Marine Biological Laboratory Library A I I I I I I L Woods Mole, Mass. Presented by the Herbert B. Rand estate Jan. 9, 1964 I I I I I A I ft O: l! LT) nj ru o a a m a READINGS IN EVOLUTION, GENETICS, AND EUGENICS THE UNIVERSITY OF CHICAGO PRESS CHICAGO, ILLINOIS THE BAKER & TAYLOR COMPANY NEW YORK THE CAMBRIDGE UNIVERSITY PRESS LONDON THE MARUZEN-KABUSHIKI-KAISHA TOKYO, OSAKA, KYOTO, FUKUOKA, SENDAI THE MISSION BOOK COMPANY SHANGHAI READINGS IN EVOLUTION, GENETICS, AND EUGENICS By HORATIO HACKETT NEWMAN Professor of Zoology in the University of Chicago THE UNIVERSITY OF CHICAGO PRESS CHICAGO, ILLINOIS COPYRIGHT 1921 BY THE UNIVERSITY OF CHICAGO All Rights Reserved Published October 1921 Second Impression December 1921 Composed and Printed By The University of Chicago Press Chicago. Illinois, U.S.A. THIS VOLUME IS AFFECTIONATELY DEDICATED TO MY MOTHER PREFACE 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 believed that the present book will furnish ade- quate reading material for a major or a semester course hi 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 modern experimental evolution, and Part V with eugenics, or genetics as applied 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, Vll Vlll PREFACE 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 religion 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, Shull, 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 fifty books from which material has been quoted is given on pages 510-512. 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 Z'LI TABLE OF CONTENTS PAGE LIST OF ILLUSTRATIONS xv-xviii 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 CHAPTER II. HISTORICAL ACCOUNT OF THE DEVELOPMENT OF THE EVOLUTION THEORY. H . H. N 10 Evolution among the Greeks 1 1 Post-Aristotelians 14 The Early Theologians 14 The Revival of Science 15 The Great Naturalists of the Eighteenth Century 16 Lamarck 18 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 32 Orthogenesis Theories 33 Mutation or Heterogenesis Theories 36 The Rise and Vogue of Biometry 38 Modern Experimental Evolution 39 Mendel's Laws 41 Hybridization and the Origin of Species 43 Neo-Mendelian Developments 43 Heredity and Sex 44 CHAPTER III. THE RELATION OF EVOLUTION TO MATERIALISM. Joseph Le Conle 46 PART II. EVIDENCES OF ORGANIC EVOLUTION CHAPTER IV. Is ORGANIC EVOLUTION AN ESTABLISHED PRINCIPLE? H.H.N 57 CHAPTER V. EVIDENCES FROM PALAEONTOLOGY 61 Strength and Weakness of the Evidence 61 ix 11630 X TABLE OF CONTENTS • PAGE Other Opinions as to the Adequacy of the Evidences from Palae- ontology • 62 What Fossils Are and How They Have Been Preserved .... 63 Fossils Classified 63 On the Conditions Necessary for Fossilization 64 On the Lapse of Time during Which Evolution Is Believed to Have Taken Place 67 On the Principal General Facts Revealed by a Study of the Fossils 69 Fossil Pedigrees of Some Well-known Vertebrates 70 Pedigree of the Horse 70 Pedigree of the Camels. W. B. Scott 73 Evolution of the Elephants. A. Franklin Shull 76 CHAPTER VI. THE EVOLUTION OF MAN: PALAEONTOLOGY. Richard Swann Lull 81 Origin of Primates 81 Origin of Man 82 Fossil Man 84 Evidences of Human Antiquity 94 Future of Humanity 95 CHAPTER VII. EVIDENCES FROM GEOGRAPHIC DISTRIBUTION . 97 Some of the More Significant Facts about the Distribution of Animals 101 The Fauna of Oceanic Islands. George John Romanes . . . 101 The Fauna of Madagascar and New Zealand. A. R. Wallace . no The Distribution of Marsupials. A. R. Wallace in The Distribution of Birds. A.R.Wallace 112 Summary of Mammalian Dispersal. Hans Gadow . . . . 114 Summary of the Argument for Evolution as Based on Geographic Distribution 115 CHAPTER VIII. EVIDENCES FROM CLASSIFICATION 117 The Principles of Classification. A. F. Shull 117 The Method of Classification. Charles Darwin 120 What Is a Species? 121 CHAPTER IX. EVIDENCE FROM BLOOD TESTS. W. B. Scott . . . 124 CHAPTER X. EVIDENCES FROM MORPHOLOGY (COMPARATIVE ANAT- OMY). George John Romanes 129 CHAPTER XI. EVIDENCES FROM EMBRYOLOGY 164 The Facts of Reproduction and Development 164 Outline of Animal Development. D. S. Jordan and V. L. Kellogg . 165 CHAPTER XII. CRITIQUE OF THE RECAPITULATION THEORY. W. B. Scott . 173 TABLE OF CONTENTS xi PART HI. THE CAUSAL FACTORS OF ORGANIC EVOLUTION PAGE CHAPTER XIII. INTRODUCTORY STATEMENT 185 What We Owe to Darwin 186 CHAPTER XIV. THE BACKGROUND OF DARWINISM — ADAPTATIONS. H.H.N 188 Laws of Adaptation 192 Adaptations Classified 195 Some Special Adaptations 196 Parasitism and Degeneration 197 Color in Animals 200 CHAPTER XV. THE BACKGROUND OF DARWINISM — Continued . . 206 The Web of Life. J. Arthur Thomson 206 CHAPTER XVI. NATURAL SELECTION. Charles Darwin .... 219 Foundation Stones of Natural Selection . 219 Darwin's Own Estimate as to the Role of Natural Selection in Evolution 219 Effects of Habits and the Use or Disuse of Parts; Correlated Variation; Inheritance .• 220 Darwin's Idea of the Causes Responsible for the Origin of Domes- tic Races 221 Darwin's Idea of the Origin of Varieties, Species, and Genera in Nature 221 The Term "Struggle for Existence" Used in a Large Sense . . 222 Geometrical Ratio of Increase 223 Natural Selection; Or the Survival of the Fittest 223 Sexual Selection 230 Illustrations of the Action of Natural Selection, or the Survival of the Fittest 232 Summary of Chapter on Natural Selection 233 Difficulties and Objections to Natural Selection as Seen by Darwin 236 CHAPTER XVII. CRITIQUE OF DARWINISM 245 Summary of Darwin's Natural-Selection Theory. Vernon L. Kellogg 245 Objections to Darwinism 247 Defense of Darwinism 252 General Defense of Darwinism. /. L. Tayler 253 Experimental Support of the Effectiveness of Natural Selection . 256 The Present Status of Natural Selection 258 The Relation of Mendelism and the Mutation Theory to Natural Selection. C. C. Nulling 258 xii TABLE OF CONTENTS PAGE CHAPTER XVIII. OTHER THEORIES OF SPECIES-FORMING ... 263 Theories Auxiliary to Natural Selection 263 Weismann's Theory of Panmixia 263 Weismann's Theory of Germinal Selection 265 Roux's Theory of Intraselection or the Battle of the Parts . . 268 Coincident Selection or Organic Selection 268 Isolation Theories 269 Theories Alternative to Natural Selection 273 CHAPTER XIX. A NEW COMPOSITE CAUSO-MECHANICAL THEORY OF EVOLUTION (THE TETRAKINETIC THEORY). Henry Fair field Osborn 275 The Energy Concept of Life 275 The Four Complexes of Energy 280 PART IV. GENETICS CHAPTER XX. THE SCOPE AND METHODS OF GENETICS .... 287 Definitions 287 The Scope and Methods of Genetics 287 The Importance of the Cell Theory in Genetics 289 CHAPTER XXI. THE BEARERS OF THE HERITAGE (an Account of the Cellular Basis of Heredity). Michael F. Guyer 290 CHAPTER XXII. VARIATION. Ernest Brown Babcock and Roy Elwood Clausen 307 CHAPTER XXIII. ARE ACQUIRED CHARACTERS (MODIFICATIONS) HEREDITARY? 323 Misunderstandings as to the Question at Issue. /. Arthur Thom- son 323 The Inheritance or Non-Inheritance of Acquired Characters. Edwin Grant Conklin 330 The Other Side to the Question • • • • 336 A Possible Mechanism for the Transmission of Acquired Characters. Michael F. Guyer 338 CHAPTER XXIV. THE MUTATION THEORY 346 New Species (Mutants) of Oenolhera. Hugo De Vries .... 348 Summary of De Vries's Mutation Theory. Thomas Hunt Morgan . 355 Criticisms 359 Causes of Mutations 360 CHAPTER XXV. BIOMETRY (THE STATISTICAL STUDY OF VARIATION AND HEREDITY). H.H.N 365 The Statistical Study of Variation 365 Bimodal and Multimodal Curves 368 The Coefficient of Correlation 369 Statistical Study of Inheritance. Edwin Grant Conklin . . . 370 TABLE OF CONTENTS xiii PAGE CHAPTER XXVI. HEREDITY IN PURE LINES. H. H. N. . . . . 376 Are Determiners (Genes) Constant or Variable ? 378 CHAPTER XXVII. MENDEL'S LAWS OF HEREDITY 380 Mendel's Life and Character. J. Arthur Thomson 380 Mendel's Discoveries. /. Arthur Thomson 380 Mendel's Explanations. /. M. Coulter and M. C. Coulter . . . 