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Marine Biological Laboratory Library
V/oods Hole, Massachusetts
Gift of Bostwick H. Ketchum - 1976
EVOLUTION, GENETICS
AND EUGENICS
THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS
THE BAKER & TAYLOR COMPANY
NEW YORK
THE CAMBRIDGE UNIVERSITY PRESS
LONDON
THE MARUZEN-K.ABUSHIKI-KAISHA
TOKYOj OSAKA, KYOTO, TVK.VOKA, SENDAI
THE COMMERCIAL PRESS, LIMITED
SHANGHAI
EVOLUTION, GENETICS ^
AND EUGENICS
By HORATIO HACKETT NEWMAN
Professor of Z,oulogy in the University of Chicago
11 % 1-
MARl
BIOLCGiCAL
LABORATORY
LIBRARY
WOODS HOLE, MASS
W. H. 0. I.
THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS
COPYRIGHT I92I AND I925 BY THE UNIVERSITY OF CHICAGO
ALL RIGHTS RESERVED. PUBLISHED OCTOBER I92I
Second Edition T>ecember ig2^
Sixth Impression October /pj/
COMPOSED AND PRINTED BY THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS, U.S.A.
THIS VOLUME
IS AFFECTIONATELY DEDICATED
TO
MY MOTHER
PREFACE TO FIRST EDITION
This book has been prepared to meet a specific demand, long
felt here and elsewhere, for an account of the various phases of evolu-
tionary biology condensed within the scope of one volume of moderate
size. The present writer has now for sixteen successive years pre-
sented in lecture form to large classes of students the subjects of
evolution, genetics, and eugenics. Never have we been able to find
a single book that would cover the required ground. In fact it has
been necessary to require, or at least to recommend, as many as
three books. It is beheved that the present book will furnish ade-
quate reading material for a major or a semester course in evolutionary
biology. Some supplementary reading may be necessary in case an
instructor wishes to emphasize one or more phases of the subject;
but for a first course in the subject we believe that all of the essential
reading material will be found within the text itself.
An effort has been made to present the subject in the best peda-
gogical order. After a general introduction, a rather long chapter
appears in which the whole history of the development of evolution-
ary science is outlined, together with the names and contributions
of the leading evolutionists. Part II is a presentation of the evi-
dences of organic evolution, beginning with the bodies of evidence
most definite and direct, and ending with the less definite and
more controversial. Part III deals with causo-mechanical theories of
evolution with Darwinism as the central topic. Part IV concerns
itself with genetics or modem experimental evolution, and Part V
with eugenics, or genetics as appUed to human improvement.
The book consists largely of excerpts, some long and some short,
from both the older classical evolutionary writers and the modem
writers. Our aim has been to select the most significant or character-
istic passages from each author. In most cases this ideal has been
attained, but it has sometimes happened that we have had to make
our selection of material to meet a real need in the book, and accord-
ingly have selected from an author a passage he himself might not
consider particularly characteristic of his work. We have succeeded,
nevertheless, in welding together out of a collection of isolated chapters
and passages what seems to us to be a close approach to a coherent
unit. Unification has been accomplished by the aid of editorial
connecting passages, introductory statements, criticisms, and sum-
maries. In certain cases it became necessary, for a variety of reasons,
vii
viii PREFACE TO FIRST EDITION
for the editor to write short chapters on certain topics that were not
presented in the available literature in sufficiently brief compass or
in sufficiently non-technical language.
The one-man textbook is only too often written to emphasize
the author's pet theories and is likely to be unduly biased. The
present work is completely non-partisan. It consists of the writ-
ings of many authors and presents many diverse theories. The
student is left to balance the various views one against another and
to form his own judgment.
It is very unfortunate, but none the less true, that even in these
scientific days, the subject of evolution has a bad name in many
communities and in many educational institutions with religious
affiliations. The mistake is made of supposing that evolution and
rehgion are diametrically opposed. The present writer has been at
some pains to make it clear that evolution and religion are strictly
compatible. We teachers of evolution in the colleges have no sinister
designs upon the religious faith of our students.
While this book is intended primarily for a college textbook,
we have also had in mind the general reader. Apart from a few of
the more technical details, the text seems to us very readable. The
language of the great classic writers — Darwin, Wallace, Romanes, De
Vries, Le Conte — is simple and lucid. Among recent biological books
few are written so freshly and vividly as those of Professor J. Arthur
Thomson. The clearness and scientific accuracy of Conklin, Saleeby,
Guyer, Walter, Lull, Osborn, the Coulters, Downing, ShuU, Tayler,
Popenoe, Johnson, and others, are familiar to American biologists.
Scrupulous care has been taken to verify all passages quoted,
but it is hardly likely that, in so large a mass of material, all errors
shall have been avoided. The author and the publishers would
welcome as a favor any suggestions or corrections submitted by
interested readers.
A list of the books from which material has been quoted is given
on pages 612, 613. To the authors and publishers of these books and
monographs we wish herewith to tender our grateful acknowledg-
ments for their generosity and co-operation. A considerable amount
of material for which permission to reprint had been granted fails
to appear in the present volume. It is hoped to incorporate this
material in an appendix to a later edition, or else to use it in the form
of a small volume of supplementary readings.
H. H. N.
August 15, 1921
PREFACE TO REVISED EDITION
A book of this sort somewhat resembles a loose-leaf encyclopedia
in that it subjects itself very readily to revision and rearrangement
and thus may be kept abreast of the times. When certain sections
prove through actual class use to need revision or restatement or when
new discoveries necessitate a change in conclusions, appropriate cor-
rections may be made, new matter added, or whole chapters re-
written. When various topics have shown themselves to be either
logically or pedagogically in the wrong order, it is easy to rearrange
chapters, for the latter are to a large degree independent. When,
finally, any new chapter of superior excellence appears in a new pub-
lication, it is usually possible through the courtesy of author and pub-
lisher to add it to the worthy collection of excerpts already gathered
together.
The writer has been fortunate in that reviewers and colleagues both
in America and in Europe have offered many constructive criticisms
of the book and suggestions for its improvement. It is hoped that the
present edition will adequately reflect this expert advice.
The order of presentation of the evidences of evolution has been
changed from one based on the degree of directness of the evidence
to one based on the logical succession of topics and their interde-
pendence. The chapters on "The Mutation Theory" and "The
Inheritance of Acquired Characters" have been placed near the end
of the book in order that they may be considered in the full light
of our present knowledge of genetics. The chapter on "Linkage
and Crossing-over" has been rewritten in a more elementary and cir-
cumstantial style in order to overcome, if possible, the difficulty that
students have always encountered in understanding the somewhat
condensed and technical account of Professor Castle. The discussion
of mutations has been modernized and considerably extended through
the addition of an article written especially for this book by Professor
R. Ruggles Gates and of a paper by Professor H. F. MuUer. The
section on eugenics has been strengthened by the addition of a lucid
ix
X PREFACE TO REVISED EDITION
chapter from Albert Edward Wiggam's book The Fruit of the Family
Tree. The writer has introduced a considerable amount of new matter
of his own which consists chiefly of relatively short introductory, con-
necting, explanatory, and summarizing statements that serve to
cement the otherwise somewhat disconnected excerpts into a coherent
whole. Because of the fact that so many of the writer's own contribu-
tions are scattered through the book, it is deemed wise to omit his
name from all such chapters and passages, with the understanding
that all matter not specifically credited to others is his own.
Excerpts from books commonly contain undefined technical terms
that perplex the beginning student. This ditficulty has been overcome
through the addition of a full glossary defining nearly all of the bio-
logical terms used in the book.
Grateful acknowledgments for the use of new materials are here-
with given to the following authors and publishers: E. G. Conklin,
R. R. Gates, S. J. Holmes, D. F. Jones, T. H. Morgan, H. F. Muller,
G. H. Thayer, A. E. Wiggam, E. B. Wilson; The Bobbs-Merrill Com-
pany, Henry Holt and Company, The Macmillan Company, The
Princeton University Press, The Williams and Wilkins Company.
H. H. Newman
University of Chicago
April 6, 1925
TABLE OF CONTENTS
PAGE
List of Illustrations • xvii
PART I. INTRODUCTORY AND HISTORICAL
Chapter I. Introduction 3
What Organic Evolution Is — Definitions 3
The Modern Attitude as to the Truth of the Evolution Doctrine . 5
What Organic Evolution Is Not 8
u Chapter II. Historical Account of the Development of the
Evolution Theory 10
Evolution among the Greeks n
.( Post-Aristotelians i4
Y J The Early Theologians . , i4
V The Revival of Science i5
The Great Naturalists of the Eighteenth Centur>^ 16
Lamarck ^"
Cuvier and Geoff roy St. Hilaire 21
Catastrophism and Uniformitarianism 22
The Reawakening of the Evolution Idea 23
Charles Darwin 24
Summary of Darwin's Theories 25
Contemporary Opinion Regarding the Validity of Darwin's Views 27
Isolation Theories 3~
Orthogenesis Theories 33
Mutation or Heterogenesis Theories 36
The Rise and Vogue of Biometry 3^
Modern Experimental Evolution 39
Mendel's Laws 4i
Hybridization and the Origin of Species 43
Neo-Mendelian Developments 43
Heredity and Sex 44
The Experimental Induction of Heredity Variations ..... 45
The Present Attack upon Evolution in the United States ... 45
Concluding Remarks 46
Chapter III. The Relation of Evolution to Materialism. Joseph
Le Conte 47
xii TABLE OF CONTENTS
PART II. EVIDENCES OF ORGANIC EVOLUTION
PAGE
Chapter IV. Is Organic Evolution an Established Principle? . 57
Chapter V. The Fundamental Assumption Underlying All Evi-
dences OF Evolution 61
Chapter VI. Evidences from Morphology (Comparative Anat-
omy). George John Romanes 66
Chapter VII. Evidences from Classification loi
The Principles of Classification. A. F. Shull loi
The Method of Classification. Charles Darwin ...... 104
What Is a Species? 105
Chapter VIII. Evidence from Blood Tests. W. B. Scott . . . 108
Chapter IX. Evidences from Embryology 113
The Facts of Reproduction and Development 113
Outline of Animal Development. D. S. Jordan and V. L. Kellogg . 114
Chapter X. Critique of the Recapitulation Theory. W.B.Scott 122
Chapter XL Evidences from Palaeontology 132
Strength and Weakness of the Evidence 132
Other Opinions as to the Adequacy of the Evidences from Palae-
ontology 133
What Fossils Are and How They Have Been Preserved .... 134
Fossils Classified 134
On the Conditions Necessary for Fossilization 135
On the Lapse of Time during Which Evolution Is Believed to Have
Taken Place 138
On the Principal General Facts Revealed by a Study of the Fossils 140
Fossil Pedigrees of Some Well-known Vertebrates 141
Pedigree of the Horse 141
Pedigree of the Camels. W . B. Scott 144
Evolution of the Elephants. A. Franklin Shidl 147
yj Chapter XII. The Evolution of Man: Palaeontology. Richard
Swann Lidl 152
Origin of Primates "" 152
Origin of Man 153
Fossil Man 155
Evidences of Human Antiquity 165
Future of Humanity 166
Chapter XIII. Evidences from Geographic Distribution. . . 168
Principles of Geographic Distribution 168
Some of the More Significant Facts about the Distribution of
Animals 172
TABLE OF CONTENTS xiil
PAGE
The Fauna of Oceanic Islands. George John Romanes . . . . 172
The Fauna of Continental Islands — Madagascar and New Zealand.
A.R.Wallace 181
The Distribution of Marsupials. .-4 ./?. M''a//ace 182
The Distribution of Birds. ^. 2?. lFfl//ace 183
Summary of Mammalian Dispersal. Hans Gadow 185
Summary of the Argument for Evolution as Based on Geographic
Distribution 186
PART III. THE CAUSAL FACTORS OF
ORGANIC EVOLUTION
Chapter XIV. Introductory Statement igi
What We Owe to Darwin 192
Chapter XV. The Background of Darwinism: Adaptations . . 194
The Nature of Adaptations . . . 194
Two Categories of Adaptations 198
Adaptations Classified 199
Some Special Adaptations 200
Parasitism and Degeneration 201
Adaptations of Deep-Sea Animals and of Cave Animals .... 204
Color and Pattern in Animals 205
Osborn's Laws of Adaptation 211
Chapter XVI. The Background of Darwinism — Continued . . 215 /^ iX
The Web of Life. J . Arthur Thomson 215
Chapter XVII. Natural Selection. Charles Darwin 228
Foundation Stones of Natural Selection 228
Darwin's Own Estimate as to the Role of Natural Selection in
Evolution 228
Effects of Habit and of the Use or Disuse of Parts; Correlated
Variation; Inheritance 229
Darwin's Idea of the Causes Responsible for the Origin of Domes-
tic Races 230
Darwin's Idea of the Origin of Varieties, Species, and Genera in
Nature 230
The Term "Struggle for Existence" Used in a Large Sense . . 231
Geometrical Ratio of Increase 232
Natural Selection; Or the Survival of the Fittest 232
Sexual Selection 239
Illustrations of the Action of Natural Selection, or the Survival
of the Fittest 241
Summary of Chapter on Natural Selection 242
Difficulties and Objections to Natural Selection as Seen by Darwin 245
XIV TABLE OF CONTENTS
PAGE
Chapter XVIII. Critique of Darwinism 254
Summary of Darwin's Natural-Selection Theory. Vernon L. Kellogg 254
Objections to Darwinism 256
Defense of Darwinism 261
General Defense of Darwinism. J. L. Tayler 262
Experimental Support of the Effectiveness of Natural Selection . . 265
The Present Status of Natural Selection . 267
The Relation of Mendelism and the Mutation Theory to Natural
Selection. C. C. Nutting 267
Chapter XIX. Other Theories of Species-Forming . . . . 272
Theories Auxiliary to Natural Selection 272
Weismann's Theory of Panmixia 272
Weismann's Theory of Germinal Selection 274
Roux's Theory of Intraselection or the Battle of the Parts . . 277
Coincident Selection or Organic Selection 277
Isolation Theories 278
Theories Alternative to Natural Selection 282
Chapter XX. A New Composite Causo-mechanical Theory of
Evolution (the Tetrakinetic Theory). Henry Fairfield Osborn 284
The Energy Concept of Life ■ 284
The Four Complexes of Energy 289
PART IV. GENETICS
Chapter XXI. The Scope and Methods of Genetics .... 295
(/ Definitions 295
The Scope and Methods of Genetics . 295
Heredity, Environment, and Training 297
Chapter XXII. How Organisms Reproduce Themselves . . . 299
V Reproductive Processes 299
Sexual or Gametic Reproduction 301
Chapter XXIII. The Bearers of the Heritage: An Account of
the Cellular Basis of Heredity. Michael F. Guyer . . . 303
Chapter XXIV. Variation and Heredity .320
Introductory Statement 320
Chapter XXV. Variation. E. B. Babcock and R. E. Clausen '. . 323
Chapter XXVI. Mendel's Laws of Heredity 339
Mendel's Life and Character. J . A. Thomson 339
Mendel's Discoveries. /. A. Thomson 339
Mendel's Explanations. John M. and Merle C. Coulter .... 345
Illustrations of Mendelian Inheritance. /. A. Thomson .... 352
TABLE OF CONTENTS XV
PAGE
Chapter XXVII. The Physical Basis or Mendelism. E. B. Bab-
cock and R. E. Clausen 360
Chapter XXVIII. The Factor Hypothesis as Applied to Plants.
John M. and Merle C. Coulter 372
Chapter XXIX. The Factor Hypothesis as Applied to Animals . 388
Chapter XXX. Review of Mendelism and Introduction to the
New Heredity 392
Chapter XXXI. Sex Determination and Sex-linked Heredity . 396
Sex Determination 39^
The Chromosomal Mechanism of Sex Determination .... 398
Sex Differentiation 404
Sex-linked Heredity 408 ^
Chapter XXXII. Linkage, Crossing-over, and the Architecture
OF THE Germ Plasm 416
Linkage 4i6
Crossing-over 4^9
Chromosome Maps Indicating the Arrangement of the Genes in the
. Chromosomes 422
Linkage in Other Organisms 427
Chapter XXXIII. Biometry (The Statistical Study of Variation
and Heredity) 43°
The Statistical Study of Variation 43°
The Statistical Study of Inheritance. E. G. Conklin 435
Chapter XXXIV. Heredity in Pure Lines 441
Chapter XXXV. The Origin of New Hereditary Characters . 445
Chapter XXXVI. Are Acquired Characters (Modifications)
Hereditary? 449
Misunderstandmgs as to the Question at Issue. /. A. Thomson. . 449
The Inheritance or Non-Inheritance of Acquired Characters. E. G.
Conklin 456
The Other Side of the Question 462
A Possible Mechanism for the Transmission of Acquired Characters.
M. F. Gnyer 464
Recent Experiments Believed to Favor the Lamarckian Theory . 471
Chapter XXXVII. The Mutation Theory 475
]<:'dc6i7e Due TO Differences in Color OF
Light 329
52. Temperature Phases of the Diurnal Peacock-Butterfly . 330
53. Morphological Cycle of Head Height in £?>'a/o(fa/>/mia . .331
•
LIST OF ILLUSTRATIONS Xix
FIGURE PAGE
54. Schematic Curves of Head Height in Hyalodaphnia as Grown
IN Media OF Three Different Food Values 332
55. Climatic Effects upon Plumage in Pigeons 333
56. Effects of Injections into Ovary of Scrophularia .... 335
57. Diagram Illustrating Behavior of Chromosomes in Men-
del's Cross of Tall and Dwarf Peas 347
58. Dlagram Illustrating Behavior of First Hybrid Genera-
tion When Inbred 34^
59. Dlagram Illustrating Dlhybrid Ratio 35 1
60. Diagram Showing the Characteristic Pairing, Size Rela-
tions, AND Shapes of the Chromosomes of Drosophila
melanogaster 3^^
61. Diagram of Mitosis in a Species Having Four Chromo-
somes IN Its Cells 363
62. The Reduction Division as Represented for a Species Whose
Diploid Number Is Four 3^5
63. Diagram of Chromatin Interchange between Homologous
Members of a Pair of Chromosomes 3^7
64. Diagram Showing Consequences of Independent Segrega-
tion of Chromosomes in Drosophila melanogaster .... 368
65. Diagram Showing Chromosome Relations in the Inheritance
OF Sex in Drosophila melanohaster 37°
66. DiAGR.\M Showing How the Original Scheme Must Be Modi-
fied to Satisfy the Presence-and-Absence Hypothesis. . 373
67. Diagram Showing How Presence-and-Absence Scheme Is
Actually Used : 374
68. Diagram Illustrating Blending Inheritance 375
69. Diagram Illustrating Complementary Factors . . . . 377
70. Diagram Illustrating Behavior of Inhibitory Factor . . 380
71. Diagram Showing Some Possible Combinations in F^ When
Fi OF Figure 70 Is Inbred 381
72. Dlagram Showing THE Heterozygote Situation 381
73. Diagram Illustrating THE Action OF A Supplementary Factor 382
74. Dlagram Illustrating Nilsson-Ehle's Explanation of the
15:1 Ratio in F2 of Hybrid between Red- and White-
grained Wheat 3^4
75. Another Method of Visualizing Nilsson-Ehle's 15:1 Ratio . 385
76. Diagram OF Nilsson-Ehle's 63 : 1 Ratio 386
XX LIST OF ILLUSTRATIONS
FIGURE I'AGE
77. An Armadillo Egg about Six Weeks after Fertilization,
Showing the Quadruplet Fetuses 397
78. Diagram Showing Chromosome Relations in Sex Determina-
tion 399
79. A Typical Opposite-sexed Pair of Cattle Twins .... 407
80. Sex-Linked Inheritance of White and Red Eyes in Drosophila 41 1
81. Recriprocal Cross TO That Shown IN Figure 80 . . . .412
82. Sex-lin^ked Inheritance of Barred and Unbarred (Black)
Plumage in Poultry . 413
83. Reciprocal Cross to That Shown in Figure 82 . . . . 414
84. Diagram Showing the Mechanism of Crossing-over . . . 422
85. Chromosome Map of Drosophila 426
86. Polygon of Variation for the Total Number of Scutes in
the Nine Bands of the Armadillo 43 1
87. Bimodal Polygon Plotted from Data on the Earwig . . . 434
88. Correlation Table of 400 Plants of Sixty-Day Oats . . . 435
89. Diagram of Galton's "Law of Ancestral Inheritance" . . 437
90. Scheme to Illustrate Galton's "Law of Filial Regression" 439
91. Oenothera lamarckiana 476
92. A Series Showing Oenothera lamarckiana and Several of Its
Mutants Growing Side by Side 481
93. Diagram Showing in Condensed Form the Genealogy of the
Oenothera lamarckiana Family and Its Various Mutants . . 486
94. Pedigree OF A Line WITH Brachydactyly 518
95. Inheritance of One Form of Cataract 519
96. Pedigree Showing Heredity of Feeble-Mindedness: Family
of Gertie K .... 521
97. Another Pedigree Showing Heredity of Feeble-Minded-
ness: Family of Charlie M 522
98. Pedigree Showing Heredity OF Insanity 523
99. Pedigree Showing Heredity of Insanity and Neurotic
Tendency 523
PART I
INTRODUCTORY AND HISTORICAL
CHAPTER I
INTRODUCTION
WHAT ORGANIC EVOLUTION IS — DEFINITIONS
The following selections are representative both of the older and
of the newer attitudes of thinkers on the subject of organic evolution.
The earlier writers were greatly impressed with the sublimity of the
idea and found it in full accord with their religious faith. The later
writers are less awed by the vastness of the process and hence adopt
a more completely materialistic attitude. It is not necessary, how-
ever, to discard one's religious beliefs in order to adopt a scientific
attitude toward the problems of organic evolution.' These points of
view are well expressed in the following quotations.
"The world has been evolved, not created; it has arisen little by
little from a small beginning, and has increased through the activity
of the elemental forces embodied in itself, and so has rather grown than
suddenly come into being at an almighty word. What a sublime idea
of the infinite might of the great Architect! the Cause of all causes,
the Father of all fathers, the Ens entiumi For if we could compare
the Infinite it would surely require a greater Infinite to cause the
causes of effects than to produce the effects themselves. .
"All that happens in the world depends on the forces that prevail
in it, and results according to law; but where these forces and their
substratum, Matter, come from, we know not, and here we have room
for faith. " — Erasmus Darwin,^ as interpreted by Weismann.
"When I first came to the notion, .... of a succession of extinc-
tion of species, and creation of new ones, going on perpetually now, and
through an indefinite period of the past, and to continue for ages to
come, all in accommodation to the changes which must continue in the
inanimate and habitable earth, the idea struck me as the grandest
which I had ever conceived, so far as regards the attributes of the
Presiding Mind. "—From a letter of Sir Charles Lyell to Sir John
Herschel, 1836.
' See Joseph Le Conte, Relation oj Evolution to Materialism, chap. iii.
' From R. S. Lull, Organic Evolution (The Macmillan Company. Reprinted
by permission).
3
4 EVOLUTION, GENETICS, AND EUGENICS
"It is interesting to contemplate a. tangled bank, clothed with
many plants of many kinds, with birds singing on the bushes, with
various insects flitting about, and with worms crawling through the
damp earth, and to reflect that these elaborately constructed forms,
so different from each other, and dependent upon each other in so com-
plex a manner, have all been produced by laws acting around us.
These laws, taken in the largest sense, being Growth with Reproduc-
tion ; Inheritance which is almost implied by reproduction ; Variability
from the indirect and direct action of the condition of hfe, and
from use and disuse ; a Ratio of Increase so high as to lead to a struggle
for Life, and as a consequence to Natural Selection, entailing Diver-
gence of Character and the Extinction of less-improved forms. Thus,
from the war of nature, from famine and death, the most exalted
object which we are capable of conceiving, namely, the production of
the higher animals, directly follows. There is a grandeur in this view
of life, with its several powers, having been originally breathed by the
Creator into a few forms or into one; and that, while this planet has
gone cycling on according to the fixed law of gravity, from so simple a
beginning endless forms most beautiful and most wonderful have been,
and are being evolved. " — Charles Darwin, Origin of Species, conclud-
ing paragraph.
" Speaking broadly we find as a fact that transmutation of species
through the geologic ages has been accompanied by increasing diver-
gence of type, by the increased specialization of certain forms, and by
the closer and closer adaptation to conditions of life on the part of the
forms most highly specialized, the more perfect adaptation and the
more elaborate specialization being associated with the greatest
variety or variation in the environment. Accepting for this process
the name organic evolution, Herbert Spencer has deduced from it the
general law, that as life endures generation after generation, its
character, as shown in structure and function, undergoes constant
differentiation and specialization. In this view, the transmutation
of species is not merely an observed process, but a primitive necessity
involved in the very organization of life itself." — D. S. Jordan and
V. L. Kellogg, Evolution and Animal Life (1908), p. 4.
"The Doctrine of Evolution is a body of principles and facts con-
cerning the present condition and past history of the living and lifeless
things that make up the universe. It teaches that natural processes
INTRODUCTION 5
have gone on in the earlier ages of the world as they do to-day, and
that natural forces have ordered the production of all things about
which we know." — Henry Edward Crampton, The Doctrine of Evolu-
tion (191 i), p. I,
"Evolution is the gradual development from the simple unorgan-
ized condition of primal matter to the complex structure of the physi-
cal universe; and in like manner, from the beginning of organic life
on the habitable planet, a gradual unfolding and branching out into
all the varied forms of beings which constitute the animal and plant
kingdoms. The first is called Inorganic, the last Organic Evolution. "
— Richard Swann Lull, Organic Evolution (1917), p. 6.
THE MODERN ATTITUDE AS TO THE TRUTH OF THE
EVOLUTION DOCTRINE
"Among that public which, though educated and intelligent, is
not yet professionally scientific, there has been, of late, a widespread
belief that naturalists have become very doubtful as to the truth of the
theory of evolution and are casting about for some more satisfactory
substitute, which shall better explain the infinitely varied and mani-
fold character of the organic world. This belief is an altogether mis-
taken one, for never before have the students of animals and plants
been so nearly unanimous in their acceptance of the theory as they are
to-day. It is true that there are still some dissentient voices, as there
have been ever since the publication of Darwin's 'Origin of Species,'
but the whole trend of scientific opinion is strongly in favor of the
evolutionary hypothesis." — ^William Berryman Scott, The Theory oj
Evolution, p. I.
"But the biological sciences were still slower [than the physical
sciences] to come to their true position as dignified science. Here was
the last stronghold of the supernaturalist. Thrust out from the field
of 'physical science' it was in the phenomena of life that the last stand
was made by those who claim that supernatural agency intervenes in
nature in such a way as to modify the natural order of events. When
Darwin came to dislodge them from this, their last intrenchment, there
was a fight, intense and bitter, but, like all attempts to stay the prog-
ress of human knowledge, this final struggle of the supernaturalists
was foredoomed to failure. The theory of evolution has taken its
place beside the other great conceptions of natural relations, and
largely through its estabhshment biology has become truly a science
6 EVOLUTION, GENETICS, AND EUGENICS
with a large group of phenomena consistently arranged and properly
classified. The discussion which followed the publication of Darwin's
'Origin of Species' lasted for nearly a generation, but it is now practi-
cally closed, so far as any attempt to discredit evolution as a true
scientific generalization is concerned. Scientists are no longer ques-
tioning the fact of evolution; they are busied rather with the attempt
to further explore and more perfectly understand the operation of the
factors that are at work to produce that development of animals and
plants which we call organic evolution. " — Maynard M. Metcalf, An
Outline oj the Theory oj Organic Evolution (191 1), pp. xxii-xxiii.
"Biologists turned aside from general theories of evolution and
their deductive application to special problems of descent, in order to
take up objective experiments on variation and heredity for their own
sake. This was not due to any doubts concerning the reality of
evolution or to any lack of interest in its problems. It was a policy
of masterly inactivity deliberately adopted; for further discussions
concerning the causes of evolution had clearly become futile until a
more adequate and critical view of existing genetic phenomena had
been attained." — E. B. Wilson (address as president of the American
Association for the Advancement of Science, 1914).
"The theory of development, as it was revived by Darwin nearly
half a century ago, is in its modern form prevailingly unhistorical.
True, it has forced beneath its sceptre the methods of investigation
of all the sciences which deal with the living world and to-day almost
completely controls scientific thought And yet science does
not sincerely rejoice in its conquests. Only a few incorrigible and
uncritically disposed optimists steadfastly proclaim what glorious
progress we have made; otherwise, in scientific as in lay circles, there
prevails a widespread feeling of uncertainty and doubt. Not as
though the correctness of the principle of descent were seriously
questioned; rather does the conviction steadily grow that it is
indispensable for the comprehension of living nature, indeed self-
evident." — Gustav Steinmann (translated by W. B. Scott from
Die Abstammungslehre [1908], pp. 1—2).
"The many converging lines of evidence point so clearly to the
central fact of the origin of forms of life by an evolutionary process
that we are compelled to accept this deduction, but as to almost all
the essential features, whether of cause or of mode, by which specific
INTRODUCTION 7
diversity has become what we perceive it to be, we have to confess an
ignorance nearly total." — William Bateson, Problems of Genetics
(1913), p. 248.
"The demonstration of evolution as a universal law of living
nature is the great intellectual achievement of the nineteenth century.
Evolution has outgrown the rank of a theory, for it has won a place
in natural law beside Newton's law of gravitation, and in one sense
holds a still higher rank, because evolution is the universal master,
while gravitation is among its many agents. Nor is the law of evolu-
tion any longer to be associated with any single name, not even with
that of Darwin, who was its greatest exponent. It is natural that
evolution and Darwinism should be closely connected in many minds,
but we must keep clear the distinction that evolution is a law, while
Darwinism is merely one of the several ways of interpreting the work-
ings of this law.
"In contrast to the unity of opinion on the law of evolution is the
wide diversity of opinion on the causes of evolution. In fact, the
causes of the evolution of life are as mysterious as the law of evolution
is certain. Some contend that we already know the chief causes of
evolution, others contend that we know little or nothing of them.
In this open court of conjecture, of hypothesis, of more or less heated
controversy the names of Lamarck, of Darwin, of Weismann figure
prominently as leaders of diflferent schools of opinion; while there are
others, like myself, who for various reasons belong to no school, and
are as agnostic about Lamarckism, as they are about Darwinism or
Weismannism, or the more recent form of Darwinism, termed Muta-
tion by De Vries.
"In truth, from the period of the earlier stages of Greek thought
man has been eager to discover some natural cause of evolution, and
to abandon the idea of supernatural intervention in the order of
nature. Between the appearance of The Origin of Species, in 1859,
and the present time there have been great waves of faith in one
explanation and then in another: each of these waves of confidence
has ended in disappointment, until finally we have reached a stage
of very general scepticism. Thus the long period of evolution, experi-
ment, and reasoning which began with the French natural philosopher,
Buffon, one hundred and fifty years ago, ends in 1916 with the general
feeling that our search for causes, far from being near completion, ba=
only just begun.
8 EVOLUTION, GENETICS, AND EUGENICS
"Our present state of opinion is this: we know to some extent
how plants and animals and man evolve; we do not know why they
evolve. We know, for example, that there has existed a more or less
complete chain of beings from monad to man, that the one-toed horse
had a four-toed ancestor, that man has descended from an unknown
ape-like form somewhere in the Tertiary. We know not only those
larger chains of descent, but many of the minute details of these
transformations. We do not know their internal causes, for none of
the explanations which have in turn been offered during the last hun-
dred years satisfies the demands of observation, of experiment, of
reason. It is best frankly to acknowledge that the chief causes of the
orderly evolution of the germ are still entirely unknown, and that our
search must take an entirely fresh start." — H. F. Osborn, The Origin
and Evolution of Life (Charles Scribner's Sons), 1918, pp. viii-x.
WHAT ORGANIC EVOLUTION IS NOT
1. The evolution doctrine is not a creed to be accepted on faith,
as are religious faiths or creeds. It appeals entirely to the logical
faculties, not to the spiritual, and is not to be accepted until proved.
2. It does not teach that man is a direct descendant of the apes
and monkeys, but that both man and the modern apes and monkeys
have been derived from some as yet unknown generalized primate
ancestor possessing the common attributes of all three groups and
lacking their specializations.
3. It is not synonymous with Darwinism, for the latter is merely
one man's attempt to explain how evolution has occurred.
4. Contrary to a very widespread idea, evolution is by no means
incompatible with religion. Witness the fact that the early Christian
theologians, Augustine and Thomas Aquinas, were evolutionists, and
the majority of thoughtful theologians of all creeds are today in
accord with the evolution idea, many of them even applying the prin-
ciple to their studies of religion; for religious ideas and ideals, like
other human characters, have evolved from crude beginnings and are
still undergoing processes of refinement.
5. The evolution idea is not degrading. Quite the contrary; it is
ennobling as is well brought out by the classic statement of Darwin
on page 4 and by that of Lyell, on page 3.
6. The evolution doctrine does not teach that man is the goal of
all evolutionary process, but that man is merely the present end
product of one particular series of evolutionary changes. The goal
INTRODUCTION 9
of evolution in general is perfection of adaptation to the conditions of
life as they happen to be at any particular time. Many a highly
perfected creature has reached the goal of its evolutionary course
only to perish because it was too highly perfected for a particular
environment and could not withstand the hardships incident to radi-
cally changed world-conditions. Many evolutions therefore ha\c
been completed, while others are still awaiting the opportunity to
speed up toward a new goal.
7. Evolution is therefore not entirely a thing of the past. Obvi-
ously some species, including Man perhaps, are nearly at the end
of their physical evolution, but there are always certain generalized
plastic types awaiting the next great opportunity for adaptive speciali-
zation.
CHAPTER n
HISTORICAL ACCOUNT OF THE DEVELOPMENT OF THE
EVOLUTION THEORY
The chief sources of material for the present chapters are: Osbom's
From the Greeks to Darwin^ and Judd's The Coming of Evolution.'^
Professor Osbom studies the evolution of the evolution idea as a
biologist would investigate the evolution of a group of species, using
all of the available sources of evidence at his disposal. The fragments
of ancient writing and the crude imaginings of early natural philoso-
phers are the fossils of the evolution idea, many of them ancestors
of modern principles; fragments of ancient or discarded ideas that
still persist, though irrelevant to modern thought, are the vestigial
structures that proclaim kinship between the past and the present;
parallelisms between the development of ideas in the minds of inde-
pendent thinkers do not prove plagiarism, but indicate common
descent from the same ancestral ideas.
This whole history is an important chapter in the story of human
evolution in general, for it deals with the evolution of a characteristic
human faculty — that of appreciating the broad relations that exist
between the past and the present. This faculty has evolved as truly
as has an organic system such as the nervous system, and is unques-
tionably closely bound up with the latter.
The evolution theory is a vast fabric of interrelated and inter-
dependent facts and principles. The fabric has been gradually woven
out of separate threads and now stands strong though flexible, with
strands reaching into all sciences and tending to unify all science.
It was only after the lesser ideas came to be cleaily apprehended
that it was possible for the master minds of Lamarck and of Darwin to
weave them together into a consistent fabric and to bring the facts
together under the one great conception, that of organic evolution.
Classification was a science, comparative anatomy had made much
progress, the principles of embryology were fairly well understood,
• H. F. Osbom, From the Greeks to Darwin (The Macmillan Company, 1908).
' John W. Judd, The Coming of Evolution (Cambridge University Press, 191 1).
10
HISTORICAL ACCOUNT OF EVOLUTION THEORY II
much palaeontological discovery had been made, before it was found
that the facts from these sources all pointed to one general principle,
and only one, that master-principle "organic evolution."
We shall now trace the development of the evolution idea from
its mception among the Greeks to its present status, and shall first
give a brief account of Greek evolution.
EVOLUTION AMONG THE GREEKS
The early Greek thinkers were sea people. " Along the shores and
in the waters of the blue Aegean," says Osborn, "teeming with what
we now know to be the earliest and simplest forms of animals and
plants, they founded their hypotheses as to the origin and succession
of life The spirit of the Greeks was vigorous and hopeful.
Not pausing to test their theories by research, they did not suffer the
disappointments and delays which come from one's own efforts to
wrest truths from Nature. "
The Greeks were anticipators of Nature. Their speculations out-
stripped the facts; in fact were usually made with "eyes closed to the
facts." Their theories were inextricably bound up with current
mythology, were naive, vague, and, from our modern point of view,
ridiculous; yet they contained many grains of truth and were the
germs out of which grew the saner ideas of subsequent thinJ<.ers.
Thales (624-548 B.C.) was the first of the Greeks to theorize about
the origin of life. "He looked upon the great expanse of mother ocean
and declared water to be the mother from which all things arose, and
out of which they exist." This idea anticipates the modem idea of
the aquatic or marine origin of life, and also the present idea as to the
indispensability of water in all vital processes.
Anaximander (611-547 B.C.) has been called the prophet of
Lamarck and of Darwin. While his theories were highly mythical in
character, he conceived the idea of a gradual evolution from a formless
or chaotic condition to one of organic coherence. He saw vaguely the
idea of transformation of aquatic species into terrestrial, even deriving
man from aquatic fishlike men (mythical mermen) who were able to
emerge from the water only after they had undergone the necessary
changes required for land life. This idea involves that of adaptation,
one of the cornerstones of the modern evolutionary structure.
Anaximenes (588-524 B.C.), a pupil of Anaximander, " found in air
the cause of all things. Air, taking the form of soul, imparts life,
motion, and thought to animals. " It is questionable whether this is a
12 EVOLUTION, GENETICS, AND EUGENICS
prophecy of the importance of oxygen and oxidation in vital processes.
Anaximenes also introduced the idea of abiogenesis (spontaneous
generation of living substance), his idea being that animals and plants
arose out of a primordial terrestrial slime wakened into life by the sun's
heat. This primordial terrestrial slime is perhaps a prophecy of
Oken's "Urschleim" or of protoplasm.
Xenophanes (576-480 B.C.), probably another pupil of Anaxi-
mander, "agreed with his master so far as to trace the origin of man
back to the transition period between the fluid or water and solid or
land stages of the development of the earth." He was the first to
recognize fossils as the remains of animals once alive, and to see
in them proof that once the seas covered the entire surface of the
earth.
Heraclitus (535-475 B.C.), the first of a group of physicists, was the
great proponent of tlie philosophy of change. He was imbued with
the idea that all was motion, that nothing was fixed. "Everything
was perpetually transposed into new shapes." Although Heraclitus
did not apply his ideas to living creatures and their evolutions, his
ohilosophy was influential in molding the ideas of his successors.
Empedocles (495-435 B.C.) " took a great stride beyond his predeces-
SOV&, and may justly be called the father of the Evolution idea
He believed in Abiogenesis, or spontaneous generation, as the explana-
tion of the origin of life, but that Nature does not produce the lower
and higher forms simultaneously or without an effort. Plant life
comes first, and animal life developed only after a long series of trials."
He thought that all creatures arose through the fortuitous combina-
tion of scattered and miscellaneous parts which were attracted or
.-epelled by the forces of love or hate (the two great forces in Nature).
Thus arose every sort of combination of parts, some more or less har-
monious and complete, others with ill-assorted organization, lacking
in some parts, double or triple in others. Some of these combinations
could not survive, because of their incompleteness and incongruity,
but "other forms arose which were able to support themselves and
multiply." This is a sort of vague prophecy of the survival of the
fittest or of natural selection. Four sparks of truth may be found in
Empedocles' philosophy, "first, that the development of life was a
gradual process; second, that plants were evolved before animals;
third, that imperfect forms were gradually replaced (not succeeded)
by perfect forms; fourth, that the natural cause of the production of
perfect forms was the extinction of the imperfect."
HISTORICAL ACCOUNT OF EVOLUTION THEORY 13
Democritus (b.450 B.C.), said to have been the first comparative
anatomist, contributed to the substructure of evolution the idea of the
"adaptation of single structures and organs to certain purposes."
Anaxagoras (500-428 B.C.) was the first of the Greeks " to attribute
the adaptations of Nature to Intelligent Design, and was thus the
founder of Teleology," an idea that has played a retarding function in
the history of evolution.
"With Aristotle (384-322 B.C.) we enter a new world," says Osborn.
"He towered above his predecessors, and by the force of his genius
created Natural History." The evolution idea took a great step
forward with Aristotle and reached a stage beyond which it did not
go for many centuries. He covered nearly the whole field, touching
upon most of the foundation stones of the complex problem. His
ideas, like those of all the Greeks, were often vague and, in the light
of present knowledge, incoherent; but, considering the meager factual
background with which he had to work he had a surprising grasp of
the whole situation. Some of his principal ideas were :
1. He had a clear idea of laws of Nature ("Necessity"), and
attributed all evolutionary changes to natural causes.
2. He opposed the ideas of Empedocles as to the fortuitous origin
of adaptive characters, and favored the idea of intelligent design in
nature. He was therefore a teleologist.
3. Hence he rejected the hypothesis of the survival of the fittest,
because it was based on chance.
4. He "had substantially the modern conception of the Evolution
of life, from a primordial soft mass of living matter. "
5. He had an idea of a Unear phylogenetic series, beginning
with plants, then plant-animals, such as sponges and sea anemones,
then animals with sensibility, and thence by graded stages up to
Man.
6. "He perceived the unity of type in certain classes of animals,
and considered rudimentary organs as tokens whereby Nature sustains
this unity. "
7. "He anticipated Harvey's doctrine of Epigenesis in embryonic
development. "
8. "He fully perceived the forces of hereditary transmission, of the
prepotency of one parent or stock, and of Atavism and Reversion."
9. He is the father of that ancient fallacy called "prenatal influ-
ences," and believed in the inheritance of acquired characters, as is
shown in the following passage:
14 EVOLUTION, GENETICS. AND EUGENICS
" Children resemble their parents not only in congenital characters,
but in those acquired later in life. For cases are known where parents
have been marked by scars and children have shown traces of these
scars at the same points; a case is also reported from Chalcedon in
which a father had been branded with a letter, and the same letter
somewhat blurred and not sharply defined appeared upon the arm of
the child."
POST-ARISTOTELIANS
With Aristotle the evolution idea reached a high watermark and
thereafter the tide steadily declined. Pliny, Epicurus, Lucretius, and
others kept the idea alive, but added nothing of importance to
Aristotle's contribution.
Lucretius (99-55 B.C.) appears to have been chiefly a follower of
Empedocles in so far as his ideas as to the origin of animals are con-
cerned. He ignored Aristotle and his much more advanced phi-
losophy of Nature, finding the earher, more mythical conceptions
better suited to poetic expression. He was not truly an evolutionist,
for he believed that all animals and plants arose fully formed from the
earth. Lucretius is of importance chiefly as a retarding factor, for
his ideas were accepted and admired even up to the eighteenth century;
witness Milton's immortal verse :
"The Earth obey'd, and straight,
Op'ning her fertile womb, teem'd at a birth
Innumerous living creatures, perfect forms,
Limb'd and full grown. "
THE EARLY THEOLOGIANS
The evolution idea made no progress from the time of Aristotle
until the revival of learning in the Middle Ages. The chief inhibiting
factor was the church, which favored traditional knowledge and the
special-creation idea in its most literal form. Yet the early theo-
logians, such as Gregory, Augustine, and Thomas Aquinas, were open-
minded about the evolution idea and attempted to reconcile it with
the scriptural account of creation.
'^Gregory of Nyssa (331-396 a.d.) taught," says Osborn, "that
Creation was potential. God imparted to matter its fundamental
properties and laws. The objects and completed forms of the Universe
developed gradually out of chaotic material."
HISTORICAL ACCOUNT OF EVOLUTION THEORY 1 5
Augustine (353-430 a.d.) conceived the idea, now so generally
adopted by theologians, that the bibUcal account of creation is alle-
gorical. "In explaining the passage 'In the beginning God created
heaven and the earth,' he says:
"In the beginning God made the heaven and the earth, as if this
were the seed of the heaven and the earth, although as yet all the
matter of heaven and of earth was in confusion, but because it was
certain that from this the heaven and the earth would be, therefore
the material itself is called by that name. "
Thomas Aquinas (1225-74), who wrote much later and was one of
the leading church authorities, satisfied himself with merely expound-
ing Augustine: "As to the production of plants, Augustine holds a
different view, .... for some say that on the third day plants were
actually produced, each in its kind — a view favoured by the superficial
reading of Scripture. But Augustme says that the earth is then said
to have brought forth grass and trees causaliter; that is, it then
received the power to produce them. For in those first days ....
God made creation primarily or causaliter, and then rested from His
work."
THE REVIVAL OF SCIENCE
During the long centuries until the awakening of science in the
Middle Ages the evolution idea smouldered along in the minds of a
few thinkers, but it was only when a few daring spirits broke the
trammels of scholasticism and began once more to give free rein to
observation and speculation that the idea once more burst into flame
and began its second great period of advance.
A small group of natural philosophers, scarcely more scientific
in their methods than the Greeks, were the first to revive interest in
the evolution idea. Of these the names of Bacon, Descartes, Leib-
nitz, and Kant are the most famous.
Francis Bacon (1561-1626) did much to revive the vogue of Aris-
totelian ideas. He also added some new ideas: (i) that the muta-
bility of species was the result of the accumulation of variations; (2)
that variations of an extreme kind, equivalent to "mutations," some-
times occur; (3) that new species might arise by a degenerative
process from old species.
Emmamiel Kant {17 24-1S04) was purely a philosopher, not an
observing naturalist, but he profited by the writings of the contem-
porary naturalists, especially those of Buflon and Maupertius. His
i6 EVOLUTION, GENETICS, AND EUGENICS
general ideas of evolution were comprehensive and summed up the
best features of all preceding writers, but he did not contribute any-
thing new to the pressing problem of the causes of evolution.
Real progress was not to be made through further speculation.
What was most needed was facts, and it was the task of the naturalists
to furnish these. The earhest of the eighteenth-century naturalists
were still anticipators of Nature in that their theories outran their
facts. Of these the names of Bonnet and Oken are the best known.
Bonnet (1720-93) was an evolutionist only in the sense that he
believed that the adult organism is present in the egg and evolves from
it by a process of unfolding or expansion. He was a zoological
observer of some note, however, and made some of the most important
contributions of his time to the general subject. He believed "that
the globe had been the scene of great revolutions, and that the chaos
described by Moses was the dosing chapter of one of these; thus the
Creation described in Genesis may be only a resurrection of animals
previously existing." This theory admits of no progress and is
scarcely wortliy of the name evolution.
Oken (1776-1851) is known chiefly for his "Urschleim" doctrine
and his ideas of cells as vesicular units of life. According to him,
"Every organic thing has arisen out of slime and is nothing but slime
in various forms. This primitive slime originated in the sea from
inorganic matter. " These ideas are purely speculative, but suggest
our modern ideas of protoplasm and cells.
THE GREAT NATURALISTS OF THE EIGHTEENTH CENTURY
Three great names stand out above all the rest during this period:
those of Linnaeus, Buffon, and Erasmus Darwin.
Linnaejis (1707-78) was the father of taxonomy. He contributed
facts rather than theories; he invented our present system of binomial
nomenclature of both animals and plants, and a great many of his
generic and specific names still persist. Unfortunately he was an
ardent advocate of the special-creation idea, holding that all of the
true species were created as they are known today, except that new
combinations may have arisen through hybridization or through
degeneration. His influence was great, but was reactionary and proved
a serious hindrance to the progress of the evolution idea.
Buffon (1707-88), bom the same year as Linnaeus, has been
recognized as the father of the modem applied form of the evolution
idea. He attempted to explain particular cases on an evolutionary
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 1 7
basis. He lived at a time when it was dangerous to express views that
might be interpreted as unorthodox, and this may account for the
apparent lack of conviction in his own ideas; for he wavered between
special creation and evolution. His chief contribution is the idea of
the direct influence of the environment in the modification of the
structure of animals and plants and the conservation of these modifi-
cations through heredity. This seems to imply that he believed in
the inheritance of acquired characters. He expressed himself as
believing that climate has had a direct effect in the production of
various races of man, that new varieties of animals have been formed
through human intervention (an idea implying artificial selection),
that similar results are produced by geographic migration and through
isolation. He expressed the view that there is a great struggle for
existence among animals and plants to prevent overcrowding and
to maintain the balance of Nature. This appears to be an anticipation
of Malthus' ideas on population, which were so influential in shaping
the theories of Charles Darwin and of Wallace.
While many of his ideas appear to be highly advanced for his time,
his special applications are open to serious criticism. He reasons,
for example, that the pig as it exists at present could not have been
formed on any original complete and perfect plan, but seems to have
been formed as a compound from other animals. It has useless parts
which could hardly have been a part of a perfect plan as originally
conceived. He thought that "the ass is a degenerate horse, and the
ape a degenerate man. "
On the whole Buffon was not a strong advocate of evolution and
his influence was far from being as important as some recent writers
appear to believe.
Erasmus Darwin (1731-1802), grandfather of Charles Darwin,
was a physician, a naturalist, and a minor poet. Undoubtedly he
transmitted to his grandson his thoughtful habit and love of science
and was influential in shaping his ideas on evolution. The elder
Darwin's theories as to the causes of evolution closely paralleled
those of Lamarck, his distinguished contemporary in France, but it
is now very generally conceded that the ideas of the two men were
independently derived from similar materials. Erasmus Darwin laid
httle emphasis on the direct action of the environment, which had been
Buffon's main dependence, and dwelt on the internal origin of adap-
tive characters. "All animals," he said, "undergo transformations
which are in part produced by their own exertions, in response to
1 8 EVOLUTION, GENETICS, AND EUGENICS
pleasures and pains, and many of these acquired forms or propensities
are transmitted to their posterity." One could ask for no clearer
statement of the idea that acquired characters are inherited.
