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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 minor
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^^Orrr-^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
Roosevelt has declared his abomination of "the land-skinner" — "the
individual whose idea of developing the country is to cut every stick
of timber off it, and then leave a barren desert for the home-maker
who comes in after him. That man is a curse, and not a blessing to the
country. The prop of the country must be the man who intends so
to run his business that it will be profitable to his children after him."
Every right-thinking man, and especially those who have grasped the
idea of the web of life, will say with Roosevelt, "I am against the land-
skinner every time."
It may be said that man must exterminate a good deal if he is to
go on peaceably with his business, and it will be admitted that there
has never been a strong enthusiasm, humanitarian or otherwise,
against the elimination of rattlesnakes, and such like. The natural-
ist's answer is that every crusade should be carefully considered on its
own merits, and that every careless and hasty destruction of life is to be
condemned. Even in regard to snakes killing may be carried too far.
Some creatures are, as it were, on the fringes of the web, while others
occupy a position where many threads meet. It is scientifically and
aesthetically deplorable that birds like the great auk and mammals
like the quagga should have been exterminated, but it is practically
much more deplorable that we have lost so many hawks and weasels
and other members of that pertinacious army whose guerilla warfare
keeps hundreds of more humdrum creatures up to the scratch, and
keeps "vermin" from becoming a plague. Moreover, it is extremely
difficult to tell what may be the consequences of exterminating any
creature — remote as it may seem from the beaten track of human
affairs. One of the obvious lessons of Darwinism is that we should be
slow to call any change unimportant. Everything counts, or may
count. A so-called unimportant animal is destroyed and no imme-
diate ill effects are seen. But who can tell ?
Very pertinent, for instance, is the question: What about the
parasites that used to complete their life-history in romantic routine
in this extinguished animal ? Have we extinguished the parasite also ?
Or is it waiting, with a whip of scorpions, to chastise mankind for
their ignorance of Darwinism ?
The practical importance of recognising the web of life has been
proved by the heavy penalties which man has often had to pay for
BACKGROUND OF DARWINISM: THE WEB OF LIFE 227
disturbing the balance of nature, careless of results and ruthless of
beauty, for not admitting that if we would master Nature we must
first understand her. How much has Australia had to pay for the
introduction of rabbits in i860, or America for sparrows? Sometimes
the introduction has been unconscious, and man has only to blame
himself for letting the intruder take hold, as in the case of the Phyl-
loxera in France, or of the Colorado Beetle in Ireland. "Ignorance
of nature," Mr. A. H. S. Lucas says, "is costly. By disturbing the
balance of nature, man has introduced foes into his own household."
Speaking of Australia, he says: "How much is needed for the eradi-
cation of Bathurst Burr, Prickly Pear, Water- hyacinth. Bramble and
Sweetbriar, Codlin Moth, Waxy Scale, Pear Slug, and Red Spider,
owing to carelessness or lack of knowledge in early days ?"
An obvious moral is that we should be careful in our introduc-
tions of new organisms — man included — into new surroundings. The
primary consequences may be predictable, but the secondary and the
tertiary consequences — who is sufficient for these things? We have
records of the unconscious introduction of rats into Jamaica, where
they became a pest. To destroy them mongooses were imported, and
the rats were soon checked. But the mongooses, having finished the
rats, began to eat up the poultry and young birds of various kinds.
As this went on the injurious insects and ticks, that the birds used to
eat, began to gain the ascendant. A recent report — which requires
confirmation — says that the increase of ticks is making life a burden
to the mongooses. Thus a balance will be again arrived at. There
is no doubt of that, but how much is often unnecessarily lost by the
way!
CHAPTER XVIT
NATURAL SELECTION
CHARLES DARWIN
Introdttctory Note. — This entire chapter is made up of carefully chosen
oassages from Darwin's Origin of Species. So much has falsely been called
" Darwinism " that it is well for the reader to have a statement of Darwin's views
in his own words. Every student of evolution should read the whole of the Origin
of Species. It is all so good that one finds it difficult to leav^e out anything. The
following excerpts will, we believe, give the gist of natural selection.
We present first certain of the ideas that underlie or are postulates of the
theory; then the theory itself is presented; the theory of sexual selection inter-
polated; and then follow examples of the way in which adaptations are accounted
for by natural selection. Darwin's own statement of the most serious difficulties
and objections to the theory, and his answers to these, bring this chapter to a close.
FOUNDATION STONES OF NATURAL SELECTION
DARWIN's own estimate as to the RdLE OF NATURAL SELECTION IN EVOLUTION
No one ought to feel surprised at much remaining as yet unex-
plained in regard to the origin of species and varieties, if he make due
allowance for our profound ignorance in regard to the mutual relations
of the many beings which Hve around us. Who can explain why one
species ranges widely and is very numerous, and why another allied
species has a narrow range and is rare ? Yet these relations are of the
highest importance, for they determine the present welfare and, as I
ueheve, the future success and modification of every inhabitant of this
»vorld. Still less do we know of the mutual relations of the innumer-
able inhabitants of the world during the many past geological epochs
in its history. Although much remains obscure, and will long remain
obscure, I can entertain no doubt, after the most deliberate study
and dispassionate judgment of which I am capable, that the view
which most naturahsts until recently entertained, and which I for-
merly entertained — namely, that each species has been independently
created — is erroneous. I am fully convinced that species are not
immutable; but that those belonging to what are called the same
genera are lineal descendants of some other and generally extinct
species, in the same manner as the acknowledged varieties of any one
species are the descendants of that species. Furthermore, I am con-
vinced that Natural Selection has been the most important, but not
the exclusive, means of modification.
s>a8
NATURAL SELECTION 229
effects of habit and of the use or disuse of parts; correlated
variation; inheritance
Changed habits produce an inherited effect, as in the period of the
flowering of plants when transported from one climate to another.
With animals the increased use or disuse of parts has had a more
marked influence; thus I find in the domestic duck that the bones of
the wing weigh less and the bones of the leg more, in proportion to the
whole skeleton, than do the same bones in the wild-duck; and this
change may be safely attributed to the domestic duck flying much
less, and walking more, than its wild parents. The great and inherited
development of the udders in cows and goats in countries where
they are habitually milked, in comparison with these organs in other
countries, is probably another instance of the effects of use. Not
one of our domestic animals can be named which has not in some
country drooping ears; and the view, which has been suggested that
the drooping is due to disuse of the muscles of the ear, from the
animals being seldom much alarmed, seems probable.
Many laws regulate variation, some few of which can be dimly
seen, and will hereafter be briefly discussed. I will here only allude
to what may be called correlated variation. Important changes in the
embryo or larva will probably entail changes in the mature animal.
In monstrosities, the correlations between quite distinct parts are
very curious; and many instances are given in Isidore Geoff roy St.
Hilaire's great work on this subject. Breeders believe that long Hmbs
are almost always accompanied by an elongated head. Some instances
of correlation are quite whimsical: thus cats which are entirely white
and have blue eyes are generally deaf; but it has been lately stated by
Mr. Tait that this is confined to the males. Color and constitutional
peculiarities go together, of which many remarkable cases could be
given amongst animals and plants. From facts collected by Heu-
singer, it appears that white sheep and pigs are injured by certain
plants, whilst dark-colored individuals escape: Professor Wyman has
recently communicated to me a good illustration of this fact; on ask-
ing some farmers in Virginia how it was that all their pigs were black,
they informed him that the pigs ate the paint-root (Lachnanthes),
which colored their bones pink, and which caused the hoofs of all but
the black varieties to drop off; and one of the "crackers "(i.e., Virginia
squatters) added, "we select the black members of a litter for raising,
as they alone have a good chance of living." Hairless dogs have
imperfect teeth; long-haired and coarse-haired animals are apt to
230 EVOLUTION, GENETICS, AND EUGENICS
have, as is asserted, long or many horns; pigeons with feathered feet
have skin between their outer toes; pigeons with short beaks have
small feet, and those with long beaks large feet. Hence if man goes
on selecting, and thus augmenting, any peculiarity, he will almost
certainly modify unintentionally other parts of the structure, owing
to the mysterious laws of correlation.
DARWm'S IDEA OF THE CAUSES RESPONSIBLE FOR THE ORIGIN OF DOMESTIC RACES
To sum up on the origin of our domestic races of animals and
plants. Changed conditions of life are of the highest importance in
causing variability, both by acting directly on the organization, and
indirectly by affecting the reproductive system. It is not probable
that variability is an inherent and necessary contingent, under all
circumstances. The greater or less force of inheritance and reversion
determine whether variations shall endure. Variabilityis governed by
many unknown laws, of which correlated growth is probably the most
important. Something, but how much we do not know, may be
attributed to the definite action of the conditions of life. Some, per-
haps a great, efifect may be attributed to the increased use or disuse
of parts. The final result is thus rendered infinitely complex. In
some cases the intercrossing of aboriginally distinct species appears to
have played an important part in the origin of our breeds. When
several breeds have once been formed in any country, their occasional
intercrossing, with the aid of selection, has, no doubt, largely aided in
the formation of new sub-breeds; but the importance of crossing has
been much exaggerated, both in regard to animals and to those plants
which are propagated by seed. With plants which are temporarily
propagated by cuttings, buds, etc., the importance of crossing is
immense ; for the cultivator may here disregard the extreme variability
both of hybrids and of mongrels, and the steriHty of hybrids; but
plants not propagated by seed are of little importance to us, for their
endurance is only temporary. Over all these causes of Change, the
accumulative action of Selection, whether applied methodically and
quickly, or unconsciously and slowly but more efficiently, seems to
have been the predominant Power.
DARWIN's IDEA OF THE ORIGIN OF VARIETIES, SPECIES, AND GENERA IN NATURE
Finally, varieties cannot be distinguished from species — except,
first, by the discovery of intermediate linking forms; and, secondly,
by a certain indefinite amount of difference between them; for two
NATURAL SELECTION 231
forms, if differing very little, are generally ranked as varieties, not-
withstanding that they cannot be closely connected; but the amount
of difference considered necessary to give to any two forms the rank
of species cannot be defined. • In genera having more than the average
number of species in any country, the species of these genera have
more than the average number of varieties. In large genera the species
are apt to be closely, but unequally, allied together, forming httle
clusters round other species. Species very closely allied to other
species apparently have restricted ranges. In all these respects the
species of large genera present a strong analogy with varieties. And
we can clearly understand these analogies, if species once existed as
varieties, and thus originated; whereas, these analogies are utterly
inexplicable if species are independent creations.
We have, also, seen that it is the most flourishing or dominant
species of the larger genera within each class which on an average yield
the greatest number of varieties; and varieties, as we shall hereafter
see, tend to become converted into new and distinct species. Thus
the larger genera tend to become larger; and tliroughout nature the
forms of life which are now dominant tend to become still more domi-
nant by leaving many modified and dominant descendants. But by
steps hereafter to be explained, the larger genera also tend to break up
into smaller genera. And thus, the forms of life throughout the uni-
verse become divided into groups subordinate to groups.
THE TERM "STRUGGLE FOR EXISTENCE" USED IN A LARGE SENSE
I should premise that I use this term in a large and metaphorical
sense including dependence of one being on another, and including
(which is more important) not only the life of the individual, but
success in leaving progeny. Two canine animals, in a time of dearth,
may be truly said to struggle with each other which shall get food and
live. But a plant on the edge of a desert is said to struggle for life
against the drought, though more properly it should be said to be
dependent on the moisture. A plant which annually produces a
thousand seeds, of which only one of an average comes to maturity,
may be more truly said to struggle with the plants of the same
and other kinds which already clothe the ground. The mistletoe is
dependent on the apple and a few other trees, but can only in a
far-fetched sense be said to struggle with these trees, for, if too many
of these parasites grow on the same tree, it languishes and dies. But
several seedling mistletoes, growing close together on the same branch,
232 EVOLUTION, GENETICS, AND EUGENICS
may more truly be said to struggle with each other. As the mistletoe
is disseminated by birds, its existence depends on them; and it may
metaphorically be said to struggle with other fruit- bearing plants,
in tempting the birds to devour and thus disseminate its seeds. In
these several senses, which pass into each other, I use for conven-
ience' sake the general term of Struggle for Existence.
GEOMETRICAL RATIO OF INCREASE
A struggle for existence inevitably follows from the high rate at
which all organic beings tend to increase. Every being, which during
its natural lifetime produces several eggs or seeds, must suffer destruc-
tion during some period of Its life, and during some season or occasional
year, otherwise, on the principle of geometrical increase, its numbers
would quiclvly become so inordinately great that no country could
support the product. Hence, as more individuals are produced than
can possibly survive, there must in every case be a struggle for exist-
ence, either one individual with another of the same species, or with
the individuals of distinct species, or with the physical conditions of
life. It is the doctrine of Malthus applied with manifold force to
the whole animal and vegetable kingdoms; for in this case there can
be no artificial increase of food, and no prudential restraint from
marriage. Although some species may be now increasing, more or
less rapidly, in numbers, all cannot do so, for the world would not
hold them.
NATURAL selection; OR THE SURVIVAL OF THE FITTEST
How will the struggle for existence, briefly discussed in the last
chapter, act in regard to variation ? Can the principle of selection,
which we have seen is so potent in the hands of man, apply under
nature ? I think we shall see that it can act most efficiently. Let the
endless number of slight variations and individual differences occurring
in our domestic productions, and, in a lesser degree, in those under
nature, be borne in mind; as well as the strength of the hereditary
tendency. Under domestication, it may be truly said that the whole
organization becomes in some degree plastic. But the variability,
which we almost universally meet with in our domestic productions,
is not directly produced, as Hooker and Asa Gray have well remarked,
by man; he can neither originate varieties, nor prevent their occur-
rence; he can only preserve and accumulate such as do occur. Unin-
tentionally he exposes organic beings to new and changing conditions
NATURAL SELECTION 233
of life, and variability ensues; , but similar changes of conditions might
and do occur under nature. Let it also be borne in mind how infinitely
complex and close-fitting are the mutual relations of all organic beings
to each other and to their physical conditions of life; and consequently
what infinitely varied diversities of structure might be of use to
each being under changing conditions of life. Can it, then, be
thought improbable, seeing thr.t variations useful to man have
undoubtedly occurred, that other variations useful in some way to
each being in the great and complex battle of life, should occur in
the course of many successive generations ? If such do occur, can
we doubt (remembering that many more individuals are born than
can possibly survive) that individuals having any advantage, however
slight, over others, would have the best chance of surviving and of
procreating their kind? On the other hand, we may feel sure that
any variation in the least degree injurious would be rigidly destroyed.
This preservation of favorable individual differences and variations,
and the destruction of those which are injurious, I have called
Natural Selection, or the Survival of the Fittest. Variations neither
useful nor injurious would not be affected by natural selection, and
would be left either a fluctuating element, as perhaps we see in certain
polymorphic species, or would ultimately become fixed, owing to the
nature of the organism and the nature of the conditions.
Several writers have misapprehended or objected to the term
Natural Selection. Some have even imagined that natural selection
induces variability, whereas it implies only the preservation of such
variations as arise and are beneficial to the being under its conditions
of Ufe. No one objects to agriculturists speaking of the potent effects
of man's selection ; and in this case the individual differences given by
nature, which man for some object selects, must of necessity first
occur. Others have objected that the term selection implies conscious
choice in the animals which become modified; and it has even been
urged that, as plants have no volition, natural selection is not applic-
able to them! In the Hteral sense of the word, no doubt, natural
selection is a false term; but who ever objected to chemists speaking
of the elective affinities of the various elements? — and yet an acid
cannot strictly be said to elect the base with which it in preference
combines. It has been said that I speak of natural selection as an
active power or Deity; but who objects to an author speaking of the
attraction of gravity as ruling the movements of the planets ? Every-
one knows what is meant and is implied by such metaphorical expres-
234 EVOLUTION, GENETICS, AND EUGENICS
sions; and they are almost necessary, for brevity. So again it is
difficult to avoid personifying the word Nature; but I mean by Nature
only the aggregate action and product of many natural laws, and by
laws the sequence of events as ascertained by us. With a little famili-
arity such superficial objections will be forgotten.
We shall best understand the probable course of natural selection
by taking the case of a country undergoing some slight physical change,
for instance, of climate. The proportional numbers of its inhabitants
will almost immediately undergo a change, and some species will prob-
ably become extinct. We may conclude, from what we have seen of
the intimate and complex manner in which the inhabitants of each
country are bound together, that any change in the numerical pro-
portions of the inhabitants, independently of the change of climate
itself, would seriously affect the others. If the country were open
on its borders, new forms would certainly immigrate, and this would
likewise seriously disturb the relations of some of the former inhabi-
tants. Let it be remembered how powerful the influence of a single
introduced tree or mammal has been shown to be. But in the case of
an island, or of a country partly surrounded by barriers, into which
new and better adapted forms could not freely enter, we should then
have places in the economy of nature which would assuredly be
better filled up, if some of the original inhabitants were in some
manner modified; for, had the area been open to immigration, these
same places would have been seized on by intruders. In such
cases, slight modifications, which in any way favored the individuals
of any species by better adapting them to their altered conditions,
would tend to be preserved; and natural selection would have free
scope for the work of improvement.
We have good reason to believe, as shown in the first chapter, that
changes in the conditions of life give a tendency to increased variability
and in the foregoing cases the conditions have changed, and this would
manifestly be favorable to natural selection, by affording a better
chance of the occurrence of profitable variations. Unless such occur,
natural selection can do nothing. Under the term of "variations," it
must never be forgotten that mere individual differences are included.
As man can produce a great result with his domestic animals and plants
by adding up in any given direction individual differences, so could
natural selection, but far more easily from having incomparably longer
time for action. Nor do I believe that any great physical change, as
of climate, or any unusual degree of isolation to check immigration,
NATURAL SELECTION
23s
is necessary in order ihat new and unoccupied places should he left,
for natural selection to fill up by improving some of the varying
inhabitants. For as all the inhabitants of each country are struggling
together with nicely balanced forces, extremely slight modifications in
the structure or habits of one species would often give it an advantage
over others; and still further modifications of the same kind would
often still further increase the advantage, as long as the species con-
tinued under the same conditions of life and profited by similar means
of subsistence and defense. No country can be named in which all the
native inhabitants are now so perfectly adapted to each other and to
the physical conditions imder which they live, that none of them could
be still better adapted or improved; for in all countries, the natives
have been so far conquered by naturalized productions, that they have
allowed some foreigners to take firm possession of the land. And as
foreigners have thus in every country beaten some of the natives, we
may safely conclude that the natives might have been modified with
advantage, so as to have better resisted the intruders.
As man can produce, and certainly has produced, a great result by
his methodical and unconscious means of selection, what may not
natural selection effect? Man can act only on external and visible
characters: Nature, if I may be allowed to personify the natural pres-
ervation or survival of the fittest, cares nothing for appearances,
except in so far as they are useful to any being. She can act on every
internal organ, on every shade of constitutional difference, on the
whole machinery of life. Man selects only for his own good : Nature
only for that of the being which she tends. Every selected character
is fully exercised by her, as is implied by the fact of their selection.
Man keeps the natives of many climates in the same country; he
seldom exercises each selected character in some peculiar and fitting
manner; he feeds a long- and a short-beaked pigeon on the same food;
he does not exercise a long-backed or long-legged quadruped in any
peculiar manner; he exposes sheep with long and short wool to the
same climate. He does not allow the most vigorous males to struggle
for the females. He does not rigidly destroy all inferior animals, but
protects during each varying season, as far as lies in his power, all
his productions. He often begins his selection by some half-monstrous
form; or at least by some modification prominent enough to catch the
eye or to be plainly useful to him. Under nature, the slightest differ-
ences of structure or constitution may well turn the nicely balanced
scale in the struggle for life, and so be preserved. How fleeting are the
236 EVOLUTION, GENETICS, AND EUGENICS
wishes and efforts of man! how short his time! and consequently how
poor will be his results, compared with those accumulated by Nature
during whole geological periods! Can we wonder, then, that Nature's
productions should be far" truer "in character than man'sproductions;
that they should be infinitely better adapted to the most complex
conditions of life, and should plainly bear the stamp of far higher
workmanship ?
It may metaphorically be said that natural selection is daily and
hourly scrutinizing, throughout the world, the slightest variations;
rejecting those that are bad, preserving and adding up all that are
good; silently and insensibly working whenever and wherever oppor-
tunity offers, at the improvement of each organic being in relation to
its organic and inorganic conditions of life. We see nothing of these
slow changes in progress, until the hand of time has marked the lapse
of ages, and then so imperfect is our view into long-past geological
ages, that we see only that the forms of life are now different from what
they formerly were.
In order that any great amount of modification should be effected
in a species, a variety when once formed must again, perhaps after a
long interval of time, vary or present individual differences of the same
favorable nature as before; and these must be again preserved, and
so onwards step by step. Seeing that individual differences of the
same kind perpetually recur, this can hardly be considered as an
unwarrantable assumption. But whether it is true, we can judge only
by seeing how far the hypothesis accords with and explains the general
phenomena of nature. On the other hand, the ordinary behef that
the amount of possible variation is a strictly limited quantity is like-
wise a simple assumption.
Although natural selection can act only through and for the good
of each being, yet characters and structures, which we are apt to con-
sider as of very trifling importance, may thus be acted on. When we
see leaf-eating insects green, and bark-feeders mottled-gray; the
alpine ptarmigan white in winter, the red-grouse the color of heather,
we must believe that tliese tints are of service to these birds and
insects in preserving them from danger. Grouse, if not destroyed at
some period of their lives, would increase in countless numbers; they
are known to suffer largely from birds of prey; and hawks are guided
by eyesight to their prey — so much so, that on parts of the Continent
persons are warned not to keep white pigeons, as being the most liable
to destruction. Hence natural selection might be effective in giving
NATURAL SELECTION 237
the proper color to each kind of grouse, and in keeping that color,
when once acquired, true and constant. Nor ought we to think that
the occasional destruction of an animal of any particular color would
produce little effect: we should remember how essential it is in a flock
of white sheep to destroy a lamb with the faintest trace of black. We
have seen how the color of the hogs, which feed on the "paint-root"
in Virginia, determines whether they shall live or die. In plants, the
down on the fruit and the color of the flesh are considered by botanists
as characters of the most trifling importance: yet we hear from an
excellent horticulturist, Downing, that in the United States smooth-
skinned fruits suffer far more from a beetle, a Curculio, than those with
down; that purple plums suffer far more from a certain disease than
yellow plums; whereas another disease attacks yellow-fleshed peaches
far more than those with other colored flesh. If, with all the aids of
art, these slight differences make a great difference in cultivating the
several varieties, assuredly, in a state of nature, where the trees would
have to struggle with other trees and with a host of enemies, such dif-
ferences would effectually settle which variety, whether a smooth or
downy, a yellow- or purple-fleshed fruit, should succeed.
In looJcing at many small points of difference between species,
which, as far as our ignorance permits us to judge, seem quite unim-
portant, we must not forget that cUmate, food, etc., have no doubt
produced some direct effect. It is also necessary to bear in mind that,
owing to the law of correlation, when one part varies, and the varia-
tions are accumulated through natural selection, other modifications,
often of the most unexpected nature, will ensue.
As we see that those variations which, under domestication, appear
at any particular period of life, tend to reappear in the offspring at the
same period; for instance, in the shape, size, and flavor of the seeds
of the many varieties of our culinary and agricultural plants; in the
caterpillar and cocoon stages of the varieties of the silk-worm; in
the eggs of poultry, and in the color of the down of their chickens; in
the horns of our sheep and cattle when nearly adult; so in a state of
nature natural selection will be enabled to act on and modify organic
beings at any age, by the accumulation of variations profitable at that
age, and by their inheritance at a corresponding age. If it profit a
plant to have its seeds more and more widely disseminated by the
wind, I can see no greater difficulty in this being effected through
natural selection, than in the cotton-planter increasing and improving
by selection the down in the pods on his cotton-trees. Natural
■j^S EVOLUTION, GENETICS, AND EUGENICS
selection may modify and adapt the larva of an insect to a score of
contingencies, wholly different from those which concern the mature
insect; and these modifications may affect, through correlation, the
structure of the adult. So, conversely, modifications in the adult may
affect the structure of the larva; but in all cases natural selection will
ensure that they shall not be injurious: for if they were so, the species
would become extinct.
Natural selection will modify the structure of the young in relation
to the parent, and of the parent in relation to the young. In social
animals it will adapt the structure of each individual for the benefit of
the whole community, if the community profits by the selected
change. What natural selection cannot do, is to modify the structure
of one species, without giving it any advantage, for the good of another
species; and though statements to this effect may be found in works
of natural history, I cannot find one case which will bear investigation.
A structure used only once in an animal's life, if of high importance
to it, might be modified to any extent by natural selection; for instance
the great jaws possessed by certain insects, used exclusively for open-
ing the cocoon — or the hard tip to the beak of unhatched birds, used
for breaking the egg. It has been asserted, that of the best short-
beaked tumbler-pigeons a greater number perish in the egg than are
able to get out of it; so that fanciers assist in the act of hatching.
Now if nature had to make the beak of a full-grown pigeon very
short for the bird's own advantage, the process of modification would
be very slow, and there would be simultaneously the most rigorous
selection of all the young birds within the egg, which had the most
powerful and hardest beaks, for all with weak beaks would inevitably
perish; or, more delicate and more easily broken shells might be
selected, the thickness of the sheU being known to vary like every
other structure.
It may be well here to remark that with all beings there must be
much fortuitous destruction, which can have little or no influence on
the course of natural selection. For instance a vast number of eggs
or seeds are annually devoured, and these could be modified through
natural selection only if they varied in some manner which protected
them from their enemies. Yet many of these eggs or seeds would
perhaps, if not destroyed, have yielded individuals better adapted to
their conditions of life than any of those which happened to survive.
So again a vast number of mature animals and plants, whether or
not they be the best adapted to their conditions, must be annually
I
NATURAL SELECTION 239
destroyed by accidental causes, which would not be in the least degree
mitigated by certain changes of structure or constitution which would
in other ways be beneficial to the species. But let the destruction of
the adults be ever so heavy, if the number which can exist in any
district be not wholly kept down by such causes, or again let the
destruction of eggs or seeds be so great that only a hundredth or a
thousandth part are developed, yet of those which do survive, the
best adapted individuals, supposing that there is any variabihty in a
favorable direction, will tend to propagate their kmd in larger numbers
than the less well adapted. If the numbers be wholly kept down by
the causes just indicated, as will often have been the case, natural
selection will be powerless in certain beneficial directions; but this is
no valid objection to its eflTiciency at other times and in other ways;
for we are far from having any reason to suppose that many species
ever undergo modification and improvement at the same time in the
same area.
SEXUAL SELECTION
Inasmuch as peculiarities often appear under domestication in one
sex and become hereditarily attached to that sex, so no doubt it will
be under nature. Thus it is rendered possible for the two sexes to be
modified through natural selection in relation to different habits of
life, as is sometimes the case; or for one sex to be modified in relation
to the other sex, as conmionly occurs. This leads me to say a few
words on what I have called Sexual Selection. This form of selection
depends, not on a struggle for existence in relation to other organic
beings or to external conditions, but on a struggle between the indi-
viduals of one sex, generally the males, for the possession of the other
sex. The result is not death to the unsuccessful competitor, but few
or no offspring. Sexual selection is, therefore, less rigorous than
natural selection. Generally, the most vigorous males, those which
are best fitted for their places in nature, will leave most progeny.
But in many cases, victory depends not so much on general vigor, as
on having special weapons, confined to the male sex. A hornless
stag or spurless cock would have a poor chance of leaving numerous
offspring. Sexual selection, by always allowing the victor to breed,
might surely give indomitable courage, length to the spur, and strength
to the wing to strike in the spurred leg, in nearly the same manner as
does the brutal cock-fighter by the careful selection of his best cocks.
How low in the scale of nature the law of battle descends, I know not;
male alligators have been described as fighting, bellowing, and whirl-
240' EVOLUTION, GENETICS, AND EUGENICS
ing around, like Indians in a war-dance, for the possession of the
females; male salmons have been observed fighting all day long; male
stag-beetles sometimes bear wounds from the huge mandibles of other
males; the males of certain hymenopterous insects have been fre-
quently seen by that inimitable observer M. Fabre, fighting for a
particular female who sits by, an apparently unconcerned beholder
of the struggle, and then retires with the conqueror. The war is,
perhaps, severest between the males of polygamous animals, and
these seem oftenest provided with special weapons. The males of
carnivorous animals are already well armed; though to them and to
others, special means of defense may be given through means of
sexual selection, as the mane of the lion, and the hooked jaw to the
male salmon; for the shield may be as important for victory as the
sword or spear.
Amongst birds, the contest is often of a more peaceful character.
All those who have attended to the subject believe that there is the
severest rivalry between the males of many species to attract, by
singing, the females. The rock-thrush of Guiana, birds of paradise,
and some others, congregate; and successive males display with the
most elaborate care, and show off m the best manner, their gorgeous
plumage; they likewise perform strange antics before the females,
which, standing by as spectators, at last choose the most attractive
partner. Those who have closely attended to birds in confinement
well know that they often take individual preferences and dislikes:
thus Sir R. Heron has described how a pied peacock was eminently
attractive to all his hen birds. I cannot here enter on the necessary
details; but if man can in a short time give beauty and an elegant
carriage to his bantams, according to his standard of beauty, I can
see no good reason to doubt that female birds, by selecting, during
thousands of generations, the most melodious or beautiful males,
according to their standard of beauty, might produce a marked effect.
Some well-known laws, with respect to the plumage of male and
female birds, in comparison with the plumage of the young, can partly
be explained through the action of sexual selection on variations
occurring at diflferent ages, and transmitted to the males alone or to
both sexes at corresponding ages; but I have not space here to enter
on this subject.
Thus it is, as I beheve, that when the males and females of any
animal have the same general habits of life, but differ in structure,
color, or ornament, such differences have been mainly caused by sexual
NATURAL SELECTION 241
selection: that is, by individual males having had, in successive gen-
erations, some slight advantage over other males, in their weapons,
means of defence, or charms, which they have transmitted to their
male offspring alone. Yet, I would not wish to attribute all sexual
differences to this agency: for we see in our domestic animals peculi-
arities arising and becoming attached to the male sex, which appar-
ently have not been augmented through selection by man. The tuft
of hair on the breast of the wild turkey-cock cannot be of any use, and
it is doubtful whether it can be ornamental in the eyes of the female
bird; indeed, had the tuft appeared under domestication, it would
have been called a monstrosity.
ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION, OR THE
SURVIVAL OF THE FITTEST
In order to make it clear how, as I beUeve, natural selection acts,
I must beg permission to give one or two imaginary illustrations. Let
us take the case of a wolf, which preys on various animals, securing
some by craft, some by strength, and some by fleetness; and let us
suppose that the fleetest prey, a deer for instance, had from any change
in the country increased in numbers, or that other prey had decreased
in numbers, during that season of the year when the wolf was hardest
pressed for food. Under such circumstances the swiftest and shmmest
wolves would have the best chance of surviving and so be preserved or
selected, provided always that they retained strength to master their
prey at this or some other period of the year, when they were compelled
to prey on other animals. I can see no more reason to doubt that this
would be the result, than that man should be able to improve the
fleetness of his greyhounds by careful and methodical selection, or
by that kind of unconscious selection which follows from each man
trying to keep the best dogs without any thought of modifying the
breed. I may add, that, according to Mr. Pierce, there are two
varieties of the wolf inhabiting the Catskill Mountains, in the United
States, one with a light greyhound-like form, which pursues deer, and
the other more bulky, with shorter legs, which more frequently attacks
the shepherd's flocks.
It should be observed that, in the above illustration, I speak of the
slimmest individual wolves, and not of any single strongly marked
variation having been preserved. In former editions of this work I
sometimes spoke as if this latter alternative had frequently occurred.
I saw the great importance of individual differences, and this led me
fuUy to discuss the results of unconscious selection by man, which
242 EVOLUTION, GENETICS, AND EUGENICS
depends on the preservation of all the more or less valuable individuals,
and on the destruction of the worst. I saw, also, that the preservation
in a state of nature of any occasional deviation of structure, such as a
monstrosity, would be a rare event; and that, if at first preserved, it
would generally be lost by subsequent intercrossing with ordinary
individuals. Nevertheless, until reading an able and valuable article
in the North British Review (1867), I did not appreciate how rarely
single variations, whether slight or strongly marked, could be per-
petuated. The author takes the case of a pair of animals, producing-
during their lifetime Iwo hundred offspring, of which, from various
causes of destruction, only two on an average survive to pro-create
their kind. This is rather an extreme estimate for most of the higher
animals, but by no means so for many of the lower organisms. He
then shows that if a single individual were born, which varied in some
manner, giving it twice as good a chance of life as that of the other
individuals, yet the chances would be strongly against its survival.
Supposing it to survive and to breed, and that half its young inherited
the favorable variation; still, as the Reviewer goes on to show, the
young would have only a slightly better chance of surviving and breed-
ing; and this chance would go on decreasing in the succeeding genera-
tions. The justice of these remarks cannot, I think, be disputed.
If, for instance, a bird of some kind could procure its food more easily
by having its beak curved, and if one were born with its beak strongly
curved, and which consequently flourished, nevertheless there would
be a very poor chance of this one individual perpetuating its kind to
the exclusion of the common form; but there can hardly be a doubt,
judging by what we see taking place under domestication, that this
result would follow from the preservation during many generations of
a large number of individuals with more or less strongly curved beaks,
and from the destruction of a still larger number with the straightest
beaks.
SUMMARY OF CHAPTER ON NATQRAL SELECTION
If under changing conditions of life organic beings present indi-
vidual differences in almost every part of their structure, and this
cannot be disputed; if there be, owing to their geometrical rate of
increase, a severe struggle for life at some age, season, or year, and
this certainly cannot be disputed; then, considering the infinite com-
plexity of the relations of all organic beings to each other and to their
conditions of life, causing an infinite diversity in structure, constitu-
tion, and habits, to be advantageous to them, it would be a most
NATURAL SELECTION 243
extraordinary fact if no variations had ever occurred useful to each
being's own welfare, in the same manner as so many variations have
occurred useful to man. But if variations useful to any organic being
ever do occur, assuredly individuals thus characterized will have the
best chance of being preserved in the struggle for life; and from the
strong principle of inheritance, these will tend to produce offspring
similarly characterized. This principle of preservation, or the survival
of the fittest, I have called Natural Selection. It leads to the im-
provement of each creature in relation to its organic and inorganic
conditions of life; and consequently, in most cases, to what must be
regarded as an advance in organization. Nevertheless, low and simple
forms will long endure if well fitted for their simple conditions of life.
Natural selection, on the principle of quahties being inherited at
corresponding ages, can modify the egg, seed, or young, as easily as
the adult. Amongst many animals, sexual selection will have given
its aid to ordinary selection, by assuring to the most vigorous and best
adapted males the greatest number of offspring. Sexual selection will
also give characters useful to the males alone, in their struggles or
rivalry with other males; and these characters will be transmitted to
one sex or to both sexes, according to the form of inheritance which
prevails.
Whether natural selection has really thus acted in adapting the
various forms of life to their several conditions and stations, must be
judged by the general tenor and balance of evidence given in the follow-
ing chapters. But we have already seen how it entails extinction ; and
how largely extinction has acted in the world's history, geology plainly
declares. Natural selection, also, leads to divergence of character;
for the more organic beings diverge in structure, habits, and constitu-
tion, by so much the more can a large number be supported on the
area, of which we see proof by looking to the inhabitants of any
small spot, and to the productions naturalized in foreign lands. There-
fore, during the modification of the descendants of any one species,
and during the incessant struggle of all species to increase in number,
the more diversified the descendants become, the better will be their
chance of success in the battle for life. Thus the small differences dis-
tinguishing varieties of the same species, steadily tend to increase, till
they equal the greater differences between species of the same genus,
or even of distinct genera.
We have seen that it is the common, the widely-diffused and
widely ranging species, belonging to the larger genera within each
244 EVOLUTION, GENETICS, AND EUGENICS
class, which vary most; and these tend to transmit to their modified
offspring that superiority which now makes them dominant in their
own countries. Natural selection, as has just been remarked, leads
to divergence of character and to much extinction of the less improved
and intermediate forms of life. On these principles, the nature of the
affinities, and the generally well-defined distinctions between the
innumerable organic beings in each class throughout the world, may
be explained. It is a truly wonderful fact — the wonder of which we
are apt to overlook from familiarity — that all animals and all plants
throughout all time and space should be related to each other in groups
subordinate to groups, in the manner which we everyivhere behold —
namely, varieties of the same species most closely related, species of
the same genus less closely and unequally related, forming sections
and sub-genera, species of distinct genera much less closely related,
and genera related in different degrees, forming sub-families, families,
orders, sub-classes and classes. The several subordinate groups in any
class cannot be ranked in a single file, but seem clustered round points,
and these round other points, and so on in almost endless cycles. If
species had been independently created, no explanation would have
been possible of this kind of classification; but it is explained through
inheritance and the complex action of natural selection, entailing
extinction and divergence of character, as we have seen illustrated in
the diagram.
The affinities of all the beings of the same class have sometimes
been represented by a great tree. I believe this simile largely speak?
the truth. The green and budding twigs may represent existing
species; and those produced during former years may represent the
long succession of extinct species. At each period of growth all the
growing twigs have tried to branch out on all sides, and to overtop and
kill the surrounding twigs and branches, in the same manner as species
and groups of species have at all times overmastered other species in
the great battle for life. The limbs divided into great branches, and
these into lesser and lesser branches, were themselves once, when the
tree was young, budding twigs; and this connection of the former and
present buds by ramifying branches may well represent the classifica-
tion of aU extinct and living species in groups subordinate to groups.
Of the many twigs which flourished when the tree was a mere bush,
only two or three, now grown into great branches, yet survive and bear
the other branches; so with the species which lived during long-past
eeological periods, very few have left living and modified descendants.
NATURAL SELECTION 245
From the first growth of the tree, many a limb and branch has decayed
and dropped off; and these fallen branches of various sizes may repre-
sent those whole orders, families, and genera which have now no living
representatives, and which are known to us only in a fossil state. As
we here and there see a thin straggUng branch springing from a fork
low down in a tree, and which b}' some chance has been favored and is
still ahve on its summit, so we occasionally see an animal like the
Omithorhynchus or Lepidosiren, which in some small degree connects
by its affinities two large branches of life, and which has apparently
been saved from fatal competition by having inhabited a protected
station. As buds give rise by growth to fresh buds, and these, if
vigorous, branch out and overtop on all sides many a feebler branch,
so by generation I beUeve it has been with the great Tree of Life, which
fills with its dead and broken branches the crust of the earth, and
covers the surface with its ever-branching and beautiful ramifications.
DIFFICULTIES AND OBJECTIONS TO NATURAL SELECTION AS
SEEN BY DARWIN
Long before the reader has arrived at this part of my work, a crowd
cf difficulties will have occurred to him. Some of them are so serious
that to this day I can hardly reflect on them without being in some
degree staggered; but, to the best of my judgment, the greater number
are only apparent, and those that are real are not, I think, fatal to the
theory.
These difficulties and objections may be classed under the follow-
ing heads: First, why, if species have descended from other species
by fine gradations, do we not everywhere see innumerable, transitional
forms? Why is not all nature in confusion, instead of the species
being, as we see them, well defined ?
Secondly, is it possible that an animal having, for instance, the
structure and habits of a bat, could have been formed by the modifica-
tion of some other animal with widely different habits and structure ?
Can we believe that natural selection could produce, on the one hand,
an organ of trifling importance, such as the tail of a giraffe, which
serves as a fly-flapper, and, on the other hand, an organ so wonderful
as the eye ?
Thirdly, can instincts be acquired and modified through natural
selection ? What shall we say to the instinct which leads the bee to
make cells, and which has practically anticipated che discoveries of
profound mathematicians ?
246 EVOLUTION, GENETICS, AND EUGENICS
Fourthly, how can we account for species, when crossed, being
sterile and producing sterile offspring, whereas, when varieties are
crossed, their fertility is unimpaired ?
ANSWER TO THE FIRST DIFFICULTY
On the Absence or Rarily of Transitional Varieties. — As natural
selection acts solely by the preservation of profitable modifications,
each new form will tend in a fully stocked country to take the place of,
and finally to exterminate, its own less improved parent-form and
other less-favored forms with which it comes into competition. Thus
extinction and natural selection go hand in hand. Hence, if we look
at each species as descended from some unknown form, both the parent
and all the transitional varieties will generally have been exterminated
by the very process of the formation and perfection of the new
form.
But, as by this theory innumerable transitional forms must have
existed, why do we not find them embedded in countless numbers in
the crust of the earth? It will be more convenient to discuss this
question in the chapter on the Imperfection of the Geological Record;
and I will here only state that I believe the answer mainly Ues in the
record being incomparably less perfect than is generally supposed.
The crust of the earth is a vast museum; but the natural collections
have been imperfectly made, and only at long intervals of time.
ANSWER TO THE SECOND DIFFICULTY: ORGANS OF EXTREME
PERFECTION AND COMPLICATION
To suppose that the eye with all its inimitable contrivances for
adjusting the focus to different distances, for admitting different
amounts' of light, and for the correction of spherical and chromatic
aberration, could have been formed by natural selection, seems, I
freely confess, absurd in the highest degree. When it was first said
that the sun stood still and the world turned round, the common sense
of mankind declared the doctrine false; but the old saying of Vox
populi, vox Dei, as every philosopher knows, cannot be trusted in
science. Reason tells me, that if numerous gradations from a simple
and imperfect eye to one complex and perfect can be shown to exist,
each grade being useful to its possessor, as is certainly the case; if
further, the eye varies and the variations be inherited, as is likewise
certainly the case; and if such variations should be useful to any ani-
mal under changing conditions of life, then the difficulty of beheving
NATURAL SELECTION 247
that a perfect and complex eye could be formed by natural selection,
though insuperable by our imagination, should not be considered as
subversive of the theory. How a nerve comes to be sensitive to light,
hardly concerns us more than how life itself originated; but I may
remark that, as some of the lowest organisms, in which nerves cannot
be detected, are capable of perceiving light, it does not seem impossible
that certain sensitive elements in their sarcode should become aggre-
gated and developed into nerves, endowed with this special sensi-
bility.
In searching for the gradations through which an organ in any
species has been perfected, we ought to look exclusively to its lineal
progenitors; but this is scarcely ever possible, and w are forced to
look to other species and genera of the same group, that is to the
collateral descendants from the same parent-form, in order to see what
gradations are possible, and for the chance of some gradations hav-
ing been transmitted in an unaltered or little altered condition. But
the state of the same organ in distinct classes may incidentally throw
light on the steps by which it has been perfected.
The simplest organ which can be called an eye consists of an optic
nerve, surrounded by pigment-cells and covered by translucent skin
but without any lens or other refractive body We m.ay, however,
according to M. Jourdain, descend even a step lower and find aggre-
gates, of pigment-cells, apparently serving as organs of vision, without
any nerves, and resting merely on sarcodic tissue. Eyes of the above
simple nature are not capable of distinct vision, and serve only to dis-
tinguish light from darkness. In certain star-fishes, small depressions
in the layer of pigment which surrounds the nerve are filled, as de-
scribed by the author just quoted, with transparent gelatinous matter,
projecting with a convex surface, like the cornea in the higher animals.
He suggests that this serves not to form an image, but only to con-
centrate the luminous rays and render their perception more easy.
In this concentration of the rays we gain the first and by far the most
important step towards the formation of a true, picture-forming eye^
for we have only to place the naked extremity of the optic nerve,
which in some of the lower animals lies deeply buried in the body, and
in some near the surface, at the right distance from the concentrating
apparatus, and an image will be formed on it.
In the great class of the Articulata, we may start from an optic
nerve simply coated with pigment, the latter sometimes forming a sort
248 EVOLUTION, GENETICS, AND EUGENICS
of pupil, but destitute of a lens or other optical contrivance. With
insects it is now known that the numerous facets on the cornea of their
great compound eyes form true lenses, and that the cones include
curiously modified nervous filaments. But these organs in the
Articulata are so much diversified that Miiller formerly made three
main classes with seven subdivisions, besides a fourth main class of
aggregated simple eyes.
When we reflect on these facts, here given much too briefly, with
respect to the wide, diversified, and graduated range of structure in the
eyes of the lower animals; and when we bear in mind how small the
number of all Hving forms must be in comparison with those which
have become extinct, the difficulty ceases to be very great in beUeving
that natural selection may have converted the simple apparatus of an
optic nerve, coated with pigment and invested by transparent mem-
brane, into an optical instrument as perfect as is possessed by any
member of the Articulate Class.
He who will go thus far, ought not to hesitate to go one step fur-
ther, if he finds on finishing this volume that large bodies of facts,
otherwise inexplicable, can be explained by the theory of modification
through natural selection; he ought to admit that a structure even as
perfect as an eagle's eye might thus be formed, although in this case
he does not know the transitional states. It has been objected that
in order to modify the eye and still preserve it as a perfect instrument,
many changes would have to be effected simultaneously, which, it is
assumed, could not be done through natural selection; but as I have
attempted to show in my work on the variation of domestic animals,
it is not necessary to suppose that the modifications were all simulta-
neous, if they were extremely slight and gradual. Different kinds of
modification would, also, serve for the same general purpose: as
Mr. Wallace has remarked, "if a lens has too short or too long a
focus, it may be amended either by an alteration of curvature, or an
alteration of density; if the curvature be irregular, and the rays do not
converge to a point, then any increased regularity of curvature will be
an improvement. So the contraction of the iris and the muscular
movements of the eye are neither of them essential to vision, but
only improvements which might have been added and perfected at any
stage of the construction of the instrument. " Within the highest
division of the animal kingdon, namely, the Vertebrata, we can start
from an eye so simple, that it consists, as in the lancelet. of a little
NATUR.\L SELECTION 249
sack of transparent skin, furnished with a nerve and lined with pig-
ment, but destitute of any other apparatus. In fishes and reptiles,
as Owen has remarked, " the range of gradations of dioptric structures
is very great. " It is a significant fact that even in man, according to
the high authority of Virchow, the beautiful crystalline lens is formed
in the embryo by an accumulation of epidermic cells, lying in a sack-
Uke fold of the skin; and the vitreous body is formed from embryonic
sub-cutaneous tissue. To arrive, however, at a just conclusion
regarding the formation of the eye, with all its marvellous yet not
absolutely perfect characters, it is indispensable that the reason should
conquer the imagination; but I have felt the difficulty far too keenly
to be surprised at others hesitating to extend the principle of
natural selection to so starthng a length.
It is scarcely possible to avoid comparing the eye with a telescope.
We know that this instrument has been perfected by the long-
continued efforts of the highest human intellects; and we naturally
infer that the eye has been formed by a somewhat analogous process.
But may not this inference be presumptuous ? Have we any right to
assume that the Creator works by intellectual powers like those of
man ? If we must compare the eye to an optical instrument, we ought
in imagination to take a thick layer of transparent tissue, with spaces
filled with fluid, and with a nerve sensitive to light beneath, and then
suppose every part of this layer to be continually changing slowly in
density, so as to separate into layers of different densities and thick-
nesses, placed at different distances from each other, and with the sur-
faces of each layer slowly changing in form. Further we must suppose
that there is a power, represented by natural selection or the survival
of the fittest, always intently watching each slight alteration in the
transparent layers; and carefully preserving each which, under varied
circumstances, in any way or in any degree, tends to produce a dis-
tincter image. We must suppose each new state of the instrument to
be multiplied by the million; each to be preserved until a better one
is produced, and then the old ones to be all destroyed. In living
bodies, variation will cause the slight alterations, generation will
multiply them almost infinitely, and natural selection will pick out
with unerring skill each improvement. Let this process go on for
millions of years; and during each year on millions of individuals of
many kinds; and may we not beUeve that a Uving optical instrument
might thus be formed as superior to one of glass, as the works of the
Creator are to those of man ?
250 EVOL-UTION, GENETICS, AND EUGENICS
DAfiWTN's SUMMARY OF HIS ANSWER TO THE THIRD DIFFICULTY, THAT OF ACCOUNTING
FOR THE ACQUISITION AND MODIFICATION OF INSTINCTS
THROUGH NATURAL SELECTION
I have endeavored in this chapter briefly to show that the mental
qualities of our domestic animals vary, and that the variations are
inherited. Still more briefly I have attempted to show that instincts
vary slightly in a state of nature. No one will dispute that instincts
are of the highest importance to each" animal. Therefore there is no
real difficulty, under changing conditions of life, in natural selection
accumulating to any extent slight modifications of instinct which are
in any way useful. Tn many cases habit or use and disuse have prob-
ably come into play. I do not pretend that the facts given in this
chapter strengthen in any great degree my theory; but none of the
cases of difficulty, to the best of my judgment, anniliilate it. On the
other hand, the fact that instincts are not always absolutely perfect
and are liable to mistakes: that no instinct can be shown to have been
produced for the good of other animals, though animals take advantage
of the instincts of others; that the canon in natural history, of
"Natura non facit saltum," is applicable to instincts as well as to cor-
poreal structure, and is plainly explicable on the foregoing views, but
is otherwise inexplicable, all tend to corroborate the theory of natural
selection.
This theory is also strengthened by some few other facts in regard
to instincts; as by that common case of closely allied, but distinct,
species, when inhabiting distant parts of the world and hvmg under
considerably different conditions of life, yet often retaining nearly the
same instincts. For instance, we can understand, on the principle of
mheritance, how it is that tlie thrush of tropical South America Unes
its nest witli mud, in the same peculiar manner as does our British
thrush; how it is that the Hornbills of Africa and India have the same
extraordinary instinct of plastering up and imprisoning the females
in a hole in a tree, with only a small hole left in the plaster through
which the males feed them and their young when hatched; how it is
that the male wrens (Troglodytes) of North America build "cock-
nests," to roost in, like the males of our Kitty- wrens, a habit wholly
unlike that of any other known bird. Finally, it may not be a logical
deduction, but to my imagination it is far more satisfactory to look
at such instincts as the young cuckoo ejecting its foster-brothers,
ants making slaves, the larvae of ichneumonidae feeding within the
live bodies of caterpillars, not as specially endowed or created
NATUR/VL SELECTION 251
Instincts, but as small consequences of one general law leading to the
advancement of all organic beings, namely, multiply, vary, let the
strongest live and the weakest die.
darwin's summary of his answer to the difficulty as to the inability of
natural selection to account for the fact that species when crossed
are sterile or produce sterile offspring, whereas when v/vrieties
are crossed their fertility is unimpaired
First crosses between forms", sufficiently distinct to be ranked as
species, and their hybrids, are very generally, but not universally
sterile. The sterility is of all degrees, and is often so slight that the
most careful experimentalists have arrived at diametrically opposite
conclusions in ranking forms by this test. The sterility is innately
variable in individuals of the same species, and is eminently suscept-
ible to the action of favorable and unfavorable conditions. The degree
of sterility does not strictly follow systematic affinity, but is governed
by several curious and complex laws. It is generally different, and
sometimes widely different in reciprocal crosses between the same two
species. It is not always equal in degree in a first cross and in the
hybrids produced from this cross.
In the same manner as in grafting trees, the capacity in one species
or variety to take on another, is incidental on differences, generally
of an unknown nature, in their vegetative systems, so in crossing, the
greater or less facility of one species to unite with another is incidental
on unknown differences in their reproductive systems. There is no
more reason to think that species have been specially endowed with
various degrees of sterility to prevent their crossing and blending in
nature, than to think that trees have been specially endowed with
various and somewhat analogous degrees of difficulty in being grafted
together in order to prevent their inarching in our forests.
The steriUty of first crosses and of their hybrid progeny has not
oeen acquired through natural selection. In the case of first crosses
it seems to depend on several circumstances; in some instances in
chief part on the early death of the embryo. In the case of hybrids,
it apparently depends on their whole organization having been dis-
turbed by being compounded from tv/o distinct forms; the sterility
being closely allied to that which so frequently affects pure species,
when exposed to new and imnatural conditions of life. He who will
explain these latter cases will be able to explain the sterility of hybrids.
This view is strongly supported by a parallehsm of another kind:
namely, that, firstly, slight changes in the conditions of life add to tbi?
252 EVOLUTION, GENETICS, AND EUGENICS
vigor and fertility of all organic beings; and secondly, that the cross-
ing of forms, which have been exposed to slightly different conditions
of life or which have varied, favors the size, vigor, and fertility of their
offspring. The facts given on the sterility of the illegitimate unions
of dimorphic and trimorphic plants and of their illegitimate progeny,
perhaps render it probable that some unknown bond in all cases con-
nects the degree of fertility of first unions with that of their offspring.
The consideration of these facts on dimorphism, as well as of the results
of reciprocal crosses, clearly leads to the conclusion that the primary
cause of the steriUty of crossed species is confined to differences in their
sexual elements. But why, in the case of distinct species, the sexual
elements should so generally have become more or less modified, lead-
ing to their mutual infertility, we do not know; but it seems to stand in
some close relation to species having been exposed for long periods of
time to nearly uniform conditions of life.
It is not surprising that the diihculty in crossing any two species,
and the steriUty of their hybrid offspring, should in most cases corre-
spond, even if due to distinct causes: for both depend on the amount
of difference between the species which are crossed. Nor is it sur-
prising that the facihty of effecting a first cross, and the fertility of the
hybrids thus produced, and the capacity of being grafted together —
though this latter capacity evidently depends on widely different cir-
cumstances— should all run, to a certain extent, parallel with the
systematic affinity of the forms subjected to experiment; for system-
atic affinity includes resemblances of all kinds.
First crosses between forms known to be varieties, or sufi&ciently
alike to be considered as varieties, and their mongrel offspring, are
very generally, but not, as is so often stated, invariably fertile. Nor
is this almost universal and perfect fertiUty surprising, when it is
remembered how liable we are to argue in a circle with respect to
varieties in a state of nature; and when we remember that the greater
number of varieties have been produced under domestication by the
selection of mere external differences, and that they have not been
long exposed to uniform conditions of Ufe. It should also be espe-
cially kept in mind that long-continued domestication tends to elimi-
nate sterility, and is therefore little likely to induce this same quahty.
Independently of the question of fertiHty, in all other respects there
is the closest general resemblance between hybrids and mongrels,
in their variability, in their power of absorbing each other by repeated
crosses, and in their inheritance of characters from both parent-forms.
NATURAL SELECTION 253
Finally, then, although we are as ignorant of the precise cause of the
sterility of first crosses and of hybrids as we are why animals and
plants removed from their natural conditions become sterile, yet the
facts given in this chapter do not seem to me opposed to the beUef that
species aboriginally existed as varieties.
CHAPTER XVIII
CRITIQUE OF DARWINISM
The last chapter deah with the central ideas of Darwin as told by
himself. Some of the chief objections to the theory were also presented
as Darwin saw them, and his own answers to these objections were
given. These four objections are not by any means all that Darwin
foresaw, for he presented in another chapter a discussion of "Miscel-
laneous Objections to the Theory of Natural Selection." Before
entering upon a general criticism of Darwinism, it would be advanta-
geous to have before us a brief and pointed summary of Darwin's
theory — natural selection — now known technically as Darwinism.
The writer knows of no better short statement of the true content of
Darwinism than the following summary by Professor Vernon L.
Kellogg.
SUMMARY OF DARWIN'S NATURAL-SELECTION THEORY*
Darwinism may be defined as a certain rational, causo-mechanical
(hence, non-teleologic) explanation of the origin of new species. The
Darwinian explanation rests on certain observed facts, and certain
inductions from these facts. The observed facts are: (i) the increase
by multipUcation in geometrical ratio of the individuals in every
species, whatever the kind of reproduction which may be pecuhar to
each species, whether this be simple division, sporulation, budding,
parthenogenesis, conjugation and subsequent division, or amphimixis
(sexual reproduction); (2) the always apparent slight (to greater)
variation in form and function existing among all individuals even
though of the same generation or brood; and (3) the transmission,
with these inevitable slight variations, by the parent to its offspring
of a form and physiology essentially like the parental. The inferred
(also partly observed) facts are: (i) a lack of room and food for all
these new individuals produced by geometrical multiplication and
consequently a competition (active or passive) among those individuals
having any ecologic relations to one another, as, for example, among
' From V. L. Kellogg, Darwinism- To-Day (copyright 1907). Used by per-
mission of the publishers, Henry Holt & Company.
254
CRITIQUE OF DARWINISM 255
those occupying the same locality, or needing the same food, or needing
each other as food; (2) the probable success in this competition of
those individuals whose sUght differences (variations) are of such a
nature as to give them an advantage over their confreres, which
results in saving their life, at least until they have produced offspring;
and (3) the fact that these "saved" individuals will, by virtue of the
already referred to action of heredity, hand down to the offspring
their advantageous condition of structure and physiology (at least, as
the "mode" or most abundantly represented condition, among the
offspring).
"The competition among individuals and kinds (species) of organ-
isms may fairly be called a struggle. This is obvious when it is active,
as in actual personal battling for a piece of food or in attempts to
capture prey or to escape capture, and less obvious when it is passive,
as in the endurance of stress of weather, hunger, thirst, and untoward
conditions of any kind. The struggle is, or may be, for each individual
threefold in nature: (i) an active struggle or competition with other
individuals of its own kind for space in the habitat, sufficient share of
the food, and opportunity to produce offspring in the way peculiar
and common to its species; (2) an active or passive struggle or compe-
tition with the individuals of other species, which may need the same
space and food as itself, or may need it or its eggs or young for food;
and (3) an active (or more usually passive) struggle with the physico-
chemical external conditions of the world it lives in, as varying
temperature and humidity, storms and floods, and natural catas-
trophes of all sorts. For any individual or group of individuals any of
these forms of struggle may be temporarily ameliorated, as is (i) the
intra-specific struggle among the thousands of honey-bee individuals
living together altruistically, in one hive, or (2) the inter-specifiC
struggle, when two species live together symbiotically as the hermit
crab Eupagurus and the sea-anemone Podocoryne, or (3) the struggle
against untoward natural conditions as in special times or places
of highly favourable climate, etc. Or for any individual or group
of individuals all forms of the struggle may be coincidently active
and severe. The resultant of these existing conditions is, accord-
ing to Darwin and his followers, an inevitable natural selection of
individuals and of species. Thousands must die where one or ten
may live to maturity (i.e., to the time of producing young). Which
ten of the thousand shall live depends on the slight but sufficient
advantage possessed by ten individuals in the comolex struggle for
256 EVOLUTION, GENETICS, AND EUGENICS
existence due to the fortuitous possession of fortunate congenital
differences (variations). The nine hundred and ninety with unfortu-
nate congenital variations are extinguished in the struggle and with
them the opportunity for the perpetuation (by transmission to the
offspring) of their particular variations. There are thux^* left ten to
reproduce their advantageous variations. The offspring of the ten of
course will vary in their turn, but will vary around the new and
already proved advantageous parental condition: among the thou-
sand, say, offspring of the original saved ten the same limitations of
space and food will again work to the killing off before maturity of
nine hundred and ninety, leaving the ten best equipped to reproduce.
This repeated and intensive selection leads to a slow but steady and
certain modification through the sucrp"=!5ive generations of the form
and functions of the species; a modification always toward adapta-
tion, toward fitness, toward a moulding of the body and its behaviour
to safe conformity with external conditions. The exquisite adapta-
tion of the parts and functions of the animal and plant as we see it
every day to our infinite admiration and wonder has all come to exist
through the purely mechanical, inevitable weeding out and selecting
by Nature (by the environmental determining of what may and what
may not live) through uncounted generations in unreckonable time.
This is Darwin's causo-mechanical theory to explain the transforma-
tion of species and the infinite variety of adaptive modification. A
rigorous automatic Natural Selection is the essential idea in Darwin-
ism, at least in Darwinism as it is held by the present-day followers
of Darwin. "
OBJECTIONS TO DARWINISM
I. Darwin in a letter to his friend Hooker (January 11, 1844)
expresses his contempt of Lamarck's ideas in the following words:
"Heaven defend me from Lamarck's nonsense of a 'tendency to pro-
gression,' 'adaptations from the slow willing of animals,' etc
Lamarck's work appeared to me to be extremely poor; I got not a
fact or idea from it."
In spit€ of these views Darwin's Origin of Species is interlarded
with Lamarckian explanations. Whenever the author feels the short-
comings of the selection factor he lapses into an explanation involving
the idea that the effects of use and disuse of organs are inherited.
Followers of Darwin, especially Weismann, felt this to be the chief
defect in the fabric of Darwinism and bent their efforts chiefly toward
purging Darwinism of all taint of Lamarckism.
CRITIQUE OF DARWINISM 257
2. Darwin insisted upon the idea that minute fluctuating varia-
tions, which we now know are to a large extent non-heritable, were
the principal, if not the sole, materials for natural selection to work
upon. He knew of a considerable number of "sports" or "saltatory
variations" (now called mutations), but considered these too infre-
quent to furnish the necessary basis for selection. We now know
that mutations may be as small as fluctuating variations or as large
as "sports" and that they are of much more frequent occurrence
than Darwin supposed.
3. Darwin considered all variations as heritable. He did not
distinguish between somatic variations and germinal variations. In
fact, as we learn from a study of his pangenesis theory, he considered
all variations as in the first instance somatic, and subsequently
transferred by means of gemmules to the germ cells. Every somatic
variation, whether induced by use, disuse, in response to environ-
mental stimulus, or through mere spontaneous variability, was sup-
posed to be able to give off gemmules into the blood stream that
would carry to the germ cells the physical basis of the varying charac-
ter. The pangenesis mechanism is now known to have no basis
in fact.
4. The natural-selection theory is based upon a mistaken concep-
tion of the methods of artificial selection. Darwin believed, without
having any proof for this beHef, that the way in which domestic
varieties had been so profoundly modified at the hands of man was
by the conscious or unconscious selection of slight fluctuating varia-
tions in favorable or desired directions, and that this resulted in the
cumulative improvement or enhancement of the desired characters
over a long series of generations. Darwin supposes that the radically
changed conditions of domestication hasten and stimulate variability,
thus offering a better opportunity for selection. Transferring this
idea to nature, he thinks that changed natural conditions stimulate
variability, just as does domestication, and that this is seized upon by
natural selection to make for adaptation to the new environment and
the resultant origin of new species.
Our modern experimental studies have shown that somatic
modifications due to environmental changes are not hereditary, and
that all of the recent domestic varieties whose origin has been observed
have been the result of suddenly appearing germinal variations or
mutations, that arrive fully formed and cannot be improved by selec-
tion, except that they usually need to be selected out or isolated in
258 EVOLUTION, GENETICS, AND EUGENICS
order to prevent swamping out through mtercrossing with the
parent-type.
5. Objection has frequently been made to Darwin's idea of the
purely .fortuitous or chance character of variations. According to
this view variations occur in all structures and in all directions at
haphazard, so that there would be the widest possible opportunity for
a given adaptive variation to occur just when the circumstances
would demand. It now appears that variations do not occur in all
directions in random fashion, but that they tend to follow certain
definite paths of change; in other words, variations are, to a consider-
able extent at least, orthogenetic. If variations really tend to follow
certain definite lines, owing to purely internal causes, natural selection
would be unnecessary, at least until orthogenesis went too far for the
good of the species, or far enough to be of real importance in the
struggle for existence.
6. The difficulty of explaining how natural selection could make
use of the initial stages of adaptive structures is obvious. It is incon-
ceivable that the first, almost imperceptible variation in a favorable
direction could be of selective value, so as to effect the survival of the
individual or the relative number of its offspring. What would be the
advantage of the first few hairs of a mammal or the first steps
toward feathers in a bird when these creatures were beginning to
diverge from their reptihan ancestors? This objection is, of course,
based on the fluctuating-variation idea. If the mutation idea were
substituted, the difficulty would, to a great extent, clear up; for a
mutation might be of sufficient importance in one generation to have
selective value from the very first.
7. Natural selection is said to be incapable of explaining the origin
of coadaptive and highly complex adaptations whose effectiveness
depends upon the perfection of their adjustments to one another. For
example, we may refer to some of the perfected adaptations described
in chapter xiv. In the case of the electric organs of certain fish, the
Darwinian assumption would be that the first step in the direction of
an electric organ would be a ver>' small one, and that it was built up
Uttle by little by means of natural selection. But, say the critics, the
electric organ would be of no value until it became powerful enough
to impart an effective shock to ihe intruder, and this would not be
possible if the character began in a small way. The whole phenome-
non of protective resemblance is open to the same type of criticism.
As a specific example of this we may cite the case of the dried-leaf
CRITIQUE OF DARWINISM 25Q
butterfly, Kallima, previously described (pp. 226-228). In its present
condition this animal has a strikingly detailed resemblance to a dried
leaf, which is therefore doubtless of some value. But of what value
would be the first tiny change in the direction of resemblance ? Until
its resemblance became close enough actually to deceive the enemies of
butterflies, the critics claim, there would be no chance for selection to act
8. It is frequently objected that a vast number of characters of
organs are useless or non-adaptive and, as such, could not have arisen
through the instrumentality of natural selection. If these useless
characters, which are sometimes quite large and prominent, are
independent of natural selection, why do we need natural selection to
explain adaptive characters? It is also claimed that a vast number
of specific peculiarities are useless and therefore could not have helped
in the differentiation of species. It should be said in defense that
Darwin realized this difficulty quite as clearly as do his critics and
was greatly puzzled by it. His idea of correlated variability, however,
helps to answer it, for it may well be that many of these apparently
useless characters are correlated, or Unked in inheritance, with charac-
ters of supreme selective value such as general hardiness or great
fecundity. Darwin also points out that we are not in a position at
present to pronounce judgment on the value of many structures or
functions that have been adjudged non-adaptive.
9. Certain characters in organisms, past and present, have been
interpreted as overspecializations, organs that have evolved beyond
the range of usefulness or that are more elaborate than is demanded
for survival under the conditions of Hfe. The case of the extinct Irish
elk is often cited as an example of overspecialization. This group of
animals went to extremes in the development of size and elaboration
of horns far beyond the range of usefulness, so that it is said to have
brought about the extinction of the race. Natural selection, which is
supposed to have brought the horns up to the point of adaptive
perfection, should have kept them within the bounds of usefulness.
Again, the enormously overgrown and overspecialized dinosaurs
of long ago are thought of as having followed their lines of evolution
far beyond the point of greatest effectiveness and adaptability.
10. The rudimentation of structures, which is such a common
phenomenon in nature, is said to meet with no adequate explanation
on a selection basis. The case of the whale's vestigial hind limbs is
a case in point. Darwin's explanation would be that under aquatic
conditions the first whale ancestors would be handicapped by hind
26o EVOLUTION, GENETICS, AND EUGENICS
legs and that any decrease in their size, which would be enhanced by
disuse, would be of advantage. This might seem reasonable during
the main period of limb reduction, but, after the limb is reduced to a
subcutaneous rudiment, there could be little advantage in carrying
the rudimentation still farther. Some whales have the hind limbs
much more profoundly reduced than others, although they are all
thoroughly out of the way and involve no hindrance in swimming.