386 Illustrations of Simple Mendelian Inheritance in Both Animals and Plants. /. Arthur Thomson 393 CHAPTER XXVIII. THE PHYSICAL BASIS OF MENDELISM. Ernest B. Babcock and Roy E. Clausen 401 CHAPTER XXIX. NEO-MENDELISM IN PLANTS. John M. Coulter and Merle C. Coulter 413 Presence and Absence Hypothesis 413 Blends 415 The Factor Hypothesis 417 CHAPTER XXX. NEO-MENDELIAN HEREDITY IN ANIMALS. H. H. N. 429 Illustrations of the Factor Hypothesis 429 The Factorial Analysis of Color in Mice 429 Different Kinds of Albinos 430 Castle's Guinea Pigs 431 CHAPTER XXXI. SEX-LINKED AND OTHER KINDS OF LINKED INHERITANCE IN Drosophila AND OTHER SPECIES. William E. Castle 433 Drosophila Type and Poultry Type of Sex-linked Inheritance . . 436 CHAPTER XXXII. LINKAGE AND CROSSING-OVER. William E. Castle 441 CHAPTER XXXIII. SEX DETERMINATION. H.H.N 449 Various Theories of Sex Determination 449 The Chromosomal Mechanism of Sex Determination .... 450 Sex Determination in Parthenogenetic Species 451 The Poultry Type of Sex Determination 452 Sex Differentiation 453 PART V. EUGENICS CHAPTER XXXIV. THE INHERITANCE OF HUMAN CHARACTERS, PHYSICAL AND MENTAL. Elliot R. Downing 459 CHAPTER XXXV. HUMAN CONSERVATION. Herbert E. Walter . . 473 How Mankind May Be Improved 473 More Facts Needed 473 Further Application of What We Know Necessary 474 The Restriction of Undesirable Germplasm 475 Control of Immigration 475 xiv TABLE OF CONTENTS PAGE More Discriminating Marriage Laws 477 An Educated Sentiment 477 Segregation of Defectives 478 Drastic Measures 479 The Conservation of Desirable Germplasm 480 By Subsidizing the Fit 480 By Enlarging Individual Opportunity 481 By Preventing Germinal Waste 481 Who Shall Sit in Judgment ? 482 CHAPTER XXXVI. EUGENICS AND EUTHENICS. Paul Popenoe and Roswell H. Johnson 484 CHAPTER XXXVII. THE PROMISE OF RACE CULTURE. Caleb Williams Saleeby 497 BIBLIOGRAPHY 510 INDEX 515 LIST OF ILLUSTRATIONS PAGE 1. TOTAL GEOLOGIC TIME SCALE . 68 2. FEET AND TEETH IN FOSSIL PEDIGREE OF THE HORSE ... 72 3. FOUR STAGES IN THE EVOLUTION OF THE CAMELINE SKULL . . 74 4. FOUR STAGES IN THE EVOLUTION OF THE CAMELINE FORE FOOT . 75 5. EVOLUTION OF HEAD AND MOLAR TEETH OF MASTODONS AND ELEPHANTS 77 6. SKULL OF JAVA APE-MAN, Pithecanthropus erectus .... 87 7. JAWS OF MAN AND OF THE APES 88 8. RESTORATION OF PREHISTORIC MEN 90 9. NEANDERTHALOID SKULL OF LA CHAPELLE-AUX-SAINTS ... 91 10. SKELETON OF NEANDERTHAL MAN 92 11. SKELETON OF SEAL 130 12. SKELETON OF GREENLAND WHALE 132 13. PADDLE OF WHALE COMPARED WITH HAND OF MAN .... 133 14. WING OF REPTILE, MAMMAL, AND BIRD 134 15. SKELETON OF Dinornis grams 137 1 6. HERMIT CRABS COMPARED WITH COCOA-NUT CRAB .... 139 17. RUDIMENTARY OR VESTIGIAL HLND LIMBS OF PYTHON ... 141 18. Apteryx australis 142 19. ILLUSTRATIONS OF THE NICTITATING MEMBRANE IN THE VARIOUS ANIMALS 147 20. RUDIMENTARY, OR VESTIGIAL AND USELESS, MUSCLES OF THE HUMAN EAR 148 21. PORTRAIT OF A YOUNG GORILLA 149 22. LOWER EXTREMITIES OF A YOUNG CHILD 150 23. AN INFANT, THREE WEEKS OLD, SUPPORTING ITS OWN WEIGHT FOR OVER Two MINUTES 151 24. SACRUM OF GORILLA COMPARED WITH THAT OF MAN . . . 152 25. DIAGRAMMATIC OUTLINE OF THE HUMAN EMBRYO WHEN ABOUT SEVEN WEEKS OLD 153 26. FRONT AND BACK VIEW OF ADULT HUMAN SACRUM . . . . 153 27. Appendix vermiformis IN ORANG AND IN MAN 154 28. Appendix vermiformis IN ORANG AND MAN, SHOWING VARIATION IN THE ORANG 154 xvi LIST OF ILLUSTRATIONS PAGE 29. HUMAN EAR MODELED AND DRAWN BY MR. WOOLNER . . . 155 30. FOETUS OF AN ORANG 156 31. VESTIGIAL CHARACTERS OF HUMAN EARS 157 32. HAIR TRACTS ON THE ARMS AND HANDS OF MAN 159 33. MOLAR TEETH OF LOWER JAW IN GORILLA, ORANG, AND MAN . 161 34. PERFORATIONS OF THE HUMERUS IN THREE SPECIES OF QUAD- RUMANA 162 35. FIRST STAGES IN THE EMBRYONIC DEVELOPMENT OF THE POND SNAIL, Lymnaeus 166 36. STAGES IN THE DEVELOPMENT OF THE PRAWN, Peneus potimirium 170 37. LATER STAGES IN THE DEVELOPMENT OF THE PRAWN, Peneus potimirium 170 38. METAMORPHOSIS OF A BARNACLE, Lepas 171 39. EMBRYOS IN CORRESPONDING STAGE OF DEVELOPMENT OF SHARK, FOWL, AND MAN 177 40. THREE AQUATIC TYPES OF VERTEBRATE, TO ILLUSTRATE CON- VERGENT ADAPTATION 193 41. Fierasfer acus, PENETRATING THE ANAL OPENINGS OF HOLO- THURIANS 199 42. Kallima, THE "DEAD-LEAF BUTTERFLY" 202 43. DIAGRAM OF A CELL, SHOWING VARIOUS PARTS 291 44. DIAGRAM SHOWING REPRESENTATIVE STAGES IN MITOTIC OR INDIRECT CELL-DIVISION 292 45. GERM CELL SET APART IN THE EIGHT-CELLED STAGE OF CLEAV- AGE IN Miastor americana 295 46. CHROMOSOMES OF THE MOSQUITO AND OF THE FRUIT FLY . . 297 47. DIAGRAM TO ILLUSTRATE SPERMATOGENESIS 298 48. DIAGRAM TO ILLUSTRATE OOGENESIS 299 49. DIAGRAM SHOWING THE PARALLEL BETWEEN MATURATION OF THE SPERM CELL AND MATURATION OF THE OVUM .... 300 50. DIAGRAM TO ILLUSTRATE FERTILIZATION 302 51. VARIATION IN Sedum spectabile DUE TO DIFFERENCES IN COLOR OF LIGHT 313 52. TEMPERATURE PHASES OF THE DIURNAL PEACOCK-BUTTERFLY . 314 53. MORPHOLOGICAL CYCLE OF HEAD HEIGHT IN Hyalodaphnia. . 315 54. SCHEMATIC CURVES OF HEAD HEIGHT IN Hyalodaphnia AS GROWN IN MEDIA OF THREE DIFFERENT FOOD VALUES . . 316 55. CLIMATIC EFFECTS UPON PLUMAGE IN PIGEONS 317 56. EFFECTS OF INJECTIONS INTO OVARY OF Scrophularia. . . . 319 LIST OF ILLUSTRATIONS xvii PAGE 57. Oenothera lamarckiana 347 58. A SERIES SHOWING Oenothera lamarckiana AND SEVERAL OF ITS MUTANTS GROWING SIDE BY SIDE 352 59. DIAGRAM SHOWING IN CONDENSED FORM THE GENEALOGY or THE Oenothera lamarckiana FAMILY AND ITS VARIOUS MUTANTS 357 60. SOME DIVERGENT TYPES (MUTATIONS) or BEETLES PRODUCED BY SUBJECTING THE GERM CELLS TO EXTERNAL INFLUENCES 361 61. Two PLANTS OF Onagra biennis, SHOWING THE EFFECT OF INJECTIONS OF ZINC SULPHATE INTO THE OVULE . . . .362 62. POLYGON OF VARIATION FOR THE TOTAL NUMBER OF SCUTES IN THE NINE BANDS OF THE ARMADILLO 366 63. BIMODAL POLYGON PLOTTED FROM DATA ON THE EARWIG . . 369 64. CORRELATION TABLE OF 400 PLANTS OF SIXTY-DAY OATS . 370 65. DIAGRAM OF GALTON'S "LAW OF ANCESTRAL INHERITANCE" . 372 66. SCHEME TO ILLUSTRATE GALTON'S" LAW OF FHJAL REGRESSION" 374 67. DIAGRAM ILLUSTRATING BEHAVIOR OF CHROMOSOMES IN MENDEL'S CROSS OF TALL AND DWARF PEAS 388 68. DIAGRAM ILLUSTRATING BEHAVIOR OF FIRST HYBRID GENERA- TION WHEN INBRED 389 69. DIAGRAM ILLUSTRATING DIHYBRID RATIO 392 70. DIAGRAM SHOWING THE CHARACTERISTIC PAIRING, SIZE RELA- TIONS, AND SHAPES OF THE CHROMOSOMES OF Drosophila ampelophila 402 71. DIAGRAM OF MITOSIS IN A SPECIES HAVING FOUR CHROMO- SOMES IN ITS CELLS 404 72. THE REDUCTION DIVISION AS REPRESENTED FOR A SPECIES WHOSE DIPLOID NUMBER Is FOUR 406 73. DIAGRAM OF CHROMATIN INTERCHANGE BETWEEN HOMOLO- GOUS MEMBERS OF A PAIR OF CHROMOSOMES . . . . ' . 408 74. DIAGRAM SHOWING CONSEQUENCES OF INDEPENDENT SEGREGA- TION OF CHROMOSOMES IN Drosophila ampelophila .... 409 75. DIAGRAM TO SHOW CHROMOSOME RELATIONS IN THE INHERIT- ANCE OF SEX IN Drosophila ampelophila 411 76. DIAGRAM SHOWING How THE ORIGINAL SCHEME MUST BE MODIFIED TO SATISFY THE PRESENCE AND ABSENCE HYPOTHE- SIS 414 77. DIAGRAM SHOWING How PRESENCE AND ABSENCE SCHEME Is ACTUALLY USED 415 78. DIAGRAM ILLUSTRATING BLENDING INHERITANCE 416 xviii LIST OF ILLUSTRATIONS PAGE 79. DIAGRAM ILLUSTRATING COMPLEMENTARY FACTORS .... 418 80. DIAGRAM ILLUSTRATING BEHAVIOR OF INHIBITORY FACTOR . . 421 81. DIAGRAM SHOWING SOME POSSIBLE COMBINATIONS IN F2 WHEN FI OF FIGURE 80 Is INBRED 422 82. DIAGRAM SHOWING THE HETEROZYGOTE SITUATION . . . .422 * 83. DIAGRAM ILLUSTRATING THE ACTION OF A SUPPLEMENTARY FACTOR 423 84. DIAGRAM ILLUSTRATING NILSSON-EHLE'S EXPLANATION OF THE 15:1 RATIO IN F2 OF HYBRID BETWEEN RED- AND WHITE- GRAINED WHEAT 425 85. ANOTHER METHOD OF VISUALIZING NILSSON-EHLE'S 15:1 RATIO 426 86. DIAGRAM OF NILSSON-EHLE'S 63 : i RATIO 427 87. SEX-LINKED INHERITANCE OF WHITE AND RED EYES IN Droso- phila 434 88. RECIPROCAL CROSS TO THAT SHOWN IN FIGURE 87 . . . .435 89. DRAWING SHOWING THE FOUR PAIRS OF CHROMOSOMES SEEN IN THE DIVIDING EGG OF Drosophila 436 90. DIAGRAM SHOWING THE LOCATION IN THE FOUR PAIRED CHROMO- SOMES OF Drosophila, OF THE GENES FOR VARIOUS MENDELIZ- ING CHARACTERS, AS DETERMINED BY MORGAN 437 91. SEX-LINKED INHERITANCE OF BARRED AND UNBARRED (BLACK) PLUMAGE IN POULTRY 438 92. RECIPROCAL CROSS TO THAT SHOWN IN FIGURE 91 . . . . 