The fierceness of the struggle for existence was clearly recognized
by Dr. Darwin. He considers that this struggle is beneficial to Nature
as a whole because it checks the too rapid increase of life. One step
farther in the argument, and he would have arrived at the idea of the
survival of the fittest, but he never took that step. He agreed with
the early Christian fathers in his belief that the powers of development
were implanted within the first organisms by the Creator and that
subsequent evolution of adaptive characters went on without further
divine intervention. The power of improvement rests v/ithin the
creature's own organizations and is due to his own efforts. The
effects of these efforts, he believes, are transmitted to offspring so
that there might be a cumulative effect throughout many generations
of the results of effort,
Erasmus Darwin was perhaps the first to express clearly the ideas
that millions of years have been required for the processes of organic
evolution and that all life arose from one primordial protoplasmic
mass. He writes as follows:
"From thus meditating upon the minute portion of time in which
many of the above changes have been produced, would it be too bold
to imagine, in the great length of time since the earth began to exist,
perhaps mallions of ages before the commencement of the history of
mankind, that all warm-blooded animals have arisen from one living
filament, which the first great Cause imbued with animality, with the
power of acquiring new parts, attended with new propensities, directed
by irritations, sensations, volitions, and associations, and thus possess-
ing the faculty of continuing to improve by its own inherent activity,
and of delivering down these improvements by generation to pos-
terity, world without end ?"
LAMARCK
Lamarck (1744-1829), the greatest of French evolutionists, is now
looked upon as "the founder of the complete modern Theory of
Descent. " Osborn considers him " the most prominent figure between
Aristotle and Darwin. One cannot compare his PJiilosophie zoologique
with all previous and contemporary contributions to the evolution
theory or learn the extraordinary difficulties under which he laboured,
and that his work was put forth only a few years after he had turned
HISTORICAL ACCOUNT OF EVOLUTION THEORY 19
from Botany to ZoOlogy, without gaining the greatest admiration for
his genius. No one has been more misunderstood, or judged with more
partiality by over or under praise. The stigma placed upon his writ-
ings by Cuvier, who greeted every fresh edition of his words as a
'nouvelle folic,' and the disdainful illusions to him by Charles Darwin
(the only writer of whom Darwin ever spoke in this tone) long placed
him in the light of a purely extravagant, speculative thinker. Yet,
as a fresh instance of the certainty with which men of science finally
obtain recognition, it is gratifying to note the admiration which has
been accorded to him in Germany by Haeckel and others, by his
countrjmien, and by a large school of American and English writers
of the present day; to note, further, that his theory was finally taken
up and defended by Charles Darwin himself, and that it forms the
very heart of the system of Herbert Spencer."
Lamarck's main theory of evolution was expressed by him in the
form of his four "laws":
I. LifC; by its proper forces, continually tends to increase the
volume of every body which possesses it, and to increase the size of its
parts, up to a limit which brings it about.
II. The production of a new organ in the animal body results
from the supervention of a new want which continues to make itself
felt, and a new movement which this want gives rise to and maintains.
III. The development of organs and their powers of action are
constantly in ratio to the employment of these organs.
rV. Everything which has been acquired, impressed upon, or
changed in the organization of individuals during the course of their
life is preserved by generation and transmitted to new individuals
which have descended from those which have undergone these
changes.
It is about the last "law" that the controversy rages, for it upholds
the idea that acquired characters are inherited, now known as the
"Lamarckian doctrine."
A somewhat more specific statement of Lamarck's theory of
evolution may be simimed up in the following list of factors which he
considered as playing an essential role in evolution.
1. "Favorable circumstances attending changes of environment,
soil, food, temperature, etc., supposed to act directly in the case of
plants, indirectly in the case of animals and man. "
2. "Needs, new physical wants or necessities induced by the
changed conditions of life. Lamarck believed that change of habits
20 EVOLUTION, GENETICS, AND EUGENICS
may lead to the origination or modification of organs; that changes
of function also modify or create new organs. By changes of environ-
ment animals become subjected to new surroundings, involving new
ways and means of living. Thus, certain land birds, driven by neces-
sity to obtain their food in the water, gradually assumed characters
adapting them for swimming, wading, or for searching for food in the
shallow water, as in the case of the long-necked kinds. "
3. "Use and disuse. To use an organ is to develop it; not to use
it is to eventually lose it. The anterior Hmbs of birds became capable
of sustained flight through use; the hind Umbs of whales are lost
through disuse, etc."
4. "Competition. Nature takes precautions not to overcrowd
the earth. The stronger and larger living things destroy the smaller
and weaker. The smaller multiply very rapidly, the larger slowly.
A physiological balance is maintained. "
$. "The transmission of acquired characters. The advantages
gained by every individual as the result of the structural changes
resulting from use or disuse are handed down to its descendants who
begin where the parent leaves off, and so are able to continue the pro-
gression or retrogression of the character. "
6. "Cross-breeding. 'If when any peculiarity of form or any
defects whatsoever are acquired, the individuals in this case, always
pairing, they will produce the same peculiarities, and if for successive
generations confined to such unions, a special distinct race will then
be formed. But perpetual crosses between individuals which have
not the same peculiarities of form result in the disappearance of all
the pecuharities acquired by the particular circumstances.'"
7. "Isolation. 'Were not man separated by distances of habita-
tion, the mixtures resulting from crossing would obliterate the general
characters which distinguish different nations.' This thought is
expressed in his account of the origin of men from apes, and is not
applied to living things in general."
In addition to his theories as to the causes of evolution, Lamarck
was the first to present the idea of the tree of life, or phylogenetic tree,
as a mode of representing animal relationships. All previous classifi-
cations had been based on the idea of a single linear phylogenetic
series, each lower group being supposedly ancestral to a higher group,
and all in a single chain.
We may best sum up Lamarck's work and influence in the words
of Osbom:
mSTORICAL ACCOUNT OF EVOLUTION THEORY 21
"Lamarck, as a naturalist,. exhibited exceptional powers of defini-
tion and description, while in his philosophical writings upon Evolu-
tion, his speculation far outran his observations, and his theory-
suffered from the absurd illustrations which he brought forward in
support of it His critics spread the unpression that he believed
animals acquired new organs simply by wishing for them. His really
sound speculation in Zoology was also injured by his earher thoroughly
worthless speculation in Chemistry and other branches of science.
Another marked defect was, that Lamarck was completely carried
away with the belief that his theory of the transmission of acquired
characters was adequate to explain all the phenomena. He did not,
Uke his contemporaries, Erasmus Darwin and Goethe, perceive and
point out, that certain problems in the origin of adaptations were still
left wholly untouched and unsolved His arguments are, in
most cases, not inductive, but deductive, and are frequently found not
to support his law but to postulate it.
"It is now a question whether Lamarck's factor is a factor in
Evolution at all! If it prove to be no factor, Lamarck will sink
gradually into obscurity as one great figure in the history of opinion.
If it prove to be a real factor, he will rise into a more eminent position
than he now holds, — into a rank not far below Darwin."
CUVIER AND GEOFFROY ST. HILAIRE
Georges Cnvier (1769-1832) deserves especial mention as one of the
strongest negative factors in the development of the evolution idea.
He was, first of all, an opponent of Lamarck, and, second, of evolution
in general. He ranged himself with Linnaeus as a special creationist
and advocated the idea of fixity of species. " AU the beings, " said he,
"belonging to one of these forms (perpetual since the beginning of all
things, that is, the Creation) constitute what we call species." So
able was Cuvier and so much in favor at the French court that he
succeeded in throwing Lamarck's views into disrepute and thus
greatly retarded the progress of evolution. He was brilliant as a
comparative anatomist and palaeontologist and wUl long be known for
his discoveries in these fields.
E. Geofroy St. Hilaire (1772-1844) did his best to defeat the
retarding influence of Cuvier. The two engaged in a long and bitter
controversy over the evolution idea. WTiile not a supporter of
Lamarckism proper, he was a thoroughgoing evolutionist, favoring
22 EVOLUTION, GENETICS, AND EUGENICS
the doctrine of BuflFon, that the direct action of the environment was
the sole cause of evolution. He also, in a sense, anticipated De Vries,
in that he believed that new species might be formed by transmutation
or sudden large variations occurring in one generation. "Hence the
underlying causes of transformations," he said, "were profound
changes induced in the egg by external influences, accidents as it were,
regulated by law, " The controversy between Cuvier and St. Hiiaire
was a losing one for the latter. The cards were stacked against him
and after him the evolution idea was retired to comparative obscurity
until revived by Charles Darwin.
CATASTROPHISM AND UNIFORMITARIANISM
The development of the science of geology had a profound influence
upon that of evolution. The prevailing theories as to historical
geology during the Middle Ages involved the idea of "catastrophism. "
According to this view all important changes in the earth's crust
represented sudden radical transformations, involving earthquakes,
volcanic outbursts, floods, sudden upliftings of submerged areas, or
equally sudden submergence of land bodies. From these ideas natu-
rally grew the related idea of great, world-wide destructions of animals
and plants, followed by re-creation of new faunas and floras. Cuvier,
for example, interpreted the more or less distinct fossil strata as being
the result of a series of tremendous cataclysms, the last of which had
been the great deluge of Scripture, in which Noah figured prominently.
He thought that at each cataclysm great floods of water had covered
the earth, that the existing animals had been buried in mud and thus
preserved as fossils, and that a new creation followed each cataclysm.
The great strength of this conception was that it appeared to give
scientific support to both special creation and the Mosaic account of
the "Flood." As compared with the pure evolutionary conception,
this alternative was highly acceptable to the church and was pro-
claimed as orthodox. The Scotch philosopher and geologist, Hutton,
who lived during the last half of the eighteenth century, combated the
idea of catastrophism by advocating the doctrine of "uniformitari-
anism," a view involving the idea that past changes on the earth
were the result of the same sort of gradual changes as are observed
to be taking place today — in brief, that there has been a strict uni-
formity of change throughout the entire period of geologic history.
There may have been, according to this view, local catastrophes.
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 23
such as volcanic outbursts, earthquakes, and floods, but the main
trend of change has been slow and constant, due largely to erosion
and allied phenomena. This view had practically no influence
on the ideas of the time and for a long period the idea of catas-
trophism triumphed over the more truly evolutionary view of uni-
formitarianism ; thus the evolution idea was destined to lie dormant
till revived by Charles Darwin.
THE REAWAKENING OF THE EVOLUTION IDEA
A number of important influences paved the way for the rehabili-
tation of the evolution idea at the hands of the younger Darwin.
Which of these was the most important it is difl&cult to say. Prob-
ably Charles Lyell's Principles of Geology and Malthus' On Population
were the most suggestive works that Darwin encountered. He was
also doubtless influenced by Robert Chambers' Vestiges of Natural
History of Creation which appeared in 1844.
Charles Lyell (1797-1875) so successfully rehabilitated the doctrine
of uniformitarianism in geology that it became very generally accepted,
thus paving the way for a more favorable consideration of the idea of
organic evolution. Charles Darwin as a very young man took Lyell's
Principles of Geology with him on his voyage on the " Beagle " and read
it with the greatest devotion, as is evidenced by his dedication of the
journal of his voyage: "To Charles Lyell, Esq., F.R.S*., this second
edition is dedicated with grateful pleasure, as an acknowledgment
that the chief part of whatever scientific merit this Journal and other
works of the author may possess, has been derived from studying the
well-known, admirable Principles of Geology. '^
Malthus' influence on Darwin's ideas is well expressed by Judd
as follows :
"Fifteen months after this 'systematic inquiry' began [referring
to Darwin's exhaustive working over of his notes taken during his
voyage on the 'Beagle'], Darwin happened to read the celebrated
work of Malthus 'On Population' for amusement, and this served as a
spark falling on a long prepared train of thought. The idea that as
animals and plants multiply in geometrical progression, while the
supplies of food and space to be occupied remain nearly constant,
and that this must lead to a struggle for existence of the most desperate
kind, was by no means new to Darwin, for the elder De Candolle,
Lyell, and others had enlarged upon it; yet the facts with regard to
24 EVOLUTION, GENETICS AND EUGENICS
the human race, so strikingly presented by Malthus, brought the
whole question with such vividness before him that the idea of
'Natural Selection' flashed upon Darwin's mind."
CHARLES DARWIN (1809-82)
Charles Darwin is without question the foremost figure in the
development of the evolution idea and probably in the development
of science in general. The publication of his book, The Origin oj
Species, in 1859, was the most important event in biological history.
As has been already shown, Darwin's chief ideas had been anticipated
not by one but by several of his predecessors. Nevertheless, he
was the first to furnish a really adequate proof of the fact of evolution
and his causo-mechanical theory to explain the method of evolution
was supported by a mass of systematically arranged data such as has
been paralleled neither before nor since. Darwin was the first evolu-
tionist effectively to employ the inductive method, that of everywhere
seeking facts first and then devising theories to fit the facts. He
never allowed speculation to outstrip observation, as nearly all of his
predecessors had done, but made theory await the amassing of facts
in its support, until the accumulation of the latter seemed almost to
speak out the theory of themselves. Our greatest debt to Darwin is
due to his establishment of the factual basis of evolution; his selection
theory was relatively of minor significance in so far as its value in the
development of the evolution idea was concerned. Yet this latter
theory gained the widest acceptance among the scientifically inclined
during the entire post-Darwinian period. It has been viciously
assailed on all sides and has tottered repeatedly under the attacks
of well-trained adversaries. Some of the weaker elements of the
theory have given way under stress, and the whole selection factor
as a primary causal factor in evolution has been seriously called into
question ; but since Darwin's time the fact of evolution has been almost
universally accepted.
The story of Darwin's life is almost a romance. "Born in 1809, "
says Lull,^ "this emancipator of human minds from the shackles of
slavery to tradition saw the light of day upon the very day that
ushered in the life of Abraham Lincoln, the emancipator of human
bodies from a no more real physical bondage. Darwin studied first
at Edinburgh, but finding medicine unsuited to his tastes, entered
Christ's College, Cambridge, as a candidate for the church. His love
' Richard Swann Lull, Organic Evolution (The Macmillan Company, 19 17).
HISTORICAL ACCOUNT OF EVOLUTION THEORY 25
of Nature, however, dominated all other interests and shortly after
graduation an opportunity came to join the ship ' Beagle ' as naturalist
in a voyage of exploration around the world. The five years spent
upon this memorable journey, the narrative of which is so admirably
set forth in the book, A Naturalist's Voyage around theWorld, resulted
in the accumulation of the first of Darwin's great series of observations,
the final decision to devote his life to zoological research, and the
beginning of that illness which made him a life-long invalid. This
last factor necessitated a retired life and thus proved of indirect bene-
fit, as it enabled him to accomplish the immense amount of work
which he did without being impeded by the distractions of a public
career."
SUMMARY OF DARWIN'S THEORIES
Since tv^ro subsequent chapters are to be devoted to Darwinism,
only an outline of Darwin's theories need be presented in the present
historical account.
Although Darwin was an all-round biologist and gave attention
to practically every phase of evolutionary biology, he is known espe-
cially for his selection theories. There are three of these : the theory
of artificial selection, the theory of natural selection, and the theory of
sexual selection.
a) Artificial selection. — According to Darwin the commonest
method of producing, under human culture, new races of animals and
plants is that of selection. The breeder selects from among the highly
variable individuals of a parent-race those which possess the begin-
nings of desired modifications, and he breeds them together, expecting
that the offspring will show the desired character, some in a more
highly perfected condition, others in a less. The ones that vary
favorably are again selected for breeding stock, and the same process
is carried on until the desired character has been perfected.
Although we now know that this is far from being a typical experi-
ence among breeders, it appeared to Darwin to be so typical that he
transferred the selection idea from the breeder to Nature, making
Nature the selecting agency responsible for the production of natural
wild species. His argument is as follows:
b) Natural selection. — The following factors are involved:
1. All animals and plants tend to multiply in geometrical ratio.
2. There is not food or room for a much larger number of animals
and plants than now exist.
26 EVOLUTION, GENETICS, AND EUGENICS
3. All members of a species vary in many if not all directions.
4. Those that vary in the more favorable directions, so as better
to fit them to meet the conditions of life, survive in larger numbers than
those varying in less favorable directions. This is Spencer's " survival
of the fittest. "
5. The survivors of one generation become the parents of the next
and, therefore, the more favorable characters are passed on more
largely than the less favorable.
6. There is in each generation a slow but definite approach toward
complete adaptation to hfe-conditions.
7. Variations neither useful nor harmful would not be affected by
natural selection, and would be left either as fluctuating variations or
as polymorphic characters.
c) Sexual selection. — This theory was offered to supplement that
of natural selection, because Darwin considered the latter as inade-
quate to explain the facts of sexual dimorphism, or secondary sexual
characters. The theory is as follows: There is always a contest
among males for possession of females, in which the inferior males are
eliminated either because they are, on the one hand, less courageous
or weaker or less well equipped with weapons of combat, or because,
on the other hand, the more attractive males, whether on account
of colors, odors, phosphorescence, behavior, etc., would succeed in
winning mates from those less endowed. Thus would be enhanced the
sexual dimorphism until it reaches extremes in many cases that are
truly remarkable.
The name of Alfred Russell Wallace (1822-1913) will always be
associated with that of Charles Darwin as co-author of the theory of
natural selection. Wallace at the age of twenty-six went on a natural-
istic expedition, primarily for collecting specimens from new regions.
He covered almost the same ground as did Darwin in his voyage
on the "Beagle." Wallace had read Lyell's Principles of Geology,
Malthus' On Population, Chambers' Vestiges of Creation. While in
Sarawak he tells us: "I was quite alone with one Malay boy as cook,
and during the evenings and wet days, I had nothing to do but to look
over my books and ponder over the problem which was rarely absent
from my thoughts. " While thus engaged the idea of natural selection
came to him as though by a sudden flash of insight. When the idea
was still in process of formation he wrote it out on thin paper and
mailed it to Darwin, stating that he considered the idea new and
asking Darwin to show it to Lyell, who had expressed interest in a
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 27
former paper of Wallace. TKe ideas were expressed under the title
On the Tendency of Varieties to Depart Indefinitely from the Original
Type, and it proved to be an unusually concise and lucid statement of
the main points of the natural-selection theory. Darwin at once
wrote to Lyell as follows:
"I never saw a more striking coincidence; if Wallace had my
MS sketch, written in 1842, he could not have made a better short
abstract ! Even his terms now stand as heads of my chapters. Please
return to me the MS which he does not say he wishes me to pubUsh
but I shall, of course, at once write and offer to send it to any journal.
So all my originality, whatever it may amount to, will be smashed,
though my book, if it ever have any value, will not be deteriorated,
as all the labour consists in the appHcation of the theory, I hope you
will approve of Wallace's sketch, that I may tell him what to say."
Lyell insisted that Darwin publish an abstract of his own work
simultaneously with ttat of Wallace, and this course was carried out.
Darwin's generosity was equaled by that of Wallace who wrote, in
1870:
"I have felt all my life and still feel the most sincere satisfaction
that Mr. Darwin had been at work long before me, and that it was not
left for me to attempt to write The Origin of Species. I have long
since measured my own strength and know well that it would be quite
unequal to the task."
Still later he wrote: "I was then (and often since) the 'young
man in a hurry,' he [Darwin] the pamstaking student, seeking ever
the full demonstration of the truth he had discovered, rather than to
achieve immediate personal fame. "
One must perforce admit the nobility of character of both men;
but there can be no serious competition between the two for the honor
of being called the originator of the natural-selection theory.
CONTEMPORARY OPINION REGARDING THE VALIDITY OF DARWIN'S VIEWS
At first Darwin was inclined to believe that the selection factor
was all-sufficient to account for the origin of species, as well as that of
adaptations; but as time passed he modified his earlier more sanguine
views and came to the conclusion " that natural selection has been the
main but not the exclusive means of modification." Many of his
followers went to such extremes in their advocacy of the all-sufficiency
of natural selection as would not have met with Darwin's approval.
28 EVOLUTION, GENETICS, AND EUGENICS
"The first effect of Darwin's works," says McFarland/ "was to
carry the world of science by storm, but at the same time to arouse
intense hostility on the part of the theologians who found the theory
of descent .... incompatible with the doctrines of Creation. In
this conflict Darwin took no part, but was championed by Huxley,
while Bishop Wilberforce led the opposition. The battle was long
and bitter, there was much acrimonious writing on both sides, but
the theory of descent — the doctrine of evolution — was found to be
invulnerable and at present the theologians themselves have accepted
it and even make use of it in their own work,
"But as the years flew by the Darwinian doctrines began to meet
with assaults from the scientists themselves, who, having endeavored
to prove their vahdity, began to find them inadequate to the require-
ments of expanding knowledge. The question was asked, 'What is
the origin of the fittest ?' Given the fittest, we easily understand how
it is perpetuated, but how does it arise ? In the striking phrase of
someone: 'Natural selection might explain the survival of the fittest
but fails to account for the arrival of the fittest!'"
Darwin's main supporters during the most trying controversial
period were Herbert Spencer and Thomas H. Huxley.
Herbert Spencer (1820-1903) was an extremely able supporter of
the general theory of evolution, but was more definitely an advocate
of Lamarckism than of natural selection. His role was that of a
champion of the whole philosophy of evolution as opposed to special
creation, and it was largely due to his forceful writings that Darwinism
won the battle against dogmatism. Spencer tried to explain the
structure of protoplasm (Hving substance) on a physicochemical
basis. He thought of the structural units of protoplasm as compa-
rable with the molecules of chemical compounds, each local region
of the protoplasm in the organism being made up of different kinds of
units, which he called "physiological units. " This conception of the
physical basis of organic structure had a considerable influence in
shaping Darwin's ideas and was probably the basis of the latter's
provisional theory of "pangenesis." This theory was probably the
first consistently worked out theory of the mechanics of heredity.
It was thought that every part of the body is continually giving off its
particular kind of units ("gemmules") into the blood. These gem-
mules are transported by the blood stream to all parts of the body and
'J. McFarknd, Biology, General and Medical (The Macmillan Company,
1918).
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 29
collect in the germ cells. This was supposed to account for the fact
that from the germ cell will develop an organism like the parent in
various details. If a part of the body was modified through func-
tioning or through changed environment, it would have modified
gemmules, which, in turn, would go to the germ cells and carry over
the modification to the next generation. This theory was not satis-
factory even to Darwin and is now only of historical interest.
Spencer is best known in the history of the evolution theory as an
ardent neo-Lamarckian. He states his belief as follows: " Change of
function produces change of structure; it is a tenable hypothesis that
changes of structure so produced are inherited. " This idea prevailed
until it was cast down by Weismann.
Thomas Henry Huxley (1825-95), one of the keenest, most analyti-
cal thinkers of the nineteenth century, not only defended the general
doctrine of evolution against Bishop Wilberforce and his aids, but was
an able investigator in the fields of comparative anatomy and embry-
ology. "At the British Association at Oxford in i860," says Judd,
"after an American professor had indignantly asked 'Are we a
fortuitous concourse of atoms?' as a comment on Darwin's views.
Dr. Samuel Wilberforce, the Bishop of Oxford, ended a clever but
flippant attack on the Origin by enquiring of Huxley, who was present
as Darwin's champion, if it ' was through his grandfather or his grand-
mother that he claimed his descent from a monkey ? '
"Huxley made the famous and well-deserved retort : *I asserted —
and I repeat' — that a man has no reason to be ashamed of having an
ape for his grandfather. If there were an ancestor whom I should
feel ashamed of recalling, it would rather be a man — a man of restless
and versatile intellect — who not content with success in his own sphere
of activity, plunges into scientific questions with which he has no real
acquaintance, only to obscure them by aimless rhetoric, and distract
the attention of his hearers from the real point at issue by eloquent
digressions and skilled appeals to reUgious prejudice!'
"Hujdey himself accepted the theory of Natural Selection — but
not without some important reservations — these, however, did not
prevent him from becoming its most ardent and successful champion.
Darwin used to acknowledge Huxley's great service to him in under-
taking the defense of the theory — a defense which his own hatred of
controversy and state of health made him unwilling to undertake —
by laughingly calling him 'my general agent' while Huxley himself in
replying to the critics, declared he was 'Darwin's bulldog.'"
30 EVOLUTION, GENETICS, AND EUGENICS
Ernst Haeckel (1834-1919) was one of the earliest and most
influential followers of Darwin in Germany. In his Generelle Mor-
phologic, pubHshed in 1866, seven years after the Origin of Species
first appeared, he applied the doctrine of evolution, and especially
the theory of natural selection, to the whole field of vertebrate mor-
phology. Beyond question Haeckel overapplied the theory and in a
sense weakened its influence by his rather uncritical use of materials.
His writings have been translated into most languages and "are
popularly beheved to represent the best scientific thought on the
matter." Biologists today, however, are apt to look askance at
Haeckel's works and to consider that they did more harm than good
to Darwinism.
August Weismann (1834-1914) was the first really original
evolutionist after Darwin. Like other thinkers of his time, he realized
that further progress in the knowledge of the causal basis of evolution
lay in further investigation of the causes of variation and the phj-sical
basis of heredity. Weismann has been classed as a neo-Darwinian
because he was a strong advocate of some form of selection, but his
"selection" was not the selection of Darwin. Realizing that the
greatest weakness of the natural-selection theory lay in its inadequacy
as an originator of variations, he proposed the "germinal-selection"
theory. He contended that aU heritable variations have their origin
in the germ cell, and therefore that a new type of organism arises only
from a changed tjq^e of germ cell. The germinal-selection theory
stands out in striking contrast with Darwin's "pangenesis" theory.
The former is centrifugal, the latter centripetal. "Determiners" of
new characters, according to Weismann, arise in the germ plasm and
work outward to aU parts of the developing body; while the "gem-
mules," Darwin's equivalent of determiners, originate in the body
tissues and are carried to the germ cells in each generation. Accord-
ing to Weismann, there is a struggle among the determiners for the
available food and favorable positions in the germ cell, and those that
receive the most food and the best positions gain an initial advantage,
so that they are able to initiate the development of larger or more
perfectly adapted organs. The descendants through cell division of
these favored determiners are in a position to compete with other
determiners on a more favorable footing in each succeeding generation,
so that the character represented by them steadily increases in a Unear
or definitely directed fashion until it reaches the state of complete
adaptation or fitness. Such a character may even continue its direct
line of advance beyond the point of maximum fitness and result in
HISTORICAL ACCOUNT OF EVOLUTION THEORY 3 1
what are known as overspecializations. The theory therefore would,
if well founded, account not only for the initial stages of new adaptive
characters, but also for overspecializations, two phenomena that
natural selection was unable to account for. Not only were pro-
gressive evolutionary changes explained by germinal selection, bu<
regressive changes seemed to be even more readily accounted for on
this basis. In the struggle among determiners in the germ cell
some of the less favored units would be handicapped at the outset by
insufficient food or unfavorable position and would produce smaller or
less effective structures. Progressively, from generation to generation,
these weakened determiners would lose ground and become less and
less successful in competition until they were weaklings among
determiners and would be able to initiate only degenerate or vestigial
structures, or else would die out and lose their place altogether, thus
accounting for total losses of structures.
This theory does not exclude natural selection, but rather increases
its importance, for every structure that arises to the threshold of
utility or disutility meets the winnowing process of natural selection.
The fitter individuals survive in the long run and these perpetuate the
germ cells in which the successful determiners reside.
A slightly different explanation of degenerating structures in-
volves the principle of "panmixia. " According to this idea, changing
environmental conditions may render certain adaptive organs of
lessened value or of no value, as would be the case in the eyes of cave
animals. In different individuals the eye determiners would vary in
their success in competition with other determiners, and since natural
selection would no longer put a premium on perfect eyes, all grades of
eyes would be equally inherited and gradually the poorer or degenerate
eyes would become more numerous, till finally there would be no
good eyes in the race. Thus it will be seen that the germinal-selection
theory was auxiliary to natural selection and tended to support the
latter at two of its weakest points. But the supporting theory itself
has the fundamental weakness of lacking a factual basis. It is purely
hypothetical and cannot be put to an experimental test. Every
time an objection to the theory was raised an auxiliary hypothesis
was added to explain away the difficulty, till finally it fell to the ground
through sheer top-heaviness, unable further to support its intricate
structure of interrelated hypotheses.
A much more valuable and lasting contribution of Weismann was
his theory of "germinal continuity" and of the "apartness of the germ
plasm. " The whole theory has come to be known as the " germ-plasm
32 EVOLUTION, GENETICS, AND EUGENICS
theory," which forms the framework of nearly all of our modem
genetics. According to this view the germ plasm is immortal in
that it is perpetuated from generation to generation through the
instrumentality of mitotic cell division, each germ cell being the prod-
uct of the division of a previous germ cell back to the first germ cell
that arose at the dawn of life. Thus a germ cell cannot be a product
of the soma, but the soma is the product of germ cells. The soma loses
its generalized characters and specializes in various ways. Once
specialized, soma cells are believed to have lost their capacity to play
a germinal role. Specialization means mortality. Thus the relation-
ship between parent and offspring is not that the parent gives rise to
the offspring, but that the same germ plasm gives rise to both parent
and offspring.
The logical conclusion to which this line of reasoning leads is that
the changes in the soma, no matter how produced, are helpless to
produce any effect upon the germ plasm, since germ cells come only
from germ cells and not from soma cells. Consequently Weismann
led the assault against Lamarckism and won the day so conclusively
that even in these modern times few biologists have the temerity to
express aloud any definite belief in the inheritance of acquired charac-
ters. Weismann's germ-plasm idea is the cornerstone of modern
genetics, though there are some forward-looking biologists who, looking
at things with a physiological bias, cannot make themselves beheve in
the total independence of any tissue — even the sacred germ plasm.
Weismann's influence was very great, especially during the last
decade of the nineteenth century, and his theories gave rise to an
immense amount of research, chiefly of a cytological and embryo-
logical character.
ISOLATION THEORIES
Among the theories subsidiary to natural selection as an aid to
species forming are the various isolation theories. One of the weak-
nesses inherent in natural selection had to do with the probable
swamping out of new types by promiscuous breeding with the more
numerous individuals of the older types. "Anything," says Metcalf,
"which divides a species into groups, which do not freely interbreed,
is said to segregate (isolate) the members of the species into these sub-
divisions."
Some American writers, especially Jordan and Kellogg, Gulick, and
Crampton, have dealt with the isolation factor in evolution and believe
HISTORICAL ACCOUNT OF EVOLUTION THEORY 33
that it is a major factor of as great importance in species forming, or
aearly so, as natural selection. But the prevailing opinion seems to be
that isolation is really a kind of selection, more like artificial selection
than anything else, which separates out certain pure lines and prevents
promiscuous interbreeding. Various agents are known to produce
isolation by erecting barriers to interbreeding between groups of
individuals within a species. These segregative factors may be
geographical, climatic, reproductive, physiological, or, in plants, the
result of soil diversity. Thus a mountain range, on the two sides of
which a species migrates, effectively separates the species into two
independent groups. Heat, cold, moisture, etc., separate others.
Reproductive incompatibility between new and older types is equally
effective, as is assortative mating of like with like. Like natural selec-
tion, isolation has nothing to do with the origin of new types, but
merely aids in the preservation of types when once formed. Were
there not spontaneous variations among animals and plants, there
would be nothing to isolate. Therefore isolation plays only an
auxiliary role, helping to preserve new races once they are formed.
ORTHOGENESIS THEORIES
"The orthogenetic evolution theories of various authors, based
upon the assumed occurrence of variations in determinate lines or
directions (a restricted and determinate variation as compared with
the nearly infinite, fortuitous, and indeterminate variation assumed
in the selection theories), are of several types. The mention of two
wUl reveal pretty well the more important characters of all. Not a
few biologists have always believed in the existence of a sort of mystic,
special vitahstic force or principle by virtue of which determination
and general progress in evolution is chiefly fixed. Such a capacity,
inherent in living matter, seems to include at once possibility of pro-
gressive or truly evolutionary change. Not all evolution is in a single
direct line, to be sure; ascent is not up a single ladder or along a single
geological branch, but these branches are few (as indeed we actually
know them to be, however the restriction may be brought about)
and the evolution is always progressive, that is, toward what we,
from an anthropocentric point of view, are constrained to call higher
and higher or more ideal life stages and conditions.
"Other naturaUsts also seeming to see this source of determinate
or orthogenetic evolution, but not inclined to surrender their dis-
belief in vitalism, in forces over and beyond the familiar ones of the
34 EVOLUTION, GENETICS, AND EUGENICS
physicochemical world, have tried to adduce a definite causomechani-
cal explanation of orthogenesis. The best and most comprehensive
types of this explanation are those essentially Lamarckian in principle,
in which the direct influence of environmental conditions, the direct
reactions of the life stuff to stimuli and influences from the world
outside, are the causal factors in such an explanation. But while
every naturalist will grant that such factors do change and control
in a considerable degree the Ufe of the indi\ddual, most see no mechan-
ism or means of extending this control directly to the species. "
The above-quoted paragraphs from Jordan and Kellogg' will
serve to place before the reader the general ideas involved in the
orthogenesis conception. A brief account of the various special
theories of orthogenesis follows:
Carl von Ndgeli's ideas of orthogenesis involve a belief in a sort of
mystical principle of progressive development, a something, quite
intangible, that exists in organic nature, which causes each organism,
to strive for or at least make for specialization or perfect adaptation.
This idea of an inner driving and directing force reminds one of the
"entelechy" of Driesch, or Bergson's "creative evolution." Nageli
believed that animals and plants would have developed essentially
as they have without any struggle for existence or natural selection.
This form of orthogenesis theory, then, is alternative to natural
selection.
Theodore Eimer^s theory of orthogenesis is more scientific and less
mystical than Nageli 's. He believed that Hues of evolution were not
miscellaneous and haphazard, but were confined to a few definite
directions, determined at their initial stages not by natural selection
but by the laws of organic growth, aided by the inheritance of acquired
characters. A new character makes a beginning as would the first
step in a slow chemical change, or series of such changes, and it must
go through to a fixed end, under given conditions, just as surely as does
the chemical process. Only when a given character or Hne of evolu-
tion results in the production of a very positive advantage or dis-
advantage to the species does natural selection step in to interfere
with orthogenesis. The causes of orthogenesis are said "to lie in the
effects of external influences, climate, nutrition, or the given constitu-
tion of the organism."
Actual species-forming, or the breaking-up into specific units of
the orthogenetic lines of change, depends, according to Eimer, upon
' Jordan and Kellogg, Evolution and Animal Life (D. Appleton and Company).
HISTORICAL ACCOUNT OF EVOLUTION THEORY 35 •
three factors: a standstill or cessation of development on the part of
some lines; sudden development by leaps (practically mutations);
and hindrance or difficulty of reproduction (the type of thing that
Romanes emphasized as physiological isolation ten years later).
Eimer illustrated his theories by the evolution of color patterns in
lizards and those on the wings of butterflies. In both he beUeved that
longitudinal stripes were primitive, that rows of dots followed these
which were in turn followed by crossbands, reticular patterns, and
finally by solid coloration. This hypothetical phylogenetic order is
more or less closely paralleled by the ontogenetic order, in the
lizards at least.
It will be noted that Elmer's theory places natural selection in a
subordinate position, but does not dismiss it altogether, as is done by
Nageh. It aids natural selection in explaining adaptations in that it
furnishes for natural selection various characters of selective value,
which may be either perpetuated or eliminated according to their
utility.
E. D. Cope, a leading American palaeontologist of the past cen-
tury, had an orthogenetic theory involving his ideas of "bathmism"
(growth force), "kinetogenesis" (direct effect of use and disuse and
environmental influence), and " archaesthetism " (influence of primi-
tive consciousness). It may be said that his ideas were Lamarckian
throughout. In common with the majority of palaeontologists of
later date — Osbom, Williston, Hyatt, Smith, and others — Cope felt
the need of some factor other than natural selection to explain the
apparent steady progress of characters in definitely directed Unes as
seen in the fossils. It is natural therefore that palaeontologists almost
universally lay hold of both Lamarckian and orthogenesis ideas.
Charles Otis Whitman, who, until his death over ten years ago, was
considered the leading American zoologist, had strong leanings toward
orthogenesis. In one of his few publications he says:
"Natural selection, orthogenesis, and mutation appear to present
fundamental contradictions; but I believe that each stands for truth,
and reconciliation is not far distant. The so-called mutations of
Oenothera are indubitable facts; but two leading questions remain to
be answered. First, are these mutations now appearing, as is agreed,
independently of variation, nevertheless the products of variations that
took place at an earher period in the history of these plants ? Secondly,
if species can spring into existence at a single leap, without the assist-
ance of cumulative variations, may they not also originate with such
36 EVOLUTION, GENETICS, AND EUGENICS
assistance ? That variation does issue a new species, and that natural
selection is a factor, though not the only factor, in determining results,
is, in my opinion, as certain as that grass grows although we cannot
see it grow. Furthermore, I believe I have found indubitable evidence
of species-forming variation advancing in a definite direction (ortho-
genesis), and likewise of variations in various directions (amphi-
genesis). If I am not mistaken in this, the reconciliation for natural
selection, and orthogenesis is at hand."
In concluding this brief account of orthogenesis, it should be said
that definitely directed evolution is now believed to be one of the laws
of organic evolution, but that we have no clear ideas as yet as to what
are its underlying causes. Therefore orthogenesis is not a causo-
mechanical theory of evolution at all.
MUTATION OR HETEROGENESIS THEORIES
The theory of "mutations" is associated with the name of Hugo
De Vries, the well-known Dutch botanist; that of "heterogenesis,"
with the name of H. Korchinsky, a Russian.
Though Korchinsky anticipated De Vries by several years, his
work was not supported by the large amount of experimental data
that characterized that of the great Dutch worker. The relative
claims for recognition as the founder of the mutation theory are
almost on a par with those of Darwin and Wallace for the natural-
selection theory. Both Darwin and De Vries held back their theo-
ries until they appeared to be adequately supported by personally
collected facts.
There is a striking parallelism between the ideas and conclusions
of De Vries and those of Korchinsky, and since this is true a resume of
De Vries's better-known work will serve to give the essentials of the
whole conception.
De Vries began his genetic experiments by a study of the variations
of plants in the field. After learning their normal variability in
nature, he transferred them to the experimental garden and there
attempted to improve them by selection. He found that the improved
living conditions due to better soil and cultivation induced a wider
range of variability in size, luxuriance, and fecundity. Such variations
were plus or minus in their character, fluctuating about a mean or
average. It was exactly this type of variability that Darwin empha-
sized as the raw material of evolution; but De Vries found by experi-
ment that selection had no permanent hereditary effect when based
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 37
to fluctuating variations, since the latter were merely somatic responses
on variable growth conditions. This negative finding led him to
renewed interest in discontinuous or saltatory variations as the only
alternative to fluctuating or continuous variations.
He looked far and wide among species of wild plants for a species
that might exhibit a significant amount of saltatory variation and
finally discovered in the evening primrose (Oenothera lamarckiana)
what seemed to exhibit exactly the hoped-for characteristics. This
large, stately plant with conspicuous yellow blooms had escaped from
cultivation and was growing wild in the fields. In addition to a large
number of plants that showed only minor differences among them-
selves, De Vries found several individuals growing among the typical
individuals which differed not merely in degree but in kind. These
were as different as distinct varieties, and, when the seeds were
planted in the garden they bred true to their kind. The only ques-
tion now was whether they had actually arisen from typical parents.
To test this possibility, seeds of several typical plants were planted
in the garden; the result being not only a repetition of the pecuhar
types observed in the field, but of about a dozen other true breed-
ing types with well-marked differences from the parent-spedes and
among themselves.
These new types De Vries considered as new elementary species
and he called them "mutants." They came into existence suddenly
in one generation and, as a rule, bred true. Whatever factors were
responsible for mutations, the seat of origin must have been in the
germ cell and not in the soma. Consequently they were inherited
fully from the start. The same mutations occurred in considerable
numbers and in successive years. In one case a given mutation
occurred only once in eight years of observation. Some mutants
were robust and successful, others were weak and incapable of hving
under natural conditions, others were sterile. On the basis of these
results, which are reported in detail in chapter xxiv, De Vries came
to the conclusion that evolution was based upon the sudden appear-
ance of new varieties or elementary species and not upon the natural
selection of fluctuating variations.
The mutation theory compared and contrasted with the natural
selection theory. — It wUl be recalled that the raw material upon which
natural selection works is the minute individual or continuous varia-
tion that is universal in all living forms and is known to be largely
somatic in character and due to differences in environment. Darwin
38 EVOLUTION, GENETICS, AND EUGENICS
did not distinguish between somatic and germinal variations. The
essential feature of mutations is that they are germinal in origin and
therefore come forth full-fledged in the first generation arising from
the changed germ. Darwin recognized "saltatory variations" or
"sports," which are mutations, but did not consider them of suffi-
ciently frequent occurrence to furnish an adequate material for
selection.
De Vries, on his side, did not discard the principle of selection,
but showed that selection acted as between mutants, serving to elimi-
nate those which are unfit and allowing the sufficiently fit to survive
alongside the parent-types. According to Darwin's view, the new
types arose only at the expense of the old, for only through the eUmina-
tion of the old (less fit) types could the new types progress toward
further fitness. Darwin's view was ill suited to explain the origin of
new distinct types, because the process of selection proceeded by
imperceptible steps. De Vries's view gives us distinctly different,
pure breeding types at once that, if isolated, would be new elementary
species from the first.
In conclusion it may be said that the mutation theory was at
first intended as a substitute for natural selection, but that later the
selection idea was adopted as a directive principle, guiding mutations
toward adaptiveness.
THE RISE AND VOGUE OF BIOMETRY
No historical account of the development of the evolution idea
would be complete without a statement of the role played by biometry
in the study of evolutionary data. Biometry is the statistical study
of variation and heredity. During the last decade of the nineteenth
century it became obvious to those who had followed the progress
of the subject that farther advance toward the solution of .the
problem of the causes of evolution must come from a better under-
standing of variation and heredity, the two fundamental factors
involved. Three main modes of attack were developed during these
years: the statistical (biometry), the experimental (chiefly breeding
work), and the microscopical (cytology or the study of the minute
structure of the germ cells).
Sir Francis Gallon, a cousin of Charles Darwin, was the founder
of biometry. He applied certain already understood principles that
had been developed mainly in the study of the laws of chance to the
study of variations, and, by comparing the boiled-down formulas
HISTORICAL ACCOUNT OF EVOLUTION THEORY 39
resulting from his computations of parental generations with those of
offspring, he arrived at two laws of heredity: the law of fiUal regres-
sion, and that of ancestral shares of inheritance. The essence of the
first was that the offspring of exceptional parents tend to regress
toward mediocrity in proportion to the degree of parental excep-
tionalness. The second law was really explanatory of the first, for it
was found that the offspring inherit not only from parents, but from
the various grades of ancestors, and it was the pulldown of a miscel-
laneous ancestry that made for regression toward mediocrity. It
appeared that half of the hereditary influence could be assigned to
parents, half of the remainder to grandparents, half of the remaining
remainder to great-grandparents, and so on down the line,
Karl Pearson, a pupil and follower of Galton, has carried the study
of biometry to a more highly refined state. His attempt has been to
apply to the study of evolution the precise quantitative methods which
are used in physics and in chemistry. While much of Pearson's work is
far beyond the range of the average professional biologist today, it
is extremely useful as a tool in handling data in which great accuracy
is demanded. Frequently, however, the methods are far too refined
for the materia], and much time is wasted in handling crude data
by means of highly refined instruments of measurement and ultra-
accurate mathematical methods.
On the whole the contributions of biometry to our understanding
of the causes of evolution are rather disappointing. About the only
clean-cut finding has been the discovery that some variations are
continuous and others discontinuous. The former are capable of being
expressed in a single curve with a single mode, while the latter are
expressed in bimodal or polymodal curves. If material is homo-
geneous to start with it is likely to give monomodal curves, but if it is
heterogeneous, its heterogeneity will be revealed by the plural modes.
In a subsequent connection (chapter xxv) some further account of the
details of biometry will be presented. We must for the present be
content with having placed biometry in its setting as one step in the
advance of the evolution idea.
MODERN EXPERIMENTAL EVOLUTION
"While De Vries," says Castle,* "was engaged in his studies of the
evening primrose he hit upon an idea far more important, as most
biologists now believe, than the idea of mutation, though De Vries
' W. E. Castle, Genetics and Eugenics (Harvard University Press, 1920), p. 82.
40 EVOLUTION, GENETICS, AND EUGENICS
himself, both before and smce, has seemed to regard it as of mmor
importance. HecSilledthis the 'law of splitting of hybrids.' The same
law, it is claimed, was independently discovered about the same time
by two other botanists, Correns in Germany, and Tschermak in
Austria. Further, historical investigations made by De Vries showed
that the same law had been discovered and clearly stated many years
previously by an obscure naturalist of Briinn, Austria, named Gregor
Mendel, and we have now come to call this law by his name, MendeVs
Law. Mendel was so little known when his discovery was published
that it attracted little attention from scientists and was soon forgotten,
only to be unearthed and duly honored years after the death of its
author. Had Mendel lived forty years later than he did, he would
doubtless have been a devotee of biometry, for he had a mathematical
type of mind and his discovery of a law of hybridization was due to the
fact that he applied to his biological studies methods of numerical
exactness which he had learned from algebra and physics. In biology
he was an amateur, being a teacher of the physical and natural sciences
in a monastic school at Briinn. Later he became head of the
monastery and gave up scientific work, partly because of other duties,
partly because of failing eyesight."
There had been plant-hybridizers before Mendel, but their lack
of exactness in technique had prevented them from discovering the
law of segregation or splitting of hybrids.
Joseph Gottlieb Kolreuter (1733-1806), who really belonged to the
period of Lamarck, barely missed making the discovery that was
afterward made by Mendel. The salient features of his work are
according to Castle:^
** I, KSlreuter estabUshed the occurrence of sexual reproduction in
plants by showing that hybrid offspring inherit equally from the
pollen plant and the seed plant.
" 2. He showed that hybrids are commonly intermediate between
their parents in nearly all characters observed, such for example as
size and shape of parts.
"3. Many hybrids are partially or wholly sterile, especially when
the parents are very dissimilar (belong to widely distinct species).
Such hybrids often exceed either parent in size and vigor of growth.
"4. Kolreuter did not observe the regular splitting of hybrids
which Mendel and De Vries record, but some of his successors did,
particularly Thomas Knight (1799) and John Goss (1822) in England,
' Op. cit., p. 86.
mSTORICAL ACCOUNT OF EVOLUTION THEORY 41
who were engaged in crossing the garden peas with a view to producing
more vigorous and productive varieties, and Naudin (1862) in France,
who made a comprehensive survey of the facts of hybridization in
plants and came very near to expressing the generalization which
Mendel reached four years later."
Mendel's laws
"The earliest experimental investigations of heredity," says
Locy' in a concise summary of Mendel's work, "were conducted with
plants, and the first epoch-making results were those of Gregor Mendel
(1822-1884), a monk and later abbot, of an Augustinian monastery at
Briiim, Austria. In the garden of the monastery, for eight years
before pubhshing his results, he made experiments on the inheritance
of individual (or unit) characters in twenty-two varieties of garden
peas. Selecting certain constant and obvious characters, as color, and
form of seed, length of stem, etc., he proceeded to cross these pure
races, thus producing hybrids, and thereafter, to observe the results of
self-fertilization among the hybrids.
"The hybrids were produced by removing the unripe stamens of
certain flowers and later fertilizing them by ripe pollen from another
pure breed having a contrasting character. The results showed that
only one of a pair of unit characters appeared in the hybrid of the next
generation, while the other contrasting character lay dormant. Thus,
in crossing a yellow-seeded with a green-seeded pea, the hybrid genera-
tion showed only yellow seeds. The character thus impressing itself
on the entire progeny was called dominant, while the other that was
held in abeyance was designated recessive.
" That the recessive color was not blotted out was clearly demon-
strated by allowing the hybrid generation to develop by self-fertiliza-
tion. Under these circumstances a most interesting result was
attained. The filial generation, derived by self-fertilization among
the hybrids, produced plants with yellow and green seeds, but in the
ratio of three yellow to one green. All green-seeded individuals and
one-third of the yellow proved to breed true, while the remaining two
thirds of the yellow-seeded plants, when self-fertilized, produced
yellow and green seeds in the ratio of three to one.
" Subsequent breedings gave an unending series of results similar
to those obtained with the first filial generation.
' William A. Locy, The Main Currents of Zoology (Henry Holt & Company,
igi8), pp. 37-30-
42 EVOLUTION, GENETICS, AND EUGENICS
"This great principle of alternative inheritance was exhibited
throughout the extensive experiments of Mendel, and it is now recog-
nized as one of the great biological discoveries of the nineteenth
century."
The essential feature of Mendel's discovery was not the phenome-
non of dominance, for relatively few instances of pure dominance have
been discovered; but it was the phenomenon of segregation. By
segregation is meant that although determiners for opposed heredi-
tary characters derived from diverse parental sources may unite in a
common germ plasm for one generation, they segregate out pure, or
unmodified by their association together, in the next and subsequent
generations. This law of segregation depends on the idea that the
germ cell is composed of bundles of separately inheritable unit charac-
ters, which may be paired or grouped, shuffled and redealt like cards,
so as to give an infinite number of permutations and combinations
without affecting the imit determiners themselves.
From the evolutionary standpoint it is supposed that new unit
characters arise by mutations and are fully hereditary. They cannot
be swamped out by interbreeding unless they are recessive, for they
wUl dominate the old characters. Even recessive characters could be
perpetuated by segregation, or by the union of two individuals possess-
ing the determiner in the recessive condition as well as the dominant.