Any number of similar cases of the same kind might be cited. Darwin
had no explanation to offer except a resort to Lamarckism; but
Weismann, the ablest neo-Darwinian, offered the theory of panmixia
to cover this objection, a theory which is mentioned in chapter i and
will be discussed later.
11. It is objected that, unless favorable variations occur in a large
number of individuals at the same time, the character would be
swamped out by intercrossing with individuals not possessing the
favorable variation. The probability that such a swampuig-out
would occur was shown mathematically by various critics. By way
of answer to this objection there arose a number of "isolation theo-
ries," according to which favorably varying individuals would be
protected from back-crossing with the non-varying individuals. We
might also point out that the Mendelian laws of dominance and
segregation would serve to prevent loss of any new favorable character.
12. It is objected that natural selection might explain the "sur-
vival, but not the arrival, of the fittest." But Darwin met this
perfectly when he said: "Some have even imagined that natural
selection induces variabihty, whereas it implies only the preservation
of such variations as arise and are beneficial to the being under its
conditions of life,"
13. Criticism has been directed against natural selection because
of the fact that some of the supporters of Darwinism, notably Weis-
mann, have made the claim that natural selection is the sole cause of
evolution. This idea of the Allmacht or all-sufficiency of natural
selection was not Darwin's, as is clear from the following statement:
"I am convinced that natural selection has been the most important,
but not the exclusive means of modification."
14. It is objected that many, if not most, of the fluctuating varia-
tions with which Darwinism deals are purely quantitative or plus-
and-minus variations; whereas the differences between species are
qualitative. This is a serious objection and difficult to meet, yet a
fair defense has been formulated by leading neo-Darwinians.
CRITIQUE OF DARWINISM 261
15. There is a growing skepticism on the part of biologists as to
the extreme fierceness of the struggle for existence and of the conse-
quent rigor of selection. It may be answered that no very obvious
fierceness is impUed in the theory. So long as overproduction and a
shortage of space and food exists the struggle for existence is inevitable.
16. Special objections are offered to the subsidiary theory of
sexual selection. It is said that the type of sexual selection involving
active rivalry and battling for mates needs no special theory, inasmuch
as this is a mere phase of the struggle for the maintenance of the full
life, including the chance to leave offspring. It is against the other
side of sexual selection, which involves passivity on the part of the
male and active choice on the part of the female of the more beautiful
or otherwise attractive male, that objection is raised. It is claimed
that such choice imphes too high aesthetic powers in animals of
relatively poor vision and mentality. Experiments have been per-
formed with moths, in which the male and female coloration is
strikingly different, in order to determine whether females actually
do exercise any choice of mates that is based on considerations of
appearance. The result proved conclusively that color patterns have
no value in mating, but that the female is passive and mates with the
first male to present himself, while the male finds the female through
his exquisitely effective sense of smell.
We know now, however, that secondary sexual characters are
intimately bound up in a physiological way with the functioning of
the sex glands and are therefore doubtless to be interpreted as mere
non-adaptive correlative variations or else as examples of obhterative
coloration.
DEFENSE OF DARWINISM
In presenting these sixteen objections, we have in most cases
indicated the lines upon which the objections have been met, if they
have been met. Not all of these objections are considered serious at
the present time, for some are based upon lack of a fuU knowledge of
what Darwin actually wrote; others are largely academic in character
and fail to stand up under actual test; still others have been more or
less adequately met by subsidiary or supporting theories which have
been advanced by various neo-Darwinians.
Most of the special objections raised in this chapter have received
the attention of various able Darwinians, and the student of evolution
would doubtless be interested in the expert and fair-minded defense
262 EVOLUTION, GENETICS, AND EUGENICS
of Darwinism at the hands of Professor V. L. Kellogg as it appears in
his book Darwinism To-Day.
A much briefer and considerably more general defense is that of
J. L. Tayler, which is as follows.
GENERAL DEFENSE OF DARWINISM^
J. L. TAYLER
To realise how far the theory of selection is capable of explaining
the facts of organic evolution, it is necessary to bear in mind the
postulates in which the theory is founded.
1. It is obvious that natural selection can only act by preserv-
ing or eliminating the complete organism. Selection must therefore
be organismal. This Darwin and other selectionists have clearly
recognised.
2. As the whole organism must survive, if the favourable variation
or variations are to be preserved, it follows that certain minor un-
favourable variations may also be preserved if they happen to exist
in an individual which survives on account of its major favourable
variations. And since no individual is completely adapted to its
environment, it follows that there must be always a variable amount
of residual unfavourable variability in every organism.
3. This residual unfavourable variability may be of considerable
utiUty under changed conditions.
4. Complementary specialisation of parts, as Spencer has shown,
is favourable to successful competition, and as it is the whole organism
that is selected or eliminated, it follows that any weakness of one
specialised part, since it would disturb the balance of all, would be
detrimental. The more complex the organism, the more specialised
the structures, the more dependent one part will be on the others for
its existence, hence a complementary specialising tendency will be
favoured by selection, and therefore all struggles of one part of an
organism with another will be reduced to a minimum.
It is clear that there must be some underlying criterion which
determines whether any given organism shall be selected or not, and
that criterion must be the net result of its adaptabiHty to its environ-
ment. One organism may conceivably survive, by its possession of
a large number of small favourable variations, while another may
survive in virtue of a single valuable one, but in each case it would be
' From J. L. Tayler, "The Scope of Natural Selection," Natural Science, i8qq.
CRITIQUE OF DARWINISM 263
the whole value of that organism which determined its survival.
This fact is continually disregarded by opponents of the neo-Darwinian
position, yet this selection of the organism as a whole is the
fundamental postulate from which the theory of selection starts.
Thus it is not uncommom to read criticisms bearing on the early
development of some organ, in which the inadequacy of selection is
supposed to be proved by the writer demonstrating, or believing he
has demonstrated, the fact that the particular variation in question
must have been too small to be by itself of selection value. In many
cases the particular variation would, no doubt, if taken alone be, as
the objector asserts, too unimportant to be selected, but as it is the
whole organism that is selected, it is not logical to make an artificial
separation and study the development of one organ or structure
irrespective of the other organs with which it is in nature associated.
Every organ in its evolution must be considered in relation to the whole
of the particular organism in which that particidar stage of development
of that organ is found.
Starting, therefore, with this fact that the net value of adaptability
of the whole organism to its environment must be the basis which
determines selection or elimination, it will follow that certain lines of
development will result from the application of this criterion. In a
series of organisms placed under new conditions, elimination will
proceed along lines essential to bring about a proper adjustment to
the new conditions. If the offspring of these adjusted organisms
merely repeated in their generation the characters of the exterminated
as well as of the surviving organisms, that temporary adjustment
would be permanent as long as the conditions were unchanged. But
since the offspring are produced only by the surviving organisms,
selection is continually raised to higher and higher planes of adapta-
tion, and, therefore, as long as conditions remain constant, the
tendency of selection must be, as Darwin clearly saw, cumulative.
He did not, however, apparently see that from this cumulative
tendency definite variability must arise out of indefinite.
Selection in direct relation to climatic conditions is, therefore, of
very minor importance, while selection among the members of a
species and all forms of inter-organismal selection is of infinitely more
importance, since it is this interaction, produced by the offspring in
different degrees inheriting the advantages of both parents (both of
whom have survived on account of certain advantages), that leads to
the cumulative development and never-ending struggle for survival.
264 EVOLUTION, GENETICS, AND EUGENICS
Darwin came very near to this conception of definite variability when
he pointed out that " if a country were changing, the altered conditions
would tend to cause variation, not but what I beUeve most beings
vary at all times enough for selection to act on." Extermination
would expose the remainder to the "mutual action of a different set of
inhabitants, which I believe to be more important to the life of each
being than mere climate," and as "the same spot will support more
life if occupied by very diverse forms," it is evident that selection
will favour very great diversity of structure.
Bearing in mind this cumulative action of selection it will follow
that under constant or relatively constant conditions the struggle for
successful living will become more and more selective in character,
even if the actual number of inhabitants remain more or less the same
as when the struggle first commenced. The selection of variations
will thus tend to pass through certain more or less ill-defined, but
nevertheless, real stages. In proportion as the struggle becomes
intense, either from the number or from the increasing adaptability
of the organisms, or both, certain major essential adaptations, which
were necessary for the climatic and other more or less comparatively
simple conditions, will be supplemented by minor auxiliary variations
which in the earUer stages would not have appeared. And still later,
as more and more rigorous conditions of life were imposed, the advan-
tage would tend to rest with those organisms which possessed highly
co-ordinated adaptations, since this would entail more rapid respon-
siveness to environment.
As evolution advances from the unspecialised to the specialised,
and higher and higher forms of life come into being, with increasing
complexity and specialisation of parts entailing an increasingly delicate
adjustment of those parts to each other's needs, the relation of each
part to the whole organism becomes of more and more importance,
and it follows that selection must become more and more generalised
in its action. No single variation could be of service to any of the
higher forms of life unless it was in more or less complete harmony
with the whole tendency of the individual. The adjustment of parts
and their mutual interdependence make it essential for adaptation
that the relation of parts be preserved; consequently, correlated
minute favourable variations will tend to be more and more selected
as evolution passes from the unspecialised to the specialised forms of
life. This response of the whole organism should be still more delicate
in those forms of Hfe that are continually subjecting themselves to
CRITIQUE OF DARWINISM 265
changed conditions; hence this delicacy of adjustment is far more
necessary in the higher forms of animal life than in more stationary
plant organisms, and in the developing nervous systems of animals we
have just the central adjusting system that is required for these condi-
tions. With evolution of type there will thus be an increasingly definite
tendency given to organic, especially the animal, forms of life, if the
acting principle of evolution has been selectional. Selection is, therefore,
able to account for the steadily progressive tendency of life as a whole
without calling to its aid any unknown and doubtful perfecting principle.
To simimarise: Natural selection, acting on the whole organism,
tends to produce more and more definite tendencies in all surviving
forms of life, which tendencies are progressive and continuous in char-
acter. Variable conditions, by partially altering tlie line of selection,
induce a temporary indefiniteness. And lastly, the process of selec-
tion being itself able to be the indirect, though not the direct, cause
of those favourable variations, which it subsequently selects from, is
able to dispense with any subsidiary factors, provided it has a certain
number of elementary properties of life which afford sufficient material
to work with.
EXPERIMENTAL SUPPORT OP THE EFFECTIVENESS
OF NATURAL SELECTION
Weldon's experiments with the shore-crabs of Plymouth Sound. —
These experiments seem to show that under changed environmental
conditions natural selection acts upon minute fluctuating variations
of linear or quantitative tj^^e so as to produce an alteration in the
species; exactly as Darwinism would hold. A large breakwater was
so placed near the mouth of Plymouth Sound that the rate of flow of
the river water was greatly slowed down in certain regions. This
allowed an increased settling of the fine china-clay sediment that is
carried by the river, and the changed condition caused the death of
numerous crabs of the species Carcinus maenas. The question arose
as to whether the survivors and those that had perished showed any
consistent differences on the basis of which selection could be operat-
ing. Careful measurements of hundreds of individuals showed that
the mean breadth of frontum is slightly less in the survivors than in
the perished. Measurements were repeated in two subsequent years
and it was found that there was a progressive narrowing of the
frontum. As an experimental check upon these conclusions Weldon
266 EVOLUTION, GENETICS, AND EUGENICS
placed a number of crabs in a large aquarium, in which china-clay was
kept partly in suspension, and found that about half of them died.
Again the survivors were compared statistically with the perished and
the same relation was found to hold: that the survivors had a mean
frontal breadth distinctly narrower than that of the perished. Wel-
don concludes that his experiments "have demonstrated two facts
about these crabs; the first that their mean frontal breadth is dimin-
ishing year by year at a measurable rate, which is more rapid in males
than in females; the second is that this diminution in frontal breadth
occurs in the presence of a material, namely, fine mud, which is
increasing in amount, and which can be shown experimentally to
destroy broad-fronted crabs at a greater rate than crabs with narrower
frontal margins .... and I see no escape from the conclusion
that we have here a case of Natural Selection acting with great
rapidity, because of the rapidity with which the conditions of life
are changing."
Cesnola's experiments with Mantis. — To test the selective value
of color markings Cesnola fixed specimens of the brown and green
Mantis religiosa on plants, some of which were against harmonious,
others against disharmonious backgrounds. The result was that most
of those which were inconspicuous because of a harmonious back-
ground escaped, while most of the others were eaten up by birds.
Poulton's and Sanders' experiments with butterfly pupae. —
Numerous pupae of various colors were placed under conditions favor-
ing protective coloration and others under opposite conditions. The
conclusion was that protective coloration is a real survival factor, and
one that operates so as to give the protectively colored individual
a decided advantage in the struggle for existence.
Davenport's experiments with chickens. — A number of chickens,
some black, some white, and some barred or checkered in color, were
allowed to wander free in the fields. Hawks killed most of the whites
and many of the blacks, but spared, to a large extent, the less con-
spicuous checkered and barred types which are harder to detect
against a mixed background.
All of these experiments merely tend to show that discriminate
survival actually occurs, but only the experiment of Weldon has a
bearing on the possibility that mere quantitative changes of small
dimensions might under certain conditions be of selective value. We
badly need more experimental evidence of this sort and until this
is forthcoming; we shall have to admit that there is very little
CRITIQUE OF DARWINISM 267
experimental evidence in favor of the type of natural selection that
Darwin stood for.
THE PRESENT STATUt> OP NATURAL SELECTION
It has come to be rather generally believed that the natural
selection that Darwin himself believed in stands almosL unscathed as
one very important causal factor. In fact it is the only explanation
ever offered for adaptation that even approaches adequacy. As an
explanation of the origin of new types or new species it falls far short
of adequacy, and I think Darwin evidently realized this, although he
was unfortunate enough to entitle his book Origin of Species. As
an explanation of the origin and perfection of adaptation natural
selection has only one rival, the far less satisfactory Lamarckian theory
of the inheritance of acquired characters. There is a strong tendency
among geneticists to conclude that the modern germ-plasm hypothe-
sis, with the aid of mutations and the mechanism of Mendelian inherit-
ance, furnishes all the necessary explanation of the causes of evolution.
There is, however, marked dissent to this extreme position. In his
critique of De Vries's rather extreme position that the mutation
theory needs no aid from natural selection, Weismann shows in most
able fashion the inadequacy of mutations to account for adaptation,
and, in contrast, how well natural selection accounts for them.
In a very recent paper Professor C. C. Nutting attempts to show
that natural selection is still an important factor in evolution and quite
in harmony with both the mutation theory and Mendelism. We
perhaps can close the present chapter no more fittingly than by
quoting Professor Nutting's paper.
THE RELATION OF MENDELISM AND THE MUTATION THEORY
TO NATURAL SELECTION'
C. C. NUTTING
Two marked tendencies are evident in the history of any important
theory after its publication.
First. The followers of the discoverer carry the theory too far
and attempt too universal an application. This is manifestly true
of Wallace and Weismann who out-Darwined Darwin in their claims
for natural selection; of the followers of Mendel, such as Morgan and
■ From an address given before the Genetics branch of the American Associa-
tion for the Advancement of Science, December, 1920; Science, N.S., Vol. LIII.
268 EVOLUTION, GENETICS, AND EUGENICS
Pearl; and of many mutationists who make much greater claims for
that theory than does De Vries himself.
Second. Each generation of biologists is so occupied with its own
work and contemporary theories that it makes no real effort to
understand preceding theories.
This second tendency seems to me most marked in the attitude of
present workers along genetic lines towards natural selection. They
reveal an apparent lack of understanding of what Darwin really meant
and of what he claimed; and when criticising that theory they are
often engaged in the classic, but unprofitable, exercise of "fighting
windmills."
In view of these facts I hope you will pardon me if I present in as
few words as possible just what I beheve to be the main factors which
Darwin presented as resulting, in their actions and reactions, in
natural selection. These factors are three in number:
First. Heredity, by which the progeny tend to resemble their
parents more than they do other individuals of the same species.
Second. Individual variation, by which the progeny tend to
depart from the parental type and sometimes from the specific type.
Third. Geometrical ratio of increase, by which each species tends
to produce more individuals than can survive.
Each of these factors is practically axiomatic, so little is it open
to argument.
No one doubts the fact of heredity, whether pangenesis, Weis-
mannism or IMendeHsm be the correct expression of the mechanism
involved. These do not affect the fact of heredity nor invahdate it
as a factor in natural selection.
No one doubts the fact of variation; whether it is the "individual
variation" of Darwin, the "fluctuating variety" or the "mutation"
of De Vries. All that is necessary for Darwin's purpose is that there
be heritable variations. That there are such things all parties agree
and it matters Httle what you call them. They are adequate to act
as a factor in the Darwinian scheme.
No one doubts the fact of geometrical ratio of increase. It is a
proposition easily capable of mathematical demonstration, and that
is sufficient for Darwin's purpose.
These three factors, then, are not debatable as facts, whatever
their mechanism or causes.
A moment's reflection will show that geometrical ratio of increase
is a quantitative factor, giving an abundance of individuals from
CRITIQUE OF DARWINISM 269
which to select; that individual variation is a qualitative factor, giving
the differences which make a selection possible; and that heredity is
a conservative factor, holding fast those characters which better fit
the organism to its environment.
Now it seems to me that there is no possible outcome of the
necessary action and interaction of these three factors that would
not be a selection of some sort. Darwin thought it comparable in a
large way to the selection by which the stock-breeder improves his
herd, and therefore called it "natural selection," carefully guarding
the phrase from misinterpretation from the teleological angle as well
as from a too close parallelism between artificial and natural selection.
And I believe no one has suggested a more acceptable term for the
process of selection resulting from the interplay of natural laws.
Three outstanding theories have been advanced since the publica-
tion of the Origin, each involving an advance in our knowledge of
the mechanism of heredity on the one hand and the origin of varia-
tions on the other.
Weismann's theory of the continuity and stability of the germ
plasm was of immense importance in its discussion of the mechanism
of heredity, and his amphimixis gave a plausible explanation of the
origin of variations. His results were almost universally regarded as
confirming and greatly extending the scope of natural selection.
Mendel's theory regarding the purity of the gametes, their segre-
gation in the sex cells, and the whole complex Mendelian mechanism
so admirably described by Morgan; all of these, fascinating and
important as they are, deal with the mechanism rather than the fact
of heredity. In my opinion their acceptance or rejection does not
affect the status of natural selection as a theory of organic evolution.
But it is the theory of mutation that has furnished most of the
ammunition for the opponents of natural selection; and this in spite
of the fact that De Vries, the originator of the mutation theory,
expresses himself with great clarity as follows:
"My work claims to be in full accord with the principles laid down
by Darwin and to give a thorough and sharp analysis to some of the
ideas of variability, inheritance, selection, and mutation which were
necessarily vague in his time."
In 1904, when these words were published, there did seem to be
a sharp distinction between the ideas of Darwin and those of De Vries.
The former believed that natural selection acted upon many small
variations and accumulated them until the differences were sufficient
270 EVOLUTION, GENETICS, AND EUGENICS
to constitute new species; while De Vries claimed that new species
were formed by the sudden appearance by mutations of forms specifi-
cally distinct from the parents. That mutants were new species!
It seems evident that Darwin did not regard " saltatory evolution "
as the common method, while De Vries did.
Darwin beUeved that individual, usually small, variations fur-
nished the material on which selection acts; while De Vries thought
that mutants, usually large variations, furnished the material. Both,
however, believed thoroughly that natural selection was a vera causa of
evolution.
But things have changed greatly since 1904. The work of
Morgan, Castle, Jennings and a host of others has shown that many
mutations are so small, from a phenotypic standpoint, that they are
quantitatively no greater than the individual variations of Darwin;
and that they are heritable in the Mendelian way.
Castle produced a perfectly graded series of hooded rats which
exhibits almost ideally the steps by which a new form might be
oroduced by natural selection. He says:
"If artificial selection can, in the brief span of a man's lifetime,
mould a character steadily in a particular direction, why may not
natural selection in unHmited time also cause progressive evolution in
directions useful to the organism ?"
Jennings says:
"Sufiiciently thorough study shows that minute heritable varia-
tions— so minute as to represent practically continuous gradations —
occur in many organisms: some reproducing from a single parent,
others by biparental reproduction It is not estabhshed that
heritable changes must be sudden large steps; while these may occur,
minute heritable changes are more frequent. Evolution according to
the typical Darwinian scheme, through the occurrence of many small
variations and their guidance by natural selection, is perfectly con-
sistent with what experimental and paleontological studies show us;
to me it appears more consistent with the data than does any other
theory."
Many believers in mutation have been needlessly befuddled by
the diverse meanings of "variations" as used by Darwin and
De Vries. Darwin included in his "individual variations" both the
"fluctuating varieties" and the "mutations" of De Vries. Pheno-
typically they cannot even now be distinguished. De Vries hmiself
candidly admits that this was Darwin's attitude, thus proving himself
CRITIQUE OF DARWIN1S:\I 271
more clear-sighted than many of his followers. All that Darwin
needed for his purpose was proof of variations that are heritable, and
these are found in mutations, be they large or small.
Just as Alendelism has to do with the mechanism and not the fact
of heredity, so the mutation theory deals with the nature and not the
fact of variations. Neither, in my opinion, has any LmpHcation that
is antagonistic to the theory of natural selection.
The statement has been made that natural selection "originates
nothing" because it does not explain the origin of variations. I
must confess scant patience with this point of view. As well say
that the sculptor does not make the statue because he does not
manufacture the marble or his chisel; or that the worker in mosaic
originates nothing because he does not make the bits of stone which
he assembles in his design!
The material corresponding to the bits of stone in the mosaic is
furnished by heredity and variation, and its quantity by geometrical
ratio of increase. Natural selection acts in selecting and putting
together this material in the formation of new species. Thus, in a
true sense, it seems evident that something new has appeared —
something that is, but was not.
Another favorite figure, introduced I beHeve by De Vries, is
"Natural selection acts only as a sieve" determining which forms
shall be retained and which shall be discarded. This also seems to
me to fall short of a complete statement of the truth. If the material
subjected to the sifting process be regarded as changing with each
generation by the addition of variations, or mutations if you prefer,
some of which are favorable to a nicer adjustment of the species to its
environment, the figure would be more nearly correct. To make it
complete, however, the mesh of the sieve must change from generation
to generation so that a quantitative variation which would be preserved
in one generation would be discarded in a later one. But in this case
natural selection would do more than a sieve could do. It would
combine a number of favorable variations in the production of
something new, a new species!
In conclusion it seems to me that we are justified in maintaining
that Mendehsm and the mutation theory, while forming the basis of
the most brilliant and important advances in biological knowledge of
the last half-century, have neither weakened nor supplanted the
Darwinian conception of the "Origin of species by means of Natural
Selection."
CHAPTER XIX
OTHER THEORIES OF SPECIES-FORMING
THEORIES AUXILIARY TO NATURAL SELECTION
The post-Darwinian causo-mechanical theories fall quite naturally
into two categories: those that were devised by Darwinians to bolster
up natural selection and to free it of some of its most obvious objec-
tions, while retaining the essential features of the principle; and those
that were meant to be substitutes for and therefore quite opposed to
natural selection. The former theories have been classed as auxiliary,
and the latter as alternative theories to natural selection.
The several theories of Weismann will be dealt with first as the
most important of the purely auxiliary theories. "Panmixia" is
designed to explain, without recourse to Lamarckism and in harmony
with natural selection, the degeneration or atrophy of organs which
seemed to be inadequately explained by Darwin. "Germinal Selec-
tion" is supposed to explain the initial stages of adaptations and
allied phenomena, and thus to aid natural selection at one of its
weakest points.
weismann's theory of panmixia
The following statement of "panmixia, " as given by S. Herbert, is
concise and to the point:
"Cessation of selection as a cause of atrophy was first proposed
by Romanes. Later on, Weismann, whilst examining the validity of
the principle of use-inheritance, adopted the same idea, called by him
'panmixia,' in order to account for the dwindling and disappearance
of useless organs without having recourse to the Lamarckian factors.
If natural selection leads to the mating of select types, so that those
below a certain standard are prevented from propagating, it follows
that, with the cessation of selection, a general crossing of all types,
including the inferior ones, must take place, and thus lower the average
quahty of the whole stock. Weismann explained in this manner, for
instance, the prevalence of short-sightedness among civilized people.
The individuals with defective eyesight not being weeded out in
modem society, the sharpness of the eyesight of the population sinks
gradually. The same would apply to the deterioration of the teeth
272
OTHER THEORIES OF SPECIES-FORMING 273
of man, of the breast-gland of modem women, etc. The fact that
degeneration generally progresses so slowly, often taking thousands
and thousands of years, seemed to him a sufficient proof of the inade-
quacy of the Li marckian explanation. For if the effect of disuse were
transmitted in accumulating ratio in the successive generations, a
useless organ ought to disappear much more quickly.
"Weismann originally attributed a great effect to panmixia, and
considered that nearly 90 per cent, of the reduction of rudimentary
organs was due to it; the remainder, up to the complete loss of the
organs, being accounted for by reversed selection. Romanes was
much more modest in his estimate, and only allowed about 10 to 20
per cent, to this cause; while Lloyd Morgan gave only 5 per cent,
reduction of the original size. The final reduction of the organ to
zero is still not accounted for by any of these theories. Calling to aid
a failure of the force of heredity, as Romanes did, can hardly be con-
sidered a solution of the problem. First of all, the force of heredity
does not explain anything in the case. It only restates the problem.
We want to know what the force of heredity is. Secondly, if the force
of heredity does fail, we should have to explain why it wanes in some
cases and not in others. For the reduction and elimination of rudimen-
tary organs occurs apparently in the most irregular, haphazard manner.
" But can panmixia really reduce an organ ? Plate, in agreement
with Spencer, Eimer, and others, denies any such possibility. An
organ in a given condition of its existence varies around a mean or
average, the plus and minus variations generally being equally fre-
quent. It follows, therefore, that if all the existing variations are
crossed in propagation, the organ remains stationary. Selection only
improves the organ by cutting off the minus variations; the absence
of selection would simply leave the organ where it was before the
selection. At most it could only sink a very Uttle below the aver-
age. That this is so is seen in organs which are not under the sway of
selection at all. There are numberless such indiJBferent species charac-
ters, which ought gradually to dwindle and disappear, yet they remain
fairly constant, though continually exposed to the swamping effect
of panmixia. Panmixia may explain the functional degeneration of
an organ, but cannot explain its actual rudimentation. •
"Weismann himseK in later times abandoned panmbda as a suffi-
cient means of explanation, and resorted to a new theory — that of
germinal selection."'
' From S. Herbert, First Principles of Evolution (1913).
274 EVOLUTION, GENETICS, AND EUGENICS
weismann's theory of germinal selection
This theory was intended to rehabihtate the selection principle
which had lost a great deal of prestige because of the serious character
of the objections that had been raised against it, most of which have
been stated in the last chapter. The theory is believed by its author
to overcome all objections and doubts and to clear away all difficulties.
"Its strength," says Plate, "shall avail in four directions. First, it
shall explain how not only degeneration (physiological) but rudimenta-
tion (morphological) occurs in panmixia; second, why' exactly those
variations needed for the development of a certain adaptation appear
at the right time; third, how correlation of adaptation comes to exist;
and fourth, how variations are able to develop orthogenetically along
a definite line without depending on the necessity of a personal selec-
tion raising them step by step."
The essential feature of germinal selection, as the name implies,
is a transfer of the struggle for existence to the germ cell. The germ
cell is assumed to be a greatly reduced and simplified sample of the
characters of the whole organism. Each independently variable part
of the organism is supposed to be represented in the germ cell by a
minute physiological unit, unique in composition and capable of
reproducing the part in question in a new organism. These hereditary
units are called "determinants." Thus there is a different kind of
determinant for each muscle of the body, for each bone, or for each
independently functioning blood vessel; but, since all red blood cor-
puscles are alike, there would be only one determinant for all of them.
These determinants have to grow, and in cell division, to divide so as to
furnish to daughter germ cells all of the necessary determinants for a
whole individual. In their process of growth and multipHcation,
which goes on very rapidly at certain periods in the germ-cell cycle,
these determinants are in competition among themselves for the
available food supply. Some may be more favorably placed than
others or may be more active chemically than others. There will thus
arise a struggle within the germ for a chance to grow and reproduce
their kind, which, for these determinants, might be as bitter as would
be the struggle in nature among the. whole organisms that are in com-
petition for a' place in the world. A ' determinant favored, perhaps
accidentally or possibly because of inherent activity, by a good food
supply would wax stronger and grow faster and would, logically, pro-
duce a larger and more effective part when that particular germ cell
developed into an adult. Other gerrn cells that would be the offspring
OTHER THEORIES OF SPECIES-FORMING 275
of this germ cell would continue the struggle among determinants, and
it would be expected that the strong determinant would continue to
gain further advantage until the structure it represents reached its
maximum efficiency. Similarly, a determinant that was for some
reason deprived of its fair share of nutriment at any time would be
weakened and would produce in cell division weakened daughter
determinants. These in turn, unless especially favored, would wage
a losing fight and continue to grow smaller and weaker. Each indi-
vidual that might develop from such germ cells would have the charac-
ters whose determinant had been weakened in a reduced and
progressively degenerating condition. Finally, certain determinants
might starve entirely, and the part for which they stood would dis-
appear entirely from the ontogeny of the indi\ddual arising from these
germ cells.
In this way Weismann tried to explain the gradual dwindling
and the final elimination of useless organs. So also he would explain
definitely directed or orthogenetic variations, because germinal selec-
tion, once started in a given direction, continues automatically till
the goal of adaptiveness is reached.
The most potent objections to the theory of germinal selection are
as follows:
1. There should be, according to this theory, certain pronounced
tendencies in variability in definite directions, whereas fluctuating
variations nearly always distribute themselves evenly about the mean
or mode, and the same specific mean or mode is stationary in succes-
sive generations.
2. The theory implies too rapid and too general modification of
parts and therefore does not accord with the fact that species are
decidedly constant, except for occasional mutations, over long periods
of time. To meet this objection Weismann proposes a new self-
correcting mechanism that checks too rapid a development of char-
acters.
3. The over- or undernourishment of determinants might con-
ceivably induce size changes in characters already present, but could
hardly be responsible for the origin of qualitatively different characters.
4. Actual experiments in over- and underfeeding of animals have
been carried on by certain experimenters in order to test out the theory
of germinal selection. In the experiments of Kellogg, for example,
involving feeding silkworm larvae only one-eighth of the normal
amount of food, the only result was that the mature individuals were
276 EVOLUTION, GENETICS, AND EUGENICS
dwarfed in size. The relative sizes of the parts were unaltered, show-
ing that there had been no real struggle a.nong the determinants; for,
on the theory of germinal selection, only the stronger determinants
would have survived and the weaker ones would have been starved
out. Partial individuals, moreover, lacking certain organs and over-
developed in others, would have been produced instead of individuals
merely smaller in all parts.
These are the specific objections to the theory,but more important
than all of these is the general objection that follows:
"Thus Weismann," says Morgan,' "has piled up one hypothesis
on another as though he could save the integrity of the theory of
natural selection by adding new speculative matter to it. The most
unfortunate feature is that the new speculation is skilfully removed
from the field of verification, and invisible germs whose sole functions
are those which Weismann's imagination bestows on them, are brought
forward as though they could supply the deficiencies of Darwin's
theory. This is, indeed, the old method of the philosophizers of
nature. An imaginary system has been invented which attempts to
explain aU difficulties, and if it fails, then new inventions are to be
thought of. Thus we see where the theory of selection of fluctuatmg
germs has led one of the most widely known disciples of the Darwin-
ian theory.
"The worsjt feature of the situation is not so much that Weismann
has advanced new hypotheses unsupported by experimental evidence,
but that the speculation is of such a kind that it is, from its very
nature, imverifiable, and therefore useless. Weismann is mistaken
when he assumes that many zoologists object to his methods because
they are largely speculative. The real reason is that the speculation is
so often of a kind that cannot be tested by observation and experiment."
It seems almost impossible that the same Professor Morgan, who
wrote the foregoing paragraphs in 1903, should now be the leading
exponent of a theory of the mechanics of hereditary transmission
which depends upon hereditary units almost identical with Weis-
mann's "determinants," for the "genes" or "factors" of Morgan are
minute corporeal bodies in the germ cells which determine the charac-
ters of the adult individual.
The difference is, however, that the "genes" of Morgan are experi-
mentally demonstrable and have behmd them a vast amount of real
evidence for their existence.
From T. H. Morgan, Evolution and Adaptation.
OTHER THEORIES OF SPECIES-FORMING 277
In this chapter the writer has purposely avoided entering into the
more elaborate intricacies of the Weismannian theories of develop-
ment and heredity. The theories have been so generally discredited
and play so small a part in modem biological thought that it seems
useless to burden the reader's mind with needless complexities.
Certain other phases of Weismann's work, especially his ideas of
the germ plasm, its separateness and its continuity, are more appro-
priately studied in connection with genetics than at the present time.
ROUX'S THEORY OF INTRASELECTION OR THE BATTLE OF THE PARTS
In point of time this theory antedates Weismann's theories, since
it was proposed in i88i. In some respects it is a more acceptable
theory than germinal selection, but in others quite unacceptable.
The theory is designed primarily to explain the origin of the "fine and
delicate inner adaptations" of organisms, which do not come in con-
tact with the external environment and therefore could not be directly
affected by it. The idea is that there is a sort of struggle among the
tissues for a chance to develop in the direction of functional perfection.
Certain contacts, stresses, and pressures of part on part aid or hinder
the development of parts. Thus, where muscular pressure on bone
is greatest or weight borne by bone is greatest there will the most bony
tissue be laid down in the form of lamellae. The result is that any
given bone improves its structure by resistance to strain and pressure,
which is a case of improvement with use. We may then inquire how
such a change in the individual could affect the evolution of the race.
The only reply involves the adoption of a distinctly Lamarckian con-
cept, and this at present is quite unacceptable.
COINCIDENT SELECTION OR ORGANIC SELECTION
This theory has been masked under various guises. In addition
to the two titles given above, it has appeared under the names "onto-
genetic selection" and "orthoplasy." The main idea, according to
Herbert, is that "the individually acquired characters, though not
transmitted to the offspring, serve to tide the successive generations
over the critical period until germinal (inborn) variations of the
same kind appear which are inheritable. Ontogenetic (individually
acquired) adaptations and natural selection work together towards the
same end.
"This hypothesis would help to account for two related difficult
points in the theory of natural selection. Firstly, it would explain
the possibUity of the slow accumulation of germinal variations in theii
278 EVOLUTION, GENETICS, AND EUGENICS
first stages before they attain selective value; secondly, it would make
correlated adaptations feasible by supplying ontogenetic (individually
acquired) modifications, until the material for the appropriate germi-
nal adaptations arose.
"It has been objected to this theory that, since the individually
acquired modifications possess the main selective value in these
instances, there is no reason why the corresponding germinal variations
should be fostered at all. The individuals with the right, but slight,
congenital variations would have no advantage over their fellows who
show no such coincident variations. Nor is there any ground to
assume that individuals with the greatest amount of plastic modifica-
tion in a given direction will tend to exhibit similar innate variations
to a greater degree than those individuals not possessing this plas-
ticity."^
ISOLATION THEORIES
One of the objections to natural selection was that a favorable
variation appearing in one or a few individuals would be lost because
the individuals possessing it would interbreed with those not possessing
it, which presumably would be much more numerous. If there were
any kind of agency whose effect would be a partial or complete inhibi-
tion of intercrossing, the favorable character would have a chance to
survive.
Several related theories have arisen that deal with possible isola-
tive or segregative agencies that might serve to prevent promiscuous
intercrossiuK. and these have received the names geographic isolation,
climatic isolation, reproductive isolation, and physiologic isolation.
Geographic isolation. — Moritz Wagner was the founder of this
theory. He was a very extensive traveler and had a vast knowledge
of the details of the geographic distribution of animals. He believed
that isolation was absolutely essential in the differentiation of species.
He at first thought of his theory as auxiliary. to natural selection, but
• later, strongly impressed by the facts he had collected, he concluded
that isolation was an independent and alternative explanation of
species-forming. The underlying idea is one that has already received
attention in chapter vii, under "Evidences from Geographic Distri-
bution." Any successful species tends to spread in all directions until
checked by barriers. Some few members of a species under favorable
conditions may surmount the barrier and become isolated. The result
• From S. Herbert, First Principles of Evolution (1913)-
OTHER THEORIES OF SPECIES-FORMING 279
will be that, if they differ in" any definite way from the main body of
the species, a new elementary species will at once gain a foothold and
will evolve independently of the parent-species. If a certain area of
land is cut off from a continent so as to form a continental island, the
members of each species that have become isolated will evolve independ-
ently of the main body of the species and will have their own peculiar
lines of variation preserved from back-crossing with the parent-species.
Professor David Starr Jordan,* the leading proponent of the theory
of geographic isolation in America says:
"It is now nearly forty years since Moritz Wagner (1868) first
made it clear that geographic isolation {raumlicke Sonderimg) was a
factor or condition in the formation of every species, race, or tribe of
animal or plant we know on the face of the earth. This conclusion
is accepted as almost self-evident by every competent student of
species or of the geographical distribution of species. But to those
who approach the subject of evolution from some other side the
principles set forth by Wagner seem less clear. They have never been
confuted, scarcely ever attacked, so far as the present writer remem-
bers, but in the literature of evolution of the present day they have
been almost universally ignored. Nowadays much of our discussion
turns on the question of whether or not minute favorable variations
would enable their possessors little by little to gain on the parent stock,
so that a new race would be established side by side with the old, or on
whether a wide fluctuation or mutation would give rise to a new species
which would hold its own in competition with the parent. In theory,
either of these conditions might exist. In fact, both of them are
virtually unknown. In nature a closely related distinct species is not
often quite side by side with the old. It is simply next to it, geo-
graphically or geologically speaking, and the degree of distinction
almost always bears a relation to the importance or the permanence
of the barrier separating the supposed new stock from the parent
stock.
"A flood of light may be thrown on the theoretical problem of the
origin of species by the study of the probable, actual origin of species
with which we are familiar or of which the actual history or the actual
ramifications may in some degree be traced.
"In regions broken by few barriers, migration and interbreeding
t)eing allowed, we find widely distributed species, homogeneous in their
character, the members showing individual fluctuation and climatic
' Science, N.S., Vol. XXII (1905).
28o EVOLUTION, GENETICS, AND EUGENICS
effects, but remaining uniform in most regards, all representatives
slowly changing together in the process of adaptation by natural
selection. In regions broken by barriers which isolate groups of indi-
viduals we find a great number of related species, though in most cases
the same region contains a smaller number of genera or families. In
other words, the new species will be formed conditioned on isolation,
though these same barriers may shut out altogether forms of life which
would invade the open district.
" Given any species in any region, the nearest related species is not
likely to be found in the same region nor in a remote region, but in a
neighboring district separated from the first by a barrier of some sort.
"Doubtless wide fluctuations or mutations in every species are
more common than we suppose. With free access to the mass of
the species, these are lost through interbreeding. Isolate them as in
a garden or an enclosure or on an island, and these may be con-
tinued and intensified to form new species or races. Any horticul-
turist will illustrate this.
"In all these and in similar cases we may confidently affirm: The
adaptive characters a species may present are due to natural selection
or are developed in connection with the demands of competition.
The characters, non-adaptive, which chiefly distinguish species do not
result from natural selection, but from some form of geographical
isolation and the segregation of individuals resulting from it."
J. T. Gulick, another exponent of the efficacy of geographic isola-
tion in species-forming, has offered in evidence of his views facts about
the distribution of Hawaiian land snails. In the island of Oahu, for
example, the volcanic ridges have been eroded out into a series of
isolated valleys in the bottoms of which grows abundant vegetation,
while on the highlands there is Uttle but barren rock. The climatic
conditions of all the numerous valleys are the same, but, remarkably
enough, each variety of snail is confined not only to one island, but to
a definite valley on an island. The degree of difference, moreover,
between varieties is in proportion to the distance that separates them.
Guhck claimed that he was able to estimate the degree of divergence
between the snails of any two valleys by measuring the number of
miles that lay between them. Gulick's findings have been extensively
corroborated by recent explorations on the snails of other oceanic
islands by Crampton.
An interesting type of isolation that hardly can be termed geo-
graphic, yet is essentially equivalent to the latter m its effects, is found
OTHER THEORIES OF SPECIES-FORMESTG 281
in connection with the extensive group of lice (Mallophaga) that live
their whole lives buried among the feathers of birds or the hair of
mammals. These animals cannot fly and are quite effectively isolated
for Ufe upon a particular bird. They do, however, during the intimate
period of nesting, pass from parent to offspring, so that they may be
said to be isolated upon definite genetic lines. In the case, especially,
of birds like the eagle, a bird of long life and monogamous habits, the
parasite becomes as isolated as might be a race on a small island. The
result is that sometimes the lice of a single bird and its offspring are
of quite a distinct variety, which has become fixed by inbreeding until
a high degree of uniformity has been attained. Such an isolated
variety may be almost as distinct as a true species. Obviously in this
case, as in others, isolation must have had a real effect upon species-
forming quite apart from natural selection, except in so far as the unfit
variants have not survived.
The writer's impression is that isolation as a factor in evolution
has been undervalued by the majority of writers on the subject. It is
a highly important and essential factor in the estabUshment of species.
If natural selection m.ay be said to be the prime factor in producing
adaptations, isolation may be said to be the prime factor in species
differentiation, guided only within moderate limits by natural selection.
Biologic isolation. — The effects of this type of isolation are not
nearly so well established as are those of geographic isolation. Accord-
ing to this theory, differences in the rate of development or earliness
or lateness of the breeding season would serve to prevent certain
varieties from intercrossing. Only those individuals which were
sexually active simultaneously would mate, and individuals with
different breeding times and seasons would be isolated from one
another and would likely maintain the variations that arose in the
isolated stocks. The main weakness of this phase of isolation is,
however, that we have so little actual evidence that it is operative in
nature.
Reproductive isolation. — A much more real type of isolation than
the last named is involved in reproduction. Several conditions may
arise of entirely distinct sorts that will tend to inhibit mating at ran-
dom. The first agency has been called "assortative mating" and
implies a sort of race feeling involving either a special attraction of like
for like, based on similarity of odors, colors, etc., or an antipathy
toward opposites or unlikes. The inhibition to general mating may
involve a mere mechanical lack of fit in certain organs necessary for
282 EVOLUTION, GENETICS, AND EUGENICS
successful mating. Such conditions are readily observable between
closely allied species. Again, the prevention of intercrossing may
result from the appearance of a lowered interfertihty between the
variant individuals and those of the parent-stock. If individuals
varying in the same direction were even slightly more fertile inter se
than those varying in different directions there would be a progressive
tendency in a series of generations for the varying individuals to
diverge more and more markedly, and ultimately to become practi-
cally sterile except with members of their own group.
That environmental changes do frequently affect the fertility of
animals is seen when wild animals are kept in confinement. Rela-
tively few wild animals breed in captivity. Such a lowering of fer-
tihty as the result of environmental changes might restrict crossing
between unlike forms, while permitting it among the like ones.
Summary on isolation theories. — There is a great divergence of
opinion as to the importance of isolation as a causal factor in species-
forming. Some writers, such as D. S. Jordan and V. L. Kellogg, con-
sider isolation an indispensable, and therefore primary, factor; others,
especially geneticists, almost ignore it as an effective factor. Still
others, Uke the present writer, take a middle ground and conclude
that isolation, especially geographic isolation, has helped greatly in the
segregation and establishment of well-defined groups such as species
or varieties, the latter developing into the former after prolonged
isolation and the addition of new variations. Isolation theories, how-
ever, have no Ught to shed upon the difficult problem of adaptation,
and it is here that isolation is auxihary to natural selection.
THEORIES ALTERNATIVE TO NATURAL SELECTION
The three theories that have been offered by their authors as sub-
stitutes for natural selection are :
1. Theory of the inheritance of acquired characters, commonly called
Lamarckism: This theory has been outHned in the chapter on the
history of evolution (pp. i8 ff.). It will again be dealt with in con-
siderable detail in chapter xxxvdi. For the present, then, we may pa^^
by this theory without further comment.
2. The orthogenesis theories: These theories have already been
presented in suflScient detail for our purposes in chapter ii (pp. ;^2 ff.).
3. The mutation theory of Hugo De Vries: This theory has been
dealt with in chapter ii, and will be discussed in further detail in
:hajiter xxxvii.
OTHER THEORIES OF SPECIES-FORMLNG 283
4. The tetrakinelic theory of'H. F. Osborn: This is a recent restate-
ment in energistic terms, of the causo-mechanical basis of evolution.
It is placed in the next chapter, but cannot fully be understood until
the subject of genetics has been presented.
It is almost impossible satisfactorily to pursue a further study of
the causal factors of evolution without encroaching upon the field that
is now called genetics, and so we shall pass without further explana-
tions to a consideration of this field of experimental and analytical
evolution.
CHAPTER XX
A NEW COMPOSITE CAUSO-MECHANICAL THEORY OF
EVOLUTION (THE TETRAKINETIC THEORY)'
HENRY FAIRFIELD OSBORN
THE ENERGY CONCEPT OF LIFE
While we owe to matter and form the revelation of the existence
of the great law of evolution, we must reverse our thought in search
for causes and take steps toward an energy conception of the origin
of life and an energy conception of the nature of heredity.
So far as the creative power of energy is concerned, we are on sure
ground: in physics energy controls matter and form; in physiology
function controls the organ; in animal mechanics motion controls
and, in a sense, creates the form of muscles and bones. In every
instance some kind of energy or work precedes some kind of form,
rendering it probable that energy also precedes and controls the
evolution of life.
The total disparity between invisible energy and visible form is
the second point which strikes us as in favor of such a conception,
because the most phenomenal thmg about the heredity-germ is its
microscopic size as contrasted with the titanic beings which may rise
out of it. The electric energy transmitted through a small copper
wire is yet capable of moving a long and heavy train of cars. The
discovery by Becquerel and Curie of radiant energy and of the proper-
ties of radium shows that the energy per unit of mass is enormously
greater than the energy quanta which we were accustomed to associate
with units of mass; whereas, in most man-made machines with metallic
wheels and levers, and in certain parts of the animal machine con-
structed of muscle and bone, the work done is proportionate to the size
and form. The slow dissipation or degradation of energy in radium has
been shown by Curie to be concomitant with the giving off of an enor-
mous amount of heat, while Rutherford and Strutt declare that in a
very minute amount of active radium the energy of degradation would
entirely dominate and mask all other cosmic modes of transformation
' From H. F. Osborn, The Origin and Evolution of Life (copyright 1916}. Used
by special permission of the publishers, Charles Scribner's Sons.
284
THE TETRAKINETIC THEORY 285
of energy; for example, it far outweighs that arising from the gravita-
tional energy which is an ample supply for our cosmic system, the
explanation being that the minutest energy elements of which radium
is composed are moving at incredible velocities, approaching often
the velocity of light, i.e., 180,000 miles per second. The energy of
radium differs from the supposed energy of life in being constantly
dissipated and degraded; its apparently unlimited power is being
lost and scattered.
We may imagine that the energy which lies in the life-germ of
heredity is very great per unit of mass of the matter which contains
it, but that the life-germ energy, unlike that of radium, is in process
of accumulation, construction, conservation, rather than of dissipation
and destruction.
Following the time (1620) when Francis Bacon divined that heat
consists of a kind of motion or brisk agitation of the particles of
matter, it has step by step been demonstrated that the energy of heat,
of light, of electricity, the electric energy of chemical configurations,
the energy of gravitation, are all utilized in living as well as in Ufeless
substances. Moreover, no form of energy has thus far been discovered
in living substances which is peculiar to them and not derived from
the inorganic world. In a broad sense all these manifestations of
energy are subject to Newton's dynamical laws which were formulated
in connection with the motions of the heavenly bodies, but are found
to apply equally to all motions great or little.
These three fundamental laws are as follows:
I I
Corpus omne perseverare in statu suo Every body perseveres in its state of
quiescendi vel movendi uniformiter in rest, or of uniform motion in a right
directum, nisi quatenus illud a viribus line, unless it is compelled to change
impressis cogitur statum suum mutare. that state by forces impressed thereon.
II II
Mutationem motus proportionalem The alteration of motion is ever
esse vi motrici impressae, et f-.eri secun- proportional to the motive force im-
dum lineam rectam qua vis ilia im- pressed; and is made in the direction of
primitur. the right line in which that force is
impressed.
m ni
Actioni contrariam semper et aequa- To every action there is always
lem esse reactionem: sive corporum opposed an equal reaction: or the
duorum actiones in se mutuo semper mutual actions of two bodies upon each
esse aequales et in partes contrarias other are always equal, and directed to
dirigi. contrary parts.
286 EVOLUTION, GENETICS, AND EUGENICS
Newton's third law of the equality of action and reaction is the
foundation of the modern doctrine of energy, not only in the Newto-
nian sense but in the most general sense. Newton divined the prin-
ciple of the conservation of energy in mechanics; Rumford (1798)
maintained the universality of the laws of energy; Joule (1843)
estabUshed the particular principle of the conservation of energy,
namely the exact equivalence between the amount of heat produced
and the amount of mechanical energy destroyed; and Helmholtz, in
his great memoir Uber die Erhaltung der Kraft, extended this system
of conservation of energy throughout the whole range of natural
phenomena. A familiar instance of the so-called transformation of
znergy is where the sudden arrest of a cool but rapidly moving body
produces heat. This was developed as \.\ie first law of thermodynamics.
At the same time there arose the distinction between potential
energy, which is stored away in some latent form or manner so that
it can be drawn upon for work — such energy being exemplified me-
chanically by the bent spring, chemically by gunpowder, and elec-
trically by a Leyden jar — and kinetic energy, the active energy of
motion and of heat.
While all active mechanical energy or work may be converted
into an equivalent amount of heat, the opposite process of turning
heat into work involves more or less loss, dissipation, or degradation
of energy. This is known as the second law of thermodynamics and is
the outgrowth of a principle discovered by Sadi Carnot (1824) and
developed by Kelvin (1852, 1853). The far-reaching conception of
cyclic processes in energy enunciated in Kelvin's principle of the
dissipation of available energy puts a diminishing limit upon the
amount of heat energy available for mechanical purposes. The avail-
able kinetic energy of motion and of heat which we can turn into work
or mechanical effect is possessed by any system of two or more bodies
in virtue of the relative rates of motion of their parts, velocity being
essentially relative.
These two great dynamical principles that ' the energy of motion
can be converted into an equivalent amount of heat, and that a certain
amount of heat can be converted into a more limited amount of power
were discovered through observations on the motions of larger masses
of matter, but they are beUeved to apply equally to such motions as
are involved in the smallest electrically charged atoms (ions) of the
chemical elements and the particles flying off in radiant energy as
phosphorescence. Such movements of infinitesimal particles underlie
THE TETRAKINETIC THEORY 287
all the physicochemical laws of action and reaction which have been
obsen^ed to occur within living things. In all physicochemical
processes witliin and without the organism by which energy is cap-
tured, stored, transformed, or released the actions and reactions are
equal, as expressed in Newton's third law.
Actions and reactions refer chiefly to what is going on between
the parts of the organism in chemical or physical contact, and are
subject to the two dynamical principles referred to above. Inter-
actions, on the other hand, refer to what is going on between material
parts which are connected with each other by other parts, and cannot
be analyzed at all by the two great dynamical principles alone without
a knowledge of the structure which connects the interacting parts.
For example, in interaction between distant bodies the cause may be
very feeble, yet the potential or stored energy which may be liberated
at a distant point may be tremendous. Action and reaction are
chiefly simultaneous, whereas interaction connects actions and reac-
tions which are not simultaneous; to use a simple illustration: when
one pulls at the reins the horse feels it a Uttle later than the moment
at which the reins are pulled — there is interaction between the hand
and the horse's mouth, the reins being the interacting part. An
interacting nerve-impulse starting from a microscopic cell in the brain
may give rise to a powerful muscular action and reaction at some
distant point. An interacting enzyme, hormone, or other chemical
messenger circulating in the blood may profoundly modify the growth
of a great organism .
Out of these physicochemical principles has arisen the conception
of a living organism as composed of an incessant series of actions and
reactions operating under the dynamical laws which govern the
transfer and transformation of energy.
The central theory which is developed in our speculation on the
Origin of Life is that every physicochemical action and reaction
concerned in the transformation, conservation, and dissipation of
energy, produces also, either as a direct result or as a by-product a
physicochemical agent of interaction ■which permeates and affects the
organism as a whole or affects only some special part. Through such
interaction the organism is made a unit and acts as one, because the
activities of all its parts are correlated. This idea may be expressed
in the following simphfied scheme of the functions or physiology of the
organism :
288 EVOLUTION, GENETICS, AND EUGENICS
Action ]
AND > Interaction .
Reaction I
Action
AND
Reaction
Functions of the Functions of the Functions of the
Capture, Storage, Coordination, Balance, Capture, Storage,
and Release of Cooperation, Compensation, and Release of
Energy Acceleration, Retardation, Energy
of Actions and Reactions
Since it is known that many actions and reactions of the organ-
ism— such as those of general and locaUzed growth, of nutrition, of
respiration — are coordinated with other actions and reactions through
interaction, it is but a step to extend the principle and suppose that
all actions and reactions are similarly coordinated; and that while
there was an evolution of action and reaction there was also a cor-
responding evolution of interaction, for without this the organism
would not evolve harmoniously.
Evidence for such universality of the interaction principle has
been accumulating rapidly of late, especially in experimental medicine
and in experimental biology. It is a further step in our theory to
suppose that the directing power of heredity which regulates the initial
and all the subsequent steps of development in action and reaction,
gives the orders, hastens development at one point, retards it at
another, is an elaboration of the principle of interaction. In lowly
organisms like the monads these interactions are very simple; in
higher organisms like man these interactions are elaborated through
physicochemical and other agents, some of which have already been
discovered although doubtless many more await discovery. Thus we
conceive of the origin and development of the organism as a con-
comitant evolution of the action, reaction, and interaction of energy.
Actions and reactions are borrowed from the inorganic world, and
elaborated through the production of the new organic chemical
compounds; it is the peculiar evolution and elaboration of the physi-
cal principle of interaction which distinguishes the living organism.
Thus the evolution of hfe may be rewritten in terms of invisible
energy, as it has long since been written in terms of visible form. All
visible tissues, organs, and structures are seen to be the more or less
simple or elaborate agents of the different modes of energy. One
after another special groups of tissues and organs are created and co-
ordinated— organs for the capture of energy from the inorganic environ-
ment and from the life environment, organs for the storage of energy,
organs for the transformation of energy from the potential state into
THE TETRAKINETIC THEORY
289
the states of motion and heat. Olher agents o' control are evolved to
bring about a harmonious balance between the various organs and
tissues in which energy is released, hastened or accelerated, slowed down
or retarded, or actually arrested or inhibited.
In the simplest organisms energy may be captured while the
organism as a whole is in a state of rest; but at an early stage of life
special organs of locomotion are evolved by which energy is sought
out, and organs of prehension by which it may be seized. Along with
these motor organs are developed organs of cfense and defense of
many kinds, by means of which stored energy is protected from cap-
ture or invasion by other organisms. Finally, there is the most
mysterious and comprehensive process of all, by which all these
manifold modes of energy are reproduced in another organism.
THE FOUR COMPLEXES OF ENERGY
The theoretic evolution of the four complexes is somewhat as
follows:
1. In the order of time the Inorganic Environment comes first;
energy and matter are first seen in the sun, in the earth, in the air,
and in the water — each very wonderful complex of energies in itself.
They form, nevertheless, an entirely orderly system, held together by
gravitation, moving under Newton's laws of motion, subject to the
more newly discovered laws of thermodynamics. In this complex we
observe actions and reactions, the sum of the taking in and giving
out of energy, the conservation of energy. We also observe inter-
actions wherein the energy released at certain points may be greater
than the energy received, which is merely a stimulus for the beginning
of the local energy transformations. This energy is distributed among
the eighty or more chemical elements of the sun and other stars.
These elements are combined in plants into complex substances, gener-
ally with a storage of energy. Such substances are disintegrated into
simple substances in animals, generally with a release of energy. All
these processes are termed by us physicochemical.
2. With life something new appears in the universe, namely, a
union of ihe internal and external adjustment of energy which we
appropriately call an Organism. In the course of the evolution of life
every law and property in the physicochemical world is turned to
advantage; every chemical element is assembled in which inorganic
properties may serve organic functions. There is an immediate or
gradual separation of the organism into two complexes of energy,
sgo EVOLUTION, GENETICS, AND EUGENICS
namely, first, the energy complex of the organism, which is perishable
with the term of life of the individual, and second, the germ or heredity
substance, which is perpetual.
3. The idea that the germ is an energy complex is an as yet un-
proved hypothesis; it has not been demonstrated. The Heredity-Germ
in some respects bears a likeness to latent or potential interacting
energy, while in other resp cts it is entirely unique. The supposed
germ energy is n(U only cumulative but is in a sense imperishable, self-
perpetuating, and continuous during the whole period of the evolution
of life upon the earth, a conception which we owe chiefly to the law of
the continuity of the germ-plasm formulated by Weismann. Some
of the observed phenomena of the germ in Heredity are chiefly
analogous to those of interaction in the Organism, namely, directive
of a series of actions and reactions, but in g ^neral we know no complete
physical or inorganic analogy to the phenomena of heredity; they are
unique in nature.
4. With the multiplication and diversification of individual or-
ganisms there enters a new factor in the environment, namely, the
energ>' complex of the Life Environment.
Thus there are combined certainly three and, possibly, four com-
plexes of energy, of which each has its own actions, reactions, and
interactions. The evolution of life proceeds by sustaining these
actions, reactions, and interactions and constantly building up new
ones: at the same time the potentiaUty of reproducing these actions, re-
actions, and interactions in the course of the development of each new
organism is gradually being accumulated and perpetuated in the germ.
From the very beginning every individual organism is competing
with other organisms of its own kind and of other kinds, and the law
of the survival of the fittest is operating between the forms and func-
tions of organisms as a whole and between their separate actions,
reactions, and interactions. This, as Weismann pointed out, while
apparently a selection of the individual organism itself, is actually a
selection of the heredity-germ complex, of its potentialities, powers,
and predispositions. Thus Selection is not a form of energy, nor a
part of the energy complex; it is an arbiter between difi"erent com-
plexes and forms of energy; it antedates the origin of life just as
adaptation or fitness antedates the origin of Ufe, as remarked by
Henderson.
Thus we arrive at a conception of the relations of organisms to
each other and to their environment as of an enormous and always
THE TETRAKINETIC THEORY 291
increasing complexity, sustained through the interchange of energy.
Darwin's principle of the survival or elimination of various forms of
living energy is, in fact, adumbrated in the survival or elimination of
various forms of lifeless energy as witnessed among the stars and
planets. In other words, Darwin's principle operates as one of the
causes of evolution in making the lifeless and living worlds what they
now appear to be, but not as one of the energies of evolution. Selec-
tion merely determines which one of a combination of energies shall
survive and which shall perish.
The complex of four interrelated sets of ph^sicochemical energies
which I have previously set forth as the most fundamental biologic
scheme or principle of development may now be restated as follows:
In each organism the phenomena of life represent the action, reaction,
and interaction of four complexes of physicochemical energy, namely,
those of (/) the Inorganic Environment, (2) the developing Organism
{protoplasm and body-chromatin) , (j) the germ or Heredity-Chromatin,
{4) the Life Environment. Upon the resultant actions, reactions, and
interactions of potential and kinetic energy in each organism Selection
is constantly operating wherever there is competition with the correspond-
ing actions, reactions, and interactions of other organisms.
This principle I shall put forth in different aspects as the central
thought of these lectures, stating at the outset and often recurring
to the admission that it involves several unknown principles and
especially the largely hypothetical question whether there is a relation
between the action, reaction, and interaction of the internal energies
of the germ or heredity-chromatin with the external energies of the
inorganic environment, of the developing organism, and of its life
environment. In other words, while this is a principle which largely
governs the Organism, it remains to be discovered whether it also
governs the causes of the Evolution of the Germ.
As observed in the preface we are studying not one but four
simultaneous evolutions. Each of these evolutions appears to be
almost infinite in itself as soon as we can examine it in detail, but of
the four that of the germ or heredity-chromatin so far surpasses all
the others in complexity that it appears to us infinite.
The physicochemical relations between these four evolutions,
including the activities of the single and of the multiplying organisms
of the Life Environment, may be expressed in diagrammatic form as
follows:
292
EVOLUTION, GENETICS, AND EUGENICS
Organism A
Under
Newton's Laws of Motion
and
Modern Thermodynamics
Actions, Reactions, and
Interactiofts
of the
1. InorganicEnvironment:
physicochemical en-
ergies of space, of the
sun, earth, air, and
water.
2. Organism:
physicochemical en-
ergies of the devel-
oping individual in
the tissues, cells,
protoplasm, and cell-
chromatin.
3. Heredity-Germ:
physicochemical en-
ergies of the heredity-
chromatin included
in the reproductive
cells and tissues.
4. Life Environment:
physicochemical en-
ergies of other or-
ganisms.
Under
Darwin's Law
of
Natural Selection
Survival of the fittest:
competition, selec-
tion, and elimination
of the energies and
forms.
OSGANISMS B-Z
Under
Newton's Laws of Motion
and
Modern Thermodynamics
Actions, Reactions, and
Interactions
of the
1. InorganicEnvironment:
physicochemical en-
ergies of space, of the
sun, earth, air, and
water.
2. Organism:
physicochemical en-
ergies of the devel-
oping individual in
the tissues, cells,
protoplasm, and cell-
chromatin.
3. Heredity-Germ:
physicochemical en-
ergies of the heredity-
chromatin included
in the reproductive
cells and tissues.
4. Life Environment:
physicochemical en-
ergies of other or-
ganisms.
If a single name is demanded for this conception of evolution it
might be termed the tetrakinetic theory in reference to the four sets of
internal and external energies which play upon and within every
individual and every race. In respect to form it is a tetraplastic
theory in the sense that every living plant and animal form is plas-
tically moulded by four sets of energies. The derivation of this
conception of life and of the possible causes of evolution from the laws
which have been developed out of the Newtonian system, and from
those of the other great Cambridge philosopher, Charles Darwin,
are clearly shown in the above diagram.
PART IV
GENETICS
CHAPTER XXI
THE SCOPE AND METHODS OF GENETICS
DEFINITIONS
"Genetics is the science which seeks to account for the resem-
blances and the differences which are exhibited among organisms
related by descent." — Babcock and Clausen.
"Genetics may be defined as the science which deals with the
coming into being of organisms. It does not refer, however, to the first
creation of organic beings, but rather to the present every-day creation
of new individuals or new races. It refers particularly to the part that
parent organisms have in bringing new organisms into being and to the
influence which parents exert on the characteristics of their ofiFspring.
In this sense it is nearly equivalent to the term heredity." — W. E.
Castle.
"Heredity may be defined as organic resemblance based on de-
scent."— W. E. Castle.
"Heredity is commonly defined as the tendency of offspring to
develop characters like those of the parents." — Babcock and Clausen.
THE SCOPE AND METHODS OP GENETICS
Genetics is the study of evolution from a new point of view. The
great evolutionists of the past were devotees of the inductive method
in science which consists of collecting data and devising theories to
explain the data. None of the older evolutionists attempted to put
their theories to experimental tests. Thus their theories, though
in some respects well founded, never reached that stage of scientific
proof which involves the use of the experimental method. The new
method in evolution is that of experiment under controlled conditions.
If new characters arise before the eyes of the investigator in a known
stock of animals or plants and the factors responsible for the change
are known and are capable of control, it may be said that man has
actually taken a hand in evolution. If new characters arise in a
known stock, but from an unknown cause, the course of the new
character in inheritance may be controlled and some knowledge of the
395
296 EVOLXjnON, GENETICS, AND EUGENICS
mechanism of heredity may be obtained by an analysis of its modes of
heredity. It is this new experimental and analytic method of study-
ing evolution that we have come to designate as genetics.
Three principal methods of attack upon the problems of genetics
have been successful in advancing our knowledge.
a) Experimental breeding. — This method was first systematized
by Mendel and consists of breeding together two individuals possessing
certain more or less contrasting characters and determining the ratios
in which the parental characters reappear in the offspring. This
method has been extremely fruitful and in connection with the second
method, that of cytology, has made clear much that was obscure to
Darwin and his followers.
b) Cytology. — This second taethod involves the microscopic
study of the germ cells during the most critical periods of their cycle.
It seems very probable that we can now view under the microscope
the actual heredity machine and see how it works.
c) The statistical method. — It is usually conceded that Sir
Francis Galton was the first to use the method of statistics in the study
of heredity. By means of correlation tables he was able to compare
large groups of parents with large groups of offspring with respect to
any unit character, and to state the degree of heredity in defin-
ite mathematical terms. The modem science of biometry is used
extensively at the present time for determining the degree of vari-
ability of characters which vary only slightly or irregularly and the
exact degree of correlation that exists between different hereditary
characters.
All three of these methods of attacking the problems of genetics
have been fruitful in results and all are essential to an adequate under-
standing of the workings of evolution.
The subject-matter of genetics consists of: (a) a knowledge of the
principles of ontogeny, the development of the individual from the
germ-ceil stage to the adult stage; (b) a knowledge of the behavior of
the germ cells from one generation to the next, involving the so-called
"origin" of germ cells, maturation and fertilization of germ cells, and
the exact behavior of the chromosomes during the entire germ-cell
cycle; (c) a knowledge of variation, including a determination of
what distinct kinds of variation occur, where in ontogeny variations
are initiated, the causes of variation, etc. ; (■
True ;
nucleolus
(plasmosome).
Chromatin 1
nucleolus. \
Linin — f
network. ^»
Plastids.
Vacuole.
M etaplasm
(passive bodies).
Fig. 43. — Diagram of a cell, showing various parts. {From Gtiyer.)
the meantime, the interior of the nucleus is undergoing a transforma-
tion. The granules and patches of chromatin begin to flow together
along the nuclear network and become more and more crowded
until they take on the appearance of one or more long deeply-
stained threads wound back and forth in a loose skein in the nucleus
(Fig. 44, h) . If we examine this thread closely, in some forms it may
be seen to consist of a series of deeply-stained chromatin granules
packed closely together, intermingled with the substance of the
original nuclear network.
