THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES This book is DUE on the la» Jate stamp" 4 below N OF CALIFORNIA, IBRARY, ANOELES, CALIF. 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 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 in evolutionary biology. Some supplementary reading may be necessary in case an instructor wishes to emphasize one or more phases of the subject; but for a first course in the subject we believe that all of the essential reading material will be found within the text itself. An effort has been made to present the subject in the best peda- gogical order. After a general introduction, a rather long chapter appears in which the whole history of the development of evolution- ary science is outlined, together with the names and contributions of the leading evolutionists. Part II is a presentation of the evi- dences of organic evolution, beginning with the bodies of evidence most definite and direct, and ending with the less definite and more controversial. Part III deals with causo-mechanical theories of evolution with Darwinism as the central topic. Part IV concerns itself with genetics or 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 modern writers. Our ami 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 hi 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, viii 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 hi 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 a'cknowledg- 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 TABLE OF CONTENTS PAGE LIST OP 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 n Post-Aristotelians 14 The Early Theologians 14 The Revival of Science 15 The Great Naturalists of the Eighteenth Century 16 Lamarck 18 Cuvier and Geoffrey 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 r TABLE OF CONTENTS PACK 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 Skull 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 III. 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. /. 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 irf 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 v . . 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 . . . . . - i' .- . 258 The Relation of Mendelism and the Mutation Theory to Natural Selection. C. C. Nutting . . . ; , . . -. . . ... 258 rii TABLE OF CONTENTS PAGE CHAPTER XVIII. OTHER THEORIES OP 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 or EVOLUTION (THE TETR AKINETIC THEORY). Henry Fairfield 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 Oenolhcra. 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 or HEREDITY 380 Mendel's Life and Character. /. 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 j 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, Pithecanthrope 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 grains 137 16. HERMIT CRABS COMPARED WITH COCOA-NUT CRAB .... 139 17. RUDIMENTARY OR VESTIGIAL HIND 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 IV xvi LIST OF ILLUSTRATIONS PACE 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, Peneiis 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 SHOEING Oenolhera lamarckiana AND SEVERAL OF ITS MUTANTS GROWING SIDE BY SIDE 352 59. DIAGRAM SHOWING IN CONDENSED FORM THE GENEALOGY OP THE Oenothera lamarckiana FAMILY AND ITS VARIOUS MUTANTS 357 60. SOME DIVERGENT TYPES (MUTATIONS) OF BEETLES PRODUCED BY SUBJECTING THE GERM CELLS TO EXTERNAL INFLUENCES 361 61. Two PLANTS OP 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 FILIAL REGRESSION " 374 67. DIAGRAM ILLUSTRATING BEHAVIOR OF CHROMOSOMES IN MENDEL'S CROSS OF TALL AND DWARP 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 or THE CHROMOSOMES OF DrosophUa ampelophUa 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 DrosophUa ampelophUa .... 409 75. DIAGRAM TO SHOW CHROMOSOME RELATIONS IN THE INHERIT- ANCE OF SEX IN DrosophUa a mpelophila 411 76. DIAGRAM SHOWING How THE ORIGINAL SCHEME MUST BE MODIFIED TO SATISFY THE PRESENCE AND ABSENCE HYPOTHE- SIS 4H 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 Fa WHEN Fj 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 Fa 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 . . . 443 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 BRACK YD ACT YLISM 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 entiuml 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. a 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 all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduc- tion; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the condition of 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 Cramp ton, 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 (IQII), 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 hi the order of nature. Between the appearance of The Origin of Species, hi 1859, and the present time there have been great waves of faith in one explanation and then in another: each of these waves of confidence has ended in disappointment, until finally we have reached a stage of very general scepticism. Thus the long period of evolution, experi- ment, and reasoning which began with the French natural philosopher, Buffon, one hundred and fifty years ago, ends in 1916 with the general feeling that our search for causes, far from being near completion, 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 monad to man, that the one-toed horse had a four-toed ancestor, that man has descended from an unknown ape-like form somewhere in the Tertiary. We know not only those larger chains of descent, but many of the minute details of these transformations. We do not know their internal causes, for none of the explanations which have in turn been offered during the last hun- dred years satisfies the demands of observation, of experiment, of reason. It is best frankly to acknowledge that the chief causes of the orderly evolution of the germ are still entirely unknown, and that our search must take an entirely fresh start." — H. F. Osborn, The Origin and Evolution of Life (Charles Scribner's Sons), 1918, pp. viii-x. WHAT ORGANIC EVOLUTION IS NOT [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 H 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.'1 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 clearly 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 Macmillan Company, 1908). * John W. Judd, The Coming of Evolution (Cambridge University Press, 1911). 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 na'ive, vague, and, from our modern point of view, ridiculous; yet they con tamed 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- 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. Empedocles (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 denned 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 hi 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 causaliter; that is, it then received the power to produce them. For hi 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 hi 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 (17 24-1804) 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 fads, 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, Buff on, 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. Bujfon (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 Buff on 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 hi shaping his ideas on evolution. The elder Darwin's theories as to the causes of evolution closely paralleled those of Lamarck, his distinguished contemporary hi 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 hi part produced by their own exertions, in response to 18 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 tune 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- 8 £ -i ALGOMIAN ill Q "i SUDBURIAN §£S SS£ 45- 8' O 1 z < 5 EVOLUTION UNICELLULAR (ARCHEAN) LAURENTIAN LY METAMORPHOSED: 1C Y SECONDARY. LIMESTO :T EVIDENCE: OF FORME 95- eo m z ARCHAEOZOIC GRENVILLE ROCKS GENERAL GRAPHITE INDIRE 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 tune at 100,000,000 years, and most geologists have tried, although with difficulty, to fit the record within these estimates. " Since the discovery of radium, all of the calculations previously made have been set aside by the new school of physicists, and now the geologists are told they can have 1,000,000,000 or more years as the time since the earth attained its present diameter Even if finally it shall turn out that the physicists have to reduce their estimates as to the age of certain minerals and rocks, geologists nevertheless appear to be on safer ground in accepting their estimates than those based either on sedimentation, chemical denudation, or loss of heat by the earth." [The last decade has seen the demise of the outworn objection to evolution based on the idea that there has not been time enough for the great changes that are believed by evolutionists to have occurred. Given 100,000,000 or 1,000,000,000 years since life began, we can then allow 1,000,000 years for each important change to arise and establish itself. We can also understand why it is that so 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 hi 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 hi an hour or a day or a year. We cannot see any movement hi 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 tune. Evolution may have been infinitely slow, but time has been infinitely long. The accompanying tune scale shows the lapse of time 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) geologic strata are most like those of the present and help to link the present with the past. 5. There is, in general, a gradual progression toward higher types as one proceeds from the lower to the higher strata. 6. Many groups of animals and plants reached the 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 OP 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 hi 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 hi length to compensate for the increased rate of wear. As in so many other groups, the evolution of these special characters has been accompanied by gradual increase in size. Thus Eohippus, of Lower Eocene times, appears to have been not more than eleven inches high at the shoulder, while existing horses measure about sixty-four inches, and the numerous intermediate genera for the most part show a regular progress in this respect. "All these changes have taken place gradually, and a beautiful series of intermediate forms indicating the different stages from Eohip- pus to the modern horse [Equus] have been discovered. The sequence of these stages in geological tune exactly fits in with the theory that each one has been derived from the one next below it by more perfect adaptation to the conditions of life. Numerous genera have been described, but it is not necessary to mention more than a few." ["The first indisputably horselike animal appears to have been Hyracotherium," of the Lower Eocene of Europe. Another Lower Eocene form is Eohippus, which lived in North America, probably having migrated across from Asia by the Alaskan land connection which was in existence at that time. In Eohippus the fore foot had four completely developed hoofed digits and a "thumb" reduced to a splint bone; hi 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 Miocene, Pliohippus of the Upper Pliocene, and finally Equus : Qua- ternary and Recent. Pliohippus Pliocene. 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 Orohippus to Equus the steady changes in fore and hind feet, bones of the forearm, bones of the lower leg, and the grinding teeth of upper and lower jaws. So definitely and clearly has the horse pedigree been worked out that, according to Dendy, " the palaeontological evidence amounts to a clear demonstration of the evolution of the horse from a five-toed ancestor along the lines indicated above." For a long time the palaeontological series of the horse was un- rivaled by other vertebrate types, but now we have almost equally complete series for several other modern types, notably the camels and the elephants. We shall present herewith accounts of the pedi- gree of the camels by Professor Scott, and that of the elephants by Professor Shull. And, to conclude the vertebrate pedigrees, we shall present hi 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 in 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 hi 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 hi the middle and its separated portions are fused with the radius. In the hind leg the shaft of the fibula has been completely xFrom 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, Proiylopus, Upper Eocene; B,Poebrotherium, Lower Oligocene; C, Procamdus, 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 D IF JT IF M FIG. 4. — Four stages in the evolution of the cameline fore foot. A , Protylopus, Upper Eocene; B, Poebrotherium, Lower Oligocene; C, Procamdus, 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 pah- 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 hi the modern species, there were two short-lived side branches which should be mentioned. One, ending hi 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 hi the Upper Miocene; these were browsers and display an increasing stature, especially hi 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 SHUIX 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, Fr, 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 hi 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 tune on each side of each jaw. The surface of these teeth bore a somewhat larger number of transverse crests (Fig. 5, £)) 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 hi 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 hi 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 hi 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 tune 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 then* 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 1From R. S. Lull, Organic Evolution (copyright 1917). Used by special permission of the publishers, The Macmillan Company. fc 82 READINGS IN EVOLUTION, GENETICS, AND EUGENICS general, are utterly dependent upon such an environment for their sustenance. Geologic record. — Primates are found in the North American sediments from Lower to Upper Eocene time, when they became extinct. Thus, while their remains constitute a relatively large per- centage of the total fauna of the Eocene, primates are utterly unknown on this continent from that time until the coming of man. In Europe the record is similar except that the extinction occurred at a somewhat later date, the 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 hi late Cenozoic time (Williston). Fifth, climatic conditions hi 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 ob tamable 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, hi 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, hi 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 whiter. There was no possibility of the accidental intrusion of the arrow-head hi 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 cohimbi, 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 in 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 hi northern India among the foothills known as the Siwaliks. Such discoveries have been heralded, but none have thus far been actually made. Yet Asia will probably prove to be the center of the human race. We have now discovered in southern Asia primitive representatives or relatives of the four existing types of anthropoid apes, namely, the gibbon, the orang, the chimpanzee, and the gorilla, and since the extinct Indian apes are related to those of Africa and of Europe, it appears probable that southern Asia is near the center of the evolution of the higher primates and that we may look there for the ancestors not only of prehuman stages like the Trinil race but of the higher and truly human types." In Europe. — It is in Europe, however, that the tale of human prehistory is the most complete, not only through the happy accident of preserval, but because it has been much more thoroughly explored than has the Asiatic evolutionary center. The latter, however, holds the greatest hopes for future exploration since, as we have emphasized, Europe is too small to be an adaptive radiation center and European 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 frontal lobes, which, as we have seen, are the seat of the higher intel- lectual faculties. Thus, as Osborn says, although touch, taste, and FIG. 6. — Skull of Java ape-man, Pithecan- thropus erectus. (From Lull, after Dubois.) 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 date as either of the Upper Plio- cene or lowermost Pleistocene period, which being rendered in terms of years gives an esti- FIG. 7.— Jaws, left outer aspect, of A , chimpanzee, Pan, sp.; B, fossil chimpanzee, Pan veins, found in association with Pilt- down man; C, Heidelberg man, Homo heidelbergensis; D, modern man, H. sapiens. (From Lull, after Woodward.) mated age of about 500,000! 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 then- apparent fashioning is not merely the result of use. Neanderthal man. — The original specimen of the Neanderthal man, Homo neanderthalensis or primigenius (Figs. 8, 9, 10) was dis- covered in 1856 not far from Dusseldorf hi Rhenish Prussia. Here the valley of the Diissel forms the deep Neanderthal ravine, whose QO 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 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. Their long depressed skulls had very strong brow-ridges; their lower jaws, of brutal depth and solidity, sloped away from the teeth down- wards and backwards in consequence of the absence of that especially characteristic feature of the higher type of man, the chin prominence." Subsequently several more specimens have come to light, at Spy in Belgium, at Krapina in Croatia, at Le Moustier, La Chapelle-aux- Saints and La Ferrassie in France, and at Gibraltar, which, while differing in various details, effectually serve to establish the race, whose main characteristics are : Heavy, overhanging brows, retreating fore- head, long upper lip; jaw less powerful than that of the Heidelberg man but very thick and massive; chin generally strongly receding but in process of forming; dentition extraordinarily massive in the La Chapelle specimen, whereas in those of Spy the teeth are small. The skull in many characteristics is nearer to the anthropoids than to modern man. The brain is large and its volume is surely human, but the pro- portions are again less like those of recent man than like the anthro- poids. The chest is large and robust, the shoulders broad, and FIG. 9.— Neanderthaloid skull of La Chapelle-aux-Saints (Homo neanderthalensis). (From Lull, after Bottle.) 92 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 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- FIG. io.— 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.) 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.) Cr6-Magnon man. — The original finds of the men of the Cr6- 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 hi 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 niches, for women 5 feet 5 niches, a great dis- parity. The lower segments of the limbs were long, hi contrast with the Neanderthal type, hence the men of Crd-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 hi Asia to the north and to the south of the Himalayas. As regards their stature the Crd-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 Cr6-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 Cr6-Magnons again show by their elaborate burial customs how old and well founded is the belief in life after death. They are supposed to be the people who left on the walls of the caverns of France and Spain the marvelous examples of Upper Palaeolithic art of which Professor Osborn's book gives so adequate a description. They lived for a while con temp oteneously 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-hoaded 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 then- 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 hi 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 hi the long run have an adverse effect upon the race. g6 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 VH 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 hi 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 hi 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 hi 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 hi 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 pf the countries in which they thrive so well. And lastly, in illustration of the fact that allied forms are not always found in adjacent regions, we have the -tapirs, which are found only on opposite sides of the globe, in tropical America and the Malayan Islands; the camels of the Asiatic deserts, whose nearest allies are the llamas and alpacas of the Andes; and the marsupials, only found in Australia and on the opposite side of the globe in America. Yet, again, although mammalia may be said to be universally distributed over the globe, being found abundantly on all the continents and on a great many of the larger islands, yet they are entirely wanting in New Zealand, and in a considerable number of other islands which are, nevertheless, per- fectly able to support them when introduced. "Now most of these difficulties can be solved by means of well- known geographical and geological facts. When the productions of remote countries resemble each other, there is almost always conti- nuity of land with similarity of climate between them. When adjacent countries differ greatly in their productions, we find them separated by a sea or strait whose great depth is an indication of its antiquity or permanence. When a group of animals inhabits two countries or regions separated by wide oceans, it is found that in past geological times the same group was much more widely distributed, and may have reached the countries it inhabits from an intermediate region in which it is now extinct. We know, also, that countries now united by land were divided by arms of the sea at a not very remote epoch, 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, with a luxuriant vegetation, extended to far within the Arctic circle, over what are now barren wastes, covered for ten months of the year with snow and ice. The ioo 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. lFrom 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 hi giving the same answer up to a certain point. For both theories would agree hi 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 nitrate of the facts which he has collected. Even as thus restricted, however, our subject matter I 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 hi 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 hi 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 in the Galapagos Archipelago, and nowhere else, bear so plainly the stamp of affinity to those created in America? There is nothing in the conditions of 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 hi all these respects. On the other hand, there is a con- siderable degree of resemblance in the volcanic nature of the soil, in the climate, height, and size of the islands, between the Galapagos and Cape de Verde Archipelagoes; but what an entire and absolute difference in their inhabitants! The inhabitants of the Cape de Verde Islands are related to those of Africa, like those of the Galapagos to America. Facts such as these admit of no sort of explanation on the ordi- nary view of independent creation; whereas in the view here main- tained it is obvious that the Galapagos Islands would be likely to receive colonists from America, and the Cape de Verde Islands from Africa; such colonists would be liable to modification — the principle of inheritance still betraying their original birthplace. " The following is a synopsis of the fauna and flora of this archi- pelago, so far as at present known. The only terrestrial vertebrates are two peculiar species of land-tortoise, and one extinct species; five species of lizards, all peculiar — two of them so much so as to constitute a peculiar genus; — and two species of snakes, both closely allied to South American forms. Of birds there are 57 species, of which no less than 38 are peculiar; and all the non-peculiar species, except one, belong to aquatic tribes. The true land-birds are represented by 31 species, of which all, except one, are peculiar; while more than half of them go to constitute peculiar genera. Moreover, while they are all unquestionably allied to South American forms, they present a beautiful series of gradations, "from perfect identity with the conti- nental species, to genera so distinct that it is difficult to determine with what forms they are most nearly allied; and it is interesting to note that this diversity bears a distinct relation to the probabilities of, and facilities for, migration to the islands. The excessively abun- dant rice-bird, which breeds in Canada, and swarms over the whole United States, migrating to the West Indies and South America, visiting the distant Bermudas almost every year, and extending its range as far as Paraguay, is the only species of land-bird which remains completely unchanged in the Galapagos; and we may therefore con- clude that some stragglers of the migrating host reach the islands 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 1 6 th, 1 7 th, and 1 8th centuries. The records of civili- zation present no more lamentable instance of this kind of destruction. io8 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 — & 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 Heleromera 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 hi number, besides 26 ferns. Forty of the former and ten of the latter are peculiar to the island, and, as Sir Joseph Hooker tells us, "cannot be regarded as very close specific allies of any other plants at all. ' ' Seventeen of them belong to peculiar genera, and the others all differ so markedly as species from their congeners, that not one comes under the category of being an insular form of a continental species. So that with respect to its plants, no less than with respect to its animals, we find that the island of St. Helena constitutes a little world of unique species, 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. no 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 hi Australia and New Guinea, while it is entirely unknown hi 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, hi 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 hi Australia, that country must have been finally separated from the Asiatic continent during the Secondary or Mesozoic period. Now during that period, hi the Upper and the Lower Oolite and hi the still older Trias, the jaw-bones of numerous small mammalia have been found, forming eight distinct genera, which ^rom 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. H4 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, half, was sure to turn up in the western, and vice versa. Lastly, the mysterious African continent. It began originally as the centre of the ancient equatorial South World; it has lost these con- nections and has become joined to the northland, after many vicissi- tudes. It is therefore most difficult to apportion its fauna rightly; moreover for fossils it is almost a blank, except Egypt. It must have had some share hi 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, "hi 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 times has become the most potent and destructive factor to the ancient faunas of the world. SUMMARY OF THE ARGUMENT FOR EVOLUTION AS BASED ON GEOGRAPHIC DISTRIBUTION [On the hypothesis of special creation or on any other hypothesis except evolution that has even been suggested, the extremely intricate patchwork of animal and plant distribution remains an unsolvable picture puzzle, without rhyme or reason. When this puzzle is attacked with the aid of the evolutionary idea, the key to the whole maze is furnished and the difficulties clear up with remarkable ease. The whole hodgepodge makes sense and we can understand many pre- viously irreconcilable facts. In no field does the working hypothesis of evolution work to such advantage as in this field. On the basis that a species arises at one place, spreads out over large areas, becoming modified as it goes, that new species are formed from old through modification after isolation from the parent-stock, how do the facts of distribution look when examined in detail ? 1. Cosmopolitan groups, those with the widest distribution, are those to whom no barriers are sufficient to check migration, e.g., strong fliers, Man, earthworms carried by Man. 2. Restricted groups are usually those to which barriers are readily set up and are frequently the last remnants of a formerly successful fauna or flora, which continue to survive only in some restricted area where the conditions are rather more favorable than elsewhere. Ii6 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 time a land connection with the nearest continent; that at this time the faunas and floras were the same on both island and continent; that, later, the continent and island were separated by an impassable barrier of ocean; and that the inhabitants of the two bodies evolved separately. 5. The faunas and floras of oceanic islands are like those of the nearest mainland and are of those types, for the most part, that might most readily have been blown there by the wind or carried on floating debris. 6. The conclusions arrived at by students of geographic distribu- tion, past and present, as to the existence of former land connections, now broken, are borne out by the independent findings of geologists and geographers. — ED.] CHAPTER EVIDENCES FROM CLASSIFICATION THE PRINCIPLES OF CLASSIFICATION1 A. F. SHULL 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 in parentheses. For example, Bascanion anthonyi Stejneger should now be written Coluber anthonyi (Stejneger), the ge- neric name of this snake having been changed. One species constitutes the type of the genus; that is, it is formally designated as typical of the genus. One genus constitutes the type of the subfamily (when a subfamily exists), and one genus forms the type of the family. The type is indicated by the describer or if not indicated by him is fixed by another author. The name of a subfamily is formed by adding the ending -inae, and the name of a family by adding -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. 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 hi 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 1 19 structural characters is the chief clue to affinities. However, the evidential value of similarity hi 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 hi 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) hi 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 hi the proper place hi a genetic system. For these reasons an important part of systematic work is the description of forms and an analysis of then- 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 hi 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 hi 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 mtergrading 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 terra '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.' " l [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. * 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 hi 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 hi 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 hi 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 annual 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 tune, 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 tune 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. An ti- whale serum gives maximum reactions only with the bloods of other whales and slight reactions with those of pigs and ruminants. EVIDENCE FROM BLOOD TESTS 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 an ti- 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 hi 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 time, there has been little change, save in size, in the structure of the body or limbs, while the teeth and skull have passed through a series of remarkable changes. It is for this reason that it is unsafe to found a scheme of classification, which is meant to be a brief expression of relationship, upon a single character, for the result is almost invariably misleading. The results of blood tests must be critically examined and checked by a comparison with the results obtained by other methods of investiga- tion, but after every allowance has been made, these tests are very remarkable. The blood tests have brought very strong confirmation to the theory of evolution and from an entirely unexpected quarter; they come as near to giving a definite demonstration of the theory as we are likely to find, until experimental zoology and botany shall have been improved and perfected far beyond their present state. 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, tiien, 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 « From G. J. Romanes, Darwin 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 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 hi 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 hi adaptation to changed conditions of life. But the same thing may be seen hi 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, hi 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 hi 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 hi 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 132 READINGS IN EVOLUTION, GENETICS, AND EUGENICS EVIDENCES FROM MORPHOLOGY 133 to perform the same functions. How, then, are we to explain these things ? By design manifested in special creation, or by descent with adaptive modification ? If it is said by design manifested in special creation, we must suppose that the Deity formed an archetypal plan of certain structures, and that he determined to adhere to this plan through all the modifications which those structures exhibit. But, if so, why is it that some structures are selected as typical and not others ? Why should the vertebral skeleton, for instance, be tortured FIG. 13. — Paddle of whale compared with hand of man. (From Romanes.} into every conceivable variety of modification in order to subserve as great a variety of functions; while another structure, such as the eye, is made in different sub-kingdoms on fundamentally different plans, notwithstanding that it has throughout to perform the same func- tion ? Will any one have the hardihood to assert that in the case of the skeleton the Deity has endeavored to show his ingenuity, by the manifold functions to which he has made the same structure sub- servient; while in the case of the eye he has endeavored to show his resources, by the manifold structures which he has adapted to serve the same function? If so, it becomes a most unfortunate circum- stance that, throughout both the vegetable and animal kingdoms, all cases which can be pointed to as showing ingenious adaptation of the 134 READINGS IN EVOLUTION, GENETICS, AND EUGENICS FIG. 14.— Wing of reptile, mammal, and bird. (From Romanes.') EVIDENCES FROM MORPHOLOGY 135 same typical structure to the performance of widely different func- tions— or cases of homology without analogy — are cases which come within the limits of the same natural group of plants and animals, and therefore admit of being equally well explained by descent from a common ancestry; while all cases of widely different structures per- forming the same function — or cases of analogy without homology, are to be found hi different groups of plants or animals, and are therefore suggestive of independent variations arising in the different lines of hereditary descent. To take a specific illustration. The octopus, or devil-fish, belongs to a widely different class of animals from a true fish; and yet its eye, in general appearance, looks wonderfully like the eye of a true fish. Now, Mr. Mivart pointed to this fact as a great difficulty in the way of the theory of evolution by natural selection, because it must clearly be a most improbable thing that so complicated a structure as the eye of a fish should happen to be arrived at through each of two totally different lines of descent. And this difficulty would, indeed, be a formidable one to the theory of evolution, if the similarity were not only analogical but homological. Unfortunately for the objection, however, Darwin clearly showed hi his reply that in no one anatomical or homologous feature do the two structures resemble one another; so that, hi point of fact, the two organs do not resemble one another in any particular further than it is necessary that they should, if both are to be analogous, or to serve the same function as organs of sight. But now, suppose that this had not been the case, and that the two structures, besides presenting the necessary superficial or analogical resemblance, had also presented an anatomical or homologous resem- blance, with what force might it have then been urged, — your hypo- thesis of hereditary descent with progressive modification being here excluded by the fact that the animals compared belong to two widely different branches of the tree of life, how are we to explain the identity of type manifested by these two complicated organs of vision ? The only hypothesis open to us is intelligent adherence to an ideal plan or mechanism. But as this cannot now be urged in any comparable case throughout the whole organic world, we may, on the other hand, present it as a most significant fact, that while within the limits of the same large branch of the tree of life we constantly find the same typical structures modified so as to perform very different functions, we never find any of these particular types of structure in other large branches of the tree. That is to say, we never find typical structures 136 READINGS IN EVOLUTION, GENETICS, AND EUGENICS appearing except in cases where their presence may be explained by the hypothesis of hereditary descent; while in thousands of such cases we find these structures undergoing every conceivable variety of adaptive modification. Consequently, special creationists must fall back upon another position and say, — Well, but it may have pleased the Deity to form a certain number of ideal types, and never to have allowed the structures occurring in one type to appear in any of the others. We 'answer,— Undoubtedly such may have been the case; but, if so, it is a most unfortunate thing for your theory, because the fact implies that the Deity has planned his types in such a way as to suggest the counter-theory of descent. For instance, it would seem most capri- cious on the part of the Deity to have made the eyes of an innumerable number of fish on exactly the same ideal type, ; nd then to have made the eye of the octopus so exactly like these other eyes in superficial appearance as to deceive so accomplished a naturalist as Mr. Mivart, and yet to have taken scrupulous care that in no one ideal particular, should the one type resemble the other. However, adopting for the sake of argument this great assumption, let us suppose that God did lay down these arbitrary rules for his own guidance in creation, and then let us see to what the assumption leads. If the Deity formed a certain number of ideal types, and determined that on no account should he allow any part of one type to appear in any part of another, surely we should expect that within the limits of the same type the same typical structures should always be present. Thus, remember what efforts, so to speak, have been made to maintain the uniformity of type in the case of the fore-limb as previously explained, and should we not expect that in other and similar cases a similar method should have been followed ? Yet we repeatedly find that this is not the case. Even in the whale, as we have seen, the hind-limbs are either alto- gether absent or dwindled almost to nothing; and it is impossible to see in what respects the hind-limbs are of any less ideal value than the fore-limbs — which are carefully preserved in all vertebrated animals except the snake, and the extinct Dinornis, where again we meet in this particular with a sudden and sublime indifference to the main- tenance of a typical structure (Fig. 15). Now I say that if the theory of ideal types is true, we have in these facts evidence of a most unrea- sonable inconsistency. But the theory of descent with continued adaptive modification fully explains all the known cases; for in every case the degree of divergence from the typical structure which an EVIDENCES FROM MORPHOLOGY 137 organism presents corresponds, in a general way, with the length of time during which the divergence has been going on. Thus we FIG. 15. — Skeleton of Dinornis gratis, -fa nat. size. Drawn from nature (British Museum). As separate cuts on a larger scale are shown, (i) the sternum as this appears in mounted specimens, and (2) the same in profile, with its (hypothetical) scapulo-coracoid attached. (From Romanes.) scarcely ever meet with any great departure from the typical form with respect to one of the organs, without some of the other organs being so far modified as of themselves to indicate, on the supposition 138 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of descent with modification that the animal or plant must have been subject to the modifying influences for an enormously long series of generations. And this combined testimony of a number of organs in the same organism is what the theory of descent would lead us to expect, while the rival theory of design can offer no explanation of the fact, that when one organ shows a conspicuous departure from the supposed ideal type, some of the other organs in the same organism should tend to keep it company by doing likewise. As an illustration both of this and of other points which have been mentioned, I may draw attention to what seems to me a particularly suggestive case. So-called soldier- or hermit-crabs are crabs which have adopted the habit of appropriating the empty shells of mollusks. In association with this peculiar habit, the structure of these animals differs very greatly from that of all other crabs. In particular, the hinder part of the body, which occupies the mollusk-shell, and which therefore has ceased to require any hard covering of its own, has been suffered to lose its calcareous integument, and presents a soft fleshy character, quite unlike that of the most exposed parts of the animal. Moreover, this soft fleshy part of the creature is especially adapted to the particular requirements of the creature by having its lateral appendages — i. e., appendages which in other Crustacea perform the function of legs — modified so as to act as claspers to the inside of the mollusk-shell; while the tail-end of the part in question is twisted into the form of a spiral, which fits into the spiral of the mollusk-shell. Now, in Keeling Island there is a large kind of crab called Birgus latro, which lives upon land and there feeds upon cocoa-nuts. The whole structure of this crab, it seems to me, unmistakably resembles the structure of a hermit-crab (Fig. 16). Yet this crab neither lives in the shell of a mollusk, nor is the hinder part of its body in the soft and fleshy condition just described; on the contrary, it is covered with a hard integument like all the other parts of the animal. Consequently, I think we may infer that the ancestors of Birgus were hermit-crabs living in mollusk-shells; but that their descendants gradually relin- quished this habit as they gradually became more and more terrestrial, while, concurrently with these changes in habit, the originally soft posterior parts acquired a hard protective covering to take the place of that which was formerly supplied by a mollusk-shell. So that, if so, we now have, within the limits of a single organism evidence of a whole series of morphological changes in the past history of its species. First, there must have been the great change from an EVIDENCES FROM MORPHOLOGY 139 140 READINGS IN EVOLUTION, GENETICS, AND EUGENICS ordinary crab to a hermit-crab in all the respects previously pointed out. Next, there must have been the change back again from a hermit-crab to an ordinary crab, so far as living without the necessity of a mollusk-shell is concerned. From an evolutionary point of view, therefore, we appear to have in the existing structure of Birgus a morphological record of all these changes, and one which gives us a reasonable explanation of why the animal presents the extraordinary appearance which it does. But, on the theory of special creation, it is inexplicable why this land-crab should have been formed on the pattern of a hermit-crab, when it never has need to enter the shell of a mollusk. In other words, its peculiar structure is not especially in keeping with its present habits, although so curiously allied to the similar structure of certain other crabs of totally different habits, in relation to which the peculiarities are of plain and obvious significance. I will devote the remainder of this chapter to considering another branch of the argument from morphology, to which the case of Birgus serves as a suitable introduction: I mean the argument from rudi- mentary structures. Throughout both the animal and vegetable kingdoms we con- stantly meet with dwarfed and useless representatives of organs, which in other and allied kinds of animals and plants are of large size and functional utility. Thus, for instance, the unborn whale has rudi- mentary teeth, which are never destined to cut the gums; and throughout its life this animal retains, in a similarly rudimentary condition, a number of organs which never could have been of use to any kind of creature save a terrestrial quadruped. The whole anatomy of its internal ear, for example, has reference to hearing in air, as Hunter long ago remarked, "is constructed upon the same principle as hi the quadruped"; yet, as Owen says, "the outer open- ing and passage leading therefrom to the tympanum can rarely be affected by sonorous vibrations of the atmosphere, and indeed they are reduced, or have degenerated, to a degree which makes it difficult to conceive how such vibrations can be propagated to the ear-drum during the brief moments hi which the opening may be raised above the water." Now, rudimentary organs of this kind are of such frequent occur- rence, that almost every species presents one or more of them— usually, indeed, a considerable number. How, then, are they to be accounted for ? Of course the theory of descent with adaptive modi- fication has a simple answer to supply — namely, that when, from EVIDENCES FROM MORPHOLOGY 141 changed conditions of life, an organ which was previously useful becomes useless, it will be suffered to dwindle away in successive generations, under the influence of certain natural causes which we shall have to consider in future chapters. On the other hand, the theory of special creation can only maintain that these rudiments are formed for the sake of adhering to an ideal type. Now, here again the former theory appears to be triumphant over the latter; for, without waiting to dispute the wisdom of making dwarfed and useless structures merely for the whimsical motive assigned, surely if such a FIG. 17. — Rudimentary or vestigial hind limbs of python, as exhibited in the skeleton and on the external surface of the animal. Drawn from nature, j nat. size. (From Romanes.) method were adopted in so many cases, we should expect that in con- sistency it would be adopted in all cases. This reasonable expectation, however, is far from being realized. We have already seen that in numberless cases, such as that of the fore-limbs of serpents, no vestige of a rudiment is present. But the vacillating policy in the matter of rudiments does not end here; for it is shown in a still more aggravated form where within the limits of the same natural groups of organisms a rudiment is sometimes present and sometimes absent. For instance, although in nearly all the numerous species of snakes there are no vestiges of limbs, in the Python we find very tiny rudiments of the hind-limbs (Fig. 17). Now, is it a worthy conception of Deity that, while neglecting to maintain his unity of ideal in the case of 142 READINGS IN EVOLUTION, GENETICS, AND EUGENICS nearly all the numerous species of snakes, he should have added a tiny rudiment in the case of the Python — and even in that case should have maintained his ideal very inefficiently, inasmuch as only two limbs, instead of four, are represented ? How much more reasonable is the naturalistic interpretation; for here the very irregularity of their appearance in different species, which constitutes rudimentary structures one of the crowning difficulties to the theory of special design, furnishes the best possible evidence in favour of hereditary FIG. 18. — Aptcryx anstralis. Drawn from life in the Zoological Gardens, | nat. size. The external wing is drawn to a scale in the upper part of the cut. The surroundings are supplied from the most recent descriptions. (From Romanes.) descent; seeing that this irregularity then becomes what may be termed the anticipated expression of progressive dwindling due to inutility. Thus, for example, to return to the case of wings, we have already seen that in an extinct genus of bird, Dinornis, these organs were reduced to such an extent as to leave it still doubtful whether so much as the tiny rudiment hypothetically supplied to Figure 15 was present in all the species. And here is another well-known case of another genus of still existing bird, which, as was the case with Dinornis, occurs only in New Zealand (Fig. 18). Upon this island there are no four-footed enemies — either existing or extinct — to escape from which the wings of birds would be of any service. Conse- EVIDENCES FROM MORPHOLOGY 143 quently we can understand why on this island we should meet with such a remarkable dwindling away of wings. Similarly, the logger-headed duck of South America can only flap along the surface of the water, having its wings considerably reduced though less so than the Apteryx of New Zealand. But here the interesting fact is that the young birds are able to fly perfectly well. Now, in accordance with a general law to be considered in a future chapter, the life-history of an individual organism is a kind of con- densed recapitulation of the life-history of its species. Consequently, we can understand why the little chickens of the logger-headed duck are able to fly like all other ducks, while their parents are only able to flap along the surface of the water. Facts analogous to this reduction of wings hi birds which have no further use for them, are to be met with also in insects under similar circumstances. Thus, there are on the island of Madeira somewhere between 500 and 600 species of beetles, which are in large part peculiar to that island, though related to other — and therefore presumably parent — species on the neighboring continent. Now, no less than 200 species — or nearly half the whole number — are so far deficient in wings that they cannot fly. And, if we disregard the species which are not peculiar to the island — that is to say, all the species which likewise occur on the neighboring continent, and therefore, as evolu- tionists conclude, have but recently migrated to the island, — we find this very remarkable proportion. There are altogether 29 peculiar genera, and out of these no less than 23 have all their species hi this condition. Similar facts have been recently observed by the Rev. A. E. Eaton with respect to insects inhabiting Kerguelen Island. All the species which he found on the island — viz., a moth, several flies, and numerous beetles — he found to be incapable of flight; and therefore, as Wallace observes, "as these insects could hardly have reached the islands hi a wingless state, even if there were any other known land inhabited by them, which there is not, we must assume that, like the Madeiran insects, they were originally winged, and lost their power of flight because its possession was injurious to them" — Kerguelen Island being "one of the stormiest places on the globe," and therefore a place where insects could rarely afford to fly without incurring the danger of being blown out to sea. Here is another and perhaps an even more suggestive class of facts. 144 READINGS IN EVOLUTION, GENETICS, AND EUGENICS It is now many years ago since the editors of Silliman's Journal requested the late Professor Agassiz to give them his opinion on the following question. In a certain dark subterranean cave, called the Mammoth Cave, there are found some peculiar species of blind fishes. Now the editors of Silliman's Journal wished to know whether Profes- sor Agassiz would hold that these fish had been specially created in these caves, and purposely devoided of eyes which could never be of any use to them; or whether he would allow that these fish had prob- ably descended from other species, but, having got into the dark cave, gradually lost their eyes through disuse. Professor Agassiz, who was a believer in special creation, allowed that this ought to constitute a crucial test as between the two theories of special design and heredi- tary descent. "If physical circumstances," he said, "ever modified organised human beings, it should be easily ascertained here." And eventually he gave it as his opinion, that these fish "were created under the circumstances in which they now live, within the limits over which they now range, and with the structural peculiarities which now characterise them." Since then a great deal of attention has been paid to the fauna of this Mammoth cave, and also to the faunas of other dark caverns, not only in the New, but also in the Old World. In the result, the following general facts have been fully established. 1. Not only fish, but many representatives of other classes, have been found in dark caves. 2. Wherever the caves are totally dark, all the animals are blind. 3. If the animals live near enough to the entrance to receive some degree of light, they may have large and lustrous eyes. 4. In all cases the species of blind animals are closely allied to species inhabiting the district where the caves occur; so that the blind species inhabiting the American caves are closely allied to American species, while those inhabiting European caves are closely allied to European species. 5. In nearly all cases structural remnants of eyes admit of being detected, in various degrees of obsolescence. In the case of some of the crustaceans of the Mammoth cave the foot-stalks of the eyes are present, although the eyes themselves are entirely absent. Now, it is evident that all these general facts are in full agreement with the theory of evolution, while they offer serious difficulties to the theory of special creation. As Darwin remarks, it is hard to imagine conditions of life more similar than those furnished by deep EVIDENCES FROM MORPHOLOGY 145 limestone caverns under nearly the same climate in the two continents of America and Europe; so that, in accordance with the theory of special creation, very close similarity in the organizations of the two sets of faunas might have been expected. But, instead of this, the affinities of these two sets of faunas are with those of their respective continents — as of course they ought to be on the theory of evolution. Again, what would have been the sense of creating the useless foot- stalks for the imaginary support of absent eyes, not to mention all the other various grades of degeneration in other cases ? So that, upon the whole, if we agree with the late Professor Agassiz in regarding these cave animals as furnishing a crucial test between the rival theories of creation and evolution, we must further conclude that the whole body of evidence which they now furnish is weighing on the side of evolution. So much, then, for a few special instances of what Darwin called rudimentary structures, but what may be more descriptively desig- nated— in accordance with the theory of descent — obsolescent or vestigial structures. It is, however, of great importance to add that these structures are of such general occurrence throughout both the vegetable and animal kingdoms that, as Darwin has observed, it is almost impossible to point to a single species which does not present one or more of them. In other words, it is almost impossible to find a single species which does not in this way bear some record of its own descent from other species; and the more closely the structure of any species is examined anatomically, the more numerous are such records found to be. Thus, for example, of all organisms that of man has been most minutely investigated by anatomists; and therefore I think it will be instructive to conclude this chapter by giving a list of the more noteworthy vestigial structures which are known to occur in the human body. I will take only those which are found in adult man, reserving for the next chapter those which occur in a transitory manner during earlier periods of his life. But, even as thus restricted, the number of obsolescent structures which we all present in our own person is so remarkable, that their combined testimony to our descent from A quadrumanous ancestry appears to me in itself conclusive. I mean, thai even if these structures stood alone, or apart from any more general evidences of our family relationships, they would be sufficient to prove our parentage. Nevertheless, it is desirable to remark that of course these special evidences which I am about to detail do not stand alone. Not only is there the general analogy 146 READINGS IN EVOLUTION, GENETICS, AND EUGENICS furnished by the general proof of evolution elsewhere, but there is likewise the more special correspondence between the whole of our anatomy and that of our nearest zoological allies. Now the force of this latter consideration is so enormous that no one who has not studied human anatomy can be in a position to appreciate it. For without special study it is impossible to form any adequate idea of the intricacy of structure which is presented by the human form. Yet it is found that this enormously intricate organisation is repeated in all its details hi the bodies of the higher apes. There is no bone, muscle, nerve, or vessel of any importance hi the one which is not answered to by the other. Hence there are hundreds of thousands of instances of the most detailed correspondence, without there being any instances to the contrary, if we pay due regard to vestigial characters. The entire corporeal structure of man is an exact anatomical copy of that which we find in the ape. My object, then, here is to limit attention to those features of our corporeal structure which, having become useless on account of our change hi attitude and habits, are in the process of becoming obsolete, and therefore occur as mere vestigial records of a former state of things. For example, throughout the vertebrated series, from fish to mammals, there occurs in the inner corner of the eye a semi- transparent eye-lid, which is called the nictitating membrane. The object of this structure is to sweep rapidly, every now and then, over the external surface of the eye, apparently in order to keep the surface clean. But although the membrane occurs hi all classes of the sub-kingdom, it is more prevalent hi some than in others — e.g., in birds than in mammals. Even, however, where it does not occur of a size and mobility to be of any use, it is usually represented, in animals above fishes, by a functionless rudiment, as here depicted in the case of man (Fig. 19). Now the organisation of man presents so many vestigial structures thus referring to various stages of his long ancestral history, that it would be tedious so much as to enumerate them. Therefore I will yet further limit the list of vestigial structures to be given as examples, by not only restricting these to cases which occur in our own organisa- tion; but of them I shall mention only such as refer us to the very last stage of our ancestral history — viz., structures which have become obsolescent since the time when our distinctively human branch of the family tree diverged from that of our immediate forefathers, the Ouadrumana. EVIDENCES FROM MORPHOLOGY 147 FIG. 19. — Illustrations of the nictitating membrane in the various animals named, drawn from nature. The letter N indicates the membrane in each case. In man it is called the plica semilunaris and is represented in the two lower drawings under this name. In the case of the shark (Galeus), the muscular membrane is shown as dissected. (From Romanes.} 148 READINGS IN EVOLUTION, GENETICS, AND EUGENICS i. Muscles of the external ear. — These, which are of large size and functional use in quadrupeds, we retain in a dwindled and useless condition (Fig. 20). This is likewise the case in anthropoid apes; but in not a few other Quadrumana (e. g., baboons, macacus, magots^ etc.) degeneration has not proceeded so far, and the ears are voluntarily movable. FIG. 20.— Rudimentary, or vestigial and useless, muscles of the human ear. (From Romanes, after Gray.) 2. Panniculus carnosis. — A large number of the mammalia are able to move their skin by means of subcutaneous muscle, as we see, for instance, in a horse, when thus protecting himself against the sucking of flies. We, in common with the Quadrumana, possess an active remnant of such a muscle in the skin of the forehead, whereby we draw up the eyebrows; but we are no longer able to use other considerable remnants of it, in the scalp and elsewhere, — or more correctly it is rarely that we meet with persons who can. But most of the Quadrumana (including the anthropoids) are still able to do so. EVIDENCES FROM MORPHOLOGY 149 There are also many other vestigial muscles, which occur only in a small percentage of human beings, but which, when they do occur, present unmistakable homologies with normal muscles in some of the Quadrumana and still lower animals. 3. Feet. — It is observable that in the infant the feet have a strong reflection inwards, so that the soles in considerable measure face one another. This peculiarity, which is even more marked in the embryo than hi the infant, and which becomes gradually less and FIG. 21. — Portrait of a young gorilla. (From Romanes, after Hartmann.) less conspicuous even before the child begins to walk, appears to me a highly suggestive peculiarity. For it plainly refers to the condition of things in the Quadrumana, seeing that in all these animals the feet are similarly curved inwards, to facilitate the grasping of branches. And even when walking on the ground apes and monkeys employ to a great extent the outside edges of their feet, as does also a child when learning to walk. The feet of a young child are also extraordinarily mobile in all directions, as are those of apes. In order to show these points, I here introduce comparative drawings of a young ape and the 150 READINGS IN EVOLUTION, GENETICS, AND EUGENICS lower extremities of a still younger child. These drawings, moreover, serve at the same time to illustrate two other vestigial characters, which have often been previously noticed with regard to the infant's foot. I allude to the incurved form of the legs and the lateral exten- sion of the great toe, whereby it approaches the thumb-like character of this organ in the Quadrumana. As in the case of the incurved position of the legs and feet, so in this case of the lateral extensibility of the great toe, the peculiarity is even more marked in embryonic FIG. 22.— Lower extremities of a young child. Drawn from life, when the mobile feet were for a short time at rest in a position of extreme inflection. (From Romanes.) . than in infant life. For, as Professor Wyman has remarked with regard to the foetus when about an inch in length, "The great toe is shorter than the others; and, instead of being parallel to them, is projected at an angle from the side of the foot, thus corresponding with the permanent condition of this part in the Quadrumana." So that this organ, which, according to Owen, "is perhaps the most characteristic peculiarity of the human structure," when traced back to the early stages of its development, is found to present a notably less degree of peculiarity. EVIDENCES FROM MORPHOLOGY 151 4. Hands. — Dr. Louis Robinson has recently observed that the grasping power of the whole human hand is so surprisingly great at birth, and during the first few weeks of infancy, as to be far in excess of present requirements on the part of a young child. Hence he con- cludes that it refers us to our quadrumanous ancestry — the young of anthropoid apes being endowed with similar powers of grasping, in order to hold on to the hair of the mother when she is using her arms for the purposes of locomotion. This inference appears to me justifiable, i:i FIG. 23. — An infant, three weeks old, supporting its own weight for over two minutes. The attitude of the lower limbs, feet, toes, is strikingly Simian. Repro- duced from an instantaneous photograph, kindly given for the purpose by Dr. L. Robinson. (From Romanes.) inasmuch as no other explanation can be given of the comparatively inordinate muscular force of an infant's grip. For experiments showed that very young babies are able to support their own weight, by holding on to a horizontal bar, for a period varying from one half to more than two minutes. With his kind permission, I here reproduce one of Dr. Robinson's instantaneous, and hitherto unpub- lished, photographs of a very young infant. This photograph was taken after the above paragraph (3) was written, and I introduce it here because it serves to show incidentally — and perhaps even better than the preceding figure — the points there mentioned with regard 152 READINGS IN EVOLUTION, GENETICS, AND EUGENICS to the feet and great toes. Again, as Dr. Robinson observes, the attitude, and the disproportionately large development of the arms as compared with the legs give all the photographs a striking resem- blance to a picture of the chimpanzee "Sally" at the Zoological Gardens. For "invariably the thighs are bent nearly at right angles to the body, and in no case did the lower limbs hang down and take the attitude of the erect position." He adds, "In many cases no sign of distress is evinced, and no cry uttered, until the grasp begins to give way." MAN GORILLA FIG. 24. — Sacrum of gorilla compared with that of man, showing rudimentary tail bones of each. Drawn from nature. (From Romanes.) 5. Tail. — The absence of a tail in man is popularly supposed to constitute a difficulty against the doctrine of his quadrumanous descent. As a matter of fact, however, the absence of an external tail in man is precisely what this doctrine would expect, seeing that the nearest allies of man in the quadrumanous series are likewise destitute of an external tail. Far, then, from this deficiency in man constituting any difficulty to be accounted for, if the case were not so— i.e., if man did possess an external tail, — the difficulty would be to understand how he had managed to retain an organ which had been renounced by his most recent ancestors. Nevertheless, as the anthro- EVIDENCES FROM MORPHOLOGY 153 poid apes continue to present the rudimentary vestiges of a tail in a few caudal vertebrae below the integuments, we might well expect to find a similar state of matters in the case of man. And this is just FIG. 25. — Diagrammatic outline of the human embryo when about seven weeks old, showing the relations of the limbs and tail to the trunk. (After Allen Thompson.) r, the radial, and «, the ulnar, border of the hand and forearm; t, the tibial, and/ the fibular, border of the foot and lower leg; au, ear; s, spinal cord; v, umbilical cord; b, bronchial gill slits; c, tail. (From Romanes.) FIG. 26. — Front and back view of adult human sacrum, showing abnormal persistence of vestigial tail muscles. (From Romanes.) what we do find, as a glance at these two comparative illustrations will show (Fig. 24). Moreover, during embryonic life, both of the anthropoid apes and of man, the tail much more closely resembles 154 READINGS IN EVOLUTION, GENETICS, AND EUGENICS that of the lower kinds of quadrumanous animals from which these higher representatives of the group have descended. For at a certain stage of embryonic life the tail, both of apes and of human beings, is C FIG. 27. — Appendix vermiformis in orang and in man. II, ilium; Co, colon; C, coecum; W, a window cut in the wall of the coecum; ***, the appendix. (From Romanes.) FIG. 28.— The same, showing variation in the orang. (From Romanes.) actually longer than the legs (see Fig. 25). And at this stage of development, also, the tail admits of being moved by muscles which later on dwindle away. Occasionally, however, these muscles persist, and are then described by anatomists as abnormalities. The illustra- EVIDENCES FROM MORPHOLOGY tions on page 153 (Fig. 26) serve to show the muscles in question, when thus found in adult man. 6. Vermiform appendix of the coecum. — This is of large size and functional use in the process of digestion among many herbivorous animals; while in man it is not only too small to serve any such purpose, but is even a source of danger to life — many persons dying every year from inflammation set up by the lodgement in this blind tube of fruit-stones, etc. In the orang it is longer than in man (Fig. 27), as it is also in the human foetus proportionally compared with the adult (Fig. 28). In some of the lower herbivorous animals it is longer than the entire body. Like the vestigial structures in general, however, this one is highly variable. Thus Figure 28 serves to show that it may some- times be almost as short in the orang as it normally is in man — both the human subjects of this illustration having been normal. 7. Ear. — Mr. Darwin writes: "The celebrated sculptor, Mr. Woolner, informs me of one little peculiarity in the external ear, which he has often observed both in men and women The peculiarity consists in a little blunt point, projecting from the inwardly folded margin, or helix. When present, it is developed at birth, and according to Professor Ludwig Meyer, more frequently in man than in woman. Mr. Woolner made an exact model of one such case, and sent me the accompanying draw- ing [Fig. 29] The helix obviously con- sists of the extreme margin of the ear folded inwards; and the folding appears to be in some manner connected with the whole external ear being permanently pressed backwards. In many monkeys, which do not stand high in the order as baboons and some species of macacus, the upper portion of the ear is slightly pointed, and the margin is not at all folded inwards; but if the margin were to be thus folded, a slight point would necessarily pro- ject towards the centre In Figure 30 is shown an accurate copy of a photograph of the foetus of an orang (kindly sent me by Dr. Nitsche), in which it may be seen how different the pointed outline of the ear is at this period from its adult condition, when it bears a close general FIG. 29. — Human ear, modeled and drawn by Mr. Woolner. a, the pro- jecting point. (From Ro- manes.) 156 READINGS IN EVOLUTION, GENETICS, AND EUGENICS resemblance to that of man (including even the occasional appear- ance of the projecting point shown in the preceding woodcut). It is evident that the folding over of the tip of such an ear, unless it is changed greatly during its further develop- ment, would give rise to a point projecting inwards."1 The woodcut on page 157 (Fig. 31) serves still further to show vestigial resemblances between the human ear and that of apes. The last two figures illustrate the general resemblance between the nor- mal ear of foetal man and the FIG. 3o.-Foetus of an orang. Exact ear of an adult orangoutang, copy of a photograph, showing the form of The Other two figures on the ear at this early stage. (From Romanes.) lower line are intended to exhibit occasional modifica- tions of the adult human ear, which approximate simian characters somewhat more closely than does the normal type. It will be observed that in their comparatively small lobes these ears resemble those of all the apes; and that while the outer margin of one is not unlike that of the Barbary ape, the outer margin of the other follows those of the chimpanzee and orang. Of course it would be easy to select individual human ears which present either of these characters in a more pronounced degree; but these ears have been chosen as models because they present both characters in conjunction. The upper row of figures likewise shows the close similarity of hair-tracts, and the direction of growth on the part of the hair itself, in cases where the human hair happens to be of an abnormally hirsute character. But this particular instance (which I do not think has been previously noticed) introduces us to the subject of hair, and hair-growth, in general. 8. Hair. — Adult man presents rudimentary hairs over most parts of the body. Wallace has sought to draw a refined distinction between this vestigial coating and the useful coating of quadrumanous animals, in the absence of the former from the human back. But even 1 Descent of Man (2d ed.), pp. 15-16. EVIDENCES FROM MORPHOLOGY 157 158 READINGS IN EVOLUTION, GENETICS, AND EUGENICS this refined distinction does not hold. On the one hand, the com- paratively hairless chimpanzee which died last year in the Zoological Gardens (T. calms') was remarkably denuded over the back; and, on the other hand, men who present a considerable development of hair over the rest of their bodies present it also on their backs and shoul- ders. Again, in all men the rudimentary hair on the upper and lower arm is directed towards the elbow — a peculiarity which occurs nowhere else in the animal kingdom, with the exception of the anthropoid apes and a few American monkeys, where it presumably has to do with arboreal habits. For, when sitting in trees, the orang, as observed by Mr. Wallace, places its hands above its head with its elbows pointing downwards; the disposition of hair on the arms and fore-arms then has the effect of thatch in turning the rain. Again, I find that in all species of apes, monkeys, and baboons which I have examined (and they have been numerous), the hair on the backs of the hands and feet is continued as far as the first row of phalanges; but becomes scanty, or disappears altogether, on the second row; while it is invariably absent on the terminal row. I also find that the same peculiarity occurs in man. We all have rudimentary hair on the first row of phalanges, both of hands and feet: when present at all, it is more scanty on the second row; and in no case have I been able to find any on the terminal row. In all cases these peculiarities are congenital, and the total absence or partial presence of hair on the second pha- langes is constant hi different species of Quadrumana. For instance, it is entirely absent in all the chimpanzees, which I have examined, while scantily present hi all the orangs. As in man, it occurs hi a patch midway between the joints. Besides showing these two features with regard to disposition of hair on the human arm and hand, the woodcut on page 159 (Fig. 32) illustrates a third. By looking closely at the arm of the very hairy man from whom the drawing was taken, it could be seen that there was a strong tendency towards a whorled arrangement of the hairs on the backs of the wrists. This is likewise, as a general rule, a marked feature in the arrangement of hair on the same places in the gorilla, orang, and chimpanzee. In the specimen of the latter, however, from which the drawing was taken this characteristic was not well marked. The downward direction of the hah: on the backs of the hands is exactly the same in man as it is hi all the anthropoid apes. Again, with regard to hair, Darwin notices that occasionally there appears hi man a few hairs in the eye- brows much longer than the others; and that they seem to be EVIDENCES FROM MORPHOLOGY 159 FIG. 32. — Hair tracts on the arms and hands of man, as compared with those of the chimpanzee. Drawn from life. (From Romanes.) 160 READINGS IN EVOLUTION, GENETICS, AND EUGENICS representative of similarly long and scattered hairs which occur in the chimpanzee, macacus, and baboons. Lastly, it may be here more conveniently observed than in the next chapter on Embryology, that at about the sixth month the human foetus is often thickly coated with somewhat long dark hair over the entire body, except the soles of the feet and palms of the hands, which are likewise bare in all quadrumanous animals. This covering, which is called the lanugo, and sometimes extends even to the whole fore- head, ears, and face, is shed before birth. So that it appears to be useless for any purpose other than that of emphatically declaring man a child of the monkey. 9. Teeth. — Darwin writes: "It appears as if the posterior molar or wisdom teeth were tending to become rudimentary in the more civilized races of man. These teeth are rather smaller than the other molars, as is likewise the case with the corresponding teeth in the chimpanzee and orang; and they have only two separate fangs They are also much more liable to vary, both in structure and in the period of their development, than the other teeth. In the Melanian races, on the other hand, the wisdom-teeth are usually furnished with three separate fangs, and are usually sound (i.e., not specially liable to decay); they also differ from the other molars in size, less than in the Caucasian races." Now, in addition to these there are other respects in which the dwindling condition of wisdom-teeth is manifested — particularly with regard to the pattern of their crowns. Indeed, in this respect it would seem that even in the anthropoid apes there is the beginning of a tendency to degeneration of the molar teeth from behind forwards. For if we compare the three molars in the lower jaw of the gorilla, orang, and chimpanzee, we find that the gorilla has five well-marked cusps on all three of them; but that in the orang the cusps are not so pronounced, while in the chimpanzee there are only four of them on the third molar. Now in man it is only the first of these three teeth which normally presents five cusps, both the others presenting only four. So that, comparing all these genera together, it appears that the number of cusps is being reduced from behind forwards; the chimpanzee having lost one of them from the third molar, while man has not only lost this, but also one from the second molar, — and it may be added, likewise partially (or even totally) from the first molar, as a frequent variation among civilized races. But, on the other hand, variations are often met with in the opposite direction, where the EVIDENCES FROM MORPHOLOGY 161 second or the third molar of man presents five cusps — in the one case following the chimpanzee, in the other the gorilla. These latter varia- tions, therefore, may fairly be regarded as reversionary. For these facts I am indebted to the kindness of Mr. C. S. Tomes. 10. Perforations of the humerus. — The peculiarities which we have to notice under this heading are two in number. First, the supra-condyloid foramen is a normal feature in some of the lower Quadrumana (Fig. 34), where it gives passage to the great nerve of NAT. SIZE FIG. 33. — Molar teeth of lower jaw in gorilla, orang, and man. Drawn from nature, nat. size. (From Romanes.) the forearm, and often also to the great artery. In man, however, it is not a normal feature. Yet it occurs in a small percentage of cases — viz., according to Sir W. Turner, in about one per cent, and therefore is regarded by Darwin as a vestigial character. Secondly, there is inter-condyloid foramen, which is also situated near the lower end of the humerus, but more in the middle of the bone. This occurs, but not constantly, in apes, and also in the human species. From the fact that it does so much more frequently in the bones of ancient — and also of some savage — races of mankind (viz. in 20 to 30 per cent of cases), Darwin is disposed to regard it also as a vestigial feature. 162 READINGS IN EVOLUTION, GENETICS, AND EUGENICS On the other hand, Prof. Flower tells me that in his opinion it is but an expression of impoverished nutrition during the growth of the bone. ii. Flattening of Tibia. — In some very ancient human skeletons there has also been found a lateral flattening of the tibia, which rarely occurs in any existing human beings, but which appears to have been usual among the earliest races of mankind hitherto discovered. According to Broca, the measurements of these fossil human tibiae resemble those of apes. Moreover, the bone is bent and strongly GAPVCHII/ FIG. 34. — Perforations of the humerus (supra-condyloid foramen) in three species of Quadrumana where it normally occurs, and in man, where it does not normally occur. Drawn from nature. (From Romanes.') convex forwards, while its angles are so rounded as to present the nearly oval section seen in apes. It is in association with these ape-like human tibiae that perforated humeri of man are found in greatest abundance. On the other hand, however, there is reason to doubt whether this form of tibia in man is really a survival from his quadrumanous ancestry. For, as Boyd-Dawkins and Hartmann have pointed out, the degree of flattening presented by some of these ancient human bones is greater than that which occurs in any existing species of anthropoid ape. Of course the possibility remains that the unknown species of ape from which man descended may have had its tibia more flattened than is now observable in any of the existing species. Never- EVIDENCES FROM MORPHOLOGY 163 theless, as some doubt attaches to this particular case, I do not press it — and, indeed, only mention it at all in order that the doubt may be expressed. Similarly, I will conclude by remarking that several other instances of the survival of vestigial structures in man have been alleged, which are of a still more doubtful character. Of such, for example, are the supposed absence of the genial tubercle in the case of a very ancient jaw-bone of man, and the disposition of valves in human veins. From the former it was argued that the possessor of this very ancient jaw-bone was probably speechless, inasmuch as the tubercle in existing man gives attachment to muscles of the tongue. From the latter it has been argued that all the valves hi the veins of the human body have reference, in their disposition, to the incidence of blood-pressure when the attitude of the body is horizontal, or quadrupedal. Now, the former. case has already broken down, and I find that the latter does not hold. But we can well afford to lose such doubtful and spurious cases, hi view of all the foregoing unquestionable and genuine cases of vestigial structures which are to be met with even within the limits of our own organization — and even when these limits are still further limited by selecting only those instances which refer to the very latest chapter of our long ancestral history. CHAPTER XI EVIDENCES FROM EMBRYOLOGY THE FACTS OF REPRODUCTION AND DEVELOPMENT [It is now definitely known that all living creatures are mortal, at least as individuals, but they all have the capacity of continuing their life by the reproduction of offspring. This physical immortality is based upon an actual transmission from parent to offspring of some material substance which is so organized chemically as to be fully representative of the race or stock to which the parent belongs. Reproduction may be asexual or sexual. In asexual development a new individual may be produced by a process of fission (dividing the parent into two or more parts, each of which has the capacity to develop into a whole new individual) ; by budding (the production of new individuals by means of outgrowths of the parent-body); or by giving off spores or eggs capable of development without fertiliza- tion (parthenogenesis}. In sexual reproduction two kinds of parent- individuals exist: one a female which is capable of giving off relatively large single cells, called eggs (ova) ; and the other a male, which is capable of producing minute, usually motile cells, called spermatozoa. A union of ovum and spermatozoon is usually necessary before the ovum can begin its development. It is the sexual method of repro- duction that will chiefly concern us here, and, for present purposes, we may omit any further mention of the various asexual methods. An ovum may be conceived of as an individual of some definite species or race reduced to the very lowest terms. It exhibits the characteristic cell structure, consisting of cytoplasm and nucleus, cell membrane, nuclear membrane, usually a centrosome (Fig. 43). Further details as to the minute structure of the nucleus are given in chapter xxvii, where the mechanism of Mendelian heredity is dealt with. — ED.] "The reproductive cells from the two sexes," says Wright,1 "have very different appearances. In mammals, the ovum is a relatively large, spherical cell, just visible to the naked eye. 1 From Sewall Wright, Principles of Livestock Breeding, United States Depart- ment of Agriculture, Bulletin No. 905. 164 EVIDENCES FROM EMBRYOLOGY 165 "In birds, the yolk of an egg is really a single ovum, distended to an enormous size by food material. The sperm cell is very much smaller and can be seen well only with a high-power microscope. It is something like a tadpole in shape, having a small cell body, containing a little nucleus, and attached to this a long, whiplike process which beats rapidly while the cell is alive, enabling it to seek out and unite with the large passive egg in the act of fertilization. Enormous num- bers of sperm cells are produced by the male, but only one takes part hi fertilization. After the first has penetrated the membrane of an egg cell, a change takes place hi the latter which prevents the entrance of others. "The sperm activates certain formerly inert substances hi the egg and the new combination cell (the zygote) starts almost at once to produce a new individual." OUTLINE OP ANIMAL DEVELOPMENT1 D. S. JORDAN AND V. L. KELLOGG The embryonic development is from the beginning up to a certain point practically alike, looked at hi its larger aspect, for all the many- celled animals. That is, there are certain principal or constant characteristics of the beginning development which are present in the development of all many-celled animals. The first stage or phenome- non of development is the simple fission of the germ cell into halves (Fig. 35, 6). These two daughter cells next divide so that there are four cells (c); each of these divides, and this division is repeated until a greater or lesser number (varying with the various species or groups of animals) of cells is produced. These cells may not all be of the same size, but in many cases they are, no structural differentiation whatever being apparent among them. The phenomenon of repeated division of the germ cell is called cleavage, and this cleavage is the first stage of development in the case of all many-celled animals. The germ or embryo in some animals consists now of a mass of few or many undifferentiated primitive cells lying together and usually forming a sphere (Fig. 35, e), or perhaps separated and scattered through the food yolk of the egg. The next stage of development is this: the cleavage cells arrange themselves so as to form a usually hollow sphere or ball, the cells lying side by side to 1 From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life (copyright 1907). Used by special permission of the publishers, D. Appleton & Company. 166 READINGS IN EVOLUTION, GENETICS, AND EUGENICS form the outer circumferential wall of this hollow sphere (/). This is called the Uastula or blastoderm stage of development, and the embryo itself is called the blastula or blastoderm. This stage also is common to all the many-celled animals. The next stage in embryonic develop- ment is formed by the bending inward of a part of the blastoderm cell layer, as shown in (g) (or the splitting off inwardly of cells from a special part of the blastula cell layer). This bending in may produce a small depression or groove; but whatever the shape or extent of the sunken-in part of the blastoderm, it results in distinguishing the blastoderm layer into two parts, a sunken-in or inner portion called FIG. 35.