Thus a knowledge of the behavior of unit characters in heredity
reveals part of the mechanism for conserving new characters if they are
advantageous or even sufficiently fit to survive.
New types or species might arise through processes of hybridiza-
tion and the survival of individuals possessing the most favorable
combinations of characters.
" Evolution from this point of view," says Morgan,' "has consisted
largely in introducing (by mutations) new factors that influence
characters aheady present in the animal or plant.
"Such a view gives us a somewhat diflferent picture of evolution
from the old idea of a ferocious struggle between the individuals of a
species with the survival of the fittest and the annihilation of the less
fit. Evolution assiunes a more peaceful aspect. New advantageous
characters survive by incorporating themselves into the race, improv-
ing it and opening to it new opportunities. In other words, the
emphasis may be placed less on the competition between the indi-
' T. H. Morgan, A Critique of the Theory of Evolution (Princeton University
Press, 1916), pp. 87, 88.
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 43
vdduals of a species (because the destruction of the less fit does not
in itself lead to anything that is new) than on the appearance of new
characters and modifications of old characters that become incorpo-
rated in the species, for on these depends the evolution of the
race."
HYBRIDIZATION AND THE ORIGIN OF SPECIES
As a consequence of the great interest aroused by Mendel's
hybridization experiments the question has arisen as to the role of
hybridization in organic evolution. Certain it is that a vast number
of animal and plant races now existing are mixed or hybrid in nature
and are continually spUtting up into various Mendelian segregates.
How many pure races are there today ? Some authors think that no
variable races today are pure. Lotsy goes so far as to claim and
attempt to prove that unit characters are fiuxed and that the only
source of variation is hybridization, or amphimixis. Biologists today
would not be willing to go thus far with Lotsy, but it seems beyond
question that hybridization has played an important role in the pro-
duction of very many groups now Hving. It is of interest to recall
that Liimaeus, though a special creationist, admitted the possibility
of the origin of new species by hybridization.
NEO-MENDELIAN DEVELOPMENTS
Since the rediscovery of Mendel's paper by De Vries and its perusal
by thousands of biologists the world over, Mendelian breeding experi-
ments with all maimer of animals and plants has been the ruling
passion of geneticists. Among the leading neo-Mendelians are Bate-
son, Morgan, Castle, Correns, East, Hurst, Shull, Tschermak, and the
pupils of these.
Perhaps the first two mentioned, Bateson and Morgan, have con-
tributed most largely to an imderstanding of the intricacies of the
Mendelian operations. Bateson has become so imbued with the idea
that all mutations are the result of the loss of factors that he proposes
the hypothesis that " evolution has taken place through the steady loss
of inhibiting factors," as Morgan puts it. "Living matter was
stopped down, so to speak, at the beginning of the world. As the
stops are lost, new things emerge. Living matter has changed only in
that it becomes simpler." It is quite probable that Bateson, in pro-
posing so radical a view, intended to be taken only half-seriously.
Apart from this, his best-known expression of opinion, Bateson is the
44 EVOLUTION, GENETICS, AND EUGENICS
author of a large amount of fine work in genetics and will rank high
in the history of the subject.
T. H. Morgan, our leading American geneticist, is best known for
his researches into the mechanism of Mendelian inheritance. Through
the statistical study of ratios and linkages of characters in the fruit fly
Drosophila, it has been possible to chart the localities of the deter-
miners or genes of at least 250 mutant characters. He has shown that
four linked groups of genes exist, corresponding to the four kinds of
chromosomes of the germ cells; one of these groups is sex-linked and
is therefore to be assigned to the X-chromosome of the mutant male.
Two other large groups are to be located in the two large autosomes,
and one very small group is assumed to be located in the microsome.
Not only have characters, or their determiners, been assigned to given
chromosomes, but they have been located in a linear series on a given
chromosome. So accurately have these loci been determined that
they may be used to predict unknown breeding ratios. It would
seem that when a theory serves so well that it may be used to predict
the results of experiments, such a theory must be founded on facts.
Morgan and his collaborators in genetics are now convinced that they
have discovered the actual mechanism of heredity in the behavior of
the chromosomes in maturation and fertilization and that it is unex-
pectedly simple. Their views have aroused considerable opposition,
but they have apparently met successfully all attacks up to the present.
If it be true that the actual machinery of variation and heredity has
Deen discovered, we are farther along in our understanding of the
causo-mechanical basis of evolution than we could have hoped to be
at so early a date.
HEREDITY AND SEX
Since Darwin's theory of sexual selection, sex has been a compli-
cating factor in evolutionary theories, and one of the chief advances
of the present century has been in connection with the factors con-
trolling sex determination and sex differentiation. The evolution of
sex has also been a subject for considerable research.
It now appears that sex is an inherited Mendelian character, the
determiner of which is carried in a definite chromosome or group
of chromosomes. Cytological examination of germ cells, under the
able leadership of E. B. Wilson, has now made it certain that sex, if
not directly the result of the presence or absence of specific chromo-
somes, at least is absolutely correlated with such chromosomes. It
appears, however, that the sex which is settled by the chromosome
fflSTORICAL ACCOUNT OF EVOLUTION THEORY 45
mechanism at the time of fertilization may or may not realize its
normal somatic differentiation, depending upon the presence or
absence of the proper environment. Cases are on record in which an
individual germinally determined as a female may be caused to
develop the secondary sexual characters of the male, or even to pro-
duce sperms instead of eggs. A great deal of extremely interesting
work on sex control and sex reversals has been done within the last
half-dozen years and new discoveries are being made almost daily. In
fact, it might be said that the genetic study of sex marks the high-tide
level of modern genetic advance.
THE EXPERIMENTAL INDUCTION OF HEREDITARY VARIATIONS
With the problem of the mechanism of the heredity of individual
differences solved, at least in its more important essentials, attention
has gradually shifted to the problem as to how individual differences
arise. They seem to arise suddenly and as though of their own accord,
and the study of their heredity does not throw much Hght on the prob-
lem of their origin. At the present time a massed attack is being made
upon the problem of the mode or modes of origin of new hereditary
characters. This inquiry strikes at the very roots of the causo-
mechanics of evolution, and it is essential that the attack upon this
problem be followed up with the utmost vigor if we are to make any
real progress in our analysis of the how and why of evolution. Some
progress has been made already, but it is the expectation of the writer
that the next two or three decades will be characterized by as impor-
tant discoveries in this field as those that have been made in the field
of heredity during the past two or three decades. When that problem
shall have been solved, it will be well to attack, in the light of these
results, the problem of how the genes produce or effect the develop-
ment of the characters of the embryo, the larva, and the adult.
When we know this we shall be in a position to attack some of the ulti-
mate problems of biology that must await the accession of such new
knowledge before their solution can be attempted.
THE PRESENT ATTACK UPON EVOLUTION IN THE UNITED STATES
The present highly advertised attack upon the validity of the
principle of evolution by certain individuals and religious bodies is
hardly to be considered as forming a part of the history of the science,
but it is significant as an influence that may serve either greatly to
accelerate or to retard the progress of our science. The writer's own
experience is that the controversy has greatly enhanced popular inter-
46 EVOLUTION, GENETICS, AND EUGENICS
est in this subject, as evidenced by the growing demand for books on
evolution and aUied subjects and the marked increase in the numbers
of students in the colleges who wish to elect courses along these lines.
CONCLUDING REMARKS
Now that we have traced the evolution of the science of organic
evolution from its crude beginnings among the Greeks up to the
present, we are in a position to go back and make a systematic study
of some of the more important phases of evolutionary science.
Charles Darwin found it necessary to prove the fact of organic evolu-
tion before attempting to discover its causes. His method of proof
was to marshal a great array of facts which agree with the idea of
descent with modification; and we shall follow Darwin's method in
the subsequent chapters deahng with the evidences of evolution.
Note. — In the first half of the present historical account many short passages
are presented in quotation marks without mentioning the source of the quotation.
In all such cases it will be understood that these passages are from H. F. Osborn's
book. From the Greeks to Darwin (The Macmillan Company).
CHAPTER III
*rHE RELATION OF EVOLUTION TO MATERIALISM'
Joseph Le Conte
It is seen in the sketch given in the previous chapter that, after
every struggle between theology and science, there has been a read-
justment of some beliefs, a giving up of some notions which really had
nothing to do with religion in a proper sense, but which had become
so associated with reUgious belief as to be confounded with the latter —
a giving up of some hne of defense which ought never to have been
held because not within the rightful domain of theology at all. Until
the present the whole difficulty has been the result of misconception,
and Christianity has emerged from every struggle only strengthened
and purified, by casting off an obstructing shell which hindered its
growth. But the present struggle seems to many an entirely different
and far more serious matter. To many it seems no longer a struggle
of theology, but of essential religion itself — a deadly hfe-and-death
struggle between religion and materialism. To many, both skeptics
and Christians, evolution seems to be synonymous with blank mate-
riahsm, and therefore cuts up by the roots every form of rehgion by
denying the existence of God and the fact of immortality. That the
enemies of religion, if there be any such, should assume and insist on
this identity, and thus carry over the whole accumulated evidence of
evolution as a demonstration of materialism, although wholly imwar-
ranted, is not so surprising; but what shall we say of the incredible
folly of her friends in admitting the same identity!
A Uttle reflection wUl explain this. There can be no doubt that
there is at present a strong and to many an overwhelming tend-
ency toward materiaUsm. The amazing achievements of modem
science; the absorption of intellectual energy in the investigation of
external nature and the laws of matter have created a current in that
direction so strong that of those who feel its influence — of those who
do not stay at home, shut up in their creeds, but walk abroad in the
Ught of modern thought — it sweeps away and bears on its bosom all
* From J. Le Conte, Evolution (copyright 1888). Used by special permission
of the publishers, D. Applcton & Company.
47
48 EVOLUTION, GENETICS, AND EUGENICS
but the strongest and most reflective minds. Materialism has thus
become a fashion of thought; and, Hke all fashions, must be guarded
against. This tendency has been created and is now guided by
science. Just at this time it is strongest in the department of biology,
and especially is evolution its stronghold. This theory is supposed by
many to be simply demonstrative of materiaUsm. Once it was the
theory of gravitation which seemed demonstrative of materiahsm.
The sustentation of the universe by law seemed to imply that Nature
operates itself and needs no God. That time is passed. Now it is
evolution and creation by law. This will also pass. The theory seems
to many the most materiahstic of all scientific doctrines only because
it is the last which is claimed by materiaUsm, and the absurdity of the
claim is not yet made clear to many.
The truth is, there is no such necessary connection between evo-
lution and materiahsm as is imagined by some. There is no dif-
ference in this respect between evolution and any other law of Nature.
In evolution, it is true, the last barrier is broken down, and the
whole domain of Nature is now subject to law; but it is only the
last; the march of science has been in the same direction all the time.
In a word, evolution is not only not identical with materiahsm, but,
to the deep thinker, it has not added a feather's weight to its proba-
bihty or reasonableness. Evolution is one thing and materiahsm
quite another. The one is an estabhshed law of Nattu-e, the other an
unwarranted and hasty inference from that law. Let no one imagine,
as he is conducted by the materialistic scientist in the paths of evo-
lution from the inorganic to the organic, from the organic to the
animate, from the animate to the rational and moral, until he lands,
as it seems to him, logically and inevitably, in universal material-
ism — let no such one unagine that he has walked aU the way in
the domain of science. He has stepped across the boundary into
the domain of philosophy. But, on account of the strong tendency
to materialism and the skilful guidance of his leaders, there seems
to be no such boimdary; he does not distinguish between the induc-
tions of science and the inferences of a shallow philosophy; the
whole is accredited to science, and the final conclusion seems to
carry with it all the certamty which belongs to scientific results.
The fact that these materiahstic conclusions are reached by some of
the foremost scientists of the present day adds nothing to then
probabihty. In a question of science, viz., the law of evolution, their
authority is deservedly high, but in a question of philosophy, viz.,
THE RELATION OF EVOLUTION TO MATERIALISM 49
materialism, it is far otherwise.. If the pure scientists smile when
theological philosophers, unacquainted with the methods of science,
undertake to dogmatize on the subject of evolution, they must
pardon the philosophers if they also smile when the pure scientists
imagine that they can at once solve questions in philosophy which
have agitated the human mind from the earliest times. I am anxious
to show the absurdity of this materialistic conclusion, but I shall try
to do so, not by any labored argument, but by a few simple illustra-
tions.
1. It is curious to observe how, when the question is concerning a
work of Nature, we no sooner find out how a thing is made than we
immediately exclaim: "It is not made at all, it became so of itself!"
So long as we knew not how worlds were made, we of course con-
cluded they must have been created, but so soon as science showed
how it was probably done, immediately we say we were mistaken —
they were not made at aU. So also, as long as we could not
imagine how new organic forms originated, we were willing to believe
they were created, but, so soon as we find that they originated by
evolution, many at once say: "We were mistaken; no creator is
necessary at all," Is this so when the question is concerning a work
of man ? Yes, of one kind — viz., the work of the magician. Here,
indeed, we beheve in him, and are delighted with his work, until we
know how it is done, and then all our faith and wonder cease. But
in any honest work it is not so; but on the contrary, when we under-
stand how it is done, stupid wonder is changed into intellectual
delight. Does it not seem, then, that to most people God is a mere
wonder-worker, a chief magician ? But the mission of science is to
show us how things are done. Is it any wonder, then, that to such
persons science is constantly destroying their superstitious illusions?
But if God is an honest worker, according to reason — i.e., according
to law — ought not science rather to change gaping wonder into
intelligent deUght, superstition into rational worship ?
2. Again, it is curious to observe how an old truth, if it come only
in a new form, often strikes us as something unheard of, and even as
paradoxical and almost impossible. A little over thirty years ago a
little philosophical toy, the gyroscope, was introduced and became
very common. At first sight, it seems to violate all mechanical laws
and set at naught the law of gravitation itself. A heavy brass wheel,
four to five inches in diameter, at the end of a horizontal axle, six oi
eight inches long, is set rotating rapidly, and then the free end of the
^O EVOLUTION, GENETICS, AND EUGENICS
axis is supported by a string or otherwise. The wheel remains
suspended in the air while slowly gyrating. What mysterious force
sustains the wheel when its only point of support is at the end of the
axle, six or eight inches away ? Scientific and popular literature were
flooded with explanations of this seeming paradox. And yet it was
nothing new. The boy's top, that spins and leans and will not fall,
although solicited by gravity, so long as it spins, which we have seen
all our lives without special wonder, is precisely the same thing.
Now, evolution is no new thing, but an old familiar truth; but,
coming now in a new and questionable shape, lo, how it startles us out
of our propriety ! Origin of forms by evolution is going on everywhere
about us, both in the inorganic and the organic world. In its more
familiar forms, it had never occurred to most of us that it was a
scientific refutation of the existence of God, that it was a demonstra-
tion of materialism. But now it is pushed one step farther in the
direction it has always been going — it is made to include also the origin
of species — only a little change in its form, and lo, how we start! To
the deep thinker, now and always, there is and has been the alterna-
tive — materialism or theism. God operates Nature or Nature
operates itself; but evolution puts no new phase on this old question.
For example, the origin of the individual by evolution. Everybody
knows that every one of us individually became what we now are by a
slow process of evolution from a microscopic spherule of protoplasm,
and yet this did not interfere with the idea of God as our individual
maker. Why, then, should the discovery that the species (or first
individuals of each kind) origmated by evolution destroy our belief
in God as the creator of species ?
3. It is curious and very interesting to observe the manner in
which vexed questions are always finally settled, if settled at all.
All vexed questions — i.e., questions which have taxed the powers of
the greatest minds age after age — are such only because there is a real
truth on both sides. Pure, unmixed error does not live to plague us
long. Error, when it continues to live, does so' by virtue of a germ of
truth contained. Great questions, therefore, continue to be argued
pro and con from age to age, because each side is in a sense — i.e.,
from its own point of view — true, but wrong in excluding the other
point of view; and a true solution, a true rational philosophy, will
always be found in a view which combines and reconciles the two
partial, mutually excluding views, showing in what they are true and
in what they are false — explaining their differences by transcending
THE RELATION OF EVOLUTION TO MATERIALISM
51
them. This is so universal and far-reaching a principle that I am sure
I will be pardoned for illustrating it in the homeliest and tritest fashion.
I will do so by means of the shield with the diverse sides, giving the
story and construing it, however, in my own way. There is, appar-
ently, no limit to the amount of rich marrow of truth that may be
extracted from these dry bones of popular proverbs and fables by
patient turning and gnawing.
We all remember, then, the famous dispute concerning the shield,
with its sides of different colors, which we shall here call white and
black. We all remember how, after vain attempts to discover the
truth by dispute, it was agreed to try the scientific method of investi-
gation. We all remember the surprising result. Both parties to the
dispute were right and both were wrong. Each was right from his
point of view, but wrong in excluding the other point of view. Each
was right in what he asserted, and each wrong in what he denied.
And the complete truth was the combination of the partial truths and
the ehmination of the partial errors. But we must not make the mis-
take of supposing that truth consists in compromise. There is an old
adage that truth lies in the middle between antagonistic extremes.
But it seems to us that this is the place of safety, not of truth. This is
the favorite adage, therefore, of the timid man, the time-server, the
fence-man, not the truth-seeker. Suppose there had been on the
occasion mentioned above one of these fence-philosophers. He would
have said: "These disputants are equally intelligent and equally
valiant. One side says the shield is white, the other that it is black;
now truth lies in the middle; therefore, I conclude the shield is gray or
neutral tint, or a sort of pepper-and-salt. " Do we not see that he is
the only man who has no truth in him? No; truth is no hetero-
geneous mixture of opposite extremes, but a stereoscopic combination
of two surface views into one solid reality.
Now, the same is true of all vexed questions, and I have given this
trite fable again only to apply it to the case in hand.
There are three possible views concerning the origin of organic
forms whether indi\adual or specific. Two of these are opposite
and mutually excluding; the third combining and reconciling. For
example, take the individual. There are three theories concerning
the origin of the individual. The first is that of the pious child who
thinks that he was made very much as he himself makes his dirt-pies;
the second is that of the street-gamin, or of Topsy, who says: "I was
not made at all, I growed"; the third is that of most intelligent
52 EVOLUTION, GENETICS, AND EUGENICS
Christians — i.e. , that we were made by a process of evolu tion. Observe
that this latter combines and reconciles the other two. and is thus the
more rational and philosophical. Now, there are also three exactly
corresponding theories concerning the origin of species. The first is
that of many pious persons and many intelligent clergymen, who say
that species were made at once by the Divine hand without natural
process. The second is that of the materialists, who say that species
were not made at all, they were derived, "they growed." The third
is that of the theistic evolutionists, who think that they were created
by a process of evolution — who believe that making is not incon-
sistent with growing. The one asserts the divine agency, but
denies natural process; the second asserts the natural process, but
denies divine agency; the third asserts divine agency by natural process.
Of the first two, observe, both are right and both wrong; each view is
right in what it asserts, and wrong in what it denies — each is right
from its own point of view, but wrong in excluding the other point
of view. The third is the only true rational solution, for it includes,
combines, and reconciles the other two; showing wherein each is right
and wherein wrong. It is the combination of the two partial truths,
and the elimination of the partial errors. But let us not fail to do
perfect justice. The first two views of origin, whether of the indi-
vidual or of the species, are indeed both partly wrong as well as
partly right; but the view of the pious child and of the Christian con-
tains by far the more essential truth. Of the two sides of the shield,
theirs is at least the whiter and more beautiful.
But, alas! the great bar to a speedy settlement of this question and
the adoption of a lational philosophy is not in the head, but in the
heart — is not in the reason, but in pride of opinion, self-conceit,
dogmatism. The rarest of all gifts is a truly tolerant, rational spirit.
In all our gettings let us strive to get this, for it alone is true wisdom.
But we must not imagine that all the dogmatism is on one side, and
that the theological. Many seem to think that theology has 2i" pre-
emptive right" to dogmatism. If so, then modern materialistic science,
has ^'jumped the claim." Dogmatism has its roots deep-bedded in the
human heart. It showed itself first in the domain of theology, because
there was the seat of power. In modern times it has gone over to the
side of science, because here now is the place of power and fashion.
There are two dogmatisms, both equally opposed to the true rational
spirit, viz., the old theological and the new scientific. The old clings
fondly to old things, only because they are old; the new grasps eagerly
THE RELATION OF EVOLUTION TO MATERIALISM 53
after new things, only because, they are new. True wisdom and true
philosophy, on the contrary, tries all things both old and new, and
holds fast only to that which is good and true. The new dogmatism
taunts the old for credulity and superstition; the old reproaches the
new for levity and skepticism. But true wisdom perceives that they
are both equally credulous and equally skeptical. The old is credulous
of old ideas and skeptical of new; the new is skeptical of old ideas and
credulous of new. Both deserve the unsparing rebuke of all right-
minded men. The appropriate rebuke for the old dogmatism has
been already put in the mouth of Job in the form of a bitter sneer:
"No doubt ye are the people, and wisdom shall die with you." The
appropriate rebuke for the new dogmatism, though not put into
the mouth of any ancient prophet, ought to be uttered — I will tmder-
take to utter it here. I would say to these modem materialists,
" No doubt ye are the men, and wisdom and true philosophy were
born with you."
Let it be observed that we are not here touching the general ques-
tion of the personal agency of God in operating Nature. This we shall
take up hereafter. All that we wish to insist on now is that the process
and the law of evolution does not differ in its relation to materialism
from all other processes and laws of Nature. If the sustentation of
the universe by the law of gravitation does not disturb our belief in
God as the sustainer of the universe, there is no reason why the origin
of the universe by the law of evolution should disturb our faith in God
as the creator of the universe. If the law of gravitation be regarded
as the Divine mode of sustentation, there is no reason why we should
not regard the law of evolution as the Divine process of creation. It
is evident that if evolution be materialism, then is gravitation also
materialism; then is every law of Nature and all science materialism.
If there be any difference at all, it consists only in this : that, as already
said, here is the last line of defense of the supporters of supernatural-
ism in the realm of Nature. But being the last line of defense —
the last ditch — it is evident that a yielding here implies not a mere
shifting of line, but a change of base; not a readjustment of details
only, but a reconstruction of Christian theology. This, I believe, is
indeed necessary. There can be little doubt in the mind of the
thoughtful observer that we are even now on the eve of the greatest
change in traditional views that has taken place since the birth of
Christianity. But let no one be greatly disturbed thereby. For
then, so now, change comes not to destroy but to fulfil all our dearest
54 EVOLUTION, GENETICS. AND EUGENICS
hopes and aspirations; as then, so now, the germ of living truth has,
in the course of ages, become so encrusted with meaningless traditions
which stifle its growth that it is necessary to break the shell to set it
free; as then, so now, it has become necessary to purge religious belief
of dross in the form of trivialities and superstitions. This has ever been
and ever will be the function of science. The essentials of rehgious
faith it does not, it cannot, touch, but it purifies and ennobles our
conceptions of Deity, and thus elevates the whole plane of religious
thought.
PART n
EVIDENCES OF OllGANIC EVOLUTION
CHAPTER IV
IS ORGANIC EVOLUTION AN ESTABLISHED PRINCIPLE ?
1. Is there definite proof of organic evolution ?
2. If so, what is the nature of the proof ?
3. What are the evidences of evolution, and in what ways do these
bear witness that evolution has occurred and is still occurring ?
Before presenting in any detail the several bodies of data that
constitute the "evidences of evolution," let us anticipate a little by
attempting to answer the three questions just propounded.
I. Reluctant as he may be to admit it, honesty compels the
evolutionist to admit that there is no absolute proof of organic
evolution. But, for that matter, there is no absolute proof of any-
thing that depends on records of past events. We have no absolute
proof that Caesar or Napoleon once lived, or fought, or conquered.
All we have are the accounts left by the historians which we accept
without question because they are the products of human thought and
imagination. There is no absolute proof for either of the more or less
directly opposed theories of the origin of the material universe: the
"nebular hypothesis" of Laplace, and the "planetesimal hypothesis"
of Chamberlin and Moulton. Both of these theories rest upon
exactly the same types of evidences as does the theory of organic evolu-
tion, viz., the amassing of facts which appear to be explicable on the
assumption that the one or the other theory is true. If all of the facts
are in accord with it, and none are found that are incapable of being
reconciled with it, a working hypothesis is said to have been advanced
to the rank of a proved theory. As yet it is impossible to say that
either of these theories as to the origin of the universe has been proved.
Yet there is much less popular opposition to the acceptance of these
theories as facts than there is to the general theory of organic evolu-
tion. Similarly, there are certain widely accepted theories of the
origin of the present conditions of the earth's crust, and its liquid and
gaseous envelopes. The accepted theory, as given us by Hutton and
especially by Lyell, is essentially an evolutionary theory and depends
for its proof on almost exactly the same types of evidence as does that
57
5^ EVOLUTION, GENETICS, AND EUGENICS
of organic evolution. The basis of the accepted theory of geological
evolution is the " uniformitarian doctrine" of Lyell, which assumes
that the key to the past lies in the present, that the changes that are
going on today are of the same order and kind as those of the past,
and, finally, that there is neither beginning nor end to the earth's
evolutionary history, but that a slow and orderly development has
gone on and will continue indefinitely. The proof of this conception
consists of an array of facts derived from a study of the earth's crust,
including its stratified structure, of traces of animal and plant hfe
preserved in the rocks, of observed changes in continental contours
going on today, of erosion going on in coasts and streams, and of a
considerable array of facts derived from a study of other worlds than
ours in the making. The theory of geologic evolution meets with
scarcely any opposition today, although its foundations are no more
securely based than are those of organic evolution.
In a sense the proofs of the atomic, ionic, and electron theories
are even less absolutely estabhshed than is that of organic evolution,
because no one has ever seen nor ever can see an atom, an ion, or an
electron. Chemical and physical fact ; are rationalized by assuming
the existence of these units with their various properties. The only
evidences of the existence of atoms, ions, and electrons appear in the
facts that, on the assumption that they exist, the whole array of
observed chemical and physical phenomena are rationalized and
bound together into a coherent, consistent, and intelHgible system.
In other words, with the atomic, ionic, and electron theories chemistry
and physics are highly rational sciences; without these theories the
phenomena of physics and chemistry would be a hopeless hodgepodge.
Yet who would say that these fundamental theories are absolutely
proved ?
The only type of proof of phenomena that cannot be directly
observed or that pertain to the remote past is circumstantial proof.
By analogy we conclude that certain changes took place thus and so
in the past because we observe similar changes going on today. Every
past event has left a trace, and it is the task of the historian, anti-
quarian, or evolutionist to discover and to interpret these traces. Some-
times the traces exist as vestiges in modern life and are meaningless
unless related to their origin in the past. The task of the student of
organic evolution is to gather all of the traces of past changes both in
hving creatures today and in the preserved remains of creatures of the
remote past. A collection of traces of evolution involves many
IS ORGANIC EVOLUTION ESTABLISHED ? 59
apparently unrelated bodies of phenomena. There are evidences of
evolution in the grouping of animals into phyla, classes, orders,
families, genera, species, varieties, and races; in the homologies tha»
exist in general structure and in particular organs between differen*^
groups of animals and plants; in the orderly process of ontogeny or
embryonic development of the individual; in actual blood relation-
ship, based upon chemical reactions; on the succession of extinct
animals and plants found as fossils imbedded in the geologic strata;
in the present geographical distribution of the various groups of
animals and plants, in the light of data derived from a study of
geological changes; and finally, in experimental evolution, which
involves the observation imder experimental control of changes in
organisms and the origin of new varieties or elementary species.
2. The nature of the proof of organic evolution, then, is this:
that, using the concept of organic evolution as a working hypothesis
it has been possible to rationalize and render intelligible a vast array
of observed phenomena, the real facts upon which evolution rests.
Thus classification (taxonomy), comparative anatomy, embryology,
palaeontology, zoogeography and phytogeography, serology, genetics,
become consistent and orderly sciences when based upon evolu-
tionary foundations, and when viewed in any other way they are
thrown into the utmost confusion. There is no other generalization
known to man which is of the least value in giving these bodies of
fact any sort of scientific coherence and unity. In other words, the
working hypothesis works and is therefore acceptable as truth until
overthrown by a more workable hypothesis. Not only does the
hypothesis work, but, with the steady accumulation of further facts,
the weight of evidence is now so great that it overcomes all intelligent
opposition by its sheer mass. There are no rival hypotheses except
the outworn and completely refuted idea of special creation, now
retamed only by the ignorant, the dogmatic, and the prejudiced.
3. In answer to the question, "What are the evidences of evolution
and in what ways do these bear witness that evolution has occurred
and is still occurring?" we may present an ordered Hst of subjects
that are to be taken up serially in detail. In connection with each of
these bodies of evidence the character of their witness-bearing will be
discussed.
Some of the evidences are more direct and freer from purely inter-
pretative construction than others. Some evidences are primary and
foundational; some are in themselves rather mconclusive, but serve
6o EVOLUTION, GENETICS, AND EUGENICS
to confirm other facts, and, when reinforced by other evidences, are
themselves strongly substantiated. Perhaps the crowning evidence
of the truth of evolution is that all of these diverse bodies or phenomena
invariably support one another and all point in the same direction and
to the same conclusion, viz., that organic evolution is a fact.
In the former edition of this book the evidences of evolution were
presented in a somewhat arbitrary order, the evidences that seemed to
furnish the most direct proof being, for pedagogical reasons, presented
first and the more controversial evidences last. Experience, however,
has shown that for an appreciation of the data from paleontology and
from geographic distribution the student must have a knowledge of
the principles of mo^ihology (comparative anatomy) and of classifica-
tion. We have, therefore, changed the order of presentation of the
evidences to one that has the authority of precedent. The order of
treatment will be as follows:
I. The fundamental assumption underlying all the evidences.
n. Comparative anatomy {homologies and vestigial structures) : the
evidence of the fact that structures in unlike organisms have a com-
mon plan and mode of origin; that changes have occurred that are in
some way related to changes in habit or environment.
in. Classification: the evidence that the present groups of animals
and plants have arisen by "descent with modification."
IV. Serology (blood-precipitation tests): the evidence that the
chemical specificity of the blood parallels taxonomic specificity.
V. Embryology (the doctrine of recapitulation) : the evidences that
the embryonic development of the individual follows the main out-
lines of the evolutionary history of its ancestors.
VI. Paleontology: the evidences afforded by a study of the distri-
bution in time (vertical distribution in the earth's strata) of the fossil
remains of extinct animals and plants.
VII. Geographic distribution: the evidences afforded by present
(also, to some extent, past) horizontal distribution of contemporaneous
animals and plants.
Vni. Genetics (experimental evolution): evidences that heritable
variations have occurred under observation in large numbers and in
many species of animals and plants, and that new varieties of animals
and plants have been produced by processes known to man and to a
large extent controlled by him.
CHAPTER V
THE FUNDAMENTAL ASSUMPTION UNDERLYING
ALL EVIDENCES OF EVOLUTION
Every science rests in last analysis upon certain postulates or justi-
fiable assumptions, certain verified or verifiable truths that must be
admitted before any progress can be made in gaining a further under-
standing of the content of that science. Geology, for example, must
assume as vahd the dynamical laws of Newton and the law of gravity,
as well as basic laws of chemistry. Biology assumes the validity of
the great laws of physics and chemistry, for biology is the fundamental
science of the transformations of form and of energy in Hving matter;
but, in addition, there are also some biological postulates that seem
to be so well established that they have come to be thought of as
truisms.
One of the truisms of biology is the famiUar fact that like produces
like. How surprised one would be if sparrows had anything but spar-
rows for offspring, or if two Caucasic parents were to have a Negro
child! Now, a careful survey of the situation reveals the fact that the
only assumption the evolutionist makes is no more nor less than a
logical extension of what the layman considers a truism or a self-evi-
dent fact, namely, that fundamental structural resemblance signifies
genetic relationship; that, generally speaking, the degree of closeness of
structural resemblance runs essentially parallel with closeness of kinship.
Most biologists would say that this is no longer an assumption, but
one of the best-estabhshed laws of Hfe. However obvious the validity
of this assumption may be, it is the plain duty of one who attempts to
justify the evolutionary prmciple to avoid taking any steps that are
open to the least bit of valid criticism. If we cannot rely upon this
assumption, which may be called the principle of homology, we can
make no sure progress in any attempt to establish the validity of
the principle of evolution.
The assumption we are now discussing is tantamount to an affirma-
tion of the fact of heredity. We rely upon this fact in our everyday life.
When we plant a certain kind of seed we expect to get a certain kind
of plant; when we breed a certain kind of dog we expect offspring
6i
62 EVOLUTION, GENETICS, AND EUGENICS
of the same breed. It would be a freak of nature were we to discover
any marked exception to the laws of heredity. Furthermore, our
ordinary daily contacts with other members of our own species have
taught us that, as a rule, the more closely alike people are, the more
closely are they related. We recognize that children of the same
family are more alike in their personal characteristics than are members
of the same race not so closely related. Whenever we see two people
whose resemblance is very great we assume a relatively close kinship.
Thus, everyone has had the experience of meeting two people so
strikingly alike that it is almost impossible to distinguish them apart,
and of immediately assuming that such persons are identical or dupli-
cate twins. Now the interesting thing about such twins is that they
are vastly more closely related than are ordinary brothers and sisters,
or even than are fraternal twins, who are only brothers and sisters
that happen to have been conceived and born simultaneously as the
result of the fertilization of two egg cells. For duplicate twins are the
products of the early division into two equivalent parts of a single
embryo derived from one fertilized egg. No closer kinship can well be
imagined than this, for the two individuals bear the same relationship
to each other as do the bilateral halves of one individual.
The writer has had an exceptional opportunity of determining the
exact degree of resemblance existing between separate offspring de-
rived from a single egg. It so happens that a peculiar species of
mammal, the nine-banded armadUlo of Texas, always gives birth to
four yoxmg at a time. These quadruplets are invariably all of the
same sex in a litter and are nearly identical even in their finest ana-
tomical details, such as the numbers and arrangements of the plates
and scales in the armor and the numbers of hairs in a given area of
the skin. A detailed study of the embryonic history of this species has
proved beyond any question that in every case the four young in a
litter result from a very early division of a single embryo derived from
a single fertilized egg (see Fig. 77). Large numbers of sets of quadru-
plets were studied statistically to determine the exact degree of their
resemblance to one another. A comparison of over two hundred sets
revealed the somewhat startling fact that on the average they were
over 93 per cent identical (more technically, they showed a coefficient
of correlation of over .93). The remarkable closeness of this degree
of resemblance may be fully appreciated when it is realized that the
only structural resemblance belonging to this order of closeness is that
existing between the right and left antimeric halves of a single indi-
ASSUMPTION UNDERLYING ALL EVIDENCES OF EVOLUTION 63
vidual, such as the right and left sides of your own face or your two
hands, and that the next degree of closeness of resemblance is that
between sibhngs (brothers and sisters), who are only 50 per cent identi-
cal (having a coefficient of correlation of only .5); while cousins of
various grades have proportionately lower and lower degrees of re-
semblance in exact ratio with their grades of kinship.
This, then, is a crucial test of the validity of the assumption that
closeness of resemblance is in proportion to closeness of kinship, for we
have in identical twins and in armadillo quadruplets the closest re-
semblance associated with the closest possible genetic relationship, and
we also see that there is an exact proportion between all other known
grades of kinship and their relative degree of resemblance.
Employing the principle of homology in a somewhat broader way,
and in a way that is hardly likely to be questioned even by the most
captious, we account for the common possession of certain structural
peculiarities by all members of a given kind or species of animal or
plant by saying that such characters have been derived from a com-
mon ancestor. It is only a short step in logic to conclude that two
similar kinds or species of animal have been derived one from the other
or both from a common ancestral species. Once having taken this
step, we are on the road that leads inevitably to an evolutionary in-
terpretation of natural groups. If the principle of heredity holds for
siblings (offspring of the same parents), for races, for species, where
are we to draw the line? It does not seem reasonable to admit that
structural resemblances between siblings, between races, between
species, are accounted for as the product of heredity, and to deny that
equally plain resemblances of essentially the same sort among the
species of a genus or among the genera of a family have a similar
hereditary basis. It is logically impossible to draw the line at any
level of organic classification and say that structural resemblance is
the product of heredity up to such and such a level, but that beyond
this arbitrarily chosen point heredity ceases to operate.
The principle of heredity and its necessary implications constitute
the only assumption that is necessary for the evolutionist to make in
order to go ahead on a sound basis with a presentation of the evidences
of evolution. Give him this one point, and he asks no further con-
cessions. And this is not so much of a concession as it might seem
at first blush, for the special creationist assumes more potency for
heredity than does the evolutionist, since he believes in descent with-
out modification, a sort of stereotyped heredity, slavishly duplicating
64 EVOLUTION, GENETICS, AND EUGENICS
forever a fixed set of structural patterns without variation or improve-
ment. Since, then, both special creationist and evolutionist find it
equally necessary to assume the principle of heredity, there should be
little argument on this score. But let the reader beware at this point
in the discussion, for if he admits the postulates already presented —
and how can he help but admit them? — he cannot avoid the inevit-
able conclusion that the theory of descent with modification is the only
reasonable explanation of organic resemblances and differences.
HOMOLOGY VERSUS ANALOGY
Much difficulty in connection with the study of resemblances and
differences in animals and plants is occasioned by a failure to under-
stand the fact that there are two kinds of resemblances and differences.
Structures that are similar in anatomical detail and in their mode of
embryonic origin, irrespective of whether they perform the same or
different functions, are known as homologous. The test of homological
equivalence is a study of the anatomical details of the adult structure
followed by a study of the developmental history of the part in ques-
tion. If the part under examination be a bone, for example, this bone
must have a certain relation to the other bones, must occur in a certain
part of the body, must be supplied with certain muscle attachments, in
order to be considered homologous with another bone that has the
same relations. If two structures have the same anatomical relations
and arise from equivalent embryonic rudiments they are said to be
homologous, in spite of small or great differences in relative size, ap-
pearance, or function. If structures are homologous it is believed that
they represent the same hereditary units and that these equivalent
hereditary units have been derived from the same or similar ancestors.
Analogous structures are of an entirely different sort. They may
be more or less superficially alike in form or in function, usually in
both, though anatomically quite different. As an example of analo-.
gous structures let us examine the three types of aquatic vertebrates
shown in Figure 42. These three kinds of vertebrates, one a fish, one
a reptile, and the third a mammal, might be mistaken by the casual
observer to be all fishes of different kinds. All have the same fusiform
body with lines best adapted for swift locomotion in the water; all
have median, paired, and caudal fins; all swim in about the same way.
Yet the resemblance is only skin-deep, as it were, for beneath the sur-
face the one is all fish, the second all reptile, and the third all mammal.
The structures that look alike and function alike are, from the stand-
ASSUMPTION UNDERLYING ALL EVIDENCES OF EVOLUTION 65
point of anatomical relations and embryonic derivation, entirely differ-
ent. The resemblances which are so obvious superficially are examples
of analogy, not of homology, and are the result of molding unlike
materials into a semblance of likeness in adaptation to a common en-
vironment. Analogous structures, while not considered as evidences
of kinship, are strong evidences of descent with modification, for their
very existence implies that they have been changed from a former
condition to one in which they are adapted to a new medium. To
illustrate this point, call to mind that both the ichythyosaur and the
porpoise (Fig, 42, 5 and C) belong to groups that are fundamentally
terrestrial air-breathing vertebrates, and that whatever they have that
is fishlike must be interpreted as adaptive modifications for aquatic
life. This type of conception and the way in which it bears witness for
organic evolution is well brought out in the next chapter by George
John Romanes, a chapter that for a generation has been considered a
classic. A few of the statements in this chapter would, in all probabil-
ity, be somewhat altered if the author were to rewrite it in the light
of newer knowledge, but on the whole the statements made would
still have the support of the most critical of modern anatomists.
I
I I
CHAPTER VI
EVIDENCES FROM MORPHOLOGY
(COMPARATIVE ANATOMY)^
GEORGE JOHN ROMANES
The theory of evolution supposes that hereditary characters
admit of being slowly modified wherever their modification will render
an organism better suited to a change in its conditions of life. Let
us, then, observe the evidence which we have of such adaptive modifi-
cations of structure, in cases where the need of such modification is
apparent. We may begin by again taking the case of the whales and
porpoises. The theory of evolution infers, from the whole structure
of these animals, that their progenitors must have been terrestrial
quadrupeds of some kind, which gradually became more and more
aquatic in their habits. Now the change in the conditions of their
life thus brought about would have rendered desirable great modifica-
tions of structure. These changes would have begun by affecting the
least typical — that is, the least strongly inherited — structures, such
as the skin, claws, and teeth. But, as time went on, the adaptations
would have extended to more typical structures, until the shape of
the body would have become affected by the bones and muscles
required for terrestrial locomotion becoming better adapted for
aquatic locomotion, and the whole outline of the animal more fish-like
in shape. This is the stage which we actually observe in the seals,
where the hind legs, although retaining all their typical bones, have
become shortened up almost to rudiments, and directed backwards,
so as to be of no use for walking, while serving to complete the fish-like
taper of the body (Fig. i). But in the whales the modification has
gone further than this so that the hind legs have ceased to be apparent
externally, and are only represented internally — and even this only
in some species — by remnants so rudimentary that it is difiicult to
make out with certainty the homologies of the bones; moreover, the
head and the whole body have become completely fish-like in shape
(Fig. 12). But profound as are these alterations, they affect only
' From G. J. Romanes, Darwin and after Darwin (copyright 1892). Used by
special permission of the publishers, The Open Court Publishing Company.
66
EVIDENCES FROM MORPHOLOGY
67
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68 EVOLUTION, GENETICS, AND EUGENICS
those parts of the organism which it was for the benefit of the organism
to have altered, so that it might be adapted to an aquatic mode of
existence. Thus the arm, which is used as a fin, still retains the bones
of the shoulder, fore-arm, wrist, and fingers, although they are all
enclosed in a fin-shaped sack, so as to render them useless for
any purpose other than swimming (Fig. 3). Similarly, the head,
although it so closely resembles the head of a fish in shape, still retains
the bones of the mammalian skull in their proper anatomical relations
to one another; but modified in form so as to offer the least possible
resistance to the water. In short, it may be said that all the modifi-
cations have been effected with the least possible divergence from the
typical mammalian type, which is compatible with securing so perfect
an adaptation to a purely aquatic mode of Ufe.
Now I have chosen the case of the whale and porpoise group,
because they offer so extreme an example of profound modification of
structure in adaptation to changed conditions of life. But the same
thing may be seen in hundreds and hundreds of other cases. For
instance, to confine our attention to the arm, not only is the limb
modified in the whale for swimming, but in another mammal — the
bat — it is modified for flying, by having the fingers enormously
elongated and overspread with a membranous web.
In birds, again, the arm is modified for flight in a wholly different
way — the fingers here being very short and all run together, while the
chief expanse of the wing is composed of the shoulder and forearm.
In frogs and lizards, again, we find hands more like our own; but in
an extinct species of flying reptile the modification was extreme, the
wing having been formed by a prodigious elongation of the fifth finger,
and a membrane spread over it and the rest of the hand (Fig. 4).
Lastly, in serpents the hand and arm have disappeared altogether.
Thus, even if we confine our attention to a single organ, how
wonderful are the modifications which it is seen to undergo, although
never losing its typical character. Everywhere we find the distinction
between homology and analogy which was explained in the last
chapter — the distinction, that is, between correspondence of structure
and correspondence of function. On the one hand, we meet with
structures which are perfectly homologous and yet in no way
analogous; the structural elements remain, but are profoundly
modified so as to perform wholly different functions. On the other
hand, we meet with structures which are perfectly analogous, and
yet in no way homologous; totally different structures are modified
EVIDENCES FROM MORPHOLOGY
69
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Fig. 7. — Rudimentary or vestigial hind limbs of python, as exhibited in the
skeleton and on the external surface of the animal. Drawn from nature, \ nat.
size. {From Romanes.)
method were adopted in so many cases, we should expect that in con-
sistency it would be adopted in all cases. This reasonable expectation,
however, is far from being realized. We have already seen that in
numberless cases, such as that of the fore-limbs of serpents, no vestige
of a rudiment is present. But the vacillating policy in the matter of
rudiments does not end here; for it is shown in a still more aggravated
form where within the limits of the same natural groups of organisms
a rudiment is sometimes present and sometimes absent. For instance,
although in nearly all the numerous species of snakes there are
no vestiges of limbs, in the Python we find very tiny rudiments of
the hind-lunbs (Fig. 7). Now, is it a worthy conception of Deity
that, while neglecting to maintain his unity of ideal in the case of
EVIDENCES FROM MORPHOLOGY
79
nearly all the numerous species-of snakes, he should have added a tiny
rudiment in the case of the Python — and even in that case should
have maintained his ideal very inefficiently, inasmuch as only two
limbs, instead of four, are represented ? How much more reasonable
is the naturalistic interpretation; for here the very irregularity of
their appearance in different species, which constitutes rudimentary
structures one of the crowning difficulties to the theory of special
design, furnishes the best possible evidence in favour of hereditary
Fig, 8. — Apkryx anstralis. Drawn from life in the Zoological Gardens,
I nat. size. The external wing is drawn to a scale in the upper part of the cut.
The surroundings are supplied from the most recent descriptions.
Romanes)
{From
descent; seeing that this irregularity then becomes what may be
termed the anticipated expression of progressive dwindling due to
inutility. Thus, for example, to return to the case of wings, we have
already seen that in an extinct genus of bird, Ditwrnis, these organs
were reduced to sucTi an extent as to leave it still doubtful whether so
much as the tiny rudiment hypothetically supplied to Figure 5 was
present in all the species. And here is another well-known case of
another genus of still existing bird, which, as was the case with
Dinornis, occurs only in New Zealand (Fig. 8). Upon this island
there are no four-footed enemies — either existing or extinct — to escape
from which the wings of birds would be of ajiy service. Conse-
So EVOLUTION, GENETICS, AND EUGENICS
quently we can understand why on this island we should meet with
such a remarkable dwindling away of wings.
Similarly, the logger-headed duck of South America can only flap
along the surface of the water, having its wings considerably reduced
though less so than the Apteryx of New Zealand. But here the
interesting fact is that the young birds are able to fly perfectly well.
Now, in accordance with a general law to be considered in a future
chapter, the life-history of an individual organism is a kind of con-
densed recapitulation of the Ufe-history of its species. Consequently,
we can understand why the little chickens of the logger-headed duck
are able to fly like all other ducks, while their parents are only able
to flap along the surface of the water.
Facts analogous to this reduction of wings in birds which have no
further use for them, are to be met with also in insects under similar
circumstances. Thus, there are on the island of Madeira somewhere
between 500 and 600 species of beetles, which are in large part peculiar
to that island, though related to other — and therefore presumably
parent — species on the neighboring continent. Now, no less than 200
species — or nearly half the whole number — are so far deficient in
wings that they cannot fly. And, if we disregard the species which
are not pecuUar to the island — that is to say, all the species which
likewise occur on the neighboring continent, and therefore, as evolu-
tionists conclude, have but recently migrated to the island, — ^we find
this very remarkable proportion. There are altogether 29 pecuUar
genera, and out of these no less than 23 have all their species in this
condition.
Similar facts have been recently observed by the Rev. A. E. Eaton
with respect to insects inhabiting Kerguelen Island. All the species
which he found on the island — ^viz., a moth, several flies, and numerous
beetles — he found to be incapable of flight; and therefore, as Wallace
observes, "as these insects could hardly have reached the islands in
a wingless state, even if there were any other known land inhabited
by them, which there is not, we must assume that, like the Madeiran
insects, they were originally winged, and lost their power of flight
because its possession was injurious to them" — Kerguelen Island
being "one of the stormiest places on the globe, " and therefore a place
where insects could rarely afford to fly without incurring the danger
of being blown out to sea.
Here is another and perhaps an even more suggestive class of
facts.
EVIDENCES FROM MORPHOLOGY ,8l
It is now many years ago since the editors of Silliman's Journal
requested the late Professor Agassiz to give them his opinion on the
following question. In a certain dark subterranean cave, called the
Mammoth Cave, there are found some peculiar species of blind fishes.
Now the editors of Silliman's Journal wished to know whether Profes-
sor Agassiz would hold that these fish had been specially created in
these caves, and purposely devoided of eyes which could never be of
any use to them; or whether he would allow that these fish had prob-
ably descended from other species, but, having got into the dark cave,
gradually lost their eyes through disuse. Professor Agassiz, who was
a believer in special creation, allowed that this ought to constitute
a crucial test as between the two theories of special design and heredi-
tary descent. "If physical circumstances," he said, "ever modified
organised human beings, it should be easily ascertained here." And
eventually he gave it as his opinion, that these fish "were created
under the circumstances in which they now live, within the limits over
which they now range, and with the structural peculiarities which now
characterise them."
Since then a great deal of attention has been paid to the fauna of
this Mammoth cave, and also to the faunas of other dark caverns, not
only in the New, but also in the Old World. In the result, the
following general facts have been fully established.
1. Not only fish, but many representatives of other classes, have
been found in dark caves.
2. Wherever the caves are totally dark, all the animals are blind.
3. If the animals live near enough to the entrance to receive some
degree of Hght, they may have large and lustrous eyes.
4. In all cases the species of blind animals are closely allied to
species inhabiting the district where the caves occur; so that the
blind species inhabiting the American caves are closely aUied to
American species, whUe those inhabiting European caves are closely
allied to European species.