439 93. DIAGRAM TO SHOW THE MECHANISM OF CROSSING OVER. . . 440 94. AN ARMADILLO EGG ABOUT Six WEEKS AFTER FERTILIZATION, SHOWING THE QUADRUPLET FOETUSES 451 95. A TYPICAL OPPOSITE-SEXED PAIR OF CATTLE TWINS .... 455 96. A PEDIGREE OF BRACHYDACTYLISM 460 97. A PEDIGREE SHOWING TRANSMISSION OF CATARACT .... 461 98. A PEDIGREE SHOWING HEREDITY OF FEEBLE-MINDEDNESS . . 463 99. ANOTHER PEDIGREE SHOWING HEREDITY OF FEEBLE-MINDED- NESS 464 100. PEDIGREE SHOWING HEREDITY OF INSANITY 465 101. PEDIGREE SHOWING HEREDITY OF INSANITY AND NEUROTIC TENDENCY 465 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.1 These points of view are well expressed in the following quotations. — ED.] '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 entium! 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,2 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. 1 See Joseph Le Conte, Relation of Evolution to Materialism, chap. iii. 2 From R. S. Lull, Organic Evolution (The Macmillan Company. Reprinted by permission). 3 4 READINGS IN 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 ah1 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 life, 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 (1911), 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 establishment biology has become truly a science 6 READINGS IN 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 of the Theory of Organic Evolution (1911), 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 different 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, Buff on, one hundred and fifty years ago, ends in 1916 with the general feeling that our search for causes, far from being near completion, has only just begun. 8 READINGS IN 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 nomad 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 [i. 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 have 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.— ED.] CHAPTER II HISTORICAL ACCOUNT OF THE DEVELOPMENT OF THE EVOLUTION THEORY H. H. NEWMAN The chief sources of material for the present chapters are : Osborn's From the Greeks to Darwin1 and Judd's The Coming of Evolution.2 Professor Osborn 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 cleai ly 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, 1 H. F. Osborn, From the Greeks to Darwin (The MacmiUan Company, 1908). 2 John W. Judd, The Coming of Evolution (Cambridge University Press, 1911). 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 inception 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 thinkers. Tholes (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 modern 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 READINGS IN 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-1 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 the 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 philosophy was influential in molding the ideas of his successors. Empedodes (495-435 B.C.) " took a great stride beyond his predeces- sors, 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 repelled 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.45o 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 linear 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 READINGS IN 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 earlier, 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 15 Augustine (353-430 A.D.) conceived the idea, now so generally adopted by theologians, that the biblical 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 Augustine says that the earth is then said to have brought forth grass and trees causaliier; 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. Emmanuel Kant (1724-1804) was purely a philosopher, not an observing naturalist, but he profited by the writings of the contem- porary naturalists, especially those of Buffon and Maupertius. His 16 READINGS IN 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 earliest 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 closing 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 worthy 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. Linnaeus (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), born the same year as Linnaeus, has been recognized as the father of the modern applied form of the evolution idea. He attempted to explain particular cases on an evolutionary HISTORICAL ACCOUNT OF EVOLUTION THEORY 17 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 little 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 l8 READINGS IN 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 within 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 millions 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 Philosophic 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 folie,' 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 countrymen, 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. "Life, 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. IV. "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 summed 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 READINGS IN 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 limbs of birds became capable of sustained flight through use; the hind limbs 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. " 5. "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 peculiarities 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 phylogenic 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 Osborn : HISTORICAL 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 impression that he believed animals acquired new organs simply by wishing for them. His really sound speculation in Zoology was also injured by his earlier 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, like 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. HILAERE Georges Cuvier (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. "All 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 will long be known for his discoveries in these fields. E. Geojjroy 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. While not a supporter of Lamarckism proper, he was a thoroughgoing evolutionist, favoring 22 READINGS IN EVOLUTION, GENETICS, AND EUGENICS the doctrine of Buffon, 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. Hilaire 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 chuich 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, HISTORICAL 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 difficult 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 READINGS IN 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 of 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,1 " 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 1 Richard Swann Lull, Organic Evolution (The Macmillan Company, 1917). 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 two 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 READINGS IN 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 life-conditions. 