— First stages in the embryonic development of the pond snail, Lymnaeus. a, egg cell; b, first cleavage; c, second cleavage; d, third cleavage; e, after numerous cleavages; /, blastula — in section; g, gastrula just forming — in section; h, gastrula completed — in section. (From Jordan and Kellogg, after Rail.) the endoblast and the other unmodified portion called the ectoblast. Endo- means within, and the cells of the endoblast often push so far into the original blastoderm cavity as to come into contact with the cells of the ectoblast and thus obliterate this cavity (h). This third well-marked stage in the embryonic development is called the gastrula stage, and it also occurs in the development of all or nearly all many- celled animals. In the case of a few of the simple many-celled animals the embryo hatches — that is, issues from the egg at the time of or very soon after reaching the gastrula stage. In the higher animals, however, develop- ment goes on within the egg or within the body of the mother until the embryo becomes a complex body, composed of many various EVIDENCES FROM EMBRYOLOGY 167 tissues and organs. Almost all the development may take place within the egg, so that when the young animal hatches there is necessary little more than a rapid growth and increase of size to make it a fully developed mature animal. This is the case with the birds; a chicken just hatched has most of the tissues and organs of a full-grown fowl, and is simply a little hen. But in the case of other animals the young hatches from the egg before it has reached such an advanced stage of development; a young starfish or young crab or young honeybee just hatched looks very different from its parent. It has yet a great deal of development to undergo before it reaches the structural condition of a fully developed and fully grown starfish or crab or bee. Thus the development of some animals is almost wholly embryonic develop- ment— that is, development within the egg or in the body of the mother — while the development of other animals is largely post- embryonic, or larval development, as it is often called. There is no important difference between embryonic and postembryonic develop- ment The development is continuous from egg cell to mature animal, and whether inside or outside of an egg it goes on regularly and uninter- ruptedly. The cells which compose the embryo in the cleavage stage and blastoderm stage, and even in the gastrula stage, are apparently all similar; there is little or no differentiation shown among them. But from the gastrula stage on, development includes three important things; the gradual differentiation of cells into various kinds to form the various kinds of animal tissues; the arrangement and grouping of these cells into organs and body parts; and finally the developing of these organs and body parts into the special condition characteristic of the species of animal to which the developing individual belongs. From the primitive undifferentiated cells of the blastoderm, develop- ment leads to the special cell types of muscle tissue, of bone tissue, of nerve tissue; and from the generalized condition of the embryo in its early stages, development leads to the specialized condition of the body of the adult animal. Development is from the general to the special, as was said years ago by von Baer, the first great student of development. A starfish, a beetle, a dove, and a horse are all alike in thei beginning — that is, the body of each is composed of a single cell, a single structural unit. And they are all alike, or very much alike through several stages of development; the body of each is first a single cell, then a number of similar undifferentiated cells, and then a 168 READINGS IN EVOLUTION, GENETICS, AND EUGENICS blastoderm consisting of a single layer of similar undifferentiated cells. But soon in the course of development the embryos begin to differ, and as the young animals get further and further along in the course of their development, they become more and more different until each finally reaches its fully developed mature form, showing all the great structural differences between the starfish and the dove, the beetle and the horse. That is, all animals begin development apparently alike, but gradually diverge from each other during the course of develop- ment. There are some extremely interesting and significant things about this divergence to which attention should be given. While all animals are apparently alike structurally at the beginning of development, so far as we can see, they do not all differ noticeably at the time of the first divergence in development. The first divergence in development is to be noted between two kinds of animals which belong to different great groups or classes. But two animals of different kinds, both belonging to some one great group, do not show differences until later in their development. This can best be understood by an example. All the butterflies and beetles and grasshoppers and flies belong to the great group or class of animals called Insecta, or insects. There are many different kinds of insects, and these kinds can be arranged in subor- dinate groups (orders), such as the Diptera, or flies, the Lepidoptera, or butterflies and moths, and so on. But all have certain structural characteristics in common, so that they are comprised in one great class — the Insecta. Another great group of animals is known as the Vertebrata, or backboned animals. The class Vertebrata includes the fishes, the batrachians, the reptiles, the birds and the mammals, each composing a subordinate group, but all characterized by the possession of a backbone or, more accurately speaking, of a notochord, a back- bonelike structure. Now, an insect and a vertebrate diverge very soon in their development from each other; but two insects, such as a beetle and a honeybee, or any two vertebrates, such as a frog and a pigeon, do not diverge from each other so soon. That is, all vertebrate animals diverge in one direction from the other great groups, but all the members of the great group keep together for some time longer. Then the subordinate groups of the Vertebrata, such as the fishes, the birds, and the others, diverge, and still later the different kinds of animals in each of these groups diverge from each other. That the course of development of any animal from its beginning to fully developed adult form is — in all its essentials — fixed and certain EVIDENCES FROM EMBRYOLOGY 169 is readily seen. All rabbits develop in the same way; every grass- hopper goes through the same developmental changes from single egg cell to the full-grown, active hopper as every other grasshopper of the same kind — that is, development takes place according to certain natural laws; the laws of animal development. These laws may be roughly stated as follows: All many-celled animals begin life as a single cell, the fertilized egg cell; each animal goes through a certain orderly series of developmental changes which, accompanied by growth leads the animal to change from a single cell to the many-celled, com- plex form characteristic of the species to which the animal belongs; this development is from simple to complex structural condition ; the development is the same for all individuals of one species. While all animals begin development similarly, the course of development in the different groups soon diverges, the divergence being of the nature of a branching, like that shown in the growth of a tree. In the free tips of the smallest branches we have represented the various species of animals in their fully developed condition, all standing more or less clearly apart from each other. But in tracing back the development of any kind of animal we soon come to a point where it very much resembles or becomes apparently identical with the development of some other kind of animal, and, in addition, the stages passed through in the developmental course may very much resemble the fully devel- oped, mature stages of lower animals. To be sure, any animal at any stage in its existence differs absolutely from any other kind of animal, in that it can develop into only its own kind of animal. There is something inherent in each developing animal that gives it an identity of its own. Although in its young stages it may be hardly distin- guishable from some other kind of animal in similar stages, it is sure to come out, when fully developed, an individual of the same kind as its parents were or are. A very young fish and a very young sala- mander are almost indistinguishably alike, but one is sure to develop into a fish and the other into a salamander. This certainty of an embryo to become an individual of a certain kind is called the law of heredity. Viewed hi the light of development, there must be as great a difference between one egg and another as between one animal and another, for the greater difference is included hi the less. The significance of the developmental phenomena is a matter about which naturalists have yet very much to learn. It is believed, how- ever, by practically all naturalists that many of the various stages in the development of an animal correspond to or repeat, in many 170 READINGS IN EVOLUTION, GENETICS, AND EUGENICS fundamental features at least, the structural condition of the animal's ancestors. Naturalists believe that all backboned or vertebrate FIG. 36. — Stages in the development of the prawn, Penens potlmirium. A Nauplius larva; B, first zoea stage; C, second zoe'a stage. (From Jordan and Kellogg, after Fritz Miillcr.) FIG. 37.— Later stages in the development of the prawn, Peneus potimirium. D, Mysis stage; E, adult stage. (From Jordan and Kellogg.) EVIDENCES FROM EMBRYOLOGY 171 animals are related to each other through being descended from a common ancestor, the first or oldest backboned animal. In fact, it is because all these backboned animals — the fishes, the batrachians, the reptiles, the birds, and the mammals — have descended from a common ancestor that they all have a backbone. It is believed that the descendants of the first backboned animal have in the course of many generations branched off little by little from the original type until there came to exist very real and obvious differences among the back- boned animals — differences which among the living backboned animals are familiar to all of us. The course of development of an individual animal is believed to be a very rapid and evidently much condensed and changed recapitulation of the history which the species or kind of animal to which the developing individual belongs has passed through in the course of its descent through a long series of gradually changing ancestors. If this is true, then we can readily understand why a fish and a salamander, a tortoise, a bird, and a rabbit, are all much alike, as they really are, in their earlier stages of development, and gradually come to differ more and more as they pass through later and later developmental stages. A crab has a tail in one of its developmental stages, so that at that time it looks like and really is like the mature stage of some tailed crustacean like a crayfish. A barnacle, which looks a little like a crayfish or crab in its ma- ture stage, is hardly to be distinguished in its immature life from a young crab or lobster. Sacculina, which is a still more degenerate crustacean, is only a sort of feeding sac with rootlet-like processes projecting into the body of the host crab on which it lives as a parasite, but the young free-swimming Sacculina is essentially like a barnacle, crayfish, or crab in its young stage. However, it is obvious that this recapitulation or repetition of ancestral stages is never perfect, and it is often so obscured and modi- fied by interpolated adaptive stages and characters that but little of an animal's ancestry can be learned from a scrutiny of its development. FIG. 38. — Metamorphosis of a barnacle, Lepas. a, larva ; b, adult. (From Jordan and Kellogg.) 172 READINGS IN EVOLUTION, GENETICS, AND EUGENICS The fascinating biogenetic law of Miiller and Haeckel summed up in the phrase, "ontogeny is a recapitulation of phytogeny," must not be too heavily leaned on as a support for any speculations as to the phyletic affinities of any species or group of species of organisms. "Embryology is an ancient manuscript with many of the sheets lost, others displaced, and with spurious passages interpolated by a later hand." CHAPTER XH CRITIQUE OF THE RECAPITULATION THEORY1 W. B. SCOTT Embryology is the study of the development of the individual organism from its beginning in the egg to the attainment of the adult condition. This individual development is called ontogeny and the question of the relation of ontogeny to the ancestral history of the species, or phytogeny, constitutes one of the main problems of embry- ology. Around this problem many controversies have raged, contro- versies which have by no means arrived at a definite solution, even to-day. Thirty years ago the "recapitulation theory" was well-nigh universally accepted, according to which the individual development, or ontogeny, was regarded as an abbreviated repetition of the ances- tral history of the species, or phylogeny. Haeckel called this theory the "fundamental biogenetic law" and upon it he established his whole "History of Creation." Nowadays, that "fundamental law" is very seriously questioned and by some high authorities is altogether denied. However, even those who take this extreme position con- cerning the recapitulation theory see in the facts of embryology one of the strongest supports of the doctrine of evolution. It was very early recognized that the recapitulation theory could not be applied with literal exactness, but was subject to certain important exceptions and qualifications. i. That the history must have been enormously abbreviated. After three weeks of incubation the tiny speck of protoplasm, which forms a circular mark on the yolk of a hen's egg, is developed into a fully formed chick, ready for hatching and able in large degree to take care of itself. On the other hand, the evolution of birds from their invertebrate ancestors, through the fishes, amphibians, and reptiles, the separation of the gallinaceous stock from other birds and the differentiation of this particular species were extremely slow processes, extending through unnumbered millions of years. Admitting reca- pitulation to the fullest extent, it is evidently a physical impossibility 1 From W. B. Scott, The Theory of Evolution (copyright 1917). Used by special permission of the publishers. The Macmillan Company. 173 174 READINGS IN EVOLUTION, GENETICS, AND EUGENICS that it should be a perfect repetition of phytogeny; very much of the long story must of necessity be omitted. 2. Through all the stages of development the embryo must be rendered able to live and grow and thrive through adaptation to its surroundings and changes in its environment. In some animals development takes place within the body of the mother; in others the embryo is protected by the hard egg-shell, as in birds, while the eggs of certain fishes and many invertebrates float freely in the sea and are almost without protection. Such differences in environment necessi- tate differences in the mode of development, while the presence or absence of a large amount of inert food-material, or yolk, exerts a great influence in determining the steps of ontogeny. 3. Many animals pass through a larval stage of development, in which the immature young leads an independent and self-sustaining existence, during which it is very different hi appearance and structure from its adult parents. Familiar instances of this mode of develop- ment are to be found in the tadpole, which is the larva of the frog, and the caterpillar, the larva of a butterfly. Larvae are fully subject to the struggle for existence and must adapt themselves to their environ- ment and to changes in that environment, exactly as do adults, if they are to survive. In this way many changes are introduced into the ontogeny which can have no phylogenetic significance. It is found in several known instances, that nearly allied species, living under different conditions, have quite different modes of ontogeny, though their ancestral history must have been substantially identical. In one and the same species of marine worms, for example, which inhabits both the warm Mediterranean and the cold waters of the North Sea, the larva of the northern form is quite distinct from that 6f the southern. In attempting to interpret the meaning of embryological facts, it is thus necessary to distinguish sharply between those features which are derived from a long inheritance, and are therefore called palingenetic, from those which have been secondarily introduced in response to the changing needs of embryonic or larval life. These secondary features are termed cenogenetlc. "If we are compelled to admit that cenogenetic characters are intermingled with palingenetic, then we cannot regard ontogeny as a pure source of evidence regarding phyletic relationships. Ontogeny accordingly becomes a field in which an active imagination has full scope for its dangerous play, but in which positive results are by no means everywhere to be obtained. To attain such results, the palin- THE RECAPITULATION THEORY 175 genetic and cenogenetic phenomena must be sifted apart, an operation which required more than one critical grain of salt. On what grounds shall this critique be based ? Assuredly not by way of a vicious circle on the ontogeny again; for if cenogenetic characters are present hi one case, who will guarantee that a second case, used for a comparison with the first, does not likewise appear in cenogenetic disguise ? If it once be admitted that not everything in development is palingenetic, that not every ontogenetic fact can be accepted at its face value, so to speak, it follows that nothing .in ontogeny is immediately available for the critique of embryonic development. The necessary critique must be drawn from another source." These remarks of Gegenbaur's were called forth by the state of wild speculation into which embryological work had fallen. As there were no generally accepted canons of interpretation for the facts of embryological development, different writers interpreted these facts in the most divergent and contradictory manner, resulting in a chaotic confusion, which led to a strong reaction against the whole method, though there can be little doubt that this reaction has gone too far. "It must be evident to any candid observer, not only that the embryological method is open to criticism, but that the whole fabric of morphology, so far as it rests upon embryological evidence, stands in urgent need of reconstruction. For twenty years embryological research has been largely dominated by the recapitulation theory; and unquestionably this theory has illuminated many dark places and has solved many a perplexing problem that without its aid might have remained a standing riddle to the pure anatomist. But while fully recognizing the real and substantial fruits of that theory, we should not close our eyes to the undeniable fact that it, like many another fruit- ful theory, has been pushed beyond its legitimate limits. It is largely to an overweening confidence in the validity of the embryological evidence that we owe the vast number of the elaborate hypothetical phylogenies which confront the modern student in such bewildering confusion. The inquiries of such a student regarding the origin of any of the great principal types of animals involve him hi a labyrinth of speculation and hypothesis in which he seeks in vain for conclusions of even an approximate certainty." Many other equally vigorous and well-deserved criticisms of the embryological method might be cited, but it should be emphasized that these criticisms are all directed against the application of the method to the solution of definite and concrete problems of descent and 176 READINGS IN EVOLUTION, GENETICS, AND EUGENICS relationship. None of them denies 'and many strongly affirm that embryology affords some of the strongest and most convincing evi- dence hi favor of the evolutionary theory. Let us examine some of this evidence. To begin with, it should be noted that, hi following out the ontogeny or individual develop- ment, the observer witnesses the formation of something new, not merely the enlargement and unfolding of a pre-existing organism, though the theory of preformation, which was widely accepted in the eighteenth century, looked upon ontogeny precisely in that way, as the growth of a germ which was the miniature of the parent. Such a theory was possible only before the development of microscopic technique had enabled the observer to detect the actual successive steps of change. The egg is a single cell, with the nucleus and all the parts of other undifferentiated cells, though it may be enormously enlarged by the presence of food-yolk. In the hen's egg this food-yolk is quite inert and the activity of development is confined to the minute disc of protoplasm on the outside of the yolk, while in the frog's egg the yolk is disseminated, though not uniformly, throughout the egg and in the mammalian egg, which is microscopic in size, there is no yolk. It is a very remarkable fact that all of the vertebrated animals, fishes, amphibians, reptiles, birds and mammals, however different their habits and modes of life, have a mode of ontogeny which is of even more characteristically and unmistakably the same plan than is the type of their adult structure, which was described in the last chapter. The egg, or the active portion of it, divides in a definite and regular manner into a very large number of cells, which arrange them- selves hi definite layers, an outer and an inner, and within these layers cell-aggregates form incipient organs, which, step by step, take on the adult condition. Not only is the plan and type of development essentially similar throughout the whole phylum of the vertebrates, but, in accordance with the recapitulation theory, many structural features which are permanent in lower forms appear in the embryos of higher and more advanced types. In the latter, however, these features are transitory and, hi the course of development, they either disappear, or are so modified as to be very different, sometimes unrecog- nizable, in the adults. At a certain stage of the ontogeny the embryo of a mammal has gill-pouches like a fish, the skeletal supports of the gill-pouches, the arteries and veins which supply them with blood, the structure of the heart, in short, the entire plan of the circulatory system is fish-like. THE RECAPITULATION THEORY 177 At a later stage most of the gill-pouches have been obliterated, but one is retained and converted into the Eustachian canal, which connects the throat with the middle ear, inside of the ear-drum. Similarly, the embryological evidence shows that the lungs of air-breathers have been derived from the swim-bladder of fishes, a conclusion which had already been reached by comparative anatomy, for in a remarkable FIG. 39. — Embryos in corresponding stage of development of shark (A), fowl (5), and man (C); g, gill slits. (From Scott.) group, known as the Dipnoi or lung-fishes, the air-bladder is utilized for purposes of respiration. It has been objected that, while embryology may prove relation- ship within a single type, it fails to demonstrate any connection between different types, but this is not altogether true. The Tuni- cata, a curious group of marine animals once referred to the Mollusca, are shown by their ontogeny to be related to the vertebrates and the same is true of certain marine worms (Balanoglossus). Indeed, most modern zoologists have adopted a scheme of classification, in which 178 READINGS IN EVOLUTION, GENETICS, AND EUGENICS the type Chordata includes not only the true vertebrates, but also the Lancelet (Amphioxus), the tunicates, and Balanoglossiis; this scheme is founded upon the embryological evidence. Among the inverte- brates even more remarkable examples have been observed. Such radically different types as the segmented worms and the shell- fish (Mollusca) are brought into relationship by their ontogeny and their closely similar types of larvae, as are also, though less distinctly, the brachiopods or lamp-shells, and the Bryozoa. The Horseshoe- crab, or King-crab, so abundant along our Atlantic coast, was long of uncertain affinities; originally referred to the Crustacea, largely because of its marine habits of life, embryology makes much more probable its relationship to the air-breathing scorpions and spiders, a result which has been examined previously from another point of view in connection with blood-tests. Even before the publication of Darwin's Origin of Species one of the great stumbling blocks in the way of the theory of special crea- tion was the existence in a great many animals of rudimentary organs, or such as are so far reduced and atrophied as to be of no service to their possessors. An analogy employed by my lamented friend, Mr. Richard Lydekker, may be advantageously repeated here. Let us suppose that a screw-steamer, with longitudinal shaft leading aft from the engine-room to the stern, where it carries the propeller, should, on close examination, reveal many signs that it has originally been a " side- wheeler," or paddle-boat. Recognizable remnants of paddle- boxes, of bearings for a transverse shaft, and the like, are found; what would be the inevitable conclusion ? No one would maintain that a naval architect, in possession of his senses, in constructing a screw- steamer would deliberately introduce features which are useful and appropriate only in a paddle-boat. The only reasonable explanation would be that the vessel had originally been built as a paddle-boat and had subsequently been converted into a screw-steamer and in the conversion it had not been found necessary completely to eradicate all traces of the original construction. Obviously, the same reasoning applies to rudimentary organs. The only satisfactory explanation of such useless remnants is that their possessors are descendants of ancestors in which those organs were fully functional. It seems quite absurd to assume that, in a separately and specially created animal, useless structures, reminiscent of other animals in which the same structures are useful and valuable, should be included, merely to indicate ideal relationships and community of plan. THE RECAPITULATION THEORY 179 It was sought to break the force of this very serious objection to the theory of special creation by saying that apparently useless organs may nevertheless have functions which are still unknown to us and may be revealed by future discovery. In certain cases, like that of the thyroid gland in the neck, this contention has been justified, but there are many others to which it does not apply. For example, in the great and varied whale-tribe (order Cetacea) which includes the right, or whalebone, whales, the sperm-whales, the porpoises, dolphins, etc., the forelimbs have been converted into swimming paddles, but the hind limbs appear to have vanished completely, leaving no externally visible trace. Internally, however, recognizable remnants of the hind limb-bones may be found in various stages of reduction, which differ in the different members of the order. In the Greenland Right Whale the hip-bone, thigh-bone and shin-bone are indicated; in the Fin whale only the hip-bones and a minute rudiment of the thigh-bone are to be found; in the toothed whales only an almost unrecognizable remnant of the hip-bone is left and in one of the dolphins even that has dis- appeared. Similarly, the snakes have lost their limbs completely, so far as external appearance is concerned, and in most members of the group no trace of limbs is to be found on dissection, but in certain snakes the rudiments of limbs are to be detected. Leaving aside all preconceptions, which is the more probable explanation of such phenomena, the theory of special creation or the theory of evolution ? Even if it were admitted that all rudimentary organs and struc- tures found in the adult have a certain unknown use and value, no one could maintain this with regard to the countless instances of structures which are developed in the embryo, but disappear entirely before birth. It is possible to mention but a very few of such instances out of the great number that have already been observed and recorded, but these few will suffice to illustrate the principle involved. " Examples of this may be cited from the most widely different groups: in the embryo of insects, especially of beetles, pairs of legs are formed within the egg, not only on the head and thorax, but also on the abdomen, but while those on the head are transformed into mouth-parts, those on the thorax are farther developed in their joint- ing and musculature to be locomotive legs, those on the abdomen are again resorbed. In many fresh-water worms, the eggs of which are laid in a cocoon, from which they are hatched as a finished, minute, crawling worm, larval organs are nevertheless formed, which recall those of the Trochophore,the larva of the original worms, which swims l8o READINGS IN EVOLUTION, GENETICS, AND EUGENICS freely in the sea. However, these larval organs .... are never properly functional, since no actually free-swimming larva is developed but the embryo merely floats in the albuminous fluid of the cocoon. "A particularly beautiful example is offered by the whales in their embryological development, which has been thoroughly studied by Kukenthal. In the adult condition they show only the anterior extremities, but in the embryo the posterior pair, with their skeletal parts, are formed,but are afterwards completely atrophied. Although they are mammals, in the adult condition they have absolutely no covering of hair, since in their aquatic life another and more effective protection against loss of heat is given by means of a thick layer of blubber; only a few coarse bristles, partly with particular functions, have persisted on a few parts of the body. But in the embryo a dense covering of hair is formed, which is later transformed in a peculiar manner and atrophied. Further, a series of whales have no teeth in the adult condition, but only the well-known, eel-trap-like, horny plates, from which whale-bone is produced. Nevertheless, in the embryo there is a dentition of numerous teeth, which are, however, resorbed, without ever piercing the gum."1 Throughout the great group of the ruminants, which includes the oxen, buffaloes, bison, sheep, goats, antelopes, deer and giraffes, the collar-bone is invariably lacking, since it is superfluous on account of the exclusively locomotive manner in which the fore legs are employed. In the embryo sheep the collar-bone is established and even, to some extent ossified, but is subsequently resorbed and disappears entirely. No doubt, the collar-bone will be found in many other embryo rumi- nants, when the proper examination shall have been made, but its demonstrated presence in the foetal sheep is sufficiently striking. In the higher mammals the number of teeth was originally 44, or 1 1 on each side of both upper and lower jaws, but in most of the modern or existing groups of these higher mammals this number has been very considerably reduced through the suppression of certain teeth. We have every reason to believe that the ancestors of the forms with reduced dentition possessed teeth in full numbers and that there has actually been a loss of teeth in the course of descent. This conclusion is abundantly confirmed by the facts of embryology. Take, for example, the great group of the gnawing mammals or Rodentia, in which the front teeth or incisors, above and below, are reduced to one on each side, except in the rabbits. The incisors are chisel-shaped and 1 Otto Maas, Die Abstammungslehre, pp. 273-74. THE RECAPITULATION THEORY 181 are faced with hard enamel, so that the action of the upper teeth upon the lower keeps the cutting edges extremely sharp; these teeth do not form roots, but continue to grow throughout the lifetime of the animal. Between the chisel-like incisors and the grinding teeth, there is a long toothless gap, which, we assume, was, hi the ancestors of the rodents, occupied by the second and third incisors, the canine and two or more grinders. This conclusion is justified by the facts of embryology; for instance, in the embryo of the squirrel several of the missing teeth are begun as distinct tooth-germs, but fail to develop, never cut the gum and are resorbed before birth. All available evidence points to the conclusion that birds are descended from reptiles, a conclusion which is especially strengthened by the facts of palaeontology and will be examined more at length in the following lecture. Such a descent explains many otherwise puzzling features in the ontogeny of birds, in which reptilian charac- teristics appear hi transitory fashion and are either modified so as to take on typically bird-like character, or are suppressed altogether. A remarkable example of this is the formation of rudimentary teeth in certain embryonic birds, followed by their resorption and disappear- ance before hatching. It can hardly be contended that these rudimentary structures, which are confined to the embryonic stages of development and of which no trace remains in the adult, are so indispensable to the processes of ontogeny, that they were specially created to serve this temporary purpose. For such a contention there is not a particle of evidence and the theory of evolution, which regards these structures as useless remnants, due to inheritance from ancestors hi which the structures are functional, offers much the most satisfactory solution of the problem that has yet been suggested. Embryology further shows that evolution is not invariably an advance from lower and simpler to higher and more complex types, but may be by way of degeneration and degradation. The adoption of a parasitic mode of life is very apt to cause such degradation, and some very remarkable instances of the degeneration of parasites have been observed. An instructive example that may be cited is that of Sacculina, a nondescript creature that is parasitic on certain species of crabs. The parasite is attached to the body of its victim, under- neath the tail, by means of root-like fibres which penetrate and ramify throughout the interior of the crab. The root-like fibres absorb nutri- ment and convey it to the body of the parasite, which is reduced to a 182 READINGS IN EVOLUTION, GENETICS, AND EUGENICS mere bag, without appendages, muscles, nervous system, sensory apparatus, digestive tract, or any determinable organs save those of reproduction. The creature has the power of assimilating the nutri- tive juices which are conveyed to it by the root-like filaments from the body of its host, and the power of reproduction, and it must have some respiratory and excretory capacity, though there are neither gills nor glands. From an examination of the adult parasite alone, it would be quite impossible to classify it and determine the type and class to which it should be referred, but embryology solves the problem. From the egg is hatched a free-swimming larva, which has jointed append- ages, nervous, muscular and digestive systems and, in short, clearly belongs to that group of the Crustacea which includes the barnacles. This is degeneration carried nearly to the utmost possible extreme and yet the individual development shows the derivation of this otherwise problematical parasite and the steps through which it passed hi its deterioration. It was stated above that several distinguished naturalists alto- gether reject the recapitulation theory as a means of interpreting the facts of embryology. They do this on the ground that, inasmuch as changes and innovations in form or structure must arise in the germ- plasm, at the very beginning of ontogeny, there is no reason why such changes might not involve the whole course of embryological develop- ment. To my mind this a priori objection to the recapitulation theory is quite without force in view of the great body of observed facts, but there is no time to enter upon a discussion of such an abstract and difficult problem. For our present purpose, however, it is important to note that these objectors are staunch evolutionists and find in the community of mode in ontogeny between different classes of organ- isms one of the strongest arguments in support of the evolutionary doctrine. PART III THE CAUSAL FACTORS OF ORGANIC EVOLUTION CHAPTER XIH INTRODUCTORY STATEMENT H. H. NEWMAN Any investigation of the causes of evolution must be preceded by a survey of the facts to be explained. Some of the principal facts which must be taken into account have already been placed before the reader in the preceding section dealing with evidences of evolution. If there were no other good reason for dealing with those materials before beginning a discussion of causal theories of evolution, the peda- gogical reason would be sufficient, because, until there is something to explain, the necessity for an explanation does not arise. We are of course aware that some writers prefer to deal with the facts of palaeon- tology, geographic distribution, classification, comparative anatomy, embryology, etc., after a discussion of the causes of evolution. Their avowed reason for this order of treatment is that the net results of a discussion of the causes underlying evolution may be used as a means of more fully analyzing the facts. This is indeed true, but it is also true that facts should come first and explanations afterward. As a final step, the facts profitably may be re-examined in the light of causal hypotheses. One of the outstanding facts of animate nature is the phenomenon of adaptation. No naturalist has failed to note and marvel at the adaptiveness or fitness of organisms to their environment and that of parts of organisms for particular functions or activities. One of the most difficult problems in evolution is the problem of the origin and the perfection of adaptations, and most causal theories of evolution have been aimed largely at an explanation of adaptation. Consequently, before we enter upon a formal discussion of the causal theories we shall introduce an outline of some of the main facts about adaptations. By way of introduction it should also be pointed out that the causes of evolution are not all of equal value. Some of the causes are to be conceived of as primary, others as secondary, or even tertiary. Variation, for example, is absolutely primary in importance. Without variation, change, which is the very essence of evolution, would of course be impossible. Not less important is heredity; for unless there be some factor which fixes variation so that it becomes a racial asset, 185 186 READINGS IN EVOLUTION, GENETICS, AND EUGENICS there can be no real racial progress; and evolution is nothing more or less than racial, as opposed to individual, progress. So obvious did this seem that Charles Darwin accepted as axiomatic the general facts of variation and heredity and proceeded at once to a discussion of the directive factors of evolution. Since variation and heredity are now universally conceded to be primary factors, and selection, the Lamarckian factor, isolation, orthogenesis, etc., as secondary or guiding factors, it would seem more natural to proceed first to a discussion of variation and heredity. So much of our present knowledge of variation and heredity, however, is dependent upon the background furnished by Darwin that it seems to us a more effective pedagogical order to consider that vast and intricate conception of evolution which was first given life and unity by Charles Darwin, and has come now to be known as "Darwinism." Just how broad the scope of Darwin's work and how important a role he played in the development of evolutionary biology is indicated in the following appreciation of Darwin which we have summarized largely from the admirable statement in Professor J. Arthur Thom- son's book Darwinism and Human Life. WHAT WE OWE TO DARWIN 1. The web of life — the idea of linkages, interdependencies, cor- relations in the living world. The idea is essentially ecological and has been expressed elsewhere as "organic equilibrium." 2. The struggle for existence — the inevitable consequence of Mal- thus' idea of overproduction. This struggle is both inter- and intra- specific, or may be a mere struggle against fate or against hard condi- tions of inorganic environment. 3. Variability of living creatures — an idea derived from the study of changes under domestication and of diversity among wild individuals belonging to the same species. 4. Natural selection — the central idea which is to be studied pres- ently. 5. Vindication of the evolution idea. — Darwin was the first effec- tively to marshal the evidences of evolution in sufficient force to com- pel the acceptance of the fact of evolution. Much that has already been presented under the head of "Evidences of Evolution" belongs to Darwin. The placing of the fact of evolution on a sure foundation is believed by many to have been Darwin's principal contribution to science. INTRODUCTORY STATEMENT 187 6. The descent and ascent of Man — " a recognition of man's solidar- ity with the rest of creation, of his affiliation to a Simian stock — that man and anthropoid apes are collateral branches from a common Pri- mate stock which remains hidden in obscurity." 7. Liberation of intelligence. — "The Origin of Species has proved a veritable Magna Charta of intellectual liberties, for, as no other single document before or since, it has released the thoughts of man from the trammels of unreasoned conservatism and dogmatism." — H. E. Crampton. 8. Ideal of scientific mood and method. — As Professor T. H. Morgan says, " It is the spirit of Darwinism, not its formulae, that we proclaim as our best heritage." Darwin was the first great evolutionist to use the inductive method, that of first securing an abundance of facts and then formulating theories to explain the facts. The above-stated eight points give us an idea of the broader con- cept of Darwinism. Today the term "Darwinism" has come to acquire a much restricted and a technical meaning. To the modern evolutionist Darwinism has come to be practically synonymous with "natural selection," or at least with the general principle of "selec- tion," some phases of which are termed "neo-Darwinism." Before we can adequately enter upon a study of Darwin's most characteristic causal theory of evolution — the natural-selection theory — it is almost imperative for us to know something of the background out of which this conception arose. Already we have presented in our survey of the evidences of evolution an array of facts most of which were known to Darwin and in accord with which he developed his causal theories. But we cannot afford to overlook the now well-known fact that what Darwinism chiefly amis to explain are the phenomena of adaptation and the web of life. These phenomena are to be conceived of as the background of Darwinism and will be dealt with as such in the next chapters. CHAPTER XIV THE BACKGROUND OF DARWINISM ADAPTATIONS H. H. NEWMAN "The adaptation of every species of animal and plant to its environment," says Jordan and Kellogg,1 "is a matter of everyday observation. So perfect is this adaptation in its details that its main facts tend to escape our notice. The animal is fitted to the air it breathes, the water it drinks, the food it finds, the climate it endures, the region which it inhabits. All its organs are fitted to its functions: all its functions to its environment. Organs and functions are alike spoken of in a half-figurative way as concessions to environment. And all structures and powers are in this sense concessions, in another sense, adaptations. As the loaf is fitted to the pan, or the river to its bed, so is each species fitted to its surroundings. If it were not so fitted, it would not live. But such fitness on the vital side leaves large room for variety in characters not essential to the life of the animal. " The authors quoted above appreciate what is perhaps the most significant fact about adaptations: that the adaptations are to a large extent molded by the environment and therefore fit the environment^ So long as the environment remains uniform, a given species will remain unchanged, except for minor fluctuations and .occasional mutations; but if the environment changes, sometimes even slightly, the development of the individual responds in such a way as to give a radically different end product. So we may conclude that a large part of the fitness of the organism to the environment is due to the fact that the development of each individual is molded by the environment so as to fit it. Thus some at least of the apparent mystery of adaptations is dispelled. When we think of the fitness of the organism to the environment we take an entirely one-sided view of the matter, for if the organism-^" fits the environment, no less certainly must the environment fit the^ organism. This idea of the "fitness of the environment" has been" 1 From D. S. Jordan and V. L. Kellogg, Evolution and Animal Life. 188 THE BACKGROUND OF DARWINISM— ADAPTATIONS 189 admirably discussed by Professor Lawrence J. Henderson in a stimu- lating volume.1 Henderson points out that the enviromisnt, no less than organ- isms, has had an evolution. The particular environmental complex as it exists today is absolutely unique. There is hardly an element of the effective environment that could be changed without causing the extinction of life or at least a transformation of it so profound that it might not be life at all as we know life. Water, for example, has a dozen unique properties that condition life. Carbon dioxide could not be replaced by any other substance. The properties of the ocean are so beautifully adjusted to life that we marvel at the exactness of its fitness. Finally, the chemical properties of carbon, hydrogen, and oxygen, the most abundant elements, are equally unique and unre- placeable. In brief, given the environment as it is, life could not be other than it is. The evolution of the environment and the evolution of organisms have gone hand in hand, or perhaps we might better say hand in glove, for this better expresses the idea of mutual fitness. Within the realm of the general environment as conceived by Henderson there are almost innumerable special environments due to particular combinations of the various environmental units. Within the aquatic environment, for example, there are variations such as differences in salinity, varying from extreme saltiness to almost total lack of salt; there are inshore conditions and open-sea conditions; there are surface conditions and those at relatively great depths; and there are great differences due to temperature. Similarly on land, there are surface conditions, subterranean conditions, caves, deserts, forests, plains, mountains, arctic, tropical conditions, and many others. No two areas on land are precisely similar hi all respects. All of this makes for a corresponding multiplicity of animal and plant forms. In the case of plants the action of the environment is remarkably direct; for the plant cannot get away from a fixed environment. If the environment undergoes material change, the plant's only response is a structural one. For example, if plants that are accustomed to a rela- tively humid climate are grown in the desert they develop numerous xerophytic adaptations such as small leaves with greatly diminished transpiration surface, a thick epidermis, hairs, or spines, small stature, deep-root system, and other similar protections against the inimical desert conditions. Similarly, plants accustomed to grow in relatively 'L. J. Henderson, The Fitness of the Environment, 1913. 190 READINGS IN EVOLUTION, GENETICS, AND EUGENICS dry soil, if grown in soil that is covered over with water, will produce aquatic leaves and roots and undergo appropriate changes in epidermis and loss of supporting tissues, for plants that are buoyed up by water need little support. Animals, on the other hand, are for the most part not so intimately related to a local environment as are plants. They are characteristi- cally mobile creatures with varying capacities for wandering about and selecting the habitat that best suits them. "By virtue of being unlike or possessing different properties," says Shelford,1 " the various animal species require different conditions for the best adjustment of their internal processes. For example, the carp lives in shallow and muddy ponds and rivers, while the brook trout lives only hi clear swift streams. These two organisms are able to move about and find places to which they are suited. The differ- ences between them are clearly indicated by the differences in the habitats which they prefer. "By observation and by experimentation it has been shown that animals select then- habitats. By this we do not mean that the animal reasons, but that selection results from regulating behavior. The animal usually tries a number of situations as the result of random movements, and stays in .the set of conditions in which its physiological processes are least interfered with. This process is called selection by trial and error. If animals are placed in situations where a number of ' conditions are equally available, they will almost always be found liv- ing in or staying most of the time in one of the places. The only reason to be assigned for this unequal or local distribution of the ani- mals is that they are not hi physiological equilibrium in all the places. However, some animals move about so much that it is with some difficulty that we determine what their true habitats are." This idea of habitat preference and habitat selection is extremely -'important for a correct understanding of adaptation, or the fitness of .^organisms to environments. Much of the observed fitness may be due to the fact that an organism has chosen out of a wide range of environ- ments the one that best suits it. We cannot in such a case say that the environment has had a direct influence in shaping the organism any more than we could say that, when a man tries on various shoes and finds a pair to fit, he has been responsible for the fitness of the shoes. Many special adaptations may be explained through habitat - choice. Thus animals such as the duckbill platypus, the lung-fishes, 1 V. E. Shelford, Animal Communities in Temperate America (1913). THE BACKGROUND OF DARWINISM— ADAPTATIONS 19 1 and others whose teeth are replaced by bony or chitinous plates that are used for crushing the hard shells of molluscs and crustaceans, may not confidently be said to have developed these crushing appliances and to have abandoned the use of teeth in adaptation to a habit of feeding upon hard-shelled prey; but rather it seems more likely that the loss of teeth and the development of crushers occurred through a degenerative process incident to racial senescence and that the pos- session of the crushing equipment enabled them to avail themselves of a new type of food, formerly unavailable to them. The organic environment. — In his admirable chapter entitled "The Web of Life," which we shall quote entire, Professor Thomson has given us a vivid picture of vast systems of interdependencies that exist throughout the organic world. No species, no creature, lives to itself alone; it is intimately tied up with a host of other creatures with interwoven destinies. Thus one species of animal is adapted to live upon certain plants or other animals, which in turn may be dependent upon still other animals or plants. The elimination of one species may cause the elimination or the radical change of a dependent species. We cannot afford ever to forget this great truth of the oneness of nature. It is the keynote of life and of evolution. Adaptation due partly to functional activity. — It is a commonplace which needs no special demonstration to say that organs improve through use and deteriorate through disuse. Many organs, then, which in the adult condition appear to us to be so admirably adapted to perform certain duties, must be thought of as having been gradually molded by functioning during the entire period of individual development. If the motor nerve running to a limb bud of a growing embryo be severed at an early stage and no secondary nerve connection be established, the limb will continue to grow up to a certain point, but, in its paralyzed condition, will be incapable of exercising its functions and will cease to develop. A certain amount of development will therefore be seen to be independent of functioning, but full develop- ment of functional efficiency is obtained only through functioning. "The relation between structure and function hi an organism," says Professor Child,1 "is similar hi character to the relation between the river as an energetic process and its banks and channel. From the moment that the river began to produce structural configurations in its environment, the products of its activity accumulated in certain 1 C. M. Child, "Regulatory Processes in Organisms," Jour. Morph., Vol. XXII (1911). IQ2 READINGS IN EVOLUTION, GENETICS, AND EUGENICS places and modified its flow It moulds its banks and bottom, forming here a bar, there an island, here a bay, there a point of land, but still flowing on, though its course, its speed, its depth, the character of the substances which its carries in suspension or in solution, all are altered, built up by its own past activity." According to this view, structure is simply the resultant of the interaction of function and en- vironment or of functional activity. Though perhaps a little extreme for most of us, this view is, we believe, essentially correct. We are prone to overemphasize structure in our discussions of adaptation and evolution and to lay too little stress upon the energy side of development. Certainly no structure is ever formed without proto- plasmic activity of a very definite sort, and in this sense adaptations are to be thought of as the results of functioning. Why, then, do we claim to be astonished at the effective way in which certain organs accomplish their functions, when functioning has taught them their task? LAWS OF ADAPTATION Adaptations have been variously classified by different writers. Perhaps the most significant classification is that of Osborn, which is based on their supposed evolutionary origin. According to this writer and others, there are two categories of adaptations to environ^ mental conditions: the first has to do with the tendency of unrelated species to assume similar structures under similar environmental conditions; the second has to do with the tendency of related species to assume different adaptive structures under different environmental conditions. In both categories the environment appears to be the determining factor. (i) A good example of the first category, which illustrates what Osborn calls "the law of convergence or parallelism of form," is seen ^ in the tendency of many aquatic types of vertebrates to assume the^ fishlike form. As is well shown in Fig. 40, the shark (a fish), the ichthyosaur (an extinct aquatic reptile), and the porpoise (a marine mammal), all possess the same fusiform body best adapted for speed under water, the same types of locomotor structures, consisting of the great propeller fin (caudal fin) and the steering and balancing fins, the dorsal fins and paired fins. Apart from these superficial adapta- tions for swift locomotion in the water, the three types are pro- foundly different. The shark breathes with gills, the reptile and mammal with lungs, the fish and reptile are cold-blooded, the THE BACKGROUND OF DARWINISM— ADAPTATIONS 193 FIG. 40. — Three aquatic types of vertebrate, to illustrate convergent adapta- tion of three wholly unrelated forms of marine life. All three show the fusiform body, median and paired fins, though the skeletal structures are radically differ- ent. A, shark (Pisces); B, ichthyosaur (Reptilia); C, porpoise (Mammalia). (From Newman, after Osborn.) 194 READINGS IN EVOLUTION, GENETICS, AND EUGENICS mammal warm-blooded. The internal anatomy of the three differs fundamentally in every detail. A list of other types of convergence will more adequately illustrate the law. Flying and parachuting animals occur among nearly all vertebrate and some invertebrate classes. Planes of some sort are found for supporting the body in the air. The plane is made in various ways in different groups, but functions much the same in all of them. Running animals of various classes have long legs, and a tendency to stand on the toes. There is also in several unrelated groups the tendency to reduce the number of toes, the culmination of which is seen in the one-toed horses. Climbing animals are all provided with clinging appendages of some sort, including such structures as hooked claws, prehensile fingers or tail, suction pads on the feet, and other similar adaptations. Burrowing animals have, as a rule, extra-heavy shoulder girdle and strong fore limbs with heavy gouging claws. Many of them also are blind or nearly so, as befits life in dark underground passages. Desert-dwelling animals as a rule are provided with heavy scales, spines, or armor, to prevent excessive loss of moisture and as a protection against spiny plants. They also usually have burrowing habits enabling them to escape the extremes of heat and cold. Cave animals are usually blind or nearly so and are relatively pale in color, sometimes without any pigmentation. Deep-sea animals of many sorts have phosphorescent organs by means of which they either attract their prey or find their way about the dark sea floor. Some of these organs, called "lanterns," can be used as searchlights. The eyes of deep-sea fish are either enormously large or are "telescope eyes," adapted for sensing light of low intensities. Ant-eating animals, belonging to several distinct groups, are heavily armored against the attacks of ants, have strong claws for digging up ant galleries, have long snouts or beaks with a long sticky tongue for capturing ants, and an arrangement of the glottis to prevent ants from crawling into the lungs. 2. There are almost innumerable examples of the law of divergence / of form, which is called also the law of adaptive radiation. Almost every successful class or order of vertebrate animals, for example, has members that have adjusted themselves to all of the main modes.-_ of living. Thus among lizards, for example, there are primitive THE BACKGROUND OF DARWINISM— ADAPTATIONS 195 running forms that prefer the surface life and swift motion; subter- ranean burrowing types that sometimes are limbless like snakes, and are blind; many arboreal or climbing types; a few volant or flying types; a few ant-eating types; and several more or less completely aquatic types. Each of these types has the customary adaptations for its own mode of life. We see, then, that whether divergent structures are molded into a semblance of similarity to fit a definite environment, or whether similar structures are modified in diverse ways to fit various divergent environments, the adaptation is related very definitely to the environ- ment and to the functional life of the organism. No wonder, then, that so many biologists consider that the environment has been a molding force in the evolution of adaptations. One of the most interesting discussions of adaptations is that of Weismann, who, it appears, is greatly impressed with the uni- versality of adaptation. His thesis apparently is that if we had complete knowledge of the field of biology, we would discover that everything is adaptive, and that many structures or habits that now appear to us useless or non-adaptive, would be found to have a definite value to the organisms possessing them. Some authors take the opposite extreme and claim that adaptation has been merely read into a vast number of so-called adaptive structures and that when these structures shall have been adequately investigated they will be found to lack the value imputed to them by uncritical observers. Some- where between these extreme views lies the truth. Thus we see that a certain amount of adaptation is inevitable and needs only a formal physiological explanation. The fitness of the environment, habitat selection, and the relationship that exists between function and structure, are adequate explanations for the, general fact of adaptation and thus take away much of the mystery that has shrouded the concept of fitness. There are, however, very many types of special adaptation which do not yield so readily to the general explanation given. Some of the most important of these will be de-^ scribed below. ADAPTATIONS CLASSIFIED Adaptations are variously classified by different authors, and that of Jordan and Kellogg is as good as any: " (a) food-securing; (6) self- defense; (c) defense of young; (d) rivalry; (e) adjustment to sur- roundings." 196 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Some very common adaptations may belong to several of these categories at once. Thus the sharp teeth and hooked claws of car- nivorous mammals serve equally well for food-securing, for self- defense, for defense of young, and for rivalry. Similarly, the horns of deer and other ungulates are equally adapted for self-defense, defense of young, and rivalry. There can be no especial advantage, in this connection, in present- ing a detailed review of adaptations of the sorts given in the foregoing classification; therefore we shall confine our efforts to a description of a few typical adaptations about which the greatest controversy has raged. SOME SPECIAL ADAPTATIONS The electric organ of the torpedo, a widely distributed elasmo- branch fish, consists of a sort of honeycomb-like structure on each side of the head. This structure acts as a storage battery and is capable of storing up electricity of considerable voltage. The animal is capable of giving a very distinct shock to an attacker and can thus defend itself quite effectively. There is also an electric eel, native to the waters of Paraguay and Brazil, that is able to give severe shocks to bathers or to horses driven through the streams. A type of catfish native to the river Nile has a similar electric equipment. In all of these cases the storage battery is made up of modified voluntary muscles and is of considerable size. The mammary glands of mammals are skin glands usually with well-defined ducts leading to the surface and terminating in teats. These glands are quite voluminous and serve admirably the purpose of feeding new-born young until the latter are able to use the more varied food normal to the adult. In the lowest mammals, the monotremes or egg-laying mammals, these glands are relatively poorly developed and diffuse; also they are known to be developed through a regional specialization of sweat glands. In the true mammals or Eutheria the glands are modified sebaceous or oil glands and may be seen to develop from the same embryonic rudiments as the latter. The marsupial pouch of the kangaroo and its allies is a pocket- like fold of the integument, folded forward or backward over the region of the abdomen in which are located the mammary glands. This pouch is used as a shelter for the tiny immature larval foetuses. Hartmann has recently described a very striking piece of behavior in connection with the birth of young opossums. The young are born THE BACKGROUND OF DARWINISM— ADAPTATIONS 197 in an exceedingly immature state and looking like tiny pink grubs. They crawl under their own power, by means of a swimming-like motion, through the hairs of the mother's abdomen, till they reach the pouch. This they enter unaided and each tiny larva finds for itself a slender tubular teat, which it swallows and holds in place by a specially adapted hold-fast mouth. The young remains attached fixedly to this teat for some weeks, feeding almost constantly on milk. After a long interval the teat is released, the mouth metamorphoses into the adult form and the young feeds only at intervals, as do the young of other mammals. This complex of adaptive structures and instincts is among the most remarkable in the annals of biology. Nest-making instincts in birds represent, on the behavior side, adaptations of extraordinary perfection. Some nests are built with the greatest care and precision, others represent a relatively crude and slovenly performance. Some nests are made of twigs, fibres, and mud, others of mud alone, still others are hollowed out in clay or sand banks, and some are made in holes in the ground. In any case, the type of nest is highly specific and due to a hereditary instinct; for birds receive no instruction in nest-making. Before bringing to a close this brief list of particularly noteworthy / adaptations let us recall to mind the series of special adaptations listed as examples of the laws of adaptation, such as aquatic, arboreal, cur- Serial, flying, burrowing, ant-eating, and, especially, adaptations of Aeep-sea animals. PARASITISM AND DEGENERATION A vast number of animals and plants have given up the active search for food and have taken up the relatively easy habits of para- sitism. In adaptation to this life certain structures have developed and many of the characters found in independent, free-roving crea- tures have disappeared or become reduced to mere vestiges. Thus the more completely dependent or parasitic an animal becomes, the more completely does it lose its organs of locomotion and its sense organs such as eyes, auditory organs, tentacles, etc. Some animals are free-living when young or in the larval condition and only settle down to a parasitic life when near the end of the life-cycle; other animals are parasitic only when young or larval and become inde- pendent in the adult condition; still others are parasitic throughout the entire life-cycle and pass from host to host without any interval of independent life. Some of these complete parasites pass one phase of the life-cycle on one species of host and the remainder on another 198 READINGS IN EVOLUTION, GENETICS, AND EUGENICS species of host. Thus the liver fluke in the adult condition lives in the gall bladder of the sheep, while the early larvae live within the body cavities of a species of land snail. The transfer from host to host in this case must be a procedure involving many chances of failure to a very few chances of success, and, in adaptation to these vicissitudes, the number of eggs and larvae produced by a single adult individual runs up into the millions. The classic case of extreme parasitic degeneration is that of Sacculina. The young larva of Sacculina is a typical entomostracan crustacean larva which swims about and leads a free life for a time, but soon attaches itself by means of its antennae to a hair pit of a crab, a small hole in the latter's armor. The internal tissues of the larva then undergo degenerative processes and are reduced to an almost fluid mass of embryonic cells, which flow through the hair pore of the crab, and into the latter's lymph spaces. The small mass of cells then rounds up and is carried about with the circulation of the crab's blood until it comes to a favorable place of lodgment, usually the wall of the intestine just back of the stomach. Here it flattens out and sends rootlike branches almost all over the crab's body, like a malignant tumor in its invasion of foreign tissues. The unbranched part of the parasite is little more than a sac of reproductive organs, and these produce eggs and sperms, which unite to produce larvae. By this time the host is killed and, with the decay of its body, the larvae escape into the sea water ready for a brief period of free life before attacking another host. Almost every group of animals and most of the groups of plants •/, have their parasitic representatives and every degree of parasitism and the accompanying degenerative changes are to be found. Of course, it is an open question whether parasitism causes degeneration or whether degenerating creatures take refuge in parasitism; but in either case the adaptive features of the situation are obvious. Commensalism. — If parasitism be defined as an association between two organisms in which one (the parasite) lives at the expense jrf and to the detriment of the other (the host), commensalism may be" ..t defined as an association hi which the two organisms exist in close association without any positive detriment to either. In some cases the claim is made that the association is mutually beneficial, but as a rule the relation is relatively one-sided. An interesting example of commensalism is that of the sea cucum- ber and the little fish Fierasfer. This strange little animal inhabits THE BACKGROUND OF DARWINISM— ADAPTATIONS 199 FIG. 41. — Fierasfer acus, penetrating the anal openings of holothurians, f natural size. (From Boulenger, after Emery.) the rectum of the sea cucumber and may be seen to lie with only its head out. From this shelter it darts forth to capture its prey; which done, it returns to its shelter. Curiously enough the vent of the little fish is situated just back of its mouth so that its wastes may be voided when in its usual position. There can be no advantage to the sea cu- cumber in such an arrange- ment, though no particular harm is done. Another case of this sort is that of several species of Remora which attach themselves by a large diskoid adaptation on top of the head to various fish such as sharks, barracudas, etc. The sucking disk is a modified dorsal fin. The remora merely gains free transportation to more favorable feeding-grounds. When the desired food is sighted the passenger leaves its conveyance tempo- rarily, but returns by a sudden swift dash and resumes its hold. The shark gets nothing except perhaps the sense of companionship, and is also undoubtedly somewhat hindered in its locomotion. Some of the most remarkable cases of commensalism are found in connection with elaborate colonies of ants. In some cases two species of ants live together in the relationship of masters and slaves. The master species is unable to perform any of the ordinary duties of the colony, such as securing food, taking care of young, etc. In extreme cases the masters are only soldiers, specialized for fighting and maraud- ing, and cannot even feed themselves unaided. The slave species would be able to carry on to some extent if not captured, but thrives exceptionally well under the protection of the soldier species. There are among ants many varieties of commensal relationship less extreme than this, but this will serve as a typical case. Communal life. — Among the higher insects and higher vertebrates"^ especially among the ants and bees, we find a very elaborate social life?^ In ants, for example, the typical colony consists of a queen (the only fertile female in the colony), several males (mates of the queen), 200 READINGS IN EVOLUTION, GENETICS, AND EUGENICS ordinary workers (sterile females of the first type), soldiers (sterile females of the second type), and sometimes officers (especially large and powerful sterile females that seem to direct the line of march in legionary ants). All of these casts are produced from the eggs of one female and are the result of various special diets permitted the larvae by the workers. Among bees, similarly, there is one queen, a number of drones (males), and the sterile female workers, who perform the functions of nursing the larvae, cleaning up the hive, collecting pollen and nectar, and making honey and wax. Detailed accounts of the lives of bees have been given by various authors, notably by Maeter- linck in his Life of the Bee. COLOR IN ANIMALS "The phenomena of color in both animals and plants," says Metcalf,1 "are among the most remarkable and interesting in the ~~- whole realm of nature. It is not so much the way in which the color A is produced, whether by pigments or by refraction, that interests us - in this connection, (as it is the uses to which colors are put. Let us first refer to the colors of animals. "According to the uses to which colors in animals are put, we may classify them, for purposes of description, as follows: " Indifferent coloration, not useful, so far as we can judge; Colors of direct physiological value; Protective coloration and resemblances; Aggressive coloration and resemblances; Alluring coloration and resemblances; Warning coloration ; Immunity coloration; Mimetic coloration and resemblances; A. Protective B. Aggressive Signals and recognition marks; Confusing coloration; Sexual coloration." A few examples of these categories of animal coloration will serve to illustrate the ways in which they are believed to be adaptive and A—thus better to fit the organism for its struggle for existence. Protective resemblance.— Many animals that live at or near the surface of the sea are practically transparent. Fishes are commonly 1 M. M. Metcalf, Organic Evolution (1911). THE BACKGROUND OF DARWINISM— ADAPTATIONS 201 dark-colored above and light-colored below, so that to the enemy above they blend with the dark bulk of the water and to the enemy below they are hidden by the fact that the shadow cast by their own bulk is sufficiently neutralized by the ventral light coloring to render them inconspicuous. A very large number of arboreal animals are green; such as grass- hoppers, leaf hoppers, spiders, green lizards, parrots, etc. Prairie and desert animals are usually dull-colored like their surroundings. Many butterflies are brightly colored like the flowers upon which they feed. Many arctic animals are white like their snowy background. Some animals, like the chameleon and the flounder, change their colors so as to keep in harmony with changing backgrounds. There are many cases of protective resemblance, involving both form and color, between an organism and some particular feature of its environment. The walking-stick insect is long and slender and colored like a twig. Many caterpillars when disturbed stand out stiff and straight like leafless twigs. A species of sea-horse (a teleost fish) has its fins fringed out into structures that closely resemble the fronds of seaweed in which the animal lives. Many insects, belonging to several orders, have very striking resemblances to leaves. The case of Kallima (Fig. 42), the dead-leaf-butterfly is a classic example of this type of protective resemblance. The resemblance is so nearly perfect that, when one has mounted specimens of butterfly and leaf before him, he has to examine them closely to detect the fraud. The details of the leaf color, veins, petiole, marginal notches, even wormholes, so common in dead leaves, are reproduced in the butterfly's wings. Many tree- frogs have a leaf-shaped pattern bordered with black to resemble the shadow cast by a leaf. These are only a few scattering examples of an exceedingly prevalent type of adaptation. Aggressive coloration and resemblance. — There is a close simi- larity between this phenomenon and the one just dealt with, but instead of being used defensively, it is used offensively, in that it enables the predaceous animal to remain hidden from its prey. Thus the polar bear and the arctic fox are white and therefore inconspicuous to seals and arctic birds, their prey. Perhaps the most striking instance of this type of coloration is that of the tiger, whose tawny coat and dark stripes resemble the reeds and their vertical shadows in the jungle. Alluring coloration and resemblance. — "In India," says Metcalf, "there is a Mantis (insect) which in shape and color resembles an 202 READINGS IN EVOLUTION, GENETICS, AND EUGENICS orchid blossom. It deceives butterflies and other insects, which it captures as they approach the seeming flower. In Java there is a spider which resembles a bit of bird excrement upon which butterflies are so apt to light. This resemblance enables it to capture the butterflies upon which it feeds." FiG.42.—Kallima, the "dead-leaf butterfly." (From Jordan and Kellogg.) Warning coloration. — Many animals that are for various reasons harmful or dangerous to other animals have strikingly distinct color patterns which have been interpreted by some authors as warning marks to keep off possible attackers. Bees, wasps, hornets, some poisonous snakes, many spiders, all of which have stings or fangs, are marked with bands of contrasting colors. Other animals that are THE BACKGROUND OF DARWINISM— ADAPTATIONS 203 nauseous if eaten, still others, like the skunk and his tribe, that pro- duce offensive odors, have well-defined markings that are classed as examples of warning coloration. Immunity coloration. — Professor Reighard has taken exception to the interpretation of conspicuous coloration as warning adaptations. His theory of "immunity coloration" furnishes an alternative interpre- tation which appears less open to criticism. According to this idea well-protected animals are relatively safe from attack and therefore may become conspicuous without endangering themselves. They are immune and therefore their conspicuous markings may be merely the result of color run riot without any check on the part of natural selection. Mimicry. — This is a special type of protective coloration in which an otherwise defenseless species has a striking resemblance to some well-protected species with warning coloration. Thus wasps and bees are "mimicked" by flies, beetles, and moths. They enhance the resemblance by similarities of behavior and habitat. Ants are pro- tected by the fact that they contain formic acid, which is distasteful to most animals (though some animals feed very largely on them). Consequently there are many ant mimics belonging to several orders of insects and to spiders. In some cases these ant mimics are inhabit- ants of ant colonies and succeed in passing themselves off as ants even among the ants themselves. The classic cases of mimicry, however, are those in which certain species of edible butterflies are said to mimic other, unrelated, nauseous species of butterflies. It is very difficult to distinguish the model from the mimic except by careful anatomical examination which, of course, could not be applied in nature. It should be said about mimicry, however, that it would work only in case the mimic occurs in much smaller numbers than the model, and that the two species occupy the same regions at the same _lme. Some critics have claimed that these conditions do not prevail in all cases. If their contention is valid, the usual expla- nations of mimicry need revision. Cases of aggressive mimicry are noted among certain predaceous animals, such as spiders which mimic flies and ants, and are therefore able to approach their prey more effectively. Signals or recognition marks. — The common cotton-tail rabbit raises its white tail when it runs. This is interpreted as a signal of danger to other rabbits. Some antelopes have a conspicuous white rump which is supposed to be a danger signal. Many distinct specific 204 READINGS IN EVOLUTION, GENETICS, AND EUGENICS markings such as the red heads of woodpeckers, distinct white or black bar? on the wings of other birds, may serve for recognition purposes within the species. Confusing coloration. — Many butterflies and moths, and not a few birds have rather conspicuous markings when in flight, which may serve as specific recognition marks; but when they alight after a zigzag course through the air, they cover up the conspicuous markings and blend with the background in various ways. They are supposed to alight when in danger of capture and they apparently disappear, much to the confusion of the pursuer. Thus Kallima, the dead-leaf butterfly, is quite conspicuous from above while in flight, but when it alights, it cannot readily be distinguished from a dead leaf. Sexual coloration. — A great many groups of animals exhibit a pronounced sexual dimorphism in color and pattern. The most conspicuous instance of this is that of birds among which the female is usually protectively colored so as to be inconspicuous when on the nest or when sheltering the young, while the male of the same species is frequently conspicuously colored. Similar situations are found among butterflies and moths in which sometimes one sex and some- times the other is the more elaborately colored. Sexual coloration is also common among teleost fishes, lizards, spiders, and many other groups. Charles Darwin devised a special "sexual selection" theory to account for just this type of adaptation. One more kind of coloration that is not specifically dealt with by Metcalf is what has now come to be known as "camouflage." Many animals when viewed out of their environment appear to be very conspicuous owing to the juxtaposition of patches of irregular colors. In their natural surroundings, however, they become practically invisible. Thus the nighthawk with its strongly contrasted patterns almost fades from view against the bark of a tree. For excellent illustrations of animal colorations the reader is referred to Professor Metcalf's book Organic Evolution, where he has gathered together in color plates many of the finest examples of the phenomena under discussion. General considerations. — Adaptations are characteristic of all living organisms and must be accounted for by any evolutionary theory that is to be acceptable. Any theory that claims to account for new species but does not account for adaptations is at best only a partial explanation. All of the phenomena which have been briefly men- tioned in this chapter, together with the more intricate phases of THE BACKGROUND OF DARWINISM— ADAPTATIONS 205 general adaptiveness involved in the idea of "the web of life," are part' of the background of Darwinism and were in the mind of Darwin when ^ he thought out the great generalization called "natural selection." - The "web of life" idea has been admirably presented by Professor Thomson, Scotland's most skilful and prolific biological writer. The present writer feels that no student of evolution should miss the oppor- tunity of getting into the spirit of Darwinism with this distinguished author, and to make this desideratum easily attainable, the chapter is quoted unchanged as part of the general text and immediately follows this discussion. CHAPTER XV THE BACKGROUND OF DARWINISM— Continued THE WEB OF LIFE1 J. ARTHUR THOMSON Naturalists, in the true sense, who study the life of living creatures in nature, have always been distinguished by a keen perception of the interrelations of things. Whether we take Gilbert White as repre- senting the old school, or W. H. Hudson as representing the new, we get from their observations the same impression of nature as a vibrat- ing system, most surely and subtly interconnected. But it seems just to say that no naturalist, before or since, has come near Darwin in his realisation of the web of life, in his clear vision and picture of the vast system of linkages that penetrates throughout the animated world. - Correlation of organisms as well as correlation of organs. — In thinking of a living body we are accustomed to the idea of the cor- relation of organs. It is of the very nature of an organism that there should be mutual dependence among its parts. The organs are all partners in the business of life, and if one member changes others also are affected. This is especially true of certain organs that have developed and evolved together, and are knit by close physiological bonds. We know in health how nerve and muscle, brain, and sense organs, heart and lungs, are closely bound together in the bundle of life. We know in disease that a change in one organ often affects another, and the fact remains though the nexus is sometimes myste- rious. The state of our liver may give colour to our whole intellectual firmament, and a slight ocular derangement may warp a wise man's philosophy. The far-reaching importance of a little organ like the thyroid gland beside the larynx is well known; our intellectual as well as our bodily health depends on its soundness. Now, just as there is a correlation of organs within the body, so there is a correlation of organisms hi that system of things which we call Nature. In both cases we are here using the word "correlation "in its deeper sense — 1 From J. A. Thomson, Darwinism and Human Life (copyright 1909). Used by special permission of the publishers, Henry Holt & Company. 306 BACKGROUND OF DARWINISM— THE WEB OF LIFE 207 that the various parts are more than mutually dependent, that they are in some measure co-ordinated, making larger systems workable. What the metaphor of "the web of life" suggests. — We may use the metaphor "web of life" hi two ways. On the one hand, Nature has a woven pattern which science seeks to read, each science following the threads of a particular colour. There is a warp and woof hi this web, which to the zoologist usually appear as "hunger" and "love." There is a changing pattern in the web, becoming more complex as the ages pass; and this is evolution. But the essential idea of a web is that of interlinking and ramifying. We can never tell where a thread will lead to. If one be pulled out, many are loosened. This is true of Nature through and through. The phrase "web of life" suggests another picture — the web of a spider — often an intricate system, with part delicately bound to part so that the whole system is made one. " The quivering fly entangled in a corner betrays itself throughout the web; often it is felt rather than seen by the lurking spinner. So in the substantial fabric of the world part is bound to part. In wind and weather, or hi the business of our life, we are daily made aware of results whose first conditions are very remote; and chains of influence, not difficult to demonstrate, link man to beast, and flower to insect. The more we know of our surroundings the more we realise that nature is a vast system of link- ages, that isolation is impossible." / Dependence of living creatures on their surroundings.— We do not know what life hi principle is, but we may describe living as action and reaction between organisms and then- environment. This is the fundamental relation — the dependence of living creatures on appro- priate surroundings, and the primary illustrations of linkages must be found here. The living creatures are real, just hi the same sense as the surroundings are real; but it is plain that we cannot abstract the living creatures from then* surroundings. When we try to do this they die — even hi our thought of them, and our biology is only necrology. Huxley compared a living creature to a whirlpool hi a river; it is always changing, yet always apparently the same; matter and energy stream hi and stream out; the whirlpool has an individuality and a certain unity, yet it is wholly dependent upon the surrounding currents. One may push the whirlpool metaphor too far, so as to give a false sim- plicity to the facts, for when vital whirlpools began to be there also emerged what cannot be discerned hi crystal or dewdrop — the will to live, a capacity of persistent experience, and the power of giving rise to 208 READINGS IN EVOLUTION, GENETICS, AND EUGENICS other lives. To ignore this is to attempt a falsely simple natural history. But what Huxley's metaphor of the whirlpool does vividly express is the dependence of living creatures on their surroundings. We cannot understand either the whirlpool or the trout apart from the stream. When we think out this fundamental dependence upon surround- ings, we see, for instance, that all our supplies of energy, all our powers of every kind — with our own hands, or by the use of animals, or by means of machinery— are traceable to the sun. Or again, it is easy to show that our society depends fundamentally not on gold, but on iron. We depend for food on plants and animals, and through these animals on plants ultimately; the plants feed upon air, water, and salts, which, with the aid of the energy of the sunlight, they build up into complex organic compounds; they cannot do this unless the sun shines through a screen of green pigment called chlorophyll; there cannot be chloro- phyll without iron; therefore our whole social framework is founded on iron. ( Nutritive chains.