5. In nearly all cases structural remnants of eyes admit of being
detected, in various degrees of obsolescence. In the case of some of
the crustaceans of the Mammoth cave the foot-stalks of the eyes are
present, although the eyes themselves are entirely absent.
Now, it is evident that all these general facts are in full agreement
with the theory of evolution, while they offer serious difficulties to
the theory of special creation. As Darwin remarks, it is hard to
imagine conditions of Ufe more similar than those furnished by deep
82 EVOLUTION, GENETICS, AND EUGENICS
<
limestone caverns under nearly the same climate in the two continents
of America and Europe; so that, in accordance with the theory of
special creation, very close similarity in the organizations of the two
sets of faunas might have been expected. But, instead of this, the
affinities of these two sets of faunas are with those of their respective
continents — as of course they ought to be on the theory of evolution.
Again, what would have been the sense of creating the useless foot-
stalks for the imaginary support of absent eyes, not to mention all the
other various grades of degeneration in other cases? So that, upon
the whole, if we agree with the late Professor Agassiz in regarding
these cave animals as furnishing a crucial test between the rival
theories of creation and evolution, we must further conclude that the
whole body of evidence which- they now furnish is weighing on the
side of evolution.
So much, then, for a few special instances of what Darwin called
rudimentary structures, but what may be more descriptively desig-
nated — ^in accordance with the theory of descent — obsolescent or
vestigial structures. It is, however, of great importance to add that
these structures are of such general occurrence throughout both the
vegetable and animal kingdoms that, as Darwin has observed, it is
almost impossible to point to a single species which does not present
one or more of them. In other words, it is almost impossible to find
a single species which does not in this way bear some record of its own
descent from other species; and the more closely the structure of any
species is examined anatomically, the more numerous are such records
found to be. Thus, for example, of all organisms that of man has
been most minutely investigated by anatomists; and therefore I think
it will be instructive to conclude this chapter by giving a hst of the
more noteworthy vestigial structures which are known to occur in the
human body. I will take only those which are found in adult man,
reserving for the next chapter those which occur in a transitory manner
during earher periods of his life. But, even as thus restricted, the
number of obsolescent structures which we all present in our own
person is so remarkable, that their combined testimony to our descent
from a quadrumanous ancestry appears to me in itself conclusive.
I mean, that even if these structures stood alone, or apart from any
more general evidences of our family relationships, they would be
sufficient to prove our parentage. Nevertheless, it is desirable to
remark that of course these special evidences which I am about to
detail do not stand alone. Not only is there the general analogy
b
EVIDENCES FROM MORPHOLOGY 83
lumished by the general proof of evolution elsewhere, but there is
likewise the more special correspondence between the whole of our
anatomy and that of our nearest zoological aUies. Now the force of
this latter consideration is so enormous that no one who has not
studied human anatomy can be in a position to appreciate it. For
without special study it is impossible to form any adequate idea of the
intricacy of structure which is presented by the human form. Yet it
is found that this enormously intricate organisation -is repeated in all
its details in the bodies of the higher apes. There is no bone, muscle,
nerve, or vessel of any importance in the one which is not answered
to by the other. Hence there are hundreds of thousands of instances
of the most detailed correspondence, without there being any instances
to the contrary, if we pay due regard to vestigial characters. The
entire corporeal structure of man is an exact anatomical copy of that
which we find in the ape.
My object, then, here is to limit attention to those features of our
corporeal structure which, having become useless on account of our
change in attitude and habits, are in the process of becoming obsolete,
and therefore occur as mere vestigial records of a former state of
things. For example, throughout the vertebrated series, from fish
to mammals, there occurs in the inner corner of the eye a semi-
transparent eye-lid, which is called the nictitating membrane. The
object of this structure is to sweep rapidly, every now and then,
over the external surface of the eye, apparently in order to keep the
surface clean. But although the membrane occurs in all classes of
the sub-kingdom, it is more prevalent in some than in others — e.g.,
in birds than in mammals. Even, however, where it does not occur
of a size and mobility to be of any use, it is usually represented, in
animals above fishes, by a functionless rudiment, as here depicted in
the case of man (Fig. 9).
Now the organisation of man presents so many vestigial structures
thus referring to various stages of his long ancestral history, that it
would be tedious so much as to enumerate them. Therefore I will
yet further Hmit the list of vestigial structures to be given as examples,
by not only restricting these to cases which occur in our own organisa-
tion; but of them I shall mention only such as refer us to the very
last stage of our ancestral history — viz., structures which have become
obsolescent since the time when our distinctively human branch of
the family tree diverged from that of our immediate forefathers, the
Quadrumana.
84
EVOLUTION, GENETICS, AND EUGENICS
Plica
Semilunaris
^.V\'
Fig. 9. — Illustrations of the nictitating membrane in the various animals
named, drawn from nature. The letter N indicates the membrane in each case.
In man it is called the plica semilunaris and is represented in the two lower drawings
under this name. In the case of the shark (Galeus), the muscular membrane is
shown as dissected. (From Romanes.)
EVIDENCES FROM MORPHOLOGY
85
I. Muscles of the external ear. — These, which are of large size
and functional use in quadrupeds, we retain in a dwindled and useless
condition (Fig. 10). This is liicewise the case in anthropoid apes;
but in not a few other Quadrumana (e. g., baboons, macacus, magots
etc.) degeneration has not proceeded so far, and the ears are
voluntarily movable.
Fig. 10. — Rudimentary, or vestigial and useless, muscles of the human ear.
{From Romanes, after Gray.)
2. Panniculus carnosis. — A large number of the mammalia are
able to move their skin by means of subcutaneous muscle, as we see,
for instance, in a horse, when thus protecting himself against the
sucking of flies. We, in common with the Quadrumana, possess an
active remnant of such a muscle in the skin of the forehead, whereby
we draw up the eyebrow^s; but we are no longer able to use other
considerable remnants of it, in the scalp and elsewhere, — or more
correctly it is rarely that we meet with persons who can.. But most
of the Quadrumana (including the anthropoids) are still able to do so.
86
EVOLUTION, GENETICS, AND EUGENICS
There are also many other vestigial muscles, which occur only in a
small percentage of human beings, but which, when they do occur,
present unmistakable homologies with normal muscles in some of
the Quadrumana and still lower animals.
3. Feet. — ^It is observable that in the infant the feet have a
strong reflection inwards, so that the soles in considerable measure
face one another. This peculiarity, which is even more marked in
the embryo than in the infant, and which becomes gradually less and
Fig. II. — Portrait of a young gorilla. {From Romanes, after Hartmunn.)
less conspicuous even before the child begins to walk, appears to me
a highly suggestive peculiarity. For it plainly refers to the condition
of things in the Quadrumana, seeing that in all these animals the feet
are similarly curved inwards, to facilitate the grasping of branches.
And even when walking on the ground apes and monkeys employ to
a great extent the outside edges of their feet, as does also a child when
learning to walk. The feet of a young child are also extraordinarily
mobile in all directions, as are those of apes. In order to show these
points, I here introduce comparative drawings of a young ape and the
EVIDENCES FROM MORPHOLOGY
87
lower extremities of a still yomiger child. These drawings, moreover,
serve at the same time to illustrate two other vestigial characters,
which have often been previously noticed with regard to the infant's
foot. I allude to the incurved form of the legs and the lateral exten-
sion of the great toe, whereby it approaches the thumb-like character
of this organ in the Quadrumana. As in the case of the incurved
position of the legs and feet, so in this case of the lateral extensibility
of the great toe, the peculiarity is even more marked in embryonic
Fig. i2.^Lower extremities of a young child. Drawn from life, when the
mobile feet were for a short time at rest in a position of extreme inflection. {From
Romanes.)
than in infant life. For, as Professor Wyman has remarked with
regard to the foetus when about an inch in length, "The great toe is
shorter than the others; and, instead of being parallel to them, is
projected at an angle from the side of the foot, thus corresponding
with the permanent condition of this part in the Quadrumana." So
that this organ, which, according to Owen, "is perhaps the most
characteristic peculiarity of the human structure," when traced back
to the early stages of its development, is found to present a notably
less degree of peculiarity.
88
EVOLUTION, GENETICS, AND EUGENICS
4. Hands. — Dr. Louis Robinson has recently observed that the
grasping power of the whole human hand is so surprisingly great at
birth, and during the first few weeks of infancy, as to be far in excess
of present requirements on the part of a young child. Hence he con-
cludes that it refers us to our quadrumanous ancestry — the young of
anthropoid apes being endowed with similar powers of grasping, in
order to hold on to the hair of the mother when she is using her arms for
the purposes of locomotion. This inference appears to me justifiable,
Fig. 13. — An infant, three weeks old, supporting its own weight for over two
minutes. " The attitude of the lower limbs, feet, toes, is strikingly simian. Repro-
duced from an instantaneous photograph, kindly given for the purpose by Dr. L.
Robinson. {From Romanes.)
inasmuch as no other explanation can be given of the comparatively
inordinate muscular force of an infant's grip. For experiments
showed that very young babies are able to support their own weight,
by holding on to a horizontal bar, for a period varying from one
half to more than two minutes. With his kind permission, I here
reproduce one of Dr. Robinson's instantaneous, and hitherto unpub-
lished, photographs of a very young infant. This photograph was
taken after the above paragraph (3) was written, and I introduce it
here because it serves to show incidentally — and perhaps even better
than the preceding figure — the points there mentioned with regard
EVIDENCES FROM MORPHOLOGY
89
to the feet and great toes. Again, as Dr. Robinson observes, the
attitude, and the disproportionately large development of the arms
as compared with the legs give all the photographs a striking resem-
blance to a picture of the chimpanzee "Sally" at the Zoological
Gardens. For " invariably the thighs are bent nearly at right angles
to the body, and in no case did the lower limbs hang down and take
the attitude of the erect position." He adds, "In many cases no
sign of distress is evinced, and no cry uttered, until the grasp
begins to give way."
MAN
Gorilla
Fig. 14. — Sacrum of gorilla compared with that of man, showing rudimentary
tail bones of each. Drawn from nature. {From Romanes.)
5. Tail. — The absence of a tail in man is popularly supposed to
constitute a difficulty against the doctrine of his quadrumanous
descent. As a matter of fact, however, the absence of an external
tail in man is precisely what this doctrine would expect, seeing that
the nearest allies of man in the quadrumanous series are likewise
destitute of an external tail. Far, then, from this deficiency in man
constituting any difficulty to be accounted for, if the case were not
so — i.e., if man did possess an external tail, — the difficulty would be
to understand how he had managed to retain an organ which had been
renounced by his most recent ancestors. Nevertheless, as the anthro-
go
EVOLUTION, GENETICS, AND EUGENICS
poid apes continue to present the rudimentary vestiges of a tail in a
few caudal vertebrae below the integuments, we might well expect to
find a similar state of matters in the case of man. And this is just
Fig. 15. — Diagrammatic outline of the human embryo when about seven
weeks old, showing the relations of the limbs and tail to the trunk. {After Allen
Thompson.) r, the radial, and 71, the ulnar, border of the hand and forearm;
/, the tibial, and/ the fibular, border of the foot and lower leg; an, ear; u , spinal
cord; «, umbiUcal cord; J, bronchial gill slits; c, tail. {From Romanes.)
ySvfl^ sh/oils Lid
doccyx:.
Fig. 16. — Front and back view of adult human sacrum, showing abnormal
persistence of vestigial tail muscles. {From Romanes.)
what we do find, as a glance at these two comparative illustrations
will show (Fig. 14). Moreover, during embryonic life, both of the
anthropoid apes and of man, the tail much more closely resembles
EVIDENCES FROM MORPHOLOGY
91
that of the lower kinds of quadrumanous animals from which these
higher representatives of the group have descended. For at a certain
stage of embryonic life the tail, both of apes and of human beings, is
Fig. 17. — Appendix vermifonnis in orang and in man. //, ilium; Co, colon;
C, coecum; IF, a window cut in the wall of the coecum; xxx, the appendix. {From
Romanes.)
Man
F(ETAL
Fig. i8. — The same, showing variation in the orang. {From Romanes.)
actually longer than the legs (see Fig. 15). And at this stage of
development, also, the tail admits of being moved by muscles which
later on dwindle away. Occasionally, however, these muscles persist,
and are then described by anatomists as abnormalities. The illustra-
92
EVOLUTION, GENETICS, AND EUGENICS
tions on page 153 (Fig. 16) serve to show the muscles in question,
when thus found in adult man.
6. Vermiform appendix of the coecum. — This is of large size and
functional use in the process of digestion among many herbivorous
animals; while in man it is not only too small to serve any such
purpose, but is even a source of danger to life^ — many persons dying
every year from inflammation set up by the lodgement in this blind
tube of fruit-stones, etc.
In the orang it is longer than in man (Fig. 17), as it is also in the
human foetus proportionally compared with the adult (Fig. 18). In
some of the lower herbivorous animals it is longer than the entire body.
Like the vestigial structures in general, however, this one is
highly variable. Thus Figure 1 8 serves to show that it may some- .
times be almost as short in the orang as it normally is in man — both
the human subjects of this illustration having been normal.
7. Ear. — Mr. Darwin writes:
"The celebrated sculptor, Mr, Woolner, informs me of one little
peculiarity in the external ear, which he has often observed both in
men and women The peculiarity consists in a little blunt
point, projecting from the inwardly folded margin, or helix. When
present, it is developed at birth, and according to Professor Ludwig
Meyer, more frequently in man than in woman.
Mr. Woolner made an exact model of one such
case, and sent me the accompanying draw-
ing [Fig. 19] The helix obviously con-
sists of the extreme margin of the ear folded
inwards; and the folding appears to be in r^
some manner connected with the whole external /
ear being permanently pressed backwards. In
many monkeys, which do not stand high in
the order as baboons and some species of
macacus, the upper portion of the ear is slightly
pointed, and the margin is not at all folded
inwards; but if the margin were to be thus
folded, a slight point would necessarily pro-
ject towards the centre In Figure 20
is shown an accurate copy of a photograph
of the foetus of an orang (kindly sent me by Dr. Nitsche), in
which it may be seen how different the pointed outline of the ear is
at this period from its adult condition, when it bears a close general
Fig. 19. — Human ear,
modeled and drawn by
Mr. Woolner. o, the pro-
jecting point. {From Ro-
manes)
EVIDENCES FROM MORPHOLOGY
.93
Fig. 20. — Foetus of an orang. Exact
copy of a photograph, showing the form of
ear at this earl}' stage. {Frojn Rcxmanes.)
resemblance to that of man (including even the occasional appear-
ance of the projecting point shown in the preceding woodcut). It is
evident that the folding over
of the tip of such an ear,
unless it is changed greatly
during its further develop-
ment, would give rise to a
point projecting inwards."*
The woodcut on page 94
(Fig. 21) serves still further to
show vestigial resemblances
between the human ear and
that of apes. The last two
figures illustrate the general
resemblance between the nor-
mal ear of foetal man and the
ear of an adult orangoutang.
The other two figures on the
lower line are intended to
exhibit occasional modifica-
tions of the adult human ear, which approximate simian characters
somewhat more closely than does the normal type. It will be observed
that in their comparatively small lobes these ears resemble those
of all the apes ; and that while the outer margin of one is not unlike
that of the Barbary ape, the outer margin of the other follows those
of the chimpanzee and orang. Of course it would be easy to select
individual human ears which present either of these characters in a
more pronounced degree; but these ears have been chosen as models
because they present both characters in conjunction. The upper row
of figures likewise shows the close similarity of hair-tracts, and the
direction of growth on the part of the hair itself, in cases where the
hmnan hair happens to be of an abnormally hirsute character. But
this particular instance (which I do not think has been previously
noticed) introduces us to the subject of hair, and hair-growth, in
general.
8. Hair. — Adult man presents rudimentary hairs over most parts
of the body. Wallace has sought to draw a refined distinction between
this vestigial coating and the useful coating of quadrumanous
animals, in the absence of the former from the human back. But even
^ Descent of Man (2d ed.), pp. 15-16.
94
EVOLUTION, GENETICS, AND EUGENICS
EVIDENCES FROM MORPHOLOGY 95
this refined distinction does not hold. On the one hand, the com-
paratively hairless chimpanzee which died last year in the Zoological
Gardens {T. calvus) was remarkably denuded over the back; and, on
the other hand, men who present a considerable development of hair
over the rest of their bodies present it also on their backs and shoul-
ders. Again, in all men the rudimentary hair on the upper and lower
arm is directed towards the elbow — a pecuUarity which occurs nowhere
else in the animal kingdom, with the exception of the anthropoid apes
and a few American monkeys, where it presumably has to do with
arboreal habits. For, when sitting in trees, the orang, as observed by
Mr. Wallace, places its hands above its head with its elbows pointing
downwards; the disposition of hair on the arms and fore-arms then
has the effect of thatch in turning the rain. Again, I find that in all
species of apes, monkeys, and baboons which I have examined (and
tliey have been numerous), the hair on the backs of the hands and feet
is continued as far as the first row of phalanges; but becomes scanty,
or disappears altogether, on the second row; while it is invariably
absent on the terminal row. I also find that the same pecuUarity
occurs in man. We all have rudimentary hair on the first row of
phalanges, both of hands and feet: when present at all, it is more
scanty on the second row; and in no case have I been able to find any
on the terminal row. In all cases these peculiarities are congenital,
and the total absence or partial presence of hair on the second pha-
langes is constant in different species of Quadrumana. For instance,
it is entirely absent in all the chimpanzees, which I have examined,
while scantily present in all the orangs. As in man, it occurs in a
patch midway between the joints.
Besides showing these two features with regard to disposition of hair
on the human arm and hand, the woodcut on pageg6 (Fig. 22) illustrates
a third. By looking closely at the arm of the very hairy man from whom
the drawing was taken, it could be seen that there was a strong tendency
towards a whorled arrangement of the hairs on the backs of the wrists.
This is likewise, as a general rule, a marked feature in the arrangement
of hair on the same places in the gorilla, orang, and chimpanzee. In
the specimen of the latter, however, from which the drawing was taken
this characteristic was not well marked. The downward direction of
the hair on the backs of the hands is exactly the same in man as it is
in all the anthropoid apes. Again, with regard to hair, Darwin
notices that occasionally there appears in man a few hairs in the eye-
brows much longer than the others; and that they seem to be
96
EVOLUTION, GENETICS, AND EUCxENICS
^s^\^^\W^
/yfAL r c7///^/'Ay^^^
Fig. 22. — Hair tracts on the arms and hands of man, as compared with those
of the chimpanzee. Drawn from life. {J^rom Romanes.)
EVIDENCES FROM MORPHOLOGY 97
representative of similarly long and scattered hairs which occur
in the chimpanzee, macacus, and baboons.
Lastly, it may be here more conveniently observed than in the
next chapter on Embrj^ology, that at about the sixth month the human
foetus is often thickly coated with somewhat long dark hair over the
entire body, except the soles of the feet and palms of the hands, which
are likewise bare in all quadrumanous animals. This covering, which
is called the lanugo, and sometimes extends even to the whole fore-
head, ears, and face, is shed before birth. So that it appears to be
useless for any purpose other than that of emphatically declaring man
a child of the monkey.
9. Teeth. — Darwin writes:
"It appears as if the posterior molar or wisdom teeth were tending
to become rudimentary in the more civiUzed races of man. These
teeth are rather smaller than the other molars, as is likewise the case
with the corresponding teeth in the chimpanzee and orang; and they
have only two separate fangs They are also much more liable
to vary, both in structure and in the period of their development,
than the other teeth. In the Melanian races, on the other hand, the
wisdom-teeth are usually furnished with three separate fangs, and are
usually sound (i.e., not specially liable to decay); they also differ from
the other molars in size, less than in the Caucasian races."
Now, in addition to these there are other respects in which the
dwindling condition of wisdom-teeth is manifested — particularly with
regard to the pattern of their crowns. Indeed, in this respect it would
seem that even in the anthropoid apes there is the beginning of a
tendency to degeneration of the molar teeth from behind forwards.
For if we compare the three molars in the lower jaw of the gorilla,
orang, and chimpanzee, we find that the gorilla has five well-marked
cusps on all three of them; but that in the orang the cusps are not so
pronounced, while in the chimpanzee there are only four of them on
the third molar. Now in man it is only the first of these three teeth
which normally presents five cusps, both the others presenting only
four. So that, comparing all these genera together, it appears that
the number of cusps is being reduced from behind forwards; the
chimpanzee having lost one of them from the third molar, while man
has not only lost this, but also one from the second molar, — and it
may be added, likewise partially (or even totally) from the first molar,
as a frequent variation among civilized races. But, on the other hand,
variations are often met with in the opposite direction, where the
98
EVOLUTION, GENT'TICS, AND EUGENICS
second or the third molar of man presents five cusps — in the one case
following the chimpanzee, in the other the gorilla. These latter varia-
tions, therefore, may fairly be regarded as reversionary. For these
facts I am indebted to the kindness of Mr. C. S. Tomes.
10. Perforations of the humerus. — The peculiarities which we
have to notice under this heading are two in number. First, the
supra-condyloid foramen is a normal feature in some of the lower
Quadrumana (Fig. 24), where it gives passage to the great nerve of
N AT. SIZE
Fig. 23. — Molar teeth of lower jaw in gorilla, orang, and man. Drawn from
nature, nat. size. {From Romanes.)
the forearm, and often also to the great artery. In man, however,
it is not a normal feature. Yet it occurs in a small percentage of
cases — viz., according to Sir W. Turner, in about one per cent, and
therefore is regarded by Darwin as a vestigial character. Secondly,
there is inter-condyloid foramen, which is also situated near the lower
end of the humerus, but more in the middle of the bone. This occurs,
but not constantly, in apes, and also in the human species. From
the fact that it does so much more frequently in the bones of ancient
— and also of some savage — races of mankind (viz. in 20 to 30 per cent
of cases), Darwin is disposed to regard it also as a vestigial feature.
EVIDENCES FROM MORPHOLOGY
99
On the other hand, Prof. Flower tells me that in his opinion it is but
an expression of impoverished nutrition during the growth of the bone.
II. Flattening of Tibia. — In some very ancient human skeletons
there has also been found a lateral flattening of the tibia, which rarely
occurs in any existing human beings, but which appears to have
been usual among the earUest races of mankind hitherto discovered.
According to Broca, the measurements of these fossil human tibiae
resemble those of apes. Moreover, the bone is bent and strongly
JAVAI7 LOR|S
CAPVCHI7
Fig. 24. .^Perforations of the humerus (supra-condyloid foramen) in three
species of Quadrumana where it normally occurs, and in man, where it does not
normally occur. Drawn from nature. {From Romanes.)'
convex forwards, while its angles are so rounded as to present the
nearly oval section seen in apes. It is in association with these
ape-like human tibiae that perforated humeri of man are found in
greatest abundance.
On the other hand, however, there is reason to doubt whether
this form of tibia in man is really a survival from his quadrumanous
ancestry. For, as Boyd-Dawkins and Hartmann have pointed out,
the degree of flattening presented by some of these ancient human
bones is greater than that which occurs in any existing species of
anthropoid ape. Of course the possibility remains that the unknown
species of ape from which man descended may have had its tibia more
flattened than is now observable in any of the existing species. Never-
lOO EVOLUTION, GENETICS, AND EUGENICS
theless, as some doubt attaches to this particular case, I do not press
it — and, indeed, only mention it at all in order that the doubt may be
expressed.
Similarly, I will conclude by remarking that several other instances
of the survival of vestigial structures in man have been alleged, which
are of a still more doubtful character. Of such, for example, are the
supposed absence of the genial tubercle in the case of a very ancient
jaw-bone of man, and the disposition of valves in human veins.
From the former it was argued that the possessor of this very ancient
jaw-bone was probably speechless, inasmuch as the tubercle in existing
man gives attachment to muscles of the tongue. From the latter it
has been argued that all the valves in the veins of the human body
have reference, in their disposition, to the incidence of blood-pressure
when the attitude of the body is horizontal, or quadrupedal. Now,
the former case has already broken down, and I find that the latter
does not hold. But we can well afford to lose such doubtful and
spurious cases, in view of all the foregoing unquestionable and genuine
cases of vestigial structures which are to be met with even within the
limits of our own organization — and even when these limits are still
further Hmited by selecting only those instances which refer to the
very latest chapter of our long ancestral history.
CHAPTER Vn
EVIDENCES FROM CLASSIFICATION
THE PRINCIPLES OF CLASSIFICATION*
A. F. SHXJLL
The International Code. — Some of the essential features of the
International Code are as follows. The first name proposed for a
genus or species prevails on the condition that it was published and
accompanied by an adequate description, definition or indication, and
that the author has applied the principles of binomial nomenclature.
This is the so-called law of priority. The tenth edition of the Sytenta
Naturae of Linnaeus is the basis of the nomenclature. The author of
a genus or species is the person who first pubHshes the same in connec-
tion with a definition, indication or description, and his name in full
or abbreviated is given with the name; thus, Bascanian anthonyi
Stejneger. In citations the generic name of an animal is written with
a capital letter, the specific and subspecific name without initial
capital letter. The name of the author follows the specific name
(or subspecific name if there is one) without intervening punctuation.
If a species is transferred to a genus other than the one under which
it was first described, or if the name of a genus is changed, the author's
name is included in parentheses. For example, Bascanion anthonyi
Stejneger should now be written Coluber anthonyi (Stejneger), the ge-
neric name of this snake having been changed. One species constitutes
the type of the genus; that is, it is formally designated as typical of
the genus. One genus constitutes the type of the subfamily (when a
subfamily exists), and one genus forms the type of the family. The
type is indicated by the describer or if not indicated by him is fixed
by another author. The name of a subfamily is formed by adding
the ending -inae, and the name of a family by adding -Uae to the root
of the name of the type genus. For example, Colubrinae and Colubri-
dae are the subfamily and family of snakes of which Coluber is the
type genus.
The basis of classification. — Early systematists largely employed
superficial characters to differentiate and classify animals, and their
' From A. F. Shull, Principles of Animal Biology (copyright 1920). Used by
special pennission of The McGraw-Hill Book Company.
lOI
I02 EVOLXmON, GENETICS, AND EUGENICS
classifications were thus largely artificial and served principally as
convenient methods of arrangement, description and cataloging.
Since the time of the development of the theory of descent with
modifications by Lamarck (1809) and Darwin (1859), there has been
an attempt to base the classification on relationships. Very nearly
related animals are put into the same species. They are related
because they descend from a common ancestry, and that common
ancestry could not in most cases have been very ancient, otherwise
evolution within the group would have occurred and the species would
have been split into two or more species. Species that are much
alike are included in one genus, being thus marked off from the species
of another genus. The similarity of the species of a genus is held to
indicate kinship, but since there is greater diversity among the indi-
viduals of a genus than among the members of a species, the common
stock from which the species of a genus have sprung must have existed
at an earher time, in order that evolution could bring about the degree
of divergence now observed. In like manner, a family is made up of
genera, and their likeness is again a sign of affinity. But to account
for the greater difference between the extreme individuals belonging to
a family, evolution must have had more time, that is, the common
source of the members of a family must have antedated the common
source of the individuals of a genus. Orders, classes, and phyla are
similarly regarded as having sprung from successively more remote
ancestors, the time differences being necessary to allow for the differ-
ences in the amount of evolution. This statement is in general correct.
However, since evolution has probably not proceeded at the same rate
at all periods, nor in all branches of the animal kingdom at any one
time, the time relations of the groups of high or low rank must not be
too rigidly assigned. Thus certain genera, in which evolution has been
slow, are probably much older than some families in which evolution
has been rapid. It is not improbable, also, that some genera are quite
as old as the famiUes which include them; but in no case can they be
older. Furthermore, different groups are classified by taxonomists of
different temperaments, so that groups of a given nominal rank may
be much more inclusive (and hence older) in one branch of the animal
kingdom than in another. Qn the whole, nevertheless, the groups of
higher rank have sprung from ancestry more remote than that of the
groups of lower rank.
The means of recognizing the kinship implied in classification
permit some differences of opinion. It is recognized that likeness in
EVIDENCES FROM CLASSIFICATION 103
structural characters is the chief clue to affinities. However, the
evidential value of similarity in one or several structures unaccom-
panied by the similarity of all parts is to be distrusted, since animals
widely separated and dissimilar in most characters may have certain
other features in common. Thus, the coots, phalaropes and grebes
among birds have lobate feet but, as indicated by other features, they
are not closely related; and there are certain lizards (Amphisbaenidae)
which closely resemble certain snakes (Typholopidae) in being blind,
limbless, and having a short tail. The early systematists were very
liable to bring together in their classification analogous forms, that is,
those which are functionally similar; or animals which are super-
ficially similar. In contrast with the early practice, the aim of
taxonomists at the present time is to group forms according to homol-
ogy, which is considered an indication of actual relationship. Since
a genetic classification must take into consideration the entire animal,
the search for affinities becomes an attempt to evaluate the results
of all morphological knowledge, and it is also becoming evident that
other things besides structure may throw light upon relationships.
The fossil records, geographical distribution, ecology and experi-
mental breeding may all assist in establishing affinities.
The method of taxonomy. — It is evident that before the relation-
ships of animals can be determined the forms must be known, for
unknown forms constitute breaks in the pedigrees of the groups to
which they belong. Moreover, as pointed out above, the structural
characters, variation and distribution must be known before a form
can be placed in the proper place in a genetic system. For these
reasons an important part of systematic work is the description of
forms and an analysis of their differences. After the Linnaean
system was adopted zoologists attacked this virgin field and for many
years "species making" predominated. Even at the present time
when other aspects of zoology have come to receive relatively more
attention it is an interesting fact that the analytical method prevails
in systematic studies, and taxonomy suffers from, and in part merits,
the criticism that it is a mere cataloging of forms and ignores the
higher goal of investigation, namely, the discovery of the course of
evolution. Many systematists, however, recognize that the ultimate
purpose of taxonomic work is to discover the relationships as well as
the differences between the described forms in order that the course of
evolution may be determined. In other words, it is appreciated that
while analytical studies are necessary they are only preliminary, and
I04 EVOLUTION, GENETICS, AND EUGENICS
that upon their results must be built synthetic studies, if taxonomy
is to fulfil its purpose.
THE METHOD OF CLASSIFICATION
CHARLES DARWIN'
Naturalists, as we have seen, try to arrange the species, genera,
and families in each class, on what is called the Natural System. But
what is meant by this system ? Some authors look at it merely as a
scheme for arranging together those living objects which are most
alike, and for separating those which are most unlike; or as an artificial
method of enunciating, as briefly as possible, general propositions, —
that is, by one sentence to give the characters common, for instance,
to all mammals, by another those common to all carnivora, by another
those common to the dog-genus, and then, by adding a single sentence,
a full description is given of each kind of dog. The ingenuity
and utiHty of this system are indisputable. But many naturalists
think that something more is meant by the Natural System; they
believe that it reveals the plan of the Creator; but unless it be specified
whether order in time or space, or both, or what else is meant by the
plan of the Creator, it seems to me that nothing is thus added to our
knowledge. Expressions such as that famous one by Linnaeus, which
we often meet with in a more or less concealed form, namely, that the
characters do not make the genus, but that the genus gives the charac-
ters, seem to imply that some deeper bond is included in our classifica-
tions than mere resemblance. I believe that this is the case, and that
community of descent — the one known cause of close similarity in
organic beings — is the bond which, though observed by various
degrees of modification, is partially revealed to us by our classifications.
Let us now consider the rules followed in classification, and the
difficulties which are encountered on the view that classification either
gives some unknown plan of creation, or is simply a scheme for
enunciating general propositions and of placing together the forms
most like each other. It might have been thought (and was in ancient
times thought) that those parts of the structure which determined the
habits of life, and the general place of each being in the economy of
nature, would be of very high importance in classification. Nothing
can be more false. No one regards the external similarity of a mouse
to a shrew, of a dugong to a whale, of a whale to a fish, as of any
^ From The Origin of Species.
EVIDENCES FROM CLASSIFICATION 105
importance^ These resemblances, though so intimately connected
with the whole life of the being, are ranked as merely "adaptive or
analogical characters": but to the consideration of these resemblances
we shall recur. It may even be given, as a general rule, that the less
any part of the organisation is concerned with special habits, the more
important it becomes for classification. As an instance: Owen, in
speakmg of the dugong, says, "The generative organs, being those
which are most remotely related to the habits and food of an animal,
I have always regarded as affording very clear indications of its true
afl&nities. We are least likely in the modifications of these organs to
mistake a merely adaptive for an essential character." With plants
how remarkable it is that the organs of vegetation, on which their
nutrition and hfe depend, are of httle signification; whereas the
organs of reproduction, with their product the seed and embryo, are
of paramount importance! So again in formerly discussing certain
morphological characters which are not functionally important, we
have seen that they are often of the highest service in classification.
This depends on their constancy throughout many aUied groups; and
theh constancy chiefly depends on any slight deviations not having
been preserved and accumulated by natural selection, which acts only
on serviceable characters.
WHAT IS A SPECIES?
"Each kind ot animal or plant, that is, each set of forms which
in the changes of the ages has diverged tangibly from its neighbors,
is called a species. There is no absolute definition for the word
species. The word kind represents it exactly in common language,
and is just as susceptible to exact definition. The scientific idea of
species does not differ materially from the popular notion. A kind of
tree or bird or squirrel is a species. Those individuals which agree
very closely in structure and function belong to the same species.
There is no absolute test, other than the common judgment of men
competent to decide. Naturalists recognize certain formal rules as
assisting in such a decision. A series of fully intergrading forms,
however varied at the extremes, is usually regarded as forming a single
species. There are certain recognized effects of climate, of climatic
isolation, and of the isolation of domestication. These do not usually
make it necessary to regard as distinct species the extreme forms of
a series concerned."*
' From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life.
io6 EVOLUTION, GENETICS, AND EUGENICS
"The terra 'species' was thus defined by the celebrated botanist
De CandoUe: 'A species is a collection of all the individuals which
resemble each other more than they resemble anything else, which can
by mutual fecundation produce fertile individuals, and which repro-
duce themselves by generation, in such a manner that we may from
analogy suppose them all to have sprung from one single individual. '
And the zoologist Swainson gives a somewhat similar definition : 'A
species, in the usual acceptation of the term, is an animal which, in
a state of nature, is distinguished by certain peculiarities of form, size,
colour, or other circumstances, from another animal. It propagates,
after its kind, individuals perfectly resembling the parent; its pecu-
Harities, therefore, are permanent.' " *
As will have become apparent, the significant assumption
underlying classification is that the closest fundamental similarities
between animals (or plants) are found in the forms most closely
related and that the greatest differences are found in those forms which
are unrelated or at best very distantly related. The assumption
implies the idea of descent with modification, which is no more nor
less than evolution. Using this evolutionary basis, we can arrive at
an extremely satisfactory classification both of living and of extinct
forms; and there is no other basis of classification that works.
The question might well be asked whether it is possible to test the
validity of the assumption that degrees of resemblance vary directly
with closeness of blood relationship ? Two direct tests of this may
be and have been made. The closest of blood relatives possible are
individuals that have been derived by the dividing of a single egg.
Armadillo' quadruplets have been shown to be thus derived, and
detailed studies of the closeness of resemblance existing between
members of a given set indicate that they are vastly more alike than
are the simultaneously born offspring of animals which give birth to
several young, but in which each young is derived from a separate egg.
If we use the index of correlation to indicate the degree of similarity
between individuals we find that ordinary brothers or sisters are only
about 50 per cent alike, while armadillo quadruplets are over 90 per
cent aUke. Identical or duplicate twins in human beings are believed
to have an origin from one egg, after the fashion of the armadillo,
» From A. R. Wallace, Darwinism.
»See H. H. Newman, The Biology of Twins (1917), University of Chicago
Press.
EVIDENCES FROM CLASSIFICATION 107
though the proof has not been forthcoming. Everyone is familiar
with the remarkable similarity, amounting almost to identity, between
such twins. Thus we are able to show that the closest blood relation-
ship known is associated with the closest resemblance. The next
degree of resemblance is between members of the same family,
brothers, sisters, cousins, etc., and we do not hesitate to explain this
resemblance as due to blood relationship. In this we merely accept
the known principles of heredity.
The second direct test of the validity of the assumption that
degrees of resemblance run parallel with degrees of blood relationship
is found in connection with "blood-precipitation tests." This evi-
dence, as presented by Professor Scott, forms the substance of the next
chapter.
CHAPTER VIII
EVIDENCE FROM BLOOD TESTS*
W. B. Scott
Here may be conveniently considered the very interesting and
significant blood tests which have been made in the last fifteen years
by various physiologists and especially by Dr. George H. F. Nuttall,
of the University of Cambridge. Though there are several methods
of making these tests, the "precipitation method" employed by
Dr. Nuttall will be quite sufficient for the ends sought in these lec-
tures. The method and significance of the tests can best be explained
by taking as an example human blood, which, of course, has been most
extensively and minutely studied, because of its legal importance as
well as its scientific interest. Ordinary chemical analysis is unable
to determine the differences in blood-composition between various
animals, but that there were important differences had long been
understood. This was shown by the fact that, in performing the
operation for the transfusion of blood, it was not practicable to
substitute animal for human blood, since the former might cause
serious injury to the patient.
The precipitation method of making blood tests is as follows:
Freshly drawn human blood is allowed to coagulate or clot, which it
will do in a few minutes, if left standing in a dish, and then the serum
is drained away from the clot. Blood-serum is the watery, almost
colourless part of the blood, which remains after coagulation. Small
quantities of this serum are injected, at intervals of one or two days,
into the veins of a rabbit and cause the formation in the rabbit's blood
of an anti-body, analogous to the anti-toxin which is produced in the
blood of a horse by the injection of diphtheria virus. After the last
injection the rabbit is allowed to live for several days and is then
killed and bled, the blood is left until it clots and the serum drained
off and preserved. The serum obtained thus from a rabbit is called
"anti-human" seriun and is an exceedingly dehcate test for human
blood, not only when the latter is fresh, but also when it is in
the form of old and dried blood-stains, or even when the blood is
»From W. B. Scott, The Theory of Evolution (copyright 1917). Used by
special permission of the publishers, The Macmillan Company.
108
EVIDENCE FROM BLOOD TESTS 109
putrid. Stains, for example, are soaked in a very weak solution of
common salt and, if necessary, the blood solution is filtered until it is
quite limpid and clear. Into the blood solution a few drops of the
anti-human serum are conveyed and, if the stains are of human blood,
a white precipitate is formed and thrown down, but if the stains are
of the blood of some domestic animal, such as a pig, sheep, or fowl,
no such reaction follows. In the same manner as above described,
we may prepare anti-pig, anti-horse, anti-fowl, etc., etc., sera by
injecting the fresh-drawn serum of a pig, horse, fowl, or any other
animal into the rabbit, instead of human blood-serum. In some
countries, notably in Germany and Austria, this test has already been
adopted by the courts of justice and has been found extremely useful
in the detection of crime.
Further investigation showed that these blood tests might be
employed to determine the degrees of relationship between different
animals, for, although a prompt and strong reaction is usually obtained
only from the blood of the same species as that from which the original
injection into the rabbit was taken, the blood of nearly allied species,
such as the horse and donkey, for example, gives a weaker and slower
precipitation. By using stronger solutions and allowing more time,
quite distant relationships may be brought out. Nuttall and his
collaborator, Graham-Smith, made many thousands of such experi-
ments bearing upon the problems of relationship and classification
and it is of great significance to note that their highly interesting
and important results contain few surprises, but, in almost all cases,
merely serve to confirm the conclusions previously reached by other
methods, such as comparative anatomy and palaeontology. It will
be instructive to quote some of these results, the quotations being
taken from "Blood Immunity and Blood Relationship, by G. H. F.
Nuttall, including Original Researches by G. L. Graham-Smith and
T. S. P. Strangeways, " Cambridge, 1904.
"In the absence of palaeontological evidence the question of the
interrelationship amongst animals is based upon similarities of struc-
ture in existing forms. In judging of these similarities, the subjective
element may largely enter." "The very interesting observations
upon the eye made by Johnson also demonstrate the close relationships
between the Old World forms and man, the macula lutea tending to
disappear as we descend in the scale of New World Monkeys and being
absent in the Lemurs. The results which I pubUshed upon my tests
with precipitins directly supported this evidence, for the reactions
no EVOLUTION, GENETICS, AND EUGENICS
obtained with the bloods of Simiidae (i.e., Man-like Apes) closely
resemble those obtained with human blood, the bloods of Cercopithe-
cidae (Old World Monkeys) came next, followed by those of Cebidae
and Hapalidae (New World Monkeys and Marmosets) which gave
but slight reactions with anti-human serum, whilst the blood of
Lemuroidea gave no indication of blood-relationship." "A perusal
of the pages relating to the tests made upon the many bloods I have
examined by means of precipitating anti-sera, will very clearly show
that this method of investigation permits of our drawing certain
definite conclusions. It is a remarkable fact .... that a common
property has persisted in the bloods of certain groups of animals
throughout the ages which have elapsed during their evolution from
a common ancestor, and this in spite of differences of food and habits
of life. The persistence of the chemical blood-relationship between
the various groups of animals serves to carry us back into geological
times, and I beheve we have but begun the work along these lines,
and that it will lead to valuable results in the study of various problems
of evolution."
The general conclusions on interrelationships, so far as they are of
particular interest for our purpose, reached by Nuttall and Graham-
Smith as the result of many thousands of blood tests, may be summa-
rized as follows:
1. If sufficiently strong solutions be used and time enough be
allowed, a relationship between the bloods of all mammals is made
evident.
2. The degrees of relationship between man, apes and monkeys
have already been noted.
3. Anti-carnivore sera show "a. preponderance of large reactions
amongst the bloods of Carnivora, as distinguished from other Mam-
malia; the maximum reactions usually take place amongst the more
closely related forms in the sense of descriptive zoology."
4. Anti-pig serum gives maximum reactions only with the bloods
of other species of the same family, moderate reactions those of rumi-
nants and camels, and moderate or sUght reactions with those of
whales. Anti-llama serum gives a moderate reaction with the blood of
the camel, and the close relationship between the deer family and the
great host of antelopes, sheep, goats and oxen is clearly demonstrated.
5. An ti- whale serum gives maximum reactions only with the
bloods of other whales and slight reactions with those of pigs and
ruminants.
EVIDENCE FROM BLOOD TESTS III
6. A close relationship is shown to exist between all marsupiak,
with the exception of the Thylacine, or so-called Tasmanian Wolf.
7. Strong anti-turtle serum gives maximum reactions only with
the bloods of turtles and crocodiles; with those of lizards and snakes
the results are almost negative. With the egg-albumins of reptiles
and birds a moderate reaction is given.
8. Anti-lizard serum produces maximum results with the bloods
of lizards and reacts well with those of snakes.
9. These experiments indicate that there is a close relationship
between lizards and snakes, on the one hand, turtles and crocodiles
on the other. They further indicate that birds are more nearly allied
with the turtle-crocodile series than with the lizard-snake series,
results for which palaeontological studies had already prepared us.
10. "Tests were made by means of anti-sera for the fowl and
ostrich upon 792 and 649 bloods respectively. They demonstrate a
similarity in blood constitution of all birds, which was in sharp con-
trast to what had been observed with mammalian bloods, when acted
upon by anti-mammalian sera. Diflfereaces in the degree of reaction
were observed, but did not permit of drawing any conclusions."
11. I have already called attention to the fact that the prob-
lematical Horseshoe-crab is indicated by its embryology to be related
to the air-breathing spiders and scorpions rather than to the marine
Crustacea. It is of exceptional interest to learn that embryology is
supported by the results of the blood tests.
It must not be supposed that there is any exact mathematical
ratio between the degrees of relationship indicated by the blood tests
and those which are shown by anatomical and palaeontological
evidence. Any supposition of the kind would be immediately nega-
tived by the contrast between the blood of mammals and that of birds.
It could hardly be maintained that an ostrich and a parrot are
more nearly allied than a wolf and a hyena and yet that would be
the inference from the blood tests. Like all other anatomical and
physiological characters, the chemical composition of the blood is
subject to change in the course of evolution and these developmental
changes do not keep equal pace in all parts of the organism. It is the
rule rather than the exception to find that one part of the structure
advances much more rapidly than other parts, such as the teeth, the
skull, or the feet. The human body is, fortunately for us, of rather
a primitive kind, while the development of the brain is far superior
to that of any other mammal and this great brain development has
112 EVOLUTION, GENETICS, AND EUGENICS
necessitated a remodeling of the skull. On the other hand, the
skeleton, limbs, hands and feet are but slightly specialized. In the
elephant tribe, so far as we can trace them back in time, there has
been little change, save in size, in the structure of the body or limbs,
while the teeth and skull have passed through a series of remarkable
changes. It is for this reason that it is unsafe to found a scheme of
classification, which is meant to be a brief expression of relationship,
upon a single character, for the result is almost invariably misleading.
The results of blood tests must be critically examined and checked by
a comparison with the results obtained by other methods of investiga-
tion, but after every allowance has been made, these tests are very
remarkable.
The blood tests have brought very strong confirmation to the
theory of evolution and from an entirely unexpected quarter; they
come as near to giving a definite demonstration of the theory as we
are likely to find, until experimental zoology and botany shall have
been improved and perfected far beyond their present state.
i
CHAPTER IX
EVIDENCES FROM EMBRYOLOGY
THE FACTS OF REPRODUCTION AND DEVELOPMENT
It is now definitely known that all living creatures are mortal, at
least as individuals, but they all have the capacity of continuing their
life by the reproduction of offspring. This physical immortality is
based upon an actual transmission from parent to offspring of some
material substance which is so organized chemically as to be fully
representative of the race or stock to which the parent belongs.
Reproduction may be asexual or sexual. In asexual development
a new individual may be produced by a process oi fission (dividing the
parent into two or more parts, each of which has the capacity to
develop into a whole new individual) ; by budding (the production of
new individuals by means of outgrowths of the parent-body) ; or by
giving off spores or eggs capable of development without fertiliza-
tion (parthenogenesis) . In sexual reproduction two kinds of parent-
individuals exist : one a female which is capable of giving off relatively
large single cells, called eggs (ova) ; and the other a male, which is
capable of producing minute, usually motile cells, called spermatozoa.
A union of ovum and spermatozoon is usually necessary before the
ovum can begin its development. It is the sexual method of repro-
duction that will chiefly concern us here, and, for present purposes, we
may omit any further mention of the various asexual methods.
An ovimi may be conceived of as an individual of some definite
species or race reduced to the very lowest terms. It exhibits the
characteristic cell structure, consisting of cytoplasm and nucleus, cell
membrane, nuclear membrane, usually a centrosome (Fig. 43).
Further details as to the minute structure of the nucleus are given in
chapter xxxiii, where the mechanism of Mendelian heredity is dealt
with.
"The reproductive cells from the two sexes," says Wright,' "have
very different appearances. In mammals, the ovum is a relatively
large, spherical cell, just visible to the naked eye.
' From Sewall Wright, Principles of Livestock Breeding, United States Depart-
ment of Agriculture, Bulletin No. 905.
"3
114 EVOLUTION, GENETICS, AND EUGENICS
"In birds, the yolk of an egg is really a single ovum, distended to
an enormous size by food material. The sperm cell is very much
smaller and can be seen well only with a high-power microscope. It is
something like a tadpole in shape, having a small cell body, containing
a little nucleus, and attached to this a long, whiplike process which
beats rapidly while the cell is alive, enabling it to seek out and unite
with the large passive egg in the act of fertilization. Enormous num-
bers of sperm cells are produced by the male, but only one takes part
in fertilization. After the first has penetrated the membrane of an
egg cell, a change takes place in the latter which prevents the entrance
of others.
"The sperm activates certain formerly inert substances in the egg
and the new combination cell (the zygote) starts almost at once to
produce a new individual."
OUTLINE or ANIMAL DEVELOPMENT'
D. S. JORDAN AND V. L. KELLOGG
The embryonic development is from the beginning up to a certain
point practically alike, looked at in its larger aspect, for all the many-
celled animals. That is, there are certain principal or constant
characteristics of the beginning development which are present in the
development of all many-celled animals. The first stage or phenome-
non of development is the simple fission of the germ cell into halves
(Fig. 25, b). These two daughter cells next divide so that there are
four cells ic) ; each of these divides, and this division is repeated until
a greater or lesser number (varying with the various species or groups
of animals) of cells is produced. These cells may not all be of the same
size, but in many cases they are, no structural differentiation whatever
being apparent among them.
The phenomenon of repeated division of the germ cell is called
cleavage, and this cleavage is the first stage of development in the
case of all many-celled animals. The germ or embryo in some animals
consists now of a mass of few or many undifferentiated primitive cells
lying together and usually forming a sphere (Fig. 2^, e), or perhaps
separated and scattered through the food yolk of the egg. The next
stage of development is this: the cleavage cells arrange themselves so
as to form a usually hollow sphere or ball, the cells lying side by side to
' From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life (copyright
1Q07). Used by special permission of the publishers, D. Appleton & Company.
EVIDENCES FROM EMBRYOLOGY
^15
form the outer circumferentiarwall of this hollow sphere (/). This is
called the blastula or blastoderm stage of development, and the embryo
itself is called the blastula or blastoderm. This stage also is common
to all the many-celled animals. The next stage in embr}^onic develop-
ment is formed by the bending inward of a part of the blastoderm cell
layer, as shown in (g) (or the splitting off inwardly of cells from a
special part of the blastula cell layer). This bending in may produce
a small depression or groove; but whatever the shape or extent of the
sunken-in part of the blastoderm, it results in distinguishing the
blastoderm layer into two parts, a sunken-in or inner portion called
Fig. 25. — First stages in the embryonic development of the pond snail,
Lymnaetis. a, egg cell; b, first cleavage; c, second cleavage; d, third cleavage;
e, after numerous cleavages; /, blastula — in section; g, gastrula just forming —
in section; h, gastrula completed — in section. (From Jordati and Kellogg, after
Rahl.)
the endoblast and the other unmodified portion called the edoblast.
