af Tm MM ms) a mu i) vi iii 7b EX. LIBRIS: VHertram C. A. Mindle, DS, MB, HSA. i dy e ustered round the Darwinian theory. it was | lated. The author’s knowledge of his sub eét is extensive, even encyclopedic and as a result of his labours he has produced a work which will be of the _ greatest value to all desirous of studying the present posi- ‘tion of the Darwinian theories, which, as he very carefully points out, do not really involve the main thesis of trans- -formism in any way. Especially useful are the excellent: “appendixes to each chapter in which the literature of the subject-matter of that chapter is surveyed and abstracted | Lad many useful contributions to knowledge which have appeared in publications not always easily accessible to _ English readers are summarized and made available, As one ‘looks through these one cannot but be struck, however, with the rapidity with which the situation changes as new faéts come to knowledge. For example: Professor Vellog holds that de Vries’ observations on Qeguthera LamarcWiana are practically unchallengeable, yet, no doubt, since this. book was written further observations on this point pub- lished in the Journal of Botany have thrown the gravest ‘doubt upon them. But to return to the point under con- sideration, what is the actual position of Darwinism to-day? Some hold that it is on its deathbed (p. 1); another, and thisa real. luminary'of science ( ch) writes: “ Darwinism now belongs to history, like that other curiosity of our century, the Hegelian philosophy; bothare variationsonthe theme: how one manages to lead a whole generation by the nose” (p. 6). On the other hand Lankester at York, in. 1906, proclaimed his belief “that the conclusions of Darwin. as to the origin of species by the survival of selected races in the struggle for existence are more firmly estab- lished than ‘ever”’ (p. 389). : _ Where such doctors differ and differ so fundamentally “it is difficult for lesser mortals to form a judgement, and Professor Vellog steers a middle course. He admits that’ “the discrediting of the sexual selection theory®”4$ an ex-- ' planation of Secondary Sexual Characters “iscertainly nearly complete” (p. 352), and he couples with it that other theory of the pangenesis of ules, both of which are “nearly” wholly discredited theories” (p. 3). | | _ And with regard to the great theory of Natural Selection: | hat “the fair truth is that the Darwinian selec tion theories, considered with regard to their claimed capa- | iteniane factor in tape reo had hence as the sufficient ; ‘explanation of descent, is discredited and cast down, At ne again, so it seems so me (p. 374). - The evidence upon which this statement rests will be ifound i in the book, and is well worthy of careful study by : all those seriously ‘interested in biological matters. : _ There is one further point to which attention must be directed. The author gives us the views of men like Naeli. and Korschinsky whose scientific evidence cannot be disba ted and whose researches have led them to the conclusion that there i is in organisms “an intrinsic tendency towards progress,” “an inner law of development,” “an inner direc- tive force” (p. 278) by which can be explained the deriva-_ tive of higher from lower forms. For views of this kind and for those of the neo-vitalistic school our author has no. sort of use. “Such a surrender of all our hardly won, actual, scientific knowledge in favour of an unknown, unproved, mystic vital force we are not prepared to make” (p.2'78).And again, “Najeli’s automatic perfecting principleis an impossibility to the pers evolutionist seeking for a causo-mechanical explanation of change” (p. 387). But why? Apparently because the “thorough-going evo- lutionist”’ of this type assumes as a first principle that there can be nothing in nature which is not explicable on chemico- physical lines. Is such an assumption legitimate? No, is the answer made by a large number of men whose eminence as biologists cannot:be gainsaid. Professor Wellog speaks with some scorn of papers written “by certain Roman Catholic priests with a considerable amateur interest in natural ee tory and a strong professional interest in anti-Darwinism”’ (p. 30). Is he, we ask him to. consider within hinheelf, | wholly ignorant of certain scientific men witha considerable. amateur interest in philosophy and a strong professional | interest in anti-Vitalism? Science means or “should mean the pursuit of truth, wherever it may lie, and since it is” ‘still possible that Najeli and others of like views, or even ‘the no doubt contemptible, though worthy, Roman Catholic priests may be right and those on the other side. wrong, would it not be well to abstain from coc sure declarations until things are a little clearer-and ; ‘more certain. than: sav. ‘those. Darwinian » views. _. OF THE DARWINIAN SELECTION THEORIES, TO- Ss GETHER WITH A BRIEF ACCOUNT OF THE ta. a PRINCIPAL OTHER PROPOSED AUXIL- IARY AND ALTERNATIVE THEO- RIES OF SPECIES-FORMING BY VERNON L. KELLOGG PROFESSOR IN LELAND STANFORD, JR., UNIVERSITY LONDON GEORGE BELL AND SONS NEW YORK: HENRY HOLT AND COMPANY 1907] COPYRIGHT, 1907, BY HENRY HOLT AND COMPANY Published August, 1907 AUG 19 1957 PREPACE, Tuts book is written for the sake of presenting simply and concisely to students of biology and to general readers the present-day standing of Darwinism in biological science, and to outline for them the various auxiliary and alternative theories of species-forming which have been proposed to aid or to replace the selection theories. Our actual knowledge of the factors and mechanism of organic evolution and our hypotheses and theories which serve to fill in the present gaps in this knowledge have been greatly added to and modified in the last few years. Much that the general reader includes in his conception of organic evolution, based on his reading of Darwin and Wallace and Spencer, has been materially modified and some of it proved untenable by modern investigation; while much which had no place in this earlier general understanding of evolutionary method and process may now be confidently added to it. The present time is one of unprecedented activity and fertility both in the discovery of facts and in attempts to perceive their significance in relation to the great problems of bio- nomics. Both destructive criticism of old, and synthesis of new hypotheses and theories, are being so energetically car- ried forward that the scientific layman and educated reader, if he stand but ever so little outside of the actual working ranks of biology, is likely to lose his orientation as to the trend of evolutionary advance. Precisely at the present mo- ment is this modification of the general point of view and attitude of philosophical biologists unusually important and far-reaching in its relation to certain long-held general con- ceptions of biology and evolution. This modification of the general trend of evolutionary thought must also necessarily ili iv PREFACE, strongly affect our conceptions of the underlying principles of such correlated sciences as sociology, pedagogy, etc. It is, then, as a means of orientation in evolutionary matters for the general reader and for the unspecialised but interested student of science that this book is prepared. That it may not be without some special usefulness to more advanced students and biological workers there are added, in appendices to the chapters, special notes (referred to in the text by small super-numbers) in which are given numerous exact references to general or special books or papers, and accounts, in more or less detail, of particular observations, experiments, or theoretical discussions, as well as references to extended bibliographic lists of the subjects under treatment. These notes will enable students, or others interested, to look up the original sources of our knowledge of the subjects of the various chapters, and to find more detailed general or special discussions of them than can be given in this book. These notes also enable the author to introduce into the book some details of his own observations and experiments touching various evolutionary subjects. bom! Bee STANFORD UNIverRsITY, /w“7é, 1907. CONTENTS. CHAPTERS. INTRODUCTORY: THE ‘“DEATH-BED OF DAR. WINISM” 7 , : ; ; Modern cies in Bistoeic eudys . Darwinism not synonymous with evolution, 3. Present-day anti-Darwin- ism, 4. Intemperate anti-Darwinism, 6. Outline of this “book, 7. ApPpENDIx: Dennert’s intemperate attack on Darwinism, 7, An anti-evolution university biologist, 8. Friedmann’s theory to replace evolution with divergence, 8. CHATTER. ff, DARWINISM AND EVOLUTION DEFINED AND DISTINGUISHED j Animal and plant kinds paetaats in one ie fares sees. 10. The theory of descent defined, 11. The theory of descent given validity by Darwin’s explanation of the cause of it, 12. Darwinism defined and analysed into its fundamental assumptions and facts, 13. Sources of scien- tific evidence for the theory of descent, 17. Relation of theology, philosophy, pedagogy, and sociology to the theory of descent, 20. APPENDIX: Accounts of history of the descent theory, 22. Books giving the evidences for descent, 23. Dis- cussions of the relation of descent and theology, 23. Discussions of the relations of biology and philosophy, 24. Biology and sociology, 24. CHAPTER L171. DARWINISM ATTACKED The attack of the theologians, oe, The present-day attack of the scientific men, 25. Some of the principal objections to natural selection summarised, 30. Darwinian or fluctuating variations too small to serve as ‘‘handles” VV. PAGE Io 25 Vi CONTENTS. for natural selection, 36. Many specific differences are indifferent, z. ¢., not adaptive, 38. The extinguishing of the extreme variations by interbreeding, 44. The im- probability of the occurrence of the right variations at the right time, 45. The difficulty of explaining the production by natural selection of specialisations useful only in highly complex condition, 49. The objection based on the over- development of specialisations, 53. The objection based on insufficient time, 54. The objection that natural selec- tion tends to preserve the type rather than the variants, and hence opposes change, 56, AppENDIX: Books and papers on variation, 57. Cases of marked variation in parthenogenetic animals, 58. Varia- tion according to the law of probabilities, 59. Quetelet, the discoverer of variation according tothe laws of chance, 61. Example of trivial variations, 62. Ndgeli’s seven objections to species-forming by selection, 62. Wolff’s attack on the selectionists’ assumption of the appearance at the right time of the needed variation, 64. Example of non-correlated variability in bilaterally repeated organs, 65. Henslow’s antagonism to selection as an explainer of floral correlations, 67. Wolff’s objection to the necessary assumption of identical and coincident variation in re- peated structures, as feathers, scales, etc., 67. Example of mal-adaption in the egg-laying habit of PAryganidia californica, 68—Pieper’s antagonism to the selection ex- planation of colour and pattern in insects, 69. CHAPTER. Jt, DARWINISM ATTACKED (Continued) Objection to the exclusively linear or quantitative anee acter of the fluctuating or Darwinian variations, 70. Galton’s law of regression, 71. Selection may produce evolution (continuous change) but not species (discontinu- ous series), 73. Pfeffer’s objection based on the slowness of species transformation, 75. The difficulty of explaining the sterility of species by selection, 76. Selection cannot explain extreme or complete degeneration of useless parts, 77. Objections to the assumed rigour of the struggle for existence and to the actuality of intra-specific or personal selection, 79. Indiscriminate extermination due to the PAGE 70 fortune of position and time, 80. The necessity of sexual CONTENTS. vil PAGE. _ selection, a discredited theory, for the support of the natural selection theory, 85. Natural selection rests on an unwarranted assumption of its homology with artificial selection, 86. Many biologists find natural selection unable to account for known biologic conditions, 89. Sig- nificance of the concessions of Darwinians, go. Kor- schinsky’s extreme anti-Darwinian doctrine, 91. Delage’s “true réle of selection,” 93. Morgan’s rejection of natural selection as a species-forming factor, 93. APPENDIX: Galton’s statement of the law of regression, 97. Wolff's criticism of panmixia, 98. Example of inef- fective panmixia, 100. Example of progressive degenera- tion inexplicable by natural selection, 100. Wolff's discussion of the selection coefficient, ror. Example of non-selection of trivial differences, 103. References to books and papers on plant breeding, 105. CHAPTER VV. DARWINISM ATTACKED (Continued): THE THEORY OF SEXUAL SELECTION é : ‘ , : . 106 Secondary sexual differences or characters, 107. Classi- ; fication of secondary sexual characters, 107. Useless and harmful characters not explicable by natural selection, 110. Theory of sexual selection to account for them: the theory defined, 111. Darwin’s assumptions as basis of the theory of sexual selection, 112. Difficulties in the way of a general application of the theory, 113. The theory appli- cable only to species in which males are more numerous than females, 113. The passivity of females, 114. Males of species in which no real pairing occurs also show strik- ing secondary sexual characters, 114. Necessity of assuming unproved esthetic development among lower animals, 114. Few recorded cases of observed choosing by female, 115. Difficult to assume utility for many secondary sexual characters, 115. Stolzmann’s case of the Andean humming-birds, 116. Howexplain the beginnings of secondary sexual characters, 117. How explain orna- mental characters appearing in both males and females, 118. Morgan’s objections to sexual selection theory, 118. Experimental evidence touching the theory is against it, 120. Mayer's experiments with Promethea and Porthetria moths, 121. Douglass’s and Diirigen’s observations on Vill CONTENTS. lizards, 123. Substitutionary theories of the origin of secondary sexual characters, 124. APPENDIX: References to books and papers discussing sexual selection, 125. Wolff’s critical exposition of weak- nesses in sexual selection, 126. CHAPTER 11. DARWINISM DEFENDED Position of the defenders of Patines va Reaction against the too speculative positions of Haeckel and Weismann, 130. ‘‘Haeckelismus,” 130. Weismannism, 131. Struggle between Neo-Darwinians and Neo-La- marckians, 133. Concessions of the Neo-Darwinians, 134. Answer to objection concerning the too slight character of fluctuating or Darwinian variations to serve as handles for natural selection, 138. Answer to the objection concern- ing the linear and quantitative character of Darwinian variation, 139. Answer to the objection that selection can- not produce many-branched descent, 142. Answer to the statement that selection can produce continuous change or evolution, but not species, 143. Answer to the objec- tion concerning the production by selection of co-adaptive and highly complex specialisations, 144. Answer to the objection concerning the over-development of specialisa- tions, 146. Discussion of the difficulty that natural selec- tion has with structural degeneration, 146. The Darwinian answer to the expressions of doubt about the rigour of selection, 148. Answer to the objections to the sexual selection theory, 148. Discussion of the objection to the derivation of evidence for natural selection from the facts of artificial selection, 150. Tayler’s general defence, 153. APPENDIX: Weldon’s experiments on Carcinus, 158. Tayler’s explanation of degeneration by natural selection, 162. Plate’s explanation of character fixity in domestic animals, 163. CHAPTER VII. DARWINISM DEFENDED (Continued): PLATE’S CON. CILIATORY DEFENCE : Plate, afair-minded Darwinian sheen aie 164. Aaawers to the objection based on the slight character and inutility of Darwinian variations, 165. Many slight differences at PAGE 129 164 CONTENTS. ix . PAGE | first glance apparently indifferent in character found on more careful inspection to be of advantage, 166. Slight characters aided by co-related differences, 167, The prin- ciple of the change of function, 168. Characters of in- different value under one condition of environment, suddenly made important by a change in life-conditions, 169. Organs of universal character which can become modified in various directions, 169. Lamarckian factors called to the aid of Darwinism, 170. Answers to the objection based on the improbability of the appearance of the right variations at the right time for the progressive perfecting or development of an organ, 170. Selection directs itself according to variation, not variation accord- ing to any assumed needs of selection, 171. Selection works with plural variations, not single ones, 172. The same selective value can often be attained through combi- nations of various peculiarities and the same effect reached by various means, 172. The element of chance _ not peculiar to the Darwinian explanation of co-adap- tations, 175. Answers to the objection based on the assumed improbability that during the course of the development of a complex organ or whole body-part, or during the perfecting of a changing adaptation the numerous necessary adaptations will occur in such a suc- cessive series as to make possible any harmonious correla- tion of the various single variations, 176. Plate’s reliance on the Lamarckian factor of the inheritance of characters acquired through use, disuse, and other functional stimuli, 178. The attainment of selective value by various means, 178. Weismann’s theory of germinal selection unaccept- able, 180. Weismann’s principle of amphimixis of great importance, 180. The necessity of concessions admitted 181. The necessity of invoking auxiliary or aiding prin- ciples to support the natural selection theory, 182. APPENDIX: Conn’s discussion of selective value, 182. References to papers on correlation, 184. Cope’s proof that natural selection cannot originate new characters, 185. CHAPTER: V 117. OTHER THEORIES OF SPECIES-FORMING: THEO- RIES AUXILIARY TO SELECTION . ; . 187 The presentation of theories to aid the selection theories or others to replace them really a continuation of the x CONTENTS. PAGE defence of, and attack on, Darwinism, 187. The Weis- mannian theories, 188. Panmixia, 190. The theory of germinal selection, 193. The physical and chemical structure of protoplasm, 194. Objections to the theory of germinal selection, 200. Roux’s theory of intra-selec- tion, or the battle of the parts, 201. Objections to Roux’s theory, 203. The theory of organic selection, or ortho- plasy, 208. APPENDIX: List of Weismann’s evolution papers, 212. Theories of ultimate protoplasmic structure, 214. Encase- ment theory, 215. Micromeric theories, 215. Buffon's theory, 216. Spencer’s theory, 217. Darwin’s theory, 218. Nadageli’s theory, 219. De Vries’s theory, 220. Hat- schek’s theory, 222. Delage’scriticisms, 224. Le Dantec’s criticisms, 224. Verworn’s biogen hypothesis, 225. De- lage’s machine theory, 225. Le Dantec’s theory of chemism, 225. Neo-vitalism, 226. Morgan’s criticism of Weismann’s method of argument, 229. References to discussions of orthoplasy, 229. CHAL IER IX, OTHER THEORIES OF SPECIES-FORMING (Continued): THEORIES AUXILIARY TO SELECTION (Continued) 232 Isolation theories, 232. Wagner’s ‘‘Separations-theorie,” 234. Jordan’s upholding of the importance in species- forming of geographic isolation, 237. Biologic and sexual isolation, or physiological selection, 243. Gulick’s work and conclusions, 249. APPENDIX: References to discussions of isolation, 253. Haacke’s summary of Wagner’s theory, 253. Grinnell’s studies of geographic differences in the chickadee, 255. Further references to discussions of isolation, 261. CHAPTER A, OTHER THEORIES OF SPECIES-FORMING (Con- tinued): THEORIES ALTERNATIVE TO SELEC- TION ‘ 3 ; 3 : : ; : ol Aas « 262 Three general groups of theories proposed to replace the selection theories as explanations of species-forming and evolution, 262. The Lamarckian theory, 262. Objections to the Lamarckian factors, especially that of the inheritance CONTENTS. 4 PAGE of acquired characters, 266. Great use could be made of the Lamarckian factors in explaining evolution phenomena if these factors could be given validity, 271. Orthogenesis and determinate variation, pointing toward orthogenesis, 271. Niageli’s theory of orthogenesis, 277. Eimer’s ortho- genetic theory, 282. Cope’s theory of bathmism and kinetogenesis, 285. Jaeckel’s theory of metakinesis, 289. APPENDIX: Referencesto Lamarck’s writings, 290. Brown- Séquard’s experiments on guinea pigs, 290. Hyatt’s studies of P/anorbis, 295. Fischer’s experiments with butterflies, 296. Experiments with silkworms, 298. Ref- erences to books and papers on inheritance of acquired characters, 305. Redfield’s position, 305. Montgomery’s explanation of inheritance of variation, 306. Scientific aspects of Burbank’s work, 310. Orthogenetic variation in paleontology, 319. A case of apparent determinate variation, 319. Pfeffer’s theory of orthogenesis, 320. Eimer’s theory of orthogenesis, 321. Apparent determi- nate evolution, 322. Snodgrass’s observances on bills of Galapagos birds, 323. Cope’s belief in orthogenetic evolu- tion, 323. Whitman’s belief in determinate variation, 325. Cunningham and orthogenesis, 326. CAAT LR AT. OTHER THEORIES OF SPECIES-FORMING (Con- tinued); THEORIES ALTERNATIVE TO SELEC- TION (Contenued) : ‘ : ~ 927 Heterogenesis or the riittations dicey. se "eae tions of heterogenesis theories by von Kolliker, Dall, Galton, and Emery, 330. Korschinsky’s heterogenesis theory, 333. De Vries’s mutations theory, 337. Present status of de Vries’s theory, 348. Alternative theories to explain secondary sexual characters, 352. APPENDIX: Mendel and his work, 356. References to recent work on Mendelism, 357. Darwin's examples of race origin from sports, 357. A recent example of race origin from a sport in cattle, 358. Galton’s discussion of specific stability, 360. References to discussions by de Vries of species-forming, 362. American opinions of the mutations theory, 362. Davenport’s example of species origin by slight continuous change, 367. Merriam’s criti- cism of the mutations theory, 367. Plate’s criticism of the Xii CONTENTS. mutations theory, 368. References to theories explaining secondary sexual characters, 373. CHAP IL AT, DARWINISM’S PRESENT STANDING Natural selection the final control in evolution, but not a sufficient explanation of species-forming, 374. Weak- nesses of the substitutionary theories, 375. The unknown factors of evolution, 377. Prime needs of evolution study; first, the intensive study, statistical and experimental, of variability, 378. Second, the means of cumulating varia- bility along definite lines, 379. Third, the investigation of adaptation, 380. A suggested argument for a belief in the transference of ontogenic changes into phylogeny, 382. A suggested automatic causal factor of variability, purposive but not purposeful, 384. Our present ignorance and the call to work, 387. AePENDIX: Wigand’s criticism of the selection theories, 387. Lankester’s upholding of Darwinism, 389. De Vries’s discussion of species-forming by selection, 389. Delage’s estimate of selection, 390. Osborn’s championship of the unknown factors of evolution, 391. Klebs’s ‘conclusions from experiments on plants, 392. Friedlander’s discussion of adaptation, 392. Loeb’s attitude toward the problem of species-forming, 393. INDEX a oe ae ee ee a PAGE 374 397 DARWINISM TO-DAY MO ae a a : a ae CC —— -é. Bis Tales —— ~~ j ; DARWINISM TO-DAY. CHAPTER I. INTRODUCTORY :-fHE-"DEATH-BED OF DARWINISM.” “Vom STERBELAGER DES DarRwinisMus!” This is the title of a recent pamphlet * lying before me. But ever since there has been Darwinism there have been occasional death- beds of Darwinism on title pages of pamphlets, addresses, and sermons. Much more worth consideration than any clerical pamphlets or dissertations, under this title, by frisch- gebackenen German doctors of philosophy—the title alone proving prejudice or lack of judgment or of knowledge— are the numerous books and papers which, with less sensa- tional headlines but infinitely more important contents, are appearing now in such numbers and from such a variety of reputable sources as to reveal the existence among biologists and philosophers of a widespread belief in the marked weakening, at least, if not serious indisposition, of Darwin- ism. A few of these books and papers from scientific sources even suggest that their writers see shadows of a death-bed. The present extraordinary activity in biology is two- phased; there is going on a most careful re-examination or Modern activ. Scrutiny of the theories connected with organic ity in biologic evolution, resulting in much destructive criti- ae: cism of certain long-cherished and widely held beliefs, and at the same time there are being developed and almost feverishly driven forward certain fascinating and fundamentally important new lines, employing new methods, J ees 2 DARWINISM TO-DAY. of biological investigation. Conspicuous among these new kinds of work are the statistical or quantitative study of variations and that most alluring work variously called developmental mechanics, experimental morphology, ex- perimental physiology of development, or, most suitably of all because most comprehensively, experimental biology.’ This work includes the controlled modification of conditions attending development and behaviour, and the pedigreed breeding of pure and hybrid generations. Now this combina- tion of destructive critical activity and active constructive ex- perimental investigation has plainly resulted, or is resulting, in the distinct weakening or modifying of certain familiar and long-entrenched theories concerning the causative factors and the mechanism of organic evolution. Most conspicuous among these theories now in the white light of scientific scrutiny are those established by Darwin, and known, col- lectively, to biologists, as Darwinism. To too many general readers Darwinism is synonymous with organic evolution or the theory of descent. The word is not to be so used or considered. Darwinism, primarily, is a most ingenious, most plausible, and, according to one’s belief, most effective or most inadequate, causo-mechanical explanation of adaptation and species-transforming. It is that factor which, ever since its proposal by Darwin in 1859, has been held by a majority of biologists to be the chief working agent in the descent, that is, the origin, of species. However worthy Darwin is of having his name applied directly to the great theory of descent—for it was only by Darwin’s aid that this theory, conceived and more or less clearly announced by numerous pre-Darwinian naturalists and philosophers, came to general and nearly immediate acceptance—the fact is that the name Darwinism has been pretty consistently applied by biologists only to those theories practically original with Darwin which offer a mechanical explanation of the accepted ‘fact of What Dar- winism is, a - + SS INTRODUCTORY: “DEATH-BED OF DARWINISM.” 3 descent. Of these Darwinian theories the primary and all- important one is that of natural selection. Included with this in Darwinism are the now nearly wholly discredited theories of sexual selection and of the pangenesis of gem- | mules. It may also be fairly said that the theory of the descent of man from the lower animals should be included in Darwinism, For Darwin was practically the first naturalist bold enough to admit the logical and obvious consequences of the general acceptance of the theory of descent, and to include man in the general chain of descending, or ascend- ing, organisms. So that the popular notion that Darwinism is in some way the right word to apply to the doctrine that man has come from the monkeys is rather nearer right than wrong. But biologists do not recognise the descent of man as a special phase of Darwinism, but rather of the whole theory of descent, or organic evolution. Darwinism, then, is not synonymous with organic evolu- tion, nor with the theory of descent (which two phases are a used by the biologist practically synonymously ). Darwinism not synonymous 9Lherefore when one reads of the “death-bed of with evolution. Parwinism,” it is not of the death-bed of or- ganic evolution or of the theory of descent that one is read- ing. While many reputable biologists to-day strongly doubt the commonly reputed effectiveness of the Darwinian selec- tion factors to explain descent—some, indeed, holding them | to be of absolutely no species-forming value—practically no naturalists * of position and recognised attainment doubt the theory of descent.“ Organic evolution, that is, the descent of species, is looked on by biologists to be as proved a part of their science as gravitation is in the science of physics or chemical affinity in that of chemistry. Doubts of Darwinism are not, then, doubts, of organic evolution. Darwinism might indeed be on its death-bed without shaking in any considerable degree the confidence of biologists and natural philosophers in the theory of descent. Li ln SII DT ae 4 DARWINISM TO-DAY. But the educated reader, the scientific layman, the thinker and worker in any line of sociologic, philosophic, or even theologic activity is bound to be disturbed and Present-day anti-Darwin- unsettled by rumours from the camp of pro- ae fessional biologists of any weakness or mortal illness of Darwinism. We have only just got ourselves and our conceptions of nature, of sociology and philosophy, well oriented and adjusted with regard to Darwinism. And for relentless hands now to come and clutch away our founda- tions is simply intolerable. Zim Teufel with these German professors! For it is precisely the German biologists who are most active in this undermining of the Darwinian theories. But there are others with them; Holland, Russia, Italy, France, and our own country all contribute their quota of disturbing questions and declarations of protest and revolt. The English seem mostly inclined to uphold the glory of their illustrious countryman. But there are rebels even there. Altogether it may be stated with full regard to facts that a major part of the current published output of general biological discussions, theoretical treatises, addresses, and brochures dealing with the great evolutionary problems, is distinctly anti-Darwinian in character. This major part of the public discussion of the status of evolution and its causes, its factors and mechanism, by working biologists and thinking natural philosophers, reveals a lack of belief in the effectiveness or capacity of the natural selection theory to serve as a sufficient causo-mechanical explanation of species-forming and evolution. Nor is this preponderance of anti-Darwinian expression in current biological literature to be wholly or even chiefly attributed to a dignified silence on the part of the believers in selection. Answers and defences have appeared and are appearing. But in practically all these defences two characteristics are to be noted, namely, a tendency to propose supporting hypotheses or theories, and a tendency to make certain INTRODUCTORY: “DEATH-BED OF DARWINISM.” = 5 distinct concessions to the beleaguering party. The fair truth is that the Darwinian selection theories, considered with regard to their claimed capacity to be an independently sufficient mechanical explanation of descent, stand to-day seriously discredited in the biological world. On the other hand, it is also fair truth to say that no replacing hypothesis: or theory of species-forming has been offered by the oppo- nents of selection which has met with any general or even considerable acceptance by naturalists. Mutations seem to: be too few and far between; for orthogenesis we can dis- cover no satisfactory mechanism; and the same is true for the Lamarckian theories of modification by the cumulation,. through inheritance, of acquired or ontogenic characters. Kurz und gut, we are immensely unsettled. Now but little of this philosophic turmoil and wordy strife has found its way as yet into current American litera- ture. Our bookshop windows offer no display, as in Ger- many, of volumes and pamphlets on the newer evolutionary study ; our serious-minded quarterlies, if we have any, and our. critical monthlies and weeklies contain no debates or discussions over “das Sterbelager des Darwinismus.” Our’ | popular magazines keep to the safe and pleasant task of telling sweetly of the joys of making Nature’s acquaintance through field-glasses and the attuned ear. But just as cer- tainly as the many material things “made in Germany” have found their way to us so will come soon the echoes and phrases of the present intellectual activity in evolutionary affairs, an activity bound to continue as long as the new lines of biological investigation continue their amazing out- put of new facts to serve as the bases for new critical attacks on the old notions and for the upbuilding of new hypotheses. If now the first of these echoes to come across the water to us prove to be, as wholly likely, those from the more vio- lent and louder debaters, they may lead to an undue dismay and panic on our part. Things are really in no such desper- 6 DARWINISM TO-DAY. ate way with Darwinism as the polemic vigour of the Ger- man and French anti-Darwinians leads them to suggest. Says one of them: “Darwinism now belongs to history, like that other curiosity of our century, the | Hegelian philosophy ; both are variations on the theme: how one manages to lead a whole gen- eration by the nose.” The same writer also speaks of “the softening of the brain of the Darwinians.’’ Another one,’ in similarly relegating Darwinism to the past, takes much pleas- ure in explaining that “we [anti-Darwinians] are now stand- ing by the death-bed of Darwinism, and making ready to send the friends of the patient a little money to insure a decent burial of the remains.’” No less intemperate and in- decent is Wolff’s " reference to the “episode of Darwinism” and his suggestion that our attitude toward Darwin should be “‘as if he had never existed.” Such absurdity of ex- pression might pass unnoticed in the mouth of a violent non-scientific debater—let us say an indignant theologian of Darwin’s own days—but in the mouth of a biologist of recognised achievement, of thorough scientific training and unusually keen mind—for this expression came from just such a man—it can only be referred to as a deplorable example of those things that make the judicious to grieve. Such violence blunts or breaks one’s own weapons. While I have said that the coming across the water of the more vigorous anti-Darwinian utterances might cause some dismay and panic in the ranks of the educated reader— really unnecessary panic, as I hope to point out—it will doubtless occur to some of my readers to say that this fear of panic is unwarranted. If the first phrases to come are as injudicious and intemperate, hence as unconvincing, as those just cited, the whole anti-Darwinian movement will be discredited and given no attention. Which, I hasten to reply, will be as much of a mistake as panic would be. There is something very seriously to be heeded in the INTRODUCTORY: “DEATH-BED OF DARWINISM.” 7 chorus of criticism and protest, and wholly to stop one’s ears to these criticisms is to refuse enlightenment and to show prejudice. I have thought it, therefore, worth while to try to anticipate the coming of fragmentary PE icery of and disturbing extracts from the rapidly in- creasing mass of recent anti-Darwinian litera- ture by presenting in this book a summary account not alone of these modern criticisms, but of the answers to them by the steadfast Darwinians, and of the concessions and supporting hypotheses which the supporters of both sides have been led to offer during the debates. I shall try to give a fair state- ment of the recent attacks on, and the defence and present scientific standing of, the familiar Darwinian theories, and to give also concise expositions, with some critical comment, of the more important new, or newly remodelled alternative and auxiliary theories of species-forming and descent, such as heterogenesis, orthogenesis, isolation, etc., and an esti- mate of their degree of acceptance by naturalists. APPENDIX. 1Dennert, E., “Vom Sterbelager des Darwinismus,” Stuttgart, 1903. An intemperate and unconvincing but interesting brief against Dennert’sin- the Darwinian factors, 1. e., the selection theories, in temperate attack evolution. Author fully accepts the theory of descent, on Darwinism: byt in no degree the Darwinian causal explanation of this descent. “‘Was ich in diesen Berichten nachzuweisen suche, ist die Tatsache, dass der, Darwinismus nunmehr bald der Ver- gangenheit, der Geschichte angehort, dass wir an seinem Sterbe- lager stehen und dass auch seine Freunde sich eben anschicken, ihm wenigstens noch ein anstandiges Begrabnis zu sichern” (p. 4). The valuable thing about the paper is that it is largely given to a gathering together of the anti-Darwinian opinions and declarations of numerous, mostly well-known and reputably placed biologists. Some of these declarations are interpreted by Dr. Dennert in a way that would probably hardly be wholly acceptable to the declarers, but for the most part the anti-Darwinian beliefs of these biologists are uumistakably revealed by their own words. Among the biologists and biological philosophers thus agglomerated into the camp of 8 DARWINISM TO-DAY. anti-Darwinism are Wigand, Haacke, von Sachs, Goette, Kor- schinsky, Haberlandt, Steinmann, Eimer, M. Wagner, von Kolliker, Nageli, Kerner, F. von Wagner, Fleischmann, O. Schultze, O. Hert- wig, and others. This list includes reputable botanists, zoologists,. and paleontologists. ? For a recent account of such work, see Morgan, T. H., ‘“Experi-. mental Zodlogy,” 1907. * A. Fleischmann, professor of zoology in the University of Er- langen, is the only biologist of recognised position, of whom I am An anti-evolu- aware, who publicly declares a disbelief in the theory tion university of descent. He seems to base his disbelief on the diologist. fact that the phyletic (genealogic) series in numerous. animal groups are as yet unexplained. See his book, “Die De- scendenztheorie,”’ Leipzig, 1901. ‘‘Allein je mehr ich mich in die vermeintlichen Beweisgriinde derselben [the theory of descent] vertiefte und durch Spezialuntersuchungen positive Anhaltspunkte fur die Stammesverwandtschaft der Tiere zu gewinnen suchte, um so klarer stellte sich mir die Erkenntniss heraus, dass jene Theorie eben doch mehr nur ein bestrickender, Ergebnisse und Aufklarung vortauschender Roman sei, als eine auf positiven Grundlagen auf- gebaute Lehre.” (From the preface of this book). *A curious attempt to formulate a scientific theory explaining the conditions as we know them in the world of life, to replace the Friedmann’s theory of descent, is contained in a recent small book theory to replace called “Die Konvergenz der Organismen” (1904), evolution with by Hermann Friedmann, The author assumes that the divergence. diversity of organisms is the primary condition, and that their similarity has been brought about through convergence, as opposed to the postulate of the theory of descent to the effect that diversity of life has grown out of primary identity or homogeneity. I quote (p. 12) as follows from Friedmann: “‘Diese Annahme, die in dem vorliegenden Buch vertreten wird, ist folgendermassen zu erlau- tern. Wir gehen von dem Hauptsatze aus, dass das Leben immer als ein bestimmter, unwandelbarer Speziescharakter auftritt. Die spezi- fisch verschiedenen Lebensformen erscheinen jedoch einander angenahert, bezw. annaherbar, durch drei (Teil-) prinzipien, von denen das Leben beherrscht wird: Das Prinzip, vermoge dessen spezifisch verschiedene Formen solche Ubereinstimmungen auf- weisen, die wir als primargesetzliche betrachten, nennen wir das Prinzip der Homologie; als einen Ausfluss des Prinzips der Analo- gie bezeichnen wir diejenigen Ubereinstimmungen, die unter dem Einfliisse gleichwirkender dusserer (mittelbar oder unmittelbar bewirkender oder selektiver) Bedingungen entstehen; und wir erkennen drittens die Macht und die Tragweite eines Prinzips der \ INTRODUCTORY: “DEATH-BED OF DARWINISM.” .