-f-Plants feed on their inanimate environment in a direct way that is impossible to animals,, so we pass insensibly from dependence on surroundings to^hose nutritive chains which bind living creatures together in long series^ of ten quaintly suggestive of "The House That Jack Built" and similar old rhymes. We have ceased to wonder at the circulation of the blood in our body; have we begun to wonder enough at the ceaseless circulation of matter hi the system of nature ? As Heraclitus said, TTOLVTO. pd, all things are in flux. "The rain falls; the springs are fed; the streams are filled and flow to the sea; the mist rises from the deep and the clouds are formed, which break again on the mountain-side. The plant captures air, water, and salts, and, with the sun's aid, builds them up by vital alchemy into the bread of life, incorporating this into itself. The animal eats the plant and a new incarnation begins. All flesh is grass. The animal becomes part of another animal, and the reincarnation continues." The silver cord of the bundle of life is loosed, and earth returns to earth. The microbes of decay break down the dead, and there is a return to air and water and salts. We may be sure that nothing real is ever lost; we are sure that all things flow. Penelope-like, Nature is continually unravelling her web and making a fresh start. Nexus between mud and clear thinking. — To keep a famous inland fish-pond from giving out, some boxes of mud and manure were placed at the sides. Bacteria — the minions of all putrefaction— BACKGROUND OF DARWINISM— THE WEB OF LIFE 209 worked in the mud and manure, making food for minute Infusorians which multiply so rapidly that there may be a million from one in a week's time. A cataract of Infusorians overflowed from box to pond, and the water-fleas and other small fry gathered at the foot of the fall and multiplied exceedingly. Thus the fishes were fed, and, as fish- flesh is said to be good for the brain, we can trace a nexus from mud to clear thinking. What was in the mud became part of the Infusorian, which became part of the Crustacean, which became part of the fish, which became part of the man. And it is thus that the world goes round. Correlation between catches of mackerel and amount of spring sunlight. — A curious and most interesting correlation has been discovered by Dr. E. J. Allen between catches of mackerel and the amount of sunlight. The more sunshine in May, the more mackerel at Billingsgate. How does this work out ? Mr. G. E. Bullen shows that "for the years 1903-1907 there appears to be a correlation between the number of mackerel taken during May, and the amount of Copepod plankton, upon which the mackerel feed, taken in the neighborhood of the fishing grounds during the same month." Mr. W. J. Dakin shows that the food of Copepods consists largely of the vegetable organisms of the plankton, such as diatoms, and of Infusoria-like organisms called Peridinidae. But the production of this microscopic plankton, the "stock" of the "seasoup," depends partly on the composition of the sea-water, partly on the tempera- ture, and partly on the amount of light available. There seems to be no correlation between the surface temperature and the abundance of mackerel, but Dr. Allen has shown a correspondence between sunshine and the catches. Thus we see that, if all flesh is grass, then in the same sense all fish is diatom. Nutritive chains in the deep sea. — If we pass from the sunlit open sea to the floor of the deep sea — that strange, dark, cold, silent, plantless world — we find carnivorous animal preying upon carnivorous animal through long series — fish feeds on fish, fish on Crustacean, Crustacean on worm, worm on still smaller fry, and all ultimately depend on the basal food-supply — the ceaseless shower of moribund atomies sinking from the surface waters many miles, it may be, over- head, like the snowflakes on a quiet winter day. Dependence of one organism on another for the continuance of ^ the species. — Passing from "nutritive chains," we may select a few illustrations of the dependence of one creature upon another for the 210 READINGS IN EVOLUTION, GENETICS, AND EUGENICS continuance of its kind. The crowning instances are to be found in in- terrelations between plants and animals which secure cross-fertilisation and the distribution of seeds.; To both of these Darwin devoted much attention, and they were always favourite subjects with him. Everyone knows that flowering plants and flower-visiting insects have grown up throughout long ages together, in alternate influence and mutual perfecting. They are now fitted to one another as hand to glove. The insects visit the flowers for food; in so doing they carry the fertilising golden dust from blossom to blossom, so that the possible seeds become real seeds. In 1793 a Berlin naturalist, Christian Konrad Sprengel, like Darwin in his perception of the web of Me, published a pioneer book entitled The Secret of Nature Discovered in the Structure and Fertili- zation of Flowers, in which he showed that most flowers have nectar which insects enjoy; that by the insects' visits polh'nation is secured; that there is no detail of the flower without its meaning — the colour is a flag to attract the insect's eye, conspicuous spots are honey-guides to the explorers, there are arrangements for keeping the pollen dry and for dusting it on the insects, and so on. If Sprengel had only discovered the utility of the cross-fertilisation, which Darwin proved experimentally, his work could hardly have been overlooked for nearly seventy years. In 1841 it came into Darwin's hands, and impressed him as being "full of truth," although "with some little nonsense." In Darwin's work Sprengel had his long-delayed reward. Darwin's instance of the connection between cats and clover. — One of Darwin's instances of the web of life — given in connection with the pollination of flowers — has become familiar all over the world. It should never become trite to us and it should never be regarded as more than a particularly clear illustration of a general fact. " Plants and animals, remote in the scale of nature, are bound together by a web of complex relations I have found, from experiments, that humble-bees are almost indispensable to the fertilisation of the heart's- ease (Viola tricolor), for other bees do not visit this flower. I have also found that the visits of bees are necessary for the fertilisation of some kinds of clover — thus, 100 heads of red clover (Trifolium pratense] produced 27,00x3 seeds, but the same number of protected heads pro- duced not a single seed. Humble-bees alone visit red clover, as other bees cannot reach the nectar Hence we may infer as highly probable that, if the whole genus of humble-bees became extinct or very rare in England, the heart's-ease and red clover would become BACKGROUND OF DARWINISM— THE WEB OF LIFE 211 very rare, or wholly disappear." We know that the red clover imported to New Zealand did not bear fertile seeds until humble-bees were also imported. "The number of humble-bees in any district depends in a great measure on the number of field-mice, which destroy their combs and nests; and Colonel Newman, who has long attended to the habits of humble-bees, believes that more than two-thirds of them are thus destroyed all over England." Now the number of mice is largely dependent, as everyone knows, on the number of cats; and Colonel Newman says: "Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice." Thus we may say, with Darwin, that next year's crop of purple clover is influenced by the number of humble-bees in the district, which varies with the number of field-mice; that is to say, with the abundance of cats! Scattering of seeds. — It is a fascinating chapter of natural history which tells us how cross-pollination is effected — here by a bee and there by a butterfly, occasionally by a long-billed humming-bird beautifully poised before the flower with almost invisibly rapid vibra- tions of its wings, and occasionally by a slowly moving snail of epicure appetite. But not less important is the part played by animals in the scattering of seeds, and here again Darwin gives us the classic case of fourscore seeds germinating out of a ball of mud from a bird's foot. From one instance you may learn all, and see that much of Darwin's work has been an eloquent commentary on that memorable saying about the sparrow that falls to the ground. Such a simple event literally sends a throb through surrounding nature; we can follow its effects a few steps, just as we follow for a few yards the ripples made when we throw a stone into a still lake; in either case can we doubt that the spreading influences are real, though they pass beyond our ken? Interrelations between fresh-water mussels and fishes. — As a striking illustration of the inter-linking of different forms of life, we may take the case of the fresh-water mussels and their larvae. The fertilised eggs develop in the outer gill-plate of the mother-mussel, and minute bivalve larvae, called Glochidia, are formed. The mussel keeps these within the cradle until a fresh-water fish — such as the minnow — comes into the vicinity, and then she sets them free. In a way that we do not understand, the simple constitution of the larvae is tuned to respond to the presence of minnows and the like, and with snapping valves they manage to fix themselves to their host. After a short 212 READINGS IN EVOLUTION, GENETICS, AND EUGENICS period of temporary parasitism, at the end of which there is a meta- morphosis, they drop off from the fish into the mud, often far from their birth-place. This is curious enough, but the idea of linkages becomes incandescent in the mind when we note that, just as the fresh- water mussel has young temporarily parasitic on fishes, so a fresh- water fish, the bitterling (Rhodeus amarus), has its young temporarily parasitic in the gills of the mussel. Life-histories of parasites. — When we pass to parasites in a stricter sense we find the most extraordinary interconnections, the most widely separated animals often sharing a parasite between them. Liver-rot, which has repeatedly killed a million sheep in a year in Britain alone, is due to a parasite which passes from sheep to water, from water to water-snail, from water-snail to grass, from grass to sheep. The tapeworm of the cat has its bladder-worm stage in the mouse, the sturdie-worm of the sheep's brain has its tape-worm stage in the dog, and similar relations hold for hundreds of species. The troublesome threadworm of human blood (Filaria sanguinis hominis) is transferred from man to man by the mosquito, and the guinea-worm which was probably the fiery serpent that vexed the Israelites in the desert, which passes into man in drinking-water, spends its youth in a minute water-flea, called by the giant's name of Cyclops. The importance of tse-tse flies in transmitting the minute animals which cause sleeping-sickness and allied diseases is known to all. We have spoken of the connection between cats and clover, and there is a not less striking connection between cats and plague. For it seems to have been shown in India that the more cats the fewer rats, and the fewer rats the fewer rat-fleas, which are the agents in passing the plague- germs to man. Far-reaching influence of certain animals; earthworms.— We realise the idea of the web of life in another way when we consider the far-reaching influence of particular kinds of activity, the best instance being the work of earthworms. In 1777 Gilbert White got at the very root of the matter. " The most insignificant insects and reptiles are of much more consequence and have more influence in the economy of nature than the incurious are aware of Earthworms, though in appearance a small and despicable link in the chain of nature, yet, if lost, would make a lamentable chasm Worms seem to be the great promoters of vegetation, which would proceed but lamely with- out them, by boring, perforating, and loosening the soil, and rendering it pervious to rains and the fibres of plants; by drawing straws and BACKGROUND OF DARWINISM— THE WEB OF LIFE 213 stalks of leaves and twigs into it; and, most of all, by throwing up such infinite numbers of lumps of earth called worm-casts, which, being their excrement, is a fine manure for grain and grass. Worms prob- ably provide new soil for hills and slopes where the rain washes the earth away; and they affect slopes probably to avoid being flooded. .... The earth without worms would soon become cold, ha/d- bound, and void of fermentation, and consequently sterile These hints we think proper to throw out, in order to set the inquisitive and discerning at work. A good monograph of worms would afford much entertainment and information at the same tims, and would open a large and new field in natural history." The monograph that Gilbert White wished for in 1777 was pub- lished by Darwin in 1881, the year before he died — " the completion," he said, " of a short paper read before the Geological Society more than forty years ago." With his characteristic thoroughness and patience he worked out the part that earthworms have played in the history of the earth, and proved that they deserve to be called the most useful animals. By their burrowing they loosen the earth, making way for the plant rootlets and the raindrops; by bruising the soil in their gizzards, they reduce the particles to more useful, powdery form; by burying the surface with castings brought up from beneath, they have been for untold ages ploughers before the plough, and by burying leaves they have made a great part of the vegetable mould over the whole earth. In illustration of the last point, we may notice that we recently found thirteen midribs of the leaves of the rowan, or mountain ash, radiating round one hole like the spokes of a wheel; the withering leaflets had been carried down, and two were sticking up at the mouth of the burrow; that meant 91 leaflets to one hole. Darwin showed that there often are 50,000 (and there may be 500,000) earthworms in an acre; that they often pass ten tons of soil per acre per annum through their bodies; and that they often cover the surface at the rate of three inches in fifteen years. Though our British worms only pass out about 20 oz. of earth hi a year, the weights thrown up in a year on two separate square yards which Darwin watched were respectively 6.75 Ib. and 8.387 lb., which correspond to 14! and 18 tons per acre per annum. We follow the work further and it becomes evident that the con- stant exposure of the soil bacteria on the surface is bound to be important, on the one hand, in allowing them to be scattered by wind and rain, on the other in exposing them to the beneficent action of the 214 READINGS IN EVOLUTION, GENETICS, AND EUGENICS sunlight— which is the most universal, effective, and economical of all germicides. In Yorubaland, on the West Coast of Africa, Mr. Alvan Millson calculated that about 62,233 tons of subsoil are brought every year to the surface of each square mile, and that every particle of earth, to the, depth of two feet, is brought to the surface once in twenty- seven years. It need hardly be added that the district is fertile and healthy. Earthworms play their part hi the disintegration of rocks, letting the solvent humus-acids of the soil down to the buried surface. Their castings on the hill-slopes are carried down by wind and rain and go to swell the alluvium of the distant valleys or the wasted treasures of the sea. The well-known parallel ledges along the slopes of grass-clad hills are partly due to earthworm castings caught on sheep-tracks, and thus we begin to connect the earthworms not only with our wheat- supply but with our scenery. Well may we say, with Darwin: "It may be doubted whether there are many other animals which have played so important a part in the history of the world as have these lowly organised creatures." Those who wish to understand Darwin- ism should always begin with Darwin's last book — The Formation of Vegetable Mould through the Action of Worms (1881). It illus- trates the web of life, the idea of which is essential to an understanding of the struggle for existence and natural selection. But it also illus- trates what Darwin had learned from Lyell — that great results may be brought about by accumulation of infinitesimal items. As Professor A. Milnes Marshall said: "The lesson to be derived from Darwin's life and work cannot be better expressed than as the cumulative im- portance of infinitely little things." Termites, or white ants. — Henry Drummond, in his Tropical Africa, tried to make out a case for the agricultural importance of termites, or white ants. It is well known that these old-fashioned insects have a pruning action in the forest, destroying dead wood with great rapidity. Houses and furniture, fences and boxes, as well as forest- trees, fall under their jaws. In some places, "if a man lay down to sleep with a wooden leg, it would be a heap of sawdust in the morning." But what of the termites' agricultural importance ? The point is that they keep the soil circulating by constructing earthen tunnels up the sides of trees and posts and by making huge obelisk-like ant-hills, or termitaries. "The earth-tubes crumble to dust, which is scattered by the wind; the rains lash the forests and soils with fury, and wash off the loosened grains to swell the alluvium of a distant BACKGROUND OF DARWINISM— THE WEB OF LIFE 215 valley." It must be noted, however, that Drummond did not prove his case with sufficient precision, and there is, as Escherich points out in his beautiful study of termites, this difficulty, that, while the cast- ings of earthworms are soft and loose, the earth-tubes and construc- tions of termites are stony. Escherich does, however, admit that the termites have some agricultural importance, and he points out that there are other serv- ices to be put to the credit side of their account. They prune off wood that has begun to go; they destroy rotting things, including the bodies of small animals; they make for cleanliness and health. In some low-lying tracts, as Silvestri has shown, there are dry stretches, "termite islands," which have been gradually built up from the broken-down remains of termitaries. Nor should it be forgotten that the white ants are often used as food. On the other hand, Escherich does not hesitate to rank them as among the great hindrances to the spread of civilisation. They insidiously devour everything wooden, from the telegraph-post to the wooden butt of the gun hanging against the wall, from books in the library to corks in the cellar. There does not seem sufficiently precise information in regard to the living plants that they attack, and no safe general statement can be made except that their appetite is large and catholic. With a centre in earthworms, what a variety of interests must be included within the radius of then: life and work! — centipedes, birds, moles, seedlings, man. The same is true of termites, and two further illustrations may be given. Observers have reported about thirty different species of termites with the habit of feeding on fungi grown within the termitary on specially constructed mazy beds. The habit is interesting in many ways; for instance, because the fungi afford a supply of nitrogenous material which is scarce hi the ordinary diet of wood, and also because a similar habit occurs in the quite unrelated true ants. Finally, the web is illustrated by the numerous boarders, mostly beetles, that are found in the termitaries — not hostile intruders or parasites, but guests which are fed and cared for apparently for the sake of a palatable exudation with a pleasant, narcotising effect on the termites. With a centre in termites, what a variety of interests must we not include within the radius of their life and work! — fungi and trees, beetles and birds, lizards and anteaters, and man more than any. The hand of life upon the earth. — The hand of life has been working upon the earth for untold ages. Take plants, for instance. The seaweeds lessen the force of the waves, the lichens eat into the 2l6 READINGS IN EVOLUTION, GENETICS, AND EUGENICS rocks, the mosses form huge sponges on the moors which keep the streams flowing in days of drought. Many little plants are forever smoothing away the wrinkleson the earth's — their mother's — face, and they adorn her with jewels. Others that have formed coal have enriched her with ages of entrapped sunlight. The grass — which began to appear in Tertiary ages — protects the earth like a garment; the forests affect rainfall and temper climate, besides sheltering multitudes of living things, to many of whom every blow of the axe is a death- knell. No plant, from bacterium to oak-tree, lives or dies to itself, or is without its influence upon the earth. So among animals there are destructive borers and burrowers and conservative agents, such as the coral-polyps and the chalk-forming Foraminifera. Practical importance of a realisation of the web t>f life. — What has Darwinism to do with human life ? The answer at this stage in our inquiry is clear: we must respect the web of life if we wish to master Nature. She must be humoured, not bullied. Emerson included in his vision of a perfected earth the absence of spiders, but the absence of spiders — which snare so many injurious insects — would mean the absence of much else, man probably included. In a northern county in Scotland the proprietors were justly annoyed at the injuries inflicted on young trees by squirrels, and they formed a squirrel club, setting a price on the beautiful rodent's head. Perhaps a wiser course would have been to begin by inquiring what disturbance of the balance of nature had allowed the squirrels to multiply so disastrously. But, after a period of squirrel-slaughter and some jubilation thereat, a cloud began to rise in the sky. The wood-pigeons were multiplying worse than ever, and the farmers, at least, said with no uncertain voice that they preferred the squirrels. An imperfect recognition of the web of life had left out of account the notable fact that squirrels destroy large numbers of young wood-pigeons. One of the hopeful symptoms of the last few years is the reawaken- ing of an interest in woods and forests. Everyone knows how terribly these have been wasted, and how the disastrous results have affected rainfall and irrigation, climate and crops, and even the character of the people. Here what was once a pleasant stream is now like a gravelly road, and there the fertile plains are flooded; here the wind is sweeping away the soil, and there both beauty and health have departed. The birds which the woods once sheltered are driven elsewhere, and the insect-pests are rife among the crops. For "the cheapest and most effective insecticides are birds." BACKGROUND OF DARWINISM— THE WEB OF LIFE 217 The recognition of consequences — often far-reaching — grows with us as we work with the idea of the web of life, as we see in proper perspective the criminality of those who are ruthless. President Roosevelt has declared his abomination of "the land-skinner" — "the individual whose idea of developing the country is to cut every stick of timber off it, and then leave a barren desert for the home-maker who comes in after him. That man is a curse, and not a blessing to the country. The prop of the country must be the man who intends so to run his business that it will be profitable to his children after him." Every right-thinking man, and especially those who have grasped the idea of the web of life, will say with Roosevelt, "I am against the land- skinner every time." It may be said that man must exterminate a good deal if he is to go on peaceably with his business, and it will be admitted that there has never been a strong enthusiasm, humanitarian or otherwise, against the elimination of rattlesnakes, and such like. The natural- ist's answer is that every crusade should be carefully considered on its own merits, and that every careless and hasty destruction of life is to be condemned. Even in regard to snakes killing may be carried too far. Some creatures are, as it were, on the fringes of the web, while others occupy a position where many threads meet. It is scientifically and aesthetically deplorable that birds like the great auk and mammals like the quagga should have been exterminated, but it is practically much more deplorable that we have lost so many hawks and weasels and other members of that pertinacious army whose guerilla warfare keeps hundreds of more humdrum creatures up to the scratch, and keeps "vermin" from becoming a plague. Moreover, it is extremely difficult to tell what may be the consequences of exterminating any creature — remote as it may seem from the beaten track of human affairs. One of the obvious lessons of Darwinism is that we should be slow to call any change unimportant. Everything counts, or may count. A so-called unimportant animal is destroyed and no imme- diate ill effects are seen. But who can tell ? Very pertinent, for instance, is the question: What about the parasites that used to complete their life-history in romantic routine in this extinguished animal ? Have we extinguished the parasite also ? Or is it waiting, with a whip of scorpions, to chastise mankind for their ignorance of Darwinism ? The practical importance of recognising the web of life has been proved by the heavy penalties which man has often had to pay for 2l8 READINGS IN EVOLUTION, GENETICS, AND EUGENICS disturbing the balance of nature, careless of results and ruthless of beauty, for not admitting that if we would master Nature we must first understand her. How much has Australia had to pay for the introduction of rabbits in 1860, or America for sparrows ? Sometimes the introduction has been unconscious, and man has only to blame himself for letting the intruder take hold, as in the case of the Phyl- loxera in France, or of the Colorado Beetle in Ireland. "Ignorance of nature," Mr. A. H. S. Lucas says, "is costly. By disturbing the balance of nature, man has introduced foes into his own household." Speaking of Australia, he says: "How much is needed for the eradi- cation of Bathurst Burr, Prickly Pear, Water-hyacinth, Bramble and Sweetbriar, Codlin Moth, Waxy Scale, Pear Slug, and Red Spider, owing to carelessness or lack of knowledge in early days ?" An obvious moral is that we should be careful in our introduc- tions of new organisms — man included — into new surroundings. The primary consequences may be predictable, but the secondary and the tertiary consequences — who is sufficient for these things ? We have records of the unconscious introduction of rats into Jamaica, where they became a pest. To destroy them mongooses were imported, and the rats were soon checked. But the mongooses, having finished the rats, began to eat up the poultry and young birds of various kinds. As this went on the injurious insects and ticks, that the birds used to eat, began to gain the ascendant. A recent report — which requires confirmation — says that the increase of ticks is making life a burden to the mongooses. Thus a balance will be again arrived at. There is no doubt of that, but how much is often unnecessarily lost by the wayl CHAPTER XVI NATURAL SELECTION CHARLES DARWIN INTRODUCTORY NOTE. — This entire chapter is made up of carefully chosen passages from Darwin's Origin of Species. So much has falsely been called " Darwinism " that it is well for the reader to have a statement of Darwin's views in his own words. Every student of evolution should read the whole of the Origin of Species. It is all so good that one finds it difficult to leave out anything. The following excerpts will, we believe, give the gist of natural selection. We present first certain of the ideas that underlie or are postulates of the theory; then the theory itself is presented; the theory of sexual selection inter- polated; and then follow examples of the way in which adaptations are accounted for by natural selection. Darwin's own statement of the most serious difficulties and objections to the theory, and his answers to these, bring this chapter to a close. FOUNDATION STONES OF NATURAL SELECTION DARWIN'S OWN ESTIMATE AS TO THE R&LE OP NATURAL SELECTION IN EVOLUTION No one ought to feel surprised at much remaining as yet unex- plained in regard to the origin of species and varieties, if he make due allowance for our profound ignorance in regard to the mutual relations of the many beings which live around us. Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare ? Yet these relations are of the highest importance, )'ar they determine the present welfare and, as I believe, the future success and modification of every inhabitant of this world. Still less do we know of the mutual relations of the innumer- able inhabitants of the world during the many past geological epochs in its history. Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists until recently entertained, and which I for- merly entertained — namely, that each species has been independently created — is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am con- vinced that Natural Selection has been the most important, but not the exclusive, means of modification. 3IQ 220 READINGS IN EVOLUTION, GENETICS, AND EUGENICS EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; CORRELATED VARIATION; INHERITANCE Changed habits produce an inherited effect, as in the period of the flowering of plants when transported from one climate to another. With animals the increased use or disuse of parts has had a more marked influence; thus I find in the domestic duck that the bones of the wing weigh less and the bones of the leg more, in proportion to the whole skeleton, than do the same bones in the wild-duck; and this change may be safely attributed to the domestic duck flying much less, and walking more, than its wild parents. The great and inherited development of the udders in cows and goats in countries where they are habitually milked, in comparison with these organs in other countries, is probably another instance of the effects of use. Not one of our domestic animals can be named which has not in some country drooping ears; and the view, which has been suggested that the drooping is due to disuse of the muscles of the ear, from the animals being seldom much alarmed, seems probable. Many laws regulate variation, some few of which can be dimly seen, and will hereafter be briefly discussed. I will here only allude to what may be called correlated variation. Important changes in the embryo or larva will probably entail changes in the mature animal. In monstrosities, the correlations between quite distinct parts are very curious; and many instances are given in Isidore Geoffrey St. Hilaire's great work on this subject. Breeders believe that long limbs are almost always accompanied by an elongated head. Some instances of correlation are quite whimsical: thus cats which are entirely white and have blue eyes are generally deaf; but it has been lately stated by Mr. Tait that this is confined to the males. Color and constitutional peculiarities go together, of which many remarkable cases could be given amongst animals and plants. From facts collected by Heu- singer, it appears that white sheep and pigs are injured by certain plants, whilst dark-colored individuals escape: Professor Wyman has recently communicated to me a good illustration of this fact; on ask- ing some farmers in Virginia how it was that all their pigs were black, they informed him that the pigs ate the paint-root (Lachnanthes), which colored their bones pink, and which caused the hoofs of all but the black varieties to drop off; and one of the "crackers" (i.e., Virginia squatters) added, "we select the black members of a litter for raising, as they alone have a good chance of living." Hairless dogs have imperfect teeth; long-haired and coarse-haired animals are apt to NATURAL SELECTION 221 have, as is asserted, long or many horns; pigeons with feathered feet have skin between their outer toes; pigeons with short beaks have small feet, and those with long beaks large feet. Hence if man goes on selecting, and thus augmenting, any peculiarity, he will almost certainly modify unintentionally other parts of the structure, owing to the mysterious laws of correlation. DARWIN'S IDEA OF THE CAUSES RESPONSIBLE FOR THE ORIGIN OP DOMESTIC RACES To sum up on the origin of our domestic races of animals and plants. Changed conditions of life are of the highest importance in" causing variability, both by acting directly on the organization, and indirectly by affecting the reproductive system. It is not probable ** that variability is an inherent and necessary contingent, under aDT" circumstances. The greater or less force of inheritance and reversion determine whether variations shall endure. Variabilityis governed by many unknown laws, of which correlated growth is probably the most important. Something, but how much we do not know, may be attributed to the definite action of the conditions of life. Some, per- haps a great, effect may be attributed to the increased use or disuse of parts. The final result is thus rendered infinitely complex. In some cases the intercrossing of aboriginally distinct species appears to have played an important part in the origin of our breeds. When several breeds have once been formed in any country, their occasional intercrossing, with the aid of selection, has, no doubt, largely aided in the formation of new sub-breeds; but the importance of crossing has been much exaggerated, both in regard to animals and to those plants which are propagated by seed. With plants which are temporarily propagated by cuttings, buds, etc., the importance of crossing is immense; for the cultivator may here disregard the extreme variability both of hybrids and of mongrels, and the sterility of hybrids; but plants not propagated by seed are of little importance to us, for their endurance is only temporary. Over all these causes of Change, the~~ accumulative action of Selection, whether applied methodically and quickly, or unconsciously and slowly but more efficiently, seems to * have been the predominant Power. DARWIN'S IDEA OP THE ORIGIN OF VARIETIES, SPECIES, AND GENERA IN NATURE Finally, varieties cannot be distinguished from species — except, ^ first, by the discovery of intermediate linking forms; and, secondly, by a certain indefinite amount of difference between them; for two> 222 READINGS IN EVOLUTION, GENETICS, AND EUGENICS forms, if differing very little, are generally ranked as varieties, not- withstanding that they cannot be closely connected; but the amount of difference considered necessary to give to any two forms the rank of species cannot be denned. In genera having more than the average number of species in any country, the species of these genera have more than the average number of varieties. In large genera the species are apt to be closely, but unequally, allied together, forming little clusters round other species. Species very closely allied to other species apparently have restricted ranges. In all these respects the species of large genera present a strong analogy with varieties. And we can clearly understand these analogies, if species once existed as varieties, and thus originated; whereas, these analogies are utterly inexplicable if species are independent creations. We have, also, seen that it is the most flourishing or dominant species of the larger genera within each class which on an average yield the greatest number of varieties; and varieties, as we shall hereafter see, tend to become converted into new and distinct species. Thus the larger genera tend to become larger; and throughout nature the forms of life which are now dominant tend to become still more domi- nant by leaving many modified and dominant descendants. But by steps hereafter to be explained, the larger genera also tend to break up into smaller genera. And thus, the forms of life throughout the uni- verse become divided into groups subordinate to groups. THE TERM "STRUGGLE FOR EXISTENCE" USED IN A LARGE SENSE I should premise that I use this term in a large and metaphorical v sense including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny. Two canine animals, in a time of dearth, may be truly said to struggle with each other which shall get food and live. But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to be dependent on the moisture. A plant which annually produces a thousand seeds, of which only one of an average comes to maturity, may be more truly said to struggle with the plants of the same and other kinds which already clothe the ground. The mistletoe is dependent on the apple and a few other trees, but can only in a far-fetched sense be said to struggle with these trees, for, if too many of these parasites grow on the same tree, it languishes and dies. But several seedling mistletoes, growing close together on the same branch, NATURAL SELECTION 223 may more truly be said to struggle with each other. As the mistletoe is disseminated by birds, its existence depends on them; and it may metaphorically be said to struggle with other fruit- bearing plants, in tempting the birds to devour and thus disseminate its seeds. In these several senses, which pass into each other, I use for conven- ience' sake the general term of Struggle for Existence. GEOMETRICAL RATIO OF INCREASE A struggle for existence inevitably follows from the high rate at" .which all organic beings tend to increase. Every being, which during its natural lifetime produces several eggs or seeds, must suffer destruc- tion during some period of its life, and during some season or occasional year, otherwise, on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. Hence, as more individuals are produced than can possibly survive, there must hi every case be a struggle for exist- ence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for hi this case there can be no artificial increase of food, and no prudential restraint from marriage. Although some species may be now increasing, more or less rapidly, hi numbers, all cannot do so, for the world would not hold them. NATURAL SELECTION; OR THE SURVIVAL or THE FITTEST How will the struggle for existence, briefly discussed hi the last chapter, act hi regard to variation ? Can the principle of selection, which we have seen is so potent in the hands of man, apply under nature ? I think we shall see that it can act most efficiently. Let the endless number of slight variations and individual differences occurring in our domestic productions, and, hi a lesser degree, hi those under nature, be borne in mind; as well as the strength of the hereditary tendency. Under domestication, it may be truly said that the whole organization becomes in some degree plastic. But the variability, which we almost universally meet with in our domestic productions, is not directly produced, as Hooker and Asa Gray have well remarked, by man; he can neither originate varieties, nor prevent their occur- rence; he can only preserve and accumulate such as do occur. Unin- tentionally he exposes organic beings to new and changing conditions 224 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of life, and variability ensues; but similar changes of conditions might and do occur under nature. Let it also be borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other and to their physical conditions of life; and consequently what infinitely varied diversities of structure might be of use to each being under changing conditions of life. Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful hi some way to each being in the great and complex battle of life, should occur in the course of many successive generations ? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind ? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest. Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions. Several writers have misapprehended or objected to the term Natural Selection. Some have even" imagined that natural selection induces variability, whereas it implies only the preservation of such variations as arise and are beneficial to the being under its conditions of life. No one objects to agriculturists speaking of the potent effects of man's selection; and in this case the individual differences given by nature, which man for some object selects, must of necessity first occur. Others have objected that the term selection implies conscious choice in the animals which become modified; and it has even been urged that, as plants have no volition, natural selection is not applic- able to them! In the literal sense of the word, no doubt, natural selection is a false term; but who ever objected to chemists speaking of the elective affinities of the various elements ?— and yet an acid cannot strictly be said to elect the base with which it in preference combines. It has been said that I speak of natural selection as an active power or Deity; but who objects to an author speaking of the attraction of gravity as ruling the movements of the planets ? Every- one knows what is meant and is implied by such metaphorical expres- NATURAL SELECTION* 225 sions; and they are almost necessary for brevity. So again it is difficult to avoid personifying the word Nature; but I mean by Nature only the aggregate action and product of many natural laws, and by laws the sequence of events as ascertained by us. With a little famili- arity such superficial objections will be forgotten. We shall best understand the probable course of natural selection by taking the case of a country undergoing some slight physical change, for instance, of climate. The proportional numbers of its inhabitants will almost immediately undergo a change, and some species will prob- ably become extinct. We may conclude, from what we have seen of the intimate and complex manner in which the inhabitants of each country are bound together, that any change in the numerical pro- portions of the inhabitants, independently of the change of climate itself, would seriously affect the others. If the country were open on its borders, new forms would certainly immigrate, and this would likewise seriously disturb the relations of some of the former inhabi- tants. Let it be remembered how powerful the influence of a single introduced tree or mammal has been shown to be. But in the case of an island, or of a country partly surrounded by barriers,' into which new and better adapted forms could not freely enter, we should then have places in the economy of nature which would assuredly be better filled up, if some of the original inhabitants were hi some manner modified; for, had the area been open to immigration, these same places would have been seized on by intruders. In such cases, slight modifications, which in any way favored the individuals of any species by better adapting them to their altered conditions, would tend to be preserved; and natural selection would have free scope for the work of improvement. We have good reason to believe, as shown in the first chapter, that changes in the conditions of life give a tendency to increased variability and in the foregoing cases the conditions have changed, and this would manifestly be favorable to natural selection, by affording a better chance of the occurrence of profitable variations. Unless such occur, natural selection can do nothing. Under the term of "variations," it must never be forgotten that mere individual differences are included. As man can produce a great result with his domestic annuals and plants by adding up in any given direction individual differences, so could natural selection, but far more easily from having incomparably longer time for action. Nor do I believe that any great physical change, as of climate, or any unusual degree of isolation to check immigration, *26 READINGS IN EVOLUTION, GENETICS, AND EUGENICS is necessary in order that new and unoccupied places should be left, for natural selection to fill up by improving some of the varying inhabitants. For as all the inhabitants of each country are struggling together with nicely balanced forces, extremely slight modifications in the structure or habits of one species would often give it an advantage over others; and still further modifications of the same kind would often still further increase the advantage, as long as the species con- tinued under the same conditions of life and profited by similar means of subsistence and defense. No country can be named in which all the native inhabitants are now so perfectly adapted to each other and to the physical conditions under which they live, that none of them could be still better adapted or improved; for hi all countries, the natives have been so far conquered by naturalized productions, that they have allowed some foreigners to take firm possession of the land. And as foreigners have thus hi every country beaten some of the natives, we may safely conclude that the natives might have been modified with advantage, so as to have better resisted the intruders. As man can produce, and certainly has produced, a great result by his methodical and unconscious means of selection, what may not natural selection effect? Man can act only on external and visible characters: Nature, if I may be allowed to personify the natural pres- ervation or survival of the fittest, cares nothing for appearances, except in so far as they are useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good: Nature only for that of the being which she tends. Every selected character is fully exercised by her, as is implied by the fact of their selection. Man keeps the natives of many climates in the same country; he seldom exercises each selected character in some peculiar and fitting manner; he feeds a long- and a short-beaked pigeon on the same food ; he does not exercise a long-backed or long-legged quadruped in any peculiar manner; he exposes sheep with long and short wool to the same climate. He does not allow the most vigorous males to struggle for the females. He does not rigidly destroy all inferior animals, but protects during each varying season, as far as lies hi his power, all his productions. He often begins his selection by some half-monstrous form; or at least by some modification prominent enough to catch the eye or to be plainly useful to him. Under nature, the slightest differ- ences of structure or constitution may well turn the nicely balanced scale in the struggle for life, and so be preserved. How fleeting are the NATURAL SELECTION 227 wishes and efforts of man! how short his time! and consequently how poor will be his results, compared with those accumulated by Nature during whole geological periods! Can we wonder, then, that Nature's productions should be far" truer "in character than man'sproductions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly bear the stamp of far higher workmanship ? It may metaphorically be said that natural selection is daily and hourly scrutinizing, throughout the world, the slightest variations; rejecting those that are bad, preserving and adding up all that are good; silently and insensibly working whenever and wherever oppor- tunity offers, at the improvement of each organic being hi relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the lapse of ages, and then so imperfect is our view into long-past geological ages, that we see only that the forms of Me are now different from what they formerly were. In order that any great amount of modification should be effected in a species, a variety when once formed must again, perhaps after a long interval of time, vary or present individual differences of the same favorable nature as before; and these must be again preserved, and so onwards step by step. Seeing that individual differences of the same kind perpetually recur, this can hardly be considered as an unwarrantable assumption. But whether it is true, we can judge only by seeing how far the hypothesis accords with and explains the general phenomena of nature. On the other hand, the ordinary belief that the amount of possible variation is a strictly limited quantity is like- wise a simple assumption. Although natural selection can act only through and for the good of each being, yet characters and structures, which we are apt to con- sider as of very trifling importance, may thus be acted on. When we see leaf-eating bisects green, and bark-feeders mottled-gray; the alpine ptarmigan white hi whiter, the red-grouse the color of heather, we must believe that these tints are of service to these birds and insects in preserving them from danger. Grouse, if not destroyed at some period of their lives, would increase in countless numbers; they are known to suffer largely from birds of prey; and hawks are guided by eyesight to their prey — so much so, that on parts of the Continent persons are warned not to keep white pigeons, as being the most liable to destruction. Hence natural selection might be effective hi giving 228 READINGS IN EVOLUTION, GENETICS, AND EUGENICS the proper color to each kind of grouse, and in keeping that color, when once acquired, true and constant. Nor ought we to think that the occasional destruction of an animal of any particular color would produce little effect: we should remember how essential it is hi a flock of white sheep to destroy a lamb with the faintest trace of black. We have seen how the color of the hogs, which feed on the " paint-root" hi Virginia, determines whether they shall live or die. In plants, the down on the fruit and the color of the flesh are considered by botanists as characters of the most trifling importance: yet we hear from an excellent horticulturist, Downing, that in the United States smooth- skinned fruits suffer far more from a beetle, a Curculio, than those with down; that purple plums suffer far more from a certain disease than yellow plums; whereas another disease attacks yellow-fleshed peaches far more than those with other colored flesh. If, with all the aids of art, these slight differences make a great difference in cultivating the several varieties, assuredly, in a state of nature, where the trees would have to struggle with other trees and with a host of enemies, such dif- ferences would effectually settle which variety, whether a smooth or downy, a yellow- or purple-fleshed fruit, should succeed. In looking at many small points of difference between species, which, as far as our ignorance permits us to judge, seem quite unim- portant, we must not forget that climate, food, etc., have no doubt produced some direct effect. It is also necessary to bear hi mind that, owing to the law of correlation, when one part varies, and the varia- tions are accumulated through natural selection, other modifications, often of the most unexpected nature, will ensue. As we see that those variations which, under domestication, appear at any particular period of life, tend to reappear in the offspring at the same period; for instance, hi the shape, size, and flavor of the seeds of the many varieties of our culinary and agricultural plants; hi the caterpillar and cocoon stages of the varieties of the silk- worm; hi the eggs of poultry, and in the color of the down of their chickens; in the horns of our sheep and cattle when nearly adult; so hi a state of nature natural selection will be enabled to act on and modify organic beings at any age, by the accumulation of variations profitable at that age, and by their inheritance at a corresponding age. If it profit a plant to have its seeds more and more widely disseminated by the wind, I can see no greater difficulty in this being effected through natural selection, than hi the cotton-planter increasing and improving by selection the down in the pods on his cotton-trees. Natural NATURAL SELECTION 229 selection may modify and adapt the larva of an insect to a score of contingencies, wholly different from those which concern the mature insect; and these modifications may affect, through correlation, the structure of the adult. So, conversely, modifications in the adult may affect the structure of the larva; but hi all cases natural selection will ensure that they shall not be injurious: for if they were so, the species would become extinct. Natural selection will modify the structure of the young in relation to the parent, and of the parent hi relation to the young. In social animals it will adapt the structure of each individual for the benefit of the whole community, if the community profits by the selected change. What natural selection cannot do, is to modify the structure of one species, without giving it any advantage, for the good of another species; and though statements to this effect may be found in works of natural history, I cannot find one case which will bear investigation. A structure used only once hi an animal's life, if of high importance to it, might be modified to any extent by natural selection; for instance the great jaws possessed by certain insects, used exclusively for open- ing the cocoon — or the hard tip to the beak of unhatched birds, used for breaking the egg. It has been asserted, that of the best short- beaked tumbler-pigeons a greater number perish in the egg than are able to get out of it; so that fanciers assist in the act of hatching. Now if nature had to make the beak of a full-grown pigeon very short for the bird's own advantage, the process of modification would be very slow, and there would be simultaneously the most rigorous selection of all the young birds within the egg, which had the most powerful and hardest beaks, for all with weak beaks would inevitably perish; or, more delicate and more easily broken shells might be selected, the thickness of the shell being known to vary like every other structure. It may be well here to remark that with all beings there must be much fortuitous destruction, which can have little or no influence on the course of natural selection. For instance a vast number of eggs or seeds are annually devoured, and these could be modified through natural selection only if they varied in some manner which protected them from their enemies. Yet many of these eggs or seeds would perhaps, if not destroyed, have yielded individuals better adapted to their conditions of life than any of those which happened to survive. So again a vast number of mature animals and plants, whether or not they be the best adapted to their conditions, must be annually 230 READINGS IN EVOLUTION, GENETICS, AND EUGENICS destroyed by accidental causes, which would not be in the least degree mitigated by certain changes of structure or constitution which would in other ways be beneficial to the species. But let the destruction of the adults be ever so heavy, if the number which can exist in any district be not wholly kept down by such causes, or again let the destruction of eggs or seeds be so great that only a hundredth or a thousandth part are developed, yet of those which do survive, the best adapted individuals, supposing that there is any variability in a favorable direction, will tend to propagate their kind in larger numbers than the less well adapted. If the numbers be wholly kept down by the causes just indicated, as will often have been the case, natural selection will be powerless in certain beneficial directions; but this is no valid objection to its efficiency at other times and in other ways; for we are far from having any reason to suppose that many species ever undergo modification and improvement at the same time in the same area. , SEXUAL SELECTION Inasmuch as peculiarities often appear under domestication hi one sex and become hereditarily attached to that sex, so no doubt it will be under nature. Thus it is rendered possible for the two sexes to be modified through natural selection in relation to different habits of life, as is some tunes the case; or for one sex to be modified in relation to the other sex, as commonly occurs. This leads me to say a few words on what I have called Sexual Selection. This form of selection depends, not on a struggle for existence hi relation to other organic beings or to external conditions, but on a struggle between the indi- viduals of one sex, generally the males, for the possession of the other sex. The result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally, the most vigorous males, those which are best fitted for their places hi nature, will leave most progeny. But in many cases, victory depends not so much on general vigor, as on having special weapons, confined to the male sex. A hornless stag or spurless cock would have a poor chance of leaving numerous offspring. Sexual selection, by always allowing the victor to breed, might surely give indomitable courage, length to the spur, and strength to the wing to strike in the spurred leg, in nearly the same manner as does the brutal cock-fighter by the careful selection of his best cocks. How low hi the scale of nature the law of battle descends, I know not; male alligators have been described as fighting, bellowing, and whirl- NATURAL SELECTION 231 ing around, like Indians in a war-dance, for the possession of the females; male salmons have been observed fighting all day long; male stag-beetles sometimes bear wounds from the huge mandibles of other males; the males of certain hymenopterous insects have been fre- quently seen by that inimitable observer M. Fabre, fighting for a particular female who sits by, an apparently unconcerned beholder of the struggle, and then retires with the conqueror. The war is, perhaps, severest between the males of polygamous animals, and these seem oftenest provided with special weapons. The males of carnivorous animals are already well armed; though to them and to others, special means of defense may be given through means of sexual selection, as the mane of the lion, and the hooked jaw to the male salmon; for the shield may be as important for victory as the sword or spear. Amongst birds, the contest is often of a more peaceful character. All those who have attended to the subject believe that there is the severest rivalry between the males of many species to attract, by singing, the females. The rock-thrush of Guiana, birds of paradise, and some others, congregate; and successive males display with the most elaborate care, and show off hi the best manner, their gorgeous plumage; they likewise perform strange antics before the females, which, standing by as spectators, at last choose the most attractive partner. Those who have closely attended to birds hi confinement well know that they often take individual preferences and dislikes: thus Sir R. Heron has described how a pied peacock was eminently attractive to all his hen birds. I cannot here enter on the necessary details; but if man can hi a short tune give beauty and an elegant carriage to his bantams, according to his standard of beauty, I can see no good reason to doubt that female birds, by selecting, during thousands of generations, the most melodious or beautiful males, according to their standard of beauty, might produce a marked effect. Some well-known laws, with respect to the plumage of male and female birds, in comparison with the plumage of the young, can partly be explained through the action of sexual selection on variations occurring at different ages, and transmitted to the males alone or to both sexes at corresponding ages; but I have not space here to enter on this subject. Thus it is, as I believe, that when the males and females of any animal have the same general habits of life, but differ in structure, color, or ornament, such differences have been mainly caused by sexual 232 READINGS IN EVOLUTION, GENETICS, AND EUGENICS selection: that is, by individual males having had, in successive gen- erations, some slight advantage over other males, in their weapons, means of defence, or charms, which they have transmitted to their male offspring alone. Yet, I would not wish to attribute all sexual differences to this agency: for we see in our domestic animals peculi- arities arising and becoming attached to the male sex, which appar- ently have not been augmented through selection by man. The tuft of hair on the breast of the wild turkey-cock cannot be of any use, and it is doubtful whether it can be ornamental in the eyes of the female bird; indeed, had the tuft appeared under domestication, it would have been called a monstrosity. ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION, OR THE SURVIVAL OF THE FITTEST In order to make it clear how, as I believe, natural selection acts, I must beg permission to give one or two imaginary illustrations. Let us take the case of a wolf, which preys on various animals, securing some by craft, some by strength, and some by fleetness; and let us suppose that the fleetest prey, a deer for instance, had from any change in the country increased in. numbers, or that other prey had decreased in numbers, during that season of the year when the wolf was hardest pressed for food. Under such circumstances the swiftest and slimmest wolves would have the best chance of surviving and so be preserved or selected, provided always that they retained strength to master their prey at this or some other period of the year, when they were compelled to prey on other animals. I can see no more reason to doubt that this would be the result, than that man should be able to improve the fleetness of his greyhounds by careful and methodical selection, or by that kind of unconscious selection which follows from each man trying to keep the best dogs without any thought of modifying the breed. I may add, that, according to Mr. Pierce, there are two varieties of the wolf inhabiting the Catskill Mountains, in the United States, one with a light greyhound-like form, which pursues deer, and the other more bulky, with shorter legs, which more frequently attacks the shepherd's flocks. It should be observed that, hi the above illustration, I speak of the slimmest individual wolves, and not of any single strongly marked variation having been preserved. In former editions of this work I sometimes spoke as if this latter alternative had frequently occurred. I saw the great importance of individual differences, and this led me fully to discuss the results of unconscious selection by man, which NATURAL SELECTION 233 depends on the preservation of all the more or less valuable individuals, and on the destruction of the worst. I saw, also, that the preservation in a state of nature of any occasional deviation of structure, such as a monstrosity, would be a rare event; and that, if at first preserved, it would generally be lost by subsequent intercrossing with ordinary individuals. Nevertheless, until reading an able and valuable article in the North British Review (1867), I did not appreciate how rarely single variations, whether slight or strongly marked, could be per- petuated. The author takes the case of a parr of animals, producing during their lifetime two hundred offspring, of which, from various causes of destruction, only two on an average survive to pro-create their kind. This is rather an extreme estimate for most of the higher animals, but by no means so for many of the lower organisms. He then shows that if a single individual were born, which varied in some manner, giving it twice as good a chance of life as that of the other individuals, yet the chances would be strongly against its survival. Supposing it to survive and to breed, and that half its young inherited the favorable variation; still, as the Reviewer goes on to show, the young would have only a slightly better chance of surviving and breed- ing; and this chance would go on decreasing hi the succeeding genera- tions. The justice of these remarks cannot, I think, be disputed. If, for instance, a bird of some kind could procure its food more easily by having its beak curved, and if one were born with its beak strongly curved, and which consequently nourished, nevertheless there would be a very poor chance of this one individual perpetuating its kind to the exclusion of the common form; but there can hardly be a doubt, judging by what we see taking place under domestication, that this result would follow from the preservation during many generations of a large number of individuals with more or less strongly curved beaks, and from the destruction of a still larger number with the straightest beaks. SUMMARY OF CHAPTER ON NATURAL SELECTION . If under changing conditions of life organic beings present indi- vidual differences in almost every part of their structure, and this cannot be disputed; if there be, owing to their geometrical rate of increase, a severe struggle for life at some age, season, or year, and this certainly cannot be disputed; then, considering the infinite com- plexity of the relations of all organic beings to each other and to their conditions of life, causing an infinite diversity in structure, constitu- tion, and habits, to be advantageous to them, it would be a most 234 READINGS IN EVOLUTION, GENETICS, AND EUGENICS extraordinary fact if no variations had ever occurred useful to each being's own welfare, in the same manner as so many variations have occurred useful to man. But if variations useful to any organic being ever do occur, assuredly individuals thus characterized will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance, these will tend to produce offspring similarly characterized. This principle of preservation, or the survival of the fittest, I have called Natural Selection. It leads to the im- provement of each creature in relation to its organic and inorganic conditions of life; and consequently, hi most cases, to what must be regarded as an advance in organization. Nevertheless, low and simple forms will long endure if well fitted for their simple conditions of life. Natural selection, on the principle of qualities being inherited at corresponding ages, can modify the egg, seed, or young, as easily as the adult. Amongst many animals, sexual selection will have given its aid to ordinary selection, by assuring to the most vigorous and best adapted males the greatest number of offspring. Sexual selection will also give characters useful to the males alone, in their struggles or rivalry with other males; and these characters will be transmitted to one sex or to both sexes, according to the form of inheritance which prevails. Whether natural selection has really thus acted in adapting the various forms of life to their several conditions and stations, must be judged by the general tenor and balance of evidence given hi the follow- ing chapters. But we have already seen how it entails extinction ; and how largely extinction has acted in the world's history, geology plainly declares. Natural selection, also, leads to divergence of character; for the more organic beings diverge in structure, habits, and constitu- tion, by so much the more can a large number be supported on the area, of which we see proof by looking to the inhabitants of any small spot, and to the productions naturalized in foreign lands. There- fore, during the modification of the descendants of any one species, and during the incessant struggle of all species to increase in number, the more diversified the descendants become, the better will be their chance of success hi the battle for life. Thus the small differences dis- tinguishing varieties of the same species, steadily tend to increase, till they equal the greater differences between species of the same genus, or even of distinct genera. We have seen that it is the common, the widely-diffused and widely ranging species, belonging to the larger genera within each NATURAL SELECTION 235 class, which vary most; and these tend to transmit to their modified offspring that superiority which now makes them dominant in their own countries. Natural selection, as has just been remarked, leads to divergence of character and to much extinction of the less improved and intermediate forms of life. On these principles, the nature of the affinities, and the generally well-defined distinctions between the innumerable organic beings in each class throughout the world, may be explained. It is a truly wonderful fact — the wonder of which we are apt to overlook from familiarity — that all animals and all plants throughout all time and space should be related to each other hi groups subordinate to groups, hi the manner which we everywhere behold — namely, varieties of the same species most closely related, species of the same genus less closely and unequally related, forming sections and sub-genera, species of distinct genera much less closely related, and genera related hi different degrees, forming sub-families, families, orders, sub-classes and classes. The several subordinate groups in any class cannot be ranked in a single file, but seem clustered round points, and these round other points, and so on in almost endless cycles. If species had been independently created, no explanation would have been possible of this kind of classification; but it is explained through inheritance and the complex action of natural selection, entailing extinction and divergence of character, as we have seen illustrated in the diagram. The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speak? the truth. The green and budding twigs may represent existing species; and those produced during former years may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, hi the same manner as species and groups of species have at all times overmastered other species hi the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was young, budding twigs; and this connection of the former and present buds by ramifying branches may well represent the classifica- tion of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear the other branches; so with the species which lived during long-past geological periods, very few have left living and modified descendants. 236 READINGS IN EVOLUTION, GENETICS, AND EUGENICS From the first growth of the tree, many a limb and branch has decayed and dropped off; and these fallen branches of various sizes may repre- sent those whole orders, families, and genera which have now no living representatives, and which are known to us only hi a fossil state. As we here and there see a thin straggling branch springing from a fork low down hi a tree, and which by some chance has been favored and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications. DIFFICULTIES AND OBJECTIONS TO NATURAL SELECTION AS SEEN BY DARWIN Long before the reader has arrived at this part of my work, a crowd of difficulties will have occurred to him. Some of them are so serious that to this day I can hardly reflect on them without being in some degree staggered; but, to the best of my judgment, the greater number are only apparent, and those that are real are not, I think, fatal to the theory. These difficulties and objections may be classed under the follow- ing heads: First, why, if species have descended from other species by fine gradations, do we not everywhere see innumerable, transitional forms? Why is not all nature in confusion, instead of the species being, as we see them, well defined ? Secondly, is it possible that an animal having, for instance, the structure and habits of a bat, could have been formed by the modifica- tion of some other animal with widely different habits and structure ? Can we believe that natural selection could produce, on the one hand, an organ of trifling importance, such as the tail of a giraffe, which serves as a fly-flapper, and, on the other hand, an organ so wonderful as the eye ? Thirdly, can instincts be acquired and modified through natural selection ? What shall we say to the instinct which leads the bee to make cells, and which has practically anticipated the discoveries of profound mathematicians ? NATURAL SELECTION 237 Fourthly, how can we account for species, when crossed, being sterile and producing sterile offspring, whereas, when varieties are crossed, their fertility is unimpaired ? ANSWER TO THE FIRST DIFFICULTY On the Absence or Rarity of Transitional Varieties. — As natural selection acts solely by the preservation of profitable modifications, each new form will tend hi a fully stocked country to take the place of, and finally to exterminate, its own less improved parent-form and other less-favored forms with which it comes Into competition. Thus extinction and natural selection go hand in hand. Hence, if we look at each species as descended from some unknown form, both the parent and all the transitional varieties will generally have been exterminated by the very process of the formation and perfection of the new form. But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers hi the crust of the earth? It will be more convenient to discuss this question hi the chapter on the Imperfection of the Geological Record; and I will here only state that I believe the answer mainly lies in the record being incomparably less perfect than is generally supposed. The crust of the earth is a vast museum; but the natural collections have been imperfectly made, and only at long intervals of time. ANSWER TO THE SECOND DIFFICULTY: ORGANS OF EXTREME PERFECTION AND COMPLICATION To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. When it was first said that the sun stood still and the world turned round, the common sense of mankind declared the doctrine false; but the old saying of Vox populi, vox Dei, as every philosopher knows, cannot be trusted in science. Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any ani- mal under changing conditions of life, then the difficulty of believing 238 READINGS IN EVOLUTION, GENETICS, AND EUGENICS that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself originated; but I may remark that, as some of the lowest organisms, in which nerves cannot be detected, are capable of perceiving light, it does not seem impossible that certain sensitive elements in their sarcode should become aggre- gated and developed into nerves, endowed with this special sensi- bility. In searching for the gradations through which an organ in any species has been perfected, we ought to look exclusively to its lineal progenitors; but this is scarcely ever possible, and w are forced to look to other species and genera of the same group, that is to the collateral descendants from the same parent-form, in order to see what gradations are possible, and for the chance of some gradations hav- ing been transmitted in an unaltered or little altered condition. But the state of the same organ in distinct classes may incidentally throw light on the steps by which it has been perfected. The simplest organ which can.be called an eye consists of an optic nerve, surrounded by pigment-cells and covered by translucent skh^ but without any lens or other refractive body. We may, however, according to M. Jourdain, descend even a step lower and find aggre- gates, of pigment-cells, apparently serving as organs of vision, without any nerves, and resting merely on sarcodic tissue. Eyes of the above simple nature are not capable of distinct vision, and serve only to dis- tinguish light from darkness. In certain star-fishes, small depressions in the layer of pigment which surrounds the nerve are filled, as de- scribed by the author just quoted, with transparent gelatinous matter, projecting with a convex surface, like the cornea in the higher animals. He suggests that this serves not to form an image, but only to con- centrate the luminous rays and render their perception more easy. In this concentration of the rays we gain the first and by far the most important step towards the formation of a true, picture-forming eye; for we have only to place the naked extremity of the optic nerve, which in some of the lower animals lies deeply buried in the body, and in some near the surface, at the right distance from the concentrating apoaratus, and an image will be formed on it. In the great class of the Articulata, we may start from an optic nerve simply coated with pigment, the latter sometimes forming a sort NATURAL SELECTION 239 of pupil, but destitute of a lens or other optical contrivance. With insects it is now known that the numerous facets on the cornea of their great compound eyes form true lenses, and that the cones include curiously modified nervous filaments. But these organs in the Articulata are so much diversified that Muller formerly made three main classes with seven subdivisions, besides a fourth main class of aggregated simple eyes. When we reflect on these facts, here given much too briefly, with respect to the wide, diversified, and graduated range of structure hi the eyes of the lower animals; and when we bear in mind how small the number of all living forms must be hi comparison with those which have become extinct, the difficulty ceases to be very great hi believing that natural selection may have converted the simple apparatus of an optic nerve, coated with pigment and invested by transparent mem- brane, into an optical instrument as perfect as is possessed by any member of the Articulate Class. He who will go thus far, ought not to hesitate to go one step fur- ther, if he finds on finishing this volume that large bodies of facts, otherwise inexplicable, can be explained by the theory of modification through natural selection; he ought to admit that a structure even as perfect as an eagle's eye might thus be formed, although hi this case he does not know the transitional states. It has been objected that in order to modify the eye and still preserve it as a perfect instrument, many changes would have to be effected simultaneously, which, it is assumed, could not be done through natural selection; but as I have attempted to show in my work on the variation of domestic animals, it is not necessary to suppose that the modifications were all simulta- neous, if they were extremely slight and gradual. Different kinds of modification would, also, serve for the same general purpose: as Mr. Wallace has remarked, "if a lens has too short or too long a focus, it may be amended either by an alteration of curvature, or an alteration of density; if the curvature be irregular, and the rays do not converge to a point, then any increased regularity of curvature will be an improvement. So the contraction of the iris and the muscular movements of- the eye are neither of them essential to vision, but only improvements which might have been added and perfected at any stage of the construction of the instrument. " Within the highest division of the animal kingdon, namely, the Vertebrata, we can start from an eye so simple, that it consists, as hi the lancelet, of a little 240 READINGS IN EVOLUTION, GENETICS, AND EUGENICS sack of transparent skin, furnished with a nerve and lined with pig- ment, but destitute of any other apparatus. In fishes and reptiles, as Owen has remarked, " the range of gradations of dioptric structures is very great. " It is a significant fact that even in man, according to the high authority of Virchow, the beautiful crystalline lens is formed in the embryo by an accumulation of epidermic cells, lying in a sack- like fold of the skin; and the vitreous body is formed from embryonic sub-cutaneous tissue. To arrive, however, at a just conclusion regarding the formation of the eye, with all its marvellous yet not absolutely perfect characters, it is indispensable that the reason should conquer the imagination; but I have felt the difficulty far too keenly to be surprised at others hesitating to extend the principle of natural selection to so startling a length. It is scarcely possible to avoid comparing the eye with a telescope. We know that this instrument has been perfected by the long- continued efforts of the highest human intellects; and we naturally infer that the eye has been formed by a somewhat analogous process. But may not this inference be presumptuous ? Have we any right to assume that the Creator works by intellectual powers like those of man ? If we must compare the eye to an optical instrument, we ought in imagination to take a thick layer of transparent tissue, with spaces filled with fluid, and with a nerve sensitive to light beneath, and then suppose every part of this layer to be continually changing slowly in density, so as to separate into layers of different densities and thick- nesses, placed at different distances from each other, and with the sur- faces of each layer slowly changing in form. Further we must suppose that there is a power, represented by natural selection or the survival of the fittest, always intently watching each slight alteration in the transparent layers; and carefully preserving each which, under varied circumstances, in any way or in any degree, tends to produce a dis- tincter image. We must suppose each new state of the instrument to be multiplied by the million; each to be preserved until a better one is produced, and then the old ones to be all destroyed. In living bodies, variation will cause the slight alterations, generation will multiply them almost infinitely, and natural selection will pick out with unerring skill each improvement. Let this process go on for millions of years; and during each year on millions of individuals of many kinds; and may we not believe that a living optical instrument might thus be formed as superior to one of glass, as the works of the Creator are to those of man ? NATURAL SELECTION 241 DARWIN'S SUMMARY or HIS ANSWER TO THE THIRD DIFFICULTY, THAT or ACCOUNTING FOR THE ACQUISITION AND MODIFICATION OF INSTINCTS THROUGH NATURAL SELECTION I have endeavored in this chapter briefly to show that the mental qualities of our domestic animals vary, and that the variations are inherited. Still more briefly I have attempted to show that instincts vary slightly in a state of nature. No one will dispute that instincts are of the highest importance to each animal. Therefore there is no real difficulty, under changing conditions of life, hi natural selection accumulating to any extent slight modifications of instinct which are in any way useful. In many cases habit or use and disuse have prob- ably come into play. I do not pretend that the facts given in this chapter strengthen in any great degree my theory; but none of the cases of difficulty, to the best of my judgment, annihilate it. On the other hand, the fact that instincts are not always absolutely perfect and are liable to mistakes: that no instinct can be shown to have been produced for the good of other animals, though animals take advantage of the instincts of others; that the canon in natural history, of "Natura non facit saltum," is applicable to instincts as well as to cor- poreal structure, and is plainly explicable on the foregoing views, but is otherwise inexplicable, all tend to corroborate the theory of natural selection. This theory is also strengthened by some few other facts in regard to instincts; as by that common case of closely allied, but distinct, species, when inhabiting distant parts of the world and living under considerably different conditions of life, yet often retaining nearly the same instincts. For instance, we can understand, on the principle of inheritance, how it is that the thrush of tropical South America lines its nest with mud, in the same peculiar manner as does our British thrush; how it is that the Hornbills of Africa and India have the same extraordinary instinct of plastering up and imprisoning the females in a hole hi a tree, with only a small hole left in the plaster through which the males feed them and their young when hatched; how it is that the male wrens (Troglodytes) of North America build "cock- nests," to roost in, like the males of our Kitty-wrens, a habit wholly unlike that of any other known bird. Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers, ants making slaves, the larvae of ichneumonidae feeding within the live bodies of caterpillars, not as specially endowed or created 242 READINGS IN EVOLUTION, GENETICS, AND EUGENICS instincts, but as small consequences of one general law leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die. DARWIN'S SUMMARY OF HIS ANSWER TO THE DIFFICULTY AS TO THE INABILITY OF NATURAL SELECTION TO ACCOUNT FOR THE FACT THAT SPECIES WHEN CROSSED ARE STERILE OR PRODUCE STERILE OFFSPRING, WHEREAS WHEN VARIETIES ARE CROSSED THEIR FERTILITY IS UNIMPAIRED First crosses between forms, sufficiently distinct to be ranked as species, and their hybrids, are very generally, but not universally sterile. The sterility is of all degrees, and is often so slight that the most careful experimentalists have arrived at diametrically opposite conclusions hi ranking forms by this test. The sterility is innately variable in individuals of the same species, and is eminently suscept- ible to the action of favorable and unfavorable conditions. The degree of sterility does not strictly follow systematic affinity, but is governed by several curious and complex laws. It is generally different, and sometimes widely different hi reciprocal crosses between the same two species. It is not always equal in degree in a first cross and hi the hybrids produced from this cross. In the same manner as in grafting trees, the capacity in one species or variety to take on another, is incidental on differences, generally of an unknown nature, in their vegetative systems, so in crossing, the greater or less facility of one species to unite with another is incidental on unknown differences hi their reproductive systems. There is no more reason to think that species have been specially endowed with various degrees of sterility to prevent their crossing and blending in nature, than to think that trees have been specially endowed with various and somewhat analogous degrees of difficulty hi being grafted together in order to prevent their inarching in our forests. The sterility of first crosses and of their hybrid progeny has not oeen acquired through natural selection. In the case of first crosses it seems to depend on several circumstances; in some instances hi chief part on the early death of the embryo. In the case of hybrids, it apparently depends on their whole organization having been dis- turbed by being compounded from two distinct forms; the sterility being closely allied to that which so frequently affects pure species, when exposed to new and unnatural conditions of life. He who will explain these latter cases will be able to explain the sterility of hybrids. This view is strongly supported by a parallelism of another kind: namely, that, firstly, slight changes in the conditions of life add to tb* NATURAL SELECTION 243 vigor and fertility of all organic beings; and secondly, that the cross- ing of forms, which have been exposed to slightly different conditions of life or which have varied, favors the size, vigor, and fertility of their offspring. The facts given on the sterility of the illegitimate unions of dimorphic and trimorphic plants and of their illegitimate progeny, perhaps render it probable that some unknown bond in all cases con- nects the degree of fertility of first unions with that of then* offspring. The consideration of these facts on dimorphism, as well as of the results of reciprocal crosses, clearly leads to the conclusion that the primary cause of the sterility of crossed species is confined to differences in their sexual elements. But why, in the case of distinct species, the sexual elements should so generally have become more or less modified, lead- ing to their mutual infertility, we do not know; but it seems to stand in some close relation to species having been exposed for long periods of time to nearly uniform conditions of life. It is not surprising that the difficulty in crossing any two species, and the sterility of their hybrid offspring, should in most cases corre- spond, even if due to distinct causes: for both depend on the amount of difference between the species which are crossed. Nor is it sur- prising that the facility of effecting a first cross, and the fertility of the hybrids thus produced, and the capacity of being grafted together — though this latter capacity evidently depends on widely different cir- cumstances— should all run, to a certain extent, parallel with the systematic affinity of the forms subjected to experiment; for system- atic affinity includes resemblances of all kinds. First crosses between forms known to be varieties, or sufficiently alike to be considered as varieties, and their mongrel offspring, are very generally, but not, as is so often stated, invariably fertile. Nor is this almost universal and perfect fertility surprising, when it is remembered how liable we are to argue in a circle with respect to varieties in a state of nature; and when we remember that the greater number of varieties have been produced under domestication by the selection of mere external differences, and that they have not been long exposed to uniform conditions of life. It should also be espe- cially kept in mind that long-continued domestication tends to elimi- nate sterility, and is therefore little likely to induce this same quality. Independently of the question of fertility, in all other respects there is the closest general resemblance between hybrids and mongrels, in their variability, in their power of absorbing each other by repeated crosses, and in their inheritance of characters from both parent-forms. 244 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Finally, then, although we are as ignorant of the precise cause of the sterility of first crosses and of hybrids as we are why animals and plants removed from their natural conditions become sterile, yet the facts given in this chapter do not seem to me opposed to the belief that species aboriginally existed as varieties. CHAPTER XVII CRITIQUE OF DARWINISM [The last chapter dealt with the central ideas of Darwin as told by himself. Some of the chief objections to the theory were also presented as Darwin saw them, and his own answers to these objections were given. These four objections are not by any means all that Darwin foresaw, for he presented in another chapter a discussion of "Miscel- laneous Objections to the Theory of Natural Selection." Before entering upon a general criticism of Darwinism, it would be advanta- geous to have before us a brief and pointed summary of Darwin's theory — natural selection — now known technically as Darwinism. The writer knows of no better short statement of the true content of Darwinism than the following summary by Professor Vernon L. Kellogg— ED.] SUMMARY OP DARWIN'S NATURAL-SELECTION THEORY* VERNON L. KELLOGG Darwinism may be denned as a certain rational, causo-mechanical (hence, non-teleologic) explanation of the origin of new species. The Darwinian explanation rests on certain observed facts, and certain inductions from these facts. The observed facts are: (i) the increase by multiplication in geometrical ratio of the individuals hi every species, whatever the kind of reproduction which may be peculiar to each species, whether this be simple division, sporulation, budding, parthenogenesis, conjugation and subsequent division, or amphimixis (sexual reproduction); (2) the always apparent slight (to greater) variation in form and function existing among all individuals even though of the same generation or brood; and (3) the transmission, with these inevitable slight variations, by the parent to its offspring of a form and physiology essentially like the parental. The inferred (also partly observed) facts are: (i) a lack of room and food for all these new individuals produced by geometrical multiplication and consequently a competition (active or passive) among those individuals having any ecologic relations to one another, as, for example, among 1 From V. L. Kellogg, Darwinism To-Day (copyright 1907). Used by per- mission of the publishers, Henry Holt & Company. 24S 246 READINGS IN EVOLUTION, GENETICS, AND EUGENICS those occupying the same locality, or needing the same food, or needing each other as food; (2) the probable success in this competition of those individuals whose slight differences (variations) are of such a nature as to give them an advantage over their confreres, which results in saving their life, at least until they have produced offspring; and (3) the fact that these "saved" individuals will, by virtue of the already referred to action of heredity, hand down to the offspring their advantageous condition of structure and physiology (at least, as the "mode" or most abundantly represented condition, among the offspring). The competition among individuals and kinds (species) of organ- isms may fairly be called a struggle. This is obvious when it is active, as in actual personal battling for a piece of food or in attempts to capture prey or to escape capture, and less obvious when it is passive, as in the endurance of stress of weather, hunger, thirst, and untoward conditions of any kind. The struggle is, or may be, for each individual threefold in nature: (i) an active struggle or competition with other individuals of its own kind for space in the habitat, sufficient share of the food, and opportunity to produce offspring in the way peculiar and common to its species; (2) an active or passive struggle or compe- tition with the individuals of other species, which may need the same space and food as itself, or may need it or its eggs or young for food; and (3) an active (or more usually passive) struggle with the physico- chemical external conditions of the world it lives in, as varying temperature and humidity, storms and floods, and natural catas- trophes of all sorts. For any individual or group of individuals any of these forms of struggle may be temporarily ameliorated, as is (i) the intra-specific struggle among the thousands of honey-bee individuals living together altruistically, in one hive, or (2) the inter-specific struggle, when two species live together symbiotically as the hermit crab Eupagurus and the sea-anemone Podocoryne, or (3) the struggle against untoward natural conditions as in special times or places of highly favourable climate, etc. Or for any individual or group of individuals all forms of the struggle may be coincidently active and severe. The resultant of these existing conditions is, accord- ing to Darwin and his followers, an inevitable natural selection of individuals and of species. Thousands must die where one or ten may live to maturity (i.e., to the time of producing young). Which ten of the thousand shall live depends on the slight but sufficient advantage possessed by ten individuals in the comolex struggle for CRITIQUE OF DARWINISM 247 existence due to the fortuitous possession of fortunate congenital differences (variations). The nine hundred and ninety with unfortu- nate congenital variations are extinguished in the struggle and with them the opportunity for the perpetuation (by transmission to the offspring) of their particular variations. There are thus left ten to reproduce their advantageous variations. The offspring of the ten of course will vary in their turn, but will vary around the new and already proved advantageous parental condition: among the thou- sand, say, offspring of the original saved ten the same limitations of space and food will again work to the killing off before maturity of nine hundred and ninety, leaving the ten best equipped to reproduce. This repeated and intensive selection leads to a slow but steady and certain modification through the successive generations of the form and functions of the species; a modification always toward adapta- tion, toward fitness, toward a moulding of the body and its behaviour to safe conformity with external conditions. The exquisite adapta- tion of the parts and functions of the animal and plant as we see it every day to our infinite admiration and wonder has all come to exist through the purely mechanical, inevitable weeding out and selecting by Nature (by the environmental determining of what may and what may not live) through uncounted generations in unreckonable time. This is Darwin's causo-mechanical theory to explain the transforma- tion of species and the infinite variety of adaptive modification. A rigorous automatic Natural Selection is the essential idea in Darwin- ism, at least in Darwinism as it is held by the present-day followers of Darwin. OBJECTIONS TO DARWINISM [i. Darwin in a letter to his friend Hooker (January u, 1844) expresses his contempt of Lamarck's ideas in the following words: "Heaven defend me from Lamarck's nonsense of a 'tendency to pro- gression,' 'adaptations from the slow willing of animals,' etc Lamarck's work appeared to me to be extremely poor; I got not a fact or idea from it." In spite of these views Darwin's Origin of Species is interlarded with Lamarckian explanations. Whenever the author feels the short- comings of the selection factor he lapses into an explanation involving the idea that the effects of use and disuse of organs are inherited. Followers of Darwin, especially Weismann, felt this to be the chief defect in the fabric of Darwinism and bent their efforts chiefly toward purging Darwinism of all taint of Lamarckism. 