As the preparations for division go on the coil in the nucleus breaks
up into a number of segments which are designated as chromosomes
(Fig. 44, c). The nuclear membrane disappears. The chromosomes
THE BEARERS OF THE HERITAGE
305
and the spindle-fibers ultimately come to lie at the equator of the
spindle as shown in Fig. 44, d. Each chromosome splits lengthwise
to form two daughter chromosomes which then diverge to pass to the
flktriTaB
Fig. 44. — Diagram showing representative stages in mitotic or indirect cell-
division, a, resting cell with reticular nucleus and single centrosome; h, the
two new centrosomes formed by division of the old one are separating and the
nucleus is in the spireme stage; c, the nuclear wall has disappeared, the spireme
has broken up into six separate chromosomes, and the spindle is forming between
the two centrosomes; d, equatorial plate stage in which the chromosomes occupy
the equator of the spindle ; e, f, each chromosome splits lengthwise and the daughter
chromosomes thus formed approach their respective poles; g, reconstruction of
the new nuclei and division of the cell body; h, cell division completed. {From
Guyer.)
poles of the spindle (Fig. 44, e and/). Thus each end of the spindle
comes ultimately to be occupied by a set of chromosomes. Moreover,
each set is a dupHcate of the other, because the substance of any
individual chromosome in one group has its counterpart in the other.
3o6 EVOLUTION, GENETICS, AND EUGENICS
In fact this whole compHcated system of indirect division is regarded
by most biologists as a mechanism for bringing about the precise
halving of the chromosomes.
The chromosomes of each group at the poles finally fuse and two
new nuclei, each similar to the original one, are constructed (Fig. 44,
g and h). In the meantime a division of the cell-body is in progress
which, when completed, results in the formation of two complete
new cells.
As all living matter, if given suitable food, can convert it into li\ing
matter of its own kind, there is no difficulty in conceiving how the
new cell or the chromatin material finally attains to the same bulk
that was characteristic of the parent cell. In the case of the chro-
matin, indeed, it seems that there is at times a precocious doubling
of the ordinary amount of material before the actual division
occurs.
Chromosomes constant in number and appearance. — With some
minor exceptions, to be noted later, which increase rather than detract
from the significance of the facts, the chromosomes are always the
same in number and appearance in all individuals of a given species
of plants or animals. That is, every species has a fixed number which
regularly recurs in all of its cell-divisions. Thus the ordinary cells
of the rat, when preparing to divide, each display sixteen chromo-
somes, the frog or the mouse, twenty-four, the lily twenty-four and
the maw-worm of the horse only four. The chromosomes of different
kinds of animals or plants may differ very much in appearance. In
some they are spherical, in others rod-like, filamentous or perhaps of
other forms. In some organisms the chromosomes of the same nucleus
may differ from one another in size, shape, and proportions, but if such
differences appear at one di\'ision they appear at others, thus showing
that in such cases the differences are constant from one generation to
the next.
Significance of the chromosomes. — -The question naturally arises
as to what is the significd,nce of the chromosomes. Why is the accur-
ate adjustment which we have noted for their division necessary ?
The very existence of an elaborate mechanism so admirably adapted
to their precise halving, predisposes one. toward the belief that the
chromosomes have an important function which necessitates the
retention of their individuaUty and their equal division. Many biolo-
gists accept this along with other evidences as indicating that in
chromatin we have a substance which is not the same throughout, that
THE BEARERS OF THE HERFTAGE . 307
different regions of the same chromosome have different physiological
values.
When the cell prepares for divisions, the granules, as we have
seen, arrange themselves serially into a definite number of strands
which we have termed chromosomes. Judging from all available
evidence, the granules are self-propagating units; that is, they can
grow and reproduce themselves. So that what really happens in mito-
■ sis in the splitting of the chromosomes is a precise halving of the series
of individual granules of which each chromosome is constituted, or in
other words each granule has reproduced itself. Thus each of the two
daughter cells presumably gets a sample of every kind of chromosomal
particle, hence, the two cells are qualitatively alike. To use a homely
illustration we may picture the individual chromosomes to ourselves
as so many separate trains of freight cars, each car of which is loaded
with different merchandise. Now, if every one of the trains could
split along its entire length and the resulting halves each grow into a
train similar to the original, so that instead of one there would exist
two identical trains, we should have a phenomenon analogous to that
of a dividing chromosome.
Cleavage of the egg. — It is through a series of such divisions as
these that the zygote or fertilized egg-cell builds up the tissues and
organs of the new organism. The process is technically spoken of as
cleavage. Cleavage generally begins very shortly after fertilization.
The fertile egg-cell divides into two, the resulting cells divide again and
thus the process continues, with an ever-increasing number of cells.
Chief processes operative in building the body. — Although of
much interest, space will not permit of a discussion in detail of the
building up of the special organs and tissues of the body. It must
suffice merely to mention the four chief processes which are operative.
These are, (i) infoldings and outfoldings of the various cell com-
plexes; (2) multiplication of the component cells; (3) special changes
(histological diferentiation) in groups of cells; and (4) occasionally
resorption of certain areas of parts.
The origin of the new germ-cells. — On account of the unusual
importance from the standpoint of inheritance, which attaches to the
germ-cells, a final word must be said about their origin in the embryo.
While the evidence is conflicting in some cases, in others it has been
well established that the germ-cells are set apart very early from the
cells which are to differentiate into the ordinary body tissues. Fig. 45,
A, shows a section through the eight-celled stage of Miastor, a fly,
3o8
EVOLUTION, GENETICS, AND EUGENICS
in which a single large, primordial germ-cell {p. g. c.) has already been
set apart at one end of the developing embryo. The nuclei of the rest
of the embryo still lie in a continuous protoplasmic mass which has
not yet divided up into separate cells. The densely stained nuclei at
the opposite end of the section are the remnants of nurse-cells which
originally nourished the egg. Fig. 45, B, is a longitudinal section
o3g
Fig. 45. — A, germ-cell (p.g.c.) set apart in the eight-celled stage of cleavage
in Miastor americana. {After Hegncr.) The walls of the remaining seven somatic
cells have not yet formed, though the resting or the dividing {M p) nuclei may be
seen; c R, chromatin fragments cast off from the somatic cells; B, section length-
wise of a later embryo of Miastor; the primordial egg-cells {oog^) are conspicuous.
{From Guyer, after Hegner.)
through a later stage in the development of Miastor; the primitive
germ-cells {oog) are plainly visible. Still other striking examples
might be cited. Even in vertebrates the germ-cells may often be
detected at a very early period.
Significance of the early setting apart of the germ-cells. — ^It is of
great importance for the reader to grasp the significance of this early
setting apart of the germ-cells because so much in our future discussion
hinges on this fact. The truth of the statement made in a previous
chapter that the body of an individual and the reproductive substance
THE BEARERS OF THE HERITAGE 309
in that body are not identical now becomes obvious. P'or in sucli
cases as those just cited one sees the germinal substance which is to
carry on the race set aside at an early period in a given individual; it
takes no part in the formation of that individual's body, but remains
a slumbering mass of potentialities which must bide its time to awaken
into expression in a subsequent generation. Thus an egg does not
develop into a body which in turn makes new germ-cells, but body and
germ-cells are established at the same time, the body harboring and
nourishing the germ-cells, but not generating them. The same must
be true also in many cases where the earliest history of the germ-cells
cannot be visibly followed, because in any event, in all higher animals,
they appear long before the embryo is mature and must therefore be
descendants of the original egg-cell and not of the functioning tissues
of the mature individual. This need not necessarily mean that the
germ-cells have remained wholly unmodified or that they continue
uninfluenced by the conditions which prevail in the body, especially
in the nutritive blood and lymph stream, although as a matter of fact
most biologists are extremely skeptical as to the probabiUty that
influences from the body beyond such general indefinite efi"ects as
might result from under-nutrition or from poisons carried in the blood,
modify the intrinsic nature of the germinal substances to any measur-
able extent.
Germinal continuity. — The germ-cells are collectively termed the
germinal protoplasm and it is obvious that as long as any race continues
to exist, although successive individuals die, some germinal protoplasm
is handed on from generation to generation without interruption.
This is known as the theory of germinal continuity. When the organ-
ism is ready to reproduce its kind the germ-cells awaken to activity,
usually undergoing a period of multiplication to form more germ-cells
before finally passing through a process of what is known as matura-
tion, which makes them ready for fertilization. The maturation
process proper, which consists typically of two rapidly succeeding
divisions, is preceded by a marked growth in size of the individual cells.
Individuality of chromosomes. — Before we can understand fully
the significance of the changes which go on during maturation we shall
have to know more about the conditions which prevail among the
chromosomes of cells. As already noted each kind of animal or plant
has its own characteristic number and types of chromosomes when
these appear for division by mitosis. In many organisms the chromo-
somes are so nearly of one size as to make it difficult or impossible to
3IO EVOLUTION, GENETICS, AND EUGENICS
be sure of the identity of each individual chromosome, but on the
other hand, there are some organisms known in which the chromo-
somes of a single nucleus are not of the same size and form (Fig. 46).
These latter cases enable us to determine some very significant facts.
Where such differences of shape and proportion occur they are constant
in each succeeding division so that similar chromosomes may be iden-
tified each time. Moreover, in all ordinary mitotic divisions where
the conditions are accurately known, these chromosomes of different
types are found to be present as pairs of similar elements; that is,
there are two of each form or size.
Pairs of similar chromosomes in the nucleus because one chromo-
some comes from each parent. — ^When we recall that the original
fertilized egg from which the individual develops is really formed by
the union of two gametes, ovum and spermatozoon, and that each
%
A B
Fig. 46. — A, chromosomes of the mosquito (Culex). (After Stevens.) B,
chromosomes of the fruit fly (Drosophila). (After Metz.) Both of these forms
have an unusually small number of chromosomes. (From Guyer.)
gamete, being a true cell, must carry its own set of chromosomes, the
significance of the pairs of similar chromosomes becomes evident; one
of each kind has probably been contributed by each gamete. This
means that the zygote or fertile ovum contains double the number of
chromosomes possessed by either gamete, and that, moreover, each
tissue-cell of the new individual will contain this dual number. For,
as we have seen, the number of chromosomes is, with possibly a few
exceptions, constant in the tissue-cells and early germ-cells in suc-
cessive generations of individuals. For this to be true it is obvious
that in some way the nuclei of the conjugating gametes have come to
contain only half the usual number. Technically the tissue-cells are
said to contain the diploid number of chromosomes, the gametes the
reduced or haploid number.
In maturation the number of chromosomes is reduced by one-
half. — -This halving, or as it is known, reduction in the number of
chromosomes is the essential feature of the process of maturation. It
THE BEARERS OF THE HERITAGE
311
is accomplished by a modification in the mitotic division in which
instead of each chromosome spHtting lengthwise, as in ordinary mito-
sis, the chromosomes unite in pairs (Fig. 47, b), a process known tech-
nically as synapsis, and then apparently one member of each pair passes
entire into one new daughter cell, the other member going to the other
daughter cell (Fig. 47, c). In the pairing preliminary to this reduction
division, leaving out of account certain special cases to be considered
Fig. 47. — Diagram to illustrate spermatogenesis, a, showing the diploid
number of chromosomes (si.x is arbitrarily chosen) as they occur in divisions of
ordinary cells and spermatogonia; b, the pairing (sjmapsis) of corresponding
mates in the primary spermatocyte preparatory to reduction; c, each secondary
spermatocyte receives three, the haploid number of chromosomes; d, division of
the secondary spermatocytes to form c, spermatids, which transform into /, sper-
matozoa. {From Guyer.)
later, according to the best evidence at our command the union always
takes place between two chromosomes which match each other in size
and appearance. Since one of these is believed to be of maternal and
the other of paternal origin, the ensuing division separates correspond-
ing mates and insures that each gamete gets one of each kind of chro-
mosome although it appears to be a matter of mere chance whether or
not a given cell gets the paternal or the maternal representative of
that kind.
312
EVOLUTION, GENETICS, AND EUGENICS
Maturation of the sperm-cell. — In the maturation of the male
gamete the germ-cell, now known as a spermatogonium, increases
greatly in size to become a primary spermatocyte. In each primary
spermatocyte the pairing of the chromosomes already alluded to
occurs as indicated in Fig. 47, where six is taken arbitrarily to indicate
the ordinary or diploid number of chromosomes, and three the reduced
or haploid number. The division of the primary spermatocyte gives
rise to two secondary spermatocytes (c), the paired chromosomes
separating in such a way that a member of each pair goes to each
Fig. 48. — Diagram to illustrate oogenesis, a, showing the diploid number of
chromosomes (six is arbitrarily chosen) as they occur in ordinary cells and in
oogonia; b, the pairing of corresponding mates preparatory to reduction; c, d,
the reduction division, giving off the first polar body; e, egg preparing to give off the
second polar body, first polar body ready for division; /, second polar body ready
for division; g, second polar body given off, division of first polar body completed.
The egg nucleus, now known as the female pronucleus, and each polar body contain
the reduced or haploid number of chromosomes. (From Guyer.)
secondary spermatocyte. Each secondary spermatocyte (d) soon
divides again into two spermatids (e), but in this second division the
chromosomes each split lengthwise as in an ordinary division so that
there is no further reduction. In some forms the reduction division
occurs in the secondary spermatocytes instead of the primary. Each
spermatid transforms into a mature spermatozoon (/). The sper-
matozoa of most animals are of Hnear form, each with a head, a
middle-piece and a long vibratile tail which is used for locomotion.
The head consists for the most part of the transformed nucleus and is
consequently the part which bears the chromosomes.
THE BEARERS OF THE HERITAGE
313
Maturation of the egg-cell. — As regards the behavior of the
chromosomes the maturation of the ovum parallels that of the sperm-
cell. There are not so many primordial germ-cells formed and only
one out of four of the ultimate cells becomes a functional egg. As in
maturation of the sperm-cell there is a growth period in which o'dgonia
enlarge to become primary oocytes (Fig. 48, b). In each primary
spermatogenesis
1
Secondary ( ^\
•ipermocd-K *^ }
Ci/ttS VJx
Sperm-
Oogenesis
1
Multiphcalion Period
Croh/th Period
]
Pairing of Chromosomes
j fiec/ucing dii/mon
^@
Oogonia
Pnmary dlc^li
Sec one/ari/ cdci/t»
ip^um and first
■~ polar doyum
fuitnumber of
(5) 9-47> (6) 7-33- Finally, Klcbs subjected similar plants
from white, red, and blue light to chemical analysis in order to secure
further evidence of the physiological effects of light of different wave
Fig. 51. — Sedum spedahile. The three shoots (taken from a single plant)
were planted in small pots on March 12, 1904, and, placed in different greenhouses,
/, in blue light; //, in mixed white light; ///, in red light. Photographed on
September 30, 1914. {Front Babcock and Clausen, after Klehs.)
lengths. Table I shows the composition of the leaves in three plants
like those shown in Fig. 5 1 . They were in their respective greenhouses
from June 6 to September 7. The percentages shown are per 100 g.
of dry substance.
In comparing these percentages it should be remembered that the
plant in white light produced 1324 flower buds and the plant in red
light 405, while the plant in blue light produced none. This explains
the higher percentage of ash, nitrogen and protein in the last. On
the other hand, the amounts of starch and sugar found in the plant
from white light are decidedly larger than the one from blue light.
330
EVOLUTION, GENETICS, AND EUGENICS
In short, according to Klebs, in comparison with normal white Hght,
the production of organic substances, such as starch and sugar, is
TABLE I
Chemical Composition of Three Plants of Scdum Spectabile Grown in
White, Red, and Blue Light
Substance
Ash
Sugar
Calcium malate.
Free nitrogen. . .
Starch
Crude protein . .
White
13.20
II .04
22
o
5
5
29
16
82
3i
Red
13.20
15-40
18.02
0.33
3.66
6. IS
Blue
18.60
2.40
iS.io
0-59
1 . 20
7.64
diminished under the influence of blue light as microchemical and
macrochemical tests distinctly show. In consequence of this dimin-
ished assimilation of carbon dioxide the rosettes become purely
Fig. 52. — -Above the diurnal peacock butterfly (Vanessa io), and below, forms
produced by subjecting the pupae to unusual temperatures. (From Babcock and
Clausen, after Goldschmidt.)
vegetative. In red light the carbon assimilation is greater than in
blue light but less than in white. These experiments prove that the
transformation of a plant "ripe to flower" into a vegetative one
VARIATION
O O T
is possible on the one hand by" an increase of temperature and of
inorganic salts, and on the other hand by a decrease of carbon
assimilation.
b) Temperature and pigmentation. IVIany experiments in the
rearing of moths and butterflies under controlled temperatures prove
that degree of pigmentation is profoundly influenced by the tempera-
ture at which the pupae are kept. Some species exhibit seasonal
dimorphism in the wild state. By taking pupae of the common
European form of the swallowtail butterfly, Papilio machaon, and
subjecting them to a temperature of 37° to 38° C, Standfuss obtained
the characteristic summer form which occurs in Palestine. Again it
has been shown by temperature experiments that many variations
28-VI
30-VII
15-IX
Fig. 53. — Morphological cycle of head height in Hyalodaphnia. Roman
numerals designate months. {From Babcock atid Clausen, after WoUereck.)
found among insects in nature are merely aberrations due to tempera-
ture effects. Goldschmidt by artificially controlled temperatures has
produced a series of forms of the diurnal peacock butterfly, Vanessa io^
which show the fading out of the "peacock eye" mark (see Fig. 52).
c) Food and structure. Woltereck was able to prove that the form
(hence the structure) of the fresh water crustacean, Hyalodaphnia,
varies directly with the food supply. These minute animals produce
many generations during a season and the successive generations from
the same water exhibit a morphological cycle, the earUer and later
generations having shorter heads and the generations produced from
midsummer to autumn having longer ones. Fig. 53 is a reproduction
of Woltereck's diagram of the morphological cycle in Hyalodaphnia
showing variation in head and shell length as found on successive
332
EVOLUTION, GENETICS, AND EUGENICS
dates from June 3 to January 3. By raising these animals under
constant temperature conditions and varying the strength of the
nutrient solution, Woltereck proved that the relative size of body
parts varied with the food. In Fig. 54 the percentages of head height
to shell in length are plotted as abscissas and the numbers of indi-
viduals as ordinates. Animals from three strengths of nutrient media
were measured, the curves of those from the weaker, the medium and
the richer media being shown at mi, mj and m3 respectively.
d) Moisture and plumage color. Beebe experimented with the
pigeon, Scardajella inca. This species, as found in North and Central
America, is very constant in color of plumage, but in the moist tropics
d^
i
I.
30
35 '40
nil
45
50
55
CO
G5
70' 75
m 2
80
85
90 95
Fig. 54. — Schematic curves of head height in Hyalodaphnia as grown in
media of three different food values. {From Babcock and Clausen, after
Woltereck.)
the following darker colored forms occur: in Honduras, dialeucos; in
Venezuela, ridgivayi; in Brazil, hraziliensis; and these differ in the
amount of pigment in the feathers. By subjecting the birds of the
northern type to an especially moist atmosphere, Beebe caused them
to be so influenced that with each new moulting, whether natural or
artificially induced, they always developed darker feathers. Thus a
wild bird having pigment in 25.9 per cent of its area, would have after
the second moulting under experimental conditions, 38 per cent and
after the third, 41 . 6 per cent. Thus during the experiment the
typical form assumed the appearance of the three other forms and
finally developed plumage markings which have never been seen in
nature. Fig. 55 shows the type form, inca, the three geographical
variants, and the darkest artificially produced form.
VARIATION
333
2. Environment conditions development of inherited characters. —
(o) Light and metabolism. In a general sense light conditions life
in all normally green plants. It certainly conditions normal develop-
ment in such plants. Potatoes sprouted in a dark room develop no
chlorophyll in the stems and the rudimentary leaves are abortive.
In many bulbous plants, however, the influence of moisture and heat
are sufficient to induce leaf growth and even development of the
inflorescense, but it is all done at the expense of the food stored up in
the bulbs.
Fig. 55. — a. Typical wild pigeon, Scardafella inca; b, the form dialcucos; c,
hraziliensis; d, ridgivayi; e, inca after three moultings in a moist atmosphere.
{After Becbe, from Babcock and Clausen.)
b) Temperature and flower color. Baur reports an experiment with
a red variety of the Chinese primrose, Primula sinensis rubra. If
plants of this variety are raised by the usual method until about one
week before time to bloom and then some of the plants are put in a
warm room under partial shade (temperature from 30° to 35° C.) and
the remainder in a cool house (temperature from 15° to 20° C), when
they bloom those in the warm temperature have pure white flowers
while those in the cool temperature have the normal red color of the
variety. Moreover, if plants are brought from the warm into the
334 EVOLUTION, GENETICS, AND EUGENICS
cool temperature the flowers which develop later on will be normal
red in color. Thus it cannot be said that this primula inherits either
red or white flowers. What it really inheiits is ability to react in
certain ways under the influence of temperature.
c) Food and fertility. It is well known that the kind of food
supplied to the larvae of bees determines whether the females shall be
fertile (queens) or infertile (workers). The striking differences ir
structure and instincts of the two classes of females are all conditioned
by the food provided for the larvae. Each larva inherited the capacity
to react in either way according to the stimulus received.
d) Moisture and structure. Morgan reports a variety of the
pomace fly, Drosophila ampelophlla, with abnormal abdomen; "the
normal black bands of the abdomen are broken and irregvilar or even
entirely absent. In flies reared on moist food the abnormality is
extreme; but even in the same culture the flies that continue to
hatch become less and less abnormal as the culture becomes more
dry and the food scarce, until finally the flies that emerge later cannot
be told from normal flies. If the culture is kept well fed (and moist)
the change does not occur, but if the flies are reared on dry food they
are normal from the beginning."
3. Environment may oause new heritable characters. — As yet
there is a dearth of evidence which can be accepted as scientific proof
that external stimuh actually cause germinal variations. At the same
time there is an abundance of data which falls into the class of circum-
stantial evidence in favor of such a doctrine. Moreover, there are
a few cases in which new heritable. characters have been artificially
produced by carefully controlled external stimuli. Hence some
germinal variations are apparently caused by known environmental
conditions and we are justified in recognizing this third category of
developmental differences due to environmental effects.
Considerable e\ddence of permanent changes in both morphologi-
cal and physiological characters has been secured from experiments
with the culture of bacteria and yeast, in unusual culture media, in
the presence of toxic solutions, or under extreme temperature condi-
tions. The significant results of four investigators who worked
independently, Hansen, Barber, Wolf, and Jordan, have been reviewed
and discussed in regard to their bearing on genetic theory by Cole
and Wright. The four investigators mentioned above used refined
methods and three of them began by isolating a single organism from
whose progeny they obtained distinct strains or biotypes which
VARIATION
33.-)
remained constant for hundreds of test-tube "generations." It must
be admitted that in most of these cases no specific influences can be
named as the direct cause of the inherited variation. But there is no
longer any doubt that permanent, discontinuous variations do occur
spontaneously in these lowest organisms, and it is highly probable
that certain incidental, external forces play an important part in
inducing such variations.
Direct experimental attack upon the germ cells themselves has
been made with plants by a number of investigators, notably by
MacDougal, who injected very dilute solutions of potassium iodide,
zinc sulphate, sugar, etc., directly into the ovaries of various plants
immediately before fertilization. Consequently somatic changes have
been produced which were inherited throughout several generations.
Fig. 56. — O, portion of leaf of Scrophularia showing branching lateral vein;
D, branching vein replaced by two laterals in leaf of seedling grown from seed
produced by an injected ovary. Also note the difference in size and margin of
leaves. {From Babcock and Clausen, after MacDougal.)
By means of check experiments and observations it was found that
these germinal variations were not caused by the wounding of the
ovary and it is thought that they must have been induced in some way
by the presence of the foreign chemical solution in the ovary. Fig. 56
shows a morphological change which appeared in a seedling of an
unnamed species of Scrophularia as a result of ovarial injection. Hav-
ing tested the species sufficiently to determine that it was a simple one,
MacDougal treated several ovaries with potassium iodide, one part
in 40,000 and secured seed. No other species of Scrophularia grew
near the cultures. From this seed only three plants were raised.
"One formed a shoot fairly equivalent to the normal, finally producing
flowers in which the anthocyans were of a noticeably deep hue. The
two remaining plantlets were characterized by a succulent aspect of
the leaves and by a lighter and yellow color of the leaves and stems.
336 EVOLUTION, GENETICS, AND EUGENICS
The flowers on one of the derivatives, as they may be called, were so
completely lacking in color as to be a cream-white, this derivative
being designated as albida, while the other showed some marginal
color and a rusty tinge and was designated as rufida Seeds of
the original two derivatives were sowed in the greenhouse. But one
plant of albida, the most extreme departure, survived, while four of
rufida were secured." MacDougal compared these second generation
seedlings with seedlings from the original stock of the species, noting
diflterences in size and margin of leaves, length of petioles and number
of marginal glands. He found that the differences shown by the first
generation appeared again in the second generation. Striking as these
results appear it must be admitted that it would be difificult, on account
of the small numbers of individuals differing from the parent tj^e, to
prove satisfactorily to the biometrician that tliey were not mutations
which would have occurred regardless of the ovarial treatment.
What appear to be germinal variations in the tomato have been
induced by intensive feeding. T. H. White tested the effect of dried
blood, dissolved phosphate rock, sulphate of potash and iron filings
all in excessive amounts, and (with the exception of the iron) in
various combinations, on the Red Cherry tomato. The lack of data
on control cultures of seedlings from the same parent as the experi-
mental cultures makes it impossible to compare the actual amount
of permanent variation produced. T. H. White states that measure-
ments "show that the plants of the sixth generation grown under the
influence of the dried blood are one-third larger in height, length of
leaf and size of fruit, than those of the second." The author con-
cludes that "there can be no doubt .... that, in the case of Red
Cherry treated with dried blood, there is permanent variation to the
third generation." If these results are corroborated by more care-
fully planned and rigidly controlled experiments they will add the
weight of scientific proof of a principle in plant breeding long since
recognized on empirical grounds, to wit, that the introduction of wild
plants into intensive cultivation induces variation. Furthermore, it
suggests a possible means for rapid permanent improvement of wild
forms with which hybridization may be impracticable.
In experiments on lower animals, e.g., the protozoa, the same
difficulty is met with as has been encountered in bacteria and yeasts,
in that it is manifestly impossible to distinguish between somatic and
germinal variations. Moreover, in most of these experiments, as with
most of those on higher animals, the necessary conditions for rigid
VARIATION 22^
scientific analysis have been lacking. Either the same strain as was
subjected to artificial conditions was not grown for comparison under
natural conditions or else the conditions themselves were not suffi-
ciently well controlled to permit of certain analysis. It is interesting
to note that the pomace fly, Drosophila ampelophila, which has pro-
duced more mutations so far as we know than any other organism,
v/as subjected to the effects of ether on a grand scale and under
controlled conditions by Morgan, but that not a single mutation was
observed to result from this treatment. However, mutations have
subsequently appeared again and again in cultures of "wild" flies not
only of this species but also of other species of Drosophila. Thus it
appears that germinal variations frequently occur independently of
external stimuU. It also seems that a tendency to produce mutations
may be inherited.
With animals the best known experiments on the artificial pro-
duction of germinal variations are those of Tower who worked with
the Colorado potato beetle, Leptinotarsa decemlineata, and related
species. Like other arthropods these beetles are more directly under
the influence of temperature changes at least than are warm-blooded
animals. Tower first determined the period in ontogeny when ex-
ternal stimuli will affect the germ cells. He found that in Leptino-
tarsa the germ cells do not become susceptible to external stimuli
until after the time in ontogeny when the color pattern of the individ-
uals subjected to the stimuli can be influenced. He found that eggs
were most susceptible just before and during maturation and this
observation is in agreement with those of Fischer, Standfuss, Weis-
mann and others who have conducted similar investigations. Tower
concluded that certain individuals from the germ cells of a stimulated
parent "show intense heritable variations, whereas those not acted
upon do not show these changes." Most of the inherited variations
involve changes in the pigmentation of the body parts. In certain
cases there was an actual change in the color pattern. It is to these
results that Tower attaches the greatest significance inasmuch as
most similar experiments have not succeeded in causing pattern
changes. In spite of the elaborateness of Tower's methods consider-
able skepticism exists regardmg the validity of his conclusions, and
this has not been lessened by the non-appearance of confirmatory
data. In a recent paper he reports the production of very striking
germinal modifications in L. decemlineata as a result of subjecting a
morphologically homogeneous race to an extreme change in environ-
338 EVOLUTION, GENETICS, AND EUGENICS
ment. However, it is still a question whether the material used may
not be heterogeneous as regards the germinal factors that condition
certain physiological characters.
Stockard's investigations on the effect of alcohol on the progeny
of guinea pigs have shown that the germ cells as well as the somatic
tissues of the alcohohzed animals are injured.
On the whole it must be admitted that the experimental induction
of heritable variations is still largely an un worked field. The complex
conditions to be considered and consequent obstacles to be overcome
are appreciated by no one more fully than by those who have at-
tempted such investigations. For, as Tower has said: "It is evident
that the problem of germinal change is one of difficulty, and involves
more of indirect than of direct methods of investigation. There is
httle reason to expect that present biochemical methods can give a
solution, but they may give valuable suggestions for further indirect
investigation. It seems not improbable, however, that this problem,
like so many others in biology, must await the solution of the larger
question of what life is before it will be possible to express in exact
terms the nature of germinal changes. Our present status, with
several methods of production and much knowledge of the behavior
of induced germinal changes available, is a basis from which great
advances in knowledge and in operation may reasonably be expected."
CHAPTER XXVI
MENDEL'S LAWS OF HEREDITY
Mendel's lite and character*
J. ARTHUR THOMSON
Gregor Johann Mendel was born in 1822, the son of well-to-do
peasants in Austrian Silesia. He became a priest in 1847, and studied
physics and natural science at Vienna from 1851 to 1853. Thence he
returned to his cloister and became a teacher in the Realschule at
Briinn. It was his hobby to make hybridisation experiments with
peas and other plants in the garden of the monastery, of which he
eventually became abbot. Apart from two papers, one dealing with
peas and a shorter one with hawkweeds, and some meteorological
observations, he does not seem to have published much. But what
he did publish, if small in quantity, was large in quality. He died in
1884.
Mendel's discoveries
In 1866 Gregor Johann Mendel, Abbot of Briinn, published what
some regard as one of the greatest of biological discoveries. After
many years of patient experimenting, chiefly with the edible pea, he
reached a very important conclusion in regard to the inbreeding of
hybrids, which is often briefly referred to as "Mendel's Law." His
publication was practically buried in the Proceedings of the Natural
History Society of Briinn; those who knew of it, as Nageli for instance
did, failed to realise its importance: in fact, Mendel's epoch-making
work was lost sight of amid the enthusiasm and controversy which the
promulgation of Darwinism (1858) had evoked. Mendel's Law seems
to have been rediscovered independently in 1900 by the botanists,
De Vries, Correns, and Tschermak ; and to Mr. Bateson we owe much,
not only for his recognition of the far-reaching importance of the
abbot's work, but also for a notable series of experiments in which he
has confirmed and extended it.
' From J. Arthur Thomson, Heredity (copyright 1907). Used by special
permission of the publishers, John Murray, London.
339
340 EVOLUTION, GENETICS, AND EUGENICS
Mendel's experiments. — What Mendel sought to discover was the
law of inheritance in hybrid varieties, and he selected for experiment
the edible pea {Pisum sativum). The trial plants, he says, must
possess constant differentiating characters, and must admit of easy
artificial pollination; the hybrids of the plants must be readily fertile,
and readily protectable from the influence of foreign pollen. These
conditions were afforded by peas, and twenty-two varieties or sub-
species of pea were selected, which remained constant during the eight
years of the experiments. Whether they were called species, or sub-
species, or varieties, is a matter of convenience; the names Pisum
quadratum, P. saccharatum, P. umbellakim, etc., do in any case repre-
sent groups of similar individuals which breed true inter se. It should
be noted that these peas have the particular advantage, for experi-
mental purposes, that they are habitually self-fertihsed — in North
Europe, at least.
In studying the different forms of peas, Mendel found that there
were seven differentia tmg characters which could be relied on:
1. The form of the ripe seeds, whether roundish, with shallow
wrinkles or none, or angular and deeply wrinkled:
2. The colour of the reserve material in the cotyledons — pale
yellow, bright yellow, orange, or green;
3. The colour of the seed-coats, whether white, as in most peas
with white flowers, or grey, grey-brown, leather brown, with or with-
out violet spots, and so on;
4. The form of the ripe pods, whether simply inflated, or con-
stricted, or wrinkled;
5. The colour of the unripe pods, whether light or dark green, or
vividly yellow, this colour being correlated with that of stalk, leaf-
veins, and blossoms;
6. The position of the flowers, whether axial or terminal; and
7. The length of the stem, whether tall or dwarfish.
Mendel's results; the Law of Dominance. — Having defined the
differentiating characteristics of the varieties, Mendel proceeded to
make crosses between these, investigating one character at a time.
Thus, pollen from a pea of the round-seeded variety was transferred
to the stigma of a pea of the angular-seeded variety, the stamens of the
artificially pollinated flower being, of course, removed before they
were ripe. The same was done all along the line.
What was the result in the hybrid or cross-bred offspring ? It was
found that they showed one of each pair of contrasted characters, to
MENDEL'S LAWS OF HEREDITY 341
the total, or almost total, exclusion of the other. No intermediaie
forms appeared.
Mendel called the character that prevailed dominant, and the
character that was suppressed, or apparently suppressed, recessive.
And the first big result was that crosses between a plant with the
dominant character and a plant with the recessive character yielded
oflfspring all resembling the dominant parent as regards the character
in question. Let us for shortness call the parents D and R, and the
first result may be expressed thus: DXR = D.
It must be carefully noted that the complete dominance which
Mendel observed has been shown in other cases to be the exception
rather than the rule. Thus a cross between a " Chinese " primula with
wavy crenated petals and a "star" primula with flat simply notched
petals is intermediate between the two parents; and yet, as the next
generation shows, the case is one of Mendelian inheritance.
In many cases the hybrid, while on the whole dominant, may show
some influence of the recessive character but not nearly enough to
warrant us in speaking of a blend. Thus, when white (dominant)
Leghorn poultry are crossed with brown (recessive) Leghorn, most of
the oflfspring have some "ticks" of colour. When these are inbred
they produce a quarter brown (extracted recessives) and three-
quarters pure white or white with a few ticks. The dominance is not
quite perfect.
The Law of Splitting or Segregation. — In the next generation the
cross-bred plants (products of D and R, or R and D, but all apparently
like D) were allowed to fertilise themselves, with the result that their
offspring exhibited the two original forms, on the average three domi-
nants to one recessive. Out of 1,064 plants, 787 were tall, 277 were
dwarfs.
When these recessive dwarfs were allowed to fertilise themselves
they gave rise to recessives only, for any number of generations. The
recessive character bred true.
When the dominants, on the other hand, were allowed to fertilise
themselves, one-third of them produced "pure" dominants, which in
subsequent generations gave rise to dominants only; and two-thirds
of them produced once again the characteristic mixture of dominants
and recessives in the proportion of 3: i.
The general results may be expressed in the scheme. The
result of the hybridisation is a generation (F,) like the dominant
parent. They may be represented by the symbol D(R), for they
342 EVOLUTION, GENETICS, AND EUGENICS
D9XR^orR$XD4 . . . Parent-forms (P')
\/
D(R) Hybrid-offspring (P)
3.D
I R . Generation of inbred hybrids (F»)
iD
+
2D(R)
SP
iR R
I D + 2 D(R)
I
D D 3D
iR R R
iD+2D(R)
I
D D D
R R R
(F4)
(Fs)
carry with them the possibility of having offspring with the recessive
character; that is to say, the recessive character remains latent in
the inheritance.
When these D(R)s are inbred (self-fertilised, in the case of peas)
they have offspring (F^), some of which resemble the recessive parent,
while others resemble the dominant parent, and these occur in the
proportion of 1:3. When those resembling the recessive parent are
inbred, they breed true — i.e., they give rise to a line of pure recessives.
Those resembUng the dominant parent are all apparently alike, but
their subsequent history shows that they may be divided into a set
which breed true to the dominant type and a set which behave like the
first generation of hybrids — -i.e., they go on splitting up into dominant-
like forms and pure recessives. These two sets occur in the propor-
tions of 1:2.
A case of peas. — Let us consider a concrete case. Peas with
rounded seeds were crossed with peas having angular wrinkled seeds.
In the offspring the character of roundness was dominant ; the angular
wrinkled character had disappeared or receded. It was not lost, as
the next generation showed.
The hybrid offspring, aU with rounded seeds, were allowed to self-
fertilise. In their progeny roundish seeds and angular wrinkled seeds
occurred in the proportions of 3:1. Here were the recessives again,
and when they were allowed to self-fertilise they produced pure reces-
sives only, with angular wrinkled seeds.
MENDEL'S LAWS OF HEREDITY
343
The dominants, however, were not all pure dominants, for when
they were allowed to self -fertilise they produced one-third pure domi-
nants and two-thirds "impure" dominants, the latter being distin-
guished by the fact that in their offspring recessives reappeared in the
proportion of one recessive to three dominants.
The outstanding facts, taking the case of yellow-seeded and green-
seeded peas, may be thus summarised: —
Parental
Generation (Pi)
First Filial {hybrid)
Generation (Fi)
Yellow-seeded "pure'
plant (dominant)
Green-seeded "pure'
plant (recessive)
All the offspring were yellow-seeded
Self-fertilised they yielded
Second Filial (inbred) Yellows
Generation (F2) (pure type)
Third Filial {inbred)
Generation (F3)
Yellows
(impure type)
Yel ows
(pure tj^pe)
Yellows
(pure)
Yellows
(impure)
Greens
(pure)
Greens
(pure type)
Greens
(pure type)
Thus intercrossing of forms with contrasted characters results not
in transitional blends, but in the dominance of one character and the
recession of another. Self-fertilisation (the extreme of inbreeding)
of the hybrids results in a number of pure recessives and a number of
dominants in the proportion 1:3; some of these dominants (one-third)
are pure, and produce only dominants ; some (two- thirds) are appar-
ently pure, but produce dominants and recessives in the old propor-
tion, 3:1.
A case of mice. — Let us take a concrete case from among animals.
A grey house-mouse is crossed with a white mouse; the offspring are
all grey. Greyness is dominant; albinism is recessive.
I G 2 G(W)
I W
(P')
W (F3)
344
EVOLUTION, GENETICS, AND EUGENICS
The grey hybrids are inbred; their offspring are grey and white
in the proportion 3:1. If these whites are inbred they show them-
selves "pure," for they produce whites only for subsequent genera-
tions. But when the greys are inbred they show themselves of two
kinds, for one-third of them produce only greys, which go on produ-
cing greys; while the other two-thirds, apparently the same, produce
both greys and whites. And so it goes on.
Summary. — In his exceedingly clear exposition of Mendelism
(1905) Mr. R. C. Punnett states the result thus: "Wherever there
occurs a pair of differentiating characters of which one is dominant
to the other, three possibilities exist: there are recessives which
always breed true to the recessive character; there are dominants
which breed true to the dominant character, and are therefore pure;
and thirdly, there are dominants which may be called impure, and
which on self-fertilisation (or in-breeding, where the sexes are separate)
give both dominant and recessive forms in the fixed proportion of
three of the former to one of the latter."
Schematic representation of Mendel's Law. — Following Mr.
Punnett's suggestion, with slight modifications, we may use the sym-
bols Px, Pa, P3 for the parental, grandparental, and great-grandparental
generations; Fi for the first filial (hybrid) generations, Fj, Fj. F^
for the subsquent inbred generations. The symbol D(R) means a
dominant with the recessive character unexpressed, but potentially
present; DD or RR means pure "extracted" dominants or reces-
sives— i.e., those pure forms which are sifted out from the inbreed-
ing of "impure" dominants.
D R
I I
D R
I I
D R
\/
D(R)
PJ — great-grandparental generation
P* — grandparental generation
P» — parental generation
P — first filial (hybrid) generation
I DD 2 D(R) I RR . F»— second filial Cin-
" Extracted" pure Impure dominants Pure recessives bred) generation
dominants I
DD iDD
2D(R)
I RR RR . FJ— third generation
DD DD I DD 2 D(R) i RR RR RR
F* — fourth generation
MENDEL'S LAWS OF HEREDITY 345
Mendel's explanations*
JOHN M. COULTER AND MERLE C. COULTER
Mendel's explanation of this behavior involved three theses which
at that time were new to biology. These theses must be kept distinct
from one another.
1. Independent unit characters. — This means that an organism,
although representing a morphological and physiological unity, from
the standpoint of heredity is a complex of a large number of independ-
ent heritable units. Thus if one pea plant is tall and another one is
dwarf the behavior of the hybrid produced from them with reference
to this character will be the same, no matter what other characters
the parent plants may have had. In other words, the characters
are independent units, unaffected by other characters or units. The
character of tallness from a tall plant with wrinkled seeds or purple
flowers will act just the same as from a tall plant with smooth seeds
or white flowers. Tallness is a unit and its behavior in inheritance is
independent of all other units.
2. Dominance. — In the germ plasm there are certain determiners
of imit characters which dominate during the development of the
body, causing these characters to dominate over others and thus
become visible. The characters dominated over and thus not allowed
to express themselves are called recessive characters. These recessive
characters are present in the germ plasm, but cannot express them-
selves and become visible as long as the dominant characters are pres-
ent. When a dominant character is absent, however, its recessive
alternate is free to express itself and become visible.
For example, in the case of tall and dwarf peas, taUness is a domi-
nant character and dwarfness is its alternative recessive. WTien a
dwarf appears, therefore, there is present no dominant tallness to
suppress it. In the F, generation all the individuals were tall because,
although they had all received the recessive character of dwarfness
from one of the parents, they had received the dominant character
of tallness from the other parent, and so dwarfness did not ap])ear in
any of them. Such pairs of alternative characters are now commonly
called allelomorphs. Thus tallness and dwarfness are allelomorphs
in the pea, one dominant over the other, which is therefore recessive.
3. Purity of gametes. — A gamete can contain only one of two
alternative characters. For example, it may contain the character
• From Coulter and Coulter, Plant Genetics (The University of Chicago Press
copyright iqi8).
346 EVOLUTION, GENETICS, AND EUGENICS
for tallness or for dwarfness, but not both. In other words, allelo-
morphs cannot be represented in the same gamete. If the gamete
having the character for tallness unites with one having the character
for dwarfness, the resulting zygote will contain both, but will produce
a tall individual because tallness is dominant over dwarfness. When
this tall hybrid produces gametes, however, one-half of them will
contain the character for dwarfness. Thus the alternative characters
are "segregated" in gamete formation and no gamete will have both
characters.
These three theses, independent unit characters, dominance, and
purity of gametes (better called segregation), make up the theoretical
explanation of Mendel's law. Independent unit characters was of
course a necessary conception. It was original with Mendel, and has
also been original with other investigators, but this conception does not
represent the essential feature of Mendel's law. The idea of domi-
nance had been somewhat vaguely proposed before Mendel's time.
In the old literature on animal breeding one meets theories of pre-
potency, which were proposed again and again before the discovery
of Mendel's work in 1900. In any event Mendel was the first to
formulate definitely the theory of dominance among unit characters.
It should be realized also that dominance is not an essential feature of
Mendel's theory. Many cases are known in which dominance fails,
but in other regards the Mendelian inheritance is strictly followed.
The essential feature of Mendel's theory is his conception of the
purity oj gametes, brought about by the segregation of alternative
characters. The striking fact is that this conception, purely theoreti-
cal with Mendel, has since been confirmed by cytology. In the
mechanism of cell division each chromosome is divided into two equal
parts and each daughter-cell receives one of these parts. It is a
reasonable inference that chromosomes are bearers of hereditary
characters. In the production of gametes the number of chromosomes,
characteristic of the organism is reduced one-half. As a consequence
each gamete carries only one-half the characters of the individual that
produced it. An application of these statements to an explanation of
Mendel's 3 : i ratio will illustrate the situation.
For convenience we will assume that the nuclei of Mendel's peas
have four chromosomes each (Fig. 57). In the case of a tall plant two
of the four chromosomes carry the character for tallness, that is, some
thing that determines the production of the tall character in the
somatoplasm, which is practically the body builder. This unknown
MENDEL'S LAWS OF HEREDITY
347
something is called by various names in the literature of genetics, the
commonest one being determiner. In our illustration, therefore, two
of the four chromosomes carry the determiner for tallness. At this
point two questions may be asked.
I . Why do just two of the four chromosomes carry the determiner
for tallness rather than all of them or only one of them ? Just here
it would be difficult to explain why no more than two of the four
chromosomes are represented as carrying the same determiner. This
will be explained later. It is easy to answer, however, why the deter-
miner is being carried by more than one chromosome. When gametes
are formed the chromosome number is reduced one-half. Since every
gamete from a pure tall plant carries the determiner for tallness there
Dwarf Parent
Fig. 57. — Diagram illustrating behavior of chromosomes in Mendel's cross
of tall and dwarf peas. Large rectangular figures, nuclei of zygotes or mature
individuals; large circles, gametes; small circles within zygotes and gametes,
chromosomes; letters on chromosomes, determiners (T, tallness; D, dwarf ness).
{From Coulter and Coulter.)
must have been at least two chromosomes carrying the determiner
before the gametes were formed.
2. Do these two chromosomes carry any other determiner than
that for tallness ? In a tentative way this question may be answered
in the affirmative, but a fuller discussion of the situation must be
deferred. There is much experimental evidence that indicates that
more than one determiner is carried on a single chromosome. In some
cases also there are more MendeHan determiners than there are
chromosomes.
The situation is represented in Fig. 57. This shows a somatic
cell with the diploid or 2x number of chromosomes. In the formation
of gametes this number is reduced to the haploid, or x number, which
in this case is two. The diagram shows that the reduction separates
348
EVOLUTION, GENETICS, AND EUGENICS
(segregates) the two chromosomes carrying the character for tallness,
so that each gamete contains one. This occurs for the other characters
as well as for that of tallness. From the tall plant, therefore, all the
gametes will contain the character for tallness, and from a dwarf plant
all of the gametes would contain the character for dwarfness. When
these two individuals are crossed the zygote will contain both charac-
ters, and these two characters will be transmitted together in the
succeeding cell generations. The individual from such a zygote of
course would be tall, but at the same time it would be carrying a
recessive determiner for dwarfness, and this fact would be shown by
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Fig. 58. — Diagram illustrating behavior of first hybrid generation (Fi) when
inbred. Illustrates meaning of "segregation" and "purity of gametes" and how
chance matings of Fi gametes result in 3:1 ratio in F, generation; dwarf indi-
vidual produced only by zygote in lower right-hand corner. {Frotn Coulter and
Coulter.)
its behavior in breeding. The result of inbreeding such hybrids is
indicated in the accompanying diagram (Fig. 58), which represents
the chance matings of two kinds of gametes. The obvious results are
three tall individuals and one dwarf. This is the so-called monohybrid
ratio, which means the ratio when a single pair of allelomorphs is
considered.
Before discussing the further development of Mendel's law it will
be necessary to explain some of the terminology of genetics. When
each gamete carries the same kind of determiner the zygote is said to
receive a double dose; when a zygote receives only a single such deter-
miner it is said to receive a single dose. In Fig. 58 one zygote receives
a double dose of tallness and two others a single dose. These phrases
are more or less common in the literature of the subject, but the more
MENDEL'S LAWS OF HEREDITY 349
frequent terminology is as follows. When two similar gametes unite
to form a zygote it is called a homozygote; when the two pairing
gametes are different the zygote is called a heterozygote. Using this
terminology it is evident that the 3:1 ratio of the F, generation is
really a 1:2:1 ratio, as follows: i homozygote for the dominant
character, 2 heterozygotes, and i homozygote for the recessive charac-
ter. The 1:2:1 ratio therefore is the significant one and appears as a
3 : 1 ratio only because of dominance.
In the experiment represented in Fig. 58 three tall individuals
appear in the F, generation. Superficially the individuals look alike,
but it is reaUzed that i differs from the other 2 in germinal constitu-
tion, for I will produce only one kind of gamete, while the other 2
will produce two kinds. To indicate this situation Johannsen has
introduced some appropriate terminology. Organisms which seem
to be alike, regardless of their germinal constitution, are said to be
phenotypically alike, or to belong to the same phenotype. On the
other hand, organisms having identical germinal constitution are said
to be genotypically alike, or to belong to the same genotype. From
the standpoint of phenotypes only, Mendel's Fj generation shows the
3:1 ratio; but if genotypes are considered, it shows the 1:2:1 ratio.
In other words, this group of forms contains two phenotypes but three
genotypes.
Referring again to Fig. 58 several things may be inferred. It can
be seen what will happen in the F3 generation when the F, individuals
are inbred. The dominant homozygote will produce only dominant
homozygotes in the F3 generation and will continue to produce them
as long as it is inbred. The two heterozygotes will split up in the
Fj generation in the same 1:2:1 ratio as did their hybrid parents of the
F, generation. The recessive homozygote will produce only recessive
homozygotes as long as it is kept pure by being inbred.
It is interesting to consider what will happen if a heterozygote
form is crossed with a homozygous recessive. It should be obvious
that one-half of the progeny would be pure recessives, while the other
half would be heterozygotes, that is, there would be a 1:1 ratio. A
similar result would be obtained by crossing a heterozygote with a
dominant homozygote, although all the immediate progeny would
show the dominant character. The real situation would be revealed,
however, when this progeny was inbred, for one-half would be homo-
zygous (pure breeders) and the other half would be heterozygous
(hybrid breeders).
35° EVOLUTION, GENETICS, AND EUGENICS
Thus far we have considered only what is called the monohybrid
ratio, that is, the ratio obtained from one pair of contrasting charac-
ters, such as tallness and dwarfness. The next step is to consider the
dihybrid ratio. Mendel also used contrasting seed characters, find-
ing, for example, that smoothness in seeds is dominant to a wrinkled
condition. Introducing this pair of contrasting characters into the
situation we have been considering, the dihybrid ratio will be the
result. Crossing a tall, smooth-seeded individual with a dwarf
wrinkled-seeded individual it is evident that all of the Fi or first hybrid
generation will be tall, smooth-seeded individuals, since both of these
characters are dominant. In the F, generation, however, the follow-
ing ratio will appear: 9 tall smooth, 3 dwarf smooth, 3 tall wrinkled,
I dwarf wrinkled; which is a 9:3:3:1 ratio. This is the dihybrid
ratio, the explanation of which may be indicated in Fig. , The
question may be raised why the characters for tallness and smoothness
are not represented on the same chromosome. If they were, the
result would be a simple monohybrid ratio, except that the tall indi-
viduals would always be smooth-seeded as well, and dwarfs would be
always wrinkled-seeded. The possibility of one chromosome carrying
two different determiners will be considered later, but at present we
shall assume that these determiners are on different chromosomes.
Fig. 59 shows that we are dealing with two homozygotes, each pro-
ducing only one kind of gamete, so that all the hybrid progeny will
be similar, both genotypically and phenotypically, that is, with the
same germinal constitution and the same appearance. By inbreeding
these F, individuals, it will be seen that four kinds of gametes are
involved. Crossing these four kinds of gametes the resulting com-
binations are indicated in Fig. 59. The result is four phenotypes, as
follows: Nos. I, 2, 3, 4, 5, 7, 9, 10, 13 are tall smooth individuals;
Nos. II, 12, 15 are dwarf smooth; Nos. 6, 8, 14 are tall wrinkled;
No. 16 is dwarf wrinkled. This is the 9:3:3:1 ratio.
It will be noticed that Nos. 1, 6, 11, 16 are homozygotes and there-
fore will breed true; but the rest are heterozygotes, either for one pair
of characters or for both, and these would spUt into various types upon
further breeding.
The next step is the trihybrid ratio. Mendel found yellow seeds
dominant over green seeds, and if this pair of characters is included
with those used above the trihybrid result can be observed. The
experiment would consist in crossing tall, smooth, yellow individuals
with dwarf, wrinkled, srreen individuals; and it is obvious that the
MENDEL'S LAWS OF HEREDITY
351
hybrid progeny would all be tall, smooth, yellow, since these three
characters are dominant. Inbreeding the hybrids gives the following
result in the F2 generation: 27 tall smooth yellow, 9 tall smooth green,
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Dwarf Wrinkled
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Fig. 59. — Diagram illustrating dihybrid ratio. Upper part shows how original
parents were crossed to give Fi hybrid; lower part shows Fi hybrid producing
four kinds of gametes; chance matings among these gametes, when Fi is inbred,
result as indicated in the large set of squares and explains the 9:3:3:1 ratio in
the F2 generation. {From Coulter a?id Coulter.)
9 tall wrinkled yellow, 9 dwarf smooth yellow, 3 tall wrinkled green,
3 dwarf smooth green, 3 dwarf wrinkled yellow, i dwarf wrinkled
green. The trihybrid ratio therefore is 27:9:9:9:3:3:3:1. This
involves 64 individuals and 8 pheno types.
352 EVOLUTION, GENETICS, AND EUGENICS
ILLUSTRATIONS OF SIMPLE MENDELIAN INHERITANCE IN
BOTH ANIMALS AND PLANTS*
J. ARTHUR THOMSON
How far has Mendel's experience been confirmed? — There has
been confirmatory work by Correns (on peas, maize, and garden-
stock), by Tschermak (on peas), by De Vries (on maize, etc.), by
Bateson and his collaborators (on a large variety of organisms), by
Darbishire (on mice), by Hurst (on rabbits), by Toyama (on silk-
moths), by Davenport (on poultry), and so on. There are some
difficulties and not a few discrepancies, but, as Bateson says, "the
truth of the law enunciated by Mendel is now estabUshed for a large
number of cases of most dissimilar characters."
In experimenting with Lychnis, Atropa, and Datura, Bateson and
Saunders found that the phenomena conformed with Mendel's law
"with considerable accuracy, and no exceptions that do not appear to
be merely fortuitous were discovered. In the case of Matthiola
(garden-stock), the phenomena are much more complex. There are
simple cases which follow Mendelian principles, but others of various
kinds which apparently do not. The latter cases fall into fairly defin-
ite groups, but their nature is obscure."
In experiments with poultry, the phenomena of dominance and
recession were detected; interbreeding of the hybrid offspring resulted
in a mixed progeny, " some presenting the dominant, others the reces-
sive character, in proportions following Mendel's Law with fair con-
sistency, though in certain cases disturbing factors are to be suspected."
The general result, so far, is that Mendel's law has received con-
firmation in a number of very dissimilar cases.
Dominant and recessive characters. — Let us first of all collect a
number of instances of contrasted characters which behave in relation
to one another as dominants and recessives.
Dominant Recessive
Pisum sativum Tallness Dwarf ness
• Round seeds Wrinkled seeds
Coloured seed-coats White seed-coats
Yellow albumen in coty- Green albumen in coty-
ledons ledons
Purple flowers White flowers
Sweet pea Tall ordinary form Dwarf or "cupid" vari-
ety
' From J. Arthur Thomson, Heredity (copyright 1907). Used by special
permission of the publisher, John Murray, London.
MENDEL'S LAWS OF HEREDITY 353
Dominant Recessive
Stocks Coloured Wliite
Wheat and barley Beardless Bearded
Later ripening Rivett Early ripening Polish
wheat wheat
Non-immune to "rust" Immune to "rust"
Maize "Starch" seed "Sugar" seed
Nettles (Urtica pihilifera a.nd
U. dodartii) Serrate leaf margin Entire leaf margin
Mirabills jalapa and M. rosea . Rose colour Other colours
Mice Coloured coat Albino coat
Normal "Waltzing" variety
Rabbits Coloured coat Albino coat
Angora fur Short fur
Poultry "Rose" comb of Ham- High serrated "single"
burghs and Wyandottes comb of Leghorns and
Andalusians
Cattle Hornlessness Horns
Snails Bandless shell Banded shell
Other instances in plants. — As is well known, there are two almost
equally common forms of wild primrose: (A) thrum- types, with
short styles and with anthers at the top of the corolla-tube; and (B)
pin-types, with long styles and with anthers half way down the tube.
The thrum-type is dominant over the pin-type.
The original species of Chinese primrose {Primula sinensis) has a
palmate leaf. About i860 a sport arose (from seed) which had a
pinnate or "fern" leaf. The palmate form is dominant, and the fern
leaf is recessive.
The deformed "Snapdragon" variety of sweet pea behaves as a
recessive to the normal type.
The 2-row barley has certain lateral flowers which are exclusively
staminate; in 6-row barley all the flowers are stamina te and pistillate,
and all set seed. Mr. Biffen crossed these forms, and found that the
more negative character was dominant. The offspring were 2-rowed.
Maize. — When the common or starchy round-seeded maize is
crossed with the wrinkled-seeded sugar-maize, the round starchy char-
acter dominates. When an egg-cell of the wrinkled sugar-maize stock
is fertilised by a pollen-cell of the round starchy stock, the result is a
round seed with starchy endosperm. If this seed is sown, it becomes
a plant which, on self-fertilisation, forms a cob with a mixture of
round starchy and wrinkled sugary seeds in the ratio 3:1. The
wrinkled seeds yield sugar-maize; the round seeds yield two "impure
rounds" to one "pure round." Correns has observed a very inter-
esting case in which two pairs of contrasted characters are implicated.
354 EVOLUTION, GENETICS, AND EUGENICS
One variety, Zea mays alba, which has smooth white seeds, was
crossed with another variety, Zea mays coeruleodulcis, which has
wrinkled blue seeds. The hybrids (Fi) had smooth blue seeds, one
character of each parent being dominant, and one character of each
parent being recessive. The hybrids were inbred, and the progeny
(Fa) showed four combinations — smooth blue, smooth white, wrinkled
blue, and wrinkled white (the dominant characters are itaUcised).
In the next generation (Fj), the wrinkled white, inbred, yielded
wrinkled white — a case of extracted recessives, breeding true. The
smooth whites and wrinkled blues, inbred, yielded partly forms like
themselves and partly wrinkled white. The smooth blues, inbred,
yielded the same combinations as in Fj.
A finer corroboration of Mendelian could hardly be wished.
Nettles. — Correns crossed two "species of stinging-nettle," Urtica
pilulijera L. and U. dodartii L., which resemble one another except as
regards leaf-margin, strongly dentate in the former, almost entire in
the latter. The hybrid offspring (Fi) have all dentate leaves like the
male or the female parent, as the case may be. The dentate character
is absolutely dominant. The inbred (self-fertilised) hybrids produce
offspring (FJ of two kinds, with dentate and with entire margins, on an
average in the Mendelian proportion, 3 : i.
"Immunity to rust in wheat. — Some kinds of wheat are very
susceptible to the fungoid disease known as ' rust ' ; others are immune.
The quality of immunity to rust is recessive to the quality of predis-
position to rust.
" When an immune and a non-iiimiune strain are crossed together
the resulting hybrids are all susceptible to * rust.' On self-fertilisation
such hybrids produce seed from which appear dominant 'rusts' and
recessive immune plants in the expected ratio of 3:1. From this
simple experiment the phrase 'resistance to disease' has acquired a
more precise significance, and the wide field of research here opened
up in this connection promises results of the utmost practical as well
as theoretical importance. To the question, ' Who can bring a clean
thing out of an unclean ? ' we are beginning to find an answer, nor is
the answer the same as that once given by Job" (R. C. Punnett).
Silkworms. — Toyama paired Siamese silkmoths with yellow or
with white cocoons; the offspring produced only yellow cocoons.
When the hybrids were inbred, the result was two sets, one producing
white cocoons, the other producing yellow cocoons, and the proportion
was Mendehan — 25.037 white and 74.96 yellow. The whites bred
MENDEL'S LAWS OF HEREDITY 355
true; the yellows when inbred showed themselves to be pure domi-
nants or "yellows" and dominant-recessives — i.e., splitting up again
into yellows and whites in the usual proportion. More intricate
experiments confirmed this general result.
It must be noted, however, that Coutagne has made much more
elaborate experiments with different results, which in many cases can-
not be interpreted on the Mendelian theory. Thus he found (i) that
the hybrid forms were sometimes blends of the parents and different
from both; (2) that in other cases the brood included some like one
parent in a particular character, some like the other parent, and some
intermediate; and (3) that in other cases the individuals showed no
fusion of characters, but resembled one or other parent. It is likely
that the discrepancy may be explained as due to considerable diversity
of origin in the domesticated races of silkworm, so that, while they
breed true when left to themselves, a disturbance of the usual routine
leads to the liberation of latent characters.
Lina lapponica. — Miss McCracken has made a fine study of the
hereditary relations in this Californian beetle, which occurs in two
types, spotted (dominant) and black (recessive). They are always
crossing in natural conditions, but there are no intermediates, and it
is easy by isolation to rear a "pure" spotted race and a "pure" black
race. When spotted forms are paired they may produce only spotted
progeny — a case of extracted dominants. In other cases, however,
they yield spotted and black forms (1,021 spotted, 345 black), i.e., in
the Mendelian proportion of 3 : i — a case of dominant-recessives inbred.
Snails. — Lang paired "pure" five-banded forms of the common
or garden snail. Helix horiensis, with bandless forms from bandless
colonies. The young of the first generation were aU bandless, the
banded character being recessive. When these were paired the off-
spring were bandless and banded in the Mendelian ratio, 3:1. Fur-
ther experiments confirmed this, not only as regards bands, but also
as regards colour (yellow or red), size, and the form of the umbiUcus.
It may be said, therefore, that common snails {Helix hortensis and Helix
nemoralis) illustrate Mendelian inheritance.
Poultry. — Numerous breeding experiments with poultry have
been made by Bateson, Bateson and Punnett, Hurst, Davenport, and
others, many of which show Mendelian phenomena with great clear-
ness, while others are strangely conflicting. One of the reasons for the
complicated results is evidently to be found in the difficulty of securing
thoroughly "pure" breeds, for many that breed true as long as they
356 EVOLUTION, GENETICS, AND EUGENICS
are inbred tend to liberate latent characters when the ordinary course
of breeding is departed from.
Hurst contrasts the following characters, which usually show them-
selves dominants and recessives; but it has to be admitted that the
dominance — always complete for some characters — is for others fre-
quently, or even always incomplete — i.e., showing traces of the corre-
sponding recessives.
Dominant Characters Recessive Characters
Rose comb Leaf comb, single comb
White plumage Black plumage, buff plumage
Extra toes Normal toes
Feathered shanks Bare shanks
Crested head Uncrested head
Brown eggs ^A^lite eggs
Broodiness Non-broodiness
Davenport's copiously illustrated work is also of great interest.
He shows in case after case that the character dominant in the first
hybrids is more or less influenced by the recessive character. Polish
fowls with a large hernia of the brain on the top of the head were
paired with Minorcas with normal heads. The hybrids showed no
hernia, but most of them showed a frontal prominence. When the
hybrids were inbred the hernia occurred in 23.5 per cent — a. close
approximation to the theoretical 25 per cent.
Single-combed black Minorcas were crossed with white-crested
black Polish fowls with a very small bifid comb. The hybrids had
combs single in front, split behind. When the hybrids were inbred
there resulted in a total of 10 1 offspring, 29.7 per cent with single
combs (like Minorcas), 46.5 per cent with Y-shaped combs, and 23.8
per cent with no combs or only papillae (like the Polish forms). Here,
again, the result is in a general way Mendelian, but the Y-like comb
is a complication.
Pigeons. — R. Staples-Browne crossed a web-footed pigeon (an
occasional discontinuous variation) with a normal form, and got six
normal young. In other words, the web-foot character is recessive
to the normal foot character. The hybrids were inbred, and in one
case produced nine with normal feet and three with webbed-feet — a
Mendelian splitting-up. But from another pair of hybrids seventeen
normal offspring resulted. Thus, the illustration of Mendelian
inheritance is inconclusive. Besides the numbers were too small.
We have noticed elsewhere that crossing different breeds of pigeons
often results in forms which more or less resemble the reputed original
MENDEL'S LAWS OF HEREDITY 357
ancestor, the wild rock dove; in other words, reversions occur. Often,
however, the results seem quite anomalous, which is probably due to
the number of latent characters which different races of pigeons appear
to carry.
Mice. — Mendelian phenomena have been carefully studied in
mice. Thus, when a grey mouse is paired with an albino, the hybrid
offspring are always grey. When these are inbred, they yield greys
and albinos, approximately in the proportion of 3:1. Thus Cuenot
obtained 198 grey, and 72 albinos.
Darbishire has obtained many results which harmonise well with
Mendelian theory, while others require some ingenuity if they are to
be fitted in with this interpretation. As a good case we may cite one
where the inbreeding of pigmented mice — derived from crossing pig-
mented and albino individuals — yielded 159 pigmented young and 55
albinos (53.5 being the theoretical anticipation). When similar
hybrids were paired with pure albinos, they yielded 69 pigmented and
69 albino forms, precisely as the theory would lead us to expect:
D R
\
D(R)
X
D(R)
1 D-l-2 D(R)-i-i R
X
3R
D(R) R
Cu^not crossed an albino AG (with latent grey) with an albmo AB
(with latent black), and obtained albinos (AGAB). He crossed a
black mouse CB with an albino AY (with latent yellow), and obtained
yellow mice (CBAY). He then paired AGAB (albino) with CBAY
(yellow) and obtained 151 young — 81 albinos, 34 yellow, 20 black, 16
grey; the theoretical anticipation being — 76 albinos, 38 yellow, 19
black, 19 grey. This is an exceedingly striking and convincing case.
Waltzing mice. — The mice of this interesting Japanese breed have
among other peculiarities the habit of waltzing round in circles. When
waltzing mice are crossed with normal mice, their abnormal quality
behaves as a recessive.
358 EVOLUTION, GENETICS, AND EUGENICS
Guinea-pigs. — If a black guinea-pig of pure race be crossed with
a white one the offspring will be all black, and if these are mated with
each other the recessive white character reappears on the average in
one in four of their offspring. These whites mated with each other
produce only white offspring, while the black are as usual of two kinds,
pure blacks and impure blacks. Similarly, as Professor Castle has
shown, a rough coat is dominant over a smooth coat, and a short coat
over a long coat.
Rabbits. — Hurst paired white Angora rabbits (with pink eyes and
silky hair) with "Belgian hare" rabbits (with pigmented skin, dark
eyes, and short yellow fur). The hybrids were pigmented like the
"Belgian hares," but the fur was grey like that of the wild rabbit.
These hybrids were inbred, and 14 distinct types resulted — an apparent
"epidemic of variation" to which Mendel's theory has supplied the
clue, for four pairs of contrasted characters are involved in the hybrid
inbreeding — namely, short hair versus long hair, pigmented coat versus
albinos, grey versus black coat, uniform versus marked coat (Dutch
marking latent in the albinos), and the 14 distinct types illustrate the
possible combinations.