- > direkten Konvergenz, welches das Entstehen von Ubereinstim- mungen zwischen den Genossen einer Biosphare aus psychischen Ursachen bewirkt. Die drei Prinzipien bilden die Grundlage der Konvergenztheorie.” * Driesch, H., Biolog. Centralb., v. 16, p. 355, 1896. * Dennert, E., ““Vom Sterbelager des Darwinismus,” p. 4, 1903. 7 Wolff, G., ‘“Beitrage zur Kritik der Darwin’schen Lehre,” p. 54, 1808. CHAPTER: it; DARWINISM AND EVOLUTION DEFINED AND DISTINGUISHED. Our manuals of zoology and botany contain the names and descriptions of about 400,000 living species of animals and 200,000 living species of plants. There are Possible = parts of the earth from which we have collected modes of origin ; P of diverse plant as yet only a few kinds of animals and plants, scabs merely the larger, more conspicuous or more abundant kinds; there are no parts of the earth from which we are not constantly receiving reports of the discovery of “new” species—new, of course, simply in the sense that we have not known them before. It is wholly certain that the number of different species, that is, kinds, of living organisms must number millions; various guesses,’ all unimportant, have been made. Of the extinct species, those hosts of strange denizens of our changing earth in the ages gone, the number of recorded forms can at best be but the veriest fraction of the grand total of species that have actually existed. Now all these millions of kinds of animals and plants can have had an origin in some one of but three ways; they have come into existence spontaneously, they \ have been specially created by some supernatural power, or ( they have descended one from the other in many-branching | series by gradual transformation. There is absolutely no scientific evidence for either of the first two ways; there is much scientific evidence for the last way. There is left for the scientific mdn, then, solely the last; that is, the method Ge) DARWINISM AND EVOLUTION DEFINED. . I1 of descent. The theory of descent (with which phrase or- ganic evolution may be practically held as a synonym) is, then, simply the declaration that the various living as well as the now extinct species of organisms are descended from one another and from common ancestors. It is the explanation of the origin of species accepted in the science of biology. (The natural Theory of descent defined, For an interesting discussion from the modern point of view of the relation between Darwinian biology and theology see Haeckel, Discrcatansot Ernst, “Der Monismus als Band zwischen Religion polation ofae- und. Wissenschatt,” 18935 also Vetter, Benjamin, scentandthe- “Die moderne Weltanschauung und der Mensch,” ology. 1903; also Wasmann, Erich, “Die moderne Biologie und die Entwicklungstheorie,” 1904. (Author is a Jesuit priest whose remarkable studies on ants and their messmates have made him well known to biologists. He accepts the theory of descent, with the ex- clusion of man from the evolution series.) See also Hutton, F. W., “The Lesson of Evolution,” 1902. In this book the author takes a strong stand for dualism, making the point that the theory of evo- lution has rescued philosophy from a rigidly monistic materialistic basis (a mind-in-all-matter theory), and has made necessary a dual- istic theory (mind-and-matter theory) because of the necessity of postulating the beginning of life and a beginning of mind. The goannas DARN A AAP AY ce pn Seen 24 DARWINISM TO-DAY. theory of evolution rescues religion from Pantheism, and puts it on a Theistic basis. ‘It is true, as Pantheists urge, that their only experi- ence of mind is in connection with matter, but so far as we know mind is connected only with one kind of matter called protoplasm, which cannot possibly exist throughout the universe. Consequently mind must either be absent in large portions of matter or it must be associated with that matter in some way which quite transcends their experience. So that we have no more experience of mind universally distributed through matter than we have of mind dis- tinct from matter. And the argument for Pantheism breaks down.” See also Le Conte, Jos., “Evolution, its Nature, its Evidences and its Relation to Religious Thought,” 1801. * Of course many books and papers concerning the relation of biology to philosophy have been written. A good introduction to Discussions of the subject is Eugen Dreher’s ‘‘Der Darwinismus und relation of biol- seine Stellung in der Philosophie,” 1877; see also Ver- ogy and philoso- worn, Max, ‘““Naturwissenschaft und Weltanschauung,” phy, 1904; also Adickes, Erich, ‘‘Kant contra Haeckel,” 1901; also Emil du Bois-Reymond’s “Uber die Grenzen des Naturer- kennens,” and “Die Sieben Weltrathsel”’; also Haeckel’s ‘‘Die Welt- rathsel” (trans. in English as “The Riddle of the Universe’) ; see also Schurman, J. G., “The Ethical Import of Darwinism,” 1888; also Huxley, “Evolution and Ethics and Other Essays,” 1894; see also Reinke, J., “‘Einleitung in die Theoretische Biologie,’ Igot. The author sets out in this book the philosophic notions of Hart- mann, Lotze, Wundt, Muller and others concerning the principles and laws of biology, and does this definitely enough to make his book a pretty good compend of philosophico-biology. "See* Herbert Spencer’s “Principles of Sociology”; also Lester Ward’s “Biological Sociology”; also Benjamin Kidd’s “Social Evo- lution”; also Curt Michaelis, “‘Prinzipien der natur- Biology and 4 : : ‘ P sociology. lichen und sozialen Entwicklungsgeschichte des Men-_ schen,” 1904; also ‘“‘Darwinismus und Sozialwissen- schaft,’ 1903; see also Schallmeyer, W., ‘“Vererbung und Auslese in Lebenslauf der Volker,’ 1903. * The books and papers referred to in notes 5, 6, and 7 are simply certain ones that have particularly interested the author. The lists of references make not the slightest pretence to guide the general reader interested in these special subjects. =a CHAPTER 11. DARWINISM ATTACKED. ATTACKs on Darwinism have been made, of course, ever since there was any Darwinism to attack. In those first days (and months and years) after the “Origin of Species” was published there were the liveliest of times for Darwin and his supporters; or rather chiefly for the supporters. Darwin wisely kept aloof from the debates. But for the first band of followers with the indefatigable, the brilliant, and wholly competent Huxley at its head, there was no lack of opportunities for jousting. The issue was never doubtful; Huxley and his informed and equipped scientific companions against the scientifically ignorant, angry, incautious, and dogmatic Bishop Wilberforces had unfair odds. The victory came swiftly and brilliantly to the Darwinians. At this time there was little distinction made between Darwinism and Evolu- tion. It was really a battle by the theologians against the theory of descent. And the theory of descent was, and is, invulnerable. Since those warring days of the ’60’s the theory of descent has been assailed no more, that is in any important or even interesting way. And the true Darwin- Picnic ism, the selection doctrine, has also been sub- of Darwinism. ject to no conspicuous and popularly recognised attack. The educated public accepted the re- sults of the first battle as final, and it quietly began to rearrange its thought and to some degree its actual ways 25 Early attacks on Darwinism. 26 DARWINISM TO-DAY. of living in accordance with these newly discovered condi- tions of life. Nevertheless there has been from the day of the close of the great first battle to the present moment a steady and cumulating stream of scientific criticism * of the Darwinian selection theories. In the last few years, it has, as already mentioned in the preface and introductory chapter of this book, reached such proportions, such strength and extent, as to begin to make itself apparent outside of strictly biological and naturo-philosophical circles. * Such older biologists and natural philosophers as von Baer, von Kolli- ker, Virchow, Nageli, Wigand, and Hartmann, and such others writing in the nineties and in the present century as von Sachs, Eimer, Delage, Haacke, Kassowitz, Cope, Haberlandt, Henslow, Goette, Wolff, Driesch, Packard, Morgan, Jaeckel, Steinmann, Korschinsky, and de Vries, are examples which show the distinctly ponderable char- acter of the anti-Darwinian ranks. Perhaps these names mean little to the general reader; let me translate them into the professors of zoology, of botany, of paleontology, and of pathology, in the universities of Berlin, Paris, Vienna, Strassburg, Tubingen, Amsterdam, Columbia University, etc., Now without knowing the man personally, or even through his particular work, the general reader can safely attribute to men of such position a certain amount of scientific training, of proved capacity, and of special ac- quaintanceship with the subject of their discussion. One does not come to be a professor of biology in Berlin or Paris or Columbia solely by caprice of ministers of educa- tion or boards of trustees; one has proved one’s competency for the place. To working biologists the names—I have given, of course, only a selection, and one particularly made to show variety of interest (botany, zoology, palzontology, pathology )—mean even more than the positions. They are mostly associated with recognised scientific attainment and general intellectual capacity. DARWINISM ATTACKED. 27 Among the critics of the selection theories we must note two groups, differing in the character of their criticism r more in degree than in kind, perhaps, but still wo groups of — : : ; : scientificat- importantly differing. One group denies in tackers, ; ; : toto any effectiveness or capacity for species- forming on the part of natural selection, while the other group, a larger one, sees in natural selection an effective factor in directing or controlling the general course of es —— descent, holding it to adaptive lines, but denies it outright | any such Allmacht of species control as the more eager selectionists, the so-called neo-Darwinians or Weismann- ians, credit it with. This larger group of critics sees in natural selection an evolutionary factor capable of initiating nothing, dependent wholly for any effectiveness on some primary factor or factors controlling the origin and direc- tion of variation, but wholly capable of extinguishing all unadapted, unfit lines of development, and, in this way, of exercising decisive final control over the general course of descent, 7. €., organic evolution. Another classification of critics may be made on the basis of pure destructiveness on the one hand as opposed to destructiveness combined with constructiveness on the other. That is, some critics of selec- tion, as Wolff, Pfeffer, Driesch, e¢ al., are content with doing their best to reveal the incapacity of Darwinism; others, on the contrary, come with certain more or less well-outlined substitutionary theories in their hands. Eimer with his theory of orthogenesis, and Korschinsky and de Vries with their theory of mutations, are examples of the latter class. The general impression left on one after a considerable course of anti-Darwinian reading ranging all the way from the extreme attitude and the violence of Den- Pigs de Be nert, Fleischmann, Wolff, and Coe, to the ee substitu- tempered and reserved criticism of Delage and de Vries, is that there is a very real and effective amount of destructive criticism for Darwinians to meet; and 28 DARWINISM TO-DAY. at the same time a curious paucity of satisfactory or at all convincing substitutionary theory offered by the anti- Darwinians to replace that which they are attempting to dethrone. The situation illustrates-admirably the varying worth of a few facts. A few stubborn facts of the wrong complexion are fatal things for a theory ; they are immensely effective offensive weapons. But these same few facts make __-a pitiable showing when they are called on to support a theory of their own. It was exactly the greatest part of Darwin's greatness, it seems to me, that he launched his. theory only after making the most remarkable collection of facts yet gathered together in biological science by any one man. Testing his theory by applying to it successively fact after fact, group after group and category after category of facts, he convinced himself of the theory’s consonance with all this vast array of observed biological actuality. Compare the grounding of any of the now offered replacing theories with the preparation and founding of Darwinism. In 1864 von Kolliker,” a great biologist, convinced of the incapacity of natural selection to do the work assigned it by its founders and friends, suggested a theory of the origin of species by considerable leaps ; in 1899, Korschinsky,’ on the basis of some few personal observations and the compiling of some others, definitely formulated a theory of species- forming by sudden considerable variations, namely, muta- tions; in 1901 and 1903 appeared the two volumes of de Vries’ s “Die Mutationstheorie,” in which are revealed the results of long years of careful personal observation, in truly Darwinian manner, directed toward the testing and better grounding of this mutationstheorie of species-origin. The results are: out of many plant species studied, a few show at certain times in the course of numerous generations a behaviour in accordance with the demands of a theory of species-forming by sudden definitive modification; that is, species-forming by mutations. The mutations-theory DARWINISM ATTACKED. 29 thus launched is offered as a substitute for the natural selection theory obviously weakening under the fire of modern scientific criticism. But however effective de Vries’s facts are in proving the possibility of the occurrence of other variations than those fortuitous ones occurring in continuous series from mean to opposite extremes which Dar- win recognised as the basis of species-forming, and however effective they are in proving the actual production of three or six or ten species by mutation, and however effective in both these capacities they are as weapons of attack on the dominance of the Darwinian theory of species-making, how really inadequate are they to serve as the basis of a . great all-answering theory explaining, in a causo-mechanical way, the facts of descent, or even the primary facts of gen- eral species-forming. And yet the first American book * (from the pen of one of America’s foremost biologists) to discuss the modern phase of unrest and dissatisfaction in evolutionary matters, practically accepts the mutations- theory as a substitute for the selection theory of species- forming. It cannot be, it seems to me, that Professor Morgan is so satisfied with the mutations-theory, that he clutches it up, hardly definitely formed and cooled, from the de Vriesian moulds, but that he is, like many another present- day biologist, so profoundly dissatisfied with the natural selection theory. For my part it seems better to go back to the old and safe Jgnoramus ° standpoint. But I have been led to anticipate my conclusions; let us make another beginning with the real undertaking of this chapter and get to the actual specifications of “Darwinism Attacked.” We shall concentrate the attacks and attackers in this and the two following chapters ; then include in the suc- ceeding two the defence and the defenders, and in the next four chapters the various supporting and substitutionary theories offered by the friends and foes of Darwinism. Finally, in the last chapter we shall set out what we can 30 DARWINISM TO-DAY. discover, in the haze of the smoke of battle, of the actual present state of the besieged and besiegers. Distinctly the most comprehensive, the fairest-minded review of gegen-und-fiir Darwinismus in recent literature is Plate’s extension of his address, “Uber die Bedeutung des Darwin’schen Selectionsprincips,’ made in Hamburg be- fore the Deutsche Zoologische Gesellschaft in 1899. To this review, as published in 1903 after being extended and brought up to date, I beg to acknowledge a special indebted- ness in my present attempt to get together the more im- portant criticism, both adverse and defensive, of Darwin. I have, however, assiduously sought out (with the help of librarians and my indefatigable Leipzig book-dealer friend Bernh. Liebisch), and perused the original pourings-forth of criticism and vilification even to the reading of some matter written by certain Roman Catholic priests with a consider- able amateur interest in natural history and a strong pro- fessional interest in anti-Darwinism! But Plate has been a guiding hand in this search for active attacks and de- fence. The natural selection theory as an all-sufficient explanation ness at its base; it depends absolutely, of course, Natural selec- on the pre-existence of variations, but it itself tion theory based : Aas on variation. | has no influence whatever on the origin or con- trol of these variations except in so far as it may determine what individuals shall be permitted to give birth to other individuals. Now one of the chief problems in biology is exactly that of the origin, the causes, and the primary control of these congenital variations.* Three principal explanations, no one of them experimentally proved or even fairly tested as yet, have been given of this actually occurring congenital variation, viz., (1) that there exists in the germ-plasm an inherent tendency or capacity to vary so that there is inevitable variation in all individuals DARWINISM ATTACKED. 35 produced from germ-plasm, this variation being wholly fortuitous and fluctuating according to some (the belief of Darwin and his followers), or, according to others, this variation following certain fixed or determinate lines (de- terminate variation, orthogenetic variation, etc.) ; (2)) that amphimixis, 1. e., bi-parental parentage, is the principal cause of variation, it seeming logical to presume that indi- viduals produced from germ-cells derived from the fusion of germ-plasm coming from two individuals more or less unlike would differ ‘slightly from either of the parental individuals ; and (3), that congenital variation is due to the influence of the ever- -varying environment of the germ-cell producing individuals. The objections to any one of these theories may be very pertinent, as when one says regarding the first that calling a thing “inherent” is not clearing up in any degree a phenomenon for which we are demanding a causo-mechanical explanation; or of the second that it has been proved * that individuals produced parthenogenetically, that is, from an unmated mother, vary and in some cases vary even more than do other individuals of the same species produced by amphimixis; or of the third that as far as our study of the actual processes and mechanism of the produc- tion of germ-cells and of embryos has gone, we have found no apparent means whereby this influence of the ambient medium can be successfully impressed on the germ-plasm. But however pertinent the objections to the why of varia- tion may be they do not in any way invalidate the fact that variations do continuously and inevitably occur in all indi- viduals, and that while many of these variations are recog- nisably such as have been impressed on the individual during its personal development as immediate results of varying temperature, amount or kind of food, degree of humidity, etc., to which it may be exposed in its young life, others seem wholly inexplicable on a basis of varying individual environment and are certainly due to some antenatal influ- ee DARWINISM TO-DAY. ence acting on the germ-plasm from which the embryo is derived. Now the natural selection theory, in its Darwinian and neo-Darwinian form, presupposes fortuitously occurring congenital variations of practically infinite ee ee in all parts of all organisms. Actual tion according to) Observation shows that all parts of all organ- neat ” isms do vary and that they vary congenitally, that is, independently of any immediate in- fluence during development exercised from without by environmental conditions, as well as in response to these environmental influences, and finally that in many cases this variation is fortuitous, that is, that it occurs according to the laws * of chance. The industrious statistical study of variations, including the tabulation of the variation con- dition in long series of individuals of the same species or race and the mathematical formulation of this variation condition, have shown that in many specific cases, studied in numerous kinds of animal and plant forms, the character of the variation in any particular character may be truly represented (with close approximation) by the mathematical expression and curve which would exactly define the condi- tion in which the variation would exist if it actually followed the law of error. It is these continuous series of slight variations, these variously called fluctuating, individual, or Darwinian variations, occurring in all organisms at all times and often following, in their occurrence, the laws of chance, on which Darwin’s theory of species-forming by natural selection is based. But this same industrious statistical and quantitative study of variation, which has proved that some variations do occur regularly, fluctuating around a mean or mode, has shown, as well, that in many cases the variations distinctly tend to heap up on one side or the other of the mean, that is, that they tend to occur along certain lines or toward certain direc- DARWINISM ATTACKED. 33 tions rather than uniformly out in all directions. Also it is true, and this has of course been long known, that by no means all variations are so slight nor in such perfectly gradatory or continuous series as is true of the gradatory Darwinian variations. “Sports” have been known to breeders of plants and animals ever since plant and animal breeding began. Bateson has filled a large book’ with records of “discontinuous varia- tions” in animals; variations, that is, of large size and not occurring as members of continuous gradatory series. So that biologists are acquainted with many cases of variation that seem to be of a kind, or to exhibit a tendency, to in- stitute special directions of development, and thus not to be of the simple, non-initiating, inert character of the fortuitous, slight, fluctuating variations, among which natural selection is presumed to choose those that are to become the be- ginnings of new lines of modification and descent. Many biologists believe firmly that variations occur in many special cases, if not in most cases, only along certain special lines. Palzontologists believe, practically as a united body, | that variation has followed fixed lines through the ages; that there has been no such unrestricted and utterly free play of variational vagary as the Darwinian natural selection theory presupposes. Now it is at least obvious that natural selection is abso- lutely limited in its work to the material furnished by varia- tion; so that if variation occurs in any cases only along certain determinate lines selection Discontinuous ‘variation. Determinate variation as8@ = =¢can do no more than make use of these lines. species-forming : Rae ; factor. Indeed if variation can occur persistently along determinate lines natural selection’s function in controlling evolution in such cases is limited to the police power of restricting or inhibiting further development along any one or more of these lines which are of a disadvan- tageous character, that is, a character which handicaps or 34 DARWINISM TO-DAY. destroys the efficiency of its members in the struggle for life. The question in many men’s mouths to-day is, Why may not variation be the actual determinant factor in species-forming, in descent? It actually is, respond many biologists and palzontologists. Even Darwin believed such determinate variation to occur, as is indicated by repeated statements in the “Origin of Species.” In chapter iv he says (to refer to but a single one of these admissions) : “It should not, however, be over- looked that certain rather strongly marked variations, which no one would rank as mere individual differences, fre- quently recur owing to a similar organisation being similarly acted on—of which fact numerous instances could be given with our domestic productions. In such cases, if the vary- ing individual did not actually transmit to its offspring its newly acquired character, it would undoubtedly transmit to them, as long as the existing conditions remain the same, a still stronger tendency to vary in the same manner. There can also be little doubt that the tendency to vary in the same manner has often been so strong that all the individuals of the same species have been similarly modified without the aid of any form of selection. Or only a third, fifth, or tenth part of the individuals may have been thus affected, of which fact several instances could be given. Thus Graba estimates that about one-fifth of the guillemots in the Faroe Islands consist of a variety so well marked, that it was formerly ranked as a distinct species under the name of Uria lacrymans. In cases of this kind, if the variation were of a beneficial nature, the original form would soon be sup- planted by the modified form, through the survival of the fittest.” This problem of the existence or non-existence of deter- minate variation is taken up in such detail in connection with the explanation and discussion of various auxiliary or alter- native theories of species-forming in later chapters of this DARWINISM ATTACKED. 35 book that it need not detain us now. But to my mind it is one of the most important matters in connection with the ee whole great problem of descent, that is, of nate variation €VOlution. It is the basic problem of evolu- bal tion, for it is the problem of beginnings. Selection, isolation, and the like factors are conditions of species-forming; variation is a prerequisite, a sine qua non. True variation must have its causes, and these causes are to be determined before an actual causo-me- chanical explanation of evolution can ever be found. But the determination of the relation of variation to species- forming is certainly the first step now necessary in our search for the basic factors, the real first causes of species change. But even in those cases where there may exist unrestricted indeterminate fluctuating variation in continuous series ac- Whatdoes COrding to the law of error, what is it that this fluctuating vati- variation really offers natural selection to ation offer selec- P tion asa basisfor WOrK on? Remember what natural selection species-forming? is : the saving of one or ten by the actual killing of the thousand or ten thousand because in the struggle for existence the variations of the one or ten are of sufficient advantage to have a life-or-death-determining value. Now between any two successive individuals in a series arranged on a basis of the variations in any one character of any one organ or function, the difference is extremely slight, too slight, one is certain, to be, in most cases, of life or death value. But even if one’s conception of the absolute inten- sity of the rigour of the personal struggle leads to a logical conception of an absolute advantage in any differ- ence, however slight, in a favourable direction, it is wholly possible that for any other characteristic equally important in the struggle the two individuals may be in exactly reversed position, the one possessing the infinitesimal advantage in strength say, possessing an infinitesimal disadvantage in 36 DARWINISM TO-DAY. sharpness of claw or in agility. What of the chances for such a necessary coincidence in the one individual of favour- able variations in all the ways necessary to create a real life- or-death-determining advantage? The law of probabilities answers that much to the dismay of the Darwinian. But, again, why not compare the chances in the struggle of two individuals not standing side by side in a variational series, but at two extremes of the range; the difference here can be considerable, can be of positive advantage or disadvantage. Yes, but again comes the necessity of presupposing a coin- cidence of other advantages or at least of no coincidence of balancing advantages and disadvantages. But even more fatal is the condition that if an extreme variation in some one character could be of a life-preserving advantage, yet by the law of probabilities (and by the tale of actual observation) those individuals standing at the extremes of the range of variation are very, very few compared with those standing nearer the mean, or mode, of the series, and there would be almost a certainty of such an extreme-charactered sur- vivor not finding a similar form with which to mate and thus insure perpetuation of the advantage, the mating of the individuals admittedly not depending on any necessary similarity in variation (unless the varying characteristics happen to be actually concerned with the mating act: see later discussion of biological isolation, chapter ix). Con- siderable variations, the only ones of apparent worth in a life-and-death struggle, are in such meagre disproportion to the less considerable that they are inevitably swamped, extinguished, in miscellaneous cross-mating. Let us consider a little more in detail each of the various objections mentioned in the last few pages. Only the student asteitheae of systematic (classificatory ) zoology or botany of fluctuating can realise how slight and insignificant are the aa various miscellaneous individual variations which make up that basis of ever-present, myriad-faced, DARWINISM ATTACKED. 37 fortuitous, fluctuating variability on which the whole great structure of the selection theory is based. Yet any one’s common sense and his intuitive comprehension of what life-and-death value is in an animal’s battle with another, with foreign enemies, or with inclement Nature, make this objection of “no handle for natural selection in mis- cellaneous slight variation” thoroughly appreciable. Polar bears are probably descended from brown; and their white fur coat is probably an advantageous adaptation in their life in the Arctic. But did the fortuitous appearance in his. coat of a spot of white hairs as large as a dollar or a pancake give some ancient brown bear such an advantage in the struggle for existence as to make him or her the fore- runner of a new and better-adapted sort of bear? The giraffe’s long neck is very much worth while to it; it gets. leaves from the higher branches unattainable by the short- necked animals who find food in the same range. But did a millimetre or even an inch of extra neck appearing as individual variation in an ancestral short-necked giraffe kind give natural selection a handle with which to grind out a new species? The consideration of the usefulness of slight variations too often leads to an argument for their usefulness on the same grounds as sustain the belief that the hound will never catch the hare which goes one-half as fast as the dog. For each time the hound covers the given stretch that lies between him and the hare at any given moment the hare will be just one-half that distance in advance—and though the distance will get ever shorter and shorter the hare will ever be one-half the last distance ahead. So say the sophists. As a matter of fact the hound gets the hare. Spencer’s example of the femur of the whale is a striking illustration of the reality of the absurdity connected with the argument of change on a basis of the selection of in- finitesimal differences. The femur of the whale, says 38 DARWINISM TO-DAY. Spencer, is evidently the atrophied rudiment of a bone once much larger. It weighs now about one ounce, less than a Bani: millionth of the weight of the whote body. ample of the Let us suppose that when it weighed two ca aa ounces an individual had a femur which by variational chance weighed but one ounce. What advantage over other whales would the difference give it? What fraction of the daily nourishment would this ad- vantageous variation permit the fortunate whale to add to its stored fat instead of spending it on an extra ounce of useless femur? Who would dare claim that this variation would aid in success in the struggle for existence? And yet this is the argument for the reduction of useless organs through the influence of natural selection. Roux and Weismann, realising the absurdity of the argument, have put forward two theories, one called the ‘battle of the parts” and the other the “theory of germinal selection” to aid the selection theory to explain the degeneration and reduction of organs. The reader will find these theories explained in chapter viii. Every student of systematic zoology or botany has a keen realisation, too, of the fact that a majority of the distinguish- ing characters which he recognises in the vari- Many species Ous species and genera that come under his characters of no P utility, eye are of a sort that reveal to him no trace of particular utility or advantage. Indeed he can go farther and express, to himself at least, his conviction that many of these slight but constant specific differences *° can actually have no special advantageousness about them. One’s experience as an observer of nature and one’s common sense combine to protest against that easy and sweeping answer of the Darwinians: “shall “poor blind man’ say what characteristic, however slight and insignificant, is or is not of advantage in the great complex of nature?’ As the whole question after all resolves itself into one for which “poor blind man” is attempting to find an answer satisfying DARWINISM ATTACKED. 