248 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 2. Darwin insisted upon the idea that minute fluctuating varia- tions, which we now know are to a large extent non-heritable, were the principal, if not the sole, materials for natural selection to work upon. He knew of a considerable number of "sports" or "saltatory variations" (now called mutations), but considered these too infre- quent to furnish the necessary basis for selection. We now know that mutations may be as small as fluctuating variations or as large as "sports" and that they are of much more frequent occurrence than Darwin supposed. 3. Darwin considered all variations as heritable. He did not distinguish between somatic variations and germinal variations. In fact, as we learn from a study of his pangenesis theory, he considered all variations as hi the first instance somatic, and subsequently transferred by means of gemmules to the germ cells. Every somatic variation, whether induced by use, disuse, hi response to environ- mental stimulus, or through mere spontaneous variability, was sup- posed to be able to give off gemmules into the blood stream that would carry to the germ cells the physical basis of the varying charac- ter. The pangenesis mechanism is now known to have no basis in fact. 4. The natural-selection theory is based upon a mistaken concep- tion of the methods of artificial selection. Darwin believed, without having any proof for this belief, that the way in which domestic varieties had been so profoundly modified at the hands of man was by the conscious or unconscious selection of slight fluctuating varia- tions hi favorable or desired directions, and that this resulted in the cumulative improvement or enhancement of the desired characters over a long series of generations. Darwin supposes that the radically changed conditions of domestication hasten and stimulate variability, thus offering a better opportunity for selection. Transferring this idea to nature, he thinks that changed natural conditions stimulate variability, just as does domestication, and that this is seized upon by natural selection to make for adaptation to the new environment and the resultant origin of new species. Our modern experimental studies have shown that somatic modifications due to environmental changes are not hereditary, and that all of the recent domestic varieties whose origin has been observed have been the result of suddenly appearing germinal variations or mutations, that arrive fully formed and cannot be improved by selec- tion, except that they usually need to be selected out or isolated in CRITIQUE OF DARWINISM 249 order to prevent swamping out through intercrossing with the parent-type. 5. Objection has frequently been made to Darwin's idea of the purely fortuitous or chance character of variations. According to this view variations occur in all structures and in all directions at haphazard, so that there would be the widest possible opportunity for a given adaptive variation to occur just when the circumstances would demand. It now appears that variations do not occur in all directions in random fashion, but that they tend to follow certain definite paths of change; in other words, variations are, to a consider- able extent at least, orthogenetic. If variations really tend to follow certain definite lines, owing to purely internal causes, natural selection would be unnecessary, at least until orthogenesis went too far for the good of the species, or far enough to be of real importance in the struggle for existence. 6. The difficulty of explaining how natural selection could make use of the initial stages of adaptive structures is obvious. It is incon- ceivable that the first, almost imperceptible variation in a favorable direction could be of selective value, so as to effect the survival of the individual or the relative number of its offspring. What would be the advantage of the first few hairs of a mammal or the first steps toward feathers hi a bird when these creatures were beginning to diverge from their reptilian ancestors? This objection is, of course, based on the fluctuating- variation idea. • If the mutation idea were substituted, the difficulty would, to a great extent, clear up; for a mutation might be of sufficient importance in one generation to have selective value from the very first. 7. Natural selection is said to be incapable of explaining the origin of coadaptive and highly complex adaptations whose effectiveness depends upon the perfection of their adjustments to one another. For example, we may refer to some of the perfected adaptations described in chapter xiv. In the case of the electric organs of certain fish, the Darwinian assumption would be that the first step hi the direction of an electric organ would be a very small one, and that it was built up little by little by means of natural selection. But, say the critics, the electric organ would be of no value until it became powerful enough to impart an effective shock to the intruder, and this would not be possible if the character began in a small way. The whole phenome- non of protective resemblance is open to the same type of criticism. As a specific example of this we may cite the case of the dried-leaf 250 READINGS IN EVOLUTION, GENETICS, AND EUGENICS butterfly, Kallima, previously described (pp. 201, 202). In its present condition this animal has a strikingly detailed resemblance to a dried leaf, which is therefore doubtless of some value. But of what value would be the first tiny change in the direction of resemblance ? Until its resemblance became close enough actually to deceive the enemies of butterflies, the critics claim, there would be no chance for selection to act. 8. It is frequently objected that a vast number of characters of organs are useless or non-adaptive and, as such, could not have arisen through the instrumentality of natural selection. If these useless characters, which are sometimes quite large and prominent, are independent of natural selection, why do we need natural selection to explain adaptive characters ? It is also claimed that a vast number of specific peculiarities are useless and therefore could not have helped in the differentiation of species. It should be said in defense that Darwin realized this difficulty quite as clearly as do his critics and was greatly puzzled by it. His idea of correlated variability, however, helps to answer it, for it may well be that many of these apparently useless characters are correlated, or linked in inheritance, with charac- ters of supreme selective value such as general hardiness or great fecundity. Darwin also points out that we are not in a position at present to pronounce judgment on the value of many structures or functions that have been adjudged non-adaptive. 9. Certain characters hi organisms, past and present, have been interpreted as overspecializations, organs that have evolved beyond the range of usefulness or that are more elaborate than is demanded for survival under the conditions of life. The case of the extinct Irish elk is often cited as an example of overspecialization. This group of animals went to extremes in the development of size and elaboration of horns far beyond the range of usefulness, so that it is said to have brought about the extinction of the race. Natural selection, which is supposed to have brought the horns up to the point of adaptive perfection, should have kept them within the bounds of usefulness. Again, the enormously overgrown and overspecialized dinosaurs of long ago are thought of as having followed their lines of evolution far beyond the point of greatest effectiveness and adaptability. 10. The rudimentation of structures, which is such a common phenomenon in nature, is said to meet with no adequate explanation on a selection basis. The case of the whale's vestigial hind limbs is a case in point. Darwin's explanation would be that under aquatic conditions the first whale ancestors would be handicapped by hind CRITIQUE OF DARWINISM 251 iegs and that any decrease in their size, which would be enhanced by disuse, would be of advantage. This might seem reasonable during the maui period of limb reduction, but, after the limb is reduced to a subcutaneous rudiment, there could be little advantage in carrying the rudimentation still farther. Some whales have the hind limbs much more profoundly reduced than others, although they are all thoroughly out of the way and involve no hindrance in swimming. Any number of similar cases of the same kind might be cited. Darwin had no explanation to offer except a resort to Lamarckism; but Weismann, the ablest neo-Darwinian, offered the theory of panmixia to cover this objection, a theory which is mentioned hi chapter i and will be discussed later. 11. It is objected that, unless favorable variations occur in a large number of individuals at the same time, the character would be swamped out by intercrossing with individuals not possessing the favorable variation. The probability that such a swamping-out would occur was shown mathematically by various critics. By way of answer to this objection there arose a number of "isolation theo- ries," according to which favorably varying individuals would be protected from back-crossing with the non-varying individuals. We might also point out that the Mendelian laws of dominance and segregation would serve to prevent loss of any new favorable character. 12. It is objected that natural selection might explain the "sur- vival, but not the arrival, of the fittest." But Darwin met this perfectly when he said: "Some have even imagined that natural selection induces variability, whereas it implies only the preservation of such variations as arise and are beneficial to the being under its conditions of life." 13. Criticism has been directed against natural selection because of the fact that some of the supporters of Darwinism, notably Weis- mann, have made the claim that natural selection is the sole cause of evolution. This idea of the Allmacht or all-sufficiency of natural selection was not Darwin's, as is clear from the following statement: " I am convinced that natural selection has been the most important, but not the exclusive means of modification." 14. It is objected that many, if not most, of the fluctuating varia- tions with which Darwinism deals are purely quantitative or plus- and-minus variations; whereas the differences between species are qualitative. This is a serious objection and difficult to meet, yet a fair defense has been formulated by leading neo-Darwinians. 252 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 15. There is a growing skepticism on the part of biologists as to the extreme fierceness of the struggle for existence and of the conse- quent rigor of selection. It may be answered that no very obvious fierceness is implied in the theory. So long as overproduction and a shortage of space and food exists the struggle for existence is inevitable. 16. Special objections are offered to the subsidiary theory of sexual selection. It is said that the type of sexual selection involving active rivalry and battling for mates needs no special theory, inasmuch as this is a mere phase of the struggle for the maintenance of the full life, including the chance to leave offspring. It is against the other side of sexual selection, which involves passivity on the part of the male and active choice on the part of the female of the more beautiful or otherwise attractive male, that objection is raised. It is claimed that such choice implies too high aesthetic powers hi animals of relatively poor vision and mentality. Experiments have been per- formed with moths, hi which the male and female coloration is strikingly different, in order to determine whether females actually do exercise any choice of mates that is based on considerations of appearance. The result proved conclusively that color patterns have no value in mating, but that the female is passive and mates with the first male to present himself, while the male finds the female through his exquisitely effective sense of smell. We know now, however, that secondary sexual characters are intimately bound up in a physiological way with the functioning of the sex glands and are therefore doubtless to be interpreted as mere non-adaptive correlative variations that need no special evolutionary explanation. DEFENSE OF DARWINISM In presenting these sixteen objections, we have in most cases indicated the lines upon which the objections have been met, if they have been met. Not all of these objections are considered serious at the present time, for some are based upon lack of a full knowledge of what Darwin actually wrote; others are largely academic in character and fail to stand up under actual test; still others have been more or less adequately met by subsidiary or supporting theories which have been advanced by various neo-Darwinians. Most of the special objections raised in this chapter have received the attention of various able Darwinians, and the student of evolution would doubtless be interested in the expert and fair-minded defense CRITIQUE OF DARWINISM 253 of Darwinism at the hands of Professor V. L. Kellogg as it appears in his book Darwinism To-Day. A much briefer and considerably more general defense is that of J. L. Tayler, which is as follows— ED.]; GENERAL DEFENSE OF DARWINISM1 J. L. TAYLER To realise how far the theory of selection is capable of explaining the facts of organic evolution, it is necessary to bear in mind the postulates hi which the theory is founded. 1. It is obvious that natural selection can only act by preserv- ing or eliminating the complete organism. Selection must therefore be organismal. This Darwin and other selectionists have clearly recognised. 2. As the whole organism must survive, if the favourable variation or variations are to be preserved, it follows that certain minor un- favourable variations may also be preserved if they happen to exist in an individual which survives on account of its major favourable variations. And since no individual is completely adapted to its environment, it follows that there must be always a variable amount of residual unfavourable variability hi every organism. 3. This residual unfavourable variability may be of considerable utility under changed conditions. 4. Complementary specialisation of parts, as Spencer has shown, is favourable to successful competition, and as it is the whole organism that is selected or eliminated, it follows that any weakness of one specialised part, since it would disturb the balance of all, would be detrimental. The more complex the organism, the more speciah'sed the structures, the more dependent one part will be on the others for its existence, hence a complementary specialising tendency will be favoured by selection, and therefore all struggles of one part of an organism with another will be reduced to a minimum. It is clear that there must be some underlying criterion which determines whether any given organism shall be selected or not, and that criterion must be the net result of its adaptability to its environ- ment. One organism may conceivably survive, by its possession of a large number of small favourable variations, while another may survive hi virtue of a single valuable one, but hi each case it would be 1 From J. L. Tayler, "The Scope of Natural Selection," Natural Science, 1899. 254 READINGS IN EVOLUTION, GENETICS, AND EUGENICS the whole value of that organism which determined its survival This fact is continually disregarded by opponents of the neo-Darwinian position, yet this selection of the organism as a whole is the fundamental postulate from which the theory of selection starts. Thus it is not uncommom to read criticisms bearing on the early development of some organ, in which the inadequacy of selection is supposed to be proved by the writer demonstrating, or believing he has demonstrated, the fact that the particular variation in question must have been too small to be by itself of selection value. In many cases the particular variation would, no doubt, if taken alone be, as the objector asserts, too unimportant to be selected, but as it is the whole organism that is selected, it is not logical to make an artificial separation and study the development of one organ or structure irrespective of the other organs with which it is in nature associated. Every organ in its evolution must be considered in relation to the whole of the particular organism in which that particular stage of development of that organ is found. Starting, therefore, with this fact that the net value of adaptability of the whole organism to its environment must be the basis which determines selection or elimination, it will follow that certain lines of development will result from the application of this criterion. In a series of organisms placed under new conditions, elimination will proceed along lines essential to bring about a proper adjustment to the new conditions. If the offspring of these adjusted organisms merely repeated hi their generation the characters of the exterminated as well as of the surviving organisms, that temporary adjustment would be permanent as long as the conditions were unchanged. But since the offspring are produced only by the surviving organisms, selection is continually raised to higher and higher planes of adapta- tion, and, therefore, as long as conditions remain constant, the tendency of selection must be, as Darwin clearly saw, cumulative. He did not, however, apparently see that from this cumulative tendency definite variability must arise out of indefinite. Selection in direct relation to climatic conditions is, therefore, of very minor importance, while selection among the members of a species and all forms of inter-organismal selection is of infinitely more importance, since it is this interaction, produced by the offspring in different degrees inheriting the advantages of both parents (both of whom have survived on account of certain advantages), that leads to the cumulative development and never-ending struggle for survival. CRITIQUE OF DARWINISM 255 Darwin came very near to this conception of definite variability when he pointed out that " if a country were changing, the altered conditions would tend to cause variation, not but what I believe most beings vary at all times enough for selection to act on." Extermination would expose the remainder to the "mutual action of a different set of inhabitants, which I believe to be more important to the life of each being than mere climate," and as "the same spot will support more life if occupied by very diverse forms," it is evident that selection will favour very great diversity of structure. Bearing in mind this cumulative action of selection it will follow that under constant or relatively constant conditions the struggle for successful living will become more and more selective in character, even if the actual number of inhabitants remain more or less the same as when the struggle first commenced. The selection of variations will thus tend to pass through certain more or less ill-defined, but nevertheless, real stages. In proportion as the struggle becomes intense, either from the number or from the increasing adaptability of the organisms, or both, certain major essential adaptations, which were necessary for the climatic and other more or less comparatively simple conditions, will be supplemented by minor auxiliary variations which hi the earlier stages would not have appeared. And still later, as more and more rigorous conditions of life were imposed, the advan- tage would tend to rest with those organisms which possessed highly co-ordinated adaptations, since this would entail more rapid respon- siveness to environment. As evolution advances from the unspecialised to the specialised, and higher and higher forms of life come into being, with increasing complexity and specialisation of parts entailing an increasingly delicate adjustment of those parts to each other's needs, the relation of each part to the whole organism becomes of more and more importance, and it follows that selection must become more and more generalised hi its action. No single variation could be of service to any of the higher forms of life unless it was in more or less complete harmony with the whole tendency of the individual. The adjustment of parts and their mutual interdependence make it essential for adaptation that the relation of parts be preserved; consequently, correlated minute favourable variations will tend to be more and more selected as evolution passes from the unspecialised to the specialised forms of life. This response of the whole organism should be still more delicate in those forms of life that are continually subjecting themselves to 256 READINGS IN EVOLUTION, GENETICS, AND EUGENICS changed conditions; hence this delicacy of adjustment is far more necessary in the higher forms of animal life than in more stationary plant organisms, and in the developing nervous systems of animals we have just the central adjusting system that is required for these condi- tions. With evolution of type there will thus be an increasingly definite tendency given to organic, especially the animal, forms of life, if the acting principle of evolution has been selectional. Selection is, therefore, able to account for the steadily progressive tendency of life as a whole without calling to its aid any unknown and doubtful perfecting principle. To summarise: Natural selection, acting on the whole organism, tends to produce more and more definite tendencies in all surviving forms of life, which tendencies are progressive and continuous in char- acter. Variable conditions, by partially altering the line of selection, induce a temporary indefiniteness. And lastly, the process of selec- tion being itself able to be the indirect, though not the direct, cause of those favourable variations, which it subsequently selects from, is able to dispense with any subsidiary factors, provided it has a certain number of elementary properties of life which afford sufficient material to work with. EXPERIMENTAL SUPPORT OF THE EFFECTIVENESS OF NATURAL SELECTION [ Weldon's experiments with the shore-crabs of Plymouth Sound. — These experiments seem to show that under changed environmental conditions natural selection acts upon minute fluctuating variations of linear or quantitative type so as to produce an alteration in the species; exactly as Darwinism would hold. A large breakwater was so placed near the mouth of Plymouth Sound that the rate of flow of the river water was greatly slowed down in certain regions. This allowed an increased settling of the fine china-clay sediment that is carried by the river, and the changed condition caused the death of numerous crabs of the species Carcinus maenas. The question arose as to whether the survivors and those that had perished showed any consistent differences on the basis of which selection could be operat- ing. Careful measurements of hundreds of individuals showed that the mean breadth of frontum is slightly less in the survivors than in the perished. Measurements were repeated in two subsequent years and it was found that there was a progressive narrowing of the frontum. As an experimental check upon these conclusions Weldon CRITIQUE OF DARWINISM 257 placed a number of crabs in a large aquarium, in which china-clay was kept partly in suspension, and found that about half of them died. Again the survivors were compared statistically with the perished and the same relation was found to hold: that the survivors had a mean frontal breadth distinctly narrower than that of the perished. Wei- don concludes that his experiments "have demonstrated two facts about these crabs; the first that their mean frontal breadth is dimin- ishing year by year at a measurable rate, which is more rapid in males than hi females; the second is that this diminution hi frontal breadth occurs in the presence of a material, namely, fine mud, which is increasing in amount, and which can be shown experimentally to destroy broad-fronted crabs at a greater rate than crabs with narrower frontal margins .... and I see no escape from the conclusion that we have here a case of Natural Selection acting with great rapidity, because of the rapidity with which the conditions of life are changing." Cesnola's experiments with Mantis. — To test the selective value of color markings Cesnola fixed specimens of the brown and green Mantis religiosa on plants, some of which were against harmonious, others against disharmonious backgrounds. The result was that most of those which were inconspicuous because of a harmonious back- ground escaped, while most of the others were eaten up by birds. Poulton's and Sanders' experiments with butterfly pupae. — Numerous pupae of various colors were placed under conditions favor- ing protective coloration and others under opposite conditions. The conclusion was that protective coloration is a real survival factor, and one that operates so as to give the protectively colored individual a decided advantage hi the struggle for existence. Davenport's experiments with chickens. — A number of chickens, some black, some white, and some barred or checkered in color, were allowed to wander free in the fields. Hawks killed most of the whites and many of the blacks, but spared, to a large extent, the less con- spicuous checkered and barred types which are harder to detect against a mixed background. All of these experiments merely tend to show that discriminate survival actually occurs, but only the experiment of Weldon has a bearing on the possibility that mere quantitative changes of small dimensions might under certain conditions be of selective value. We badly need more experimental evidence of this sort and until this is forthcoming we shall have to admit that there is very little 258 READINGS IN EVOLUTION, GENETICS, AND EUGENICS experimental evidence in favor of the type of natural selection that Darwin stood for. THE PRESENT STATUS OF NATURAL SELECTION It has come to be rather generally believed that the natural selection that Darwin himself believed in stands almost unscathed as one very important causal factor. In fact it is the only explanation ever offered for adaptation that even approaches adequacy. As an explanation of the origin of new types or new species it falls far short of adequacy, and I think Darwin evidently realized this, although he was unfortunate enough to entitle his book Origin of Species. As an explanation of the origin and perfection of adaptation natural selection has only one rival, the far less satisfactory Lamarckian theory of the inheritance of acquired characters. There is a strong tendency among geneticists to conclude that the modern germ-plasm hypothe- sis, with the aid of mutations and the mechanism of Mendelian inherit- ance, furnishes all the necessary explanation of the causes of evolution. There is, however, marked dissent to this extreme position. In his critique of De Vries's rather extreme position that the mutation theory needs no aid from natural selection, Weismann shows in most able fashion the inadequacy of mutations to account for adaptation, and, hi contrast, how well natural selection accounts for them. In a very recent paper Professor C. C. Nutting attempts to show that natural selection is still an important factor in evolution and quite in harmony with both the mutation theory and Mendelism. We perhaps can close the present chapter no more fittingly than by quoting Professor Nutting's paper. — ED.] THE RELATION OF MENDELISM AND THE MUTATION THEORY TO NATURAL SELECTION1 C. C. NUTTING Two marked tendencies are evident in the history of any important theory after its publication. First. The followers of the discoverer carry the theory too far and attempt too universal an application. This is manifestly true of Wallace and Weismann who out-Darwined Darwin in their claims for natural selection; of the followers of Mendel, such as Morgan and 1 From an address given before the Genetics branch of the American Associa- tion for the Advancement of Science, December, 1020; Science, N.S., VoL LIII. CRITIQUE OF DARWINISM 259 Pearl; and of many mutationists who make much greater claims for that theory than does De Vries himself. Second. Each generation of biologists is so occupied with its own work and contemporary theories that it makes no real effort to understand preceding theories. This second tendency seems to me most marked in the attitude of present workers along genetic lines towards natural selection. They reveal an apparent lack of understanding of what Darwin really meant and of what he claimed; and when criticising that theory they are often engaged in the classic, but unprofitable, exercise of "fighting windmills." In view of these facts I hope you will pardon me if I present in as few words as possible just what I believe to be the main factors which Darwin presented as resulting, in their actions and reactions, hi natural selection. These factors are three in number: First. Heredity, by which the progeny tend to resemble their parents more than they do other individuals of the same species. Second. Individual variation, by which the progeny tend to depart from the parental type and sometimes from the specific type. Third. Geometrical ratio of increase, by which each species tends to produce more individuals than can survive. - Each of these factors is practically axiomatic, so little is it open to argument. No one doubts the fact of heredity, whether pangenesis, Weis- mannism or Mendelism be the correct expression of the mechanism involved. These do not affect the fact of heredity nor invalidate it as a factor in natural selection. No one doubts the fact of variation; whether it is the "individual variation" of Darwin, the "fluctuating variety" or the "mutation" of De Vries. All that is necessary for Darwin's purpose is that there be heritable variations. That there are such things all parties agree and it matters little what you call them. They are adequate to act as a factor hi the Darwinian scheme. No one doubts the fact of geometrical ratio of increase. It is a proposition easily capable of mathematical demonstration, and thaf is sufficient for Darwin's purpose. These three factors, then, are not debatable as facts, whateve' then- mechanism or causes. A moment's reflection will show that geometrical ratio of increasp is a quantitative factor, giving an abundance of individuals fron* 260 READINGS IN EVOLUTION, GENETICS, AND EUGENICS which to select; that individual variation is a qualitative factor, giving the differences which make a selection possible; and that heredity is a conservative factor, holding fast those characters which better fit the organism to its environment. Now it seems to me that there is no possible outcome of the necessary action and interaction of these three factors that would not be a selection of some sort. Darwin thought it comparable in a large way to the selection by which the stock-breeder improves his herd, and therefore called it "natural selection," carefully guarding the phrase from misinterpretation from the teleological angle as well as from a too close parallelism between artificial and natural selection. And I believe no one has suggested a more acceptable term for the process of selection resulting from the interplay of natural laws. Three outstanding theories have been advanced since the publica- tion of the Origin, each involving an advance hi our knowledge of the mechanism of heredity on the one hand and the origin of varia- tions on the other. Weismann's theory of the continuity and stability of the germ plasm was of immense importance in its discussion of the mechanism of heredity, and his amphimixis gave a plausible explanation of the origin of variations. His results were almost universally regarded as confirming and greatly extending the scope of natural selection. Mendel's theory regarding the purity of the gametes, their segre- gation hi the sex cells, and the whole complex Mendelian mechanism so admirably described by Morgan; all of these, fascinating and important as they are, deal with the mechanism rather than the fact of heredity. In my opinion their acceptance or rejection does not affect the status of natural selection as a theory of organic evolution. But it is the theory of mutation that has furnished most of the ammunition for the opponents of natural selection; and this hi spite of the fact that De Vries, the originator of the mutation theory, expresses himself with great clarity as follows: " My work claims to be in full accord with the principles laid down by Darwin and to give a thorough and sharp analysis to some of the ideas of variability, inheritance, selection, and mutation which were necessarily vague hi his tune." In 1904, when these words were published, there did seem to be a sharp distinction between the ideas of Darwin and those of De Vries. The former believed that natural selection acted upon many small variations and accumulated them until the differences were sufficient CRITIQUE OF DARWINISM 261 to constitute new species; while De Vries claimed that new species were formed by the sudden appearance by mutations of forms specifi- cally distinct from the parents. That mutants were new species! It seems evident that Darwin did not regard " saltatory evolution " as the common method, while De Vries did. Darwin believed that individual, usually small, variations fur- nished the material on which selection acts; while De Vries thought that mutants, usually large variations, furnished the material. Both, however, believed thoroughly that natural selection was a vera causa of evolution. But things have changed greatly since 1904. The work of Morgan, Castle, Jennings and a host of others has shown that many mutations are so small, from a phenotypic standpoint, that they are quantitatively no greater than the individual variations of Darwin; and that they are heritable in the Mendelian way. Castle produced a perfectly graded series of hooded rats which exhibits almost ideally the steps by which a new form might be oroduced by natural selection. He says: "If artificial selection can, in the brief span of a man's lifetime, mould a character steadily in a particular direction, why may not natural selection in unlimited time also cause progressive evolution in directions' useful to the organism ?" Jennings says: "Sufficiently thorough study shows that minute heritable varia- tions— so minute as to represent practically continuous gradations — occur hi many organisms: some reproducing from a single parent, others by biparental reproduction It is not established that heritable changes must be sudden large steps; while these may occur, minute heritable changes are more frequent. Evolution according to the typical Darwinian scheme, through the occurrence of many small variations and their guidance by natural selection, is perfectly con- sistent with what experimental and paleontological studies show us; to me it appears more consistent with the data than does any other theory." Many believers hi mutation have been needlessly befuddled by the diverse meanings of "variations" as used by Darwin and De Vries. Darwin included in his "individual variations" both the "fluctuating varieties" and the "mutations" of De Vries. Pheno- typically they cannot even now be distinguished. De Vries himself candidly admits that this was Darwin's attitude, thus proving himself 262 READINGS IN EVOLUTION, GENETICS, AND EUGENICS more clear-sighted than many of his followers. All that Darwin needed for his purpose was proof of variations that are heritable, and these are found in mutations, be they large or small. Just as Mendelism has to do with the mechanism and not the fact of heredity, so the mutation theory deals with the nature and not the fact of variations. Neither, in my opinion, has any implication that is antagonistic to the theory of natural selection. The statement has been made that natural selection "originates nothing" because it does not explain the origin of variations. I must confess scant patience with this point of view. As well say that the sculptor does not make the statue because he does not manufacture the marble or his chisel; or that the worker in mosaic originates nothing because he does not make the bits of stone which he assembles hi his design! The material corresponding to the bits of stone in the mosaic is furnished by heredity and variation, and its quantity by geometrical ratio of increase. Natural selection acts in selecting and putting together this material in the formation of new species. Thus, in a true sense, it seems evident that something new has appeared — something that is, but was not. Another favorite figure, introduced I believe by De Vries, is "Natural selection acts only as a sieve" determining which forms shall be retained and which shall be discarded. This also seems to me to fall short of a complete statement of the truth. If the material subjected to the sifting process be regarded as changing with each generation by the addition of variations, or mutations if you prefer, some of which are favorable to a nicer adjustment of the species to its environment, the figure would be more nearly correct. To make it complete, however, the mesh of the sieve must change from generation to generation so that a quantitative variation which would be preserved in one generation would be discarded in a later one. But in this case natural selection would do more than a sieve could do. It would combine a number of favorable variations hi the production of something new, a new species! In conclusion it seems to me that we are justified hi maintaining that Mendelism and the mutation theory, while forming the basis of the most brilliant and important advances hi biological knov/ledge of the last half-century, have neither weakened nor supplanted the Darwinian conception of the "Origin of species by means of Natural Selection." CHAPTER XVIH OTHER THEORIES OF SPECIES-FORMING H. H. N. THEORIES AUXILIARY TO NATURAL SELECTION The post-Darwinian causo-mechanical theories fall quite naturally into two categories: those that were devised by Darwinians to bolster up natural selection and to free it of some of its most obvious objec- tions, while retaining the essential features of the principle; and those that were meant to be substitutes for and therefore quite opposed to natural selection. The former theories have been classed as auxiliary, and the latter as alternative theories to natural selection. The several theories of Weismann will be dealt with first as the most important of the purely auxiliary theories. "Panmixia" is designed to explain, without recourse to Lamarckism and in harmony with natural selection, the degeneration or atrophy of organs which seemed to be inadequately explained by Darwin. "Germinal Selec- tion" is supposed to explain the initial stages of adaptations and allied phenomena, and thus to aid natural selection at one of its weakest points. WEISMANN'S THEORY OF PANMIXIA The following statement of "panmixia, " as given by S. Herbert, is concise and to the point: "Cessation of selection as a cause of atrophy was first proposed by Romanes. Later on, Weismann, whilst examining the validity of the principle of use-inheritance, adopted the same idea, called by him 'panmixia,' in order to account for the dwindling and disappearance of useless organs without having recourse to the Lamarckian factors. If natural selection leads to the mating of select types, so that those below a certain standard are prevented from propagating, it follows that, with the cessation of selection, a general crossing of all types, including the inferior ones, must take place, and thus lower the average quality of the whole stock. Weismann explained hi this manner, for instance, the prevalence of short-sightedness among civilized people. The individuals with defective eyesight not being weeded out in modern society, the sharpness of the eyesight of the population sinks gradually. The same would apply to the deterioration of the teeth 263 264 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of man, of the breast-gland of modern women, etc. The fact that degeneration generally progresses so slowly, often taking thousands and thousands of years, seemed to him a sufficient proof of the inade- quacy of the Lamarckian explanation. For if the effect of disuse were transmitted in accumulating ratio hi the successive generations, a useless organ ought to disappear much more quickly. "Weismann originally attributed a great effect to panmixia, and considered that nearly 90 per cent, of the reduction of rudimentary organs was due to it; the remainder, up to the complete loss of the organs, being accounted for by reversed selection. Romanes was much more modest in his estimate, and only allowed about 10 to 20 per cent, to this cause; while Lloyd Morgan gave only 5 per cent, reduction of the original size. The final reduction of the organ to zero is still not accounted for by any of these theories. Calling to aid a failure of the force of heredity, as Romanes did, can hardly be con- sidered a solution of the problem. First of all, the force of heredity does not explain anything hi the case. It only restates the problem. We want to know what the force of heredity is. Secondly, if the force of heredity does fail, we should have to explain why it wanes hi some cases and not in others. For the reduction and elimination of rudimen- tary organs occurs apparently in the most irregular, haphazard manner. "But can panmixia really reduce an organ ? Plate, in agreement with Spencer, Eimer, and others, denies any such possibility. An organ hi a given condition of its existence varies around a mean or average, the plus and minus variations generally being equally fre- quent. It follows, therefore, that if all the existing variations are crossed hi propagation, the organ remains stationary. Selection only improves the organ by cutting off the minus variations; the absence of selection would simply leave the organ where it was before the selection. At most it could only sink a very little below the aver- age. That this is so is seen in organs which are not under the sway of selection at all. There are numberless such indifferent species charac- ters, which ought gradually to dwindle and disappear, yet they remain fairly constant, though continunlly exposed to the swamping effect of panmixia. Panmixia may explain the functional degeneration of an organ, but cannot explain its actual rudimentation. "Weismann himself hi later tunes abandoned panmixia as a suffi- cient means of explanation, and resorted to a new theory— that of germinal selection."1 1 From S. Herbert, First Principles of Evolution (1913). OTHER THEORIES OF SPECIES-FORMING 265 WEISMANN'S THEORY OP GERMINAL SELECTION This theory was intended to rehabilitate the selection principle which had lost a great, deal of prestige because of the serious character of the objections that had been raised against it, most of which have been stated in the last chapter. The theory is believed by its author to overcome all objections and doubts and to clear away all difficulties. "Its strength," says Plate, "shall avail in four directions. First, it shall explain how not only degeneration (physiological) but rudimenta- tion (morphological) occurs in panmixia; second, why exactly those variations needed for the development of a certain adaptation appear at the right time; third, how correlation of adaptation comes to exist; and fourth, how variations are able to develop orthogenetically along a definite line without depending on the necessity of a personal selec- tion raising them step by step." The essential feature of germinal selection, as the name implies, is a transfer of the struggle for existence to the germ cell. The germ cell is assumed to be a greatly reduced and simplified sample of the characters of the whole organism. Each independently variable part of the organism is supposed to be represented in the germ cell by a minute physiological unit, unique in composition and capable of reproducing the part in question in a new organism. These hereditary units are called "determinants." Thus there is a different kind of determinant for each muscle of the body, for each bone, or for each independently functioning blood vessel; but, since all red blood cor- puscles are alike, there would be only one determinant for all of them. These determinants have to grow, and in cell division, to divide so as to furnish to daughter germ cells all of the necessary determinants for a whole individual. In their process of growth and multiplication, which goes on very rapidly at certain periods in the germ-cell cycle, these determinants are in competition among themselves for the available food supply. Some may be more favorably placed than others or may be more active chemically than others. There will thus arise a struggle within the germ for a chance to grow and reproduce their kind, which, for these determinants, might be as bitter as would be the struggle in nature among the whole organisms that are in com- petition for a place in the world. A determinant favored, perhaps accidentally or possibly because of inherent activity, by a good food supply would wax stronger and grow faster and would, logically, pro- duce a larger and more effective part when that particular germ cell developed into an adult. Other germ cells that would be the offspring 266 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of this germ cell would continue the struggle among determinants, and it would be expected that the strong determinant would continue to gain further advantage until the structure it represents reached its maximum efficiency. Similarly, a determinant that was for some reason deprived of its fair share of nutriment at any time would be weakened and would produce in cell division weakened daughter determinants. These in turn, unless especially favored, would wage a losing fight and continue to grow smaller and weaker. Each indi- vidual that might develop from such germ cells would have the charac- ters whose determinant had been weakened in a reduced and progressively degenerating condition. Finally, certain determinants might starve entirely, and the part for which they stood would dis- appear entirely from the ontogeny of the individual arising from these germ cells. In this way Weismann tried to explain the gradual dwindling and the final elimination of useless organs. So also he would explain definitely directed or orthogenetic variations, because germinal selec- tion, once started in a given direction, continues automatically till the goal of adaptiveness is reached. The most potent objections to the theory of germinal selection are as follows: 1. There should be, according to this theory, certain pronounced tendencies in variability in definite directions, whereas fluctuating variations nearly always distribute themselves evenly about the mean or mode, and the same specific mean or mode is stationary in succes- sive generations. 2. The theory implies too rapid and too general modification of parts and therefore does not accord with the fact that species are decidedly constant, except for occasional mutations, over long periods of time. To meet this objection Weismann proposes a new self- correcting mechanism that checks too rapid a development of char- acters. 3. The over- or undernourishment of determinants might con- ceivably induce size changes in characters already present, but could hardly be responsible for the origin of qualitatively different characters. 4. Actual experiments in over- and underfeeding of animals have been carried on by certain experimenters in order to test out the theory of germinal selection. In the experiments of Kellogg, for example, involving feeding silkworm larvae only one-eighth of the normal amount of food, the only result was that the mature individuals wtre OTHER THEORIES OF SPECIES-FORMING 267 dwarfed in size. The relative sizes of the parts were unaltered, show- ing that there had been no real struggle among the determinants; for, on the theory of germinal selection, only the stronger determinants would have survived and the weaker ones would have been starved out. Partial individuals, moreover, lacking certain organs and over- developed in others, would have been produced instead of individuals merely smaller hi all parts. These are the specific objections to the ..heory, but more important than all of these is the general objection that follows: "Thus Weismann," says Morgan,1 "has piled up one hypothesis on another as though he could save the integrity of the theory of natural selection by adding new speculative matter to it. The most unfortunate feature is that the new speculation is skilfully removed from the field of verification, and invisible germs whose sole functions are those which Weismann's imagination bestows on them, are brought forward as though they could supply the deficiencies of Darwin's theory. This is, indeed, the old method of the philosophizers of nature. An imaginary system has been invented which attempts to explain all difficulties, and if it fails, then new inventions are to be thought of. Thus we see where the theory of selection of fluctuating germs has led one of the most widely known disciples of the Darwin- ian theory. "The worst feature of the situation is not so much that Weismann has advanced new hypotheses unsupported by experimental evidence, but that the speculation is of such a kind that it is, from its very nature, unverifiable, and therefore useless. Weismann is mistaken when he assumes that many zoologists object to his methods because they are largely speculative. The real reason is that the speculation is so often of a kind that cannot be tested by observation and experiment" It seems almost impossible that the same Professor Morgan, who wrote the foregoing paragraphs in 1903, should now be the leading exponent of a theory of the mechanics of hereditary transmission which depends upon hereditary units almost identical with Weis- mann's "determinants," for the "genes" or "factors" of Morgan are minute corporeal bodies hi the germ cells which determine the charac- ters of the adult individual. The difference is, however, that the "genes" of Morgan are experi- mentally demonstrable and have behind them a vast amount of rea) evidence for then* existence. 'From T. H. Morgan, Evolution and Adaptation. 268 READINGS IN EVOLUTION, GENETICS, AND EUGENICS In this chapter the writer has purposely avoided entering into the more elaborate intricacies of the Weismannian theories of develop- ment and heredity. The theories have been so generally discredited and play so small a part in modern biological thought that it seems useless to burden the reader's mind with needless complexities. Certain other phases of Weismann's work, especially his ideas of the germ plasm, its separateness and its continuity, are more appro- priately studied in connection with genetics than at the present tune. ROUX'S THEORY OF INTRASELECTION OR THE BATTLE OF THE PARTS In point of tune this theory antedates Weismann's theories, since it was proposed hi 1881. In some respects it is a more acceptable theory than germinal selection, but in others quite unacceptable. The theory is designed primarily to explain the origin of the "fine and delicate inner adaptations" of organisms, which do not come in con- tact with the external environment and therefore could not be directly affected by it. The idea is that there is a sort of struggle among the tissues for a chance to develop in the direction of functional perfection. Certain contacts, stresses, and pressures of part on part aid or hinder the development of parts. Thus, where muscular pressure on bone is greatest or weight borne by bone is greatest there will the most bony tissue be laid down in the form of lamellae. The result is that any given bone improves its structure by resistance to strain and pressure, which is a case of improvement with use. We may then inquire how such a change in the individual could affect the evolution of the race. The only reply involves the adoption of a distinctly Lamarckian con- cept, and this at present is quite unacceptable. COINCIDENT SELECTION OR ORGANIC SELECTION This theory has been masked under various guises. In addition to the two titles given above, it has appeared under the names "on to- genetic selection" and "orthoplasy." The main idea, according to Herbert, is that "the individually acquired characters, though not transmitted to the offspring, serve to tide the successive generations over the critical period until germinal (inborn) variations of the same kind appear which are inheritable. Ontogenetic (individually acquired) adaptations and natural selection work together towards the same end. "This hypothesis would help to account for two related difficult points in the theory of natural selection. Firstly, it would explain the possibility of the slow accumulation of germinal variations in their OTHER THEORIES OF SPECIES-FORMING 269 first stages before they attain selective value; secondly, it would make correlated adaptations feasible by supplying ontogenetic (individually acquired) modifications, until the material for the appropriate germi- nal adaptations arose. " It has been objected to this theory that, since the individually acquired modifications possess the main selective value in these instances, there is no reason why the corresponding germinal variations should be fostered at all. The individuals with the right, but slight, congenital variations would have no advantage over their fellows who show no such coincident variations. Nor is there any ground to assume that individuals with the greatest amount of plastic modifica- tion hi a given direction will tend to exhibit similar innate variations to a greater degree than those individuals not possessing this plas- ticity."1 ISOLATION THEORIES One of the objections to natural selection was that a favorable variation appearing hi one or a few individuals would be lost because the individuals possessing it would interbreed with those not possessing it, which presumably would be much more numerous. If there were any kind of agency whose effect would be a partial or complete inhibi- tion of intercrossing, the favorable character would have a chance to survive. Several related theories have arisen that deal with possible isola- tive or segregative agencies that might serve to pre\*ent promiscuous intercrossing, and these have received the names geographic isolation, climatic isolation, reproductive isolation, and physiologic isolation. Geographic isolation. — Moritz Wagner was the founder of this theory. He was a very extensive traveler and had a vast knowledge of the details of the geographic distribution of animals. He believed that isolation was absolutely essential hi the differentiation of species. He at first thought of his theory as auxiliary to natural selection, but later, strongly impressed by the facts he had collected, he concluded that isolation was an independent and alternative explanation of species-forming. The underlying idea is one that has already received attention hi chapter vii, under "Evidences from Geographic Distri- bution." Any successful species tends to spread hi all directions until checked by barriers. Some few members of a species under favorable conditions may surmount the barrier and become isolated. The result 1 From S. Herbert, First Principles of Evolution (1913). 270 READINGS IN EVOLUTION, GENETICS, AND EUGENICS will be that, if they differ in any definite way from the main body of the species, a new elementary species will at once gain a foothold and will evolve independently of the parent-species. If a certain area of land is cut off from a continent so as to form a continental island, the members of each species that have become isolated will evolve independ- ently of the mam body of the species and will have their own peculiar lines of variation preserved from back-crossing with the parent-species. Professor David Starr Jordan,1 the leading proponent of the theory of geographic isolation in America says: "It is now nearly forty years since Moritz Wagner (1868) first made it clear that geographic isolation (raumlicke Sender ung) was a factor or condition hi the formation of every species, race, or tribe of animal or plant we know on the face of the earth. This conclusion is accepted as almost self-evident by every competent student of species or of the geographical distribution of species. But to those who approach the subject of evolution from some other side the principles set forth by Wagner seem less clear. They have never been confuted, scarcely ever attacked, so far as the present writer remem- bers, but in the literature of evolution of the present day they have been almost universally ignored. Nowadays much of our discussion turns on the question of whether or not minute favorable variations would enable their possessors little by little to gain on the parent stock, so that a new race would be established side by side with the old, or on whether a wide fluctuation or mutation would give rise to a new species which would hofd its own in competition with the parent. In theory, either of these conditions might exist. In fact, both of them are virtually unknown. In nature a closely related distinct species is not often quite side by side with the old. It is simply next to it, geo- graphically or geologically speaking, and the degree of distinction almost always bears a relation to the importance or the permanence of the barrier separating the supposed new stock from the parent stock. "A flood of light may be thrown on the theoretical problem of the origin of species by the study of the probable, actual origin of species with which we are familiar or of which the actual history or the actual ramifications may in some degree be traced. "In regions broken by few barriers, migration and interbreeding being allowed, we find widely distributed species, homogeneous in their character, the members showing individual fluctuation and climatic 1 Science, N.S., Vol. XXII (1905). OTHER THEORIES OF SPECIES-FORMING 271 effects, but remaining uniform in most regards, all representatives slowly changing together in the process of adaptation by natural selection. In regions broken by barriers which isolate groups of indi- viduals we find a great number of related species, though in most cases the same region contains a smaller number of genera or families. In other words, the new species will be formed conditioned on isolation, though these same barriers may shut out altogether forms of life which would invade the open district. " Given any species in any region, the nearest related species is not likely to be found in the same region nor in a remote region, but in a neighboring district separated from the first by a barrier of some sort. "Doubtless wide fluctuations or mutations in every species are more common than we suppose. With free access to the mass of the species, these are lost through interbreeding. Isolate them as in a garden or an enclosure or on an island, and these may be con- tinued and intensified to form new species or races. Any horticul- turist will illustrate this. "In all these and in similar cases we may confidently affirm: The adaptive characters a species may present are due to natural selection or are developed in connection with the demands of competition. The characters, non-adaptive, which chiefly distinguish species do not result from natural selection, but from some form of geographical isolation and the segregation of individuals resulting from it." J. T. Gulick, another exponent of the efficacy of geographic isola- tion in species-forming, has offered in evidence of his views facts about the distribution of Hawaiian land snails. In the island of Oahu, for example, the volcanic ridges have been eroded out into a series of isolated valleys in the bottoms of which grows abundant vegetation, while on the highlands there is little but barren rock. The climatic conditions of all the numerous valleys are the same, but, remarkably enough, each variety of snail is confined not only to one island, but to a definite valley on an island. The degree of difference, moreover, between varieties is in proportion to the distance that separates them. Gulick claimed that he was able to estimate the degree of divergence between the snails of any two valleys by measuring the number of miles that lay between them. Gulick's findings have been extensively corroborated by recent explorations on the snails of other oceanic islands by Crampton. An interesting type of isolation that hardly can be termed geo- graphic, yet is essentially equivalent to the latter hi its effects, is found 272 READINGS IN EVOLUTION, GENETICS, AND EUGENICS in connection with the extensive group of lice (Mallophaga) that live their whole lives buried among the feathers of birds or the hair of mammals. These animals cannot fly and are quite effectively isolated for life upon a particular bird. They do, however, during the intimate period of nesting, pass from parent to offspring, so that they may be said to be isolated upon definite genetic lines. In the case, especially, of birds like the eagle, a bird of long life and monogamous habits, the parasite becomes as isolated as might be a race on a small island. The result is that sometimes the lice of a single bird and its offspring are of quite a distinct variety, which has become fixed by inbreeding until a high degree of uniformity has been attained. Such an isolated variety may be almost as distinct as a true species. Obviously in this case, as in others, isolation must have had a real effect upon species- forming quite apart from natural selection, except in so far as the unfit variants have not survived. The writer's impression is that isolation as a factor in evolution has been undervalued by the majority of writers on the subject. It is a highly important and essential factor in the establishment of species. If natural selection may be said to be the prune factor in producing adaptations, isolation may be said to be the prime factor in species differentiation, guided only within moderate limits by natural selection. Biologic isolation. — The effects of this type of isolation are not nearly so well established as are those of geographic isolation. Accord- ing to this theory, differences in the rate of development or earliness or lateness of the breeding season would serve to prevent certain varieties from intercrossing. Only those individuals which were sexually active simultaneously would mate, and individuals with different breeding tunes and seasons would be isolated from one another and would likely maintain the variations that arose in the isolated stocks. The main weakness of this phase of isolation is, however, that we have so little actual evidence that it is operative in nature. Reproductive isolation. — A much more real type of isolation than the last named is involved in reproduction. Several conditions may arise of entirely distinct sorts that will tend to inhibit mating at ran- dom. The first agency has been called "assortative mating" and implies a sort of race feeling involving either a special attraction of like for like, based on similarity of odors, colors, etc., or an antipathy toward opposites or unlikes. The inhibition to general mating may involve a mere mechanical lack of fit in certain organs necessary for OTHER THEORIES OF SPECIES-FORMING 273 successful mating. Such conditions are readily observable between closely allied species. Again, the prevention of intercrossing may result from the appearance of a lowered interfertility between the variant individuals and those of the parent-stock. If individuals varying hi the same direction were even slightly more fertile inter se than those varying hi different directions there would be a progressive tendency hi a series of generations for the varying individuals to diverge more and more markedly, and ultimately to become practi- cally sterile except with members of their own group. That environmental changes do frequently affect the fertility of animals is seen when wild animals are kept hi confinement. Rela- tively few wild animals breed hi captivity. Such a lowering of fer- tility as the result of environmental changes might restrict crossing between unlike forms, while permitting it among the like ones. Summary on isolation theories. — There is a great divergence of opinion as to the importance of isolation as a causal factor hi species- forming. Some writers, such as D. S. Jordan and V. L. Kellogg, con- sider isolation an indispensable, and therefore primary, factor; others, especially geneticists, almost ignore it as an effective factor. Still others, like the present writer, take a middle ground and conclude that isolation, especially geographic isolation, has helped greatly hi the segregation and establishment of well-defined groups such as species or varieties, the latter developing into the former after prolonged isolation and the addition of new variations. Isolation theories, how- ever, have no light to shed upon the difficult problem of adaptation, and it is here that isolation is auxiliary to natural selection. THEORIES ALTERNATIVE TO NATURAL SELECTION The three theories that have been offered by their authors as sub- stitutes for natural selection are: 1. Theory of the inheritance of acquired characters, commonly called Lamarckism: This theory has been outlined hi the chapter on the history of evolution (pp. 19 ff.). It will again be dealt with hi con- siderable detail hi chapter xxii. For the present, then, we may pass by this theory without further comment. 2. The orthogenesis theories: These theories have already been presented hi sufficient detail for our purposes hi chapter ii (pp. 33 ff.). 3. The mutation theory of Hugo De Vries: This theory has been dealt with hi chapter ii, and will be discussed hi further detail hi chapter xxiv. 274 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 4. The tetr akinetic theory of H. F. Osborn: This is a recent restate- ment in energistic terms, of the causo-mechanical basis of evolution. It is placed in the next chapter, but cannot fully be understood until the subject of genetics has been presented. It is almost impossible satisfactorily to pursue a further study of the causal factors of evolution without encroaching upon the field that is now called genetics, and so we shall pass without further explana- tions to a consideration of this field of experimental and analytical evolution. CHAPTER XIX A NEW COMPOSITE CAUSO-MECHANICAL THEORY OF EVOLUTION (THE TETRAKINETIC THEORY)1 HENXY FAIEPIELD OSBORN THE ENERGY CONCEPT OF LIFE While we owe to matter and form the revelation of the existence of the great law of evolution, we must reverse our thought in search for causes and take steps toward an energy conception of the origin of life and an energy conception of the nature of heredity. So far as the creative power of energy is concerned, we are on sure ground: hi physics energy controls matter and form; in physiology function controls the organ; in animal mechanics motion controls and, in a sense, creates the form of muscles and bones. In every instance some kind of energy or work precedes some kind of form, rendering it probable that energy also precedes and controls the evolution of life. The total disparity between invisible energy and visible form is the second point which strikes us as hi favor of such a conception, because the most phenomenal thing about the heredity-germ .is its microscopic size as contrasted with the titanic beings which may rise out of it. The electric energy transmitted through a small copper wire is yet capable of moving a long and heavy train of cars. The discovery by Becquerel and Curie of radiant energy and of the proper- ties of radium shows that the energy per unit of mass is enormously greater than the energy quanta which we were accustomed to associate with units of mass; whereas, in most man-made machines with metallic wheels and levers, and in certain parts of the animal machine con- structed of muscle and bone, the work done is proportionate to the size and form. The slow dissipation or degradation of energy in radium has been shown by Curie to be concomitant with the giving off of an enor- mous amount of heat, while Rutherford and Strutt declare that in a very minute amount of active radium the energy of degradation would entirely dominate and mask all other cosmic modes of transformation 1 From H. F. Osborn, The Origin and Evolution of Life (copyright 1916). Used by special permission of the publishers, Charles Scribner's Sons. 275 276 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of energy; for example, it far outweighs that arising from the gravita- tional energy which is an ample supply for our cosmic system, the explanation being that the minutest energy elements of which radium is composed are moving at incredible velocities, approaching often the velocity of light, i.e., 180,000 miles per second. The energy of radium differs from the supposed energy of life in being constantly dissipated and degraded; its apparently unlimited power is being lost and scattered. We may imagine that the energy which lies hi the life-germ of heredity is very great per unit of mass of the matter which contains it, but that the life-germ energy, unlike that of radium, is in process of accumulation, construction, conservation, rather than of dissipation and destruction. Following the tune (1620) when Francis Bacon divined that heat consists of a kind of motion or brisk agitation of the particles of matter, it has step by step been demonstrated that the energy of heat, of light, of electricity, the electric energy of chemical configurations, the energy of gravitation, are all utilized hi living as well as in lifeless substances. Moreover, no form of energy has thus far been discovered in living substances which is peculiar to them and not derived from the inorganic world. In a broad sense all these manifestations of energy are subject to Newton's dynamical laws which were formulated in connection with the motions of the heavenly bodies, but are found to apply equally to all motions great or little. These three fundamental laws are as follows: I I Corpus omne perseverare in statu suo Every body perseveres in its state of quiescendi vel movendi uniformiter in rest, or of uniform motion in a right directum, nisi quatenus illud a viribus line, unless it is compelled to change impressis cogitur statum suum mutare. that state by forces impressed thereon. II II Mutationem motus proportionalem The alteration of motion is ever esse vi motrici impressae, et fieri secun- proportional to the motive force im- dum lineam rectam qua vis ilk im- pressed; and is made in the direction of primitur. the right line in which that force is impressed. in m Actioni contrariam semper et aequa- To every action there is always lem esse reactionem: sive corporum opposed an equal reaction: or the duorum actiones in se mutuo semper mutual actions of two bodies upon each esse aequales et in partes contrarias other are always equal, and directed to dirigi. contrary parts. THE TETRAKINETIC THEORY 277 Newton's third law of the equality of action and reaction is the foundation of the modem doctrine of energy, not only in the Newto- nian sense but in the most general sense. Newton divined the prin- ciple of the conservation of energy in mechanics; Rumford (1798) maintained the universality of the laws of energy; Joule (1843) established the particular principle of the conservation of energy, namely the exact equivalence between the amount of heat produced and the amount of mechanical energy destroyed; and Helmholtz, in his great memoir Uber die Erhaltung der Kraft, extended this system of conservation of energy throughout the whole range of natural phenomena. A familiar instance of the so-called transformation of energy is where the sudden arrest of a cool but rapidly moving body produces heat. This was developed as the first law of thermodynamics. At the same time there arose the distinction between potential energy, which is stored away in some latent form or manner so that it can be drawn upon for work — such energy being exemplified me- chanically by the bent spring, chemically by gunpowder, and elec- trically by a Leyden jar — and kinetic energy, the active energy of motion and of heat. While all active mechanical energy or work may be converted into an equivalent amount of heat, the opposite process of turning heat into work involves more or less loss, dissipation, or degradation of energy. This is known as the second law of thermodynamics and is the outgrowth of a principle discovered by Sadi Carnot (1824) and developed by Kelvin (1852, 1853). The far-reaching conception of cyclic processes hi energy enunciated in Kelvin's principle of the dissipation of available energy puts a diminishing limit upon the amount of heat energy available for mechanical purposes. The avail- able kinetic energy of motion and of heat which we can turn into work or mechanical effect is possessed by any system of two or more bodies hi virtue of the relative rates of motion of their parts, velocity being essentially relative. These two great dynamical principles that the energy of motion can be converted into an equivalent amount of heat, and that a certain amount of heat can be converted into a more limited amount of power were discovered through observations on the motions of larger masses of matter, but they are believed to apply equally to such motions as are involved in the smallest electrically charged atoms (ions) of the chemical elements and the particles flying off in radiant energy as phosphorescence. Such movements of infinitesimal particles underlie 278 READINGS IN EVOLUTION, GENETICS, AND EUGENICS all the physicochemical laws of action and reaction which have been observed to occur within living things. In all physicochemical processes within and without the organism by which energy is cap- tured, stored, transformed, or released the actions and reactions are equal, as expressed in Newton's third law. Actions and reactions refer chiefly to what is going on between the parts of the organism in chemical or physical contact, and are subject to the two dynamical principles referred to above. Inter- actions, on the other hand, refer to what is going on between material parts which are connected with each other by other parts, and cannot be analyzed at all by the two great dynamical principles alone without a knowledge of the structure which connects the interacting parts. For example, in interaction between distant bodies the cause may be very feeble, yet the potential or stored energy which may be liberated at a distant point may be tremendous. Action and reaction are chiefly simultaneous, whereas interaction connects actions and reac- tions which are not simultaneous; to use a simple illustration: when one pulls at the reins the horse feels it a little later than the moment at which the reins are pulled — there is interaction between the hand and the horse's mouth, the reins being the interacting part. An interacting nerve-impulse starting from a microscopic cell in the brain may give rise to a powerful muscular action and reaction at some distant point. An interacting enzyme, hormone, or other chemical messenger circulating in the blood may profoundly modtfy the growth of a great organism. Out of these physicochemical principles has arisen the conception of a living organism as composed of an incessant series of actions and reactions operating under the dynamical laws which govern the transfer and transformation of energy. The central theory which is developed in our speculation on the Origin of Life is that every physicochemical action and reaction concerned in the transformation, conservation, and dissipation of energy, produces also, either as a direct result or as a by-product a physicochemical agent of interaction which permeates and affects the organism as a whole or affects only some special part. Through such interaction the organism is made a unit and acts as one, because the activities of all its parts are correlated. This idea may be expressed in the following simplified scheme of the functions or physiology of the organism : THE TETRAKINETIC THEORY 279 ACTION 1 f ACTION AND V INTERACTION \ AND REACTION J I REACTION Functions of the Functions of the Functions of the Capture, Storage, Coordination, Balance, Capture, Storage, and Release of Cooperation, Compensation, and Release of Energy Acceleration, Retardation, Energy of Actions and Reactions Since it is known that many actions and reactions of the organ- ism— such as those of general and localized growth, of nutrition, of respiration — are coordinated with other actions and reactions through interaction, it is but a step to extend the principle and suppose that all actions and reactions are similarly coordinated; and that while there was an evolution of action and reaction there was also a cor- responding evolution of interaction, for without this the organism would not evolve harmoniously. Evidence for such universality of the interaction principle has been accumulating rapidly of late, especially in experimental medicine and in experimental biology. It is a further step in our theory to suppose that the directing power of heredity which regulates the initial and all the subsequent steps of development in action and reaction, gives the orders, hastens development at one point, retards it at another, is an elaboration of the principle of interaction. In lowly organisms like the monads these interactions are very simple; in higher organisms like man these interactions are elaborated through physicochemical and other agents, some of which have already been discovered although doubtless many more await discovery. Thus we conceive of the origin and development of the organism as a con- comitant evolution of the action, reaction, and interaction of energy. Actions and reactions are borrowed from the inorganic world, and elaborated through the production of the new organic chemical compounds; it is the peculiar evolution and elaboration of the physi- cal principle of interaction which distinguishes the living organism. Thus the evolution of life may be rewritten in terms of invisible energy, as it has long since been written in terms of visible form. All visible tissues, organs, and structures are seen to be the more or less simple or elaborate agents of the different modes of energy. One after another special groups of tissues and organs are created and co- ordinated— organs for the capture of energy from the inorganic environ- ment and from the life environment, organs for the storage of energy, organs for the transformation of energy from the potential state into 28o READINGS IN EVOLUTION, GENETICS, AND EUGENICS the states of motion and heat. Other agents of control are evolved to bring about a harmonious balance between the various organs and tissues in which energy is released, hastened or accelerated, slowed down or retarded, or actually arrested or inhibited. In the simplest organisms energy may be captured while the organism as a whole is in a state of rest; but at an early stage of life special organs of locomotion are evolved by which energy is sought out, and organs of prehension by which it may be seized. Along with these motor organs are developed organs of ofense and defense of many kinds, by means of which stored energy is protected from cap- ture or invasion by other organisms. Finally, there is the most mysterious and comprehensive process of all, by which all these manifold modes of energy are reproduced in another organism. THE FOUR COMPLEXES OF ENERGY The theoretic evolution of the four complexes is somewhat as follows: 1. In the order of time the Inorganic Environment comes first; energy and matter are first seen in the sun, in the earth, in the air, and in the water— each i very wonderful complex of energies in itself. They form, nevertheless, an entirely orderly system, held together by gravitation, moving under Newton's laws of motion, subject to the more newly discovered laws of thermodynamics. In this complex we observe actions and reactions, the sum of the taking in and giving out of energy, the conservation of energy. We also observe inter- actions wherein the energy released at certain points may be greater than the energy received, which is merely a stimulus for the beginning of the local energy transformations. This energy is distributed among the eighty or more chemical elements of the sun and other stars. These elements are combined in plants into complex substances, gener- ally with a storage of energy. Such substances are disintegrated into simple substances in animals, generally with a release of energy. All these processes are termed by us physicochemical. 2. With life something new appears in the universe, namely, a union of the internal and external adjustment of energy which we appropriately call an Organism. In the course of the evolution of life every law and property in the physicochemical world is turned to advantage; every chemical element is assembled in which inorganic properties may serve organic functions. There is an immediate or gradual separation of the organism into two complexes of energy, THE TETRAKINETIC THEORY 281 namely, first, the energy complex of the organism, which is perishable with the term of life of the individual, and second, the germ or heredity substance, which is perpetual. 3. The idea that the germ is an energy complex is an as yet un- proved hypothesis; it has not been demonstrated. The Heredity-Germ in some respects bears a likeness to latent or potential interacting energy, while in other respects it is entirely unique. The supposed germ energy is not only cumulative but is in a sense imperishable, self- perpetuating, and continuous during the whole period of the evolution of life upon the earth, a conception which we owe chiefly to the law of the continuity of the germ-plasm formulated by Weismann. Some of the observed phenomena of the germ hi Heredity are chiefly analogous to those of interaction in the Organism, namely, directive of a series of actions and reactions, but in general we know no complete physical or inorganic analogy to the phenomena of heredity; they are unique in nature. 4. With the multiplication and diversification of individual or- ganisms there enters a new factor hi the environment, namely, the energy complex of the Life Environment. Thus there are combined certainly three and, possibly, four com- plexes of energy, of which each has its own actions, reactions, and interactions. The evolution of life proceeds by sustaining these actions, reactions, and interactions and constantly building up new ones : at the same time the potentiality of reproducing these actions, re- actions, and interactions in the course of the development of each new organism is gradually being accumulated and perpetuated in the germ. From the very beginning every individual organism is competing with other organisms of its own kind and of other kinds, and the law of the survival of the fittest is operating between the forms and func- tions of organisms as a whole and between their separate actions, reactions, and interactions. This, as Weismann pointed out, while apparently a selection of the individual organism itself, is actually a selection of the heredity-germ complex, of its potentialities, powers, and predispositions. Thus Selection is not a form of energy, nor a part of the energy complex; it is an arbiter between different com- plexes and forms of energy; it antedates the origin of life just as adaptation or fitness antedates the origin of life, as remarked by Henderson. Thus we arrive at a conception of the relations of organisms to each other and to their environment as of an enormous and always 282 READINGS IN EVOLUTION, GENETICS, AND EUGENICS increasing complexity, sustained through the interchange of energy. Darwin's principle of the survival or elimination of various forms of living energy is, in fact, adumbrated in the survival or elimination of various forms of lifeless energy as witnessed among the stars and planets. In other words, Darwin's principle operates as one of the causes of evolution in making the lifeless and living worlds what they now appear to be, but not as one of the energies of evolution. Selec- tion merely determines which one of a combination of energies shall survive and which shall perish. The complex of four interrelated sets of physicochemical energies which I have previously set forth as the most fundamental biologic scheme or principle of development may now be restated as follows: In each organism the phenomena of life represent the action, reaction, and interaction of four complexes of physicochemical energy, namely, those of (i) the Inorganic Environment, (2) the developing Organism (protoplasm and body-chromatin), (3) the germ or Heredity-Chromatin, (4) the Life Environment. Upon the resultant actions, reactions, and interactions of potential and kinetic energy in each organism Selection is constantly operating wherever there is competition with the correspond- ing actions, reactions, and interactions of other organisms. This principle I shall put forth in different aspects as the central thought of these lectures, stating at the outset and often recurring to the admission that it involves several unknown principles and especially the largely hypothetical question whether there is a relation between the action, reaction, and interaction of the internal energies of the germ or heredity-chromatin with the external energies of the inorganic environment, of the developing organism, and of its life environment. In other words, while this is a principle which largely governs the Organism, it remains to be discovered whether it also governs the causes of the Evolution of the Germ. As observed in the preface we are studying not one but four sirhultaneous evolutions. Each of these evolutions appears to be almost infinite in itself as soon as we can examine it in detail, but of the four that of the germ or heredity-chromatin so far surpasses all the others in complexity that it appears to us infinite. The physicochemical relations between these four evolutions, including the activities of the single and of the multiplying organisms of the Life Environment, may be expressed in diagrammatic form as follows: THE TETRAKINETIC THEORY ORGANISM A Under Newton's Laws of Motion and Modern Thermodynamics Actions, Reactions, and Interactions of the 1. Inorganic Environment: physicochemical en- ergies of space, of the sun, earth, air, and water. 2. Organism: physicochemical en- ergies of the devel- oping individual in the tissues, cells, protoplasm, and cell- chromatin. 3. Heredity-Germ: physicochemical en- ergies of the heredity- chromatin included in the reproductive cells and tissues. 4. Life Environment: physicochemical en- ergies of other or- ganisms. Under Darwin's Law of Natural Selection Survival of the fittest: competition, selec- tion, and elimination of the energies and forms. ORGANISMS B-Z Under Newton's Laws of Motion and Modern Thermodynamics Actions, Reactions, and Interactions of the 1. InorganicEnvironment: physicochemical en- ergies of space, of the sun, earth, air, and water. 2. Organism: physicochemical en- ergies of the devel- oping individual in the tissues, cells, protoplasm, and cell- chroma tin. 3. Heredity-Germ: physicochemical en- ergies of theheredity- chromatin included in the reproductive cells and tissues. 4. Life Environment: physicochemical en- ergies of other or- ganisms. If a single name is demanded for this conception of evolution it might be termed the tetrakinetic theory in reference to the four sets of internal and external energies which play upon and within every individual and every race. In respect to form it is a tetraplastic theory in the sense that every living plant and animal form is plas- tically moulded by four sets of energies. The derivation of this conception of life and of the possible causes of evolution from the laws which have been developed out of the Newtonian system, and from those of the other great Cambridge philosopher, Charles Darwin, are clearly shown in the above diagram. PART IV GENETICS CHAPTER XX THE SCOPE AND METHODS OF GENETICS H. H. N. DEFINITIONS " Genetics is the science which seeks to account for the resem- blances and the differences which are exhibited among organisms related by descent." — Babcock and Clausen. "Genetics may be denned as the science which deals with the coming into being of organisms. It does not refer, however, to the first creation of organic beings, but rather to the present every-day creation of new individuals or new races. It refers particularly to the part that parent organisms have in bringing new organisms into being and to the influence which parents exert on the characteristics of their offspring. In this sense it is nearly equivalent to the term heredity." — W. E. Castle. "Heredity may be defined as organic resemblance based on de- scent."