Endo- means within, and the cells of the endoblast often push so far
into the original blastoderm cavity as to come into contact with the
cells of the ectoblast and thus obliterate this cavity Qi). This third
well-marked stage in the embryonic development is called the gastrula
stage, and it also occurs in the development of all or nearly all many-
celled animals.
In the case of a few of the simple many-celled animals the embryo
hatches — that is, issues from the egg at the time of or very soon after
reaching the gastrula stage. In the higher animals, however, develop-
ment goes on within the egg or within the body of the mother until
the embr}'0 becomes a complex body, composed of many various
Il6 EVOLUTION, GENETICS, AND EUGENICS
tissues and organs. Almost all the development may take place within
the egg, so that when the young animal hatches there is necessary little
more than a rapid growth and increase of size to make it a fully
developed mature animal. This is the case with the birds; a chicken
just hatched has most of the tissues and organs of a full-grown fowl,
and is simply a little hen. But in the case of other animals the young
hatches from the egg before it has reached such an advanced stage of
development; a young starfish or young crab or young honeybee just
hatched looks very different from its parent. It has yet a great deal
of development to undergo before it reaches the structural condition
of a fully developed and fully grown starfish or crab or bee. Thus
the development of some animals is almost wholly embryonic develop-
ment — that is, development within the egg or in the body of the
mother — ^while the development of other animals is largely post-
embryonic, or larval development, as it is often called. There is no
important difference between embiyonic and postembryonic develop-
ment. The development is continuous from egg cell to mature animal,
and whether inside or outside of an egg it goes on regularly and uninter-
ruptedly.
The cells which compose the embryo in the cleavage stage and
blastoderm stage, and even in the gastrula stage, are apparently all
similar; there is little or no differentiation shown among them. But
from the gastrula stage on, development includes three important
things; the gradual differentiation of cells into various kinds to form
the various kinds of animal tissues; the arrangement and grouping
of these cells into organs and body parts; and finally the developing of
these organs and body parts into the special condition characteristic
of the species of animal to which the developing individual belongs.
From the primitive undifferentiated cells of the blastoderm, develop-
ment leads to the special cell types of muscle tissue, of bone tissue, of
nerve tissue; and from the generalized condition of the embryo in its
early stages, development leads to the specialized condition of the
body of the adult animal. Development is from the general to the
special, as was said years ago by von Baer, the first great student of
development.
A starfish, a beetle, a dove, and a horse are all alike in their
beginning — that is, the body of each is composed of a single cell, a
single structural unit. And they are all alike, or very much alike
through several stages of development; the body of each is first a
single cell, then a number of similar undifferentiated cells, and then a
EVIDENCES FROM EMBRYOLOGY 1 1?
blastoderm consisting of a single layer of similar undifferentiated cells.
But soon in the course of development the embryos begin to differ, and
as the young animals get further and further along in the course of
their development, they become more and more different until each
finally reaches its fully developed mature form, showing all the great
structural differences between the starfish and the dove, the beetle and
the horse. That is, all animals begin development apparently alike,
but gradually diverge from each other during the course of develop-
ment.
There are some extremely interesting and significant things about
this divergence to which attention should be given. While all animals
are apparently alike structurally at the beginning of development, so
far as we can see, they do not all differ noticeably at the time of the first
divergence in development. The first divergence in development is to
be noted between two kinds of animals which belong to different great
groups or classes. But two animals of different kinds, both belonging
to some one great group, do not show differences until later in their
development. This can best be understood by an example. All the
butterflies and beetles and grasshoppers and flies belong to the great
group or class of animals called Insecta, or insects. There are many
different kinds of insects, and these kinds can be arranged in subor-
dinate groups (orders), such as the Diptera, or flies, the Lepidoptera,
or butterflies and moths, and so on. But all have certain structural
characteristics in common, so that they are comprised in one great
class — the Insecta. Another great group of animals is known as the
Vertebrata, or backboned animals. The class Vertebrata includes the
fishes, the batrachians, the reptiles, the birds and the mammals, each
composing a subordinate group, but all characterized by the possession
of a backbone or, more accurately speaking, of a notochord, a back-
bonelike structure. Now, an insect and a vertebrate diverge very
soon in their development from each other; but two insects, such as a
beetle and a honeybee, or any two vertebrates, such as a frog and a
pigeon, do not diverge from each ither so soon. That is, all vertebrate
animals diverge in one direction from the other great groups, but all
the members of the great group keep together for some time longer.
Then the subordinate groups of the Vertebrata, such as the fishes, the
birds, and the others, diverge, and still later the different kinds of
animals in each of these groups diverge from each other.
That the course of development of any animal from its beginning
to fully developed adult form is — in all its essentials — fixed and certain
Ii8 EVOLUTION, GENETICS, AND EUGENICS
is readily seen. All rabbits develop in the same way; every grass-
hopper goes through the same developmental changes from single egg
cell to the full-grown, active hopper as every other grasshopper of the
same kind — that is, development takes place according to certain
natural laws; the laws of animal development. These laws may be
roughly stated as follows: All many-celled animals begin life as a
single cell, the fertilized egg cell; each animal goes through a certain
orderly series of developmental changes which, accompanied by growth
leads the animal to change from a single cell to the many-celled, com-
plex form characteristic of the species to which the animal belongs;
this development is from simple to complex structural condition; the
development is the same for all individuals of one species. While all
animals begin development similarly, the course of development in
the different groups soon diverges, the divergence being of the nature
of a branching, like that shown in the growth of a tree. In the free
tips of the smallest branches we have represented the various species
of animals in their fully developed condition, all standing more or less
clearly apart from each other. But in tracing back the development
of any kind of animal we soon come to a point where it very much
resembles or becomes apparently identical with the development of
some other kind of animal, and, in addition, the stages passed through
in the de \'elopmental course may very much resemble the fully devel-
oped, mature stages of lower animals. To be sure, any animal at any
stage in its existence differs absolutely from any other kind of animal,
in that it can develop into only its own kind of animal. There is
something inherent in each developing animal that gives it an identity
of its own. Although in its young stages it may be hardly distin-
guishable from some other kind of animal in similar stages, it is sure
to come out, when fully developed, an individual of the same kind as
its parents were or are. A very young fish and a very young sala-
mander are almost indistinguishably alike, but one is sure to develop
into a fish and the other into a salamander. This certainty of an
embryo to become an individual of a certain kind is called the law of
heredity. Viewed in the light of development, there must be as great
a difference between one egg and another as between one animal and
another, for the greater difference is included in the less.
The significance of the developmental phenomena is a matter about
which naturalists have yet very much to learn. It is believed, how-
ever, by practically all naturalists that many of the various stages in
^he development of an animal correspond to or repeat, in many
EVIDENCES FROM EMBRYOLOGY
119
fundamental features at least,"the structural condition of the animal's
ancestors. Naturalists believe that all backboned or vertebrate
Fig. 26. — Stages in the development of the prawn, Pencils potimirium. A
Nauplius larva; B, first zoea stage; C, second zoea stage. {From Jordan and
Kellogg, after Fritz Miiller.)
Fig. 27. —Later stages in the development of the prawn, Peneus potimirium.
Z?, Mysis stage; £, adult stage. {Fro7n Jordan and Kellogg.)
I20
EVOLUTION, GENETICS, AND EUGENICS
animals are related to each other through being descended from a
common ancestor, the first or oldest backboned animal. In fact, it is
because all these backboned animals — the fishes, the batrachians, the
reptiles, the birds, and the mammals — have descended from a common
ancestor that they all have a backbone. It is believed that the
descendants of the first backboned animal have in the course of many
generations branched off Httle by little from the original type until
there came to exist very real and obvious differences among the back-
boned animals — differences which among the living backboned animals
are familiar to all of us. The course of development of an individual
animal is believed to be a very rapid and evidently much condensed and
changed recapitulation of the history
which the species or kind of animal to
which the developing individual belongs
has passed through in the course of its
descent through a long series of gradually
changing ancestors. If this is true, then
we can readily understand why a fish
and a salamander, a tortoise, a bird, and
a rabbit, are all much alike, as they
really are, in their earlier stages of
development, and gradually come to
differ more and more as they pass
through later and later developmental
stages. A crab has a tail in one of its
developmental stages, so that at that
time it looks like and really is like the
mature stage of some tailed crustacean
like a crayfish. A barnacle, which looks
a little like a crayfish or crab in its ma-
ture stage, is hardly to be distinguished in its immature life from a
young crab or lobster. Sacculina, which is a still more degenerate
crustacean, is only a sort of feeding sac with rootlet-hke processes
projecting into the body of the host crab on which it lives as a
parasite, but the young free-swimming Sacculina is essentially like a
barnacle, crayfish, or crab in its young stage.
However, it is obvious that this recapitulation or repetition of
ancestral stages is never perfect, and it is often so obscured and modi-
fied by interpolated adaptive stages and characters that but little of an
animal's ancestry can be learned from a scrutiny of its development.
Fig. 2 8. — Metamorphosis of a
barnacle, Lepas. a, larva ; b, adult.
{From Jordan and Kellogg.)
EVIDENCES FROM EMBRYOLOGY I2i
The fascinating biogenetic law of Miiller and Haeckel summed up
in the phrase, "ontogeny is a recapitulation of phylogeny'' must not
be too heavily leaned on as a support for any speculations as to the
phyletic affinities of any species or group of species of organisms.
"Embryology is an ancient manuscript with many of the sheets lost,
others displaced, and with spurious passages interpolated by a later
hand."
CHAPTER X
CRITIQUE OF THE RECAPITULATION THEORY'
W. B. SCOTT
Embryology is the study of the development of the individual
organism from its beginning in the egg to the attainment of the adult
condition. This individual development is called ontogeny and the
question of the relation of ontogeny to the ancestral history of the
species, or phytogeny, constitutes one of the main problems of embry-
ology. Around this problem many controversies have raged, contro-
versies which have by no means arrived at a definite solution, even
to-day. Thirty years ago the "recapitulation theory" was well-nigh
universally accepted, according to which the individual development,
or ontogeny, was regarded as an abbreviated repetition of the ances-
tral history of the species, or phylogeny. Haeckel called this theory
the "fundamental biogenetic law" and upon it he established his
whole "History of Creation." Nowadays, that "fundamental law"
is very seriously questioned and by some high authorities is altogether
denied. However, even those who take this extreme position con-
cerning the recapitulation theory see in the facts of embryology one
of the strongest supports of the doctrine of evolution.
It was very early recognized that the recapitulation theory could
not be applied with literal exactness, but was subject to certain
important exceptions and qualifications.
I. That the history must have been enormously abbreviated.
After three weeks of incubation the tiny speck of protoplasm, which
forms a circular mark on the yolk of a hen's egg, is developed into a
fully formed chick, ready for hatching and able in large degree to take
care of itself. On the other hand, the evolution of birds from their
invertebrate ancestors, through the fishes, amphibians, and reptiles,
the separation of the gallinaceous stock from other birds and the
differentiation of this particular species were extremely slow processes,
extending through unnumbered millions of years. Admitting reca-
pitulation to the fullest extent, it is evidently a physical impossibihty
' From W. B. Scott, The Theory of Evolution (copyright 1917). Used by
special permission of the publishers. The Macmillan Company-
122
THE RECAPITULATION THEORY 12;
that it should be a perfect repetition of phylogeny; very much of the
long story must of necessity be omitted.
2. Through all the stages of development the embryo must be
rendered able to Uve and grow and thrive through adaptation to it?
surroundings and changes in its environment. In some animals
development takes place within the body of the mother; in others the
embryo is protected by the hard egg-shell, as in birds, while the eggs
of certain fishes and many invertebrates float freely in the sea and are
almost without protection. Such differences in environment necessi-
tate differences in the mode of development, while the presence or
absence of a large amount of inert food-material, or yolk, exerts a great
influence in determining the steps of ontogeny.
3. Many animals pass through a larval stage of development, in
which the immature young leads an independent and self-sustaining
existence, during which it is very different in appearance and structure
from its adult parents. Familiar instances of this mode of develop-
ment are to be found in the tadpole, which is the larva of the frog, and
the caterpillar, the larva of a butterfly. Larvae are fully subject to
the struggle for existence and must adapt themselves to their environ-
ment and to changes in that environment, exactly as do adults, if they
are to survive. In this way many changes are introduced into the
ontogeny which can have no phylogenetic significance. It is found in
several known instances, that nearly aUied species, Uving under
different conditions, have quite different modes of ontogeny, though
their ancestral history must have been substantially identical. In one
and the same species of marine worms, for example, which inhabits
both the warm Mediterranean and the cold waters of the North Sea,
the larva of the northern form is quite distinct from that of the
southern. In attempting to interpret the meaning of embryological
facts, it is thus necessary to distinguish sharply between those features
which are derived from a long inheritance, and are therefore called
palingenetic, from those which have been secondarily introduced in
response to the changing needs of embryonic or larval life. These
secondary features are termed cenogenetic.
"If we are compelled to admit that cenogenetic characters are
mtermingled with palingenetic, then we cannot regard ontogeny as a
pure source of evidence regarding phyletic relationships. Ontogeny
accordingly becomes a field in which an active imagination has full
scope for its dangerous play, but in which positive results are by no
means everywhere to be obtained. To attain such results, the palin-
124 EVOLUTION, GENETICS, AND EUGENICS
genetic and cenogenetic phenomena must be sifted apart, an operation
which required more than one critical grain of salt. On what grounds
shall this critique be based ? Assuredly not by way of a vicious circle
on the ontogeny again; for if cenogenetic characters are present in one
case, who will guarantee that a second case, used for a comparison with
the first, does not Ukewise appear in cenogenetic disguise ? If it once
be admitted that not everything in development is palingenetic, that
not every ontogenetic fact can be accepted at its face value, so to
speak, it follows that nothing in ontogeny is immediately available
for the critique of embryonic development. The necessary critique
must be drawn from another source."
These remarks of Gegenbaur's were called forth by the state of
wild speculation into which embryological work had fallen. As there
were no generally accepted canons of interpretation for the facts of
embryological development, different writers interpreted these facts
in the most divergent and contradictory manner, resulting in a chaotic
confusion, which led to a strong reaction against the whole method,
though there can be little doubt that this reaction has gone too far.
"It must be evident to any candid observer, not only that the
embryological method is open to criticism, but that the whole fabric
of morphology, so far as it rests upon embryological evidence, stands
in urgent need of reconstruction. For twenty years embryological
research has been largely dominated by the recapitulation theory;
and unquestionably this theory has illuminated many dark places and
has solved many a perplexing problem that without its aid might have
remained a standing riddle to the pure anatomist. But while fully
recognizing the real and substantial fruits of that theory, we should not
close our eyes to the undeniable fact that it, like many another fruit-
ful theory, has been pushed beyond its legitimate limits. It is largely
to an overweening confidence in the validity of the embryological
evidence that we owe the vast number of the elaborate hypothetical
phylogenies which confront the modern student in such bewildering
confusion. The inquiries of such a student regarding the origin of any
of the great principal types of animals involve him in a labyrinth of
speculation and hypothesis in which he seeks in vain for conclusions
of even an approximate certainty."
Many otiier equally vigorous and well-deserved criticisms of the
embryological method might be cited, but it should be emphasized that
these criticisms are aU directed against the appUcation of the method
to the solution of definite and concrete problems of descent and
THE RECAPITULATION THEORY 125
relationship. None of them denies and many strongly affirm that
embryology affords some of the strongest and most convincing evi-
dence in favor of the evolutionary theory.
Let us examine some of this evidence. To begin with, it should
be noted that, in following out the ontogeny or individual develop-
ment, the observer witnesses the formation of something new, not
merely the enlargement and unfolding of a pre-existing organism,
though the theory of preformation, which was widely accepted in the
eighteenth century, looked upon ontogeny precisely in that way, as
the growth of a germ which was the miniature of the parent. Such a
theory was possible only before the development of microscopic
technique had enabled the observer to detect the actual successive
steps of change. The egg is a single cell, with the nucleus and all the
parts of other undifferentiated cells, though it may be enormously
enlarged by the presence of food-yolk. In the hen's egg this food-yolk
is quite inert and the activity of development is confined to the minute
disc of protoplasm on the outside of the yolk, while in the frog's egg
the yolk is disseminated, though not uniformly, throughout the egg
and in the mammalian egg, which is microscopic in size, there is no
yolk. It is a very remarkable fact that all of the vertebrated animals,
fishes, amphibians, reptiles, birds and mammals, however different
their habits and modes of hfe, have a mode of ontogeny which is of
even more characteristically and unmistakably the same plan than is
the type of their adult structure, which was described in the last
chapter. The egg, or the active portion of it, divides in a definite and
regular manner into a very large number of cells, which arrange them-
selves in definite layers, an outer and an inner, and within these layers
cell-aggregates form incipient organs, which, step by step, take on the
adult condition. Not only is the plan and type of development
essentially similar throughout the whole phylum of the vertebrates,
but, in accordance with the recapitulation theory, many structural
features which are permanent in lower forms appear in the embryos of
higher and more advanced types. In the latter, however, these
features are transitory and, in the course of development, they either
disappear, or are so modified as to be very different, sometimes unrecog-
nizable, in the adults.
At a certain stage of the ontogeny the embryo of a manmial has
gill-pouches like a fish, the skeletal supports of the gill-pouches, the
arteries and veins which supply them with blood, the structure of the
heart, in short, the entire plan of the circulatory system is fish-like.
126
EVOLUTION, GENETICS, AND EUGENICS
At a later stage most of the gill-pouches have been obUterated, but one
is retained and converted into the Eustachian canal, which connects
the throat with the middle ear, inside of the ear-drum. Similarly, the
embryological evidence shows that the lungs of air-breathers have been
derived from the swim-bladder of fishes, a conclusion which had
already been reached by comparative anatomy, for in a remarkable
Fig. 29. — Embryos in corresponding stage of development of shark (A),
fowl (J5), and man (C); g, gill slits. {From Scott.)
group, known as the Dipnoi or lung-fishes, the air-bladder is utilized
for purposes of respiration.
It has been objected that, while embryology may prove relation-
ship within a single type, it fails to demonstrate any connection
between different types, but this is not altogether true. The Tuni-
cata, a curious group of marine animals once referred to the Mollusca,
are shown by their ontogeny to be related to the vertebrates and the
same is true of certain marine worms {Balanoglossus). Indeed, most
modern zoologists have adopted a scheme of classification, in which
THE RECAPITULATION THEORY 12?
the type Chordata includes not only the true vertebrates, but also the
Lancelet {Amphioxus), the tunica tes, and Balanoglosstis; this scheme
is founded upon the embryological evidence. Among the inverte-
brates even more remarkable examples have been observed. Such
radically different types as the segmented worms and the shell-
fish (Mollusca) are brought into relationship by their ontogeny and
their closely similar types of larvae, as are also, though less distinctly,
the brachiopods or lamp-shells, and the Bryozoa. The Horseshoe-
crab, or King-crab, so abundant along our Atlantic coast, was long
of uncertain affinities; originally referred to the Crustacea, largely
because of its marine habits of life, embryology makes much more
probable its relationship to the air-breathing scorpions and spiders, a
result which has been examined previously from another point of view
in connection with blood-tests.
Even before the publication of Darwin's Origin of Species one
of the great stumbling blocks in the way of the theory of special crea-
tion was the existence in a great many animals of rudimentary organs,
or such as are so far reduced and atrophied as to be of no service to
their possessors. An analogy employed by my lamented friend,
Mr. Richard Lydekker, may be advantageously repeated here. Let us
suppose that a screw-steamer, with longitudinal shaft leading aft from
the engine-room to the stern, where it carries the propeller, should, on
close examination, reveal many signs that it has originally been a
" side- wheeler," or paddle-boat. Recognizable remnants of paddle-
boxes, of bearings for a transverse shaft, and the like, are found; what
would be the inevitable conclusion ? No one would maintain that a
naval architect, in possession of his senses, in constructing a screw-
steamer would deliberately introduce features which are useful and
appropriate only in a paddle-boat. The only reasonable explanation
would be that the vessel had originally been built as a paddle-boat and
had subsequently been converted into a screw-steamer and in the
conversion it had not been found necessary completely to eradicate all
traces of the original construction. Obviously, the same reasoning
applies to rudimentary organs. The only satisfactory explanation of
such useless remnants is that their possessors are descendants of
ancestors in which those organs were fully functional. It seems quite
absurd to assume that, in a separately and specially created anixnal,
useless structures, reminiscent of other animals in which the same
structures are useful and valuable, should be included, merely to
indicate ideal relationships and community of plan.
128 EVOLUTION, GENETICS, AND EUGENICS
It was sought to break the force of this very serious objection to
the theory of special creation by saying that apparently useless organs
may nevertheless have functions which are still unknown to us and
may be revealed by future discovery. In certain cases, like that of the
thyroid gland in the neck, this contention has been justified, but there
are many others to which it does not apply. For example, in the great
and varied whale-tribe (order Cetacea) which includes the right, or
whalebone, whales, the sperm-whales, the porpoises, dolphins, etc.,
the forelimbs have been converted into swimming paddles, but the
hind limbs appear to have vanished completely, leaving no externally
visible trace. Internally, however, recognizable remnants of the hind
limb-bones may be found in various stages of reduction, which diJQFer
in the different members of the order. In the Greenland Right Whale
the hip-bone, thigh-bone and shin-bone are indicated; in the Fin whale
only the hip-bones and a minute rudiment of the thigh-bone are to be
found; in the toothed whales only an almost unrecognizable remnant
of the hip-bone is left and in one of the dolphins even that has dis-
appeared. Similarly, the snakes have lost their limbs completely, so
far as external appearance is concerned, and in most members of the
group no trace of limbs is to be found on dissection, but in certain
snakes the rudiments of limbs are to be detected. Leaving aside all
preconceptions, which is the more probable explanation of such
phenomena, the theory of special creation or the theory of evolution ?
Even if it were admitted that all rudimentary organs and struc-
tures found in the adult have a certain unknown use and value, no one
could maintain this with regard to the countless instances of structures
which are developed in the embryo, but disappear entirely before
birth. It is possible to mention but a very few of such instances out
of the great number that have already been observed and recorded,
but these few will suffice to illustrate the principle involved.
" Examples of this may be cited from the most widely different
groups: in the embryo of insects, especially of beetles, pairs of legs
are formed within the egg, not only on the head and thorax, but also
on the abdomen, but while those on the head are transformed into
mouth-parts, those on the thorax are farther developed in their joint-
ing and musculature to be locomotive legs, those on the abdomen are
again resorbed. In many fresh-water worms, the eggs of which are
laid in a cocoon, from which they are hatched as a finished, minute,
crawling worm, larval organs are nevertheless formed, which recall
those of the Trochophore,the larva of the original worms, which swims
THE RECAPITULATION THEORY
129
freely in the sea. However, these larval organs .... are never
properly functional, since no actually free-swimming larva is developed
but the embryo merely floats in the albuminous fluid of the cocoon.
"A particularly beautiful example is offered by the whales in their
embryological development, which has been thoroughly studied by
Kukenthal. In the adult condition they show only the anterior
extremities, but in the embryo the posterior pair, with their skeletal
parts, are formed,but are afterwards completely atrophied. Although
they are mammals, in the adult condition they have absolutely no
covering of hair, since in their aquatic life another and more effective
protection against loss of heat is given by means of a thick layer of
blubber; only a few coarse bristles, partly with particular functions,
have persisted on a few parts of the body. But in the embryo a dense
covering of hair is formed, which is later transformed in a peculiar
manner and atrophied. Further, a series of whales have no teeth in
the adult condition, but only the well-known, eel-trap-like, horny
plates, from which whale-bone is produced. Nevertheless, in the
embryo there is a dentition of numerous teeth, which are, however,
resorbed, without ever piercing the gum."^
Throughout the great group of the ruminants, which includes the
oxen, buffaloes, bison, sheep, goats, antelopes, deer and giraffes, the
collar-bone is invariably lacking, since it is superfluous on account of
the exclusively locomotive manner in which the fore legs are employed.
In the embryo sheep the collar-bone is established and even, to some
extent ossified, but is subsequently resorbed and disappears entirely.
No doubt, the collar-bone will be found in many other embryo rumi-
nants, when the proper examination shall have been made, but its
demonstrated presence in the foetal sheep is sufficiently striking. In
the higher mammals the number of teeth was originally 44, or 1 1 on
each side of both upper and lower jaws, but in most of the modern or
existing groups of these higher mammals this number has been very
considerably reduced through the suppression of certain teeth. We
have every reason to beheve that the ancestors of the forms with
reduced dentition possessed teeth in full numbers and that there has
actually been a loss of teeth in the course of descent. This conclusion
is abundantly confirmed by the facts of embryology. Take, for
example, the great group of the gnawing mammals or Rodentia, in
which the front teeth or incisors, above and below, are reduced to one
on each side, except in the rabbits. The incisors are chisel-shaped and
' Otto Maas, Die Abstammungslehre, pp. 273-74.
I30 EVOLUTION, GENETICS, AND EUGENICS
are faced with hard enamel, so that the action of the upper teeth upon
the lower keeps the cutting edges extremely sharp; these teeth do not
form roots, but continue to grow throughout the lifetime of the animal.
Between the chisel-like incisors and the grinding teeth, there is a long
toothless gap, which, we assume, was, in the ancestors of the rodents,
occupied by the second and third incisors, the canine and two or more
grinders. This conclusion is justified by the facts of embryology;
for instance, in the embryo of the squirrel several of the missing teeth
are begun as distinct tooth-germs, but fail to develop, never cut the
gum and are resorbed before birth.
All available evidence points to the conclusion that birds are
descended from reptiles, a conclusion which is especially strengthened
by the facts of palaeontology and will be examined more at length
in the following lecture. Such a descent explains many otherwise
puzzling features in the ontogeny of birds, in which reptilian charac-
teristics appear in transitory fashion and are either modified so as to
take on typically bird-like character, or are suppressed altogether. A
remarkable example of this is the formation of rudimentary teeth in
certain embryonic birds, followed by their resorption and disappear-
ance before hatching.
It can hardly be contended that these rudimentary structures,
which are confined to the embryonic stages of development and of
which no trace remains in the adult, are so indispensable to the
processes of ontogeny, that they were specially created to serve this
temporary purpose. For such a contention there is not a particle
of evidence and the theory of evolution, which regards these structures
as useless remnants, due to inheritance from ancestors in which the
structures are functional, offers much the most satisfactory solution
of the problem that has yet been suggested.
Embryology further shows that evolution is not invariably an
advance from lower and simpler to higher and more complex types,
but may be by way of degeneration and degradation. The adoption
of a parasitic mode of life is very apt to cause such degradation, and
some very remarkable instances of the degeneration of parasites have
been observed. An instructive example that may be cited is that of
Sacculina, a nondescript creature that is parasitic on certain species
of crabs. The parasite is attached to the body of its victim, under-
neath the tail, by means of root-like fibres which penetrate and ramify
throughout the interior of the crab. The root-like fibres absorb nutri-
ment and convey it to the body of the parasite, which is reduced to a
THE RECAPITULATION THEORY 131
mere bag, without appendages, muscles, nervous system, sensory
apparatus, digestive tract, or any determinable organs save those of
reproduction. The creature has the power of assimilating the nutri-
tive juices which are conveyed to it by the root-like filaments from the
body of its host, and the power of reproduction, and it must have some
respiratory and excretory capacity, though there are neither gills nor
glands. From an examination of the adult parasite alone, it would be
quite impossible to classify it and determine the type and class to
which it should be referred, but embryology solves the problem. From
the egg is hatched a free-swimming larva, which has jointed append-
ages, nervous, muscular and digestive systems and, in short, clearly
belongs to that group of the Crustacea which includes the barnacles.
This is degeneration carried nearly to the utmost possible extreme and
yet the individual development shows the derivation of this otherwise
problematical parasite and the steps through which it passed in its
deterioration.
It was stated above that several distinguished naturalists alto-
gether reject the recapitulation theory as a means of interpreting the
facts of embryology. They do this on the ground that, inasmuch as
changes and innovations in form or structure must arise in the germ-
plasm, at the very beginning of ontogeny, there is no reason why such
changes might not involve the whole course of embryological develop-
ment. To my mind this a priori objection to the recapitulation theory
is quite without force in view of the great body of observed facts, but
there is no time to enter upon a discussion of such an abstract and
difficult problem. For our present purpose, however, it is important
to note that these objectors are staunch evolutionists and find in the
community of mode in ontogeny between different classes of organ-
isms one of the strongest arguments in support of the evolutionary
doctrine.
CHAPTER XI
EVIDENCES FROM PALAEONTOLOGY
STRENGTH AND WEAKNESS OF THE EVIDENCE
The word palaeontology means literally the science of ancient
life. Practically, it is the study of the fossil remains of extinct animals
and plants, including any traces of their existence, such as footprints,
impressions in slate, clay, or coal. The evidence from the fossils has
definite elements of strength in that it deals with actual organisms that
formerly inhabited the earth's surface. Many of these species must
have left descendants, some of which are doubtless living in a modified
condition today. Palaeontology should be able either strongly to
support or to contradict the idea of evolution. If its data accord with
the evolution idea and are opposed to the special creation idea, the
fossils may be said to be evidences of evolution.
The weakness of the study of fossils lies in the fact that extremely
few samples of the living forms that have existed in the past have
been preserved, and of those that have been preserved only a very
small percentage have been dug up and studied by capable scientists.
Many types of animals and plants, moreover, are soft and capable
of preservation only under such exceptional conditions that but
a rare specimen here and there over the world, scattered through
various widely separated strata, has been found. Only very common
or abundant types are likely to have been preserved and discovered,
for the chances of an uncommon form being preserved would be small
and the further chances of these infrequently preserved specimens
being found would be infinitely smaller.
The great majority of fossil remains are fragmentary or preserved
very incompletely, so that only the hard parts have come down
to us. There are, of course, many important exceptions to this rule,
and these are our chief reliance in interpreting ancient Ufe.
That Darwin fully realized the vulnerable points in the palaeonto-
logical record is shown by the following quotation from the Origin oj
Species:
"I look at the geological record as a history of the world imper-
fectly kept and written in a changing dialect; of this history we possess
132
EVIDENCES FROM PALAEONTOLOGY 133
the last volume alone, relating only to two or three countries. Of
this volume only here and there a short chapter has been preserved;
and of each page only here and there a few lines. Each word of the
slowly changing language, more or less different in the successive
chapters, may represent the forms of Hfe which are entombed in our
successive formations and which falsely appear to us to have been
abruptly introduced."
OTHER OPINIONS AS TO THE ADEQUACY OF THE EVIDENCES
FROM PALAEONTOLOGY
"The primary and direct evidence in favour of evolution can be
furnished only by palaeontology. The geological record, so soon as
it approaches completeness, must, when properly questioned, yield
either an affirmative or a negative answer: if Evolution has taken
place there wiU its mark be left; if it has not taken place there will
lie its refutation." — T. H. Huxley.
"The geological record is not so hopelessly incomplete as Darwin
believed it to be. Since The Origin of Species was written our knowl-
edge of that record has been enormously extended, and we now possess
no complete volumes, it is true, but some remarkably full and illvmii-
nating chapters. The main significance of the whole lies in the fact
that, JM5/ in proportion to the completeness of the record is the unequivocal
character of its testimony to the truth of the evolutionary theory." —
W. B. Scott.
"On the other hand, matters have greatly improved since Darwin
wrote his oft-cited Chapter X; many lands then geologically unknown
have been explored and many of the missing chapters and paragraphs
in the history of life have been brought to Ught. The most ancient
biologically intelligible period of the earth's history is called the
Cambrian and, compared with the succeeding periods, the Cambrian
has always been poor in fossils, great areas and thicknesses of rocks
being entirely barren. No one could doubt that our knowledge of
Cambrian life was most incomplete and inadequate. A few years ago
Dr. C. D. Walcott, Secretary of the Smithsonian Institution, dis-
covered in the Canadian Rockies a most marvelous series of Cambrian
fossils of an incredible deUcacy and beauty of preservation, which
have thrown a flood of new and unexpected Ught into very dark places.
It is clear that the Cambrian seas swarmed with a great variety and
profusion of life, but that in only a few places, so far known to us,
134 EVOLUTION, GENETICS, AND EUGENICS
were conditions such that these delicate creatures could be preserved.
It is not possible to say how far the difficulty caused by the imperfec-
tion of the geological record will be removed by the progress of dis-
covery. Even as matters stand to-day, the astonishing fact is that
so much has been preserved, rather than that the story is so incom-
plete. Notwithstanding all the difficulties, the palaeontological
method remains one of the most valuable means of testing the theory
of evolution, because certain chapters in the history of hfe have been
recorded with a minuteness that is really very surprising." —
W. B. Scott, Theory of Evolution. (The Macmillan Company. Re-
printed by permission).
WHAT FOSSILS ARE AND HOW THEY HAVE BEEN PRESERVED
"Fossils are only animals and plants which have been dead rather
longer than those which died yesterday." — T. H. Huxley.
"Fossils are either actual remains of bones or other parts preserved
intact in soil or rocks, or else, and more commonly, parts of animals
which have been turned into stone, or of which stony casts have been
made. All such remains buried by natural causes are called fossils." —
Jordan and Kellogg.
FOSSILS CLASSIFIED
Class I. The actual remains of recently extinct animals and
plants which have been buried or surrounded by some sort of preserv-
ing material constitute the first type under consideration. Such
remains have undergone Uttle or no change of the original organic
matter into inorganic. Thus we find the complete bodies of great
hairy mammoths frozen in the arctic ice. These are so well preserved
that dogs have fed upon their flesh. Nearly a thousand species of
extinct insects, including many ants, have been obtained practically
intact from amber, a form of petrified resin. Innumerable mollusk
shells, teeth of sharks, pieces of buried logs, bones of animals buried
in asphalt lakes and bogs, have been found in a well-preserved
condition.
Class 2. Petrified fossils. — The process of petrification involves
the replacement, particle for particle, of the organic matter of a dead
animal or plant by mineral matter. So completely is the finer
structure preserved that microscopic sections of preserved tissues,
especially of plants, have practically the same appearance as sections
made from living organisms. Various mineral materials have been
employed in petrification, such as quartz, limestone, or iron pyrites.
EVIDENCES FROM PALAEONTOLOGY 13S
Class 3. Casts and impressions. — ^Very frequently the animal or
plant has been buried in mud or has lain on a soft mud flat only
long enough to have left its impress in the plastic material. Sub-
sequently the entire organism has decayed and been dissolved away,
and its place has been taken by a mineral deposit. Thus only the
external appearance has been preserved, as would be the case in
making plaster-of-paris casts. Sometimes traceries of soft-bodied
animals have been left upon forming slate or coal that are almost as
accurate in detail as a lithograph.
Perhaps the most remarkable fossils known are those found by
Professor Charles D. Walcott m the marine oily shales of British
Columbia. A large number of soft-bodied invertebrates of Cambrian
age have been found so wonderfully preserved that not only are
the external features revealed, but sometimes even the details of
the internal organs may be seen through the transparent integu-
ment.
Some authorities include among fossils such traces of extinct life
as footprints, utensils and tools of extinct man, and even the
vestiges of archaic sea beaches. Perhaps this is stretching the
definition of the term "fossil" too far.
ON THE CONDITIONS NECESSARY FOR FOSSILIZATION
"Examination and study of the rocks of the earth reveal the fact
that fossils or the remains of animals and plants are found in certain
kinds of rocks only. They are not found in lava, because lava
comes from volcanoes and rifts in the earth's crust, as a red-hot,
viscous liquid, which cools to form a hard rock. No animal or plant
caught in a lava stream will leave any trace. Furthermore, fossils
are not found in granite, nor in ores of metals, nor in certain other of
the common rocks. Many rocks are, like lava, of igneous origin;
others, like granite, although not originally in the melted condition,
have been so heated subsequent to their formation, that any traces of
animal or plant remains in them have been obliterated. Fossils are
found almost exclusively in rocks which have been formed by the slow
deposition in water of sand, clay, mud, or lime. The sediment which
is carried into a lake or ocean by the streams opening into it sinks
slowly to the bottom of the lake or ocean and forms there a layer
which gradually hardens under pressure to become rock. This is called
sedimentary rock, or stratified rock, because it is composed of sedi-
136 EVOLUTION, GENETICS, AND EUGENICS
ment, and sediment always arranges itself in layers or strata. In
sedimentary or stratified rocks fossils are found. The commonest
rocks of this sort are limestone, sandstone, and shales. Limestone is
formed chiefly of carbonate of lime; sandstone is cemented sand, and
shales, or slaty rocks, are formed chiefly of clay.
"The formation of sedimentary rocks has been going on since land
first rose from the level of the sea; for water has always been wearing
away rock and carrying it as sediment into rivers, and rivers have
always been carrying the wom-off lime and sand and clay downward
to lakes and oceans, at the bottoms of which the particles have been
piled up in layers and have formed new rock strata. But geologists
have shown that in the course of the earth's history there have been
great changes in the position and extent of land and sea. Sea bottoms
have been folded or upheaved to form dry land, while regions once
land have simk and been covered by lakes and seas. Again, through
great foldings in the cooHng crust of the earth, which resulted in
depression at one point and elevation at another, land has become
ocean and ocean land. And in the almost unimaginable period of
time which has passed since the earth first shrank from its hypo-
thetical condition of nebulous vapor to be a ball of land covered with
water, such changes have occurred over and over again. They have,
however, mostly taken place slowly and gradually. The principal
seat of great change is in the regions of mountain chains, which, in
most cases, are simply the remains of old folds or wrinkles in the
crust of the earth,
"When an aquatic animal dies, it sinks to the bottom of the lake
or ocean, unless, of course, its flesh is eaten by some other animal.
Even then its hard parts will probably find their way to the bottom.
There the remains will soon be covered by the always dropping sedi-
ment. They are on the way to become fossils. Some land animals
also might, after death, get carried by a river to the lake or ocean,
and find their way to the bottom, where they, too, will become fossils,
or they may die on the banks of the lake or ocean and their bodies
may get buried in the soft mud of the shores. Or, again, they are
often trodden in the mire about salt springs or submerged in quick-
sand. It is obvious that aquatic animals are far more likely to be
preserved as fossils than land animals. This inference is strikingly
proved by fossil remains. Of all the thousands and thousands of
kinds of extinct insects, mostly land animals, comparatively few speci-
mens are known as fossils. On the other hand, the shell-bearing
EVIDENCES FROM PALAEONTOLOGY 137
mollusks and crustaceans are represented in almost all rock deposits
which contain any kind of fossil remains." — Jordan and Kellogg.^
The study of geology teaches us that the earth's outer zones have
undergone within the period of vertebrate history numerous profound
changes which in general we may term climatic changes. There have
been periods of continental subsidence, accompanied by ocean-floor
elevations, during which great continental plains have been covered
with comparatively shallow seas. The marine faunas of the seas have
migrated into these shallows and representatives of them have been
buried in sediment. When the reverse change has occurred and the
continental plain has been again elevated, the sedimentation of the
shallow-sea period forms a great rocky stratum laden with marine
fossils. Between periods of subsidence millions of years elapsed, and
therefore a break in the continuity of the entombed fossils is to be
expected. Discontinuity between the fossil faunas in adjacent strata
is the invariable rule. Were it not for this periodicity of subsidence
and elevation there would be no boundaries between consecutive
geologic strata.
In addition to the methods of fossilization mentioned, a few others
deserve notice. Many animals of the arid plains have been fossilized
by becoming imbedded in dust or sand drifts which have piled up
against rocky outcrops or have filled in dried-up arroyos. Some very
valuable fossils have been recovered from asphaltic deposits as the
result of animals falling into liquid or semiliquid lakes or pools of
asphalt.
Not only are external organs preserved with precision, but even
delicate internal structures, such as the brains or the viscera of verte-
brates, have been found in such a perfectly natural shape that the
comparative anatomy could be worked out with confidence.
On the whole, then, we must conclude that the earlier pessimism
regarding the inadequacy and insufficiency of fossil data is giving way
before a steadily increasing optimism, due to the very rapid advance
in technique and the surprisingly abundant discoveries of the modern
palaeontologist. The more enthusiastic of the new scliool of fossil-
hunters do not despair of ultimately bringing to light all of the really
essential links in the chain of evidence necessary to place the evolution
theory beyond the reach of controversy.
'From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life (copy-
right 1907). Used by special permission of the publishers, D. Appleton & Company.
138 EVOLUTION, GENETICS, AND EUGENICS
ON THE LAPSE OF TIME DURING WHICH EVOLUTION IS BELIEVED
TO HAVE TAKEN PLACE
"Independently of our not finding fossil remains of such infinitely
numerous connecting links [referring to the objection that all steps in
the evolution of modern types should be revealed in the fossils], it
may be objected that time cannot have sufficed for so great an amount
of organic change, all changes having been effected slowly. It is
hardly possible for me to recall to the reader who is not a practical
geologist, the facts leading the mind feebly to comprehend the lapse
of time. He who has read Sir Charles Lyell's grand work on the
Principles of Geology, which the future historian will recognize as
having produced a revolution in natural science, and yet does not
admit how vast have been the past periods of time, may at once close
this volume. Not that it suffices to study the Principles of Geology,
or to read special treatises by different observers on separate forma-
tions, and to mark how each author attempts to give an inadequate
idea of the duration of each formation, or even of each stratum. We
can best gain some idea of past time by knowing the agencies at work,
and learning how deeply the surface of the land has been denuded,
and how much sediment has been deposited. As Lyell has well
remarked, the extent and thickness of our sedimentary formations are
the result and the measure of the denudation which the earth's crust
has elsewhere undergone. Therefore a man should examine for him-
self the great piles of superimposed strata, and watch the rivulets
bringing down the mud, and the waves wearing away the sea-cliffs, in
order to comprehend something about the duration of past time, the
monuments of which we see all around us."' — Charles Darwin, Origin
of Species.
"In 1862," says Schuchert,' "the physicist, Lord Kelvin ....
held that as our planet was continually losing energy in the form of
heat, the globe was a molten mass somewhere between 20,000,000 and
400,000,000 years ago, with a probability of this state occurring about
98,000,000 years ago. Finally in 1897 he concurred in Clarence King's
conclusion that the globe was a molten mass about 24,000,000 years ago.
Both of these conclusions, however, were wrought out under the Lap-
lacian hypothesis, and now many geologists hold that the earth never
was molten. While geologists have not been able to fit their evidence
into so short a time, they have ever since been trying to keep their
' C. Scbuchert, Text-Book of Geology, Part II, Historical Geology (19 15).
EVIDENCES FROM PALAEONTOLOGY
139
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I40 EVOLUTION, GENETICS, AND EUGENICS
estimates within the bounds of Lord Kelvin's older calculations. Wal-
cott, in 1893, on the basis of the stratigraphic record and the known
discharge of sediment by rivers, concluded that 70,000,000 years had
elapsed since sedimentation began in the Archeozoic. Sir Archibald
Giekie places the time at 100,000,000 years, and most geologists have
tried, although with difficulty, to fit the record within these estimates.
" Since the discovery of radium, all of the calculations previously
made have been set aside by the new school of physicists, and now
the geologists are told they can have 1,000,000,000 or more years as
the time since the earth attained its present diameter Even
if finally it shall turn out that the physicists have to reduce their
estimates as to the age of certain minerals and rocks, geologists
nevertheless appear to be on safer ground in accepting their estimates
than those based either on sedimentation, chemical denudation, or loss
of heat by the earth."
The last decade has seen the demise of the outworn objection to
evolution based on the idea that there has not been time enough for
the great changes that are believed by evolutionists to have occurred.
Given 100,000,000 or 1,000,000,000 years since life began, we can then
allow 1,000,000 years for each important change to arise and establish
itself. We can also understand why it is that so Uttle change can be
noted in the majority of wild animals and plants within the historic
period. A thousand years in the development of the race is like a
second in the development of an individual and, though no one can
notice any change in a growing creature in a second or a minute, very
radical changes can be noted in an hour or a day or a year. We cannot
see any movement in an hour hand of a clock, but it moves with
certainty around the dial in a relatively short time. There is there-
fore no shortage of time. Evolution may have been infinitely slow,
but time has been infinitely long. The accompanying time scale
shows the lapse of time and the distribution in time of the main
groups of animals (Fig. 30).
ON THE PRINCIPAL GENERAL FACTS REVEALED BY A
STUDY OF THE FOSSILS
1. None of the animals or plants of the past are identical with
those of the present. The nearest relationship is between a few species
of the past and some living species which have been placed in the same
families.
EVIDENCES FROM PALAEONTOLOGY 141
2. The animals and plants of each geologic stratum are at least
generically different from those of any other stratum, though belonging
in some cases to the same families or orders.
3. The animals and plants of the oldest (lowest) geologic strata
represent all of the existing phyla, except the Chordata, but the
representatives of the various phyla are relatively generalized as
compared with the existing types.
4. The animals and plants of the newest (highest) geologic strata
are most like those of the present and help to link the present with
the past,
5. There is, in general, a gradual progression toward higher types
as one proceeds from the lower to the higher strata.
6. Many groups of animals and plants reached the cHmax of
specialization at relatively early geologic periods and became extinct.
7. Only the less specialized relatives of the most highly specialized
types survived to become the progenitors of the modern representa-
tives of their group.
8. It is very common to find a new group arising near the end of
some geologic period during which vast cHmatic changes were taking
place. Such an incipient group almost regularly becomes the domi-
nant group of the next period, because it developed under the
changed conditions which ushered in the new period and was therefore
especially favored by the new environment.
9. The evolution of the vertebrate classes is more satisfactorily
shown than that of any other group, probably because they represent
the latest phylum to evolve, and most of their history coincides with
the period within which fossils are known.
10. Most of the invertebrate phyla had already undergone more
than half of their evolution at the time when the earliest fossil remains
were deposited.
FOSSIL PEDIGREES OF SOME WELL-KNOWN VERTEBRATES
PEDIGREE OF THE HORSE
Of all fossil pedigrees that of the horse is most often mentioned in
evolutionary Uterature. The main facts have been known for about
forty years, and there is a rather general consensus of opinion as to the
history as a whole. It appears practically certain that the horse
family (Equidae) arose from a group of primitive five-toed ungulates
or hoofed mammals called Condylarthra that lived in Eocene times.
142 EVOLUTION, GENETICS, AND EUGENICS
No particular member of this extinct group has been found that fulfils
all the requirements of a primitive horse ancestor, so the chances are
that the real ancestral condylarthran has not been discovered.
"The course of their [Equidae] evolution," says Dendy,' "has
evidently been determined by the development of extensive, dry,
grass-covered, open plains on the American continent. In adap-
tation to life on such areas structural modification has proceeded
chiefly in two directions. The limbs have become greatly elongated
and the foot upUfted from the ground, and thus adapted for rapid
flight from pursuing enemies, while the middle digit has become more
and more important and the others, together with the ulna and the
fibula, have gradually disappeared or become reduced to mere vestiges.
At the same time the grazing mechanism has been gradually perfected.
The neck and head have become elongated so that the animal is able
to reach the ground without bending its legs, and the cheek teeth have
acquired complex grinding surfaces and have greatly increased in
length to compensate for the increased rate of wear. As in so many
other groups, the evolution of these special characters has been
accompanied by gradual increase in size. Thus Eohippus, of Lower
Eocene times, appears to have been not more than eleven inches high
at the shoulder, while existing horses measure about sixty-four inches,
and the numerous intermediate genera for the most part show a
regular progress in this respect.
"All these changes have taken place gradually, and a beautiful
series of intermediate forms indicating the different stages from Eohip-
pus to the modern horse [Equus] have been discovered. The sequence
of these stages in geological time exactly fits in with the theory that
each one has been derived from the one next below it by more perfect
adaptation to the conditions of life. Numerous genera have been
described, but it is not necessary to mention more than a few."
The first indisputably horselike animal appears to have been
Hyracotherium, of the Lower Eocene of Europe. Another Lower
Eocene form is Eohippus, which lived in North America, probably
having migrated across from Asia by the Alaskan land connection
which was in existence at that time. Li Eohippus the fore foot had
four completely developed hoofed digits and a "thumb" reduced to
a splint bone; in the hind foot the great toe had entirely disappeared
and the little toe is represented by a vestigial structure or spHnt bone.
' Arthur Dendy, Outlines of Evolutionary Biology (D. Appleton & Company,
[916).
EVIDENCES FROM PAL.\EONTOLOGY
143
Then came in succession Orohippus, of the Upper Eocene, Mesohippus
ot the Lower Miocene, Pliohippus of the Upper PHocene, and, finally
Equus ; Qua-
ternary and
Recent.
Pliohippus :
Pliocene.
Protohippus ;
Lower Plio-
cene.
Miohippus :
Miocene.
Mesohippus :
Lower Mio-
cene.
Orohippus :
Eocene.
Fig. 31. — Feet and teeth in fossil pedigree of the horse. {After Marsh.)
a, Bones of the fore foot; b, bones of the hind foot; c, radius and ulna; d, fibula
and tibia; c, roots of a tooth; / and g, crowns of upper and lower teeth.
Equus of the Quaternary and Recent. Other genera might be men-
tioned, but the history of this series has been pictured in a classic
144 EVOLUTION, GENETICS, AND EUGENICS
diagram by Marsh, and in this (Fig. 31) the reader may trace upward
from Orohippus to Equus the steady changes in fore and hind feet,
bones of the forearm, bones of the lower leg, and the grinding teeth
of upper and lower jaws.