39 to his own understanding, however short of perfection and — omniscience that is, he is bound to answer the subsidiary -problems such as usefulness or non-usefulness on a basis of his own seeing and understanding capacity. As a matter of fact the indifference of many specific characteristics of organisms is not denied by selectionists. Romanes ** was perhaps the first representative Darwinian, after Darwin himself, to admit this. But many biologists say, further, on a basis of their experience as observers, that these very indifferent, meaningless (as far as utility goes) mor- phological characteristics and differences are much more constant in their character than the obviously adaptive, 7. ¢., useful ones. However, as pointed out first by Nageli, accord- ing to the selection theory the characteristics of organisms should be just in that degree the more constant, the more useful they are. Hence there is here a serious discrepancy between theory and fact. Darwin himself felt the force of this objection and met it in a manner not at all acceptable to the ultra-Darwinians, that is the strict selectionists of post-Darwinian times. He admitted that these trivial, ap- parently non-useful, but constant specific characters could not be explained by natural selection, and must be due to a fixation in the species of these characters at one time or another through the nature of the organism and the influ- ence of extrinsic influences; a true Lamarckian or at least anti-Weismannian * explanation. This objection to the selection theory based on the ad- * Students and readers who have not read Darwin recently, or in the light of the controversy between the neo-Darwinians and the neo-Lamarckians, that is, between those who disbelieve and those who believe in the inheritance of acquired characters, will be sur- prised to note on a careful re-reading of the “Origin of Species,” with this post-Darwinian sharp distinction in mind, how often Dar- win calls on the Lamarckian factors to help his species-forming theories out of tight places. Morgan in his “Evolution and Adap- tation” points out many cases of this. 40 DARWINISM TO-DAY. mitted existence of indifferent species characters is well stated phe Oe “as follows: “But how is it with char- ment of theob- acters that have no utility? It is, of course, a er great achievement to be able to point out the trivial charace method by which adaptations have been pro- i duced, but if animals have some characters that are not useful, natural selection does not explain them. Natural selection can develop useful organs only. The real problem which our naturalists are trying to solve is not the origin of adaptations simply but the origin of species also. Now while many of the characters and organs of animals. and plants are of utility to the individual there are others that appear to be useless. As animals and plants are studied, it is found that the different species differ from each other by certain definite characters. These distinctive peculiarities that distinguish species are called ‘specific characters, and this term will be hereafter used in this sense. The explanation of the origin of species must then account for the origin of specific characters. Now specific characters are frequently trivial in nature. This was long ago recognised by Darwin, who saw that the characters by which species are distinguished are frequently so trivial as to be apparently useless. If, however, we are to explain the origin of species we must find an explanation of these trivial characters as well as the more important ones. If these trivial characters are of no use to their possessors, then manifestly the principle of the survival of the fittest does. not account for them. The fact that species are so com- monly separated by characters that seem to be absolutely useless has led some of our keenest naturalists to insist that the survival of the fittest does not explain the origin of species, but explains only the origin of adaptations. At all events, it is clear that the problem of the utility of specific characters is a very fundamental one to the discussion of the principle of survival. DARWINISM ATTACKED. ai “We here come to the first parting of the ways between scientists of different schools. On the one hand we find those who are so thoroughly convinced of the universality of the principle of natural selection that they insist that all specific characters are useful, however useless they may seem. It is beyond question that they are led to this belief in the utility of all characters, not from observation, but simply from their belief in the sufficiency of the law of natural selection. They tell us that we know too little of the actual life of organisms in nature to enable us to say that any given character is not of use; and to make a claim that any- thing, no matter how trivial, is useless, is simply to confess ignorance. We must acknowledge that many seemingly useless organs have been found to have utility as soon as the life habits of animals are better understood. Certainly, utility has been found more universal than was believed to be possible a quarter of a century ago. The followers of Darwin have given very much attention to this matter. They have pointed out many lines of utility hitherto not dreamed of. They have considered great multitudes of cases of seemingly useless characters, and by a little imagina- tion have suggested some use to which they may be adapted. If one reads the recent works of Wallace, the most promi- nent advocate of this position, he will not fail to be im- pressed with the fact that utility is much more widely applicable as an explanation of seemingly trivial characters than might have been thought possible. The position held by this writer is, that inasmuch as the law of natural selection is a universal force which all admit, while all other forces of evolution are yet in dispute, and inasmuch as many seemingly useless organs have been shown to be of use, it is perfectly legitimate to claim that when we come to under- stand them, we shall find that all characters are of value, and that the principle of survival of the fittest has been concerned in the development of them all. If this is true, the survival 42 DARWINISM TO-DAY. of the fittest explains the origin of species as well as the origin of adaptations, since all specific characters are really adaptations. “But on the other hand, many naturalists think that there are specific characters for which we cannot only see no utility, but which are demonstrably of no use. A few illus- trations will serve to make the matter clearer. Certain in- sects are distinguished from each other in accordance with whether they possess one or two bristles on the head. Here is a character which appears to be constant, and which must therefore be explained by any complete theory of the origin of species. Can we imagine that the question of whether the animal has one or two hairs should ever have been of selective value? But if developed by natural selection, this character must at some time have been a matter of life and death. Again among snails, the shells commonly coil in the same direction in the same species, this fact making the direction of the coiling of the shell a specific character. But clearly this is not a matter of selective value, since living among the rest of the individuals will frequently be found some with their shells coiled in the opposite direction. Again, horses have small horny callosities on their feet. No one has suggested any possible use for them, but neverthe- less they are present on the feet of all the species of the horse family. But the most curious fact is that while the horse has them on all four feet, the ass has them on only two. Now, upon the principle that utility is universal, it would be neces- sary to claim, not only that the presence of four callosities has been a matter of selective value in the horse, an ex- tremely difficult thing to believe, but also that the presence of only two instead of four has been of selective value in the ass. This position approaches absurdity. Again, there are molluscs characterised by special markings of the shell, which markings are constant enough to be specific char- acters, and must, of course, be included in any explanation DARWINISM ATTACKED. 43 of the origin of species. But these marks are demonstrably of no use, since they are entirely covered by the epidermis | of the animal when alive, and absoiutely invisible. Again, some birds have slight differences in colour markings which separate species. Now these differences may perhaps be re- garded as of use as protective or as recognition marks. But in some cases the colour markings are entirely con- cealed by other feathers and, being invisible, can be of no possible utility. It is hardly possible for one, unless he has decided previously to accept the all-sufficiency of natural selection, to believe that there can be any utility in the very slight differences in the shape of leaves of plants, in the micro- scopic markings of the hairs of different species of mammals, the exact numbers of the feathers in the tails of birds, the peculiar distribution of the veins in the wings of a butter- fly, the microscopic markings in the scales on its wings, or a host of other similar trivial characters. When it is re- membered that the selection principle would force us to insist that all of these characters are of value sufficient to protect their possessors at the expense of other individuals not possessing them, it is evident that the burden thrown upon the principle of survival becomes very great. When finally we come to characters of specific nature connected with colour markings which are invisible when the animal is alive, there is apparently no resource left except to con- clude that the principle of survival because of utility does not account for everything.” It is indeed the general recognition by naturalists of the fact of the triviality or indifference of a majority of specific characters that has led to the recent renewal of the import- ance of isolation theories, particularly of geographical isolation. The rehabilitation of Moritz Wagner’s theory of species-forming by migration and isolation is a conspicuous feature in present-day evolution discussion. The way in ‘which isolation comes to the aid of selection, or even sup- 44 DARWINISM TO-DAY. plants it in the minds of some, in species-forming is pointed out in chapter ix, to which the interested reader may FeTer, But in those cases where the differences or variation among individuals may be or obviously are of the character The swamping Of useful ones, and where by comparing ex- or extinguishing tremes of this variation the life-and-death- of favourable va- riations by inter- determining worth of this utility might be crectine: conceded, still. what chance is there for the perpetuation of this advantage? Nageli long ago pointed out that the extreme variations, that is, the rare variations, would in almost every case be inevitably extinguished by interbreeding. If a certain considerable variation occurred in one individual of a hundred born, in 20,000 individuals of the species 200 would have this worth-while variation. Now if the chances of mating are the same for all there would be 9,801 parings of individuals not showing the variations, 198 pairings between a varying individual and a non-varying one, and a single mating between two indi- viduals both preserving the considerable variation. In fact every rare variation will, as Delage says, be immediately effaced by the dilution of the blood of the varying individual by that of the great mass of individuals not possessed of the particular variation. This inevitable swamping of the ad- vantageous variations of individuals has long ago led to the practical giving up by Darwinians of any claims to species- forming or evolution on the basis of extreme or rare varia- tions and to the restriction of the selecting influence to masses. The species must be changed through the selection of it as a mass or unit rather than through the selection of special scattered individuals of it. But for the selection of masses of individuals sufficiently considerable to avoid the extinguishing of the fortunate variations by interbreeding, and to insure a repetition of the advantage and an opportunity for its fostering and DARWINISM ATTACKED. 45 increase, there is necessary an extraordinary coincidence in the appearance of the needed variations in many forms at The needed co- the right time. That is,atheory based on chance incident occur- or accidental phenomena demands after all the ‘rence of several : variations atone assumption of the occurrence of phenomena ‘time, of the right kind at the right moment, and the persistence of such occurrences through a definite time-period. This is too much to assume, too much to ask even of those of the true faith, say the antagonists ** ** of the selection theory. Kronig ** makes sport of the selection ‘doctrine by having his rather frivolous character, Sabtich- winski, undertake to have made, by a foolish clown, various trifling changes in all kinds of industrial products with the expectation of bringing them into the market. He is con- vinced that he will win a fortune by this, for he says to himself that the struggle for supremacy must work out the same in the industries as in nature, and in his case with the added advantage that the changes effected by even the most slender-witted boor must result better than those which are the outcome of perfectly blind chance. Indeed, from the very heart of the neo-Darwinian ranks come signs of dis- may when this objection is faced. Weismann, leader of the ultra-selectionists, practically concedes the irrefutability of this objection to the Allmacht of selection when he intro- duces a statement of his latest theory, that of Germinal Selection, by saying :** “Knowing this factor [that of germi- nal selection] we remove, it seems to me, the Weismann’s eps . admission of the Patent contradiction of the assumption that the nu paar general fitness of organisms or the adaptations necessary to their existence are produced by accidental variations—a contradiction which formed a seri- ous stumbling-block to the theory of selection.” And the formulation of the theory of germinal selection is of itself a practical confession on the part of the foremost neo- Darwinian of the inability of natural selection to explain 46 DARWINISM TO-DAY. species-forming without calling to its aid some effective factor to control in its beginnings the variation essential as the basis of the selective action. Pfeffer ** and Wolff ** have been particularly keen and severe in their criticism of the selection theory on the basis of this objection. And Morgan” in this country has also made effective use of this weapon in his destructive con- sideration of the Darwinian theories. There is an additional point about this difficulty of the necessity for a certain regularity or reliability of variation etinein tee in order to make a beginning basis for the action coincident ap- of selection. It is this. Close scrutiny reveals pearance of other the necessity often of the occurrence of several variations to make acertain coincident variations in order to make any one one effective, characteristic positively advantageous. What advantage in the way of increased speed is a slight added length of leg without a simultaneously added strength of musculation; or an increase in size of antlers without a simultaneous increase in strength of neck muscles to sup- port and manipulate the heavier head? What faint prob- ability of the occurrence coincidently of the necessary varia- tions (if determined only by chance, that is, the law of prob- ability) to produce a gradual perfecting of so complex a structure as the vertebrate eye? Or, more, how incon- ceivable the coincidences, if variation is purely fortuitous, necessary to the simultaneous development of two exactly similar eyes: two eyes so intimately associated physio- logically that normal sight is a function of both these separated organs working perfectly together. Is variation to be assumed to be governed by some law of bilateral symmetry? But I have shown for many cases *° that in such perfectly and fundamentally bilaterally symmetrical animals as insects neither the usual Darwinian fluctuating variation nor the rarer discontinuous or sport variation is governed at all by sucha law. In fact the independence of the varia- DARWINISM ATTACKED. 47 tion phenomena in right and left members of bilaterally arranged pairs of organs as wings, antenne, legs, etc., is a noticeable fact. This denial of the capacity of the selection of fortuitous slight variations to account for coadaptation and for the continuous perfecting of complex organs has been stated as follows: “It is highly improbable that for the steady perfecting of an organ, the variations needed by selection will always appear just at the right time.” Or in more expanded form: “It is highly improbable that during the modification of a complex organ such as a whole body part, or during the gradual perfecting of an adaptive modi- fication, the numerous necessary variations will appear suc- cessively in such series that a harmonious combination of the single variations will be possible.” The objection cer- tainly needs no elaboration. The Darwinian variations ap- pear in all directions at all times in slight degrees with no determinate direction nor correlation. Selection is to find in these variations its only material with which to build up to wonderful complexity and perfection of coadaptation and correlation of parts ** on a basis of constant advantage, such an intricate but harmoniously adjusted compound organ as the human eye, in which the failure or imperfectness of a single minute part can at any time, during the course of development, rob the whole of any advantage whatever to the organism possessing: it. Wolff ** enlarges on the difficulty of explaining any identical structures of the animal body which appear in one Difficulty of and the same organism to the number of two explaining re- or more. “It cannot be explained,” he says, “by peated identical P : structures by Selection, how the carnivores, for example, can selection. have developed through fortuitous yet always similar variations, two-such structures agreeing in all de- tails as the back teeth, which have developed in course of time from small skin teeth. That a tooth can develop into such an admirable biting organ through chance variation may 48 DARWINISM TO-DAY. be explicable by selection, because we are accustomed to postulate thoroughly fortuitous and all-inclusive variation ; but that the tooth standing next to it shall have varied al- ways in exactly the same way so that the result of its de- velopment shall make it identical with the other one, is inexplicable by selection on a basis of fortuitous variation, but rather indicates that the change of form is ruled by law which we do not know. The attempt to discover it is the most imperative task for biologists to undertake.” Wolff * follows this argument farther by discussing other particular examples, but they are all of the type of the one Spencer’s pic. JuSt set out. Spencer pictures the situation of ture ofthe inu- the herbivorous animals in a country of in- tility of advan- ‘ tageinasingle Clement climate and populated by numerous eerie carnivores. Now those herbivores which have the finest hearing will be soonest aware of the approach of the tiger, but those with keenest sight or most perfect sense of smell will also perceive, as soon, that it is time to flee. But what advantage over others will the first start in flight give them? Others less delicately endowed with sense organs but swifter of foot will, although starting a little later, have as good a chance to escape because of their more rapid run- ning. Later may come snow and terrible cold. Those in- dividuals best endowed with sense-organs or swiftest of foot will not necessarily be the most enduring or the best equipped with instincts to find shelter. The climate may decimate those which selection on the basis of special senses or speed has saved. But after the cold may come the sum- mer drought. Those most heavily furred or warmest- blooded which have successfully endured the low temperature and snow and ice of winter should be the first to suffer from the attacks of sun and drought and lack of food in the summer. Thus no individual has, because of advantage in any one character, any real and complete superiority which guarantees it success in all the phases of the struggle for DARWINISM ATTACKED, ees existence: the advantages are scattered and compensated by disadvantages.** | In connection with the objection stated in the preceding paragraphs is that specially pressed by Wolff, although long Numerous use- 2£0 strongly stated by Mivart,** and one that Papeete has long appealed strongly to me particularly in in highly per- COmnection with the study of the utility of fected staten = colour and pattern among insects. This ob- jection is, that numerous useful characteristics or adapta- tions of organisms are useful only in a highly perfected state, often involving a complex and considerable structural development of old (then much modified) or quite new parts, and hence could not have arisen by gradual modification by the selection of slight variations. Darwin himself says that . if a single complex organ can be referred to whose full de- velopment cannot possibly be explained through numerous small successive modifications, then his theory must indubi- tably fall. For example, the electric organ of the torpedoes, the brood-sacks or cells on the back of Pipa dorsigera, the chameleon’s tongue, and many other organs can be recalled which could not possibly exercise their particular advanta- geous function in an undeveloped and beginning state. In my own eyes has for long stood the familiar case of the mimicry, of our common American monarch butterfly, Mimicry of Anosia plexippus, by the viceroy butterfly, Anosia by Basilarchia archippus. The viceroy belongs to a epearule group of species in which the prevailing (almost certainly the ancestral) colour and pattern are white and black (or iridescent purplish and bluish) arranged as a broad white continuous transversal bar across both fore and hind wings, on a black (to purplish) ground. The colour and pattern of Anosia are radically different; brick-red ground, black longitudinal lines following the veins and small white spots in an irregular black submarginal band. Examine the viceroy butterfly. You find no suggestion of typical Bast- 5° DARWINISM TO-DAY. larchia type of colour and pattern; on the contrary, you find an extraordinarily faithful imitation (duplication) of Anosia’s colour and pattern. Only in a narrow black trans- versal streak across the outer disc of each hind wing is there any divergence in the viceroy from the Anosia pattern. Now Anosia is distasteful to birds; after a few experiments with Anosia a bird recognising this ill-tasting morsel in its conspicuous red-brown livery leaves the monarchs alone. Not only monarchs, however, but also viceroys, which are to all external seeming only slightly smaller monarchs. The viceroy is, however, not distasteful; it would be a welcome bonne bouche to any bird that could distinguish it. But thanks to its perfectly mimicking colour-pattern it wings its deceitful way unmolested. There is huge usefulness here, and selec- tion can well be the steadfast maintainer of the viceroy’s dissimulation. But of what avail for this purpose of deceit was the first tiny tinge or fleck of red-brown on the staring black and white wings of the ancestral viceroy? How can one possibly conceive of an attainment of this identity of pattern between mimicker and mimicked by selection on a basis of life-or-death-determining advantage of slight chance appearances of brown or reddish flecks or tinges in suc- cessive viceroys? Not until practically full development of the mimicry pattern existed can this pattern have worked its advantage. It is, indeed, a different matter with many, per- haps most, cases of general or special protective resemblance. A little green, a little brown could obviously help the insect living in green foliage, or on the ground. Every change of tinge toward the general environing colour is worth while; it helps melt the insect into its inanimate surroundings. But with mimicry it must be the whole thing or nothing; or at least near enough to the whole thing to pass for it. Wolff puts the objection about as follows: There are compound organs and complex adaptations, whose complication (he would better say, whose advantage due to complication) can DARWINISM ATTACKED. 51 only be reached by a leap, while the selection theory pre- supposes slight gradual stages of complication. Wolff ** expresses another phase of this objection by re- ferring to a few of many cases of complex relations between Difficulty og entirely distinct organs in the body, which explaining com- relations constitute some of the most important ae functions of the body. For the successful parts by selec- establishment of these relations it has been tion. , necessary, as Wolff expresses it, “that for each advance in development or complexity of one definite pecu- liarity in an organ there must appear corresponding and exact definite advance in development or complexity of a peculiarity in another entirely distinct organ.” Wolff’s first example is the relationship existing between the muscles and nerves of the higher animals. The intimate, delicate, and precise character of the relations between the nerve-end- ings and the muscle cells, to be explicable by selection of fortuitous variations, must have required coincident varia- tions both in structure and functions of each muscle cell and each nerve-ending that are impossible to conceive of. “It might be,” says Wolff, “possible to picture the gradual development of the relations between one muscle cell and one nerve-ending on the basis of a selection among infinitely fortuitous variations, but that such variation shall occur coincidently in time and character in hundreds or thousands of cases in one organism is inconceivable.” In the case of organs whose functions are regulated from a common centre, the development of centre and of organs must have gone on coincidently and could not have been independent. The development of the eye is useless if the development of the optic centre did not go hand in hand with it. Without the one the other has no reason, no significance, therefore selection could have brought neither to its proper development independently. The coincident appearance, however, of organ and centre can 52 DARWINISM TO-DAY. be explained by the selection theory only when there is postulated a definite degree of complexity of the fortu- itously appearing slight variations, that is, when this theory is in condition to assume that which would be a denial in terms that variations are wholly fortuitous. Wolff goes on to give certain examples of such complex relations which involve a dependence of the use upon an instinct, as the performance by the queen honey-bee of her particular functions in the hive, etc. , “Out of this discussion,’ says Wolff, “finally we must postulate that structures which are to be explained by the selection theory must possess at the least two certain charac- teristics. Such a structure, namely, must occur but once in an organism [that is, must not be a serially or bilaterally repeated organ, nor indeed appear in any condition of plural number]; further, it must not stand in any necessary relation to any other part of the same organism, that is, in a relation which one can interpret as a relation not existing from the beginning, therefore one which must be looked on as an acquired relation. But if we survey the whole animal king- dom it will be very difficult for us to find any structures which satisfy both these requirements. It might be possible to find some which perhaps seem to satisfy the second re- quirement, but with regard to the first requirement I may declare,” says Wolff, “that there is scarcely a single structure which fulfils it. Symmetry alone, which rules almost all organisms, makes organs which appear in the singular num- ber rarities, and even such as the pancreas, etc., are com- posed of many finer structures, which are homodynamous among themselves. When we find two similar organs in different animal groups we seek for a causal explanation of this similarity and find it in common ancestry. It is absurd to seek a causal explanation for the origin of homologous structures and yet postulate a purely chance or fortuitous explanation for the origin of homodynamous structures.” 2 s c : ; ’ DARWINISM ATTACKED. 53 Another objection which the study of the utility of col- our and pattern ** also has impressed upon me is that of the Pbisdtita based carrying too far of certain lines of modification. on over-speciali- Classic examples are the fatal over-development saa of the antlers of the extinct Irish stag, the un- wieldiness of the giant Cretaceous reptiles, the intimate identity of the halves of bilaterally symmetrical animals. Let me call attention to an overdone case of “protective resemblance’ among the insects. It is that of the famous Kallimas, the dead-leaf butterflies of the Malayan and gen- eral south tropical regions. These butterflies (there are several species which show the marvellous imitation) have the under sides of both fore and hind wings so coloured and streaked that when apposed over the back in the manner common to butterflies at rest, the four wings combine to Kellima, the resemble with absurd fidelity a dead leaf still dead-leaf butter- attached by a short petiole to the twig or branch. a I say absurd, for it seems to me the resemblance is over-refined. Here for safety’s sake it is no question of mimicking some one particular kind of other organism or inanimate thing in Nature which birds do not molest. It is simply to produce the effect of a dead leaf; any dead leaf; a brown, withering leaf on a branch. Leaf-shape and gen- eral dead-leaf colour scheme are necessary for this illusion. But are these following things necessary? namely, an extraordinarily faithful representation of mid-rib and lateral veins even to faint microscopically-tapering vein tips; a perfect short petiole produced by the apposed “tails” of the hind wings; a concealment of the head of the butterfly so that it shall not mar the outlines of the lateral margin of the leaf; and, finally, delicate little flecks of purplish or yellow- ish brown to mimic spots of decay and fungus-attacked spots in the leaf (!) and, as culmination, a tiny circular clear spot in the fore wings (terminal part of the leaf) which shall represent a worm-eaten hole, or a piercing of the dry leaf 54 DARWINISM TO-DAY, by flying splinter, or the complete decay of a little spot due to fungus growth! A general and sufficient seeming of a dead leaf, object of no bird’s active interest, yes, but not a dead leaf modelled with the fidelity of the wax-workers in the modern natural history museums. When natural selec- tion had got Kallima along to that highly desirable stage when it was so like a dead leaf in general seeming that every bird sweeping by saw it only as a brown leaf clinging precariously to a _ half-stripped branch, it was natural selection’s bounden duty, in conformance with its obligations to its makers, to stop the further modelling of Kallima and just hold it up to its hardly won advantage. But what happens? Kallima continues its way, specifically and ab- surdly, dead-leafwards, until to-day it is a much too fragile thing to be otherwise than very gingerly handled by its rather anxious foster-parents, the neo-Darwinian selec- tionists. An objection which was long ago pointed out, and which has been emphasised strongly by some biologists and almost overlooked by others, is that of the incom- Soe patibility of the results concerning the age of selection oppor- life on this earth as propounded by physicists sind tedoits and astronomers with the demand made by the theory of descent. This objection of the lack of time for the production of the hosts of kinds of plants and animals through the slow workings of natural selection was brought forward against Darwin from the very begin- ning and has never been given up. De Vries,”’ for example, in a recent paper, refers to it as follows: “The deductions made by Lord Kelvin and others from the central heat of the earth, from the rate of the production of the calcareous deposits, from the increase in the amount of salt in the water of the seas, and from various other sources, indicate an age for the inhabitable surface of the earth of some millions of years only. The most probable estimates DARWINISM ATTACKED. 55 lie between twenty and forty millions of years. The evolu- tionists of the gradual line, however, have supposed many thousands of millions of years to be the smallest amount that would account for the whole range of evolution, from the very beginning until the appearance of mankind. This large discrepancy has always been a source of doubt and a weapon in the hands of opponents of the evolutionary idea, and it is especially in this country that much good work has been done to overcome this difficulty. The theory of descent had to be remoulded. On this point conviction has grown in America during the last decades with increasing rapidity.” However (according to a newspaper clipping), Professor Lankester,” a present-day Darwinian champion, in the aoe of an interesting outline of the advance- sibleanswerto ment of science in the past twenty-five years the objection. == Which he gave at the opening meeting of the British Association at York recently (September, 1906) again raised the question of the age of the earth. Refer- ring to the discovery of radium as one far exceeding in importance all other modern scientific discoveries he said that if the sun contained a fraction of one per cent. of radium, this radium would account for and make good the heat that is annually lost by the sun. “This is a tremendous fact, upsetting all calculations of physicists as to duration in past and future of the sun’s heat and the temperature of the earth’s surface. The geologists and the biologists have long contended that some thousand million years must have passed during which the earth’s surface has presented ap- proximately the same conditions of temperature as at pres- ent, in order to allow time for the evolution of living things and the formation of aqueous deposits of the earth’s crust. The physicists,’ contended Professor Lankester, “notably Professor Tait and Lord Kelvin, refused to allow more than ten million years (which they have subsequently increased to a hundred million, basing the estimate on the rate of 56 DARWINISM TO-DAY. cooling of a sphere of the size and composition of the earth). They have assumed that its material is self-cooling. But as Huxley pointed out, mathematics will not give a true result when applied to erroneous data. It has now, within the last five years, become evident that the earth’s material is not self-cooling, but on the contrary self-heating, and away go the restrictions imposed by physicists on geological time. They are now willing to give us not merely a thou- sand million years, but as many more as we want.” In this connection should be mentioned the position taken by Ammon *’ and others who argue that the real effect or Claim that se. result of natural selection is to preserve the lection hinders type at the expense of the variants, which would rather than pro- ~ ; motes species: Make it a retarder rather than accelerator of change, species-change. Bumpus’s ** observations on, and conclusions concerning, his storm-beaten English spar- rows is an example of what Ammon claims must be the real result of selection. Bumpus, in statistical studies of the variation of two animal species introduced from Europe into the United States, viz., the English sparrow and the peri- winkle, Littorina littorea, shows that the eggs of the sparrow and the periwinkles themselves are much more variable in Bengurk cb America than in their native regions, and the au- servationson thor attributes this increased variability to their ai ies “presumable emancipation from many of the re- straining influences of natural selection.” In the case of the English sparrows, also, Bumpus believes himself able to show on a basis of the examination of 136 birds brought in wounded or stunned after a severe storm of snow, rain, and sleet (Feb. 1, 1898), that the sixty-four birds that perished (seventy-two revived), “perished not through acci- dent, but because they were physically disqualified, and that the birds which survived, survived because they possessed certain physical characters. These characters enabled them to withstand the intensity of this particular phase of selective DARWINISM ATTACKED. 57 elimination and distinguish them from their more unfortu- hate companions.” The fortunate characters were mas- culinity, shortness of body, lightness, longer humerus, longer femur, longer tibio-tarsus, longer sternum, greater brain capacity. But more important for survival than favourable variations was the fact of’ approach to the species type or mode of variability. The extreme variants perished. “The process of selective elimination is most severe with ex- tremely variable individuals, no matter in what directions the variations may occur. It is quite as dangerous to be con- spicuously above a certain standard of organic excellence as it is to be conspicuously below the standard. It is the type that nature favours.” APPENDIX, * For a fairly complete bibliography, with excellent abstracts, of all important critical discussions of Darwinism since 1895, see L’Année Biologique (ed. Y. Delage), 1895-1903; for good bibliog- raphy also see Zoologischer Jahresbericht, issued annually. See also discussions and notes in such journals as Natural Science, Bio- logisches Centralblatt, Nature, Science, American Naturalist, etc. *Von Kolliker, A., “Uber die Darwin’sche Schépfungstheorie,” Zeitsch. f. wiss. Zool., Vol. XIV, pp.. 174-186, 1864. ® Korschinsky, S., “Heterogenesis und Evolution,’ Naturw. Wo- chenschrift, Vol. XIV, pp. 273-278, 1899. *Morgan, T. H., “Evolution and Adaptation,” 1903. A vigorous anti-Darwinian argument, somewhat sophisticated in its lawyer- like handling of Darwin’s own words, but keen and trenchant in its exposure of the weaknesses of the selection theories as species- forming explanations. It is also a brief for de Vries’s theory of species-forming by mutation. (See chap. xi of this book.) ° “See Osborn, H. F., “Biol. Lectures,” Wood’s Holl Lab., 1894, Pp. 79-100, for suggestive plea for the recognition of “the unknown factors of evolution.” © The subject of variation, an absolutely fundamental one in any consideration of the factors and mechanism of organic evolution, has a very large literature pertaining to it which the serious student of evolution must make considerable acquaintance with at the very outset. Of this litera- oo the following books and papers may be suggested to serve aS Books and pa- me on variation, 58 DARWINISM TO-DAY. a means of introduction to the subject, not alone in its broad out- lines, but in its extensive ramifications of relation to other evolution problems. Some of these books and papers include extended biblio- graphic lists sufficient to enable one to follow up the subject in any of its special phases. Darwin, Chas., “The Origin of Species,” 1859. Darwin, Chas., “The Variation of Animals and Plants under Domestication” (Amer. ed.), 1868. Wallace, A. R., Darwinism,” chaps. iii and iv, 1891. Allen, J. A., “On the Mammals and Winter Birds of East Florida,” Bull. Mus. Comp. Zool., Il, pp. 161-450, Plates IV-VIII, 1871. Galton, F., ““Natural Inheritance,” 1880. Bateson, W., “Materials for the Study of Variation,” 1894. Duncker, G., “Die Methode der Variationsstatistik,” Archiv f. Entwick. Mech., Vol. VIII, pp. 112-183, 1899. (Full bibliography.) Rosa, D., “La riduzione progressiva della variabilita i suoi rap- porti coll’ esstinzione e coll’ origine delle specie,” 1899. Conn, H. W.. “The Method of Evolution,” chap. iv, 1900. Davenport, C. B., “A History of the Development of the Quan- titative Study of Variation,” Science, N. S., Vol. XII, pp. 864-870, 1900. De Vries, H., “Die Mutationstheorie,” Vol. I, pp. 7-150, pp. 412-648, I90I. Ewart, J. C., “Variation; Germinal and Environmental,” Trans. Roy. Dublin Soc., Ser. II, Vol. VII, pp. 353-378, 1901. Vernon, H. M., “Variation in Animals and Plants,” 1903. Delage, Y., “L’Hérédité,” pp. 283-310, pp. 826-843, 2d ed., 1903. Davenport, C. B., “Statistical Methods in the Study of Varia- tion,” 2d ed., 1904. (Full bibliography. ) Kellogg and Bell, “Studies of Variation in Insects,” Proc. Wash. Acad. Sci., Vol. VI, pp. 203-332, 1904. Lotsy, J. P., “Vorlesungen ttber Descendenztheorien,” Vol. I, chap. 1x, 1906. Biometrika, 1go1-1906. A journal devoted chiefly to the sta- tistical study of variation. "See Kellogg, “Variation in Parthenogenetic Insects,” Science, N. S., Vol. XXIV, pp, 695-699, 1906, in which it is shown that the Cases of marked Parthenogenetically produced drone honey-bees vary variation in par- Much more than do the workers which are of bi- thenogenetic ani- sexual parentage, and that parthenogenetically pro- mals. duced plant-lice (Aphidids) vary as markedly as insects of bisexual parentage. See also Warren, Proc. Roy. Soc., Vol. LXV, 1899. in which the variation in parthenogenetic varia- tions of Daphnia magna is shown to be little, if any, smaller than DARWINISM ATTACKED. 