7. Variations neither useful nor harmful would not be affected bv r 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 HISTORICAL ACCOUNT OF EVOLUTION THEORY 27 former paper of Wallace. The 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 publish 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 application 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 that 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 painstaking 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 READINGS IN EVOLUTION, GENETICS, AND EUGENICS "The first effect of Darwin's works," says McFarland,1 "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 validity, 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 (living 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 XJ. McFarland, Biology, General and Medical (The Macmillan Company, 1918). HISTORICAL 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 1860," 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 religious prejudice!' "Huxley 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 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Ernst Hacckel (1834-1919) was one of the earliest and most influential followers of Darwin in Germany. In his Generelle Mor- phologic, published 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 believed 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 physical 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 all heritable variations have their origin in the germ cell, and therefore that a new type of organism arises only from a changed type 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 all 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 linear 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 31 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, but 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 hi 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 READINGS IN EVOLUTION, GENETICS, AND EUGENICS theory," which forms the framework of nearly all of our modern 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 believe in the total independence of any tissue1— 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 nearly 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 will 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 vitalistic force or principle by virtue of which determination and general progress in evolution is chiefly fixed. Such a capacity, inherent hi 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 naturalists 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 READINGS IN 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 life of the individual, most see no mechan- ism or means of extending this control directly to the species." The above-quoted paragraphs from Jordan and Kellogg1 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 Nageli'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 lines 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 line 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 1 Jordan and Kellogg, Evolution and Animal Life (D. Apple ton 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 believed 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 Eimer's theory places natural selection in a subordinate position, but does not dismiss it altogether, as is done by Nageli. 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— Osborn, 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 lines 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 earlier 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 READINGS IN 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 HISTORICAL 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 lamarckiand) 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 peculiar types observed in the field, but of about a dozen other true breed- ing types with well-marked differences from the parent-species 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 living 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 will 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 READINGS IN 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 elimina- 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. t 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 filial 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 material, 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,1 "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 1 W. E. Castle, Genetics and Eugenics (Harvard University Press, 1920), p. 82. 40 READINGS IN EVOLUTION, GENETICS, AND EUGENICS himself, both before and since, has seemed to regard it as of minor importance. He called this 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, Mendel's 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 Kb'lr enter (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:1 " i. Kolreuter established 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, 1 Op. cit., p. 86. HISTORICAL 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 LAW "The earliest experimental investigations of heredity," says Locy1 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 Briinn, Austria. In the garden of the monastery, for eight years before publishing 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. 1 William A. Locy, The Main Currents of Zoology (Henry Holt & Company, 1918), pp. 37-39- 42 READINGS IN 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 unit 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 will 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,1 "has consisted largely in introducing (by mutations) new factors that influence characters already present in the animal or plant. " Such a view gives us a somewhat different 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 assumes 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- 1 T. H. Morgan, A Critique of the Theory of Evolution (Princeton University Press, 1916), pp. 87, 88. HISTORICAL ACCOUNT OF EVOLUTION THEORY 43 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 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 splitting 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 fixed 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 living. It is of interest to recall that Linnaeus, 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 manner 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 understanding 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 READINGS IN 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 150 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 been 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 HISTORICAL 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. 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 dealing 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 THE RELATION OF EVOLUTION TO MATERIALISM1 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 religious belief as to be confounded with the latter— a giving up of some line 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 life-and-death struggle between religion and materialism. To many, both skeptics and Christians, evolution seems to be synonymous with blank mate- rialism, and therefore cuts up by the roots every form of religion 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 unwar- ranted, is not so surprising; but what shall we say of the incredible folly of her friends in admitting the same identity! A little reflection will explain this. There can be no doubt that there is at present a strong and to many an overwhelming tend- ency toward materialism. The amazing achievements of modern 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 light of modern thought — it sweeps away and bears on its bosom all 1 From J. Le Conte, Evolution (copyright 1888). Used by special permission of the publishers, D. Appleton & Company. 46 THE RELATION OF EVOLUTION TO MATERIALISM 47 but the strongest and most reflective minds. Materialism has thus become a fashion of thought; and, like 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 materialism. Once it was the theory of gravitation which seemed demonstrative of materialism. 