—W. E. Castle. "Heredity is commonly defined as the tendency of offspring to develop characters like those of the parents." — Babcock and Clausen. THE SCOPE AND METHODS OF GENETICS Genetics is the study of evolution from a new point of view. The great evolutionists of the past were devotees of the inductive method hi science which consists of collecting data and devising theories to explain the data. None of the older evolutionists attempted to put then- theories to experimental tests. Thus their theories, though hi some respects well founded, never reached that stage of scientific proof which involves the use of the experimental method. The new method hi evolution is that of experiment under controlled conditions. If new characters arise before the eyes of the investigator hi a known stock of animals or plants and the factors responsible for the change are known and are capable of control, it may be said that man has actually taken a hand in evolution. If new characters arise in a known stock, but from an unknown cause, the course of the new character in inheritance may be controlled and some knowledge of the 387 288 READINGS IN EVOLUTION, GENETICS, AND EUGENICS mechanism of heredity may be obtained by an analysis of its modes of heredity. It is this new experimental and analytic method of study- ing evolution that we have come to designate as genetics. Three principal methods of attack upon the problems of genetics have been successful in advancing our knowledge. a) Experimental breeding. — This method was first systematized by Mendel and consists of breeding together two individuals possessing certain more or less contrasting characters and determining the ratios in which the parental characters reappear in the offspring. This method has been extremely fruitful and in connection with the second method, that of cytology, has made clear much that was obscure to Darwin and his followers. b) Cytology. — This second method involves the microscopic study of the germ cells during the most critical periods of their cycle. It seems very probable that we can now view under the microscope the actual heredity machine and see how it works. c) The statistical method. — It is usually conceded that Sir Francis Galton was the first to use the method of statistics in the study of heredity. By means of correlation tables he was able to compare large groups of parents with large groups of offspring with respect to any unit character, and to state the degree of heredity in defin- ite mathematical terms. The modern science of biometry is used extensively at the present time for determining the degree of vari- ability of characters which vary only slightly or irregularly and the exact degree of correlation that exists between different hereditary characters. All three of these methods of attacking the problems of genetics have been fruitful in results and all are essential to an adequate under- standing of the workings of evolution. The subject-matter of genetics consists of: (a) a knowledge of the principles of ontogeny, the development of the individual from the germ-cell stage to the adult stage; (b) a knowledge of the behavior of the germ cells from one generation to the next, involving the so-called "origin" of germ cells, maturation and fertilization of germ cells, and the exact behavior of the chromosomes during the entire germ-cell cycle; (c) a knowledge of variation, including a determination of what distinct kinds of variation occur, where in ontogeny variations are initiated, the causes of variation, etc. ; (d) what kinds of variations are inherited and according to what laws — the whole subject of Men- delian heredity; (e) the determination of sex and the relation of sex THE SCOPE AND METHODS OF GENETICS 289 to heredity; (/) theories as to the mechanism that brings about the observed regularity in heredity, including theories of linkage, cross- overs, and other phases of neo-Mendelian heredity. THE IMPORTANCE OF THE CELL THEORY IN GENETICS All organisms are composed of minute units called cells. A cell is the smallest particle of living matter capable of growing and multi- plying. The only continuity between two successive generations is a cellular continuity, involving a continuous series of cell divisions. All cells are the offspring by division of previous cells. We distinguish two main categories of cells: body or somatic cells and germ ceHs. In germinal reproduction, the only kind of reproduction possible in the more highly differentiated animals, the material continuity between parent and offspring is through the germ cell. A parental germ cell produces an offspring. The germ cell therefore is called the hereditary bridge. The only way, then, in which a parent can transmit his or her characteristics to an offspring is through the germ cell. Every hereditary character, whether old or new, must have its differential cause in the germ cell. The germ cells are therefore called the bearers of the heritage, and in the next chapter Professor M. F. Guyer gives an account of the cellular basis of variation and heredity. CHAPTER XXI THE BEARERS OF THE HERITAGE AN ACCOUNT OF THE CELLULAR BASIS OF HEREDITY1 MICHAEL F. GUYER Structure of the cell. — Before we can understand certain necessary details of the physical mechanism of inheritance we must inquire a little further into the finer structure of the cell and into the nature of cell-division. A typical cell, as it would appear after treatment with various stains which bring out the different parts more dis- tinctly, is shown in Fig. 43. Typical, not that any particular kind of living cell resembles it very closely in appearance, but because it shows in a diagrammatic way the essential parts of a cell. In the diagram, there are two well-marked regions: a central nucleus and a peripheral cell-body or cytoplasm. Other structures are pictured, but only a few of them need command our attention at present. At one side of the nucleus one observes a small dot or granule surrounded by a denser area of cytoplasm. This body is called the centrosome. The nucleus in this instance is bounded by a well-marked nuclear membrane and within it are several substances. What appear to be threads of a faintly staining material, the linin, traverse it in every direction and form an apparent network. The parts on which we wish particularly to rivet our attention are the densely stained substances scattered along or imbedded in the strands of this network in irregular granules and patches. This substance is called chromatin. It takes its name from the fact that it shows great affinity for certain stains and becomes intensely colored by them. This deeply colored portion of the cell, the chromatin, is by most biologists regarded as of great importance from the standpoint of heredity. One or more larger masses of chromatin or chromatin-like material, known as chromatin nucleoli, are often present, and not infrequently a small spheroidal body, differing in its staining reactions from the chromatin-nucleolus and sometimes called the true nucleolus, exists. Cell-division. — In the simplest type of cell-division the nucleus first constricts in the middle, and finally the two halves separate. 'From M. F. Guyer, Being Well Born (copyright 1916). Used by special permission of the publishers, The Bobbs-Merrill Company. 290 THE BEARERS OF THE HERITAGE 291 This separation is followed by a similar constriction and final division of the entire cell-body, which results in the production of two new cells. This form of cell-division is known as simple or direct division. Such a simple division, while found in higher animals, is less frequent and apparently much less significant than another type of division which involves profound changes and rearrangements of the nuclear contents. The latter is termed mitotic or indirect cell-division. Fig. 44 illustrates some of the stages which are passed through in indirect cell-division. The centrosome which lies passively at the side of the nucleus in the typical cell (Fig. 44, a) awakens to activity, divides and the two components come to lie at the ends of a fibrous spindle. In Centrosome. Chromatin. — — True nucleolus Nucleus. £ (plasmosome). Chromatin ——— nucleolus. Linin network. (passive bodies). FIG. 43. — Diagram of a cell, showing various parts. (From Guyer.) the meantime, the interior of the nucleus is undergoing a transforma- tion. The granules and patches of chromatin begin to flow together along the nuclear network and become more and more crowded until they take on the appearance of one or more long deeply- stained threads wound back and forth in a loose skein in the nucleus (Fig. 44, &). If we examine this thread closely, in some forms it may be seen to consist of a series of deeply-stained chromatin granules packed closely together, intermingled with the substance of the original nuclear network. As the preparations for division go on the coil in the nucleus breaks up into a number of segments which are designated as chromosomes (Fig. 44, c). The nuclear membrane disappears. The chromosomes 292 READINGS IN EVOLUTION, GENETICS, AND EUGENICS and the spindle-fibers ultimately come to lie at the equator of the spindle as shown in Fig. 44, d. Each chromosome splits lengthwise to form two daughter chromosomes which then diverge to pass to the FIG. 44. — Diagram showing representative stages in mitotic or indirect cell- division, a, resting cell with reticular nucleus and single centrosome; b, the two new centrosomes formed by division of the old one are separating and the nucleus is in the spireme stage; c, the nuclear wall has disappeared, the spireme has broken up into six separate chromosomes, and the spindle is forming between the two centrosomes; d, equatorial plate stage in which the chromosomes occupy the equator of the spindle; e,f, each chromosome splits lengthwise and the daughter chromosomes thus formed approach their respective poles; g, reconstruction of the new nuclei and division of the cell body; h, cell division completed. (From Guyer.) poles of the spindle (Fig. 44, e and/). Thus each end of the spindle comes ultimately to be occupied by a set of chromosomes. Moreover, each set is a duplicate of the other, because the substance of any individual chromosome in one group has its counterpart in the other. THE BEARERS OF THE HERITAGE 293 In fact this whole complicated system of indirect division is regarded by most biologists as a mechanism for bringing about the precise halving of the chromosomes. The chromosomes of each group at the poles finally fuse and two new nuclei, each similar to the original one, are constructed (Fig. 44, g and h). In the meantime a division of the cell-body is in progress which, when completed, results hi the formation of two complete new cells. As all living matter, if given suitable food, can convert it into living matter of its own kind, there is no difficulty hi conceiving how the new cell or the chroma tin material finally attains to the same bulk that was characteristic of the parent cell. In the case of the chro- matin, indeed, it seems that there is at times a precocious doubling of the ordinary amount of material before the actual division occurs. Chromosomes constant in number and appearance. — With some minor exceptions, to be noted later, which increase rather than detract from the significance of the facts, the chromosomes are always the same hi number and appearance in all individuals of a given species of plants or animals. That is, every species has a fixed number which regularly recurs in all of its cell-divisions. Thus the ordinary cells of the rat, when preparing to divide, each display sixteen chromo- somes, the frog or the mouse, twenty-four, the lily twenty-four and the maw- worm of the horse only four. The chromosomes of different kinds of animals or plants may differ very much hi appearance. In some they are spherical, in others rod-like, filamentous or perhaps of other forms. In some organisms the chromosomes of the same nucleus may differ from one another in size, shape, and proportions, but if such differences appear at one division they appear at others, thus showing that in such cases the differences are constant from one generation to the next. Significance of the chromosomes. — The question naturally arises as to what is the significance of the chromosomes. Why is the accur- ate adjustment which we have noted for their division necessary? The very existence of an elaborate mechanism so admirably adapted to their precise halving, predisposes one toward the belief that the chromosomes have an important function which necessitates the retention of their individuality and their equal division. Many biolo- gists accept this along with other evidences as indicating that hi chromatin we have a substance which is not the same throughout, that 294 READINGS IN EVOLUTION, GENETICS, AND EUGENICS different regions of the same chromosome have different physiological values. When the cell prepares for divisions, the granules, as we have seen, arrange themselves serially into a definite number of strands which we have termed chromosomes. Judging from all available evidence, the granules are self -propagating units; that is, they can grow and reproduce themselves. So that what really happens in mito- sis in the splitting of the chromosomes is a precise halving of the series of individual granules of which each chromosome is constituted, or in other words each granule has reproduced itself. Thus each of the two daughter cells presumably gets a sample of every kind of chromosomal particle, hence, the two cells are qualitatively alike. To use a homely illustration we may picture the individual chromosomes to ourselves as so many separate trains of freight cars, each car of which is loaded with different merchandise. Now, if every one of the trains could split along its entire length and the resulting halves each grow into a train similar to the original, so that instead of one there would exist two identical trains, we should have a phenomenon analogous to that of a dividing chromosome. Cleavage of the egg. — It is through a series of such divisions as these that the zygote or fertilized egg-cell builds up the tissues and organs of the new organism. The process is technically spoken of as cleavage. Cleavage generally begins very shortly after fertilization. The fertile egg-cell divides into two, the resulting cells divide again and thus the process continues, with an ever-increasing number of cells. Chief processes operative in building the body. — Although of much interest, space will not permit of a discussion in detail of the building up of the special organs and tissues of the body. It must suffice merely to mention the four chief processes which are operative. These are, (i) infoldings and outfoldings of the various cell com- plexes; (2) multiplication of the component cells; (3) special changes (histological differentiation) in groups of cells; and (4) occasionally resorption of certain areas of parts. The origin of the new germ-cells. — On account of the unusual importance from the standpoint of inheritance, which attaches to the germ-cells, a final word must be said about their origin in the embryo. While the evidence is conflicting in some cases, in others it has been well established that the germ-cells are set apart very early from the cells which are to differentiate into the ordinary body tissues. Fig. 45, A, shows a section through the eight-celled stage of Miastor, a fly, THE BEARERS OF THE HERITAGE 295 in which a single large, primordial germ-cell (p. g. c.} has already been set apart at one end of the developing embryo. The nuclei of the rest of the embryo still lie in a continuous protoplasmic mass which has not yet divided up into separate cells. The densely stained nuclei at the opposite end of the section are the remnants of nurse-cells which originally nourished the egg. Fig. 45, B, is a longitudinal section 08* FIG. 45. — A, germ-cell (p.g.c.) set apart in the eight-celled stage of cleavage in Miastor americana. (After Hegner.) The walls of the remaining seven somatic cells have not yet formed, though the resting or the dividing (M p) nuclei may be seen; c R, chromatin fragments cast off from the somatic cells; B, section length- wise of a later embryo of Miastor; the primordial egg-cells (oog^j are conspicuous. (From Guyer, after Hegner.} through a later stage in the development of Miastor; the primitive germ-cells (oog) are plainly visible. Still other striking examples might be cited. Even in vertebrates the germ-cells may often be detected at a very early period. Significance of the early setting apart of the germ-cells. — It is of great importance for the reader to grasp the significance of this early setting apart of the germ-cells because so much in our future discussion hinges on this fact. The truth of the statement made in a previous chapter that the body of an individual and the reproductive substance 296 READINGS IN EVOLUTION, GENETICS, AND EUGENICS in that body are not identical now becomes obvious. For in such cases as those just cited one sees the germinal substance which is to carry on the race set aside at an early period in a given individual; it takes no part in the formation of that individual's body, but remains a slumbering mass of potentialities which must bide its time to awaken into expression in a subsequent generation. Thus an egg does not develop into a body which in turn makes new germ-cells, but body and germ-cells are established at the same tune, the body harboring and nourishing the germ-cells, but not generating them. The same must be true also in many cases where the earliest history of the germ-cells cannot be visibly followed, because in any event, in all higher animals, they appear long before the embryo is mature and must therefore be descendants of the original egg-cell and not of the functioning tissues of the mature individual. This need not necessarily mean that the germ-cells have remained wholly unmodified or that they continue uninfluenced by the conditions which prevail in the body, especially in the nutritive blood and lymph stream, although as a matter of fact most biologists are extremely skeptical as to the probability that influences from the body beyond such general indefinite effects as might result from under-nutrition or from poisons carried hi the blood, modify the intrinsic nature of the germinal substances to any measur- able extent. Germinal continuity. — The germ-cells are collectively termed the germinal protoplasm and it is obvious that as long as any race continues to exist, although successive individuals die, some germinal protoplasm is handed on from generation to generation without interruption. This is known as the theory of germinal continuity. When the organ- ism is ready to reproduce its kind the germ-cells awaken to activity, usually undergoing a period of multiplication to form more germ-cells before finally passing through a process of what is known as matura- tion, which makes them ready for fertilization. The maturation process proper, which consists typically of two rapidly succeeding divisions, is preceded by a marked growth in size of the individual cells. Individuality of chromosomes. — Before we can understand fully the significance of the changes which go on during maturation we shall have to know more about the conditions which prevail among the chromosomes of cells. As already noted each kind of animal or plant has its own characteristic number and types of chromosomes when these appear for division by mitosis. In many organisms the chromo- somes are so nearly of one size as to make it difficult or impossible to THE BEARERS OF THE HERITAGE 297 be sure of the identity of each individual chromosome, but on the other hand, there are some organisms known in which the chromo- somes of a single nucleus are not of the same size and form (Fig. 46). These latter cases enable us to determine some very significant facts. Where such differences of shape and proportion occur they are constant in each succeeding division so that similar chromosomes may be iden- tified each time. Moreover, in all ordinary mitotic divisions where the conditions are accurately known, these chromosomes of different types are found to be present as pairs of similar elements; that is, there are two of each form or size. Pairs of similar chromosomes in the nucleus because one chromo- some comes from each parent. — When we recall that the original fertilized egg from which the individual develops is really formed by the union of two gametes, ovum and spermatozoon, and that each A B FIG. 46. — A, chromosomes of the mosquito (Culex). (After Stevens.) B, chromosomes of the fruit fly (Drosophila). (After Metz.) Both of these forms have an unusually small number of chromosomes. (From Guyer.) gamete, being a true cell, must carry its own set of chromosomes, the significance of the pairs of similar chromosomes becomes evident; one of each kind has probably been contributed by each gamete. This means that the zygote or fertile ovum contains double the number of chromosomes possessed by either gamete, and that, moreover, each tissue-cell of the new individual will contain this dual number. For, as we have seen, the number of chromosomes is, with possibly a few exceptions, constant in the tissue-cells and early germ-cells in suc- cessive generations of individuals. For this to be true it is obvious that in some way the nuclei of the conjugating gametes have come to contain only half the usual number. Technically the tissue-cells are said to contain the diploid number of chromosomes, the gametes the reduced or haploid number. In maturation the number of chromosomes is reduced by one- half. — This halving, or as it is known, reduction in the number of chromosomes is the essential feature of the process of maturation. It 298 READINGS IN EVOLUTION, GENETICS, AND EUGENICS is accomplished by a modification in the mitotic division in which instead of each chromosome splitting lengthwise, as in ordinary mito- sis, the chromosomes unite in pairs (Fig. 47, b), a process known tech- nically as synapsis, and then apparently one member of each pair passes entire into one new daughter cell, the other member going to the other daughter cell (Fig. 47, c}. In the pairing preliminary to this reduction division, leaving out of account certain special cases to be considered FIG. 47. — Diagram to illustrate spermatogenesis. a, showing the diploid number of chromosomes (six is arbitrarily chosen) as they occur in divisions of ordinary cells and spermatogonia; b, the pairing (synapsis) of corresponding mates in the primary spermatocyte preparatory to reduction; c, each secondary spermatocyte receives three, the haploid number of chromosomes; d, division of the secondary spermatocytes to form e, spermatids, which transform into /, sper- matozoa. (From Guyer.) later, according to the best evidence at our command the union always takes place between two chromosomes which match each other in size and appearance. Since one of these is believed to be of maternal and the other of paternal origin, the ensuing division separates correspond- ing mates and insures that each gamete gets one of each kind of chro- mosome although it appears to be a matter of mere chance whether or not a given cell gets the paternal or the maternal representative of that kind. THE BEARERS OF THE HERITAGE 299 Maturation of the sperm-cell. — In the maturation of the male gamete the germ-cell, now known as a spermatogonium, increases greatly in size to become a primary spermatocyte. In each primary spermatocyte the pairing of the chromosomes already alluded to occurs as indicated in Fig. 47, where six is taken arbitrarily to indicate the ordinary or diploid number of chromosomes, and three the reduced or haploid number. The division of the primary spermatocyte gives rise to two secondary spermatocytes (c), the paired chromosomes separating in such a way that a member of each pair goes to each FIG. 48. — Diagram to illustrate oogenesis. a, showing the diploid number of chromosomes (six is arbitrarily chosen) as they occur in ordinary cells and in oogonia; b, the pairing of corresponding mates preparatory to reduction; c, d, the reduction division, giving off the first polar body; e, egg preparing to give off the second polar body, first polar body ready for division; /, second polar body ready for division; g, second polar body given off, division of first polar body completed. The egg nucleus, now known as the female pronucleus, and each polar body contain the reduced or haploid number of chromosomes. (From Guyer.) secondary spermatocyte. Each secondary spermatocyte (d) soon divides again into two spermatids (e), but in this second division the chromosomes each split lengthwise as in an ordinary division so that there is no further reduction. In some forms the reduction division occurs in the secondary spermatocytes instead of the primary. Each spermatid transforms into a mature spermatozoon (/). The sper- matozoa of most animals are of linear form, each with a head, a middle-piece and a long vibratile tail which is used for locomotion. The head consists for the most part of the transformed nucleus and is consequently the part which bears the chromosomes. 300 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Maturation of the egg-cell. — As regards the behavior of the chromosomes the maturation of the ovum parallels that of the sperm- cell. There are not so many primordial germ-cells formed and only one out of four of the ultimate cells becomes a functional egg. As in maturation of the sperm-cell there is a growth period in which oogonia enlarge to become primary oocytes (Fig. 48, b). In each primary Spermatogenesis V3X I\ Multiplication Period Croh/th period Pairing of Chromosor, / \ } Reducing division Obgcnesis J A FIG. 49. — Diagram showing the parallel between maturation of the sperm- cell and maturation of the ovum. (From Guyer.) oocyte as in the primary spermatocyte the chromosomes pair and two rapidly succeeding divisions follow in one of which the typical numeri- cal reduction in the chromosomes occurs. A peculiarity in the maturation of the ovum is that there is a very unequal division in the cytoplasm in cell-division so that three of the resulting cells usually termed polar bodies are very small and appear like minute buds on the side of the fourth or egg-cell proper. THE BEARERS OF THE HERITAGE 301 The scheme of this formation of the polar bodies is indicated in Fig. 48. In Fig. 48, b the chromosomes are seen paired and ready for the first division; that is, for the formation of the first polar body. Figs. 48, c, d show the giving off of this body. Note that while only a small proportion of the cytoplasm passes into this tiny cell, its chro- matin content is as great as that of the ovum. A second polar body (Fig. 48, e) is formed by the egg, but in this case each chromosome splits lengthwise, as in ordinary mitosis, and there is no further numeri- cal reduction. In the meantime, typically, a third polar body is formed by division of the first. (Stages e, f, g.) Parallel between the maturation of sperm- and egg-cell. — This rather complex procedure of the germ-cells will be rendered more intelligible through a careful study of Figs. 47, 48, and 49, which indicates the parallel conditions in spermatogenesis and oogenesis. The view now generally held regarding the polar bodies is that they are really abortive eggs. They later disappear, taking no part in embryo-formation. It can readily be seen how such an unequal division is advantageous to the large cell, for it receives all of the rich store of food material that would be distributed among the four cells if all were of equal size. This increased amount of food is a favorable provision for the forthcoming offspring whose nourishment is thus more thoroughly insured. On the other hand, all of the sperm-cells develop into complete active forms, which, as aforesaid, usually become very much elongated and develop a motile organ of some kind. In such cells an accumula- tion of food to any large extent would hinder rather than help them, because it would seriously interfere with their activity. Fertilization. — In fertilization (Fig. 50) the spermatozoon pene- trates the wall of the ovum and after undergoing considerable altera- tion its nucleus fuses with the nucleus of the egg. In some forms only the head (nucleus) and middle-piece enter, the tail being cut off by a so-called fertilization membrane which forms at the surface of the egg and effectually blocks the entrance of other spermatozoa. Thus normally only one spermatozoon unites with an egg. In some forms while several may enter the egg only one becomes functional. As soon as the nucleus of the spermatozoon, now known as the male promicleus, reaches the interior of the egg, it enlarges and becomes simi- lar in appearance to the female pronucleus. It swings around in such a way (Fig. 50, b] that the middle piece, now transformed into a centro- some, lies between it and the female pronucleus. The two pronuclei 302 READINGS IN EVOLUTION, GENETICS, AND EUGENICS (c,d,e),ea.ch containing the reduced number of chromosomes, approach, the centrosome divides, the nuclear walls disappear, the typical division spindle forms, and the chromosomes of paternal and maternal origin respectively come to lie side by side at the equator of the spindle ready for the first division or cleavage (/, g). It will be noted that the FIG. 50. — Diagram to illustrate fertilization; <5, male pronucleus; $, female pronucleus; observe that the chromosomes of maternal and paternal origin respectively do not fuse.' (From Guyer.) individual chromosomes do not intermingle their substance at this time, but each apparently retains its own individuality. There is considerable evidence which indicates that throughout life the chro- mosomes contributed by the male parent remain distinct from those of the female parent. Inasmuch as each germ-cell, after maturation, contains only half the characteristic number of chromosomes, the original number is restored in fertilization. Significance of the behavior of chromosomes. — The question confronts us as to what is the significance of this elaborate system THE BEARERS OF THE HERITAGE 303 which keeps the chromosomes of constant size, shape and number; which partitions them so 'accurately in ordinary cell-division; and which provides for a reduction of their numbers by half in the germ-cell while yet securing that each mature gamete gets one of each kind of chromosome. Most biologists look on these facts as indicating that the chromosomes are specifically concerned in inheritance. In the first place it is recognized that as regards the definable characters which separate individuals of the same species, offspring may inherit equally from either parent. And it is a very significant fact that while the ovum and spermatozoon are very unequal in size themselves, the chromosomes of the two germ-cells are of the same size and number. This parity in chromosomal contribution points clearly to the means by which an equal number of character deter- miners might be conveyed from each parent. Moreover it is mainly the nucleus of the sperm-cell in some organisms which enters the egg, hence the determiners from the male Una must exist wholly or largely somewhere hi the nucleus. And the bulk of the nucleus in the sper- matozoon consists of the chromosomes or their products. A single set of chromosomes derived from one parent only is sufficient for the production of a complete organism. — That a single or haploid set of chromosomes as seen in the gametes is sufficient contribution of chromatin for the production of a complete organism is proved by the fact that the unfertilized eggs of various animals (many echinoderms, worms, mollusks, and even the frog) may be artificially stimulated to development without uniting at all with a spermatozoon. The resulting individual is normal in every respect except that instead of the usual diploid number it has only the single or haploid number of chromosomes. Its inheritance of course is wholly of maternal origin. The converse experiment hi echinoderms in which a nucleus of male origin (that is, a spermatozoon) has been introduced into an egg from which the original nucleus has been removed shows that the single set of chromosomes carried by the male gamete is also sufficient to cooperate with the egg-cytoplasm in developing a complete individual. The duality of the body and the singleness of the germ. — Since every maternal chromosome in the ordinary cell has an equivalent mate derived from the male parent, it follows therefore, supposing the chromosomes do have the significance in inheritance attributed to them, that as regards the measurable inheritable differences between two individuals, the ordinary organism produced through the union 304 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of the two germ-cells is, potentially at least, dual in nature. On the other hand through the process of reduction the gametes are provided with only a single set of such representatives. This duality of the body and singleness of the mature germ is one of the most striking facts that come to light in embryology. How well the facts fit in with the behavior of certain hereditary characters will be seen later in our dis- cussions of Mendelism. The cytoplasm not negligible in inheritance. — Just what part is played by the cytoplasm in inheritance is not clear, but it is probably by no means a negligible one. The cytoplasm of a given organism is just as distinctive of the species or of the individual of which it forms a part as are the chromosomes. It is well established that neither nucleus nor cytoplasm can fully function or even exist long without the other, and neither can alone produce the other. They undoubtedly must cooperate in building up the new individual, and the cytoplasm of the new individual is predominantly of maternal origin. It is obvious that all of the more fundamental characters which make up an organism, such, for instance, as make it an animal of a certain order or family, as a human being or a dog or a horse, are common to both parents, and there is no way of measuring how much of this fundamental constitution comes from either parent, since only closely related forms will interbreed. In some forms, moreover, the broader fundamental features of embryogeny are already established before the entrance of the spermatozoon. It is probable therefore that instead of asserting that the entire quota of characters which go to make up a complete individual are inherited from each parent equally, we are justified only in maintaining that this equality is restricted to those measurable differences which veneer or top off, as it were, the individual. We may infer that in the development of the new being the chromosomes of the egg together with those derived from the male work jointly on or with the other germinal contents which are mostly cytoplasmic materials of maternal origin. The chromosomes possibly responsible for the distinctiveness of given characters. — It seems probable that in the establishment of certain basic features of the organism the cooperation of the cytoplasm with chromatin of either maternal or paternal origin might accomplish the same end, but that certain distinctive touches are added or come cumulatively into expression through influences carried, predomi- nantly at least, in the chromatin from one as against the other parent. These last distinctive characters of the plant or animal constitute the THE BEARERS OF THE HERITAGE 305 individual differences of such organisms. In this connection it is a significant fact that in young hybrids between two distinct species the early stages of development, especially as regards symmetry and regional specifications, are exclusively or predominantly maternal in character, but the male influence becomes more and more apparent as development progresses until the final degree of intermediacy is attained. From the evidence at hand this much seems sure, that the paternal and maternal chromosomes respectively carry substances, be they ferments, nutritive materials or what not, that are instrumental in giving the final parity of personal characters which we observe to be equally heritable from either line of ancestry. It is clear that most of the characters of an adult organism cannot be merely the outcome of any unitary substance of the germ. Each is the product of many cooperating factors and for the final outcome any one cooperant is probably just as important hi its way as any other. The individual characters which we juggle to and fro in our breeding experiments seem apexed, as it were, on more fundamental features of organic chemical constitution, polarity, regional differentiation, and physiological balance, but since such individual characters parallel so closely the visible segregations and associations which go on among the chromo- somes of the germ-cells it would seem that they, at least, are repre- sented hi the chromosomes by distinctive cooperants which give the final touch of specificity to those hereditary characters which can be shifted about as units of inheritance. Sex and heredity. — Whatever the origin of fertilization may have been in the world of life, or whatever its earliest significance, the important fact remains that to-day it is unquestionably of very great significance in relation to the phenomena of heredity. For in all higher animals, at least, offspring may possess some of the character- istics originally present in either of two lines of ancestry, and this commingling of such possessions is possible only through sexual repro- duction. As has already been seen, in the pairing of chromosomes previous to reduction, the corresponding members of a pair always come together so that in the final segregation each gamete is sure to have one of each kind although whether a given chromosome of the haploid set is of maternal or paternal origin seems to be merely a matter of chance. Thus, for instance, if we arbitrarily represent the chromosomes of a given individual by ABC, abc, and regard A, B and C as of paternal and a, b, and c as of maternal origin, then in synapsis 306 READINGS IN EVOLUTION, GENETICS, AND EUGENICS only A and a can pair together, B and b, and C and c, but each pair operates independently of the other so that in the ensuing reduction division either member of a pair may get into a cell with either member of the other pairs. That is, the line up for division at a given reduc- tion might be any one of the following, ABC ABc Abe AbC _-. T T^. ™^. T> • This would yield the following eight kinds of abc aoL aBL anc gametes, ABC, abc, ABc, abC, Abc, aBC, AbC, aBc, each bearing one of each kind of chromosome required to cover the entire field of characters necessary to a complete organism. And since each sex would be equally likely to have these eight types of gametes and any one of the eight in one individual might meet any one of the eight of the other, the possible number of combinations in the production qf a new individual from such germ-cells would be 8X8, or 64. With the larger numbers of chromosomes which exist in most animals it is readily seen that the number of possible combinations becomes very great. Thus any individual of a species with twenty chromosomes — and many animals, including man, have more — would have ten pairs at the reduction period and could therefore form (z)10, or 1,024 different gametes in each sex. And since any one of these in one sex would have an equal chance of meeting with any one in the oppo- site sex, the total number of possible different zygotes that might be produced would be (i,o24)2, or 1,048,576. Sex, therefore, through recombinations of ancestral materials, undoubtedly means, among other things, the production of great diversity in offspring. CHAPTER XXII VARIATION1 ERNEST BROWN BABCOCK AND ROY ELWOOD CLAUSEN Organic differences, their nature and causes, have furnished abundant material for speculative enquiry since tune immemorial. The great significance of the fact of organic individuality was not fully grasped until Lamarck founded his theory of evolution which postu- lated the progressive, imperceptible change of one species into another. It remained for Darwin to scrutinize all phases of organic life, past and present, wild and domesticated, in his search for a guiding prin- ciple which should explain the course of evolution. Darwin's hypothe- sis of natural selection assumes variability without enquiring into its causes, but this does not mean that Darwin was not concerned with the problem of causes. In both his Origin of Species and Variation in Animals and Plants under Domestication the causes of variability are often referred to and he suggested among others, the kind and amount of food, climatic changes and hybridization. Our respect for the great naturalist's keen perception deepens when we realize that very little has been added as yet to our knowledge of the causes of variation. The universality of variation. — Individuality is common to all organisms. No two trees, no two leaves, no two cells in a leaf are identical in every respect. Individuals sometimes appear exactly alike but even identical twins will be found to differ in some features. The shepherd knows his sheep individually and the orchardist his trees. Were there no differences in individuals there would be no changes in species and there could be no improvement of cultivated plants. "Variation is at once the hope and despair of the breeder," the hope because without it no improvement would be possible, the despair because very often, when improvement has been made, variation results in a tendency to fall below the standard previously reached. In the sugar beet, for example, a high percentage of sugar has been maintained by continually testing and selecting the "mother" beets for the next crop of seed. However, this necessity for continual 1 From E. R. Babcock and R. E. Clausen, Genetics in Relation to Agriculture (copyright 1918). Used by special permission of the publishers, The McGraw- Hill Book Company. 30? 308 READINGS IN EVOLUTION, GENETICS, AND EUGENICS selection does not exist in respect to all important field crops although they are subject to the general law of variation. That this must be so is clear when we realize that many natural species as well as culti- vated varieties of plants are really mixtures of sub-species, varieties, or races and that upon being isolated these distinct forms reproduce their own particular type. This is most easily demonstrated in plants normally self-fertilized, yet in all naturally cross-fertilized plants and in higher animals this same endless diversity among individuals is even more marked. The variation concept. — As we have implied in the above remarks the term variation may be used in very different senses in referring to different phenomena. Thus variation within a species or variety means that the group in question is heterogeneous. Among indi- viduals variation may consist of differences between members of the same generation or between parents and offspring. Even when thus restricted, however, the term is apt to prove ambiguous. Hence it is necessary to give some thought to the sources, nature and causes of these individual differences in order that we may use clear-cut expres- sions which shall always convey to one another a concept of the same particular sort of organic difference. Classification of variations. — i. Eeritdbility. Character differ- ences either represent something specific in the germ or they are merely the effect of external stimuli upon the individual soma. In the first case they are inherited, although they will not reappear necessarily in all later generations or in all the progeny. In the second case they will not be inherited. This is a fundamental dis- tinction and may well serve as our primary basis of classification. According to heritability variations are either germinal or somatic. Under germinal variations we recognize two sub-classes, combinations and mutations. Purely somatic variations will be referred to here- after as modifications. Modifications are non-heritable differences between the individuals of a race caused by the unequal influence of different environmental factors. Such variations frequently approximate continuity and, when studied statistically, display the normal variability curve, which will be explained in a subsequent chapter. [See chap, xxv.] Combinations are heritable differences between the individuals of a race or between the offspring of a pair of parents caused by segrega- tion and recombination of hereditary units. They also frequently display the normal variability curve. VARIATION 309 Mutations are heritable differences between parents and offspring which do not depend upon segregation and recombination. These three categories, as Baur has shown, are not to be recognized and separated merely according to appearances. The cause of any individual differences can usually be established only by careful breeding experiments; but by this means the separation of the three categories is always possible as the boundaries between them are quite sharp. Modifications are somatic effects of environmental differences and should not be confused with germinal changes which are some- times induced by natural or artificial means and which result in the production of mutations. Within this first category must be included all place-effects hi plants and somatic environmental effects hi ani- mals. Modifications comprise a large portion of what are commonly spoken of as fluctuations due to environment, but all cases of fluctua- ting variation are not modifications inasmuch as variations due to combinations frequently display the normal variability curve also. Modifications are not heritable. The second category, variation by combination of hereditary units is often confused with modification, as already stated, because of the fact that variations caused by segregation and recombination when studied statistically often dis- play the normal variability curve. This is especially apt to be the case hi quantitative characters (those of size or weight) and segrega- tion and recombination may be the cause of gradation in color inten- sity. In autogamous (self-fertilized) organisms hybridization between races is sufficiently rare to be negligible in this connection, i. e., in such species the fluctuating variations are caused by the environment. But in allogamous organisms (those hi which two individuals are necessary to accomplish sexual reproduction) fluctuating variations may be caused either by the environment, by segregation and recombination of factors, or by both causes acting together. We shall take up the third category, mutations, in a later chapter. For the present it is sufficient to remember that mutations are no doubt the least frequent of the three classes, that easily distinguishable mutations are comparatively rare, but that there may also occur true mutations of such moderate extent, as compared with the population, that their existence would only be detected by breeding tests, since their progeny would exhibit a different range of fluctuation from that of the population. 2. Nature. We may next enquire into the nature of variation as it affects the organism. Upon this basis we may distinguish between 310 READINGS IN EVOLUTION, GENETICS, AND EUGENICS four classes: morphological, physiological, psychological and eco- logical. Morphological variations are differences in size and form. In general morphological variations have more significance for the biologist than for the agriculturist. However, in many products of the farm, size and conformation are of decided importance. Two sub-classes under morphological variations are meristic and homeotic variations. Meristic variations are differences in number of repeated parts such as the petals in a flower, the leaflets in a compound leaf or number of phalanges. Homeotic variations are differences caused by the replacement of one part by another, as the production of an antenna in place of an eye in an insect. Physiological variations are differences in quality and performance. Examples of qualitative variations are difference in degree of hardness of bone, flavor of meat, richness of milk, difference in normal color, resistance to drouth, frost or alkali. Variations in performance con- stitute the most important group for the producer. Differences in performance are sometimes, though not necessarily, associated with certain details of structure. Psychological variations are differences in mental traits. That mental and nervous conditions have very definite effects upon physical conditions is well known, but the problem of distinguishing between purposeful action and automatic response, between manifestations of reason and manifestations of instinct, is set for the students of animal behavior. While variations in mental characteristics have an impor- tant place in eugenics and merit the attention of livestock breeders, yet the inheritance of psychological characters must be more exten- sively investigated before the subject can be considered with profit in a fundamental study of genetics. Ecological variations are those differences between individuals that result from their fixed relation to the environment. These differences are especially noticeable in plants and are known as place-effects or place variations. This category includes some of the phenomena of variation in crop yield and hence is of immediate significance to agriculture. 3. According to differences between them there are two general classes of variations: first, the slight differences in every character which are always to be observed even among individuals of identical heredity; second, unusual, striking differences commonly known as sports. The first class are called normal, indefinite fluctuating or VARIATION 311 continuous variations and the second, abnormal, definite and discon- tinuous variations. It should be noted, however, that all discontin- uous variations are not necessarily definite or even distinguishable. Continuous variations when examined statistically are found to con- form to the law of statistical regularity. That is, if measured and plotted the graph will approximate the normal curve of variability. Continuous variations are either heritable (combinations) or non- heritable (modifications) and, as was stated above, the only certain method of determining the class in which a given case may fall is the breeding test. Discontinuous variations are essentially discrete dif- ferences whether they be large or small. They are also either herit- able or non-heritable, and there is no correlation between size and heritability. Thus the extremely large and small mustard plants, con- sidered by themselves, are discontinuous variations, but they are almost certainly due entirely to environmental differences and seed from the small plant if grown under optimum conditions would pro- duce plants of normal size. On the other hand, it is known that many minute differences in organisms are heritable. 4. According to direction variations are classed as orthogenetic and fortuitous. Orthogenetic variations are those differences found in individuals related by descent which form progressive series tending in a definite direction. Many remarkable illustrations are found among paleontological records of the evolution of animals. Occa- sional examples are found among short-lived or vegetatively propa- gated species. The remarkable series of variations of the Boston fern is a good example. Fortuitous variations are chance differences occurring in all directions. 5. According to cause variations are either ectogenetic, differences arising from conditions acting upon the organism from without; or autogenetic, differences resulting from strictly internal relations be- tween germ and soma. Variation and development. — Somatogenesis, in sexually produced multicellular organisms, includes the entire history of cellular multi- plication and specialization from the first cleavage of the fertilized (or parthenogenetic) egg to the completion of all adult features. From the standpoint of individual development it includes gameto- genesis, for the production of sexual glands and of secondary sexual characters are merely phases of differentiation. Cell growth and cell function depend directly upon the activity of the living substance within the cell. The nature and degree of his activity depends upon 312 READINGS IN EVOLUTION, GENETICS, AND' EUGENICS two sets of determining causes acting simultaneously. First, there are the specific hereditary determiners or genetic factors, which react with the other elements of the protoplasm and, under favorable circumstances, condition normal development. Second, there are all the conditions external to the cell which stimulate or inhibit proto- plasmic activity. These "developmental stimuli" are chemical and physical changes wrought by energy from without the organism or caused by its own physiological activities. Chemical stimuli are exerted mainly through the medium of the circulating liquid which surrounds each living cell. Normally this fluid contains the elements essential for maintenance of life as well as various waste products. It may also bear toxic substances that suppress or inhibit the cell functions and in higher animals it contains the secretions of the duct- less, sexual and other glands that profoundly affect development. Physical stimuli are exerted chiefly from without and upon the organ- ism as a whole. They include changes in temperature, light and density of medium, the effects of electric and radiant energy, force of gravity, etc. Obviously, so many interrelated causes acting simulta- neously, each being independently capable of inducing a change in the end product, may cause an infinite number of differences in substance and in degree of development. Variation and environment. — External stimuli affect the develop- ment of characters in three ways: (i) they modify the development of inherited characters; (2) they actually condition the production of characters whose hereditary determiners are present in the germ- plasm; (3) they may cause germinal variations which result in the appearance of new heritable characters. The following are illustra- tions of these effects with reference to particular environmental factors. i. Environment modifies development of inherited characters. — (a) Light and Function. Klebs reports the result of growing the Showy Sedum (Sedum spectabile) in white, red, and blue light. The diverse effects of the three kinds of light are clearly shown in Fig. 51. Although the visible differences between the three plants were very pronounced the experiment was carried much farther. During 1905-6 observations were made on the numbers of stamens in the flowers of plants similarly propagated under white, red, and blue light and under variations, conditions of temperature, moisture, and food. About 20,000 flowers were examined and six distinct types were found, according to the variation in number of stamens. These had the VARIATION 313 following average numbers of stamens: (i) 9.68, (2) 8.45, (3) 6.54, (4) 5.05, (5) 9.47, (6) 7.33. Finally, Klebs subjected similar plants from white, red, and blue light to chemical analysis in order to secure further evidence of the physiological effects of light of different wave FIG. 51. — Sedum spectdbile. The three shoots (taken from a single plant) were planted in small pots on March 12, 1904, and placed in different greenhouses, 7, in blue light; II, in mixed white light; III, in red light. Photographed on September 30, 1914. (From Babcock and Clausen, after Klebs.) lengths. Table I shows the composition of the leaves in three plants like those shown in Fig. 5 r . They were in their respective greenhouses from June 6 to September 7. The percentages shown are per 100 g. of dry substance. In comparing these percentages it should be remembered that the plant in white light produced 1324 flower buds and the plant in red light 405, while the plant in blue light produced none. This explains the higher percentage of ash, nitrogen and protein in the last. On the other hand, the amounts of starch and sugar found in the plant from white light are decidedly larger than the one from blue light. 314 READINGS IN EVOLUTION, GENETICS, AND EUGENICS In short, according to Klebs, in comparison with normal white light, the production of organic substances, such as starch and sugar, is . TABLE I CHEMICAL COMPOSITION OF THREE PLANTS OF Sedum Spectabile GROWN IN WHITE, RED, AND BLUE LIGHT Substance White Red Blue Ash Sugar Calcium malate Free nitrogen 13.20 11.04 22. 29 13.20 15-40 18.02 18.60 2.40 18.10 Starch e 82 3 66 Crude protein 5-33 6. 15 7.64 diminished under the influence of blue light as microchemical and macrochemical tests distinctly show. In consequence of this dimin- ished assimilation of carbon dioxide the rosettes become purely FIG. 52.— Above the diurnal peacock butterfly (Vanessa id), and below, forms produced by subjecting the pupae to unusual temperatures. (From Babcock and Clausen, after Goldschmidt.) vegetative. In red light the carbon assimilation is greater than in blue light but less than in white. These experiments prove that the transformation of a plant "ripe to flower" into a vegetative one VARIATION 315 is possible on the one hand by an increase of temperature and of inorganic salts, and on the other hand by a decrease of carbon assimilation. b} Temperature and pigmentation. Many experiments in the rearing of moths and butterflies under controlled temperatures prove that degree of pigmentation is profoundly influenced by the tempera- ture at which the pupae are kept. Some species exhibit seasonal dimorphism in the wild state. By taking pupae of the common European form of the swallowtail butterfly, Papilio machaon, and subjecting them to a temperature of 37° to 38° C., Standfuss obtained the characteristic summer form which occurs in Palestine. Again it has been shown by temperature experiments that many variations 3-VI 28-VI 18-X 3-1 30-VII FIG. 53. — Morphological cycle of head height in Hyalodaphnia. Roman numerals designate months. (From Bdbcock and Clausen, after Woltereck.) found among insects in nature are merely aberrations due to tempera- ture effects. Goldschmidt by artificially controlled temperatures has produced a series of forms of the diurnal peacock butterfly, Vanessa io, which show the fading out of the "peacock eye" mark (see Fig. 52). c) Food and structure. Woltereck was able to prove that the form (hence the structure) of the fresh water crustacean, Hyalodaphnia, varies directly with the food supply. These minute animals produce many generations during a season and the successive generations from the same water exhibit a morphological cycle, the earlier and later generations having shorter heads and the generations produced from midsummer to autumn having longer ones. Fig. 53 is a reproduction of Woltereck's diagram of the morphological cycle in Hyalodaphnia showing variation in head and shell length as found on successive 316 READINGS IN EVOLUTION, GENETICS, AND EUGENICS dates from June 3 to January 3. By raising these animals under constant temperature conditions and varying the strength of the nutrient solution, Woltereck proved that the relative size of body parts varied with the food. In Fig. 54 the percentages of head height to shell in length are plotted as abscissas and the numbers of indi- viduals as ordinates. Animals from three strengths of nutrient media were measured, the curves of those from the weaker, the medium and the richer media being shown at mx, m2 and m3 respectively. d) Moisture and plumage color. Beebe experimented with the pigeon, Scardafella inca. This species, as found in North and Central America, is very constant in color of plumage, but in the moist tropics 30 35 '40 45 50 55 CO 05 70 ' 75 80 85 90 95 FIG. 54. — Schematic curves of head height in Hyalodaphnia as grown in media of three different food values. (From Babcock and Clausen, after Woltereck.) the following darker colored forms occur: in Honduras, dialeucos; in Venezuela, ridgivayi; in Brazil, braziliensis; and these differ in the amount of pigment in the feathers. By subjecting the birds of the northern type to an especially moist atmosphere, Beebe caused them to be so influenced that with each new moulting, whether natural or artificially induced, they always developed darker feathers. Thus a wild bird having pigment in 25.9 per cent of its area, would have after the second moulting under experimental conditions, 38 per cent and after the third, 41 . 6 per cent. Thus during the experiment the typical form assumed the appearance of the three other forms and finally developed plumage markings which have never been seen in nature. Fig. 55 shows the type form, inca, the three geographical variants, and the darkest artificially produced form. VARIATION 317 2. Environment conditions development of inherited characters. — (a) Light and metabolism. In a general sense light conditions life in all normally green plants. It certainly conditions normal develop- ment in such plants. Potatoes sprouted in a dark room develop no chlorophyll in the stems and the rudimentary leaves are abortive. In many bulbous plants, however, the influence of moisture and heat are sufficient to induce leaf growth and even development of the inflorescense, but it is all done at the expense of the food stored up in the bulbs. FIG. 55. — a, Typical wild pigeon, Scardafella inca; b, the form dialeucos; c, braziliensis; d, ridgwayi; e, inca after three moultings in a moist atmosphere. (After Beebe, from Babcock and Clausen.) b) Temperature and flower color. Baur reports an experiment with a red variety of the Chinese primrose, Primula sinensis rubra. If plants of this variety are raised by the usual method until about one week before time to bloom and then some of the plants are put in a warm room under partial shade (temperature from 30° to 35° C.) and the remainder in a cool house (temperature from 15° to 20° C.), when they bloom those in the warm temperature have pure white flowers while those in the cool temperature have the normal red color of the variety. Moreover, if plants are brought from the warm into the 318 READINGS IN EVOLUTION, GENETICS, AND EUGENICS cool temperature the flowers which develop later on will be normal red in color. Thus it cannot be said that this primula inherits either red or white flowers. What it really inherits is ability to react in certain ways under the influence of temperature. c) Food and fertility. It is well known that the kind of food supplied to the larvae of bees determines whether the females shall be fertile (queens) or infertile (workers). The striking differences in structure and instincts of the two classes of females are all conditioned by the food provided for the larvae. Each larva inherited the capacity to react in either way according to the stimulus received. d) Moisture and structure. Morgan reports a variety of the pomace fly, Drosophila ampelophila, with abnormal abdomen; "the normal black bands of the abdomen are broken and irregular or even entirely absent. In flies reared on moist food the abnormality is extreme; but even in the same culture the flies that continue to hatch become less and less abnormal as the culture becomes more dry and the food scarce, until finally the flies that emerge later cannot be told from normal flies. If the culture is kept well fed (and moist) the change does not occur, but if the flies are reared on dry food they are normal from the beginning." 3. Environment may cause new heritable characters. — As yet there is a dearth of evidence which can be accepted as scientific proof that external stimuli actually cause germinal variations. At the same time there is an abundance of data which falls into the class of circum- stantial evidence in favor of such a doctrine. Moreover, there are a few cases in which new heritable characters have been artificially produced by carefully controlled external stimuli. Hence some germinal variations are apparently caused by known environmental conditions and we are justified in recognizing this third category of developmental differences due to environmental effects. Considerable evidence of permanent changes in both morphologi- cal and physiological characters has been secured from experiments with the culture of bacteria and yeast, in unusual culture media, in the presence of toxic solutions, or under extreme temperature condi- tions. The significant results of four investigators who worked independently, Hansen, Barber, Wolf, and Jordan, have been reviewed and discussed in regard to their bearing on genetic theory by Cole and Wright. The four investigators mentioned above used refined methods and three of them began by isolating a single organism from whose progeny they obtained distinct strains or biotypes which VARIATION 319 remained constant for hundreds of test-tube "generations." It must be admitted that in most of these cases no specific influences can be named as the direct cause of the inherited variation. But there is no longer any doubt that permanent, discontinuous variations do occur spontaneously in these lowest organisms, and it is highly probable that certain incidental, external forces play an important part in inducing such variations. Direct experimental attack upon the germ cells themselves has been made with plants by a number of investigators, notably by MacDougal, who injected very dilute solutions of potassium iodide, zinc sulphate, sugar, etc., directly into the ovaries of various plants immediately before fertilization. Consequently somatic changes have been produced which were inherited throughout several generations. FIG. 56. — 0, portion of leaf of Scrophularia showing branching lateral vein; D, branching vein replaced by two laterals in leaf of seedling grown from seed produced by an injected ovary. Also note the difference in size and margin of leaves. (From Babcock and Clausen, after MacDougal.) By means of check experiments and observations it was found that these germinal variations were not caused by the wounding of the ovary and it is thought that they must have been induced in some way by the presence of the foreign chemical solution in the ovary. Fig. 56 shows a morphological change which appeared in a seedling of an unnamed species of Scrophularia as a result of ovarial injection. Hav- ing tested the species sufficiently to determine that it was a simple one, MacDougal treated several ovaries with potassium iodide, one part in 40,000 and secured seed. No other species of Scrophularia grew near the cultures. From this seed only three plants were raised. "One formed a shoot fairly equivalent to the normal, finally producing flowers in which the anthocyans were of a noticeably deep hue. The two remaining plantlets were characterized by a succulent aspect of the leaves and by a lighter and yellow color of the leaves and stems. 320 READINGS IN EVOLUTION, GENETICS, AND EUGENICS The flowers on one of the derivatives, as they may be called, were so completely lacking in color as to be a cream-white, this derivative' being designated as albida, while the other showed some marginal color and a rusty tinge and was designated as rufida Seeds of the original two derivatives were -sowed in the greenhouse. But one plant of albida, the most extreme departure, survived, while four of rufida were secured." MacDougal compared these second generation seedlings with seedlings from the original stock of the species, noting differences in size and margin of leaves, length of petioles and number of marginal glands. He found that the differences shown by the first generation appeared again in the second generation. Striking as these results appear it must be admitted that it would be difficult, on account of the small numbers of individuals differing from the parent type, to prove "satisfactorily to the biometrician that they were not mutations which would have occurred regardless of the ovarial treatment. What appear to be germinal variations in the tomato have been induced by intensive feeding. T. H. White tested the effect of dried blood, dissolved phosphate rock, sulphate of potash and iron filings all in excessive amounts, and (with the exception of the iron) in various combinations, on the Red Cherry tomato. The lack of data on control cultures of seedlings from the same parent as the experi- mental cultures makes it impossible to compare the actual amount of permanent variation produced. T. H. White states that measure- ments "show that the plants of the sixth generation grown under the influence of the dried blood are one-third larger in height, length of leaf and size of fruit, than those of the second." The author con- cludes that "there can be no doubt .... that, in the case of Red Cherry treated with dried blood, there is permanent variation to the third generation." If these results are corroborated by more care- fully planned and rigidly controlled experiments they will add the weight of scientific proof of a principle in plant breeding long since recognized on empirical grounds, to wit, that the introduction of wild plants into intensive cultivation induces variation. Furthermore, it suggests a possible means for rapid permanent improvement of wild forms with which hybridization may be impracticable. In experiments on lower animals, e.g., the protozoa, the same difficulty is met with as has been encountered in bacteria and yeasts, hi that it is manifestly impossible to distinguish between somatic and germinal variations. Moreover, in most of these experiments, as with most of those on higher animals, the necessary conditions for rigid VARIATION 321 scientific analysis have been lacking. Either the same strain as was subjected to artificial conditions was not grown for comparison under natural conditions or else the conditions themselves were not suffi- ciently well controlled to permit of certain analysis. It is interesting to note that the pomace fly, Drosophila ampelopkila, which has pro- duced more mutations so far as we know than any other organism, was subjected to the effects of ether on a grand scale and under controlled conditions by Morgan, but that not a single mutation was observed to result from this treatment. However, mutations have subsequently appeared again and again in cultures of "wild" flies not only of this species but also of other species of Drosophila. Thus it appears that germinal variations frequently occur independently of external stimuli. It also seems that a tendency to produce mutations may be inherited. With animals the best known experiments on the artificial pro- duction of germinal variations are those of Tower who worked with the Colorado potato beetle, Leptinotarsa decemtineata, and related species. Like other arthropods these beetles are more directly under the influence of temperature changes at least than are warm-blooded animals. Tower first determined the period in ontogeny when ex- ternal stimuli will affect the germ cells. He found that hi Leptino- tarsa the germ cells do not become susceptible to external stimuli until after the time in ontogeny when the color pattern of the individ- uals subjected to the stimuli can be influenced. He found that eggs were most susceptible just before and during maturation and this observation is in agreement with those of Fischer, Standfuss, Weis- mann and others who have conducted similar investigations. Tower concluded that certain individuals from the germ cells of a stimulated parent "show intense heritable variations, whereas those not acted upon do not show these changes." Most of the inherited variations involve changes in the pigmentation of the body parts. In certain cases there was an actual change in the color pattern. It is to these results that Tower attaches the greatest significance inasmuch as most similar experiments have not succeeded in causing pattern changes. In spite of the elaborateness of Tower's methods consider- able skepticism exists regarding the validity of his conclusions, and this has not been lessened by the non-appearance of confirmatory data. In a recent paper he reports the production of very striking germinal modifications in L. decemlineata as a result of subjecting a morphologically homogeneous race to an extreme change in environ- 322 READINGS IN EVOLUTION, GENETICS, AND EUGENICS ment. However, it is still a question whether the material used may not be heterogeneous as regards the germinal factors that condition certain physiological characters. Stockard's investigations on the effect of alcohol on the progeny of guinea pigs have shown that the germ cells as well as the somatic tissues of the alcoholized animals are injured. On the whole it must be admitted that the experimental induction of heritable variations is still largely an unworked field. The complex conditions to be considered and consequent obstacles to be overcome are appreciated by no one more fully than by those who have at- tempted such investigations. For, as Tower has said: "It is evident that the problem of germinal change is one of difficulty, and involves more of indirect than of direct methods of investigation. There is little reason to expect that present biochemical methods can give a solution, but they may give valuable suggestions for further indirect investigation. It seems not improbable, however, that this problem, like so many others in biology, must await the solution of the larger question of what life is before it will be possible to express in exact terms the nature of germinal changes. Our present status, with several methods of production and much knowledge of the behavior of induced germinal changes available, is a basis from which great advances in knowledge and in operation may reasonably be expected." CHAPTER XXIH ARE ACQUIRED CHARACTERS (MODIFICATIONS) HEREDITARY? INTRODUCTORY NOTE. — In the previous chapter, under the heading " Classifica- tion of Variations," the authors pointed out that germinal variations are hereditary, and somatic variations (modifications) are not hereditary. That germinal varia- tions are hereditary and may be produced hi a number of different ways was made clear in the last chapter, but the statement that somatic modifications are never in the least hereditary is equivalent to a total denial of the doctrine of the "Inheritance of Acquired Characters," the so-called Lamarckian theory, which was briefly presented hi chapter ii. This is not a closed question and the final answer has been given neither in the negative nor in the affirmative. The problem is of utmost import for evolu- tionists and for all who are interested in race improvement. So important is it to view this question fairly that we shall quote extensively from several of the leading students of the problem. MISUNDERSTANDINGS AS TO THE QUESTION AT ISSUE1 J. ARTHUR THOMSON The precise question is this: Can a structural change in the body induced by some change in use or disuse, or by a change in surrounding influence, affect the germ-cells in such a specific or representative way that the offspring will through its inheritance exhibit, even in a slight degree, the modification which the parent acquired ? Before we pass to discuss the evidence pro and con it will be useful to notice some frequently recurring misunderstandings, the persistence of which would make further argument futile. Misunderstanding I. — How can there be progressive evolution if acquired characters are not transmitted ? — Those who have not thought clearly on the subject often shake their heads sagely and remark that they "do not see how evolution could have been possible at all unless what is acquired by one generation is handed on to the next." To this we have simply to answer (i) that our first business is to find out the facts of the case, careless whether it makes our interpretation of the history of life more or less difficult, and (2) that in the supply of germinal variations, whose transmissibility is unquestioned, there is ample raw material for evolution. We know a li ttle about the abundant 1 From J. A. Thomson, Heredity (copyright 1907). Used by special permis- sion of the publisher, John Murray, London. 323 324 READINGS IN EVOLUTION, GENETICS, AND EUGENICS crop of variations at present supplied; there is no reason to believe that it was less abundant hi the past. Misunderstanding II. — Interpretations are not facts. — There are many adaptive characters in plants and animals which may be super- ficially interpreted as due to the direct result of use and disuse or of environmental influence. The Lamarckians have so interpreted them, and the Lamarckian way of looking at adaptations has become habitual to many uncritical minds. They see on modern flowers the footprints of insects which have visited them for untold ages; they speak of the dwindling of the whale's hind-limbs through disuse, of the hardening of the ancestral horses' hoofs as they left the marshes and ran on harder ground; they picture the giraffe by persistent effort lengthening out its neck a few millimetres every century, as the acacia raised its leaves higher and higher off the ground; and they say that animate nature is so full of evidences of the inheritance of acquired characters that no further argument is needed. But all this is a begging of the question. It is easy to find struc- tural features which may be interpreted as entailed acquired characters, if acquired characters can be entailed. Obviously, however, we must deal with what we can prove to be modifications, or with what we can plausibly regard as modifications because we find their analogues in actual process of being effected to-day. It is easy to say that the blackness of the negro's skin was produced by the tropical sun, and that it is now part of his natural inheritance. It is easy to say this, but absolutely futile. Let us first catch our modifications. The Golden Rod (Solidago mrgaured) growing on the Alps is pre- cocious in its flowering when compared with representatives of the same species growing in the lowlands. Hoffmann found that Alpine forms transplanted to Giessen remained precocious, therefore the acquired precocity had become heritable. But there is no .evidence that the precocity was acquired; it may have been the outcome of the selection of germinal variations. The African Wart-hog (Phacochoerus) has the peculiar habit of kneeling down on its fore-limbs as it routs with its huge tusks in the ground and pushes itself forward with its hind-limbs. It has strong horny callosities protecting the surfaces on which it kneels, and these are seen even in the embryos. This seems to some naturalists to be a satisfactory proof of the inheritance of an acquired character. It is to others simply an instance of an adaptive peculiarity of germinal origin wrought out by natural selection. ARE ACQUIRED CHARACTERS HEREDITARY? 325 Misunderstanding HI. — Begging the question by starting with what is not proved to be a modification. — There is no relevancy in citing cases where an abnormal bodily peculiarity re-appears generation after generation, unless it be shown that the peculiarity is a modifica- tion, and not an inborn variation whose transmissibility is admitted by all. Short-sightedness may recur hi a family-series generation after generation, but there is no evidence to prove that the original short-sightedness was a modification. In all probability, short- sightedness is in its origin a germinal variation, like so many other bodily idiosyncrasies. In regard to some diseases, such as rheumatism, it is often said dogmatically by those who know little about the matter that the original affection hi the ancestor was brought about by some definite external influence — such as a cold drive or a damp bed; but it seems practically certain that hi all such cases we have to do with an inborn predisposition, to the expression of which the cold drive or the damp bed were merely the liberating stimulus, comparable to the pulling of the trigger in a loaded gun. The liberating stimulus is, of course, of great importance, both in the case of the gun's discharge and the organism's disease, but it only goes a little way towards a satisfactory interpretation in either case. Not that we can explain the origin of rheumatism or shortsightedness or any such thing — there is no expla- nation hi calling them germinal variations that cropped up; but we are almost certain that they never are modifications or acquired characters. Herbert Spencer twits those who are sceptical as to the trans- mission of acquired modifications with assigning the most flimsy reasons for rejecting a conclusion they are averse to; but when Spencer cites the prevalence of short-sightedness among the "notoriously studious " Germans, the inheritance of a musical talent, and the inheri- tance of a liability to consumption, as evidence of the inheritance of modifications, we are reminded of the pot calling the kettle black. Over and over again in the prolific literature of this discussion the syllogism is advanced, either in regard to gout or something analogous — Gout is a modification of the body, an acquired character; Gout is transmissible; Modifications are sometimes transmissible. It may be formally a good argument, but there is every reason to deny the major premise. There is no proof that the gouty habit had an exogenous origin — that it was, to begin with, for instance, the direct result of high living; though it is generally admitted that 326 READINGS IN EVOLUTION, GENETICS, AND EUGENICS excesses in eating or drinking may give a stimulus to its expression. "The conclusion that I have arrived at," says Prof. D. J. Hamilton, " is that the gouty habit of body has arisen as a variation, and as such is hereditarily transmissible, and that excess of diet and alcohol merely renders the habit of body apparent." It may also be pointed out that gout and rheumatism and the like are rather processes of metabolism than structural modifications, though the latter may ensue. After pointing out the irrelevancy of citing cases of the hereditary recurrence of polydactylism, haemophilia, colour-blindness in man, or the absence of horns in cattle or of tails in cats, as instances of the transmission of acquired characters, Prof. Ernst Ziegler says: "Only that can be regarded as ' acquired ' which is produced in the course of the individual life, during and after the period of development, exclu- sively under the influence of external conditions; the term is in no wise applicable to peculiarities which, as one says, arise of themselves from a predisposition already present in the germ." Misunderstanding IV. — Mistaking the reappearance of a modifica- tion for transmission of a modification. — It is of h'ttle service to cite cases where a particular modification reappears generation after gen- eration unless it be shown that the change recurs as part of the inheri- tance, and not simply because the external conditions which evoked it in the first generation still persisted to evoke it in those that followed. Reappearance is not synonymous with inheritance. Misunderstanding V. — Mistaking re-infection for transmission. — A particular form of the fourth misunderstanding has to do with facts so special that it may be conveniently treated of separately. It has to do with microbic diseases. It is admitted that a parent infected with tubercle-bacillus or with the microbe of syphilis may. have off- spring also infected. But such cases are irrelevant in the discussion. Infection, whether before or after birth, has nothing to do with inheri- tance. As Dr. Ogilvie says, " Wherever the transmission of infectious disease from parent to offspring has been adduced to support the doctrine of the inheritance of acquired characters, it has been done in utter misconception of its meaning and scope." Medical men have sometimes condescended to make a subtle distinction between "hereditary" and "congenital" syphilis — the latter manifested at birth, the former some time afterwards! It seems strange that they have failed to recognise that there is no reason to use the word "hereditary" at all in this connection. What occurs is an infection, and it is theoretically immaterial at what stage the infection occurs. A microbe cannot be part of an inheritance. ARE ACQUIRED CHARACTERS HEREDITARY? 327 Misunderstanding VI. — Transmission in unicellular s is not to the point. — It is not to the point to cite cases where unicellular organisms, such as bacteria or monads, have been profoundly and heritably modi- fied by artificial culture, so that, for instance, the descendants of a virulent microbe have been made to lose their evil potency. It is irrelevant because in regard to unicellular organisms we cannot draw the distinction between body and germinal matter, apart from which the concept of modifications is of no value. In artificial culture the whole character of the unicellular organism — its particular metabolism — is altered; it multiplies by dividing into two or more parts, which naturally retain the altered constitution. But this is worlds away from the supposed case of an alteration in the structure of the little toe so affecting the germ-cells that the offspring inherit a corresponding deformation. Professor L. Errera (1899) reported an experiment with a simple but multicellular mould (Aspergillus niger), which adapted itself to a medium more concentrated than the normal. The second generation of the mould was more adapted than the first, and the adaptation to the concentrated medium was not wholly lost after rearing in the nor- mal medium again. This looks like evidence of the inheritance of the acquired adaptive quality which was brought about as a direct modifi- cation. But the case does not really help us, since the distinction between soma and germ-plasm is not more than incipient in the mould in question. And even if the distinction were more marked, it would only show that the germ-plasm is capable of being affected along with the body, by a deeply saturating influence, which nobody has ever denied. Misunderstanding VII. — Changes in the germ-cells along with changes in the body are not relevant. — Another misunderstanding is due to a failure to appreciate the distinction between a change of the repro- ductive cells along with the body, and a change in the reproductive cells conditioned by and representative of a particular change in bodily structure. The supporters of the hypothesis that modifications may be transmitted point to the tragic cases where some poisoning of the parent's system, by alcohol, opium, or some toxin, is followed by some deterioration in the offspring. There is no doubt as to the fact; the question is as to the correct interpretation. i. In some cases it may be that the whole system of the parent is poisoned — reproductive cells as well as body; the effect may be as direct on the germ-cells as on the nerve-cells. These, therefore, are not cases on which to test the transmissibility of an acquired character — i.e., 328 READINGS IN EVOLUTION, GENETICS, AND EUGENICS of a particular somatic modification. If a local poisoning had a structural effect on some particular organ, and if that structural effect was reproduced in any degree in the offspring, the case would be relevant; but when the whole organism is soaked in a poison the case is irrelevant. If it could be said that the sunshine, which brings about sun-burning in the skin, soaks through the organism even to its repro- ductive cells and specifically affects them, hi a manner analogous to the saturating poison, we should have a physiological basis for expect- ing the inheritance of sun-burning. But we cannot make this assump- tion. We have no warrant for believing that the modification of a part re-echoes in a definite specific way through the organism until even the penetralia of the germ-cells reverberate. 2. A parent organism is poisoned, and there are structural results of that poisoning. The offspring are born poisoned, and show similar structural peculiarities. This may be due to the fact that the germ- cells were poisoned along with the parental body; but it may also be due, in the case of a mother, to a poisoning of the embryo before birth, hi a manner comparable to a pre-natal infection. 3. In some cases — e.g., of alcoholism in successive generations — there may be poisoning of the germ-cells along with the body, there may be poisoning of the embryo before birth, and of the infant after; but it may also be that what is really inherited is a 'specific degeneracy of nature, an innate deficiency of control, perhaps, which led the parent to alcoholism, and which may find the same or some other expression hi the child. Cases are known hi which the children of a dipsomaniac father and a quite normal mother have exhibited a tendency to alcoholism, insanity, and the like. In this case the possibility of poisoning the unborn child is eliminated, but there remain three possibilities of interpretation — that there was specific poisoning of the paternal germ- cells; that what was inherited was the constitutional weakness which expressed itself as alcoholism in the father; and that there were detri- mental influences in the early nutrition, environment, education — "nurture," in short — of the offspring. But while we have admitted a good deal, we have not admitted the transmissibility of a particular structural modification brought about hi the parental body as a result of the toxin. Misunderstanding VIII. — Failure to distinguish between the possible inheritance of a particular modification and the possible inheri- tance of indirect results of that modification, or of changes correlated with ARE ACQUIRED CHARACTERS HEREDITARY? 