59 jin sexually produced generations; also, Biometrika, Vol. I, pp. 129- 154, 1902, in which Warren shows the variation in parthenogenetic series of the plant-louse Hyalopterus trirhodus to be as large as the variability exhibited in sexual forms. See also Haycraft, J. B., “The Role of Sex,” Nat. Science, Vol. VII, pp. 245-250, 342-344, 1895, in which paper is presented an ingen- ious argument to show that sexual reproduction tends not merely not to increase variation but to decrease it: “the convergence to the mean is, then, a result of sexual reproduction: it may be termed the role of sex, and one indeed of no secondary order. The tendency con- stantly to vary is a property inherent in protoplasm, yet often for long periods of time the environment may be the same. In order that a species may continue to live in such a constant environment, the effects of variation must be checked. Sexual multiplication, a conservative function, antagonises the progressive tendency of varia- tion: * Other naturalists have also held strongly to this view of the role of amphimixis. See Bailey, L. H., “The Plant Individual in the Light of Evolution,” address before the Biological Society of Wash- ington, January 12, 1895, Science, N. S., Vol. I, p. 281, 1895, in which paper the author points out the importance of a clear recognition of the tremendous possibilities and actuality of asexual variation in plants. In a paper by Winslow and Rogers (Science, N. S., Vol. XXI,, p. 486, 1905), referring to the classification of bacteria, there is the following statement: ‘Since the swamping of minor differences by sexual reproduction is absent from bacteria, every inheritable variation is maintained, and instead of true species, we find an infi- nite series of minutely differing but constant races. The only prac- tical method of handling and systematising these, is to establish cer- tain fairly distinct groups and types about which the individual ‘variations may be grouped.” * By using a large series of individuals, and carefully tabulating the noted conditions of variation of one or more parts, using, pref- Nae erably, attributes whose variability is capable of being pets hea mathematically expressed, such as dimensions, num- of probabilities, bers of spines, or spots, etc. many students have shown that these variations seem to occur in most ‘cases according to the law of probabilities, and that a curve plotted so as to express graphically the actual conditions of variation for a given character would be nearly identical with the curve that could be plotted so as to express what variation would exist in the given case if this variation occurred exactly according to the laws of chance. This means that in a thousand individuals collected at 60 DARWINISM TO-DAY. random and examined for variation in any character, say total length of body, not only would there be found a larger number of individuals of medium length than of any other length between the two extremes, represented by the longest and shortest individuals, but that the various lengths between the mean and the longest and between the mean and the shortest, would be represented by groups of individuals regularly decreasing in number as the length in- creased or decreased on either side of the mean, but of equal number if compared at equal amounts of difference away from the mean. The curve expressing graphically the law of probabilities or, better, the frequency of error, is determined by the formula for this frequency deduced originally by Gauss at the beginning of the last century. It would lead us too far afield to reproduce here the mathematical proof of the formula or method of its determination, but Vernon’s excellent concrete illustration of how such a formula could be deduced directly from a study of biologic variation may be quoted. “Supposing,” says Vernon in “Variation in Animals and Plants,” pp. 11 and 12, 1903, “a group of developing organisms be taken, of which the growth can be affected in a favourable or an unfavourable manner by their surroundings. Let us suppose that there are twenty different agencies, each of which would produce an equal, favourable effect on growth, and twenty which would pro- duce just as great an effect in the opposite direction. Suppose, also, that each organism is subjected to only half of these forty different agencies; then it would follow, according to the laws of chance, that a larger number of the organisms would be acted upon by 10 favourable and to unfavourable agencies, than by any other com- bination; @.e., they would, on our hypothesis, remain absolutely unaffected in their growth. A somewhat smaller number would be acted upon by 11 favourable and 9 unfavourable agencies, or on the whcle, would have their growth slightly increased. A still smaller proportion would be acted on by 12 favourable and 8 unfavourable agencies, or would have their growth rather more increased. Finally, the number of organisms acted on by 20 favourable and o unfa- vourable agencies would be extraordinarily small, but in this case the effect on growth would be extremely large. Similar relationships, ~ only in the reverse direction, would of course be found in those cases in which the number of unfavourable agencies exceeded the number of favourable. If desired, the proportional numbers of organ- isms acted on by all the different combinations of agencies may be readily determined by expanding the binomial (% + %)’°. It is found, for instance, that for each single time the organisms are acted on by the whole 20 favourable agencies, they are acted on 190 times by 18 favourable and 2 unfavourable; 15,504 times by I5 DARWINISM ATTACKED. — 6r . favourable and 5 unfavourable; and no less than 184,756 times by 10 favourable and 10 unfavourable. Let us consider that the organ- isms acted on by 20 favourable and o unfavourable agencies have their size increased 20 per cent.; those acted on by 15 favourable and 5 unfavourable by 15 — 5 = Io per cent.; and so on. If now these percentage increments and decrements be plotted out at equal distances on a base line, and” ordinates corresponding to the theo- retical frequencies erected from each, then by joining these ordinates we shall obtain a curve which is practically identical in form with the probability curve of the law of frequency of error. Thus, by a simple arithmetical method, we obtain a series approximating more and more closely to the probability curve, the greater the number of times the expression (% + %) is expanded. Expanded 20 times, the average error is less than .5 per cent., and for a greater number of times it becomes rapidly smaller and smaller.” This discovery and formulation of the law of individual varia- tion—namely, that such variation occurs according to the law of probabilities—was first made by the Belgian anthro- Quetelet, the ; sf por Meravccoretvaric DOlOgISt, Quetelet (‘‘Lettres sur la théorie des Proba- ation according bilités,’ Brussels, 1846), on a basis of the examina- ‘to the law of tion of the height and chest measurements of soldiers. chance. It was later elaborately confirmed by Francis Galton (numerous papers and the book, “Natural Inheritance,” 1870-1890), by quantitative determinations of the height, weight, span of arms, breathing capacity, strength of pull, strength of squeeze, swiftness of blow, and keenness of sight in men and women. It has been most illuminatingly discussed by Karl Pearson in ‘‘The Chances of Death, and other Studies in Evolution,” 2 vols., 1897. Since then the recognised necessity of a more thorough study and understand- ing of variation, as the indispensable foundation of species-forming has led to a large development of the statistical and mathematical study of variation, under the name of biometry, a study largely due to the initiative and genius of the English mathematician and natural philosopher, Karl Pearson (numerous papers from 1894 to present). Most of the methods and formule for determining precise mathe- matical expression of variation conditions have been devised by him. These methods and formule permit of an actual mathematical com- parison of variation among various parts in one species (immensely enlarging our definite knowledge of structural correlations), or among similar or wholly different parts in various species. With the statistical facts or data of variation thus put into precise mathe- matical expression, these expressions may be submitted to a deal of independent mathematical treatment; rather bewildering, it must -be confessed, to most biologists, but presented by the biometricians 62 DARWINISM TO-DAY. as the first step toward making biology, in part, at least, an exact science. But there is no question at all that the statistical and quantitative study of variation, and the use of authoritatively deduced mathematical expressions (and the graphic representation of these by plotted frequency curves, polygons, etc.), have immensely advanced our understanding of variation conditions, and given us. definiteness and concreteness in a fiindamental field of evolution study, where before were a mass of uncoordinated data and a haze of loose generalising. * Bateson, Wm., “Materials for the Study of Variation,” 1894. *® See Kellogg and Bell, ‘Studies of Variation in Insects,” Proc. Wash. Acad. Sct., Vol. VI, pp. 203-332, 1904, in which are discussed. (pp. 257-273) variation conditions existing in the lady- esind gee bird beetle, Hippodamia convergens. The variations. in the number and character of the elytral pattern (small black spots on a brown ground) noted in a thousand speci- mens examined, were such that eighty-four “aberrations,” or pat- tern-variates, could be distinguished and described, and yet, an intensity of scrutiny demanding the use of a lens was necessary to: distinguish properly these varying types. Such a scrutiny, needless. to say, will never be given these beetles by bird or lizard, the active agents representing natural selection, as far as pattern is to be tested. Nevertheless, these pattern variations, if not so completely connected by gradatory steps, would be exactly the characters on which several Hippodamia species would be based, for they range all the way from no spots to eighteen spots, although twelve is the species character of convergens. ** Romanes discusses this subject of the indifference, or triviality,. of many specific characters at some length in chap. vii of his “Dar- win and After Darwin,” II, ‘““Post-Darwinian Questions,” “Heredity and Utility,” 1895. ** Conn, H. W., “Method of Evolution,” pp. 78-83, 1900. ** Nageli, Carl, ‘“Mechanisch-physiologische Theorie der Abstam- mungslehre,”’ 1884. Nageli, an eminent botanist, formulated many Nageli’s seven Years ago the following famous seven objections to objections to spe- the natural selection theory of species-forming (pp. cies-forming by 289-290) : selection, “Tech hebe folgende sieben Gesichtspunkte hervor, welche uns die Abstammung durch Zuchtwahl unannehmbar machen : “tT. Bezuglich der allgemeinen Bedeutung der Selectionstheorie ist die unbestimmte Wirkung unbestimmter Ursachen und die dem Zufall allzusehr tiberlassene Entscheidung durch die nattrliche Zuchtwahl unserem naturwissenschaftlichen Bewusstsein weniger zusagend. Ferner setzt sich die Selectionstheorie, welche ihrem DARWINISM ATTACKED. 63 Princip gemass nur nach dem erreichten Nutzen einer Erscheinung fragt, um dieselbe zu rechtfertigen, in Widerspruch mit der wahren und exacten Naturforschung, welche vor allem die bewirkenden Ur- sachen der Dinge zu erkennen sucht. “2. Die Folgerung von der (kiinstlichen) Rassenbildung auf die (nattrliche) Varietatenbildung, welche die Grundlage der Selec- tionstheorie ausmacht, ist unzulassig, da beide wesentlich verschie- den sind und namentlich sich riicksichtlich der Kreuzung ungleich verhalten. Die Varietaten namlich vermischen sich sehr schwer mit einander und nehmen kein fremdes Blut in irgend wirksamer Menge auf, werden somit auch durch die ihnen gebotene Gelegenheit zur Kreuzung nicht verandert; mit diesen Eigenschaften stimmen ihre Vorkommensverhaltnisse genau tberein. “3. Nutzliche Veranderungen kénnen erst, wenn sie eine bemerk- bare Hohe erreicht haben und in zahlreichen Individuen vorhanden sind, eine ausgiebige Verdrangung der Mitbewerber bewirken. Da sie aber im Anfange durch eine lange Reihe von Generationen jeden- falls noch sehr unbedeutend und nach der Selectionstheorie auch nur in einer kleinen Zahl von Individuen vertreten sind, so bleibt die Verdrangung aus und eine nattirliche Zuchtwahl kommt, da ihr der wirksame Hebel mangelt, uberhaupt nicht zu Stande. “4. Die Ernahrungseinflusse, welche die Selectionstheorie voraus- setzt, bewirken thatsachlich keine erblichen Veranderungen, und wenn sie es thaten, so konnte eine Steigerung der begonnenen Abian- derung nicht eintreten, weil die unvermeidliche Kreuzung eine naturliche Zuchtwahl unmoglich machen wiirde. Ferner lasst sich aus den unbestimmten, in allen denkbaren Richtungen wirkenden Ernahrungseinfllissen der so stetige phylogenetische Fortschritt zu einer complicirteren Organisation nicht erklaren. Ebenso wenig werden durch dieselben die Erscheinungen der Anpassung verur- sacht; dies ergibt sich einerseits aus dem Umstande, dass Gebrauch und Nichtgebrauch die Zu- und Abnahme der Organe bedingen, da diese Ursache fiir sich vollkommen ausreicht und daher die Mit- wirkung einer zweiten andersartigen Ursache ausschliesst,—und andrerseits durch den ferneren Umstand, dass Anfange von Organen bis zu der Grosse, wo sie in Gebrauch kommen und ihre Nuitzlich- keit zu erproben verm6gen, mangeln, obgleich sie durch die Ernah- rungseinfitisse in Menge hervorgebracht werden mussten. “5. Die Ejigenschaften der Organismen mtssten in Folge der naturlichen Zuchtwahl um so constanter sein, je ntitzlicher sie sind, und Einrichtungen, die keinen Vortheil gewahren, konnten keine Bestandigkeit erlangen. Im Widerspruche hiermit gehGren gewisse, rein morphologische, mit Ricksicht auf den Nutzen indifferente Merkmale zu den allerbestandigsten. 64 DARWINISM TO-DAY. “6. Aus der Selectionstheorie, nach welcher von den eintretenden richtungslosen Veranderungen bloss die ntitzlichen festgehalten wiir- den, lassen sich weder die Divergenz der Reihen in den organischen Reichen, noch die bestehenden Lucken in und zwischen den Reihen erklaren, indem vielmehr eine netzformige Anordnung der Sippen zu Stande kommen musste. ‘7 Ebenso widersprechen jener Theorie das Nichtvorhandensein der von ihr behaupteten gegenseitigen Anpassung der Bewohner eines Landes und die bestehenden Naturalisationen fremder Erzeugnisse. “Diese Einwtirfe gegen die Selectionstheorie, die ich hier bloss ganz allgemein formulirt habe, sollen im folgenden des Naheren begriindet werden.” *4 Wolff, G., “Beitrage zur Kritik der Darwin’schen Lehre,” 1808. From this caustic attack on the Darwinian position, I quote as fol- lows (pp. 56-57): “Wenn wir sagen, die Selektion schafft Zweckmassiges dadurch, dass eben nur das Zweckmassige erhalten wird, das andre zu Grunde geht, so wird in dieser Fassung das Zweckmassige Wolff's attack nattirlich vorausgesetzt, aber nicht sein Zustandekom- on the selection~- men erklirt. Dass Zweckmissiges iiberhaupt da war, ists’ assumption ... ‘ ie of the appearance 1st im héchsten Grade unwahrscheinlich und unver- at the right time Standlich. Mochte auch unter den vielen Variie- of the needed rungen manchmal etwas Zweckmassiges zufallig Variation. vorgekommen sein, so ist die Wahrscheinlichkeit eines solchen Eintreffens so gering, dass ich nicht das Recht habe, diesen Faktor als einen gegebenen in meine Rechnung ein- zusetzen. Diese Wahrscheinlichkeit sucht nun der Darwinismus dadurch zu vergrossern, dass er alle moglichen Falle annimmt, unter welchen nattrlich auch das Zweckmassige als Spezialfall enthalten sein muss. Der Darwinismus sucht also den Treffer sich dadurch zu sichern, dass er den ganzen Gluckshafen mit nach Hause nimmt. “Um ein Beispiel zu nehmen: es sei von Vorteil, dass die Schna- belform entsteht, wie sie beim Kreuzschnabel vorhanden ist. Der Darwinismus nimmt an, dass durch gluckliche Variierung ein bezw. mehrere oder sogar viele gekreuzten Schnabel auftraten. Sagt nun der Gegner: das spontane Auftreten einer Schnabelkreuzung scheint mir so unwahrscheinlich, dass ich diese Voraussetzung eben nicht zugebe, so antwortet der Darwinist: unter allen mdglichen Schnabel- varlierungen ist auch der gekreuzte, darf ich alle, so darf ich auch diesen voraussetzen; da aber die Variierung, wie die Beobachtung lehrt, nach allen Richtungen beliebig wirkt, so sind alle Variierungen moglich, folglich darf ich auch jene spezielle voraussetzen. “Der Gegner wtirde jetzt vielleicht so erwidern: Gewiss, moglich sind alle Variierungen, aber gegeben ist deren doch immer nur eine DARWINISM ATTACKED. 65 begrenzte Anzahl. Die Zahl aller moglichen Variierungen ist = ©, die Zahl der gegebenen ist eine endliche Grosse. Die Wahrschein- lichkeit des Ejintretens einer speziellen zweckmassigen Variierung (in unserm Beispiel der zweckmassigen Schnabelkreuzung) ist End- liches dividiert durch Unendliches, d. h. eine Zahl, welche sich der ' Null ohne Ende nahert; mithin ist die Wahrscheinlichkeit, dass unter den gegebenen Fallen sich eine gtinstige Variierung befindet, so ungeheuer klein, dass nicht die geringste wissenschaftliche Be- rechtigung besteht, den betreffenden Fall vorauszusetzen. Und nun witirde allerdings demjenigen Darwinisten, welchem die Ktihnheit fehlte, die Zahl der ihm zur Verfuigung stehenden Variierungen ein- fach = © zu setzen, wohl kaum etwas andres tbrig bleiben, als sich darauf zu berufen, dass es eine Sorte von Variierungen giebt, bei denen die Zahl der gegebenen Falle gross genug ist, um alle mogli- chen zu enthalten, gross genug also, um die Voraussetzung jedes einzelnen wissenschaftlich zu rechtfertigen, namlich diejenigen Vari- ierungen, welche nur in graduellen Veranderungen bestehen, bei denen es sich also nur darum handelt, dass ein Vorhandenes grosser oder kleiner wird. Hier ist die Zahl der modglichen Falle gleich 2, die der gegebenen ebenfalls, die Wahrscheinlichkeit, sich unter den gegebenen zu befinden, ist also ftir jeden der mdglichen Falle gleich 1.” ** Kronig, “Das Dasein Gottes und das Gliick des Menschen,” p. 109, 1874. ** Weismann, Aug., “On Germinal Selection as a Source of Defi- nite Variation,” trans. McCormack, p. 3 (preface), 1896. *" Pfeffer, Georg, “Die Umwandlung der Arten,” 1894. ** Wolff, G., “Der gegenwartige Stand des Darwinismus,” 1896; also, “Beitrage zur Kritik der Darwin’schen Lehre,” 1808. *® Morgan, T. H., “Evolution and Adaptation,” 1903. *’ Kellogg and Bell, “Studies of Variation in Insects,’ Proc. Wash. Acad. Sci., Vol. VI, pp. 203-332, 1904. The following is quoted from pp. 330-332: “Insects are bilaterally symmetrical and metameric animals. There are thus right and left and fore and aft structural correlations. Do the Example of non- variations, continuous and discontinuous, show similar correlated varia- bilateral and metameric correlation? Evidence regard- bility in bilater- ing this question will be found on many pages in the ane present paper, right and left correlation, at least, hav- ing been considered and briefly discussed in connection with almost all of the various cases studied. And the evidence is curiously conflicting. For example, in the male black ant in which were studied the variations of the venation and number of hooks, a close correlation in the variation conditions of right and left wings 66 DARWINISM TO-DAY. exists. On the other hand, in the honey-bee the bilateral correla- tion of variation seems surprisingly small (see pp. 214-222). In the case of variations in pattern, also, there is no uniformity among the various cases studied. In Hippodamia convergens (p. 257 et seq.) the two elytra show pattern-variations quite independently ; in Diabrotica soror (p. 274 et seq.), on the contrary, there seems to be a marked right and left correlation in the elytral pattern- variation. In the cases of the variation in number of tibial spines on the right and left hind tibie of locusts (p. 301) and cicadas (p. 306), we have simply made a brief statement, in each case, of the actual conditions of correlation, leaving the reader to draw his own conclusions. In the case of the variation in actual and relative length of the antennal segments of the scale insect, Ceroputo yucce (?) (p. 310), there is a surprising lack of correlation between the right and left antenne. ““We have not attempted to determine the mathematical expression (coefficient of correlation) for any of the cases studied. The data presented, however, will enable any biometrician, who sees an advantage in doing this, to do it. But without checking our results by the use of that method there seems, on the whole, to be a sur- prising lack of that fine degree of correlation in variation which we should expect to find existing, if we believe that the actual existing conditions of structure and pattern in these bilaterally sym- metrical animals are an expression of the result of the action of a rigorous natural selection. If one condition of pattern or structure is the most advantageous (of the many conditions which selection among a host of fluctuating variations could have established), surely this condition ought to be pretty closely similar on both sides of the insect. That as much bilateral variety as actually exists, in many of the species examined by us, should exist—a variety comparable in certain cases even with the degree of variety revealed by the comparison of considerable series of individuals—is a state of affairs that only confirms us in the belief that these innumerable small continuous variations, on which for so long the thorough- going selectionists have put their faith as the sufficient bases for natural selection’s species-forming work, are clearly not competent to serve as such bases. If these ‘continuous’ variations are the foun- dation stones of new species, some other agents than selection must be found or invoked to build several courses on them, to produce some cumulation of them, before natural selection finds them of that life-and-death worth which is the prerequisite for her potent interference.” *? Henslow, the botanist, has maintained a constant attitude of antagonism to natural selection on the basis of his belief that the DARWINISM ATTACKED. 67 complex correlations of floral structures cannot possibly be accounted for by the natural selection of fortuitous variations. Henslow’s Whe clow's tn- observations and ideas are exploited in detail in tagonism to selec- two books called, “The Origin of Floral Structures tion as explain- through Insect and Other Agencies,’ 1895, and _ eroffloral corre- “The Origin of Plant Structures by Self-Adaptation sasions. to the Environment,” 1895. 72 Wolff, G., “Beitrage zur Kritik der Darwin’schen Lehre,” p. 6, 1808. *8 Wolff, G., “Beitrage zur Kritik der Darwin’schen Lehre,” 1898. I quote the following, pp. 6-8: “Solche Erscheinungen, welche der Erklarung durch die Selek- tionstheorie widerstreben, weil sie hier eine gesetzmassige kom- plizierte Veranderung der Formen voraussetzen wurde, Wolff's objection statt sie zu erklaren, sind aber nicht etwa nur verein- to the necessary 7elte Fille, sondern von solchen wird die ganze Sa Formgestaltung beherrscht, wie z. B. von symme- incident varia- trischer Anlage. Auch brauchen wir uns bei dieser tion in repeated Betrachtung nicht nur auf solche Gebilde zu_be- structures as schranken, die in geringer Mehrheit vorhanden sind, ae scaler, sondern es giebt ja Gebilde, die in hundert-, ja tau- sendfacher Anzahl an einem und demselben Or- ganismus sich finden, wie Schuppen, Haare, Federn. Betrachten wir z. B. gerade die Federn. Wie viel Millionen Variierungen musste eine Reptilienschuppe durchmachen, bis sie sich in eine Feder verwandelt hatte, vollends noch in ein so kompliziertes Gebilde wie z. B. die Schwanzfeder des Pfaues. Aber dies ware immer noch nach der Selektionstheorie erklarlich. Nicht erklarlich dage- gen ware, dass die anderen Schwanzfedern immer gleichzeitig dieselben Variierungen durchmachten. Ein Gesetz, welches ein einheitliches Variieren dieser Hautgebilde vorschreibt, giebt es nicht, denn es variieren ja nicht alle gleich. Es entstehen viele gleiche Flaumfedern, viele gleiche Schwanzfedern etc., an einigen Stellen bleiben die Schuppen sogar erhalten, namlich an den hinteren Extremitaten. “Wir konnen noch weiter gehen. Eine Masse von einzelnen Zel- len musste bei den verschiedenen Differenzierungen, bei Entstehung des Darms, des Nervensystems, der Muskulatur etc. in ganz genau der gleichen Weise variieren. Wenn wir hier die Selektionstheorie zur Erklarung herbeiziehen wollen, so ist die Kompliziertheit des einzelnen Variierungsinkrementes so gross, dass damit die ganze weitere Erklarung tberflissig wird. “Interessant sind ferner solche homodynamen Gebilde, die nicht zu gleicher Zeit auftreten, wie der dritte halbzirkelformige Kanal ! \ i | ' 68 DARWINISM TO-DAY. im Gehororgan der Wirbeltiere, welcher bekanntlich erst in der Klasse der Fische auftritt. Dieser dritte Kanal ist den beiden andern vollig gleich, hat Crista, Ampulle, Macula etc., ist aber spater entstanden; die namlichen zufalligen Variierungen, die stattfanden bei der Entstehung der beiden ersten Kanale, mussten viele Generationen spater ganz genau in derselben Art sich wieder- holen! Dass diese Variierungen wieder auftreten, dies erklart die Darwinsche Lehre nicht; denn die Selektion kann ja keinen Ein- fluss auf die Variierung ausuben. ‘“‘Aehnlich sind die Resultate der Kowalevskyschen Untersuch- ungen tuber fossile Huftiere zu betrachten, welche sich auf die im Lauf der phylogenetischen Entwicklung stattgehabten Umwand- lungen des Extremitatenskelettes dieser Tiere beziehen. Hier kann bekanntlich eine allmahlich eintretende Verringerung der Anzahl der Metatarsal- und Metakarpalknochen sowie der Phalangen verfolgt werden. Diese Verringerung tritt zuerst an den hintern, erst spater an den vordern Extremitaten auf!” °* A moth, Phryganidia californica, whose larve live abundantly on the oak trees in California, shows very clearly how a conspicuous Example of mal- disadvantage does not seem to interfere much with adaptation in egg- Successful life; for the “success” of this moth is only laying habit of too well proved by the serious injuries which it pro- Phryganidia cali- quces, because of its great numbers, on the beautiful fornica, a 4 trees it infests. For several years the live-oaks and white oaks of the Santa Clara Valley were defoliated to a dangerous extent. The life history of the moth is told in detail in ‘The Californian Phryganidian,” by Kellogg and Jack, Proc. Cal. Acad. Sct., Ser. 2, Vol. V, pp. 562-570, 1895. From this account I quote the following: ‘‘Although most abundant on the live-oaks (Q. agrifolia), the larve attack other oaks. We have found them on Quercus lobata, Q. kelloggii, Q. dumosa, and Q. douglasti. The live-oaks in this vicinity begin to put out new leaves about January I, but in the case of many of the trees badly defoliated by the larve in the autumn, new leaves appeared much earlier than the first of Janu- ary. The wintering of the insect in a larval condition is only possi- ble in the evergreen oaks, and they are thus the natural and usual host of the pest. At the time of the hatching of the first of the autumn brood of eggs (latter part of November), the leaves of the deciduous oaks begin to fall. But, oddly, the eggs were found to be deposited on the leaves of both the white oak and Douglas’s oak (deciduous oaks), and the larve hatched only to die of starvation. By this suicidal means the pest aids in depleting its own numbers. The new leaves of the deciduous oaks appear about April 1, before the eggs for the summer brood of larve are deposited. These eggs, % DARWINISM ATTACKED. 69 therefore, can safely be laid on the leaves of these trees, but the eggs laid by the fall moths on the foliage of these trees give up their young to certain destruction.” 25 Mivart, St. G., “On the Genesis of Species,” 1871. *° Wolff, G., eBeltege zur Kritik der Darwin’schen Lehre,” p. 8 ff., 1898. *7 In Piepers, M. C, “Mimikry, Selektion und Darwinismus,” 1903, the author strongly antagonises the Darwinian explanation Pi ; of protective warning and mimicking colour patterns. iepers’s an- : ; ae tagonism to selec- Piepers claims to show (1) that the so-called mimicry tion explanation is a phenomenon or appearance whose _ biological of colour and pat- value is greatly over-praised; (2) that the causes of tern of insects. this appearance are not entirely known, yet can in most cases be very well explained without having recourse to this natural selection theory; and (3) that, therefore, mimicry makes natural selection in no wise necessary, and hence lends no basis for its establishing. The author also, in a long discussion of nearly one hundred pages, criticises adversely the selection theories and Darwin in general. He holds that the Darwinian theory of species- building from varieties is very ill-grounded, but finds also de Vries’s mutations-theory incompetent to explain species, at least, in the large degree in which they actually exist. The author presents a theory or explanation of his own for species-forming, which is essentially this: Variation is not simply a fluctuation about a stable mean; it 7s evolution in small steps. Evolution is the principle of life; it is determinate, i.e., progressive, yet with rapid, slow, or even standstill periods. There are differences in the rapidity of evolu- tion among similar groups, as classes, orders, families, genera, species, races, even individuals, and the two sexes of a kind. This accounts for the great variety of life. There is a great variety of stages of evolution rather than a great variety of adaptation. 28 De Vries, Hugo, “The Evidence of Evolution,’ Science, N. S., Vol. XX, pp. 395-401, 1904. °° Lankester, Prof. Ray, Address by, reported in the London Mail, September, 1906. °° Ammon O., “Der Abdnderungsspielraum,” Naturw. Wochen- schr., Vol. XI, pp. 137-143, 149-155, 161-166, 1894. *1 Bumpus, H. C., “The Variations and Mutations of the Intro- duced Sparrow, Passer domesticus,’ in Biological Lectures, Wood’s Holl Laboratory, 1897; also, ‘““The Elimination of the Unfit as illus- trated by the Introduced Sparrow, Passer domesticus,” in Biological Lectures, Wood’s Holl Laboratory, 1899; also, “The Variations and Mutations of the Introduced Littorina,’ Zool. Bull., Vol. I, pp. 247- 259, 1808. CHAPTERAY. DARWINISM ATTACKED (CONTINUED): THE THEORY OF NATURAL SELECTION (CON- TINUED). CERTAIN objections urged by various authors may be said to concern themselves more with the character of the varia- Objection based tions themselves and the possibilities of their on the linear and 4 ccymulation by selection, than with the manner quantitative and non-qualitative of their occurrence. For example, de Vries * npr hs denies the species-forming capacity of Dar- tions. winian selection of Darwinian (fluctuating) variation, on the ground that these variations are only “linear,” and thus cannot afford a basis for the creation of new forms. Already existing bodies, organs, and parts can be enlarged or made smaller, made smoother or rougher, made bluer or less blue, greener or less green, that is de- veloped plus-ward or minus-ward, but by this nothing really mew is created. But, declares de Vries, the differentiation of organs consists, taken by and large, in the development of actually new characteristics ; therefore in such material as that presented by the linear variations of Darwin, selection cannot have the necessary basis for this production of new characteristics. Gustav Wolff * reiterates the same objection in his declara- tion that while the theory of natural selection may get on decently well when modifications embodying only quan- titative changes in parts or organs are concerned, it is com- pletely at a loss to account for modifications or adaptations requiring as basis qualitative changes. Even the warmest 70 . DARWINISM ATTACKED. | 1 advocates of the selection theory have to admit, says Wolff, that they face a serious matter here. Weismann’ is quoted as follows: “Wenn man sich die Umwandlung deshalb in grésseren Schritten und durch Variationen von qualitativer Natur geschehend denkt, so wird man uber dieses Hindernis nicht wegkommen. Ich glaube aber, dass man von den Variationen grosseren Betrages, wie sie bei domestizierten Tieren und Pflanzen nicht selten vorkommen, bei den Pro- zessen der Artumwandlung, wie sie in der freien Natur vor sich gehen, vollstandig abgesehen hat, dass Mer tiberhaupt nicht qualitative sondern nur quantitative Unterschiede der Individuen das Material der Naturztchtung bilden, solche aber sind immer vorhanden.” Wolff holds that there can simply be no doubt that if natural selection can do any modifying at all it has at most to limit itself solely to work possible on a basis of quantitative variation of already ex- isting structures. Variation also of whatever kind is subject to Galton’s * law of regression. This is, put briefly, that the young of Galton'’s law Parents varying from the mean of their species of regression. or race tend to vary also in the same direction but less so than the parent, so that the mean or mode among the young is nearer the species or race type (mean or mode) than the parental type was. Or as Morgan’ has stated it: “The facts of observation show that when a new variety ap- pears its descendants are more likely, on the average, to produce proportionately more individuals that show the same variation, and some even that may go still farther in the same direction. If these latter are chosen to be the parents of the next generation, then once more the offspring may show the same advance; but little by little the advance slows down, until before long it may cease altogether. Unless, then, a new kind of variation appears, or a new standard of variation develops of a different kind, the result of selection of fluctuating variations has reached its limit. Our experi- 72 DARWINISM TO-DAY. ence seems, therefore, to teach us that selection of fluctuating variations leads us to only a certain point, and then stops in this direction. We get no evidence from the facts in favour of the view that the process, if carried on for a long time, could ever produce such great changes, or the kind of changes, as those seen in wild animals and plants.” There is something inherent in the make-up of the organ- ism and something inevitably in incident to the phenomena of variation which prohibit, even in ‘the most favourable cases, the indefinite movement of variation. Johannsen,’ pro- fessor of plant physiology in the University of Copenhagen, finds that beans bred in pure lines, 7. e., not crossed, conform perfectly with Galton’s law of regression. And Johannsen holds that this regression must be a serious brake on the species-modifying, 7. e., species-forming, activity of natural selection. That is, while the species mode can be moved in one direction or another by pure line breeding it can be so moved only very slowly. And this same law of regression will tend to break up a “mixed population” resulting from crossed and miscellaneous breeding into distinct pure lines; that is, each independent form-type tends to be constant, not constantly moving, 1. e., transforming. New types must arise chiefly then through (a) the crossing of races or species (= hybridisation) or (b) through mutations. Delage ‘ in his criticism of selection makes the point that because the causes of variation are more feeble than the Delage's eriti- CAUSES of fixity (as evidenced by the massing of cism of Delbeuf’s variations around and close to the mean or mode, mm and their increasing scarcity as they recede in any direction from the mode (species type) ), the species tends always to stand still rather than to change. If in the first generation a thousandth of the individuals vary in the same way, in the second generation only 1-1000 of the thousandth part will show the same variation, reasons Delage. But, as pointed out in chapter vi (“Darwinism De- DARWINISM ATTACKED. 73 fended”’), this criticism was long ago met by Delbceuf, who claimed to show mathematically that, however feeble may be the number of varying individuals compared with those non-varying, the number of the varying will always be increasing and will finish by being greater than that of the individuals holding to the type. Delage holds “Delbceuf’s law” to be false as regards its attempted general applica- tion to the selection of variation, conceding it to hold true only in the hypothetical case where a persistent active modi- fying cause influences for some reason but a part of the individuals of a species. And Delage cannot conceive of a cause endowed with such an attribute. An objection that has been often made to the natural selection theory may be put in the following general form: It may be granted that selection can make evolu- Selection may ., 4 ’ . produce evolution tion, 7. ¢., adaptive change or progress, but this eee not Will be done in such a way as to leave a con- specieg (discon- tinuous chain or series. How is the chain tinuous series)» broken into species? Areall our species simply the existent ends of series or chains? But we see many chains or series of discontinuous but obviously connected species. Natural selection can make evolution but not species. Darwin himself couched this objection more con- cisely as follows: “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 ?” Professor Morgan, in his “Evolution and Adaptation,” discusses this objection in the following paragraphs (pp. 129-131): “The answer that Darwin gives [to his own just quoted query] is, that by competition the new form will crowd out its own less-improved parent form, and other less-favoured forms. But is this a sufficient or satisfactory answer? If 74 DARWINISM TO-DAY. we recall what Darwin has said on the advantage that those forms will have in which a great number of new variations appear to fit them to the great diversity of natural conditions, and if we recall the gradations that exist in external conditions, I think we shall find that Darwin’s reply fails to give a satisfactory answer to the question. “Tt is well known, and Darwin himself has commented on it, that the same species often remains constant under very diverse external conditions, both inorganic and organic. Hence I think the explanation fails, in so far as it 1s based on the accumulation by selection of small individual varia- tions that are supposed to give the individuals some slight advantage under each set of external conditions. Darwin admits that ‘this difficulty for a long time quite confounded me. But I think it can be in large part explained.’ The first explanation that is offered is that areas now continuous may not have been so in the past. This may be true in places, but the great continents have had continuous areas for a long time, and Darwin frankly acknowledges that he ‘will pass over this way of explaining the difficulty.” The second attempt is based on the supposed narrowness of the area, where two species, descended from a common parent, overlap. In this region the change is often very abrupt, and Darwin adds: “To those who look at climate and the physical condi- tions of life as the all-important elements of distribution, these facts ought to cause surprise, as climate and height or depth graduate away insensibly. But when we bear in mind that almost every species, even in its metropolis, would increase immensely in numbers, were it not for other com- peting species; that nearly all either prey on or serve as prey for others; in short, that each organic being is either directly or indirectly related in the most important manner to other organic beings,—we see that the range of the in- habitants of any country by no means exclusively depends DARWINISM ATTACKED. 75 on insensibly changing physical conditions, but in a large part on the presence of other species, on which it lives, or by which it is destroyed, or with which it comes into com- petition; and as these species are already defined objects, not blending one into another by insensible gradations, the range of any one species, depending as it does on the range of others, will tend to be sharply defined.’ “Here we have a petitio principu. The sharp definition of species, that we started out to account for, is explained by the sharp definition of other species! “A third part of the explanation is that, owing to the relative fewness of individuals at the confines of the range during the fluctuations of their enemies, or of their prey, or in the nature of the seasons, they would be extremely liable to utter extermination. If this were really the case, then new species themselves which, on the theory, are at first few in numbers ought to be exterminated. On the whole, then, it does not appear that Darwin has been very successful in his attempt to meet this objection to the theory.” A rather surprising objection is that of Pfeffer,’ who contends that selection cannot be the cause of the formation of species, for if it were real, however feeble Pfeffer’s objec- . ‘ : tion based on the its effects, it would transform species much 2 areal more rapidly than they are transformed; and in order to transform a species in a long time the protection afforded by the selection of small additions or modifications is so feeble as to be illusory. And adequate protection under such a system of species transformation is imperative. This is a curious argument, for it has always ‘been one of the claims of the mutationists that a “hurry- up” theory is needed in order to satisfy the familiar objec- tion that the physicists’ estimate of the actual age of the world is too low to admit of the production of the hosts of kinds of animals and plants which we know to have existed 76 DARWINISM TO-DAY. by the process of natural selection. But Pfeffer, who is an ingenious debater, makes out a very plausible case for his contention. Of the many special questions that have been asked of the selectionists two may be mentioned, simply as examples illus- trative of a rather formidable category of objections most of which are concerned with certain particular phases of evolution or groups of evolution phenomena rather than with the whole problem of species-forming. Many such special objections or questions touching specific cases were taken up and answered by Darwin in his “Origin of Species.””. Morgan has recently (“Evolution and Adapta- tion’) gone over critically many of these special objections and Darwin’s answers to them, and pointed out clearly that in numerous cases Darwin relied for his answers on evolution factors which the neo-Darwinians have attempted to read out of court. In many tight places Darwin availed himself of the Lamarckian factor of the cumulation, through inheritance, of the effects of use and disuse, or of other functional stimuli originating either in internal or ex- trinsic conditions. That is, Darwin, while constantly trying to rely, and whenever possible relying on natural selection as the species-forming and adaptation-explaining cause, never hesitated, when it seemed necessary, to admit the influence and effect of the inheritance of acquired characters or the influence of other, to him, unknown factors. In most cases of degeneration, for example, he adopted a Lamarckian explanation. The question of how sterility between species could have arisen is a case in point. “That this property of species is useful to them in the somewhat unusual sense at ak that it keeps them from freely mingling with species sterility other species is true,’ says Morgan; “but this by selection. ; : ; would be a rather peculiar kind of adaptation. If, however, it be claimed that this property is useful to DARWINISM ATTACKED. 77 species, as Darwin himself claims, then, as he also points out, it is a useful acquirement that cannot have arisen through natural selection. It is not difficult to show why this must be so. If two varieties were to some extent at the start less fertile, inter se, than with their own kind, the only way in which they could become more infertile through selection would be by selecting those individuals in each generation that are still more infertile, but the forms of this sort would, ex hypothese, become less numerous than the descendants of each species itself, which would, therefore, supplant the less fertile ones.” Darwin admits that this situation cannot apparently be explained by natural selection, and simply says that to him it appears “that the sterility both of first crosses and of hybrids is simply incidental or dependent on unknown differences in their reproductive systems.” Wolff * has urged strongly the objection that natural selec- tion does not explain the degeneration or atrophy of parts, Objection that at least not large or nearly complete reduction. selection cannot And Weismann and other selectionists long eee ago conceded that some sort of auxiliary prin- generationof ciple was necessary to explain degeneration on Le a Darwinian basis. This principle was supplied by Weismann, under the name of panmixia, which is, simply, that a constantly active selection is necessary not only for the evolutionary development or specialisation of an organ but as well for its retention in specialised condition.”’ *’ So that an organ which is no longer used and is therefore useless comes no longer under the supporting influence of selection (on the basis of advantage) and must consequently degenerate. But, as Wolff says, it seems obvious that such an influence or effect of the cessation of selection or of panmixia (so-called by Weismann because all variations good and bad alike mix and compensate each other) can at best lead to degeneration or atrophy only when the negative or reducing variations are in the majority, for when 78 DARWINISM TO-DAY. this is not the case the average of the survivors cannot change. Weismann himself has in recent years recognised the inadequacy of panmixia alone to explain degenerative phenomena. He says:* ... “In most retrogressive pro- cesses active selection in Darwin’s sense plays no part, and advocates of the Lamarckian principle, as above re- marked, have rightly denied that active selection, that is, the selection of individuals possessing the useless organ in its most reduced state, is sufficient to explain the process of degeneration. I, for my part, have never assumed this, and have on this very account enunciated the principle of panmiria. Now, although this, as I have still no reason for doubting, is a perfectly correct principle, which really does have an essential and indispensable share in the process of retrogression, still it is not alone sufficient for a full ex- planation of the phenomena. My opponents, in advancing this objection, were right, to the extent indicated, and as I expressly acknowledge, although they were unable to substitute anything positive in its stead or to render my explanation complete. The very fact of the cessation of control over the organ is sufficient to explain its degenera- tion, that is, its deterioriation, the disharmony of its parts, but not the fact which actually and always occurs where an organ has become useless—viz., its gradual and unceasing diminution continuing for thousands and thousands of years and culminating in its final and absolute effacement.” To supply the lack in the present neo-Darwinian explana- tion of retrogression Weismann calls on his new theory of germinal selection, the “rehabilitator of the natural selec- tion theory” (for an account of this theory see chapter viii). But Wolff and Morgan and others have shown how unsatis- factory and inadequate this third attempt at an explanation is, even if we grant the actuality of germinal selection, a hypothesis which has by no means met with any general acceptance by biologists. DARWINISM ATTACKED. 79 In all our discussion of the effectiveness of the natural selection theory one feature of it has so far not been ques- tioned. And that is the actual selecting power when the variations or differences among individuals are large enough to be conceivably of real advantage or disadvantage to the respective organisms. That is to say, we have not brought into question the alleged rigour of the struggle for existence upon which rigour depends, of course, the selection and the survival of the fittest. The very phrases “struggle for ex- istence” and “‘survival of the fittest” presuppose and assume a rigour of competition and a life-and-death-determining value of the variations or differences that are fundamental features of the natural selection theory. Let us, however, not hesitate to scrutinise these basic assumptions of the Darwinians. What of the actual rigour of the struggle that must be presupposed in order to give small variations a life-and- Eorutiny of the death-determining worth? Does it exist? Has claimed extreme it been observed? Is the actual (admitted) Se dali production of thousands or millions of eggs. consequent per- or embryos in localities capable of supporting aa but tens or hundreds of individuals, sufficient reason for deducing an endless, searching, utterly rigorous competition sufficient to give the slightest variations a weight in the balances determining death or life? In the first place, this tremendous competition must be largely over, if it exists, before the individuals come to maturity. Especially is this absolutely true of all species that live for a long time in immature stages and a very short time in the adult stage, as the Mayflies ** with only a night- long adult life. Many insects of complete metamorphosis (i. e., those whose adult stage, assumed during a quiescent encased pupal stage, is very different from their larval stage) which have very elaborate structural specialisations in the adult stage have had their fate as offspring-producing 80 DARWINISM TO-DAY. agents decided for them in immature, 7. e., egg, larval, or pupal, life, and this immature life is in most cases by far the larger part of the insect’s duration of existence. Henslow ** sowed together the same quantity of two kinds of wheat in a square yard of ground. The young wheat plants that came up were many times as many as the soil could support; the passive struggle for life was intense. In the end twenty heads ripened and these were all of one of the two kinds sown. The experiment was repeated in the following year with the same result. In the struggle one kind of wheat had a distinct advantage over the other. But this selection depended wholly on special characters or strength of the young stages. None of the adult characters cut any figure in this selection, which was decided before ever the plants came to maturity. And this is true, it seems to me, of most of struggle and selection. It is not in the adult state that the oppressive abundance exists: in the forest to-day are about as many crows as last year; in the meadows as many yellow butterflies as in sum- mers by. The eggs and the young are the stages which figure in mortality tables. They need the variations and adaptations ; the pressure is largely gone before maturity is reached. However, the adaptations of the fully-developed body, in structure and function, certainly do not fall behind those of the embryonic and immature stages. Indeed they obviously are more complex and perfected. } But after all what determines just what millions of trout’s Indiscriminate CGZs Shall be destroyed and what thousands death. shall hatch small fry? Many a sharp-eyed trout fisherman, many a keen-witted nature observer, many a trained biologist will answer: Chiefly chance, the luck of position, the good fortune of not being devoured by the roaming things that paddle or crawl in the upper reaches of trout streams. What shall decide when the big whale opens his mouth in the nudst of a shoal of myriads of tiny DARWINISM ATTACKED. 81 Copepods floating in the pelagic waters of the Aleutian seas, what Copepods shall disappear forever? Mainly, we may say, the chance of position. A bit more or less of size, or strength, or redness, or yellowness, or irritability or what not of form and function is going to avail little when the water rushes into the yawning throat. Now this chance and this luck are the luck and chance of the law of prob- abilities; that is, luck and chance capable of being mathe- matically determined. Given so much ocean, with so many whales swimming about in such and such curves at such and such rates and opening and closing their mouths inter- mittently at such and such intervals, and just so many shoals of so many million Copepods, these shoals at such and such distances apart, and any mathematical friend will reckon for you the chances any one Copepod individual has at any given moment of being swallowed. But Darwinian variations in the Copepod body will be represented by no function in the mathematician’s formula. When the scores of little streams dry in California every summer, what deter- mines whether millions of Californian water-insects of scores of kinds shall die in July or not? Mainly life or death is determined for them by their good or ill luck in being in one of the few streams that do not dry up, or in one of the many that do dry. Kelsey Creek runs into Clear Lake, in northern California; it is usually ever-living, but some summers it suddenly dries up. Fish play back and forth between this stream and the lake; at the time of the sudden drying a few hundreds of thousands out of many hundreds of thousands that habitually live in the stream and adjacent lake waters find themselves one awful day gasping painfully for water to wet their drying gills. They gasp a short while and then die. Did they all have the same num- ber of scales, the same shape and size of body, the same tinges of fleeting colour? No, they represented most of the possible gamut of Darwinian variation for their particular ae DARWINISM TO-DAY. species. But they were dead all together, by the ill-chance of position. In Lagunita, a small artificial lake on the campus of Stanford University, water pours in from two or three rivulets during the rainy season so as to fill it and make it an abiding place for many aquatic organisms that swim in or are washed in through the dikes. And thou- sands of little fishes and water beetles and dragon-fly nymphs and the like live contentedly there for seven or eight months. But with the rainless summer months come swift evaporation and steady leakage, and by September all the thousands of little fishes and insects lie dying there together in the last few puddles. It is the hard luck of a fatal chance against which all the variations in colour, in size, in scales, in spines, and what not are as one as far as helping or sav- ing any of the gasping possessors is concerned. One might go on tiresomely but one does not need to point the moral of these tales. Wolff *’ has clearly fancied how the fate of millions of tapeworms may hang on the recep- tion in the German Reichstag of a clever speech for or against meat laws. To go so far isn’t necessary: the very life-history of the tapeworm and of hundreds of similarly- lived vermian parasites shows to what nearly absolute de- gree chance rules their fate, and how utterly insignificant a part in it miscellaneous individual variation can possibly play. But aside from the part that what we may call fortune *° of position plays in determining life or death among indi- viduals, what of the actual rigour of the strug- gle in those cases where death does not come to thousands at a moment;—in the whale’s mouth, by catastrophe of flood or drouth, or by the elephant’s tread on the ant-hill? To this question of the rigour of intra-specific struggle I have given some personal attention in insect life, and while to detail observations here would be impossible, I may say baldly that no such rigour of in- How real is per- sonal selection ? DARWINISM ATTACKED. 83 7 dividual selection based on variation “* in colour, in pattern, in venation and other wing characters, in hairs and in numerous other structural characters, as demanded by the needs of the selection theory, is to be detected. I find just as much variation represented in series of mature individuals collected miscellaneously after having lived for more ‘or less time a free life exposed to all the dangers of this life, exposed, that is, to the rigour of the individual: struggle for existence, as among series of similar extent of individuals of the same species collected just at the time of reaching maturity but before enjoying any opportunity to be weeded out (on a basis of disadvantageous variation) by the rigour of the life-struggle. Just as many varying individuals, with variations of just as much extent and va- riety, were found in series exposed to the struggle, in which these variations are presumably capable of saving or losing life, as among series not yet exposed; in other words, just as much variation exists after enduring the selective rigour of the struggle as existed on the day when the insects are hrst.exposed to it, Conn ** expresses his belief concerning destruction by chance and the rigour of the struggle as follows: Conn’s discus: 4s eiscriminate destruction occurs con- sionof the chances Stantly, and certainly influences the problem of ae survival. Of the hundreds of individuals that are produced where few can live, many are destroyed in- discriminately, independent of the principle of survival of the fittest, and of these that are thus killed doubtless some are superior to those that survive. This principle of indis- criminate elimination does not in the slightest deny the force of the principle of survival of the fittest, but only indi- cates that its action is not absolutely rigid. The fittest do not always survive, for many of them are destroyed. “On the other hand the least fit do not always perish. Whether an individual shall live or die in the struggle is 34 DARWINISM TO-DAY. largely a matter of accident. Many a well-equipped indi- vidual will die, while many another, even though handi- capped by decidedly unfavourable characters, will continue to live and produce offspring because of some specially favourable conditions. Nothing could seem to be more decidedly disadvantageous than a broken leg, and, if the principle of elimination of the unfit were rigid, broken-legged individuals should be speedily destroyed. But it is quite common to find animals with broken legs or arms which yet succeed in living perfectly well. They have repaired their broken members by processes of bone growth, and have been able to carry on their part in the struggle for life and survive competition. J have found a frog with the whole of both feet bitten off, and yet with the wounds healed, the animal living without feet, and hence hardly able to swim, but side by side in competition with other well-developed animals. JI have found a clam that in its young condition had received a severe rent in one gill, through which, by some twist the body had been thrust, giving rise to the extraordinary condition of three gills on one side of the body and one on the other, a truly monstrous abnormity. But this clam had lived to maturity and produced eggs in quantities equal to any other clam. “Now such instances simply show the complexity of the conditions which determine survival. They indicate that these animals were favoured in some respects sufficiently to counteract the disadvantage of their mutilations. But the fact that so many instances are found does show that single characters do not always determine survival or elimination. The question whether an individual survive is dependent upon many factors, of which utility of various organs may be one and accident another. What would seem more sure from a logical standpoint, than that, in the intense struggle for life due to numerous individuals seeking for food, a frog who was unable to swim because of the loss of his DARWINISM ATTACKED. 85 feet would be sure to be a loser? Even if the inflammation caused by the wound did not destroy him, it would seem impossible for the animal to obtain his share of food. Of course, a footless race would be eliminated in a compara- tively short time, but the survival of so many mutilated individuals shows that selection is not so rigid as to eliminate all unfit individuals, even though their disadvantage be very great. “Tf a very disadvantageous character may thus fail to pro- duce destruction it must be still more true that a favour- able character, occurring in a single individual, has really little chance for survival. The individual possessing it will have to compete with accident, with indiscriminate slaughter, and with other conditions which we have just seen may be sufficient to preserve even a broken-legged individual. Nothing can seem more evident than that the web of the foot and the muscles of the legs are of use in swimming, and have therefore been developed by the preserving influ- ence of natural selection. If anything is of selective value, these characters certainly are. But when we find that a frog with no feet can survive the struggle for existence, it is evidently difficult to believe that single variations, either of use or disadvantage, will have any special likelihood of sur- viving at the expense of other members of the race, so as eventually to replace all others. But only thus can they be ‘seized upon by natural selection and preserved.’ ”’ There are two important objections to the natural selec- tion theory based on the relations of this theory with the oo is other selection theories, namely sexual tion needs the Selection and artificial selection. Wolff *’ has leant , made the criticism that natural selection must theory, which is be supported by the sexual selection theory ache in order to stand. It makes no pretension of explaining those extraordinary secondary sexual characters such as ornamentation, songs, dances, odours, etc., which 86 DARWINISM TO-DAY. not only are of no conceivable utility in the struggle for existence but are in many cases of obvious disadvantage. It relies wholly on sexual selection to explain them, and yet in Wolff’s eyes, and indeed in the eyes of most biologists, sexual selection is practically discredited. It certainly can- not explain some or many of these characters. (See account of the sexual selection theory and the criticisms of it in the next chapter.) Therefore, say Wolff and other anti- Darwinians, natural selection 1s undermined in just so far as it relies on the sexual selection theory to sustain it. The other objection is that the natural selection theory rests altogether too largely on an unwarranted analogy with Pine - tion rests too = has graphicaily expressed the contrast between largely on an . analogy witharti- the facts and processes of the two kinds of cial selection. selection in the following double-column table: Natural selec: the phenomena of artiScial selection. ARTIFICIAL SELECTION. (1) rests on the wish (Willen) and intelligence of the breeder, except in a certain few cases of “unintentional breeding’ (See Darwin, ‘Origin of Species.’’) (2) selects exceptional, most widely divergent characters, which appear only in a few individuals. (3) complete isolation (pure breeding) of the selected indi- viduals. (4) often leads to exaggerated development and to a sickly dis- position, so that the whole con- stitution suffers. (5) leads comparatively rapidly to new forms. (6) The = artificially-produced NATURAL SELECTION. (1) rests on the unvolitional and umnreasoning resultant of natural forces. (2) is a selection of slight dif- ferences, appearing simultane- ously in many individuals. (3) pure breeding is often very difficult through the possibility of crossing with the parental type. (4) effects no injury to the whole constitution, but on the contrary a strengthening and bettering of it. (5) The modification of species is effected, presumably almost always, very slowly, for if it were otherwise the appearance of new species would be often observed. (6) The natural races (varie- traces are unstable; they revert easily to the ancestral type if allowed to run wild; this is so probably because of their recent origin. DARWINISM ATTACKED. 87 ties) are stable; they do not revert if the outer conditions (environment) remain constant; this is so probably because they are more firmly established by reason of greater age. (7) The = artificially-produced (7) Natural varieties do not traces of the same species are cross in nature, either with in most cases fertile among each other or with the ancestral themselves. type. The most important contrast between the two kinds of selection lies, in my eyes at least, in the results obtained in the character of the new forms. As Morgan** well says, “we should not lose sight of the fact that even after the most rigorous selective process has been brought to bear on organisms, namely, by isolation under domestication, we do not apparently find ourselves gradually approaching nearer and nearer to the formation of new species, but we find, on the contrary, that we have produced something quite differ- ent. Inthe light of this truth, the relation between the two selective theories may appear quite different from the inter- pretation that Darwin gives of it. We may well doubt whether nature does select so much better than does man, and whether she has ever made new species in this way.” De Vries expresses very positively his belief that no artifi- cial races are fixed and constant forms, in the sense that natural varieties are. And this difference he believes to rest on the radically different method *’ of origin of the two kinds of forms; the domestic ones through carefully main- tained selection; the natural ones through definitive imme- diately fixed and enduring mutations. If one stops to recall his own familiar knowledge of the cultivated plants ** and will roughly classify the cultivated fruits and vegetables and ornamental plants with which he is acquainted into two categories depending upon the mode of reproduction, that is whether by division or by seeds, one will be struck by the great preponderance of the first of the 88 ‘’ DARWINISM TO-DAY. two categories,—the category, namely, of cultivated plant races which are reproduced practically exclusively by division (1. ¢., by cuttings, roots, scions, buds, etc.). The reason for relying upon this kind of reproduction is, in nearly every case, that these races do not breed true to seed, i. e., the races are not fixed, are unstable. And even among those races which we are accustomed to allow to reproduce by seed how necessary it is to maintain the unusual environ- ment, the exaggerated excellence of conditions of food supply, humidity, protection from natural enemies, etc., if we are to be successful in maintaining the parental characters of the plant. Let a few individuals escape from the hothouse or fertilised and sprinkled garden and see how soon, if they can persist at all, they lose their characters of amelioration, and become most pitifully unadorned. In Pfeffer’s “* eyes the fundamental difference between the two selection processes rests on the fact that the breeder or plant ameliorator selects his individuals (the “to be saved’’) on the basis of the character or condition of single characteristics, while in nature survival is not determined by such conditions, but on a basis of total or all-around fitness or advantage. ‘‘The moment,” says Pfeffer, ‘that one be- lieves one’s self to be able to place in parallel, simply and directly and in general, the activity of the breeder and the activity of the struggle for existence, and from this false generalisation deductively to compare the selective work of the breeder based on definitive special characters with the automatic selective work of nature based on similar specific characteristics, that moment one enters the camp of the teleologists, whether he is doing it knowingly and will- ingly, or not. In short it is a logical fallacy when one as- sumes to substitute for the selective action of the breeder a mechanically-working natural selection. Only in a single kind of case has this position any justification, and this not on account of logical correctness but on account of the pecu- DARWINISM ATTACKED. 89 liar identity of the circumstances. And this is when a single definitive characteristic is so all-important and dominant in the life of a race or species that its presence really has a life-and-death-determining value in the struggle for exist- ence; in this case the killing out of all the individuals not provided with this specific character has the same re- sult as an actual selection of the possessors of this char- acter. The farther, however, the actual circumstances differ from this case, in so far as a number of characteristics, and not a single one, determines the outcome of survival, by just so much less can the Darwinian explanation be made to cover the situation.” De Vries sums up a full and careful discussion ** of natural as compared with artificial selection as follows: “In conclusion, summing up all our arguments we may state that there is a broad analogy between breeding-selection in the widest sense of the word, including variety-testing, race- improvement, and the trial of the breeding ability on one side, and natural selection on the other. This analogy, how- ever, points to.the importance of the selection between ele- mentary species,and the very subordinate roleof intra-specific selection in nature. It strongly supports our view of the origin of species by mutation instead of continuous selec- tion. Or to put it in the terms chosen lately by Mr. Arthur Harris in a friendly criticism of my views: ‘Natural selection may explain the survival of the fittest, but it cannot explain the arrival of the fittest.’ ”’ Finally I desire to add an objection that has real weight with me, whatever may be the personal attitude of other Anircreasing naturalists or students to it. And that is, that number of work- ing biologists 2 Constantly increasing number of working unsatisfied with biologists find themselves, on a basis of their the selection theories. cumulative individual observation and experi- ence and thought, unsatisfied with the explanation of adapta- tion and species-forming offered by the selection theories. go DARWINISM TO-DAY. Men using, or rather, testing, these theories every day in their work in field and laboratory, find selection insufficient to explain the conditions that their observation and experi- ments reveal to them. These men are students in all the different lines of biological work; they are zoologists, bota- nists, palzontologists; they are students of anatomy, physi- ology, cecology, and taxomony (classification); they are embryologists, pathologists, animal and plant breeders. From all these lines of work come increasing complaints ; selection cannot explain for me what I see to exist. From some the cry is more bitter: selection is a delusion and false guide; I reject it utterly. For me, I repeat, this is an objection of much significance and importance. Just as modern chemistry seems to be finding its long useful atoniic theory now a restraint and a hindrance in understanding the wonderful new facts that have followed the pushing out of investigation into the rich fields of physical chemistry, so the biological experimentalists, the students of variation and heredity, of life mechanics, of physico-chemical biology, are finding the rigid theory of selection’s control of all processes and phenomena a rack on which they will no longer be bound. Coupled with the significance of this general objection to the reign of the selection theory—a general objection that ___ the selectionists will say is simply the objection The concessions ; ; : - of the selection- that the selection theory is objected to—is the sic added significance of the concessions in the way of supporting theories that the neo-Darwinians have made to the general increase and sharpness of scientific criticism of selection ; conspicuous examples are Roux’s theory of the battle of the parts, and Weismann’s theory of germinal selection. This latter is no less than a neo-Darwinian ex- planation of how determinate variation, that is ortho- genesis, may be explained non-teleologically. Which is practically to rob natural selection of all influence in the DARWINISM ATTACKED. gi primary determination of lines of descent. But to these supporting and concessionary theories we shall come in a later chapter. To show how definitive and positive an anti-Darwinian position is taken by some biologists I shall quote some para- osineey's graphs from an interesting short paper by Kor- radical anti-se- schinsky,*° a Russian botanist whose formula- lection position, tion of the theory of species-forming by hetero- genesis preceded that of de Vries by two years. In this paper (which is a vorlaufige Mitteilung published in Ger- man preliminary to the issuance, in the publications of the Royal Academy of Sciences of St. Petersburg, of a larger, more detailed paper) Korschinsky arranges in parallel columns the various corresponding or contrasting items of the selection theory compared with the heterogenesis theory of the author himself (for this full table see chapter xi). From this table I quote only the following statements to show how differently from the Darwinian view the probable effects of the struggle for existence may appear to another naturalist and to what radically anti-Darwinian conclusions a man may come who interprets the effects of selection in this way: “The origin of new forms can only occur under condi- tions favourable for them, and the more favourable such conditions are, that is, the less severe the struggle for ex- istence is, the more energetic is their development. Under severe external conditions new forms do not arise, or if they appear they are extinguished. “The struggle for existence, and the selection which goes hand in hand with it, compose a factor which restricts new- appearing forms and restrains wider variations, and which is in no way favourable to the production of new forms. It is indeed an inimical factor in evolution. “Were there no struggle for existence, then there would be no extinguishing of arising or already arisen forms. The g2 DARWINISM TO-DAY. organic world could then develop into a mighty tree, whose branches could all remain in blooming condition, so that the now isolated extremest species would be united with all others through gradatory forms. “The adaptation resulting from the effects of the struggle for existence is absolutely not identical with advance, for higher-standing, more complex forms are by no means always better adapted to outer conditions than the lower ones. The evolution [used here by the author as synony- mous with advance or progressive complexity] of organisms cannot be explained in a purely mechanical way. In order to explain the origin of higher forms from lower it is neces- sary to postulate in the organisms a special tendency to ad- vance which is nearly related to or identical with the tendency to vary, which tendency compels the organisms to advance so far as the outer conditions permit.” These declarations sound strange and perhaps almost absurd in the ears of one accustomed for years to hear only the Darwinian interpretation of the effects of the strugele for existence and natural selection. But taken up one by one, as they are by Korschinsky, and developed and explained, they begin to have a kind of plausibility, an appeal to our reason, of much that sort which the Dar- winian interpretation has and makes. After all the Darwin- lan interpretation is proved only in so far as it possesses a high degree of plausibility and makes a convincing appeal to our reason. Of exact proof, in the nature of observed fact or result of experiment, or of mathematical demonstra- tion, there is little in the case either of the Darwinian or the Korschinskian interpretation. Those other biologists “" who, like Korschinsky, take the extreme and positive stand that the struggle and selection are not factors in evolution, or if factors are really hinder- ing and opposing ones, constitute, however, by far the smaller body in the ranks of the anti-Darwinian critics when DARWINISM ATTACKED. 93 compared with those whose arraignment of selection is chiefly a protest against its assumption of altogether an undue share of influence in species-forming, and whose principal attempt is to reduce selection to a secondary place among evolutionary factors, giving first place to that influ- ence or those influences which determine the character and direction of variation. Still the totally anti-Darwinian critics are not few, and are not without ingenuity and capacity in debate. But better justified by what we know to-day and far saner in their estimate of the Darwinian factors are such critics _ as Delage and Morgan. “The conclusion of Dirty lial this criticism,” says Dglage,”* at the end of a detailed critical discussion of the “true role of selection,” “is that selection is powerless to form Species. Its role, however, is not nul, but it is limited to the sup- pression of variations radically bad, and to the maintaining of the species in its normal character. Far from being an instrument for the evolution of species it guarantees their fixity.” And elsewhere he says: “Species come from fixed variations. The formation of species is due ordinarily to general variation [a conception of change much like that of de Vries’s mutations and sudden fixed origin of elementary species], very rarely to strong individual variation [sports or discontinuous variations], and never to weak individual variation [fluctuating or Darwinian variation]. Morgan * in a recent popular essay in which he takes a strong stand against natural selection as a species-forming Morgan's ad- factor and in favour of “definite variations” verse criticism of (de Vriesian mutations) concludes as follows: the species-form- ,, ing value ofse- | 1” the preceding pages I have tried to bring lection: into contrast the point of view of the Darwinian school and the newer conception of the sur- vival of elementary species. I have tried to show what selection has meant to the selectionists. They have 79 1662 94 DARWINISM TO-DAY. never hesitated to take each particular character of an animal or plant, and dress it up in more perfect gar- ments, while the body of the species, if I may so speak, has been left as it was before. There has been a con- tinual tampering with the characters of the organism with the laudable intention of doing with them that which na- ture herself seems unable to do, namely, to dissociate them from the rest of the organisation and perfect them in this way or in that. It is this meddling with the fluctuating characters of the species that has been the characteristic procedure of the Darwinians, in their attempt to show how new species have been created. In contrast to this method, the theory of the survival of species assumes that a form once made does not have its individual parts later disso- ciated and adjusted to better fit the external needs of the species. Such a new form can change only by becoming again a new species with a new combination of characters; some of which may be more developed in one direction than before, others less, etc. “New forms on the Darwinian theory are supposed to be created by a process of picking out of individual differences. If, in addition to this, Darwin supposed that at times varie- ties and species crowd each other out nothing new is thereby created.