As regards short hair versus long hair, Hurst found that when the
short-coated hybrids were inbred they produced short-haired forms
like the Belgian hare grandparent, and long-haired forms like the
Angora grandparent. Out of 70 which reached the age of two months
or more, 53 were short-haired and 17 long-haired — a close approxi-
mation to the Mendelian anticipation, 52.5 : 17.5. Similarly, as
regards pigmented coat versus albino, the hybrids, when inbred,
yielded 132 pigmented and 39 albino forms — a close approximation to
the Mendelian expectation, 129 : 43; and so on.
Cats. — There are some interesting results as to colour (Doncaster).
Thus, "pure" orange $ crossed by "pure" black $, gives tortoiseshell
females and yellow males, but black crossed by orange gives black
males or females, tortoiseshell females, and orange males. It seems
that orange usually dominates over black in males, while in females
the orange (for some unknown reason) is less dominant and tortoise-
shell results. Male tortoiseshell cats are very rare. In this case the
results are complicated by some pecuharity wrapped up with "sex."
When a male tortoiseshell is paired with a female tortoiseshell the
kittens are tortoiseshell, orange, and black — which is what Mendelian
theory would lead us to expect.
Man. — Evidence of Mendelian phenomena in man is as yet very
scanty. It appears that the condition known as brachydactylism.
MENDEL'S LAWS OF HEREDITY 359
where the fingers are all thumbs with two joints instead of three,
is dominant over the normal. In five generations chronicled by Fara-
bee about half of the offspring were of the abnormal type, though the
marriages were apparently always with unrelated normal individuals.
Moreover, no normal member of the Uneage is known to have trans-
mitted the abnormality. Another good case has been recently dis-
cussed by Drinkwater.
Of great interest also is Mr. Nettleship's account of the descend-
ants of one Jean Nougaret (bom 1637), who was afflicted with "night-
blindness" — a condition apparently due to loss of visual pvirple. It
seems to behave like a unit character. There are records of over 2,000
individuals; and the night-blindness is dominant over normal eye-
sight. The notable point is that during two and a half centuries no
normal member of the lineage who married another normal, whether
related or not, ever transmitted the disease.
Human eye-colour affords another illustration. It is largely
determined by the presence or absence of two distinct layers of pig-
ment. In the true blue eye only one of these pigmentary layers is
visibly present, the posterior purple pigment of the choroid, which,
being reflected through the fibrous structure of the iris, produces the
blue colour. In the absence or partial absence of this pigment the
eye appears to be "pink," as in albinos. In the ordinary brown eye
two layers of pigment are present, for in addition to the posterior
purple layer there is also an anterior brown layer, in front of the iris.
Major C. C. Hurst found that the eye with two layers of visible pigment
(duplex) is dominant and the eye with one layer of visible pigment
(simplex) recessive. Or, putting it in another way, the presence of the
brown front layer is dominant to its absence. Practically the same con-
clusion was reached independently by Professor and Mrs. Davenport.
The Davenports and Major Hurst have also brought forward some
evidence illustrating in typical Caucasians the dominance of dark to
fair skins, their segregation in the same family, and the apparent
purity of the extracted fair individuals. Hurst also gives evidence
that "fiery red" hair behaves as a recessive to brown, and that the
musical sense or temperament is also recessive. It seems as if an
individual is non-musical owing to the presence of an inhibitory factor
preventing the expression of musical temperament which is poten-
tially present in everyone (Hurst, 191 2).
It would be interesting to have precise information as to the pro-
geny of Eurasians who intermarry, for here the original hybrids result
from the mixture of two very distinct races.
CHAPTER XXVII
THE PHYSICAL BASIS OF MENDELISM*
ERNEST B. BABCOCK AND ROY E. CLAUSEN
Recent investigations in heredity have focused attention upon the
chromosome mechanism as the physical basis for the segregation and
recombination of the units of MendeUan inheritance. The importance
of cytological phenomena to students of genetics is admirably summed
up by E. E. Wilson in the brief statement that "heredity is a conse-
quence of the genetic continuity of cells by division, and the germ cells
form the vehicle of transmission from one generation to another." It
is appropriate, therefore, to introduce the subject of Mendelism with a
formal and brief treatment of the chromosome mechanism and its
mode of operation, on the one hand, in the building up of the body
from the single cell with which the individual begins its existence, and,
on the other hand, in the production of germ cells when the individual
reaches the reproductive period of its Ufe cycle. It is the purpose of
this chapter merely to deal with the fundamental facts of cytology
which are necessary to an understanding of the connection between
cell behavior and Mendelian phenomena. Details unessential to such
an understanding, however well established cytologically, will not be
dealt with in this treatment to the end that the cardinal points may be
presented as simply and as clearly as possible.
The chromosomes. — With few exceptions the number of chromo-
somes in the cells of any individual is constant and characteristic of
the species to which the individual belongs. Thus it is characteristic
of Drosophila ampelophila that the cells contain eight chromosomes.
In maize the cells contain twenty chromosomes, in wheat sixteen, and
in man forty-eight, and so on through the entire plant and animal
kingdoms.
Not only is the 'number of chromosomes in a particular species
constant, but the chromosomes themselves possess a definite indi-
viduality. Man and tobacco have cells with the same number of
chromosomes. It is needless to point out that these chromosomes,
« From E. B. Rabcock and R. E. Clausen, Genetics in Relation to Agriculture
(copyright iQiS). Used by special permission of the publishers, The McGraw-
Hill Book Company.
360
THE PHYSICAL BASIS OF MENDELISM 361
however, are qualitatively very different. Similarly within the species
the chromosomes are not all alike; on the contrary, especially in
certain forms, they exhibit very marked differences in size and shape.
This is peculiarly well illustrated in Drosophila as shown in Fig. 60.
Here it is possible to recognize in the female two large pairs of curved
chromosomes very similar in size and shape. There is also a very smaU
pair of chromosomes, and finally there is a pair of straight ones about
two-thirds as long as the large curved chromosomes. In the male the
same relations hold except that instead of the pair of straight chromo-
somes there is a pair consisting of one straight and one somewhat
larger hooked chromosome. The significance of this difference in
chromosome content in the sexes will be pointed out in a consideration
FEHllE HILC
Fig. 60. — Diagram showing the characteristic pairing, size relations, and
shapes of the chromosomes of Drosophila melanogaster. In the male an X and a
Y chromosome correspond to the X pair of the lemale. On the basis of X ioq
the length of each long autosome 159, of each small autosome 12, and of Y 112, of
the long arm of F 71, and of the short arm of Y 41. (From Babcock and Clausen,
after Bridges.)
of the inheritance of sex. The pair of straight chromosomes we call
the sex or X-chromosomes, the unequal mate of the X-chromosome in
the male of this species is called the Y-chromosome. The other
chromosomes are called autosomes when it is desired to distinguish
them as a class from the sex chromosomes. Drosophila is not unique
in possessing chromosomes of such characteristic shapes and sizes; but
more and more as cytology advances it is becoming possible to dis-
tinguish chromosomes, and to recognize them at every cell division.
Moreover, the characteristic paired relations which exist among
the chromosomes of Drosophila are of general significance. When
mature germ cells are formed in an individual, reduction divisions
occur by means of which the chromosome number is reduced in the
germ cells to one-half that characteristic of the body cells. Thus the
362 EVOLUTION, GENETICS, AND EUGENICS
germ cells of Drosophila contain four chromosomes as the result of a
reduction which takes place in such a manner that each germ cell con-
tains one member of each pair of chromosomes. As a consequence,
the germ cell of Drosophila contains two large curved autosomes,
representing the two pairs of these chromosomes, one small autosome,
and one X- or one Y-chrojuosome. The same thing is true for other
species of plants and animals — in the reduction divisions the
chromosomes are distributed in such a manner that each germ cell
receives one member of each pair of chromosomes. It follows from
this that in general a definite number of pairs of chromosomes is
characteristic of the body cells of individuals of a given species, and,
taking the chromosomes by pairs, one member of each pair is derived
from one parent and the other from the other parent.
From the standpoint of interpretation the chromosomes are aggre-
gates of chromatin material which in itself is definitely and highly
organized. Our conceptions of this feature of cell organization are
based on appearances of the cytological preparations from certain of
the more favorable plants and animals and further interpreted by
investigations on heredity. Accordingly the entire chromatin con-
tent of the nucleus is regarded as made up of a definite number of indi-
vidual chromatin elements called chromomeres. The number of
chromomeres in a cell of any species must run into the thousands. A
certain definite group of these elements make up each chromosome,
and at every cell division this chromosome is reformed from the same
group of chromomeres, but the chromosome is definitely organized
with respect to the position or locus occupied by each chromomere.
At certain stages in the history of chromosomes, they are simply Unes
of chromomeres, very much like single strings of beads with each bead
corresponding to a chromomere. Now it appears probable that all
the chromomeres in a chromosome are different, as though our string
of beads had no duplicates throughout its length. Moreover, each
chromomere has a definite place or locus in the particular chromosome
in which it belongs and it is always found at that particular locus.
The chromomeres of this discussion are identified with the factors of
Mendelian heredity, and how closely this conception of the nature of
chromatin and its complex organization corresponds to the modern
view of Mendelian phenomena will be pointed out as each new phase
of MendeUsm is taken up.
Somatic cell division. — The phenomena of cell division (called
mitosis) are represented in outHne in Fig. 61, for a species having four
THE PH\'SIC.\L BASIS OF MENDELISM
363
chromosomes in its body cell. Bearing in mind the description which
has just been given of the organization of the chromatin material we
may follow the steps involved in mitosis as they are outlined in this
figure. In the " resting " cell at A the chromatin is scattered through-
out the nucleus in clumps or knots loosely strung together to form an
irregular network. As the cell prepares for division the chromatin
elements appear in more definite form until at B the chromomeres have
Fig. 61. — Diagram of mitosis in a species having four chromosomes in its
cells, yl, the "resting" cell; 5, formation of the spireme thread; C, longitudinal
division of the spireme thread and transverse segmentation into four chromosomes;
D, separation of the daughter chromosomes formed by longitudinal spHtting
of spireme thread; E, beginnings of nuclear reconstruction and di\dsion of the cell
body; F, cell division complete and daughter nuclei in the "resting" stage.
(From Babcock and Clausen.)
arranged themselves in a single row in a long continuous spireme-
thread. This spireme-thread may be considered to be made up of the
four chromosomes united end to end with the chromomeres arranged
in a linear series. As mitosis progresses to the next stage represented
at C, each chromomere of the spireme-thread divides into two, so that
a double spireme-thread results from the longitudinal splitting of the
original thread. Both parts of the thread are quantitatively and quali-
tatively equal, for, by the spHtting of all the chromomeres both of the
364 EVOLUTION, GENETICS, AND EUGENICS
threads come to possess all of the individual elements of the original
spireme thread. Following the splitting of the chromomeres and the
formation of a double spireme, the spireme-thread contracts and seg-
ments transversely forming four double chromosomes, the number
characteristic of the cells of this individual. This is the stage shown
at C where also is shown the origin of the spindle, a part of the mechan-
ism in mitosis. The chromosomes now still further contract until
they assume their characteristic shapes and sizes. They next appear
in an equatorial position on the spindle as shown at D, where the two
pairs of double chromosomes, one larger and one smaller, are dia-
grammed and the nucleolus, the large black body of the previous steps,
is shown cast out and degenerating. The daughter chromosomes of
each pair now separate from each other until at E they have moved
nearly to the opposite poles of the spindles and are beginning to fray
out and seemingly to lose their identity. At this stage actual division
of the cell body has begun. Finally at F, the chromosomes have com-
pletely lost all appearance of their identity, the chromatin material
is distributed thruout the nucleus as in the original cell shown at A,
and the nucleolus has been reformed in each nucleus. Division of the
cell-body has resulted in two daughter cells, each of which, so far as
chromomeres are concerned, contains exactly the same chromatin
elements as the original cell.
There are many variations in this process particularly in the order,
of occurrence of the steps, but these variations in nowise modify the
essential fact of mitosis which is that the chromatin material of the
cell is converted into a thread which spUts thruout its entire length
into two halves so that the daughter nuclei receive exactly equivalent
portions of chromatin material. This precise division of the chro-
matin is brought about by a division of each chromomere so that not
only do the daughter nuclei receive equivalent portions of chromatin
but these portions are also equivalent quaUtatively to the entire
chromatin content of the mother cell. By this method then each of
the cells of the body finally comes to possess not only the whole num-
ber of chromosomes contributed by the two parents, but also the
entire set of chromatin elements which it received from them. The
extreme care with which the cell mechanism partitions the chromatin
material in each successive cell division is in itself eloquent testimony
of the fundamental importance of this material.
The production of germ cells. — In the production of germ cells a
different set of phenomena occur which result in a reduction of this
THE PHYSICAL BASIS OF MENDELISM
365
number of chromosomes to one-half that characteristic of the somatic
cells. Preceding the actual reduction division the chromatin passes
through a complex series of steps which may be included under the
term synapsis. (This term is sometimes applied in a specific sense
to the pairing of homologous chromosomes and sometimes to the con-
traction of the chromatin threads in the conjugation stage.) The
essential steps in the prereduction process are shown in outline in
Fig. 62. At A is diagrammed a " resting " nucleus at the completion of
Fig. 62. — The reduction division as represented for a species whose diploid
number is four. A, "resting" nucleus of a primary germ cell; B, formation of
paired threads of chromomeres; C, conjugation of homologous chromosomes
(synapsis) ; D, loosening of the synaptic knots; E, condensation of the chromosomes
and disappearance of the nuclear membrane; F, homologous chromosomes about
to pass to opposite poles, thus giving each secondary germ cell a member of each
pair and one-half the somatic number. {From Babcock and Clausen.)
the multiplication divisions in the germ plasm. As a result of the exact
type of mitosis which has been outlined above it contains the full num-
ber of chromosomes characteristic of the species. The chromatin of
the nucleus next becomes organized into threads of chromomeres
which pair as shown at B. In this diagram the paired threads are
taken to represent homologous chromosomes, and the opposite chro-
momeres of the two chromosomes. The paired threads contract and
366 EVOLirnON, GENETICS, AND EUGENICS
fuse along their entire length giving the figure diagrammed at C in
which the two loops represent two pairs of homologous chromosomes
in the conjugation stage, the essential step in synapsis. Following
this stage the two contracted loops of chromatin split lengthwise and
unravel in somewhat the manner shown in D. These filaments con-
tract again forming the intertwined pairs of chromosomes shown at E,
and the nuclear membrane thereupon begins to disappear. Further
contraction and the formation of a spindle results in the reduction
figure at F, the significant feature of which is the fact that each of the
daughter nuclei resulting from this division receives only two chromo-
somes instead of the four which the original cell at A contained. Since
the original cell contained one pair of larger and one pair of smaller
chromosomes, the daughter cells which are formed each receive one
larger and one smaller chromosome.
Cytological investigation is not yet in agreement as to the inter-
pretation of synapsis especially as to the manner in which the phe-
nomena therein concerned are connected with preceding mitotic divi-
sions. Considering certain cytological investigations and the results
of research in heredity together, it appears that the thi^eads which pair
in stage B represent pairs of chromosomes with homologous chromo-
meres occupying corresponding positions along their entire length.
Likewise the contraction stage at C is taken to represent a conjugation
of the members of pairs of chromosomes which later again separate.
Other cytological evidence indicates that in some forms the conjuga-
tion of pairs of homologous chromosomes is brought about in anothei
way. However, the essential fact is the same in either case. In the
reduction figure the members of each pair of chromosomes are dis
tributed to the opposite poles of the spindle so that the daughter
nuclei received only one member of each pair.
The significance of synapsis lies in the conjugation of homologous
chromosomes. In the mitoses which have preceded this particular
division, the chromosomes were each time conceived to be reformed
from the identical group of chromomeres which they contained origi-
nally. In synapsis, however, as shown at B there is a certain amount
of intertwining of the paired threads and in the unraveling of the
chromosomes after the contraction stage there is likewise a twisting
of the filaments about each other. The indications are, therefore,
that in, synapsis there is a possibility of interchange of chromatin
material between the members of a pair of homologous chromosomes.
In all cases, however, in order to uphold our conception of the definite
THE PHYSICAL BASIS OF MENDELISM
367
I
Fig. 6j. — Diagram of chromatin inter-
change between homologous members of a
pair of chromosomes. {From Babcock and
Clausen, after Midler.)
organization of the chromosomes with respect to the chromomeres
which they contain, this interchange of material must involve exactly
equivalent portions of the two chromosomes. The chromosomes of
the reduction division shown at
F may not, therefore, be identi-
cal with the four originally
present in /I, but may represent
various combinations of portions
of both members of a particular
pair of chromosomes. The re-
sults of such interchange between
members of homologous pairs of
chromosomes is shown in Fig. 63.
At the left is shown a pair of
chromosomes, one in outline, the
other in full black. In the middle the steps in chromatin interchange
are diagrammed and finally at the right this interchange results in
a pair of chromosomes each of which is made up of parts of both
members of the original pair of chromosomes. Various combinations
may result depending on the points at which interchange takes place,
but in every case the exchange involves corresponding portions of
the two chromosomes.
Independent distribution of chromosomes. — ^In Fig. 64 are illus-
trated diagranmiatically the chromosomes of Drosophila, with particu-
lar reference to their size and form relations and to their character-
istic pairing in the cell. One member of each of these pairs of chro-
mosomes was contributed by the female parent and one member by
the male parent. In the reduction divisions these chromosomes are
separated so that each germ cell contains one member of each pair of
chromosomes. The simplest condition which could obtain is that of
independent distribution in each pair of chromosomes such that the
particular member of one pair which went to a given pole of the reduc-
tion spindle would have no influence on the distribution of the mem-
bers of any other pair. Such independent distribution of chromo-
somes appears to be actually the type followed in reduction. As a
consequence the germ cells contain various combinations of chromo-
somes with respect to their original parental derivation. In Fig. 64
the types of combinations of maternal and paternal chromosomes and
their mode of derivation in Drosophila are shown diagrammatically.
Two germ cells, one from the female with the chromosomes in outline,
368
EVOLUTION, GENETICS, AND EUGENICS
and the other from the male with the chromosomes in full black, unite
to form the female zygote shown in the middle of the figure. The
combinations of maternal and paternal chromosomes which result in
the production of germ cells in such an individual are shown diagram-
FiG. 64. — Diagram showing consequences of independent segregation of
chromosomes in Drosophila melanogaster. {From Bahcock and Clausen.)
matically in the lower portion of the figure. There are eight different
ways in which the chromosomes may be grouped in the reduction
figures and on the basis of chance any one of these types is as likely
to occur as any other. As a result there are sixteen possible combi-
nations of chromosomes in the germ cells with respect to the original
THE PHYSICAL BASIS OF MENDELISM 3^9
derivation of the chromosomes, whether from the female or from the
male parent. This of course represents only the total number of
possible combinations of entire chromosomes. By exchange of
chromatin material between homologous chromosomes resulting in the
formation of combination-chromosomes the number of actual com-
binations is greatly increased.
The number of chromosome combinations resulting from inde-
pendent distribution is that number possible when each pair of chro-
mosomes is considered separately, and every combination has an equal
chance of occurrence. With a form having but two pairs of chromo-
somes there would be only four possible combinations, three pairs
would give eight, four pairs sixteen, and in general the number of
possible combinations is given by the expression 2" in which n is the
number of pairs of chromosomes in the individual in question. In
tobacco which has 24 pairs of chromosomes the num.ber of possible
combinations in the germ cells reaches the enormous total of 16,777,-
216. This means that in the formation of zygotes in a self-fertilized
tobacco plant the actual parental combinations, i.e., combinations
identical with those of the germ cells which united to form the indi-
vidual in question, occur only twice in over sixteen million times, and
this proportion is still further lessened when the interchange of chro-
matin material between homologous chromosomes is taken into
account. The condition of independent distribution although simple
in itself results in a rapid increase in complexity with the increase in the
number of pairs of chromosomes involved.
Chromosomes and sex in Drosophila. — The relation between
inheritance and the chromosome mechanism is perhaps most simply
displayed in the inheritance of sex in those animal forms in which the
sexes occur in approximately equal proportions. Thus in Drosophila
as indicated in Fig. 65 there are three pairs of autosomes which are
alike in both the male and the female. The remaining pair of chromo-
somes, however, differ, for the female possesses two X-chromosomes
whereas in the male a single X-chromosome is paired with a Y-chromo-
some and these differences are characteristic of all normal males and
females of this species. The bearing of these differences on the
inheritance of sex is shown diagrammatically in Fig. 6^. Beginning
with the parents, the diploid number is shown in the circles represent-
ing the female and the male.
In the female the three pairs of autosomes are outlined and the
X-chromosomes only are drawn in black to indicate that they are
the ones primarily concerned in the determination of sex. Similarly in
370
EVOLUTION, GENETICS, AND EUGENICS
the male the three pairs of autosomes which are exactly like those in the
female are outlined, but the X-chromosome and the Y-chromosome are
drawn in black. The reduction division in the female results in a
Fig. 6^. — Diagram showing chromosome relations in the inheritance of sex
in Drosophila malanogastct {From Bahcock and Clausen.)
separation of the members of each pair of chromosomes, so that every
secondary germ cell (or egg) contains two large curved autosomes,
a small autosome, and an X-chromosome. Consequently as far as
chromosome content goes the eggs are all exactly alike. In the male,
THE PHYSICAL BASIS OF MENDELISM 371
however, the separation of the members of the chromosome pairs
results in sperms half of which contain an X-chromosome and half a
Y-chromosome in addition to the three autosomes. The reduction
division in the male insures an equality in numbers for the two kinds
of sperm cells and the chances that either kind of sperm will fertilize
an egg-cell are equal. By this arrangement the numerical equaUty
of the sexes is maintained. When, later, the egg cells of the female are
fertilized by the sperm cells of the male, as shown in the lower portion
of the figure, half of them being fertilized by sperm cells which contain
an X-chromosome will give females, and half uniting with sperm cells
which contain Y-chromosomes will produce males. The inheritance
of sex in Drosophila provides a beautiful illustration of the parallel
behavior of the chromosome mechanism and a somatic difference, in
this case, sex.
To recapitulate, the essential phenomena of cell behavior which fur-
nish the mechanism for the distribution of hereditary factors are these:
1. Every species is characterized by a definitely organized group
of chromosomes. The chromosomes occur in pairs, in each of which
one member is derived from each parent. In ordinary somatic mitosis
the distribution of chromatin is such that each daughter cell receives
a full complem.ent of chromosomes which are equivalent qualitatively
to those of the mother cell.
2. In germ cell formation the homologous chromosomes conjugate
during synapsis, then separate, and pass into a division figure in which
entire homologous chromosomes are opposed to each other. The
resulting reduction division gives daughter cells with half the number
of chromosomes characteristic of the species, the half number being
made up of one member of each pair of chromosomes. During synap-
sis there is an opportunity for the members of a pair of chromosomes
to exchange chromatin material. WHien such interchange takes place
equivalent portions of chromosomes both quaHtatively and quantita-
tively are involved. In the reduction division segregation within one
pair of chromosomes is entirely independent of that of any other pair
so that the combinations of parental chromosomes in the germ cell?
represent all those to be expected on the basis of chance distribution.
The student should constantly endeavor to harmonize this con-
ception of the distributing mechanism of the chromatin material with
the Mendelian interpretations of hereditary phemomena which will be
presented in what follows, to the end that he may obtain a clear and
definite idea of the interrelations between the known facts of heredity
and cell behavior.
CHAPTER XXVIII
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS
JOHN M. COULTER AND MERLE C COULTER
Thus far we have been considering Mendel's law in its simple form
and have enlarged but little upon Mendel's original statement. The
value of the law is apparent. Upon its republication in 1900 it was
taken up by biologists and numerous breeders set to work to test it.
As a consequence data for and against it began to accumulate. As
might be expected, there was much apparent evidence against the law,
but as geneticists developed a better conception of the mechanism the
contradictory evidence was explained away. Almost every type of
inheritance has now been explained according to Mendel's law. Some
of the explanations are very complicated and cannot be in eluded in
this presentation. A few of the more important cases, however, will
be presented.
I. PRESENCE AND ABSENCE HYPOTHESIS
This may be regarded as a new method of Mendehan thought. It
was first suggested by Correns, but later was worked out in detail by
other geneticists, especially Hurst, Bateson, ShuU, and East. It is
merely a modification of the mechanism involved. For example, in
the case of a hybrid obtained by crossing tall and dwarf parents the
result had been explained as due to the fact that one chromosome bears
a determiner for tallness and the other one of the pair carries the deter-
miner for dwarfness. In other words, each one of a pair of allelo-
morphs is represented by a determiner, two determiners thus being
present. Dwarfness in this case would be the result of the interaction
of that determiner and its environment during the development of the
body; and the same for tallness. When both were present, however,
the conception of the situation was as follows. The determiner for
dwarfness, setting up its usual series of reactions, early became para-
lyzed by the determiner for tallness or its products. This result was
called the dominance of the character for tallness. It was as if the
determiner for tallness completely prevented the activity of the deter-
miner for dwarfness. This conception was apparently borne out
' From Coulter and Coulter, Plant Genetics (The University of Chicago Press,
copyright 1918).
372
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS 373
by the facts and was the explanation of the mechanism generally
accepted.
According to the presence and absence hypothesis, however, the
situation is looked at from an entirely different point of view. Tall-
ness is the result of a determiner, but dwarfness is merely the result
of the absence of the determiner for tallness. The dominant character
is produced by an inheritable determiner, but the recessive character
appears only when the dominant determiner is lacking. This con-
ception has some evident advantages and may modify the previous
Mendehan diagram, as shown in Fig. 66. This appears to be a simpler
mechanism to account for the phenomenon called dominance. In the
case of the dwarf form there is a normal course of development; in the
case of the tall parent or hybrid, however, an additional determiner
Dwarf Parent
Gamete
Fig. 66. — Diagram showing how the original scheme must be modified to
satisfy the presence and absence hypothesis. (From Coulter and Coulter.)
stimulates cell growth, or cell division, or both. It is a simpler and
more useful conception, so long as it fits the facts. Some investigators,
however, claim that it cannot be applied to all the situations that have
been discovered.
This hypothesis introduces some additional terminology suggested
by Bateson. In our illustration the tall parent has two determiners
for tallness and therefore Bateson calls it duplex, having a double dose.
For the same reason the Fi individuals, having only one determiner for
tallness, he calls simplex. According to the same terminology the
dwarf parent is nulliplex with respect to its character of tallness.
Additional advantages of the presence and absence hypothesis will
appear in connection with a consideration of blending inheritance and
of cumulative factors in inheritance. Attention, however, should be
called to the fact that those who accept the presence and absence
374
EVOLUTION, GENETICS, AND EUGENICS
hypothesis do not use the form of notation thus far used in explaining
MendeHan inheritance. Assume that T is used to express the deter-
miner for tallness, its same letter (/) is used to express the absence.
For example, instead of using D for dwarfness, t is used for "lack of
tallness" (Fig. 67). It is a matter of convenience to have a symbol
to represent the recessive, the absence of something that is present in
another individual.
In summary, the essential difference between the presence and
absence hypothesis and that of dominant and recessive- is that in
the former case the recessive determiner has no existence at all,
while in the latter case it exists, but is in a latent condition when
associated with the dominant.
Dwarf Parent
Gamete
Fig. 67. — Diagram showing how presence and absence scheme is actually
used, with small letter representing "absence." {From Coulter and Coulter.)
II. BLENDS
This type of inheritance when first discovered was thought to be
in direct conflict with Mendel's law. It is a case in which dominance
seems to fail, for the two alternative characters both express them-
selves and the result is an average between them. It is easy to explain
this situation in accordance with the presence and absence hypothesis
without any violation of Mendel's law.
The classic example of blending inheritance was presented by
Correns in breeding work upon Mirabilis Jalapa, the common four-
o'clock. Correns crossed red and white varieties, and all the hybrid
progeny had rose pink flowers. This was a color blend, distinctly
intermediate between the colors of the two parents. The Fi genera-
tion, therefore, seemed to contradict Mendel's law in that one color
character was not completely dominant over the other. The real situa-
tion, however, appeared in the F2 generation obtained by inbreeding
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS
375
individuals of the Fi generation which showed the blend. By
inbreeding the pink hybrids Correns obtained the perfect 1:2:1 ratio,
that is, I red like one grandparent, 2 pink like the hybrid parent, and
I white like the other grandparent. Segregation was evidently taking
place, the only unusual thing being the appearance of the Fi indi-
viduals, and that was explained immediately as failure of dominance
(see Fig. 68 .
The question this introduces, therefore, is that of a mechanism
which could account for such a result. The easiest explanation
offered is that the red parent was a homozygote for redness (double
dose) and the hybrid a heterozygote (single dose) ; the inference is that
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0 0
White Parent
F,
0p;.k0
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0«®
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0 0
Fig. 68.— Diagram illustrating blending inheritance, discovered by Correns
in Mirahilis Jalapa. {From Coulter a-nd Coulter.)
a single dose produces pink while a double dose produces red. A
theoretical explanation of this occasional difference in the result of
double and single doses is as follows. Imagine that the body cells
of a plant have a certain capacity for expressing hereditary characters.
In such a case, just as a given quantity of solvent can dissolve only a
given amount of solute, so the body cells can express hereditary charac-
ters only to a definite limited extent. In the four-o'clock a single dose
of redness may be thought of as half saturating the body cells, while a
double dose completely saturates them. In cases showing complete
dominance, however, a single dose completely saturates the cells and a
double dose can do nothing more. This analogy assists in visualizing
on the one hand the necessary mechanism of blends (apparent failure
376 EVOLUTION, GENETICS, AND EUGENICS
of dominance) and on the other hand that for cases of complete domi-
nance.
Another example of simple blending inheritance is the case of
Adzuki beans, described by Blakeslee. In this bean the mottling of
the seed coat is dominant to the lack of mottling. In the hybrid
condition, however, the mottling is lighter than in the pure or homo-
zygous condition. Heterozygous plants, therefore, can be easily dis-
tinguished from homozygous plants, so that the 1:2:1 ratio is evident
on external inspection rather than the usual 3 : i ratio.
III. THE FACTOR HYPOTHESIS
Mendel concluded that each plant character depends upon a single
determiner. Inheritance, however, has proved to be a much more
complex phenomenon than indicated by Mendel's peas. Ratios have
appeared that were puzzling, and geneticists were forced to the conclu-
sion that there may be a compound determiner for a single character.
This conception is called the factor hypothesis, and the growing com-
plexity of genetics has developed in connection with this hypothesis.
With the consideration of factors instead of determiners one passes
from elementary to advanced genetics. Previously we have used the
word determiner, implying Mendel's idea that a single determiner is
responsible for the development of a plant character, and this
has been true of the examples of inheritance previously considered.
It is understood now, however, that a character is frequently deter-
mined by the interaction of two or more separately heritable factors,
and hence the factor hypothesis. The distinction between factors and
determiners should be made clear. In case only one factor is involved
in determining a character, there is no distinction between factor and
determiner; and in such a case the term factor should not be used.
I. Complementary factors. — This is the simplest expression of
the factor hypothesis and it may be illustrated by some of East's work.
Crossing red-grained and white-grained corn he obtained all red in
the Fi generation. This would suggest that the F, generation would
show 3 red to i white; but it showed 9 reds to 7 whites, which did not
suggest Mendelian inheritance. It is in accord with Mendel's law,
however, if we consider that two complementary factors are necessary
to produce the red character, and that each of these factors is inherited
separately. Such a situation would give a dihybrid ratio, as indicated
in Fig. 69. It will be seen that out of 16 progeny 9 will be red, for they
alone contain the complementary factors; the other 7 will be white.
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS
377
The situation is thus explained by the dihybrid ratio, but although
only one character is involved that character depends upon two com-
plementary factors.
Another situation is worth noting. No. 6 of the diagram is white
because it contains only one of the necessary factors; No. ii is white
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between red-grained and white-grained corn. R and C must both be present to
produce red-grained corn. {From Coulter and Coulter.)
for the same reason, but its germinal constitution is just the opposite.
What would happen if these two are crossed? There is only one
possibility, since each is a homozygote producing only one kind of
gamete. The result would be red, and thus a cross between two whites
would produce only reds. What would happen from crossing Nos. 6
and 15, the former being a homozygote and the latter a heterozygote ?
378 EVOLUTION, GENETICS, AND EUGENICS
It is obvious that the resulting progeny would be one-half white and
one-half red, although both parents are white. The same result would
be secured in crossing Nos. ii and 14. A cross between Nos. 14 and
15, both of which are heterozygotes, would result in 3 whites and i red,
the ordinary 3 : i ratio. These illustrations show how differently the
same phenotype may behave in inheritance. In each case two whites
were crossed, that is, the same phenotypes, but three different ratios
were obtained because the genotypes were different.
The striking feature of this situation is that one can cross two
whites and get a red. This gives an insight into the so-called phenome-
non of reversion. For example, in the course of numerous breeding
experiments Bateson obtained two strains of white sweet peas, each
of which when normally "selfed" bred true to the white color; but
when these two were artificially crossed all the progeny had purple
flowers, like the wild Sicilian ancestors of all cultivated varieties of
the sweet pea. This appeared to be a typical case of reversion. Fur-
ther breeding, however, showed that this was just such a case of com-
plementary factors as we have been considering. One of Bateson's
white strains had one of the factors for purple and the other strain had
the other factor.
Complementary factors have been defined and the method of their
inheritance described, but is there any mechanism to explain the
situation ? A suggestion may be obtained from plant chemistry.
The most prominent group of pigments in plants is the group of antho-
cyanins, which are produced as follows. Plants contain compounds
called chromogens, which are colorless themselves but which produce
pigments when acted upon by certain oxidizing enzymes or oxidases.
This is a sufficient mechanism for the behavior of complementary
factors. If one of East's white strains of corn contained a chromogen
capable of producing red but lacked the necessary oxidase it would
remain colorless. If the other white strain contained the oxidase but
no chromogen it would remain colorless. In crossing them, however,
chromogen and oxidase would be brought together and a red-grained
hybrid would be the result. Inbreeding such red-grained individuals
of course would give red and white progeny in a ratio of 9:7, as
explained in connection with East's corn. This seems to be the explana-
tion of the behavior of complementary factors in many cases of color
inheritance.
Where other characters are involved the mechanism must be some-
what different. In some cases the two factors may be the enzyme
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS 379
and the compound the enzyme attacks, as in the oxidase and chromo-
gen situation just described. On the other hand, we might be dealing
with two chemical compounds that are inert when occurring separately
but active when brought together, active in such a way as to produce
a distinctly new character. Also two active substances might neutral-
ize one another when brought together in a hybrid, and the failure in
their acti\aty might result either in a new character or the failure of
some parental character to develop. Such are some of the possible
mechanisms to explain the behavior of complementary factors.
Hybridizing, therefore, is much like mixing chemicals in a test
tube. We know that very wide crosses cannot be made successfully;
but the surprising thing is that certain very close crosses are constantly
unsuccessful, even though both parents may cross freely with closely
related types. We obtain a glimpse of the possibiUty of such appar-
ently inconsistent behavior when we consider the chemical possibilities
suggested by the behavior of complementary factors.
The origin of complementary factors is an interesting field of
speculation. Did they originate together or separately? A natural
inference would be that they originated together, for neither would be
of any use without the other. It should be remembered, however,
that the idea of use as explaining the occurrence of everything in a
plant is being abandoned; one must think rather of a plant as a com-
plex physico-chemical laboratory. No one claims that all chemical
reactions are useful; they are simply inevitable; and plant characters
are the result of chemical reactions and physical necessities. Even
though we assume the simultaneous origin of two complementary
factors, they would have to be put on separate chromosomes, for the
factors are separately inherited.
The other alternative is to suppose that these factors originated
independently in the history of a plant. In this case, of course, the
first one to be produced would remain functionless until finally its
complement came into existence. This might be an explanation of what
are called latent characters. Also they might have not only originated
independently but in different varieties or species. In this case if
natural hybridizing should bring them together the result would be
the appearance of a new character, and this may have been a very
important factor in the origin of species.
This may serve as an introduction to the factor hypothesis, with
complementary factors as an illustration, simply because it is the
simplest situation. There are many other kinds of factors recognized.
38o
EVOLUTION, GENETICS, AND EUGENICS
but we shall not attempt to list all of the proposed types. A simple
illustration of the better known types is as follows :
a) A complementary factor is added to a dissimilar factor to pro-
duce a particular character.
b) An inhibitory factor prevents the action of some other factor.
c) A supplementary factor is added to a dissimilar factor with the
result that the character is modified in some way.
d) A cumulative factor, when added to another similar factor,
affects the degree of development of the character.
Some examples of these types will make them clear, those for
complementary factors having been given previously.
R
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Pure Red Parent
Gamete
Gamete
White Parent with
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Fig. 70. — Diagram illustrating behavior of inhibitory factor. {From Coulter
and Coulter.)
2. Inhibitory factors. — Recalling East's experiment with red-
grained corn it will be remembered that when both factors for red
were present the grain was red, but when either factor was absent the
grain was white. Later he crossed these strains with a new white
strain, and the result was surprising. The pure red strain produced
gametes carrying both the red factors, and it would be expected that
whatever such a gamete mated with would result in red progeny; but
when this pure red was crossed with the new strain of white the pro-
geny were all white, although the hybrids certainly contained both
factors for red. The explanation which first occurred to East, and
which later experiments confirmed, was that the new white strain con-
tained an inhibitory factor, which prevented the development of red
even though both the complementary factors for red were present.
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS
381
Fig. 70 illustrates the situation and shows why all the individuals of
the Fi generation are white. It is interesting to note further the
possibiUties of white and red in the F2 generation. They would be
0 0
0 0
White
White
Fig. 71. — Diagram showing some possible combinations in F2 when Fi of
Figure 70 is inbred. Individual on left end of upper set red-grained, because R
and C both present and / absent; other individuals in upper set white, because
lacking C or i? or both; individuals in lower set with inhibitory factor and there-
fore white, whatever other combinations of factors they may contain. (From
Coulter and Coulter.)
numerous, since we are dealing with trill ybrid ratios (see Fig. 71).
This does not exhaust the possibilities, for the cases given were
homozygotes, each producing a single kind of
gamete. There remains for consideration the
heterozygote situation (see Fig. 72).
The possible mechanism of the inhibitory
factor is as follows. We have assumed that red is
produced only when the enzyme is present to
oxidize the chromogen. Enzymes are very sensi-
tive; their activities may be affected or com-
pletely checked by various agents. Suppose that
/ of the diagram be such an agent and the neces-
sary mechanism is apparent. When / is present R is paralyzed, so
that it cannot oxidize C.
3. Supplementary factors. — -A supplementary factor is one that is
added to a dissimilar factor, with the result that a character is modified
in some wav.
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382
EVOLUTION, GENETICS, AND EUGENICS
In his work upon red-grained races of corn East found occasionally
a few purple grains. His conception of the situation is as follows.
The pure red plant contains two complementary factors, one (C) a
chromogen, and the other (R) an enzyme, which when brought
together produced the red color. The purple grains, however, must
be explained by the presence of still another factor (P), the resulting
situation being represented in Fig. 73. Of course when C is absent
no pigment whatsoever can be produced. As a consequence we will
assume that the presence of C is constant, and that P and R are vari-
ables. For a similar reason we will assume that the absence of I is
constant. The figure shows three possibilities, from which the follow-
ing conclusions may be drawn: (i) when P and R are both present
the result is purple grains; (2) red appears only in the absence of P;
(3) P although present will not develop any color in the absence of R.
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Puiple
Red
White
Fig. 73. — Diagram illustrating action of supplementary factor. (From
Coulter and Coulter.)
This is a typical case of a supplementary factor, that is, one which
is added to a dissimilar factor, with the result that the color character
is modified. The mechanism of this situation will make clearer the
behavior of the supplementary factor. If C is the chromogen and R
the enzyme, what is P? The suggested answer can be obtained
from plant chemistry. It is found that the purple pigment is produced
by the same substance as the red, but represents a higher state of
oxidation. The conclusion is obvious. C is oxidized by i? up to a
certain point, where red is produced; but if P is also present it repre-
sents an additional enzyme, which attacks the red pigment and oxidizes
it still further into purple. P is incapable of attacking the original
chromogen, but when R carries the attack to a certain point, P can
function and carry the oxidation further. As a consequence P without
R gives white grains, while R gives red grains only in the absence of P.
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS 383
4. Cumulative factors. — These will be considered under the next
heading, "Inheritance of quantitative characters."
In addition to the four types of factors given, the literature of
genetics also contains discussions on intensifying factors, diluting
factors, distribution factors, etc. These, however, do not introduce
any new mechanisms.
5. Inheritance of quantitative characters. — This phase of the
factor hypothesis, if true, is of fundamental importance not only to
genetics but to general biology. It is based upon the conception of
cumulative factors, and as it is presented it will be realized that it
throws hght not only upon numerous breeding experiments but also
upon variation in general, which means evolution also. A cumulative
factor was defined as one which, when added to another similar factor,
affects the degree of development of the character.
It will be recalled that Correns crossed red and white strains of
Mirabilis and obtained pink hybrids. The suggested explanation of
this result was that a single dose of the red determiner gives pink while
a double dose gives red. When Correns inbred these pink hybrids,
he obtained the result presented in Fig. 68, that is, i red, 2 pink,
I white. This result is obvious and the mechanism is plain.
With this diagram in mind we shall consider some of the experi-
ments of Nilsson-Ehle at the Swedish Experiment Station. He
crossed two strains of wheat with red and white kernels. The Fj
individuals had light red kernels, which of course suggests a repetition
of the situation shown by Mirabilis in the experiment of Correns.
The Fa generation, however, showed a very different result. The reds
and whites appeared in the ratio of 15:1; but in addition to this,
among the 15 reds there could be distinguished varying degrees of
redness. Nilsson-Ehle suspected that 15:1 meant a dihybrid ratio,
16 individuals being necessary to give the ratio, so that he constructed
the tentative scheme shown in Fig. ,74.
This shows a regular dihybrid ratio, except that the two factors
involved are similar. Applying the single dose and double dose con-
ception, as used In the case of Corren's pink Mirabilis, we reach the
following conclusions: No. i only has four doses and therefore it only
is deep red; Nos. 2, 3, 5, 9 have three doses and are somewhat lighter
red; Nos. 4, 6, 7, 10, 11, 13 have two doses and are still lighter red;
Nos. 8, 12, 14, 15 have one dose and are very light red; while No. 16
alone has no dose and is the only pure white. This accounts for
the 15:1 ratio, and the different shades of red. This is entirely in
384
EVOLUTION, GENETICS, AND EUGENICS
accord with the conceptions that have been presented, and only two
assumptions are necessary: (i) that dominance is absent, and two
doses have twice the effect of one: (2) that the independent similar
factors are cumulative in their operation, and are paired with their
absence in the hybrid. This was Nilsson-Ehle's conception, and of
Fig. 74. — Diagram illustrating Nilsson-Ehle's explanation of 15:1 ratio
obtained in F2 generation from cross between red-grained and white-grained
wheat. {From Conlkr and Coulter.)
course he tested it by further experimental work, the results consist-
ently confirming the conception.
Since it is important to fix this conception clearly in mind, another
type of diagram may represent the facts even more clearly. The
proportion of individuals showing the various degrees of redness in the
F2 is graphically recorded in Fig. 75, each dot representing one dose
of the factors in question.
THE FACTOR HYPOTHESIS AS APPLIED TO PL.ANTS
385
Continuing these investigations, Nilsson-Ehle next discovered a
new strain of red-grained wheat, which, when crossed with the pure
white strain, yielded Fi hybrids of intermediate intensity of red as
before. The F2 generation, however, showed a different situation.
Reds and whites were obtained in the proportion of 63 : i ; the 63 reds
as before falUng naturally into different groups on the basis of degree
of redness. Applying the same conception as before Nilsson-Ehle
• • •
Pure Red
Grades of Pink
White
Fig. 75. — Another method of \asualizing Nilsson-Ehle's 15:1 ratio (see
Fig. 74). {From Coulter and Coulter.)
discovered that in this case he was dealing with a trihybrid situation.
Without constructing the usual Mendelian diagram, which would have
to be extensive enough for 64 individuals, the situation as it appeared
in the F2 generation may be represented by Fig. 76. If the graph is
surmounted by a curve we recognize the regular "probability curve,"
exactly the kind of curve biometricians use to represent the fluctuating
individuals about a specific type.
This conception of cumulative factors, therefore, has far-reaching
significance. For a long time biologists have recognized individual
386
EVOLUTION, GENETICS, AND EUGENICS
variation within the species. Darwin depended upon it as the basis of
his theory of natural selection as the origin of species; in fact, ever
J*
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• • •
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White
Fig. 76. — Diagram illustrating Nilsson-Ehle's 63:1 ratio. (From Coulter
and Coulter.)
since Darwin's Origin of Species, individual variation has been funda-
mental in our conceptions. To account for this universally recog-
nized phenomenon, Darwin proposed his transportation hypothesis as
THE FACTOR HYPOTHESIS AS APPLIED TO PLANTS 387
a possible explanation, which, as will be recalled, did not long sur-
vive. Weismann oflFered in explanation his genninal selection, which
was soon discarded because it was beyond the possibility of experi-
mental testing. Aside from these two attempts to explain individual
variation no other comprehensive scheme had been presented. Biolo-
gists had simply recognized the fact of individual variation without
any conception of the mechanism. They knew that individual varia-
tion existed but had even stopped asking why it existed.
The importance of this new theory, therefore, is obvious. It is
an ingenious explanation of the inheritance of quantitative characters
and of the existence of individual variations. Furthermore, the theorv
has not been developed through meditation, but has its basis in
scientific experiments. It is imaginative to a certain extent, of course,
as is every other valuable theory, but unlike most such theories it has
a substantial foundation, namely, Mendel's law.
CHAPTER XXIX
THE FACTOR HYPOTHESIS AS APPLIED TO ANIMALS
Immediately after the announcement by De Vries in 1900 of the
rediscovery of Mendel's paper, zoologists in Europe and in America
began experiments in animal breeding with the idea of discovering to
what extent Mendel's laws were applicable. It was soon found that
the principles of unit characters, dominance, segregation, mono-
hybrid, dihybrid, and trihybrid ratios were of practically universal
appUcation. A number of instances of Mendelian heredity in animals
have already been presented in the preceding chapter and no more
simple Mendelian cases need be described. For a considerable period
the animal-breeders proceeded no farther in their analysis of the
mechanism of heredity than Mendel had done so many years before.
In time, however, new facts came to light that needed further analysis,
and the older Mendelism was superseded by neo-Mendelism. This
new phase in the study of heredity is m the forefront of interest today.
Neo-Mendelian heredity in plants has already been discussed. It
remains for us to present the data on some phases of neo-Mendelism
in animals.
ILLUSTRATIONS OF THE FACTOR HYPOTHESIS
THE FACTORIAL ANALYSIS OF COLOR IN MICE
Miss Durham, after extensive breeding experiments with numer-
ous strains of differently colored mice, has been able to show that
the appearance of a particular color in an individual mouse is depend-
ent upon the presence or absence of sevwal independently inherited
factors, evidently represented by genes in as many different chromo-
somes. It seems possible to classify these factors as follows:
jB = black pigment, which masks chocolate pigment
b = absence of B, which gives chocolate
I = intensity factor
i = absence of intensity, or dilution factor
C =a complementary color factor acting with P
P=a complementary pigment factor acting with C
If either C or P is absent, albino mice result no matter what other
color factors may be present.
388
THE FACTOR HYPOTHESIS AS APPLIED TO ANIM.\LS 389
The factorial make-up of the various mice in Miss Durham's
experiments would, then, be represented as follows:
^JCP = black
BiCP =blue (dilute black)
6/CP= chocolate (absence of black)
biCP = silver fawn (dilute chocolate)
The following experiments indicate the mode of heredity on the
factorial basis:
1. P Black (3/CP)XSUver-fawn (biCP)
F, 100 per cent Black (BlCP-biCP)
F, Black {BICP) Blue (BiCP) Chocolate (blCP) Silver-fawn
(biCP)
9331
2. P Blue (5CP)X Chocolate (bICP)
F, 100 per cent Black (BiCP-blCP)
Fa Black {BICP) Blue (BiCP) Chocolate (bICP) Silver-fawn
(biCP)
9331
3. P Blue (^iCP)X Silver-fawn (biCP)
Fx 100 per cent Blue (BiCP-biCP)
F, Blue (BiCP) Silver-fawn (hiCP)
3 I
DIFFERENT KINDS OF ALBINOS
Any one of the color types mentioned, if lackin^: in the factor C.
*rill be an albino, though carrying the other factors for color. For
example, there may be a Black-albino (BIcP), a Blue-albino (BicP),
a Chocolate-albino (bIcP), or a Silver-fawn-albino (bicP).
That color factors are present in albinos may be shown by the
following experiment. An albino had appeared in a Black stock and
was crossed with a Silver-fawn, thus:
4. P Silver-fawn (^)/CP)X Albino extracted from Black (BIcP)
F, 100 per cent Black (biCP-BIcP)
Black Blue Chocolate Albino-Black Silver-fawn
(BICP) (BiCP) (bICP) (BIcP) (biCP)
27 9 9 9 3
Albino-Blue Albino-Chocolate Albino-Silver-fawn
(BicP) (bIcP) (bicP)
390
EVOLUTION, GENETICS, AND EUGENICS
The ratios given are the theoretical ratios for a trihybrid Mendel -
ian experiment, and the actual results have closely approximated these.
Asa matter of fact, sixteen albinos appeared, and it is not possible,
except by breeding, to tell one kind from another. Breeding each
with, for example, Silver-fawn would readily repeal the differences;
for the F, generation would all be of the color that is masked by the
lack of C in these albinos. In the language of Johanssen there is only
one albino phenotype, but there are four albino genotypes. Similarly
m experiments (i) and (4), which have just been described, the indi-
viduals are all Black (phenotypically identical), but that they are not
genotypically alike is clearly shown by inbreeding them. In experi-
ment (i) we get only individuals of the four color types, while in
experiment (4) we get, in addition to the four color types, four albino
t3^es.
castle's guinea pigs
Professor W. E. Castle was one of the first zoologists to use Men-
del's methods. He soon discovered that in the determination of the
coat characteristics of guinea pigs at least three sets of factors were
necessary, as follows:
C= colored fur
c= albinism (absence of C)
5= short fur
5= long fur (recessive to S)
i?=rosetted fur
r = smooth fur (absence of R)
An example will show how these factors segregate:
P Colored, Short, Smooth X Albino, Long, Rosetted
iCSr) (csR)
F, 100 per cent Colored, Short, Rosetted (CSr-csR)
F,
Colored
Short
Rosetted
27
Albino
Long
Rosetted
Colored
Long
Rosetted
9
Albino
Long
Smooth
Colored
Short
Smooth
9
Albino
Short
Rosetted
9
Colored
Long
Smooth
3
Albino
Short
Smooth
3
THE FACTOR HYPOTHESIS AS APPLIED TO ANIMALS 391
The ratio of 27, 9, 9, 9, 3, 3, 3, i shows clearly that the three factors
independently segregate and are all three concerned in the determi-
nation of the characters of the fur. A fourth factor, a pattern factor,
is often present that further complicates the factorial analysis. Usually
the self-color dominates the pattern, but certam special patterns are
dominant over self-color.
These two examples for animals are sufl&cient to illustrate the
nature of Menddian factors and their workings. Numerous other
factors have been discovered. Castle, for example, found a factor
associated with the occurrence of brown pigment in guinea pigs.
Some rabbits have the pigment distributed evenly over the body;
others have it in the eye only. These conditions are allelomorphic to
each other, E (extension) being dominant over e (restriction to eyes).
Inhibiting factors are distinguished, the presence of which prevents
the appearance of a char: cter represented in the germ plasm. Lethal
factors result in the loss of something necessary for the life of the
individual. Modifying factors change the expression of a character
that depends on another gene. These and various other types of
factors have been discovered by the large school of neo-Mendelians
now so actively at work.
CHAPTER XXX
REVIEW OF MENDELISM AND INTRODUCTION
TO THE NEW HEREDITY
At this point it seems weU to pause and to take stock of what we
have learned about heredity by following Mendel's lead. Let us first
enumerate some of the rules or laws of heredity discovered by Mendel.
These are commonly known as Mendel's laws.
Mendel's first law: the law of dominance. — When two parent-
types differing from each other with reference to a single unit character
are crossed, the "hybrid-character resembles that of one of the parent
forms so closely that the other either escapes observation completely
or cannot be detected with certainty." The character that appears in
the first-generation hybrids is called "dominant" and that which ap-
parently becomes latent is called "recessive." The law of dominance
has been shown to be far from universal in its application. In fact,
complete dominance is relatively rare, and almost entire lack of domi-
nance is not uncommon. Evidently, then, dominance is not an essen-
tial feature of Mendelian heredity.
Mendel's second law: the law of segregation or purity of ga-
metes.— While the body cells and the germ cells of the Fi parent, prior
to the reduction divisions involved in gamete formation, contain the
determiners (genes) of both alternative characters and are therefore
hybrid in character, a segregation of the alternative genes (allelo-
morphs) takes place during maturation so that only one or the other
gene comes to be present in any gamete. Thus gametes are pure for
any gene. A gamete has one or the other of a pair of allelomorphs
and is never hybrid with reference to any single character. This law
is by far the most important of Mendel's discoveries. In fact, it might
be called the discovery of Mendel, for it is almost unsurpassed among
biological generalizations on account of its far-reaching applicability.
The law has sometimes been called the law of the splitting of hybrids.
Whether dominance is present or not, the law of segregation always
holds. The second law, therefore, is much more important than the
first.
Mendel's third law: the law of independent assortment of dififer-
39»
MENDELISM AND INTRODUCTION TO THE NEW HEREDITY 393
ent allelomorphs. — To use Mendel's own expression, "the relation of
each pair of different characters in hybrid union is independent of the
other differences m the two original parental stocks." This third
law is only discoverable when we try to follow the assortment and
recombination of at least two pairs of allelomorphs up to the second
hybrid generation (F,). If each allelomorph be studied by itself, it
will show nothing more than the facts indicated in the first two laws,
but as soon as we try to follow the modes of inheritance of more than
one character simultaneously, we find that we are merely dealing with
the independent shuffling and assorting of two or more genes. The way
in which we explain the third law is that all genes that exhibit mde-
pendent assortment are located in different chromosomes. If two
allelomorphs were in the same chromosome, it is obvious that their
association with each other in heredity would be much closer than
if they were in different chromosomes. Remember this when we come
to consider a later proposition called linkage.
Mendel's fourth law: the law of recombination. — According to
Mendel, this law means "that the constant characters which appear in
the several varieties of a group of plants (or animals) may be obtained
in all the associations which are possible according to the mathematical
laws of combination." The genes carried by the chromosomes are
shuffled about like a pack of cards and dealt out in all possible combina-
tions according to the laws of chance. The result of this is that the
particular deal, or "hand," that happened to be possessed by the parent
is likely not to be repeated in any of the offspring if the number of
differences involved is at all large. Of course, if there is only one point
of dift'erence between the two parents, the character of the parent will
be repeated in one out of each four individuals of the Fj generation. If
there are two pairs of allelomorphs concerned, there will be one in
sixteen in the F2 with the same combination as each original parent;
if three pairs of allelomorphs, one in sixty-four; if four pairs, one in two
hundred fifty-six; if ten or more pairs, one in hundreds of thousands
or milUons. Nearly all human beings differ from one another with
regard to hundreds of allelomorphs. Is it not remarkable, then, that
there is as much resemblance between two brothers as there sometimes
is? This condition will be better understood when we come to discuss
the limitations of the law of mdependent assortment, which Mendel
failed to discover, and which is explained by the law of linkage.
The concepts expressed in the above laws may be considered to
have originated with Mendel. It must be remembered, however, that
394 EVOLUTION, GENETICS, AND EUGENICS
Mendel had no knowledge of chromosomes or of the chromosomal
mechanism of maturation, which now seems to be the machine respon-
sible for the regularities seen in the various Mendelian ratios and for
segregation in general. It is remarkable, however, that Mendel fore-
saw a mechanism within the genetic apparatus of plants that coin-
cides in principle with that subsequently discovered. Among the great
discoveries that have resulted from the use of Mendelian methods
and procedures are the factor hypothesis, the chromosome theory of
heredity and of sex determination, linkage and crossing-over, and the *
finer details of the heredity machine.
THE FACTOR HYPOTHESIS
The factor hypothesis is a neo-Mendelian concept, by which we
mean that it was unknown to Mendel. According to Mendel, each
unit character was determined by a single determiner in the germ cell.
Also, the determiners of a pair of allelomorphs were both positive in
character and opposed to each other in their effects. The presence-
and-absence hypothesis, according to which a recessive gene differs from
a dominant gene merely in lacking something possessed by the domi-
nant gene, opened the way toward a much more satisfactory under-
standing of the ways in which germinal determiners (genes or factors)
influence characters than was possible under the view of Mendel.
When once we learn that a single character may depend upon the mter-
action of two or more independently inherited and segregating factors
or genes, it becomes possible to understand all sorts of puzzling and
apparently non-Mendelian ratios. The adoption of the factor hypoth-
esis has justified itself over and over again, for it has been the instru-
ment that has led to a really scientific genetics and has served to bring
under one category all sorts of hereditary phenomena that had formerly
been considered fundamentally different. Thus there is now no fur-
ther need for the three categories of heredity: alternative, blending,
and particulate. All three are now seen to be phases of alternative or
Mendelian heredity. Especially striking is the way in which the idea
of multiple factors ("cumulative" or "duplicate factors" of some au-
thors) has served to rationalize and to bring into line with other
Mendelian phenomena the data about the inheritance of quantitative
characters. Another service of the factor hypothesis comes out in con-
nection with the discovery of lethal factors. There is a large number of
genes or factors whose presence in the homozygous condition (i.e.,
when a given factor is present in both gametes that unite to form a
MENDELISM AND INTRODUCTION TO THE NEW HEREDITY 395
zygote) leaves the individual derived from such a zygote lacking in
something essential for life. All such individuals in any breeding
experiment will fail to survive, and their absence will be noted when
the ratios of the various combinations are worked out. The failure
of a certain expected combination to appear in the F2 generation is
attributed to the presence of a lethal factor in the stock. It can readily
be proven that many of the surviving individuals possess the lethal
factor in a heterozygous condition, having one dose of the normal
allelomorph along with the lethal factor. These lethal factors can be
identified and located as readily as characters that actually appear.
The subsidiary hypothesis of lethal factors has had a far-reaching in-
fluence upon some of the most advanced phases of modern genetic
practice.
THE RELATION OF SEX TO GENETICS
Not many years after the rediscovery of Mendel's work, the chro-
mosome theory of sex determination, already outlined in chapters xxiv
and xxviii, grew out of our knowledge of MendeUan heredity. It came
to be recognized that sex is inherited in Mendelian fashion, as follows:
If we suppose that the male sex is a heterozygous dominant and the
female sex pure recessive, we can understand why males and females
are produced in equal numbers, for it is equivalent to the familiar
condition where an Fi hybrid is back-crossed with the pure recessive
parent: the F2 offspring are half hybrid dominants (Dr) and half pure
recessive (rr). The discovery that, as a rule, the male is hetero-
zygous (produces two kinds of gametes) and the female is homozygous
(produces but one kind of gamete) was confirmed by cytological study
and went a long way toward the establishment of the chromosome
theory of heredity. It is because of the discovery of the sex chromo-
somes that it became later possible to locate many other genes in the
same chromosomes as those responsible for sex; and the fact that the
heredity of these characters could be followed along with sex made it
possible to develop the hypotheses of linkage and crossing-over, as well
as several important hypotheses that now form essential links in the
series of generaUzations that make up modern genetics.
CHAPTER XXXI
SEX DETERMINATION AND SEX-LINKED HEREDITY
SEX DETERMINATION
In earlier chapters it has been necessary to introduce a few neces-
sary facts about sex determination and sex-Unked heredity. The
mechanism of sex determination has been clearly described and illus-
trated for Drosophila (pp. $6^ ff.), and the close connection that exists
between sex-linked heredity and sex determination has been shown in
chapters xxiii and xxviii. A more detailed consideration of sex deter-
mination and sex differentiation is now to come.
The question as to what determines whether an animal shall be a
male or a female is a very ancient one, and it is only during the present
century that we have solved the puzzle.
A great many theories of sex determination have been proposed,
some of which are as follows :
c) Hippocrates and some subsequent theorists beheved that the
sex of the offspring depended on the relative vigor of the parents, the
more vigorous parent giving his or her sex to the offspring.
h) Thury thought that the sex of the offspring depended on the
degree of ripeness of the ovum at the time of fertilization.
c) Various writers claim that statistics show that germ cells from
the right ovary produce males and those from the left ovary females.
d) The nutrition theory. — The egg is a much more highly nourished
cell than the spermatozoon, and the idea seems natural that high
degrees of nourishment of the mother produce female offspring and
lower degrees of nourishment male offspring. Professor Schenk of
Vienna gained a huge reputation by controlling the diet of certain
royal prospective mothers and predicting the sex of the offspring
accordingly. He was correct in his predictions several times, but his
success was short-lived. His early predictions were merely lucky,
just as one might be who could guess heads or tails correctly several
times in succession.
Some color is lent to the nutrition hypothesis by the fact, if it is a
fact, that after war or famine, when the nutrition of mothers has been
396
SEX DETERMINATION AND SEX-LINKED HEREDITY
397
low, more males than females are born. This is probably a case of
differential prenatal mortality. By that we mean that more females
die unborn than males, because the latter are hardier and stand pre-
natal malnutrition better.
e) Sex is determined at the time of fertilization. — Perhaps the best
evidence that sex is determined at the very beginning of development
Fig. 77. — An armadillo egg about six weeks after fertilization, showing the
quadruplet foetuses deriv^ed from the single egg and all destined to be of the same
sex. {Front Newman.)
is derived from one-egg twins and quadruplets. In the nine-banded
armadillo practically every female gives birth to quadruplets four
essentially identical young being produced in each litter. All in a
given set of quadruplets are invariably of the same sex, either four
males or four females. Newman and Patterson have shown that each
set of quadruplets comes from a single egg which at a very early stage
398 EVOLUTION, GENETICS, AND EUGENICS
divides into four parts to form four fetuses (Fig. 77). The conclusion
is that sex was determined before the separation took place. Human
identical twins, also always of the same sex, furnish further evidence
in favor of very early sex determination. These and numerous other
similar facts justify the conclusion that sex is determined at the time
of fertilization.
THE CHEOMOSOMAL MECHANISM OF SEX DETERMINATION
In two previous chapters (chaps, xxiv and xxix) descriptions of the
typical modes of chromosomal sex determination have been given. In
order to facihtate a clear understanding of this important matter,
it seems well to recapitulate one typical instance. Perhaps the best-
known instance of sex determination is that of Drosophila melanogaster,
already described and figured (Fig. 78) by Babcock and Clausen. In
this insect the female body cells and the unmaturated germ cells are
characterized by the presence of two sex chromosomes (X-chromo-
somes), which are shown in black at the top of the left-hand column
of the accompanying figure. The chromosomes are readily dis-
tinguishable by being of medium size and straight. The male body
cells and immaturated germ cells (top of right colimin) are just like
those of the female except that there is substituted for one of the
X-chromosomes a hook-like chromosome, known as a Y-chromosome.
Now in the process of maturation of the germ cells, which results in
the formation of gametes with the haploid or half-somatic number of
chromosomes, each of the eggs (female gametes) receives an X-chromo-
some. AU eggs are therefore alike in their chromosome content, in-
cluding the sex chromosome. The case is different on the male side;
for two kinds of gametes are formed, one kind with an X-chromosome
and the other with a Y-chromosome. These are formed in exactly
equal numbers, as one of each is produced at every reduction division.
Each egg must be fertilized by one or the other of these two kinds of
sperms, and in the long run as many eggs will receive an X-chromosome
as will receive a Y-chromosome. Those that receive an X-chromosome
wiU be characterized by having two X-chromosomes, which is the
typical female condition, and thus a new female individual is started
in life; while those that receive no X-chromosome, but a Y-chromo-
some, wiU have the XY composition characteristic of the male sex,
and will give rise to males. The female sex may thus be designated
as XX and the male sex as XY. We have shown for Drosophila the
exact mechanism that operates in determining whether an individual
SEX DETERMINATION AND SEX-LINKED HEREDITY
399
shall be a male or a female, and in addition we have explained why
equal numbers of both sexes are continuously produced.
How general is the chromosomal mechanism of sex-determina-
FiG. 78. — Diagram showing chromosome relations in the determination of sex
in Drosophila ampelophila. (From Babcock and Clausen.)
tion? — "To what extent," says E. B. Wilson, "sex may be determined
by an automatically operating nuclear mechanism such as has been
here described is unknown; but a mechanism that exists in the same
400 EVOLUTION, GENETICS, AND EUGENICS
general form in organisms as diverse as bryophytes, nematodes, echi-
noderms, arthropods and vertebrates is beyond a doubt of far-reaching
significance, and may be as widely distributed as Mendelian heredity
generally." While the same general scheme holds for all forms that
have been investigated, there exist many interesting differences in the
details of operation of the sex-determining machine. Some of the
simpler variations of the process are as follows:
a) Variations of the Y -chromosome. — Beginning with a condition
such as that described for Drosophila, in which the Y-chromosome is
larger than the X-chromosome, there is a long series of species in
which the Y-chromosome becomes smaller and smaller until it dwindles
away to nothing and the male chromosome condition becomes XO in-
stead of XY. In the females of such species the condition remains XX.
b) Variations of the X-chromosome. — In a number of species of
animals the X-chromosome may be represented by from two to nine
components, each of which at times has the appearance of a separate
chromosome. In a species of roundworms, Ascaris canis, for example,
the diploid chromosome number of the female is thirty-six and that of
the male is thirty, the difference being due to the fact that there are
two sets of six X-components in the female and only one set in the male.