So definitely and clearly has the horse pedigree been worked out
that, according to Dendy, " the palaeontological evidence amounts to
a clear demonstration of the evolution of the horse from a five-toed
ancestor along the lines indicated above."
For a long time the palaeontological series of the horse was un-
rivaled by other vertebrate types, but now we have almost equally
complete series for several other modern types, notably the camels
and the elephants. We shall present herewith accounts of the pedi-
gree of the camels by Professor Scott, and that of the elephants by
Professor Shull. And, to conclude the vertebrate pedigrees, we shall
present in the next chapter that of man as given by Professor Lull.
In extenuation of the use of vertebrate material to the exclusion
of invertebrate, the present writer has only this to oflFer, that verte-
brate material is more intelligible to the non-biological reader and is
more in his own field of knowledge and interest.
PEDIGREE OF THE CAMELS'
W. B. SCOTT
There remains one family of mammals with which it is necessary
to deal and that is the camel tribe. This family has two well-defined
subdivisions, the camels of the Old World and the llamas, guanacos,
etc., of South America. For a very long time, the family was entirely
confined to North America and did not reach its present homes until
the Pliocene epoch of the Tertiary period. The skeleton of a Patago-
nian guanaco may be taken as the starting point of our mquiry. In
this animal the third incisor and the canine are retained m the upper
jaw, all the incisors and the canine in the lower. The anterior two
grinding teeth have been lost and the others are moderately high-
crowned. The skull is broad and capacious behind, narrow and
tapering in front. The neck is long and its vertebrae very curiously
modified. The limbs are long and slender and have undergone nearly
the same modifications as m the horses; the uhia is greatly reduced,
interrupted in the middle and its separated portions are fused with the
radius. In the hind leg the shaft of the fibula has been completely
'From W. B. Scott, The Theory of Evolution (copyright 1917)- Used by
special permission of the publishers, The Macmillan Company.
EVIDENCES FROM PALAEONTOLOGY
145
suppressed ; the upper end fuses with the tibia, while the lower remains
as a small separate bone, wedged in between the tibia and the heel-
bone, Thefeetare very long and slender, with two toes in each; the
B A
Fig. 32, — Four stages in the evolution of the cameline skull. A, Protylopus,
Upper Eocene; B, Poebrotherium, Lower Oligocene; C, Procamelus, Upper Miocene;
D, guanaco, Recent. (From Scott.)
long bones of the foot are co-ossified to form a "cannon-bone," the
very young skeleton showing that this co-ossification does actually take
place. The toes proper are free, giving the "cloven hoof," but the
hoofs are very small and the weight is carried upon a soft, thick pad.
146
EVOLUTION, GENETICS, AND EUGENICS
IT
M
c
m
JV^
B
jr M
Tig. 33. — Four stages in the evolution of the cameline fore foot. A , Protylopus,
Upper Eocene; B, Poebrotherium, Lower Oligocene; C, Frocamelus, Upper Miocene;
0. guanaco, Recent. (From Scott.)
EVIDENCES FROM PALAEONTOLOGY 147
Were there time enough to do so, we might trace the development
of this family backward, step by step, through all the many stages
between the Pleistocene and the Upper Eocene in quite as unbroken
sequence and in as full detail as can be done for the horses. We must,
however, pass over all the intermediate steps and consider the ances-
tral camels of the Upper Eocene. These were very little animals,
hardly larger than a jack rabbit, which had the full complement of
teeth, 44 in total number, and all with very low crowns. The Umbs,
and especially the feet, are relatively short, the ulna is complete and
separate, as is also the fibula; there are four toes m each foot, though
the lateral pair of the hind foot are extremely slender, and there is no
co-ossification to form cannon-bones. The hoofs are well developed,
in form like those of an antelope, so that there can have been no pad.
For the present, the line cannot be carried back of the Upper Eocene,
the probable ancestors from the middle and Lower Eocene being, as
yet, represented only by fragmentary specimens.
In addition to this main stem of cameline descent which resulted
in the modem species, there were two short-lived side branches which
should be mentioned. One, ending in the Lower Miocene, was the
series descriptively called "gazelle-camels," small animals with very
long and slender legs, evidently swift runners. The other series, the
so-called "giraffe-camels," terminated in the Upper Miocene; these
were browsers and display an increasing stature, especially in the
length of the neck and fore Umbs. They adapted themselves to the
growing aridity of the western plains.
EVOLUTION OF THE ELEPHANTS*
A. FRANKLIN SHTJLL
The mastodon-elephant series shows a larger number of obvious
changes than most of the other series named, all of these changes
except that of the body having to do with features of the head.
From the numerous specimens of elephant-like forms available, the
following are selected (following Lull) as probably representing a
direct line of evolution: Moeritherium from the Upper Eocene of
Egypt; Palaeomastodon from the Lower Oliogocene of Egypt, also
from Lidia; Trilophodon from the Miocene of Europe, Africa, and
North America; Mastodon from the Pliocene and Pleistocene of
• From A. F.' ShuU, Principles of Atiimal Biology (copyright 1920). Used by
special permission of the publishers, The McGraw-Hill Book Company.
148
EVOLUTION, GENETICS, AND EUGENICS
North America, Europe and Asia; Stegodon from the Pliocene of
southern Asia; and Elephas from the Pleistocene of the Americas,
Europe, and Asia, as well as the living elephants of Asia and Africa.
Fig. 34.— Evolution of head and molar teeth of mastodons and elephants.
A, A', Elephas, Pleistocene; B, Stegodon, PHocene; C, C, Mastodon, Pleistocene;
D, D', Trilophodon, Miocene; E, E' , Palacomastodon, Oligocene; F, F', Mac-
ritherium, Eocene. {From Lull.)
EVIDENCES FROM PALAEONTOLOGY
149
A study of Figure 34 in connection with the following account will dis-
close the more striking steps of evolution. These forms differed from
one another in a number of features, but the differences between any
member of the series and the one that precedes or that which follows
were so small that the series is obviously a continuous one. Moerithe-
rium was very different from the modern elephant, but the inter-
mediate forms completely bridged the gap. The series exhibits an
enormous increase in size of body, changes in the form and size of
the teeth, a reduction in the number of teeth, an alteration in the
method of tooth succession, the enlargement of certain teeth to
become tusks, the elongation and subsequent shortening of the
lower jaw, the development of the upper lip and nose into a proboscis,
and an increase in the height of the skull through the development
of large cavities in the substance of the bone. These features are
described in the several forms seriatim.
Moeritherium. — The earliest animal recognized as belonging to
the elephant series, Moeritherium by name, was recovered from the
late Eocene and early Oligocene deposits of northern Egypt.
It was slightly over three feet in height. The features suggesting
elephantine affinities are the high posterior portion of the skull (Fig.
34, F); composed of somewhat cancellate bone, that is, bone containing
open spaces; the elongation of the second pair of incisors in each jaw
to form short tusks; the indication of transverse ridges on the molar
teeth (Fig.34,F) ; and the position of the nasal openings some distance
back of the tip of the upper jaw, indicating probably a prehensile
upper lip. There were 24 teeth, and the neck was long enough to
enable the animal to put its head to the ground. It probably fed
upon tender shoots and swamp vegetation.
Palaeomastodon. — This form also lived in Egypt, but has recently
been found in India. It dates irom early Oligocene time. Palaeo-
mastodon was of somewhat larger size than the preceding form, the
posterior part of the skull was distinctly higher (Fig.34,£') — with a
greater development of cancellate bone, and the neck was somewhat
shortened. The upper incisors of the second pair were more elongated
as tusks and bore a band of enamel on their front surfaces. The lower
second incisors were present, but not enlarged. All other incisors and
the canines had disappeared. The molar teeth (£) reseinbled those
of Moeritherium but were larger. The lower jaw was considerably
elongated, and the total number of teeth was still high (26). The
nasal openings had receded until tJiey were just in front of the eyes,
I50 EVOLUTION, GENETICS, AND EUGENICS
which is believed to indicate the existence of a short probosci^i
extending at least to the tips of the tusks.
Trilophodon. — Trilophodon, a great migrant and consequently
wide-spread over several continents as stated above, exhibited in
several respects a striking advance over Palaeomastodon; but this
advance was in the main in the same direction as was indicated by
the change from Moeritherium to Palaeomastodon. Trilophodon was a
huge animal, nearly as large as modem Indian elephants. The tusks
were considerably longer (Fig.34, D') and still bore a band of enamel.
The molar teeth were large and greatly reduced in number, so
that only two were present at any one time on each side of each
jaw. The surface of these teeth bore a somewhat larger number of
transverse crests (Fig. 34, D) than were present in the earlier forms.
The lower jaw was enormously elongated, so that it projected as far
forward as the tusks. The great weight of the lower jaw and tusks
was associated with a considerable development of cancellate bone
in the skull, to which the supporting muscles of the neck were
attached. Presumably there was a proboscis which extended to or
beyond the tips of the tusks and lower jaw.
Mastodon. — The mastodons on the whole represent a line of
development which became extinct; but in their incipient stages they
appear to have given rise to the succeeding forms leading to the
elephants. The body was somewhat larger than that of Trilophodon,
being about the size of the Indian elephant. The tusks (C) were
much elongated (9 feet or more), but the lower jaw was greatly short-
ened and the lower incisor teeth were reduced or wanting. The molar
teeth (Fig. 34 J C) were scarcely more complex than earlier forms, and
numbered two on each side of each jaw. They were still crushing
teeth, and the food must have been tender twigs and succulent plants;
indeed, remains of such objects have been found in the region of the
stomach of the fossil mastodons.
Stegodon. — This animal is of interest chiefly because the molar
teeth bore five or six well-defined transverse ridges (Fig.34,5). These
ridges were due to plates of enamel extending up through the tooth,
and inclosing a substance known as dentine. Over the enamel in ah
unworn tooth was a thin coat of a third substance called cement, but
there was not much of this substance between the ridges. In the
latter respect Stegodon differed, as is pointed out below, from the
elephants and manunoths. On the whole, Stegodon was intermediate
between the mastodons and elephants.
EVIDENCES FROM PALAEONTOLOGY 151
Elephas. — In this genus are included a number of extinct forms
(the mammoths) from three or four continents, and the living ele-
phants. The extinct forms, though called mammoths, were not large
animals, being no larger than the Indian elephant of today, and not
so large as the living African species. Some of the features of the
elephants, their size, the short neck, the long proboscis, and the heavy
tusks are matters of common observation. The skull is very high
and short (Fig. 34, A'). The height is due chiefly to the development
of cancellate bone, not to the enlargement of the brain, which is still
quite small. As stated above, the high skull affords the necessary
leverage for the muscles that support the weight of the tusks. The
molar teeth are distinctly grinding teeth {V'l^. 34, A). Each tooth
bears a number of transverse ridges, about ten in the African elephant
and two dozen or more in the Indian species. These ridges are worn
down by the chewing of harsh food, so that the upper surface displays
a number of flattened tubular plates of enamel inclosing dentine and
bound together by cement. A tooth is completely worn out by use,
and is replaced by another. The method of replacement, however,
is peculiar. While the tusks (incisors) are of two sets, one following
the other liJve milk and permanent teeth of other mammals, the
grinders succeed one another in continuous fashion. There are never
more than two visible grinders on each side of each jaw. As they
wear out they move forward in the jaw, and are replaced by new teeth
appearing behind. New molars thus enter at intervals of two to four
years in young elephants, and at intervals of 15 to 30 years in later
life. If an elephant lives long enough (60 years or more) it develops
a total of 28 teeth, including tusks, but has not more than ten (often
less) at any one time.
Correlated with the nature of the teeth of the elephants are their
food and chewing habits. WTiereas the ancestral forms whose molars
bore prominent elevations lived on twigs and tender herbage which
they crushed in mastication, the mammoths with their flattened tooth
surfaces devoured grasses, sedges, and other harsh vegetation which
they ground with lateral motion of the teeth upon one another. In
this respect modem elephants are like the mammoths.
In the changes described above is found one of the most beautiful
and best established evolutionary series with which the palaeontolo-
gist is acquainted. Only a few others equal or approach it in clearness
and completeness.
CHAPTER XII
THE EVOLUTION OF MAN: PALAEONTOLOGY*
Richard Swann Lull
ORIGIN OP PRIMATES
Stock. — There is but little doubt that two important orders of
modem mammals, the Carnivora and the Primates, had a common
origin, diverging mainly along lines determined by a dietary contrast,
as the former have become more strictly flesh-eating or predaceous,
the latter largely fruit-eating and as a consequence more completely
arboreal. Back of each group lie as annectant forms the Insectivora,
not perhaps such as are alive to-day, as all these are highly specialized
along diverse Unes, but generalized insectivores possessing, because
of their primitiveness, a wider range of potential adaptation. Mat-
thew is "disposed to think of these, our distant ancestors, at the dawn
of the Tertiary, as a sort of hybrid between a lemur and a mongoose,
rather catholic in their tastes, living among and partly in the trees,
with sharp nose, bright eyes, and a shrewd little brain behind them,
looking out, if you will, from a perch among the branches, upon a
world that was to be singularly kind to them and their descendants."
Thus we can define the stock as a relatively large-brained arboreal
insectivore, of primitive but adaptable dentition, and especially of
progressive mentality.
Time. — The time of primate origin must have been not later
than basal Eocene, as prunates, clearly definable as such, are found in
the Lower Eocene rocks of both Europe and North America.
Place. — The simultaneous appearance of the primate in the
Old World and the New gives rise to the same conclusions as to their
place of origin and their migrations thence as with other modernized
mammals. It sufl&ces now to say that their ancestral home was
boreal Holarctica, probably within the limits of the present continent
of Asia, whence they migrated southward along the three great
continental radii. The impelling cause of this migration was the
increasing northern cold, before which the boreal limitations of the
tropical forests retreated, carrying with them the primates which, in
'From R. S. Lull, Organic Evolution (copyright 1917). Used by special
permission of the publishers. The Macmillan Company.
152
THE EVOLUTION OF MAN 153
general, are utterly dependent upon such an environment for their
sustenance.
Geologic record. — Primates are found in the North American
sediments from Lower to Upper Eocene time, when they became
extinct. Thus, while their remains constitute a relatively large per-
centage of the total fauna of the Eocene, primates are utterly unknown
on this continent from that time until the coming of man. In Europe
the record is similar except that the extinction occurred at a somewhat
later date, the OUgocene. Furthermore, they reappear in Europe in
the Lower Miocene, at the time of the proboscidean migration out of
Africa, whence these primates may also have come. Their second
European extinction was in the Upper Pliocene shortly before the first
appearance of mankind.
But in southern Asia, Africa, and South America the evolution of
primates seems to have been continuous since the first great southward
migration. The evidence, however, is not so much the historical
documents as the presence of primates in those places at the present
time, the fossil record is not entirely lacking although highly incom-
plete. The South American monkeys may have had their origin in
the ancient North American primates, or more doubtfully, the stock
may have come by way of Africa. Scott inclines toward the latter
view although he says the evidence is by no means conclusive.
ORIGIN or MAN
Stock. — ^According to W. K. Gregory, the stock from which man
arose was some big-brained anthropoid related most nearly to the
chimpanzee-gorilla group, an assumption based upon anatomical
evidences, in spite of wide differences in habitus and consequent
adaptation.
Place. — Evidences point to central Asia as the place of descent
from the trees of the human precursor, the reasons for this belief being
several. First, it was central for migrations elsewhere; Europe, on
the other hand, where the most conclusive, in fact almost the exclusive
evidence for fossil man is found, is too small an area for the divergent
evolution of the several human species. Second, Asia is contiguous
to the oldest known human remains, which, as we shall see, were found
in Java. Third, it was the seat of the oldest civiUzations, not only of
the existing nations which, like the Chinese, trace their recorded
history back to a hoary antiquity, but of nations which preceded them
by thousands of years, and whose records have not yet come to light.
154 EVOLUTION, GENLTICS, AND EUGENICS
This antiquity vastly exceeds that of the nations of Europe or of the
Americans or of Africa. Fourth, central Asia is the source of almost
all of our domestic animals, many of which have been subjected to
human will and control for thousands of years, and this is equally true
of many of our domestic plants. This is not due to the fact that man
first reached civilization in Asia, but rather that he chose for his corn-
panions the highest and best of their several evolutionary lines, and
Asia was the place of all others upon earth where the evolution in
general of organic hfe reached its highest development in late Cenozoic
time (Williston). Fifth, cHmatic conditions in Asia in the Miocene
or early Pliocene were such as to compel the descent of the prehuman
ancestor from the trees, a step which was absolutely essential to
further human development.
Impelling cause. — We look for a geologic cause back of this most
momentous crisis in the evolution of humanity and we find it in conti-
nental elevation and consequent increasing aridity of climate, espe-
cially to the northward of the Himalayas. With this increased aridity
and tempering of tropical heat came the dwindling of the forested
areas suitable to primate occupancy. Barrell has suggested that this
diminution left residual forests comparable to the diminishing lakes
and ponds of the Devonian, which upon final desiccation compelled
their denizens to become terrestrial or perish. The dwindling of the
residual forests would have an effect upon the tree-dwellers which may
be expressed in precisely the same words. Once upon the ground the
effect upon even a conservative type — and the primates in general,
where constant conditions prevail, are slow of change — would be the
rapid acquisition of such adaptations as were necessary to insure sur-
vival under the new conditions. The other man-like apes had,
unfortunately for their further evolution, reached a region where
tropical forests continued to be available and hence have retained their
arboreal hfe and with it a stagnation of progress. The result has been,
at any rate on the part of the three larger forms, a degeneracy from
the estate of their common ancestry with mankind; the gibbons seem
to have deteriorated less, while terrestrial man has risen to the summit
of primate evolution.
Time. — The time of the descent is not later than early Pliocene
nor ear her than Miocene time; when the terrestrial ape-man became
what we would call human was perhaps later, but certainly during the
Phocene, which makes the age of man as such measurable in terms of
hundreds of thousands of years 1
THE EVOLUTION OF MAN
155
Significance of the descent from trees. — As a result of the descenl
from the trees, certain definite factors were called into play, each of
which had its effect on the further evolution. Briefly enumerated,
these are: (i) Assumption of the erect posture; (2) liberation of the
hands from their ancient locomotor function to become organs of the
mind; (3) loss of the easily obtainable food of the tropical forests,
necessitating the search for sustenance, both plant and animal, and
man became a hunter; (4) need of clothing with increasing inclemency
of the weather, especially during the long winters; (5) freedom from
climatic restrictions — when an omnivorous diet and clothing were
acquired man was no longer limited to one definite habitat and the
result was dispersal; (6) the development of communal life, rendered
possible by the terrestrial habitat. Primates are at best gregarious,
submitting, as in the gorilla, to the leadership of the strongest male,
but it is only by communal life with its attendant division of labor
that man can rise above the level of utter savagery.
Evolutionary changes. — Human evolutionary changes which are
recorded are: more erect posture, shorter arms, perfection of
thumb opposability, reduction of muzzle and of size of teeth, loss
of jaw power, development of chin prominence, increase in skull
capacity, diminution of brow-ridges, diminution in strength of zygo-
matic or temporal arch, increase in size and complexity of brain,
especially frontal lobes, development of articulate speech.
FOSSIL MAN
Fossil remains of man are found under two conditions, in river
valley deposits and in limestone caverns which served first as a
dwelling-place and later as a sepulture. Of these the caverns
have been by far the most productive, but they contain only the
remains of the later races, as the caverns according to Penck did not
become available for human occupancy before middle Pleistocene
time.
The rarity of human fossils may be explained, first, by the various
burial customs which seldom are sufl&ciently perfect to preclude the
possibility of alternate wetting and drying or of rapid oxidation, both
of which are prohibitive of fossilization. If man lived and died in the
forests the chances for his fossilization, in common with other forest
creatures, was very remote, for the remains of such are almost invari-
ably destroyed by other animals, by dampness, or by fungi, and rarely
attain a natural burial in sediment. If, on the other hand, he dwelt
156 EVOLUTION, GENETICS, AND EUGENICS
in the open, the chances of so shrewd a creature being caught in
the flood waters and thus buried in sediment were not very great.
However we account for it, the fact remains that relics of ancient man
are rare and are valued accordingly.
In North America. — Repeated instances of seemingly ancient
man have been brought to light in North America, such as the "Cale-
veras skull" of the California gold-bearing gravels, which was satirized
by Bret Harte; the Nebraska "Loess man," and those of the Trenton
gravels; none of which, with the possible exception of the last-men-
tioned, has proved to be really old in the geologic sense. Indirect
evidence of human antiquity, that is, the association of North Ameri-
can man with animals which are now extinct, while very rare, has been
reported in at least two highly authentic instances. The first of these
was at Attica, New York, and is attested by Doctor John M. Clarke,
the New York state geologist. Four feet below the surface of the
ground, in a black muck, he found the bones of the mastodon (Masto-
don americaniis) , and 12 inches below this, in undisturbed clay, pieces
of pottery and thirty fragments of charcoal. The charcoal may have
been of natural origin, but the presence of the pottery seems conclu-
sive. The other instance was that of the remains of a herd of extinct
bison {Bison antiquus) found near Smoky Hill River, Logan County,
Kansas, and thus described by Professor WiUiston: An "arrow-head
was found underneath the right scapula of the largest skeleton,
embedded in the matrix, but touching the bone itself. The skeleton
was lying upon the right side The bone bed when cleared off
.... contained the skeletons of five or sLx adult animals, and two or
three younger ones, together with a foetal skeleton within the pelvis
of one of the adult skeletons. The animals had evidently all perished
together, during the winter. There was no possibility of the accidental
intrusion of the arrow-head in the place where found It must
have been within the body of the animal at the time of death, or have
been lying on the surface beneath its body."
What at this writing is claimed to be another genuine case of such
an association, this time of the actual human bones, has just been
aimounced from Florida. This find, which has been reported by
State Geologist Sellards, was made at Vero, eastern Florida, in 1913
The fossil human bones are from two incomplete skeletons and are
found in strata which also contain remains of the following extinct
species: Elephas columbi, Equus leidyi, a fox, a deer, the ground-sloth,^
Megalonyx jeffersoni, and the American mastodon.
THE EVOLUTION OF MAN 157
In South America. — A number of finds have been recorded from
South America, notably by the late Florentino Ameghino of Buenos
Aires, who contributed so largely to our knowledge of South American
prehistoric life. An expert from Washington, Doctor Ales Hrdlick£|„
has studied with the utmost care the locality and character of each of
these finds in the Western World, and has expressed the opinion that
none is of an antiquity greater than that of the pre-Coliunbian
Indians.
Further evidence lies in the uniformity of type, except for m inor
distinctions, of all native American peoples. There is no such racial
difi'erentiation as that seen in the Old World, and the argument is that
there has not been time for such a deployment. The area and condi-
tions as an adaptive radiation center are surely ample.
In Africa. — The only African relics thus far reported are those
of prehistoric cultures, comparable to those of Southern Europe, in
certain caverns of the Barbary States. There has also been reported
from Oldoway ravine, German East Africa, a human skeleton of
undoubted antiquity. It is described, however, as being neither a
very early nor a primitive type.
In Asia. — Asia has given us in Pithecanthropus the oldest known
relic of the Hominidae, found at Trinil in the island of Java. Osbom
says: "It is possible that within the next decade one or more of the
Tertiary ancestors of man may be discovered in northern India among
the foothills known as the Siwaliks. Such discoveries have been
heralded, but none have thus far been actually made. Yet Asia will
probably prove to be the center of the human race. We have now
discovered in southern Asia primitive representatives or relatives of
the four existing types of anthropoid apes, namely, the gibbon, the
orang, the chimpanzee, and the gorilla, and since the extinct Indian
apes are related to those of Africa and of Europe, it appears probable
that southern Asia is near the center of the evolution of the higher
primates and that we may look there for the ancestors not only of
prehuman stages like the Trinil race but of the higher and truly
human types."
In Europe. — It is in Europe, however, that the tale of human
prehistory is the most complete, not only through the happy accident
of preserval, but because it has been much more thoroughly explored
than has the Asiatic evolutionary center. The latter, however, holds
the greatest hopes for future exploration since, as we have emphasized,
Europe is too small to be an adaptive radiation center and European
158 EVOLUTION. GENETICS, AND EUGENICS
prehistoric man represents waves of migration from the greater
continent.
Nevertheless the European record has enabled us to name and
define a number of distinct human species, and here the record of the
cultural evolution of man is also unusually complete. Hence Euro-
pean chronology is taken as a standard in describing discoveries from
any portion of the world.
CHRONOLOGICAL TABLE
(Adapted from Osborn, 1915)
Postglacial Time 25,000 years
Upper Palaeolithic culture
Cro-Magnon man
Fourth Glacial Stage (Wiirm, Wisconsin) 50,000 years
Close of Lower Palaeolithic culture
Neanderthal man
Third Interglacial Stage 150,000 years
Beginning of Lower Palaeolithic culture
Piltdown and pre-Neanderthaloid men
Third Glacial Stage (Riss, lUinoian) 175,000 years
Second Interglacial Stage 375,000 years
Heidelberg man
Second Glacial Stage (Mindel, Kansas) 400,000 years
First Interglacial Stage 475,000 years
Pithecanthropus, ape-man
First Glacial Stage (Giinz, Nebraskan) 500,000 years
Pithecanthropus. — The Java ape-man, Pithecanthropus erectus
(Fig. 35) was discovered in Trinil, on the Solo or Bengawan
River in central Java, in
1894. The type consists of
a calvarium or skull cap, a
left thigh bone, and two
upper molar teeth. The /y "^^
skull is characterized by its /"K
limited capacity, about two- y"^ \ — -f ^^•s-' ~-vf> ^ — ' \
thirds that of man ; and by U^^Or rr-^r^ I \^^..-s::l_>
the low flat forehead and 'r'^^~^^
beetling brows. Hence not
only was the brain limited
in its total size, but this ^^^- 35-^Skull of Java ape-man, Pithecan-
was especially true of the '^'''^"' '''''"'■ ^^'"''' ^"^^' °^''' ^"^"''-^
frontal lobes, which, as we have seen, are the seat of the higher intel-
lectual faculties. Thus, as Osborn says, although touch, taste, and
THE EVOLUTION OF MAN
I5V
vision were well developed there was a limited faculty for profiting
by experience and accumulated tradition. The femur associated with
the skull is remarkable for its
length and slight curvature as
compared with the primitive
Neanderthal race of Europe
and indicates a creature fully
as erect and nearly as tall as the
average European of today,
the height being estimated at 5
feet 7 inches as compared with
5 feet 3 inches for the Nean-
derthals and 5 feet 8 inches,
the average height of modem
males. The erect posture of
course implies the liberation
of the hands from any part in
the locomotor function. The
teeth are somewhat ape-like,
but are more human than are
those of the gibbon, and the
human mode of mastication
has been acquired. Certain
authorities have tried to prove
that Pithecanthropus is nothing
but a large gibbon, but the
weight of authority considers
it prehuman, though not in
the line of direct development
into humanity. It is neverthe-
less a highly important transi-
tional form.
Associated with the Pithe-
canthropus remains are those
of a number of the contem-
porary animals which fix the
Fig. 36 —Jaws, left outer aspect, of A, date as either of the Upper Plio-
chimpanzee,PaK,sp.; B, fossil chimpanzee, cene or lowermost Pleistocene
,Pan veins, found in association with Pilt- -^^^ ^j^j^j^ ^^^ rendered
down man; C, Heidelberg man. Homo . .
. -J ,1. . r» J Tj J.- m terms 01 years gives an esti-
hetdeloergensis; D, modern man, H. sapiens. •' °
{From Lull, after Woodward.) mated age of about 500,000!
i6o EVOLUTION, GENETICS, AND EUGENICS
Heidelberg man. — Homo heidelbergensis, the Heidelberg man,
represents the oldest recorded European race, geologically speaking.
The type was discovered in 1907 in river sands, 79 feet below the
surface, at Mauer, near Heidelberg, South Germany. The reHc
consists of a perfect lower jaw with the dentition (Fig. 36, C). The
description by the discoverer, Doctor Schoetensack, follows (from
Osborn) :
"The mandible shows a combination of features never before
found in any fossil or recent man. The protrusion of the lower jaw
just below the front teeth (the chin prominence) which gives shape to
the human chin is entirely lacking. Had the teeth been absent it
would have been impossible to diagnose it as human. From a fragment
of the symphysis of the jaw it might well have been classed as some
gorilla-like anthropoid, while the ascending ramus resembles that of
some large variety of gibbon. The absolute certainty that these
remains are human is based on the form of the teeth — molars, pre-
molars, canines, and incisors are all essentially human and although
somewhat primitive in form, show no trace of being intermediate
between man and the anthropoid apes but rather of being derived from
some older common ancestor. The teeth, however, are small for the
jaw; the size of the border would allow for the development of much
larger teeth. We can only conclude that no great strain was put on
the teeth, and therefore the powerful development of the bones
of the jaw was not designed for their benefit. The conclusion is that
the jaw, regarded as unquestionably human from the nature of the
teeth, ranks not far from the point of separation between man and the
anthropoid apes. In comparison with the jaws of the Neanderthal
races .... we may consider the Heidelberg jaw as pre-Neander-
thaloid; it is, in fact, a generalized type."
Associated with the Heidelberg jaw is an extensive warm-climate
fauna: straight-tusked elephant {E. antiquus), Etruscan rhinoceros,
primitive horse, bison, wild cattle (urus), bear, lion, and so on, all of
which aid in establishing the date of the jaw as Second Interglacial
and its age, conservatively estimated, at from 300,000 to 375,000 years.
The cultural evolution of Heidelberg man is indicated by the presence
of eoUths, flint implements of the crudest workmanship, if indeed their
apparent fashioning is not merely the result of use.
Neanderthal man. — The original specimen of the Neanderthal
man. Homo neanderthalensis or primigenius (Figs.37, 38^39) was dis-
covered in 1856 not far from Diisseldorf in Rhenish Prussia. Here
the valley of the Diissel forms the deep Neanderthal ravine, whose
THE EVOLUTION OF MAN
i6i
limestone walls are penetrated by caverns, in one of which the remains
were found. What was doubtless a perfect skeleton at the time of its
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discovery was so injured by its finders that only a portion of it, which
is now preserved in the Provincial Museum at Bonn, was saved. " This
prophet of an unknown race was for a time utterly without honor
l62
EVOLUTION, GENETICS, AND EUGENICS
though of course the subject of a most heated controversy, being con-
sidered as non-human, or, as Virchow beheved, owing its distinctive
characters to disease. The sagacity of Huxley threw true light upon
the problem, though it was not until the mute testimony of other
representatives of the race (the men of Spy) was offered that even
Huxley's masterful conception of the Neanderthal characters was
taken as an accepted fact.
Professor Huxley's descrip-
tion of the Neanderthal
type is classic. He says:
"The anatomical char-
acters of the skeletons bear
out conclusions which are
not flattering to the appear-
ance of the owners. They
were short of stature but
powerfully built, with
strong, curiously curved
thigh bones, the lower ends
of which are so fashioned
that they must have walked
with a bend at the knees.
Their long depressed skulls had very strong brow-ridges; their lower
jaws, of brutal depth and solidity, sloped away from the teeth down-
wards and backwards in consequence of the absence of that especially
characteristic feature of the higher type of man, the chin prominence."
Subsequently several more specimens have come to light, at Spy
in Belgium, at Krapina in Croatia, at Le Moustier, La Chapelle-aux-
Saints and La Ferrassie in France, and at Gibraltar, which, while
differing in various details, effectually serve to establish the race, whose
main characteristics are : Heavy, overhanging brows, retreating fore-
head, long upper lip; jaw less powerful than that of the Heidelberg
man but very thick and massive; chin generally strongly receding but
in process of forming; dentition extraordinarily massive in the La
Chapelle specimen, whereas in those of Spy the teeth are small. The
skull in many characteristics is nearer to the anthropoids than to
modern man.
The brain is large and its volume is surely human, but the pro-
portions are again less like those of recent man than like the anthro-
poids. The chest is large and robust, the shoulders broad, and
Fig. 38. — Neanderthaloid skull of La
Chapelle-aux-Saints {Homo neanderthalensis) .
{From Lull, after Boulc.)
THE EVOLUTION OF MAN
163
the hand large, but the fingers are relatively short, the thumb lacking
the range of movement seen in modern man. The knee was some-
what bent, the leg powerful, with a short shin and clumsy foot, clearly
not of cursorial adaptation. The
curve of the bent leg was correlated
with a similar curvature of the
spine, so that the man could not
stand fully erect, as he lacked the
fourth or cervical curvature of
Homo sapiens. The average stature
was 5 feet 3 inches, with a range
from 4 feet 10.3 inches to 5 feet
5.2 inches, partly sex differences.
Neanderthal man lived in Eu-
rope from the Third Interglacial
stage through the Fourth Glacial,
a duration of thousands of years,
and then became extinct, from
twenty to twenty-five millenniums
ago. He seems to have been an
actual lineal successor of the man
of Heidelberg, but was throughout
his long career an unprogressive
static race. One of the most
remarkable features in connection
with this race, however, was the
very reverent way in which the
dead were buried, with an abun-
dance of ornaments and finely
Fig. 39. — Skeleton of Neanderthal
man. A , Homo neanderthalensis , com-
pared with that of a living native
AustraUan; B ,H omo sapiens ,thQ\a.i\.tx
the lowest existing race. {From Lull,
after Woodward.)
worked flints. This can have but one interpretation, the awakening
within this ancient type of the instinctive belief in immortality!
Piltdown man. — In 191 2 was announced the discovery of a very
ancient man from the Thames gravels at Piltdown, Sussex, England.
Here again the skull was injured and partly lost, so that the question
of its proper restoration has been the subject of considerable contro-
versy. The material consists of portions of the cranial walls, nasal
bones, a canine tooth, and part of a lower jaw. The brain-case in this
instance is typically human, except for the remarkably thick cranial
walls. The forehead is high and lacks the superorbital ridges of
Neanderthal man and Pithecanthropus. While the skull is of com-
1 64 EVOLUTION, GENETICS, AND EUGENICS
paratively high human type, the associated jaw and canine tooth
clearly are not, and some difficulty was met in explaining their evolu-
tionary discrepancy. That has apparently been answered, however,
by the conclusion that the association of the material is purely acci-
dental and that the jaw not only does not belong with the skull, but
that it is not even human but is that of a fossil chimpanzee. That
being the case, there seems to be no reason for the exclusion of the
Piltdown man, who has been named Eoanthropiis dawsoni, from the
direct line of human ancestry. The specimen is not, perhaps, so surely
dated as are those of the other European races, but it is associated with
a warm-climate fauna and is generally considered to belong to the
Third Interglacial stage — from 100,000 to 150,000 years old, and
hence vastly more ancient than the more primitive Homo neander-
thalensis. (See Fig. 36, B.)
Cr8-Magnon man. — The original finds of the men of the Cro-
Magnon race, Homo sapiens, were made at Gower, Wales, and at
Aurignac, France. In the latter place seventeen skeletons came to
light in 1852, but were buried in the village cemetery and thus lost to
science, and not until 1868, when five more skeletons were discovered
at Cr6-Magnon, France, was the race established. These individuals,
an old man, two young men, a woman and a child, are thus the
types of the race. This magnificent race is thus characterized:
Skull large but narrow, with a broad face, hence disharmonic.
Facial angle equalling the highest type of Homo sapiens. Jaw thick
and strong, with a narrow but very prominent chin. Forehead high
and orbital ridges reduced. Brain not only of high type but very
large, that of the women exceeding the average male of to-day.
The stature of the old man was 6 feet 4.5 inches; the average for
males being 6 feet r.5 inches, for women 5 feet 5 inches, a great dis-
parity. The lower segments of the limbs were long, in contrast with
the Neanderthal type, hence the men of Cr6-Magnon were swift-
footed, while those of Neanderthal were slow. Osbom says: "The
wide, short face, the extremely prominent cheekbones, the spread of
the palate and a tendency of the upper cutting teeth and incisors to
project forward, and the narrow, pointed chin recall a facial type
which is best seen to-day in tribes living in Asia to the north and to
the south of the Himalayas. As regards their stature the Cr6-Magnon
race recall the Sikhs living to the south of the Himalayas. In the
disharmonic proportions of the face, that is, the combination of
broad cheekbones and narrow skull, they resemble the Eskimo. The
THE EVOLUTION OF MAN 165
sum of the Cro-Magnon characters is certainly Asiatic rather than
African, whereas in the Grimaldis (of which specimens have been
found in association with Cr6-Magnons at the Grotte des Enfants,
Mentone) the sum of the characters is decidedly negroid or African."
The Cr6-Magnons again show by their elaborate burial customs
how old and well founded is the belief in life after death. They are
supposed to be the people who left on the walls of the caverns of France
and Spain the marvelous examples of Upper Palaeolithic art of which
Professor Osborn's book gives so adequate a description. They
lived for a while contemporaneously with the men of Neanderthal and
may have contributed somewhat to the final extinction of the latter.
In the course of time, however, they too declined, although to this
day survivors of the race may be seen in Dordogne, at Landes, near
the Garonne in Southern France, and at Lannion in Brittany. Osborn
says:
The decUne of the Cr6-Magnons, with their artistic culture,
"may have been partly due to environmental causes and the abandon-
ment of their vigorous nomadic mode of life, or it may be that they had
reached the end of a long cycle of psychic development We
know as a parallel that in the history of many civilized races a period
of great artistic and industrial development may be followed by a
period of stagnation and decline without any apparent environmental
cause."
Europe was repopulated after Cr6-Magnon decHne by later
invaders from the Asiatic realm, the so-called Mediterranean narrow-
headed and the Alpine broad-headed types, etc., probably differen-
tiated in Asia in early Palaeolithic times. The repopulation took
place in the Upper Palaeolithic.
EVIDENCES OF HUMAN ANTIQUITY
Great variation. — These, briefly summarized, are, first, great
variation. If man is monophyletic, that is, derived from a single
prehuman species, and there is no reason to believe otherwise, he must
be old, for while the adaptations to ground-dwellmg after the descent
from the trees were doubtless relatively rapidly acquired, the differen-
tiation into the various races, due perhaps largely to climatic influ-
ences rather than to any notable environmental change, must have
been slowly attained. As corroborative evidence we have but to
point to the mural paintings on Egyptian monuments, dating back
l66 EVOLUTHJN, GENETICS, AND EUGENICS
several thousand years, in which are depicted the Ethiopian, Caucasian,
and the like, which are in some instances striking likenesses of the
present-day Egyptians.
Universal distribution is, in animals, another mark of antiquity:
in man, it is probably less so because of his greater intelligence.
And yet before transportation had become a science man's spread
over land and sea was extremely slow.
High intelligence as compared with that of the anthropoids is also
a mark of antiquity, for the brain, especially the type of brain found
in the higher human races, must have been very slow of development.
Our study of fossil man shows this.
Communal life, division of labor and all of the complicated
interactions which it brings about, and the development of law and
rehgions all have taken time. When we realize that Babylonian texts,
twice as remote as the patriarch Abraham, give evidence of highly
perfect laws and of a civilization which must have antedated their
production by centuries, we gain another yet more emphatic im-
pression of human antiquity. Add to all this the palaeontological
evidence of man's association with various genera and numerous
successive species of prehistoric animals of which he alone survives,
and the evidence is complete.
FUTURE OF HUMANITY
Because of his intelligence and communal co-operation man is no
longer subject to the laws which govern the adaptation of animals
to their environment. Osbom's law of adaptive radiation, which, as
we have seen, applies equally well to the insects, reptiles, and mam-
mals, fails in its application to mankind ; and yet man has become as
thoroughly adapted to speed, flight, to the fossorial and aquatic as
they; but his adaptation is artificial and to a very small extent only
affects his physical frame, while theirs is natural and the stamp of
environment is deeply impressed upon the organism.
Man's physical evolution has virtually ceased, but in so far as any
change is being effected, it is largely retrogressive. Such changes are :
Reduction of hair and teeth, and of hand skill; and dulling of the
senses of sight, smell, and hearing upon which active creatures depend
so largely for safety. That sort of charity which fosters the physi-
cally, mentally, and morally feeble, and is thus contrary to the law of
natural selection, must also in the long run have an adverse effect upon
the race.
THE EVOLUTION OF MAN 167
Man is hardly as yet subject to Malthus' law, for while he is
increasing more rapidly than any other animal, owing largely to the
care of the young which makes the expectation of life of the new-born
relatively very high, his migratory abihty, but above all his intelli-
gence, save him from the application of the law. A single new dis-
covery such as that of electricity may increase his food supply and
other Ufe necessities several fold. His future evolution, in so far as
it is progressive, will be mental and spiritual rather than physical, and
as such will be the logical conclusion of the marvelous results of
organic evolution.
L
CHAPTER XIII
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION
PRINCIPLES OF GEOGRAPHIC DISTRIBUTION
Just as palaeontology may be said to be a study of the vertical
distribution (distribution in time) of organisms, so geographic distribu-
tion may be called a study of the horizontal distribution of organisms,
on the earth's surface at any given time (spatial distribution). We are
chiefly to be concerned with the present spatial distribution of animal
and plant species, but equally interesting studies have been and still
may be made of the horizontal or contemporaneous existence of
extinct forms. Much new knowledge has been gained by combining
the data of palaeontology with those of geographic distribution. In
fact, neither field can be studied profitably without recourse to the
other. This fact was clearly perceived by J. A. Thomson in his little
manual on Evolution when he combined the two types of evidence in
one chapter under the title "Evidences of Evolution from Explorer
and Palaeontologist."
It was a consideration of the present and of the past distribution
of Edentates that led Charles Darwin to his first clear concept of
descent with modification. In his voyage on the "Beagle" he found
that present-day Edentates (armadillos, sloths, anteaters), a very
peculiar group of archaic mammals, are practically confined to South
America. When he also found that the only fossil Edentates, resem-
bling but also differing from the existing types, are also confined to
South America, he easily arrived at the only inference permitted by
the facts: that the present Edentates are the modified descendants
of the Edentates of the past.
The following quotations from both an older and a recent writer
will give the reader a clear idea of the ways in which the general facts
of geographic distribution bear witness to the truth of the evolutionary
principle.
"The theory," says Wallace,' "which we may now take as estab-
lished — that all the existing forms of life have been derived from other
forms by a natural process of descent with modification, and that this
same process has been in action during past geological time — should
' From A. R. Wallace, Darwinism (1889). Used by special permission of the
publishers, The Macmillan Company.
168
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION X69
enable us to give a rational- account not only of the peculiarities of
form and structure presented by animals and plants, but also of their
grouping together in certain areas, and their general distribution over
the earth's surface.
"In the absence of any exact knowledge of the facts of distribution,
a student of the theory of evolution might naturally anticipate that all
groups of allied organisms would be found in the same region, and that,
as he travelled farther and farther from any given centre, the forms
of life would differ more and more from those which prevailed at the
starting-point, till, in the remotest regions to which he could penetrate,
he would find an entirely new assemblage of animals and plants,
altogether unlike those with which he was familiar. He would also
anticipate that diversities of chmate would always be associated with a
corresponding diversity in the forms of life.
"Now these anticipations are to a considerable extent justified.
Remoteness on the earth's surface is usually an indication of diversity
in the fauna and flora, while strongly contrasted climates are always
accompanied by a considerable contrast in the forms of life. But
this correspondence is by no means exact or proportionate, and the
converse propositions are often quite untrue. Countries which are
near to each other often differ radically in their animal and vegetable
productions; while similarity of cUmate, together with moderate
geographical proximity, are often accompanied by marked diversi-
tiss in the prevailing forms of life. Again, while many groups of
animals — genera, families, and sometimes even orders — are confined
to limited regions, most of the families, many genera, and even
some species are found in every part of the earth. An enumeration
of a few of these anomalies will better illustrate the nature of the
problem we have to solve.
"As examples of extreme diversity, notwithstanding geographical
proximity, we may adduce Madagascar and Africa, whose animal and
vegetable productions are far less alike than are those of Great Britain
and Japan at the remotest extremities of the great northern continent;
while an equal, or perhaps even a still greater, diversity exists between
Australia and New Zealand. On the other hand. Northern Africa
and South Europe, though separated by the Mediterranean Sea, have
faunas and floras which do not differ from each other more than do
the various countries of Europe. As a proof that similarity of climate
and general adaptability have had but a small part in determining the
forms of life in each country, we have the fact of the enormous increase
I70 EVOLUTION, GENETICS, AND EUGENICS
of rabbits and pigs in Australia and New Zealand, of horses and cattle
in South America, and of the common sparrow in North America,
though in none of these cases are the animals natives of the
countries in which they thrive so well. And lastly, in illustration of
the fact that allied forms are not always found in adjacent regions,
we have the tapirs, which are found only on opposite sides of the
globe, in tropical America and the Malayan Islands; the camels of
the Asiatic deserts, whose nearest allies are the llamas and alpacas
of the Andes; and the marsupials, only found in Australia and on
the opposite side of the globe in America. Yet, again, although
mammalia may be said to be universally distributed over the globe,
being found abundantly on all the continents and on a great many of
the larger islands, yet they are entirely wanting in New Zealand, and
in a considerable number of other islands which are, nevertheless, per-
fectly able to support them when introduced.
"Now most of these difficulties can be solved by means of well-
known geographical and geological facts. When the productions of
remote countries resemble each other, there is almost always conti-
nuity of land with similarity of climate between them. When adjacent
countries differ greatly in their productions, we find them separated by
a sea or strait whose great depth is an indication of its antiquity or
permanence. When a group of animals inhabits two countries or
regions separated by wide oceans, it is found that in past geological
times the same group was much more widely distributed, and may
have reached the countries it inhabits from an intermediate region
in which it is now extinct. We know, also, that countries now united
by land were divided by arms of the sea at a not very remote epoch,
jvhile there is good reason to believe that others now entirely isolated
by a broad expanse of sea were formerly united and formed a single land
area. There is also another important factor to be taken account of
in considering hov/ animals and plants have acquired their present
peculiarities of distribution, — changes of climate. We know that
quite recently a glacial epoch extended over much of what are now the
temperate regions of the northern hemisphere, and that consequently
the organisms which inhabit those parts must be, comparatively
speaking, recent immigrants from more southern lands. But it is a
yet more important fact that, down to middle Tertiary times at all
events, an equable temperate climate, with a luxuriant vegetation,
extended to far within the Arctic circle, over what are now barren
wastes, covered for ten months of the year with snow and ice. The
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 171
Arctic zone has, therefore, been in past times capable of supporting
almost all of the forms of life of our temperate regions; and we must
take account of this condition of things whenever we have to specu-
late on the possible migration of organisms between the old and new
continents."
"Many of the facts of distribution," says Shull,^ "are capable of
interpretation by the assumption that evolution has operated with the
other factors. If each kind of animal has arisen from a pre-existing
kind, then each group of related animals must have had an ancestral
form, and if the component parts of the groups are widespread the
range of the ancestral form may be considered to be the center of
dispersal of the group. The facts of distribution can apparently be
interpreted only on this basis.
"Accepting evolution, along with the other factors which can be
recognized, the method of distribution is generally conceived to be as
follows. The ancestral form tends to spread in all directions. In
some directions it is limited by unfavourable conditions either through-
out its life or for some time. In other directions it extends its range.
Anywhere within its range new types of individuals may arise through
the process of evolution. These new types may be fitted to occupy
new regions, and if they are formed near the limits of the range they
may find opportunity to spread into areas which are inaccessible to
the unaltered members of the species. Thus may arise recognizably
distinct forms coincident in range with certain environmental condi-
tions. If particular forms, or the individuals of a single form, are
accidentally (or possibly by sporadic migration) transferred across
barriers the distribution of the group becomes discontinuous. If
these processes have been going on for a long time, that is, if the
common ancestors of a group of forms existed long ago, the range may
have had time to become very extensive, or its discontinuity very
marked. If, contrariwise, the ancestors were comparatively recent,
the range is likely to be much smaller. For this reason, groups that
have diverged far enough to have attained the rank of families are on
the whole more widespread than those so nearly allied as to be con-
sidered genera. Should the environment become altered within a
given range, the occupying form might be driven from it or destroyed.
'From A. F. Shull, Principles of Animal Biology (copyright 1920). Used by
special pennission of the publishers, The McGraw-Hill Book Company.
172 EVOLUTION, GENETICS, AND EUGENICS
If the environment in a region adjoining a range should change in a
favourable manner, the range might be extended at that point without
any alteration on the part of the animals.
" The distribution of animals is inferred to be in harmony with this
method, which involves, it will be noted, the factors of migration,
evolution, physiological and morphological dependence upon the
environment, the diversity and changeableness of the earth's surface,
and extinction; and in this manner are explained the differences in
geographical position, differences in size of range, differences in the
continuity of range and the fact that ranges are at first continuous,
differences in physical and biological conditions which characterize
the ranges of different forms, and the geographical proximity of
apparently related forms."
SOME OF THE MORE SIGNIFICANT FACTS ABOUT THE
DISTRIBUTION OF ANIMALS
THE FAUNA OF OCEANIC ISLANDS'
GEORGE JOHN ROMANES
Turning now from aquatic organisms to terrestrial, the body of
facts from which to draw is so large, that I think the space at my dis-
posal may be best utilized by confining attention to a single division
of them — that, namely, which is furnished by the zoological study of
oceanic islands.