* On the other hand the theory of the survival of definite variations refers the creation of new forms to an- *“Tf the survival of certain species determines, in a metaphorical sense, the kinds of future mutations that occur, the course of evo- lution may appear to be guided by selection or survival; but, how- ever true it may be that selection acts by lopping off certain branches, and limits to this extent the kinds of possible future muta- tions, the origin of the new forms remains still a different question from the question of the survival of certain species. This negative action of selection is not the process that most Darwinians have had in mind as the source of the origin of new species. It is true that Weismann believes that selection of individual differences deter- mines the origin of new species. and that the creation of these new species determines the future course of variations in the same direc- tion, but his argument that fluctuating variations can go on indefi- DARWINISM ATTACKED. 95: other process, namely, to a sudden change in the character of the germ. The creating has already taken place before the question of the survival of the new form comes up. After the new form has appeared the question of its per- sistence will depend on whether it can get a foothold. The result is now the same as when species crowd each other out. This distinction appears to me to be not a matter of secondary interest, but one of fundamental importance, for it involves the whole question of the ‘origin of species.’ So far as a phrase may sum up the difference, it appears that new species are born; they are not made by Darwinian methods, and the theory of natural selection has nothing to do with the origin of species, but with the survival of already formed species. Not selection of the fittest individuals, but the survival of the sufficiently fit species. “There is a fundamental difference between the idea that fluctuating variations become specific characters through accumulation by selection, and the idea that new species arise as definite variations, which, with their appearance, characterise the new form as a new species. According to the Darwinian theory, natural selection performs a double duty, first, to build up new species, and second, to maintain them in competition with other species. According to the other view, species are not formed by any kind of selection, and the question of survival only concerns the maintenance of species already formed. The primary problem is the problem of the ‘origin of species.’ The central idea is not nitely varying in the direction of selection is refuted by what has. been actually found to be the case when the process of selection of fluctuating variations is carried out. Most of the individuals of a species may be brought in this way to show the particular character selected in its highest degree as a fluctuating variation, but it appears: not possible to transgress this limit; and rigorous selection in every generation is necessary to hold the individuals to the highest point. reached. Only by the appearance of new definite variations can a given character be permanently fixed, or a new species created that. will show fluctuating variations around the new standard. 96 DARWINISM TO-DAY. what species survive, but how species originate; no matter whether they are going to become victorious or not. “After a species has appeared it will surely be admitted by every one, that forms that can survive will survive! If Darwin’s theory meant only this to those who adopted it, is it not surprising that such a truism should have been hailed as a great discovery? Was not the theory heralded because it seemed to explain how new species arose? What shall we say then when we find a situation like that existing at the present time, when we are told that after all the only difference between Darwin’s theory of natural selection and the theory of the survival of definite variations is that in the one case fluctuating variations are selected, and in the other mutations, and that in both cases natural selection is the key to the evolutionary process! Is not the ‘origin of species’ still the real point at issue? “T yield to no one in admiration for what Darwin has done in behalf of the biological sciences, for he succeeded, where the great French zoologists failed, in establishing the prin- ciple of evolution. Furthermore no other hypothesis, that has as yet been proposed, accounts so well for the wide- spread occurrence of adaptation of organisms to the environ- ment as does the principle of natural selection. But appre- ciation of Darwin’s claims in these directions need not blind us to the insufficiency of the theory of natural selection to account for the origin of species; nor to the fact that his followers have been especially concerned in propounding and making application of this side of the theory. They have shown little interest in selection as the great conserv- ing factor of evolution, and the reason for this is not far to seek, because of the much greater importance that they have attributed to natural selection as a creative factor in building up individual differences into specific characters.” DARWINISM ATTACKED. 97 APPENDIX. * De Vries, H., ‘Die Mutationstheorie,” Vol. I, pp. 83 ff., 1901. * Wolff, Gustav, “Der gegenwartige Stand des Darwinismus,” p. 9, 1896. * Weismann, A., ‘““Aufsatze tiber Vererbung,” p. 116, 1892. * Galton, Francis, ‘‘Natural Inheritance.” I quote from Galton as follows: : “As soon as the character of the problem of filial descent had become well understood, it was seen that a general equation of Galton’s state- the same form as that by which it was expressed, mentofthelaw also expressed the connection between kinsmen in of regression. == every degree. The unexpected law of universal re- gression became a theoretical necessity, and on appealing to facts, its existence was found to be conspicuous. If the word ‘‘peculiarity” be used to signify the difference between the amount of any faculty possessed by a man and the average of that possessed by the popu- lation at large, then the law of regression may be described as follows: Every peculiarity in a man is shared by his kinsmen, but on the average in a less degree. It is reduced to a definite fraction of its amount quite independently of what its amount might be. The fraction differs in different orders of kin, becoming smaller as they are more remote. When the kinship is so distant that its effects are not worth taking into account, the peculiarity of the man, however remarkable it may have been, is reduced to zero in his kinsmen. This apparent paradox is fundamentally due to the greater frequency of mediocre deviations than of extreme ones, occurring between limits separated by equal widths” (pp. 194-195). “The law of regression in respect to stature may be phrased as follows: namely, that the deviation of the sons from P are on the average equal to one-third of the deviation of parent from P, and in the same direction or more briefly still; if P + (+D) be the stature of a parent, the stature of the offspring will on the average be P + (+1-3 D)” (p. 104). “Thus, however paradoxical it may appear at first sight, it is theoretically a necessary fact, and one that is clearly confirmed by observation, that the stature of the adult offspring must, on the whole, be more mediocre than the stature of their parents; that is to say, more near to the M of the general population” (p. 95). “The law of regression tells heavily against the full hereditary transmission of any gift. Only a few of many children would be likely to differ from mediocrity so widely as their mid-parent, and still fewer would differ as widely as the more exceptional of 98 DARWINISM TO-DAY. the two parents. The more bountifully the parent is gifted by Nature, the more rare will be his good fortune if he begets a son who is as richly endowed as himself, and still more so if he has a son who is endowed yet more largely” (p. 106). ° Morgan, T. H., “Evolution and Adaptation,” p. 104, 1903. * Johannsen, W., “Uber Erblichkeit in Populationen und in reinen Linien,” 1903. ” Delage, Yves, “L’Hérédité,” 2d ed., p. 398, 1903. ® Pfeffer, G., “Die Umwandlung der Arten,” p. 26, 1894. * Wolff, G., ‘“Beitrage zur Kritik der Darwin’schen Lehre,” pp. 50 ff. I quote as follows: “Fir jeden, der sich den Grundgedanken der Selektionstheorie auch nur einigermassen klar gemacht hat, kann kein Zweifel daru- Wolff's criticism ber bestehen, dass die nattrliche Selektion immer of panmixia. nur ein einziges Anpassungsgebilde, niemals aber zwei oder gar noch mehr zu gleicher Zeit ztichten kann. Es konnen z. B. Auge und Ohr nicht gleichzeitig geztichtet werden, denn sonst miissten ja die ausgelesenen Individuen mit den besten Augen zugleich auch diejenigen mit den besten Ohren sein, eine Vorausset- zung, die wir um so weniger machen durfen, als dieselbe ja auf alle ubrigen Organe ausgedehnt werden musste. Die Naturzuchtung wird sich immer auf die Ziuchtung desjenigen Organes verlegen, dessen bessere Ausbildung fur das Tier den grosseren Vorteil bietet.. Ist ein gutes Auge niitzlicher, als ein gutes Ohr, so sind die Individuen mit den besten Augen denen mit den besten Ohren gegenuber in Vorteil: sie werden gezitichtet. Wahrend also das Auge geztuchtet wird, steht das Ohr nicht unter dem Einfluss der Selektion, also unter dem Einfluss der Panmixie. Unter diesem Einflusse stehen aber samtliche Organe mit Ausnahme des ein- zigen, welches gerade geziichtet wird, sie fangen daher alle an, einen Ruckbildungsprozess einzugehen. Sobald nun eines der nicht gezuchteten Organe bereits so weit rtickgebildet ist, dass der Zu- stand desselben eine Gefahr fur den Organismus in sich schliesst, alsdann wird sich die Naturztichtung diesem Organe zuwenden, denn dann ist eine bessere Ausbildung dieses Organes ein grosserer Vorteil als die des andern. Die Selektion iiberlasst also dieses letztere seinem Schicksal, d. h. der riickbildenden Panmixie, unter deren Einflusse die andern Organe immer noch stehen. * Jedes Gebilde, welches durch Naturztichtung hervorgebracht ist, auch wenn es jetzt von untergeordneter Bedeutung ist, muss einmil Generationen hindurch, d. h. so lange als die Selektion zu seiner Herstellung brauchte, das allerwichtigste gewesen sein, eine Konse- hae die allein gentigt, den ganzen Darwinismus ad absurdum zu uhren. DARWINISM ATTACKED. 99 “Wem die Absurditat dieser ganz unvermeidlichen Konsequenzen noch nicht einleuchtet, der mdge sich die Sache an einem Bilde versinnlichen. Wenn ein Lehrer eine Klasse von Schilern zu unterrichten hat und dabei so verfahrt, dass er immer einen Schiler zu sich auf sein Zimmer nimmt und dort unterrichtet, unterdessen aber die tbrigen treiben lasst, was sie wollen, so wird er bei einer Inspizierung durch den Schulrat mit seiner Klasse wenig Staat machen konnen, weil die Schtiler weit mehr Zeit auf das Vergessen, als auf das Behalten und Lernen verwendet haben. Sie werden daher nicht nur das, was sie bei diesem Lehrer in den wenigen Einzellektionen, sondern auch das, was sie in den friithern Klassen gelernt hatten, vergessen haben. Genau so beim Organismus. Alle Organe stehen eine weit langere Zeit unter dem Einflusse der Pan- mixie, als unter dem der Selektion; wenn also die Panmixie einen Einfluss ausubt, so wird dieser Einfluss der titberwiegende sein, und wenn dieser Einfluss dem der Selektion entgegengesetzt ist, so wird der Einfluss der Selektion ganzlich aufgehoben werden, d. h. der ruckbildende Einfluss wtirde die Oberhand behalten, das ganze Tier musste sich mit Stumpf und Stiel—zuriickbilden, ein Vorgang, bei welchem die Panmixie zu vergleichen ware einem Feuer, das ein Dorf ergriffen hat, die Selektion dagegen einer Feuerwehr, welche mit der Spritze immer wieder an dasjenige Haus fahrt, aus dem gerade die starksten Flammen herausschlagen. Diese Feuer- wehr wird gewiss nicht viel von dem Dorfe retten. “Der Darwinismus muss also, wenn er der Absurditat dieser Konsequenzen entgehen will, notwendig annehmen, dass diejenigen Organe, welche jeweilig nicht unter dem Einflusse der Selek- tion stehen, ruhig und unbeschadet warten k6nnen, bis die miitter- liche Sorgfalt der Selektion, welche sich immer nur einem ihrer Kinder widmen kann, sich ihrer wieder annimmt. Das heisst der Darwinismus muss annehmen, dass die Panmixie keinen Einfluss auf die Organisation hat. “Da aber die Variierung eine Thatsache ist, so muss er anneh- men, dass gunstige und ungiinstige Variierung die gleiche * Wahr- scheinlichkeit haben, womit ein weiterer Beweis geliefert ist, dass der Darwinismus nur mit graduellen Veranderungen rechnen kann. “Die Lehre von der Panmixie und die Selektionstheorie vertragen sich nicht mit einander. Aus der Richtigkeit der einen folgt die Falschheit der andern. Und insofern die Selektionstheorie eigentlich die Voraussetzung zur Lehre von der Panmixie ist, vernichtet diese letztere sich selbst durch ihre blosse Existenz. Ihre Bejahung *Ist man, wie Emery, der Ansicht, dass ungiinstige Variierungen grossere Wahrscheinlichkeit haben als giinstige, so muss man hieraus allein die Unrichtigkeit der Selektionstheorie folgern. 100 DARWINISM TO-DAY. schliesst ihre Verneinung in sich, d. h. sie leidet an einem unl6sbaren inneren Widerspruch.” *°? This necessity of constantly active selection must apply as well to specialised function as to specialised organ. But it is not diffi- Example of inef- cult to call attention to certain functions or physio- fective panmixia. logical capacities of various animals which seem to negative this deciaration of the need of constant selection to main- tain specialisation. For example, I have shown (‘‘Regeneration in Larval Legs of Silkworms,” Jour. Exper. Zool., Vol. I, pp. 593-599, Io figs., 1904) that the long ‘‘domesticated” mulberry silkworm larva possesses the capacity of regenerating any of its legs, if the mutila- tion has not removed the whole appendage. Now the assumption of most selectionists is that this capacity for regenerating injured legs and other parts is a specialisation, adaptive and advantageous. But in connection with this particular case, it should be borne in mind that the silkworm has been for approximately 5,000 years a domesticated animal, cared for under such conditions as to make the natural loss of legs almost an impossible occurrence. Perfectly protected against such natural enemies as bite off legs, there has certainly been nothing of that sharp necessity, during all the life of countless generations of silkworms, which is supposed to be the basis for maintaining the advantageous capacity for regeneration. There has been a clear field for panmixia. But the regenerative capacity still exists in effective degree. 11 See a recent paper by Vejdovsky (“Uber einige Stisswasser- Amphipoden, III. Die Augenredtiktion bei einem neuen Gam- Example of pro- mariden aus Irland und uber Niphargus caspary eh rae Pratz aus den Brunnen von Munchen,” in S. B. Kgl. cable by sie ln Bohm. Ges. d. Wiss., 1905), embodying the results of selection. his studies on the reduction of the size in certain small Crustaceans (Gammaridz), which he found living in the Irish Sea at a depth of from 130 to 150 feet. These Crustaceans form an interesting series showing a gradual reduction of the eyes. It is shown clearly that this reduction proceeds very regularly from the periphery toward the interior. First, there is apparent a high degree of variability of all parts, then the optic parts of the eye disappear, and finally the nervous, or retinal, parts. This course of reduction is only explicable, according to the author, on a basis of the inherited degenerative results of a lack of use, for in any decreas- ing use exactly this course of individual degeneration of the eye is what is met with; that is, the active external optic elements degenerate first, and later the nervous, or retinal, elements. ** Weismann, A., “On Germinal Selection as a Source of Definite Variation,” trans. McCormack, pp. 38 ff., 1896. DARWINISM ATTACKED. IO *® The Mayflies, or lake-flies, constitute an order (Ephemerida) of insects which spend from several months to perhaps a couple of years in their immature life (as crawling, gill-bearing, wingless aquatic larve), and from a few hours to at most a few days as free-flying adult creatures. Many other insects (indeed most in- sects) have a much shorter adult life than immature life, and most of them have very different structures in the two life-periods. Hundreds of insect kinds take no food in the adult stage and many others that do have food-habits quite different from the larval habits. ** Henslow, G. W., “Origin of Flowering Structures,” 1895. *® Wolff, G., “Beitrage zur Kritik der Darwin’schen Lehre,” pp. 41,. ff., 1898. I quote as follows: “Ware die Wahrscheinlichkeit einer niitzlichen Variierung wirk- lich so klein, wie Emery behauptet, ware sie wirklich so klein, wie Wolff's discus- die Wahrscheinlichkeit, dass in dem Satz einer sion of the selec- Druckseite durch beliebiges Ersetzen eines beliebigen. tion coefficient. Biuchstaben durch einen beliebigen andern ein Druck- fehler verbessert wird, dann k6nnte sich der Darwinismus gleich von vornherein begraben lassen. Er konnte dann nicht mehr sagen: die Auslese des Bessern muss notwendig eine Steigerung des. Niitzlichen ergeben. Die erforderlichen Voraussetzungen waren dann noch viel verwickelter; es mtisste dann auch noch tuber den Inten- sitatsgrad’* des Selektionsprozesses eine Voraussetzung gemacht werden: er muss so hoch sein, dass die Summe aller ttberlebenden + dx?” (unter denen vor Eintritt des Selektionsprozesses die unge- heure Mehrzahl negativ, das Vorhandensein positiver dagegen ausserst unwahrscheinlich war) eine positive Zahl wird. Der Kampf ums Dasein an und fir sich niitzt also noch gar nichts; erst wenn er jenen ganz bestimmten Intensitatsgrad erreicht, dann erst wirkt die Selektion verbessernd. Und wie hoch ist dieser von * Dieser Intensitatsgrad ist eine genau bestimmte, wenn auch selten bestimmbare Zahl. Sie giebt das Verhaltnis der erzeugten zu den sich fortpflanzenden Nachkommen an. Man konnte diese Verhaltniszahl den Selektionskoeffizienten nennen. Ich muss trotz der Einwendungen Emerys meine Schreibweise dx beibehalten. Sage ich, dass der Darwinismus mit dem Vari- ierungsinkrement nur dann rechnen diirfe, wenn er von ihm keine bestimmte Grosse voraussetzt, sondern ihm gestattet, sich der Null beliebig zu nahern, und will ich dies durch ein mathematisches Zeichen ausdriicken, so ist das einzig richtige dx. Ob die wirk- lichen Variierungsinkremente messbar sind oder nicht, ist dabei ganz gleichgiltig. Ubrigens ist Emery im Irrtum, wenn er meint, alle seien messbar. Die wenigsten sind es. Die Differenz in der Disposition zur Tuberkulose zwischen zwei vollig gesunden Indi- viduen ist z. B. gewiss nicht messbar, und doch kann gerade hier eine, wenn auch noch so kleine Differenz, im Kampf ums Dasein den Ausschlag geben. 102 DARWINISM TO-DAY. Emery geforderte Intensitatsgrad! Nimmt man an, ein Tier habe 40,000 Millionen Kinder, von welchen nur 2 Individuen sich fort- pflanzen, so ware nach Emerys Rechnung dieser Selektionsprozess noch nicht einmal intensiv genug, um es wahrscheinlich werden zu lassen, dass diese 2 im Durchschnitt sich irgendwie verbessert haben.* Und dabei ist noch vorausgesetzt, dass die Selektion von den 40,000 Millionen wirklich ganz genau die 2 Besten heraus- gefunden hat. Dies wird nattrlich nie der Fall sein. Denn je geringer die Prozentzah! der gtinstigen Variierungen ist, um so weniger wird das Resultat der Selektion von Variierungsvorteilen, um so mehr dagegen von Situationsvorteilen abhangen. Nehmen wir z. B. eine Tierklasse, bei welcher die Verhaltniszahl der erzeug- ten und der erhaltungsfahigen Individuen der von Emery geforderten Zahl vielleicht am nachsten kommt: die Bandwiirmer. Nehmen wir also an, ein Bandwurm erzeuge wahrend seines ganzen Lebens 40.000 Millionen Eier. Unter den abgehenden Eiern findet eine Selektion statt: nur die, welche vom Zwischenwirt gefressen werden konnen sich zur Finne entwickeln. Es werden aber ungeheuer wenige gefressen, die meisten gehen ungefressen zu Grunde. Wir haben also eine intensive Selektion. Wovon hangt es aber ab, ob das Ei gefressen wird? Ganz ausschliesslich von aussern Umstan- den. Die individuellen Eigenschaften der Eier kommen nicht in Betracht. Wir haben also hier einen Selektionsprozess, bei welchem ein Einfluss der Variierungsvorteile absolut ausge- schaltet ist, bei welchem ausschliesslich Situationsvorteile in Be- tracht kommen. Nur in Bezug auf die Resistenzfahigkeit konnten Variierungsvorteile von Belang sein, die wir aber ausschalten konnen, indem wir uns auf ein bestimmtes Anpassungsgebilde beschranken (was ttberhaupt bei jeder Darwinistischen Betrachtung notig ist), z. B. die Entstehung der Saugnapfe, etc. Dass unter den relativ wenigen gefressenen Eiern sich eines von den 2 mit einer in Bezug auf die Saugnapfe vorteilhaften Keimesanlage befinde, ist ausserst unwahrscheinlich. Die gefressenen Embryonen kommen nun ‘zur engeren Wahl.’ Nicht alle werden in fremden Organismus bleiben. Viele werden einfach abgehen. Bei diesem Selektionsprozess, der lange nicht so intensiv ist, als der erste, 1 Wobei noch zu beachten ist, dass die Zahl 100 der Elemente, in welche Emery ein Organ sich aufgelost denkt, selbstverstandlich eine willktrliche ist, und dass diese Zahl der Wirklichkeit naturlich um so naher kommen wird, je grosser sie angenommen wird. Wie enorm wiirde sich dann erst die Zahl der Kombinationen vermehren! Ubrigens kommt es auf die Zahlen gar nicht an: das Wichtige ist, dass mit der Emeryschen Annahme der Hypothesenkomplex, welchen die Selektionstheorie darstellt, um eine neue und zwar das Fundament betreffende Hypothese vermehrt wurde. DARWINISM ATTACKED. 103 konnen auch (aber keineswegs ausschliesslich) Variierungsvorteile mitwirken. Die soweit gelangten Finnen kommen nun zu einer noch engern Wahl. Nur diejenigen entwickeln sich weiter, deren Zwischenwirte gefressen oder gegessen werden. Diesen Selektions- prozess konnen wieder eine Unzahl der verschiedensten Faktoren beeinflussen. Mehr oder weniger grosser Geschmack an rohem Fleisch, mehr oder weniger grosse Achtsamkeit der Sanitatsbehor- den, diplomatischer Notenwechsel tber Grenzverkehr: das sind alles Faktoren, die in Betracht kommen konnen. Eine schneidige Reichs- tagsrede kann unter Umstanden uber Tod und Leben von Tau- senden von Bandwiirmern entscheiden. Eine Klasse von Faktoren kommt aber ganz gewiss nicht in Betracht, das sind individuelle Vorteile der Finnen. Auch hier ist also die Wirkung der Vari-. ierungsvorteile ausgeschaltet. Unter den gefressenen oder geges- senen Finnen findet wahrscheinlich wiederum ein Selektionsprozess statt, bei welchem Variierungsvorteile (aber keineswegs ausschliess- lich) mitwirken k6nnen. Von den 2 Individuen mit vorteilhaft variierten Saugnapfen wird aber aller Wahrscheinlichkeit nach kein einziges zur letzten Wahl gekommen sein. Also selbst bei denjeni- gen Tieren, bei welchen die Uberproduktion die grosste ist, konnte nach der Emeryschen Rechnung die Selektionstheorie zur Erkla- rung der Anpassungserscheinungen nicht mehr verwendet werden.” *® See Piepers, M. C., “Mimikry, Selektion, Darwinismus,” 1903, pp. 376 ff. Author shows how an enormous mortality among oysters can occur without any reference to their fitness for lite, and also gives other interesting cases of indiscriminate non- selective mortality. ™ Kellogg and Bell, “Studies of Variation in Insects,’ Proc. Wash Acad. Sci., Vol. VI, pp. 203-332, 1904. I quote the follow- ing: | “There are certainly few selectionists left who honestly believe that the minute fluctuating variations in pattern, in size, in curve Example of non- of a vein, in length of a hair, etc., have that life- selection of trivial and-death value which is the sole sort of value that differences. an ‘advantageous variation’ must have to be a ser- viceable handle for the action of natural selection. As a matter of fact, no systematist will have escaped having had it distinctly -impressed on him that he recognises differences in the pattern of lady-bird beetles, in the number of fin rays in fishes, in the branch- ing of a vein in flies’ wings, that no enemy, no agent of natural selection, can recognise, at least to the extent of pronouncing sentence of death (or not pronouncing it) on its basis. And further, no biologist really satisfies himself with the worn state- ment, ‘We must not presume to judge the value of these trivial, 104 DARWINISM TO-DAY. these microscopic differences, for we do not know all the complex interrelation and interaction of the organism and its environment.’ We do not, but we do know for many cases that such differences are actually not of life-and-death selective value, and reason compels us to believe to a moral certainty that in other cases these fortuitous trivialities have similar lack of life-and-death importance. The case of the variation of the convergent lady-bird beetle, Hip- podamia convergens (p. 275 et seq.), is distinctly in point. In our account of this variation we have called attention to the suggestive- ness, in its light on the rigour of the ‘struggle for existence’ among individuals, of the fact that armong several thousand individuals, gathered together to hibernate after an active life, having been exposed to the attacks of bird and insect enemies, to the rigours of climatic conditions and to the necessities of obtaining food (other smaller insects, as aphids, etc., caught alive), such a range of variation in pattern is found as enables us to describe (so that they may be actually readily distinguished by verbal description), eighty-four ‘aberrations’ or pattern-variates; lady-birds with no spots, with one, with two, with three, with each of all the numbers up to and including eighteen distinct small black spots, the different numbers usually being represented by several different combinations of spots. Systematic entomologists describe Hippodamia convergens as a brown-red beetle with six black spots on each elytron, and this description is true for most beetles of this species. But not at all for all; nor even approximately for many. After a season of ex- posure to the struggle for existence, to the rigours of selection, individuals with one spot, with six spots, with twelve spots, with eighteen, find themselves alive and healthy; they come together to pass a quiet winter under the fallen oak leaves on a mountain side, ready to mate miscellaneously in the spring, and produce young of all manner of pattern (as far as number and arrangement of spots go); which young, whether twelve-spotted as they ought to be, or no-spotted, or eighteen-spotted as they may be, will appa- rently go safely through life despite the malevolent search of the all-powerful Inquisitor, Rigour of Selection! “Directly touching this point, too, are our data of the variation of series of honey-bees collected from free-flying individuals after exposure as adults to the rigours of outdoor life, as compared with the variation in the series of bees, adult, but collected just as issu- ing from the cells before being exposed as adults in any way to the external dangers of living. Series of both drones and workers representing both exposed and unexposed individuals were studied. The results of this examination are, put in one statement, that the variation among the exposed individuals is no less than that among DARWINISM ATTACKED. 105 the unexposed individuals. This means that these various, mostly slight, blastogenic variations (although in such important organs as the wings) which occur among bees at the time of their issuance as active, winged creatures, are not of sufficient advantage or dis- advantage to the individuals to lead to a weeding out (by death) or saving of such varying individuals by immediate selective action. Whatever the rigour and danger of the outdoor bee life, these variations seem to be insufficient to cut any figure in the persist- ence or non-persistence of any individual in the face of this rigour.” ** Conn, H. W., “The Method of Evolution,” pp. 72 ff., 1900. 7° Wolff, G., ‘“Beitrage zur Kritik der Darwin’schen Lehre,” pp. 24 et seq., 1808. 2° Plate, L., “Uber die Bedeutung des Darwin’schen Selections- prinzip,” pp. 17-18, 1903. 2+ Morgan, T. H., ‘Evolution and Adaptation,” 1903. 2 De Vries, in a recent paper (‘“Altere und Neuere Selektions- methode,” Biol. Centralbl., Vol. XXVI, pp. 385-395, 1906), describes the new methods of plant amelioration adopted by the Svalfor Ver- suchsstation (Sweden). These methods have been determined largely by the acceptance of De Vries’s mutations theory as a working hypothesis. 7? For account of the breeding and amelioration (artificial selec- tion) of plants see Darwin, ‘Variation of Animals and Plants Dee cenccn to. Undet Domestication,” many editions; Bailey, L. books and papers i, “‘Plant-breeding,” 4th ed., 1900 ; Hays, W. M., on plant-breed- ‘‘Plant-breeding,” Bull. 29, Div. Veg. Phys. and me Path, U. S. Dept. Agric., 1901; Webber, H. J., and Bessey, E. A., “Progress of Plant-breeding in the United States,” Yearbook of U. S. Dept. Agric., for 18809, pp. 465-490; Kellogg, V. L., “The Scientific Aspects of Luther Burbank’s Work,” Pop. Sci. Mo., pp. 363-374, Oct., 1906 (reprinted in Appendix to chapter ix of this book). ** Pfeffer, Georg, ‘“‘Die Umwandlung der Arten,” pp. 19-20, 1894. 25 De Vries, H., “Species and Varieties, their Origin by Mutation,” pp. 798-826, 1905. *° Korschinsky, S., ‘“Heterogenesis und Evolution,” Naturwiss, Wochenschrift, Vol. XIV, p. 276, 1899. ?™ Coe, C. G., ‘‘Nature versus Natural Selection,” 1894. A book devoted wholly to denying any validity at all to natural selection. 78 Delage, Yves, “L’Hérédité,” 2d ed,, p. 419, p. 843, 1903. *° Morgan, T. H., ‘‘The Origin of Species through Selection Con- trasted with their Origin through the Appearance of Definite Variations,’ Pop. Sci. Mo., pp. 54-65, May, 1905. CHAP ER yy. DARWINISM ATTACKED (CONTINUED): THE THEORY OF SEXUAL SELECTION. THE differences between male and female individuals of a single species are often striking; recall the gorgeous colouring, the plumes and tufts and tail-feathers Secondary s , sexual difer- Of many male birds compared with the sober cy and quiet plumage of their mates; the antlers of the stag, the mane of the lion and bison, the beard of the goat, many monkeys, and of man. Recall the mamme of the female quadrupeds, the brood pouches of the female kangaroos and opossums, the small size, compared with their mates, of many female birds, the winglessness of many fe- male insects. Other less familiar kinds of animals show sexual dimorphism or dichromatism in even more striking degree, while in many others the differences are less con- spicuous but nevertheless perfectly obvious if some attention is given to looking for them. These differences in size, colour, general appearances, and various specific structural details in head, trunk, wings, feet, plumage, etc., are over and beyond those primary radical differences existing in all species in which the two sexes are differentiated. Some of these differences may, however, have obvious relation to the primary differences, in that they may be connected im- mediately with the act of pairing or with the work of rear- ing the young. The presence in male insects of complexly developed holding organs, and in female mammals of milk glands exemplifies differences of this category. A great many sexual differences, however, have no such obvious direct relation to the function of producing and rearing the young. 106 DARWINISM ATTACKED. 107 Such are the metallic purple and bronze colours of the male grackles compared with the dull brown of the females; the long tails and brilliant coloration of the male pheasants, the great, spreading, patterned tail of the peacock, the larger size or the winglessness of many female insects, etc. All these differences between male and female of the same species of animal, beyond or in addition to the differences between the actual primary reproductive organs, are known as secondary sexual differences, or the characters themselves, which may be characteristics of physiology and habit as well as the more familiar ones of structure, are called sec- ondary sexual characters. The layman may not readily appreciate the abundance and the great variety of these char- acters, but it is a fact that almost all species of animals, excepting those in the lower invertebrate branches, show them, and if one will try to recall the aspect of the two sexes in one after another of the species of animals with which one is familiar, mammals, birds, insects, etc., one will begin to realise how widespread and significant are these secondary sexual characters. Various biologists have made up classifications, from various points of view, of the different kinds of these char- Classifications 2cters; one classification, like that of Kramer ’ of secondary sex- for the secondary sexual characters of insects, ual characters. ray be based on the different parts of the body showing the differences between male and female indi- viduals, as head, antenne, thorax, wings, legs, abdomen, etc., and on the character of the differences themselves, as whether differences in structure or in colour and pattern. Another type of classification, and one more useful for our present discussion, is that based on the apparent significance or actual use of the differing characters. An excellent classification of this type is that of Plate.* The following are the principal subdivisions of this classification with a few examples illustrating each: 108 DARWINISM TO-DAY. CLASSIFICATION OF THE EXTERNAL SECONDARY SEXUAL CHARACTERS. Group A. Characters which are useful to the possessor, or to its young, or have an indirect relation to reproduction. Sub-group 1. Specialisations in organs which aid in the finding of individuals of the other sex. Examples, the extra-develop- ment of the antenne in many male moths and beetles, the enlarged and divided eyes of certain flies and May-flies, the enlarged tactile feelers of male Daphnias, the larger or better wings of many male insects, the swimming membrane, in the breeding season, on the hind-legs of Molge paradoxa. Sub-group 2. Specialisations that aid in mating. Examples, the clasping organs of many male crabs, the hectocotylus of octopuses, the expanded tarsi of many male insects, and in general, the accessory copulatory organs of innumerable vari- ous animal species. Sub-group 3. Special size and form of the female due to the extra- development of the ovaries. Examples, in Psychid moths and parasitic Crustaceans. Sub-group 4. Differences connected with care of the young. Ex- amples, mammz of female mammals, brood-pouch of mar- suplals, brood-sacs of male sea-horses, and brood-cavities in the back of male Pipa (a frog). Sub-group 5. Specialisations for defence or offence. Examples, protective coloration of female birds and insects, mimicry by female butterflies, antlers of the stag, strong canines of many male mammals (wild boars, etc.), sting of the female honey-bee, spurs of the cock, greater size and strength of many male mammals and birds. Sub-group 6. Differences in coloration which aid in the recogni- tion of the sexes (“recognition marks” of Wallace). Sub-group 7. Differences connected with various special habits of life. Examples, the pollen-baskets of the worker honey-bees, the winglessness of male fig-caprifying insects (Blastophaga), the large differences between males and females of certain insects where one sex lives parasitically, the other independ- ently, as the scale insects, the Strepsiptera, etc., the beak differences in the New Zealand bird, Heteralocha acutiros- tris, whose male chisels out the hard wood with a short, broad beak, while the female extracts insect larve from decay- ing wood by means of a long, curved beak. Group B. Exciting organs. These are found almost exclusively in the males only, and serve to indicate the sexual excitement of their possessors, and at the same time to stimulate or excite DARWINISM ATTACKED. 