In the reduction division of the male germ cell, the six X-components
all go in a group to one gamete and none to the other, so that two
kinds of gametes are produced, one with eighteen chromosomes and
the other with twelve chromosomes. AU the female gametes have
eighteen chromosomes. Apart from the fact that the X-chromosome
is in six pieces instead of but one, the mechanism of sex determination
is the same as it is in a group that has but one X-chromosome.
c) Linkage of sex chromosome with autosome. — In a great many
species of insects the X-chromosome has been found to be imited to
one end of one of the autosomes, never losing this relation during the
entire chromosome cycle. Apart from this apparently secondary
union with an autosome, the behavior of the X-chromosome is the same
as in the XO cases described above. Hence the mode of sex deter-
mination is in line with the types already discussed.
d) Female digamety. — In this mode of sex determination two differ-
ent kinds of eggs are produced, while the sperms are all alike. In other
words, there is simply an exchange between the sexes of the nuclear
differences characterizing males and females. Thus in the Lepidoptera
(butterflies and moths) the females have either the XY or the XO type
of chromosome complex, while the males always have the XX condi-
SEX DETERMINATION AND SEX-LINKED HEREDITY ^qj
tion. Though the cytological evidence is still incomplete, it is prac-
tically certain that birds have the same peculiar method of chromo-
somal sex determination as the Lepidoptera, for they have the same
type of sex- linked heredity as the latter and the opposite of that seen
in mammals and most insects. Apart from the change of the digametic
condition from one sex to the other, the mechanism remains the same.
Sex chromosomes in parthenogenesis. — When it became known
that parthenogenetic species (those in which eggs are capable of de-
veloping without fertilization) in some cases produce males and in
other cases produce females from parthenogenetic eggs, this seemed to
be out of accord with the theory of the chromosome mechanism of sex
determination. It is interesting to know, however, that, now that we
know the histories of the chromosome cycles in these species, the facts
are not only fully in accord with the chromosome theory, but greatly
strengthen it and enlarge its range of applicability. Two kinds of
parthenogenesis are known, which may be designated diploid and
Iiaploid. In the former, the developing egg and embryo has the full
somatic number of chromosomes; in the latter, only half the somatic
number characteristic of the species is present.
a) Diploid parthenogenesis. — In these species only one maturation
division occurs, and this division is not the reduction division; hence
each egg retains the diploid number of chromosomes, including two
X-chromosomes (XX). The result is that all eggs that behave in this
way develop into females. Thus in aphids and phyloxerans many suc-
cessive generations of all females are produced. After a series of
female generations, a mixed generation appears in which males are
produced parthenogenetically along with females, but from smaller
eggs. Examination reveals the fact that male-producing eggs have,
after maturation, two less chromosomes than the female-producing
eggs. This was explained by the observation that when the first
maturation takes place, two chromosomes (obviously consisting of a
double X-element) are cast out into the polar body, while all the auto-
somes and two of the X-chromosomes remain in the egg nucleus. In
this way the male produced from this egg comes to have only two
X-chromosomes, while the female has four. This is really the equiv-
alent of XX for the female and XO for the male. In gamete forma-
tion the males produce two kinds of gametes, one with the double
X-element and the other with no X-element. Only the former of
these is viable; and this accounts for the fact that all fertilized eggs
produce females, for both gametes supply double X-elements. This
402 EVOLUTION, GENETICS, AND EUGENICS
whole rather intricate story is thus seen to be merely a variant upon
the typical scheme of chromosomal sex determination.
b) Haploid parthenogenesis. — This kind of parthenogenesis is now
known to occur in rotifers, in several orders of insects, and in arach-
nids. It is practically universal among the Hymenoptera (bees, wasps,
ants, etc.), and we may use the case of the honey bee as an illustration.
In haploid parthenogenesis the egg develops after having undergone the
reduction division; it therefore has only half the somatic number of chro-
mosomes, including but one X-chromosome. Invariably the progeny
from haploid parthenogenesis are males, which we might expect from
the fact that they have but one X-chromosome. In the bees the queen
seems to be able to determine whether an egg gets fertilized or not.
An egg descends the oviduct, passes the seminal receptacle containing
a supply of sperms acquired during the mating act, and if sperms are
given off, fertilization occurs and a female is produced; but if an egg
slips past the seminal receptacle without being fertilized, the result is
a male (drone). Now these drones are the mates of the future queens,
and must supply the spermatozoa for the next generation of eggs. They
already possess the reduced number of chromosomes, so they cannot
well undergo the reduction division in forming gametes. It is inter-
esting to note, however, that a sort of vestigial reduction division takes
place resulting in the formation of a tiny cell without any nucleus and
a larger cell with all the chromosomes (including one X-chromosome)
characteristic of males of the species. Since all gametes, both male
and female, contain an X-chromosome, fertilization always results
in a female. Thus once more the general sex-determination formula
is confirmed.
Sex-chromosomes in hermaphrodites and gynandromorphs. —
Hermaphrodites are individuals which are functionally both male and
female, that produce both eggs and sperms in the same body. Her-
maphroditism is common in snails, flatworms, earthworms, nematodes,
tunicates, and in several other phyla of animals. We have unfortu-
nately very little information about the chromosome situations in
these forms. In one species of nematode {Angiostomum ftigrovenosum) ,
however, it is known that there is an alternation of generations between
a parasitic hermaphroditic generation and a free-Uving dioecious gen-
eration (with separate males and females). In the dioecious genera-
tion males and females are about equally numerous. AU fertilized
eggs of this generation produce parasitic hermaphrodites. These pro-
duce from their gonads first oogonia and later spermatogonia, the form-
SEX DETERMINATION AND SEX-LINKED HEREDITY 403
er producing eggs and the latter spermatozoa. It is known that all
eggs of the hermaphrodite generation have six chromosomes, while the
sperms have either five or six. Self-fertilization takes place, and half
of the fertilized eggs produce males with (eleven chromosomes) and
half produce females (with twelve chromosomes) of the free-living gen-
eration. The males of the dioecious generation produce two kinds of
gametes with respectively five and six chromosomes, and one would
expect males and females to be produced from fertilization; but this
is not what happens, for only hermaphrodite individuals with twelve
chromosomes are produced. It seems certain that only one of the
two kinds of spermatozoa (that with six chromosomes) is viable, and
that the hermaphrodite generation is chromosomally female. How
can a female produce spermatozoa of two kinds, one with six and the
other with five chromosomes? This is explained by the fact that in
the second maturation division one of the X-chromosomes remains
near the equator of the spindle, and does not become included within
the daughter-nucleus. Thus one of the daughter-cells is without an
X-chromosome and is male-producing when fertilization takes place.
Further investigation of the chromosomes of hermaphrodites will
doubtless be in agreement with what we already know.
Gynandromorphs are individuals made up of some female body
regions and some male body regions. Thus, an insect may have male
secondary sexual characters on one half of the body and female char-
acters on the other; or the anterior end may be male and the posterior,
female. The chromosomal basis for these conditions is not entirely
clear, but Morgan and Bridges have shown that all of the peculiarities
of the hereditary behavior can be explained on the assumption that
in the first or second cleavage division one of the X-chromosomes lags
behind and is excluded from one of the daughter-cells. Thus one
daughter-cell gets XX and the other X, which accounts for the fact
that all the cell descendants of one cell have the female characters and
all those of the other cell, male characters.
Intersexes and their bearing on sex determination. — Bridges, dur-
ing his experiments with Drosophila, encountered in certain strains
anomalous individuals that were neither male nor female, but inter-
sexes. On cytological examination these were found to have a changed
chromosome complex. One type, for example, was found to have
three of one kind of autosomes (instead of the usual two) but only two
X-chromosomes. The interesexual condition in this case might be
explained by the assumption that the autosomes have a male-produc-
404 EVOLUTION, GENETICS, AND EUGENICS
ing tendency and that one set of extra autosomes is sufficient partially
to overcome the female tendency of two X-chromosomes, thus produc-
ing intersexes. Again, individuals with three X-chromosomes but
only the usual supply of autosomes were super- females somatically,
but unbalanced in their physiology and non-viable. These results
show that, in the words of E. B. Wilson, 'Hhe actual performance of
the zygote, therefore, is the common effect of the whole group, aiid is turned
this way or that as the result of a quantitative balance betiveen X-chromo-
somes and autosomes. ^^
SEX DIFFERENTIATION
It now becomes necessary to distinguish clearly between sex
determination and sex differentiation. When we say that by means
of a chromosomal mechanism sex is determined, exactly what do we
mean ? We answer that the sex of an individual arising from a fertil-
ized egg (in the case of parthenogenesis, an unfertilized egg) has been
settled. Now as a matter of fact only one thing has been settled irrevo-
cably, and that is that one individual will have the chromosome
composition characteristic of a male and another individual that of a
female. A male is usually an individual that produces spermatozoa
and a female one that produces ova. Is it irrevocably settled beyond
possibility of reversal that a zygote with the XX chromosome com-
position must produce eggs and one with the X composition, sper-
matozoa ? This question has apparently been answered by Geoffrey
Smith in his work on parasitically castrated crabs and by Richard
Goldschmidt on Gypsy moths. In the first case, individual crabs
whose testes had been infested by the parasitic cirripede, Sacculijia,
were gradually changed over in their whole metabolism to such an
extent that cells destined to produce spermatozoa produced ova. In
the second case, when certain varieties of moth were crossed, all of
the germ cells produced females with ova, whereas half of the eggs
had the XX and half the X chromosome content. This evidently
means that some individuals with the male chromosome character
produced eggs. From these results we may be justified in conclud-
ing that not even this most fundamental difference of sexes, that of
the female producing ova and the male spermatozoa, is irrevocal^Iy
predetermined at fertilization.
Lest the reader be confused, however, we hasten to add that under
natural conditions of life an individual with the male chromosomal
content produces spermatozoa and one with the female chromosomal
content produces eggs, and that only rare accidental or unnatural
SEX DETERMINATION AND SEX-LINKED HEREDITY 405
conditions disturb the normal course of events. For purposes of
practical genetics we may then define a female as an individual that
produces ova and a male as one that produces spermatozoa.
Secondary sexual characters. — Usually males and females differ
from each other in many other characters besides the production of
eggs or sperm. Often one sex is larger, stronger, more elaborately
ornamented and colored than the other and possesses characteristic
accessory sex organs whose function it is to facilitate the bringing
together of the eggs and the sperm. All of the differences between the
sexes other than the primary difference of egg or sperm production are
called secondary sexual characters. Usually very young animals show
only slight differences in secondary sexual characters and the differ-
ences increase markedly at sexual maturity. We speak of the gradual
divergent development of the two sex types as sex differentiation.
The question arises as to whether or not the chromosomal differences
are the causes of the differentiation of secondary sexual characters.
These secondary sexual characters are all somatic, and, since the soma
is the product of cell division of the zygote, the soma cells must have
either the male or the female chromosomal character. That the
chromosomal mechanism in the somatic cells is not sufficient of itself
to bring about, unaided, the differentiation of secondary sexual charac-
ters can be shown readily in at least many animals.
In the mammals, for example, it is known that the early removal
of the testes or ovaries results in a retention of the juvenile or undif-
ferentiated condition of secondary sexual characters. Evidently some
influence is exerted by the tissues of the gonad that is necessary for the
full differentiation of sex characters. The current theory is that
certain glandular cells that form part of the body of ovary or testes
excrete materials into the blood that stimulate various tissues in
different ways and produce dimorphic results. The specific sub-
stances produced by these glands are called "hormones," for want
of a better name. To test the efficiency of these hormones the crucial
experiment of taking out the gonads of a young rat or guinea pig and
implanting the gonad of an individual of the opposite sex has been
many times performed. For example, Steinach castrated young male
rats and then successfully grafted into them ovaries from young
female rats. The result was that these young rats which started to
be males became much altered in a female direction, the mammary
glands becoming greatly enlarged, their instincts more feminine than
masculine, and in a number of other particulars they showed more
or less pronounced evidences of feminization. Conversely, spayed
4o6 EVOLUTION, GENETICS, AND EUGENICS
females with engrafted testes showed a tendency toward male differ-
entiation, especially in instincts. These experiments have been
largely confirmed by C. R. Moore.
In birds it is of interest to note that practically complete reveraal
of secondary sexual characters may be induced if young females are
entirely deprived of the ovary. The condition is described by L. V.
Domm as follows:
"The larger percentage of our birds have assumed additional male
characters following removal of the ovaries, until they are practically
complete replicas of the male, and, to those not familiar with their
history, they are regarded as unmistakable males. Thus we find that
they assume the complete male plumage, spurs grow as they do in the
normal cock, head furnishings increase in size until they can not be
distinguished from those of the normal male.
"Other birds in the pen regard them as males and when a strange
cock is introduced they fight as would other cocks, very frequently
assuming the initiative, some of them having been observed to come
off victorious in such a combat. Many of these birds crow regularly.
When aroused by a disturbance, it was found that their reaction is
very similar to that of the male; the sounds they make, together with
their reaction on such occasions, reminds one very much of the young
male just prior to maturity.
"One set of experiments may be mentioned as an example: Out
of the one lot of fourteen females of the same hatch, one was kept as
control and thirteen were operated upon between the ages of six weeks
and six months; twelve of these have developed all the characteristics
of the male mentioned above, some being completely cock-feathered,
while the others are fast becoming so. The other one of the thirteen
is very capon-like in appearance except perhaps for size and can not
be readily distinguished from her capon brothers by those not know-
ing her history. This bird has assumed complete male plumage, is
developing spurs; but the comb, wattles and earlobes are pale and
small, resembling those of the capon.
"In some of our cases individuals which have assumed more or
less complete male characters as concerns head furnishings, plumage
and spurs, are reverting toward the female type as shown by the female
type of plumage reappearing.
"Our results indicate that the female in the brown leghorn fowl
has many potentialities of the male, which are normally inhibited by
the presence of the ovary, and that these potentialities can assert
SEX DETERMINATION AND SEX-LINKED HEREDITY
407
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4o8 EVOLUTION, GENETICS, AND EUGENICS
Ihemselves approximately fully after the complete removal of the
ovary at an early age."
A beautiful experiment conducted by nature herself helps to drive
home the hormone theory of sex differentiation. In cattle, as shown
recently by F. R. Lillie, twins occur in a small percentage of cases and
involve the simultaneous fertilization of two eggs. These eggs lie as
a rule in opposite horns of the forked uterus, but owing to the growth
of their embryonic membranes the two individuals come to fuse cir-
culations so that there is an admixture of blood (Fig. 79). The result
is that if the twins are zygotically of the same sex no untoward effect
of blood admixture is apparent, but when the twins are zygotically a
male and a female, the female individual is always stopped in its
female differentiation and becomes more or less completely trans-
formed in a male direction. It appears, however, that at the time
when blood admixture occurs, the female individual has already
differentiated so far with respect to the external genitalia and in other
respects that, even though subsequent development be entirely male
in character, the resultant individual is always a sterile creature,
neither fully a female nor a complete male. Such individuals have
long been known as " freemartins." As a rare exception to the general
rule an occasional case has appeared in which a male and a female pair
fail to undergo blood admixture. In such cases both develop into
normal animals. It now appears that the reason why the female sex
is the one to suffer is that the male gonads differentiate precociously,
before the female, and inhibit the subsequent development of female
gonads. Hence the only hormones in the blood of both twins are
the male hormones.
In conclusion we may say then that, in mammals, though
chromosomes tend to determine the primary sex differences, they
have no effect on the differentiation of secondary sexual characters.
These are due to substances secreted by the gonads that have been
called a hormones.
SEX-LINKED HEREDITY
Certain characters that are definitely heritable but have no obvious
relation to sex have been found to be more or less closely linked with
one or the other sex. A well-known instance of the kind of character
in question is color blindness in man. It has long been known that
color-blind individuals are almost invariably males, that such males
marrying normal women never have any color-blind offspring, but that
SEX DETERMINATION AND SEX-LINKED HEREDITY
40Q
their daughters when mated with normal men have some color-blind
sons, but never color-blind daughters. Thus color blindness shows a
strong predilection for males, and is called a sex-linked character.
Free bleeding, night blindness, and several other human characters
are known to be inherited in the same fashion.
The mechanics of this form of heredity was worked out by Pro-
fessor T. H. Morgan as the result of his work on the classic fruit fly
Drosophila melanogaster. In this valuable little insect the eyes are
typically bright red. In a stock of typical red-eyed flies Morgan one
day noted one white-eyed male. This had been born of typical red-
eyed ancestry, so the white-eye character in addition to being sex-
linked was a mutant, appearing suddenly without any preliminary
steps. To test the heritability of this new character, the white-eyed
male was mated to a normal red-eyed female. The offspring of this
mating were all red-eyed in appearance (phenotypically), but tlie
females were obviously all genotypically hybrid red-and- white eyed,
for when mated with normal red-eyed males half of their sons were
white eyed and half red eyed, but all daughters were red eyed. Sub-
sequent experiments showed that half of the daughters were pure red
eyed and half hybrid red-and-white eyed. Now what sort of mech-
anism in the germ cells could account for this peculiar but very uniform
type of hereditary behavior?
Professor Morgan explained the whole thing in a beautifully simple
way by assuming that the gene of the sex-Hnked character was situated
in the X-chromosome of the mutant male, for the male has but one
X-chromosome along with a Y-chromosome (see Fig. 78). In the
reduction division of the germ ceUs of this individual two kinds of male
gametes (spermatozoa) are formed in equal numbers, one carrying the
X-chromosome with the white-eyed gene and the other the Y-chromo-
somes. Now, whenever a female gamete (egg) of the normal red-eyed
female used as a mate is fertilized by a sperm with the X-chromosome,
an XX individual or female will result, and aU of these females will
get the white-eye gene along with the X-chromosome from their
white-eyed father. But whenever an egg is fertilized by a sperm- with
the Y-chromosome, a male wiU be produced, and all of these will be red
eyed because they get their X-chromosome from their mothers. Why
are not these female offspring possessing the white-eye factor white
eyed? Because they have also inherited an X-chromosome contain-
ing the red-eyed factor from their mothers, and red eye is dominant
over white eye. These red-and-white-eyed hybrid daughters are now
4IO EVOLUTION, GENETICS, AND EUGENICS
bred to normal red-eyed males, whose X-chromosome carries the red-
eye factor. The females will produce two kinds of gametes in equal
numbers, one with the X-chromosome carrying the red-eye gene, the
other with the X-chromosome carrying the white-eye gene; while the
male will produce two kinds of gametes, one with an X-chromosome
carrying the red-eye gene and the other with only a Y-chromosome.
Each kind of male gamete will unite equally often with each kind
of female gamete, and the result will be four kinds of zygotes in equal
numbers: one in which two red-eyed X-chromosomes come together
and produce a pure red-eyed female, one in which a red-eyed and a
white-eyed X-chromosome come together and produce a hybrid female;
one in which a red-eyed X-chromosome and a Y-chromosome unite
to produce a red-eyed male; and finally, one in which a white-
eyed X-chromosome and a Y-chromosome unite to produce a white-
eyed male. This is the detailed procedure followed by all sex-
linked characters of this sort, and is shown diagrammatically in Fig-
ure 80.
We have seen that white eyes seem to be purely a male character,
inasmuch as it does not seem to express itself in females even when
present in the germ plasm. Why is this not just a secondary sexual
character like the differences in size and shape of the body that char-
acterize the two sexes? The answer to this query is that, if we perform
the proper breeding experiment, it is possible to transfer the white-
eye character to the female. For example, let us take one of the daugh-
ters of a white-eyed male and mate her with a white-eyed male.
The female is a hybrid carrying the white-eye gene in one of her
X-chromosomes and the red-eye gene in the other X-chromosome.
She will produce equal numbers of gametes with the two eye-color
genes. The male will also have two kinds of gametes, one with a white-
eye-bearing X-chromosome and one with a Y-chromosome. Random
pairing of the types of gametes of the two parents will produce
four classes of individuals in equal numbers: one female with a red-
eyed X and a white-eyed X (phenotypically red-eyed) ; one female with
two white-eyed X-chromosomes, and therefore white-eyed; one
male with a red-eyed X, and therefore red-eyed; and one male
with a white-eyed X, and therefore white-eyed. It is clear, then,
that the white-eye character is not limited to one sex, but merely
closely linlced to the male sex under normal breeding conditions. AH
sex-linked characters are recessive, for were they dominant they would
express themselves somatically when either one dose or two doses of
SEX DETERMINATION AND SEX-LINKED HEREDITY 41 j
the gene are present. The reason why the character appears normally
in males only is that males have only one X-chromosome, a situation
which makes it possible for any recessive gene located in the X-chromo-
some to express itself. The female, however, has always two X-
chromosomes, and miless she inherits the recessive gene from both
parents — a condition that would rarely occur in nature — she would
Flies
Chromosomes
iXi
X n ?
XX XI X
$ $ c?
Fi
Gametes
F2
d
Fig. 80. —Sex-linked inheritance of white and red eyes in Drosophila. Parents
white-eyed male and red-eyed female; Fi, red-eyed males and females; Fj, red-
eyed females and equal numbers of red-eyed and white-eyed males. A black
X indicates an X chromosome bearing the gene for red eye, a white X bears white
eye. @ indicates that X is wantmg; in recent publications Morgan replaces it
by Y. (From Conklin, after Morgan.)
always have the corresponding dominant character in one X-chromo-
some to mask or offset the recessive character in the other X-chromo-
some. In man it is also the unfortunate male that falls heir to all of
the rather detrimental sex-Unked characters, while the female, though
inheriting the character more often than the male, practically never
shows the effects of it.
An interesting variant upon the usual type of sex-linked breeding
experiment is the so-called reciprocal cross, starting out with a white-
412
EVOLUTION, GENETICS, AND EUGENICS
eyed female, derived from such an experiment as that just described,
and breeding her to a normal red-eyed male. The Fj hybrids will be
white-eyed males and red-eyed females, the two eye colors simply
changing sexes. This is explained by the fact that females always in-
herit an X-chromosome from their fathers, while males always get their
X-chromosome from their mothers. We speak of this phenomenon
Flies
CliTomosomes
5X0 : 5 XX
'
NEW SPECIES (mutants) OF OENOTHERA'^
HUGO DE VRIES
This striking species {Oenothera lamarckiana) was found in a
locaHty near Hilversum, in the vicinity of Amsterdam, where it grew
in some thousands of individuals. Ordinarily biennial, it produces
rosettes in the first, and stems in the second year. Both the stems
and the rosettes were at once seen to be highly variable, and soon
distinct varieties could be distinguished among them.
The first discovery of this locality was made in 1886. Afterwards
I visited it many times, often weekly or even daily during the first
few years, and always at least once a year up to the present time.
This stately plant showed the long-sought pecuHarity of producing a
number of new species every year. Some of them were observed
directly on the field, either as stems or as rosettes. The latter could
be transplanted into my garden for further observation, and the stems
yielded seeds to be sown under like control. Others were too weak
to live a sufficiently long time in the field. They were discovered by
sowing seed from indifferent plants of the wild locality in the
garden. A third and last method of getting still more new species
from the original strain was the repetition of the sowing process, by
saving and sowing the seed which ripened on the introduced plants.
These various methods have led to the discovery of over a dozen new
types never previously observed or described.
Leaving the physiological side of the relations of these new forms
for the next lecture, it would be profitable to give a short description
of the several novelties. To this end they may be combined under
five different heads, according to their systematic value. The first
head includes those which are evidently to be considered as varieties,
' From H. De Vries, Species and Varieties (copyright 1904). Used by special
permission of the publishers, The Open Court Publishing Company.
478 EVOLUTION, GENETICS, AND EUGENICS
in the narrower sense of the word, as previously given. The second
and third heads indicate the real progressive elementary species, first
those which are as strong as the parent-species, and secondly a group
of weaker types, apparently not destined to be successful. Under
the fourth head I shall include some inconstant forms, and under
the last head those that are organically incomplete.
Of varieties with a negative attribute, or real retrograde varieties,
I have found three, all of them in a flowering condition in the field.
I have given them the names of laevifolia, brevistylis and nannella.
The laevifolia, or smooth-leaved variety, was one of the very first
deviating types found in the original field. This was in the summer
of 1887, seventeen years ago. It formed a little group of plants grow-
ing at some distance from the main body, in the same field. I found
some rosettes and some flowering stems and sowed some seed in the
fall. The variety has been quite constant in the field, neither increas-
ing in number of individual plants nor changing its place, though now
closely surrounded by other lamarckianas. In my garden it has
proved to be constant from seed, never reverting to the original
lamarckiana, provided intercrossing was excluded.
It is cliiefly distinguished from Lamarck's evening-primrose by its
smooth leaves, as the name indicates. The leaves of the original
form show numerous sinuosities in their blades, not at the edge, but
anywhere between the veins. The blade shows numbers of convexi-
ties on either surface, the whole surface being undulated in this
manner; it lacks also the brightness of the ordinary evening-primrose
or Oenothera biennis.
These undulations are lacking or at least very rare on the leaves
of the new laevifolia. Ordinarily they are wholly wanting, but at
times single leaves with slight manifestations of this character may
make their appearance. They warn us that the capacity for such
sinuosities is not wholly lost, but only lies dormant in the new variety.
It is reduced to a latent state, exactly as are the apparently lost
characters of so many ordinary horticultural varieties.
Lacking the undulations, the laevifolia-lesives are smooth and
bright. They are a httle narrower and more slender than those of
the lamarckiana. The convexities and concavities of leaves are a
useful character in dry seasons, but during wet summers, such as those
of the last few years, they must be considered as very harmful, as they
retain some of the water which falls on the plants, prolonging the
action of the water on the leaves. This is considered by some writers
THE MUTATION THEORY 479
to be of some utility after slight showers, but was observed to be a
source of weakness during wet weather in my garden, preventing the
leaves from drying. Whether the laevlfolia would do better under
such circumstances, I have, however, omitted to test.
The flowers of the laevifolia are also in a slight degree different
from those of lamarckiana. The yellow color is paler and the petals
are smoother. Later, in the fall, on the weaker side branches these
differences increase. The laevifolia petals become smaller and are
devoid of the emargination at the apex, becoming ovate instead of
obcordate. This shape is often the most easily recognized and most
striking mark of the variety. In respect to the reproductive organs,
the fertility and abundance of good seed, the laevifolia is by no means
inferior or superior to the original species.
0. brevistylis, or the short-styled evening-primrose, is the most
curious of all my new forms. It has very short styles, which bring
the stigmas only up to the throat of the calyx-tube, instead of upwards
of the anthers. The stigmas themselves are of another shape, more
flattened and not cylindrical. The pollen falls from the anthers
abundantly on them, and germinates in the ordinary manner.
The ovary which in lamarckiana and in all other new forms is
wholly underneath the calyx-tube, is here only partially so. This tube
is inserted at some distances under its summit. The insertion divides
the ovary into two parts: an upper and a lower one. The upper part
is much reduced in breadth and somewhat attenuated, simulating a
prolongation of the base of the style. The lower part is also reduced,
but in another manner. At the time of flowering it is like the ovary
of lamarckiana, neither smaller nor larger. But it is only reached by
very few pollen-tubes, and is therefore always very incompletely
fertilized. It does not fall off after the fading away of the flower, as
unfertilized ovaries usually do; neitlier does it grow out, nor assume
the upright position of normal capsules. It is checked in its develop-
ment, and at the time of ripening it is nearly of the same length as in
the beginning. Many of them contain no good seeds at all; from
others I have succeeded in saving only a hundred seeds from thousands
of capsules.
These seeds, if purely pollinated, and with the exclusion of the
visits of insects, reproduce the variety entirely and without any
reversion to the lamarckiana type.
Correlated with the detailed structures is the form of the flower-
buds. They lack the high stigma placed above the anthers, which in
48o EVOLUTION, GENETICS, AND EUGENICS
the lamarckiana, by the vigorous growth of the style, extends the calyx
and renders the flower-bud thinner and more slender. Those of the
brevistylis are therefore broader and more swollen. It is quite easy
to distinguish the individuals by this striking character alone, although
it differs from the parent in other particulars.
The leaves of the 0. brevistylis are more rounded at the tip, but
the difference is only pronounced at times, slightly in the adult
rosettes, but more clearly on the growing summits of the stems and
branches. By this character the plants may be discerned among the
others some weeks before the flowers begin to show themselves.
But the character by which the plants may be most easily recog-
nized from a distance in the field is the failure of the fruits. They
were found nearly every year in varying, but always small numbers.
Leaving the short-styled primrose, we come now to the last of
our group of retrograde varieties. This is the 0. nannella, or the
dwarf, and is a most attractive little plant. It is very short of stature,
reaching often a height of only 20-30 cm., or less than one-fourth of
that of the parent. It commences flowering at a height of 10-15 cm.,
while the parent-form often measures nearly a meter at this stage of
its development. Being so very dwarfed the large flowers are all the
more striking. They are hardly inferior to those of the lamarckiana,
and agree with them in structure. When they fade away the spike
is rapidly lengthened, and often becomes much longer than the lower
or vegetative part of the stem.
The dwarfs are one of the most common mutations in my garden,
and were observed in the native locality and also grown from seeds
saved there. Once produced they are absolutely constant. I have
tried many thousands of seeds from various dwarf mutants, and never
observed any trace of reversion to the lamarckiana type. I have also
cultivated them in successive generations with the same result. In a
former lecture we have seen that contrary to the general run of
horticultural belief, varieties are as constant as the best species, if
kept free from hybrid admixtures. This is a general rule, and the ex-
ceptions, or cases of atavism, are extremely rare. In this respect it is of
great interest to observe that this constancy is not an acquired quality,
but is to be considered as innate, because it is already fully developed
at the very moment when the original mutation takes place.
From its first leaves to the rosette period, and through this to the
lengthening of the stem, the dwarfs are easily distinguished from any
other of their congeners. The most remarkable feature is the shape
THE MUTATION THEORY
481
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Gen. 2 J
1888-89
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9
Gen. I
1886-87
Mutants and Number observed in
different years
O.La
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1 form
Mutants and Number
observed in different years
Fig. 93. — Diagram showing in condensed form the genealogy of the Oc7zo;//crfl
Lamarckiana family and its various mutants during successive years. The numbers
under each type represent the number of new types observed each year. {From
Tower.)
From the seeds of one of the new forms, 0. laevifoUa, collected
in the field, plants were reared, some of which were O. lamarckiana and
others 0. laevifoUa. They were allowed to grow together, and their
descendants gave rise to the same forms found in the lamarckiana
THE MUTATION THEORY 487
family, described above, namely, 0. lata, elliplica, nannella, rubri-
nervis, and also two new species, 0. spahdata and leptocarpa.
In the lata family, only female flowers are produced, and, there-
fore, in order to obtain seeds they were fertilized with pollen from
other species. Here also appeared some of the new species already
mentioned, namely, alhida, nannella, lata, oblonga, rubrinervis , and
also two new species, elliptica and snbovata.
De Vries also watched the field from which the original forms
were obtained, and found there many of the new species that appeared
under cultivation. These were found, however, only as weak young
plants that rarely flowered. Five of the new forms were seen either
in the Hilversum field, or else raised from seeds that had been collected
there. These facts show that the new species are not due to cultiva-
tion, and that they arise year after year from the seeds of the parent
form, 0. lamarckiana.
Conclusions. — From the evidence given in the preceding pages it
appears that the line between fluctuating variations and mutations
may be sharply drawn. If we assume that mutations have furnished
the material for the process of evolution, the whole problem appears
in a different light from that in which it was placed by Darwin when
he assumed that the fluctuating variations are the kind which give
the material for evolution.
From the point of view of the mutation theory, species are no
longer looked upon as having been slowly built up through the selec-
tion of individual variations, but the elementary species, at least,
appear at a single advance, and fully formed. This need not neces-
sarily mean that great changes have suddenly taken place, and in
this respect the mutation theory is in accord with Darwin's view that
extreme forms that rarely appear, "sports," have not furnished the
material for the process of evolution.
As De Vries has pointed out, each mutation may be different from
the parent form in only a slight degree for each point, although all
the points may be different. The most unique feature of these muta-
tions is the constancy with which the new form is inherited. It is
this fact, not previously fully appreciated, that De Vries's work has
brought prominently into the foreground. There is another point of
great interest in this connection. Many of the groups that Darwin
recognized as varieties correspond to the elementary species of De
Vries. These varieties, Darwin thought, are the first stages in the
formations of species, and, in fact, cannot be separated from species
in most cases. The main difference between the selection theory and
488 EVOLUTION, GENETICS, AND EUGENICS
the mutation theory is that the one supposes these varieties to arise
through selection of individual variations, the other supposes that
they have arisen spontaneously and at once from the original form.
The development of these varieties into new species is again sup-
posed, on the Darwinian theory, to be the result of further selection,
on the mutation theory, the result of the appearance of new muta-
tions.
In consequence of this difference in the two theories, it will not
be difficult to show that the mutation theory escapes some of the
gravest difficulties that the Darwinian theory has encountered.
Some of the advantages of the mutation theory may be briefly
mentioned here.
1. Since the mutations appear fully formed from the beginning,
there is no difficulty in accounting for the incipient stages in the
development of an organ, and since the organ may persist, even when
it has no value to the race, it may become further developed by later
mutations and may come to have finally an important relation to the
life of the individual.
2. The new mutations may appear in large numbers, and of the
different kinds those will persist that can get a foothold. On account
of the large number of times that the same mutations appear, the
danger of becoming swamped through crossing with the original form
will be lessened in proportion to the number of new individuals that
arise.
3. If the time of reaching maturity in the new form is different
from that in the parent forms, then the new species will be kept from
crossing with the parent form, and since this new character will be
present from the beginning, the new form will have much better
chances of surviving than if a difference in time of reaching maturity
had to be gradually acquired.
4. The new species that appear may be in some cases already
adapted to live in a different environment from that occupied by the
parent form; and if so, it will be isolated from the beginning, which
will be an advantage in avoiding the bad effects of intercrossing.
5. It is well known that the differences between related species
consist largely in differences of unimportant organs, and this is in
harmony with the mutation theory, but one of the real difficulties of
the selection theory.
6. Useless or even slightly injurious characters may appear as
mutations, and if they do not seriously affect the perpetuation of the
race, they may persist.
THE MUTATION THEORY 489
LATER INVESTIGATIONS OF MUTATIONS
Since the publication of De Vries's classic investigations a large
amount of attention has been paid both by botanists and by zoologists
to the subject of mutations. Some of the mvestigators, notably B. M.
Davis, went far toward discrediting the whole of the exceptionally
careful work of De Vries by claiming that Oenothera lamarckiana is of
hybrid origin. It was pointed out that the form worked with is a
domestic type escaped from cultivation and that there is nowhere in
the known world any wild species comparable with it. It is supposed
to have been brought to Europe from America many years ago, bui
there is no such species in America today. Davis claims that he has
succeeded in producing, by crossing two American wild species, a
hybrid form distinctly resembling Oenothera lamarckiana, and that
when inbred this hybrid produces offspring showing various combina-
tions of the two parent-species that are not unlike some of the mutants
observed by De Vries. Jeffreys has also pointed out that the pollen
grains of Oenothera lamarckiana exhibit a high percentage of sterility,
which he beheves to be a stigma of hybridity. The general tenor of
this type of destructive criticism is to invahdate the whole mutation
theory as developed by De Vries and to reduce his mutants to the level
of mere Mendelian recombinations of characters once introduced from
two or more parental species.
The large amount of work on the cytology of Oenothera by Gates and
others has, however, served to show that the mutants of De Vries are
more than hybrid segregates. Moreover, the beautiful work of
Blakeslee on the Jimson weed {Datura) and the work of many other
botanists, whose findings are reported by Gates in a contribution
quoted below, serve to indicate that the type of evolutionary behavior
first observed in Oenothera is by no means exceptional, but is probably
a conmion thing at least among plants and may be commoner than we
at present know in animals. It may be said by way of anticipation
of Gates' detailed account that nearly all of the mutations observed in
various species of plants may be definitely correlated with observable
changes in the chromosomes of the germ cells, involving changes in
number or changes in arrangement of these nuclear elements.
While the botanists busied themselves with their type of mutations,
the zoologists, especially T. H. Morgan and his able collaborators, were
making discoveries of equal moment in connection with their studies
of the mechanism of Mendelian heredity in Drosophila. As has al-
490 EVOLUTION, GENETICS, AND EUGENICS
ready been shown in previous chapters, hundreds of new hereditary
types arose, apparently spontaneously, in pure-pedigreed stock. Each
new type is designated a mutant, and the cause of the changed heredi-
tary condition is not a gross chromosomal change, but an invisible
change at a definite point in a definite chromosome, whose cause is
unknown but whose location can be exactly determined. Such muta-
tions are known as gene mutations. Like the mutants of Oenothera,
these Drosophila mutants do not differ from the parent species in just
one or two characters, but in several or many characters. Usually some
one or two characters in any given mutant are especially character-
istic, and these serve to give a name to each mutant and make it easier
to identify them. Both morphological and physiological characters
are involved in these mutants, and every part of the body may be
involved. Sometimes the change is so slight as to require an eye
sensitized by much training to detect them. It may happen, for ex-
ample, that two mutants of the eye are so much alike that the human
eye is not sufficiently keen to tell them apart, but they may be dis-
tinguished by differences in their hereditary behavior. A large per-
centage of the mutants discovered in Drosophila are "lethals," which
means that the change is decidedly for the worse, under the prevailing
conditions of life, and that they render the individual unfit to live.
Possibly under decidedly different conditions some of these lethal
mutants might be better adapted than the normal individuals. A
further discussion of the role of mutants in evolution will be given in a
later connection.
The following two rather technical, but very interesting, discus-
sions as to the nature, causes, and significance of mutations are from
two men who are recognized as perhaps the leaders in the two branches
of mutation study. R. R. Gates has done a large amount of important
tvork especially upon the cytology of Oenothera, and H. J. Muller has
done and is still doing much to enrich our understanding of the muta-
tional phenomena exhibited by Drosophila. WhUe these two workers
do not agree as to the relative emphasis that should be placed upon the
two types of mutation, it is obvious that both types are of very great
importance in evolution.
THE NEO-MUTATIONIST POSITION
E. RUGGLES GATES
Since the original work of De Vries, the subject of mutation in
Oenothera has advanced in many directions and the explanation of the
phenomena has taken on various aspects. Mutation has become
THE MUTATION THEORY 491
essentially a cell problem. Cytological investigations have shown
that many of the mutations are concerned with new chromosome num-
bers, and the precise nature of the change which has led to the appear-
ance of forms with a new number is known with more or less certainty
in the various cases. The new number is in each case present through-
out the plant and will be found whether the chromosomes be counted
in growing petals, root tips or anthers. These discoveries led in 191 5
to the conception that each mutation with its new external characters
is the result of nuclear changes transmitted by mitosis to every cell of
the plant during development. A fundamental advance in the analysis
of mutations has thus been made.
Mutations can now be classified into two types, (i) Mutations
which are inherited as Mendelian differences, and which may be looked
upon provisionally as the result of a chemical change in one gene or
locus of a chromosome. The great majority of the mutations in
Drosophila are of this type. On the other hand, very few Mende-
lian mutations are known in Oenothera. The two best known are
rubricalyx, which is a dominant in crosses, and brevistylis, which is
inherited as a recessive. (2) Mutations resulting from a visible nuclear
change involving a new number of chromosomes. Probably the major-
ity of Oenothera mutations belong here. Similar mutations have been
discovered in Drosophila and also in Datura. Examination of the
chromosome numbers in related species of wild and cultivated plants
shows that such changes have been of relatively frequent occurrence
in the evolution of many plant genera, but they appear to be less com-
mon in animals.
CHROMOSOME MUTATIONS
The mutations with new chromosome numbers, which are partic-
ularly characteristic of Oenothera, may be classified into three
types: — (i) tr is omic forms, i.e., mutations with one or sometimes two
extra chromosomes (2W+1); (2) triploid forms (3»); and (3) tetraploid
(4«) forms. Other forms with different numbers, as 20 or 30, may be
regarded as derivatives from these types.
Trisomic forms are known to arise through non-disjunction, or a
reduction division in which both members of one pair of chromosomes
enter the same daughter nucleus. The best known mutation of this
kind is Oenothera lata with 15 chromosomes (0. lamarckiana having
14). But a number of others are now known, including scintillans,
albida, oUonga, subovata, and more recently cana, pallescens, ladiica,
and liquida. Several other derivatives of Oenothera lamarckiana are
also from their behavior almost certainly trisomic. When pollinated
492 EVOLUTION, GENETICS, AND EUGENICS
trom 0. lamarckiana they give the two parental types of offspring hav-
ing presumably 14 and 15 chromosomes. Since there are only seven
pairs of chromosomes these trisomic types can not all be accounted
for by duplication of a different chromosome in each case.
The genetic relationships between these trisomic mutants are also
interesting and peculiar. Thus lata can give rise to scintillans in its
offspring, and scintillans can similarly produce lata. Also lata (polli-
nated from lamarckiana) can give rise to several other trisomic muta-
tions. Many of these relationships can be explained by the assump-
tion of double non-disjunction, i.e., both members of one chromosome
pair entering one germ cell while both members of another pair enter
the opposite cell. It is highly probable that such cases occur. Thus
germ cells would be produced with the chromosome content
AACDEFG and BBCDEFG. It can be shown that by such a process
one trisomic mutation could give rise to another in its offspring. It
is very probable that lata is a primary trisomic mutation, e.g.,
AABCDEFG . . . ,, . ,
"ABrnFFr' ^■^■' ^ three A chromosomes, while some other
^ . . . , ^ , ,. , , , , AABCDEFG
trisomic (2W+ 1) mutations are probably secondary, e.g., —
ACCDEr G
i.e., with for example three A and three C chromosomes but only one
B chromosome. All such irregular chromosome distributions are
probably enabled to occur through a weakness in the attraction which
normally leads to close pairing of homologous chromosomes during
synapsis or on the heterotypic spindle. There is much evidence of
variation in the strength of this attraction in Oenothera.
Cleland has recently found that the chromosomes in various
Oenothera species retain their end-to-end connections even on the
heterotypic spindle. He has also shown that in several species the
arrangement of the chromosomes is more or less constant and char-
acteristic during the stages immediately preceding the reduction
division. Thus in 0. franciscana four of the chromosomes form a ring
while the other ten are arranged in five ring pairs which are at first
linked to the circle of four in a definite way. In a form called O.
franciscana sulphur ea, which is derived from 0. biennisXfranciscana,
12 chromosomes end-to-end form a circle and the other two form a
pair which is at first linked round the larger chain of 12, and this
arrangement is said to be constant. Thus in the derived form a re-
arrangement of the chromosomes with relation to each other has taken
place. Cleland finds similar fixed arrangements in other species.
THE MUTATION THEORY 493
Thus in a race identified with 0. muricata the 14 chromosomes all form
a single circle; in 0. biennis they are usually in two interlocking circles,
one with 6 and the other with 8 chromosomes; while in the mutant
oblonga with 15 chromosomes the arrangement is more variable but
frequently shows a ring of 5 single chromosomes with 5 pairs attached
to it. In a trisomic mutant from 0. rubricalysXhewettii a varying
number of ring pairs was found by the writer. If the relative con-
stancy of these arrangements is confirmed, it will show an essentially
new type of integration in nuclear structure, that is, a fixed positional
arrangement of the chromosomes in the nucleus with relation to one
another. This wUl also confirm the hypothesis of the writer years ago,
that the homologous maternal and paternal chromosomes in Oenothera
are usually arranged alternately on the spireme thread before the
reduction division. The fact that also, as observed by the writer in
ipo8, pairs of chromosomes are frequently detached from the rest of
the spireme in certain forms at an early stage of diakinesis, would make
it easier for double non-disjunction to occur on the heterotypic spindle
in these forms. The further study of the chromosome arrangements
in hybrids and mutants will throw more light on these rearrangements,
and perhaps also on the nature of the forces which bring them about
Such rearrangements without change of number, if they prove to be
constant, are to be considered as mutations of another kind.
Whether non-disjunction has played a part in the appearance of
species in nature with a different chromosome number is as yet un-
certain. But there are certain genera, such as Carex, in which the
haploid numbers usually increase by one from species to species.
Heilbom suggests that this may have happened by non-disjunction, as
in Oenothera lata, followed by the division of the extra chromosome to
form a pair.
Polyploidy. — An increase in the chromosome number by multiples
of the haploid number (polyploidy) is a phenorhenon of considerable
phylogenetic significance in plants, although it appears to be relativel>
uncommon in animals. There has been a burst of new knowledge on
this subject m the last few years. Since the original mutant Oenothera
gigas has been shown to be tetraploid, and setnigigas mutations triploid,
we have an experimental basis for the interpretation of all such cases.
It appears probable that the triploid condition in Oenothera arises
through the union of two male nuclei with the egg, as this condition
has been actually observed in 0. lamarckiana by Ishikawa, and in other
plants as well.
494 EVOLUTION, GENETICS, AND EUGENICS
A difference of opinion has long existed as to whether 0. gigas
arose from the fusion of two diploid cells or from a suspended mitosis
with division of the chromosomes in the fertilized egg. I am still in-
clined to adhere to the latter view as more probable, with perhaps a
sudden lowering of temperature just after fertilization as the cause.
Although it is a fact that diploid germ cells do sometimes occur,
diploid pollen grains are not known to be viable in plants.
The frequency of polyploidy in flowering plants, and also in other
groups of plants, is one of the surprises of recent years. Not only does
the condition occur in such cultivated plants as pineapples, bananas,
mulberries, wheat, oats, sugar-cane, dahlias, and tobacco, but also in
such genera of wild plants as the roses, maples, chrysanthemums,
Erigeron, Hieracium, Rumex, Rubus, Crataegus, Spiranthus, and a
number of others. The multiplication of chromosome sets runs as
high as 8w in Rosa and in Acer, and even as high as ion in certain
species of Rumex (80 chromosomes) and chrysanthemums (90 chromo-
somes). Such a widespread phenomenon must be of fundamental
significance in the evolution of the genera in which it occurs. The
higher degrees of polyploidy are probably often connected with hybrid-
ization, but there the higher chromosome numbers are usually accom-
panied by apogamous (asexual) reproduction, which renders constant
even forms with an unbalanced chromosome number. This is true
even of the triploid mulberries and Erigerons, etc. In every case of
polyploidy the higher numbers have not arisen gradually by the addi-
tion of single chromosomes, but one or more complete sets have been
added each time and the process is a mutation involving considerable
discontinuity.
That still other kinds of chromosome change occur, is shown both
from experimental work and by comparison of the chromosomes of
related species. Thus transverse segmentation of all chromosomes
has taken place in Primula kewensis, and end-to-end fusion of certain
pairs has evidently occurred in some species of Drosophila. In the
Japanese violets there is some indication that the small number of
large chromosomes in certain species may have been derived by the
fusion of smaller chromosomes found in other species. A process sug-
gesting transverse fragmentation of certain pairs of long chromosomes
appears to have occurred in various genera of Liliaceae. Further
study wUl no doubt throw Hght on the nature of these processes. It
appears already that the passage from one genus to another has not
infrequently been marked by a visible change in the chromatin mor-
THE MUTATION THEORY 495
phology of the nucleus. Such alterations in the conformation of the
nuclear material are to be regarded as germinal changes, even though
they are not accompanied by external changes in the organism.
MUTATION"
H. J. MULLER
Beneath the imposing building called "Heredity" there has been a
dingy basement called "Mutation." Lately the searchlight of genetic
analysis has thrown a flood of illumination into many of the dark
recesses there, revealing some of them as ordinary rooms in no wise
different from those upstairs, that merely need to have their blinds
flung back, while others are seen to be subterranean passageways of
quite a different type. In other words, the term mutation originally
included a number of distinct phenomena, which, from a genetic point
of view, have nothing in common with one another. They were classed
together merely because they all involved the s.udden appearance of a
new genetic type. Some have been found to be special cases of
Mendelian recombination, some to be due to abnormalities in the
distribution of entire chromosomes, and others to consist in changes in
the individual genes or hereditary units. It seems incumbent upon us,
however, in the interests of scientific clarity, to agree to confine our use
of the term mutation to one coherent class of events. The usage most
serviceable for our modern purpose would be to limit the meaning of
the term to the cases of the third type — that is, to real changes in the
gene. This would also be most in conformity with the spirit of the
original usage, for even in the earlier days, mutations were conceived
of as fundamental changes in the hereditary constitution, and there
were never intentionally included among them cases merely involving
redistribution of hereditary units — when these cases were recogniz-
able as such. In accordance with these considerations, our new defini-
tion would be: "mutation is alteration of the gene." And "alteration,"
as here used, is of course understood to mean a change of a transmissible,
or at least of a propagable, sort.
In thus trimming down the scope of our category of mutation we
do not deprive it of the material of most fundamental evolutionary
significance. For all changes due to the redistribution of individual
genes or of groups of genes, into new combinations, proportions, or
quantities, are obviously made possible only by the prior changes that
' Reprinted from Eugenics, Genetics and the Family, Vol. I (1923). Courtesy of
the Williams and Wilkins Company.
496 EVOLUTION, GENETICS, AND EUGENICS
make these genes differ from each other in the first place. It should in
addition be noted that changes due merely to differences in the gross
proportions of entire groups of genes must be relatively incapable of
that delicate adjustment which is required for evolutionary adaptation.
And as to the question, frequently raised, whether all evolution is ulti-
mately due to mutation, this is necessarily answered in the affirma-
tive by our definitions of the gene and of mutation, which designate the
gene as any unit of heredity, and mutation as any transmissible change
occurring in the gene. The question of the basic mechanism of evolu-
tion thus becomes transferred to the problem of the character, fre-
quency, and mode of occurrence of mutation, taken in this precise,
yet comprehensive sense. And since eugenics is a special branch of
evolutionary science it must be equally concerned with this problem.
In choosing the body of data wherewith to attack these questions of
mutation, in their new form, it must imfortunately be recognized that
the results with the evening primrose, Oenothera, although they formed
the backbone of the earlier mutation theory, can no longer be regarded
as having a direct bearing on the modern problem, since they cannot
be shown to be due directly to changes in the genes. Certain of them,
such as gigas, lata, scintillans, etc., have been proved by Geerts, Lutz,
Gates, and others, to be due to abnormaUties in the apportionment of
the chromosomes. Very valuable information on the genetics of cases
of this sort is now being obtained, especially in the work of Blakeslee,
Belling, and Farnham on much clearer cases of similar character in the
Jimson weed, and, finally, in the work of Bridges on the fruit fly Droso-
phila. Most of the other so-called mutations in the evening primrose
appear to be due to the normal hereditary processes of segregation and
crossing over, working on a genetic constitution of a special type. Evi-
dence for this was obtained in my analysis of the analogous case exist-
ing in the fly Drosophila, as follows. It had previously been shown by
de Vries, and further elaborated by Renner, that germ cells or indi-
viduals of Oenothera bearing certain genes always died, in such a way
that all the surviving individuals were heterozygous (hybrid) in regard
to these genes. I later showed, through work on Drosophila, that
when such a condition (there called "balanced lethal factors") exists,
the situation tends to become still further compHcated through the
presence of other heterozygous genes, which are linked to those which
cause death. When one or a group of these non-lethal genes crosses
over (separates) from the lethals, as they occasionally do, they may
oecome homozygous, producing a visible effect. Thus new types of
individuals appear which may be ascribed to "mutatiop" whereas thej
THE MUTATION THEORY 497
are really due to crossing over. The work of Frost on stocks has shown
that a precisely analogous situation exists in that form also, and G. H.
Shull is obtaining direct evidence for the same conclusion in the eve-
ning primrose itself. In any event, it must be granted that so long as
this interpretation cannot be definitely refuted, these variations can-
not be used as examples on which to base our theory of gene change.
In place, then, of the elaborate system of conclusions which has derived
its support chiefly from the results in the evening primrose, it will be
necessary for our present theory of gene change to erect an independent
structure, built upon an entirely new basis.
The data upon which the new theory must be built consist of two
main sorts, which may be called direct and indirect, (i) In the cases
giving the direct evidence, the occurrence of the gene change can be
proved, and it is possible to exclude definitely all alternative explana-
tions, such as contamination of the material, emergence of previously
"latent" factors, non-disjunction, etc. So far, the only considerable
body of such evidence is that gotten in the Drosophila work, where
mutations have (in this sense) been actually observed in at least loo
loci. Considered collectively, however, there exist in other organisms
enough scattered data to afford ample corroborative evidence for the
generality of occurrence of mutations like those observed in the Dro-
sophila work. In addition several specially mutable genes have been
found in a number of plants (as well as in Drosophila) that are giving
highly valuable information along their particular lines. And a num-
ber of selection experiments that have been performed on non-segregat-
ing lines of various organisms have also given us direct evidence, if
not of the frequency, then at least of the infrequency, of mutations.
(2) As for the indirect data, these may be gotten by examination of
Mendelian factor-differences of all kinds, on the assumption that they
must have arisen through mutation. Although this assumption can be
shown to be fully justified, these cases cannot provide information
concerning the manner of origin of the mutants, nor can they furnish
a reliable index of the frequency of mutations, since the mutant genes
may have been subjected to an unknown amount of selective elimina-
tion or selective propagation before the observations were taken. As
for the still more indirect data, derived from studies of phylogenetic
series and comparisons between different species, genera, etc., these
occasionally give suggestive results, but where crosses cannot be made
or where the differences cannot be traced down to the individual genes,
such facts can seldom lead to trustworthy genetic conclusions.
On these various data, duly weighted, we may found our new muta-
498 EVOLUTION, GENETICS, AND EUGENICS
tion theory. We know nothing, as yet, about the mechanism of muta-
tion, or about the nature of the gene — aside from the fact that nearly
all genes hitherto studied behave like material particles existing in the
chromosomes. Nevertheless there is already evidence for a number of
empirical principles regarding the changes of the genes, some of which
may conveniently be listed here in the form of 14 statements. I shall
have opportunity merely to present these principles, without attempt-
ing any adequate explanations of how they have been derived from the
data.
1. The first and probably most important principle is that most
genes — ^both mutant and "normal" — are exceedingly stable. Some
idea of the degree of this stability may be obtained from some quantita-
tive studies of mutation which Altenburg and I have made in the fruit
fly Drosophila. It may be calculated from these experiments that
a large proportion of the genes in Drosophila must have a stability
which — at a minimum value — is comparable with that of radium
atoms. Radium atoms, it may be recalled, have a so-called "mean
life" of about two thousand years.
2. Certain genes are, however, vastly more mutable than others.
For example, a gene causing variegation in com, studied by Emerson,
and another in the four-o'clock, studied by Maryatt, ordinarily have a
mean life of only a few years; and that causing bar eye in Drosophila
has a mean life of only about 65 years, as is shown by the results of
Zeleny. (In expressing these results we are here using the physicists'
index of stability, which seems most appropriate for the present pur-
pose also.)
3. External agents do not ordinarily increase the mutability sufii-
ciently (if at all) to cause an obvious "production" of mutation.
4. The changes are not exclusively of the character of losses; this
is shown by the well established occurrence of reverse mutations, in
bar-eyed and white-eyed Drosophila, in Blakeslee's dwarf Portulaca,
Emerson's variegated corn, and probably in a number of other recorded
instances. It is known that mutations having an effect similar to that
of losses do occur, however, and they may be relatively frequent.
5. The change in a given gene is not in all cases in the same direc-
tion, and it does not even, in all cases, involve the same characters.
The latter pomt is illustrated by a series of mutations which I am
investigating in Drosophila, which all involve one gene, but which pro-
duce, as the case may be, either a shortened wing, an eruption on the
thorax, a lethal effect, or any combination of these three.
THE MUTATION THEORY 499
6. The direction of mutation in a given gene is, however, preferen-
tial, occurring oftener in some directions than in others. This is well
illustrated in the studies on variegated corn and four-o 'clocks, and on
the bar eye and white eye and other series in Drosophila.
7. The mutability and preferential direction may themselves be-
come changed through mutation, as illustrated by some of the same
cases.
8. The mutations do not ordinarily occur in two or more different
genes at once. In only two instances in Drosophila have mutations
been found in two different, separated' genes in the same line of cells
of one individual. But a recurrent case, apparently of this kind, has
recently been described in oats, by Nillson-Ehle.
9. Not only does the mutation usually involve but one kind of
gene — it usually involves but one gene of that kind in the cell. That is,
the allelomorphs mutate independently of one another, just as totally
dififerent genes do. There is evidence for this derived from corn,
Portulaca, and Drosophila.
10. Mutations are not limited in their time of occurrence to any
particular period of the life history. This has been proved in the above
mentioned studies on mutable plants, in Drosophila, and in other cases.
11. Genes normal to the species tend to have more dominance than
the mutant genes arising from them. This is very markedly the case
in Drosophila, where even the relatively few mutant genes that have
been called dominant are very incompletely so, and might more justly
be called recessive. In other organisms, the same condition of things
is strongly suggested, although the direct data on occurrence of muta-
tions is as yet too meagre to allow of certainty.
12. Most mutations are deleterious in their effects. This applies
not only to the organism as a whole but also to the development of any
particular part: the delicate mechanisms for producing characters
are more likely to be upset than strengthened, so that mutations
should more often result in apparent losses or retrogressions than in
"progressive" changes. This is both an a priori expectation and a
phenomenon generally observed.
13. Mutations with slight effects are probably more frequent than
those with more marked effects. This must not be understood as re-
ferring to the different mutations of each given gene, but it applies in a
comparison of the mutations occurring in different genes. Thus, there
' Contiguous genes may be affected in the rare cases known as "deficiencies,"
found by Bridges and Mohr.
500 EVOLUTION, GENETICS, AND EUGENICS
are more than a dozen mutations, in different loci, which reduce the
size of the wing in Drosophila so slightly as to leave it more than half
its original length, whereas only four reduce it to less than half-length.
Mutant genes with effects so sUght as to be visible only by the aid of
specific co-genes seem to arise still more frequently. It is reasonable
to conclude that the mutations with slighter effects would more often
take part in evolution, because they should usually be less deleterious,
and this conclusion is born out by observations on the multipUcity
with which such factor-differences with relatively slight effects are
found in species crosses.
14. The range of those mutations which are of appropriate magni-
tude to be visible is probably very small, in comparison with the entire
"spectrum" of mutations, so that there are many more lethals than
visible mutations, and probably more subliminal than visible.
The above empirical and semi-empirical principles must be re-
garded as a mere preliminary scaffolding, for the erection of a later^
more substantial, theory of mutation. Time does not permit me here
to discuss which directions of research, and what methods, seem the
most promising for future results. Suffice it to say that it is especially
important to obtain accurate data concerning the effect of various
conditions upon the rate of mutation. This seems one of the logical
routes by which to work towards the artificial production of mutation
and consequent more perfect control of evolution. At the same time
such results should also give a further insight into the structure of the
gene. The way is now open, for the first time, to such studies on
mutation rate, first through the finding, by Emerson, Baur, Maryatt,
Zeleny, and Blakeslee, of a number of specially mutable factors in
different organisms, and second, through certain special genetic meth-
ods which I have elaborated in Drosophila, for the detection of lethal
and other mutations there.
It has now become recognized that advances in theoretical or
"pure" science eventually carry in their train changes in practice of the
most far reaching nature — changes which are usually far more radical
than those caused by progress in the appHed science directly concerned.
It may therefore be asked at this point by eugenists: "Are there any
applications of the knowledge which has akeady been gained about
mutation in general, to eugenics and to the principles which should
govern us in guiding human reproduction?" I think that one such
application is already clearly indicated.
In order to understand the nature of this application it will be nee-
THE MUTATION THEORY
501
essary first to consider the proposition — emphasized by East and
Jones in their book, "Inbreeding and Cross-breeding" — that the only
way for a genetically sound stock to be formed is by its going through
a course of inbreeding, with elimination, by natural or artificial selec-
tion, of the undesirable individuals that appear in the course of this
inbreeding. The truth of this proposition depends upon the fact that
many recessive genes of undesirable character are apt to exist in a
population. Since the frequency with which these genes are able to
produce their characteristic effects, i.e., to "come to light," depends on
the closeness of the inbreeding, it is evident that inbreeding will be
necessary in order to recognize the genes adequately, and hence to
eliminate them.
Our present theory of mutation, however, carries us further than
the proposition just considered. It shows that these undesirable
genes have arisen by mutation; in fact, as stated in point 12, the great
majority of mutations are deleterious, probably even to the degree of
being lethal, and it is also known, as noted in point 11, that many —
probably the great majority — are recessive. In other words, our
mutation theory shows that probably the majority of the mutations
that are occiurring are giving rise to genes of just the type specified in
the above discussion. This immediately shows us that not only are
inbreeding and selection desirable for raising the genetic level of a
population, but they are absolutely necessary merely in order to main-
tain it at its present standard. For the same process of mutation
which was responsible for the origination of these undesirable genes in
the past must be producing them now, and will continue to produce
them in the future. Therefore, without selection, or without the in-
breeding that makes effective selection possible, these lethals and other
undesirable genes will inevitably accumulate, until the germ plasm
becomes so riddled through with defect that pure lines cannot be ob-
tained, and progress through selection of desirable recessive traits can
never more be effected, since each of them wiU have become tied up
with a lethal. To avoid such a complete and permanent collapse of the
evolutionary process, it is accordingly necessary for man or nature to
resort to a periodically repeated, although not continuous, series of
inbreedings and selections in the case of any biparental organism.
This conclusion is more than a mere speculation, or even a deduc-
tion from our principles. The reality of this process of mutational
deterioration has been directly proved, in the case of Drosophila,
through experiments that I have conducted on lines in which the
502 EVOLUTION, GENETICS, AND EUGENICS
processes that are essential for the effectiveness of inbreeding and selec-
tion were prevented: in these lines there was found an accumulation
of lethal genes so rapid that it would have taken but a few decades to
have brought about the presence of a lethal gene in practically every
chromosome of every fly. Although the same general thesis un-
doubtedly applies also to mankind we do not yet know the speed of the
process here. Its speed depends upon the actual frequency of muta-
tions, which it will be very unportant — and extremely difficult — to de-
termine in the case of mankind. Meanwhile, no matter what this rate
may be, the process remams a real one, which must eventually be
reckoned with, and either grappled in tune, and conquered, or else
yielded to.
I have dwelt at length upon this particular appUcation to eugenics,
of some of the mutation studies. I beUeve, however, that this is but
one example of such appHcations, and that from an increasing knowl-
edge of our theoretical science there will inevitably flow an increasingly
adequate technique for coping with our refractory human material.
Meanwhile, the crying need is for more of the theoretical knowledge —
and for the support of pure science, in its investigation of the processes
lying at the root of the germ plasm.
THE CAUSES OF MUTATIONS
In attempting to determine the causes of the appearance of new
hereditary characters, we must first of all learn which of the categories
of variation we are dealing with. If we find that a so-called mutant
has a different number or arrangement of chromosomes, we may say
that this change in the chromosomes is the cause of the somatic differ-
ences seen in the mutant, for it would be strange if a relatively large
change in the hereditary material did not affect the somatic expression
of specific characters. As has already been suggested by Gates, the
cause of chromosomal aberrations may be environmental, as for ex-
ample sudden lowering of temperature durmg critical periods of the
germ-cell cycle. We have, however, no controlled experiments that
prove this to be the case. Again, there is a tendency to account for
non-disjunction and other types of chromosomal aberration through
purely internal causes, such as weakness of attraction between homolo-
gous chromosomes resulting in a failure of synapsis. In general it may
be said that, apart from being able to note a definite correlation
between a changed somatic condition and a changed chromosomal
THE MUTATION THEORY 503
condition, we do not know very much about the causes of this kind of
mutation.
We are also almost entirely in the dark as to the causes of gene
mutations. In Drosophila the hundreds of mutations seem to occur
over and over again under highly standardized environmental condi-
tions. Moreover, attempts to increase the rate or the character of
mutations by radical changes of the environment have given nega-
tive results. The experiments of Tower described in chapter xxvii
stood for a long time as the only instance of the successful production
of mutations under experimental conditions. Even these experiments
that have been the chief reliance of the environmentalist now seem to
be untenable, for it has not been possible to get any confirmation of
Tower's results. Using the same apparatus and the same stock, no
such mutants as he described, nor any other certain mutants, appeared.
It seems likely that Tower happened to get a strain of beetles that were
mutating of their own accord and that their mutations happened to
coincide with the experiment. MacDougal's experiments, cited in the
same chapter, now seem to be far from satisfactory as evidence that
true mutations may be induced by rather gross experimental means.
Apart from the fact that the percentage of changed individuals was
very small, although a great many experiments were performed, it is
now reported that the effects faded out in subsequent generations of
progeny; and this, of course, would mean that the changed condition
should be called an induction, not a mutation.
The most promising attack upon the problem of the causes of muta-
tions has been made by Guyer and Smith, by Stockard, by Bagg and
Little, and a few others, who have succeeded in reaching the germ cells
with agents from without that seem to be capable of producing per-
manent or hereditary changes. Of these, Guyer and Smith are the
only ones who appear to have produced anything like a specific change
by means of a specific agent. It will be recalled that these investi-
gators produced defects of the eye, particularly of the lens, by injecting
anti-lens serum into the mother at a time when the lenses of the
fetuses were undergoing differentiation, and that the induced defect
became definitely hereditary. Guyer also reports that the same results
were obtained by needling the lens of the mother, thus inducing directly
the production of lens antibodies that seem to be inherited. It has
already been pointed out that similar eye defects have been induced
by non-specific agents, such as alcohol and X-rays, and that these
conditions are inherited in similar fashion. In addition to eye defects
504 EVOLUTION, GENETICS, AND EUGENICS
there were several other associated defects, and this was more or less
true of the results of Guyer and Smith, for not only were lenses defec-
tive, but the whole eye was often much smaller than normal and defec-
tive in other parts besides the lens. But it should be remembered that
Morgan and others make no claim that a gene change is confined to
one part of the body, and gene changes probably represent the limit of
possible specificity. It would not be strange, then, if a lens antibody
modified a certain gene that particularly affected the lens, but affected
other structures to a less extent.
In closing the discussion about causes of new hereditary conditions,
we are forced to admit that at the present time we know practically
nothing as to causes. It seems highly probable that the environment
has had some controlling effect upon evolution, for changes in organ-
isms have run closely parallel with changes in climate in past geological
ages. The apparent effect may be due to natural selection, in that
radical changes in climate might merely eliminate most of the special-
ized types and open up the world for the plastic types to diversify and
by mutation to produce new adaptive forms. At the present time it
looks as though the heredity material, both through chromosomal
aberrations and through gene changes, is slowly differentiating inter-
nally through inherent forces and is very Uttle affected by the environ-
ment. This does not mean that the environment may not exercise
through selection an important guiding influence. It is still open to
question whether there may not be a long-time effect of somatic func-
tioning upon the germ plasm. In the very nature of the case it is
impossible either to prove or to disprove this possibility.
MUTATION AND EVOLUTION
T. H. MORGAN'
What bearing has the appearance of these new types of Drosophila
on the theory of evolution may be asked. The objection has been
raised in fact that in the breeding work with Drosophila we are dealing
with artificial and unnatural conditions. It has been more than im-
plied that the results obtained from the breeding pen, the seed pan, the
flower pot and the milk bottle [used as breeding-container for Droso-
phila] do not apply to evolution in the "open," nature "at large" or
to "wild" types. To be consistent, this same objection should be
extended to the use of the spectroscope in the study of the evolution
' From A Crilique of the Theory of Evolution. Princeton University Press, i g 1 6.