329 it. — At first sight this seems hair-splitting, but it is a crucial point. Through his vigorous exercise the blacksmith develops a muscular arm worthy of admiration; the shoemaker acquires skeletal and muscular peculiarities less admirable. There are many permanent and profound modifications associated with particular occupations. Are we to believe, it is asked, that the occupation of the parents has no influence on the offspring? Are we to believe, it is asked, that the children of soldier, sailor, tinker, tailor, are in no way affected by the parental functions ? It would be interesting to have precise data in regard to this, but it is generally admitted that when parents have healthful occupations their offspring are likely to be more vigorous. The matter is compli- cated by the difficulty of estimating how much is due to good nurture before and after birth. It is not unlikely, too, that some profound parental modifications may influence the general constitution, may even affect the germ-cells, and may thus have results in the offspring. But unless the offspring show peculiarities in the same direction as the original modifications, we have no data bearing precisely on the ques- tion at issue. A belief in the inheritance of modifications was perhaps expressed in the old proverb, "The fathers have eaten sour grapes, and the children's teeth are set on edge" — a proverb which Ezekiel with such solemnity said was not any more to be used in Israel. Now if " setting on edge" was a structural modification, and if the children's teeth were "set on edge" as their fathers' had been before them, there would be a presumption in favour of the transmission of this acquired character, though it would be still necessary to inquire carefully whether the children had not been hi the vineyard too. But if, as Romanes said, the children were born with wry necks, we should have to deal with the inheritance of an indirect result of the parent's vagaries of appetite, and not with any direct representation hi inheritance of the particular modification produced in the paternal dentition. Misunderstanding IX. — Appealing to data from not more than two generations. — It has often been pointed out that animals transported to a new country or environment may exhibit some modification apparently the result of the novel influence, and that their offspring in the same environment may exhibit the same modification in a greater degree. Thus sheep may show a change in the character and length of their fleece, and their progeny may show the same change more markedly. 330 READINGS IN EVOLUTION, GENETICS, AND EUGENICS But it is perfectly clear that if the evidence does not go beyond this, nothing is proved that affects the question at issue. It was to be expected that the offspring should show the modification hi a more marked degree than their parents did, since the offspring were sub- jected to the modifying influences from birth, whereas their parents were influenced only from the date of their importation. What would be welcome is evidence that the third generation is more markedly modified than the second; then there would be data worth considering. Only then would it be necessary to consider Weismann's somewhat subtle discussion as to the influence of climate. THE INHERITANCE OR NON-INHERITANCE OF ACQUIRED CHARACTERS1 EDWIN GRANT CONKLIN Few questions in biology have been discussed so fully and so fruitlessly as this. It is a problem of the greatest interest not only to students of biology but also to sociologists, educators and philan- thropists and yet it is still to a certain extent an unsolved problem. Opinions of Lamarck and Darwin. — It is well known that Lamarck taught that characters due to desire or need, use or disuse, and to changed environment or conditions of life were inherited and thus brought about progressive evolution. Long ago desire or need was repudiated as a factor of evolution. Lowell satirized it in his Biglow Papers in these words: "Some filosifers think that a fakkilty's granted The minnit it's felt to be thoroughly wanted. That the fears of a monkey whose holt chanced to fail Drawed the vertibry out to a prehensile tail. " Darwin wrote to Hooker, "Heaven forfend me from Lamarck's non- sense of adaptation from the slow willing of animals"; but although he repudiated this feature of Lamarckism he held that characters due to use or disuse and to changed conditions of life might be inherited and he proposed his hypothesis of pangenesis in order to explain the process of the transmission of such characters to the germ cells. Weismann's theories. — Weismann introduced a new era in biology by denying the inheritance of all kinds of acquired characters, and by challenging the world to produce evidence that would stand a 1 From E. G. Conklin, Heredity and Environment (copyright 1919). Used by special permission of the publishers, The Princeton University Press. ARE ACQUIRED CHARACTERS HEREDITARY? 331 rigorous analysis. But Weismann's greatest service lay in his con- structive theories rather than in destructive criticism; he forever disposed of theories of pangenesis and the like by showing that the germ cells are not built up by contributions from the body and that characters are not transmitted from generation to generation; but on the other hand that there is transmitted a germ plasm which is relatively independent of the body and which is relatively very stable in organization. This epoch-making theory of Weismann's has natu- rally undergone some changes, as the result of new discoveries. It is no longer believed that the germ plasm is really independent of the body, nor that it is absolutely stable, as Weismann at one time held. There is no doubt that the germ cells and the germ plasm are physiologically related to other cells and to other plasms, and similarly there is no doubt that the germ plasm although very stable can and does change its constitution under some rare conditions. But hi the mam the germ plasm theory is accepted by the great majority of biologists to-day, and recent work in genetics and cytology has brought many confirmations of this theory. Distinctions between hereditary and acquired characters. — As long as it was believed that the developed characters of an organism could be transmitted as such to its descendants it was customary to speak of developed characters as hereditary or acquired and to talk of the inheritance or non-inheritance of acquired characters. This dis- tinction is not a logical one for all developed characters are invariably the result of the responses of the germinal organization to environ- mental stimuli; and of course no developed character can be purely hereditary or purely environmental. But when a given character arises in many individuals of the same genotype under different environmental conditions it is probable that heredity, which is the constant factor in this case, is also the determining factor for that character. On the other hand if a character develops hi response to peculiar stimuli and does not appear in other individuals of the same genotype hi which such stimuli are lacking it is said to be an environ- mental or acquired character. In fine, inherited characters are those whose distinctive or differential causes are in the germ cells, while acquired characters are those whose differential causes are environ- mental. Statement of problem. — Briefly stated the question of the inheri- tance of acquired characters is this: Can the differential cause of a character be shifted from the environment to the germ plasm ? Can 332 READINGS IN EVOLUTION, GENETICS, AND EUGENICS peculiarities of the environment which influence the development of somatic characters so affect the germ cells that they will produce these somatic characters in the absence of the peculiar environment ? Can the characteristics of a developed organism enter into its germ cells and be born again in the next generation ? Considering the fact that germ cells are cells and contain no adult characteristics, it seems very improbable that any peculiarity of environment whether of nutri- tion, use, disuse or injury, which brings about certain peculiarities of developed characters in the adult, could so change the structure of the germ cells as to cause them to produce this same character in subse- quent generations in the absence of its extrinsic cause. How, for example, could defective nutrition, which leads to the production of rickets, affect the germ cells, which contain no bones, so as to produce rickets in subsequent generations, although well nourished ? Or how can over-exertion, leading to hypertrophy of the heart, so affect the germ cells that they, in turn, would produce hypertrophied hearts in the absence of over-exertion, seeing that germ cells have no hearts ? Or how could the loss or injury of eyes or teeth or legs lead to the absence or weakened development of these organs in future generations, seeing that inheritance must be through germ cells which possess none of these structures ? Lack of evidence for inheritance of acquired characters. — But, apart from these general objections to the doctrine of the inheritance of acquired characters, there are many special difficulties. There is no conclusive and satisfactory evidence in favor of such inheritance. Almost all the evidence adduced serves to show only that characters are acquired, not that they are inherited. It is a matter of common observation that mutilations are not inherited; wooden legs do not run in families, although wooden heads do. The evidence for the inheritance of peculiarities due to use or disuse is wholly inconclusive; for example, did the giraffe get his long neck because he browsed on trees, or does he browse on trees because he has by inheritance a long neck ? Did attempts to fly lead to the development of wings in birds, or do birds fly because heredity has given them wings ? Did life in caves make cave animals blind, or did blind animals resort to caves because the struggle for existence there was less severe for them ? The evidence is in favor of the second of each of these alternatives rather than of the first. There still remains the question of the inheritance of certain characters due to environment, though hcxe also the most clear-cut ARE ACQUIRED CHARACTERS HEREDITARY? 333 evidence is against this proposition. That unusual conditions of food, temperature, moisture, etc., may affect the germ cells so as to produce general and indefinite variations in offspring is probable, but this is a very different thing from the inheritance of acquired characters. The germ cells being a part of the parental organism may be modified by such changes in the environment as affect the body as a whole, they may be well nourished or starved, they may be modified by changed conditions of gravity, salinity, pressure, temperature, etc., and these modifications of the germ cells probably lead to certain general modi- fications of the adult, which may be larger or smaller, stronger or weaker, according as the germ is well or poorly nourished, but it is incredible that the environment which produces rickets, or hyper- trophied heart, or loss of sight in one generation should modify the germ cells in such a peculiar and definite way that they should give rise in the next generation to these particular peculiarities, in the absence of the extrinsic cause which first produced them. The inheritance of acquired characters is incredible, because the egg is a cell and not an adult organism; and in this case there is no suffi- cient evidence that the thing which is incredible really does happen. No inherited influence of stock on graft. — If specific changes of environment produced specific changes in heredity we should expect to find that where different plants or animals are grafted together each would modify more or less the hereditary constitution of the other. But this does not occur. Everybody knows that when a branch of a particular kind of fruit tree is grafted upon a tree of a different variety the quality of the fruit borne by that branch is not altered by its close union with the new stock. The same is true of all forms of animal grafts. Harrison cut in two young tadpoles of two species of frog, Rana sylvatica and Rana palustris, and spliced the anterior half of one to the posterior half of the other. These frogs and their tadpoles differ in color as well as hi other respects, R. sylvatica being more deeply pigmented than R. palustris. In the grafted tadpoles each half pre- served its own peculiarities even up to the adult condition. A still more striking case of the persistence of heredity in spite of environmental changes is found in experiments in which the ovaries are removed from one variety of animal and transplanted to another variety. Guthrie made such transplantation in the case of fowls and concluded that there was some influence of the foster mother upon the transplanted ovary, but Davenport, who repeated his experiments, was unable to confirm his resu. ,s. Finally Castle and Phillips furnished 334 READINGS IN EVOLUTION, GENETICS, AND EUGENICS the most conclusive demonstration that the hereditary character- istics of the transplanted ova are in no wise changed by the foster mother. They removed the ovary from a pure black guinea-pig and put it in the place of the ovary of a pure white animal. After recover- ing from the operation this white female with the "black" ovary was bred to a pure white male. Three litters of offspring from these parents were all pure black. Although both parents were pure white all the offspring of the Fi generation were black because they came from "black" eggs and black is dominant over white. The fact that these "black" eggs developed in the body of a white female did not in the least change their hereditary constitution. Dominants and recessives remain pure. — A still more intimate union takes place when the dominant and recessive characters come together in any zygote. These characters, or rather the factors which determine them, may be intimately associated in every cell of the organism throughout an entire generation and yet we may get a clean separation of these characters hi the next generation; hi many cases neither the dominant nor the recessive character has been at all modi- fied by its most intimate association with the other. Climatic effects not inherited. — A striking instance of the purely temporary effect of the environment and of the long persistence of hereditary constitution amidst new environmental conditions, which have greatly changed the appearance of the developed organisms, is found in the case of alpine plants. Nageli says that such plants, which have preserved the characters of high mountain plants since the ice age, lose these characters perfectly during then* first summer in the lowlands. Summary. — If acquired characters were really inherited we should expect to find many positive evidences of this instead of a few sporadic and doubtful cases. In particular why do we not find in plant or animal grafting that the influence of the stock changes the hereditary potencies of the graft ? Why do we not find that transplanted ovaries show the influence of the foster mother as Guthrie supposed — a thing which has been disproved by Castle ? Why do dominant and recessive characters remain pure, even after their in tuna te union in a hybrid, so that pure dominants and pure recessives may be obtained in subse- quent generations from this mixture ? Why does every child have to learn anew what his parents learned so laboriously before him ? Even the strongest defenders of the inheritance of acquired characters are constrained to admit that it occurs only sporadically and excep- tionally. ARE ACQUIRED CHARACTERS HEREDITARY? 335 Neo-Lamarckism. — Many modifications of the Lamarckian hypothesis of the inheritance of acquired characters have been pro- posed in recent years. Foremost among those are the "mneme" theory of Semon and the " centro-epigenesis " theory of Rignano. To Semon as to many other biologists the apparent resemblance between memory and heredity has seemed significant, and this furnishes the basis of his theory. Semon holds that every condition of life, every functional activity of an organism leaves a permanent record of itself in what he calls an "engramme." If these conditions or activities are long continued their engrammes are heaped up and affect heredity. Semon does not ask if "acquired characters" are inherited, but rather "Are the hereditary potencies of the germ cells altered by stimuli acting on the parental body?" This is a very different thing from the inheritance of a particular acquired character, and there is some evidence that such stimuli may in rare instances produce changes in the hereditary constitution of the germ plasm though these evidences are by no means conclusive. Temporary effects of environment; "induction." — On the other hand certain changes may be produced in germ cells or embryos which last for only a generation or two and then disappear. It is well known that plants grown in poor soil are smaller and produce smaller seeds than those grown in good soil, and De Vries, Bauer and Harris find that such seeds produce smaller plants having smaller seeds than do seed of normal size. This is an after effect of poor nutrition which changes the amount of food material in the seeds and through this the size of the plant which develops from the seed, but it does not change the hereditary constitution. Woltereck found that in Daphnia there is an after effect of cold lasting for one or two generations, and this he calls "induction," when the effect lasts for one generation, or "pre- induction " when it lasts for two or three generations. Whitney found that rotifers poisoned with alcohol were weaker in resistance to copper salts and were less fertile than others, and when brought back to normal conditions the first generation was weak but the second was normal. On the other hand Stockard finds that the injurious effects of alcohol on guinea pigs persist through two or more generations. In man alcohol may have an "induction" effect on offspring, but fortu- nately it does not seem to alter hereditary constitution. Probably of a similar character are Sumner's results; he found that mice raised in the cold have shorter tails than those raised in higher temperatures and this modified character appears in the next generation. If this is an after effect or "induction" it should disappear in the following generations. 336 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Kammerer found that salamanders with black and yellow spots when reared on yellow soil gradually lose their black color, becoming more yellow, and their young continue to grow more yellow until finally almost all black may disappear. The offspring of such sala- manders are said to be more yellow than normal; but this work has been called in question and needs confirmation. Even if confirmed the result may be an after effect or "induction" which would soon disappear under usual conditions, and there is no evidence that it is really inherited. Such cases are not instances of true inheritance; they do not signify a change in the hereditary constitution but an influence on the germ cells of a nutritive or chemical sort comparable with what takes place when fat stains are fed to animals; the eggs of such animals are stained, and the young which develop from such eggs are also stained, though the germinal constitution remains unchanged. The very fact that the changed condition is reversible and that it disappears within a short time is evidence that it is not really inherited. In conclusion: (i) Developed characters, whether "acquired" or not, are never transmitted by heredity, and the hereditary constitu- tion of the germ is not changed by changes in such characters. (2) Possibly environmental stimuli acting upon germ cells at an early stage in their development may rarely cause changes in hereditary constitution, but changes produced in somatic cells do not cause corresponding changes in the hereditary constitution of the germ cells. (3) Germ cells like somatic cells may undergo modifications which are not hereditary; if starved they may produce stunted individuals and this effect may last for two or three generations; they may be stained with fat stains and the generation to which they give rise be similarly stained; they may be poisoned with alcohol or modified by tempera- ture and such influence be carried over to the next generation without becoming hereditary. All such cases are known as "induction" and many instances of the supposed inheritance of acquired characters come under this category. (4) Environment may profoundly modify individual development but it does not generally modify heredity. THE OTHER SIDE TO THE QUESTION [It will have been noted that the chief objection to the idea of the possibility of acquired characters being inherited comes to us as a heritage of the rather extreme Weismannian concept of the "germ ARE ACQUIRED CHARACTERS HEREDITARY? 337 plasm." According to this view as brought out by Professor Guyer (p. 296), there is an unbroken continuity from generation to generation of the germ plasm. Germ cells are thought of as remaining entirely undifferentiated for any somatic function and as therefore capable of starting at the beginning to develop a new individual. The germ cell is supposed to be "set apart at an early period in a given individual; it takes no part in the formation of the individual's body, but remains a slumbering mass of potentialities which must bide its time to awaken into expression in a subsequent generation." Physiologists object to this idea that the germ cells are so dis- tinctly different from body cells and that they are so insulated, as it were, from the soma as to be immune to any changes that may affect the latter. Two kinds of data are offered in opposition to this con- cept. A few observers, notably Professor C. M. Child, have described cases in which somatic cells, that already had become differentiated as primitive muscle cells, lost their differentiation and returned to a germinal condition. If this kind of thing were general, and it is probably not, germ cells might conceivably be produced from func- tioning soma cells and might therefore furnish a mechanism for the transmission of the effects of use and disuse. It should be empha- sized, however, that, among animals at least, there is extremely little evidence in support of the idea that differentiated body cells give rise to germ cells. Among plants, however, a different situation prevails. In the Begonia, for example, any part of a plant if cut off is capable of pro- ducing a whole new plant. Even a purely vegetative organ like a leaf, if cut off and partially buried in soil, will bud off a new plant which will produce flowers with perfectly typical germ cells. We have to admit, in this case, either that leaf tissues contain undifferentiated germ cells or that somatic tissues give rise to germ cells. The first alterna- tive is in harmony with the germ-plasm hypothesis, the second is the preferred view of the opponents of this hypothesis. Among animals, as for example annelid worms, it is quite common to find the germ cells aggregated in a few segments of the body. If a part of the body in which there are no recognizable germ cells be cut off, it will, under proper conditions, regenerate the lost parts and become a complete worm with functional germ cells. The same alternative explanations that were offered for the Begonia case apply equally well here. Numerous other cases of the same sort are well known to all zoologists. To the advocate of the " germ-plasm " theory 338 READINGS IN EVOLUTION, GENETICS, AND EUGENICS they offer no difficulties because he can always fall back upon the statement that, among the lower forms at least, there is reserve germ plasm equally distributed over the whole body ready to differentiate into definite germ cells when needed. This type of appeal is abhor- rent to the physiologist, and with some justification, for it really begs the question by assuming that any cell that is capable of form- ing germ cells belongs to the more or less sacred lineage of germ plasm. If we confine the application of the germ-plasm idea to the higher animals, such as vertebrates and insects, we would obviate these chief objections, and the present writer would take the view that it is only among the upper ranges of highly specialized animals that the con- tinuity of the germ-plasm concept holds solidly. Another chief objection to the germ-plasm concept has to do with the supposed insulation or apartness of the germ plasm. Physiolo- gists have found that there is an extremely intimate correlation in function between practically all parts of a living organism. Many of the structures, such as the rudimentary pituitary body, the thyroids, the adrenal body, and various other bodies whose function was long unknown, have now been shown to exercise a profound effect on the development of the whole body. Since practically all tissues are known to affect at least some other tissues, is it likely, the physiologist asks, that none of the other tissues affect the germinal tissues? The organism is to be viewed, it is said, not as a collection of independently functioning parts, but as a single coherent unit. On this view no tissue can be thought of as beyond the influence of organic changes. The classic argument of the Weismannians was that we can con- ceive of no mechanism by means of which somatic changes can be carried back into the germ cells, and therefore there is no such mechanism. Now the fallacy of this argument is obvious; even if we could con- ceive of no suitable mechanism for this purpose, this does not preclude the existence of such a mechanism. Moreover, according to Professor Guyer, just such a mechanism actually exists, as will be brought out in the following quotation from one of his recent publications. — ED.] A POSSIBLE MECHANISM FOR THE TRANSMISSION OF ACQUIRED CHARACTERS1 MICHAEL F. GUYER Some selectionists glibly assert that new characters arise as the result of spontaneous changes in the germ. What is meant by this ? 1 From M. F. Guyer, "Immune Sera and Certain Biological Problems," American Naturalist, Vol. LV (1921). ARE ACQUIRED CHARACTERS HEREDITARY? 339 Just what is a spontaneous change? No one has ever succeeded in telling us. And we may suspect, though perhaps it is heresy to do so, that it is a well-sounding phrase that is the equivalent of the three words, "I don't know." Unwilling to admit of the modifying influence of external agencies on the germ, such theorists resort to the fiction of a spontaneous change. Coleridge somewhere has said, "What's gray with age becomes religion." We have toyed so long with this idea of germinal continuity and the invulnerability of the germ, that it has become for some of us wellnigh sacrosanct. Living matter is living matter wherever it may be found, but when it happens to be in the germ-cells, verily, " this corruptible has put on incorruption and this mortal immortality"! Now, no one to-day, qualified by his knowledge of embryology and genetics to the right of an opinion, would, I think, deny that the new organism is in the main the expression of what was hi the germ- line, rather than of what it got directly from the body of its parents, but does this fact necessarily carry with it the implication that the germ is insusceptible to modification from without ? Is not the serum of organisms with blood or lymph an excellent medium through which external influences may operate upon it ? Is it not more reasonable to postulate the origination of germinal changes through some such mechanism as this than to attribute it to mysterious "spontaneous changes"? With such thoughts hi mind I and my research associate, Dr. E. A. Smith, set about making various tests. Without attempting to tell you of our as yet unsuccessful attempts to secure cytolysins which will operate in the developmental stages of such periodically renewed structures as feathers, or to weary you with the history of our various other failures — of which there are an abundance — I wish to speak briefly about certain antenatal effects we secured in rabbits by means of fowl-serum sensitized against rabbit crystalline lens, and of the fact that such induced defects may become heritable. The crystalline lens of the rabbit was selected as antigen, and fowls as the source of the antibodies. The lenses of newly killed rabbits were pulped thoroughly in a mortar and diluted with normal saline solution. About four cubic centimeters of this emulsion was then injected intraperitoneally or intravenously into each of several fowls. Four or five weekly treatments with such lens-emulsions were given. Then a week or ten days after the last injection the blood-serum of one or more of the fowls was used for injection into pregnant rabbits. The rabbits had been so bred as to have the young advanced to about 340 READINGS IN EVOLUTION, GENETICS, AND EUGENICS the tenth day of pregnancy, since from the tenth to the thirteenth day seems to be a particularly important period in the development of the lens. It is then growing rapidly and becomes surrounded by a rich vascular network that later disappears. From four to seven cubic centimeters of the sensitized fowl-serum were injected intravenously into the pregnant rabbits at intervals of two or three days for from ten days to two weeks. Several rabbits died from the treatment and many young were killed in utero. Of sixty-one surviving young from mothers thus treated, four had one or both eyes conspicuously defect- ive and five others had eyes which were clearly abnormal. It is possible that still others were more or less affected, since we judged only by obvious, visible effects. We found later hi some of the descendants of these individuals that rabbits which passed for normal during their earlier months subsequently manifested traces of defects in their lenses or in other parts of the eye. The commonest abnormality seen in both the original subjects and hi their descendants was partial or complete opacity of the lens, usually accompanied by reduction in size. Other defects were cleft iris, persistent hyaloid artery, bluish or silvery color instead of the characteristic red of the albino eye, microphthalmia and even almost complete disappearance of the eyeball. Taking into account the method of embryological development, however — the relation of lens, optic cup, and choroid fissure — the defects are probably all attributable to the early injury of the lens. In some cases, both among originals and descendants, an eye micr ophthalmic at birth may undergo fur- ther degeneration such as collapse of the ball and what appears to be a resorption as if some solvent were operating upon it. The eyes of the mothers apparently remained unaffected. This is probably due to the fact that the lens tissue of the adult rabbit is largely avascular and therefore did not come into contact with the injected anti- bodies. That the changes in the eyes of the fetuses resulted from the action of lens antibodies is indicated by the fact that in not one of the forty- eight controls obtained from mothers which had been treated with unsensitized fowl-serum or with fowl-serum sensitized to rabbit tissue other than lens, was there evidence of eye-defects, and I may add, that among the hundred or more young obtained later from mothers which were being experimented upon with various types of sera or protein extracts, for other purposes, not a single case of eye-defect has appeared. ARE ACQUIRED CHARACTERS HEREDITARY? 341 As already stated, once the anomaly is secured it may be trans- mitted to subsequent generations through breeding. So far we have succeeded in passing it to the eighth generation without any other than the original treatment. The imperfection, indeed, tends to become worse hi succeeding generations and also to occur in a proportionately greater number of young. Though not analyzed completely as to its exact mode of inheritance, it has in general, the characteristics of a Mendelian recessive. Like such anomalies as brachydactyly or poly- dactyly hi man, the transmission is not infrequently of an irregular, unilateral type, sometimes only the right, at others only the left eye showing the defect. In the later generations, probably hi some measure as the result of selective breeding, there is an increasing num- ber of young which have both eyes affected. To determine whether the reappearance of the defect was due merely to the passing on of antibodies or kindred substances from the blood stream of the mother, or to true inheritance, we mated defective- eyed males to normal females from strains of rabbits unrelated to our defective-eyed stock. The first generations produced hi this way were invariably normal-eyed, but when females of this generation were mated to defective-eyed males again, we secured defective-eyed young after the manner of an extracted Mendelian recessive. It is obvious that hi such cases the abnormality could only have been conveyed through the germ-cells of the male, and that it is, therefore, an example of true inheritance. Subsequent matings have shown that these young transmit the eye-anomalies as effectively as do individuals of the original lines. A new strain of defective-eyed young, estab- lished about the time our original paper went to press, is also flourish- ing and, as regards transmission of the defect, seems to differ in no way from the earlier stock. But now, let us inquire as to where all this leads. Without enter- ing into a discussion of just what, serologically, is taking place hi the body or in the germ of fetuses borne by the lens-treated mothers, the point I wish to emphasize is that a certain specific effect has been pro- duced; and, what is of greater moment, once the condition is estab- lished it may be not merely transmitted, but inherited. Whether the lens of the uterine young is first changed and then in turn induces a change hi the lens-producing antecedents hi the germ-cells of these young, or whether the specific antibody simultaneously affects the eyes and the germ-cells of the young is not clear. In any event it is evident that there is some constitutional identity between the 342 READINGS IN EVOLUTION, GENETICS, AND EUGENICS substance of the mature organ in question and the material ante- cedents of such an organ as it exists in the germ. Biologically considered, the most significant fact is that specific antibodies can induce specific modifications in the germ-cell. Whether these antibodies are transmitted from the mother's blood or engen- dered in that of the young would seem to be of secondary importance. It stands to reason that antibodies originated in an animal's own blood will modify germinal factors if corresponding antibodies introduced from without can accomplish this. The whole question as to how important such a fact may be in contributing to an understanding of the causes of the germinal changes in organisms hi general, which lead to variation and evolution, hinges on the question of whether changes in an animal's tissue will induce the formation of antibodies or kindred active substances in its own body. We have been steadily accumulating evidence that such react ions do occur. In our own laboratory, for example, after many attempts we have succeeded in securing a defective-eyed young rabbit from a mother of normal stock by injecting her repeatedly with pulped rabbit lens before and during pregnancy. Since the young rabbit in question has both eyes badly affected there can be no question that a rabbit can build antibodies against rabbit-tissue which are as effective as those engendered in a foreign species such as the fowl. We have likewise found it relatively easy to secure spermatoxins by directly injecting rabbits, both male and female, with rabbit spermatozoa. Moreover, a given male will develop antibodies against his own spermatozoa if he is injected intravenously with the latter. We are also securing evidence that serologic reactions induced in the fetus through operations on the mother are not mere passive trans- missions, but may become actively participated in by the tissues of the fetus. For example, female rabbits sensitized with typhoid vaccine followed by living typhoid germs may transmit to their young and even to their grand descendants the ability to agglutinate typhoid bacilli in serum diluted from 60 to 160 times. From the standpoint of heredity we have no reason so "Far for maintaining that this is anything but placental transmission, though we are going to practice immunization generation after generation for a number of generations to determine if a truly hereditary immunity will be established. How- ever, facts have come to light which show that there is more concerned in the operation than a mere transfer of antibodies from mother to ARE ACQUIRED CHARACTERS HEREDITARY? 343 fetus. For instance, the blood of young shortly after birth may show a higher titer than that of the mother. Again, after two or three months of development the young of certain of the sensitized mothers have shown a rather sudden rise in titer, much above that of the mothers. In such cases it would seem that some mechanism in the young rabbit itself is constructing antibodies which supplement those passively derived from the mother. Possibly in the process of develop- ment some organ important hi such reactions just came into function- ing. If this is true further experiments may throw some light on the perplexing question of the source or sources of the antibodies in an animal. After a few weeks, in such cases, the titer drops back again. In still another set of experiments we found that young from a sen- sitized mother, when nursed by a normal untreated mother, retained a fairly high titer for several months and even showed the rise of titer mentioned. On the other hand, young of an untreated mother when nursed by a sensitized mother acquired a fairly high titer from the milk of the foster mother but lost it rapidly after weaning time. Thus there are evidently constitutional factors operative in the young which have acquired their immunity through the placenta which are absent in the young whose antibodies were conveyed through food. That changes hi the blood serum may be caused by changed con- ditions hi the tissues is further attested by many facts. For example, in pregnancy, the newly forming placenta may set free cells or cell- products which, sometimes at least, cause changes in the blood-serum of the mother, though the exact nature of these changes is in dispute. Romer, using the complement-fixation technique, found that the serum of adult human beings may possess antibodies for their own lens proteins. Bradley and Sansum, employing anaphylactic reactions, found that guinea-pigs injected with guinea-pig tissue-proteins (liver, heart, muscle, testicle, kidney) develop immunity reactions. Again during the late war, the type of toxic action to which anaphylactic shock conforms was found to exist after extensive injury of the soft tissues. It resulted apparently from the absorption of poisonous substances of tissue origin into the circulation. In fact, various cells and tissues when injured liberate such poisons, and even blood hi clot- ting is known to acquire a transient toxicity of this type. With facts such as these before us, is it not a rational hypothesis to assume that changes in various parts of a body may on occasion influence the representatives of such parts in the germ-cells borne by that body? This appears all the more probable when we recall the 344 READINGS IN EVOLUTION, GENETICS, AND EUGENICS facts learned from a study of precipitins and of anaphylaxis that each species of animal has a thread of fundamental similarity underlying the proteins of all its tissues. There is no reason to suppose that germi- nal tissue forms an exception. The further fact that homologous tissues, though existing in different species of animals, possess similar chemical characteristics, shows that to get an effect there need not be absolute chemical identity between the substance of such a tissue as the lens and the germinal constituents of which it is the expres- sion. And if this is true for lens, why not for other tissues ? The blood-serum of any organism with blood thus affords a means of conveying the effects of changes in a parental organ to the germ- cell which contains the antecedent of such an organ. As long as there is little change in the somatic element its germinal correlative would presumably remain constant, but any alternations of the soma which give rise to the formation of anti-bodies or other active agents, par- ticularly if long continued, might induce changes in the germ. Such a hypothesis would seem to be plausible at least hi accounting for degenerative changes such as the deterioration of eyes in such forms as the mole, or in fact, hi the formation of vestigial organs in general. On the other hand, there is no reason to infer that changes induced in the blood-serum may not also be instrumental in leading to pro- gressive as well as regressive evolution. If we may have germinally destructive constituents engendered in the blood there is no valid reason for supposing that we may not also have constructive ones. When we learn more about what initiates and promotes growth in a part through exercise, or what causes hypertrophy of an organ, we may likewise find how corresponding germinal antecedents of that part may be enhanced. Until such time we shall probably remain in the dark regarding the mechanism of progressive germinal changes. As already indicated, in the hormones and chalones we have a wonderful series of secretions normally circulating in the blood and maintaining general physiological equilibrium. That reciprocal stimulations of various organs occur by this means is a well-established fact. Hyper- trophy or atrophy of an endocrine gland may produce pronounced effects in the furthermost reaches of the body. Again we may inquire, is it reasonable to suppose that the germinal tissues will be inviolate to all this ebb and flow of chemical influence ? Should we not expect specific reactions or selections here no less surely than in other tissues ? Destruction of the pars buccalis of the hypophysis in the frog-tadpole will cause profound alteration in other endocrine organs such as the . ARE ACQUIRED CHARACTERS HEREDITARY? 345 adrenals and thyroids, will retard the growth rate, render the entire organism albinous, and produce in the individual pigment cells a con- dition of sustained contraction. Shall we conclude that such a far- reaching influence as this, particularly in a developing organism, will pass the germ-cells by unscathed ? Similarly, growth in man is known to be controlled by a pituitary secretion that is carried by the blood to the various organs. The normal development of secondary sexual characters is determined by products from the testes or ovaries, and the activities of the generative organs themselves are ultimately associated with the functioning of the adrenal and other glands. The periods of ovulation are inhibited by secretions from the corpus luteum; lactation is incited by products of the corpus luteum, the involuting uterus and the placenta; the car- bohydrate metabolism in the liver and even in the most distant muscles is profoundly influenced by substances formed in the pan- creas; the pancreas, liver, and intestinal glands are set to secreting through the stimulus of a product formed in the duodenal and jejunal mucosae. And still others of such remarkable interrelations can be cited. Truly one may pronounce that social complex of reciprocating individuals termed cells which make up an organism, "members one of another." And with all of these co-operative activities of the various parts of the body it is inconceivable to me, at least, that the germ-cells, bathed in the same fluid, nourished with the same food, stand wholly apart. May we not surmise then that as regards inheritance and evolu- tion, Lamarck was not wholly in error when he stressed the importance of use and disuse of a part, or of modifications due to environmental change, in altering the course of the hereditary stream, particularly if we conceive of these influences as being prolonged, possibly over many generations ? Have we not in the serological mechanism of the body of animals an adequate means for the incitement of the germinal changes which underly certain aspects of evolution ? CHAPTER XXIV THE MUTATION THEORY [It will be recalled that Darwin, although depending upon the ever-present fluctuating variations as the material for natural selection to work upon, recognized the occasional occurrence of "sports" or "saltatory variations." These, however, seemed to him to be so rare in nature as to offer no adequate basis for selection. During the latter part of the nineteenth century several investigators, feeling the inadequacy of fluctuating variations to produce qualitatively new characters, decided to make a more careful examination of animals and plants in nature in order to discover whether saltatory variations might not be of more frequent occurrence than Darwin had supposed. In England William Bateson collected a large number of instances of a type of variation which he called discontinuous hi contradistinc- tion to the continuous type which we have been calling fluctuations. Such variations, instead of being in a closely graded series with the typical variations of a species, were frequently quite sharply different from the majority. Although no experiments were conducted in order to test the hereditability of these "discontinuous variations," it is probable that some of them were "mutations" in the sense of De Vries. At about the same time Hugo De Vries in Holland, probably as the result of his rediscovery of Mendel's work and his confirmation of the latter's laws of heredity, became convinced that new species arise not by the accumulation, through natural selection, of minute fluc- tuating variations, but by the sudden appearance in one generation of fully formed new elementary species. He began a systematic research for species of plants in nature that were giving rise to new species. Many species were examined in their natural surroundings and were then brought into the experimental garden for more careful observation, but for a long time the search for a species throwing off new elementary species was unsuccessful. Finally, however, in a field near Hilversum, in the vicinity of Amsterdam, he found what seemed to him to be just the kind of plant he had been looking for in the evening primrose (Oenothera lamarckiana) . 346 THE MUTATION THEORY 347 "Lamarck's evening-primrose" (Fig. 57), says De Vries, "is a stately plant, with a stout stem, attaining often a height of 1.6 meters and more. When not crowded the main stem is surrounded by a large FIG 57. — Ocnothera lamarckiana, the original type used by DeVries in his experiments. This is the stock from Hilversum, from which arose in successive generations a series of mutants. (From De Vries,) 348 READINGS IN EVOLUTION, GENETICS, AND EUGENICS circle of smaller branches, growing upwards from its base so as to form a dense brush The flowers are large and bright yellow attract- ing immediate attention even from a distance. They open toward evening, as the name indicates, and are pollinated by bumble-bees and moths." On account of the classic character of De Vries's mutants of Oenothera lamarckiana we shall follow his own detailed description of the more significant of these. — ED.] NEW SPECIES (MUTANTS) OF OENOTHERA* HUGO DE VRIES This striking species (Oenathera lamarckiana) was found in a locality near Hilversum, in the vicinity of Amsterdam, where it grew in some thousands of individuals. Ordinarily biennial, it produces rosettes in the first, and stems in the second year. Both the stems and the rosettes were at once seen to be highly variable, and soon distinct varieties could be distinguished among them. The first discovery of this locality was made in 1886. Afterwards I visited it many tunes, often weekly or even daily during the first few years, and always at least once a year up to the present time. This stately plant showed the long-sought peculiarity of producing a number of new species every year. Some of them were observed directly on the field, either as stems or as rosettes. The latter could be transplanted into my garden for further observation, and the stems yielded seeds to be sown under like control. Others were too weak to live a sufficiently long tune in the field. They were discovered by sowing seed from indifferent plants of the wild locality in the garden. A third and last method of getting still more new species from the original strain was the repetition of the sowing process, by saving and sowing the seed which ripened on the introduced plants. These various methods have led to the discovery of over a dozen new types never previously observed or described. Leaving the physiological side of the relations of these new forms for the next lecture, it would be profitable to give a short description of the several novelties. To this end they may be combined under five different heads, according to their systematic value. The first head includes those which are evidently to be considered as varieties, 1 From H. De Vries, Species and Varieties (copyright 1904). Used by special permission of the publishers, The Open Court Publishing Company. THE MUTATION THEORY 349 in the narrower sense of the word, as previously given. The second and third heads indicate the real progressive elementary species, first those which are as strong as the parent-species, and secondly a group of weaker types, apparently not destined to be successful. Under the fourth head I shall include some inconstant forms, and under the last head those that are organically incomplete. Of varieties with a negative attribute, or real retrograde varieties, I have found three, all of them hi a flowering condition hi the field. I have given them the names of laewfolia, brevistylis and nannella. The laevifolia, or smooth-leaved variety, was one of the very first deviating types found in the original field. This was hi the summer of 1887, seventeen years ago. It formed a h'ttle group of plants grow- ing at some distance from the main body, in the same field. I found some rosettes and some flowering stems and sowed some seed in the . fall. The variety has been quite constant in the field, neither increas- ing in number of individual plants nor changing its place, though now closely surrounded by other lamarckianas. In my garden it has proved to be constant from seed, never reverting to the original lamarckiana, provided intercrossing was excluded. It is chiefly distinguished from Lamarck's evening-primrose by its smooth leaves, as the name indicates. The leaves of the original form show numerous sinuosities in their blades, not at the edge, but anywhere between the veins. The blade shows numbers of convexi- ties on either surface, the whole surface being undulated in this manner; it lacks also the brightness of the ordinary evening-primrose or Oenothera biennis. These undulations are lacking or at least very rare on the leaves of the new laevifolia. Ordinarily they are wholly wanting, but at tunes single leaves with slight manifestations of this character may make their appearance. They warn us that the capacity for such sinuosities is not wholly lost, but only lies dormant in the new variety. It is reduced to a latent state, exactly as are the apparently lost characters of so many ordinary horticultural varieties. Lacking the undulations, the laevifolia-leswes are smooth and bright. They are a little narrower and more slender than those of the lamarckiana. The convexities and concavities of leaves are a useful character in dry seasons, but during wet summers, such as those of the last few years, they must be considered as very harmful, as they retain some of the water which falls on the plants, prolonging the action of the water on the leaves. This is considered by some writers 350 READINGS IN EVOLUTION, GENETICS, AND EUGENICS to be of some utility after slight showers, but was observed to be a source of weakness during wet weather in my garden, preventing the leaves from drying. Whether the laevifolia would do better under such circumstances, I have, however, omitted to test. The flowers of the laevifolia are also in a slight degree different from those of lamarckiana. The yellow color is paler and the petals are smoother. Later, in the fall, on the weaker side branches these differences increase. The laevifolia petals become smaller and are devoid of the emargination at the apex, becoming ovate instead of obcordate. This shape is often the most easily recognized and most striking mark of the variety. In respect to the reproductive organs, the fertility and abundance of good seed, the laevifolia is by no means inferior or superior to the original species. 0. brevistylis, or the short-styled evening-primrose, is the most curious of all my new forms. It has very short styles, which bring the stigmas only up to the throat of the calyx-tube, instead of upwards of the anthers. The stigmas themselves are of another shape, more flattened and not cylindrical. The pollen falls from the anthers abundantly on them, and germinates in the ordinary manner. The ovary which in lamarckiana and in all other new forms is wholly underneath the calyx-tube, is here only partially so. This tube is inserted at some distances under its summit. The insertion divides the ovary into two parts: an upper and a lower one. The upper part is much reduced in breadth and somewhat attenuated, simulating a prolongation of the base of the style. The lower part is also reduced, but hi another manner. At the time of flowering it is like the ovary of lamarckiana, neither smaller nor larger. But it is only reached by very few pollen-tubes, and is therefore always very incompletely fertilized. It does not fall off after the fading away of the flower, as unfertilized ovaries usually do; neither does it grow out, nor assume the upright position of normal capsules. It is checked in its develop- ment, and at the time of ripening it is nearly of the same length as in the beginning. Many of them contain no good seeds at all; from others I have succeeded hi saving only a hundred seeds from thousands of capsules. These seeds, if purely pollinated, and with the exclusion of the visits of insects, reproduce the variety entirely and without any reversion to the lamarckiana type. Correlated with the detailed structures is the form of the flower- buds. They lack the high stigma placed above the anthers, which in THE MUTATION THEORY 351 the lamarckiana, by the vigorous growth of the style, extends the calyx and renders the flower-bud thinner and more slender. Those of the brevistylis are therefore broader and more swollen. It is quite easy to distinguish the individuals by this striking character alone, although it differs from the parent hi other particulars. The leaves of the 0. brevistylis are more rounded at the tip, but the difference is only pronounced at times, slightly in the adult rosettes, but more clearly on the growing summits of the stems and branches. By this character the plants may be discerned among the others some weeks before the flowers begin to show themselves. But the character by which the plants may be most easily recog- nized from a distance in the field is the failure of the fruits. They were found nearly every year in varying, but always small numbers. Leaving the short-styled primrose, we come now to the last of our group of retrograde varieties. This is the 0. nannella, or the dwarf, and is a most attractive little plant. It is very short of stature, reaching often a height of only 20-30 cm., or less than one-fourth of that of the parent. It commences flowering at a height of 10-15 cm-> while the parent-form often measures nearly a meter at this stage of its development. Being so very dwarfed the large flowers are all the more striking. They are hardly inferior to those of the lamarckiana, and agree with them in structure. When they fade away the spike is rapidly lengthened, and often becomes much longer than the lower or vegetative part of the stem. The dwarfs are one of the most common mutations in my garden, and were observed in the native locality and also grown from seeds saved there. Once produced they are absolutely constant. I have tried many thousands of seeds from various dwarf mutants, and never observed any trace of reversion to the lamarckiana type. I have also cultivated them in successive generations with the same result. In a former lecture we have seen that contrary to the general run of horticultural belief, varieties are as constant as the best species, if kept free from hybrid admixtures. This is a general rule, and the ex- ceptions, or cases of atavism, are extremely rare. In this respect it is of great interest to observe that this constancy is not an acquired quality, but is to be considered as innate, because it is already fully developed at the very moment when the original mutation takes place. From its first leaves to the rosette period, and through this to the lengthening of the stem, the dwarfs are easily distinguished from any other of their congeners. The most remarkable feature is the shape 3$2 READINGS IN EVOLUTION, GENETICS, AND EUGENICS THE MUTATION THEORY 353 of the leaves. They are broader and shorter, and especially at the base they are broadened in such a way as to become apparently sessile. The stalk is very brittle, and any rough treatment may cause the leaves to break off. The young seedlings are recognizable by the shape of the first two or three leaves, and when more of them are produced, the rosettes become dense and strikingly different from others. Later leaves are more nearly like the parent-type, but the petioles remain short. The bases of the blades are frequently almost cordate, the laminae themselves varying from oblong-ovate to ovate in outline. The stems are often quite unbranched, or branched only at the base of the spike. Strong secondary stems are a striking attribute of the lamarckiana parent, but they are lacking, or almost so in the dwarfs. The stem is straight and short, and this, combined with the large crown of bright flowers, makes the dwarfs eminently suitable for bed or border plants. Unfortunately they are very sensitive, especially to wet weather. Oenothera gigas and 0. rubrinervis, or the giant, and the red-veined evening primroses, are the names given to two robust and stout species, which seem to be equal hi vigor to the parent-plant, while diverging from it in striking characters. Both are true elementary species, differentiated from lamarckiana in nearly all their organs and qualities, but not showing any preponderating character of a retrograde nature. Their differences may be compared with those of the elemen- tary species of other genera, as for instance, of Draba, or of violets, as will be seen by then* description. The giant evening-primrose, though not taller in stature than 0. lamarckiana, deserves its name because it is so much stouter in all respects. The stems are robust, often with twice the diameter of lamarckiana throughout. The internodes are shorter, and the leaves more numerous, covering the stems with a denser foliage. This shortness of internodes extends itself to the spike, and for this reason the flowers and fruits grow closer together than on the parent-plant. Hence the crown of bright flowers, opening each evening, is more dense and more strikingly brilliant, so much the more so as the individual flowers are markedly larger than those of the parents. In connection with these characters, the flower-buds are seen to be much stouter than those of lamarckiana. The fruits attain only half the normal size, but are broader and contain fewer, but larger seeds. 354 READINGS IN EVOLUTION, GENETICS, AND EUGENICS The rubrinervis is in many respects a counterpart to the gigas, but its stature is more slender. The spikes and flowers are those of the lamarckiana, but the bracts are narrower. Red veins and red streaks on the fruits afford a striking differentiating mark, though they are not absolutely lacking in the parent-species. A red hue may be seen on the calyx, and even the yellow color of the petals is somewhat deepened in the same way. Young plants are often marked by the pale red tinge of the mid-veins, but in adult rosettes, or from lack of sunshine, this hue is often very faint. The leaves are narrow, and a curious feature of this species is the great brittleness of the leaves and stems, especially on annual indi- viduals, for example, on those that make their stem and flowers in the first year. High turgidity and weak development of the mechani- cal and supporting tissues are the anatomical cause of this deficiency, the bast-fibres showing thinner walls than those of the parent-type under the microscope. Young stems of rubrinervis may be broken off by a sharp stroke, and show a smooth rupture across all the tissues, while those of lamarckiana are very tough and strong. Both the giant and the red-veined species are easily recognized in the rosette-stage. The very young seedlings of the latter are not clearly differentiated from the lamarckiana, and often a dozen leaves are required before the difference may be seen. Under ordinary circumstances the young plants must reach an age of about two months before it is possible to discern their characters, or at least before these characters have become reliable enough to enable us to judge of each individual without doubt. But the divergencies rapidly become greater. The leaves of 0. gigas are broader, of a deeper green, the blade more sharply set off against the stalk, the whole rosettes becoming stout and crowded with leaves. Those of 0. rubri- nervis on the contrary are thin, of a paler green and with a silvery white surface; the blades are elliptic, often being only 2 cm. or less in width. They are acute at the apex and gradually narrowed into the petiole. It is quite evident that such pale narrow leaves must produce smaller quantities of organic food than the darker green and broad organs of the gigas. Perhaps this fact is accountable partly, at least, for the more robust growth of the giant in the second year. Perhaps also some relation exists between this difference in chemical activity and the tendency to become annual or biennial. The gigas, as a rule, produces far more, and the rubrinervis far less biennial plants, than the lamarckiana. Annual culture for the one is as unreliable as THE MUTATION THEORY 355 biennial culture for the other. Rubrinervis may be annual in appar- ently all specimens, in sunny seasons, which would allow a large part of the gigas to remain in the state of rosettes during the entire first summer. It would be very interesting to obtain a fuller insight into the relation of the length of life to other qualities, but as yet the facts can only be detailed as they stand. Both of these stout species have been found quite constant from the very first moment of their appearance. I have cultivated them from seed in large numbers, and they have never reverted to the lamarckiana. From this they have inherited the mutability or the capacity of producing in their turn new mutants. But they seem to have done so incompletely, changing in the direction of more absolute constancy. This was especially observed in the case of rubrinervis, which is not of such rare occurrence as 0. gigas, and which it has been possible to study in large numbers of individuals. So for instance, "the red- veins" have never produced any dwarfs, notwithstanding they are produced very often by the parent-type. And in crossing experiments the red-veins gave proof of the absence of a mutative capacity for their production. [Besides the mutants just described there occurred two weak forms that could survive only if reared under protection and would have failed to survive in nature. Here we have a place for the action of natural selection, but operating with mutations instead of with fluctuating variations. These two mutants are " the whitish and the oblong-leaved evening-primroses or the Oenothera albida and oblonga." All of the mutants so far mentioned are constant forms that breed true to type. Certain other types were either incapable of being bred or else were decidedly inconstant. Oenothera lata had only pistillate flowers and therefore could not be fertilized by pollen of the same mutant. Oenothera scintillous and 0. elliptica are fertile to their own pollen, but produce progeny only partly like the parent, the rest reverting to the original typeflenothera lamarckiana. — ED.] SUMMARY OF DE VRIES'S MUTATION THEORY1 THOMAS HUNT MORGAN We may now proceed to examine the evidence from which De Vries has been led to the general conclusions given in the preceding pages. De Vries found at Hilversum, near Amsterdam, a locality *T. H. Morgan, Evolution and Adaptation (1903). Used by special permission of the publishers, The Macmillan Company. 356 READINGS IN EVOLUTION, GENETICS, AND EUGENICS where a number of plants of the evening primrose, Oenothera lamarck- iana, grow in large numbers. This plant is an American form that has been imported into Europe. It often escapes from cultivation, as is the case at Hilversum, where for ten years it had been growing wild. Its rapid increase in numbers in the course of a few years may be one of the causes that has led to the appearance of a mutation period. The escaped plants showed fluctuating variations in nearly all of their organs. They also had produced a number of abnormal forms. Some of the plants came to maturity in one year, others in two, or in rare cases, in three, years. A year after the first finding of these plants De Vries observed two well-characterized forms, which he at once recognized as new elemen- tary species. One of these was 0. brevistylis, which occurred only as female plants. The other new species was a smooth-leafed form with a more beautiful foliage than 0. lamarckiana. This is 0. laevifolia. It was found that both of these new forms bred true from self- fertilized seeds. At first only a few specimens were found, each form in a particular part of the field, which looks as though each might have come from the seeds of a single plant. These two new forms, as well as the common 0. lamarckiana, were collected, and from these plants there have arisen the three groups of families of elementary species that De Vries has studied. In his garden other new forms also arose from those that had been brought under cultivation. The largest group and the most important one is that from the original 0. lamarckiana form. The accompanying table shows the mutations that arose between 1887 and 1899 from these plants. The seeds were selected in each case from self -fertilized plants of the lamarckiana form, so that the new plants appearing in each horizontal line are the descendants hi each generation of lamarckiana parents. It will be observed that the species, 0. oblonga, appeared again and again in considerable numbers, and the same is true for several of the other forms also. Only the two species, 0. gigas and 0. scintillans, appeared very rarely (Fig. 59). Thus De Vries had, in his seven generations, about fifty thousand plants, and about eight hundred of these were mutations. When the flowers of the new forms were artificially fertilized with pollen from the flowers of the same plant, or of the same kind of plant, they gave rise to forms like themselves, thus showing that they are true elemen- tary species. It is also a point of some interest to observe that all these forms differed from each other hi a large number of particulars. THE MUTATION THEORY 357 Only one form, 0. scintillans, that appeared eight times, is not constant as are the other species. When self-fertilized its seeds produce always three other forms, O. scintillans, O. oblonga, and O. lamarckiana. It differs in this respect from all the other elementary species, which mutate not more than once in ten thousand individuals. Genera- 0. rubri- OJ.amarck- 0. scintil- tions 0. gigas O. alblda 0. oblonga nervis iana 0. nandla 0. lala. lans Gen. 8 1899 Gen. 7 Gen. 6 1897 Gen. 5 1896 Gen. 4 1895 Gen. 3 1890-91 Gen. 2 1888-89 Gen. i 1886-87 .5 1 0 1700 21 1, .9 0 3700 11. ~TTZ .11 2,9 3 1800 9 5 I ~J .25 135 20 ^000 49 142 6, ] .1 15 176 8 J4000 60 75 L .1 10000 3 3, - _.J__, .15000 5 K JL~ 1 Mutants and Number obser different years O. Lamarck- Mutants and Number iana observed in different years The mu- tating stem form FIG. 59. — Diagram showing in condensed form the genealogy of the Oenothera Lamarckiana family and its various mutants during successive years. The numbers under each type represent the number of new types observed each year. (From Tower.) From the seeds of one of the new forms, 0. laevifolia, collected in the field, plants were reared, some of which were O. lamarckiana and others O. laevifolia. They were allowed to grow together, and their descendants gave rise to the same forms found in the lamarckiana 358 READINGS IN EVOLUTION, GENETICS, AND EUGENICS family, described above, namely, 0. lata, elliptica, nannella, rubri- nervis, and also two new species, 0. spatulata and leptocarpa. In the lata family, only female flowers are produced, and, there- fore, in order to obtain seeds they were fertilized with pollen from other species. Here also appeared some of the new species already mentioned, namely, albida, nannella, lata, oblonga, rubrinervis, and also two new species, elliptica and subovata. De Vries also watched the field from which the original forms were obtained, and found there many of the new species that appeared under cultivation. These were found, however, only as weak young plants that rarely flowered. Five of the new forms were seen either in the Hilversum field, or else raised from seeds that had been collected there. These facts show that the new species are not due to cultiva- tion, and that they arise year after year from the seeds of the parent form, 0. lamarckiana. Conclusions. — From the evidence given in the preceding pages it appears that the line between fluctuating variations and mutations may be sharply drawn. If we assume that mutations have furnished the material for the process of evolution, the whole problem appears hi a different light from that in which it was placed by Darwin when he assumed that the fluctuating variations are the kind which give the material for evolution. From the point of view of the mutation theory, species are no longer looked upon as having been slowly built up through the selec- tion of individual variations, but the elementary species, at least, appear at a single advance, and fully formed. This need not neces- sarily mean that great changes have suddenly taken place, and in this respect the mutation theory is in accord with Darwin's view that extreme forms that rarely appear, "sports," have not furnished the material for the process of evolution. As De Vries has pointed out, each mutation may be different from the parent form in only a slight degree for each point, although all the points may be different. The most unique feature of these muta- tions is the constancy with which the new form is inherited. It is this fact, not previously fully appreciated, that De Vries's work has brought prominently into the foreground. There is another point of great interest in this connection. Many of the groups that Darwin recognized as varieties correspond to the elementary species of De Vries. These varieties, Darwin thought, are the first stages in the formations of species, and, in fact, cannot be separated from species in most cases. The main difference between the selection theory and THE MUTATION THEORY 359 the mutation theory is that the one supposes these varieties to arise through selection of individual variations, the other supposes that they have arisen spontaneously and at once from the original form. The development of these varieties into new species is again sup- posed, on the Darwinian theory, to be the result of further selection, on the mutation theory, the result of the appearance of new muta- tions. In consequence of this difference in the two theories, it will not be difficult to show that the mutation theory escapes some of the gravest difficulties that the Darwinian theory has encountered. Some of the advantages of the mutation theory may be briefly mentioned here. 1. Since the mutations appear fully formed from the beginning, there is no difficulty in accounting for the incipient stages in the development of an organ, and since the organ may persist, even when it has no value to the race, it may become further developed by later mutations and may come to have finally an important relation to the life of the individual. 2. The new mutations may appear in large numbers, and of the different kinds those will persist that can get a foothold. On account of the large number of times that the same mutations appear, the danger of becoming swamped through crossing with the original form will be lessened in proportion to the number of new individuals that arise. 3. If the time of reaching maturity in the new form is different from that hi the parent forms, then the new species will be kept from crossing with the parent form, and since this new character will be present from the beginning, the new form will have much better chances of surviving than if a difference in time of reaching maturity had to be gradually acquired. 4. The new species that appear may be in some cases already adapted to live hi a different environment from that occupied by the parent form; and if so, it will be isolated from the beginning, which will be an advantage in avoiding the bad effects of intercrossing. 5. It is well known that the differences between related species consist largely in differences of unimportant organs, and this is in harmony with the mutation theory, but one of the real difficulties of the selection theory. 6. Useless or even slightly injurious characters may appear as mutations, and if they do not seriously affect the perpetuation of the race, they may persist. 360 READINGS IN EVOLUTION, GENETICS, AND EUGENICS CRITICISMS [Oenothera lamarckiana has fallen under suspicion of being of impure stock due to the crossing of two or more original species. The basis for this suspicion is that the type found in Holland is not a truly wild indigenous species, but a domestic type escaped from cultivation. It seems probable that the species was imported from America a great many years ago. B. M. Davis has succeeded in producing by cross- ing two American wild species a hybrid form distinctly resembling Oenothera lamarckiana in numerous respects, and this hybrid, like any other hybrid, produces numerous combinations of the parental charac- ters when inbred, and these hybrid progeny sometimes resemble the mutants observed by De Vries. It is also said that the pollen grains of Oenothera lamarckiana exhibit a high degree of sterility, which is a characteristic defect of hybrid plants. Whether or not, however, the Oenothera situation be taken as valid evidence of the occurrence of mutations, the idea of mutations and their role in evolution will stand up on quite independent grounds. Numerous mutations have been observed in all sorts of animals and plants. Professor T. H. Morgan and his able corps of collaborators have observed in their carefully controlled breeding experiments with the fruit fly Drosophila melanogaster hundreds of suddenly appearing new characters which are classed by them as mutants, and whose heredity has been most accurately studied. These mutants involve single characters of the organism which are sometimes of a prominent and readily recognizable sort and sometimes of so slight a degree as to be imperceptible except to the trained eye of the expert student of genetics. It also frequently occurs that two mutants are to the eye practically identical, but may be distinguished by differences in hereditary behavior. The great majority of the mutants discovered in Drosophila are termed "lethals" because they involve the death of the mutants possessing the variation. A further discussion of Drosophila "mutants" appears in a later chapter. — ED.] CAUSES OF MUTATIONS [Various mutations have been produced experimentally by subject- ing the germ cells to radically changed environmental conditions. VV. L. Tower claims to have produced at least two new elementary species of potato beetle by subjecting the already grown and unchange- able parents to radically changed temperature and humidity conditions. Although the parents could undergo no change themselves they THE MUTATION THEORY 361 produced a small number of offspring with distinctly changed charac- ters. These turned out to be mutants because they bred true to the new characters. Three of Tower's mutants of the potato beetle (Leptinotarsa decemlineata) are shown in Figure 60. MacDougal injected into the ovules of various species of plants such foreign materials as solutions of zinc salts, cane sugar, etc. The seeds produced from these plants developed into plants with radically FIG. 6c. — Some divergent types (mutations) of beetles produced by subject- ing the germ cells to external influences. A, normal decemlineata; B, the form pallida; C, tortuosa; D, defectopunctata. (From Tower.) new characters (Fig. 61) which bred true to type for four or more gener .tions. Whether or not the changes persisted longer we do not kno\ , since MacDougal has not published any further details. Gager discovered that the action of radium rays on the pollen grains of various plants had a profound effect upon the chromatin. Seme of the latter was apparently lost during mitotic cell division. 362 READINGS IN EVOLUTION, GENETICS, AND EUGENICS The same writer exposed the ovules of plants to radium rays and pro- duced marked changes in the germ cells so that they grew into various stunted and otherwise abnormal plants, some of which bred true for several generations. The work was not followed long enough to determine whether the change was one involving a rather prolonged induction or was a permanent mutation. — ED.] FIG. 61. — Two plants of Onagra bicnnis, showing the effect of injections of zinc sulphate into the ovule. A, normal; B, the modified plant, which arose from seeds that had been modified by zinc sulphate. (From MacDougal.) THE MUTATION THEORY 363 "Baur's third category of variations," say Babcock and Clausen,1 "comprises all inheritable changes due to causes other than segregation and recombination of genetic factors. Although comparatively little is known concerning the specific causes of mutations, yet it is possible to distinguish between two general classes of such inheritable varia- tions according to the nature of the genetic units involved. These classes are (i) alterations in genetic factors, and (2) deviations in the number of chromosomes. We designate the first group as factor mutations and the second as chromosome aberrations. Since the first group is of vastly greater importance to agriculture than the second, we shall consider the latter very briefly before engaging hi discussion of the former, which we deem worthy of recognition as mutations in the strict sense. "Chromosome aberrations. — By the aid of cytology it has been demonstrated that inheritable changes are occasionally induced, in plants at least, by irregularities in the behavior of the chromosomes during mitosis or meiosis, such that certain germ cells contain fewer or more chromosomes than the number typical of the species. Aber- rant forms in several plant families are now known to differ from the parent species in chromosome number. Some have only a single chromosome more or less than the parent, while a few are known in which the original number is doubled. It is possible that aberrations occur involving all combinations of numbers between these two extremes. In various forms of Lamarck's evening primrose (Oenothera lamarckiana) , whose typical number is 14, according to Gates the following aberrant numbers have been reported — 15, 20, 21, 22, 23, 27, 28, 29, 30. Aberrations involving the doubling of the number of chromosomes typical of the species is known as tetraploidy because there are four times the haploid number typical of the parent. Oc- casionally aberrations or hybridization between diploid and tetraploid forms result in triploidy. "There is a limited amount of evidence which indicates that groups of species have arisen by progressive alterations in chromosome number. Thus in Drosophila, Metz has found ten species in which the chromosome numbers range from 6 to 12 and the larger numbers appear to have arisen by subdivision of the large dumbbell-shaped chromosomes found in the species having smaller numbers. Evidence that doubling of the chromosome number may occur during somato- genesis has been found by Farmer and Digby in the interesting hybrid, 1 From E. B. Babcock and R. E. Clausen, Genetics in Relation to Agriculture (copyright 1918). Used by special permission of the publishers, The McGraw- Hill Book Company. 364 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Primula kewensis. The original plant, which was sterile, 'had 18 and 9 chromosomes in its premeiotic and postmeiotic nuclei respec- tively,' but in the fertile plants which were propagated asexually from it, as well as in similar fertile hybrids which were produced in later experiments, the diploid and haploid numbers were 36 and 18 respectively. Having found by means of careful measurements of the chromosomes in the two forms that the nuclei in both forms contain the same volume of chromatin, the authors conclude that the increase in number may be attributed to transverse fission of the 18 larger chromosomes and not to the fusion of two nuclei. "From a study of chromosomal dimensions in relation to phylo- geny, Meek 'arrived at the conclusion that the widths of chromosomes are successively greater in higher zoological phyla, and that this dimension is constant for very large groups of animals.' But Farmer and Digby have shown that such a conclusion is without foundation since 'closely related form's may possess chromosomes diff ering widely in shape and size and character.' Hence they conclude 'that phylo- genetic affinity is not, necessarily, correlated with chromosome width.' They also point out that 'unfortunately we know practically nothing about the phylogeny of the chromosomes. No convincing hypothesis has been put forward to explain how these remarkable bodies have become organized, nor how their peculiarities have either been brought into existence or are kept so true for a given species.' However, we are reminded by Glaser that chromatin is present in bacteria though not in the form of a nucleus and it may not be too much to hope that cytology may yet discover the principal stages in the development of the chromosomes and establish such correlation as may exist between this development and organic evolution. Certainly extended investi- gations of chromosome numbers must be made before chromosome aberrations can be considered an important factor in evolution. Except that certain chromosome aberrations, such a tetraploidy causing gigantism, might be of economic value, in general this class of mutations is of minor importance in breeding." [Conclusion. — In bringing this discussion of the causes of heritable variations (mutations) to a close, we find ourselves in a somewhat pessimistic frame of mind. When all is said, it is found that our knowledge of what actually causes mutations is almost nothing. We think we know something about the mechanism of heredity, but we do not know the mechanism of variation. The really great evolution- ary discovery of the future will probably be the finding out of the cause or the causes of mutations. — ED.] CHAPTER XXV BIOMETRY (THE STATISTICAL STUDY OF VARIATION AND HEREDITY) THE STATISTICAL STUDY OF VARIATION H. H. NEWMAN The pioneer workers in the application of statistical methods to biological study were Sir Francis Galton and his leading disciple, Karl Pearson. The use to which Galton and Pearson put their statistical methods appears later in this chapter. For present purposes we may limit our study of biometry to that part of it which has to do with variation. We have already discussed fluctuating variations, the small plus and minus differences that exist between the different mem- bers of the same species or variety. This was the type of variation that Darwin considered the main raw material of evolution. Exam- ples of fluctuating variations are not far to seek. Pearson cites as an illustration of fluctuating variation the number of veins in two sets of beech leaves, each set from a different tree: Number of veins *3 14 15 16 17 T8 19 20 First tree i 4 7 9 4 I 26 Second tree R 2 ?6 Total 12 4 i It will be noted that though there were i6-veined leaves on both trees, as well as 15- and ly-veined, the general distribution is quite different in the two trees. In the first tree the most frequently occur- ring type is the i8-veined leaf, and the other types may be said to fluctuate about this (the "mode"). In the second tree the mode is the i5-veined type and the other types fluctuate about it. It will be seen also at a glance that the types that differ most from the mode are the least frequent and that those nearest the mode are the most fre- quent. Some years ago the writer had occasion to study the heredity of scale numbers in the banded region of the nine-banded armadillo. As a preliminary to this study it was necessary to know the degree and 365 366 READINGS IN EVOLUTION, GENETICS, AND EUGENICS extent of variability present in the species. Consequently 508 indi-. viduals were taken at random and their scale or scute number counted. It was found that the total number of scutes in the nine bands ranged from 517 to 625 and that the commonest number was about 557. In order to get a definite idea of the distribution of the different types, FIG. 62. — Polygon of variation for the total number of scutes in the nine bands of the armadillo (Dasypus novcmcinctus), as determined by the seriation of 508 individuals. Class range = 8 scutes. The solid line represents the observa- tional, and the broken line the theoretical, normal curve. The abscissae refer to the number of scutes, and the ordinates to the number of individuals. (From Newman.} they were arranged in a variation polygon as shown in Figure 62. On the abscissa are arranged groups including individuals between 517 and 524 scutes inclusive, those between 525 and 532, those between 533 and 540, on up to a group of those from 621 to 625. All of these except the last included a small class with a range of 8 scutes. This arranging in classes was essential, for without it there would have been BIOMETRY 367 1 13 classes and a very irregular and meaningless distribution. On the ordinate we find by tens the numbers of individuals in each class. It will be noted that the solid line is one connecting the points of inter- section between the class of scute numbers and the number of indi- viduals in these classes. The dotted line represents an ideal fluctuat- ing variation curve, which is practically a mathematical curve of chance. The closeness of fit between the actual and the theoretical curve is very good. The mode is the class including individuals with a scute count of 557-64, and there is a fairly even balance of individuals in the plus and the minus directions. It seems fairly evident from examination of the curve that the individuals with 613 scutes and over are beyond the limits of the theoretical distribution. A further study of these exceptional individuals shows that they are mutations, in which a splitting up of single scutes into paired and twinned scutes has taken place to such an extent as greatly to increase the total num- ber of scutes. From the data used hi constructing this variation polygon several significant constants may be obtained. The "arithmetical mean" (average number of scutes hi the entire 508 individuals) is 558.2. The "median" or halfway point between the extremes is 558. The "mode"' or most frequently occurring single type is 557 (the theoreti- cal value being 557.6). If we wished to compare a large group of parents with a large group of offspring, or if it were necessary to compare the armadillos of Texas with those of Mexico or Brazil, we could compare them as to mean, median, and mode, and also as to the shape of the polygon of variation. This would give us a very good idea as to whether or not the old species present in these three regions is tending to evolve hi different directions under different conditions of life. Instead of having to depend on the visual comparison between the variation polygon of two or more different populations, we can reduce the facts about the distribution of the different types about the mean or mode to a simple arithmetical constant, called the "standard deviation," which is usually given the symbol a. This constant is computed as follows: •nl In this formula * represents the deviation of each class from the arithmetical mean; /, the number of individuals in each separate class; 2, the sum of all the classes, and n, the total number of individuals. 