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 materialistic of all scientific doctrines only because it is the last which is claimed by materialism, 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 materialism 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 materialism, but, to the deep thinker, it has not added a feather's weight to its proba- bility or reasonableness. Evolution is one thing and materialism quite another. The one is an established law of Nature, 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 imagine that he has walked all 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 boundary; 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 certainty which belongs to scientific results. The fact that these materialistic conclusions are reached by some of the foremost scientists of the present day adds nothing to their probability. In a question of science, viz., the law of evolution, their authority is deservedly high, but in a question of philosophy, viz., 48 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 all. 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 believe 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 delight, 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 or eight inches long, is set rotating rapidly, and then the free end of the THE RELATION OF EVOLUTION TO MATERIALISM 49 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) originated 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 $0 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 elimination 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 individual 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 THE RELATION OF EVOLUTION TO MATERIALISM 51 Christians — i.e. , that we were made by a process of evolution. 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 \vhat 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 rational 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 a," 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 52 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 under- take to utter it here. I would say to these modern 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 THE RELATION OF EVOLUTION TO MATERIALISM 53 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 religious 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 ORGANIC EVOLUTION CHAPTER IV IS ORGANIC EVOLUTION AN ESTABLISHED PRINCIPLE ? H. H. NEWMAN 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 58 READINGS IN 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 life 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 established 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 intelligible 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 living 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 that exist in general structure and in particular organs between different 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 under 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 retained 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 list 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 inconclusive, but serve 60 READINGS IN 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 of 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 presenting the evidences of evolution, those evidences that are believed to furnish the most direct proof are discussed first and those whose evidence is subsidiary and confirmatory are dealt with later. The order of treatment, therefore, will be as follows: I. Palaeontology — the evidence afforded by a study of the dis- tribution in time (vertical distribution in the earth's strata) of the fossil remains of extinct animals and plants. II. Geographic distribution- — the evidence afforded by present (also, to some extent, past) horizontal distribution of contemporaneous animals and plants. III. Classification — the evidence that the present groups of animals and plants have arisen by "descent with modification," which is an evolutionary conception. IV. Comparative anatomy (homologies and vestigial structures)— the evidence derived from the fact that structures in unlike organisms have a common plan and mode of origin; that»changes have occurred which are in some way related to changes of habit or of environment. V. Serology (blood-transfusion tests] — the evidence that the chemical specificity of the blood parallels taxonomic specificity. VI. Embryology (the doctrine of recapitulation) — the evidence that the embryonic development of the individual follows the main outlines of the evolutionary history of its ancestors. VII. Experimental evolution (genetics)- — evidences that heritable variations can be produced experimentally and that these are of the same general character as those which occur spontaneously in Nature. (This material will be presented in some detail in Part IV of this book.) CHAPTER V 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 condi Lions 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 life. That Darwin fully realized the vulnerable points in the palaeonto- logical record is shown by the following quotation from the Origin oj Species: — ED.] "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 61 62 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 life 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 OF 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 will 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 illumi- nating chapters. The main significance of the whole lies in the fact that, just 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 light. 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 delicacy and beauty of preservation, which have thrown a flood of new and unexpected light 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, EVIDENCES FROM PALAEONTOLOGY 63 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 life 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 little 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. 64 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 in 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. — ED.] 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, becauae it is composed of sedi- EVIDENCES FROM PALAEONTOLOGY 65 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 worn-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 sunk and been covered by lakes and seas. Again, through great foldings in the cooling 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 66 READINGS IN EVOLUTION, GENETICS, AND EUGENICS mollusks and crustaceans are represented in almost all rock deposits which contain any kind of fossil remains." — Jordan and Kellogg.1 [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 school 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. — ED.] 'From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life (copy- right 1907). Used by special permission of the publishers, D. Apple ton & Company. EVIDENCES FROM PALAEONTOLOGY 67 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 I/yell'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 sliould 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,1 "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 1 C. Schuchert, Text-Book of Geology, Part, II, Historical Geology (1915). 