THE MUTATION THEORY 505
of the stars, to the use of the test tube and the balance by the chemist,
and of the galvanometer by the physicist. All these are unnatural
instruments used to torture Nature's secrets from her. I venture to
think that the real antithesis is not between unnatural and natural
treatment of Nature, but rather between controlled or verifiable data
on the one hand, and unrestrained generalization on the other.
If a systematist were asked whether these new races of Drosophila
are comparable to wild species, he would not hesitate for a moment.
He would call them all one species. If he were asked why, he would
say, I think, "These races differ only in one or two striking points, while
in a hundred other respects they are identical even to the minutest
details. " He would add, that as large a group of wild flies would show
on the whole the reverse relations, viz., they would differ in nearly
every detail and be identical in only a few points. In all this I en-
tirely agree with the systematist, for I do not think such a group of
types differing by one character each, is comparable to most wild
groups of species because the difference between wild species is due to
a large number of such single differences. The characters that have
been accumulated in wUd species are of significance in the maintenance
of the species, or at least we are led to infer that even though the visible
character we attend to may not itself be important, one at least of the
other effects of the factors that represent these characters is significant.
It is, of course, hardly to be expected that any random change in as
complex a mechanism as an insect would improve the mechanism, and
as a matter of fact it is doubtful whether any of the mutant types so
far discovered are better adapted to those conditions to which a fly
of this structure and habitat is already adjusted. But this is beside
the mark, for modern genetics shows very positively that adaptive
characters are inherited in exactly the same way as are those that are
not adaptive; and I have already pointed out that we cannot study a
single mutant factor without at the same time studying one of the
factors responsible for normal characters, for the two together con-
stitute the Mendelian pair.
And, finally, I want to urge upon your attention another question.
Evolution of wild species appears to have taken place by modifying
and improving bit by bit the structures and habits that the animal or
plant already possessed. We have seen that there are thirty mutant
factors 3 1 least that have an influence on eye color, and it is probable
that there are at least as many normal factors that are involved in the
production of the red eye of the wild fly.
5o6 EVOLUTION, GENETICS, AND EUGENICS
Evolution from this point of view has consisted largely in introduc-
ing new factors that influence characters already present in the animal
or plant.
Such a view gives us a somewhat different picture of the process of
evolution from the old idea of a ferocious struggle between individuals
of a species with the survival of the fittest and the annihilation of the
less fit. Evolution assumes a more peaceful aspect. New and ad-
vantageous characters survive by incorporating themselves into the
race, improving it and opening to it new opportunities. In other words,
the emphasis may be placed less on the competition between the indi-
viduals 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 char-
acters and modifications of old characters that become incorporated
in the species, for on those depend the evolution of the race.
CHAPTER XXXVIII
CROSS-BREEDING AND INBREEDING
CROSS-BREEDING
Cross-breeding is essentially hybridization, and we have already
studied various phases of hybridization in connection with MendeUan
heredity. There are, however, certain other aspects of cross-breeding
that have only a more or less remote connection with Mendelian
analysis. In this place we shall confine our attention to two questions :
(c) What is the role of hybridization as an evolutionary factor? (b) To
what extent is hybridization advantageous?
The role of hybridization in evolution. — "This," says R. R. Gates,
"is a thorny subject, on which different investigators have taken quite
different attitudes to the same facts. The extreme view that all flower-
ing plants, or even all sexual organisms are hybrids, has been held.
This has been accompanied in some cases (Lotsy) by the denial of any
true germinal change, though why such labile substance as protoplasm
should be incapable of undergoing a permanent or germinal change is
difficult to understand. Jeffries and others appear to hold that poly-
ploidy and other changes in which hybridization may be a factor, have
nothing to do with evolution. A more reasonable view would appear
to be that crossing has occiurred in various groups from time to time,
with more or less frequency and between sometimes more and some-
times less closely related forms. Crossing is therefore a condition
under which much evolution has taken place. It by no means follows
that crossing, any more than gravitation, is a vera causa, still less the
vera causa, of evolution, but it is a contributing condition. Polyploidy,
frequently accompanied by hybridization, appears to be a common
occurrence among flowering plants, but it would be futile to deny on
this account that flowering plants have had an evolution; nor would
it be safe to assume at present that the evolution of this group differs
very essentially from that of any other."
The exact role of hybridization in the formation of new species is
at present merely a matter for speculation, but that many new races
have been the result of favorable combinations of the genetic factors
of different strains can scarcely be doubted. In a sense, it may be said
507
5o8 EVOLUTION, GENETICS, AND EUGENICS
that hybridization is the rule in all organism? that reproduce sexually,
for no completely homozygous individuals exist in such groups, and
therefore there will always be a certain amount of factor segregation
in gamete formation and of recombination in the process of zygote
formation. Also it must be admitted that there are aU grades of
heterozygosity within a species and between one species and another.
Moreover, sexual reproduction as an adaptation operates chiefly
through bringing together a variety of combinations of characters
possessed by strains genetically diverse; it is, in fact, a hybridizing
mechanism. It seems probable therefore that hybridization as a factor
in evolution operates up to the limit of the adaptive possibilities inherent
in its mechanism. We may therefore conclude that hybridization is
and has been an important evolutionary factor, though we have at
present little information as to its precise mode of operation as an
agent in species formation.
Hybrid vigor (heterosis). — It has long been known that the
crossing of different races, varieties, or even species of animals or plants
result in the production of first-generation hybrids characterized by
a greater sturdiness, vitality, and size than either parent-species. This
effect has received the name hybrid vigor or heterosis. A good example
of this effect is the common mule, which is large and strong, thrives
under adverse conditions, and is hardier than either parent. It has
the disadvantage, or possibly advantage, of being sterile, a fact which
makes it necessary to hybridize two species every time we want another
mule.
Some of the manifestations of hybrid vigor as observed in various
crosses are as follows:
a) Hastening of maturity. — This is particularly advantageous in
plants reared in regions where the growing-period is short. Thus
hybrid strains of cereals may be valuable because they can be harvested
sooner than pure-bred strains. It is also true that hybrid plants, such
for example as tomatoes, have a larger as well as an earlier yield.
h) Increased longevity. — Pearl has shown that hybrid strains of fruit
flies have a longer average life-span than pure races. The same is
true for a number of hybrid races of plants, as brought out by Gaertner.
c) Better viability. — The writer has shown that the hybrids pro-
duced by crossing the eggs of the fish Fundidus heteroditus with the
sperm of F. majalis were frequently more viable, faster growing, and
more vigorous than the pure-bred young of either species; but the
hvbrids from the reciprocal cross showed much-reduced viability.
CROSS-BREEDING AND INBREEDING 509
Similarly, he has shown that some of the hybrids produced by cross-
ing the eggs of the sea-urchin Strongylocentrotus purpuratus with the
sperm of S. franciscanus hved nearly twice as long under cultural con-
ditions as did either pure breed, while the reciprocal cross showed
very low viability.
d) Augmented facility of vegetative propagation. — Many hybrid plants
are noted for their success in vegetative propagation. It is believed
that plants such as strawberries, brambles, grasses, etc., that propa-
gate so successfully by vegetative methods, are the products of hybrid-
ization. The vegetative method of reproduction not only maintains
a fortunate combination of genetic characters that could hardly be
repeated by gametic reproduction, but maintains their hybrid vigor
as well.
These and perhaps some other effects, all of which are essentially
beneficial, have been noted in both animals and plants. The follow-
ing explanation of hybrid vigor has been given by D. F. Jones:
^'Explanation of hybrid vigor. — From the illustrations given it is
evident that there is a tendency for the features of both parents to be
expressed in the offspring. This is the basis for an understanding of
the vigor derived from crossing. There is a greater number of differ-
ent hereditary factors in a hybrid individual than in either pure parent.
Nearly all variations that are recessive are less favorable to the de-
velopment of the organism than their dominant mates Since
crossing brings out those qualities which help the individual in its
growth and suppresses the abnormal and unfavorable characters, it
is to be expected that hybrids will tend to be strong and vigorous.
This will be true, however, only if each parent is able to supply the
deficiency of the other, and if the forms crossed are not so diverse
that their union is incompatible with normal growth. If the parents
are themselves hybrids, further crossing may bring together no great
number of dominant favorable growth factors but may even uncover
recessive characters. Hence further crossing can not usually increase
size and vigor, and in fact may even result in the appearance of weak-
nesses. This is clearly understandable from the operation of Mendel's
principles of heredity."
The question now arises as to whether hybridization in general is
advantageous or the reverse. Undoubtedly first-generation hybrids
are generally an improvement upon either parent-race, especially if
the parents belong to races not too distantly related. If we could stop
hybridization after one generation, as Nature stops it in the case of the
5IO EVOLUTION, GENETICS, AND EUGENICS
mule, nothing but good would apparently come out of it; but in man
and among other animals and plants where mating is more or less
indiscriminate, cross-breeding is sure to continue into the F2, Fj, and
subsequent generations, entailing the production of all sorts of unfortu-
nate combinations and the outcropping of all sorts of unbalanced
recessive weaknesses. In view of these considerations it is practically
certain that hybridization, unless accompanied by rigid selection and
the elimination from parentage of the less desirable combinations, is
on the whole disadvantageous. In nature, natural selection serves to
eliminate sooner or later the worst combinations resulting from con-
tinuous cross-breeding, but in man, little is done to prevent the worst
racial admixtures from predominating, the result being that the popu-
lations of some parts of the New World are made up mainly of a rather
homogeneous hybrid type possessing little more than the worst traits
of the various races that have contributed to the melting-pot.
By way of a general summary let us quote the following paragraphs
from D. F. Jones,' by whose book Genetics in Plant and Animal Im-
provement this discussion has been largely suggested:
"Summary. — From the foregoing it will be realized that if any
individual is deficient or handicapped in its hereditary make-up, there
is a good chance that its needs will be supplied when it is crossed with
other individuals, because all are not apt to be wanting in the same
things. What one lacks is furnished by the other, and conversely. In
other words, there is a pooling of hereditary resources, with the result
that the combined effect is better than either could produce alone.
"It should now be clear that the beneficial effects of crossing follow
from the workings of the laws of heredity and not from any mysterious
stimulus from the act of crossing itself. If good qualities exist in the
parents, but not in sufficient amount or not in their proper association,
then there is a good opportunity for the offspring to bring together
the favorable factors from both and surpass their parents in develop-
ment. This is a temporary and transitory effect, however. The in-
creased vigor is shown at its best only in the first generation following
the cross, and is quickly lost in later generations unless it can be
perpetuated by some form of asexual reproduction."
INBREEDING
There is a widespread and deep-seated feeling among men that the
mating of close relatives is unnatural and harmful. In most civilized
countries there are laws both religious and civic forbidding the mar-
' Loc. cil.
CROSS-BREEDING AND INBREEDING 511
riage of close relatives. The aversion to the marriage of relatives has
sometimes gone beyond the Kmits of genetic relationship and has in-
vaded the realm of merely legal or conventional relationships, as in
England, where it is, or at least once was, illegal to marry one's deceased
wife's sister.
"Only exceptionally, as in the case of the royal families of Egypt
and ancient Peru," says Castle, "has the marriage of brother and
sister been sanctioned. The underlying reason in such cases was the
belief that the family in question constituted a superior race whose
members could find no fit mates outside their own number. There
was probably no thought that inbreeding itself was beneficial but only
the desire to conserve the superior excellence beUeved to reside in cer-
tain individuals. The same considerations probably have led to the
occasional practice of inbreeding in animal husbandry, viz., the desire
to conserve and perpetuate the superiority of particular individuals."
It appears that Robert Bakewell, a stock-breeder of the eight-
eenth century, was the first to show the value of close inbreeding in
maintaining a uniform type of sheep and cattle. Bakewell adopted
the plan of mating brother with sister or parent with offspring, much
to the horror of his neighbors, who considered such a procedure im-
moral; but their scruples were soon broken down by the obvious im-
provements obtained and the greatly increased revenue that accrued.
The practice of inbreeding has been a favorite one for a long time, and
many fine breeds of standard character have been produced mainly in
this way.
Opinions among breeders differ as to whether inbreeding if prac-
ticed expertly is injurious. Some believe that inbreeding itself in-
volves no possible injury; others hold that it is always more or less
harmful. In order to settle this question, geneticists have carried out
extensive experiments under conditions of rigid control. • Even these
do not agree in their results. One group of workers (Crampe and
Ritzema-Bos) found after extensive inbreeding of rats that there was
a steady falling off in fertility and general health during the first six
generations of inbreeding. The material used, however, was a mixed
or hybrid stock to start with, a fact that makes a satisfactory conclu-
sion difficult. Weismann inbred a race of white mice for twenty-nine
generations. In the first ten generations the average number of young
was 6.1; in the second ten generations it was 5.6; and in the last nine
generations it was 4.2. Again, nothing was known about the genetic
constitution of the original parents.
Recent experiments carried out by Dr. Helen Dean King at the
512 EVOLUTION, GENETICS, AND EUGENICS
Wistar Institute are entirely contrary to those of the workers just
mentioned. This piece of work was carried out in a most precise
manner, with large numbers of individuals. The original stock con-
sisted of four rather undersized but otherwise normal albino Norway
rats. Brothers and sisters were mated throughout the experiment.
For six generations no selective mating was practiced, with the re-
sult that many of the defects previously noted were in evidence; but
after the sixth generation some twenty females from about a thousand
were selected for their superior qualities. From this stock the result
of inbreeding for twenty-five generations was very good. Dr. King
seems to have produced an essentially homozygous race of white rats
that are superior in many ways to the race from which they have been
derived. It seems probable that selection has rid the race of all or
nearly all of the residual recessive characters, so that the present com-
bination is highly normal and standard. Sewall Wright, under the
auspices of the United States Department of Agriculture, has carried
out a very extensive program of inbreeding with guinea pigs. His
results are more in harmony with those of earlier workers than with
those of Dr. King. In general, the result of brother- and sister-mating
was a steady loss of vigor both bodily and reproductive. Both prena-
tal and postnatal mortality was increased. Some families, however,
remained quite strong after long inbreeding; while other families de-
clined so rapidly that it was impossible to perpetuate them after a few
generations. Some strange combinations of traits appeared in differ-
ent stocks. One stock was characterized by very low vitality, but
remained normal in body size and in number of young produced.
Another stock showed undiminished vitality but greatly lowered re-
productivity and reduced size. The chief difference in method used
in these two modern experiments seems to be that only the best were
bred in Dr. King's experiments, while in Dr. Wright's experiments no
such precautions were taken, probably because he preferred to approxi-
mate natural conditions.
A large amount of experimentation in inbreeding has been carried
out with domestic animals and plants of all sorts, and the results have
shown as much diversity as those already reported; consequently,
opinions are still at variance as to the question whether inbreeding is
injurious per se. D. F. Jones, who seems to have given this matter
very careful consideration, takes the position that "the only injury that
comes from inbreeding comes from the inheritance received. ^^ If the indi-
viduals inbred possess many vmdesirable recessive characters, nothing
CROSS-BREEDING AND INBREEDING 513
is surer than that inbreeding will bring these to the surface. Cross-
breeding might succeed in masking such recessive characters, but they
remain in the germ plasm, nevertheless. All inbreeding does is to
reveal that which was masked behind dominant characters. Therefore
it is not inbreeding itself that is to blame, but a poor heredity. In-
breeding is a valuable instrument for detecting the unfavorable heredi-
tary characters in a race and giving the breeder a chance to cull out the
defective factors from his stock.
Inbreeding should be followed by cross-breeding inbred stocks. —
Whatever loss of vigor or productiveness may be incidental to the in-
breeding method of standardizing stock may be entirely done away
with by suitable cross-breeding or outbreeding. No matter how good
an inbred stock may be, great improvement can be brought about by
introducing new blood even from an apparently very similar strain
which is unrelated. It is well known that when two pure breeds are
crossed there is an effect quite equivalent to that which we have called
hybrid vigor. The animal-breeder commonly practices close inbreed-
ing in building up families of superior excellence, which he maintains as
pure-line stock, used for crossing with other stocks in order to produce
exceptional F, offspring. Man, of course, cannot practice this scheme
in the present state of society, but it seems obvious that there lie in
this method almost untold possibilities for racial improvement.
PART V
EUGENICS
CHAPTER XXXIX
THE INHERITANCE OF HUMAN CHARACTERS,
PHYSICAL AND MENTAL^
ELLIOT E. DOWNING
Anyone who undertakes to trace the ancestry of an mdividual is
soon impressed with the fact that it is a difficult task even to find the
names of the persons involved three or four generations back; it is
much more difficult to determine with certainty their physical and
mental characteristics. One can more surely find the pedigree of a
horse or hog that he may own than he can of a child in whom he is
interested, for we do have registry books for good stock, but none
ordinarily for human family relations (in Illinois not even compulsory
birth registrations until very recently), so that a child bom in this
state may not even legally prove his existence or parentage by official
records. It is not an easy matter, therefore, to find human data that
illustrate the various phases of heredity concerning which we are
reasonably sure in deaUng with animals and plants.
Fortunately, there are some studies of the inheritance of physical
characters that are quite satisfactory. There is an increasing number
of studies of the inheritance of insanity, feeble-mindedness, epilepsy,
and alcohoUsm by the scientific staff of institutions dealing with such
cases, and we do have a fairly good mass of material in the lines of
descent of the royal families of Europe, where the matings and the
characters of the individuals are more or less matters of history.
Thanks to the generosity of some men of wealth and foresight, appre-
ciative of the importance of a better knowledge of the laws of human
heredity, we have in several countries well-endowed laboratories with
expert staffs founded on purpose to study this topic; such as the
Gal ton Laboratory of Eugenics in England and the Eugenics Labora-
tory of the Carnegie Institution, Cold Springs Harbor, New York.
Occasionally a family is found in which one or more members have
five fingers instead of four; such a condition is known as polydactyl-
ism. Sometimes a case is recorded in which a person has fingers with
* From E. R. Downing, Tlie Third and Fourth Generation (The University of
Chicago Press, copyright 1920).
517
5i8
EVOLUTION, GENETICS, AND EUGENICS
two joints instead of three and a thumb with one joint in place of two
(brachydactylism). Such human abnormalities are inherited. There
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individuals on a scale of lo. Ten represents very high ability, as
determined by the comparative amount of space and laudation given
to the individual in such standard works as Lippincott's Biographical
Dictionary. Five out of eight of Isabella's great-grandparents rank
very high. John the Great of Portugal, twice her great-grandfather,
has a grade of lo. John of Gault, twice her great-grandfather, has a
grade of 8, as does also John of Castile, while Henry III of Castile, one
of her grandparents, is designated the model king. Ferdinand I of
Aragon, the grandfather of Ferdinand, is a brother of this same
Henry III of Castile, and is also an exceedingly able king. Of the
children of Ferdinand and Isabella, most were mediocre or distinctly
inferior. Joanna was insane. In the next generation, however, appears
Charles V, whose reign marked the acme of Spain's greatness, partially
due to his own ability, partially due to the momentum of those move-
ments that were instituted by his illustrious grandparents. Charles V
married his own cousin, as did also John III. Children of these two
matings married, and Don Carlos, child of this latter marriage, was
madly depraved and cruel.
When insanity and brilliancy are found in the ancestry it seems
merely a matter of chance as to whether the determiners for greatness
will be thrown together in the union of sperm and egg or those for
insanity. We can predict with some certainty, that, in a large number
of offspring, ability will reappear and insanity will reappear, but just
what individual each will strike it is impossible to prophesy without
knowing much more definitely the nature of the germ plasm involved.
One may say that the convergence of a number of lines of descent from
great ancestors toward one individual makes it probable that he will
be exceptionally able.
This is nowhere better illustrated than in the family tree of
Frederick the Great of the Prussian house of Hohenzollem, as will be
seen from the chart on page 524. Of his great-grandparents, three
scale 10, one 9, one 8, two 7, and one 6. Not one is below mediocrity,
and the majority are of very high grade. Of his fourteen ancestors
back three generations, only one is distinctly inferior. Of his brothers
and sisters, four are distinctly great, three mediocre, and one inferior.
It is interesting to trace the effect of the mating of such splendid
stock with another brilliant Une, that of the Swedish royal house.
Gustavus I, or Gustavus Vasa, is another instance of the brilliant
mutant, with some taint of neurosis. He married a gentle and tactful
princess; their son Charles IX was a very able man, although of their
528
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three other children one was insane and two weak. The children of
Charles EX were both remarkably able. The daughter Catherine
becomes the mother of a later succession of kings. Her son Charles X
and his son Charles XI were rather mediocre; but Charles XI, with
this fine stock behind him, married Ulrica Eleanor (7), granddaughter
of Christian IV of Denmark, the most brilliant of all Danish sovereigns,
and Charles XII, their son, is pronounced by Voltaire the most
remarkable man who ever existed. Charles XII had no children:
the succession passed to his sister's son, Adolph Frederick of Holstein-
Gottorp, who married Louisa Ulrica, sister of Frederick the Great
of Prussia. ^ The result of this union of two great lines of hereditary
abihty was Gustavus III, a fit successor of Gustavus Vasa, Gustavus
Adolphus, and Charles XII; he was " a prodigy of talents," statesman,
poet, dramatist.
CHAPTER XL
TWINS AND THE RELATIVE POTENCY OF
HEREDITY AND ENVIRONMENT
IN DEVELOPMENT'
Two sets of factors are involved in the development of an indi-
vidual, and doubtless the same two sets of factors are responsible for
racial development or revolution. One category of factors is intrinsic
and seems to depend upon the physical organization of the germinal
protoplasm or upon the mechanisms that are involved in cell multi-
plication and differentiation: all such factors are included under the
term heredity. The other category of factors is extrinsic and seems to
involve both environment and training: these factors are usually in-
cluded together under the term environment. The controversy as to
the relative importance of these two sets of factors is so old as to be
time-honored. In the case of man especially the question as to what
characters are due to nature and what to nurture has long been an
active issue.
Before the rise and growth of democracy the opinion was very com-
monly held that man was born noble or base, with high qualities or
low, according as he came from good or bad stock. The various well-
defined strata of society were believed to have a basis in blood. Blue
blood was the criterion of nobility or of high character. With the
rise of democracy, however, the view has come to prevail that "all
men are created equal" and that inequalities arise only as the result of
inequitable distribution of environmental and educational advantages.
This has been until recently the prevailing opinion in educational,
sociological, and political circles. This ignoring of hereditary differ-
ences and overemphasizing of the potency of environment have
caused the pendulum to swing to the opposite extreme.
The present century has seen such a surprising advance in our
knowledge of the laws and the mechanism of heredity that it is no
wonder that biologists have come to feel that heredity is far and away
the chief factor in human development and that environment and
training are only minor modifying factors.
' Reprinted from the Publications of the American Sociological Society, Vol
XVII (1Q22). An address given before the American Sociological Society by
H. H. Newman.
531
532 EVOLUTION, GENETICS, AND EUGENICS
No one can deny the equality of heredity and environment in one
sense: for both are absolutely essential. No organism can develop
without a basis of germinal substance; neither can any development
take place in the absence of the proper environment. The hereditary
material is, however, what we are and the environment and training
are what we have and what we do. What we are is really more funda-
mental in determining character. This is the opinion of the great body
of biologists.
Geneticists have ceased to consider a man as a whole unit. He is a
highly elaborate complex of characters. It is futile to attempt to de-
termine whether a man as a whole is more the product of nature than
of nurture, but it is quite reasonable to attempt to measure the relative
contributions of nature or nurture to any single human character, such
as eye color, stature, brain power, well-defined idiosyncrasies.
A natural form of experiment to test the relative potency of two
co-operating factors would be to keep one factor uniform and modify
the other, and vice versa. We might conceivably rear several indi-
viduals with identical heredity under varying environmental condi-
tions and compare the end results. Or we might place individuals of
unlike heredity under identical environmental conditions and compare
the end results. If the former tended to remain alike despite the en-
vironmental differences, it would appear that environment was im-
potent materially to affect heredity. Similarly, if individuals with
different heredity fail to grow more alike under the same environment,
a similar conclusion would be justified. The crux of such an experi-
ment is to discover individuals with identical heredity, and it is to the
insight and ingenuity of Sir Francis Galton that we owe the first crucial
test of the problem along the lines proposed.
TWO KINDS OF TWINS
Galton was perhaps the first to recognize that there are two kinds
of twins: identical twins and ordinary or fraternal twins. Ordinary
twins are merely brothers and sisters that happen to be born together.
Each comes from a separate fertilized egg, and they differ in their
hereditary complex as widely as do brothers and sisters in general.
Such twins may be both male, both female, or a male and a female.
Identical twins have an origin quite different from this. It is practi-
cally certain, though not as yet fully demonstrated for human beings,
that the two individuals are derived from the two halves of a single
egg which had been fertilized by a single sperm. They constitute,
RELATIVE POTENCY OF HEREDITY AND ENVTRONMENT 533
therefore, just the type of material we need: two indrviduals with
identical heredity.
Thus we have twins with identical heredity and twins with quite
different heredity. If we could always distinguish the two types, we
should be able to determine the effects of diversified environment in
the former and similar environment in the latter. Galton assmned
that if the environment has the power to modify the inborn character
of individuals, identical twins that arise from one germ cell and have
identical heredity ought to become progressively more and more unlike
if separated and reared under different conditions. Fraternal twins,
on the other hand, though quite different in heredity, should, if reared
under the same environmental and educational conditions, tend to be-
come progressively more and more alike. If, however, the identical
twins remain alike and fraternal twins remain different, it would ap-
pear that environment has little if any power to modify inborn con-
stitution,
galton's use or data from two kinds or twins
In order to put this matter to the test, Galton collected data on one
hundred pairs of twins, eighty of which he classed as identical and
twenty as fraternal.
After a considerable amount of comment on the extraordinary close-
ness of resemblance between identical twins, some instances of which are
rather comical, he comes to a study of a number of cases where the
twins were separated early in life and reared under diverse environ-
mental conditions. The resemblances in physical appearance, in ideas,
in habits underwent no divergence, but the twins remained as much
alike as ever up to old age. Only serious illness or accident to one
twin seemed to have any effect upon their inborn resemblance.
With reference to the twenty pairs of fraternal twins who were
unlike from birth, the conclusion was equally striking. In no case
was there any tendency for unlike twins to grow alike when reared to-
gether under the same environmental conditions. The comments of
the two parents are typical:
o) "They have had exactly the same nurture from their birth up to
the present time; they are both perfectly healthy and strong, yet they
are otherwise as dissimilar as two boys could be physically, mentally,
and in their emotional nature."
b) "They had never been separated, never the least differently
treated in food, '•Nothing, education; both teethed at the same time,
534 EVOLUTION, GENETICS, AND EUGENICS
both had measles, whooping cough, and scarlatina at the same time,
and neither has had any other serious illness. Both are and have been
exceedingly healthy, and have good abilities, yet they differ as much
from each other in mental cast as any one of my family differs from
another."
Gal ton finally concludes as follows: "There is no escape from the
conclusion that nature prevails enormously over nurture when the
differences of nurture do not exceed what is commonly to be found
among persons of the same rank in society and in the same country."
This was a strong statement and needed to be confirmed and made
more exact. Two American specialists set out to put this conclusion
on a firmer basis.
Professor Thorndike used biometrical methods, especially the co-
efficient of correlation. He studied fifty pairs of twins in the New
York City schools with reference to their closeness of resemblance in
eight physical and six mental characters. He found that on the aver-
age twins, not distinguishing between fraternals and identicals, were
from two to three times as similar as were ordinary children of the
same ages brought up under similar environment; that twins from
twelve to fourteen years old were no more alike than twins nine to
eleven years old, although they had been several years longer under
similar environment during an extremely plastic period; that twins
were no more alike in traits subject to much training than those sub-
ject to little or no training. Thorndike concludes:
"The facts are easily, simply and completely explained by one
simple hypothesis; namely, that the nature of the germ-cells — the
conditions of conception — cause whatever similarities and differences
exist in the original natures of men, that these conditions influence
mind and body equally, and that in life the differences in modification
of mind and body produced by such differences as obtain between the
environments of present-day New York City public school children
are slight." ■
It will be noted that Thorndike, although he used the data of twin
resemblance to test the relative powers of nature and nurture, makes
no clear distinction between fraternal and duplicate twins. In ex-
perience he discovered that in many cases the twins were obviously of
one category or the other, but that there were many marginal cases
that he was unable to classify.
About the same time, or possibly a little earlier, Piofessor Wilder
was making a very elaborate comparison of duplicate twins with refer-
RELATIVE POTENCY OF HEREDITY AND ENVIRONMENT 535
ence especially to such minute details as finger prints. He showed
that in some cases the resemblance between the palm and sole patterns
of twins was startlingly close, but that in other cases, although the
twins appeared to be duplicate twins, there was not much resemblance
between their finger-print patterns. One cannot but be impressed
with Wilder's feelings of uncertainty as he attempts to classify certain
pairs. The following extract makes my point clear. Speaking of
Case VII, Wilder says:
"This case caused me considerable trouble owing to the precon-
ceived notion that the marks ought to be found identical. The family
emphasized the facial resemblance of these twins and when I first saw
them they certainly looked much alike. One was, however, an inch
taller than the other, and the facial resemblance, after a short ac-
quaintance did not seem as great The case is plainly one of
fraternal twins that resemble one another somewhat more than the
average."
This is t)Apical of the method used in gathering statistics on this
problem of twins and the relative values of nature and nurture as
factors in development. We assume that twms that come from one
egg are nearly identical and that two-egg twins are no more alike than
ordinary brothers and sisters. From this we conclude that heredity
is almost the sole factor in determining the character of the individual.
Then we infer that strikingly similar twins are one-egg and those less
similar are two-egg derivatives. We assume that identical heredity
should give identical characters and then turn around and assume that
identical individuals, and only those, have identical heredity, while
individuals that fall considerably short of identity have unlike heredity.
This is reasoning in a vicious circle with a vengeance. If we find that
twins are sufficiently alike to meet our preconceived ideas of what one-
egg twins ought to be, we class them as duplicate twins. If we find
that they are less alike than we think they ought to be, we class them
as fraternal twins. Unless we can be certain at the outset whether
twins are of the one-egg or the two-egg types, no safe conclusions can
possibly be based upon their degrees of resemblance or difference.
The only way in which one could at all safely determine whether
twins have the same or different heredity is to observe the placental
connections of the twins at birth. Authorities such as Spaeth and
Schatz agree that one-egg twins are attached to a single placenta, while
two-egg twins have separate placentas which may be more or less fused,
but even when fused show no intercommunication of placental blood
53^ EVOLUTION, GENETICS, AND EUGENICS
vessels. There are on record no data as to the degrees of resemblances
and differences between twins in which the placental connections are
known. Hence there are but few definite data upon which to measure
the relative proportion of hereditary and environmental factors in the
case of human twins.
One interesting set of comparisons has, however, been made by
Frederick Schatz, who more than any other writer has gone into the
details of the consequences of human twinning. This author had a
large amount of gynecological material at his disposal and was able to
deal statistically with the resemblances and differences between one-
egg and two-egg twins before and after birth. He found, strangely
enough, that one-egg twins, though they have the same hereditary
composition, are considerably less alike in size and weight at about the
middle of pregnancy that are two-egg twins. The cause of the great
inequality is associated with the fact that the placental blood vessels
of the two individuals struggle for supremacy in the single placental
area and undergo more or less extensive anastomoses, so that one twin
sends blood over to the other and vice versa. There is great oppor-
tunity for unfairness of give and take and, as a rule, one twin is dis-
advantaged at an early time. At the time of birth, however, the differ-
ences in size and weight of the one-egg twins are essentially equal to
those of the two-egg twins; which means that the one-egg twins have
grown more alike and the two-egg twins have grown less alike in spite
of all the environmental factors that have been at work to make the
one-egg twins less alike and the two-egg twins more aUke. This is in-
deed a test of the relative potency of heredity and environment, and
the result is greatly in favor of heredity; but we have information only
about matters of size and weight, which are perhaps the least valuable
characters for comparison because they are so notoriously changeable
and seem to depend so largely upon nutrition, a factor of the environ-
ment. The fact that even these characters seem to be so definitely
governed by heredity is at least not in favor of the environment side
of the discussion.
ARMADILLO QUADRUPLETS
On the whole, then, we may say that human twins furnish little
or no conclusive evidence of the exact relative values of the factors of
heredity and environment. What we need to find is some species,
preferably a mammal, in which we know that one-egg twins occur and
in which there is no doubt that we are dealing with individuals with
identical heredity. Some years ago I was fortunate in finding just
RELATIVE POTENCY OF HEREDITY AND ENVIRONMENT 537
the right animal for this purpose — the nine-banded armadillo of Texas.
This armored mammal, belonging to an archaic race, abounds in south-
west Texas. We discovered that it always produces not merely twins
but quadruplets at every pregnancy and always only one egg is fertilized
at each pregnancy. Over two hundred litters sufficiently advanced for
detailed comparisons were examined, and in this material we have the
data for determining just exactly what are the extreme Hmits of hered-
ity and how much leeway there may be for environmental modification.
The animals are beautifully designed for detailed comparison. Their
nine bands of armor, composed of definite scutes, the rings of scutes on
the tail, the definite scale pattern of the head, all these and many other
characters lend themselves to exact statistical treatment.
Some of the results of such a comparison are these:
a) All individuals of a given litter, derived from one egg, are of
the same sex. There are no exceptions.
b) The coefficient of correlation of a considerable number of body
characters for 115 sets of quadruplets which showed no marked anom-
alies of scute pattern was approximately .93, where i is complete
correlation or exact correspondence. This may be taken to prove that
heredity accounts for 93 per cent of the bodily characteristics and other
factors for about 7 per cent.
c) WTien, however, individual sets of offspring were examined, very
great differences revealed themselves. With regard to certain char-
acters some sets showed .99+ resemblance and others showed very Ut-
tle more resemblance than would be expected in unrelated individuals.
Yet every set of quadruplets is beyond question the product of the
division of a single fertilized egg.
d) In some of these sets of quadruplets where the differences
among individuals were great, it was found that one, two, or three
individuals closely resembled the mother, while the others were quite
unlike the mother, and presumably like the unknown father.
e) In several sets where the mother had some rare pecuUar arrange-
ment of the scutes, one, two, or three offspring repeated the maternal
character more or less definitely, while the others failed to show any
trace of such peculiarity.
/) Frequently an asymmetrical peculiarity inherited from the
mother was found on the left side of one twin, the right side of another,
sometimes on both sides of a third, and wanting in the fourth.
All of these results indicate that there is operating here a third
factor, neither heredity nor environment, but what we might call a
538 EVOLUTION, GENETICS, AND EUGENICS
distributional factor associated with the mechanism of cell division and
body formation. This factor involves some profound inaccuracy in
the supposedly exact mechanism of mitosis which should equally
distribute hereditary materials to all cell products of a single zygote.
Whatever this third factor is, call it developmental inaccuracy if you
will, it tends to interfere with the degree of resemblance between twins
and is consequently to be thought of as explaining a considerable part
of the failure of the quadruplets to show complete identity. In spite
of this factor and in spite of whatever influence may be exerted by en-
vironment, the average potency of heredity is about 93 per cent, as
compared with 7 per cent for both environment and the third or distri-
butional factor. We have no basis for estimating how much of the 7
per cent is environmental and how much distributional, but I suspect
that very little of it is environmental. In the case of the armadillo,
therefore, we are forced to the conclusion that environmental factors
such as may be concerned in the development of bodily characters are
largely ineSective in modifying heredity. The environmental differ-
ences of position, variations in food, or any other developmental
variables are not suflliciently great to disturb at all seriously the equal-
ity of the quadruplets, all of which start out with a common heredity.
We know nothing about the mental qualities of the armadillo. Whether
his mentality is more or less plastic than his body is hidden from us.
TWINS THAT ARE MODIFIED BY THE ENVIRONMENT
Quite the opposite conclusion with reference to the influence of en-
vironment upon heredity is brought out by a beautiful experiment of
Nature upon cattle twins. Twins are very rare in cattle. When they
do occur they are two-egg twins with a different hereditary make-up
from the start. They may or may not be of the same sex. When they
are both of the same sex, they are merely like ordinary brothers and
sisters; but when they are of opposite sexes, a male and a female, the
male is always normal and the female is nearly always an anomalous
creature, partly male and partly female, called a freemartin. This
much has been known for some time, but it remained for Professor
F. R. Lillie to work out the details and to solve the problem. Using
the unexampled opportunities of the Chicago stockyards, he obtained
large numbers of cattle twins at all stages of their development. The
situation is this: Sex in cattle, as in other animals, is inherited. An
individual is zygotically determined as either a male or a female when
the egg is fertilized. The uterus of cattle is bicornate, consisting of two
long horns communicatine with a common region. One egg usuallv
RELATIVE POTENCY OF HEREDITY AND ENVIRONMENT 539
ovulates from each ovary when twins are produced. Each twin
develops separately for some time in its own horn of the uterus, and
their membranes grow down toward the united part of the uterus. As
a rule the chorionic membranes of the two fuse and the blood vessels
unite so that their blood supply is in common. It is now known that
the male at a very early period develops glandular tissues in its
gonads that are a necessary agent in differentiating the characteristic
male features, while the female does not develop ovarian gland tissues
till a late fetal period. The result is that the substances given off from
the male gonads, which we call hormones, pass through the common
blood supply to the individual that is by heredity a female, and so
profoundly transform this prospective female that in many cases she
has more male qualities than female. Apparently it is not possible
completely to reverse the sexes, but in some cases reversal is approxi-
mated. The male hormones that come to the prospective female
from outside her body are obviously environmental factors, and that
heredity is profoundly modified by environment cannot be denied in
such cases as these.
What light is thrown upon the human situation by the study of
these various types of twins? The influence of environment as an
agent capable of modifying heredity is not denied as a general proposi-
tion, but it appears that the organism is in general so plastic, almost
elastic one might say, that environmental effects within the range of
ordinary human experience are able to affect heredity only very slightly
or temporarily. By the time an individual is born its characters are
already so far advanced toward the definitive condition that only such
radical disturbances as serious illness or gross poisoning of one kind or
another are capable of altering the course of differentiation that has
been shaped by heredity. If we could change the environment during
an early embryonic period, we might hope effectively to modify hered-
ity, but no such control is yet within our power. Prenatal influences
through maternal impressions are believed in by many, but the genet-
icist looks upon this notion as among the most patent fallacies with
which he comes in contact.
I suppose that the motive actuating the invitation given me to
speak before this representative body of sociologists was the hope that
I would emphasize the factor of heredity and thus tend to neutralize to
some extent the prevailing overemphasis upon the factor of environ-
ment. Perhaps I have in turn overemphasized heredity. Somewhere
between these extremes of overemphasis lies the truth.
CHAPTER XLI
DOES HEREDITY OR ENVIRONMENT MAKE MEN?'
ALBERT EDWARD WIGGAM
All men are born unequal. When the Declaration of Independence
made its pronunciamento, it was merely to serve notice upon King
George that the American colonists were equal in their social, political
and human rights to the citizens of England. It was not meant as a
scientific formula from some laboratory of psychology which had tested
several thousand human beings and found them all exactly equal. In
all the common rights of man, the right to life, liberty and the pursuit
of happiness, the world now concedes that one man is as good as
another.
But, when we study not men's rights, but men's natures and capa-
cities, nothing is more obvious than that all men are unequal; they
are born unequal; they will always be unequal ; nature intended them
to be unequal; and no system of government, social control, or educa-
tion has yet been devised or ever will be devised, that will make them
equal. Indeed, the astonishing and delightful discovery of modern
psychology and biology is that the more you educate men the more
unequal you make them. The more you equalize opportunity, the
more you unequalize men. The more nearly you treat men alike, the
more unlike they become. It was Henry van Dyke, I think, who said
that there is one thing in which all men are exactly alike, and that is
that they are aU different. And the more you educate and develop
these differences, the more they grow into larger differences.
As a matter of fact, that is what education and good environment
are for, to draw out and develop each man's individual and particular
capacities and powers. The old Romans invented the word "educa-
tion"— edtico — a leading out of what was in a man, and not a pouring
in of some magic fire from Heaven to melt and mold his soul into a
likeness to other men. You can teach three boys the same knowledge
of history. You can inform them of exactly the same facts of the past.
But I do not believe any school-teacher in the world would maintain
that he had filled them with the same spirit and viewpoint. One boy
' Reprinted from The Fruit of the Family Tree. Copyright 1924 by the Bobbs-
Merrill Company.
S40
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 541
will be inspired by these facts to write historical novels and dramas;
another will find them helpful in shaping economic and social legisla-
tion; while the third may remain almost wholly unaffected and devote
his life to keeping a country grocery, or to inventing a new method of
making soap. They all had the same facts, the same teacher, the same
school-room. But they all reacted differently, each according to his
own ability and temperament — that is, his inborn make-up.
So an unalterable fact of human nature is that men are different.
The whole question at issue in this world-old heredity-environment
debate is, what causes these differences?
All modern biology and psychology support the view that heredity
plays a great part, and probably a preponderant part, in shaping a
man's actions and reactions, his goings and comings, his health and
happiness in this world. We found in the chapters on twins and on the
royal famiUes that this is true. But it may be of interest to present
here some of the main arguments on both sides of this question, with
these scientific discoveries as their background.
It is commonly said that it is impossible to separate heredity from
environment. This is probably true when we consider merely one
individual. I doubt if we shall ever be able to determine whether a
particular act by a particular individual, say whether he takes a drink
of alcohol on some particular occasion or whether he commits a crime,
is due to his heredity or to his environment. The causes are so hope-
lessly intertwined that no one so far as I am aware has presented the
slightest hope of measuring the relative influence of the two forces
within the individual. As I have already pointed out in a foot-note to
a previous chapter, the Behaviorists — a school of psychologists founded
by Doctor John B. Watson — assert (at least some of the leading ex-
ponents of this school assert) that "ninety per cent, of a man's behavior
is due to his environment."
This may be entirely true, but so far it seems to me it has not been
removed from the realm of assertion into the realm of exact measure-
ment. No one doubts that a man's early education is of great influ-
ence in determining his character and behavior in later life, but exactly
how great — whether ninety per cent, or twenty per cent. — has not as
yet so far as I am aware been measured. And I do not believe we can
speak of percentages until we have measurements. Environment is
important in determining behavior, but precisely how important I doubt
very much if we have any means at present for determining, when it
comes to one individual, whether we consider one particular act or the
542 EV.OLUTION, GENETICS, AND EUGENICS
sum total of his character. Indeed, it seems to me it would be pretty
difficult to determine what one hundred per cent, of a man's character
really is, and when we had measured either ten per cent, or ninety
per cent, of its total.
I am inclined to believe from what Thorndike and his students,
especially Doctor Paul F. VoeUcer, have proved as to the enormous in-
fluence of moral education and as to how much more we can influence
the moral character than we can develop the purely intellectual traits,
that by proper education and environment we could prevent nearly
aU individuals from committing actual crimes. Crime is not itself in-
herited, because crime is a particular act by a particular individual.
And whether he commits that act, no doubt depends very greatly upon
previous education, habits, the particular stimulus before him and all
the forces of his environment. For all we know a man may commit a
particular crime or take a particular drink entirely from environment.
And it may be that he can be prevented from these particular acts
entirely by environment. We know that moral ideas tend to diffuse
themselves very widely over the mental life — or as the psychologists
say, there is a very large "transfer of learning" from one set of brain
centers to others. No doubt moral ideals set up wider transfers of
learning and thus influence larger areas of behavior than the cultiva-
tion of particular mental abilities or aptitudes. For this reason teach-
ing a boy trustworthiness, as Voelker has proved, influences his conduct
far more widely than teaching him algebra improves his proficiency
even in algebra. All of this is granted.
What we know of heredity, therefore, should not in the least dis-
courage us (indeed, when deeply considered it ought to encourage us)
from throwing every possible good influence about our youth. The
very stability of society depends on our doing this. But when it
comes to the question as to which one of two individuals is the more
likely to commit crime at some time in his life or to take to excessive
drink, we are in reality dealing with a different set of scientific prob-
lems. And when we come to the question as to which family is likely
to have more members who, in any one age of the world, will be unable
to adjust themselves to sound social behavior or who will easily be
filled with aspirations for building a worthy character and maintaining
the social and political order, we are in a field where we can measure
the factors involved by fairly exact methods, and predict results with
considerable confidence.
Doctor Charles F. Goring, of the Galton Eugenics Laboratory of
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 543
London, has shown in the most exact and elaborate study ever made
of the influence of heredity upon the criminal tendencies of men — or
what more technically is called the "etiology of crime" — that heredity
is by all means the more important factor in the problem. Some
families easily react, naturally, to high social ideals, and some lack
the foresight and the power to develop that true synthetic wisdom of
life which we call in a general way self-control. Education and en-
vironment will alter the weight and influence of these factors within
each individual, but I am not aware of sufficient evidence to prove
that they will much alter the central tendencies either of such indi-
viduals or of such families.
Perhaps Woods's iUustration will illuminate this problem. As he
pointed out in 191 2 at the First Eugenics Congress in London (the first
time, I think, this distinction had been made), it is only when we
come to measure the differences between one or two groups of indi-
viduals, that we can really separate heredity from environment.
When we consider, as Woods suggests, what causes a white man to be
white or a negro to be black, or one person to have brown eyes and one
blue, it is evident that these characteristics are the resultant of all the
combined forces of heredity and environment. We can not, therefore,
by any means now known, separate the two sets of forces within any
one individual. But that the differences in pigmentation between the
white and black races are almost wholly due to the differences in their
germ plasm, no one can very well doubt. True, a tropical sun will
develop all the skin pigment a white man has the power to produce,
and rearing a negro in a northern climate will reduce his pigmentation;
but when placed in the same climate their differences are almost wholly
due to heredity.
Therefore we can not consider the heredity-environment problem
with much assurance of success, either in method or logic, unless we
consider it as the problem of the differences among men. And since,
as Thorndike pointed out long ago in his Educational Psychology, the
prizes of life, whether of health or wealth or social position, are nearly
all relative matters, the result is that heredity is the most important
factor in determining who shaU secure these prizes and who shall not.
n the ideal of human health were an individual who could barely
hobble about, then to attain this minimmn of energy would be our
highest ambition. The healthiest man would be one who was almost
helpless. Health would still be, as it is now, a relative matter. Just
so wealth and influence are relative matters. Among our ancestors a
544 EVOLUTION, GENETICS, AND EUGENICS
man with a few shells or arrow heads was rich. The fact, as Thorn-
dike suggests, that Croesus and Rockefeller were the two richest men
in the world is due almost wholly to their superior natural powers over
those of other men to acquire wealth. But the fact that Croesus ac-
cumulated only a few thousands, or at most a few millions, while
Rockefeller has accumulated perhaps a billion, is almost wholly a
matter of the differences in enviroimient between the ancient and
modern world.
The differences among men, therefore, as I trust we have shown
throughout this book, are almost entirely due to their differences in
natural powers and aptitudes. But none of this remotely discourages
us from stimulating and educating those powers and aptitudes, nor
should it discourage the individual from developing his own inner
natural capacities and tendencies to the utmost. To do this is the
only way to attain his prize in life. And whether he starts with one
talent, two, five or a hundred, makes very little real difference. We
all regret that we do not have greater natures than we have. I should
really like to be such a man in intellect as was Plato or Pericles. I
should like especially to have the musical appreciation of Fritz Kreisler
and the power to play the piano like Josef Hofmann. But as William
James pointed out, we can not be everything. And to want to be
everything is as foolish and as much a waste of good energy as it is for
a dog to bay at the moon. If we had everything we would probably
lose that immense incentive of ambition and rivalry which, just be-
cause men are different, probably leads them to make nearly all the
practical achievements and moral conquests of life.
In his wonderful little book. Talks to Teachers and Sitidents, James
relates a story that goes to the heart of the problem. He says that one
day he had an old carpenter making some repairs on his house at Cam-
bridge. They were talking about the differences among men — why it
is that some men begin at the bottom of the ladder and climb up, while
others start at the top and slide down. Incidentally I remember that
Josh Billings said, when a man starts down-hill in this world, it seems
that all creation is greased for the occasion. However, the old carpen-
ter finally made a remark which James states was one of the most pro-
found observations upon human life he had ever heard or read in all the
philosophies of men. "There is very Uttle difference," said the car-
penter, "between one man and another; but, what httle there is, is
very important."
Have we not here the crux of the whole matter? I suppose, if,
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 545
when a baby, Abraham Lincoln had been placed by the side of all the
other babies in the world of that time, the best baby-show judges on
earth could have found very little difference between him and the thou-
sands of others. And I am sure that if all the germ-cells from which
these babies were born had been weighed and measured and analyzed
and peered at through microscopes by all the biologists on earth, they
could not have told which one would produce Abraham Lincoln. Yet
existing somewhere, somehow, within this tiny microscopic cell, which
had been handed down to his parents and which represented his com-
bined ancestry, were mighty and resplendent forces which ordained in
advance that the child born from it would be one of the greatest human
beings in all the tide of time.
But it will be said that the Civil War "gave Lincoln his oppor-
tunity." Certainly it gave him this particular opportunity. No
man could ask for a greater chance to serve mankind and enter among
the human immortals. But the same opportunity existed for the four
or five million other men who were born and grew up about the same
time. The Civil War discovered Lincoln, but Lincoln also discovered
the Civil War. Even the men in his Cabinet who had the stimulus of
his overwhelming personality did not become Lincolns. Millions of
men since then have taken him as their example and striven to be
like him.
Of course we are all better because of the example of Lincoln.
That is the value of a rich environment full of high ideals. I am a
better man and so are you because this great soul lived and blessed
the world. And I do not doubt that Lincoln himself was stimulated
by his studies in the firelight of the lives of the men of the great gen-
erations gone. I do not doubt he tried to emulate them. Just in pro-
portion to his own greatness does a man try to be like other great men.
He does not try to copy them, he tries to expand his own powers in the
light of their radiant examples. And I have noticed that the greater
men are in real character, the more they have blessed the world with
beauty, and truth and happiness, men such as Lincoln and Washing-
ton, and Foch and William the Silent, and Gustavus Adolphus, and
Faraday and Huxley and Darwin and Pasteur and WilHam James, the
more nearly do they approach in their lives and personal characters to
the Supreme Teacher — that other Carpenter who two thousand years
ago also uttered some sayings that have changed the whole course of
human history, Huxley, a thoroughgoing agnostic in philosophy, was
almost fierce in his admiration of the character of Tesus.
546 EVOLUTION, GENETICS, AND EUGENICS
As Professor Thorndike has pointed out, when it comes to the
absolute achievements of men, the outward performance to which they
can attain, environment is well-nigh all powerful. But when it comes
to determining which individuals in that civilization will profit the
most by it and contribute the most richly to its expansion and con-
tinuance, the all-important thing is each individual's heredity. A
man gives to his environment and receives from it just in proportion
to the richness of his own nature. Was any great environment ever
built by a race of fools? No. Was any truly small and mean environ-
ment ever built by a race teeming with genius? No. Where there is
no vision, no genius, the people perish.
As another example, I walked down the street a while ago upon a
pavement which took all the combined physics, chemistry, social,
political and economic organization of a great industrial age to con-
struct. I had nothing to do with it. It was a part of my environment.
But I was able to walk faster and reach my journey's end earlier — that
is, make a greater absolute achievement — because of it. By my side
walked a laboring man with a basket of groceries for his family. Now,
it may be that this man has a son in college who will some day write a
much better book on heredity and eugenics than this one. But it cer-
tainly would surprise me to find that all the students in colleges and
all writers of books were laboring men's sons, and all the sons of the
abler and more successful classes should to-morrow be handling the
picks and shovels of our civilization.
The whole point of this is that the things which men can do depend
upon the tools that are at hand in the forms of environment, ma-
chinery, social organization, ideals and systems of education — in short,
what we call the social heritage. But the relative performances of
one man as compared with another, that is, what each man does with
these tools — this social heritage, depends almost entirely upon his in-
dividual, inborn heritage. Consequently, it is the duty of all men to
improve the general social heritage because this furnishes multiplied
opportunities for each man to develop and express his personal
heritage.
Let us see if, in a rough way, we can not measure this. The other
day I motored through the western part of the state of New York,
where I had learned the lives and histories of the farmers in consider-
able detail. I was being driven by a man who knew them ail inti-
mately. We passed a farm which a few years ago had been one of the
model farms of western New York. At the death of the owner, whom
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 547
we shall call John Crosby, its broad acres were divided into three equal
shares for his sons. Within three years the appearance of two of the
farms had changed. The fences were run down, the stoclc was run
down, the buildings were run down, while the weeds and underbrush
had run up. But on the third farm, which fell to the youngest son,
the conditions were better than when the father died. This son,
Joseph, was rapidly acquiring the lands of his two brothers, William
and Alexander. The parts which he acquired promptly became models
of successful tillage. I have no doubt that, as the neighbors proph-
esied, within a short time William and Alexander will be working as
hired laborers for Joseph.
Now here is a clear case where the environment remained un-
changed, while the heredity did change and had a chance to reveal its
overwhelming power. All the stimulus was there for each one of the
sons. But only one reacted to it. Any biologist would say in the
light of his own studies, that Joseph was the only son who inherited
his father's vigor and decision of character. However they came by it,
no one could talk with the three brothers without discerning that they
were radically different men.
But let us drive on and see a like phenomenon on another farm.
We passed down the road and stopped in front of a large, handsome
frame house. Two different men had been on this farm within the
last twenty years and "couldn't make it pay." It had grown up in
thickets and underbrush, the buildings had become dilapidated, the
fruit trees were wind broken and worm eaten, until finally a poor immi-
grant named Conrad from Switzerland had bought it for a song.
Within ten years he had developed it into one of the finest dairy farms
in the region. And when I looked at his five-thousand-doUar Holstein
bull and his prize cows giving from ten to fifteen thousand pounds of
milk a year, I thought on the one hand of what glorious achievements
American environment permits men to make, and on the other of what
a small percentage of the millions of job-hunting immigrants America
has admitted in the past forty years could do as well as Conrad. Had
we had the wit to select and admit only the Conrads and the Joseph
Crosbys, what a glorious future for our country! What wonderful
cows, what splendid hogs, what brilliant poets, painters, inventors,
politicians and statesmen would fill this country for all the generations
to come!
It always straightens out this whole tangle of heredity and environ-
ment for me to think of two boys I knew in a western state — let us
54S EVOLUTION, GENETICS, AND EUGENICS
call them George and James. There was no great outward difference
in them as boys. Their parents tried their utmost to treat them exact-
ly alike, but the more they treated them alike, the more amazingly
unlike they grew. When their mother sent them on an errand James
would always loiter and show up an hour late, while George was on
time. George was always devising new ways of doing the farm work,
while James was content to get by in any old way or not get by at all.
When they went to school the teacher saw no great difference be-
tween them, but soon discovered that while James was two years
older, still, George could do his class work better and within a year was
one grade ahead of his brother. In spite of expending very Httle effort
on George and every possible effort on James, it was impossible to make
them progress alike. Of course two or three hundred years ago James
and perhaps George also, might have been mere ignorant louts about
the village. Quite possibly both might have been bandits and
criminals according to the ideas of crime in that day. But if so,
George would have been the leader and James the follower. Conse-
quently the absolute mental and moral achievements of both were
enormously increased by the wonderful modern environment. But
their achievements and character remained relatively the same.
However, the community saw no outstanding differences between
these two boys. They were both good, well-behaved lads. But let us
look thirty years later. George was in the United States Senate, one
of the great orators, one of the great political and economic thinkers
of our time, one of the keenest and most graceful writers of the day
and, had he not made a political blunder, would probably have been
president of the United States; while James was keeping a fourth-
class pie counter in western Illinois.
Now this world is made up of Jameses and Georges. And in the
careers of these men and these families, the Crosbys, and the Conrads,
the Jameses and Georges, are exhibited in simple relief the vast forces
that make and unmake empires, that create and separate social classes,
that evolve great cultures and intellectual disciplines and overthrow
them — in short, the forces that make our lives, and make history and
civiUzation what they are. I might add that George married into one
of the great families of the world and his two children show promise of
helping to glorify the age. James married a woman of his own type
and his two children show every promise of continuing in pie-counter
channels. Now it is necessary to have pie counters as well as Senates.
And I have Uttle doubt that James blames his situation on his environ-
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 549
ment or upon 'Tjad luck," or complains that "things went against
him." We all blame our misfortunes upon something or somebody
else and lay our successes to ourselves.
The inspiring thing about all this to me is that it gives us such an
exalting view of life. It proves, not that we are slaves, but that we are
masters of our environment. Look back at your own schoolboy or
schoolgirl friends. Have they not all carved out their own fortunes,
in the main? Have they not all developed about as you would expect
from your own intimate knowledge of their natures, their heredity?
The point is, have they not selected, chosen and built their own en-
vironments? There are seeming exceptions; but is not this the general
rule? It would fill me with despair if I thought that enviroment was
the main shaping influence of my life. It has some influence on my
character, and immense influence on my outward career; but if it had
the overwhelming power that many people ascribe to it, the power to
change my fundamental character then I should not have the slightest
idea what sort of man I would be twenty years from now. I have not
the slightest fear of the future because I know that my environment,
and above all my own inner character are mainly in my own hands.
I might be thrown to-morrow among criminals. I have not the sUght-
est doubt that if I were I would begin at once to try to reform them,
probably without great results. But if I am the mere victim of my
environment, I have precisely the same mathematical chance as any
criminal has, of committing murderand being hanged within the year.
Do you suppose that your grandchildren are going to be the victims
of their environment as far as their inner characters and mental ca-
pacities are concerned? Wars may disrupt the nation. Civilization
may go to pieces. But if you marry the right mate and endow your
children with your own royal nature and your marked abilities, you
may be sure they will rise amid its ashes and build a great and heroic
life.
I have no doubt that there were great men among the cave men.
But they lived a poor and mean life. In a poor environment men must
live a poor life, as we look at it, although men always find excitement,
interest and adventure under any set of circumstances. We see that
in the case of our Puritan forefathers. Compared to the great build-
ings, laboratories and libraries of Yale, Harvard or Columbia, their
Uttle log academy looks poor indeed. Yet I doubt seriously if the men
within this little structure lived a life of less mental excitement or of
less true inner glory.
55° EVOLUTION, GENETICS, AND EUGENICS
As Karl Pearson has said, "It is man who makes his own environ-
ment, and not environment that makes the man." Now while, in the
main, this is true, it is not altogether true. The choice of a man's
profession is often seemingly a matter of mere accident. I chanced to
read a sentence in a book thirty years ago that seems to me was the
cause of my devoting my life to the study of heredity. But it was not
this sentence nor any sentence that determined whether I should be a
success or a failure at the undertaking. Nor was it this sentence nor
any sentence that caused me from boyhood to have an overpowering
ambition to be a professional scholar of some sort. My parents left
me a heredity, an inner urge, to do the best I could in the study of
science and in lecturing and writing for my fellow-men. I could not
stop this inner urge any more than I could stop Niagara with a pitch-
fork.
Of course people always say, "But don't you think you can take
children from the slums and do wonders for them?" Most assuredly.
You can do a great deal for them. But you can, as has been shown by
experience, take the same number of children from good homes, which
have been built by the good heredity of their parents, and do vastly
greater wonders for them with the same money, effort and time.
Many children from the slums rise by their own heredity and become
ornaments to our civilization. This proves that you can put good
heredity into bad environment and not wreck the heredity. The
trouble is that many people assume that all the children in the slums
are bad. You will find many in the slums that are good and many
on the avenue that are bad. But you will find a vastly higher percen-
tage of poorly endowed, mentally, morally and physically — that is to
say, the poor heredity — in the slums than on the avenue. Slums are
the product of many injustices in our social and industrial organiza-
tions; but if we have slums, it is those with poor heredity who, in the
main, fall into them.
To test this, go if you will, into some small town in a rich farming
region. It would surely seem that there opportunity is wide open to
all; every tub stands on its own bottom; there is almost no actual
want. I was in one town in Iowa where they took up a collection for
the poor. But the preacher told me he did not know what to do with
the money, as they had no poor. I went into many homes in that town
and found some with lace curtains at the front windows and Victrolas
in the "settin'-room," and yet their houses were truly the dirtiest, most
ill-smelling places I have ever seen. I have scarcely seen such utter
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 55^
cess-pool dirt in the lowest sections of New York. The "settin'-
room" was properly named, for they seemed to do nothing but just
"set."
Now honestly, my uplifting environmental friend, what can you
do for such people? They had plenty of money and ample oppor-
tunity. They went to picture shows, and their children attended, or
rather were forced to attend, school. "The old man" got three to ten
dollars a day. The farmers about the town were crying for tenants,
and willing, practically, to set a man and his family up in business if
they would only properly till the land. But their poverty was pure
biological poverty, inborn, ineradicable. Their real poverty was poor
heredity. And do you suppose that if those people drifted into the
larger cities they would build residences on the avenue, or would they
simply fall naturally into the slums? Many a strong man goes into
the slums, under the wicked crush of modern industrialism. But such
stock does not long remain there. Many of the children or the grand-
children fight their way out. The vast slums of the world are in the
main inhabited by breeds that have been there for centuries. Sydney,
Australia, has probably the largest slums relative to its size of any city
in Anglo-Saxon countries. The belief of Doctor Charles B. Daven-
port, who investigated it, is that this is largely due to the fact that
Sydney was originally settled chiefly by criminals and lower stocks
deported from England one hundred and fifty years ago. Anyone
who will read the account of the character of these shipments of slums
stocks which England sent for many years to Sydney in ship loads,
as given in the Encyclopedia Britannica, will, I think, be impressed with
the high probability of the truth of Doctor Davenport's conclusion.
We have seen then that heredity is the preponderant factor in the
relative character of men, and almost the whole factor in mental ca-
pacity; and that our success as compared with that of our fellows is
largely a matter of our natural endowments. But the real lessons that
emerge for us all are, first, that you "can't make a silk purse out of a
sow's ear"; and second, that human success and human happiness are
largely relative things. "We are not trying to get ahead in this
world," as Professor Thorndike says, "but to get ahead of somebody."
To be tlie most beautiful girl in the county is beauty enough. The
most beautiful girl in Podunk feels no envy of Agnes Soret, long the
reigning beauty of France. I suppose President Wilson and Theodore
Roosevelt were eager to get ahead of each other. But you and I never
gave a thought about getting ahead of either one of them. The third
552 EVOLUTION, GENETICS, AND EUGENICS
conclusion is that environment does not much change the relative
situations and achievements and characters of men. But a rich en-
vironment gives all men the chance for greater achievements and a
wider life. If Roosevelt had been born in Africa he would not have
been the Roosevelt he was. But even in Africa he would have been
the "Buanna Tumbo" — the big hunter as the natives called him, the
mighty man with the big stick with the power to move things and men.
And he would have had a "perfectly corking time."
You should remember always that by the hereditarian view you
are not mastered by fate, but you are the masters of fate. You make
your environment to a far greater extent than it makes you. Life is
self-expression, self-realization. Every one should study his heredity,
and the lives of his immediate ancestors. He should choose his voca-
tion with a view of avoiding their failures and imitating their successes.
If they drank to excess, it should be a special warning. If they had
particular talents, these should be emulated. You probably have some
or all of them. Let your natural, inborn Ught shine, to be seen of all
men. You are always going to live with yourself. Then make your-
self a good person to live with. You probably have a great deal of
good heredity going to waste. Explore yourself and find out. You
can not express anybody else's heredity. You must express your own.
For there is no antagonism between heredity and environment.
Heredity has furnished you with untold powers and no one ever
develops all of them as much as he could and ought. It is your duty
to use those powers in building an environment amid which and with
which both you and your descendants may make the noblest possible
practical achievements.
It seems to me that this view of life, far from being fatalistic, as
the extreme environmental view surely is, is filled with the most inspir-
ing optimism. A boy may never hear the chance sermon, or read the
inspiring book which our environmental friends often point out as
being the "cause" of his fine career in life. If such things are the
"causes" of the success or failure of men, then we are mere pawns upon
the chess-board of environment, mere marionettes upon the stage
whose wires are pulled by this mysterious and awful hand of doom.
In a bad environment a boy would be bound to turn out to be bad,
and in a good environment he would be bound to turn out to be good.
Whatever the optimism or pessimism of such a view may be, we see
simply that this is not true. Good boys constantly come up out of
bad environment, and boys turn out badly amid the best environment
that human wisdom can devise.
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 553
But the thing to reflect upon is that every child who is not posi-
tively idiotic has within him those glorious powers by which he can
seek out the inspiring man who will preach to him the inspiring sermon ;
he has the power to seek out the good book and read it; he has the
power to choose his companions, his teachers, the way he spends his
time and money, and in the long run build his own sm-roundings.
Obviously, however, even here environment plays a very strong
hand; for the more choices that are opened before a child, the more it is
encouraged to make this choice instead of that, the more surely will it
be enabled in the end to form those right habits of choosing the good
instead of the bad, and also have those right objects and courses before
it to choose which lead to self-mastery and success. And self-mastery
is merely success in the utilization of one's heredity. For success itself
by and by becomes a habit, ingrained in the very motor patterns of
the nerve system itself. Every child should be guarded against, and
should guard itself against the habit of failure. As James says, you
may forget the fine resolution you made and failed to carry out, but
the nerve cells do not forget. Down in the very depths of our bodily
organization, each tiny nerve cell is registering every act and thought,
and laying it up in store for some future occasion, either for or against
you. "Make your nervous system," he says, "your ally instead of
your enemy." This contains almost the whole basis of moral educa-
tion. And one should always remember with old Spinoza, the German
philosopher, that "if you can keep from doing a thing because it is
bad, you can keep from doing the same thing because something else
is good." This is the whole difference between living the positive and
the negative life. One can not build a successful and happy life unless
he has filled his mind and tuned his nerves to be up and alive with the
things he must do, instead of always holding them back with the checks,
inhibitions and prohibitions of the things he must not do. The theo-
logical hell which is pictured for lost souls in the future, says James,
can be no worse than the hell which many of us build for ourselves in
this world by continually fashioning our nervous systems — our wills —
in the wrong way. And, granted that there is in us a power of choos-
ing at all, granted that thinking has any purpose in it, then the oppor-
tunity to build daily more stately mansions for our souls in this world
at least, is every morning opened anew to us all.