368 READINGS IN EVOLUTION, GENETICS, AND EUGENICS By the use of this formula we have calculated the standard devia- tion (cr) of the individuals represented in Figure 62 to be 14.89 ± 0.31 scutes. This means that the average deviation from the mean is about 14.89 scutes. The ='=0.31 scutes is called the "probable error" and means that the figure 14.89 is inaccurate to the extent of being 0.31 scutes too high or too low. The probable error is an essential feature of such computations, as, without it, we would not be able to rely on the signifi- cance of small differences. Suppose, for example, we should find that the armadillos of Brazil had a standard deviation of 15.43 ±0.44 scutes, we might conclude that the variability of the Brazilian individuals was 0.54 scutes greater than that of the Texas individuals. In view of the fact, however, that the probable error in one case is ±0.31 scutes and in the other=fco.44 scutes we would have to conclude that there was no significant difference. In actual practice it has been decided that unless the actual difference between two constants is about 4.6 times as great as the probable error, the difference is not significant. The method of determining the probable error of any calculated constant is difficult to understand, but easy to put into practice. For example, the formula for calculating the probable error of the standard deviation is as follows: ±0.6745* Ea- / V2H where E is the probable error, and n the number of individuals. It will be seen that the probability of error diminishes steadily with the increase in number of individuals studied. With very large numbers the error due to what is known as "random sampling" practically disappears. BIMODAL AND MULTIMODAL CURVES If we confine our biometrical studies to homogeneous populations, we get only fairly simple monomodal curves that resemble the normal curve of variation, which is a curve of chance; but when we study ordinary wild populations, we frequently find that we are dealing with a complex of several races, each of which has its own mode and stand- ard deviation. Bateson has given us a classic example of this type of phenomenon. In studying the length of pinchers in the common earwig (Forficulata auricularia) , he found that he got a two-humped or bimodal curve as shown in Figure 63. It then became evident that there were two distinct varieties as figured above. Such studies have frequently revealed the heterogeneity of supposedly homogeneous BIOMETRY 369 populations. Opinion differs as to the significance of these findings. The more optimistic evolutionists look upon such instances as that of Bateson's earwigs as visual demonstrations of a species actually split- ting up into two or more species. It seems quite likely that one of these types is a successful mutant type that has not fully segregated itself as a true species from the parent-type. Another view of the significance of bimodal curves is that the condition results from hybridi- zation and that the bimodality is the result of the segregation of dominant and recessive types. FIG. 63. — Bimodal polygon plotted from data on the earwig. Mean types ( X f ) indicated above corresponding modes. Numbers below the base line indicate length of pincers in millimeters. (From Bateson and Johannsen.) THE COEFFICIENT OF CORRELATION Only one more biometrical constant need be mentioned here: the "coefficient of correlation." It is often necessary to discover the exact relation that exists between two sets of variables in order to discover whether they are totally independent or partially correlated with each other. For example, we have found that there is a close correlation between stature and head length in man, also between color of hau: and color of eyes; but it is very important to be able to reduce the degree of correlation to a simple arithmetical constant. This is called the "coefficient of correlation" (commonly expressed as rxy, where x is one variable and y the other). The formula for com- puting Txy is as follows: \ 370 READINGS IN EVOLUTION, GENETICS, AND EUGENICS where d represents the actual deviation and S the sum, n the number of individuals; a the standard deviation. "Correlation tables" show graphically whether or not there is correlation. If, as in Figure 64, we want to find out what is the rela- tionship between total yield of oats and number of culms to the plant, we may make a table with subject classes arranged perpendicularly, and the relative classes, horizontally. If the individuals tend to group themselves about a diagonal ranging from upper left- to lower right- hand corners, the amount of correlation is quite marked. Complete correlation would be represented by a single line of points along this diagonal. No correlation would be shown by random distribution 0-1 3 3 1-2 28 19 3 50 2-3 18 66 20 1 1 106 3-4 1 42 58 7 1 109 4-5 7 59 11 3 80 5-6 26 14 2 42 6-7 4 3 7 7-8 1 1 2 8-9 1 1 50 134 107 38 10 1 400 FIG. 64. — Correlation table of 400 plants of Sixty-Day oats. Total yield of plant in grams, subject. Number of culms per plant, relative. 1910. Coefficient of correlation = 0.712 ±0.017. (From Love and Leighty, 1914.) over the whole rectangle. Inverse correlation would tend to give a grouping about a diagonal ranging from the upper right- to lower left-hand corners. In the particular correlation table used for illustration, the coeffi- cient of correlation (rxy) turns out to beo.7i2±o.oiy. Since com- plete correlation would be i, the degree of positive correlation is very high, as we might expect. The correlation table was used quite effectively by Galton, as we shall now show. STATISTICAL STUDY OF INHERITANCE1 EDWIN GRANT CONKLIN Francis Galton was one of the first who attempted to reduce the mass of conflicting observations on heredity and variation to some 1 From E. G. Conklin, Heredity and Environment (copyright 1920). Used by special permission of the publishers, The Princeton University Press. BIOMETRY 371 system and to establish certain principles as a result of statistical study. He was the real founder of the scientific study of inheritance; he studied characters singly and he introduced quantitative measures. Galton's researches, which were published in several volumes, con- sisted chiefly in a study of certain families with regard to several selected traits, viz., genius or marked intellectual capacity, artistic faculty, stature, eye color and disease. As a result of his very exten- sive studies two main principles appeared to be established: i. The Law of Ancestral Inheritance which he stated as follows: The two parents contribute between them on the average one-half of each inherited faculty, each of them contributing one-quarter of it. The four grandparents contribute between them one-quarter, or each of them one-sixteenth; and so on,thesumof the series 1+1+1+^ being equal to i, as it should be. It is a property of this infinite series that each term is equal to the sum of all those that follow: thus i = lH-HiV • • • • , l = l+iV+ • • • • , and so on. The pre- potencies of particular ancestors in any given pedigree are eliminated by a law which deals only with average contributions, and the various prepotencies of sex with respect to different qualities are also presum- ably eliminated. The average contribution of each ancestor was thus stated defi- nitely, the contribution diminishing with the remoteness of the ances- tor. This Law of Ancestral Inheritance is represented graphically in Figure 65. Pearson has somewhat modified the figures given by Galton, holding that in horses and dogs the parents contribute f , the grandparents f , the great-grandparents f , etc. Number of ancestors. — Theoretically the number of ancestors doubles in each ascending generation; there are two parents, four grandparents, eight great grandparents, etc. If this continued to be true indefinitely the number of ancestors in any ascending generation would be (2)", in which n represents the number of generations. There have been about 57 generations since the beginning of the Chris- tian Era, and if this rule held true indefinitely each of us would have had at the time of the birth of Christ a number of ancestors repre- sented by (2)" or about 120 quadrillions — a number far greater than the entire human population of the globe since that time. As a matter of fact, owing to the intermarriage of cousins of various degrees, the actual number of ancestors is much smaller than the theoretical number. For example, Plate says that the late Emperor of Germany had only 162 ancestors in the zoth ascending generation, instead of 372 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 512, the theoretical number. Nevertheless this calculation will serve to show how widespread our ancestral lines are, and how nearly related are all people of the same race. • Davenport concludes that no people of English descent are more distantly related than 3oth cousins, while most people are much more closely related than that. If we allow three generations to a century, and calculate that the degree of cousinship is determined by the num- ber of generations less two, since first cousins appear only in the third generation, the first being that of the parents and the second that of the sons and daughters, we find that 3oth cousins at the present time d1 $ Parents Grand Pte Gt Gd Pts & Gt Gd J d1 $ d1 ? c? ? d1 ? d1 ? d1 ? c? 9 c? ? Ji S o ^ )a 1 § <-> 2 **~> <^ to *^ *0 . i4TARd g I d 1 1 ••..O^OTJGH ^ ^ S | £ *" & -^ ° '•0.0 SPECK. • OT.OHORULA. 438 READINGS IN EVOLUTION, GENETICS, AND EUGENICS breeding true for a sex-linked character, the female is homozygous for the character in question while the male is heterozygous and incap- able of becoming homozygous. Reciprocal crosses with such a race give unlike results, because the female transmits the character to all her offspring, but the male transmits it to only half his offspring, viz., the females. FIG. 91. — Sex-linked inheritance of barred and unbarred (black) plumage in poultry. P, parents, barred male, unbarred female; F,, barred males and females; F2, males all barred, females in equal numbers barred and unbarred. (After Morgan.) 2. Poultry type. — Another type of sex-linked inheritance exists in which the sex relations are exactly reversed. This was first observed in the moth, Abraxas, but more familiar cases occur hi poultry, for which reason it may be called the poultry type of sex-linked inherit- ance. Here the male is the homozygous sex, the female being hetero- zygous. This condition is found in moths and in certain birds, viz., SEX-LINKED INHERITANCE 439 in domestic fowls, pigeons, ducks, and canaries. As an example we may take the inheritance of the color pattern, barring, in crosses of barred Plymouth Rock fowls. In reciprocal crosses between pure- bred barred Plymouth Rocks and black Langshans (or another unbarred breed), the results are not identical. If the barred parent is the male (Fig. 91 and Table III), all Ft offspring are barred and in F2 all males are barred, but half the females are black and half are barred. If, however, the barred parent is the female (Fig. 92 and Table III), TABLE III RECIPROCAL CROSSES OF BARRED AND BLACK BREEDS OF FOWLS Male Female Male Female P Barred X Black Black X Barred Fj Barred Barred Barred Black Fj Barred i Barred: i Black i Barred: i Black i Barred: i Black (See Fig. 91) (See Fig. 92) FIG. 92. — Reciprocal cross to that shown in Figure 91. P, parents, unbarred male, barred female; FI( barred males, unbarred females (crisscross inheritance); F2, barred and unbarred birds equally numerous in both sexes. (From Castle.) 440 READINGS IN EVOLUTION, GENETICS, AND EUGENICS all FI males are barred, but all Fx females are black. In F2 barred birds and black birds occur in both sexes. These curious facts, which have been repeatedly verified, suggest the occurrence of a vehicle of inherit- ance which is duplex in males but simplex in females. What this is we do not know. No chromosome has been found which has a distribu- tion of this sort in fowls, but it is possible that some chromosome component, or other cell constituent has such a distribution and may be the actual vehicle of inheritance in such cases. The most important character economically, which appears to be affected by some sex- linked factor in poultry, is fecundity. Pearl has shown that when reciprocal crosses are made between Cornish Indian Games, a poor breed for winter egg production, and barred Plymouth Rocks, a fairly good breed for winter egg production, the Fx females in each case resemble the father's race more strongly than the mother's race as regards egg production. Pearl did not maintain, however, nor do his experiments suggest, that the inheritance of fecundity depends exclu- sively upon a sex-linked factor. Goodale, however, has not been able to confirm Pearl's observations, in the case of Rhode Island Red fowls. He finds no evidence of superior influence of the sire in the transmission of racial fecundity. CHAPTER XXXH LINKAGE AND CROSSING-OVER1 WILLIAM E. CASTLE In ordinary Mendelian inheritance, if two characters, A and B, enter a cross in the same gamete (either egg or sperm), it will be wholly a matter of chance whether they continue together or are found apart in the following generation. If in the formation of gametes by the cross-bred, A and B separate from each other and pass into differ- ent gametes, it is evident that one of them has crossed over from the gametic group in which both originally lay to enter the alternative group. This event may be called simply a crossover. Crossovers and non-crossovers will be equally numerous (50 per cent each) where no linkage occurs. Also, if A and B enter a cross in different gametes, one in the egg, the other in the sperm, it will in ordinary Mendelian inheritance be a matter of- chance whether they emerge from the cross together or apart. If together, it is evident that a crossover has occurred; if apart, a non-crossover, that is a persistence of their previous relations. Again, crossovers and non-crossovers will be equally numerous '(50 per cent each) if no linkage occurs. Linkage may be defined as the tendency sometimes shown by genes to maintain in hereditary transmission their previous relations to each other. Thus if two linked genes, A and B, enter a cross together in the same gamete, they will oftener than not be found* together in the gametes formed by the cross-bred individual. Crossovers hi that case will be less than 50 per cent, and non-crossovers more. And if the same two genes enter the cross separately, one in the egg, the other in the sperm, then oftener than not they will be found apart, in different gametes formed by the cross-bred individual. Again crossovers will be less than 50 per cent. The number of genes in a linkage group varies hi known cases from 2 to 50 or more. However many genes there are in a linkage group, each gene shows linkage with every other gene belonging to the same group, but the apparent strength of the linkage varies greatly. Under uniform environmental conditions, A and B show a fairly constant 1 From W. E. Castle, Genetics and Eugenics (copyright 1920). Used by special permission of the publishers, The Harvard University Press. 442 READINGS IN EVOLUTION, GENETICS, AND EUGENICS linkage with each other, A and C show a different and likewise fairly constant linkage strength, and so on through the entire group. This leads to the conclusion that the genes of a linkage system are bound together, gene with gene, with bonds of definite strength in each case. In order to visualize the matter and get a more objective view of link- age relations, Morgan and his associates have developed the chromo- some theory of linkage. Its essential parts are: 1. Genes which show linkage with each other are located in the same pair of chromosomes. It is the substance of the chromosome which binds the genes to each other and causes A to be inherited when B is. 2. Genes close together in the same chromosome show strong link- age, genes farther apart show less linkage. 3. Homologous chromosomes, those containing corresponding sets of genes, one set derived from the father, one from the mother, lie side by side (in synapsis) previous to the formation of gametes. At this time breaks are likely to occur in the chromosomes and parts of one are likely to replace corresponding parts of the other. 4. Such replacement is called crossing-over. 5. Breaks are commoner hi long chromosomes than in short ones, and between distant points than between near points on the same chromosome. 6. The genes occur in a chromosome, like beads on a string, hi a single row and in definite order. The supposed order of the genes in the four linkage groups of Dro- sophila and their relative distances apart are shown in Fig. 90 (p. 437). In these diagrams or "maps," when the probable order of the genes in a system has once been determined, the supposed end gene of the system is placed at position o and the gene next to it is placed at a distance (in centimeters or other units) corresponding to the average cross-over percentage between the two, this process being repeated from gene to gene until the whole chain is plotted. The "map" is thus based on a summation of the distances (measured in cross-over per- centages) from gene to gene. But if we compare the " map distances" between genes not adjacent to each other in the chain with the observed cross-over percentages between the same genes, we find that the map distance is regularly greater than the cross-over percentage, except for very short distances (5 or less). Thus if three genes occur hi the order ABC, it is usually found that AB+BC is greater than AC. In other words, the cross-over percentage between B and C is commonly LINKAGE AND CROSSING-OVER 443 greater than the cross-over percentage between A and C, and the dis- crepancy increases with the magnitude of the values involved. This fact has been accounted for in two different ways. First, it may be supposed that the arrangement of the genes is really not linear, that B lies out of line with A and C, so that AC will be less than the sum of AB and BC, and that the more distant genes are no farther apart than indicated by the cross-over percentages between them. This expla- nation has met with more difficulties than it has cleared away. The second explanation is that the map-distances indicate proportionate numbers of breaks in the linkage chain between points, not propor- tionate numbers of changes of relation between genes at particular pouits. Thus, suppose genes ABCDE of a linkage system meet their allelomorphs, abcde, hi a cross and gametes are later formed by the cross-bred as follows, (i) ABcde, (2) ABcdE, and (3) AbcDe. Assum- ing that the arrangement is linear, we must suppose that one break hi the linkage chain has occurred hi (i), two breaks hi (2), and three FIG. 93. — B and C illustrate Morgan's idea of the linear arrangement of the genes in the chromosomes. A and D show how the composition of the chromo- somes is supposed to change as the result of the crossover. On the right, a pair of chromosomes, a, before; b, during; and c, after a double crossover. (After Morgan.) breaks hi (3). But if we did not have genes BCD under observation, and merely noted the relation of A to E, we should infer that in case (i) and in case (3) a single crossover had occurred. We should on that basis underestimate the amount of breaking in the linkage chain. 444 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Accordingly the construction of maps on the basis of short distances summated is justifiable, provided the arrangement is linear, as it seems to be. But it must be borne in mind that the map distances do not correspond with cross-over percentages (although they are based on them) except in the case of very short distances. Map distances often exceed 50, but cross-over percentages cannot do so, as already pointed out. To get a distinctive name for the map units, Haldane has called them units of Morgan or simply "morgans." Haldane has computed a formula for converting cross-over percentages into "morgans" and vice versa. He finds that the two correspond only for very low values (5 or less) and diverge more and more as the observed cross-over per- centages approach 50. Haldane's formula may be stated thus. If three genes, A, B, and C, occur in a common linkage group, and the cross-over percentages are known between A and B and between B and C, we may predict with a probable error of not over 2 per cent, what cross-over percentage will be found to occur between A and C. Call- ing the cross-over percentage between A and B, m, and that between B and C, n, the cross-over percentage between A and C will lie between (m-}-n) and (m-\-n— imn). It will approach the former for amounts of 5 or less, and the latter for amounts of 45 or over. In a useful table Haldane shows the calculated map distances (morganc) for all cross- over percentages between 5 and 50. This table is based on the rela- tions of the genes observed hi the sex-linked group of Drosophila, but it applies equally well to the second linkage group of Drosophila, and to a group of three genes in the plant, Primula. Provisionally it may be considered to apply generally to linkage systems in animals and plants. TABLE IV A TABLE FOR CONVERTING CROSS-OVER PERCENTAGES INTO MAP DISTANCES ("MORGANS") AND VICE VERSA (AFTER HALDANE) Cross-over percentage o.o 5 .0 8.0 IO.O 1 1 . o 12. 0 13.0 Map distance o o , i 8.2 10 3 1 1 . 4 12.5 13.6 14.0 14.7 23.0 25-3 32-0 37-7 41.0 54-4 49-5 99.2 IS-O iS-9 24.0 26.6 33-o 39-3 42.0 56.8 49-7 109.4 16.0 17.0 25.0 27.9 34-0 40.9 43-0 59-6 49.8 117.7 • 17- 18, 26 29 55 42 44 62, 49 1 28 o ,1 .0 ,2 .0 .0 .0 .0 • 9 .1 18.0 19-3 27.0 3°-S 36.0 44-3 45-0 66.0 50.0 Aw> O 19.0 20.5 28.0 31-9 37-0 46.1 46.0 70.1 20 21 29 53 38 48 47 75 .0 • 7 .0 •3 .0 .0 0 .1 21.0 22.9 30.0 34-7 39-0 50.0 48.0 8x.9 22.0 24.1 31-0 36.2 4O.O 52.2 49.0 93-o As an example of how the table may be used in predicting undeter- mined linkage values, suppose that A is linked with B, and B with C LINKAGE AND CROSSING-OVER 445 and that between A and B there are 10 per cent of crossovers. What will be the cross-over percentage between A and C ? Converting the observed cross-over percentages into map distances with the aid of the table, we find the distance AB to be 10.3 and the distance BC to be 15.9. On the linear theory the distance AC will equal either the sum or the difference of AB and BC, that is will be either 26.2 or 5.4. Converting these distances into cross-over percentages by interpola- tion in the table, we find that the cross-over percentage between A and C should be either 23.7 or 5.1, according as the linear arrangement is ABC or ACB. Measurement of linkage. — It will be observed that as the strength of linkage increases, the cross-over percentage decreases. With a cross-over percentage of 50, there is no linkage. With a cross-over percentage of o, the linkage is complete, two characters so related behaving as allelomorphs. Accordingly we depend upon the observed cross-over percentage both for the detection of linkage and for the measurement of its strength. But unfortunately the linkage strength varies inversely as the cross-over percentage. This makes the cross- over percentage directly considered, a rather poor measure of linkage strength. It is really the amount by which the cross-over percentage falls below 50 that measures directly the strength of linkage. Thus with cross-over percentages of 50, 40, 30, 20, 10, and o, we should have linkage strengths of o, 10, 20, 30, 40, and 50. We should then have a standard for measuring linkage strength directly, on a scale of 50. But as we are more accustomed to grading on a scale of 100, it seems preferable to double the values indicated above. We then have grades of linkage strength on a scale of 100, as follows: Cross-over percentage 50 40 30 20 10 o Linkage strength o 20 40 60 80 100 Accordingly, to estimate the strength of linkage in a particular case, we multiply by 2 the difference between the observed cross-over per- centage and 50. But suppose the observed cross-over percentage were greater than 50, what then? Such an occurrence would not indicate linkage, a tendency of characters to remain grouped as they were, but an oppo- site tendency, to assume new groupings. No such tendency has been observed. If it should be, it would need a different name and method of measurement. We may now consider some further examples of linkage. 446 READINGS IN EVOLUTION, GENETICS, AND EUGENICS In the plant, Primula sinensis, Gregory observed the occurrence of linkage in a group of five characters, viz., Dominant Recessive 1. Short style vs. long style (1) 2. Magenta corolla vs. red corolla (r) 3. Tinged corolla vs. full-colored corolla 4. Green stigma vs. red stigma (s) 5. Pale stem vs. full red stem Altenburg later determined the strength of the linkage existing between three of these five pairs of characters, viz., i, 2, and 4 of the above list. His results may be expressed in a linkage map as follows : 1 - r s o 34.0 45.6 The cross-over percentage between 1 and r was found to be 34.02, between r and s, 11.62. The sum of these two, 45.64, is the total (uncorrected) map distance. The observed cross-over percentage between 1 and s was 40.6, which falls short of the map distance by almost exactly the amount indicated by Haldane's table. In the sweet pea the earliest discovered examples of linkage are found. Here are known two linkage groups containing each three pairs of characters as follows: Dominant Recessive Dominant Recessive Dark vs. light leaf-axil Fertile vs. sterile anthers Normal vs. cretin flowers !i. Blue vs. red flower color f i. 2. Long vs. round pollen Group 2 < 2. 3. Erect vs. hooded standard [ 3. Results described by Bateson and by Punnett indicate that in Group i the map relations of the three genes are: E— B L o .78 12.5 The group is a compact one, with E and B very closely linked, cross- over percentage less than one, with B and L showing between n and 12 per cent crossovers, and with E and L showing about 12.5 per cent of crossovers. In Group 2, the cross-over percentage between D and F is about 6.2, between F and N about 25.0. Until the cross-over percentage between D and N has been experimentally determined, it cannot be stated whether the "map" order is FDN or FND. In the former case, the total map distance will be 25, or about double the length of Group i; in the latter case, it will be still longer, or about 31.2. LINKAGE AND CROSSING-OVER 447 TABLE V CASES OF LINKAGE IN PLANTS OR IN ANIMALS OTHER THAN DROSOPHILA Species I Linked Characters Cross-over Percentage Linkage Strength Authority Sweet pea i i i 2 2 Purple flowers, long pollen Purple flowers, erect standard Long pollen, erect standard Dark axil, fertile anthers Dark axil, normal (not cretin) flower ii or 12 0.78 "-S 6.2 ? 76-78 98.4 75 87.6 Bateson and Punnett 2 Fertile anthers, normal (not cretin) flowers 25.0 So Primula sinensis I I I I Short style, magenta corolla Short style, green stigma Magenta corolla, green stigma Tinged corolla, green stigma Pale stem, green stigma 34-0 40.0 ii. 6 ? ? 8.8 76.8 Altenburg Gregory Garden pea I 2 Round seeds, tendrils on leaves Late flowering, colored flow- ers i-5 1 2-1 6 97 68-76 Bateson and Vilmorin Hoshino Antirrhinum I Red flower color, "pictur- atum" pattern ao.o 60 Baur Maize I 2 2 2 3 Waxy endosperm, Aleurone C Aleurone R, Chlorophyl G Aleurone R, Chlorophyl L Chlorophyl G, Chlorophyl L Starchy endosperm, tunicate seed 26.7 19.0 o.o 23.0 8-3 46.6 62? ] 100 \ 54 J 83-4 Breggar Lindstrom Jones Tomato I 2 Vine habit, fruit shape Green foliage, 2-celled fruit 20. o 0? 60 \ 100? / Jones Beans I Seed pattern, vine habit 0? IOO? Surface Silkworm I Pattern Q of larva, yellow silk 26.1 47-8 Tanaka Apotettix I I I I I I I I Patterns G and M Patterns M and K Patterns K and Y Patterns Y and R Patterns Y and T Patterns R and T Patterns M and R Patterns Y and Z 4 (in?; i (inS) 6 (in?) 10 (in9) 12 (in?) o(in9) 10 (in2) 10 (in?) 92 98 88 80 76 IOO 80 80 Nabours Pigeon I Sex-linked factors I and A 40 (in<$) 20 Cole and Kelley Rat X I I Albinism, red-eye Albinism, pink-eye Red-eye, pink-eye I.O? 21. 0 I8.3 98? 58 63-4 Castle and Dunn Mouse I Albinism, pink-eye 14-3 71.4 Castle and Dunn 448 READINGS IN EVOLUTION, GENETICS, AND EUGENICS In garden peas two independent pairs of linked characters are known and two more are suspected (White). In one of the established cases close linkage is found between round starchy seeds and tendrils on the leaves, with about 1.5 per cent of crossing-over. In the other case a gene for late flowering is linked with red flower color with an estimated cross-over percentage of between 12 and 16. In the snapdragon, Antirrhinum, two factors for flower color were found by Baur to be linked, with about 20 per cent of cross-overs occur- ring. In maize three linkage groups are known, one of four factors and two of two factors each. Group i includes a factor for waxy endo- sperm and the factor C for aleurone color. These show a cross-over percentage of 26.7. Group 2 includes four linked factors, aleurone factor R, chlorophyll factor G, chlorophyll factor L, and aleurone spotting factor, S. No crossovers have been observed between R and L which behave as if they were allelomorphs, or "completely linked." The cross-over percentage between L and G has been determined as 23, that between R and Ghas been determined less accurately as 19, and that between R and S as 12.5. The order of the genes is accordingly R— L S G. Group 3 includes the two characters, starchy endosperm and tunicate ("podded") seeds. The cross-over percentage in this case is 8.3 (Jones and Gallastegui). In the cultivated tomato two cases of linkage have been reported. A gene for "standard" vine habit and a gene for "constricted" fruit shape show about 20 per cent of crossing over. In another linkage group, no crossovers have been observed between green foliage color and two-celled fruit, as opposed to yellow foliage color and many- celled fruit, in a total of 24 F2 plants. It seems probable that the linkage in this latter case is close, though the number of observations is too small to do more than establish a probability. In rats a group of three linked characters has been found, albinism (c), red-eye (r) and pink-eye (p), which may be mapped, thus C— r- O I In mice albinism (c) and pink-eye (p) are linked, as they are in rats, but the cross-over percentage is less, viz., 14.3. [Castle cites further examples.1] 1 See Genetics and Eugenics. CHAPTER XXXIII SEX DETERMINATION VARIOUS THEORIES OF SEX DETERMINATION H. H. NEWMAN In earlier chapters it has been necessary to introduce a few neces- sary facts about sex determination and sex-linked heredity. The mechanism of sex determination has been clearly described and illus- trated for Drosophila (pp. 410 ff.), and the close connection that exists between sex-linked heredity and sex determination has been shown in chapters xxxi and xxxii. A more detailed consideration of sex deter- mination and sex differentiation is now to come. The question as to what determines whether an animal shall be a male or a female is a very ancient one, and it is only during the present century that we have solved the puzzle. A great many theories of sex determination have been proposed, some of which are as follows: a) Hippocrates and some subsequent theorists believed that the sex of the offspring depended on the relative vigor of the parents, the more vigorous parent giving his or her sex to the offspring. b) Thury thought that the sex of the offspring depended on the degree of ripeness of the ovum at the time of fertilization. c) Various writers claim that statistics show that germ cells from the right ovary produce males and those from the left ovary females. d) The nutrition theory. — The egg is a much more highly nourished cell than the spermatozoon, and the idea seems natural that high degrees of nourishment of the mother produce female offspring and lower degrees of nourishment male offspring. Professor Schenk of Vienna gained a huge reputation by controlling the diet of certain royal prospective mothers and predicting the sex of the offspring accordingly. He was correct in his predictions several times, but his success was short-lived. His early predictions were merely lucky, just as one might be who could guess heads or tails correctly several times in succession. Some color is lent to the nutrition hypothesis by the fact, if it is a fact, that after war or famine, when the nutrition of mothers has been 450 READINGS IN EVOLUTION, GENETICS, AND EUGENICS low, more males than females are born. This is probably a case of differential prenatal mortality. By that we mean that more females die unborn than males, because the latter are hardier and stand pre- natal malnutrition better. e) Sex is determined at the time of fertilization. — Perhaps the best evidence that sex is determined at the very beginning of development is derived from one-egg twins and quadruplets. In the nine-banded armadillo practically every female gives birth to quadruplets, four essentially identical young being produced in each litter. All hi a given set of quadruplets are invariably of the same sex, either four males or four females. Newman and Patterson have shown that each set of quadruplets comes from a single egg which at a very early stage divides into four parts to form four foetuses (Fig. 94). The conclusion is that sex was determined before the separation took place. Human identical twins, also always of the same sex, furnish further evidence in favor of very early sex determination. These and numerous other similar facts justify the conclusion that sex is determined at the tune of fertilization. THE CHROMOSOMAL MECHANISM OF SEX DETERMINATION The well-established case of Drosophila (pp. 410 ff .) will serve as a basis for comparison. Many cases similar to that of Drosophila have been worked out. The chief differences have to do with the X and Y chromosomes. Sometimes the X chromosome is distinct and inde- pendent during synapsis and maturation, but cases are known hi which the X chromosome is attached to the end of one of the ordinary chromosomes, and will, of course, always follow this chromosome in reduction division. The Y chromosome varies considerably in dif- ferent species. Sometimes the Y chromosome and the X chromosome are optically indistinguishable. Sometimes the Y element is repre- sented by a group of as many as five small chromosomes which keep together in a group and always go either one way or the other in the reduction division. Again, the Y element may be very small or vesti- gial, or, finally, it may be wanting altogether, so that X is an entirely unpaired chromosome that goes to one cell only at the reduction division. In spite of all of these various modifications of the X-Y type of chromosomal sex-determining mechanism, the method of producing male-forming and female-forming spermatozoa is the same in each case. The female gametes all have one X chromosome, while half of SEX DETERMINATION 451 the male gametes have one X chromosome and the other half have no X, but sometimes Y and sometimes simply one chromosome less than the first type of male gametes. We can then speak of the two FIG. 94. — An armadillo egg about six weeks after fertilization, showing the quadruplet foetuses derived from the single egg and all destined to be of the same sex. (From Newman.) sexes produced by union of male and female gametes simply in terms of the X chromosomes, females being characterized by XX (duplex) and males by X (simplex). SEX DETERMINATION IN PARTHENOGENETIC SPECIES Although it was at first thought that the facts of parthenogenesis (development of eggs without fertilization) was opposed to the chromosomal mechanism of sex determination, further study of this 452 READINGS IN EVOLUTION, GENETICS, AND EUGENICS phenomenon only served to line up this category of sex determina- tion with the type already explained. In the bees and wasps it has long been known that eggs which are extruded without fertilization produce drones (males), while fertilized eggs produce workers or queens (both females). It has now been dis- covered that the bee egg undergoes the reduction division before fertilization so that all eggs will have only one X chromosome. The eggs that are fertilized always have the XX condition and will produce only females, while the eggs that are not fertilized keep the X con- dition and produce males. These males with only half the normal number of chromosomes cannot carry out the reduction division, but produce spermatozoa always with an X chromosome. In aphids parthenogenetic individuals are always females and in this case it has been discovered that the egg develops without under- going the reduction division, thus retaining the XX condition. In all of the cases hitherto mentioned the female is said to be homo- zygous for sex, because she produces gametes of only one kind, from the sex standpoint, each matured egg having the X chromosome pres- ent. The male, on the contrary, is said to be heterozygous for sex since two kinds of sperms are produced, one with X and the other with- out X. The great majority of animals appear to have a similar mechanism, but there are a few groups of animals which are just the reverse of what we have described, since the female is heterozygous for sex and the male homozygous. THE POULTRY TYPE OF SEX DETERMINATION There is now evidence both cytological and genetic that in poultry, and probably in all birds, there are two kinds of maturated eggs, one having the X chromosome and the other with the Y chromosome, or at least without an X chromosome. All of the spermatozoa are believed to have the X chromosome. As has already been seen (chapter xxxi), the sex linkage is just the reverse of that seen in the majority of animals when the male is the heterozygous sex. Moths and butterflies are also probably of the same type as poultry. In the classic case of Abraxas, the currant moth, a pale mutant occurred which was female and was sex-linked to females just as white eye color was linked to males in Drosophila. Apart from the fact that the XX con- dition seems to have shifted from one sex to the other hi these two groups (birds and butterflies) the mechanism of sex determination seems to be exactly the same as in the majority of animals studied. SEX DETERMINATION 453 SEX DIFFERENTIATION It now becomes necessary to distinguish clearly between sex determination and sex differentiation. When we say that by means of a chromosomal mechanism sex is determined, exactly what do we mean ? We answer that the sex of an individual arising from a fertil- ized egg (in the case of parthenogenesis, an unfertilized egg) has been settled. Now as a matter of fact only one thing has been settled irrevo- cably, and that is that one individual will have the chromosome composition characteristic of a male and another individual that of a female. A male is usually an individual that produces spermatozoa and a female one that produces ova. Is it irrevocably settled beyond possibility of reversal that a zygote with the XX chromosome com- position must produce eggs and one with the X composition, sper- matozoa ? This question has apparently been answered by Geoffrey Smith in his work on parasitically castrated crabs and by Richard Goldschmidt on Gypsy moths. In the first case, individual crabs whose testes had been infested by the parasitic cirripede, Sacculina, were gradually changed over in their whole metabolism to such an extent that cells destined to produce spermatozoa produced ova. In the second case, when certain varieties of moth were crossed, all of the germ cells produced females with ova, whereas half of the eggs had the XX and half the X chromosome content. This evidently means that some individuals with the male chromosome character produced eggs. From these results we may be justified in conclud- ing that not even this most fundamental difference of sexes, that of the female producing ova and the male spermatozoa, is irrevocably predetermined at fertilization. Lest the reader be confused, however, we hasten to add that under natural conditions of life an individual with the male chromosomal content produces spermatozoa and one with the female chromosomal content produces eggs, and that only rare accidental or unnatural conditions disturb the normal course of events. For purposes of practical genetics we may then define a female as an individual that produces ova and a male as one that produces spermatozoa. Secondary sexual characters. — Usually males and females differ from each other in many other characters besides the production of eggs or sperm. Often one sex is larger, stronger, more elaborately ornamented and colored than the other and possesses characteristic accessory sex organs whose function it is to facilitate the bringing together of the eggs and the sperm. All of the differences between the 454 READINGS IN EVOLUTION, GENETICS, AND EUGENICS sexes other than the primary difference of egg or sperm production are called secondary sexual characters. Usually very young animals show only slight differences in secondary sexual characters and the differ- ences increase markedly at sexual maturity. We speak of the gradual divergent development of the two sex types as sex differentiation. The question arises as to whether or not the chromosomal differences are the causes of the differentiation of secondary sexual characters. These secondary sexual characters are all somatic, and, since the soma is the product of cell division of the zygote, the soma cells must have either the male or the female chromosomal character. That the chromosomal mechanism in the somatic cells is not sufficient of itself to bring about, unaided, the differentiation of secondary sexual charac- ters can be shown readily in at least many animals. In the mammals, for example, it is known that the early removal of the testes or ovaries results in a retention of the juvenile or undif- ferentiated condition of secondary sexual characters. Evidently some influence is exerted by the tissues of the gonad that is necessary for the full differentiation of sex characters. The current theory is that certain glandular cells that form part of the body of ovary or testes excrete materials into the blood that stimulate various tissues in different ways and produce dimorphic results. The specific sub- stances produced by these glands are called "hormones," for want of a better name. To test the efficiency of these hormones the crucial experiment of taking out the gonads of a young rat or guinea pig and implanting the gonad of an individual of the opposite sex has been many times performed. For example, Steinach castrated young male rats and then successfully grafted into them ovaries from young female rats. The result was that these young rats which started to be males became much altered in a female direction, the mammary glands becoming greatly enlarged, their instincts more feminine than masculine, and in a number of other particulars they showed more or less pronounced evidences of feminization. Conversely, spayed females with engrafted testes showed a tendency toward male differ- entiation, especially hi instincts. These experiments have been largely confirmed by C. R. Moore. Similar experiments with similar results have been performed with fowls and ducks. All indicate that the glandular part of the gonads has a determinative effect on sex differentiation, and this in spite of the chromosome make-up of the somatic cells; for the male differentiation in cells with the male chromosome characters can be SEX DETERMINATION 455 4S& READINGS IN EVOLUTION, GENETICS, AND EUGENICS inhibited and female differentiation superimposed if the female gonad is introduced in the absence of the male gonad. A beautiful experiment conducted by nature herself helps to drive home the hormone theory of sex differentiation. In cattle, as shown recently by F. R. Lillie, twins occur in a small percentage of cases and involve the simultaneous fertilization of two eggs. These eggs lie as a rule in opposite horns of the forked uterus, but owing to the growth of their embryonic membranes the two individuals come to fuse cir- culations so that there is an admixture of blood (Fig. 95). The result is that if the twins are zygotically of the same sex no untoward effect of blood admixture is apparent, but when the twins are zygotically a male and a female, the female individual is always stopped in its female differentiation and becomes more or less completely trans- formed in a male direction. It appears, however, that at the time when blood admixture occurs, the female individual has already differentiated so far with respect to the external genitalia and in other respects that, even though subsequent development be entirely male hi character, the resultant individual is always a sterile creature, neither fully a female nor a complete male. Such individuals have long been known as " freemartins." As a rare exception to the general rule an occasional case has appeared in which a male and a female pair fail to undergo blood admixture. In such cases both develop into normal animals. It now appears that the reason why the female sex is the one to suffer is that the male gonads differentiate precociously, before the female, and inhibit the subsequent development of female gonads. Hence the only hormones in the blood of both twins are the male hormones. In conclusion we may say then that, in mammals, though chromosomes tend to determine the primary sex differences, they have no effect on the differentiation of secondary sexual characters. These are due to substances secreted by the gonads that have been called a hormones. PARTY EUGENICS CHAPTER XXXIV THE INHERITANCE OF HUMAN CHARACTERS, PHYSICAL AND MENTAL1 ELLIOT R. DOWNING Anyone who undertakes to trace the ancestry of an individual is soon impressed with the fact that it is a difficult task even to find the names of the persons involved three or four generations back; it is much more difficult to determine with certainty their physical and mental characteristics. One can more surely find the pedigree of a horse or hog that he may own than he can of a child in whom he is interested, for we do have registry books for good stock, but none ordinarily for human family relations (in Illinois not even compulsory birth registrations until very recently), so that a child born in this state may not even legally prove his existence or parentage by official records. It is not an easy matter, therefore, to find human data that illustrate the various phases of heredity concerning which we are reasonably sure in dealing with animals and plants. Fortunately, there are some studies of the inheritance of physical characters that are quite satisfactory. There is an increasing number of studies of the inheritance of insanity, feeble-mindedness, epilepsy, and alcoholism by the scientific staff of institutions dealing with such cases, and we do have a fairly good mass of material in the lines of descent of the royal families of Europe, where the matings and the characters of the individuals are more or less matters of history. Thanks to the generosity of some men of wealth and foresight, appre- ciative of the importance of a better knowledge of the laws of human heredity, we have in several countries well-endowed laboratories with expert staffs founded on purpose to study this topic; such as the Galton Laboratory of Eugenics in England and the Eugenics Labora- tory of the Carnegie Institution, Cold Springs Harbor, New York. Occasionally a family is found in which one or more members have five fingers instead of four; such a condition is known as polydactyl- ism. Sometimes a case is recorded in which a person has fingers with * From E. R. Downing, The Third and Fourth Generation (The University of Chicago Press, copyright 1920). 459 460 READINGS IN EVOLUTION, GENETICS, AND EUGENICS two joints instead of three and a thumb with one joint in place of two (brachydactylism). Such human abnormalities are inherited. There is given on this page a chart (Fig. 96) of a family tree in which brachydactylism is very common; it is based on a study made by Drinkwater. Males in the chart are represented by 6, females by ?, INHERITANCE OF HUMAN CHARACTERS 461 matings by = . The circles are of solid color • in individuals affected with the deformity, open O in normal individuals. The character seems to behave like a Mendelian dominant, though one could make no very positive assertion on this point from so few individuals. But it is very evident that such a physical character once in the stock is transmitted generation after generation, reappearing continually in the offspring. Below there is presented a chart (Fig. 97) of the transmission of cataract. This disease is characterized by the appearance of an opaque area in the usually transparent parts of the eye, FIG. 97. — Inheritance of one form of cataract. Modified from Nettleship's chart. The diagram reads thus : A man with cataract married a normal woman; of their eight children six were affected with the disease. One of these married an unaffected man; three of the children of this union were normal, sex unrecorded, two defective. This same man married a second wife who was normal; their eight children were all unaffected. So continue reading through five generations. (From Downing.) ultimately rendering the person blind. In the particular form of the disease here considered it does not develop until middle life. Clarence Loeb in a study of hereditary blindness published in 1909 tabulated the results of a study of 304 families in which such blindness occurs. There were 1,012 children, of whom 58 per cent were afflicted, which is about the percentage expected when hybrid defectives mate with normal individuals and the defect is a dominant character. Similar extensive studies of congenital deafness and deaf-mutism show that these are similarly heritable, though just how the character behaves is not yet known, for undoubtedly under "deafness" are included a variety of diseased conditions that must be 462 READINGS IN EVOLUTION, GENETICS, AND EUGENICS studied separately before we shall know how each is inherited. Care must be taken, too, to distinguish between congenital deafness and blindness — that which inheres in the germ plasm — and those forms, due to accident or contagious disease, which are acquired modifications and so not heritable. Thus measles often produces deafness as one of its after effects. Persons so rendered deaf would not transmit the affliction to their children any more than they would transmit blind- ness if the eyes of the parents were put out by accident. Feeble-mindedness apparently behaves as a Mendelian recessive. Goddard's studies of the family pedigree of the inmates of the Vine- land, New Jersey, institution for the care of the feeble-minded gives us an abundance of material to show the heritability of this defect and its relation to alcoholism, insanity, syphilis, etc. Briefly, syphilitic infection is a fairly common cause of feeble-mindedness in children. There is a higher percentage of feeble-mindedness in the offspring of alcoholic parents than among those of parents not addicted to it. There seems little or no causal relation between feeble-mindedness and insanity. But aside from feeble-mindedness that may be pro- duced by such causes or by occasional accidents such as falls, blows on the head, there is the great mass of feeble-mindedness that is wholly a matter of heredity. If a feeble-minded individual comes from parents both of whom are congenitally feeble-minded or who both have a great deal of feeble- mindedness in their ancestry, such a one is taken to be a pure recessive as far as this character is concerned, and his germ cells have a double dose of the factor for feeble-mindedness (FF). When two such per- sons mate, their offspring would be expected to be all feeble-minded, for all eggs and sperm contain the factor F, and when any egg is fertil- ized the person produced is an FF individual. Out of 144 such mat- ings resulting hi 482 offspring whose records are known, Goddard found that 476 were feeble-minded. This type of mating as well as others cited below are illustrated in the family pedigrees shown on pages 463 and 464, selected from Goddard's book. If a person comes from parents one of whom is entirely normal and one is feeble-minded with many feeble-minded ancestors, it is probable that such an individual is a hybrid with germ cells that, as far as this one character is concerned, can be designated NF. Such a person will pass for normal, since feeble-mindedness is recessive. If such a one mates with the type described above (FF), it would be expected that hah" the offspring would be normal, half feeble-minded. Out of INHERITANCE OF HUMAN CHARACTERS 463 122 such mailings producing 371 children, 193 were found to be feeble- minded, 178 normal, which is remarkably close to expectation con- sidering the difficulty of determining with certainty the real character of the parents. When two individuals of the NF type mate, their offspring would be expected to give 3 normals to i feeble-minded. Out of 146 children produced by 33 such matings Goddard found 39 were feeble-minded. The first of Goddard's charts (Fig. 98) illustrates the family tree of Gertie K., a girl of 12 years, with the mental development of a child of 7. Males in this and the following chart are represented by squares, females by circles. Note that this girl has a feeble-minded brother and that both her parents are feeble-minded and see the appalling array of feeble-minded cousins, aunts, uncles, and other relatives. Her grandmother passed for a normal individual, although it would seem from her children she must have been an NF individual. The T '_l 'O • •;••••••• ••00 • •» • • •••••••• B BOO •[•• • ® O B= t Gum* FIG. 98. — Family of Gertie K. '(From Downing, after Goddard.) second chart (Fig. 99) is quite exactly Mendelian, if we suppose the grandparents were NF individuals. This case is particularly interest- ing, for the parents of these six feeble-minded children were high-grade morons, both immigrants. The public must support the children because we have as yet instituted no expert examinations to detect such defectives among our immigrants in order to refuse them admis- sion to this country. See what a single unfortunate alliance can produce. A young man to whom Goddard gives the fictitious name of Martin Kallikak had children by a feeble-minded girl in the days before the Civil War. There have been traced some 480 descendants from this mating, and all of them are below normal intelligence. Later this same man married a good Quaker girl, and 496 of the descendants of this marriage have been traced, all of normal mentality. The contrast is strikingly instructive, for the conditions are almost those demanded by a scien- tific demonstration. 464 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Such cases as those cited are interesting from the standpoint of the student of heredity. They are tremendously significant to the average citizen because there is in the United States a very large feeble-minded population, estimated at 200,000, nine-tenths of whom are at large, free to reproduce their kind, and very prone to interbreed, because the feeble-minded are seldom sought as legitimate mates by persons of normal mentality. The number of feeble-minded is apparently increasing much more rapidly than the general population. How rapidly, it is impossible to determine, for we have no exact data on the number of feeble-minded; we are not yet awake to the enormity of the problem involved. From these feeble-minded come some FIG. 99. — Family of Charlie M. (From Downing, after Goddard.} 40 per cent of our prostitutes, a fourth of our criminals, and at least a half of the inmates of our almshouses. A generation ago the valley of Aosta, in Northern Italy, was over- run with feeble-minded and idiotic individuals of the type known as cretins. It was estimated that fully 60 per cent of the population were affected with this abnormality. A law was passed and enforced segregating the really irresponsible cases and prohibiting the marriage of cretin with cretin. Now the condition has almost disappeared, and it is estimated that only a very small percentage of the population are cretins, these nearly all old, so that this particular form of idiocy will there very soon be a thing of the past. It seems only a rational proce- dure to accomplish at least a segregation of feeble-minded in this INHERITANCE OF HUMAN CHARACTERS 465 country, even if no more drastic action is taken. Otherwise the group is bound to be an increasing burden on the community, adding con- stantly to the tax needed for their support. Investigations of competent officials in the employ of insane hos- pitals have accumulated a mass of evidence demonstrating the herit- ability of many forms of nervous diseases which most commonly behave as recessives. Rosanoff and Orr,1 in a study of 206 matings between individuals from more or less insane stock, found 1,097 children, 146 of whom died in childhood. There were 351 afflicted offspring to 586 normal. The theoretical expectations, knowing with more or less certainty the character of the parents, were 359 to 578. There are presented (Figs. 100, 101) two typical family pedi- grees. In the first an insane man was twice married, each tune to an FIG. 100. — (i) Ignorant, "queer"; (2) Insane, was in sanitarium, com- mitted suicide; (3) eccentric, violent temper, ideas of persecution against neighbors; (4) eccentric, not well bal- anced; (5) alcoholic, lazy, indolent; (6) dementia praecox, paranoid, in state hospital; (7) violent temper, queer, extreme dolichocephaly; (8) defective, cranial malformation; (9) inferior, "slow." (From Downing, after Rosanoff and Orr.) 6 . • .* 6 MM O 0 FIG. 101. — (i) epileptic; (2) insane for a time, recovered; (3) epileptic, imbecile; (4) imbecile; (5) melancholy in early married life, recovered; (6) insane five years, was in state hospital, recovered; (7) insomnia, neuralgia; (8) daughter had spells of excitement; (9) feeble-minded; (10) dementia praecox, katatonic, in state hospital; (n) died of marasmus, had one convulsion. (From Downing, after Rosanof and Orr.) eccentric woman, undoubtedly mildly insane. All the offspring were unbalanced. In the second case, those distinctly neurotic are indi- cated in solid color; those having a neurotic element in the germ material are shaded. It might seem as if insane individuals would scarcely add materially to the general population, since they are com- monly in asylums. Often, however, the inherited insanity does not 'Eugenics Record Office (Cold Springs Harbor, N.Y.) Bulletin No. 5, 1911. 466 READINGS IN EVOLUTION, GENETICS, AND EUGENICS manifest itself until past middle life, when they have already married and started a family. Moreover, those hybrid individuals in whom the insane tendency is present alongside of the normal determiner appear as normal individuals. Frequently they can be detected only by an examination of the pedigree. If such individuals mate, one- fourth of the offspring would be expected to be insane. Early modern European history centers about the doings of a few great men and women. Peter the Great of Russia, Ferdinand and Isabella and Charles V of Spain, Frederick the Great of Prussia, Gusta- vus Adolphus and Charles XII of Sweden, are among the most brilliant of these potent individuals that shaped the destinies of Europe during this period. It is interesting to note how their characters are deter- mined (and through them national destinies are apparently decided in no small measure) by the hereditary concentration of ability due to lucky royal matings, and how their genius is dissipated by unwise ma tings. Peter the Great of Russia came as a brilliant type from a good stock, though with a very evident taint of epilepsy and feeble- mindedness. He himself was an epileptic. His father, grandfather, and great-grandfather had been men of large ability. They had married peasant girls, as was the custom of the czars. Peter's own brothers and sisters were in no way remarkable. His half-sister Sophia was a woman of marked ability, although two of her brothers were imbeciles, one also an epileptic. As will be seen from the pedigree, the epilepsy, imbecility, and mediocrity appear in both Peter's children and grand- children, as well as in those of his imbecile half-brother, Ivan. It is interesting to note from the pedigree that the feeble-mindedness and epilepsy seem to cling to the males quite persistently. The females of the family are much more apt to be brilliant and virtuous. Peter the Great's own son Alexis was a poor dissolute specimen, and although he married Charlotte, the angelic daughter of a great line, the house of Brunswick, the son of this mating was Peter II, of unstable mind, while the daughter Natalia was as sweet as she was energetic. Isabella and Ferdinand were both descendants from lines of very great individuals, although in each case there is insanity in the family. Isabella herself comes from an insane mother and an imbecile father, but her grandparents and great-grandparents were well-balanced and able. The data for the charts of these royal families were taken largely from F. A. Woods's Mental and Moral Heredity in Royalty, supplemented with information from other sources. He grades the INHERITANCE OF HUMAN CHARACTERS 467 i i i™ -« a-gfc 111 -IS* *J ei! EJ; fl r fft B| P -i« -Hi ili 468 READINGS IN EVOLUTION, GENETICS, AND EUGENICS -31 INHERITANCE OF HUMAN CHARACTERS 469 Individuals on a scale of 10. Ten represents very high ability, as determined by the comparative amount of space and laudation given to the individual hi such standard works as Lippincott's Biographical Dictionary. Five out of eight of Isabella's great-grandparents rank very high. John the Great of Portugal, twice her great-grandfather, has a grade of 10. John of Gault, twice her great-grandfather, has a grade of 8, as does also John of Castile, while Henry III of Castile, one of her grandparents, is designated the model king. Ferdinand I of Aragon, the grandfather of Ferdinand, is a brother of this same Henry III of Castile, and is also an exceedingly able king. Of the children of Ferdinand and Isabella, most were mediocre or distinctly inferior. Joanna was insane. In the next generation, however, appears Charles V, whose reign marked the acme of Spain's greatness, partially due to his own ability, partially due to the momentum of those move- ments that were instituted by his illustrious grandparents. Charles V married his own cousin, as did also John III. Children of these two matings married, and Don Carlos, child of this latter marriage, was madly depraved and cruel. When insanity and brilliancy are found in the ancestry it seems merely a matter of chance as to whether the determiners for greatness will be thrown together hi the union of sperm and egg or those for insanity. We can predict with some certainty, that, in a large number of offspring, ability will reappear and insanity will reappear, but just what individual each will strike it is impossible to prophesy without knowing much more definitely the nature of the germ plasm involved. One may say that the convergence of a number of lines of descent from great ancestors toward one individual makes it probable that he will be exceptionally able. This is nowhere better illustrated than in the family tree of Frederick the Great of the Prussian house of Hohenzollern, as will be seen from the chart on page 470. Of his great-grandparents, three scale 10, one 9, one 8, two 7, and one 6. Not one is below mediocrity, and the majority are of very high grade. Of his fourteen ancestors back three generations, only one is distinctly inferior. Of his brothers and sisters, four are distinctly great, three mediocre, and one inferior. It is interesting to trace the effect of the mating of such splendid stock with another brilliant line, that of the Swedish royal house. Gustavus I, or Gustavus Vasa, is another instance of the brilliant mutant, with some taint of neurosis. He married a gentle and tactful princess; their son Charles DC was a very able man, although of their 470 READINGS IN EVOLUTION, GENETICS, AND EUGENICS INHERITANCE OF HUMAN CHARACTERS 471 472 READINGS IN EVOLUTION, GENETICS, AND EUGENICS three other children one was insane and two weak. The children of Charles IX were both remarkably able. The daughter Catherine becomes the mother of a later succession of kings. Her son Charles X and his son Charles XI were rather mediocre; but Charles XI, with this fine stock behind him, married Ulrica Eleanor (7), granddaughter of Christian IV of Denmark, the most brilliant of all Danish sovereigns, and Charles XII, their son, is pronounced by Voltaire the most remarkable man who ever existed. Charles XII had no children: the succession passed to his sister's son, Adolph Frederick of Holstein- Gottorp, who married Louisa Ulrica, sister of Frederick the Great of Prussia. The result of this union of two great lines of hereditary ability was Gustavus III, a fit successor of Gustavus Vasa, Gustavus Adolphus, and Charles XII; he was " a prodigy of talents," statesman, poet, dramatist. CHAPTER XXXV HUMAN CONSERVATION1 HERBERT E. WALTER I. HOW MANKIND MAY BE IMPROVED There are two fundamental ways to bring about human better- ment, namely, by improving the individual and by improving the race. The first method consists in making the best of whatever heritage has been received by placing the individual in the most favorable environment and developing his capacities to the utmost through education. The second method consists in seeking a better heritage with which to begin the life of the individual. The first method is immediate and urgent for the present generation. The second method is concerned with ideals for the future, and consequently does not usually present so strong an appeal to the individual. The first is the method of euthenics, or the science of learning to live well. The second is eugenics, which Gal ton defines as " the science of being well born." These two aspects of human betterment, however, are inseparable. Any hereditary characteristic must be regarded, not as an independent entity, but as a reaction between the germplasm and its environment. The biologist who disregards the fields of educational endeavor and environmental influence, is equally at fault with the sociologist who fails sufficiently to realize the fundamental importance of the germ- plasm. Without euthenic opportunity the best of heritages would never fully come to its own. Without the eugenic foundation the best opportunity fails of accomplishment. The euthenic point of view, however, must not distract the attention now, for the present chapter is particularly concerned with the program of eugenics. 2. MORE FACTS NEEDED Since the point of attack in human heredity must be largely statistical, it is of the first importance to collect more facts. Our actual knowledge is confused with a mass of tradition and opinion, 1 From H. E. Walter, Genetics (copyright 1913). Used by special permission of the publishers, The Macmillan Company. 474 READINGS IN EVOLUTION, GENETICS, AND EUGENICS much of which rests upon questionable foundations. The great present need is to learn more facts; to sift the truth from error in what is already known ; and to reduce all these data to workable scientific form. Much progress is being made hi this direction, owing to the impetus given by the revival of Mendel's illuminating work, but as yet the science of eugenics is in its infancy. The most systematic and effective attempt in this country to collect reliable data concerning heredity in man has been initiated by the Eugenics Section of the American Breeders' Association under the secretaryship of Dr. C. B. Davenport. In 1910 the Eugenics Record Office, with a staff of expert field and office workers and an adequate equipment of fire-proof vaults, etc., for the preservation of records, was opened at Cold Spring Harbor, Long Island, New York, with Mr. H. H. Laughlin as superintendent. "The main work of this office is investigation into the laws of inheritance of traits hi human beings and their application to eugenics. It proffers its services free of charge to persons seeking advice as to the consequences of pro- posed marriage matings. In a word, it is devoted to the advance- ment of the science and practice of eugenics." The publication of results from the Eugenics Record Office has already been begun. The Volta Bureau, founded about twenty-five years ago in Washington by Dr. Alexander Graham Bell, is collecting data with reference to deafness and has now systematically arranged particu- lars concerning the history of over 20,000 individuals. In England, also, the Galton Laboratory for Eugenics, founded in 1905, is system- atically collecting facts about human pedigrees and publishing the results in a compendious "Treasury of Human Inheritance." Besides these special bureaus of investigation, innumerable facts about the inheritance of particular traits are being incidentally brought together and made available in various institutions and asylums throughout the world which are immediately concerned with the care of defectives of different types. It is hi connection with such institu- tions for defectives that much of the most successful "field work" of the Eugenics Section of the American Breeders' Association is being accomplished in the United States. 3. FURTHER APPLICATION OF WHAT WE KNOW NECESSARY Human performance always lags behind human knowledge. Many persons who are fully aware of the right procedure do not put their knowledge into practice. It follows, therefore, that any pro- HUMAN CONSERVATION 475 gram of eugenics which does not grip the imagination of the common people in such a way as to become an effective part of their very lives is bound to remain largely an academic affair for Utopians to quarrel and theorize over. It is not enough to collect facts and work out an analysis and interpretation of them, for, important as this preliminary step is, it must be followed by a convincing campaign of education. The lives of the unborn do not force themselves upon the average man or woman with the same insistency as the lives already begun. In the midst of the overwhelming demands of the present, the appeal of posterity for better blood is vague and remote. If every individual regarded the germplasm he carries as a sacred trust, then it would be the part of an awakened eugenic conscience to restrain that germplasm when it is known to be defective or, when it is not defective, to hand it on to posterity with at least as much foresight as is exercised in breeding domestic animals and cultivated plants. The eugenic conscience is hi need of development, and it is only when this becomes thoroughly aroused in the rank and file of society as well as among the leaders, that a permanent and increasing better- ment of mankind can be expected. 4. THE RESTRICTION OF UNDESIRABLE GERMPLASM A negative way to bring about better blood hi the world is to follow the clarion call of Davenport, and "dry up the streams that feed the torrent of defective and degenerate protoplasm." This may be partially accomplished, at least in America, by employing the following agencies: control of immigration; more discriminating marriage laws; a quickened eugenic sentiment; sexual segregation of defectives; and finally, drastic measures of asexualization or steriliza- tion when necessary. a) CONTROL OF IMMIGRATION The enforcement of immigration laws tends to debar from the United States not only many undesirable individuals, but also inci- dentally to keep out much potentially bad germplasm that, if admitted, might play havoc with future generations. For example, during the year of 1908, 65 idiots, 121 feeble-minded, 184 insane, 3,741 paupers, 2,900 individuals having contagious dis- eases, 53 tuberculous individuals, 136 criminals, and 124 prostitutes were caught hi the sieve at Ellis Island alone and turned back from this country by the immigration officials. These 7,000 and more 476 READINGS IN EVOLUTION, GENETICS, AND EUGENICS individuals probably were the bearers of very little germplasm that we are nationally not better off without. Eugenically, the weak point in the present application of immi- gration laws is that criteria for exclusion are phenotypic in nature rather than genotypic, and consequently much bad germplasm comes through our gates hidden from the view of inspectors because the bearers are heterozygous, wearing a cloak of desirability over undesir- able traits. It is not enough to lift the eyelid of a prospective parent of Ameri- can citizens to discover whether he has some kind of an eye-disease or to count the contents of his purse to see if he can pay his own way. The official ought to know if eye-disease runs in the immigrant's family and whether he comes from a race of people which, through chronic shiftlessness or lack of initiative, have always carried light purses. In selecting horses for a stock-farm an expert horseman might rely to a considerable extent upon his judgment of horseflesh based upon inspection alone, but the wise breeder does more than take the chances of an ordinary horse trader. He wants to be assured of the pedigree of his prospective stock. It is to be hoped that the time will come when we, as a nation, will rise above the hazardous methods of the horse trader in selecting from the foreign applicants who knock at our portals, and that we will exercise a more fundamental discrimination than such a haphazard method affords, by demanding a knowledge of the germplasm of these candidates for citizenship, as displayed hi their pedigrees. This may possibly be accomplished by having trained inspectors located abroad in the communities from which our immigrants come, whose duty it shall be to look up the ancestry of prospective applicants and to stamp desirable ones with approval. The national expense of such a program of genealogical inspection would be far less than the maintenance of introduced defectives, in fact it would greatly decrease the number of defectives in the country. At the present time this country is spending over one hundred million dollars a year on defectives alone, and each year sees this amount increased. The United States Department of Agriculture already has field agents scouring every land for desirable animals and plants to intro- duce into this country, as well as stringent laws to prevent the importa- tion of dangerous weeds, parasites, and organisms of various kinds. Is the inspection and supervision of human blood less important ? HUMAN CONSERVATION 477 b) MORE DISCRIMINATING MARRIAGE LAWS Every people, including even the more primitive races, make customs or laws that tend to regulate marriage. Of these, the laws which relate to the eugenic aspect of marriage are the only ones that concern us in this connection. "Marriage," says Davenport, "can be looked at from many points of view. In novels as the climax of human courtship; hi law largely as two lines of property descent; in society, as fixing a certain status; but hi eugenics, which considers its biological aspect, marriage is an experiment hi breeding." Certain of the United States have laws forbidding the marriage of epileptics, the insane, habitual drunkards, paupers, idiots, feeble- minded, and those afflicted with venereal diseases. It would be well if such laws were not only more uniform and widespread, but also more rigidly enforced. It is quite true that marriage laws hi themselves do not necessarily control human reproduction, for illegitimacy is a factor that must always be reckoned with; nevertheless such laws do have an important influence in regulating marriage and consequent reproduction. Marriage laws may, however, sometimes bring about a deplor- able result eugenically, as hi the case of forced marriage of sexual offenders in order to legalize the offense and "save the woman's honor." To compel, under the guise of legality, two defective streams of germplasm to combine repeatedly and thereby result in defective offspring just because the unfortunate event happened once illegiti- mately, is fundamentally a mistake. Darwin says: "Except in the case of man himself hardly any one is so ignorant as to allow his worst animals to breed." tf) AN EDUCATED SENTIMENT A far more effective means of restricting bad germplasm than placing elaborate marriage laws upon our statute-books is to educate public sentiment and to foster a popular eugenic conscience, hi the absence of which the safeguards of the law must forever be largely without avail. Such a sentiment already generally exists to a large extent with respect to incest, and the marriage of persons as noticeably defective as idiots or those afflicted with insanity, and also in America with respect to miscegenation, but a cautious and intelligent examination of the more obscure defective traits, exhibited in the somatoplasms of the various members of families hi question, is largely an ideal of the 478 READINGS IN EVOLUTION, GENETICS, AND EUGENICS future. Under existing conditions non-eugenic considerations such as wealth, social position, etc., often enter into the preliminary negotia- tions of a marriage alliance, but an equally unromantic caution with reference to the physical, moral, and mental characters that make up the biological heritage of contracting parties is less usual. The scientific attitude is not necessarily opposed to the romantic way of looking at things. Science is simple "organized common sense," and romance, that dispenses with this balance-wheel, although it may be entertaining and always exciting at first, is sure to be dis- appointing in the end. Marriages may be "made hi heaven," but, as a matter of fact, children are born and have to be brought up on earth. It follows without saying that it will be much easier to stamp out bad germplasm when an educated sentiment becomes common among all people everywhere. d) SEGREGATION OF DEFECTIVES Persons with hereditary defects, such as epileptics, idiots, and certain criminals, who become wards of the state, should be segregated so that then- germplasm may not escape to furnish additional burdens to society. " We have become so used to crime, disease and degener- acy that we take them for necessary evils. That they were hi the world's ignorance, is granted. That they must remain so, is denied" (Davenport). "The great horde of defectives once in the world have the right to live and enjoy as best they may whatever freedom is compatible with the lives and freedom of other members of society," says Kellicott, but society had a right to protect itself against repetitions of hereditary blunders. There is one grave danger connected with the administration of our humane and commendable philanthropies toward the unfortunate, for it frequently happens that defectives are kept hi institutions until they are sexually mature or are partly self-supporting, when they are liberated only to add to the burden of society by reproducing their like. Furthermore, if defectives of the same sort are collected together hi the same institutions, unless sexual segregation is strictly main- tained, they may by the very circumstance of proximity tend to reproduce their kind just as defectives hi any isolated community tend to multiply. David Starr Jordan cites the interesting case of cretinism which occurs in the valley of Aosta hi northern Italy, to prove the wisdom HUMAN CONSERVATION 479 of the sexual segregation of defectives. Cretinism is an hereditary defect connected with an abnormal development of the thyroid gland which results hi a peculiar form of idiocy usually associated with goitre. "In the city of Aosta the goitrous cretin has been for centuries an object of charity. The idiot has received generous support, while the poor farmer or laborer with brains and no goitre has had the severest of struggles. In the competition of life a premium has thus been placed on imbecility and disease. The cretin has mated with cretin, the goitre with goitre, and charity and religion have presided over the union. The result is that idiocy is multiplied and intensified. The cretin of Aosta has been developed as a new species of man. In fair weather the roads about the city are lined with these awful paupers — human beings with less intelligence than a goose, with less decency than the pig." Whymper, writing hi 1880, further observes: "It is strange that self-interest does not lead the natives of Aosta to place their cretins under such restrictions as would prevent their illicit intercourse; and it is still more surprising to find the Catholic Church actually legalizing their marriage. There is something horribly grotesque in the idea of solemnizing the union of a brace of idiots, and, since it is well known that the disease is hereditary and develops in successive generations the fact that such marriages are sanctioned is scandalous and infamous." Since 1890 the cretins have been sexually segregated, and in 1910 Jordan reported that they were nearly all gone, 6) DRASTIC MEASURES A fifth method of restricting undesirable germplasm hi the case of confirmed criminals, idiots, imbeciles, and rapists may be mentioned, namely, the extreme treatment of either asexualization or vasectomy. The latter is a minor operation confined to the male which occupies only a few moments and requires at most only the application of a local anaesthetic, such as cocaine. There are no disturbing or even inconvenient after effects from this operation. It consists in removing a small section of each sperm duct, and is entirely effectual in prevent- ing subsequent parenthood. In the female the corresponding operation, which consists in removing a portion of each Fallopian tube, is much more severe, but not impracticable or dangerous. Eight states already have sterilization laws providing for certain cases and "could such a law be enforced in the whole United States, 480 READINGS IN EVOLUTION, GENETICS, AND EUGENICS less than four generations would eliminate nine tenths of the crime, insanity and sickness of the present generation hi our land. Asylums, prisons and hospitals would decrease, and the problems of the unem- ployed, the indigent old and the hopelessly degenerate would cease to trouble civilization." 5. THE CONSERVATION OF DESIRABLE GERMPLASM Not only negatively by the restriction of undesirable germplasm, but also positively by the conservation of desirable germplasm, may the eugenic ideal be approached. It is possible that if some of the philanthropic endeavor now directed toward alleviating the condition of the unfit should be directed to enlarging the opportunity of the fit, greater good would result in the end. In breeding animals and plants the most notable advances have been made by isolating and developing the best, rather than by attempting to raise the standard of mediocrity through the elimination of the worst. One leader is worth a score of followers in any community, and the science of genetics surely gives to educators the hint that it is wiser to cultivate the exceptional pupil who is often left to take care of him- self than to expend all the energies of the instructor in forcing the indifferent or ordinary one up to a passing standard. The campaign for human betterment in the long run must do more than avoid mis- takes. It must become aggressive and take advantage of those human mutations or combinations of traits which appear in the exceptionally endowed. There are various ways hi which this improvement of society may be brought about. a) BY SUBSIDIZING THE FIT The following unconfirmed newspaper clipping illustrates the point of what is meant by subsidizing the fit so far as certain physical characteristics are concerned. "Berlin, Dec. n, 1911. The Emperor is reported to be interested in a plan proposed by Professor Otto Hauser for the propagation of a fixed German type of humanity — a type which will be as fixed as the Jewish in its characteristics, if the suggestions of the professor can ever be carried out. The fixed type is to be produced as follows: — Only ' typical' couples are to be allowed to mate. The man is to be not more than thirty years old, the woman not over twenty-eight, and each have a perfect health certificate. The man should be at least five feet seven inches tall ; the woman not under HUMAN CONSERVATION 481 five feet six inches. Neither the man nor the woman should have dark hair. Its tint may range from blonde to auburn. The eyes of the pair should be pure blue without any tint of brown. The complexion should be fair to ruddy without any suggestion of heaviness or ' beefi- ness.' The nose ought to be strong and narrow, the chin square and powerful, and the skull well developed at the back. The man and the woman must be of German descent and must bear a German name and speak the language of Germany. These 'mated couples' are to get a wedding gift of $125 and an additional grant for each child born. The couples may settle in the United States if they prefer." This reported attempt to establish a Prussian type of "Hauser blondes "at least points the way to one sort of a positive eugenic method that might possibly be employed with respect to certain physical charac- teristics. It should be remembered, however, that the eugenic ideal is not by any means confined to physical traits alone. ft) BY ENLARGING INDIVIDUAL OPPORTUNITY Much good human germplasm goes to waste through ineffective- ness on account of unfavorable environment or lack of a suitable opportunity to develop. Every agency which contributes toward increasing the opportunity of the individual to attain to a better development of his latent possibilities is in harmony with a thoroughly positive eugenic practice. Thus better schools, better homes, better living conditions, hi short, all euthenic endeavor, directly serves the eugenic ideal by making the best out of whatever germinal equipment is present in man. C) BY PREVENTING GERMINAL WASTE Much good protoplasm fails to find expression hi the form of off- spring because one or the other of possible parents is cut off either by preventable death or by social hindrances. To avoid such calamities is a part of the positive program of eugenics. i. Preventable death. — War, from the eugenic point of view, is the height of folly, since presumably the brave and the physically fit march away to fight, while in general the unqualified stay at home to reproduce the next generation. When a soldier dies on the battlefield or hi the hospital, it is not alone a brave man who is cut off, but it is the termination of a probably desirable strain of germplasm. The Thirty Years' War hi Germany cost 6,000,000 lives, while Napoleon in his campaigns drained the best blood of France. 482 READINGS IN EVOLUTION, GENETICS, AND EUGENICS David Starr Jordan has presented the matter very clearly. He points out that the "man with a hoe" among the European peasantry is not the result of centuries of oppression, as he has been pictured, but rather the dull progeny resulting from generations of the unfit who were left behind when the fit went off to war never to return. Benjamin Franklin, with characteristic wisdom, sums up the situation in the following epigram: "Wars are not paid for in war time; the bill comes later." 2. Social hindrances. — There are many conditions of modern society which act non-eugenically. For instance, the increasing demands of professional life prolong the period necessary for preparation, which, with the "cost of high living," tends toward late marriage. In this way much of the best germplasm is very often withheld from circulation until it is too late to be effective hi providing for the succeeding generation. Certain occupations such as school- teaching and nursing by women are filled by the best blood obtainable, yet this Hood is denied a direct part in molding posterity, since marriage is either forbidden or regarded as a serious handicap in such lines of work. Advertisements concerning " unincumbered help" and "childless apartments" tell their own deplorable tale. One of the darkest features of the dark ages from a eugenic stand- point was the enforced celibacy of the priesthood, since this resulted, as a rule, in withdrawing into monasteries and nunneries much of the best blood of the times, and this uneugenic custom still obtains in many quarters today. 6. WHO SHALL SIT IN JUDGMENT? In the practical application of a program of eugenics there are many difficulties, for who is qualified to sit hi judgment and separate the fit from the unfit ? There are certain strongly marked characteristics in mankind which are plainly good or bad, but the principle of the independence of unit characters demonstrates that no person is wholly good or wholly bad. Shall we then throw away the whole bundle of sticks because it contains a few poor or crooked ones ? The list of weakling babies, for instance, who were apparently physically unfit and hardly worth raising upon first judgment, but who afterwards became powerful factors in the world's progress, is a notable one and includes the names of Calvin, Newton, Heine, Voltaire, Herbert Spencer, and Robert Louis Stevenson. HUMAN CONSERVATION 483 Or, take another example. Elizabeth Tuttle, the grandmother of Jonathan Edwards whose remarkable progeny was referred to in a preceding chapter, is described as a "woman of great beauty, of tall and commanding appearance, striking carriage, of strong will, extreme intellectual vigor and mental grasp akin to rapacity," but with an extraordinary deficiency in moral sense. She was divorced from her husband "on the ground of adultery and other immoralities The evil trait was hi the blood, for one of her sisters murdered her own son and a brother murdered his own sister." That Jonathan Edwards owed his remarkable qualities largely to his grandmother rather than to his grandfather is shown by the fact that Richard Edwards, the grandfather, married again after his divorce and had five sons and one daughter, but none of their numerous progeny " rose above mediocrity, and their descendants gained no abiding reputa- tion." As shown by subsequent events, it would have been a great eugenic mistake to have deprived the world of Elizabeth Tuttle's germplasm, although it would have been easy to find judges to con- demn her. Dr. C. V. Chapin recently said with reference to the eugenic regulation of marriage by physician's certificate: "The causes of heredity are many and very conflicting. The subject is a difficult one, and I for one would hesitate to say, hi a great many cases where I have a pretty good knowledge of the family, where marriage would, or would not, be desirable." Desirability and undesirability must always be regarded as rela- tive terms more or less indefinable. In attempting to define them, it makes a great difference whether the interested party holds to a puritan or a cavalier standard. To show how far human judgment may err as well as how radically human opinion changes, there were in England, as recently as 1819, 233 crimes punishable by death accord- ing .to law. One needs only to recall the days of the Spanish Inquisition or of the Salem witchcraft persecution to realize what fearful blunders human judgment is capable of, but it is unlikely that the world will ever see another great religious inquisition, or that hi applying to man the newly found laws of heredity there will ever be undertaken an equally deplorable eugenic inquisition. It is quite apparent, finally, that although great caution and broadness of vision must be exercised hi bringing about the fulfilment of the highest eugenic ideals, nevertheless in this direction lies the future path of human achievement. CHAPTER XXXVI EUGENICS AND EUTHENICS' PAUL POPENOE AND ROSWELL H. JOHNSON Emphasis has been given, in several of the foregoing chapters, to the desirability of inheriting a good constitution and a high degree of vigor and disease-resistance. It has been asserted that no measures of hygiene and sanitation can take the place of such inheritance. It is now desirable to ascertain the limits within which good inheritance is effective, and this may be conveniently done by a study of the lives of a group of people who inherited exceptionally strong physical con- stitutions. The people referred to are taken from a collection of histories of long life made by the Genealogical Record Office of Washington. One hundred individuals were picked out at random, each of whom had died at the age of ninety or more, and with the record of each indi- vidual were placed those of all his brothers and sisters. Any family was rejected in which there was a record of wholly accidental death (e.g., families of which a member had been killed in the Civil War). The 100 families, or more correctly fraternities or sibships, were classified by the number of children per fraternity, as follows: Number of Fraternities Number of Children per Fraternity Total Number of Children in Group I 2 2 II 3 33 8 4 32 17 5 85 13 6 78 14 7 98 9 8 72 ii 9 99 10 10 IOO 3 ii 33 2 12 24 I 13 13 loo 669 1 From P. Popenoe and R. H. Johnson, Applied Eugenics (copyright 1918). Used by special permission of the publishers, The Macmillan Company. 