In the comparatively limited — but in itself extensive — class of
facts thus presented, we have a particularly fair and cogent test as
between the alternative theories of evolution and creation. For
where we meet with a volcanic island, hundreds of miles from any
other land, and rising abruptly from an ocean of enormous depth, we
may be quite sure that such an island can never have formed part of a
now submerged continent. In other words, we may be quite sure that
it always has been what it now is — an oceanic peak, separated from all
other land by hundreds of miles of sea, and therefore an area supplied
by nature for the purpose, as it were, of testing the rival theories of
creation and evolution. For, let us ask, upon these tiny insular
specks of land what kind of life should we expect to find ? To this
question the theories of special creation and of gradual evolution
would agree in giving the same answer up to a certain point. For
both theories would agree in supposing that these islands would, at all
' From G. J. Romanes, Darwin and after Darwin (copyright 1892). Used by
special permission of The Open Court Publishing Company.
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 173
events in large part, derive their inhabitants from accidental or occa-
sional arrivals of wind-blown or water-floated organisms from other
countries — especially, of course, from the countries least remote. But,
after agreeing upon this point, the two theories must part company in
their anticipations. The special-creation theory can have no reason
to suppose that a small volcanic island in the midst of a great ocean
should be chosen as the theatre of any extraordinary creative activity,
or for any particularly rich manufacture of peculiar species to be
found nowhere else in the world. On the other hand, the evolution
theory would expect to find that such habitats are stocked with more
or less peculiar species. For it would expect that when any organisms
chanced to reach a wholly isolated refuge of this kind, their descendants
should forthwith have started upon an independent course of evolu-
tionary history. Protected from intercrossing with any members of
their parent species elsewhere, and exposed to considerable changes in
their conditions of life, it would indeed be fatal to the general theory
of evolution if these descendants, during the course of many genera-
tions, were not to undergo appreciable change. It has happened on
two or three occasions that European rats have been accidentally
imported by ships upon some of these islands, and even already it is
observed that their descendants have undergone a slight change of
appearance, so as to constitute them what naturalists call local
varieties. The change, of course, is but shght, because the time
allowed for it has been so short. But the longer the time that a
colony of a species is thus completely isolated under changed condi-
tions of life the greater, according to the evolution theory, should
we expect the change to become. Therefore, in all cases where we
happen to know, from independent evidence of a geological kind, that
an oceanic island is of very ancient formation, the evolution theory
would expect to encounter a great wealth of peculiar species. On the
other hand, as I have just observed, the special-creation theory can
have no reason to suppose that there should be any correlation
between the age of an oceanic island and the number of peculiar species
which it may be found to contain.
Therefore, having considered the principles of geographical distri-
bution from the widest or most general point of view, we shall pass to
the opposite extreme, and consider exhaustively, or in the utmost
possible detail, the facts of such distribution where the conditions are
best suited to this purpose — that is, as I have akeady said, upon
oceanic islands, which may be metaphoriraTlv regarded as having been
174 EVOLUTION, GENETICS, AND EUGENICS '
formed by nature for the particular purpose of supplying naturalists
with a crucial test between the theories of creation and evolution.
The material upon which my analysis is to be based will be derived
from the most recent works upon geographical distribution — espe-
cially from the magnificent contributions to this department of science
which we owe to the labours of Mr. Wallace. Indeed, all that follows
may be regarded as a condensed filtrate of the facts which he has
collected. Even as thus restricted, however, our subject matter
would be too extensive to be dealt with on the present occasion,
were we to attempt an exhaustive analysis of the floras and faunas
of all oceanic islands upon the face of the globe. Therefore, what I
propose to do is to select for such exhaustive analysis a few of what
may be termed the most oceanic of oceanic islands — that is to say,
those oceanic islands which are most widely separated from main-
lands, and which, therefore, furnish the most unquestionable of
test cases as between the theories of special creation and genetic
descent.
Azores. — A group of volcanic islands, nine in number, about 900
miles from the coast of Portugal, and surrounded by ocean depths of
1,800 to 2,500 fathoms. There is geological evidence that the origin
of the group dates back at least as far as Miocene times. There is a
total absence of all terrestrial Vertebrata, other than those which are
known to have been introduced by man. Flying animals, on the
other hand, are abundant : namely, 53 species of birds, one species of
bat, a few species of butterflies, moths and hymenoptera, with 74
species of indigenous beetles. All these animals are unmodified
Eurc^ean species, with the exception of one bird and many of the
beetles. Of the 74 indigenous species of the latter, 36 are not found
in Em-ope; but 19 are natives of Madeira or the Canaries, and 3 are
American, doubtless transplanted by drift-wood. The remaining 14
species occur nowhere else in the world, though for the most part
they are allied to other European species. There are 69 known
species of land-shells, of which 37 are European, and 32 peculiar,
though all allied to European forms. Lastly, there are 480 known
species of plants of which 40 are peculiar, though allied to European
species.
Bermudas. — A small volcanic group of islands, 700 miles from
North Carolina. Athough there are about 100 islands in the group,
their total area does not exceed 50 square miles. The group is sur-
rounded by water varying in depth from 2,500 to 3,800 fathoms. The
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 175
only terrestrial Vertebrate (unless the rats and mice are indigenous)
is a lizard allied to an American form, but specifically distinct from it,
and therefore a solitary species which does not occur anywhere else in
the world. None of the birds or bats are pecuUar, any more than in
the case of the Azores; but, as in that case, a large percentage of the
land-shells are so — namely, at least one quarter of the whole. Neither
the botany nor the entomology of this group has been worked out;
but I have said enough to show how remarkably parallel are the cases
of these two volcanic groups of islands situated in different hemispheres
but at about the same distance from large continents. In both there
is an extraordinary paucity of terrestrial Vertebrata, and of any
peculiar species of bird or beast. On the other hand, there is in both
a marvellous wealth of pecuUar species of insects and land -shells.
Now these correlations are all abundantly intelligible. It is a difficult
matter for any terrestrial animal to cross 900, or even 700 miles of
ocean : therefore only one lizard has succeeded in doing so in one of the
two parallel cases; and living cut off from intercrossing with its
parent form, the descendants of that lizard have become modified so as
to constitute a peculiar species. But it is more easy for large flying
animals to cross those distances of ocean: consequently, there is only
one instance of a peculiar species of bird or bat — namely, a bull-finch
in the Azores, which, being a small land-bird, is not likely ever to have
had any other visitors from its original parent species coming over
from Europe to keep up the original breed. Lastly, it is very much more
easy for insects and land-moUusca to be conveyed to such islands by
wind and floating timber than it is for terrestrial mammals, or even
than it is for small birds and bats; but yet such means of transit are
not sufficiently sure to admit of much recruiting from the mainland
for the purpose of keeping up the specific types. Consequently, the
insects and the land-shells present a much greater proportion of
peculiar species — namely, one half and one fourth of the land-shells in
the one case, and one eighth of the beetles in the other. All these cor-
relations, I say, are abundantly intelligible on the theory of evolution;
but who shall explain, on the opposite theory, why orders of beetles
and land-mollusca should have been chosen from among all other
animals for such superabundant creation on oceanic islands, so that
in the Azores alone we find no less than 32 of the one and 14 of the
other? And, in this connection, I may again allude to the peculiar
species of beetles in the island of Madeira. Here there are an enor-
mous number of peculiar species, though they are nearly all related to,
176 EVOLUTION, GENETICS, AND EUGENICS
or included under the same genera, as beetles on the neighboring conti-
nent. Now, as we have previously seen, no less than 200 of these
species have lost the use of their wings. Evolutionists explain this
remarkable fact by their general laws of degeneration under disuse,
and the operation of natural selection, as will be shown later on; but
it is not so easy for special creationists to explain why this enormous
number of peculiar species of beetles should have been deposited on
Madeira, all aUied to beetles on the nearest continent, and nearly all
deprived of the use of their wings. And similarly, of course, with all
the peculiar species of the Bermudas and the Azores. For who will
explain, on the theory of independent creation, why all the peculiar
species, both of animals and plants, which occur on the Bermudas
should so unmistakably present American affinities, while those which
occur on the Azores no less unmistakably present European affinities ?
But to proceed to other, and still more remarkable, cases.
The Galapagos Islands. — This archipelago is of volcanic origin,
situated under the equator between 500 and 600 miles from the West
Coast of South America. The depth of the ocean around them varies
from 2,000 to 3,000 fathoms or more. This group is of pecuUar
interest, from the fact that it was the study of its fauna which first
suggested to Darwin's mind the theory of evolution. I will, therefore,
begin by quoting a short passage from his writings upon the zoological
relations of this particular fauna.
"Here almost every product of the land and of the water bears the
unmistakable stamp of the American continent. There are twenty-six
land birds; of these, twenty-one, or perhaps twenty- three, are ranked
as distinct species, and would commonly be assumed to have been here
created; yet the close affinity of most of these birds to American
species is manifest in every character, in their habits, gestures, and
tones of voice. So it is with the other animals, and with a large pro-
portion of the plants, as shown by Dr. Hooker in his admirable Flora
of this archipelago. The naturalist, looking at the inhabitants of
these volcanic islands in the Pacific, distant several hundred miles
from the continent, feels that he is standing on American land. Why
should this be so? Why should the species which are supposed to
have been created in the Galapagos Archipelago, and nowhere else,
bear so plainly the stamp of affinity to those created in America?
There is nothing in the conditions of Ufe, in the geological nature of the
islands, in their height or cHmate, or in the proportions in which the
several classes are associated together, which closely resembles the
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 177
conditions of the South American coast; in fact, there is a considerable
dissimilarity in all these respects. On the other hand, there is a con-
siderable degree of resemblance in the volcanic nature of the soil, in the
climate, height, and size of the islands, between the Galapagos and Cape
de Verde Archipelagoes; but what an entire and absolute difference
in their inhabitants! The inhabitants of the Cape de Verde Islands
are related to those of Africa, like those of the Galapagos to America.
Facts such as these admit of no sort of explanation on the ordi-
nary view of independent creation; whereas in the view here main-
tained it is obvious that the Galapagos Islands would be likely to
receive colonists from America, and the Cape de Verde Islands from
Africa; such colonists would be liable to modification — the principle of
inheritance still betraying their original birthplace. "
The following is a synopsis of the fauna and flora of this archi-
pelago, so far as at present known. The only terrestrial vertebrates
are two peculiar species of land-tortoise, and one extinct species; five
species of lizards, all peculiar — two of them so much so as to constitute
a peculiar genus; — and two species of snakes, both closely allied to
South American forms. Of birds there are 57 species, of which no less
than 38 are peculiar; and all the non-peculiar species, except one,
belong to aquatic tribes. The true land-birds are represented by 31
species, of which all, except one, are peculiar; while more than half
of them go to constitute peculiar genera. Moreover, while they are
all unquestionably allied to South American forms, they present a
beautiful series of gradations, "from perfect identity with the conti-
nental species, to genera so distinct that it is difficult to determine with
what forms they are most nearly allied; and it is interesting to note
that this diversity bears a distinct relation to the probabilities of,
and facilities for, migration to the islands. The excessively abun-
dant rice-bird, which breeds in Canada, and swarms over the whole
United States, migrating to the West Indies and South America,
visiting the distant Bermudas almost every year, and extending its
range as far as Paraguay, is the only species of land-bird which remains
completely unchanged in the Galapagos; and we may therefore con-
clude that some stragglers of the migrating host reach the islands
sufiiciently often to keep up the purity of the breed" [Wallace].
Again, of the thirty peculiar land-birds, it is observable that the
more they differ from any other species or genera on the South
American continent, the more certainly are they found to have their
nearest relations among those South American forms which have the
178 EVOLUTION, GENETICS, AND EUGENICS
more restricted range, and therefore the least likely to have found
their way to the islands with any frequency.
The insect fauna of the Galapagos Islands is scanty, and chiefly
composed of beetles. These number 35 species, which are nearly all
peculiar, and in some cases go to constitute peculiar genera. The
same remarks apply to the twenty species of land-shells. Lastly, of
the total number of flowering plants (332 species) more than one
half (174 species) are peculiar. It is observable in the case of
these peculiar species of plants — as also of the pecuhar species of
birds — that many of them are restricted to single islands. It is also
observable that with regard both to the fauna and flora, the Galapagos
Islands as a whole are very much richer in peculiar species than either
the Azores or Bermudas, notwithstanding that both the latter are
considerably more remote from the nearest continents. This differ-
ence, which at first sight appears to make against the evolutionary
interpretation, really tends to confirm it. For the Galapagos Islands
are situated in a calm region of the globe, unvisited by those periodic
storms and hurricanes which sweep over the North Atlantic, and which
every year convey some straggling birds, insects, seeds, etc., to the
Azores and Bermudas. Notwithstanding their somewhat greater
isolation geographically, therefore, the Azores and Bermudas are
really less isolated biologically than are the Galapagos Islands; and
hence the less degree of peculiarity on the part of their endemic
species. But, on the theory of special creation, it is impossible to
understand why there should be any such correlation between the
prevalence of gales and a comparative inertness of creative activity.
And, as we have seen, it is equally impossible on this theory to under-
stand why there should be a further correlation between the degree
of peculiarity on the part of the isolated species, and the degree in
which their nearest allies on the mainland are there confined to narrow
ranges, and therefore less likely to keep up any biological communi-
cation with the islands.
St. Helena. — A small volcanic island, ten miles long by eight
wide, situated in mid-ocean, 1,100 miles from Africa, and 1,800 from
South America. It is very mountainous and rugged, bounded for the
most part by precipices, rising from ocean depths of 17,000 feet, to a
height above the sea-level of nearly 3,000. When first discovered it
was richly clothed with forests; but these were all destroyed by human
agency during the i6th, 17th, and i8th centuries. The records of civili-
zation present no more lamentable instance of this kind of destruction.
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 179
From a merely pecuniary point of view the abolition of these pri-
meval forests has proved an irreparable loss; but from a scientific
point of view the loss is incalculable. These forests served to harbour
countless forms of life, which extended at least from the Miocene age,
a,nd which, having found there an ocean refuge, survived as the last
remnants of a remote geological epoch. In those days, as Mr. Wallace
observes, St. Helena must have formed a kind of natural museum or
vivarium of archaic species of all classes, the interest of which we can
now only surmise from the few remnants of those remnants, which are
still left among the more inaccessible portions of the mountain peaks
and crater edges. These remnants of remnants are as follows:
There is a total absence of all indigenous mammals, reptiles,
fresh-water fish, and true land-birds. There is, however, a species of
plover, allied to one in South Africa; but it is specifically distinct, and
therefore peculiar to the island. The insect life, on the other hand,
is abimdant. Of beetles, no less than 129 species are believed to be
aboriginal, and, with one single exception, the whole number are
peculiar to the island. "But in addition to this large amount of
specific peculiarity (perhaps unequalled anywhere else in the world)
the beetles of this island are remarkable for their generic isolation, and
for the altogether exceptional proportion in which the great divisions of
the order are represented. The species belong to 39 genera, of which
no less than 25 are peculiar to the island; and many of these are such
isolated forms that it is impossible to find their allies in any particular
country" [Wallace], More than two-thirds of all the species belong
to one group of weevils — a circumstance which serves to explain the
great wealth of beetle-population, the weevils being beetles which live
in wood, and St. Helena having been originally a densely wooded
island. This circumstance is also in accordance with the view that the
peculiar insect fauna has been in large part evolved from ancestors
which reached the island by means of floating timber; for, of course,
no explanation can be suggested why special creation of this highly
peculiar insect faima should have run so disproportionately into the
production of weevils. About two-thirds of the whole number of
beetles, or over 80 species, show no close afi&nity with any existing
insects, while the remaining third have some relations, though often
very remote, with European and African forms. That this high
degree of peculiarity is due to high antiquity is further indicated,
according to our theory, by the large number of species which some of
the types comprise. Thus, the 54 species of Cossonidae mav be
l8o EVOLUTION, GENETICS, AND EUGENICS
referred to three types; the ii species of Bembidium form a group by
themselves; and the Heteromera form two groups. "Now, each of
these types may well be descended from a single species, which origi-
nally reached the island from some other land; and the great variety
of generic and specific forms into which some of them have diverged
is an indication, and to some extent a measure, of the remoteness of
their origin" [Wallace]. But, on the counter-supposition that all these
128 peculiar species were separately created to occupy this particular
island, it is surely unaccountable that they should thus present
such an arborescence of natural affinities amongst themselves.
Passing over the rest of the insect fauna, which has not yet been
sufficiently worked out, we next find that there are only 20 species of
indigenous land-shells — which is not surprising when we remember by
what enormous reaches of ocean the land is surrounded. Of these 20
species no less than 13 have become extinct, three are allied to Euro-
pean species, while the rest are so highly peculiar as to have no near
allies in any other part of the globe. So that the land-shells tell
exactly the same story as the insects.
Lastly, the plants likewise tell the same story. The truly indige-
nous flowering plants are about 50 in number, besides 26 ferns. Forty
of the former and ten of the latter are peculiar to the island, and, as
Sir Joseph Hooker tells us, "cannot be regarded as very close specific
allies of any other plants at all." Seventeen of them belong to peculiar
genera, and the others all differ so markedly as species from their
congeners, that not one comes under the category of being an insular
form of a continental species. So that with respect to its plants, no
less than with respect to its animals, we find that the island of
St. Helena constitutes a little world of unique species, alhed among
themselves, but diverging so much from all other known forms that
in many cases they constitute unique genera.
Sandwich Islands. — These are an extensive group of islands,
larger than any we have hitherto considered — the largest of the group
being about the size of Devonshire. The entire archipelago is vol-
canic, with mountains rising to a height of nearly 14,000 feet. The
group is situated in the middle of the North Pacific, at a distance of
considerably over 2,000 miles from any other land, and surrounded by
enormous ocean depths. The only terrestrial vertebrates are two
lizards, one of which constitutes a pecuhar genus. There are 24
aquatic birds, five of which are peculiar; four birds of prey, two
of which are peculiar; and 16 land-birds, all of which are pecuUar.
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION
i8i
Moreover, these i6 land-birds constitute no less than lo peculiar
genera, and even one peculiar family of five genera. This is an amount
of peculiarity far exceeding that of any other islands, and, of course,
corresponds with the great isolation of this archipelago. The only
other animals which have here been carefully studied are the land-
shells, and these tell the same story as the birds. For there are no less
than 400 species which are all, without any exception, pecuhar; while
about three-quarters of them go to constitute peculiar genera.
Again, of the plants, 620 species are believed to be endemic; and of
these 377 are pecuhar, yieldmg no less than 39 pecuUar genera.
THE FAUNA OF CONTINENTAL ISLANDS — MADAGASCAR AND NEW ZEALAND'
A. R. WALLACE
The two exceptions just referred to are Madagascar and New
Zealand, and all the evidence goes to show that in these cases the land
connection with the nearest continental area was very remote in time.
The extraordinary isolation of the productions of Madagascar — almost
all the most characteristic forms of mammalia, birds, and reptiles of
Africa being absent from it — renders it certain that it must have been
separated from that continent very early in the Tertiary, if not as far
back as the latter part of the Secondary period; and this extreme
antiquity is indicated by a depth of considerably more than a thousand
fathoms in the Mozambique Channel, though this deep portion is less
than a hundred miles wide between the Comoro Islands and the main-
land. Madagascar is the only island on the globe with a fairly rich
mammalian fauna which is separated from a continent by a depth
greater than a thousand fathoms; and no other island presents so
many pecuUarities in these animals, or has preserved so many lowly
organised and archaic forms. The exceptional character of its pro-
ductions agrees exactly with its exceptional isolation by means of a
very deep arm of the sea.
New Zealand possesses no known mammals and only a single
species of batrachian; but its geological structure is perfectly conti-
nental. There is also much evidence that it does possess one mammal,
although no specimens have been yet obtained. Its reptiles and birds
are highly peculiar and more numerous than in any truly oceanic
island. Now the sea which directly separates New Zealand from
Australia is more than 2,000 fathoms deep, but in a north-west direc-
' From A. R. Wallace, Darwinism (copyright 1889). Used by special permis-
sion of the publishers, The Macmillan Company.
l82 EVOLUTION, GENETICS AND EUGENICS
tion there is an extensive bank under i,ooo fathoms, extending to and
including Lord Howe's Island, while north of this are other banks
of the same depth, approaching towards a submarine extension of
Queensland on the one hand, and New Caledonia on the other, and
altogether suggestive of a land union with Australia at some very
remote period. Now the peculiar relations of the New Zealand fauna
and flora with those of Australia and of the tropical Pacific Islands to
the northward indicate such a connection, probably during the Cre-
taceous period; and here, again, we have the exceptional depth of the
dividing sea and the form of the ocean bottom according well with the
altogether exceptional isolation of New Zealand, an isolation which has
been held by some naturalists to be great enough to justify its claim
to be one of the primary Zoological Regions.
THE DISTRIBUTION OF UARSOPIAT^'
A. R. WALLACE
This singular and lowly organised type of mammals constitutes
almost the sole representative of the class in Australia and New
Guinea, while it is entirely unknown in Asia, Africa, or Europe. It
reappears in America, where several species of opossums are found;
and it was long thought necessary to postulate a direct southern con-
nection of these distant countries, in order to account for this curious
fact of distribution. When, however, we look to what is known of the
geological history of the marsupials the difficulty vanishes. In the
Upper Eocene deposits of Western Europe the remains of several
animals closely allied to the American opossums have been found;
and as, at this period, a very mild climate prevailed far up into the
arctic regions, there is no difficulty in supposing that the ancestors of
the group entered America from Europe or Northern Asia during early
Tertiary times.
But we must go much further back for the origin of the AustraUan
marsupials. AU the chief types of the higher mammalia were in
existence in the Eocene, if not in the preceding Cretaceous period,
and as we find none of these in Australia, that country must have been
finally separated from the Asiatic continent during the Secondary or
Mesozoic period. Now during that period, in the Upper and the
Lower OoUte and in the still older Trias, the jaw-bones of numerous
small mammalia have been found, forming eight distinct genera, which
'From A. R. Wallace, Darwinism (copyright i88q). Used by special per-
mission of the publishers, The Macmillan Company.
EVIDENCES FROM GEOGR/\PHIC DISTRIBUTION 183
are believed to have been either marsupials or some allied lowly forms.
In North America also, in beds of the Jurassic and Triassic formations,
the remains of an equally great variety of these small mammalia have
been discovered; and from the examination of more than sixty speci-
mens, belonging to at least six distinct genera, Professor Marsh is of
the opinion that they represent a generalised type, from which the
more specialised marsupials and insectivora were developed.
From the fact that very similar mammals occur both in Europe
and America at corresponding periods, and in beds which represent a
long succession of geological time, and that during the whole of this
time no fragments of any higher forms have been discovered, it seems
probable that both the northern continents (or the larger portion of
their area) were then inhabited by no other mammalia than these,
with perhaps other equally low types. It was, probably, not later
than the Jurassic age when some of these primitive marsupials were
able to enter Australia, where they have since remained almost com-
pletely isolated; and, being free from the competition of higher forms,
they have developed into the great variety of types we now behold
there. These occupy the place, and have to some extent acquired
the form and structure of distinct orders of the higher mammals — the
rodents, the insectivora, and the carnivora — while still preserving the
essential characteristics and lowly organisation of the marsupials.
At a much later period — probably in late Tertiary times — the ances-
tors of the various species of rats and mice which now abound in
Australia, and which, with the aerial bats, constitute its only forms
of placental mammals, entered the country from some of the adjacent
islands. For this purpose a land connection was not necessary, as
these small creatures might easily be conveyed among the branches
or in the crevices of trees uprooted by floods and carried down to the
sea, and then floated to a shore many miles distant. That no actual
land connection with, or very close approximation to, an Asiatic
island had occurred in recent times, is sufficiently proved by the fact
that no squirrel, pig, civet, or other widespread mammal of the Eastern
hemisphere has been able to reach the Australian continent.
THE UISTKIBUTION OF BIRDS'
A. R. WALLACE
These vary much in their powers of flight, and their capability of
traversing wide seas and oceans. Many swimming and wading birds
' From A. R. Wallace, Darwinism (copyright iSgi). Used by special per-
mission of the publishers, The Macniillan Company.
1 84 EVOLUTION, GENETICS, AND EUGENICS
can continue long on the wing, fly swiftly, and have, besides, the
power of resting safely on the surface of the water. These would
hardly be limited by any width of ocean, except for the need of food;
and many of them, as the gulls, petrels, and divers, find abundance of
food on the surface of the sea itself. These groups have a wide distri-
bution across the oceans; while waders — especially plovers, sandpipers,
snipes, and herons — are equally cosmopolitan, travelling along the
coasts of all the continents, and across the narrow seas which separate
them. Many of these birds seem unaffected by climate, and as the
organisms on which they feed are especially abundant on arctic, tem-
perate, and tropical shores, there is hardly any limit to the range even
of some of the species.
Land-birds are much more restricted in their range, owing to their
usually limited powers of flight, their inability to rest on the surface
of the sea or to obtain food from it, and their greater specialisation,
which renders them less able to maintain themselves in the new coun-
tries they may occasionally reach. Many of them are adapted to Uve
only in woods, or in marshes, or in deserts; they need particular kinds
of food or a limited range of temperature; and they are adapted to
cope only with the special enemies or the particular group of competi-
tors among which they have been developed. Such birds as these may
pass again and again to a new country, but are never able to estabHsh
themselves in it; and it is this organic barrier, as it is termed, rather
than any physical barrier, which, in many cases, determines the
presence of a species in one area and its absence from another. We
must always remember, therefore, that, although the presence of a
species in a remote oceanic island clearly proves that its ancestors
must at one time have found their way there, the absence of a species
does not prove the contrary, since it also may have reached the island,
but have been unable to maintain itself, owing to the inorganic or
organic conditions not being suitable to it. This general principle
appUes to all classes of organisms, and there are many striking illus-
trations of it. In the Azores there are eighteen species of land-birds
which are permanent residents, but there are also several others which
reach the islands almost every year after great storms, but have never
been able to establish themselves. In Bermuda the facts are stiU more
striking, since there are only ten species of resident birds, while no less
than twenty other species of land-birds, and more than a hundred
species of waders and aquatics are frequent visitors, often in great
numbers, but are never able to establish themselves.
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 185
SUMMARY QF MAMMALIAN DISPERSAL'
HANS GADOW
Australia as the earliest great mass of land permanently severed
from the rest is in almost undisturbed possession of the lowest mam-
mals. It is the sole refuge of the monotremes, and the marsupials
have narrowly escaped a similar fate. They take us to the next
independent continent, South America. This had three chances, or
epochs, of being stocked with mammals. Within the Cretaceous period
it seems to have received its marsupial stock from the north, the pro-
genitors of all modern marsupials. A second influx during the early
Tertiary brought edentates and rodents as its first Placentals from
Africa, and those queer Ungulates, the Toxodonts and Pyrotheria,
unless we prefer to look upon these Eocene extinct orders as truly
aboriginal to South America, when this was still continuous with tlie
ancient Brazil- Afro-Indian Gondwanaland. The third and last inroad
came once more from the north, when with the close of the Miocene
permanent connection with North America was re-estabhshed. This
brought the modern odd-toed and pair-toed Ungulates, with dogs, cats
and bears in their wake, and lastly man.
There remains the huge North World. Eurasia and North America
have always formed a wide circumpolar ring, which repeatedly broke
and joined again. Whatever group of terrestrial creatures was
developed in the eastern, Asiatic, half, was sure to turn up in the
western, and vice versa.
Lastly, the mysterious African continent. It began originally as
the centre of the ancient equatorial South World; it has lost these con-
nections and has become joined to the northland, after many vicissi-
tudes. It is therefore most difficult to apportion its fauna rightly;
moreover for fossils it is almost a blank, except Egypt. It must have
had some share in the evolution of mammals, like edentates, rodents,
insectivores, hyrax, elephants, sirenians and lemurs, all groups with
an ancient stamp. But what share it had, against Eurasia, in the
development of say ungulates, carnivores, monkeys, we do not know.
Not much is likely to have originated in Europe; the elephants, rhinos,
hippos, Hons and hyaenas were migrants rather from than to Africa,
rarely across some Mediterranean bridge, usually by Asia Minor.
The more dominant forms of our present fauna have originated, to
use an expression of Darwin's, "in the larger areas and more efficient
' From Hans Gadow, Wanderings of Animals (1913), Cambridge University Press.
l86 EVOLUTION, GENETICS, AND EUGENICS
workshops of the north," and the balance is in favour of Asia as the
cradle of modem mammals.
Is it an idle dream to think of the future ? A survey of the past
reveals the vanishing of whole faunas from extensive countries, which
were then repeopled by other forms from elsewhere. What has
happened before, may happen in times to come. Countless groups,
once flourishing, are no more; many others have had their day and are
now on the decline, whilst others are flourishing now, are even in the
increase and seem to have a future before them. Such favoured
assemblies are the toads and frogs, lizards and snakes. Passerine birds
and rodents, mostly the small-sized members of their tribes; the days
of giants are past. All this has happened in the natural course of
events, without the influence of man, who only within most recent
times has become the most potent and destructive factor to the ancient
faunas of the world.
SUMMARY OF THE ARGUMENT FOR EVOLUTION AS BASED ON
GEOGRAPHIC DISTRIBUTION
On the hypothesis of special creation or on any other hypothesis
except evolution that has even been suggested, the extremely intricate
patchwork of animal and plant distribution remains an unsolvable
picture puzzle, without rhyme or reason. When this puzzle is attacked
with the aid of the evolutionary idea, the key to the whole maze is
furnished and the difficulties clear up with remarkable ease. The
whole hodgepodge makes sense and we can understand many pre-
viously irreconcilable facts. In no field does the working hypothesis
of evolution work to such advantage as in this field.
On the basis that a species arises at one place, spreads out over
large areas, becoming modified as it goes, that new species are formed
from old through modification after isolation from the parent-stock,
how do the facts of distribution look when examined in detail ?
1. Cosmopolitan groups, those with the widest distribution, are
those to whom no barriers are sufficient to check migration, e.g.,
strong fliers, Man, earthworms carried by Man.
2. Restricted groups are usually those to which barriers are
readily set up and are frequently the last remnants of a formerly
successful fauna or flora, which continue to survive only in some
restricted area where the conditions are rather more favorable than
elsewhere.
EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 187
3. The study of the distribution of species belonging to a single
genus reveals that the more primitive or generalized species occupy a
central position and the most specialized species are at the outer
boimdaries of the distributional area.
4. The faunas and floras of continental islands are just what we
should expect on the basis that there was at one time a land connection
with the nearest continent; that at this time the faunas and floras were
the same on both island and continent; that, later, the continent and
island were separated by an impassable barrier of ocean ; and that the
inhabitants of the two bodies evolved separately.
5. The faunas and floras of oceanic islands are like those of the
nearest mainland and are of those types, for the most part, that might
most readily have been blown there by the wind or carried on floating
debris.
6. The conclusions arrived at by students of geographic distribu-
tion, past and present, as to the existence of former land connections,
now broken, are borne out by the independent findings of geologists
and geographers.
PART III
THE CAUSAL FACTORS OF ORGANIC EVOLUTION
CHAPTER XIV
INTRODUCTORY STATEMENT
Any investigation of the causes of evolution must be preceded by a
survey of the facts to be explained. Some of the principal facts
which must be taken into account have already been placed before the
reader in the preceding section dealing with evidences of evolution.
If there were no other good reason for dealing with those materials
before beginning a discussion of causal theories of evolution, the peda-
gogical reason would be sufficient, because, until there is something
to explain, the necessity for an explanation does not arise. We are of
course aware that some writers prefer to deal with the facts of palaeon-
tology, geographic distribution, classification, comparative anatomy,
embryology, etc., after a discussion of the causes of evolution. Their
avowed reason for this order of treatment is that the net results of a
discussion of the causes underlying evolution may be used as a means
of more fully analyzing the facts. This is indeed true, but it is also
true that facts should come first and explanations afterward. As a
final step, the facts profitably may be re-examined in the light of causal
hypotheses.
One of the outstanding facts of animate nature is the phenomenon
of adaptation. No naturalist has failed to note and marvel at the
adaptiveness or fitness of organisms to their environment and that of
parts of organisms for particular functions or activities. One of the
most difficult problems in evolution is the problem of the origin and the
perfection of adaptations, and most causal theories of evolution have
been aimed largely at an explanation of adaptation. Consequently,
before we enter upon a formal discussion of the causal theories we shall
introduce an outline of some of the main facts about adaptations.
By way of introduction it should also be pointed out that the
causes of evolution are not all of equal value. Some of the causes are
to be conceived of as primary, others as secondary, or even tertiary.
Variation, for example, is absolutely primary in importance. Without
variation, change, which is the very essence of evolution, would of
course be impossible. Not less important is heredity; for unless there
be some factor which fixes variation so that it becomes a racial asset,
IQI
192 EVOLUTION, GENETICS, AND EUGENICS
there can be no real racial progress; and evolution is nothing more oi
less than racial, as opposed to individual, progress. So obvious did
this seem that Charles Darwin accepted as axiomatic the general facts
of variation and heredity and proceeded at once to a discussion
of the directive factors of evolution. Since variation and heredity
are now universally conceded to be primary factors, and selection,
the Lamarckian factor, isolation, orthogenesis, etc., as secondary
or guiding factors, it would seem more natural to proceed first to
a discussion of variation and heredity. So much of our present
knowledge of variation and heredity, however, is dependent upon the
background furnished by Darwin that it seems to us a more effective
pedagogical plan to consider first that vast and intricate conception of
evolution which was first given Ufe and unity by Charles Darwin,
and has come now to be known as "Darwinism."
Just how broad the scope of Darwin's work and how important a
role he played in the development of evolutionary biology is indicated
in the following appreciation of Darwin which we have summarized
largely from the admirable statement in Professor J. Arthur Thom-
son's book Darwinism and Human Life.
WHAT WE OWE TO DARWIN
1. The web of life — the idea of linkages, interdependencies, cor-
relations in the living world. The idea is essentially ecological and has
been expressed elsewhere as "organic equilibrium."
2. The struggle for existence — the inevitable consequence of Mal-
thus' idea of overproduction. This struggle is both inter- and intra-
specific, or may be a mere struggle against fate or against hard condi-
tions of inorganic environment.
3. Variability of living creatures — an idea derived from the study of
changes under domestication and of diversity among wild individuals
belonging to the same species.
4. Natural selection — the central idea which is to be studied pres-
ently.
5. Vindication of the evolution idea. — Darwin was the first eflfec-
tively to marshal the evidences of evolution in sufficient force to com-
pel the acceptance of the fact of evolution. Much that has already
been presented under the head of "Evidences of Evolution" belongs
to Darwin. The placing of the fact of evolution on a sure foundation
is believed by many to have been Darwin's principal contribution to
science.
INTRODUCTORY STATEMENT 193
6. The descent and ascent of Man — " a recognition of man's solidar-
ity with the rest of creation, of his affihation to a Simian stock — that
man and anthropoid apes are collateral branches from a common Pri-
mate stock which remains hidden in obscurity."
7. Liberation of intelligence. — "The Origin oj Species has proved
a veritable IVIagna Charta of intellectual liberties, for, as no other
single document before or since, it has released the thoughts of man
from the trammels of unreasoned conservatism and dogmatism." —
H. E. Crampton.
8. Ideal of scientific mood and method. — ^As Professor T. H. Morgan
says, "It is the spirit of Darwinism, not its formulae, that we proclaim
as our best heritage." Darwin was the first great evolutionist to use
the inductive method, that of first securing an abundance of facts and
then formulating theories to explain the facts.
The above-stated eight points give us an idea of the broader con-
cept of Darwinism. Today the term "Darwinism" has come to
acquire a much restricted and a technical meaning. To the modern
evolutionist Darwinism has come to be practically synonymous with
"natural selection," or at least with the general principle of "selec-
tion," some phases of which are termed "neo-Darwinism." Before
we can adequately enter upon a study of Darwin's most characteristic
causal theory of evolution — the natural-selection theory — it is almost
imperative for us to know something of the background out of which
this conception arose. Already we have presented in our survey of the
evidences of evolution an array of facts most of which were known to
Darwin and in accord with which he developed his causal theories.
But we cannot afford to overlook the now well-known fact that what
Darwinism chiefly aims to explain are the phenomena of adaptation
and the web of life. These phenomena are to be conceived of as the
background of Darwinism and will be dealt with as such in the next
chapters.
CHAPTER XV
THE BACKGROUND OF DARWINISM:
ADAPTATIONS
THE NATURE OF ADAPTATIONS
"The adaptation of every species of animal and plant to its
environment," says Jordan and Kellogg,' "is a matter of everyday
observation. So perfect is this adaptation in its details that its main
facts tend to escape our notice. The animal is fitted to the air it
breathes, the water it drinks, the food it finds, the climate it endures,
the region which it inhabits. All its organs are fitted to its functions:
all its functions to its environment. Organs and functions are aUke
spoken of in a half-figurative way as concessions to environment. And
all structures and powers are in this sense concessions, in another
sense, adaptations. As the loaf is fitted to the pan, or the river to its
bed, so is each species fitted to its surroundings. If it were not so
fitted, it would not live. But such fitness on the vital side leaves large
room for variety in characters not essential to the life of the animal. "
The authors quoted above appreciate what is perhaps the most
significant fact about adaptations: that the adaptations are to a large
extent molded by the environment and therefore fit the environment.
So long as the environment remains uniform, a given species will
remain unchanged, except for minor fluctuations and occasional
mutations; but if the environment changes, sometimes even slightly,
the development of the individual responds in such a way as to give a
radically diflferent end product. So we may conclude that a large part
of the fitness of the organism to the environment is due to the fact that
the development of each individual is molded by the environment so as
to fit it. Thus some at least of the apparent mystery of adaptations is
dispelled.
When we think of the fitness of the organism to the environment
we take an entirely one-sided view of the matter, for if the organism
fits the environment, no less certainly must the environment fit the
organism. This idea of the "fitness of the environment" has been
' From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life.
194
THE BACKGROUND OF DARWINISM: ADAPTATIONS 195
admirablv discussed by Professor Lawrence J. Henderson in a stimu-
lating volume.'
Henderson points out that the environment, no less than organ-
isms, has had an evolution. The particular environmental complex
as it exists today is absolutely unique. There is hardly an element of
the eflfective environment that could be changed without causing the
extinction of life or at least a transformation of it so profound that it
might not be life at all as we know life. Water, for example, has a
dozen unique properties that condition life. Carbon dioxide could not
be replaced by any other substance. The properties of the ocean are
so beautifully adjusted to life that we marvel at the exactness of its
fitness. Finally, the chemical properties of carbon, hydrogen, and
oxygen, the most abundant elements, are equally unique and unre-
placeable. In brief, given the environment as it is, life could not be
other than it is. The evolution of the environment and the evolution
of organisms have gone hand m hand, or perhaps we might better say
hand in glove, for this better expresses the idea of mutual fitness.
Within the realm of the general environment as conceived by
Henderson there are almost innumerable special environments due to
particular combinations of the various environmental units. Within
the aquatic environment, for example, there are variations such as
differences in salinity, varying from extreme saltiness to almost total
lack of salt; there are inshore conditions and open-sea conditions; there
are surface conditions and those at relatively great depths; and
there are great differences due to temperature. Similarly on land,
there are surface conditions, subterranean conditions, arctic, tropical
conditions, caves, deserts, forests, plains, mountains, and many others.
No two areas on land are precisely similar in all respects. All of this
makes for a corresponding multiplicity of animal and plant forms. In
the case of plants the action of the environment is remarkably direct;
for the plant cannot get away from a fixed environment. If the
envir.onment undergoes material change, the plant's only response is a
structural one. For example, if plants that are accustomed to a rela-
tively humid climate are grown in the desert they develop numerous
xerophytic adaptations such as small leaves with greatly diminished
transpiration surface, a thick epidermis, hairs, or spines, smaU stature,
deep-root system, and other similar protections against the inimical
desert conditions. Similarly, plants accustomed to grow in relatively
• L. J. Henderson, The FUnes: of the Environment, 1913.
196 EVOLUTION, GENETICS, AND EUGENICS
dry soil, if grown in soil that is covered over with water, will produce
aquatic leaves and roots and undergo appropriate changes in epidermis
and loss of supporting tissues, for plants that are buoyed up by water
need little support.
Animals, on the other hand, are for the most part not so intimately
related to a local environment as are plants. They are characteristi-
cally mobile creatures with var3dng capacities for wandering about and
selecting the habitat that best suits them.
"By virtue of being unlike or possessing different properties,"
says Shelford,* " the various animal species require different conditions
for the best adjustment of their internal processes. For example, the
carp lives in shallow and muddy ponds and rivers, while the brook
trout Hves only in clear swift streams. These two organisms are able
to move about and find places to which they are suited. The differ-
ences between them are clearly indicated by the differences in the
habitats which they prefer.
"By observation and by experimentation it has been shown that
animals select their habitats. By this we do not mean that the
animal reasons, but that selection results from regulating behavior.
The animal usually tries a number of situations as the result of random
movements^ and stays in the set of conditions in which its physiological
processes are least interfered with. This process is called selection by
trial and error. If animals are placed in situations where a number of
conditions are equally available, they will almost always be found liv-
ing in or staying most of the time in one of the places. The only
reason to be assigned for this unequal or local distribution of the ani-
mals is that they are not in physiological equilibrium in all the places.
However, some animals move about so much that it is with some
difficulty that we determine what their true habitats are."
This idea of habitat preference and habitat selection is extremely
important for a correct understanding of adaptation, or the fitness of
organisms to environments. Much of the observed fitness may be due
to the fact that an organism has chosen out of a wide range of environ-
ments the one that best suits it. We cannot in such a case say that the
environment has had a direct influence in shaping the organism any
more than we could say that, when a man tries on various shoes and
finds a pair to fit, he has been responsible for the fitness of the shoes.
Many special adaptations may be explained through habitat
choice. Thus animals such as the duckbill platypus, the lung-fishes,
' V. E. Shelford, Animal Communities in Temperate America (igi3).
THE BACKGROUND OF DARWINISM: ADAPTATIONS
197
and others whose teeth are replaced by bony or chitinous plates that
are used for crushing the hard shells of molluscs and crustaceans, may
not confidently be said to have developed these crushing appliances
and to have abandoned the use of teeth in adaptation to a habit of
feeding upon hard-shelled prey; but rather it seems more likely that the
loss of teeth and the development of crushers occurred through a
degenerative process incident to racial senescence and that the pos-
session of the crushing equipment enabled them to avail themselves of
a new type of food, formerly unavailable to them.
The organic environment. — In his admirable chapter entitled
''The Web of Life," which we shall quote entire, Professor Thomson
has given us a vivid picture of vast systems of interdependencies that
exist throughout the organic world. No species, no creature, lives to
itself alone; it is intimately tied up with a host of other creatures with
interwoven destinies. Thus one species of animal is adapted to live
upon certain plants or other animals, which in turn may be dependent
upon still other animals or plants. The ehmination of one species may
cause the elimination or the radical change of a dependent species.
We cannot afford ever to forget this great truth of the oneness of
nature. It is the keynote of life and of evolution.
Adaptation due partly to functional activity. — It is a commonplace
which needs no special demonstration to say that organs improve
through use and deteriorate through disuse. Many organs, then,
which in the adult condition appear to us to be so admirably
adapted to perform certain duties, must be thought of as having been
gradually molded by functioning during the entire period of individual
development. If the motor nerve running to a limb bud of a growing
embryo be severed at an early stage and no secondary nerve connection
be established, the limb will continue to grow up to a certain point, but,
in its paralyzed condition, will be incapable of exercising its functions
and will cease to develop. A certain amount of development will
therefore be seen to be independent of functioning, but full develop-
ment of functional efficiency is obtained only through functioning.
"The relation between structure and function in an organism,"
says Professor Child,^ "is similar in character to the relation between
the river as an energetic process and its banks and channel. From the
moment that the river began to produce structural configurations
in its environment, the products of its activity accumulated in certain
» C. M. Child, "Regulatory Processes in Organisms," Jour. Morph., Vol.
XXII (191 1).
198 EVOLUTION, GENETICS, AND EUGENICS
places and modified its flow It moulds its banks and bottom,
forming here a bar, there an island, here a bay, there a point of land,
but still flowing on, though its course, its speed, its depth, the character
of the substances which its carries in suspension or in solution, all are
altered, built up by its own past activity." According to this view,
structure is simply the resultant of the interaction of function and en-
vironment or of functional activity. Though perhaps a little extreme
for most of us, this view is, we believe, essentially correct. We are
prone to overemphasize structure in our discussions of adaptation
and evolution and to lay too little stress upon the energy side of
development. Certainly no structure is ever formed without proto-
plasmic activity of a very definite sort, and in this sense adaptations
are to be thought of as the results of functioning. , Why, then, do we
claim to be astonished at the efi'ective way in which certain organs
accomphsh their functions, when functioning has taught them their
task?
TWO CATEGORIES OF ADAPTATIONS
There are, according to E. G. Conklin, two categories of adapta-
tions: (a) racial or inherited adaptations, and (b) individual, acquired,
or contingent adaptations. All of the direct molding effects of environ-
ment or of developmental functioning, together with adaptative rela-
tions resulting from habitat selection or from learning and experience,
may well be classed as individual, acquired, or contingent adaptations.
As such they do not offer any particular problem to the evolutionist,
for they concern themselves with individuals, not with races. The
adaptive condition is simply made over afresh in each generation, and
the only thing that seems to extend beyond the immediate individual
or generation is a general plasticity or responsiveness of the specific
protoplasm which enables it to adjust itself to special life conditions.
There is nothing mysterious or baffling about this situation, for it in-
volves merely a repetition of certain appropriate responses by each
individual. It is a problem of individual development, not of racial
development or evolution.
Inherited Adaptations. — There is, however, a large category of
adaptations which appear in the organism as though in anticipation
of the role they are to play some time in the future and not in response
to any present need. In this category are the eyes, the lungs, the vocal
organs, the taste buds, and many other organs of the human fetus.
THE BACKGROUND OF DARWINISM: ADAPTATIONS 199
Thus, the eyes of the new-born infant are essentially finished mech-
anisms before they ever function as organs of vision. They cannot
therefore have been molded for their visual function by functioning
in a visual manner. Of course they must have been functioning in
some way, as all living protoplasm must function, but they cannot
have functioned in a way that would in itself account for the fact that
the eye is a very intricate optic mechanism. Similarly, the human
infant has good lungs and good vocal cords before it ever takes the
first breath of air or gives the first cry. Such adaptive structures as
these are said to be racial or inherited adaptations. Any theory of
evolution worthy of the name must account for the origin and per-
petuation of such inborn adaptations. It was partly to explain the
origin and perfection of adaptations such as these that Lamarck pro-
posed his theory of the inheritance of acquired characters and Charles
Darwin devised his theory of natural selection. It is still unsettled as
to which of these theories is the more adequate, but the consensus of
expert opinion favors Darwin's explanation.
It would be impossible to give any comprehensive account of ani
mal or of plant adaptations in the brief space of such a chapter as this.
Let it suffice to classify adaptations and to describe a few representa-
tive adaptations, confining our attention to those which are obvious-
ly racial or inherited in character.
ADAPTATIONS CLASSIFIED
Adaptations are variously classified by different authors, and that
of Jordan and Kellogg is as good as any: "(c) food-securing; (6) self-
defense; (c) defense of young; {d) rivah-y; {e) adjustment to sur-
roundings."
Some very common adaptations may belong to several of these
categories at once. Thus the sharp teeth and hooked claws of car-
nivorous mammals serve equally well for food-securing, for self-
defense, for defense of young, and for rivalry. Similarly, the horns
of deer and other ungulates are equally adapted for self-defense,
defense of young, and rivalry.
There can be no especial advantage, in this connection, in preseni-
ing a detailed review of adaptations of the sorts given in the foregoing
classification; therefore we shall confme our efforts to a description
of a few typical adaptations about which the greatest controversy
has raged.
200 EVOLUTION, GENETICS, AND EUGENICS
SOME SPECIAL ADAPTATIONS
The electric organ of the torpedo, a widely distributed elasmo-
branch fish, consists of a sort of honeycomb-like structure on each side
of the head. This structure acts as a storage battery and is capable
of storing up electricity of considerable voltage. The animal is
capable of giving a very distinct shock to an attacker and can thus
defend itself quite effectively. There is also an electric eel, native to
the waters of Paraguay and Brazil, that is able to give severe shocks to
bathers or to horses driven through the streams. A type of catfish
native to the river Nile has a similar electric equipment. In all of
these cases the storage battery is made up of modified voluntary
muscles and is of considerable size.
The mammary glands of mammals are skin glands usually with
well-defined ducts leading to the surface and terminating in teats.
These glands are quite voluminous and serve admirably the purpose of
feeding new-born young until the latter are able to use the more varied
food normal to the adult. In the lowest mammals, the monotremes
or egg-laying mammals, these glands are relatively poorly developed
and diffuse; also they are known to be developed through a regional
specialization of sweat glands. In the true mammals or Eutheria the
glands are modified sebaceous or oil glands and may be seen to develop
from the same embryonic rudiments as the latter.
The marsupial pouch of the kangaroo and its allies is a pocket-
like fold of the integument, folded forward or backward over the region
of the abdomen in which are located the mammary glands. This
pouch is used as a shelter for the tiny immature larval foetuses
Hartmann has recently described a very striking piece of behavior in
connection with the birth of young opossums. The young are born
m an exceedingly unmature state and looking like tiny pink grubs.
They crawl under their own power, by means of a swimming-like
motion, through the hairs of the mother's abdomen, till they reach the
pouch. This they enter unaided and each tiny larva finds for itself
a slender tubular teat, which it swallows and holds in place by a
specially adapted hold-fast mouth. The young remains attached
fixedly to this teat for some weeks, feeding almost constantly on milk.
After a long interval the teat is released, the mouth metamorphoses
into the adult form and the young feeds only at intervals, as do the
young of other mammals. This complex of adaptive structures and
instincts is among the most remarkable in the annals of biology.