68 READINGS IN EVOLUTION, GENETICS, AND EUGENICS MILLIONS • §^ AGE OF MAN' L> O QUARTERNARY OF YEARS 82 °. ^ (*)" AGE OF MAMMALS 0 Ul U TERTIARY 3— tn CE < UJ >- o UPPER CRETACEOUS H Z < Z O AGE o N LOWER CRETACEOUS (COMANCHEAN) ° 3 Q J UJ IT . § oT u> REPTILES in u JURASSIC tr ui "• 5 >- a K O IO - o »— < QC TRIASSIC $ "- ul .0 = aB • o PERMIAN Q < Z SiS 15- in AGE OF AMPHIBIANS PAUEOZO PENNSYLVANIAN (UPPER CARBONIFEROUS) D°> Sjyu O1"^ i§i5 . K < Ul >• u « MISSISSIPPIAN (LOWER CARBONIFEROUS) ttro = O u Q 2 Z u) <0-l c""3 2O- I AGE OF o N O UJ u 0 2 DEVONIAN " Ul i o Z u. 3 0 • £ FISHES < < S o SILURIAN 5 S "- 7 y o 25- M O 1- c AGE OF INVERTEBRATES 0. PALAEOZOIC ORDOVICIAN ROCKS ce ENl oe w CAMBRIAN MILLIONS OF YEARS u o KEWEENAWAN u § il 0 o £ ° ANIMIKIAN .. UI 1- U 35- U) £ < EVOLUTION OF INVERTEBRATES o c UJ H 3 HURONIAN Z K SgS ll« o • "! U >- O K Q. u o 53 ALGOMIAN QUJz! UJ K U) n: O ui Q. -, O uio"" 40- §• ^l SUDBURIAN g?S gufJ Sz* 45 § o" OJ 0 < K Z < EVOLUTION UNICELLULAR (ARCHEAN) LAURENTIAN LY METAMORPHOSED: l< Y SECONDARY. LIMESTO IT EVIDENCE OF FORME 35 6O PRECAMBF LIFE ARCHAEOZOIC GRENVILLE (KEEWATIN) (COUTCH1CHING) ROCKS GENERAL SEDIMENTAR GRAPHITE INDIRE •O 6 o X °t/J *J rt l/l 4) V3 u 'So "o D o EVIDENCES FROM PALAEONTOLOGY 69 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 los 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 little 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 tune and the distribution in time of the main groups of animals (Fig. i). — ED.] ON THE PRINCIPAL GENERAL FACTS REVEALED BY A STUDY OF THE FOSSILS [i. 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. 70 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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) geolog:c 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 climax 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 climatic 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. — ED.] 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 literature. 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. EVIDENCES FROM PALAEONTOLOGY 71 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. — ED.] 'The course of their [Equidae] evolution," says Dendy,1 "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 uplifted 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 Eo/tippus, 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 Hyracoiherium" 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. In 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 splint bone. 1 Arthur Dendy, Outlines of Evolutionary Biology (D. Appleton & Company, 1916). 72 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Then came in succession Orohippus, of the Upper Eocene, Mesohippus of the Lower Oligocene, Pliohippus of the Upper Pliocene, and finally Equus: Qua- ternary and Recent. Pliohippus : Pliocene. Protohippus : Lower Plio- cene. Miohippus : Miocene. Mesohippus : Lower Mio- /i/^ cene. Orohippus : Eocene. FIG. 2. — 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; e, 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 EVIDENCES FROM PALAEONTOLOGY 73 diagram by Marsh, and in this (Fig. 2) the reader may trace upward from OroJiippus to Eqims 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 offer, that verte- brate material is more intelligible to the non-biological reader and is more hi his own field of knowledge and interest. — ED.] PEDIGREE OF THE CAMELS1 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 inquiry. In this animal the third incisor and the canine are retained in 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 in the horses; the ulna 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. 74 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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. The feet are very long and slender, with two toes in each ; the FIG. 3. — 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. EVIDENCES FROM PALAEONTOLOGY 75 C IF M FIG. 4. — Four stages in the evolution of the cameline fore foot. A , Protylopns, Upper Eocene; B, Poebr other ium, Lower Oligocene; C, Procamelus, Upper Miocene; D, guanaco, Recent. (From Scott.) 76 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 limbs, and especially the feet, are relatively short, the ulna is complete and separate, as is also the fibula; there are four toes in 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 modern 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 limbs. They adapted themselves to the growing aridity of the western plains. EVOLUTION OF THE ELEPHANTS1 A. FRANKLIN SHULL 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 India; Trilophodon from the Miocene of Europe, Africa, and North America; Mastodon from the Pliocene and Pleistocene of 1 From A. F. Shull, Principles of Animal Biology (copyright 1920). Used by special permission of the publishers, The McGraw-Hill Book Company. EVIDENCES FROM PALAEONTOLOGY 77 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. 5. — Evolution of head and molar teeth of mastodons and elephants. A, A', Elephas, Pleistocene; B, Stegodon, Pliocene; C, C', Mastodon, Pleistocene; D, D', Trilophodon, Miocene; E, E' , Palaeomastodon, Oligocene; F, Ff, Moe- ritherium, Eocene. (From Lull.) 78 READINGS IN EVOLUTION, GENETICS, AND EUGENICS A study of Figure 5 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. 5, 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. 5, 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 from early Oligocene time. Palaeo- mastodon was of somewhat larger size than the preceding form, the posterior part of the skull was distinctly higher (Fig. 5, £')' — 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 (£) resembled 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 they were just in front of the eyes, EVIDENCES FROM PALAEONTOLOGY 79 which is believed to indicate the existence of a short proboscis 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 modern Indian elephants. The tusks were considerably longer (Fig. 5, 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. 5, 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. 5, 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. 5, B). These ridges were due to plates of enamel extending up through the tooth, and inclosing a substance known as dentine. Over the enamel in an 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 mammoths. On the whole, Stegodon was intermediate between the mastodons and elephants. 8o READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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. 5, 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 (Fig. 5, 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 like 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. Whereas 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 modern 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 VI THE EVOLUTION OF MAN: PALAEONTOLOGY1 RICHARD SWANN LULL ORIGIN OF PRIMATES Stock. — There is but little doubt that two important orders of modern 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 lines, 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 primates, 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 suffices 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. 81 82 READINGS IN EVOLUTION, GENETICS, AND EUGENICS general, are utterly dependent upon such an environment for their sustenance. Geologic records — 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 Oligocene. 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 OF 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 civilizations, 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. THE EVOLUTION OF MAN 83 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 com- 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 life reached its highest development in late Cenozoic time (Williston). Fifth, climatic 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 life 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 earlier than Miocene time; when the terrestrial ape-man became what we would call human was perhaps later, but certainly during the Pliocene, which makes the age of man as such measurable in terms of hundreds of thousands of years! 84 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Significance of the descent from trees. — As a result of the descent 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 sufficiently 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 THE EVOLUTION OF MAN 85 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 americanus) , 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 Williston: 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 six 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 announced 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. 