Thus, notwithstanding our belief, and I think our demonstration,
that a man's inborn nature is the chief cause of his being different from
other men, the cause of his making different choices, building a differ-
ent "personality picture" of himself and his life, from the personality
554 EVOLUTION, GENETICS, AND EUGENICS
picture of other men, our enthusiasm for environment continues as
great as ever. The poorest soil will increase its yield somewhat if
fertilized; but the same stimulus given to rich soil will increase its
yield many fold. The one- talent man will improve a great deal by
education; but the five- talent man will improve enormously. This
should be the chiefest source of comfort to the environmentalist him-
self— that the better the heredity upon which he expends his efforts the
richer will be his rewards. It takes all the skill of teachers trained in
the best pedagogy in the world to teach some children to read and
write, while other children practically teach themselves. By doubling
our educational efforts we would likely quadruple men's achievements,
their generosity, integrity, courage, determination, and thus quadruple
what Woodrow Wilson called "the world's fitness for affairs"; but if
we could double men's hereditary powers, their inborn virtue and excel-
lence, the range and deli.cacy of their imaginations, the sweetness and
charm of their personalities, and the exaltation of their natural desires,
the humanism that would result — and what is civilization for except
for a larger and finer humanism — would be beyond our power to fore-
see. And this difference between the two alternatives that are always
before mankind — the alternative of building either a better heredity or
devoting all their efforts to building a better environment — is not a fan-
ciful difference; for we see always before us that some men have many
times — Galton thought thirty times — as great natural endowments as
have others. Some men have in some directions a thousand or a
million times greater powers than have other men.
The millennium, therefore, will be hastened by better education;
but it will be vastly more accelerated by better men. And after all,
is not this the final answer to the whole tangle of heredity and environ-
ment? Better social machinery will make better men and better men
will enormously enhance the efficiency of the social machinery. Our
enthusiasm for environment will increase as we see more clearly
through the improved education the modern world has given us how
a well-born race would use education for still more exalted ends.
Instead, therefore, of being antagonistic, heredity and environ-
ment are reciprocal agencies, both placed at last by science within the
grasp of man, by which he can lift his species out of the bloody sea
of natural selection and fare happily forward to richer and more fruit-
ful goals. The Garden of Eden is not in the past, it is in the future.
And the trees of knowledge grow along the whole highway that leads
to it. It is an arduous highway; but its hardships need not be those,
DOES HEREDITY OR ENVIRONMENT MAKE MEN? 555
as in the past, of the red tooth and claw of nature, but the striving
passions of men to realize in richer cultures higher values for which to
Uve.
A rightly directed environment, not by brute death-selection but
by the happier method of birth-selection, will improve man's heredity
and in turn this better heredity will enrich the social heritage. To in-
stil the "will to believe" in a hvmianity naturally better than ours is
as necessary an aim for education as to instil merely, as education
does now, the will to believe in better conditions amid which humanity
shall live. Education will be doubly effective when it learns this great
lesson.
The ancient Greeks pictured ambition as a beautiful goddess rolUng
golden apples down the pathway of pursuing youth. Like these
fleeting prizes the Eden of eugenics can never be attained. But science
and progress has at least stamped the picture of that Eden upon the
imagination of mankind : the Eden of a perfect humanity dwelling in
an environment of paradise. And, while it is unattainable it is not a
mirage. It is merely the great dream of human destiny and possi-
bility which men began to dream back in that mysterious time when
they started their organic journey from the jungle to their present high
estate. Only science and progress have drawn it for us in clearer out-
lines, drawn it nearer, and made it the conscious goal of the world's
desire. And while it can not be attained any more than Heaven can
be here on earth attained, yet the passion for it, the going toward it,
the belief in it, the training and education of men for it, constitute that
"new religion" of a better humanity which Galton said would "sweep
the world." The goddess of humanity's ambitions can never be
captured nor embraced; but as Thackeray said of the woman that a
man loves, on that last noble page of Henry Esmond, "To think of her
is to praise God."
Note. — The reader must understand that what is handed from one genera-
tion to the next is merely these little packets or genes in the germ-cell and not
the completed character such as tallness or black color. Neither the tall character
nor black color nor any other feature will develop unless proper environment is
supplied, and if there should be a radical change in the environment it might be
some other color than black would develop. If either the hereditary material in
the germ-cell is changed ever so slightly or the environment changed some other
character develops than the one which we commonly speak of as "inherited." The
reader must not gain the idea that these determiners will develop into some certain
characteristics irrespective of the environment. Professor Herbert S. Jennings, of
The Johns Hopkins University, has brilliantly and profoundly argued this whole
556 EVOLUTION, GENETICS, AND EUGENICS
matter in an article in The Scientific Monthly for September, 1924, entitled Heredity
and Environment. As Professor Jennings puts it: "Clearly it is not necessary to
have a characteristic merely because one inherits it. Or more properly, character-
istics are not inherited at all; what one inherits is certain material that under certain
conditions will produce a particular characteristic; if those conditions are not
supplied, some other characteristic is produced."
In this sense a man's knowledge of Latin grammar is just as much an inherited
character as is his bald head. Both developed because certain packets of chemicals
called factors were in the germ-cell from which he was bom, and these factors
under the conditions that he met in life developed into these characteristics. Had
he met different conditions he would have developed other characteristics in their
stead. It is not true that a man is predetermined in or by the germ-cell and that
a foreordained man with foreordained characteristics is going to grow up willy-
nilly. However, because of merely practical difficulties we can not very radically
alter men by education and environment, partly because we do not as yet have the
proper technical means and partly because the environment is fairly uniform for
all human beings during the first nine months of their lives and they come into the
world as quite far advanced organisms. But in frogs and fruit flies and other ani-
mals where the egg itself and the early embryo can be radically interfered with,,
changes can easily be produced which make the adult animal strikingly different
from what it would have been in the usually expected environment. We predict
a certain kind of man by studying his ancestry merely because we expect for him
a certain tjrpe of general environment not profoundly different from that of his
ancestors. It is the expected enviromnent which leads us to count pretty strongly
on heredity and not that the heredity in the germ package predetermines all he shall
be. F. A. Woods pointed this out nearly fifteen years ago. Of course there are
limits to the alterations possible by envirormient, but they are far from being reached
as yet with human beings. None of this alters the fact that very moderate environ-
mental measures, such as education and moral suasion, expended on rich hereditary
material yield far greater results than when expended on poor material. Other
measures might produce as marked results with poor material, but in society as
a practical matter there is neither the time nor money as yet to try to make imbeciles
into geniuses when by proper marriages they can be produced free of charge. The
differences among men are, I think, largely due to differences in the original heredi-
tary packets in the germ-cells because so much of the environment of men is common
io them all. I can not reproduce all of Professor Jenniags' fine presentation and
can only urge the thoughtful to study it with care as the most penetrating dis-
cussion of the heredity-environment problem that has been made from the stand-
point of a geneticist and embryologist.
CHAPTER XLII
EUGENICS AND EUTHENICS*
PAXIL POPENOE AND ROSWELL H. JOHNSON
Emphasis has been given, in several of the foregoing chapters, to
the desirability of inheriting a good constitution and a high degree
of vigor and disease-resistance. It has been asserted that no measures
of hygiene and sanitation can take the place of such inheritance. It
is now desirable to ascertain the limits within which good inheritance
is effective, and this may be conveniently done by a study of the lives
of a group of people who inherited exceptionally strong physical con-
stitutions.
The people referred to are taken from a collection of histories of
long Ufe made by the Genealogical Record Office of Washington.
One hundred individuals were picked out at random, each of whom had
died at the age of ninety or more, and with the record of each indi-
vidual were placed those of all his brothers and sisters. Any family
was rejected in which there was a record of wholly accidental death
(e.g., families of which a member had been killed in the Civil War).
The loo families, or more correctly fraternities or sibships, were
classified by the number of children per fraternity, as follows:
Number
of
Fraternities
Number of
Children per
Fraternity
Total Number
of Children
in Group
I
2
2
II
3
33
8
4
3a
17
5
85
13
6
78
14
7
98
9
8
72
II
9
99
10
10
100
3
II
33
a
12
24
I
13
13
100 66q
' From P. Popenoe and R. H. Johnson, Applied Eugenics (copyright 1918).
Used by special permission of the publishers, The Macmillan Company.
SS7
558 EVOLUTION, GENETICS, AND EUGENICS
The average at death of these 669 persons was 64.7 years. The
child mortality (first 4 years of life) was 7.5 per cent of the total
mortality, 69 families showing no deaths of that kind. The group
is as a whole, therefore, long-lived.
The problem was to measure the resemblance between brothers and
sisters in respect of longevity — to find whether knowledge of the age
at which one died would justify a prediction as to the age at death of
the others — or technically, it was to measure the fraternal correlation
of longevity. A zero coefficient here would show that there is no
association; that from the age at which one dies, nothing whatever
can be predicted as to the age at which the others will die. Since it is
known that heredity is a large factor in longevity, such a finding would
mean that all deaths were due to some accident which made the
inheritance of no account.
In an ordinary population it has been found that the age at death
of brothers and sisters furnishes a coefficient of correlation of the order
of .3, which shows that heredity does determine the age at which one
shall die to considerable extent, but not absolutely.'
The index of correlation^ between the lengths of life within the
fraternity in these 100 selected families, furnished a coefficient of
— .0163='= .0672, practically zero. In other words, if the age is known
at which a member of one of these families died, whether it be one
month or 100 years, nothing whatever can be predicted about the age
at which his brothers and sisters died.
' Mary Beeton, and Karl Pearson, Biometrika, I, p. 60. The actual correlation
varies with the age and sex: the following are the results:
COLLATERAL INHERITANCE
Elder adult brother and younger adult brother 2290=*^ .0194
Adult brother and adult brother 2853* .0196
Minor brother and minor brother 1026=*= .0294
Adult brother and minor brother — .0262=*= .0246
Elder adult sister and younger adult sister 3464=*= -0183
Adult sister and adult sister 3322=*= .0185
Minor sister and minor sister 1 74^ =*= • 0307
Adult sister and minor sister — .0260=*= .0291
Adult brother and adult sister 2319=^= .0145
Minor brother and minor sister 1435=*= -0251
Adult brother and minor sister — .0062=1= .0349
Adult sister and minor brother — .0274=*= .0238
"The method used is the ingenious one devised by J. Arthur Harris
(Biometrika, IX, p. 461). The probable error is based on «= 100.
EUGENICS AND EUTHENICS 559
Remembering that longevity is in general inherited, and that it is
found in the families of all the people of this study (since one in each
fraternity hved to be 90 or over) how is one to interpret this zero
coefficient? Evidently it means that although these people had
inherited a high degree of longevity, their deaths were brought about
by causes which prevented the heredity from getting full expression.
As far as hereditary potentialities are concerned, it can be said that all
their deaths were due to accident, using that word in a broad sense to
include all non-selective deaths by disease. If they had all been able
to get the full benefit of their heredity, it would appear that each of
these persons might have Uved to 90 or more, as did the one in each
family who was recorded by the Genealogical Record Office. Geneti-
cally, these other deaths may be spoken of as premature.
In an ordinary population, the age of death is determined to the
extent of probably 50 per cent by heredity. In this selected long-
lived population, heredity appears not to be responsible in any meas-
urable degree whatsoever for the differences in age at death.
The result may be expressed in another, and perhaps more striking,
way. Of the 669 individuals studied, a hundred — namely, one child
in each family — Hved beyond 90; and there were afew others who did.
But some 550 of the group, though they had inherited the potentiaUty
of reaching the average age of 90, actually died somewhere around 60;
they failed by at least one-third to live up to the promise of their
inheritance. If we were to generalize from this single case, we would
have to say that five-sixths of the population does not make the most
of its physical inheritance.
This is certainly a fact that discourages fatalistic optimism. The
man who tells himself that, because of his magnificent inherited
constitution, he can safely take any risk, is pretty sure to take too
many risks and meet with a non-selective — i.e., genetically, a pre-
mature— death, when he might in the nature of things have lived
almost a generation longer.
It should be remarked that most of the members of this group
seem to have Hved in a hard environment. They appear to belong
predominantly to the lower strata of society; many of them are immi-
grants and only a very few of them, to judge by a cursory inspection
of the records, possessed more than moderate means. This necessi-
tated a frugal and industrious life which in many ways was favorable
to longevity but which may often have led to overexposure, overwork,
lack of proper medical treatment, or other causes of a non-selective
560 EVOLUTION, GENETICS, AND EUGENICS
death. We would not push the conclusion too far, but we can not
doubt that this investigation shows the folly of ignoring the environ-
ment— shows that the best inherited constitution must have a fair
chance. And what has here been found for a physical character,
would probably hold good in even greater degree for a mental charac-
ter. All that man inherits is the capacity to develop along a certain
line under the influence of proper stimuU, food and exercise. The
object of eugenics is to see that the inherent capacity is there. Given
that, the educational system is next needed to furnish the stimuli.
The consistent eugenist is therefore an ardent euthenist. He not only
works for a better human stock but, because he does not want to see
his efforts wasted, he always works to provide the best possible envi-
ronment for this better stock.
In so far, then, as euthenics is actually providing man with more
favorable surroundings — not with ostensibly more favorable sur-
roundings which, in reality, are unfavorable — there can be no antago-
nism between it and eugenics. Eugenics is, in fact, a prerequisite of
euthenics, for it is only the capable and altruistic man who can con-
tribute to social progress; and such a man can only be produced
through eugenics.
Eugenic fatalism, a blind faith in the omnipotence of heredity
regardless of the surroundings in which it is placed, has been shown
by the study of long-Uved families to be unjustified. It was found
that even those who inherited exceptional longevity usually did not
Uve as long as their inheritance gave them the right to expect. If they
had had more euthenics, they should have Uved longer.
But this illustration certainly gives no ground for a belief that
euthenics is sufficient to prolong one's life beyond the inherited limit.
A study of these long-lived famiUes from another point of view will
reveal that heredity is the primary factor and that good environment,
euthenics, is the secondary one.
For this purpose we augment the 100 families of the preceding
section by the addition of 240 more families like them, and we examine
each family history to find how many of the children died before com-
pleting the fourth year of life. The data are summarized in the table
on page 488.
The addition of the new families (which were not subjected to any
different selection than the first 100) has brought down the child
mortaUty rate. For the first 100, it was found to be 7.5 per cent. If
in the above table the number of child deaths, 1 19, be divided by the
EUGENICS AND EUTHENICS 561
total number of children represented, 2,259, the child mortality rate
for this population is found to be 5.27 per cent or 53 per 1,000.
The smallness of this figure may be seen by comparison with the
statistics of the registration area, U.S. Census of 1880, when the child
mortality (0-4 years) was 400 per thousand, as calculated by Alexan-
der Graham Bell. A mortality of 53 for the first four years of life is
smaller than any district known in the United States, even to-day, can
show for the first year of life alone. If any city could bring the deaths
of babies during their first twelve months down to 53 per 1,000, it
would think it had achieved the impossible; but here is a population
CHILD MORTALITY IN FAMILIES OF LONG-LIVED STOCK,
GENEALOGICAL RECORD OFFICE DATA
Size
Number of
Number of Families
Total Nun
of
Families
Showing Deaths
of
"amily
Investigated
under Five Years
Deaths
I child
6
0
0
2 children
6
0
0
3
38
4
5
4
40
6
7
5
38
4
4
6
44
12
13
7
34
8
II
8
46
13
18
9
31
14
20
10
27
14
14
II
13
6
9
12
13
9
16
13
I
0
0
14
3
0
0
17
I
I
2
340 91 119
in which 53 per 1,000 covers the deaths, not only of the fatal first 12
months, but of the following three years in addition.
Now this population with an unprecedentedly low rate of child
mortality is not one which had had the benefit of any Baby Saving
Campaign, nor even the knowledge of modern science. Its mothers
were mostly poor, many of them ignorant; they lived frequently
under conditions of hardship ; they were peasants and pioneers. Their
babies grew up without doctors, without pasteurized milk, without ice,
without many sanitary precautions, usually on rough food. But they
had one advantage which no amount of applied science can give after
birth — namely, good heredity. They had inherited exceptionally
good constitutions.
502
EVOLUTION, GENETICS, AND EUGENICS
It is not by accident that inherited longevity in a family is associ
ated with low mortality of its children. The connection between th >.
two facts was first discovered by Mary Beeton and Karl Pearson ii>
their pioneer work on the inheritance of duration of life. They found
that high infant mortality was associated with early death of parents,
while the offspring of long-lived parents showed few deaths in child-
hood. The correlation of the two facts was quite regular, as will be
evident from a glance at the following tables prepared by A. Ploetz:
LENGTH OF LIFE OF MOTHERS AND CHILD MORTALITY OF THEIR
DAUGHTERS (ENGLISH QUAKER FAMILIES, DATA OF
BEETON AND PEARSON, ARRANGED BY PLOETZ)
Year of Life in Which Mothers Dikd
to 38
39-S3
54-68
69-83
84 up
At
All
Ages
Number of daughters
Number of them who died in first five
years
Per cent of daughters who died. .
234
122
521
304
114
37-5
395
118
29.9
666
131
19.7
247
26
lo.s
1,846
511
27.7
LENGTH OF LIFE OF FATHERS AND CHILD MORTALITY OF
THEIR DAUGHTERS
Number of daughters
Number of them who died in first five
years
Per cent of daughters who died. .
I KAK (
jr LiltIS, L
N ^^ uiUH
TAXaXK
S JJIED
At
All
to 38
39-53
S4-68
69-83
84 up
Ages
los
284
58s
797
236
2,009
SI
48.6
98
34S
26.7
177
22.2
40
17.0
522
26.0
To save space, we do not show the relation between parent and
son ; it is similar to that of parent and daughter which is shown in the
preceding tables. In making comparison with the 340 famihes from
the Genealogical Record Office, above studied, it must be noted that
Dr. Ploetz's tables include one year longer in the period of child mor-
tality, being computed for the first five years of life instead of the first
four. His percentages would therefore be somewhat lower if com-
puted on the basis used in the American work.
These various data demonstrate the existence of a considerable
correlation between short life {brachybioty, Karl Pearson calls it) in
parent and short life in offspring. Not only is the tendency to live
long inherited, but the tendency not to live long is likewise inherited.
EUGENICS AND EUTHENICS 563
But perhaps the reader may think they show nothing of the sort.
He may fancy that the early death of a parent left the child without
sufficient care, and that neglect, poverty, or some other factor of
euthenics brought about the child's death. Perhaps it lacked a
mother's loving attention, or perhaps the father's death removed the
wage-earner of the family and the child thenceforth lacked the
necessities of life.
Dr. Ploetz has pointed out that this objection is not valid, because
the influence of the parent's death is seen to hold good even to the
point where the child was too old to require any assistance. If the
facts appHed only to cases of early death, the supposed objection
might be weighty, but the correlation exists from one end of the age-
scale to the other. It is not credible that a child is going to be deprived
of any necessary maternal care when its mother dies at the age of 69;
the child herself was probably married long before the death of the
mother. Nor is it credible that the death of the father takes bread
from the child's mouth, leaving it to starve to death in the absence of a
pension for widowed mothers, if the father died at 83, when the " child "
herself was getting to be an old woman. The early death of a parent
may occasionally bring about the child's death for a reason wholly
unconnected with heredity, but the facts just pointed out show that
such cases are exceptional. The steady association of the child death-
rate and parent death-rate at all ages demonstrates that heredity is a
common cause.
But the reader may suspect another fallacy. The cause of this
association is really environmental, he may think, and the same
poverty or squalor which causes the child to die early may cause the
parent to die early. They may both be of healthy, long-lived stock,
but forced to live in a pestiferous slum which cuts both of them
off prematurely and thereby creates a spurious correlation in the
statistics.
We can dispose of this objection most effectively by bringing in
new evidence. It will probably be admitted that in the royal families
of Europe, the environment is as good as knowledge and wealth can
make it. No child dies for lack of plenty of food and the best medical
care, even if his father or mother died young. And the members of
this caste are not exposed to any such unsanitary conditions, or such
economic pressure as could possibly cause both parent and child to die
prematurely. If the association between longevity of parent and
child mortality holds for the royal families of Europe and their princely
564
EVOLUTION, GENETICS, AND EUGENICS
relatives, it can hardly be regarded as anything but the effect of
heredity — of the inheritance of a certain type of constitution.
Dr.Ploetz studied the deaths of 3,210 children in European royalty,
from this viewpoint. The following table shows the relation between
father and child:
LENGTH OF LIFE OF FATHERS AND CHILD MORTALITY OF
THEIR CHILDREN IN ROYAL AND PRINCELY
FAMILIES (PLOETZ DATA)
Year of Life in Which Fathers Died
At
All
Ages
16-2S
26-35
36-45
46-53
56-65
66-75
76-85
86 up
Number of children
23
12
52.2
90
29
32.2
367
313
545
171
31-4
725
200
27.6
983
254
25.8
444
105
23.6
333210
I 887
3.0 27.6
Number who died in first five years.
Per cent who died
Allowing for the smallness of some of the groups, it is evident that the
amount of correlation is about the same here as among the English
Quakers of the Beeton-Pearson investigation, whose mortality was
shown in the two preceding tables. In the healthiest group from the
royal families — the cases in which the father lived to old age — the
amount of child mortality is about the same as that of the Hyde family
in America, which Alexander Graham Bell has studied — namely,
somewhere around 250 per 1,000. One may infer that the royal
families are rather below par in soundness of constitution.
All these studies agree perfectly in showing that the amount of
child mortality is determined primarily by the physical constitution
of the parents, as measured by their longevity. In the light of these
facts, the nature of the extraordinarily low child mortality shown in
the 340 families from the Genealogical Record Office, with which we
began the study of this point, can hardly be misunderstood. These
famiHes have the best inherited constitution possible and the other
studies cited would make us certain of finding a low child mortality
among them, even if we had not directly investigated the facts.
If the interpretation which we have given is correct, the conclusion
is inevitable that child mortality is primarily a problem of eugenics,
and that all other factors are secondary. There is found to be no
warrant for the statement so often repeated in one form or another,
that " the fundamental cause of the excessive rate of infant mortality
in industrial communities is poverty, inadequate incomes, and low
standards of living." Royalty and its princely relatives are not
EUGENICS AND EUTHENICS 565
characterized by a low standard of li\ing, and yet the child mortality
among them is very high — somewhere around 400 per 1,000 in cases
where a parent died young. If poverty is responsible in the one case,
it must be in the other— which is absurd. Or else the logical absurdity
is involved of inventing one cause to explain an effect today and a
wholly different cause to explain the same effect tomorrow. This is
unjustifiable in any case, and it is particularly so when the single cause
that explains both cases is so evident. If weak heredity causes high
mortality in the royal families, why, similarly, cannot weak heredity
cause high infant mortahty in the industrial communities? We
beUeve it does account for much of it, and that the inadequate income
and low standard of Hving are largely the consequence of inferior
heredity, mental as well as physical. The parents in the Genealogical
Record Office files had, many of them, inadequate incomes and low
standards of living under frontier conditions, but their children grew
up while those of the royal famihes were dying in spite of every
attention that wealth could command and science could furnish.
If the infant ^mortality problem is to be solved on the basis of
knowledge and reason, it must be recognized that sanitation and
hygiene cannot take the place of eugenics any more than eugenics
can dispense with sanitation and hygiene. It must be recognized that
the death-rate in childhood is largely selected, and that the most
effective way to cut it down is to endow the children with better
constitutions. This cannot be done solely by any euthenic cam-
paign; it cannot be done by swatting the fly, abolishing the mid-wife,
sterilizing the milk, nor by any of the other panaceas sometimes
proposed.
But, it may be objected, this discussion ignores the actual facts.
Statistics show that infant mortality campaigns have consistently
produced reductions in the death-rate. The figures for New York,
which could be matched in dozens of other cities, show that the num-
ber of deaths per 1,000 births, in the first year of life, has steadily
declined since a determined campaign to "Save the Babies" was
started:
1902 181 iQog 129
1903 152 1910 125
1904 162 IQII 112
1905 159 1912 105
1906 153 I913 102
1907 144 1914 Q5
IQ08 128
566 EVOLUTION, GENETICS, AND EUGENICS
To one who cannot see beyond the immediate consequences of an
action, such figures as the above indeed give quite a different idea of
the effects of an infant mortaUty campaign, than that which we have
just tried to create. And it is a great misfortune that euthenics so
often fails to look beyond the immediate effect, fails to see what
may happen next year, or lo years from now, or in the next generation.
We admit that it is possible to keep a lot of children alive who
would otherwise have died in the first few months of life. It is being
done, as the New York figures, and pages of others that could be
cited, prove. The ultimate result is twofold:
1. Some of those who are doomed by heredity to a selective death,
but are kept alive through the first year, die in the second or third or
fourth year. They must die sooner or later; they have not inherited
sufficient resistance to survive more than a limited time. If they are
by a great effort carried through the first year, it is only to die in the
next. This is a statement which we have nowhere observed in the
propaganda of the infant mortality movement; and it is perhaps a
disconcerting one. It can only be proved by refined statistical
methods, but several independent determinations by the English
biometricians leave no doubt as to the fact. This work of Karl
Pearson, E. C. Snow, and Ethel M. Elderton, was cited in our chapter
on natural selection; the reader will recall how they showed that
nature is weeding out the weaklings, and in proportion to the strin-
gency with which she weeds them out at the start, there are fewer
weakhngs left to die in succeeding years.
To put the facts in the form of a truism, part of the children bom
in any district in a given year are doomed by heredity to an early
death; and if they die in one year they will not be alive to die in the
succeeding year, and vice versa. Of course there are in addition
infant deaths which are not selective and which if prevented would
leave the infant with as good chance as any to live.
In the light of these researches, we are forced to conclude that
baby-saving campaigns accomplish less than is thought; that the
supposed gain is to some extent temporary and illusory.
2. There is still another consequence. If the gain is by great
exertions made more than temporary; if the baby who would other-
wise have died in the first months is brought to adult life and repro-
duction, it means in many cases the dissemination of another strain
of weak heredity, which natural selection would have cut off ruthlessly
EUGENICS AND EUTHENICS 567
in the interests of race betterment. In so far, then, as the infant
mortality movement is not futile it is, from a strict biological view-
point, often detrimental to the future of the race.
Do we then discourage all attempts to save the babies ? Do we
leave them all to natural selection ? Do we adopt the "better dead"
gospel ?
Unquahfiedly, no! The sacrifice of the finer human feelings,
which would accompany any such course, would be a greater loss to
the race than is the eugenic loss from the perpetuation of weak strains
of heredity. The abolition of altruistic and humanitarian sentiment
for the purpose of race betterment would ultimately defeat its own end
by making race betterment impossible.
But race betterment will also be impossible unless a clear distinc-
tion is made between measures that really mean race betterment of a
fundamental and permanent nature, and measures which do not.
We have chosen the Infant Mortality Movement for analysis in this
chapter because it is an excellent example of the kind of social better-
ment which is taken for granted, by most of its proponents, to be a
fundamental piece of race betterment; but which, as a fact, often
means race impairment. No matter how abundant and urgent are
the reasons for continuing to reduce infant mortality wherever pos-
sible, it is dangerous to close the eyes to the fact that the gain from it
is of a kind that must be paid for in other ways; that to carry on the
movement without adding eugenics to it will be a short-sighted policy,
which increases the present happiness of the world at the cost of
diminishing the happiness of posterity through the perpetuation of
inferior strains.
While some euthenic measures are eugenically evils, even if
necessary ones, it must not be inferred that all euthenic measures are
dysgenic. Many of them, such as the economic and social changes we
have suggested in earlier chapters, are an important part of eugenics.
Every euthenic measure should be scrutinized from the evolutionary
standpoint; if it is eugenic as well as euthenic, it should be whole-
heartedly favored; if it is dysgenic but euthenic it should be con-
demned or adopted, according to whether or not the gain in all ways
from its operation will exceed the damage.
In general, euthenics, when not accompanied by some form of
selection (i.e., eugenics) ultimately defeats its own end. If it is accom-
panied by rational selection, it can usually be indorsed. Eugenics,
568 EVOLUTION, GENETICS, AND EUGENICS
on the other hand, is likewise inadequate unless accompanied by
constant improvement in the surroundings; and its advocates must
demand euthenics as an accompaniment of selection, in order that the
opportunity for getting a fair selection may be as free as possible. If
the euthenist likewise takes pains not to ignore the existence of the
racial factor, then the two schools are standing on the same ground,
and it is merely a matter of taste or opportunity, whether one empha-
sizes one side or the other. Each of the two factions, sometimes
thought to be opposing, will be seen to be getting the same end result,
namely, human progress.
Not only are the two schools working for the same end, but each
must depend in still another way upon the other, in order to make
headway. The eugenist cannot see his measures put into effect except
through changes in law and custom — i.e., euthenic changes. He must
and does appeal to euthenics to secure action. The social reformer, on
the other hand, cannot see any improvements made in civilization
except through the discoveries and inventions of some citizens who are
inherently superior in abiUty. He in turn must depend on eugenics
for every advance that is made.
It may make the situation clearer to state it in the customary
terms of biological philosophy. Selection does not necessarily result
in progressive evolution. It merely brings about the adaptation of
a species or a group to a given environment. The tapeworm is the
stock example. In human evolution, the nature of this environment
will determine whether adaptation to it means progress or retro-
gression, whether it leaves a race happier and more productive, or the
reverse. AU racial progress, or eugenics, therefore, depends on the
creation of a good environment, and the fitting of the race to that
environment. Every improvement in the enviromnent should bring
about a corresponding biological adaptation. The two factors in
evolution must go side by side, if the race is to progress in what the
human mind considers the direction of advancement. In this sense,
euthenics and eugenics bear the same relation to human progress as
a man's two legs do to his locomotion.
Social workers in purely euthenic fields have frequently failed to
remember this progress of adaptation, in their efforts to change the
environment. Eugenists, in centering their attention on adaptation,
have sometimes paid too little attention to the kind of environment to
which the race was being adapted. The present book holds that the
EUGENICS AND EUTHENICS 569
second factor is just as important as the first, for racial progress; that
one leg is just as important as the other, to a pedestrian. Its only con-
flict with euthenics appertains to such euthenic measures as impair the
adaptability of the race to the better environment they are trying to
make.
Some supposedly euthenic measures opposed by eugenics are not
truly euthenic, as for instance the hmitation of a superior family in
order that all may get a college education. For these spurious
euthenic measures, something truly euthenic should be substituted.
IVIeasures which show a real conflict may be typified by the infant
mortality movement. There can be no doubt but that sanitation and
hygiene, prenatal care and intelligent treatment of mothers and babies,
are truly euthenic and desirable. At the same time, as has been
shown, these euthenic measures result in the survival of inferior
children, who directly or through their posterity will be a drag on the
race. Euthenic measures of this type should be accompanied by
counterbalancing measures of a more eugenic character.
Barring these two types, euthenics forms a necessary concomitant
of the eugenic program; and, as we have tried to emphasize, eugenics
is likewise necessary to the complete success of every euthenic program.
How foolish, then, is antagonism between the two forces! Both are
working toward the same end of human betterment, and neither can
succeed without the other. When either attempts to eliminate the
other from its work, it ceases to advance toward its goal. In which
camp one works is largely a matter of taste. If on a road there is a
gradient to be leveled, it will be brought down most quickly by two
parties of workmen, one cutting away at the top, and the other filling
in the bottom. For the two parties to indulge in mutual scorn and
recrimination would be no more absurd than for eugenics and euthenics
to be put in opposition to each other. The only reason they have been
in opposition is because some of the workers did not clearly understand
the nature of their work. With the dissemination of a knowledge of
biology, this ground of antagonism will disappear.
CHAPTER XLIII
HUMAN CONSERVATION*
HERBERT E. WALTER
I. HOW MANKIND MAY BE IMPROVED
There are two fundamental ways to bring about human better-
ment, namely, by improving the individual and by improving the race.
The first method consists in making the best of whatever heritage
has been received by placing the individual in the most favorable
environment and developing his capacities to the utmost through
education. The second method consists m seeking a better heritage
with which to begin the Ufe of the individual. The first method is
immediate and urgent for the present generation. The second method
is concerned with ideals for the future, and consequently does not
usually present so strong an appeal to the individual.
The first is the method of eulhenics, or the science of learning to
live well. The second is eugenics, which Gal ton defines as " the science
of being well born."
These two aspects of human betterment, however, are inseparable.
Any hereditary characteristic must be regarded, not as an independent
entity, but as a reaction between the germplasm and its environment.
The biologist who disregards the fields of educational endeavor and
environmental influence, is equally at fault with the sociologist who
fails sufficiently to realize the fundamental importance of the germ-
plasm.
Without euthenic opportunity the best of heritages would never
fully come to its own. Without the eugenic foundation the best
opportunity fails of accomplishment. The euthenic point of view,
however, must not distract the attention now, for the present chapter
is particularly concerned with the program of eugenics.
2. MORE FACTS NEEDED
Since the point of attack in human heredity must be largely
statistical, it is of the first importance to collect more facts. Our
actual knowledge is confused with a mass of tradition and opinion,
• From H. E. Walter, Genetics (copyright 1913). Used by special permission
.f the publishers, The Macmillan Company.
570
HUMAN CONSERVATION 57 1
much of which rests upon questionable foundations. The great
present need is to learn more facts; to sift the truth from error in what
is already known ; and to reduce all these data to workable scientific
form. Much progress is being made in this direction, owing to the
impetus given by the revival of Mendel's illuminating work, but as yet
the science of eugenics is in its infancy.
The most systematic and effective attempt in this country to
collect reliable data concerning heredity in man has been initiated by
the Eugenics Section of the American Breeders' Association under the
secretaryship of Dr. C. B. Davenport. In 1910 the Eugenics Record
Office, with a staff of expert field and office workers and an adequate
equipment of fire-proof vaults, etc., for the preservation of records,
was opened at Cold Spring Harbor, Long Island, New York, with
Mr. H. H. Laughlin as superintendent. "The main work of this
office is investigation into the laws of inheritance of traits in human
beings and their application to eugenics. It proffers its services free
of charge to persons seeking advice as to the consequences of pro-
posed marriage matings. In a word, it is devoted to the advance-
ment of the science and practice of eugenics." The publication of
results from the Eugenics Record Office has already been begun.
The Volta Bureau, founded about twenty-five years ago in
Washington by Dr. Alexander Graham Bell, is collecting data with
reference to deafness and has now systematically arranged particu-
lars concerning the history of over 20,000 individuals. In England,
also, the Galton Laboratory for Eugenics, founded in 1905, is system-
atically collecting facts about human pedigrees and pubHshing the
results in a compendious "Treasury of Human Inheritance."
Besides these special bureaus of investigation, innumerable facts
about the inheritance of particular traits are being incidentally brought
together and made available in various institutions and asylums
throughout the world which are immediately concerned with the care
of defectives of different types. It is in connection with such institu-
tions for defectives that much of the most successful "field work" of
the Eugenics Section of the American Breeders' Association is being
accomplished in the United States.
3. FURTHER APPLICATION OF WHAT WE KNOW NECESSARY
Human performance always lags behind human knowledge.
Many persons who are fully aware of the right procedure do not put
their knowledge into practice. It follows, therefore, that any pro-
572 EVOLUTION, GENETICS, AND EUGENICS
gram of eugenics which does not grip the imagination of the common
people in such a way as to become an effective part of their very lives
is bound to remain largely an academic affair for Utopians to quarrel
and theorize over.
It is not enough to collect facts and work out an analysis and
interpretation of them, for, important as this preliminary step is, it
must be followed by a convincing campaign of education.
The lives of the unborn do not force themselves upon the average
man or woman with the same insistency as the lives already begun.
In the midst of the overwhelming demands of the present, the appeal
of posterity for better blood is vague and remote. If every individual
regarded the germplasm he carries as a sacred trust, then it would be
the part of an awakened eugenic conscience to restrain that germplasm
when it is known to be defective or, when it is not defective, to hand
it on to posterity with at least as much foresight as is exercised in
breeding domestic animals and cultivated plants.
The eugenic conscience is in need of development, and it is only
when this becomes thoroughly aroused in the rank and file of society
as well as among the leaders, that a permanent and increasing better-
ment of mankind can be expected.
4. THE RESTRICTION OF UNDESIRABLE GERMPLASM
A negative way to bring about better blood in the world is to
follow the clarion call of Davenport, and "dry up the streams that
feed the torrent of defective and degenerate protoplasm." This may
be partially accomplished, at least in America, by emplo3dng the
following agencies: control of immigration; more discriminating
marriage laws; a quickened eugenic sentiment; sexual segregation of
defectives; and finally, drastic measures of asexuaUzation or steriliza-
tion when necessary.
a) CONTROL OF IMMIGRATION
The enforcement of immigration laws tends to debar from the
United States not only many undesirable individuals, but also inci-
dentally to keep out much potentially bad germplasm that, if admitted,
might play havoc with future generations.
For example, during the year of 1908, 65 idiots, 121 feeble-minded,
184 insane, 3,741 paupers, 2,900 individuals having contagious dis-
eases, 53 tuberculous individuals, 136 criminals, and 124 prostitutes
were caught in the sieve at Ellis Island alone and turned back from
this country by the immigration ojfficials. These 7,000 and more
HUMAN CONSERVATION 573
individuals probably were the bearers of very little germplasm that
we are nationally not better off without.
Eugenically, the weak point in the present application of immi-
gration laws is that criteria for exclusion are phenotypic in nature
rather than genotypic, and consequently much bad germplasm comes
through our gates hidden from the view of inspectors because the
bearers are heterozygous, wearing a cloak of desirability over undesir-
able traits.
It is not enough to hft the eyelid of a prospective parent of Ameri-
can citizens to discover whether he has some kind of an eye-disease or
to count the contents of his purse to see if he can pay his own way.
The official ought to know if eye-disease runs in the immigrant's family
and whether he comes from a race of people which, through chronic
shiftlessness or lack of initiative, have always carried light purses.
In selecting horses for a stock-farm an expert horseman might rely
to a considerable extent upon his judgment of horseflesh based upon
inspection alone, but the wise breeder does more than take the chances
of an ordinary horse trader. He wants to be assured of the pedigree
of his prospective stock. It is to be hoped that the time will come
when we, as a nation, will rise above the hazardous methods of the
horse trader in selecting from the foreign applicants who knock at our
portals, and that we will exercise a more fundamental discrimination
than such a haphazard method affords, by demanding a knowledge of
the germplasm of these candidates for citizenship, as displayed in
their pedigrees.
This may possibly be accomplished by having trained inspectors
located abroad in the communities from which our immigrants come,
whose duty it shall be to look up the ancestry of prospective applicants
and to stamp desirable ones with approval. The national expense
of such a program of genealogical inspection would be far less than
the maintenance of introduced defectives, in fact it would greatly
decrease the number of defectives in the country. At the present
time this country is spending over one hundred million dollars a year
on defectives alone, and each year sees this amount increased.
The United States Department of Agriculture already has field
agents scouring every land for desirable animals and plants to intro-
duce into this country, as well as stringent laws to prevent the importa-
tion of dangerous weeds, parasites, and organisms of various kinds.
Is the inspection and supervision of human blood less important ?
574 EVOLUTION, GENETICS, AND EUGENICS
b) MORE DISCRIMINATING MARRIAGE LAWS
Every people, including even the more primitive races, make
customs or laws that tend to regulate marriage. Of these, the laws
which relate to the eugenic aspect of marriage are the only ones that
concern us in this connection. "Marriage," says Davenport, "can
be looked at from many points of view. In novels as the climax of
human courtship; in law largely as two lines of property descent; in
society, as fixing a certain status; but in eugenics, which considers its
biological aspect, marriage is an experiment in breeding."
Certain of the United States have laws forbidding the marriage
of epileptics, the insane, habitual drunkards, paupers, idiots, feeble-
minded, and those afflicted with venereal diseases. It would be well
if such laws were not only more uniform and widespread, but also more
rigidly enforced.
It is quite true that marriage laws in themselves do not necessarily
control human reproduction, for illegitimacy is a factor that must
always be reckoned with; nevertheless such laws do have an important
influence in regulating marriage and consequent reproduction.
Marriage laws may, however, sometimes bring about a deplor-
able result eugenically, as in the case of forced marriage of sexual
offenders in order to legalize the offense and "save the woman's
honor." To compel, under the guise of legaUty, two defective streams
of germplasm to combine repeatedly and thereby result in defective
offspring just because the unfortunate event happened once illegiti-
mately, is fundamentally a mistake. Darwin says: "Except in the
case of man himself hardly any one is so ignorant as to allow his worst
animals to breed."
c) AN EDUCATED SENTIMENT
A far more effective means of restricting bad germplasm than
placing elaborate marriage laws upon our statute-books is to educate
public sentiment and to foster a popular eugenic conscience, in the
absence of which the safeguards of the law must forever be largely
without avail.
Such a sentiment already generally exists to a large extent with
respect to incest, and the marriage of persons as noticeably defective
as idiots or those afflicted with insanity, and also in America with
respect to miscegenation, but a cautious and intelligent examination
of the more obscure defective traits, exhibited in the somatoplasms of
the various members of families in question, is largely an ideal of the
HUMAN CONSERVATION 575
future. Under existing conditions non-eugenic considerations such
as wealth, social position, etc., often enter into the preliminary negotia-
tions of a marriage alliance, but an equally unromantic caution with
reference to the physical, moral, and mental characters that make up
the biological heritage of contracting parties is less usual.
The scientific attitude is not necessarily opposed to the romantic
way of looking at things. Science is simple "organized common
sense," and romance, that dispenses with this balance-wheel, although
it may be entertaining and always exciting at first, is sure to be dis-
appointing in the end. Marriages may be "made in heaven," but,
as a matter of fact, children are bom and have to be brought up on
earth. It follows without saying that it will be much easier to stamp
out bad germplasm when an educated sentiment becomes common
among all people everywhere.
d) SEGREGATION OF DEFECTIVES
Persons with hereditary defects, such as epileptics, idiots, and
certain criminals, who become wards of the state, should be segregated
so that their germplasm may not escape to furnish additional burdens
to society. "We have become so used to crime, disease and degener-
acy that we take them for necessary evils. That they were in the
world's ignorance, is granted. That they must remain so, is denied"
(Davenport).
" The great horde of defectives once in the world have the right to
hve and enjoy as best they may whatever freedom is compatible with
the lives and freedom of other members of society," says Kellicott, but
society had a right to protect itself against repetitions of hereditary
blunders.
There is one grave danger connected with the administration of
our humane and commendable philanthropies toward the unfortunate,
for it frequently happens that defectives are kept in institutions until
they are sexually mature or are partly self-supporting, when they are
hberated only to add to the burden of society by reproducing their like.
Furthermore, if defectives of the same sort are collected together
in the same institutions, unless sexual segregation is strictly main-
tained, they may by the very circumstance of proximity tend to
reproduce their kind just as defectives in any isolated community tend
to multiply.
David Starr Jordan cites the interesting case of cretinism which
occurs in the valley of Aosta in northern Italy, to prove the wisdom
576 EVOLUTION, GENETICS, AND EUGENICS
of the sexual segregation of defectives. Cretinism is an hereditary
defect connected with an abnormal development of the thyroid gland
which results in a pecuUar form of idiocy usually associated with goitre.
"In the city of Aosta the goitrous cretin has been for centuries an
object of charity. The idiot has received generous support, while the
poor farmer or laborer with brains and no goitre has had the severest
of struggles. In the competition of hfe a premium has thus been
placed on imbecility and disease. The cretin has mated with cretin,
the goitre with goitre, and charity and religion have presided over
the union. The result is that idiocy is multiplied and intensified. The
cretin of Aosta has been developed as a new species of man. In fair
weather the roads about the city are lined with these awful paupers —
human beings with less intelligence than a goose, with less decency
than the pig."
Whymper, writing in 1880, further observes: "It is strange that
self-interest does not lead the natives of Aosta to place their cretins
under such restrictions as would prevent their illicit intercourse; and
it is still more surprising to find the Catholic Church actually legalizing
their marriage. There is something horribly grotesque in the idea of
solemnizing the union of a brace of idiots, and, since it is well known
that the disease is hereditary and develops in successive generations the
fact that such marriages are sanctioned is scandalous and infamous."
Since 1890 the cretins have been sexually segregated, and in 19 10
Jordan reported that they were nearly all gone.
e) DRASTIC MEASURES
A fifth method of restricting undesirable germplasm in the case of
confirmed criminals, idiots, imbeciles, and rapists may be mentioned,
namely, the extreme treatment of either asexualization or vasectomy.
The latter is a minor operation confined to the male which occupies
only a few moments and requires at most only the application of a
local anaesthetic, such as cocaine. There are no disturbing or even
inconvenient after effects from this operation. It consists in removing
a small section of each sperm duct, and is entirely effectual in prevent-
ing subsequent parenthood.
In the female the corresponding operation, which consists in
removing a portion of each Fallopian tube, is much more severe, but
not impracticable or dangerous.
Eight states already have sterilization laws providing for certain
cases and " could such a law be enforced in the whole United States,
HUMAN CONSERVATION 577
less than four generations would eliminate nine tenths of the crime,
insanity and sickness of the present generation in our land. Asylums,
prisons and hospitals would decrease, and the problems of the unem-
ployed, the indigent old and the hopelessly degenerate would cease to
trouble civilization."
5. THE CONSERVATION OF DESIRABLE GERMPLASM
Not only negatively by the restriction of undesirable germplasm,
but also positively by the conservation of desirable germplasm, may
the eugenic ideal be approached.
It is possible that if some of the philanthropic endeavor now
directed toward alleviating the condition of the unfit should be directed
to enlarging the opportunity of the fit, greater good would result in the
end. In breeding animals and plants the most notable advances have
been made by isolating and developing the best, rather than by
attempting to raise the standard of mediocrity through the elimination
of the worst.
One leader is worth a score of followers in any community, and the
science of genetics surely gives to educators the hint that it is wiser
to cultivate the exceptional pupil who is often left to take care of him-
self than to expend all the energies of the instructor in forcing the
indifferent or ordinary one up to a passing standard. The campaign
for human betterment in the long run must do more than avoid mis-
takes. It must become aggressive and take advantage of those human
mutations or combinations of traits which appear in the exceptionally
endowed.
There are various ways in which this improvement of society may
be brought about.
a) BY SUBSIDIZING THE FIT
The following unconfirmed newspaper chpping illustrates the
point of what is meant by subsidizing the fit so far as certain physical
characteristics are concerned. "Berlin, Dec. 11, igii. The Emperor
is reported to be interested in a plan proposed by Professor Otto
Hauser for the propagation of a fixed German type of humanity —
a tj^e which will be as fixed as the Jewish in its characteristics, if the
suggestions of the professor can ever be carried out. The fixed type
is to be produced as follows: — Only ' typical ' couples are to be allowed
to mate. The man is to be not more than thirty years old, the woman
not over twenty-eight, and each have a perfect health certificate. The
man should be at least five feet seven inches tall ; the woman not under
578 EVOLUTION, GE>rETICS, AND EUGENICS
five feet six inches. Neither the man nor the woman should have dark
hair. Its tint may range from blonde to auburn. The eyes of the
pair should be pure blue without any tint of brown. The complexion
should be fair to ruddy without any suggestion of heaviness or 'beefi-
ness.' The nose ought to be strong and narrow, the chin square and
powerful, and the skull well developed at the back. The man and the
woman must be of German descent and must bear a German name and
speak the language of Germany. These 'mated couples' are to get
a wedding gift of $125 and an additional grant for each child born.
The couples may settle in the United States if they prefer." This
reported attempt to establish a Prussian type of "Hauser blondes "at
least points the way to one sort of a positive eugenic method that
might possibly be employed with respect to certain physical charac-
teristics.
It should be remembered, however, that the eugenic ideal is not
by any means confined to physical traits alone.
b) BY ENLARGING INOrVIDUAL OPPORTUNITY
Much good human germplasm goes to waste through ineffective-
ness on account of unfavorable environment or lack of a suitable
opportunity to develop.
Every agency which contributes toward increasing the opportunity
of the individual to attain to a better development of his latent
possibihties is in harmony with a thoroughly positive eugenic practice.
Thus better schools, better homes, better hving conditions, in short,
all euthenic endeavor, directly serves the eugenic ideal by making the
best out of whatever germinal equipment is present in man.
c) BY PREVENTING GERMINAL WASTE
Much good protoplasm fails to find expression in the form of off-
spring because one or the other of possible parents is cut off either by
preventable death or by social hindrances. To avoid such calamities
is a part of the positive program of eugenics.
I, Preventable death. — War, from the eugenic point of view, is the
height of folly, since presumably the brave and the physically fit
march away to fight, while in general the unqualified stay at home to
reproduce the next generation. When a soldier dies on the battlefield
or in the hospital, it is not alone a brave man who is cut off, but it is
the termination of a probably desirable strain of germplasm. The
Thirty Years' War in Germany cost 6,000,000 lives, while Napoleon
in his campaigns drained the best blood of France.
HUMAN CONSERVATION ^jg
David Starr Jordan has presented the matter very clearly. He
points out that the "man with a hoe" among the European peasantry
is not the result of centuries of oppression, as he has been pictured, but
rather the dull progeny resulting from generations of the unfit who
were left behind when the fit went off to war never to return.
Benjamin Franklin, with characteristic wisdom, sums up the
situation in the following epigram: "Wars are not paid for in war
time; the bill comes later."
2. Social hindrances. — There are many conditions of modern
society which act non-eugenically.
For instance, the increasing demands of professional hfe prolong
the period necessary for preparation, which, with the "cost of high
living," tends toward late marriage. In this way much of the best
germplasm is very often wthheld from circulation until it is too late
to be effective in providing for the succeeding generation.
Certain occupations such as school-teaching and nursing by
women are filled by the best blood obtainable, yet this blood is denied
a direct part in molding posterity, since marriage is either forbidden or
regarded as a serious handicap in such lines of work. Advertisements
concerning "unincumbered help" and "childless apartments" tell
their own deplorable tale.
One of the darkest features of the dark ages from a eugenic stand-
point was the enforced ceUbacy of the priesthood, since this resulted,
as a rule, in withdrawing into monasteries and nunneries much of the
best blood of the times, and this uneugenic custom still obtains in
many quarters today.
6. WHO SHALL SIT IN JUDGMENT?
In the practical application of a program of eugenics there are
many difficulties, for who is qualified to sit in judgment and separate
the fit from the unfit ?
There are certain strongly marked charac'^eristics in mankind
which are plainly good or bad, but the principle of the independence
of unit characters demonstrates that no person is wholly good or
wholly bad. Shall we then throw away the whole bundle of sticks
because it i^ on tains a few poor or crooked ones?
The Ust of weakUng babies, for instance, who were apparently
physically unfit and hardly worth raising upon first judgment, but who
afterwards became powerful factors in the world's progress, is a notable
one and includes the names of Calvin, Newton, Heine, Voltaire,
Herbert Spencer, and Robert Louis Stevenson.
SSo EVOLUTION, GENETICS, AND EUGENICS
Or, take another example. Elizabeth Tuttle, the grandmother of
Jonathan Edwards whose remarkable progeny was referred to in a
preceding chapter, is described as a " woman of great beauty, of tall
and commanding appearance, striking carriage, of strong will, extreme
intellectual vigor and mental grasp akin to rapacity," but with an
extraordinary deficiency in moral sense. She was divorced from her
husband "on the ground of adultery and other immoralities
The evil trait was in the blood, for one of her sisters murdered her
own son and a brother murdered his own sister." That Jonathan
Edwards owed his remarkable qualities largely to his grandmother
rather than to his grandfather is shown by the fact that Richard
Edwards, the grandfather, married again after his divorce and had
five sons and one daughter, but none of their numerous progeny " rose
above mediocrity, and their descendants gained no abiding reputa-
tion." As shown by subsequent events, it would have been a great
eugenic mistake to have deprived the world of EUzabeth Tuttle's
germp!asm, although it would have been easy to find judges to con-
demn her.
Dr. C. V. Chapin recently said with reference to the eugenic
regulation of marriage by physician's certificate: "The causes of
heredity are many and very conflicting. The subject is a difficult one,
and I for one would hesitate to say, in a great many cases where I have
a pretty good knowledge of the family, where marriage would, or
would not, be desirable."
Desirability and undesirability must always be regarded as rela-
tive terms more or less indefinable. In attempting to define them, it
makes a great difference whether the interested party holds to a
puritan or a cavalier standard. To show how far human judgment
may err as well as how radically human opinion changes, there were in
England, as recently as 1819, 233 crimes punishable by death accord-
ing to law.
One needs only to recall the days of the Spanish Inquisition or of
the Salem witchcraft persecution to realize what fearful blunders
human judgment is capable of, but it is unlilvely that the world will
ever see another great religious inquisition, or that in applying to man
the newly found laws of heredity there will ever be undertaken an
equally deplorable eugenic inquisition.
It is quite apparent, finally, that although great caution and
broadness of vision must be exercised in bringing about the fulfilment
of the highest eugenic ideals, nevertheless in this direction Ues the
future path of human achievement.
CHAPTER XLIV
THE PROMISE OF RACE CULTURE*
CALEB WILLIAMS SALEEBY
The best is yet to be.
In its form of what we have called negative eugenics, the practice
of our principle would assuredly reduce to an incalculable extent the
amount of human defect, mental and physical, which each generation
now exhibits. This alone, as has been said, would be far more than
sufficient to justify us. A world without hereditary disease of mind
and body would alone warrant the hint of Ruskin that posterity may
some day look back upon us with " incredulous disdain." Yet, assum-
ing that this could be accomplished, as it will be accompUshed, what
more is to be hoped for ? Must race-culture cease merely when it has
raised the average of the community by reducing to a minimum the
proportion of those who are thus grossly defective in mind or body ?
Such disease apart, are we to be content, must we be content, with
the present level of mediocrity in respect of intelligence and temper
'and moral sentiment? Can we anticipate a London in which the
present ratio of musical comedy to great opera will be reversed, in
which the works of Mr. George Meredith will sell in hundreds of
thousands, whilst some of our popular novelists will have to find other
means of earning a hving? Can we make for a critical democracy
which no political party can fool, and which will choose its best to
govern it ? Yet more, can we undertake, now or hereafter, to provide
every generation with its own Shakespeare and Beethoven and
Tintoretto and Newton ? What, in a word, is the promise of positive
eugenics? It is to this aspect of the question that Mr. Galton has
mainly directed himself. Indeed he was led to formulate the princi-
ples and ideals of the new science by his study of hereditary genius
some four decades ago. Let us now attempt to answer some of these
questions.
The production of genius. — And first as to the production of
genius. It is this, perhaps, that has been the main butt of the jesters
who pass for philosophers with some of us 'today. It may be said
' From C. W. Saleeby, PareiitJwod and Race Culture (copyright 1909). Used by
special permission of the publishers, Moffat, Yard, and Company.
581
582 EVOLUTION, GENETICS, AND EUGENICS
at once that neither Mr. Galton nor any other responsible person has
ever asserted that we can produce genius at will. The difficulties in
the way of such a project — at present — are almost innumerable.
One or two may be cited.
In the first place, there is the cardinal — but by no means univer-
sal— difficulty that the genius is too commonly so occupied with the
development and expansion of his own individuality that he has little
time or energy for the purposes of the race. This, of course, is an
example of Spencer's great generalization as to the antagonism or
inverse ratio between individuation and genesis.
Again, there is the generalization of heredity formulated by
Mr. Galton, and named by him the /aw of regression towards mediocrity.
It asserts that the children of those who are above or below the mean of
a race, tend to return towards that mean. The children of the born
criminal will be probably somewhat less criminal in tendency than he,
though more criminal than the average citizen. The children of the
man of genius, if he has any, wiU probably be nearer mediocrity than
he, though on the average possessing greater talent than the average
citizen. It is thus not in the nature of sheer genius to reproduce on its
own level. It is only the critics who are totally ignorant of the elemen-
tary facts of heredity that attribute to the eugenist an expectation of
which no one knows the absurdity so well as he does.
On the other hand, it is impossible to question that the hereditary
transmission of genius or great talent does occur. One may cite at
random such cases as that of the Bach family, Thomas and Matthew
Arnold, James and John Stuart Mill; and the reader who is inclined
to believe that there is no law or likeUhood in this matter, must
certainly make himself acquainted with Mr. Galton's Hereditary
Genius, and with such a paper as that which he printed in Sociological
Papers, 1904, furnishing an "index to achievements of near kinsfolk
of some of the Fellows of the Royal Society." There is, of course, the
obvious fallacy involved in the possibiUty that not heredity but
environment was really responsible for many of these cases. It must
have been a great thing to have such a father as James Mill. But it
would be equally idle to imagine that the evidence can be dismissed
with this criticism. A Matthew Arnold, a John Stuart Mill, could not
be manufactured out of any chance material by an ideal education
continued for a thousand years.
The transmission of genius. — One single instance of the trans-
mission of genius or great talent in a family may be cited. We shall
THE PROMISE OF RACE CULTURE 583
take the family which produced Charles Darwin, the discoverer of the
fundamental principle of eugenics, and his first cousin, Francis Galton.
Darwin's grandfather was Erasmus Darwin, physician, poet and
philosopher, and independent expounder of the doctrine of organic
evolution. Darwin's father was a distinguished physician, described
by his son as "the wisest man I ever knew." Darwin's maternal
grandfather was Josiah Wedgwood, the famous founder of the pottery
works. Amongst his first cousins is Mr, Francis Galton. He has five
living sons, each a man of great distinction, including Mr. Francis
Darwin and Sir George Darwin, both of them original thinkers,
honored by the presidency of the British Association. No one will
put such a case as this down to pure chance or to the influence of
environment alone. This is evidently, like many others, a greatly
distinguished stock. The worth of such families to a nation is wholly
beyond any one's powers of estimation. What if Erasmus Darwin
had never married !
No student of human heredity can doubt that, however limited
our immediate hopes, facts such as those alluded to furnish promise
of great things for the future. But let us turn now from genius to
what we usually call talent.
The production of talent.— There can be no question that amongst
the promises of race-culture is the possibility of breeding such things
as talent and the mental energy upon which talent so largely depends.
In the Inquiries into Human Faculty, Mr. Galton shows the remark-
able extent to which energy or the capacity for labor underlies intellec-
tual achievement. He says, of energy:
"It is consistent with all the robust virtues, and makes a large
practice of them possible. It is the measure of fullness of life ; the more
energy the more abundance of it; no energy at all is death; idiots are
feeble and listless. In the enquiries I made on the antecedents of men
of science no points came out more strongly than that the leaders of
scientific thought were generally gifted with remarkable energy, and
that they had inherited the gift of it from their parents and grand-
parents Itmaybeobjectedthatif the race were too heal thy and
energetic there would be insufficient call for the exercise of the pitying
and self-denjang virtues, and the character of men would grow harder
in consequence. But it does not seem reasonable to preserve sickly
breeds for the sole purpose of tending them, as the breed of foxes is
preserved solely for sport and its attendant advantages. There is
little fear that misery will ever cease from the land, or that the
584 EVOLUTION, GENETICS, AND EUGENICS
compassionate will fail to find objects for their compassion; but at
present the supply vastly exceeds the demand; the land is over-stocked
and over-burdened with the listless and the incapable. In any scheme
of eugenics, energy is the most important quality to favor; it is, as we
have seen, the basis of living action, and it is eminently transmissible
by descent."
Need it be pointed out that any political system which ceases to
favor or actively disfavors energy, making it as profitable to be lazy as
to be active, is antieugenic, and must inevitably lead to disaster?
That, however, by the way. Our present point is that eugenics can
reasonably promise, when its principles are recognized, to multiply
the human and diminish the vegetable type in the community. In so
doing, it will greatly further the production of talent, and therefore
of that traditional or acquired progress which men of talent and
genius create. Such a result will also further, though indirectly, the
production of genius itself. For, as Mr. Gal ton points out, " men of an
order of ability which is now very rare, would become more frequent,
because the level out of which they rose would itself have risen."
This is by no means the only fashion in which an effective and
practicable race-culture would serve genius, and I shall not be blamed
for considering this matter further by any reader who realizes, however
faintly, what the man of genius is worth to the world. If it were shown
possible to establish such social conditions that genius could never
flower in them, we should realize that their establishment would
mean the putting of an end to progress and the blasting of all the
highest hopes of the highest of all ages.
The immediate need of this age, as of all ages, is perhaps not so
much the birth of babies capable of developing into men and women of
genius, as the full exploitation of the possibilities of genius with which,
as I fancy, every generation on the average is about as well endowed as
any other. There is, of course, the popular doctrine that there are no
mute inglorious Miltons, that "genius will out," and that therefore
if it does not appear, it is not there to appear. In expressing the com-
pelling power of genius in many cases this doctrine is not without
truth. Yet history abounds in instances where genius has been de-
stroyed by environment — and we can only guess how many more
instances there are of which history has no record. To take the single
case of musical genius, it is a lamentable thought that there may be
those now living whose natural endowments, in a favorable environ-
ment, would have enabled them to write symphonies fit to place
THE PROMISE OF RACE CULTURE 585
beside Beethoven's, but whom some environmental factors — conven-
tional, economic, educational, or what not — have silenced; or worse,
have persuaded to write such sterile nullities as need not here be
instanced. There is surely no waste in all this wasteful world so
lamentable as this waste of genius.
If, then, anyone could devise for us a means by' which the genius,
potentially existing at any time, were realized, he would have per-
formed in effect a service equivalent to that of which eugenics repudi-
ates the present possibility — the actual creation of genius. But if we
consider what the conditions are which cause the waste of genius, we
realize at once that they mainly inhere in the level of tlie human
environment of the priceless potentiality in question. As we noted
elsewhere, in an age like that of Pericles genius springs up on all hands.
It is encouraged and welcomed because the average level of the human
environment in which it finds itself is so high. But if eugenics can
raise the average level of intelligence, in so doing not merely does it
render more likely, as Mr. Galton points out, the production of men of
the highest abihty, but it provides those conditions in which men of
genius, now swamped, can swim. We could not undertake to produce
a Shakespeare, but we might reasonably hope to produce a generation
which would not destroy its Shakespeares. And even if men of genius
still found it necessary, as men of genius have found it necessary, to
"play to the gallery," they would play, as Mr. Galton says of the
demagogue in a eugenic age, "to a more sensible gallery than at
present."
Darwin somewhere points out that it is not the scientific, but the
unscientific man who denies future possibilities. Thus though an
advocate of eugenics may be applauded for his judgment if he declares
that the creation of genius will forever be impossible, yet I should not
care to assert that the ultimate limitations of eugenics can thus be
defined. We have yet to hear the last of Mendelism.
Eugenics and unemployment. — Let us look now at another aspect
of the promise of race-culture. When the time comes that quahty
rather than quantity is the ideal of those who concern themselves with
the population question, it is quite evident that not a few of the social
problems which we now find utterly insoluble will disappear. In
this brief outline, we can only allude to one or two points. Take, for
instance, the question of unemployment. We know that some by no
means small proportion of the unemployed were really destined to be
unemployable from the first, as for instance by reason of hereditary
586 EVOLUTION, GENETICS, AND EUGENICS
disease. It were better for them and for us that they had never been
born. Many more of the unemployed have been made unemployable
by the influence of over-crowding, to which they were subjected in their
years of development. Is there, can there be, any real and permanent
remedy for overcrowding, but the erection of parenthood into an act
of personal and provident responsibility ?
Eugenics and woman. — Take, again, the woman question. No
one will deny that in many of its gravest forms, especially in its
economic form, and the question of the employment of women, wisely
or horribly, this depends (to a degree which few, I think, realize) upon
the fact that there are now (1909), for instance, 1,300,000 women in
excess in this country. Is it then proposed, the reader will say, by
means of race-culture to exterminate the superfluous woman ? Indeed,
no. But is the reader aware that Nature is not responsible for the
existence of the superfluous woman ? There are more boys than girls
born in the ratio of about 103 or 104 to 100; and Nature means them all
to live, boys and girls alike. If they did so Uve, we should have merely
the problem of the superfluous man, which would not be an economic
problem at all. But we destroy hosts of all the children that are born,
and since male organisms are in general less resistant than female
organisms, we destroy a disproportionate number of boys, so that the
natural balance of the sexes is inverted. Unlike ancient societies we
largely practice male infanticide. Can the reader beUeve that there
is any permanent and final means of arresting this wastage of child-
life, with its singular and far-reaching consequences, other than the
elevation of parenthood, wholly apart from the question of the selec-
tion of parents ? We shall not succeed in keeping all the children alive
(with a trivial number of exceptions), thereby abolishing the super-
fluous woman by keeping alive the boy who should have grown up to
be her partner, until we greatly reduce the birth-rate; as it must and
win be reduced when the ideal of race-culture is realized, and no child
comes into the world that is not already loved and desired in antici-
pation.
Eugenics and cruelty to children. — ^This ideal, also, ofEers us in
its realization the only complete remedy for the present ghastly cruelty
under which so many children suffer even in Great Britain, even in the
twentieth century. Is the reader aware that the National Society
for the Prevention of Cruelty to Children inquired into the ill-treat-
ment or cruel neglect of 115,000 children in the year beginning April
isL, igo6 ? It has been reasonably and carefully estimated that " over
THE PROMISE OF RACE CULTURE 587
half a million children are involved in the total of the wastage of child-
life and the torture and neglect of child-life in a single year." Surely
Mr. G. R. Sims, to whom I would offer a hearty tribute for his recent
services to childhood, is justified in saying, "Against the guilt of race
suicide our men of science are everywhere preaching their sermons
to-day. It is against the guilt of race murder that the cry of the
children should ring through the land." As regards race suicide and
the men of science, I am not so sure as to the assertion. But the truth
of the second sentence quoted is as indisputable as it is horrible.
Now no legislation conceivable will wholly cure this evil nor avert
its consequences. At bottom it depends upon human nature, and
you can cure it only by curing the defect of human nature. This, in
general, is of course beyond the immediate powers of man, but evi-
dently we should gain the same end if only we could confine the advent
of children to those parents who desired them — that is to say, those in
whom human nature displayed the first, if not indeed almost the only,
requisite for the happiness of childhood. To this most beneficent
and whoUy moral end we shall come, notwithstanding the blind and
pitiable guidance of most of our accredited moral teachers today. By
no other means than the realization of the ideal defined, that every
new baby shall be loved and desired in anticipation — an ideal which is
perfectly practicable — can the black stain of child murder and child
torture and child neglect be removed from our civilization.