THE BACKGROUND OF DARWINISM: ADAPTATIONS 20I
The fetal membranes of higher mammals constitute one of the
most efficient adaptive complexes known. Surrounding the embryo is
a fluid-filled sack (amnion) which furnishes an aquatic environment for
the soft and delicate body, preventing harmful contacts and allowing
ample free space for expansion. The placenta is a co-operative struc-
ture, developed out of both fetal and maternal materials, that furnishes
an excellent medium for nutritive and other metabolic exchanges be-
tween mother and fetus. Although there is no direct vascular connection
between them, the mother gives of her nutritive materials to the fetus
and takes up from the fetus and eliminates its wastes. As an adapta-
tion for carrying out an intricate set of physiological exchanges between
two otherwise entirely separate individuals the placenta is unexcelled.
Nest-making- instincts in birds represent, on the behavior side,
adaptations of extraordinary perfection. Some nests are built with
the greatest care and precision, others represent a relatively crude and
slovenly performance. Some nests are made of twigs, fibres, and mud,
others of mud alone, still others are hollowed out in clay or sand banks,
and some are made in holes in the ground. In any case, the type of
nest is highly specific and due to a hereditary instinct; for birds
receive no instruction in nest-making.
Before bringing to a close this brief list of particularly noteworthy
adaptations let us recall to mind the series of special adaptations listed
as examples of the laws of adaptation, such as aquatic, arboreal, cur-
sorial, flying, burrowing, ant-eating, and, especially, adaptations of
deep-sea animals.
PARASITISM AND DEGENERATION
A vast number of animals and plants have given up the active
search for food and have taken up the relatively easy habits of para-
sitism. In adaptation to this life certain structures have developed
and many of the characters found in independent, free-roving crea-
tures have disappeared or become reduced to mere vestiges. Thus
the more completely dependent or parasitic an animal becomes, the
more completely does it lose its organs of locomotion and its sense
organs such as eyes, auditory organs, tentacles, etc. Some animals
are free-living when young or in the larval condition and only settle
down to a parasitic life when near the end of the hfe-cycle; other
animals are parasitic only when young or larval and become inde-
pendent in the adult condition; still others are parasitic throughout
the entire life-cycle and pass from host to host without any interval
of independent Hfe. Some of these complete parasites pass one phase
of the life-cycle on one species of host and the remainder on another
202 EVOLUTION, GENETICS, AND EUGENICS
species of host. Thus the liver fluke in the adult condition lives in the
gall bladder of the sheep, while the early larvae live within the body
cavities of a species of land snail. The transfer from host to host in
this case must be a procedure involving many chances of failure to a
very few chances of success, and, in adaptation to these vicissitudes,
the niunber of eggs and larvae produced by a single adult individual
runs up into the millions.
The classic case of extreme parasitic degeneration is that of
Sacculina. The young larva of Sacculina is a typical entomostracan
crustacean larva which swims about and leads a free Ufe for a time,
but soon attaches itself by means of its antennae to a hair pit of a crab,
a small hole in the latter's armor. The internal tissues of the larva
then undergo degenerative processes and are reduced to an almost
fluid mass of embryonic cells, which flow through the hair pore of the
crab, and into the latter's lymph spaces. The small mass of cells then
rounds up and is carried about with the circulation of the crab's blood
until it comes to a favorable place of lodgment, usually the wall of the
intestine just back of the stomach. Here it flattens out and sends
rootlike branches almost all over the crab's body, like a maUgnant
tumor in its invasion of foreign tissues. The unbranched part of the
parasite is little more than a sac of reproductive organs, and these
produce eggs and sperms, which unite to produce larvae. By this
time the host is killed and, with the decay of its body, the larvae escape
into the sea water ready for a brief period of free life before attacking
another host.
Almost every group of animals and most of the groups of plants
have their parasitic representatives and every degree of parasitism
and the accompanying degenerative changes are to be found. Of
course, it is an open question whether parasitism causes degeneration
or whether degenerating creatures take refuge in parasitism; but in
either case the adaptive features of the situation are obvious.
Commensalism. — If parasitism be defined as an association
between two organisms in which one (the parasite) lives at the expense
of and to the detriment of the other (the host), commensalism may be
defined as an association in which the two organisms exist in close
association without any positive detriment to either. In some cases
the claim is made that the association is mutually beneficial, but as a
rule the relation is relatively one-sided.
An interesting example of commensalism is that of the sea cucum-
ber and the little fish Fierasfer. This strange little animal inhabits
THE BACKCxROUND OF DARWINISM: ADAPTATIONS
203
^■^:m
Fig. 40. — Fierasfer acus, penetrating the
anal openings of holothurians, f natural size.
{From Boitlcnger, after Emery.)
the rectum of the sea cucumber and may be seen to He with only its
head out. From this shelter it darts forth to capture its prey; which
done, it returns to its shelter.
Curiously enough the vent
of the little fish is situated
just back of its mouth so
that its wastes may be
voided when in its usual
position. There can be no
advantage to the sea cu-
cumber in such an arrange-
ment, though no particular
harm is done. Another case
of this sort is that of several
species of Remora which
attach themselves by a large
diskoid adaptation on top of
the head to various fish such
as sharks, barracudas, etc.
The sucking disk is a modified dorsal fin. The remora merely gains
free transportation to more favorable feeding-grounds. When the
desired food is sighted the passenger leaves its conveyance tempo-
rarily, but returns by a sudden swift dash and resumes its hold.
The shark gets nothing except perhaps the sense of companionship,
and is also undoubtedly somewhat hindered in its locomotion.
Some of the most remarkable cases of commensalism are found in
connection with elaborate colonies of ants. In some cases two species
of ants live together in the relationship of masters and slaves. The
master species is unable to perform any of the ordinary duties of the
colony, such as securing food, taking care of young, etc. In extreme
cases the masters are only soldiers, specialized for fighting and maraud-
ing, and cannot even feed themselves unaided. The slave species
would be able to carry on to some extent if not captured, but thrives
exceptionally well under the protection of the soldier species. There
are among ants many varieties of commensal relationship less extreme
than this, but this will serve as a typical case.
Communal life. — Among the higher insects and higher vertebrates,
especially among the ants and bees, we find a very elaborate social life.
In ants, for example, the typical colony consists of a queen (the only
fertile female in the colony), several males (mates of the queen),
204 EVOLUTION, GENETICS, AND EUGENICS
ordinary workers (sterile females of the first type), soldiers (sterile
females of the second type), and sometimes officers (especially large
and powerful sterile females that seem to direct the line of march in
legionary ants). All of these casts are produced from the eggs of one
female and are the result of various special diets permitted the larvae
by the workers. Among bees, similarly, there is one queen, a number
of drones (males), and the sterile female workers, who perform the
functions of nursing the larvae, cleaning up the hive, collecting pollen
and nectar, and making honey and wax. Detailed accounts of tlie
lives of bees have been given by various authors, notably by Maeter-
linck in his Life of the Bee.
ADAPTATIONS OF DEEP-SEA ANIMALS AND OF
CAVE ANIMALS
One of the weirdest environments the world affords is the bottom
of the sea at great depths. There it is dark and cold and almost devoid
of oxygen, while the pressure is almost unbelievably high. Yet in these
vast and forbidding abysses there dwell in apparent comfort represen-
tatives of most of the animal phyla. Fishes of many sorts, crabs,
mollusks, worms, and many other forms thrive and multiply in this
seemingly cheerless environment. We do not at all understand the
nature of the adaptive mechanism that enables these animals to with-
stand with their frail bodies the steel-crushing pressures that prevail
at all such depths. We do know, however, how some of the deficien-
cies of the environment are made good by these denizens of the deep.
Thus many abysmal forms produce their own light by means of
phosphorescent organs placed at advantageous points of their bodies.
Not only fishes of the depths, but some mollusks possess forms of
artificial lighting equipment. One species of cephalopod (related to
the octopus) is described by Wiesmann as bordered with twenty large
phosphorescent lanterns that present the aspect of a display of varie-
gated gems, colored ultramarine, ruby red, sky blue, and silvery white.
Equally highly adapted to life in a world of darkness, the monotony
of which is broken only by the occasional spots of light emanating
from the various living lanterns just referred to, are the strange eyes
of some of the abysmal fishes. Sometimes these eyes are enormously
large, and thus adapted to bring to the perception of the animal the
weak light of the depths, or again they may be modified still further
in a strikingly peculiar manner, each being drawn out into a cylinder
and projecting from the side of the head like a telescope. Such eyes
are in fact not telescopes, though they are called "telescope eyes," but
are merely adaptations for concentrating the lights of low intensity
THE BACKGROUND OF DARWINISM: ADAPTATIONS 205
and making the environment visible. Could man view the sea bottom
through some of these instruments, he would doubtless add something
very novel and weird to his scenic repertoire.
Other creatures of the darkness live strange lives in caves, such as
jhe Mammoth Cave of Kentucky. Most cave dwellers are blind or
nearly so, and usually have a pale and ghostlike appearance because of
their lack of pigment. All grades of defective eyes are found, ranging
from those that are merely somewhat smaller than normal to those
that remain deeply imbedded in the head in a relatively undifferen-
tiated state. It goes without saying that such animals are better
adapted to life in caves than they would be outside. One pressing
problem of biology is: How did the cave animals become blind? Did
they wander into the caves as normal animals and become blind be-
cause their eyes were disused, or did they become blind outside through
no fault of their own, as the result of a mutation, and by chance find
safety in an underground stream or a cave? The first explanation is
Lamarckian, the second Darwinian.
COLOR AND PATTERN IN ANIMALS
"The phenomena of color in both animals and plants," says
Metcalf,' "are among the most remarkable and interesting in the
whole realm of nature. It is not so much the way in which the color
is produced, whether by pigments or by refraction, that interests us
in this connection, as it is the uses to which colors are put. Let us
first refer to the colors of animals.
"According to the uses to which colors in animals are put, we
may classify them, for purposes of description, as follows:
"IndiiTerent coloration, not useful, so far as we can judge;
Colors of direct physiological value;
Protective coloration and resemblances;
Aggressive coloration and resemblances;
Alluring coloration and resemblances;
Warning coloration;
Immunity coloration;
Mimetic coloration and resemblances;
A. Protective
B. Aggressive
Signals and recognition marks;
Confusing coloration;
Sexual coloration."
' M. M. Metcalf, Organic Evolution (igii).
2o6 EVOLUTION, GENETICS, AND EUGENICS
Much has been written about these various categories of animai
coloration nearly all of which assumes some special adaptive value for
each type of color or pattern.
The above classification is typical of the older views as to animal
coloration in that it recognizes no colors as merely incidental by-
products of metabolism, but assumes that all colors are valuable as
adaptations. Modern critics ar^ inclined to consider that at least
many colors are to be explained as the result of the fact that certain
chemical materials are formed in the elaboration of tissues and in the
physiological processes that must go on in these tissues, which, because
of their light-absorptive properties, appear to our eyes as colored.
The color may chance to enhance the protective resemblance of the
animal or it may make it more conspicuous than it should be; in either
case it may have an incidental value. But colors may come and colors
may go irrespective of adaptive value, for many colors are so placed
in the organism that they can never be visible; and color is only in
the seeing. While we have no intention of denying the adaptive value
of animal colors, it seems wise to get away from the extreme anthro-
pomorphic interpretation of these colors, for some of the categories of
coloration listed in the previous paragraph are largely, if not wholly,
anthropomorphic. It has been the habit of students of coloration to
assume that insects, birds, lizards, and other animals see colors and
patterns as man sees them, that what is attractive to man must also
be attractive to the lower animals, that what is confusing to man would
also be confusing to a lizard or an owl. Experiments with lizards,
which are supposed to be chief among the factors giving adaptive sig-
nificance to insect coloration, have shown that the lizard apparently
takes no notice of colors, at least when they are at rest, but will jump
at any moving object of about the right size.
Modern students are inclined to think that many of the minor
categories of animal coloration listed above are, at best, of very ques-
tionable significance and that practically all categories simmer down
to one: obliterative coloration or camouflage.
"All naturalists," says G. H. Thayer,' "perceive the wonderful
perfection of the twig mimicry by an inchworm, or of bark by a moth,
or of a dead leaf by the Kallima butterfly. It is now apparent that
almost equally marvelous concealment-devices, in one shape or
another, are general throughout the animal kingdom; the most gorgeous
■ G. H. Thayer, Concealing Coloration in the Animal Kingdom. The Macnaillan
Company, 1918.
THE BACKGROUND OF DARWINISM: ADAPTATIONS 207
costumes being, in their own way, climaxes of obliterative coloration
scarcely surpassed even by moths or by inchworms.
"This discovery that patterns and utmost contrasts of color (not
to speak of appendages) on animals make wholly for their 'obUteration,'
is a fatal blow to the various theories that these patterns exist mainly
as nuptial dress, warning colors, mimicry devices (i.e., mimicry of one
species by another), etc., since these. are all attempts to explain an
entirely false conception that such patterns make their wearers con-
spicuous. So immeasurably great, in the case of most animals, must
be the value of inconspicuousness, tliat such devices as achieve this to
the utmost imaginable degree, upon almost every living creature, de-
mand no further reason for being (although doubtless serving count-
less minor purposes) Apparently, not one 'mimicry' mark, nor
one 'warning color' or 'barmer mark' nor one of Gadow's light-and-
shadow-begotten marks, nor any 'sexually selected' color, exists any-
where in the world where there is not every reason to believe it is the
very best conceivable device for the concealment of its wearer, either
throughout the main part of this wearer's life, or under certain pecu-
Harly important circumstances The so-called 'nuptial' cos-
tumes of animals are demonstrably an increase of such potency of
obliterative coloration as belongs to all gorgeously varied costumes,
and this at the very period when concealment is most needed.'^
Thayer believes "that the colors, patterns, and appendages of
animals are the most perfect imaginable eilacers under the very cir-
cumstances wherein such effacement would most serve the wearer."
Many animals, when observed in a museum show case or in a menag-
erie, appear to us to be most conspicuous, but the elements that lend
conspicuousness in the artificial environment may be the very ones
that tend to efface the wearer when in his native haunts. The most
brilliant birds, such as mandarin ducks, birds of paradise, flamingoes,
peacocks, parrots, etc., are shown to be almost invisible in their
natural surroundings.
The schemes for producing obHterative protection are much the
same as those made use of during the recent war. The simplest scheme
of all is that of having the same color and pattern as the background.
Thus many green insects, amphibia, reptiles, birds, and a few mammals
that Hve in trees, smaller plants, or grass, are colored green. Many
desert animals are sand colored. Many marine animals living near
the surface are transparent or nearly so. Another scheme is known
as counter-shading, according to which most animals with Httle variety
2o8 EVOLUTION, GENETICS, AND EUGENICS
of color are concealed by having the upper surfaces dark, the lower sur-
faces light, and a blending of one into the other on the sides. Nearly
all birds of the open, such as sea birds and soaring birds, use this
method of concealment. The same is true for fishes that live near the
surface, and for many mammals that are likely to be seen against a
sky line. Actual demonstrations have shown that this method of
concealment is highly effective, no matter from what point of view the
animal may be seen. A third scheme is one that was used most effec-
tively during the war in concealing battleships, heavy artillery, and
other large objects, namely, destroying the continuity of outline by
using large, irregular patches of contrasting or light and dark colors.
In this way a broken, irregular patchwork of color takes the place of
a coherent, regular contour. It is probably in this way that many of
the most brilliant coral-reef fishes attain concealment. Instead of the
fish as a whole being the center of vision, the bright patches stand out
against the dark, and these fail to give any picture likely to be inter-
preted as a fish either by enemies or by prey. Professor Reighard in-
terpreted the brilliant patterns of reef fishes as examples of "immunity
coloration," the idea being that these fishes were so safe from attack
and so little in need of concealment from prey that they simply went
the Umit in color display, unchecked by natural selection. Longley
has recently shown that the patterns and colors of such fishes are in
reality obhterative, and if this be true, there is no need of introducing
the idea of "immunity coloration."
In view of the above considerations, it now seems likely that essen-
tially all types of animal coloration that have any adaptive value at all
— and by no means all have any demonstrable adaptive significance —
may be classed under the general head of conceaUng coloration; and if
this be so, it greatly simplifies the problem of the evolutionist. Much
of the controversy as to the efficacy of natural selection has been waged
about some of the questionable categories of animal coloration, such
as "warning coloration," "mimicry," "confusing coloration," "sexual
coloration." If all of these turn out to be merely phases of conceal-
ment coloration, their origin could be explained as readily as that of
any other adaptive character of definite selective value.
The Case of Kallima. — With this general introduction to the sub-
ject of animal coloration, it does not seem necessary to Hst examples of
all the categories of color mentioned. Let us close the discussion with
what appears to be the classic instance in biological Uterature of perfect
protective resemblance: that of the "dead-leaf butterfly," Kallima
(Fig. 41).
THE BACKGROUND OF DARWINIS:\I: ADAPTATIONS
209
*^Its wings," says Herbert, "when upturned, represent on their
underside a perfect copy of a leaf with a midrib and a regular suc-
cession of side veinings. Differently colored spots on the wing imi-
tate patches of decay and mildew, while the prolonged tail of the hind-
wing, which touches the stem in the sitting posture of the butterfly,
Fig. 41. — Kallima, the "dead-leaf butterfly." (From Jordan and Kellogg.)
makes it appear as though the leaf was directly growing out of the
stem." It is only when at rest upon the stem of a tree that the re-
semblance to a leaf would be effective, for it is only the under surfaces
of the wings that are protectively colored. The upper surfaces of the
wings are brightly colored and would supposedly be quite conspicuous
when the insect is in flight. "These insects," says IMetcalf, "are very
noticeable when in flight, but when they light and close the wings, their
2IO EVOLUTION, GENETICS, AND EUGENICS
sudden disappearance is most startling and confusing, greatly increas-
ing the difficulty of observing their resting-place." According to this
idea of "confusing coloration," a butterfly is supposed to mystify or
confuse its enemies by first attracting their attention and then suddenly
becoming invisible. One is reminded of the prestidigitator of his
favorite remark: "Now you see it and now you don't." But why
attract attention in the first place, when continued inconspicuousness
would be much less risky? The best answer to this question is to use
Thayer's interpretation, namely, that what looks like a conspicuous
coloration when observed in the stationary insect held against an alien
background is probably almost invisible when the animal is moving
its wings and flying through the air in the bright sunlight.
The case of Kallima is probably more or less typical of the some-
what uncritical tendency on the part of naturalists to invent adaptive
explanations for every striking color or pattern seen among animals.
Let us examine the situation a httle further. Much has been said
about the minute details of resemblance to a dead and decaying leaf
on the part of this butterfly, yet, if its habits are at all like those of
other members of its order, it is hardly likely that its most active period
would coincide with that in which the leaves of trees would be decayed
and mildewed or even brown. Butterflies are active when flowers,
whose nectar forms their chief food, are numerous, and are usually in
their pupa cases when the leaves have died on the trees. It has also
been stated by critical observers that Kallimas do not frequently light
on trees whose leaves are very similar in shape to the folded wings of
a butterfly. Furthermore, there are many kinds of butterflies that
are more or less like leaves; in fact, it would be difficult for a butterfly
not to look somewhat like a leaf, since the wings are shaped like leaves.
Again, many species of butterflies have the swallowtails on the lower
wings without in other ways much resembling a leaf; others have spots
that might be interpreted as resembling decay and mildew without in
other ways being more than in general leaflike; and there are many
other species that show all degrees of leaf resemblance, some very im-
perfect and others almost as perfect as that of Kallima, yet they all
seem to be essentially successful in the life-struggle in spite of their less
perfect protective resemblance.
Alleged cases of mimicry have failed also to meet critical examina-
tion. When a poisonous butterfly is mimicked by an edible species
several conditions must be met in order that the deception be effec-
tive. The model and the mimic must both occupy the same range,
THE BACKGROUND OF DARWINISM: ADAPTATIONS 211
have the same period of activity and the same general habits. The
model must be much more numerous than the mimic. Unfortunately
for the proponents of mimicry, it has sometimes been found that
several of these requirements are lacking. Attempts to explain away
the discrepancies have been far from satisfactory.
All these considerations should make us cautious about reading
into the colors and patterns of animals too many adaptive details. It
is more than likely that the majority, if not all, of these apparently
marvelously exact instances of imitative resemblance would turn out,
when critically examined, to be no more nor less adaptive in special
ways than is Kallima and the mimics.
One lesson that the naturalist may well learn from the present
discussion is this: There is enough in the way of adaptations for the
evolutionist to explain without burdening him with hypothetical or
interpretative adaptations. First find and prove your adaptation;
then try to explain it. Don't explain it first and then find out later
that it was not so much of an adaptation after all.
osborn's laws of adaptation
Adaptations have been variously classified by different writers.
Perhaps the most significant classification is that of Osborn, which
is based on their supposed evolutionary origin. According to this
writer and others, there are two categories of adaptations to environ-
mental conditions: the first has to do with the tendency of unrelated
species to assume similar structures under similar environmental
conditions; the second has to do with the tendency of related species
to assume different adaptive structures under different environmental
conditions. In both categories the environment appears to be the
determining factor.
(i) A good example of the first category, which illustrates what
Osborn calls "the law of convergence or parallelism of form," is seen
in the tendency of many aquatic types of vertebrates to assume the
fishlike form. As is well shown in Fig. 42, the shark (a fish), the
ichthyosaur (an extinct aquatic reptile), and the porpoise (a marine
mammal), all possess the same fusiform body best adapted for speed
under water, the same types of locomotor structures, consisting of the
great propeller fin (caudal fin) and the steermg and balancing fins,
the dorsal fins and paired fins. Apart from these superficial adapta-
tions for swift locomotion in the water, the three types are pro-
foundly different. The shark breathes with gills, the reptile and
mammal with lungs, the fish and reptile are cold-blooded, the
212
EVOLUTION, GENETICS, AND EUGENICS
Fig. 42. — Three aquatic types of vertebrate, to illustrate convergent adapta-
tion of three wholly unrelated forms of marine life. All three show the fusiform
body, median and paired fins, though the skeletal structures are radically differ-
ent. A, shark (Pisces); B, ichthyosaur (Reptilia); C, porpoise (Mammalia).
{From Newman, after Osborn.)
TIIE BACKGROUND OF DARWINISM: ADAPTATIONS 213
mammal warm-blooded. The internal anatomy of the three differs
fundamentally in every detail.
A list of other types of convergence will more adequately illustrate
the law.
Flying and parachuting animals occur among nearly all vertebratt
and some invertebrate classes. Planes of some sort are found for
supporting the body in the air. The plane is made in various ways
in different groups, but functions much the same in all of them.
Running animals of various classes have long legs, and a tendency
to stand on the toes. There is also in several unrelated groups the
tendency to reduce the number of toes, the culmination of which is
seen in the one-toed horses.
Climbing animals are all provided with clinging appendages of
some sort, including such structures as hooked claws, prehensile
fingers or tail, suction pads on the feet, and other similar adaptations.
Burrowing animals have, as a rule, extra-heavy shoulder girdle
and strong fore limbs with heavy gouging claws. Many of them also
are blind or nearly so, as befits life in dark underground passages.
Desert-dwelling animals as a rule are provided with heavy
scales, spines, or armor, to prevent excessive loss of moisture and as a
protection against spiny plants. They also usually have burrowing
habits enabling them to escape the extremes of heat and cold.
Cave animals are usually blind or nearly so and are relatively
pale in color, sometimes without any pigmentation.
Deep-sea animals of many sorts have phosphorescent organs by
means of which they either attract their prey or find their way about
the dark sea floor. Some of these organs, called "lanterns," can be
used as searchlights. The eyes of deep-sea fish are either enormously
large or are "telescope eyes," adapted for sensing Ught of low
intensities.
Ant-eating animals, belonging to several distinct groups, are
heavily armored against the attacks of ants, have strong claws for
digging up ant galleries, have long snouts or beaks with a long sticl^^y
tongue for capturing ants, and an arrangement of the glottis to prevent
ants from crawling into the lungs.
2. There are almost innumerable examples of the law of divergence
of form, which is called also the law of adaptive radiation. Almost
every successful class or order of vertebrate animals, for example,
has members that have adjusted themselves to all of the main modes
of living. Thus among lizards, for example, there are primitive
214 EVOLUTION, GENETICS, AND EUGENICS
running forms that prefer the surface life and swift motion; subter-
ranean burrowing t5^es that sometimes are limbless like snakes, and
are blind; many arboreal or climbing types; a few volant or flying
types; a few ant-eating types; and several more or less completely
aquatic types. Each of these types has the customary adaptations
for its own mode of life.
We see, then, that whether divergent structures are molded into a
semblance of similarity to fit a definite environment, or whether
similar structures are modified in diverse ways to fit various divergent
environments, the adaptation is related very definitely to the environ-
ment and to the functional fife of the organism. No wonder, then,
that so many biologists consider that the environment has been a
molding force in the evolution of adaptations.
General considerations. — Adaptations are characteristic of all
living organisms and must be accounted for by any evolutionary theory
that is to be acceptable. Any theory that claims to account for new
species but does not account for adaptations is at best only a partial
explanation. All of the phenomena which have been briefly men-
tioned in this chapter, together with the more intricate phases of
general adaptiveness involved in the idea of "the web of Ufe," are part
of the background of Darwinism and were in the mind of Darwin when
he thought out the great generalization called "natural selection."
The "web of life" idea has been admirably presented by Professor
Thomson, Scotland's most skilful and prolific biological writer. The
present writer feels that no student of evolution should miss the oppor-
tunity of getting into the spirit of Darwinism with this distinguished
author, and to make this desideratum easily attainable, the chapter
is quoted unchanged as part of the general text and immediately
follows this discussion.
CHAPTER XVI
TIIE BACKGROUND OF DARWWISM—Conlinued
THE WEB OF LIFE'
J. AKTHUR THOMSON
Naturalists, in the true sense, who study the Hfe of living creatures
in nature, have always been distinguished by a keen perception of the
interrelations of things. Whether we take Gilbert White as repre-
senting the old school, or W. H. Hudson as representing the new, we
get from their observations the same impression of nature as a vibrat-
ing system, most surely and subtly interconnected. But it seems
just to say that no naturalist, before or since, has come near Darwin
in his realisation of the web of life, in his clear vision and picture of the
vast system of linkages that penetrates throughout the animated
world.
Correlation of organisms as well as correlation of organs. — In
thinking of a living body we are accustomed to the idea of the cor-
relation of organs. It is of the very nature of an organism that there
should be mutual dependence among its parts. The organs are all
partners in the business of life, and if one member changes others also
are affected. This is especially true of certain organs that have
developed and evolved together, and are knit by close physiological
bonds. We know in health how nerve and muscle, brain, and sense
organs, heart and lungs, are closely bound together in the bundle of
life. We know in disease that a change in one organ often affects
another, and the fact remains though the nexus is sometimes myste-
rious. The state of our Uver may give colour to our whole intellectual
firmament, and a slight ocular derangement may warp a wise man's
philosophy. The far-reaching importance of a Httle organ like the
thyroid gland beside the larynx is well known; our intellectual as well
as our bodily health depends on its soundness. Now, just as there is a
correlation of organs within the body, so there is a correlation of
organisms in that system of things which we call Nature. In both
cases we are here using the word " correlation " in its deeper sense —
' From J. A. Thomson, Darwinism and Human Life (copyright rgoo). Useu
by special permission of the publishers, Henry Holt & Company.
2I.S
2i6 EVOLUTION, GENETICS, AND EUGENICS
that the various parts are more than mutually dependent, that they
are in some measure co-ordinated, making larger systems workable.
What the metaphor of "the web of life" suggests. — We may use
the metaphor "web of life" in two ways. On the one hand. Nature
has a woven pattern which science seeks to read, each science following
the threads of a particular colour. There is a warp and woof in this
web, which to the zoologist usually appear as "hunger" and "love."
There is a changing pattern in the web, becoming more complex as the
ages pass; and this is evolution. But the essential idea of a web is that
of interlinking and ramifying. We can never tell where a thread will
lead to. If one be pulled out, many are loosened. This is true of
Nature through and through.
The phrase "web of life" suggests another picture — the web of a
spider — often an intricate system, with part delicately bound to part
so that the whole system is made one. "The quivering fly entangled
in a corner betrays itself throughout the web; often it is felt rather
than seen by the lurking spinner. So in the substantial fabric of the
world part is bound to part. In wind and weather, or in the business
of our life, we are daily made aware of results whose first conditions are
very remote; and chains of influence, not difficult to demonstrate,
link man to beast, and flower to insect. The more we know of our
surroundings the more we reahse that nature is a vast system of link-
ages, that isolation is impossible."
Dependence of living creatures on their surroundings. — We do
not know what life in principle is, but we may describe living as action
and reaction between organisms and their environment. This is the
fundamental relation — the dependence of living creatures on appro-
priate surroundings, and the primary illustrations of linkages must be
found here. The living creatures are real, just in the same sense as the
surroundings are real; but it is plain that we cannot abstract the living
creatures from their surroundings. When we try to do this they die —
even in our thought of them, and our biology is only necrology.
Huxley compared a living creature to a whirlpool in a river; it is always
changing, yet always apparently the same; matter and energy stream
in and stream out; the whirlpool has an individuality and a certain
unity, yet it is wholly dependent upon the surrounding currents. One
may push the whirlpool metaphor too far, so as to give a false sim-
plicity to the facts, for when vital whirlpools began to be there also
emerged what cannot be discerned in crystal or dewdrop — the will to
Uve, a capacity of persistent experience, and the power of giving rise to
BACKGROUND OF DARWINISM : THE WEB OF LIFE 217
Other lives. To ignore this is to attempt a falsely simple natural
history. But what Huxley's metaphor of the whirlpool does vividly
express is the dependence of living creatures on their surroundings.
We cannot understand either the whirlpool or the trout apart from
the stream.
When we think out this fundamental dependence upon surround-
ings, we see, for instance, that all our supplies of energy, all our powers
of every kind — with our own hands, or by the use of animals, or by
means of machinery — are traceable to the sun. Or again, it is easy to
show that our society depends fundamentally not on gold, but on iron.
We depend for food on plants and animals, and through these animals
on plants ultimately; the plants feed upon air, water, and salts, which,
with the aid of the energy of the sunlight, they build up into complex
organic compounds; they cannot do this unless the sun shines through
a screen of green pigment called chlorophyll; there cannot be chloro-
phyll without iron; therefore our whole social framework is founded I
on iron.
Nutritive chains. — Plants feed on their inanimate environment
in a direct way that is impossible to animals, so we pass insensibly
from dependence on surroundings to those nutritive chains which bind
living creatures together in long series often quaintly suggestive of
"The House That Jack Built" and similar old rhymes. We have
ceased to wonder at the circulation of the blood in our body; have we
begun to wonder enough at the ceaseless circulation of matter in the
system of nature ? As HeracUtus said, iravra pel, all things are in flux.
"The rain falls; the springs are fed; the streams are filled and flow to
the sea; the mist rises from the deep and the clouds are formed, which
break again on the mountain-side. The plant captures air, water, and
salts, and, with the sun's aid, builds them up by vital alchemy into the
bread of life, incorporating this into itself. The animal eats the plant
and a new incarnation begins. All flesh is grass. The animal becomes
part of another animal, and the reincarnation continues." The silver
cord of the bundle of Ufe is loosed, and earth returns to earth. The
microbes of decay break down the dead, and there is a return to air
and water and salts. We may be sure that nothing real is ever lost; ^^
we are sure that all things flow. Penelope-like, Nature is continually
unravelling her web and making a fresh start.
Nexus between mud and clear thinking. — To keep a famous
inland fish-pond from giving out, some boxes of mud and manure were
placed at the sides. Bacteria — the minions of all putrefaction —
2i8 EVOLUTION, GENETICS, AND EUGENICS
worked in the mud and manure, making food for minute Infusorians
which multiply so rapidly that there may be a million from one in a
week's time. A cataract of Infusorians overflowed from box to pond,
and the water-fleas and other small fry gathered at the foot of the fall
and multiplied exceedingly. Thus the fishes were fed, and, as fish-
flesh is said to be good for the brain, we can trace a nexus from mud to
clear thinking. What was in the mud became part of the Infusorian,
which became part of the Crustacean, which became part of the fish,
which became part of the man. And it is thus that the world goes
round.
Correlation between catches of mackerel and amount of spring
sunlight. — A curious and most interesting correlation has been
discovered by Dr. E. J. Allen between catches of mackerel and the
amount of sunlight. The more sunshine in May, the more mackerel
at Billingsgate. How does this work out ? Mr. G. E. Bullen shows
that "for the years 1903-1907 there appears to be a correlation
between the number of mackerel taken during May, and the amount
of Copepod plankton, upon which the mackerel feed, taken in the
neighborhood of the fishing grounds during the same month."
Mr. W. J. Dakin shows that the food of Copepods consists largely
of the vegetable organisms of the planlcton, such as diatoms, and of
Infusoria-like organisms called Peridinidae. But the production of
this microscopic plankton, the "stock" of the "seasoup," depends
partly on the composition of the sea-water, partly on the tempera-
ture, and partly on the amount of light available. There seems to be
no correlation between the surface temperature and the abundance
of mackerel, but Dr. Allen has shown a correspondence between
sunshine and the catches. Thus we see that, if all flesh is grass,
then in the same sense all fish is diatom.
Nutritive chains in the deep sea. — If we pass from the sunUt
open sea to the floor of the deep sea — that strange, dark, cold, silent,
plantless world — ^we find carnivorous animal preying upon carnivorous
animal through long series — fish feeds on fish, fish on Crustacean,
Crustacean on worm, worm on still smaller fry, and all ultimately
depend on the basal food-supply — the ceaseless shower of moribund
atomies sinking from the surface waters many miles, it may be, over-
head, like the snowflakes on a quiet winter day.
Dependence of one organism on another for the continuance of
the species. — Passing from "nutritive chains," we may select a few
illustrations of the dependence of one creature upon another for the
BACKGROUND OF DARWINISM: THE WEB OF LIFE 219
continuance of its kind. The crowning instances are to be found in in-
terrelations between plants and animals which secure cross-fertilisation
and the distribution of seeds. To both of these Darwin devoted much
attention, and they were always favourite subjects with him.
Everyone knows that flowering plants and flower-visiting insects
have grown up throughout long ages together, in alternate influence
and mutual perfecting. They are now fitted to one another as hand
to glove. The insects visit the flowers for food ; in so doing they carry
the fertilising golden dust from blossom to blossom, so that the
possible seeds become real seeds.
In 1793 a Berlin naturaUst, Christian Konrad Sprengel, like
Darwin in his perception of the web of life, pubHshed a pioneer book
entitled The Secret of Nature Discovered in the Structure aitd Fertili-
zation of Flowers, in which he showed that most flowers have
nectar which insects enjoy; that by the insects' visits pollination is
secured; that there is no detail of the flower without its meaning —
the colour is a flag to attract the insect's eye, conspicuous spots are
honey-guides to the explorers, there are arrangements for keeping the
pollen dry and for dusting it on the insects, and so on. If Sprengel
had only discovered the utility of the cross-fertilisation, which Darwin
proved experimentally, his work could hardly have been overlooked
for nearly seventy years. In 1841 it came into Darwin's hands, and
impressed him as being "full of truth," although "with some little
nonsense." In Darwin's work Sprengel had his long-delayed reward.
Darwin's instance of the connection between cats and clover. —
One of Darwin's instances of the web of life — given in connection with
the pollination of flowers — has become familiar all over the world.
It should never become trite to us and it should never be regarded as
more than a particularly clear illustration of a general fact. " Plants
and animals, remote in the scale of nature, are bound together by a
web of complex relations I have found, from experiments, that
humble-bees are almost indispensable to the fertilisation of the heart's-
ease {Viola tricolor), for other bees do not visit this flower. I have also
found that the visits of bees are necessary for the fertilisation of some
kinds of clover — thus, 100 heads of red clover {Trifolium pratense)
produced 27,000 seeds, but the same number of protected heads pro-
duced not a single seed. Humble-bees alone visit red clover, as other
bees cannot reach the nectar Hence we may infer as highly
probable that, if the whole genus of humble-bees became extinct or
«rery rare in England, the heart's-ease and red clover would become
220 EVOLUTION, GENETICS, AND EUGENICS
very rare, or wholly disappear." We know that the red clover
imported to New Zealand did not bear fertile seeds until humble-bees
were also imported. "The number of humble-bees in any district
depends in a great measure on the number of field-mice, which destroy
their combs and nests; and Colonel Newman, who has long attended
to the habits of humble-bees, believes that more than two-thirds of
them are thus destroyed all over England." Now the number of
mice is largely dependent, as everyone knows, on the number of cats;
and Colonel Newman says: "Near villages and small towns I have
found the nests of humble-bees more numerous than elsewhere, which I
attribute to the number of cats that destroy the mice." Thus we may
say, with Darwin, that next year's crop of purple clover is influenced
by the number of humble-bees in the district, which varies with the
number of field-mice; that is to say, with the abundance of cats!
Scattering of seeds. — It is a fascinating chapter of natural history
which tells us how cross-polUnation is effected — here by a bee and
there by a butterfly, occasionally by a long-billed humming-bird
beautifully poised before the flower with almost invisibly rapid vibra-
tions of its wings, and occasionally by a slowly moving snail of epicure
appetite. But not less important is the part played by animals in the
scattering of seeds, and here again Darwin gives us the classic case of
fourscore seeds germinating out of a ball of mud from a bird's foot.
From one instance you may learn all, and see that much of Darwin's
work has been an eloquent commentary on that memorable saying
about the sparrow that falls to the ground. Such a simple event
literally sends a throb through surrounding nature; we can follow its
effects a few steps, just as we follow for a few yards the ripples made
when we throw a stone into a still lake; in either case can we doubt
that the spreading influences are real, though they pass beyond
our ken?
Interrelations between fresh-water mussels and fishes. — As a
striking illustration of the inter-linking of different forms of Ufe, we
may take the case of the fresh-water mussels and their larvae. The
fertilised eggs develop in the outer gill-plate of the mother-mussel, and
minute bivalve larvae, called Glochidia, are formed. The mussel keeps
these within the cradle until a fresh-water fish — such as the minnow —
comes into the vicinity, and then she sets them free. In a way that
we do not understand, the simple constitution of the larvae is tuned
to respond to the presence of minnows and the like, and with snapping
valves they manage to fix themselves to their host. After a short
BACKGROUND OF DARWINISM: THE WEB OF LIFE 221
period of temporary parasitism, at the end of which there is a meta
morphosis, they drop off from the fish into the mud, often far from
their birth-place. This is curious enough, but the idea of linkages
becomes incandescent in the mind when we note that, just as the fresh-
water mussel has young temporarily parasitic on fishes, so a fresh-
water fish, the bitterling {Rhodeus amarus), has its young ternporarily
parasitic in the gills of the mussel.
Life-histories of parasites. — When we pass to parasites in a
stricter sense we find the most extraordinary interconnections, the
most widely separated animals often sharing a parasite between them.
Liver- rot, which has repeatedly killed a million sheep in a year in
Britain alone, is due to a parasite which passes from sheep to water,
from water to water-snail, from water-snail to grass, from grass to
sheep. The tapeworm of the cat has its bladder-worm stage in the
mouse, the sturdie-worm of the sheep's brain has its tape-worm stage
in the dog, and similar relations hold for hundreds of species. The
troublesome threadworm of human blood (Filaria sanguinis hominis)
is transferred from man to man by the mosquito, and the guinea-worm
which was probably the fiery serpent that vexed the IsraeUtes in the
desert, which passes into man in drinking-water, spends its youth
in a minute water-flea, called by the giant's name of Cyclops. The
importance of tse-tse flies in transmitting the minute animals which
cause sleeping-sickness and allied diseases is known to all. We have
spoken of the connection between cats and clover, and there is a not
less striking connection between cats and plague. For it seems to have
been shown in India that the more cats the fewer rats, and the fewer
rats the fewer rat-fleas, which are the agents in passing the plague-
germs to man.
Far-reaching influence of certain animals; earthworms. — We
realise the idea of the web of life in another way when we consider the
far-reaching influence of particular kinds of activity, the best instance
being the work of earthworms. In 1777 Gilbert White got at the very
root of the matter. "The most insignificant insects and reptiles are of
much more consequence and have more influence in the economy of
nature than the incurious are aware of Earthworms, though in
appearance a small and despicable link in the chain of nature, yet, if
lost, would make a lamentable chasm Worms seem to be the
great promoters of vegetation, which would proceed but lamely with-
out them, by boring, perforating, and loosening the soil, and rendering
it pervious to rains and the fibres of plants; by drawing straws and
22 2 EVOLUTION, GENETICS, AND EUGENICS
stalks of leaves and twigs into it; and, most of all, by throwing up such
infinite numbers of lumps of earth called worm-casts, which, being
their excrement, is a fine manure for grain and grass. Worms prob-
ably provide new soil for hills and slopes where the rain washes the
earth away; and they affect slopes probably to avoid being flooded.
.... The earth without worms would soon become cold, hard-
bound, and void of fermentation, and consequently sterile
These hints we think proper to throw out, in order to set the inquisitive
and discerning at work. A good monograph of worms would afford
much entertainment and information at the same tims, and would
open a large and new field in natural history."
The monograph that Gilbert White wished for in 1777 was pub-
Hshed by Darwin in 1881, the year before he died — " the completion,"
he said, " of a short paper read before the Geological Society more than
forty years ago." With his characteristic thoroughness and patience
he worked out the part that earthworms have played in the history
of the earth, and proved that they deserve to be called the most useful
animals. By their burrowing they loosen the earth, making way for
the plant rootlets and the raindrops; by bruising the soil in their
gizzards, they reduce the particles to more useful, powdery form; by
burying the surface with castings brought up from beneath, they have
been for untold ages ploughers before the plough, and by burying leaves
they have made a great part of the vegetable mould over the whole
earth. In illustration of the last point, we may notice that we recently
found thirteen midribs of the leaves of the rowan, or mountain ash,
radiating round one hole like the spokes of a wheel; the withering
leaflets had been carried down, and two were sticking up at the mouth
of the burrow; that meant 91 leaflets to one hole. Darwin showed
that there often are 50,000 (and there may be 500,000) earthworms
in an acre; that they often pass ten tons of soil per acre per annum
through their bodies; and that they often cover the surface at the rate
of three inches in fifteen years. Though our British worms only pass
out about 20 oz. of earth in a year, the weights thrown up in a year on
two separate square yards which Darwin watched were respectively
6.75 lb. and 8.387 lb., which correspond to 14I and 18 tons per acre
per annum.
We follow the work further and it becomes evident that the con-
stant exposure of the soil bacteria on the surface is bound to be
important, on the one hand, in allowing them to be scattered by wind
and ram, on the other in exposing them to the beneficent action of the
BACKGROUND OF DARWINISM- THE WEB OF LIFE 223
sunlight — which is the most universal, effective, and economical of all
germicides.
In Yorubaland, on the West Coast of Africa, Mr. Alvan Millson
calculated that about 62,233 tons of subsoil are brought every year
to the surface of each square mile, and that every particle of earth, to
the depth of two feet, is brought to the surface once in twenty-seven
years. It need hardly be added that the district is fertile and healthy.
Earthworms play their part in the disintegration of rocks, letting
the solvent humus-acids of the soil down to the buried surface. Their
castings on the hill-slopes are carried down by wind and rain and go
to* swell the alluvium of the distant valleys or the wasted treasures of
the sea. The well-known parallel ledges along the slopes of grass-clad
hills are partly due to earthworm castings caught on sheep-tracks, and
thus we begin to connect the earthworms not only with our wheat-
supply but with our scenery. Well may we say, with Darwin: "It
may be doubted whether there are many other animals which have
played so important a part in the history of the world as have these
lowly organised creatures." Those who wish to understand Darwin-
ism should always begin with Darwin's last book — The Formation
of Vegetable Mould through the Action oj Worms (1881). It illus-
trates the web of life, the idea of which is essential to an understanding
of the struggle for existence and natural selection. But it also illus-
trates what Darwin had learned from Lyell — that great results may
be brought about by accumulation of infinitesimal items. As Professor
A. Milnes Marshall said: "The lesson to be derived from Darwin's
life and work cannot be better expressed than as the cumulative im-
portance of infinitely little things."
Termites, or white ants.— Henry Drummond, in his Tropical
Africa, tried to make out a case for the agricultural importance of
termites, or white ants. It is well known that these old-fashioned
insects have a pruning action in the forest, destroying dead wood with
great rapidity. Houses and furniture, fences and boxes, as well as
forest- trees, fall under their jaws. In some places, "if a man lay
down to sleep with a wooden leg, it would be a heap of sawdust in the
morning." But what of the termites' agricultural importance ? The
point is that they keep the soil circulating by constructing earthen
tunnels up the sides of trees and posts and by making huge obelisk-like
ant-hills, or termitaries. "The earth-tubes crumble to dust, which is
scattered by the wind; the rains lash the forests and soils with fury,
and wash off the loosened grains to swell the alluvium of a distant
2 24 EVOLUTION, GENETICS, AND EUGENICS
valley." It must be noted, however, that Drummond did not prove
his case with sufficient precision, and there is, as Escherich points out
in his beautiful study of termites, this difHculty, that, while the cast-
ings of earthworms are soft and loose, the earth-tubes and construc-
tions of termites are stony.
Escherich does, however, admit that the termites have some
agricultural importance, and he points out that there are other serv-
ices to be put to the credit side of their account. They prune oflf
wood that has begun to go; they destroy rotting things, including the
bodies of small animals; they make for cleanliness and health. In
some low-lying tracts, as Silvestri has shown, there are dry stretches,
"termite islands," which have been gradually built up from the
broken-down remains of termitaries. Nor should it be forgotten that
the white ants are often used as food. On the other hand, Escherich
does not hesitate to rank them as among the great hindrances to the
spread of civilisation. They insidiously devour everything wooden,
from the telegraph-post to the wooden butt of the gun hanging against
the wall, from books in the library to corks in the cellar. There does
not seem sufficiently precise information in regard to the Uving plants
that they attack, and no safe general statement can be made except
that their appetite is large and cathohc.
With a centre in earthworms, what a variety of interests must be
included within the radius of their Ufe and work! — centipedes, birds,
moles, seedlings, man. The same is true of termites, and two further
illustrations may be given. Observers have reported about thirty
different species of termites with the habit of feeding on fungi grovni
within the termitary on specially constructed mazy beds. The habit
is interesting in many ways; for instance, because the fungi afford
a supply of nitrogenous material which is scarce in the ordinary diet
of wood, and also because a similar habit occurs in the quite unrelated
true ants. Finally, the web is illustrated by the numerous boarders,
mostly beetles, that are found in the termitaries — not hostile intruders
or parasites, but guests which are fed and cared for apparently for the
sake of a palatable exudation with a pleasant, narcotising effect on the
termites. With a centre in termites, what a variety of interests must
we not include within the radius of their life and work! — fungi and
trees, beetles and birds, lizards and anteaters, and man more than any.
The hand of life upon the earth. — The hand of life has been
working upon the earth for untold ages. Take plants, for instance.
The seaweeds lessen the force of the waves, the lichens eat into the
BACKGROUND OF DARWINISM: TIIE WEB OF LIFE 225
rocks, the mosses form huge sponges on the moors which keep the
streams flowing in days of drought. Many little plants are forever
smoothing away the wrinkleson the earth's — their mother's — face, and
they adorn her with jewels. Others that have formed coal have enriched
her with ages of entrapped sunlight. The grass — which began to
appear in Tertiary ages — protects the earth like a garment; the
forests affect rainfall and temper cUmate, besides sheltering multitudes
of living things, to many of whom every blow of the axe is a death-
knell. No plant, from bacterium to oak-tree, lives or dies to itself,
or is without its influence upon the earth. So among animals there
are destructive borers and burrowers and conservative agents, such
as the coral-polyps and the chalk-forming Foraminifera.
Practical importance of a realisation of the web of life. — What
has Darwinism to do with human life ? The answer at this stage in
our inquiry is clear: we must respect the web of life if we wish to
master Nature. She must be humoured, not bullied. Emerson
included in his vision of a perfected earth the absence of spiders, but
the absence of spiders — which snare so many injurious insects — would
mean the absence of much else, man probably included. In a northern
county in Scotland the proprietors were justly annoyed at the injuries
inflicted on young trees by squirrels, and they formed a squirrel club,
setting a price on the beautiful rodent's head. Perhaps a wiser course
would have been to begin by inquiring what disturbance of the balance
of nature had allowed the squirrels to multiply so disastrously. But,
after a period of squirrel-slaughter and some jubilation thereat, a
cloud began to rise in the sky. The wood-pigeons were multiplying
worse than ever, and the farmers, at least, said with no uncertain voice
that they preferred the squirrels. An imperfect recognition of the
web of life had left out of account the notable fact that squirrels
destroy large numbers of young wood-pigeons.
One of the hopeful symptoms of the last few years is the reawaken-
ing of an interest in woods and forests. Everyone knows how terribly
these have been wasted, and how the disastrous results have affected
rainfall and irrigation, climate and crops, and even the character of the
people. Here what was once a pleasant stream is now like a gravelly
road, and there the fertile plains are flooded; here the wind is sweeping
away the soil, and there both beauty and health have departed. The
birds which the woods once sheltered are driven elsewhere, and the
insect-pests are rife among the crops. For " the cheapest and most
effective insecticides are birds."
226 EVOLUTION, GENETICS, AND EUGENICS
The recognition of consequences — often far-reaching — grows with
us as we work with the idea of the web of life, as we see in proper
perspective the criminality of those who are ruthless. President
Rooseve