86 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 Hrdlicka, 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-Columbian Indians. Further evidence lies hi the uniformity of type, except for minor distinctions, of all native American peoples. There is no such racial differentiation 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. Osborn 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 wfll 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 THE EVOLUTION OF MAN 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, Illinoian) 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 (Figs. 6 and 7, A), 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 skull is characterized by its limited capacity, about two- thirds that of man; and by the low flat forehead and beetling brows. Hence not only was the brain limited in its total size, but this was especially true of the FIG. 6. — Skull of Java ape-man, Pithecan- thropus erectus. (From Lull, after Dnbois.) frontal lobes, which, as we have seen, are the seat of the higher intel- lectual faculties. Thus, as Osborn says, although touch, taste, and 88 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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. 7. — Jaws, left outer aspect, of A, date as either of the Upper Plio- chimpanzee, Pan, sp. ; B, fossil chimpanzee, cene or lowermost Pleistocene Pan veins, found in association with Pilt- • j i • r u • j period, which being rendered down man; C, Heidelberg man, Homo , . heidelbergcnsis; D, modern man, H. sapiens. m terms of years §ives an estl- (From Lull, after Woodward.) mated age of about 500,000! c THE EVOLUTION OF MAN 89 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 relic consists of a perfect lower jaw with the dentition (Fig. 7, 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 eoliths, 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 neanderthal ens is or primigenius (Figs. 8, 9, 10) was dis- covered in 1856 not far from Diisseldorf in Rhenish Prussia. Here the valley of the Diissel forms the deep Neanderthal ravine, whose go READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 u f^ & • <2 o o o Sf 5 rill -38 B •>-> O ii -r ?N «» '£? 2 all 2 PH O C CO | to 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 THE EVOLUTION OF MAN though of course the subject of a most heated controversy, being con- sidered as non-human, or, as Virchow believed, 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. FIG. g. — Neanderthaloid skull of La Chapelle-aux-Saints (Homo neanderthalensis). (From Lull, after Boitle.) 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 g 2 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 FIG. 10. — Skeleton of Neanderthal man. A , Homo neanderthalensis, com- pared with that of a living native Australian; B, Homo sapiens, the latter the lowest existing race. (From Lull, after Woodward.) dead were buried, with an abun- dance of ornaments and finely worked flints. This can have but one interpretation, the awakening within this ancient type of the instinctive belief in immortality! Piltdown man.— In 1912 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- THE EVOLUTION OF MAN 93 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 Eoanthropus 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. 7, B.} Cro-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 Cro-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 1.5 inches, for women 5 feet 5 inches, a great dis- parity. The lower segments of the limbs were long, hi contrast with the Neanderthal type, hence the men of Cro-Magnon were swift- footed, while those of Neanderthal were slow. Osborn 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 Cro-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 94 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 Cro-Magnons at the Grotte des Enfants, Mentone) the sum of the characters is decidedly negroid or African." The Cro-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 decline of the Cro-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 Cro-Magnon decline 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-dwelling 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 THE EVOLUTION OF MAN 95 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 religions 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. Osborn'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. Q6 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 ability, 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 life 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. CHAPTER VII EVIDENCES FROM 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. — ED.] "The theory," says Wallace,1 "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 1 From A. R. Wallace, Darwinism (1889). Used by special permission of the publishers, The Macmillan Company. 97 g8 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 climate 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 climate, 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 EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 99 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 hi 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, while 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 how 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, writh 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 too READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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,1 "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. 1 From A. F. Shull, Principles of Animal Biology (copyright 1920). Used by special permission of the publishers, The McGraw-Hill Book Company. EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 101 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 ISLANDS1 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 1 From G. J. Romanes, Darwin and after Darwin (copyright 1892). Used by special permission of The Open Court Publishing Company. 102 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 slight, 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 already said, upon oceanic islands, which may be metaphorically regarded as having been EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 103 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 i, 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 European 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 Europe; 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 104 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 peculiar, 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 peculiar 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-mollusca 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, EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 105 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 allied 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 peculiar 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 hi the Galapagos Archipelago, and nowhere else, bear so plainly the stamp of affinity to those created m America ? There is nothing in the conditions of life, in the geological nature of the islands, in their height or climate, or in the proportions in which the several classes are associated together, which closely resembles the 106 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 ana 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 sufficiently 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 EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 107 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 peculiar 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, i7th, and i8th centuries. The records of civili- zation present no more lamentable instance of this kind of destruction. loS READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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, and 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 abundant. 