109 the females. The excitation of the male is manifest to the female through her senses of sight, hearing, and smell (in each case through one or more of these), and this perception gives rise reflexively to an excitation on the part of the female. Sub-group 1. The male characters may appeal to the sense of sight of the female: (a) by colours, as in the breeding plumage, or coloration, of many birds, fishes, amphibians, and reptiles, or, as in the constant brilliancy of colour and pattern in many butterflies, other insects, and spiders; or (b) by striking form, as the beard and hairy tufts of many monkeys and the extraordinary “horns” and processes of certain lamellicorn beetles ; or (c) by movable processes (often strongly coloured), as the wattles and movable feathers (tail, etc.) of certain birds, swelling cheek or neck sacs of turkeys, etc.; or (d) by strik- ing movements, as the dancing on the ground or tumbling and whirling in flight of certain birds, the mating-time bat- tles of mammals, birds, and fishes, and the “love-dances” of spiders. Sub-group 2. The male characters appeal to the sense of hearing of the females, as the song of birds, the cries and calls of many mammals, frogs, and insects. Sub-group 3. The male characters appeal to the sense of smell of the females, as the odours given off by goats, chamois, musk- deer, beaver, etc., and from the scent-scales (androconia) of many male butterflies. Group C. Reciprocal organs; that is, organs which exist in func- tional condition in one sex but are inherited by the other only in rudimentary and often non-functional form. Examples; the reduced mammz of male mammals, the brood pouch of the male Thylacinus; wingless female butterflies often have a rudimentary sucking proboscis, which in some cases is in- herited by the males without any reduction of the wings; in cases of mimicry by female butterflies, the males often show some traces of the changed colour-pattern; traces of spurs in female pheasants, reduced horns of female antelopes and goats, small “horns” on female lamellicorn beetles, undeveloped stridu- lating apparatus in female crickets, katydids, etc. Group D. Indifferent characters, without any apparent utility. Sub-group 1. Rudimentary organs, which are wholly non-func- tional in one sex, although still functional in the other. Examples, the reduced wings of many female insects, the rudimentary alimentary canal of male Rotatoria. Sub-group 2. Negative characters, that is, those wholly failing in one sex, although present in the other. This lack can be a 110 DARWINISM TO-DAY. primary one, that is, indicate an older phyletic condition, as the absence of antlers in the female deer; or be a secondary one, that is, gradually acquired by progressive reduction, as the loss of wings by many female insects. Sub-group 3. Atavistic characters, as the more marked hairiness on the breast of men as compared with women. Sub-group 4. Correlated characters, which may be called into ex- istence by other organs present; with the female mollusc Anodonta, the shell is more strongly bowed in adaptive correlation with the expanded brood chamber between the gills. Sub-group 5. A large number of secondary sexual characters which are incapable of specific classification, as the minute differences between the sexes in size and habitus; slight dif- ferences in wing form in humming-birds, dragon-flies, and butterflies; small differences in character and number of tarsal and antennal segments of many insects. As Plate justly remarks the foregoing classification can, of course, make no pretension to completeness. But it jeer indicates sufficiently clearly certain important nificance of tke differences among the secondary sexual char- pac acters; differences especially important in con- nection with any attempt to get at an explanation of the why and how of these characters. Such a classification shows that many of these characters have uses which are of a kind directly helpful in the struggle for existence, as the strong antlers of the stags, useful in defence against attacking enemies; the brood sacs of the kangaroos and opossum, use- ful in caring for their helpless young; the milk-glands and teats of all female mammals, the pollen-baskets and wax- glands of the honey-bee which make the workers more effective food-gatherers and food-storers, and the protective colours and patterns of many insects and birds. But others, many others, indeed, of these secondary sexual characters, are either of a kind apparently useless in the struggle for life, or even of a kind actually harmful. Of apparent useless- ness are the reduced wings of some male insects, and the host of slight differences in coloration, pattern, size, or DARWINISM ATTACKED. 11! shape, of different body-parts or of the whole body, the beards and hair-tufts of many male mammals and the combs and wattles of male gallinaceous birds. Of apparent harm- fulness are those ultra-developed pro-thoracic and head processes, “horns,” of stag and other lamellicorn beetles, the conspicuous staring colours of many male birds, the long dangling plumes, the weighty crests, and heavy dragging tails of others, all these parts also usually being dangerously conspicuously coloured. The lively loud song of many male birds, and the dancing and leaping of numerous male spiders and some male birds must also involve some danger to the performers by attracting the attention of their enemies. In fact most of those secondary sexual characters that are classified under the general head of “exciting organs” are apparently of a sort that should be actually disadvantageous in the struggle for existence. They are of a character tend- ing to make their possessors conspicuous and thus readily perceived by their carnivorous enemies. How 1s to be explained the existence of so many and such highly de- veloped structural and physiological characters of this kind, a condition that seems to stand in direct opposition to the theory of natural selection? Darwin’s answer to this ques- tion is contained in his theory of sexual selection. This theory, in few words, is that there is practically a competition or struggle for mating, and that those males are Bee ine. successful in this struggle which are the stron- ory ofsexual gest and best equipped for battle among them- spies selves, or which are most acceptable, by reason of ornament or other attractiveness, to the females. In the former case mating with a certain female depends upon overcoming in fight the other suitors, the female being the passive reward of the victor; in the second case the female is presumed to exercise a choice, this choice depending upon the attractiveness of the male (due to colour, pattern, plumes, processes, odour, song, etc.). The actual fighting among 112 DARWINISM TO-DAY. males and the winning of the females by the victor, are ob- served facts in the life of numerous animal species. But a special sexual selection theory is hardly necessary to explain the development of the fighting equipment, antlers, spurs, claws, etc. This fighting array of the male is simply a special phase of the already recognised intra-specific struggle; it is not a fight for room or food, but for the chance to mate. But this chance often depends on the issue of a life-and- death struggle. Natural selection would thus account for the development of the weapons for this struggle. For the development, however, of such secondary sexual characters as ornament, whether of special plumage, colour, pattern, or processes, and song, and special odours, and “love-dancing,”’ the natural selection theory can in no way account; the theory of sexual selection was the logical and necessary auxiliary theory, and when first proposed by Darwin met with quick and wide acceptance. Wallace in particular took up the theory and applied it to explain many cases of remarkable plumage and pattern development among birds. Later as he analysed more carefully his cases, and those proposed by others, he became doubtful, and finally wholly sceptical * of the theory. The theory as proposed by Darwin was based on the fol- lowing general assumptions, for the proof of each of which a Pursiniad few to many facts were adduced. First, many bases of the secondary sexual characters are not explicable gah by natural selection; they are not useful in the struggle for life. Second, the males seek the females for the sake of pairing. Third, the males are more abundant than the females. Fourth, in many cases there is a struggle among the males for the possession of the females. Fifth, in many other cases the females choose, in general, those males specially distinguished by more brilliant colours, more conspicuous ornaments, or other attractive characters. Sixth, many males sing, or dance, or otherwise draw to DARWINISM ATTACKED. 113 themselves the attention of the females, Seventh, the sec- ondary sexual characters are especially variable. Darwin believed that he had observed certain other conditions to ex- ist which helped make the sexual selection theory probable, but the conditions noted are sufficient if they truly exist. Exposed to careful scrutiny and criticism—an admira-_ ble and convincing example of such scientific and impar- tial criticism is Kramer’s analysis of the Scrutiny and criticism of the Secondary sexual characters of European in- as sects—the theory of sexual selection has been relieved of all necessity of explaining any but two categories of secondary sexual characters, namely the special weapons borne by males, and the special ornaments and excitatory organs of the males and females. For examination has disclosed the fact that males are not alone ° in the possession of special characters of attraction or excitation. Regarding these two categories Plate,’ in his able recent defence of Darwinism, says, “the first part of this theory, the origin of the special defensive and offensive weapons of males through sexual selection is nearly universally accepted. The second part of the theory, the origin of exciting organs has given rise to much controversy. Undoubtedly the presumption that the females compare the males and then choose only those which have the most attractive colours, the finest song, or the most agreeable odour, presents great difficulties, but it is doubtful if it is possible to replace this explanation by a better.” Some of these difficulties may be briefly enumerated. The theory can be applied only to species in which the males are markedly more numerous than the femaies, or in ene which the males are polygamous. In other morenumerous cases there will be a female for each male Sohreenae whether he be ornamented or not; and the unornamented males can leave as many progeny as the ornamented ones, which would prevent any cumula- 114 DARWINISM TO-DAY. tion of ornamental variations by selection. As a matter of fact-in a majority of animal species, at least among the vertebrates, males and females exist in approximately equal numbers. Observation shows that in most species the female is wholly passive in the matter of pairing, accepting the first Female is usy- Male that offers. Note the cock and hens in ally passive. the barnyard. 3 Ornamental colours are as often a characteristic of males of kinds of animals in which there is no real pairing, as ieiacie ces POMS those which pair. How explain by cur on males that Sexual selection the remarkable colours in the tall Jeo breeding season of many fishes, in which the female never, perhaps, even sees the male which fertilises her dropped eggs? Choice on a basis of ornament and attractiveness implies a high degree of esthetic development on the part of the females of animals for whose development in Assumption of er : esthetic develop- this line we have no (other) proof. Indeed this ment inlower choice demands esthetic recognition among animals, : : pad animals to which we distinctly deny such a development, as the butterflies and other insects in which secondary sexual characters of colour, etc., are abundant and conspicuous. Similarly with practically all invertebrate animals. Further, in those groups of higher animals where esthetic choice may be presumed possible we have repeated evidence that preferences vary with individuals. Certainly they do with man, the animal species in which such prefer- ences certainly and most conspicuously exist. In some human races hair on the face is thought beautiful; in others, ugly. Besides even if we may attribute fairly a certain amount of zsthetic feeling to such animals as mammals and birds, is this feeling to be so keen as to lead the female to make choice among only slightly differing patterns of songs? Yet this assumption is necessary if the development DARWINISM ATTACKED, 115 of ornament and other attracting and exciting organs is to be explained by the selection and gradual cumulation through generations of slight fortuitously appearing fluctuating variations in the males. There are actually very few recorded cases where the observer believes that he has noted an actual choice by a Pos spaced. Lemale. Darwin records eight cases among cases of choice birds. Since Darwin not more than half a br emele dozen other cases, all doubtful, have been recorded. Also a few instances, all more illustrative of sexual excitation of females resulting from the perception of odour or actions, than any degree of choice by females, have been listed. In numerous cases the so-called attractive characters of the males, described usually from preserved (museum) specimens, have been found, in actual life, to Some so-called attractive char- be Of such a character that they cannot be noted acters not visible hy the female. For example, the brilliant 1n nature. : colours and the curious horns of the males of the dung beetles are, in life, always so obscured by dirt and filth that there can be no question of display to the female eyes about them. The dancing swarms of many kinds of insects are found to be composed of males alone with no females near enough to see; it is no case of an excitatory flitting and whirling of many males before the eyes of the impressionable females. Of many male katy- dids singing in the shrubbery will not for any female that particular song be the loudest and the most convincing that proceeds from the nearest male, not the most expert or the strongest stridulator? Similarly with the flitting male fire- flies; will not the strongest gleam be, for any female, that from the male which happens to fly nearest her, and not from the distant male with ever so much better, stronger light? Stolzmann finds it difficult to understand, when nearly 116 DARWINISM TO-DAY. related species differ widely in their ornamental plumage, that this should be attributed to a difference in Problem of preference among the females of the related the Andean ; : : : humming-birds, Species. The humming-bird, Schistes perso- natus, lives in Ecuador on the west side of the Andes, in a restricted range of four degrees of latitude. It is distinguished from the nearly related Schistes geoffroy especially in the possession by its male of a brilliant spot over each eye. Schistes geoffroyi lives on the east side of the Andes from Colombia to Central Peru, with a range cover- ing over twenty degrees of latitude, which range is divided into two completely separated regions by the Maranon valley. Now if isolation alone is sufficient to produce a change in the taste of the females, one would expect to find two sorts of males (as far as ornamental pattern goes) in- side this one species. But there is but one kind of male through the whole range. Why is the taste of the female constant through twenty degrees of latitude, while it is changed on the other side of the Andes in a limited range of four degrees of latitude? Another case presented by Stolzmann is even more striking. The Chilian hummer, Eustephanus galeritus, which is green in both sexes, has migrated from the continent to the Juan Fernandez Islands. On Masatierra Island it has changed to Eust. fernandensis, in Masafuera Island to Eust. leyboldi. These two species agree in the females with the original continental form (that is, are green) while the males have become red, but in different pattern in the two species. Eust. galeritus (the Continental form) also occurs on Masatierra Island, in the same form as on the continent, that is, with green male. Now one must presume from this state of affairs that this species (galeritus) has been able to reach Masatierra twice, once long ago—the descendants of the invasion having changed to Eust. fernandensis—and once more recently— the descendants of these later migrants showing as yet no DARWINISM ATTACKED. 117 sign of a transformation of the malecolour. Shall one in this case and others like it, asks Stolzmann, assume a change of beauty-ideal on the part of the females? Much simpler and much more reasonable, according to Stolzmann, is it to see in the change of colour of the males of the earlier migrants the results of the direct influence of the new environment; the islands are distinctly milder and warmer than the continent. Even if the females do choose among the males on a basis of attractiveness, how are the characters of the more at- tractive males to become especially fostered How are more , attractive char- amd accumulated by selection? Do such males acters to be produce more offspring or more vigorous ones fostered ? ; / than the other males, which, though rejected by the first females, find their mates among the females not already mated? Are we to attribute to the more ornamental males a particular vigour? If so, may not that very vigour be the cause of the extra-production of colour or plumage or wattles, etc.? Darwin admits, in order to explain the beginnings of colour and ornament development, a certain degree of differ- _ | ence between the male and female in regard to Darwin's sig- é f : : nifcantadmis- their reaction to environmental influences. If ut so, may not these admitted differences be really sufficient to account for even a pretty high degree of differ- ence in development of secondary sexual characters? The special display of colours, tufts, plumes, spreading tails, and other secondary sexual characters by the males at mating time is an observed fact; the “dances” of cranes and storks, the serenades of the song- birds, the evolutions of the male spiders are all familiar phenomena in the mating season of these animals. And they probably do exercise an exciting effect on the females, and are probably actually displayed for this pur- pose. But does this in any way prove, or even give basis for a reasonable presumption for belief in a discriminating Does display prove choice ? 118 DARWINISM TO-DAY. and definitive choice among the males on the part of the female? And it is this actual choosing which is the neces- sary basis for the theory of sexual selection. How explain the well-known cases of a similar extra- development of plumage in the nuptial season by both Bow éxplald males and females, as in certain herons and ornamentsin other birds? And what of those other cases in females or : — : f common to both Which it is the female that is the brighter-cq- sexes 7 oured individual of the pair? To explain the lat- ter case Darwin assumes that in these cases the males have done the selecting, but even this rather too easy reversal of the situation postulated as a fundamental generalisation of the theory does not explain the first of the questions in this paragraph. Do both sexes among the herons do selecting? Morgan‘ lists twenty objections to the sexual selection theory, several of which are identical with those already mentioned in the foregoing paragraphs, but Pevionites among which are several to which we have not referred. One of these is that “some of the objections that apply to the theory of natural selection apply also with equal force to the theory of sexual selection in so far as the results in both cases are supposed to be the outcome of the selection of individual, or fluctuating, varia- tions. If these variations appear in only a few individuals, their perpetuation is not possible, since they will soon dis- appear through crossing. It would be, of course, preposter- ous to suppose that at any one time only those few indi- viduals pair and leave descendants that have secondary sexual characters developed to the highest point, but if something of this sort does not occur, the extreme of fluctuating variations cannot be maintained. Even if half of the individuals are selected in each generation, the ac- cumulation of a variation in a given direction could not go very far. The assumption, however, that only half of all DARWINISM ATTACKED. 11g the individuals that reach maturity breed, and that all of these are chosen on account of the special development of their secondary sexual characters, seems _ preposterous. Furthermore, if it is assumed that the high development of the new character appears in a large number of individuals, then it is not improbable that its continued appearance might be accounted for without bringing in, at all, the hypothesis of sexual selection.” Again, Morgan well points out that “the development, or the presence, of the esthetic feeling in the selecting sex is not accounted for on the theory. There is just as much need to explain why the females are gifted with an appreciation of the beautiful as why the beautiful colours develop in the males. Shall we assume that still another process of selection is go- ing on, as a result of which those females are selected by the males that appreciate their unusual beauty, or that those females whose taste has soared a little higher than that of the average (a variation of this sort having appeared) select males to correspond, and thus the two continue heaping up the ornaments on one side and the appreciation of these ornaments on the others No doubt an interesting fiction could be built up along these lines, but would any one be- lieve it, and if he did, could he prove it? “Darwin assumes that the appreciation on the part of the female is always present, and he thus simplifies, in appearance, the problem, but he leaves half of it un- explained. “There is another side to the question,” also says Morgan, “the importance of which is so great, that it is surprising that Darwin has not taken any notice of it. If, in order to bring about, or even maintain, the results of sexual selection, such a tremendous elimination of individuals must take place, it is surprising that natural selection would not counteract this by destroying those species in which a process, so useless for the welfare of the species, is going 120 DARWINISM TO-DAY. on. It is curious that this has not been realised by those who believe in both of these two hypotheses. “What has just been said applies also with almost equal force to the development of such structures as the horns of the deer, bison, antelopes, and the brilliant colours of many insects and birds. If in nature, competition between species takes place on the scale that the Darwinian theory of natural selection postulates, such forms, if they are much exposed, would be needlessly reduced in numbers in the process of acquiring these structures. So many individuals would have been at such a disadvantage in breeding, that if competition is as severe as the theory of natural selection postulates, these species could hardly be expected to compete successfully with other species in which sexual selection was not taking place.” Finally to make an end of miscellaneous objections and come to that one which promises to be, if it is not already, . the most serious obstacle in the way of the Experimental ; eae evidence is op- | S€Xual selection theory, it is a fact that all the posed tosextal evidence (though it be little as yet) based on selection theory. ; ; actual experiment is strongly opposed to the validity of the assumption that the females make a choice among males based on the presence in the males of ornament or attractive colours, pattern, or special structures. I may mention especially the striking experiments of Mayer ‘ (which, published in a small entomological journal of limited circulation, have not received the attention that they deserve) on the large Bombycine moth, Callosamia pro- methea. This well-known American moth expands about three and one-half inches and shows unusually pronounced secondary sexual differences as to colour and pattern. The females are reddish-brown in ground colour, while the males are blackish and in the two sexes the pattern is distinctly different. If there is any moth species in which the colours and general pattern of the male ought to be readily obvious 1. Fe DARWINISM ATTACKED. “yer to the female, and in which sexual selection might be pre- sumed to have been the influence in producing a pronounced aa male type 40! preferred pattern, it As this perimentson Species. Mayer’s simple and convincing ex- PIERCE: periments were as follows: Mayer took four hundred and forty-nine pupz (in cocoons) of the moth Callosamia promethea, which had been collected in Massa- chusetts and New Jersey, south to Loggerhead Key in the Dry Tortugas Islands off Florida. This island is separated by many miles of ocean from other land, and is hundreds of miles south of the range of the species. Evidently no interference with Mayer’s experiments could come from outside individuals of this species. The moths issued during May and June in the proportion of about two males for each female. The males of this species seek out the female for pairing and can do this for a considerable distance. As many as several dozen males will find a single female and hover, fluttering, about her. Mayer’s first experiments were directed to the end of determining if the males found the females by sight or by smell. By enclosing females in numerous jars variously arranged and covered or uncovered, it was readily determinable that males never pay any attention to females enclosed in transparent jars so closed as to prevent the escape of any odours from the female, while to females enclosed in boxes or wrapped in cotton so as to be invisible but yet capable of giving odour off into the air males came promptly and hovered about. To locate the organs of scent in the female Mayer cut off abdomens from various females and then placed abdomens and ab- domenless females at some little distance apart. Males came to the abdomens and not to the thorax plus wings, legs, and head parts. Females were proved to increase in attractive power with age, and virgins are a little, but only a little, more attractive than already fertilised females. It was readily proved, by experiments with males whose an- 122 DARWINISM TO-DAY. tennz were covered with shellac, photographic paste, glue, paraffin, etc., that the sense of smell is seated in the antennz. Males with antenne covered with photographic paste did not find females, while the same males with this paste dis- solved off did. Mayer now tried to test the selective action of the female. The male promethea has blackish wings while the females are reddish-brown. In accordance with the theory of sexual selection, the peculiar coloration of the male should be due to the selection of dark-coloured males, so that under this influence the males would become, in successive generations, darker and darker until the present coloration has been attained. Mayer’s own account of his experi- ments and conclusions to test the preferences and selective action of the females is as follows: “In order to test this hypothesis I cut off the wings of a number of females, leaving only short stumps, from which all the scales were carefully brushed. Male wings were then neatly glued to the stumps, and thus the female pre- sented the appearance of a male. Under these circum- stances the males mated with the female quite as readily as they would have done under normal conditions. “T then tried the experiment of gluing female wings upon the male. Here again the mating seemed to occur with normal frequency, and I was unable to detect that the females displayed any unusual aversion toward their effeminate-looking consorts. “It 1s also interesting to note that normal males pay no attention to males with female wings. “In another series of experiments the wings were cut entirely off of males and females and the scales brushed off their bodies; and yet these shabby males were readily accepted by normal females, nor could I see that normal males displayed any aversion to mating with wingless females. DARWINISM ATTACKED. 123 “We are therefore forced to conclude that the melanic coloration of the male has not been brought about through the agency of sexual selection on the part of the female.” More recently Mayer (and Soule) * repeated these experi- ments on a more extensive scale and with some variations woe in character. Fifteen hundred cocoons of Soule’s experi- Promethea were collected in the winter of 1go1- ae o2 and hung in trees so that the issuing moths might fly about unconfined. “About six hundred males emerged from the cocoons and the wings of about one-half of them were painted with scarlet or green ink, while the others were allowed to remain normal in colour. It was evident that the males whose wings were scarlet and green succeeded fully as well in their attempts to mate as did the normal males.” Experiments were also tried with the moth Porthetria dispar, in which the male is brown and the female white. The experiments showed that males with wings painted scarlet or green were accepted as readily as normal males, but that males with the wings cut off were more apt to meet with resistance from the females than perfect males were. From these experiments Mayer and Soule conclude that the mating instinct in the males of C. promethea and P. dispar is a phenomenon of chemotaxis. Sexual selection on the ground of colour alone does not affect it, and there is no associative memory connected with it. To these experiments may be added the observations of Douglass,*” who found that females of the wall-lizard, Lacerta muralis, showed no preference what- ever among the variable patterns exhibited by males in breeding-coat. Diurigen ** observed that male lizards without tails are accepted readily by females. Finally, also, of the nature of objections to the sexual selection theory are the replacing or substutionary explana- Experiments on lizards, 124 DARWINISM TO-DAY. tions of secondary sexual characters which various biol- ogists have offered. These explanations will be presented Alternative ex- in some detail in chapter xi, which is devoted ee ar to an exposition of the various alternative characters, theories proposed to replace or partially to re- place the Darwinian theories. It must be sufficient to say here that the theories proposed to account for secondary sexual characters mostly rest on one or both of two principal basic assumptions; first, that the secondary sexual characters are produced as the result of the immediate stimulus (naturally different) of the sexually differing primary reproductive organs, this stimulus being usually considered to result from an internal secretion of the genital organs acting on certain tissues of the organism; and, second, that the males in most species possess an excess of energy which manifests itself in extra-growths, extra-development of pigment, plumage, etc., and that displays by the males of special move- ments, sound-making, etc., are direct effects or manifesta- tions of sexual excitation. To these explanations should be added the rather far-fetched one of Emery, who believes that many cases of secondary sexual differences are explained by the sudden appearance (mutation) of another form of male or female, the persistence for a while of the two forms side by side, as now exists in numerous dimorphic species (espe- cially among insects), and then the gradual dying out (kill- ing out by natural selection) of one of the two old original forms (the one like the other sex), thus leaving the other, or aberrant form. The ideas of Cunningham,” who does. not believe that any selection of fortuitous variation can account for secondary sexual characters, may also be re- ferred to. In a book of over three hundred pages this author lists and describes—according to principal animal groups—a host of secondary sexual characters, and pro- poses a theory to account for them. “The direct effects,” writes Cunningham, “of regularly recurrent stimulations are DARWINISM ATTACKED. 125 sooner or later developed by heredity, but only in associa- tion with the physiological conditions under which they were originally produced. This is the explanation of the limita- tions of particular modifications not ‘merely to particular species or kinships, but to particular periods in the life of the individual, to a particular sex and even to a particular season of the year in that sex.”’ The author believes that an examination of secondary sexual characters shows that they develop at places and in parts which are at the time of sexual excitement unusually directly stimulated by exertion or contact or use. These secondary sexual characters are “in many cases not merely limited to the period of mature life but actually to that part of the year in which the repro- ductive organs are active, that is to the breeding season.” In closing this chapter given up to objections to the Dar- winian theories of natural and sexual selection, attention may be called to Wolff’s ** objection to natural Importance of selection based upon the dependence of the na- the sexual selec- . : tion theory asa tural selection theory on the sexual selection support ofthe theory for explanation of the existence of orna- natural selection theory, mental characters, and of all these secondary sexual characters, which are useless or even apparently disadvantageous in the life-and-death inter- ‘specific struggle for space and food. As Wolff looks on the ‘sexual selection theory as wholly discredited, he finds this necessary dependence on it by believers in natural selection for the explanation of those characters just mentioned strong evidence for the weakness of the natural selection theory. — APPENDIX. * Kramer, Paul, “Theorie u. Erfahrung ; Beitrage zur Beurtheilung ‘des Darwinismus,” 1877, Halle. An interesting paper criticising ‘the selection theories from two points of view; first, on the basis of a mathematical treatment of the Darwinian hypothesis (especially that of sexual selection), the author taking Darwin’s premises and -by a mathematical handling of them showing that they do not lead 126 DARWINISM TO-DAY. to the Darwinian conclusions; and, second, on a basis of the care- ful scrutiny of the facts of secondary sexual differences, the author finding sexual selection wholly unable to account for the great majority of secondary sexual characters among animals. 7 A ate, x, “Uber die Bedeutung des Darwin’schen Selections- prinzips,”’ pp. 107-111, 2d. ed., 1903, Leipzig. * Darwin outlined the theory of sexual selection in the “Origin of Species” (1859), but first treated it at length in the “Descent of Man” €Parts- Il :and Ill), 187%, * Wallace, A. R., “Tropical Nature,” chap. v, 1878; and “Darwin- ism,’ chap. x, 1891, London. * Doane (Ent. News, Vol. XVIII, pp. 136-138, 1907) has described the striking behaviour during mating of certain Dolichopodid flies (Scellus virago, n. sp.) observed by him on the salt marsh flats of San Francisco Bay, near Stanford University. In these matings it is the female which is the active sex in pursuing and exciting the other. * See note 2. "Morgan, T. H., “Evolution and Adaptation,” chap. vi, 1903, New York. This chapter is an exhaustive attack on the theory of sexual selection. * Mayer, A. G., “On the Mating Instinct in Moths,” Psyche, Vol. IX, pp. 15-20, 1900. °* Mayer, A. G., and Soule. C. G, ‘Some Reactions of Cater- pillars and Moths,” Jour. Exper. Zool., Vol. III, pp. 427-431, 1906. *? Douglass, N. G. “On the Darwinian Hypothesis of Sexual Selection,’ Nat. Science, Vol. VII, pp., 398-406, 1895. ‘' Duirigen, ‘““Deutschlands Amphibien u. Reptilien,” p. 89, 1897. * Cunningham, J. T., “Sexual Dimorphism in the Animal King- dom,” 1900. ‘8 Wolff, Gustav, “Beitrage zur Kritik der Darwin’schen Lehre,” p. 21 ff., 1898, Leipzig. A bitter but keen and trenchant critical ex- position of certain weaknesses in the selection theories. He criti- cises the theory of sexual selection in the following words: “An diese Falle reiht sich vielleicht am besten die Betrachtung der Folgen, welche frithzeitige Sterilitat auf die Ausbildung von Wolf's exposi- sekundaren Geschlechtscharakteren ausubt. Wir kon- tion of weak- nen ja diese Erscheinungen auch in gewissem Sinne nesses insexual zu den Rickbildungen rechnen; sie haben aber insbe- selection. sondere auch das mit den vorigen Fallen gemeinsam, dass wir hier ebenfalls einen im individuellen Leben des Organismus sich abspielenden Vorgang beobachten konnen, der nach der Selek- tionstheorie nicht eintreten durfte. “Nach der Selektionstheorie entstehen ja sekundare Geschlechts- DARWINISM ATTACKED. 127 merkmale dadurch, dass eben Individuen des einen Geschlechts, bei welchen durch zufallige Variierung eine Andeutung solch eines Merkmals da war, mehr Chancen hatten, sich fortzupflanzen und diese Eigenttmlichkeit auf die Nachkommen ihres Geschlechts zu vererben, von denen dann durch den gleichen Prozess immer diejenigen zur Fortpflanzung ausgewahlt wurden, welche die betref- fende Eigentiimlichkeit am starksten besassen. Es soll also zwischen jenen Gebilden und dem Geschafte der Zeugung an und fiir sich nicht der geringste Zusammenhang existieren. Dann ist aber schwer erklarlich, warum jene sekundaren Geschlechtsmerkmale sich haufig nur zur Zeit der Geschlechtsthatigkeit bilden und nachher wieder verschwinden, wie z. B. der Hochzeitskamm der Tritonen. Aber geben wir einmal zu, das sei bloss ein zufalliges Zusammen- treffen, indem eben diejenigen zur Fortpflanzung gelangten, welche gerade zufallig um die Zeit der Brunst eine bald wieder zufallig verschwindende Verstarkung des Kammes besassen. Es ist zwar unmoglich, sich dies, insbesondere das Verschwinden des Kammes, vorzustellen, weil ja, wenn auch das spatere Verschwinden des: Kammes dem Tiere irgend einen Vorteil gebracht haben sollte, dieser bei der Selektion in keiner Weise sich geltend machen konnte, oder doch nur in Bezug auf das Individuum aber nicht auf dessen. Nachkommen, aber nehmen wir einmal an, das sei alles in Ordnung:. wie erklart sich dann, dass, z. B. beim kastrierten Hirsch kein Geweih sich entwickelt, dass der kastrierte Mensch hohe Stimme behalt, keinen Bart bekommt u. s. w., u. s. w.? “Auch andere Riickbildungen, welche nach AufhGren der Ge- schlechtsthatigkeit normal sich einstellen (z. B. Aufhéren der Flim- merbewegung im Uterus des Weibes nach Aufhoren der Menstrua- tion, Verlust der Flugel nach der Begattung bei Insekten,* etc. ), bieten. der Selektion die grossten Schwierigkeiten, denn wenn hier die Ruckbildung einen Vorteil bote, welcher die Auswahl der Indi- viduen, bei welchen diese Riickbildung auftrat, herbeifiihrte, so konnte dieser Selektionsprozess doch erst nach der Fortpflanzungs- zeit eintreten, auf die nachfolgenden Geschlechter daher von keinem Einflusse mehr sein. “Der unbestreitbare Zusammenhang, welcher zwischen der Ge- schlechtsthatigkeit und den sekundaren ’ Geschlechtsmerkmalen besteht, ist nun aber nicht etwa durch das Wort “Korrelatior’ erklart. Es ist natiirlich richtig, dass eine Anderung irgend eine andere im Gefolge haben kann, dass es also korrelative Abande- rungen giebt, aber ist denn damit vielleicht erklart, dass eine bestimmte zweckmassige Abanderung nun auch eine andere fir *In diesem letzteren Fall ist vielleicht doch ein Vorteil ftir die Art durch Vermittlung der Brutpflege denkbar. 