Ruskin and race-culture. — The name of Ruskin, perhaps, would
not occur to the reader as likely to afford support to the fair hopes of
the eugenist. Consider then, these words from Time and Tide:
"You leave your marriages to be settled by supply and demand,
instead of wholesome law. And thus, among your youths and maid-
eiis, the improvident, incontinent, selfish, and foolish ones marry,
whether you will or not; and beget famiUes of children necessarily
inheritors in a great degree of these parental dispositions; and for
whom, supposing they had the best dispositions in the world, you have
thus provided, by way of educators, the foolishest fathers and mothers
you could find; (the only rational sentence in their letters, usually, is
the invariable one, in which they declare themselves 'incapable of
providing for their children's education'). On the other hand, who-
soever is wise, patient, unselfish, and pure among your youth, you
keep maid or bachelor; wasting their best days of natural life in pain-
ful sacrifice, forbidding them their best help and best reward, and care-
fully excluding their prudence and tenderness from any ofiices of
588 EVOLUTION, GENETICS, AND EUGENICS
parental duty. Is not this a beatific and beautifully sagacious system
for a Celestial Empire, such as that of these British Isles ?"
Apart from the point as to wholesome law rather than the educa-
tion of opinion as the eugenic means, the foregoing passage must win
the assent and respect of every eugenist. It indicates the promise of
race-culture as it appeared to John Ruskin. The passage has been
quoted in full, not for the benefit of the ordinary thoughtful reader but
for that of the professional literary man who, in this remarkable age,
so far as I can judge, reads nothing but what he writes, and thus quali-
fies himself for dismissing Spencer or Darwin or Galton by any casual
phrase.
Race-culture and human variety. — Now let us turn to another
question. Let it be asserted most emphatically that, if there is any-
thing in the world which eugenics or race-culture does not promise or
desire, it is the production of a uniform type of man. This delusion,
for which there has never been any warrant at all, possesses many of
the critics of eugenics, and they have made pretty play with it, just
as they do with their other delusions. Let us note one or two facts
which bear upon this most undesirable ideal.
In the first place, it is unattainable because of the existence of
what we call variation. No apparatus conceivable would suffice to
eliminate from every generation those who varied from the accepted
type.
In the second place, this uniformity is supremely undesirable from
the purely evolutionary point of view, because its attainment would
mean the arrest of all progress. All organic evolution, as we know,
depends upon the struggle between creatures possessing various varia-
tions and the consequent selection of those variations which con-
stitute their possessors best adapted or fitted to the particular environ-
ment. If there is no variation there can be no evolution. To aim at
the suppression of variation, therefore, on supposed eugenic grounds
(which would be involved in aiming at any uniform type of mankind)
would be to aim at destroying the necessary condition of all racial
progress. The mere fact that all the critics of race-culture attribute
to evolutionists, of all people, the desire to suppress variation, is a
pathognomonic symptom of their critical quality.
And, of course, quite independently of the evolutionary function of
variation — though this is cardinal and must never be forgotten by the
politician of any school, since what we call individuality is variation
on the human plane — the value of variation in ordinary life is wholly
THE PROMISE OF RACE CULTURE 589
incalculable. It is not merely that, as Mr. Galton says, "There are a
vast number of conflicting ideals, of alternative characters, of incom-
patible civilizations; but they are wanted to give fullness and interest
to life. Society would be very dull if every man resembled the highly
estimable Marcus Aurelius or Adam Bede." The question is not
merely as to the interest of life. Much more important is the fact
that it takes all sorts to make a world. What is the development of
society but the result of the psychological division of labor in the social
organism? And how could such division of labor be carried out if
we had not various types of laborers ? What would be the good of
science if there were no poetry or music to live for? How would
poetry and music help us if we had not men of science to protect our
shores from plague ? Obviously the existence of men of most various
types is a necessity for any highly organized society. Even if eugenics
were capable — as it is not — of producing a complete and balanced
type, fit up to a point to turn out a satisfactory poem, a satisfactory
symphony or a satisfactory sofa, the utmost could not be expected of
such a man in any of these directions. In a word, as long as their
activities are not antisocial, men cannot be of too various types. We
require mystic and mathematician, poet and pathologist. Only, we
want good specimens of each. "The aim of eugenics," says
Mr. Galton, "is to represent each class or sect by its best specimens;
that done, to leave them to work out their common civilization in their
own way Special aptitudes would be assessed highly by those
who possessed them, as the artistic faculties by artists, fearlessness
of inquiry and veracity by scientists, reUgious absorption by mystics,
and so on. There would be self-sacrificers, self-tormentors, and
other exceptional ideaHsts." But at least it is better to have good
rather than bad specimens of any kind, whatever that kind may be.
Mr. Galton thinks that all except cranks would agree as to including
health, energy, ability, manliness, and courteous disposition amongst
qualities uniformly desirable — alike in poet and pathologist. We
should desire also uniformity as to the absence of the antisocial
procHvities of the born criminal. So much uniformity being granted,
let us have with it the utmost conceivable variety — more, mdeed,
than most of us can conceive.
This point, of course, is cardinal from the point of view of practice.
No progress could be made with eugenics, it would be impossible even
to form a Eugenics Education Society, if each of us were to regard
the particular type he belongs to as the ideal, and were to seek merely
590 EVOLUTION, GENETICS, AND EUGENfCS
to obtain the best specimens of that type. The doctrine that it takes,
all sorts to make a world — a doctrine very hard for youth to learn, yei
unconsciously learnt by all who are capable of learning at all — must
be regarded as cardinal truth for the eugenist. All he asks for, all he
is wise in seeking, is good specimens rather than bad. Poets certainly
but not poetasters; jesters certainly, but not clever fools.
Time and its treasure. — -Taking the modern estimates of the
physicists, we are assured that the total period of past human existence
is very brief compared with what may reasonably be predicted.
Granted, then, practically unlimited time, what inherent limits are
there to the upward development of man as a moral and intellectual
being? Shall we answer this question by a study of the nature of
matter ? Plainly not. Shall we answer it by a study of the nature
of mind ? Surely not, for the study of the mind cannot inform us as
to what mind might be. One source of guidance alone we have, and
this is the amazing contrast which exists between the mind of man at
its highest, and mind in its humblest animal forms; or shall we say
even between the highest and lowest manifestations of mind within
the human species ? The measureless height of the ascent thus indi-
cated offers us no warrant for the conclusion that, as we stand on the
heights of our life, our "glimpse of a height that is higher" is only a
hallucination. On the contrary.
There is no warrant whatever for supposing that the forces which
have brought us thus far are yet exhausted; they have their origin in
the inexhaustible. Who, gazing on the earth of a hundred milUon
years ago, could have predicted life^ — ^could have recognized, in the
forces then at work and the matter in which they were displayed, the
promise and potency of all terrestrial hfe ? Who, contemplating Ufe
at a much later stage, even later mammalian, could have seen in the
simian the prophecy of man ? WTio, examining the earUest nervous
ganglia, could have foreseen the human cerebrum ? The fact that we
can imagine nothing higher than ourselves, that we make even our gods
in our own image, offers no warrant for supposing that nothing higher
will ever be. What ape could have predicted man, what reptile the
bird, what amoeba the bee ? " There are many events in the womb of
time which will be deHvered " and the fairest of her sons and daughters
are yet to be.
But even grant, for the sake of the argument, that the intelligence
of a Newton, the musical faculty of a Bach, the moral nature of any
good mother anywhere, represent the utmost hmits of which the
THE PROMISE OF RACE CULTURE 591
evolution of the psychical is capable. There is every reason to deny
this, but let us for the moment assume it true. There still remains
the thought of Wordsworth, "What one is, why may not millions
be?" — a thought to which Spencer has also given utterance. VVliat
is shown possible for human nature here and there, he says, is con-
ceivable for human nature at large. It is possible for a human being,
whilst still remaining human, to be a Shakespeare or a St. Francis;
these things are thus demonstrably within the possibilities of human
nature. It is therefore at the least conceivable that, in the course of
almost infinite time (even assuming, say, that intelligence must ever
be hmited, as even Newton's intelligence was limited) — some such
capacities as his may be common property amongst men of the
scientific type; and so with other types. We may answer Words-
worth that there is no bar thrown by Nature in the way of such a hope.
What is possible. — This of course is speculation and of no
immediate value. I would merely remind the reader that the doctrine
of optimism, as regards the future of mankind, which the principles of
race-culture assume and which they desire to justify, was definitely
shared by the great pioneers to whom we owe our understanding
of those principles. Notwithstanding grave nervous disorder, such
as makes pessimists of most men, both Darwin and Spencer were
compelled by their study of Nature to this rational optimism as
regards man's future. The doctrine of organic evolution, and of the
age-long ascent of man through the selection of the fittest (who have,
on the whole, been the best) for parenthood, is one not of despair but
of hope. Exactly half a century ago it struck horror into the minds of
our predecessors. Man, then, is only an erected ape, they thought —
as if any historical doctrine, however true, could shorten the dizzy
distance to which man has climbed since he was simian; and man
being an ape, they thought his high dreams palpably vain. But the
measure of the accomplished hints at the measure of the possible, and
the value of the historical facts lies not in themselves, all facts as
such being as dead as are the individual atoms of the living body, but
in the principles which grow out of them. It is of no importance as
such that man has simian ancestors; it is of immeasurable importance
that he should learn by what processes he has become human, and by
what, indeed, they became simian — ^which would have been a proud
adjective for its own day. The principles of organic progress matter
for us because they are the principles of race-culture, the only sure
means of human progress. Our looking backwards does not turn as
592 EVOLUTION, GENETICS, AND EUGENICS
into pillars of salt, but teaches us that the best is yet to be, and how
alone it is to be attained.
Elsewhere the optimistic argument of Wordsworth is quoted.
Here also John Ruskin:
"There is as yet no ascertained limit to the nobleness of person
and mind which the human creature may attain, by persevering
observance of the laws of God respecting its birth and training."
And Herbert Spencer:
" What now characterizes the exceptionally high may be expected
eventually to characterize all. For that which the best human nature
is capable of, is within the reach of human nature at large."
And Francis Galton:
"There is nothing either in the history of domestic animals or in
that of evolution to make us doubt that a race of sane men may be
formed, who shall be as much superior, mentally and morally, to the
modern European, as the modern European is to the lowest of the
Negro races.
"It is earnestly to be hoped that inquiries will be increasingly
directed into historical facts, with the view of estimating the possible
effects of reasonable political action in the future, in gradually raising
the present miserably low standard of the human race to one in which
the Utopias in the dreamland of philanthropists may become practical
possibilities."
Conclusion — eugenics and religion. — In an early chapter it wa^
attempted to show that eugenics is not merely moral, but is of the
very heart of morality. We saw that it involves taking no life, that
rather it desires to make philanthrophy more philanthropic, that, at
any rate so far as this eugenist is concerned, it recognizes and bows
to the supreme law of love; and claims to serve that law, and the
ideal of social morality, which is the making of human worth. Eugen-
ics may or may not be practicable, it may or may not be based upon
natural truth, but it is assuredly moral; though I, for one, would pro-
claim eternal war between this real morality and the damnable sham,
which approves the unbridled transmission of the most hideous
diseases, rotting body and soul, in the interests of good.
And if reUgion, whatever its origin and the more questionable
chapters in its past, be now "morality touched with emotion,"
I claim that eugenics is religious, is and will ever be a religion. Else-
where I have attempted to show that religion has survived and will
survive because of its survival-value — its services to the Ufe of the
THE PROMISE OF RACE CULTURE 593
societies wherein it flourishes. The religion of the future, it was
sought to argue, will be that which "best serves Nature's unswerving
desire — fullness of life." The Founder of the Christian religion said,
"I am come that ye might have Ufe, and that ye might have it more
abundantly." It is higher and more abundant life that is the eugenic
ideal. Progress I define as the emergence and increasing dominance
of mind. Of progress, thus conceived, man is the highest fruit hitherto.
He is also its appointed agent and eugenics is his instrument.
To this end he must use all the powers which have blossomed in
him from the dust. He must claim Art: and indeed in Wagner's
great music-drama, at the moment when the prophetic Briinnhilde
tells Sieglinde who has just lost her mate that she, the expectant
mother, may look for the resurrection of the dead and the Ufe of the
world to come in the child Siegfried; and when the heroic theme is
pronounced for the first time and followed by that which signifies
redemption by love; then, I think, the eugenist may thrill not merely
to the music, nor the humanity of the story, but to the spiritual and
scientific truth which it symbolizes.
If the struggle towards individual perfection be religious, so,
assuredly, is the struggle, less egoistic indeed, towards racial perfection.
If the historic meaning and purport of religion are as I conceive them,
and if its future evolution may thence be inferred, there can be no
doubt in the prophecy that in ages to come those high aspirations and
spiritual visions which astronomy has dishoused from amongst the
stars, and which, at their best, were ever selfish, will find a place on this
human earth of ours. If we have transferred our hopes from heaven
to earth and from ourselves to our children, they are not less religious.
And they that shall be of us shall build up the old waste places; for we
shall raise up the foundations of many generations,
"We feel the high tradition of the world
And leave our spirits on our children's breasts."
BIBLIOGRAPHY
Babcock, Ernest Brown, and Clausen, Roy Elwood. Genetics in Rela-
tion to Agriculture. The McGraw-Hill Book Co., 1918.
Bateson, William. Problems of Genetics. Yale University Press, 1913.
Castle, William E. Genetics and Eugenics. Harvard University Press,
3d ed., 1924.
Child, Charles Manning. "Regulatory Processes in Organisms." Jotir.
Morph., XXII (1911).
Conklin, Edwin Grant. Heredity and Environment. Princeton Univer-
sity Press, 3d ed., 1920.
Coulter, John M., and Coulter, Merle C. Plant Genetics. University
of Chicago Press, 1918.
Crampton, Henry Edward. The Doctrine of Evolution. The Columbia
University Press, 191 1.
Darwin, Charles. The Origin of Species. D. Appleton & Co., with addi-
tions from the sixth and last edition, 1893.
Darwin, Francis. Life and Letters of Charles Danvin. John Murray,
London, 1888.
Dendy, Arthur. Outlines of Evolutionary Biology. D. Appleton & Co.,
1916.
De Vries, Hugo. Species and Varieties. The Open Court PubUshing Co..
1904.
Downing, Elliot Rowland. The Third and Fourth Generation. Univer-
sity of Chicago Press, 1918.
Eimer, Theodore. On Orthogenesis. The Open Court Publishing Co.,
1898.
Eugenics, Genetics and the Family. (Papers of the Second International
Congress of Eugenics.) Williams & Wilkins Co., 1923.
Gadow, Hans. The Wanderings of Animals. Cambridge University Press,
1913-
GuYER, Michael F. Being Well-Born. Bobbs-Merrill Co., 191 8.
. "Immune Sera and Certain Biological Problems." Amer. Natur.,
LV (1921).
Henderson, Lawrence J. The Fitness of the Environment. The Mac-
millan Co., 1913.
Herbert, S. The First Principles of Evolution. Adarn and Charles Black,
London, 1913.
Jones, Donald F. Genetics in Plant and Animal Improvement. John
Wiley & Sons, 1925.
594
BIBLIOGRAPHY 595
Jordan, David Starr, and Kellogg, Vernon L. Evolution and Animal
Life. D. Appleton & Co., 1908.
JuDD, John W. The Coming of Evolution. Cambridge University Press,
1911.
Kellogg, Vernon L. Darwinism To-Day. Henry Holt & Co., 1907.
Le Conte, Joseph. Evolution. D. Appleton & Co., 2d ed., 1897.
LocY, W1LLLA.M A. The Main Currents of Zoology. Henry Holt & Co., 1918.
Lull, Richard Swann. Organic Evolution. The Macmillan Co., 191 7.
McFarland, Joseph. Biology, General and Medical. W. B. Saunders Co.,
3d ed., 1918.
Metcalf, Maynard M. An Outline of the Theory of Organic Evolution.
The Macmillan Co., 191 1.
Morgan, Thomas H. Evolution and Adaptation. The Macmillan Co.,
1903.
. A Critique of the Theory of Evolution. Princeton University Press,
1916.
Morgan, Sturtevant, Muller, and Bridges. The Mechanism of Men-
delian Heredity. Henry Holt & Co., 191 5.
Newman, Horatio H. "The Limits of Hereditary Control in Armadillo
Quadruplets: A Study of Blastogenic Variation." Jour. Morph.,
XXII (1911).
. The Biology of Twins. University of Chicago Press, 1915.
. Vertebrate Zoology. The Macmillan Co., 1920.
. "Twins and the Relative Potency of Heredity and Environment
in Development." Publications of the American Sociological Society,
1922.
. The Physiology of Twinning. University of Chicago Press, 1923.
NuTTALL, G. H. F. Blood Immunity and Blood Relationship. Cambridge
University Press, 1904.
Nutting, C. C. "The Relation of MendeHsm and the Mutation to Theory
Natural Selection." Science, N.S., LIII (Feb. 11, 1921).
OsBORN, Henry Fairfield. From the Greeks to Darwin. The Macmillan
Co., 1908.
. The Origin and Evolution of Life. Charles Scribner's Sons, 1918.
Plate, Ludwig. Uber die Bedeutimg des Darwin' schen Selectionsprincips
und Proleme der Artbildung. Engelmann, Leipzig, 2d ed., 1903.
Popenoe, Paul, and Johnson, Roswell H. Applied Eugenics. The Mac-
millan Co., 1918.
Romanes, George J. Darwin and after Darwin. The Open Court Pub-
lishing Co., 1892.
Saleeby, Caleb Williams. The Promise of Race Culture. Moffat, Yard
& Co., 1909.
Schuchert, Charles. Text-Book of Geology: Part II, Historical Geology.
John Wiley & Sons, 191 5.
596 EVOLUTION, GENETICS, AND EUGENICS
Scott, William Berryman. The Theory of Evolution. The Macmillan
Co., 1911.
Shelford, Victor E. Animal Communities in Temperate America. Uni-
versity of Chicago Press, 1913.
Shull, a. Franklin. Principles of Animal Biology. The McGraw-Hill
Book Co., 1920.
Steinmann, Gustav. Die Abstammungslehre. Engelmann, Leipzig, 1908.
Taylee, J. L. "The Scope of Natural Selection." Natural Science, Vol.
XV., 1899.
Thayer, Gerald H. Concealing Coloration in the Animal Khigdom. The
Macmillan Co., 1918.
Thomson, J. Arthur. Darwinism and Human Life. Henry Holt & Co.,
1909.
. Heredity. John Murray, London, 1907.
Walter, Herbert Eugene. Genetics. Revised ed. The Macmillan Co.,
1922.
Whitman, Charles Otis. "The Problem of the Origin of Species." Pro-
ceedings of Congress of Arts and Science, Universal Exposition, St. Louis,
1906.
WiGGAM, Albert Edward. The Fruit of the Family Tree. Bobbs-Merrill
Co., 1924.
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ture, Bull. 905, 1920.
GLOSSARY
Acquired character. — Any change in the body (soma) of an individua
due to change of function or change of environment. Same as Modification.
Adaptation. — Any character, structural or functional, in an organism
that helps to enhance the fitness of that organism.
Agamic reproduction. — See Asexual reproduction.
Allelomorph. — One of a pair of contrasted characters; one of a pair of
genes (factors) determining the development of such characters, and be-
lieved to occupy equivalent loci in homologous chromosomes: a Mendelian
pair.
Analogous structures. — Any two or more structures that subserve the
same function in the different kinds of animals or plants, but which arise
from different embryonic rudiments and have fundamentally different
structural constitutions. Contrast with Homologous structures.
Anthropoid. — Literally, manlike; refers especially to the manlike apes.
Apogamy. — A term used by botanists, synonymous with Partheno-
genesis.
Asexual reproduction. — Any method of reproduction that does not in-
volve the union of gametes. (Some authorities consider parthenogenesis
as a phase of asexual reproduction.)
Atavism, — The cropping out of ancestral characters in an individual.
Atrophy. — The dwindling away of a structure in an individual or in a
race.
Autosome. — .\ny chromosome other than those that are recognized as
especially involved in the heredity of sex. See Sex chromosome.
Biometry. — That branch of biology that investigates organic differences
by statistical methods.
Blastula. — An early embryonic stage consisting tj^Dically of a hollow ball
of cells.
Castration. — The removal from an organism of the gonads (testes or
ovaries).
Catastrophism. — The idea, held by Cuvier and others, that the geologic
strata were sharply marked off from one another because great catastrophies
had brought each era to an end, and that all life was destroyed in each
catastrophe. Contrast with Uniformitarianism.
Cell. — The smallest unit of living substance that can exist in a free
state; the unit out of which tissues are composed.
Centrosome. — An organ of a cell which seems to be a center of forces
that express themselves in mitotic cell division.
Character. — One of many structural or functional details that character-
ize an individual or a race.
597
598 EVOLUTION, GENETICS, AND EUGENICS
Chromatin. — The substance of which chromosomes are largely com-
posed, the chemical composition of which is not exactly known; supposed
to be the hereditary substance; so called because it stains readily with certain
dyes and can be easily seen under the microscope.
Chromosomes. — The definite masses of chromatin that have a char-
acteristic number, size, and shape in any given species.
Combinations. — New organic conditions due to a new assortment of old
factors already present in the germ plasm of parents.
Commensalism. — The habitual living together of two or more different
species of animals or plants, involving more or less interdependence.
Crossing-over. — Exchange of genes (factors) between homologous chro-
mosomes, believed to occur during synapsis.
Cytology. — The detailed microscopic study of the structure of cells,
especially of germ cells.
Cytoplasm. — All of the living material of the cell outside of the nucleus.
Determiner. — See Gene or Factor.
Dihybrid cross. — A crossing of two parents diflfering from each other
in only two pairs of allelomorphs.
Diploid. — The maximum or full (duplex) number of chromosomes, found
in body cells and in the unmaturated germ cells; twice the gametic or
haploid number.
Dominant. — A term applied to that member of an allelomorphic pair of
characters that has the capacity of manifesting an effect wholly or partly
to the exclusion of the effect of the other member (the recessive).
Duplicate factors (genes). — Two or more factors located in different
chromosomes, either of which produces the same result.
Egg. — The female germ cell; more precisely, the female gamete.
Environment. — The sum of all influences upon the organism that have
their origin outside of the body.
Epigenesis. — The doctrine that the germ cell is absolutely or relatively
structureless and that differentiation arises de novo through the interaction
of the protoplasm and the environment. Contrast with Preformation.
Fi generation. — The first hybrid generation of a hybrid cross; exhibits
only the dominant characters of the two parents.
Fa generation. — The offspring resulting from the interbreeding o\ indi-
viduals of the F, generation.
Fj generation. — The offspring resulting from the interbreeding of indi-
viduals of the Fj generation.
Factor. — A unit of inheritance situated at some particular locus of a
particular chromosome and transmitted according to the laws of Mendel,
a determiner, or gene.
Faunas. — Groups of animals inhabiting a given geographic region ur
geologic period.
GLOSSARY 5<)9
Fertilization. — The union of male and female gametes and the conse-
quent initiation of development of a new individual.
Floras. — Groups of plants inhabiting a given geographic region or
geologic period.
Gamete. — A mature male or female reproductive cell, containing the
haploid number of chromosomes; an egg or a spermatozoon.
Gametic Reproduction. — See Sexual reproduction.
Gastrula. — A stage in the development of metazoan animals in which
the embryo consists of two germ layers, ectoderm and endoderm.
Gemmules. — Hypothetical inheritance units involved in Darwin's pro-
visional theory of pangenesis.
Gene. — See Factor.
Genetics. — The science which seeks to explain the resemblances and
differences in organism related by descent; the modem analytic and experi-
mental study of variation, heredity, and sex.
Genotype. — A group of individuals all of which are alike in their genes
or factors. Contrast with Phenotype.
Genotypic. — Pertaining to the germinal or hereditary constitution of an
organism. Contrast with Phenotypic.
Genus. — An arbitrary group in the systematic classification of animals
or plants, ranking above the species and containing one or more species
possessing structural characters differing from those of other genera.
Germ cell. — A cell specialized for sexual reproduction. Matured germ
cells are known as gametes.
Germ plasm. — That part ot tlie cell protoplasm which is believed to be
the material basis of heredity and is transferred from one generation to the
next. Contrast with Somotoplasm or Soma.
Germinal continuity. — The concept of an unbroken stream of germ plasm
from generation to generation back to the beginning of life.
Gonads. — The organs (ovaries or testes) that contain the reproductive
cells or germ cells, and sometimes also contain glandular tissue that func-
tions in the differentiation of secondary sexual characters.
Gynandromorph. — An animal in which one part exhibits male characters
and another part female characters.
Habitat. — The complex of environmental factors making up the sur-
roundings of any species or race.
Haploid. — -The reduced (one-half) number of chromosomes present only
in gametes. See Diploid.
Hermaphrodite. — An individual organism possessing both ovaries and
testes.
Heterogenesis. — See Mutation.
Heterozygote. — An individual or a zygote resulting from the union of
unlike gametes.
6oo EVOLUTION, GENETICS, AND EUGENICS
Heterozygous. — Having the allelomorphic pairs composed of dissimilar
elements, resulting in the production of more than one kind of gametes.
Heterozygous sex. — The sex in which the members of the chromosome
pair that determines sex are unlike.
Homologous structures. — Any two structures either in the same or in
different individuals or species that arise from equivalent embryonic rudi-
ments and have the same structural relations to other parts, irrespective of
the function subserved. Contrast with Analogous structures.
Homozygote. — An individual or a zygote resulting from the union of like
gametes.
Homozygous. — Having the allelomorphic pairs composed of similar ele-
ments, resulting in the production of only one kind of gamete.
Homozygous sex. — The sex in which the members of the chromosome
pair that determines sex are alike.
Hormone. — A substance, secreted by one of the endocrine glands, that
affects the development of or the functioning of some other part or parts of
the body.
Indigenous. — ^Living naturally in any country or climate. Contrast
with Introduced.
Induction. — Any change in a germ cell or an embryo that persists for
only a few generations and then disappears. Contrast with Mutation.
Introduced. — Brought in from another coimtry and living more or less
successfully under foreign conditions. Contrast with Indigenous.
Isolation. — The process of separating one section or strain of a species
from another section or from the main body of the species; believed to
facilitate the establishment of new species.
Lamarckian. — Pertaining to Lamarck's doctrine of the inheritance of
acquired characters.
Lamarckism. — The theory of the inheritance of acquired characters.
Larva. — A self-supporting embryo; a developmental stage of an animal
in which various adaptive structures for self-support appear that may or
may not be significant for the development of adult structures.
Lethal. — Producing death; destructive of life.
Linin. — ^An achromatic or non-chromatin substance that forms a net-
work of threads in the nucleus.
Linkage. — The type of inheritance in which genes (factors) tend to
remain together in transmission from generation to generation, owing to
their location in the same chromosome.
Locus {pi. loci). — A definite point or region in a given chromosome at
which is located a genetic factor or gene.
Maturated germ cell. — See Gamete.
Maturation. — The process through which germ cells pass in preparation
for fertilization, usually resulting in the formation of gametes.
Mitosis. — The normal process of cell division, involving the formation
GLOSSARY 60 1
of spindle, chromosomes, etc., and resulting in longitudinal splitting of each
chromosome.
Modification. — A change in the body or soma of an individual due to
functioning or to use and disuse; same as Acquired character.
Monohybrid cross. — A cross between two individuals differing in only
one pair of allelomorphs.
Morphological. — Structural; opposed to physiological.
Multiple allelomorphs. — Different factors or genes occupying the same
locus of homologous chromosomes; the character conditioned by such factors.
Multiple factors. — Two or more factors, usually alike in character, which
unite in various numbers to produce different quantitative expressions of
one character. Same as DupUcate factors.
Mutant. — An individual having a different genotypic constitution from
its parents, as the result of a change in the germ plasm, and not as the result
of segregation or crossing-over. Some authorities include the type of
changes due to chromosomal aberrations under the head of mutants, while
others limit mutants to those resulting from factor changes.
Mutation. — The germinal change resulting in the production of a
mutant. The definition of mutation differs according to differences of
opinion as to what should be included under the definition of a mutant.
Contrast with Induction.
Neo-Darwinian. — A descriptive term applied to theories based on
Darwin's theory of natural selection.
Neo-Lamarckian. — A descriptive term applied to theories based on
Lamarck's theory of the inheritance of acquired characters.
Neo-mutationist. — A modem adherent of the mutation theory; especial-
ly one who is interested chiefly in tracing the origin of germinal changes that
are responsible for the appearance of mutants.
Non-disjunction. — The failure of the two members of a pair of homolo-
gous chromosomes to separate in cell division, with the result that they both
pass into one daughter-cell, making one too many chromosomes in one
gamete and one too few in the other.
Nucleus. — The body within a cell that contains the chromatin.
Ontogenetic. — Pertaining to the life history of the individual. Con-
trast with Phylogenetic.
Ontogeny. — The developmental history of the individual; same as
development or somatogenesis. Contrast with Phylogeny.
Orthogenesis. — The apparent fact that races or groups of animals or
plants vary progressively along definite lines, each variation forming the
threshold of departure for the next and the whole series forming a definite
sequence; definitely directed evolution.
Ovule. — The body that contains the egg of flowering plants and becomes
the seed after fertilization and maturation.
Ovum {pi. ova). — The egg; the type of gamete produced by a female.
Paneenesis. — A provisional theory as to the mechanism of hereditary
6o2 EVOLUTION, GENETICS, AND EUGENICS
transmission devised by Charles Darwin. It implies the idea that the germ
cells are made up through the process of collecting from the blood stream
"gemmuJes" or representatives of all parts of the body. In this way each
structure of the adult parent would be present in the germ cell and would be
transmitted to the ofTspring.
Panmixia. — An early theory of Weismann designed to account for the ru-
dimentation of structures; almost equivalent to cessation of natural selection.
Parthenogenesis. — The development of an egg without fertilization.
A process in animals equivalent to Apogamy in plants.
Peculiar. — A term used technically to describe a species or higher group
of organisms occurring in one region and nowhere else.
Pedigree. — An ancestral history; a genealogical tree.
Phenotype. — A group of individuals which are alike somatically and
look alike, but which may differ germinaily; the sum of the visible features
of an individual or a race. Contrast with Genotype.
Phenotypic. — Pertaining to the somatic appearance of the individual
or group of individuals. Contrast with Genotypic.
Phylogenetic. — Pertaining to the ancestral history of a group. Con-
trast with Ontogenetic.
Phylogeny. — ^The history of the evolution of a species or a group, as
distinguished from Ontogeny.
Preformation. — A theory that the individual is preformed in the egg
and needs only to grow or to unfold in order to reach its definitive state.
Contrast with Epigenesis.
Protoplasm. — The living substance of cells.
Pure line. — The descendants of a single individual that have not under-
gone any germinal change.
Quadrumana. — An old name for apes and monkeys implying that their
hands and feet are both grasping appendages like hands.
Recessive. — The opposite of dominant.
Reduction division. — That division in germ cells when the chromosome
number is reduced from the diploid to the haploid condition; usually one
of the two maturation divisions of a germ cell.
Segregation. — -The separation into separate gametes of the two members
of a pair of allelomorphs, resulting in gametes pure for one or the other of a
pair of allelomorphic genes.
Serology. — That branch of experimental biology or medicine that deals
with the reactions of the blood to foreign materials and the production of
antibodies; the science of serums.
Sex chromosome. — The particular chromosome (the X-chromosome, for
example) that seems to carry the factors for sex and through which sex is
inherited.
Sex linked.— A term applied to characters located in the sex chromo-
somes.
Sex ratio. — The relative proportion of the two sexes in a population
GLOSSARY
603
Sexual reproduction. — That mode of reproduction that involves the
union of gametes to form a zygote. Same as Gametic reproduction.
Simian. — Pertaining to apes.
Soma. — The body of an organism as contrasted with the germ cells.
Somatic. — Pertaining to the body. Contrast with Germinal.
Somatoplasm. — Same as Soma. Contrast with Germ plasm.
Special creation. — A popular doctrine holding that all species existing
today were created by divine fiat within a few days and that they have not
materially changed.
Species. — A group of varieties or a single variety which, in botanical or
zoological characters and genetic relationship, can be differentiated from all
other groups or varieties.
Sperm. — A short term for the male gamete.
Spermatozoon. — The longer technical term for the functional male
gamete.
Sporadic. — Occurring singly, scatteringly, or apart from others of the
same kind.
Symbiosis. — See Commensalism.
Systematist. — A taxonomist or specialist in the science of classification.
Synapsis. — The pairing off and lying together of homologous chromo-
somes, prior to the maturation division.
Taxonomy. — The science of classification.
Teleology. — The doctrine that the processes of nature were originally
purposed or planned; the doctrine of design.
Tetraploidy. — That chromosomal condition where the germ cells in some
way acquire four times the haploid number of chromosomes; thus some so-
called plant mutants are tetraploid.
Trihybrid cross. — A hybridization experiment in which the parents differ
with regard to three pairs of allelomorphs.
Triploidy. — That chromosomal condition where the germ cells in some
way acquire three times the haploid number of chromosomes; some so-called
plant mutants are triploid.
Uniformitarianism. — The theory that the changes of the past may be
interpreted in terms of the changes of the present, and that most changes
are of a slow, gradual kind. Contrast with Catastrophism.
Variety. — A group of individuals within a species which resemble one
another but differ in some respects from other members of the species.
X-chromosome. — The so-called sex-chromosome.
Y-chromosome. — The chromosome that usually pairs off with the X-
chromosome in synapsis. It does not seem to carry any genetic factors
except possibly that of fertility.
Zygote. — ^A combination germ cell formed by the fusion of two gametes;
the individual, with the diploid number of chromosomes, that result from
the development of a fertilized egg.
Zygotically. — Pertaining to the zygote or fertilized egg.
INDEX
INDEX
Abiogenesis, 12
Abraxas, 415
Acer, 494
Acquired characters: inheritance of , 19-
20, 445-47; discussion by E. G. Conk-
lin, 456-62; lack of evidence for, 458-
59; misunderstandings concerning,
449-56; other side of the question,
462-64; recent experiments appar-
ently favoring, 464-74; statement of
the problem, 449, 457-6o
Adaptation, 11, 30, 194-214; classifica-
tion of adaptations, 199-200; Osbom's
laws of, 211-14
Adaptive radiation, law of, 81-2
Agassiz, L., 213-14
Albinos, different kinds of, 389-90
AUelomorphic, characters in heredity,
345, 393
Allen, E. J., 191
Altenburg, 448
Amphioxus, 127
Amphisbaenidae, 103
Analogous, versus homologous struc-
tures, 64-65
Analogy, principle of, 64-65; versus
homology, 64-65
Anaxagoras, 12
Anaximander, 11
Anaximenes, 11-12
Ancestral inheritance, Galton's law of,
436-37
Angioslomum nigrovenosum, 402
Anti-evolution campaign, 45-46
Anti-lens serum, Guyer's experiments
with, 464-72
Apartness of the germ plasm, 31, 308,
463, 464 •
Aphids, 401
Appendix vermiformis, in man and apes,
91-92
Apleryx aiislralis, 79-So
Aquinas, Thomas, 8, 15
Aristotle, 13-14, 18
Arithmetical mean, 432
Armadillo quadruplets: and classifica-
tion, 106-7; and the fundamental
assumption about evolution, 62-63;
and the relative potency of heredity
and environment, 536-38; and sex-
determination, 397-98
Armadillos, 62-63, 16S
Artificial selection, 25-26
Asexual reproduction, 300
Aspergillus nigcr, 453
Assortment, independent, 392-93
Atavism, 13
Atropa, 352
Augustine, 8, 15
Autosomes, 400, 403-4
Azores, fauna of, 174
Babcock, E. B., 295, 323-38, 383-94, 399
Bacon, F., 15, 285
Bagg, H. J., 472, 503
Bakewell, R., 511
Balanoglossus, 126-27
Bascanion antlionyi, loi
Bat, wing of, 71
Bateson, W., 7, 21, 43-46, 339, 355, 372,
434-35, 475
Bathmism, 35
Bauer, E., 500
"Beagle," Darwin's voyage on the, 23,
25-26
Beebe, W., 332-33
Beeton, ]\I., 462, 468
Begonia, 463
Bell, A. G., 464, 471, 473
Bellamy, A. W., 427
Belling, 496
Bembidium, 180
Bequerel, A. H., 284
Bergson, H., 34
Bermudas, fauna of, 174-76
Bibliography, 594-96
Bimodal and multimodal curves, 434-35
607
6o8
EVOLUTION, GENETICS, AND EUGENICS
Biometry: discussion of, 430-40; rise
and vogue of, 38-39
Birds: rudimentary teeth of, 130; wing
of, 71
Birgiis latro, 75-76, 78
Bison aniiquus, 156
Blakeslee, A. F., 376, 489, 496, 500
Blastoderm, 125
Blastula, 125
Blends, in heredity, 374-76
Blood-precipitation tests, evidences
from, 60, 108-12
Bonnet, R., 16
Boyd-Dawkins, 98
Brachydactylism, 518-19; inheritance
of, 358-59
Bridges, C. B., 359, 403, 416, 421, 496
Briinn, 40, 41
Buffon, G. L. L., 7, 15-17
Bullen, G. E., 228
Cameline: forefoot, 146: skull, evolu-
tion of, 145
Camels, fossil pedigree of, 144-46
Cape de Verde Islands, fauna of, 177
Carex, 493
Carnot, S., 286
Carsinas maenas, 265
Castle, W. E., 39, 40, 41, 43, 270, 295,
358, 390-91, 424, 427-28, 443-44,
459-60
Cataract, inheritance of, 519
Catastrophism, 22-23
Cave animals, eyes of, 81-82, 204-5
Cebidae, no
Cell: diagram of typical, 304; division,
direct, 303-4, division, indirect or
mitotic, 303-4, 362-65; division, so-
matic, 362-65
Cenogenetic, 123
Centrosome, 303-5
Cesnola, 266
Cetacea, 128
Chamberlin, T. C, 57
Chambers, R., 23, 26
Chapin, C. V., 580
Child, C. M., 196-97, 463
Child mortality in long-lived families,
561
Chimpanzee, 159
Chromatin, 303; interchange between
homologous chromosomes, 367; nu-
cleolus, 303
Chromosomes, 303, 304-5, 326-27; con-
jugation of pairs of, 366; of Drosophila,
310; in heredity, 315-16; independent
distribution of, 367-68; individuality
of, 309; maps to show loci of genes,
422-23, 426; of mosquito, 327; num-
ber and appearance, 306; pairs of,
305, 366; reduction of, 310-11, 365;
and sex in Drosophila, 368-82; sig-
nificance of, 274-75
Clark, J. M., 155
Classification: basis of, 101-3; evi-
dences from, 60, 101-3; international
code of, loi; method of, 104-5
Clausen, R. E., 295, 323-38, 360-71, 399
Cleavage of egg, 307
Cocoa-nut crab, 75-76, 78
Coefficient of correlation, 435-36
Coincident selection, 277-7S
Color blindness, heredity of, 408-9
Color in animals, 205-11
Coluber anthonyi, loi
Colubridae, loi
Colubrinae, loi
Commensalism, as adaptation, 202-3
Communal life, as adaptation, 203-4
Comparative anatomy, evidences from,
60, 66-100
Conklin, E. G., 411-12, 435, 440, 456-
63
Conjugation, of homologous chromo-
somes, 366
Convergence, Osborn's law of, 211-13
Cope, E. D., 39
Correlation: coefficient of, 434-35;
tables, 435
Correns, C, 40, 43. 339, 352-53, 374-75,
383
Cossonidae, 179
Coulter, J. M., 345-51. 372-8?
Coulter, M. C, 345-51, 372-87
Crampe, H., 511
Crampton, H. E., 5, 32, 2S0
Crataegus, 4
Cretins of Aosta, 460-61, 522-23, 575-
76
INDEX
609
Crisscross inheritance, 412
Cross-breeding, 507-10
Crossing-over, in Mendelian heredity,
419-22
Cuenot, L., 357
Cumulative factors, 394
Curie, P., 284
Cuvier, G., 19, 21-22
Cytogenic reproduction, 300-301
Cytoplasm, 325; in inheritance, 310
Dakin, W. J., 218
Daphnia, 461
Darbishire, A. D., 352, 357
Darwin, C, 4-6, 8, lo-ii, 17, 19, 23-31)
45, 97, 102, 104-5, 132-33, 138, 168,
214, 219-20, 222, 228-53, 267-68,323,
386, 456, 521, 586
Darwin, E., 3, 16-17, 18, 21, 446
Darwinism, 7, 8; background of, 194-
227; critique of, 254-71; defense of,
general, 262-66; objections to, 256-
6x
Dasypus novenicinclus, 62-63, 106-7,
397-98
Datura, 339, 489
Davenport, C. B., 288, 374, 377, 459,
482, 493-94, 573
Davis, B. M., 489
De Candolle, A., 23, 106
Defectives, segregation of, 575-76
Democritus, 12
Dendy, A., 142, 144
Descartes, R., 15
Determinants (Weismann's), 30-32, 274
Determination of sex, 396-404
Detlefson, J. A., 472-73
Development: facts of, 1 13-14; outline
of animal development, 114, 121
De Vries, H., 7, 36-39, 43, 267, 269-70,
282, 339, 352, 388, 461, 477-90
Difficulties and objections to natural
selection as seen by Darwin, 56-62
Difflugia, 443
Digamety, female, 400-401
Dinornis gravis, 73-74, 79, 124
Dominance, Mendel's law of, 40-42,
340-41, 345, 392
Domm, L. V., 406-8
Doncaster, L., 358
Downing, E. R., 517-30
Driesch, H., 34
Drinkwater, H., 359, 528
Drosophila melanogaster, 334, 337-38;
chromosomes of, 360-62; sex-linked
heredity in, 409-12; mutations in, 448
Drummond, H., 223-24
Duplicate factors, 394
Durham, F. M., 388-89
Ears of man and apes, 92-94
Earthworms and vegetable mold, 221-23
East, E. M., 43, 376, 501
Eaton, Rev. A. E., 80
Ectoblast, 115
Edentates, distribution of, 169
Edwards, J., 580
Eimer, T., 34, 35, 273
Elderton, E. M., 566
Electric organ, of fishes, 200
Elephants, evolution of, 147-51
Elephas, 148-52; E. antiqiius, 160; E.
colunihi, 156; E. leidyi, 156
Embryology, evidences from, 1 13-21
Emerson, R. A., 500
Empedocles, 12-13
Endoblast, 125
Engrammes of Rignano, 461
Enteleche, 34
Environment: effects of, on develop-
ment, 333-34; effects of, on heredity,
328-32, 334-36; and heredity, 328-29
Eanthropus dawsoni, 164
Epicurus, 14
Epigenesis, 13
Epilepsy, inheritance of, 523
Equidae, 141-44
Equus, 142-44; E. leidyi, 156
Erigeron, 494
Escherich, 224
Eugenics: Carnegie Laboratory' of, 517;
and cruelty to children, 484, 485, 507;
defined, 570; Education Society, 509;
and Euthenics, 470-87; Gallon Labo-
ratory of, 517; positive, 577-80; and
religion, 490, 491; restrictive, 572-77;
and unemployment, 483-84; and wo-
man, 4S4
Eupagurus, 255
Euthenics, 557-80
6io
EVOLUTION, GENETICS, AND EUGENICS
Evolution, organic: causal factors of,
191; definitions of, 3-5; evidences of,
59-60; experimental, 60; nature of
proof of, 59; proof of, 57-59; and reli-
gion, 8; what it is not, 8, 9
Fabre, M., 240
Factor hypothesis, 372-91, 394-95
Factorial analysis of color in mice, 388-
89
Factors, in Neo-Mendelian heredity;
complementary, 376-80; cumulative,
382; inhibitory, 380-81; lethal, 391;
in quantitative inheritance, 382-86
Farnham, 496
Feeble-mindedness, inheritance of, 521-
22
Fertilization, 315-16
Fetal membranes, as adaptations, 201
Fierasfer acus, 202-3
Filaria sanguinis hominis, 221
Filial regression. Gallon's law of, 437-40
Flower, Professor, 99
Forficulata auricularia, 433-34
Franklin, B., 479
Freemartin, 407-8, 538-39
Fossils: actual remains, 135; Cambrian,
133; casts and impressions, 136; classi-
fication of, 135; conditions necessary
for, 136-38; Darwin's opinion as to
the adequacy of the record of the,
132-34; definition of (by T. H. Hux-
ley), 135; first recognized, 12; general
facts revealed by, 140-42; pedigrees
of well-known vertebrates, 141-51;
petrifications, 135
Fundamental assumption underlying
evidences of evolution, 61-65
Fundulus, 508
Gadow, H., 185-86
Gaertner, 508
Galapagos Islands, fauna of, 176-78
Gal ton Laboratory of Eugenics, 521,
571
Galton, Sir F., 38-39, 430, 435-40, 44i,
487, 490, 532-34, 581-85
Gametic reproduction, 301-2
Gastrula, 115
Gates, R. R., 489, 490-95, 496, 502-7
Gazelle-camels, 147
Geerts, 4
Gegenbaur, 124
Gemmules, 28, 30
Genealogical Records Office, 557, 564-65
Genetics: definitions of, 295; evidences
from, 28; methods of study of, 296;
scope and methods of, 295-97; sub-
ject matter of, 296-97
Genius: hereditary, 582; production of,
581-82; transmission of, 582-83
Genotype, 442-45
Genotypic, 442-45
Geographic distribution, evidences from,
60, 168-87
Geologic time: lapse of, 138-39; scale in
millions of years, 139
Germ-cells: early setting apart of, 309-
10; origin of new, 308-9; production
of, 364-67
Germinal continuit>% 31, 310
Germinal selection, 30-31
Germ-plasm theory, 31-32
Giekie, Sir A., 140
Gill arches in vertebrates, 125-26
Giraffe-camels, 147
Glochidia, 220
Goddard, H. H., 520-22
Goethe, J. W., 21
Goldschmidt, R., 330-31. 404
Gorilla, 86
Goring, C. F., 542-43
Goss, J., 40, 322
Graham-Smith, G. L., 109
Gray, A., 232
Greek evolutionists, 11-14
Gregory of Nyssa, 14
Gregory, W. K., 153
Griffith, C. R., 472-73
Guacanos, 144
Guhck, J. T., 32, 282
Guthrie, C. C, 459
Guyer, M. F., 310-42, 486-93, 493-94
525-26
Gynandromorphs, sex-chromosomes in.
402-3
Habitat: preference, 196-97; selection
196-97
Haeckel, E., 19, 30, 121-22
Hair of man and apes, 93-97
Haldane, 423
Hamilton, D. J., 452
INDEX
6ii
Hanson, F. B., 472
Hapalidae, no
Harris, J. A., 461, 538
Harrison, R. G., 459
Harte, Bret, 156
Harvey, W., 13
Hauser blonds, 578
Hegner, R. W., 309
Heilbom, 493
Helix hortensis, 355; H. nemoralis, 355
Henderson, L. J., 195
Heraclitus, 12, 217
Herbert, S., 209, 272-73, 277-78
Heredity: environment and training,
297-98; Galton's laws of, 436-40; in
man, 368-69; in pure lines, 442-44;
statistical study of, 435-40
Hermaphrodites, sex-chromosomes in,
402-3
Hermit crabs, 75-77
Heron, Sir R., 240
Herschel, Sir J., 3
Hesperotettix, 427
Heterogenesis theory, 36
Heterosis, 508-10
Heterozygote, 349
Hieracium, 494
Hippocrates, 396
Homo: H. heidelbergensis, 159; H. sa-
piens, 159, 161, 163-64; H. neander-
thalensis, 160-64; H. primagenius, 160
Homologies: evidences from, 60; vaHd-
ity of the principle of, 63-64; versus
analogy, 64-65
Homozygote, 349
Hooker, Sir J., 202, 254, 278, 478
Hormone theory of sex differentiation,
405-8
Hormones, 405-8
Horse: ancestry of, 8; feet and teeth in
fossil pedigree of, 143; fossil pedigree
of, 141-43, 145
Horseshoe-crab, 121
HrdU(^ka, A., 137
Hudson, W. H., 213
Human antiquity, evidences of, 164-65
Human conservation, 570-80
Humanity, future of, 166-67
Humerus, perforations of, in Quadru-
mana, 99
Hurst, C. C, 43, 352, 355, 358-59
Hutton, J., 22, 57
Huxley, T. H., 28-29, 133-34, 162, 217
Hyalodaphnia, 331, 332
Hyatt, A., 35
Hybrid vigor, 309-10
Hydra, 300
Hybridization: and the origin of species,
43; role of, in evolution, 507-8
Hymenoptera, parthenogenesis in, 402
Hyracotherium, 142
Immigration and eugenics, 572-73
Inbreeding, 510-13
Induction : a temporary change in germ-
cells, 461-62; of hereditary variations,
45
Infant mortaUty movement, 567
Inheritance: of acquired characters {see
Acquired characters); of brachydac-
tylism, 518; of cataract, 519; of feeble-
mindedness, 420-22, 317; of human
characters, 417-30; of insanity, epi-
lepsy, etc., 517, 523-24; in royalty,
523-30; sex-Unked, 408-13
Insanity, inheritance of, 323
Interference, in crossing-over, 423
Intersexes: in birds, 406-8; in cattle,
407-8; in Drosophila, 403-4; in
gypsy moth, 404
Intraselection, 277-78
Isolation: biologic, 281; geographic
278-81 ; theories of, 20, 32-33, 278-82;
reproductive, 281-82
James, W., 344
Jeffries, E. C, 407
Jennings, H. S., 270, 442-43, SSSS^)
Johannsen, W., 441-42
Johnson, R. H., 558-80
Jones, D. F., 134, 137, 297, 415, 501,
509, 510, 512
Jordan, D. S., 4, 32-34, 103, 114-21,
194, 279-80, 282, 373-76, 579
Joule, J. P., 286
Judd, J. W., 10, 23-24
Kallima, 208-10, 259
Kammerer, P., 462
Kant, E., 13-16
Kellogg, V. S., 4, 32-34, 105, 114-21,
134-38, 194, 254-56, 262, 273, 282
5l2
EVOLUTION, GENETICS, AND EUGENICS
Kelvin, Lord, 138-39, 286
Kinetogenesis, 35
King, C, 138
King, Helen D., 511-12
Klebs, E., 328-29
Knight, T., 40, 322
Kolilreuter, J. G., 40-41, 322
Korchinsky, H., 36
Lamarck, J. P., 7, lo-ii, 18-21, 102,
256, 323. 446-47, 456, 471
Lamarckism, 7, 21, 256, 446-47
Lang, A., 355
Laplace, P. S., 57
Laplacian hypothesis, 138
Laughlin, H. H., 571
Le Conte, J., 3
Leibnitz, 15
Leighty, C. E., 435
Lemuroidea, no
Lepas, metamorphosis of, 120
Lepidosiren, 245
Leptinotarsa decern! iniata, 337, 442
Liliaceae, 494
Lethal factors, 394-9S, 427
Lillie, F. R., 407-8, 538-39
Lina lapponica, 355
Lincoln, A., 24
Linkage: in Mendelian heredity, 407-8;
chromosome theory of, 417-18; in
many species, 427-29; measurements
of, 419-21
Linnaeus, 16, 43, loi
Little, C. C, 472, 503
Locy, W. A., 41-43
Loeb, C, 519
Loess Man, 156
Lotsy, J. P., 43, S07
Love, H. H., 435
Lowell, J. R., 456
Lucas, A. H. S., 227
Lucretius, 14
Lull, R. S., 3, 5, 24, 25, 144, 147, ISO-
IS 2-67
Lutz, 496
Lychnis, 352
Lydekker, R., 127
Lyell, Sir C, 3, 8, 23, 26, 57-58, 138
MaaS; O., 129
Macdougal, D. T., 335-36, 503
McCracken, I., 355
McFarland, J., 28
McGregor, J. H., 161
Madagascar, fauna of, 181-82
MaeterUnck, 204
Mallophaga, 389-81
Malthus, 17, 23-24, 26, 232
Mammalian dispersal, 285-86
Mammary glands, as adaptations, 20c
Man: of Chappelle-aux-Saints, 162
Cro-Magnon Man, 164-65; chrono-
logical table of fossil man, 158; de-
scent from trees, significance of, 155;
evolution of, 152-67; evolutionary
changes of, 155; fossil man, 155-65;
Heidelberg Man, 159-60, 162; im
pelling cause, of origin, 154; Nean-
derthal Man, 160-63; origin of, 153-
55; Piltdown Man, 163-64; place of
origin, 153-54; of Spy, 162; stock of,
153; time of origin, 154-55
Mantis religiosa, 266
Marriage laws and eugenics, 574
Marsh, O. C, 143
Marshall, A! M., 223
Marsupial pouch, as adaptation, 200-
201
Maryatt, 498-500
Mastodon, 147-51, 156
Materialism, the relation of evolution
to, 47-54
Matthew, W. T., 152
Matthiola, 352
Maturation: of egg-cell, 313-15; of
sperm-cell, 312, 314
Maupertius, 15
Median, in variation, 454
Megalonyx jejfersoni, 1 78
Mendel, G., 40, 269, 322, 475; his con-
ception of purity of gametes, 345-46;
iiis conception of unit characters, 345;
his experiments, 340; his explana-
tions, 345-51; his law of dominance,
40-42, 340-41, 345; his law of segre-
gation, 40-42, 341-42; his life and
character, 339; his results, 340-41
Mendelian heredity, 302, 321; in cats,
368; in guinea-pigs, 368, 391 ; in Helix,
355; laws of, 302, 311, 322, 392-94;
in Lina lapponica, 355; linkage in.
INDEX
613
416-29; in maize, 353-54; in man,
358-59; in mice, 343-44, 357; in
nettles, 354; in numerous species, 352-
53; in peas, 342-43; in pigeons, 356-
57; in poultry, 355-56; in rabbits,
358; in silkworms, 354-55
MendeKsm: physical basis of, 360-71;
review of, 392-94
Mesohippus, 143
Metcalf, M. M., 6, 32, 205, 209-10
Metz, C. E. v., 311
Meyer, L., 92 ,
Miastor americana, 308-9
Millson, A., 223
Milton, J., 14
Mimicry, 205, 207-8, 210-11
Miohippus, r43
Mirabilis jalapa, 355, 374-75, 383-84;
M. rosea, 353
Misconceptions about evolution, 8, 9
Mivart, 72-73
Mneme theory of Semon, 461
Mode, in variation, 432
Modifications, 325-26
Moeritherium, 147-49
Monohybrid ratio, 348
Moore, C. R., 406
Morgan, L., 273
Morgan, T. H., 42-44, 291-92, 298, 356,
359, 425, 431, 433-34, 438, 443, 448,
466, 506-11, 526-28
Morphology, evidences from, 88-122
Moulton, F. R., 79
Miiller, F., 141, 143, 270
Muller, H. J., 389, 438, 443, 446, 5"
Multiple allelomorphs, 447-49
Multiple factor hypothesis, 405-9, 416
Mutation theory, 469-70, 4Q7-528; ad-
vantages over natural selection, 510;
alternative to natural selection, 304;
criticism of, 511-12; De Vries' own ac-
count of, 499-506; historical account
of, 36-38; Morgan's summary of,
506-10
Mysis larva of Peneus, 141
Nabours, R. K., 427
Nageli, C. von, 38-39, 339
Natural selection, 4, 12, 24-26, 35, 37-
38, 232-71; experimental support of,
265-67; present status of, 267; rela-
tion of Mendelism and mutation to,
267-80
Naudin, C, 41, 222
Nauplius larva of Peneus, 119
Neanderthal Man, 169-73
Nebular hypothesis, 57
Neo-Lamarckism, 29, 244-45, 445-46
Neo-Mendehsm, 43-45, 445-46
Nest-making instincts, as adaptations,
201
Nettleship, E., 359-519
Newman, Colonel, 220
Newton, Sir F., 7, 61, 286-89, 289, 292
New Zealand, fauna of, 181-82
Nictitating membranes of vertebrates,
83-84
Nilsson-Ehle, H., 383-87, 499
Nitsche, Dr., 82
Nucleolus: chromatin, 303; true, 303
Nutritive chains, 217
NuttaU, G. H. F., 108-9
Nutting, C. C, 267-71
Obhterative coloration, 207-8
Oceanic islands, fauna of, 172-81
Octopus, eye of, 72
Oenothera, 35; 0. albida, 506, 513; O.
biennis, 500, 514; 0. brevistylis, 500,
513; 0. cana, 513; 0. elliptica, 506; 0.
franciscana, 514; O. gigas, 357 ff.,
515-16; O. hewdiii, 515; 0. lactuca,
513; 0. lacvifolia, 500; 0. lamarckiana,
37, 497-512, 514; 0. lata, 506, 514;
0. leptocarpa, 509; 0. liquida, 513;
0. muricata, 515; O. nannella, 500; 0.
oblonga, 513; 0. pubescens, 513; 0.
rubricalyx, 513; O. rubrinervis, 504;
0. scintillans, 506, 513-14; O. spatu-
lala, 509; 0. siibovala, 513
Oglivie, Dr., 474
Oken, L., 12, 16
Oocyte, 336
Oogenesis, 335-36
Oogonium, 336
Organic selection, 299-300
Origin of new hereditary characters,
467-70
Origin of Species, The, 4, 5, 7, 24, 27,
132-33, 138
Ornithorhynchus, 245
Orohippus, 143-44
6i4
EVOLUTION, GENETICS, AND EUGENICS
Orr, H. B., 523
Orthogenesis, 33-36, 282
Orthoplasy, 277
Osborn, H. F., 8, lo-ii, 13, 20-21, 45,
158-59, 161, 165-66, 211-14, 282,
284-92
Overspecializations, 31
Ovum, 113
Owen, R., 87, 105, 249
Pagiiriis bernhardus, 76
Palaeomastodon, 147-49
Palaeontology, evidences from, 60; opin-
ions as to the adequacy of, 133-34;
strength and weakness of, 132-33
Palingenetic, 123
Pan vetus, 159
Pangenesis, 28, 30
Panmixia, 31, 272-73
Panniculus carnosis, 85-86
Papilio machaon, 331
Paramecium, 442
Parasitism, as adaptation, 201-2
Parthenogenesis: diploid, 401-2; hap-
loid, 402; as a method of asexual de-
velopment, 112; sex determination in
connection with, 401-2
Pavlov, I. P., 473
Pearson, K., 43, 430, 436, 438, 450, 558,
562, 564, 566
Pedigree: of brachydactylism, 518; of
cataract, 519; of Charles the Great of
Sweden, 529; of feeble-mindedness,
521-22; of Ferdinand and Isabella,
526; of Hohenzollerns of Prussia,
528; of insanity, epilepsy, etc., 523;
of Romanoils of Russia, 525
Peneus polimirium, 119-20
Phaseolus, 441
Phenotype, 349, 390, 442-44
Phenotypic, 349, 390, 442-44
Phillips, J. C, 459-60
Phocochaerus, 450-51
Phylaxerans, 401
Physiological units, 28
Pisum quadratmn, 340; P. saccharatum,
340; P. sativum, 352; P. umbellatum,
340
Pithecanthropus er edits, 157-61, 164
Placenta, 201
Plane tesimal hjqjothesis, 57
Plate, L., 273-74, 436
PHny, 14
Pliohippus, 143
Ploetz, A., 562-64
Podocoryne, 255
Poebrotherium, 143-46
Polar bodies, 313-15
Polyploidy, 493-94, 5°?
Popenoe, P., 557-69
Post-Aristotelians, 14
Poulton, E. B., 266
Poultry, sex-linked heredity in, 413-14
Preformation doctrine, 125
Prenatal influences, 13-14
Presence and absence hypothesis, 372-
73, 394
Primates: geologic record of, 153; origin
of, 152-53; place of origin, 152; stock
of, 152; time of origin of, 152
Primula kewensis, 494; P. sinensis, S33<
353
Priority, law of, loi
Probable error, 433
Procamelus, 145-46
Promise of race culture, 581-92
Pronucleus: male, 315; female, 316
Protective resemblance, 205-11
Protohippus, 143
Protylopus, 145-46
Pterodactyl, wing of, 71
Punnett, R. C, 344, 354, 355
Pure lines, heredity in, 441-44
Purity of gametes, 345-46
Python, hind limbs of, 78-79
Quadrumana, 85-87
Rabl, C, IIS
Race culture and human variety, 588-89
Rana sylvatica, 459; R. palustris, 459
Recapitulation, doctrine of, 60, 120-21;
critique of, 122-30
Recombination, Mendel's law of, 393-94
Reduction divisions in maturation,
364-65
Reighard, J., 208
Remora, 203
Renner, 496
Reproductive processes, 499-502
Reversion, 13
INDEX
615
Revival of science, the, 15-16
Rhodeus amarus, 221
Rignano, E., 461
Ritzema-Bos, J., 511
Robinson, L., 88-89
Rodentia, loss of teeth in, 1 29
Romanes, G. J., 35, 65, 66-100, i72-8i,_
272-73
Roosevelt, T., 226
Rosa, 494
Rosanoff, A. J., 523
Roux, W., 277
Rubus, 494
Rumex, 494
Rumford, B. T., 286
Ruminants, collar-bone of, 129
Ruskin, J., 587-88, 592
Ruskin and race culture, 587-88
Rutherford, E., 284
Sacculina, 120, 130, 202, 404
Saleeby, C. W., 581-92
Salatory, variations, 38
Sandwich Islands, fauna of, 180-81
Saunders, 352
Scardafella inca, 332-33; S. dialeucos,
332-33; S. braziliensis, 332-33; -S
ridgwayi, 332-33
Schatz, F., 536
Schoetensack, Dr., 160
Schuchert, C, 138-40
Scott, W. B., s, 6, 108-12, 122-31, 133-
34, 144-47, 153
Scrophularia, 335-36
Seals, comparative anatomy of, 66-67
Secondary sexual characters, 405
Sedum spectabile, 328-30
Segregation, Mendel's law of, 40-42,
341-44, 392
Semon, R., 461
Serology, evidences from, 60
Sex determination, 396-404; chroino-
some mechanism of, in Drosophila,
398 ff.; in parthenogenetic species,
401-2; nutrition theory of, 418; rela-
tion of, to genetics, 395; at time of
fertilization, 396-97; various theories
of, 396 ff.
Sex differentiation, 404-8
Sex, heredity and, 44, 319-20
Sex-linked inheritance, 408-15; rules for
41S
Sexual coloration, 205
Sexual reproduction, 301-2
Sexual selection, 26, 249-51
Shelford, V. E., 196
ShuU, A. F., 101-4, 144, 147-51, 171-72
ShuU, G. H., 43, 497
Sims, G. R., 587
Smith, E. A., 465, 471-72, 503, S04
Smith, G., 404
Snow, E. C., 566
Solidago vigiiarea, 450
Somatogenic reproduction, 300
Species, definitions of, 105-6
Spencer, H., 4, 19, 28-29, 273, 451, 591
Spermatid, 312-13
Spermatocyte, 312-13
Spermatogenesis, 312-13
Spermatogonium, 312-13
Spermatozoon, 114, 312-13
Spiranthus, 494
Spontaneous generation, 12
Sports, 38
Sprengel, C. K., 219
Standard deviation, 432-33
Staples-Brown, R., 356
Statistical study: of variation, 436-40;
of heredity, 435-4©
Stegodon, 148-51
Steinach, E., 405
Steinmann, G., 6
Stejneger, loi
Sterilization laws, 576-77
Stock on graft, no influence of, 459-60
Stockard, C. R., 338, 461, 503
St. Helena, fauna of, 178-80
St. Hilaire, E. G., 21-22, 229
Strangeways, T. S. P., 109
Strongylocentrotus, 509
Sturtevant, A. H., 416, 421
Subsidizing the fit, 577-579
Survival of the fittest, 232-39
Swainson, 106
Synapsis, 312, 366
Systema Naturae, of Linnaeus, loi
Tail, vestigial in man, 89-90
6i6
EVOLUTION, GENETICS, AND EUGENICS
Talent, the pnviuction of, 583-84
Tasmanian wolf, in
Tayler, J. L., 262-65
Taxonomy, the method of, 103-4
Teleology, 13
Termites, 196-97
Tetrakinetic theory of Osborn, 283, 284-
92
Tetraploid mutations, 491
Thales, 11
Thayer, G. H., 206-8
Theologians, the early Christian, 14, 15
Thompson, A., 90
Thomson, J. A., 168, 197, 215-27, 339-
44, 352-59, 449-56
Thorndike, E. L., 534, 544, 546
Tibia, flattening of, in man, 99
Tomes, C. S., 98
Tower, W. L., 337-38, 442, 503
Toyama, K., 352-54
Trihybrid ratio, 350-51
Trilophodon, 147-50
Triploid mutations, 491
Trisomic mutations, 491
Tschermak, 40, 43, 339, 352
Turner, Sir W., 98
Tuttle, E., 580
Twins: evidences from, in support of
classification, 106; and the funda-
mental assumption of evolution, 62-
63; and the relative potency of hered-
ity and environment, 531-49
Typhlopidae, 103
Uniformitarianism, 22-23
Unit characters, Mendelian, 345
Urtica dodarti, 353-54; U. pilulifera
353-54
Urschleim, 12, 16
van Dyke, H., 540
Vanessa io, 330-31
Variation, 323-38; classification of, 324-
27; concept of, 324; continuous and
discontinuous, 327, 475; and develop-
ment, 327; and environment, 328;
germinal, 324; and heredity, 320-22;
nature of, 325, 326; polygons of, 431-
32; somatic, 324; statistical study of,
43"-35; universality of, 323-24
Vasectomy, 576
Vestigial structures, evidences from, 60,
77-100
Virchow, R., 162, 240
Voelkor, P. F., 542
Volta Bureau, 571
Wagner, M., 278-79
Walcott, C. W, 133-34, 140
Wallace, A. R., 17, 26-27, 36, 106, 168-
71, 181-84, 248
Walter, H. E., 416, 570-80
Watson, J. B., 541
Weismann, A., 3, 7, 30-32, 256, 267, 269,
272-77, 290,387,456-57, 511
Weismannism, 7
Weldon, W. F. R., 265-66
Whales, comparative anatomy of, 68-
70; embryology of, 128-29
White, G., 215, 221-22
White, T. H., 336
Whitman, C. O., 35
Whitney, D. D., 461
Whymper, E., 576
Wiggam, A. E., 540-56
Wilberforce, Bishop, 28-29
Wilder, H. H., 534-35
Williston, S. W., 35, 154, 156
Wilson, E. B., 6, 44, 299, 300, 360, 399-
400, 404
Wings, comparative anatomy of, 71
Wistar Institute, 512
Woltereck, R., 331-32, 461
Woods, F. A., 524-30, 543
Woodard, 159, 163
Woolner, 92
Wordsworth, W., 591
Wright, Sewall, 113-14, 512
Wyman, Professor, 87
X-chromosome, 398-404, variations of,
400; linkage with autosome, 400
Xonephanes, 12
Y-chromosome, 398-404
Yellow mice, lethal factors in, 427
Zea mays, 354
Zeleny, 498, 510
Ziegler, E., 452
Zoea larva of Peneus, 119
Zygote, 114, 311, 394-95
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