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 fauna 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 affinity 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 may be EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 109 referred to three types; the n 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 Kooker 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, allied 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 peculiar 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 peculiar. HO READINGS IN EVOLUTION, GENETICS, AND EUGENICS Moreover, these 16 land-birds constitute no less than 10 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, peculiar; 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 peculiar, yielding no less than 39 peculiar genera. THE FAUNA OF MADAGASCAR AND NEW ZEALAND1 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 peculiarities 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- 1 From A. R. Wallace, Darwinism (copyright 1889). Used by special permis- sion of the publishers, The Macmillan Company. EVIDENCES FROM GEOGRAPHIC DISTRIBUTION in tion there is an extensive bank under 1,000 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 MARSUPIALS1 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 Australian marsupials. All 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 Oolite and in the still older Trias, the jaw-bones of numerous small mammalia have been found, forming eight distinct genera, which 1 From A. R. Wallace, Darwinism (copyright 1889). Used by special per- mission of the publishers, The Macmillan Company. 112 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 DISTRIBUTION OF BIRDS1 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 1 From A. R. Wallace, Darwinism (copyright 1891). Used by special per- mission of the publishers, The Macmillan Company. EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 113 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 live 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 establish 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 applies 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 still 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. 114 READINGS IN EVOLUTION, GENETICS, AND EUGENICS SUMMARY OF MAMMALIAN DISPERSAL1 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 the 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-established. 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, hah0, 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, lions 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 1 From Hans Gadow, Wanderings of Animals (1913), Cambridge University Press. EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 115 workshops of the north," and the balance is in favour of Asia as the cradle of modern 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 tunes 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. Il6 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 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 boundaries 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 tune 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. — ED.] CHAPTER EVIDENCES FROM CLASSIFICATION THE PRINCIPLES OF CLASSIFICATION1 A. F. SHTJLL 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 Sytema Naturae of Linnaeus is the basis of the nomenclature. The author of a genus or species is the person who first publishes 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 hi 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 -idae 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 1 From A. F. Shull, Principles of Animal Biology (copyright 1920). Used by special permission of The McGraw-Hill Book Company. 117 Il8 READINGS IN EVOLUTION, 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 earlier 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 families 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. On 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 119 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 120 READINGS IN 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 DARWIN1 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 utility 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 1 From The Origin of Species. EVIDENCES FROM CLASSIFICATION 12 1 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 speaking 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 affinities. 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 life depend, are of little 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 allied groups ; and their 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 of 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."1 1 From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life. 122 READINGS IN EVOLUTION, GENETICS, AND EUGENICS "The term 'species' was thus defined by the celebrated botanist De Candolle: '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- liarities, therefore, are permanent.' " x [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. Armadillo2 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 alike. Identical or duplicate twins in human beings are believed to have an origin from one egg, after the fashion of the armadillo, 1 From A. R. Wallace, Darwinism. 3 See H. H. Newman, The Biology of Twins (1917), University of Chicago Press. EVIDENCES FROM CLASSIFICATION 123 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-transfusion tests." This evidence, as presented by Professor Scott, forms the substance of the next chapter. — ED.] CHAPTER IX EVIDENCE FROM BLOOD TESTS1 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" serum and is an exceedingly delicate 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 1 From W. B. Scott, The Theory of Evolution (copyright 1917). Used by special permission of the publishers, The Macmillan Company. 124 EVIDENCE FROM BLOOD TESTS 125 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 published upon my tests with precipitins directly supported this evidence, for the reactions 126 READINGS IN 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 believe 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 slight 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. Anti- 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 127 6. A close relationship is shown to exist between all marsupials, 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. Differences 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 128 READINGS IN 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 tune, 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. CHAPTER X EVIDENCES FROM MORPHOLOGY (COMPARATIVE ANATOMY)1 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. n). 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 difficult 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 1 From G. J. Romanes, Damnn and after Darwin (copyright 1892). Used by special permission of the publishers, The Open Court Publishing Company. 129 130 READINGS IN EVOLUTION, GENETICS, AND EUGENICS <0 « I G nj l). a o EVIDENCES FROM MORPHOLOGY 131 • 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. 13). 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 life. 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. 14). 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 READINGS IN EVOLUTION, GENETICS, AND EUGENICS g in a ri •S3 i I J3 b ca •4-> d "l/l 4-> 8 •s i e • O OX) •S C •-! 1- T3 w