484 EUGENICS AND EUTHENICS 485 The average at death of these 669 persons was 64.7 years. The child mortality (first 4 years of life) was 7.5 per cent of the total mortality, 69 families showing no deaths of that kind. The group is as a whole, therefore, long-lived. The problem was to measure the resemblance between brothers and sisters hi respect of longevity — to find whether knowledge of the age at which one died would justify a prediction as to the age at death of the others — or technically, it was to measure the fraternal correlation of longevity. A zero coefficient here would show that there is no association; that from the age at which one dies, nothing whatever can be predicted as to the age at which the others will die. Since it is known that heredity is a large factor in longevity, such a finding would mean that all deaths were due to some accident which made the inheritance of no account. In an ordinary population it has been found that the age at death of brothers and sisters furnishes a coefficient of correlation of the order of .3, which shows that heredity does determine the age at which one shall die to considerable extent, but not absolutely.1 The index of correlation2 between the lengths of life within the fraternity in these 100 selected families, furnished a coefficient of — .0163 =*= .0672, practically zero. In other words, if the age is known at which a member of one of these families died, whether it be one month or 100 years, nothing whatever can be predicted about the age at which his brothers and sisters died. 1 Mary Beeton, and Karl Pearson, Biometrika, I, p. 60. The actual correlation varies with the age and sex: the following are the results: COLLATERAL INHERITANCE Elder adult brother and younger adult brother 2200* .0194 Adult brother and adult brother 2853* .0196 Minor brother and minor brother 1026* .0294 Adult brother and minor brother — .0262=*= .0246 Elder adult sister and younger adult sister 3464=*= .0183 Adult sister and adult sister 3322=* .0185 Minor sister and minor sister 1748=*= .0307 Adult sister and minor sister — .0260^= .0291 Adult brother and adult sister 2319=41 .0145 Minor brother and minor sister 1435=*= -0251 Adult brother and minor sister — .0062=*= .0349 Adult sister and minor brother — .0274* .0238 "The method used is the ingenious one devised by J. Arthur Harris (Biometrika, IX, p. 461). The probable error is based on w= 100. 486 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Remembering that longevity is in general inherited, and that it is found in the families of all the people of this study (since one in each fraternity lived to be 90 or over) how is one to interpret this zero coefficient? Evidently it means that although these people had inherited a high degree of longevity, their deaths were brought about by causes which prevented the heredity from getting full expression. As far as hereditary potentialities are concerned, it can be said that all their deaths were due to accident, using that word in a broad sense to include all non-selective deaths by disease. If they had all been able to get the full benefit of their heredity, it would appear that each of these persons might have lived to 90 or more, as did the one in each family who was recorded by the Genealogical Record Office. Geneti- cally, these other deaths may be spoken of as premature. In an ordinary population, the age of death is determined to the extent of probably 50 per cent by heredity. In this selected long- lived population, heredity appears not to be responsible hi any meas- urable degree whatsoever for the differences in age at death. The result may be expressed in another, and perhaps more striking, way. Of the 669 individuals studied, a hundred — namely, one child in each family — lived beyond 90; and there were a few others who did. But some 550 of the group, though they had inherited the potentiality of reaching the average age of 90, actually died somewhere around 60; they failed by at least one-third to live up to the promise of their inheritance. If we were to generalize from this single case, we would have to say that five-sixths of the population does not make the most of its physical inheritance. This is certainly a fact that discourages fatalistic optimism. The man who tells himself that, because of his magnificent inherited constitution, he can safely take any risk, is pretty sure to take too many risks and meet with a non-selective — i.e., genetically, a pre- mature— death, when he might hi the nature of things have lived almost a generation longer. It should be remarked that most of the members of this group seem to have lived in a hard environment. They appear to belong predominantly to the lower strata of society; many of them are immi- grants and only a very few of them, to judge by a cursory inspection of the records, possessed more than moderate means. This necessi- tated a frugal and industrious life which in many ways was favorable to longevity but which may often have led to overexposure, overwork, lack of proper medical treatment, or other causes of a non-selective EUGENICS AND EUTHENICS 487 death. We would not push the conclusion too far, but we can not doubt that this investigation shows the folly of ignoring the environ- ment— shows that the best inherited constitution must have a fair chance. And what has here been found for a physical character, would probably hold good in even greater degree for a mental charac- ter. All that man inherits is the capacity to develop along a certain line under the influence of proper stimuli, food and exercise. The object of eugenics is to see that the inherent capacity is there. Given that, the educational system is next needed to furnish the stimuli. The consistent eugenist is therefore an ardent euthenist. He not only works for a better human stock but, because he does not want to see his efforts wasted, he always works to provide the best possible envi- ronment for this better stock. In so far, then, as euthenics is actually providing man with more favorable surroundings — not with ostensibly more favorable sur- roundings which, in reality, are unfavorable — there can be no antago- nism between it and eugenics. Eugenics is, in fact, a prerequisite of euthenics, for it is only the capable and altruistic man who can con- tribute to social progress; and such a man can only be produced through eugenics. Eugenic fatalism, a blind faith hi the omnipotence of heredity regardless of the surroundings in which it is placed, has been shown by the study of long-lived families to be unjustified. It was found that even those who inherited exceptional longevity usually did not live as long as their inheritance gave them the right to expect. If they had had more euthenics, they should have lived longer. But this illustration certainly gives no ground for a belief that euthenics is sufficient to prolong one's life beyond the inherited limit. A study of these long-lived families from another point of view will reveal that heredity is the primary factor and that good environment, euthenics, is the secondary one. For this purpose we augment the 100 families of the preceding section by the addition of 240 more families like them, and we examine each family history to find how many of the children died before com- pleting the fourth year of life. The data are summarized hi the table on page 488. The addition of the new families (which were not subjected to any different selection than the first 100) has brought down the child mortality rate. For the first 100, it was found to be 7.5 per cent. If in the above table the number of child deaths, 119, be divided by the 488 READINGS IN EVOLUTION, GENETICS, AND EUGENICS total number of children represented, 2,259, the child mortality rate for this population is found to be 5.27 per cent or 53 per 1,000. The smallness of this figure may be seen by comparison with the statistics of the registration area, U.S. Census of 1880, when the child mortality (0-4 years) was 400 per thousand, as calculated by Alexan- der Graham Bell. A mortality of 53 for the first four years of life is smaller than any district known in the United States, even to-day, can show for the first year of life alone. If any city could bring the deaths of babies during their first twelve months down to 53 per 1,000, it would think it had achieved the impossible; but here is a population CHILD MORTALITY IN FAMILIES OF LONG-LIVED STOCK, GENEALOGICAL RECORD OFFICE DATA Size Number of Number of Families Total Number of Families Showing Deaths of Family Investigated under Five Years Deaths 1 child 600 2 children 600 3 38 4 5 4 40 6 7 5 38 4 4 6 44 12 13 7 34 . 8 ii 8 46 13 18 9 3i 14 20 10 27 14 14 11 13 6 9 12 13 9 16 13 100 14 200 17 112 340 91 119 in which 53 per 1,000 covers the deaths, not only of the fatal first 12 months, but of the following three years in addition. Now this population with an unprecedentedly low rate of child mortality is not one which had had the benefit of any Baby Saving Campaign, nor even the knowledge of modern science. Its mothers were mostly poor, many of them ignorant; they lived frequently under conditions of hardship ; they were peasants and pioneers. Their babies grew up without doctors, without pasteurized milk, without ice, without many sanitary precautions, usually on rough food. But they had one advantage which no amount of applied science can give after birth — namely, good heredity. They had inherited exceptionally good constitutions. EUGENICS AND EUTHENICS 489 It is not by accident that inherited longevity in a family is associ- ated with low mortality of its children. The connection between the two facts was first discovered by Mary Beeton and Karl Pearson in their pioneer work on the inheritance of duration of life. They found that high infant mortality was associated with early death of parents, while the offspring of long-lived parents showed few deaths in child- hood. The correlation of the two facts was quite regular, as will be evident from a glance at the following tables prepared by A. Ploetz: LENGTH OF LIFE OF MOTHERS AND CHILD MORTALITY OF THEIR DAUGHTERS (ENGLISH QUAKER FAMILIES, DATA OF BEETON AND PEARSON, ARRANGED BY PLOETZ) YEAR OF Lira IN WHICH MOTHERS DIED Ax ALL AGES to 38 39-S3 S4-68 69-83 84 up Number of daughters Number of them who died in first five years 234 122 52-1 304 114 37-5 395 118 29.9 666 131 19.7 247 26 10.5 1,846 5" 27.7 Per cent of daughters who died. . . LENGTH OF LIFE OF FATHERS AND CHILD MORTALITY OF THEIR DAUGHTERS YEAR OF LIFE IN WHICH FATHERS DIED AT ALL AGES to 38 30-53 S4-68 60-83 84 up 105 51 48.6 284 98 34-5 585 156 26.7 797 177 22.2 236 40 17.0 2,009 522 26.0 Number of them who died in first five Per cent of daughters who died. . . To save space, we do not show the relation between parent and son; it is similar to that of parent and daughter which is shown in the preceding tables. In making comparison with the 340 families from the Genealogical Record Office, above studied, it must be noted that Dr. Ploetz's tables include one year longer in the period of child mor- tality, being computed for the first five years of life instead of the first four. His percentages would therefore be somewhat lower if com- puted on the basis used in the American work. These various data demonstrate the existence of a considerable correlation between short life (brachybioty, Karl Pearson calls it) in parent and short life hi offspring. Not only is the tendency to live long inherited, but the tendency not to live long is likewise inherited. 490 READINGS IN EVOLUTION, GENETICS, AND EUGENICS But perhaps the reader may think they show nothing of the sort. He may fancy that the early death of a parent left the child without sufficient care, and that neglect, poverty, or some other factor of euthenics brought about the child's death. Perhaps it lacked a mother's loving attention, or perhaps the father's death removed the wage-earner of the family and the "child thenceforth lacked the necessities of life. Dr. Ploetz has pointed out that this objection is not valid, because the influence of the parent's death is seen to hold good even to the point where the child was too old to require any assistance. If the facts applied only to cases of early death, the supposed objection might be weighty, but the correlation exists from one end of the age- scale to the other. It is not credible that a child is going to be deprived of any necessary maternal care when its mother dies at the age of 69; the child herself was probably married long before the death of the mother. Nor is it credible that the death of the father takes bread from the child's mouth, leaving it to starve to death in the absence of a pension for widowed mothers, if the father died at 83, when the " child " herself was getting to be an old woman. The early death of a parent may occasionally bring about the child's death for a reason wholly unconnected with heredity, but the facts just pointed out show that such cases are exceptional. The steady association of the child death- rate and parent death-rate at all ages demonstrates that heredity is a common cause. But the reader may suspect another fallacy. The cause of this association is really environmental, he may think, and the same poverty or squalor which causes the child to die early may cause the parent to die early. They may both be of healthy, long-lived stock, but forced to live in a pestiferous slum which cuts both of them off prematurely and thereby creates a spurious correlation in the statistics. We can dispose of this objection most effectively by bringing in new evidence. It will probably be admitted that in the royal families of Europe, the environment is as good as knowledge and wealth can make it. No child dies for lack of plenty of food and the best medical care, even if his father or mother died young. And the members of this caste are not exposed to any such unsanitary conditions, or such economic pressure as could possibly cause both parent and child to die prematurely. If the association between longevity of parent and child mortality holds for the royal families of Europe and their princely EUGENICS AND EUTHENICS 491 relatives, it can hardly be regarded as anything but the effect of heredity— of the inheritance of a certain type of constitution. Dr.Ploetz studied the deaths of 3,210 children inEuropean royalty, from this viewpoint. The following table shows the relation between father and child: LENGTH OF LIFE OF FATHERS AND CHILD MORTALITY OF THEIR CHILDREN IN ROYAL AND PRINCELY FAMILIES (PLOETZ DATA) YEAR OF Lira IN WHICH FATHERS DIED AT ALL AGES 16-25 26-35 36-45 46-55 56-65 66-75 76-85 86 up Number of children *3 12 52.2 00 29 32.2 367 "5 3i-3 545 171 3i-4 725 200 27.6 983 254 2S.8 444 i°5 23.6 33 I 3-o 3210 887 27.6 Number who died in first five years. Per cent who died Allowing for the smallness of some of the groups, it is evident that the amount of correlation is about the same here as among the English Quakers of the Beeton-Pearson investigation, whose mortality was shown in the two preceding tables. In the healthiest group from the royal families — the cases in which the father lived to old age — the amount of child mortality is about the same as that of the Hyde family in America, which Alexander Graham Bell has studied — namely, somewhere around 250 per 1,000. One may infer that the royal families are rather below par in soundness of constitution. All these studies agree perfectly in showing that the amount of child mortality is determined primarily by the physical constitution of the parents, as measured by their longevity. In the light of these facts, the nature of the extraordinarily low child mortality shown hi the 340 families from the Genealogical Record Office, with which we began the study of this point, can hardly be misunderstood. These families have the best inherited constitution possible and the other studies cited would make us certain of finding a low child mortality among them, even if we had not directly investigated the facts. If the interpretation which we have given is correct, the conclusion is inevitable that child mortality is primarily a problem of eugenics, and that all other factors are secondary. There is found to be no warrant for the statement so often repeated hi one form or another, that " the fundamental cause of the excessive rate of infant mortality in industrial communities is poverty, inadequate incomes, and low standards of living." Royalty and its princely relatives are not 492 READINGS IN EVOLUTION, GENETICS, AND EUGENICS characterized by a low standard of living, and yet the child mortality among them is very high — somewhere around 400 per 1,000 in cases where a parent died young. If poverty is responsible hi the one case, it must be in the other — which is absurd. Or else the logical absurdity is involved of inventing one cause to explain an effect today and a wholly different cause to explain the same effect tomorrow. This is unjustifiable in any case, and it is particularly so when the single cause that explains both cases is so evident. If weak heredity causes high mortality in the royal families, why, similarly, cannot weak heredity cause high infant mortality in the industrial communities? We believe it does account for much of it, and that the inadequate income and low standard of living are largely the consequence of inferior heredity, mental as well as physical. The parents in the Genealogical Record Office files had, many of them, inadequate incomes and low standards of living under frontier conditions, but their children grew up while those of the royal families were dying in spite of every attention that wealth could command and science could furnish. If the infant mortality problem is to be solved on the basis of knowledge and reason, it must be recognized that sanitation and hygiene cannot take the place of eugenics any more than eugenics can dispense with sanitation and hygiene. It must be recognized that the death-rate in childhood is largely selected, and that the most effective way to cut it down is to endow the children with better constitutions. This cannot be done solely by any euthenic cam- paign; it cannot be done by swatting the fly, abolishing the mid- wife, sterilizing the milk, nor by any of the other panaceas sometimes proposed. But, it may be objected, this discussion ignores the actual facts. Statistics show that infant mortality campaigns have consistently produced reductions in the death-rate. The figures for New York, which could be matched in dozens of other cities, show that the num- ber of deaths per 1,000 births, in the first year of life, has steadily declined since a determined campaign to ''Save the Babies" was started: I2S 162 112 icx 1006 JC7 IO2 . . . 144 • 05 1008. . . ...128 EUGENICS AND EUTHENICS 493 To one who cannot see beyond the immediate consequences of an action, such figures as the above indeed give quite a different idea of the effects of an infant mortality campaign, than that which we have just tried to create. And it is a great misfortune that euthenics so often fails to look beyond the immediate effect, fails to see what may happen next year, or 10 years from now, or in the next generation. We admit that it is possible to keep a lot of children alive who would otherwise have died in the first few months of life. It is being done, as the New York figures, and pages of others that could be cited, prove. The ultimate result is twofold: 1. Some of those who are doomed by heredity to a selective death, but are kept alive through the first year, die in the second or third or fourth year. They must die sooner or later; they have not inherited sufficient resistance to survive more than a limited time. If they are by a great effort carried through the first year, it is only to die in the next. This is a statement which we have nowhere observed in the propaganda of the infant mortality movement; and it is perhaps a disconcerting one. It can only be proved by refined statistical methods, but several independent determinations by the English biometricians leave no doubt as to the fact. This work of Karl Pearson, E. C. Snow, and Ethel M. Elderton, was cited in our chapter on natural selection; the reader will recall how they showed that nature is weeding out the weaklings, and in proportion to the strin- gency with which she weeds them out at the start, there are fewer weaklings left to die in succeeding years. To put the facts in the form of a truism, part of the children born in any district in a given year are doomed by heredity to an early death; and if they die in one year they will not be alive to die in the succeeding year, and vice versa. Of course there are in addition infant deaths which are not selective and which if prevented would leave the infant with as good chance as any to live. In the light of these researches, we are forced to conclude that baby-saving campaigns accomplish less than is thought; that the supposed gain is to some extent temporary and illusory. 2. There is still another consequence. If the gain is by great exertions made more than temporary; if the baby who would other- wise have died in the first months is brought to adult life and repro- duction, it means in many cases the dissemination of another strain of weak heredity, which natural selection would have cut off ruthlessly 494 READINGS IN EVOLUTION, GENETICS, AND EUGENICS in the interests of race betterment. In so far, then, as the infant mortality movement is not futile it is, from a strict biological view- point, often detrimental to the future of the race. Do we then discourage all attempts to save the babies ? Do we leave them all to natural selection ? Do we adopt the " better dead " gospel ? Unqualifiedly, no! The sacrifice of the finer human feelings, which would accompany any such course, would be a greater loss to the race than is the eugenic loss from the perpetuation of weak strains of heredity. The abolition of altruistic and humanitarian sentiment for the purpose of race betterment would ultimately defeat its own end by making race betterment impossible. But race betterment will also be impossible unless a clear distinc- tion is made between measures that really mean race betterment of a fundamental and permanent nature, and measures which do not. We have chosen the Infant Mortality Movement for analysis in this chapter because it is an excellent example of the kind of social better- ment which is taken for granted, by most of its proponents, to be a fundamental piece of race betterment; but which, as a fact, often means race impairment. No matter how abundant and urgent are the reasons for continuing to reduce infant mortality wherever pos- sible, it is dangerous to close the eyes to the fact that the gain from it is of a kind that must be paid for in other ways; that to carry on the movement without adding eugenics to it will be a short-sighted policy, which increases the present happiness of the world at the cost of diminishing the happiness of posterity through the perpetuation of inferior strains. While some euthenic measures are eugenically evils, even if necessary ones, it must not be inferred that all euthenic measures are dysgenic. Many of them, such as the economic and social changes we have suggested hi earlier chapters, are an important part of eugenics. Every euthenic measure should be scrutinized from the evolutionary standpoint; if it is eugenic as well as euthenic, it should be whole- heartedly favored; if it is dysgenic but euthenic it should be con- demned or adopted, according to whether or not the gain hi all ways from its operation will exceed the damage. In general, euthenics, when not accompanied by some form of selection (Le., eugenics) ultimately defeats its own end. If it is accom- panied by rational selection, it can usually be indorsed. Eugenics, EUGENICS AND EUTHENICS 495 on the other hand, is likewise inadequate unless accompanied by constant improvement in the surroundings; and its advocates must demand euthenics as an accompaniment of selection, in order that the opportunity for getting a fair selection may be as free as possible. If the euthenist likewise takes pains not to ignore the existence of the racial factor, then the two schools are standing on the same ground, and it is merely a matter of taste or opportunity, whether one empha- sizes one side or the other. Each of the two factions, sometimes thought to be opposing, will be seen to be getting the same end result, namely, human progress. Not only are the two schools working for the same end, but each must depend hi still another way upon the other, in order to make headway. The eugenist cannot see his measures put into effect except through changes in law and custom — i.e., euthenic changes. He must and does appeal to euthenics to secure action. The social reformer, on the other hand, cannot see any improvements made hi civilization except through the discoveries and inventions of some citizens who are inherently superior in ability. He in turn must depend on eugenics for every advance that is made. It may make the situation clearer to state it in the customary terms of biological philosophy. Selection does not necessarily result in progressive evolution. It merely brings about the adaptation of a species or a group to a given environment. The tapeworm is the stock example. In human evolution, the nature of this environment will determine whether adaptation to it means progress or retro- gression, whether it leaves a race happier and more productive, or the reverse. All racial progress, or eugenics, therefore, depends on the creation of a good environment, and the fitting of the race to that environment. Every improvement in the environment should bring about a corresponding biological adaptation. The two factors hi evolution must go side by side, if the race is to progress hi what the human mind considers the direction of advancement. In this sense, euthenics and eugenics bear the same relation to human progress as a man's two legs do to his locomotion. Social workers hi purely euthenic fields have frequently failed to remember this progress of adaptation, in their efforts to change the environment. Eugenists, hi centering their attention on adaptation, have sometimes paid too little attention to the kind of environment to which the race was being adapted. The present book holds that the 496 READINGS IN EVOLUTION, GENETICS, AND EUGENICS second factor is just as important as the first, for racial progress; that one leg is just as important as the other, to a pedestrian. Its only con- flict with euthenics appertains to such euthenic measures as impair the adaptability of the race to the better environment they are trying to make. Some supposedly euthenic measures opposed by eugenics are not truly euthenic, as for instance the limitation of a superior family in order that all may get a college education. For these spurious euthenic measures, something truly euthenic should be substituted. Measures which show a real conflict may be typified by the infant mortality movement. There can be no doubt but that sanitation and hygiene, prenatal care and intelligent treatment of mothers and babies, are truly euthenic and desirable. At the same time, as has been shown, these euthenic measures result hi the survival of inferior children, who directly or through their posterity will be a drag on the race. Euthenic measures of this type should be accompanied by counterbalancing measures of a more eugenic character. Barring these two types, euthenics forms a necessary concomitant of the eugenic program; and, as we have tried to emphasize, eugenics is likewise necessary to the complete success of every euthenic program. How foolish, then, is antagonism between the two forces! Both are working toward the same end of human betterment, and neither can succeed without the other. When either attempts to eliminate the other from its work, it ceases to advance toward its goal. In which camp one works is largely a matter of taste. If on a road there is a gradient to be leveled, it will be brought down most quickly by two parties of workmen, one cutting away at the top, and the other filling in the bottom. For the two parties to indulge in mutual scorn and recrimination would be no more absurd than for eugenics and euthenics to be put hi opposition to each other. The only reason they have been in opposition is because some of the workers did not clearly understand the nature of their work. With the dissemination of a knowledge of biology, this ground of antagonism will disappear. CHAPTER XXXVH THE PROMISE OF RACE CULTURE' CALEB WILLIAMS SALEEBY The best is yet to be. In its form of what we have called negative eugenics, the practice of our principle would assuredly reduce to an incalculable extent the amount of human defect, mental and physical, which each generation now exhibits. This alone, as has been said, would be far more than sufficient to justify us. A world without hereditary disease of mind and body would alone warrant the hint of Ruskin that posterity may some day look back upon us with " incredulous disdain." Yet, assum- ing that this could be accomplished, as it will be accomplished, what more is to be hoped for ? Must race-culture cease merely when it has raised the average of the community by reducing to a minimum the proportion of those who are thus grossly defective in mind or body ? Such disease apart, are we to be content, must we be content, with the present level of mediocrity in respect of intelligence and temper and moral sentiment? Can we anticipate a London hi which the present ratio of musical comedy to great opera will be reversed, hi which the works of Mr. George Meredith will sell in hundreds of thousands, whilst some of our popular novelists will have to find other means of earning a living? Can we make for a critical democracy which no political party can fool, and which will choose its best to govern it ? Yet more, can we undertake, now or hereafter, to provide every generation with its own Shakespeare and Beethoven and Tintoretto and Newton ? What, hi a word, is the promise of positive eugenics ? It is to this aspect of the question that Mr. Galton has mainly directed himself. Indeed he was led to formulate the princi- ples and ideals of the new science by his study of hereditary genius some four decades ago. Let us now attempt to answer some of these questions. The production of genius. — And first as to the production of genius. It is this, perhaps, that has been the main butt of the jesters who pass for philosophers with some of us today. It may be said 1 From C. W. Saleeby, Parenthood and Race Culture (copyright 1909). Used by special permission of the publishers, Moffat, Yard, and Company. 497 498 READINGS IN EVOLUTION, GENETICS, AND EUGENICS at once that neither Mr. Galton nor any other responsible person has ever asserted that we can produce genius at will. The difficulties in the way of such a project — at present — are almost innumerable. One or two may be cited. In the first place, there is the cardinal — but by no means univer- sal—difficulty that the genius is too commonly so occupied with the development and expansion of his own individuality that he has little time or energy for the purposes of the race. This, of course, is an example of Spencer's great generalization as to the antagonism or inverse ratio between individuation and genesis. Again, there is the generalization of heredity formulated by Mr. Galton, and named by him the law of regression towards mediocrity. It asserts that the children of those who are above or below the mean of a race, tend to return towards that mean. The children of the born criminal will be probably somewhat less criminal in tendency than he, though more criminal than the average citizen. The children of the man of genius, if he has any, will probably be nearer mediocrity than he, though on the average possessing greater talent than the average citizen. It is thus not in the nature of sheer genius to reproduce on its own level. It is only the critics who are totally ignorant of the elemen- tary facts of heredity that attribute to the eugenist an expectation of which no one knows the absurdity so well as he does. On the other hand, it is impossible to question that the hereditary transmission of genius or great talent does occur. One may cite at random such cases as that of the Bach family, Thomas and Matthew Arnold, James and John Stuart Mill; and the reader who is inclined to believe that there is no law or likelihood in this matter, must certainly make himself acquainted with Mr. Galton's Hereditary Genius, and with such a paper as that which he printed in Sociological Papers, 1904, furnishing an "index to achievements of near kinsfolk of some of the Fellows of the Royal Society." There is, of course, the obvious fallacy involved in the possibility that not heredity but environment was really responsible for many of these cases. It must have been a great thing to have such a father as James Mill. But it would be equally idle to imagine that the evidence can be dismissed with this criticism. A Matthew Arnold, a John Stuart Mill, could not be manufactured out of any chance material by an ideal education continued for a thousand years. The transmission of genius. — One single instance of the trans- mission of genius or great talent hi a family may be cited. We shall THE PROMISE OF RACE CULTURE 499 take the family which produced Charles Darwin, the discoverer of the fundamental principle of eugenics, and his first cousin, Francis Gallon. Darwin's grandfather was Erasmus Darwin, physician, poet and philosopher, and independent expounder of the doctrine of organic evolution. Darwin's father was a distinguished physician, described by his son as "the wisest man I ever knew." Darwin's maternal grandfather was Josiah Wedgwood, the famous founder of the pottery works. Amongst his first cousins is Mr. Francis Galton. He has five living sons, each a man of great distinction, including Mr. Francis Darwin and Sir George Darwin, both of them original thinkers, honored by the presidency of the British Association. No one will put such a case as this down to pure chance or to the influence of environment alone. This is evidently, like many others, a greatly distinguished stock. The worth of such families to a nation is wholly beyond any one's powers of estimation. What if Erasmus Darwin had never married ! No student of human heredity can doubt that, however limited our immediate hopes, facts such as those alluded to furnish promise of great things for the future. But let us turn now from genius to what we usually call talent. The production of talent. — There can be no question that amongst the promises of race-culture is the possibility of breeding such things as talent and the mental energy upon which talent so largely depends. In the Inquiries into Human Faculty, Mr. Galton shows the remark- able extent to which energy or the capacity for labor underlies intellec- tual achievement. He says, of energy: "It is consistent with all the robust virtues, and makes a large practice of them possible. It is the measure of fullness of life ; the more energy the more abundance of it; no energy at all is death; idiots are feeble and listless. In the enquiries I made on the antecedents of men of science no points came out more strongly than that the leaders of scientific thought were generally gifted with remarkable energy, and that they had inherited the gift of it from their parents and grand- parents It maybe objected that if the race were too healthy and energetic there would be insufficient call for the exercise of the pitying and self-denying virtues, and the character of men would grow harder hi consequence. But it does not seem reasonable to preserve sickly breeds for the sole purpose of tending them, as the breed of foxes is preserved solely for sport and its attendant advantages. There is little fear that misery will ever cease from the land, of that the 500 READINGS IN EVOLUTION, GENETICS, AND EUGENICS compassionate will fail to find objects for their compassion; but at present the supply vastly exceeds the demand; the land is over-stocked and over-burdened with the listless and the incapable. In any scheme of eugenics, energy is the most important quality to favor; it is, as we have seen, the basis of living action, and it is eminently transmissible by descent." Need it be pointed out that any political system which ceases to favor or actively disfavors energy, making it as profitable to be lazy as to be active, is antieugenic, and must inevitably lead to disaster? That, however, by the way. Our present point is that eugenics can reasonably promise, when its principles are recognized, to multiply the human and diminish the vegetable type in the community. In so doing, it will greatly further the production of talent, and therefore of that traditional or acquired progress which men of talent and genius create. Such a result will also further, though indirectly, the production of genius itself. For, as Mr. Galton points out, " men of an order of ability which is now very rare, would become more frequent, because the level out of which they rose would itself have risen." This is by no means the only fashion in which an effective and practicable race-culture would serve genius, and I shall not be blamed for considering this matter further by any reader who realizes, however faintly, what the man of genius is worth to the world. If it were shown possible to establish such social conditions that genius could never flower in them, we should realize that their establishment would mean the putting of an end to progress and the blasting of all the highest hopes of the highest of all ages. The immediate need of this age, as of all ages, is perhaps not so much the birth of babies capable of developing into men and women of genius, as the full exploitation of the possibilities of genius with which, as I fancy, every generation on the average is about as well endowed as any other. There is, of course, the popular doctrine that there are no mute inglorious Miltons, that "genius will out," and that therefore if it does not appear, it is not there to appear. In expressing the com- pelling power of genius in many cases this doctrine is not without truth. Yet history abounds in instances where genius has been de- stroyed by environment — and we can only guess how many more instances there are of which history has no record. To take the single case of musical genius, it is a lamentable thought that there may be those now living whose natural endowments, in a favorable environ- ment, would have enabled them to write symphonies fit to place THE PROMISE OF RACE CULTURE 501 beside Beethoven's, but whom some environmental factors — conven- tional, economic, educational, or what not — have silenced; or worse, have persuaded to write such sterile nullities as need not here be instanced. There is surely no waste in all this wasteful world so lamentable as this waste of genius. If, then, anyone could devise for us a means by which the genius, potentially existing at any time, were realized, he would have per- formed in effect a service equivalent to that of which eugenics repudi- ates the present possibility — the actual creation of genius. But if we consider what the conditions are which cause the waste of genius, we realize at once that they mainly inhere in the level of the human environment of the priceless potentiality in question. As we noted elsewhere, in an age like that of Pericles genius springs up on all hands. It is encouraged and welcomed because the average level of the human environment in which it finds itself is so high. But if eugenics can raise the average level of intelligence, in so doing not merely does it render more likely, as Mr. Galton points out, the production of men of the highest ability, but it provides those conditions in which men of genius, now swamped, can swim. We could not undertake to produce a Shakespeare, but we might reasonably hope to produce a generation which would not destroy its Shakespeares. And even if men of genius still found it necessary, as men of genius have found it necessary, to "play to the gallery," they would play, as Mr. Galton says of the demagogue in a eugenic age, "to a more sensible gallery than at present." Darwin somewhere points out that it is not the scientific, but the unscientific man who denies future possibilities. Thus though an advocate of eugenics may be applauded for his judgment if he declares that the creation of genius will forever be impossible, yet I should not care to assert that the ultimate limitations of eugenics can thus be defined. We have yet to hear the last of Mendelism. Eugenics and unemployment. — Let us look now at another aspect of the promise of race-culture. When the time comes that quality rather than quantity is the 'ideal of those who concern themselves with the population question, it is quite evident that not a few of the social problems which we now find utterly insoluble will disappear. In this brief outline, we can only allude to one or two points. Take, for instance, the question of unemployment. We know that some by no means small proportion of the unemployed were really destined to be unemployable from the first, as for instance by reason of hereditary 502 READINGS IN EVOLUTION, GENETICS, AND EUGENICS disease. It were better for them and for us that they had never been born. Many more of the unemployed have been made unemployable by the influence of over-crowding, to which they were subjected in their years of development. Is there, can there be, any real and permanent remedy for overcrowding, but the erection of parenthood into an act of personal and provident responsibility ? Eugenics and woman. — Take, again, the woman question. No one will deny that hi many of its gravest forms, especially in its economic form, and the question of the employment of women, wisely or horribly, this depends (to a degree which few, I think, realize) upon the fact that there are now (1909), for instance, 1,300,000 women in excess in this country. Is it then proposed, the reader will say, by means of race-culture to exterminate the superfluous woman ? Indeed, no. But is the reader aware that Nature is not responsible for the existence of the superfluous woman ? There are more boys than girls born in the ratio of about 103 or 104 to 100; and Nature means them all to live, boys and girls alike. If they did so live, we should have merely the problem of the superfluous man, which would not be an economic problem at all. But we destroy hosts of all the children that are born, and since male organisms are in general less resistant than female organisms, we destroy a disproportionate number of boys, so that the natural balance of the sexes is inverted. Unlike ancient societies we largely practice male infanticide. Can the reader believe that there is any permanent and final means of arresting this wastage of child- life, with its singular and far-reaching consequences, other than the elevation of parenthood, wholly apart from the question of the selec- tion of parents ? We shall not succeed in keeping all the children alive (with a trivial number of exceptions), thereby abolishing the super- fluous woman by keeping alive the boy who should have grown up to be her partner, until we greatly reduce the birth-rate; as it must and will be reduced when the ideal of race-culture is realized, and no child comes into the world that is not already loved and desired in antici- pation. Eugenics and cruelty to children. — This ideal, also, offers us in its realization the only complete remedy for the present ghastly cruelty under which so many children suffer even hi Great Britain, even in the twentieth century. Is the reader aware that the National Society for the Prevention of Cruelty to Children inquired into the ill-treat- ment or cruel neglect of 115,000 children in the year beginning April ist, 1906 ? It has been reasonably and carefully estimated that "over THE PROMISE OF RACE CULTURE 503 half a million children are involved in the total of the wastage of child- life and the torture and neglect of child-life in a single year." Surely Mr. G. R. Sims, to whom I would offer a hearty tribute for his recent services to childhood, is justified hi saying, "Against the guilt of race suicide our men of science are everywhere preaching their sermons to-day. It is against the guilt of race murder that the cry of the children should ring through the land." As regards race suicide and the men of science, I am not so sure as to the assertion. But the truth of the second sentence .quo ted is as indisputable as it is horrible. Now no legislation conceivable will wholly cure this evil nor avert its consequences. At bottom it depends upon human nature, and you can cure it only by curing the defect of human nature. This, hi general, is of course beyond the immediate powers of man, but evi- dently we should gam the same end if only we could confine the advent of children to those parents who desired them — that is to say, those hi whom human nature displayed the first, if not indeed almost the only, requisite for the happiness of childhood. To this most beneficent and wholly moral end we shall come, notwithstanding the blind and pitiable guidance of most of our accredited moral teachers today. By no other means than the realization of the ideal defined, that every new baby shall be loved and desired in anticipation — an ideal which is perfectly practicable — can the black stain of child murder and child torture and child neglect be removed from our civilization. Ruskin and race-culture. — The name of Ruskin, perhaps, would not occur to the reader as likely to afford support to the fair hopes of the eugenist. Consider then, these words from Time and Tide: "You leave your marriages to be settled by supply and demand, instead of wholesome law. And thus, among your youths and maid- ens, the improvident, incontinent, selfish, and foolish ones marry, whether you will or not; and beget families of children necessarily inheritors in a great degree of these parental dispositions; and for whom, supposing they had the best dispositions in the world, you have thus provided, by way of educators, the foolishest fathers and mothers you could find; (the only rational sentence in their letters, usually, is the invariable one, in which they declare themselves 'incapable of providing for their children's education'). On the other hand, who- soever is wise, patient, unselfish, and pure among your youth, you keep maid or bachelor; wasting their best days of natural life in pain- ful sacrifice, forbidding them their best help and best reward, and care- fully excluding their prudence and tenderness from any offices of 504 READINGS IN EVOLUTION, GENETICS, AND EUGENICS parental duty. Is not this a beatific and beautifully sagacious system for a Celestial Empire, such as that of these British Isles?" Apart from the point as to wholesome law rather than the educa- tion of opinion as the eugenic means, the foregoing passage must win the assent and respect of every eugenist. It indicates the promise of race-culture as it appeared to John Ruskin. The passage has been quoted in full, not for the benefit of the ordinary thoughtful reader but for that of the professional literary man who, in this remarkable age, so far as I can judge, reads nothing but what he writes, and thus quali- fies himself for dismissing Spencer or Darwin or Galton by any casual phrase. Race-culture and human variety. — Now let us turn to another question. Let it be asserted most emphatically that, if there is any- thing in the world which eugenics or race-culture does not promise or desire, it is the production of a uniform type of man. This delusion, for which there has never been any warrant at all, possesses many of the critics of eugenics, and they have made pretty play with it, just as they do with their other delusions. Let us note one or two facts which bear upon this most undesirable ideal. In the first place, it is unattainable because of the existence of what we call variation. No apparatus conceivable would suffice to eliminate from every generation those who varied from the accepted type. In the second place, this uniformity is supremely undesirable from the purely evolutionary point of view, because its attainment would mean the arrest of all progress. All organic evolution, as we know, depends upon the struggle between creatures possessing various varia- tions and the consequent selection of those variations which con- stitute their possessors best adapted or fitted to the particular environ- ment. If there is no variation there can be no evolution. To aim at the suppression of variation, therefore, on supposed eugenic grounds (which would be involved in aiming at any uniform type of mankind) would be to aim at destroying the necessary condition of all racial progress. The mere fact that all the critics of race-culture attribute to evolutionists, of all people, the desire to suppress variation, is a pathognomonic symptom of their critical quality. And, of course, quite independently of the evolutionary function of variation — though this is cardinal and must never be forgotten by the politician of any school, since what we call individuality is variation on the human plane — the value of variation in ordinary life is wholly THE PROMISE OF RACE CULTURE 505 incalculable. It is not merely that, as Mr. Gallon says, " There are a vast number of conflicting ideals, of alternative characters, of incom- patible civilizations; but they are wanted to give fullness and interest to life. Society would be very dull if every man resembled the highly estimable Marcus Aurelius or Adam Bede." The question is not merely as to the interest of life. Much more important is the fact that it takes all sorts to make a world. What is the development of society but the result of the psychological division of labor hi the social organism ? And how could such division of labor be carried out if we had not various types of laborers ? What would be the good of science if there were no poetry or music to live for? How would poetry and music help us if we had not men of science to protect our shores from plague ? Obviously the existence of men of most various types is a necessity for any highly organized society. Even if eugenics were capable — as it is not — of producing a complete and balanced type, fit up to a point to turn out a satisfactory poem, a satisfactory symphony or a satisfactory sofa, the utmost could not be expected of such a man in any of these directions. In a word, as long as their activities are not antisocial, men cannot be of too various types. We require mystic and mathematician, poet and pathologist. Only, we want good specimens of each. "The ami of eugenics," says Mr. Gal ton, "is to represent each class or sect by its best specimens; that done, to leave them to work out their common civilization in then- own way Special aptitudes would be assessed highly by those who possessed them, as the artistic faculties by artists, fearlessness of inquiry and veracity by scientists, religious absorption by mystics, and so on. There would be self-sacrificers, self -tormentors, and other exceptional idealists." But at least it is better to have good rather than bad specimens of any kind, whatever that kind may be. Mr. Galton thinks that all except cranks would agree as to including health, energy, ability, manliness, and courteous disposition amongst qualities uniformly desirable — alike in poet and pathologist. We should desire also uniformity as to the absence of the antisocial proclivities of the born criminal. So much uniformity being granted, let us have with it the utmost conceivable variety — more, indeed, than most of us can conceive. This point, of course, is cardinal from the point of view of practice. No progress could be made with eugenics, it would be impossible even to form a Eugenics Education Society, if each of us were to regard the particular type he belongs to as the ideal, and were to seek merely 506 READINGS IN EVOLUTION, GENETICS, AND EUGENICS to obtain the best specimens of that type. The doctrine that it takes all sorts to make a world — a doctrine very hard for youth to learn, yet unconsciously learnt by all who are capable of learning at all — must be regarded as cardinal truth for the eugenist. All he asks for, all he is wise in seeking, is good specimens rather than bad. Poets certainly but not poetasters; jesters certainly, but not clever fools. Time and its treasure. — Taking the modern estimates of the physicists, we are assured that the total period of past human existence is very brief compared with what may reasonably be predicted. Granted, then, practically unlimited tune, what inherent limits are there to the upward development of man as a moral and intellectual being? Shall we answer this question by a study of the nature of matter ? Plainly not. Shall we answer it by a study of the nature of mind ? Surely not, for the study of the mind cannot inform us as to what mind might be. One source of guidance alone we have, and this is the amazing contrast which exists between the mind of man at its highest, and mind hi its humblest animal forms; or shall we say even between the highest and lowest manifestations of mind within the human species ? The measureless height of the ascent thus indi- cated offers us no warrant for the conclusion that, as we stand on the heights of our life, our "glimpse of a height that is higher" is only a hallucination. On the contrary. There is no warrant whatever for supposing that the forces which have brought us thus far are yet exhausted; they have their origin in the inexhaustible. Who, gazing on the earth of a hundred million years ago, could have predicted life — could have recognized, in the forces then at work and the matter in which they were displayed, the promise and potency of all terrestrial life ? Who, contemplating life at a much later stage, even later mammalian, could have seen in the simian the prophecy of man ? Who, examining the earliest nervous ganglia, could have foreseen the human cerebrum ? The fact that we can imagine nothing higher than ourselves, that we make even our gods in our own image, offers no warrant for supposing that nothing higher will ever be. What ape could have predicted man, what reptile the bird, what amoeba the bee ? " There are many events in the womb of time which will be delivered " and the fairest of her sons and daughters are yet to be. But even grant, for the sake of the argument, that the intelligence of a Newton, the musical faculty of a Bach, the moral nature of any good mother anywhere, represent the utmost limits of which the THE PROMISE OF RACE CULTURE 507 evolution of the psychical is capable. There is every reason to deny this, but let us for the moment assume it true. There still remains the thought of Wordsworth, "What one is, why may not millions be?" — a thought to which Spencer has also given utterance. What is shown possible for human nature here and there, he says, is con- ceivable for human nature at large. It is possible for a human being, whilst still remaining human, to be a Shakespeare or a St. Francis; these things are thus demonstrably within the possibilities of human nature. It is therefore at the least conceivable that, hi the course of almost infinite time (even assuming, say, that intelligence must ever be limited, as even Newton's intelligence was limited) — some such capacities as his may be common property amongst men of the scientific type; and so with other types. We may answer Words- worth that there is no bar thrown by Nature in the way of such a hope. What is possible. — This of course is speculation and of no immediate value. I would merely remind the reader that the doctrine of optimism, as regards the future of mankind, which the principles of race-culture assume and which they desire to justify, was definitely shared by the great pioneers to whom we owe our understanding of those principles. Notwithstanding grave nervous disorder, such as makes pessimists of most men, both Darwin and Spencer were compelled by their study of Nature to this rational optimism as regards man's future. The doctrine of organic evolution, and of the age-long ascent of man through the selection of the fittest (who have, on the whole, been the best) for parenthood, is one not of despair but of hope. Exactly half a century ago it struck horror into the minds of our predecessors. Man, then, is only an erected ape, they thought — as if any historical doctrine, however true, could shorten the dizzy distance to which man has climbed since he was simian; and man being an ape, they thought his high dreams palpably vain. But the measure of the accomplished hints at the measure of the possible, and the value of the historical facts lies not -hi themselves, all facts as such being as dead as are the individual atoms of the living body, but in the principles which grow out of them. It is of no importance as such that man has simian ancestors; it is of immeasurable importance that he should learn by what processes he has become human, and by what, indeed, they became simian — which would have been a proud adjective for its own day. The principles of organic progress matter for us because they are the principles of race-culture, the only sure means of human progress. Our looking backwards does not turn us 5©8 READINGS IN EVOLUTION, GENETICS, AND EUGENICS into pillars of salt, but teaches us that the best is yet to be, and how alone it is to be attained. Elsewhere the optimistic argument of Wordsworth is quoted. Here also John Ruskin: "There is as yet no ascertained limit to the nobleness of person and mind which the human creature may attain, by persevering observance of the laws of God respecting its birth and training." And Herbert Spencer: "What now characterizes the exceptionally high may be expected eventually to characterize all. For that which the best human nature is capable of, is within the reach of human nature at large." And Francis Galton: " There is nothing either in the history of domestic animals or hi that of evolution to make us doubt that a race of sane men may be formed, who shall be as much superior, mentally and morally, to the modern European, as the modern European is to the lowest of the Negro races. " It is earnestly to be hoped that inquiries will be increasingly directed into historical facts, with the view of estimating the possible effects of reasonable political action in the future, in gradually raising the present miserably low standard of the human race to one in which the Utopias in the dreamland of philanthropists may become practical possibilities." Conclusion — eugenics and religion. — In an early chapter it was attempted to show that eugenics is not merely moral, but is of the very heart of morality. We saw that it involves taking no life, that, rather it desires to make philanthrophy more philanthropic, that, at any rate so far as this eugenist is concerned, it recognizes and bows to the supreme law of love; and claims to serve that law, and the ideal of social morality, which is the making of human worth. Eugen- ics may or may not be practicable, it may or may not be based upon natural truth, but it is assuredly moral; though I, for one, would pro- claim eternal war between this real morality and the damnable sham, which approves the unbridled transmission of the most hideous diseases, rotting body and soul, in the interests of good. And if religion, whatever its origin and the more questionable chapters in its past, be now "morality touched with emotion," I claim that eugenics is religious, is and will ever be a religion. Else- where I have attempted to show that religion has survived and will survive because of its survival-value — its services to the life of the THE PROMISE OF RACE CULTURE 509 societies wherein it flourishes. The religion of the future, it was sought to argue, will be that which " best serves Nature's unswerving desire — fullness of life." The Founder of the Christian religion said, "I am come that ye might have life, and that ye might have it more abundantly." It is higher and more abundant life that is the eugenic ideal. Progress I define as the emergence and increasing dominance of mind. Of progress, thus conceived, man is the highest fruit hitherto. He is also its appointed agent and eugenics is his instrument. To this end he must use all the powers which have blossomed hi him from the dust. He must claim Art: and indeed hi Wagner's great music-drama, at the moment when the prophetic Briinnhilde tells Sieglinde who has just lost her mate that she, the expectant mother, may look for the resurrection of the dead and the life of the world to come hi the child Siegfried; and when the heroic theme is pronounced for the first tune and followed by that which signifies redemption by love; then, I think, the eugenist may thrill not merely to the music, nor the humanity of the story, but to the spiritual and scientific truth which it symbolizes. If the struggle towards individual perfection be religious, so, assuredly, is the struggle, less egoistic indeed, towards racial perfection. If the historic meaning and purport of religion are as I conceive them, and if its future evolution may thence be inferred, there can be no doubt in the prophecy that in ages to come those high aspirations and spiritual visions which astronomy has dishoused from amongst the stars, and which, at their best, were ever selfish, will find a place on this human earth of ours. If we have transferred our hopes from heaven to earth and from ourselves to our children, they are not less religious. And they that shall be of us shall build up the old waste places; for we shall raise up the foundations of many generations. "We feel the high tradition of the world And leave our spirits on our children's breasts." BIBLIOGRAPHY LIST OF FIFTY BOOKS FROM WHICH EXCERPTS HAVE BEEN QUOTED BABCOCK, ERNEST BROWN, and CLAUSEN, ROY ELWOOD. Genetics in Relation to Agriculture. The McGraw-Hill Book Co., 1918. BATESON, WILLIAM. Problems of Genetics. Yale University Press, 1913. CASTLE, WILLIAM E. Genetics and Eugenics. Harvard University Press, sd ed., 1920. CHILD, CHARLES MANNING. "Regulatory Processes in Organisms." Jour. Morph., XXII (1911). CONKXIN, EDWIN GRANT. Heredity and Environment. Princeton Uni- versity Press, 3d ed., 1920. COULTER, JOHN M., and COULTER, MERLE C. Plant Genetics. The University of Chicago Press, 1918. CRAMPTON, HENRY EDWARD. The Doctrine of Evolution. The Columbia University Press, 1911. DARWIN, CHARLES. The Origin of Species. D. Appleton & Co., with additions from the sixth and last edition, 1893. DARWIN, FRANCIS. Life and Letters of Charles Darwin. John Murray, London, 1888. DENDY, ARTHUR. Outlines of Evolutionary Biology. D. Appleton & Co., 1916. DEVRTES, HUGO. Species and Varieties. The Open Court Publishing Co., 1904. DOWNING, ELLIOT ROWLAND. The Third and Fourth Generation. The University of Chicago Press, 1918. EIMER, THEODORE. On Orthogenesis. The Open Court Publishing Co., 1898. GADOW, HANS. The Wanderings of Animals. Cambridge University Press, 1913. GUYER, MICHAEL F. Being Well-Born. The Bobbs-Merrill Co., 1918. . "Immune Sera and Certain Biological Problems." Amer. Natur., LV (1921). HENDERSON, LAWRENCE J. The Fitness of the Environment. The Mac- millan Co., 1913. HERBERT, S. The First Principles of Evolution. Adam and Charles Black, London, 1913. JORDAN, DAVID STARR, and KELLOGG, VERNON L. Evolution and Animal Life. D. Appleton & Co., 1908. JUDD, JOHN W. The Coming of Evolution. Cambridge University Press, .1911. 510 BIBLIOGRAPHY 511 KELLOGG, VERNON L. Darwinism To-Day. Henry Holt & Co., 1907. LE CONTE, JOSEPH. Evolution. D. Appleton & Co., zd ed., 1897. LOCY, WILLIAM A. The Main Currents of Zoology. Henry Holt & Co., 1918. LULL, RICHARD SWANN. Organic Evolution. The Macmillan Co., 1917. MCFARLAND, JOSEPH. Biology, General and Medical. W. B. Saunders Co., 3d ed., 1918. METCALF, MAYNARD M. An Outline of the Theory of Organic Evolution. The Macmillan Co., IQII. MORGAN, THOMAS H. Evolution and Adaptation. The Macmillan Co., 1903. . A Critique of the Theory of Evolution. Princeton University Press, 1916. NEWMAN, HORATIO H. "The Limits of Hereditary Control in Armadillo Quadruplets: A Study of Blastogenic Variation." Jour. Morph., XXII (1911). . The Biology of Twins. The University of Chicago Press, 1915. . Vertebrate Zoology. The Macmillan Co., 1920. NUTTALL, G. H. F. Blood Immunity and Blood Relationship. Cambridge, at the University Press, 1904. NUTTING, C. C. "The Relation of Mendelism and the Mutation to Theory Natural Selection." Science, N.S., LIII (Feb. n, 1921). OSBORN, HENRY FAIRFIELD. From the Greeks to Darwin. The Macmillan Co., 1908. . The Origin and Evolution of Life. Charles Scribner's Sons, 1918. PLATE, LUDWIG. Vber die Bedeutung des Darwin'schen Selectionsprincips und Proleme der Artbildung. Engelmann, ad ed., 1903. POPENOE, PAUL, and JOHNSON, ROSWELL H. Applied Eugenics. The Macmillan Co., 1918. ROMANES, GEORGE J. Darwin and after Darwin. The Open Court Publishing Co., 1892. SALEEBY, CALEB WILLIAMS. The Promise of Race Culture. Moffat, Yard & Co., 1909. SCHUCHERT, CHARLES. Text-Book of Geology: Part II, Historical Otology. John Wiley, 1915. SCOTT, WILLIAM BERRYMAN. The Theory of Evolution. The Macmillan Co., 1911. SHELFORD, VICTOR E. Animal Communities in Temperate America. The University of Chicago Press, 1913. SHULL, A. FRANKLIN. Principles of Animal Biology. The McGraw-Hill Book Co., 1920. STEINMANN, GUSTAV. Die Abstammungslehre. Engelmann, Leipzig, 1908. TAYLER, J. L. "The Scope of Natural Selection." Natural Science, Vol. XV., 1899. 512 READINGS IN EVOLUTION, GENETICS, AND EUGENICS THOMSON, J. ARTHUR. Darwinism and Human Life. Henry Holt & Co., 1909. . Heredity. John Murray, London, 1007. WALTER, HERBERT EUGENE. Genetics. The Macmillan Co., 1911. WHITMAN, CHARLES OTIS. "The Problem of the Origin of Species." Proceedings of Congress of Arts and Science, Universal Exposition, St. Louis, 1906. WRIGHT, SEWALL. Principles of Livestock Breeding. U.S. Dept. Agri- culture, Bull. 905, 1920. INDEX INDEX Abiogenesis, 12 Abraxas, 438, 452 Acquired characters, inheritance of, 19, 20, 273; discussion by E. G. Conklin, 330-36; lack of evidence for, 332, 333; misunderstandings concerning, 323-30; other side of the question, 336-38; statement of the problem, 323, 331-32 Adaptation, n, 30, 188-205; classi- fication of adaptations, 195, 196; Osbom's laws of, 192-95 Adaptive radiation, law of, 194, 195 Agassiz, L., 144, 145 Aggressive resemblance, 201 Albinos, different kinds, of, 431, 432 Allelomorphic, characters in heredity, 433 Allen, E. J., 209 Alluring coloration, 201 Ameghino, F., 86 Amphioxus, 178 Amphisbaenidae, 119 Analogous, versus homologous struc- tures, 136 Anaxagoras, 12 Anaximander, n Anaximenes, n, 12 Ancestral inheritance, Gallon's law of, 371,372 Anti-lens serum, Guyer's experiments with, 338-45 Antirrhinum, 446 Apartness of the germ plasm, 31, 295, 296, 337 Apotetix, 448 Appendix vermiformis, in man and apes, 154, 155 Apteryx australis, 142, 143 Aquinas, Thomas, 8, 15 Archaesthetism, 35 Aristotle, 13, 14, 18 Arithmetical mean, 367 Armadillo quadruplets: and classifica- tion, 122, 123; and sex-determina- tion, 451 Armadillos, 97 Artificial selection, 25, 26 Aspergillus niger, 327 Atavism, 13 Atropa, 393 Augustine, 8, 15 Azores, fauna of, 103 Babcock, E. B., 287, 307-22, 363, 364, 401-12 Bacon, F., 15, 276 Balanoglossus, 177, 178 Bascanion anthonyi, 117 Bat, wing of, 134 Bateson, W., 7, 43, 346, 368, 369, 380, 393, 396> 414, 446 Bathmism, 35 Bauer, E., 335 "Beagle," Darwin's voyage on the, 23, 25, 26 Beebe, W., 316, 317 Beeton, M., 485, 489, 491 Begonia, 337, 338 Bell, A. G., 474, 4QI Bembidium, 109 Bequerel, A. H., 275 Bergson, H., 34 Bermudas, fauna of, 103-5 Bibliography, 510-13 Biffen, R. H., 394 Bimodal and multimodal curves, 368, 369 Biometry: discussion of, 365-75; rise and vogue of, 38, 39 Birds: rudimentary teeth of, 181; wing of, 134 Birgus latro, 138, 139, 140 Bison antiquus, 85 Blakeslee, A. F., 417 Blastoderm, 166 Blastula, 166 Blends, in heredity, 416-18 Blood-transfusion tests, evidences from 60, 124-28 Bonnet, R., 16 516 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Boyd-Dawkins, 162 Brachydactylism, 399, 400; inheritance of, 460 Bridges, C. B., 402, 437 Briinn, 40, 41 Bryonia, 436 Buffon, G. L. L., 7, 15, 16, 17 Bullen, G. E., 209 Cameline: forefoot, 75; skull, evolu- tion of, 74 Camels, fossil pedigree of, 73-76 Cape de Verde Islands, fauna of, 106 Carnivora, 126 Carnot, S., 277 Carsinas maenas, 256 Castle, W. E., 39, 40, 41, 43, 261, 287, 333, 334, 3?8, 379, 399, 43*, 432, 433-48 Cataract, inheritance of, 461 Catastrophism, 22, 23 Cave animals, eyes of, 144, 145 Cebidae, 126 Cell: diagram of typical cell, 291; division, direct, 290, 291; division, indirect or mitotic, 291, 292, 403-5; division, somatic, 403-5; theory, 289 Cenogenetic, 174 Centrosome, 290, 291, 292 Cesnola, 257 Cetacea, 179 Chamberlin, T. C., 57 Chambers, R., 23, 26 Chapin, C. V., 483 Child, C. M., 191, 192, 337 Child mortality in long-lived families, 488 Chimpanzee, 88 Chromatin, 290; interchange between homologous chromosomes, 408; nu- cleolus, 290 Chromosomes, 291, 292; conjugation of pairs of, 407; of Drosophila, 297; in heredity, 304, 305; independent distribution of, 408, 409; individual- ity of, 296; maps to show loci of genes, 437, 442; of mosquito, 297; number and appearance, 293; pairs of, 297, 407; reduction of, 297-98, 406; and sex in Drosophila, 410-12; significance of, 292, 293 Circooithecidae, 126 Clark, J. M., 85 Classification: basis of, 117-19; evi- dences from, 60, 117-23; inter- national code of, 117; method of, 120-21 Clausen, R. E., 287, 307-22, 363, 364, 401-12 Cleavage of egg, 294 Cocoanut crab, 138, 139, 140 Coefficient of correlation, 369, 370 Coincident selection, 268, 269 Color in animals, 200-204 Coluber anthonyi, 117 Colubridae, 117 Colubrinae, 117 Commensalism, as adaptation, 198, 199 Communal life, as adaptation, 199, 200 Comparative Anatomy, evidences from, 60, 129-63 Confusing coloration, 204 Conklin, E. G., 33°~37, 37°-75, 434, 435 Conjugation, of homologous chromo- somes, 407 Convergence, Osborn's law of, 192-94 Cope, E. D., 35 Correlation: coefficient of, 369, 370; tables, 370 Correns, C., 40, 43, 380, 393, 394, 415, 416, 424 Cossonidae, 108 Coulter, J. M., 386-92, 413-28 Coulter, M. C., 386-92, 413-28 Coutagne, G., 396 Crampton, H. E., 5, 32, 271 Cretins of Aosta, 464, 465, 478, 479 Crossing-over, in Mendelian heredity, 441-48 Cu6not, L., 398 Curie, P., 275 Cuvier, G., 19, 21, 22 Cytoplasm, 290; in inheritance, 304 Dakin, W. J., 209 Daphnia, 335 Darbishire, A. D., 393, 398 Darwin, C., 4, 5, 6, 8, 10, n, 17, 19, 23, 24, 25, 26, 27, 28, 29, 30, 31, 45, 61, 67, 97, 118, 120, 121, 160, 205, 210, 211, 213, 219-44, 259, 260, 307, 330, 427, 477, 501 Darwin, E., 3, 16, if, 18, 21 INDEX 517 Darwinism, 7, 8; background of, 188- 216; critique of, 245-62; defense of, general, 252-56; objections to, 247- 52 Dasypus novemcinctus, 366, 375-78 Datura, 395 Davenport, C. B., 257, 333, 372, 393, 396, 474, 475 Davenport, G. C., 400 Davis, B. M., 360 De Candolle, A., 23, 122 Defectives, segregation of, 479-80 Democritus, 12 Dendy, A., 71, 73 Descartes, R., 15 Determinants (Weismann's), 30, 31, 32, 265 Determination of sex, 440-56 Development: facts of, 164, 165; out- line of animal development, 165-72 De Vries, H., 7, 36, 37, 38, 39, 43, 258, 260, 261, 273, 335, 346-60, 380, 393, 429 Difficulties and objections to Natural Selection as seen by Darwin, 236-42. Difflugia, 378 Digby, L., 363, 364 Dihybrid ratio, 391 Dinornis gravis, 136, 137, 142 Dominance, Mendel's Law of, 40-42, 381, 382, 386 Doncaster, L., 399 Downing, E. R., 459-72 Driesch, H., 34 Drinkwater, H., 400, 460 Drosophila ampelophila, 318, 321, 380, 444; chromosomes of, 401, 402, 403; sex-linked heredity in, 433-38 Drummond, H., 214, 215 Durham, F. M., 429, 430 Ears of man and apes, 155, 156, 157 Earthworms and vegetable mold, 214 East, E. M., 43, 419 Eaton, Rev. A. E., 143 Ectoblast, 1 66 Edentates, distribution of, 98 Edwards, J., 483 Eimer, T., 34, 35, 264 Elderton, E. M., 493 Electric organ, of fishes, 196 Elephants, evolution of, 76-80 Elephas, 76, 77, 78, 79, 80; E. antiquus, 89; E. columbi, 85; E. leidyi, 85 Embryology, evidences from, 60, 164-72 Empedocles, 12, 13 Endoblast, 166 Engrammes of Rignano, 335 Enteleche, 34 Environment: effects of, on develop- ment, 317, 318; effects of, on heredity, 312-16, 318-20; and heredity, 312, 3i3 Eoanthropus dawsoni, 93 Epicurus, 14 Epigenesis, 13 Epilepsy, inheritance of, 465 Equidae, 70, 71, 72, 73 Equus, 71, 72, 73; E. leidyi, 85 Escherich, 215 Eugenics: Carnegie Laboratory of, 459; and cruelty to children, 502, 503; defined, 473; Education Society, 505 ; and Euthenics, 484-96; Galton Laboratory of, 459; positive, 480-83; and religion, 508, 509; restrictive, 475-480; and unemployment, 501, 502; and woman, 502 Eupagurus, 246 Euthenics, 473, 484-96 Evolution, organic: causal factors of, 185; definitions of, 3, 4, 5; evidences of, 59, 60; experimental, 60; nature of proof of, 59; proof of, 57, 58, 59; what it is not, 8, 9 Fabre, M., 231 Factor hypothesis, 417-28 Factorial analysis of color in mice, 429- 30 Factors, in Neo-Mendelian heredity: complementary, 417-20; cumulative, 424; inhibitory, 421-23; lethal, 432; in quantitative inheritance, 424-28 Farmer, J. B., 363, 364 Farrabee, W. C., 400 Feeble-mindedness, inheritance of, 463. 464 Fertilization, 301, 302 Fierasfer acus, 198, 199 Filaria sanguinis hominis, 212 Filial Regression, Gallon's Law of, 372-74 Flower, Professor, 162 518 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Forficulata auricularia, 368, 369 Franklin, B., 482 Freemartin, 455, 456 Fossils: actual remains, 63 ; Cambrian, 62; casts and impressions, 64; classi- fication of, 63; conditions necessary for, 64, 65, 66; Darwin's opinion as to the adequacy of the record, of the, 61, 62; definition of (by T. H. Huxley), 63; first recognized, 12; general facts revealed by, 69, 70; pedigrees of well-known vertebrates, 70-80; purifications, 63 Gadow, H., 114, 115 Gager, C. S., 361 Galapagos Islands, fauna of, 105-7 Gallastegui, 448 Gallon Laboratory of Eugenics, 459, 474 Galton, Sir F., 38, 39, 365, 370-75, 376, 473. 497-5°r> 5°5> 5°8 Gastrula, 166 Gates, R. R., 363 Gazelle-camels, 76 Gegenbaur, 175 Gemmules, 28, 30 Genealogical Records Office, 484, 491, 492 Genetics: definitions of, 287; evi- dences from, 60; importance of cell theory in, 289; methods of study, 288; scope and methods of, 287-89; subject-matter of, 288-89 Genius: hereditary, 498; production of 497, 498; transmission of, 498, 499 Genotype, 377-79 Genotypic, 377-79 Geographic distribution, evidences from, 60, 97-116 Geologic time: lapse of, 67, 68; scale in millions of years, 68 Germ-cells: early setting apart of, 295, 296; origin of new, 294, 295; pro- duction of, 405-8 Germinal continuity, 31, 296 Germinal selection, 30, 31, 265-68 Germ-plasm theory, 31, 32 Giekie, Sir A., 69 Gill arches in vertebrates, 176, 177 Giraffe-camels, 76 Glaser, O. C., 365 Glochidia, 211 Goddard, H. H., 462-64 Goethe, J. W., 21 Goldschmidt, R., 314, 315, 453 Goodale, H. D., 440 Gorilla, 149 Goss, J., 40 Graham-Smith, G. L., 125 Gray, A., 223 Greek evolutionists, 1 1-14 Gregory of Nyssa, 14 Gregory, R. P., 445 Gregory, W. K., 82 Guacanos, 73 Gulick, J. T., 32, 271 Guthrie, C. C., 333 Guyer, M. F., 289, 290-306, 336, 338-45 Habitat: preference, 190, 191; selec- tion, 190, 191 Haeckel, E., 19, 30, 172, 173 Hair of man and apes, 156-61 Haldane, 443, 444 Hamilton, D. J., 326 Hapalidae, 126 Harris, J. A., 335, 485 Harrison, R. G., 333 Harte, Bret, 85 Hartmann, C. G., 162 Harvey, W., 13 Ilauser blonds, 481 Hegner, R. W., 295 Helix hortensis, 396; H. nemordlis, 396 Henderson, L. J., 189 Heraclitus, 12, 208 Herbert, S., 263, 264, 269 Heredity: Gallon's Laws of, 371-75; in man, 398-400; in pure lines, 376, 379; statistical study of, 370-75 Hermit-crabs, 138 Heron, Sir R., 231 Herschel, Sir J., 3 Heterogenesis theory, 36 Heteromera, 106 Heterozygote, 390 Hialodaphnia, 315, 316 Hippocrates, 449 Homo: H. heidelbergensis, 88; H. sa- piens, 88, 90, 92, 93; H. neander- thalcnsis, 89, 90, 91, 92, 93; H. primagenius, 89 INDEX 519 Homologies, evidences from, 60 Homozygote, 390 Hooker, Sir J., 109, 223, 247, 330 Hormone theory of sex differentiation, 454-56 Hormones, 454 Horse: ancestry of, 8; feet and teeth in fossil pedigree of, 72; fossil pedigree of, 70, 71, 72, 73 Horseshoe-crab, 127 Hrdlicka, A., 86 Hudson, W. H., 206 Human antiquity, evidences of, 93, 94 Human conservation, 473-83 Humanity, future of, 95, 96 Humerus, perforations of, in Quadru- mana, 162 Hurst, C. C., 43, 393, 396, 399, 400 Hutton, J., 22, 57 Huxley, T. H., 28, 29, 62, 63, 91, 208 Hyatt, A., 35 Hybridization and the origin of species, 43 Hyracotherium, 71 Immigration and eugenics, 475-76 Immunity coloration, 203 Induction, a temporary change in germ-cells, 335, 336 Infant mortality movement, 494 Inheritance: of acquired characters (see Acquired characters); of brachy- dactylism, 460; of cataract, 461; of feeble-mindedness, 459, 462-64; of human characters, 459-72; of insanity, epilepsy, etc., 459, 465, 466; in royalty, 466-72 ; sex-linked, 433-40 Insanity, inheritance of, 465 Intraselection, 268 Isolation: biologic, 272; geographic, 269-72; theories of, 20, 32, 33, 260- 73; reproductive, 272, 273 Jennings, H. S., 261, 377, 378 Johannsen, W., 369, 376, 377 Johnson, R. H., 484-96 Jones, D. F., 448 Jordan, D. S.,4, 32, 33, 34, 63, 64, 65, 66, 121, 165-74, 188, 195, 202, 270, 271, 273, 478, 479> 482 Joule, J. P., 277 Judd, J. W., 10, 23, 24 Kallima, 201, 204, 250 Kammerer, P., 336 Kant, E., 15, 1 6 Kellogg, V. S., 4, 32, 33, 34, 63, 64, 65, 66, 121, 165-74, 188, 195, 202, 245- 47, 253, 266, 273 Kelvin, Lord, 67, 68, 277 Kinetogenesis, 35 King, C., 67 Klebs, E., 312, 313 Knight, T., 40 Kohlreuter, J. G., 40, 41 Korchinsky, H., 36 Lamarck, J. P., 7, 10, n, 18, 19, 20, 21, 118, 247, 307, 330, 345 Lamarck ism, 7, 21, 247 Lang, A., 395 Laplace, P. S., 57 Laplacian hypothesis, 67 Laughlin, H. H., 474 • Le Conte, J., 3, 46-53 Leibnitz, 15 Leighty, C. E., 370 Lemuroidea, 126 Lepas, metamorphosis of, 171 Lepidosiren, 236 Leptinotarsa decemliniata, 321, 361, 377 Lillie, F. R., 455, 456 Lino, lapponica, 396 Lincoln, A., 24 Linkage, in Mendelian heredity, 441- 48; chromosome theory of, 442; measurements of, 444, 445 Linnaeus, 16, 43, 117 Locy, W. A., 41, 42, 43 Loeb, C., 461 Loess Man, 85 Lotsy, J. P., 43 Love, H. H., 370 Lowell, J. R., 330 Lucas, A. H. S., 218 Lucretius, 14 Lull, R. S., 3, 5, 24, 25, 73, 76, 79, 81-96 Lychnis, 393, 436 Lydekker, R., 178 Lyell, Sir C., 3, 8, 23, 26, 57, 58, 67 Maas, O., 180 Macdougal, D. T., 319, 320, 361, 362 McCracken, I., 396 520 READINGS IN EVOLUTION, GENETICS, AND EUGENICS McFarland, J., 28 McGregor, J. H., 90 Madagascar, fauna of, no, in Maeterlinck, 200 Mallophaga, 271, 272 Malthus, 17, 23, 24, 26, 223 Mammalian dispersal, 114-15 Mammary glands, as adaptations, 196 Man: of Chappelle-aux-Saints, 91; Crd-Magnon Man, 93, 94; chrono- logical table of fossil man, 87 ; descent from trees, significance of, 84; evolu- tion of, 81-96; evolutionary changes of, 84; fossil man, 84-94; Heidel- berg Man, 88, 89, 91; impelling cause of origin, 83; Neanderthal Man, 89-92; origin of, 82-84; PHt- down Man, 92, 93; place of origin, 82, 83; of Spy, 91; stock of, 82; time of origin, 83, 84 Mantis religiosa, 257 Marriage laws and eugenics, 477 Mareh, O. C., 72 Marshall, A. M., 214 Marsupial pouch, as adaptation, 196, 197 Mastodon, 76, 77, 78, 79, 85 Materialism, the relation of evolution to, 46-53 Matthew, W. T., 81 Matthiola, 394 Maturation: of egg-cell, 299, 300, 301; of sperm-cell, 298, 300 Maupertius, 15 Median, in variation, 367 Meek, 364 Megalonyxjefersoni, 85 Mendel, G., 40, 260, 346; his concep- tion of purity of gametes, 386, 387; his conception of unit characters, 386 ; his experiments, 381; his explana- tions, 386-92; his Law of Domi- nance, 40-42, 381, 382, 386; his Law of Segregation, 40-42, 382-385; his life and character, 380; his results, 381, 382 Mendelian heredity: in cats, 399; crossing-over in, 441-48; in guinea- pigs, 399, 432, 433; in Helix, 396; in Lino, lapponica, 396; linkage in, 441-48; in maize, 394, 394; in man, 399, 400; in mice, 384, 385, 398; in nettles, 395; in numerous species, 393. 394; in peas, 384; in pigeons, 397, 398; in poultry, 396, 397; in rabbits, 399; in silkworms, 395, 396 Mendelism: physical basis of, 401-12 Mesohippus, 72 Metcalf, M. M., 6, 32, 200-204 Metz, C. E. V., 297, 363, 436 Meyer, L., 155 Miastor americana, 294, 295 Millson, A., 214 Milton, J., 14 Mimicry, 203 Miohippus, 72 Mirabilis jalapa, 394, 415, 416, 4*45 M. rosea, 394 Mivart, 135, 136 Mneme theory of Semon, 335 Mode, in variation, 367 Modifications, 308, 309 Moeritherium, 76, 77, 78 Monohybrid ratio, 389 Moore, C. R., 454 Morgan, L., 264 Morgan, T. H., 42, 43, 44, 260, 261, 267, 318, 321, 355-60, 379, 433-38, 442, 443 Morphology, evidences from, 120-63 Moulton, F. R., 57 Miiller, F., 170, 172, 239 Miiller, H. J., 408, 437 Multiple factor hypothesis, 424-28 Mutation theory, 346-64; advantages over Natural Selection, 359; alterna- tive to Natural Selection, 272; criticism of, 360; De Vries' own account of, 348-55; historical account of, 36-38; Morgan's sum- mary of, 355-59 Mysis larva of Peneus, 170 Nabours, R. K., 448 Nageli, C. von, 34, 35, 333, 380 Natural Selection, 4, 12, 24, 25, 26, 35, 37, 38, 223-43; experimental sup- port of, 256-58; present status of, 258; relation of Mendelism and mutation to, 258-62 Naudin, C., 41 Nauplius larva of Peneus, 170 Neanderthal Man, 88-92 Nebular hypothesis, 57 Neo-Lamarckism, 29, 335, 336 INDEX Neo-Mendelism, 43, 44, 45, 413-32 Nest-making instincts, as adaptations, 197 Nettleship, E., 400, 461 Newman, Colonel, 211 Newton, Sir F., 7, 276, 277, 280, 283 New Zealand, fauna of, no, in Nictitating membranes of vertebrates, 146, 147 Nilsson-Ehle, H., 424-28 Nitsche, Dr., 155 Nudeolus: chroma tin, 290; true, 290 Nutritive chains, 208 Nuttall, G. H. F., 124, 125 Nutting, C. C., 258-62 Oceanic islands, fauna of, 101-10 Octopus, eye of, 13 5 Oenothera, 35; O. albida, 355; 0. biennis, 349; O. brevistylis, 349 ff.; O. ettiptica, 355; O. gigas, 353 ff.; O. lata, 355; O. laevifolia, 349 ff.; O. lamarckiana, 37, 346-60; O. leptocarpa, 358; 0. nannetta, 3498.; O. rubrinervis, 353 ff.; 0. scinttilans, 355', O. spatulata, 358 Oglivie, Dr., 326 Oken, 1 2, 16 Onagra biennis, 362 Ontogenetic selection, 268 Oocyte, 300 Oogenesis, 299, 300 Oogonium, 300 Organic selection, 268, 269 Origin of Species, The, 4, 5, 7, 24, 27, 61, 62, 67 Ornithorhynchus, 236 Orohippus, 72, 73 Orr, H. B., 465 Orthogenesis, 33, 34, 35, 3<5, 273 Orthoplasy, 268 Osborn, H. F., 8, 10, n, 13, 20, 21, 45, 86, 87, 89, 94, 95, 192-95, 273, 274-83 Overspecializations, 31 Ovum, 164 Owen, R., 121, 150, 240 Pagurus bernhardus, 139 Palaeomastodon, 76, 77, 78 Palaeontology, evidences from, 60; opinions as to the adequacy of, 62, 63; strength and weakness of, 61, 62 Palingenetic, 174 Pan velus, 88 Pangenesis, 28, 30 Panmixia, 31, 263, 264 Panniculus carnosis, 148, 149 Papilio machaon, 315 Paramecium, 377 Parasitism, as adaptation, 197, 198 Parthenogenesis : as a method of asexual development, 164; sex deter- mination in connection with, 451, 452 Pearl, R., 440 Pearson, K., 39, 365, 371, 373, 484, 489, 491, 493 Pedigree: of brachydactylism, 460; of cataract, 461; of Charles the Great of Sweden, 471; of feeble- mindedness, 463, 464; of Ferdinand and Isabella, 468; of Hohenzollems of Prussia, 470; of insanity, epilepsy, etc., 465; of Romanoffs of Russia, 467 Peneus potimirium, 170, 171 Phaseolus, 376 Phenotype, 377~79, 39°, 43* Phenotypic, 377~79, 39<>, 43* Phillips, J. C., 333 Phocochaerus, 324, 325 Physiological units, 28 Pisum quadratum, 381; P. saccharatum, 381; P. sativum, 393; P . umbellatum, 381 Pithecanthropus erectus, 86, 87, 88, 90, 93 Planetesimal hypothesis, 57 Plate, L., 264, 265, 371 Pliny, 14 Pliohippus, 72 Ploetz, A., 489, 490, 491 Podocoryne, 246 Poebrotherium, 74, 75 Polar bodies, 299, 300, 301 Popenoe, P., 484-96 Post-Aristotelians, 14 Poulton, E. B., 257 Preformation doctrine, 176 Prenatal influences, 13, 14 Presence and absence hypothesis, 413- 15 Primates: geologic record of, 82; origin of, 81, 82; place of origin; stock of, 81; time of origin, 81 522 READINGS IN EVOLUTION, GENETICS, AND EUGENICS Primula kiwensis, 364; P. sinensis, 317, 394, 445 Priority, law of, 117 Probable error, 368 Procamelus, 74, 75 Promise of Race Culture, 497-509 Pronucleus: malt, 301; female, 302 Protective resemblance, 200, 201 Protohippus, 72 Protylopus, 74, 75 Pterodactyl, wing of, 134 Punnett, R. C., 385, 395, 396, 446 Pure lines, heredity in, 376-79 Purity of gametes, 386, 387 Python, hind limbs of, 141, 142 Quadrumana, 148 Rabl, C., 166 Race culture and human variety, 504, 5°S Rana sylvatica, 333 ; R. palustris, 333 Recapitulation, doctrine of, 60, 171, 172; critique of, 173-82 Reduction divisions, in maturation, 405 Reighard, J., 203 Remora, 199 Reversion, 13 Revival of Science, the, 15, 16 Rhodeus amarus, 212 Rignano, E., 335 Robinson, L., 151, 152 Rodentia, loss of teeth in, 180 Romanes, G. J., 35, 101-10, 129-63, 263, 264, 329 Roosevelt, T., 217 Rosanoff, A. J., 465 Roux, W., 268 Rumford, B. T., 277 Ruminants, collar-bone of, 180 Ruskin, J., 503, 504, 508 Ruskin and race culture, 503, 504 Rutherford, E., 275 Sacculina, 171, 181, 198, 453 Saleeby, C. W., 497~5°9 Saltatory, variations, 38 Sandwich Islands, fauna of, 109, no Saunders, 393 Scardafella inca, 316, 317; 5. dialeucos, 316, 317; S. braziliensis, 316, 317; S. ridgwayi, 316, 317 Schoetensack, Dr., 89 Schuchert, C., 67, 68, 69 Scott, W. B., 5, 6, 62, 63, 73-6, 82, 123- 28, 173-82 Scrophularia, 319, 320 Seals, comparative anatomy of, 129, 130 Secondary sexual characters, 453, 454 Sedum spectabile, 312-14 Segregation, Mendel's Law of, 40-42, 382-85 Semon, R., 335 Serology, evidences from, 60 Sex determination, 449-56; chromo- some mechanism of, in Drosophila, 410 ff.; in parthenogenetic species. 451, 452; nutrition theory of, 449; at time of fertilization, 449, 450; various theories of, 449-51 Sex differentiation, 453-56 Sex, Heredity and, 44, 305, 306 Sex-linked inheritance, 433, 440 Sexual coloration, 204 Sexual Selection, 26, 230-32 Shelford, V. E., 190 Shull, A. F., 73, 76-80, 100, 101, 117-20 Shull, G. H., 43 Signals and recognition marks, 203, 204 Sims, G. R., 503 Smith, E. A., 339 Smith, G., 453 Snow, E. C., 493 Solidago virguarea, 324 Species, definitions of, 121, 122 Spencer, H., 4, 19, 28, 29, 264, 325, 508 Spermatid, 298, 299 Spermatocyte, 298, 299 Spermatogenesis, 298, 299 Spermatogonium, 298, 299 Spermatozoon, 165, 298, 299 Spontaneous generation, 12 Sports, 38 Sprengel, C. K., 210 Standard deviation, 367, 368 Staples-Brown, R., 397 Statistical study: of variation, 365-70; of heredity, 370-75 Stegodon, 76, 77, 78, 79 INDEX 523 Steinach, E., 454 Steinmann, G., 6 Stejneger, 117 Sterilization laws, 479, 480 Stock on graft, no influence of, 333, 334 Stockard, C. R., 322, 335 St. Helena, fauna of, 107-9 St. Hilaire, E. G., 21, 22, 220 Strangeways, T. S. P., 125 Sturtevant, A. H., 437 Subsidizing the fit, 480-82 Survival of the Fittest, 223-30 Swainson, 122 Synapsis, 298, 407 Systema Naturae, of Linnaeus, 117 Tail, vestigial hi man, 152, 153 Talent, the production of, 499, 500 Tasmanian Wolf, 127 Tayler, J. L., 253-56 Taxonomy, the method of, 119-20 Teleology, 13 Termites, 214, 215 Tetrakinetic theory of Osborn, 274, 275- 83 Thales, n Theologians, the early Christian, 14, 15 Thompson, A., 153 Thomson, J. A., 97, 191, 205-18, 323- 30, 380-85, 393-4oo Tibia, flattening of, in man, 162 Tomes, C. S., 161 Tower, W. L., 321, 322, 360, 361, 377 Toyama, K., 393, 395 Trihybrid ratio, 391, 392 Trilophodon, 76, 77, 78, 79 Tschermak, 40, 43, 380, 393 Turner, Sir W., 161 Tuttle, E., 483 Twins, evidences from in support of classification, 122 Typhlopidae, 119 Uhrschleim, 12, 16 Uniformitarianism, 22, 23 Unit characters, Mendelian, 386 Urtica dodarti, 394, 395; U. pilulifera, 394, 395 Vanessa to, 314, 315 Variation, 307-22; classification of, 308-11; concept of, 308; continuous and discontinuous, 311, 346; and development, 311; and environment, 312; germinal, 308; nature of, 309, 310; polygons of, 366, 367; somatic, 308; statistical study of, 365-70; universality of, 307, 308 Vasectomy, 479 Vestigial structures, evidences from 60, 140-63 Virchow, R., 91, 240 Volta Bureau, 474 Wagner, M., 269, 270 Walcott, C. W., 62, 64, 67 Wallace, A. R., 17, 26, 27, 36, 97-100, 110-13, I22> 239 Walter, H. E., 373, 473-83 Warning coloration, 202, 203 Weismann, A., 3, 7, 30, 31, 32, 195, 247, 258, 260, 263-68, 281, 330-31, 428 Weismannism, 7 Weldon, W. F. R., 256, 257 Whales, comparative anatomy of, 131- 33; embryology of, 179, 180 White, G., 206, 212, 213 White, T. H., 320 Whitman, C. O., 35 Whitney, D. D., 335 Whymper, 479 Wilberforce, Bishop, 28, 29 Williston, S. W., 35, 83, 85 Wilson, E. B., 6, 44, 401 Wings, comparative anatomy of, 134 Woltereck, R., 315, 316, 335 Woods, F. A., 466-72 Woodward, 88, 92 Woolner, 155 Wordsworth, W., 507 Wright, Sewall, 164, 165 Wyman, Professor, 150 Xenophancs, 12 Zea mays, 395 Ziegler, E., 326 Zoea larva of Peneus, 170 Zygote, 165, 297 PRINTED IN THE U.S.A. UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. JAN 2 5 1956 rm 8 1951 JUN7-RECD B10MEDPEB2375 BfOMPO III FEBl9fi£(TO Biowpy MAY 3 1-1978 MAR 1 8 1968 m°MFO Ua -JfXHlf^70 FEB14RK'Q WRR27^2 APR 1RECTJ B. 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