128 DARWINISM TO-DAY. den jeweilig vorliegenden ganz speziellen Fall nititzliche Abande- rung bedingt? Korrelative Abanderungen beziehen sich ja in den meisten Fallen, wo wir von solchen sprechen, auf ganz bestimmte Verhaltnisse der Aussenwelt. Sich zur Erklarung solcher Erschein- ungen mit der Konstatierung eines Gesetzes der Korrelation zufrieden geben, heisst einfach eine praestabilierte Harmonie zwischen der Entwicklung der Organismen und den Verhaltnissen der Aussenwelt annehmen. Das Ratselhafte ist ja zunachst nicht der Umstand, dass es uberhaupt Korrelationserscheinungen giebt (wenngleich wir naturlich auch hierflr ebensowenig, wie fur irgend eine andere Lebenserscheinung eine Erklarung haben), sondern der Umstand, dass eine Eigenttimlichkeit eine andere korrelativ im Gefolge hat, die eben gerade fiir besondere aussere Zwecke vorteilhaft ist. Hier kann die Selektionstheorie nichts ausrichten, denn der Selektionsprozess hat doch keinen Ein- fluss auf die Variierungsgesetze, zu welchen die Korrelationsge- setze gehoren; diese mtssen vielmehr vorausgesetzt werden. “Es giebt ubrigens Thatsachen, die mir darauf hinzudeuten schei- nen, dass die korrelativen Beziehungen noch viel verwickelter sind, und dass korrelative Beziehungen gar nicht immer auf die Ent- stehung korrelativer Abanderungen zurtickzufthren sind, sondern dass, was ja noch viel ratselhafter ist, eine Korrelation erst sekundar erworben werden kann, wie folgendes Beispiel zeigen diirfte. “Von den drei verschiedenen Individuen des Bienenstaates hat nur die Arbeitsbiene an der Innenflache des Tarsus regelmassige Borstenreihen, sogenannte Burstchen. Da die Arbeitsteilung immer eine hohere Differenzierung ist, so kann es keinem Zweifel unter- liegen, dass urspriinglich bei allen Formen die Beine gleich waren. Kaum zu entscheiden dtrfte wohl die Frage sein, ob ursprunglich sich die Btirstchen sowohl bei mannlichen als auch bei weiblichen Individuen differenzierten. sodass das Fehlen derselben bei den Drohnen als Riickbildung betrachtet werden miusste, oder ob die Biirstchen gleich von vornherein als sekundares Geschlechtsmerkmal der Weibchen auftraten. Im erstern Fall ware also die Bildung primar in keinerlei Korrelation zum Geschlechtsapparate gestanden, diese miisste vielmehr erst spater erworben worden sein. Im zweiten Fall waren die Biirstchen als zum Geschlechtsapparate korrelative Bildungen entstanden, aber in beiden Fallen musste eine Anderung des Korrelationsverhaltnisses eingetreten sein, die Korrelation musste namlich eine reziproke werden: die Entstehung von Biirstchen ist zwar an das weibliche Geschlecht geknupft, jedoch in der Weise, dass die Biirstchen nur auftreten, wenn die Geschlechtsorgane nicht zur Ausbildung kommen.” CHAPTER Vik. DARWINISM DEFENDED. In taking up the defence of Darwinism it should be noted in the first place that the anti-Darwinians are without the walls; that theirs is the burden of attack; that Renata. against them is the presumption of right. The defendersof § J)arwinians are in the castle, theirs simply the Darwinism. : . ; ; é necessity of withstanding or repelling really significant and truly threatening attack; theirs the strength of possession and the presumption of truth. Much anti- Darwinism is futile and easily answered; much was an- swered by Darwin * himself before ever the anti-Darwinians formulated it; much other anti-Darwinism is directed against a position which Darwinism, true Darwinism, has long seen the inadvisability, indeed the impossibility, of holding. With certain concessions made, what use of further struggle over them? Thus by answering briefly the insignificant and undamaging part of anti-Darwinian attack, or by referring to Darwin’s own answers of this, and by indicating clearly and definitely the concessions that Darwinism is ready to make, has made, indeed—these humiliating concessions, if humiliation is in them, only being made necessary because *Darwin’s anticipation of the criticisms of his theories, and his own open-minded and detailed answers to these criticisms, should, of course, be held clearly in mind by any student of fiur-und- gegen Darwinismus. but many of these answers concern objections which present-day Darwinism has largely conceded as valid, and most of the others touch matters on which modern biological re- search has thrown much new light. So that it is perhaps fairer to the Darwinian theories to set out the attitude of present-day Darwinians. For a detailed critical consideration of Darwin’s own answers, see Morgan, “Evolution and Adaptation” (1903). 129 130 DARWINISM TO-DAY. of the ill judgment and rash enthusiasm of certain too ardent and too conspicuous friends of Darwinism, the so- called neo-Darwinians—with this salutary restriction of diffuseness in account, “Darwinism Defended” may be con- fined to fewer pages than have been devoted to “Darwinism Attacked” without suggesting by this brevity any necessary weakness in the Darwinian position. Let us give our first attention to the Darwinian conces- sions—those concessions which the biological world has Mechs practically agreed have been made necessary by against ultra- the steady criticism of the exaggeration and oe magnification, almost wholly post-Darwinian in appearance, of the Darwinian factors in evolution. It is strange, but wholly true, that the modern reaction and revolt against Darwinism is chiefly due to the activity and attitude taken by certain of its over-ardent friends. Weismann, by denying validity to any other evolutionary factor than the natural selection of purely congenital variations, and by the development to an illogical and untenable extreme of his theory of the independence and continuity of the germ- plasm, precipitated the revolt and furnished the enemy with the very weapons needed to overcome neo-Darwinism. The evolution champion Haeckel, although not at all a Weismannian Darwinian, has also by his daring and reck- less speculative development of certain phases of evolution- ary thought, especially in its relation to sociology and religious philosophy, and by his obstinate adherence to, and reiteration of, certain long discredited more strictly biological dogmas of evolutionary science, contributed to produce an irritation and antagonistic activity among biologists, especially in Germany, which has helped make many friends for the anti-Darwinian party. “Der Haeckelismus in der Zoologie,’* as Semper originally phrased it, is the object of a curiously bitter and often- expressed contempt in German biological circles. I fancy Haeckel. > pst fe Lsyyv AhyvVi, Fs } q ) 2rpael frra—o> | ay DARWINISM DEFENDED. 131 that this feeling really depends not so much on Haeckel’s attitude and speculative writing in zoology as in his unpar- donable intrusion into politics and religion; the Social- Democrats and the Free-Thinkers have found a helpful and willing scientific champion in Haeckel. And this is sin superlative in rigorous minds! As a matter of fact, how- ever, biologists generally are agreed that Haeckel’s daring speculations and reckless progress in advance of positions grounded on observed fact have been, in a way, always repre- hensible and dangerous to the fair fame of biological science. But, to my mind, biologists may also fairly agree that this very activity and speculative daring of Haeckel have in- spired much genuine biological investigation (for the sake of denying or confirming his speculations) and have led to a salutary reactionary critical attitude toward other biologi- cal speculations and hypotheses. It is a rare ism in any science or philosophy that yields nothing good. Weismannism is wholly different from Haeckelism. It has only in common with it that it is, in part, also daringly speculative. But the speculations primarily interest neither Free-Thinkers nor Social-Democrats. They have to do with the ultimate structure and behaviour of protoplasm, especially germinal protoplasm, and with the intimate proc- esses of heredity and variation. Weismann first attempted to free Darwin’s general theory of modification and species-forming from all taint of La- marckism; an attempt which resulted in his apparently successful overthrowal of the com- monly accepted theory of the inheritance of acquired characters, a theory or assumption which is a fundamental and indispensable part of the general Lamarck- ian theory. (Lamarckism and the inheritance of acquired characters are explained and briefly discussed in chapter x of this book.) On the strength of this success Weismann pro- posed the doctrine of the Allmacht of natural selection; that Weismann’s theories. 132 DARWINISM TO-DAY. is, that natural selection alone is capable of explaining all the phenomena and facts of species-forming and descent. At ‘the same time he developed and announced the theory of the continuity of the germ-plasm,’ which, in a word, is the theory of an absolute separation of the germ-plasm from the soma-plasm and consequently the thorough independ- ence of this germ-plasm from all influence and control of the soma-plasm, 7. ¢., all that part of the body other than the germ cells. This carried with it the assumption that all the phenomena of heredity and variation depended solely on the germ-plasm and that the germ-plasm of any individual is derived, unmodified by any somatic influences, directly from the germ-plasm of its ancestors. This assumption in turn led to the logical but startling conclusion that all the capacity or possibility of variation for all time was present in that primitive ancestral germ-plasm from which the germ- plasm of all many-celled animals has been derived. But such a nearly infinite capacity for furnishing variations demanded the postulation of an equally nearly infinite capacity for ac- tual physical or structural complexity on the part of the germ- plasm itself, for biologists insist on a physical mechanism for all the physiological phenomena they find in life. So Weis- mann assumed an interesting but invisible and apparently non-testable composition of germ-plasm out of life-units, called biophors, grouped into particles of.a second order called determinants. The biophors are taken to be much larger and more complex units than chemical atoms, or even than molecules. They are groups of several to many molecules, each biophor, however, still ultra-microscopic, and represent- ing a single characteristic of cell-life. Each biophor is as- sumed to possess the essential attributes of living substance, viz., the capacity to assimilate food, to grow, and to repro- duce itself. The groups of biophors called determinants are larger, of course, but yet invisible to our best micro- scopes, and each represents all the characteristics which a DARWINISM DEFENDED. 133 cell of any particular single kind has. Thus one kind of determinant represents all the attributes of the red blood corpuscles, another of the nerve-ganglion cells, another of a certain type of epithelial cells, and so on. Each determinant has also the power of assimilating food, growing and re- producing itself by division. Now the possibility of repre- senting in the germ-plasm the nearly infinite capacity to vary characteristic of this plasm has for its physical or mechanical basis the minute size of the biophors and deter- minants coupled with the inconceivably many combinations of different kinds of biophors possible in the make-up of the determinants which are, as already said, the actual structural representatives of, or better, controllers or producers of, the various kinds of body tissue and organs. These three general assumptions of Weismann, namely, (1) the composition of germ-plasm out of ultimate life-units called biophors (grouped into determinants) which deter- mine all the physical characteristics of the individuals into which the germ-plasm develops; (2) the isolation (from the soma) and the continuity (from generation to generation, from beginning to end) of the germ-plasm; and (3) the Allmacht of natural selection, which involves the discarding of all other factors of modification and species-forming than the natural selection of the slight fluctuating congenital variations produced (in an unknown manner) by infinitest- mal changes in the determinants of the germ-plasm—these three fundamental and important Weismannian assumptions, accepted more or less nearly completely by Wallace and a See number of other English biologists, and by a ism and Neo- few naturalists of Europe and America, con- Lamarckism. = ctitute the essential position of what is called neo-Darwinism. This neo-Darwinism immediately found many capable antagonists, and as most of the antago- nists were believers in some parts of the general theory of adaptation and species-forming first proposed by 134 DARWINISM TO-DAY. Lamarck, their position came to be known as _ neo- Lamarckism. Herbert. Spencer in Eneland, Packard, Osborn, and others in America, and Eimer in Ger- many were prominent exponents of the anti-Weisman- nian views. The debate was spirited, and engaged many biological writers, and interested the general reading public in the larger problems of biology more than it has been interested at any other time since the great struggle immediately following the publication of Darwin’s “Origin of Species.” The best known part of the general debate was that carried on directly by Weismann and Spencer in the Contemporary Review (1893 and 1894). The general result of the struggle between neo-Darwin- ism and neo-Lamarckism can be fairly stated to be, that Weismann’s assault on the theory of the in- secre a heritance of acquired characters was in general successful; while, on the other hand, the assault of the anti-Weismannians on the assumptions of the isola- tion and continuity of the germ-plasm and of the Allmacht of natural selection forced from Weismann and his follow- ers, one by one and slowly, such radical concessions as to make the latter doctrine utterly untenable, and to rob the other of most of its significance in the consideration of modi- fication and species-forming. The assumption of the com- position of germ-plasm out of biophors and determinants is of course merely an interesting speculation, or tentative hypothesis, which, because it is untestable by scientific ob- servation or experiment, cannot be debated to any particular advantage. Weismann himself, in 1895, definitely conced- ing that natural selection is radically weak at its base, being incapable of explaining the beginnings of useful variations and the development (which actually occurs) of indifferent ones, proposed a new and radically un-Darwinian theory under the name of Germinal Selection. This theory (ex- plained in chapter viii of this book) although including the ey ea DARWINISM DEFENDED. 135 _word selection in its name is fundamentally different from natural selection in the Darwinian sense, and is indeed an admission of the existence of variations maintained (not by means of natural selection) along definite lines, result- ing in a real orthogenesis. It attempts to offer a causo- mechanical explanation of such un-Darwinian development. By the theory of germinal selection, which is based abso- lutely on the assumption that the plasm is composed of biophors and determinants or at least of physical life units of similar type and function, Weismann hopes to strengthen four weak places in the general position of neo-Darwinism. The theory explains (1) how in Panmixia (another Weis- mannian contribution to neo-Darwinism, for account of which see chapter viii) the degeneration of useless organs is brought about, (2) how it is that for the continued development of any certain complex adaptation exactly the right variations shall appear at the needed time, (3) how co- adaptation comes to exist, and finally (4) how variations may come to be developed along fixed lines or in definite directions without the aid of personal selection. Whether the theory of germinal selection explains these four things or not, what is to us for the moment the chief interest of the theory is that it is put forward by Weismann, who is dis- tinctly the foremost neo-Darwinian, to explain just these things. For that makes of these things concessions that the neo-Darwinians, the ultra-selectionists, feel forced to offer. It should be noted, however, that perhaps Weismann does not speak for all ultra-selectionists, for example, Lloyd Morgan, Ray Lankester, and other English * Darwinians. Certainly his theory of germinal selection is accepted by few of them. On the whole, however, I think I speak perfectly fairly in saying that the believers and defenders of the natural selection theory to-day admit in large measure the valid- ity of those criticisms which are directed at the inca- 136 DARWINISM TO-DAY. pacity of Darwinism, in its long familiar form, to account for the development of variations and modifications up to the advantageous or disadvantageous stage. They admit also the actual existence, and in abundant measure, of species differences which are of indifferent character, that is, of no especial utility, and make the consequent admission that such species differences cannot for the most part be explained by natural selection. And they also concede, or at least most of them, including Weismann, do, the force of the criticism that the assumption of the occurrence of the tight variations at the right time is a necessity for the development by selection of many if not most specialisations of qualitative and of coadaptive character, which assump- tion in turn demands an explanation of causes anterior to selection. And finally most selectionists concede that selection can- not make new species by relying on the extremes of series of fluctuating or Darwinian variations because of the inevitable extinguishing or swamping of these extreme variations by inter-breeding with the far more abundant average or modal individuals of the species. Hence all those objections recorded in the chapters on “Darwin- ism Attacked” which have to do solely with this inca- pacity of natural selection to make use of variations too small or too few or purely fortuitous, or with the incapacity of selection to explain hosts of indifferent, non-adaptive species differences which actually exist, and hence with the certainty of its not being the only factor, if indeed a prin- cipal factor, in the formation of species, need not be re- discussed, at least to any length, in this chapter. We may also largely neglect those objections which are directed against the purely hypothetical assumptions and the extreme positions of the neo-Darwinians. Many of these assump- tions, such as that of the absolute isolation and independence from the soma of the germ-plasm, are not a part of Dar- Po DARWINISM DEFENDED. 137 winism proper, and the extreme position of the believers in the Allmacht of selection was certainly never taken by Dar- win himself. In fact, most of neo-Darwinism has been. deserted by its one-time followers, and most conspicuously and perhaps most radically by Weismann himself. Thus, with these two categories of objections listed in the “Darwinism Attacked” chapter put to one side, for the moment at least, by admitting the validity of one category and showing the inapplicability of the other as regards its relation to true Darwinism, we have left to us. The objections to consider those remaining objections which needing answer. ; eqe are made (1) against the capability of selec- tion’s making any use at all of the familiar and always occurring fluctuating variations called Darwinian, (2) against its capacity to explain coadaptive and highly com- plex adaptations, especially those which seem as if they could be of advantage to the organism only in fully developed or specialised state, (3) against its inability to account for overdeveloped specialisations, (4) against the possibility of selection’s explaining qualitative differences in species, and many-branched descent (quantitative differ- ences and linear descent seeming to be the only kinds pos- sible to it), (5) against its capacity to explain complete or extreme structural degeneration of useless organs and parts, (6) against the reality and extreme rigour of the struggle for existence and personal selection (an essential foundation of the selection theory), (7) against the sexual selection theory, particularly in its capacity as a supporting prop of the natural selection theory, (8) against the reliance by the selectionists on the homology or analogy which they hold to exist between natural selection and artificial selec- tion, and finally to consider those curiously positive and definite declarations of such radical anti-Darwinians as Wolff, Korschinsky, and others that natural selection is a vagary, having no claims to existence either on a basis of 138 DARWINISM TO-DAY. observation or logical reasoning, or that if it exists its whole influence is directly inimical to changes and evolution rather than of a nature to produce and foster them. The most comprehensive, fairest, and most effective recent attempt to gather together and meet seriatim the objections and criticisms of Darwinism is (as already stated in the chapter on “Darwinism Attacked”) that of Ludwig Plate,’ and I have therefore given considerable space in this chapter to direct quotations from the answers and discussions of this modern Darwinian champion. The objection made that natural selection can make no use at all of the small fluctuating Darwinian variations is really Poke wider application of the really valid objection objection that that such variations cannot, or can only rarely, fuctuating vari- Offer material for the production by selection of ations are too slight tobeof new organs and that for many adaptations pi bea they are too slight to be of use and hence cannot serve as handles for selection. As a matter of fact, however, many adaptive modifications are purely quan- titative, not necessarily involving any qualitative change at all. Increase in general size, or in any one dimension of an organ or part, meaning often an increase of strength on the part of the animal, in the capacity for aggres- sion or defence, in swiftness, in flight, running or swim- ming, in reaching or digging or climbing or leaping— such an adaptive modification might well be brought about by selection of even very inconsiderable enlargements or strengthenings of one or more organs or parts. Wherever the modification is in a directly linear path, and an advantage is possible through even slight advances or regressions along this line, natural selection will find in the Darwinian varia- tions a means of fostering and perfecting this modification. There are just two requirements necessary for the Darwin- ian variations to meet in order to serve as handles for natural selection: they must be variations actually suff- DARWINISM DEFENDED. 139 ciently useful and advantageous to turn the scale in the intra- or inter-specific struggle for existence in favour of the individuals possessing them, and they must occur in suffi- ciently many individuals to avoid being swamped or extinguished by cross-breeding: that is, they must be useful enough to be selected and numerous enough to perpetuate themselves. Do Darwinian variations ever meet these re- quirements? Unfortunately our proof is rather indirect: observation reveals their abundance, but does not actually show their utility.” To answer the question our judgment and reason, based on our knowledge and experience of the existing conditions of animal and plant life, will have to be trusted for answer. How real is the rigour; how keen the struggle ; how crowded the square yard or square mile; how great or how little must be the differences in a part to give a life-or-death decision in the competition? Each naturalist must answer this for himself, and the layman must take the general consensus of opinion of the natural- ists, if there is one, for his answer. The objection to the linear and quantitative character of the Darwinian variations has been recently especially urged by de Vries in connection with his exposition eee a of the theory of species-forming by mutations. cerning the The selection theory reckons with linear hence linear and quan- ; ate Sate titative charac- Strictly quantitative variations, says he, and yet ees is presumed to create new forms for which in reality qualitative variations are necessary as a basis, so that in fact selection can only increase or diminish, add to or subtract from characters already in existence and cannot create anything new, this appear- ance of new characteristics being, however, precisely the principal peculiarity of new species, taken by and large. This position of de Vries has been discussed by Plate’ as follows: “T call attention in advance to the fact that de Vries understands by ‘linear variations’ what are more usually 140 DARWINISM TO-DAY. known as individual, fluctuating or continuous variations. He has chosen this name because the single characteristic can change toward but two directions; that is, toward the plus, or toward the minus direction. In contrast to this kind of variation stand the sudden and discontinuous leap- like changes or mutations which have been for the first time carefully investigated by the praiseworthy labour of de Vries, hitherto having been familiar indeed under the names ‘single variations’ or ‘sports,’ but little studied. Con- cerning these linear variations de Vries writes: “The statis- tical method of the study of variation has now been so generally followed as to make its principles familiar without further discussion, and they may be considered as accepted. The chief principle indicated by the use of the frequency curves is that the characteristics vary in but two directions, that 1s toward plus or toward minus. The old vague con- ception of an all-sided variation of the single characters has disappeared of its own self.’ “As highly as I appreciate the great service of de Vries in relation to our knowledge of the suddenly appearing changes, heritable in high degree, I must nevertheless op- pose him in his conclusions touching the selection theory. In the first place this theory does not reckon alone with linear variations, but also with mutations, if they appear, for it takes the changes as given material without troubling itself about differences in their mode of origin. In the second place it is not correct that a character cannot so change itself through simple addition or reduction that it may not be, in the customary classificatory limits, looked on as a new character. A smooth leaf, a leaf with few small hairs, and one with a thick wool show only linear variations, but in spite of that they may very well serve as character- istic of different species. Nearly related butterflies—recall the Vanessas and Lycenas—often show the same funda- - mental characters of pattern and form, so that they are dis- DARWINISM DEFENDED. 141 tinguished only by plus or minus variations. Indeed one may consider the whole endless manifoldness of organic combinations as only representing greater or lesser num- bers of atoms of the same few elements which are bound to- gether in one molecule. In the third place the statistical studies of variation have not shattered in any respect the conception of an all-sided variation of the single characters, but indeed on the contrary have rather shown that all the parts and attributes of organisms that are accessible to observation appear to us more or less different in different individuals. This all-sided variability has nothing to do with the statement that each single variable element can vary always only toward plus or toward minus. Blue flower petals can appear more or less blue and at the same time reveal their indeterminate, fortuitous, or all-sided variability in differences of form, hairiness, thickness, structure, etc. The same indeterminateness which de Vries claims for his mutations is characteristic also of linear variations.” Tayler,” a Darwinian defender, has discussed this objec- tion as follows: “This objection appears to me to be one of the most weighty of all the objections which have been raised to the selectional hypothesis, and it is further an extremely | difficult objection to satisfactorily reply to; first, because it is almost impossible to say in what form of organism the earli- est variations appeared, and without this no judgment on the value of any small variation can be of use; secondly, it is equally essential to know the kind of environment which such an organism was living in; and lastly, if we were fully acquainted with the character of the organism and its environment it would still be difficult to form any adequate opinion on the value of such a variation, owing to the fact that this apparently simple organism would differ so widely from our own functional activity and life that any conclu- sions formed on comparative methods of testing its powers, 142 DARWINISM TO-DAY. etc., would be extremely likely to be fallacious. If, however, we keep in mind the facts that (1) the whole and not merely a part of the organism is selected, and that, therefore, each variation does not require to be of the same value as if selection depended on it alone; (2) specialisations are largely quantitative, between man at one extreme of de- velopment and a simple unicellular organism at the other, the difference, though very great, is mainly due to the fact that man is a huge multicellular colony; this difficulty will be much simplified. To estimate the quantitative difference it is necessary to endeavour to determine the specialisation of an individual cell in one of those collective specialisations or organs: the difference between a cell in, for instance, the cerebral cortex of man and the character of an ameeba is no doubt great, but the amceba reacts to stimuli, though in a less specialised form, just as the cortex cell does ; in the same way the reaction to light in the mammalian eye is not a new development—it has its beginnings in the preference for light or darkness shown by many unicellular organisms. These two points, that selection is organismal and that specialisations are as, or more, largely quantitative than qualitative, weaken if they do not abolish all those diff- culties to natural selection that are founded on this objec- tion, and it is further necessary to recollect that no specialisa- tion has yet been found which has not a primitive counter- part in the earliest known forms of life.” With regard to the objection that because natural selec- tion working with fluctuating Darwinian variations 1s working only with linear or quantitative varia- Answer tothe tions and therefore cannot produce many- objection that selection cannot branched descent (which is certainly the kind ‘samen lent Of descent that exists) but only straight-line or and discontinuity mono-typic descent, it is obvious that the Dar- ciaeataa winian answer to this is partly that of the answer to the objection discussed in the last paragraph. In “it pn > 7 en 3 n 1 DARWINISM DEFENDED. 143 addition it is partly that of the answer to the objection to be mentioned in the next sentence. This related objection is that while natural selection may produce continuous gradatory adaptive change or evolution it cannot produce discontinuity in the series, 7. e., cannot produce separated distinct species. This objection receives an answer which is of the nature of an admission that natural selection wholly unaided really cannot differentiate species. It must call to its aid some isolation or segregation factor, and as isolation is certainly most commonly effected through migration and geographic means, it is usually this factor of geographic isolation that natural selection must be accompanied by to form new species. As Plate says: “Any particular phase of the struggle for existence extinguishes all those indi- viduals which do not possess certain absolutely necessary characteristics. By this means there is produced a common type. And only when some means of isolation is added can the splitting of the species into two or more forms result. Natural selection can only transform a species gradually and develop it in a continuous forthright line; alone it cannot produce a divergent, tree-like evolution. This results from geographic, biologic, or sexual isolation, which is in most cases a form of the extensive manner of working of the struggle for existence. But selection can aid in the differ- entiation of a species into two or more forms, as the following examples show. When all average or median-sized in- dividuals of a species are killed out there remain only the smallest and the largest, by which we may assume that the first are saved because they can most readily conceal them- selves, while the latter find in their ereat size a sufficient protection. On the ground of this difference in size perhaps both forms will be inclined to keep apart from each other and if to this is added a somewhat differing habit of life, two races can arise which in course of time will become distinct species. From a butterfly kind of very variable 144 DARWINISM TO-DAY. ‘colour-tone all brown individuals might disappear for some special reason while both the lighter and darker individuals might persist. Now if in consequence of this contrast a racial feeling should develop between the light individuals on the one hand and the dark ones on the other, the differ- entiation into two species is already begun. If a snail species living in fresh water is so harassed that it can only maintain itself when its individuals move either into the region be- tween tide-lines or into the deeper water, this would lead to morphological differentiation, as we can indeed actually note in the case of the chitons.”’ The objection that the existence of coadaptive and highly complex adaptations, especially those which seem as if they could be of no possible advantage to their pos- Prarieneum sessors except in their present fully developed cerning complex Or specialised state, is one which. unfortunately aera cannot be definitely refuted or proved by ever so much ingenious explaining or discussion in the face of the lack of what we certainly do not now possess, namely, direct observational or experimental evi- dence. For such specialisations as elaborate mimickry, or the electric organ of the torpedo, etc., which are of appa- rent advantage only in perfected state, the selectionist is forced to admit that the objector has apparently a good case, but for the gradual specialisation of many highly complex structures and specialisations through the long-continued selection of slight advantageous variations, Darwin and his followers have offered ingenious and plausible explanations. For the case of so complex and coadaptive a specialisation as the eye and its function in the vertebrates or in the insects and crustaceans, the possible evolution, by slight additions and modifications, from simple pigment fleck to the present marvellous visual organ, a logically irrefutable Darwinian argument can be made out on the basis of the real and constant utility and advantage of even very slight steps DARWINISM DEFENDED. 145 forward. And so with many other complex specialisations, although in almost all these cases it is necessary, as Darwin says, to let the reason conquer the imagination. That is, the reasoned explanation explains, although one recoils con- stantly before the almost inconceivable actuality of the phenomenon. Plate has recognised this objection as one of the really weighty ones and has given much attention to its considera- tion. His conclusion is that it is necessary to rely to a ereater or less extent on the Lamarckian factor of the inheritance of somatogenic characters acquired in the life- time of the individual through the effects of use, or disuse, or other functional stimuli. This is, of course, direct aban- donment of the position maintained by such strict selection- ists as Weismann and Wallace, although Weismann himself, in order to answer the objection without having recourse to reliance on Lamarckian factors, introduces his new theory or hypothesis of germinal selection to aid natural selection in the difficulty presented by the objection. Lloyd Morgan’s* answer to this objection consists chiefly of the formulation of the theory of orthoplasy (explained in chapter viii of this book). It is, briefly, that every organism, from its somatic and germinal aspects, exhibits two tendencies of variability. The somatic variability is determined largely or at least modified largely by environmental influences ; therefore those organisms whose somatic tendency is pre- dominantly plastic will survive under altered conditions of environment, where those organisms of a less easily mod- ifiable tendency will be eliminated. Now if somatic changes rarely or never become germinal, 7.e., are inherited, the mod- ifications of the parental organisms cannot be transmitted to their offspring, but those offspring that happen to be endowed with germinal variations in the same direction as the acquired but not transmitted modifications would start their life with a predisposition favourable to their 146 DARWINISM TO-DAY. environment and therefore favourable to more complete modification of the somatic side of the organism; this tend- ency being accumulative under constant conditions, coinci- dent variability would arise by the process of selective elimination and preservation, without the need of the assumption of use-inheritance, which assumption facts appear to negative. Against the criticism that natural selection cannot explain over-developments of specialisation, that is, the carrying unnecessarily far of advantageous structural Answer to the . . objection con- aNd functional development, as illustrated by cerningover- the great antlers of stags and moose, the micro- specialisation, . : ; ‘ mee scopic fidelity of simulation and mimicry, and the nearly identical equivalence of the right and left halves. of bilaterally symmetrical animals, the selectionist has little to offer except the always pertinent questions: Are we sure that the case in point is one of over-development, of unnec- essary specialisation? And although the paleo-zoologists may be pretty emphatic in their declarations that the ex- tinction of the Irish stag and of the unwieldy cretaceous reptiles was directly due to over-specialisation, they cannot prove it. And there you are, says the Darwinist. The difficulty that natural selection has with structural degeneration is admittedly a real one. The strict Darwinian answer has to be that retrogression is produced Consideration . ; ‘ of the objection ¢ither by reversed selection, that is, that when concerning de- by a change in the life habits or external condi- i datas tions a certain function or organ becomes inju- rious, as in the case of insects on small exposed islands where the wind might carry the flying ones off into the ocean, selection, on the basis of advantage, would tend to preserve the ones most poorly equipped for flight; or it has to be that when the function of an organ is, because of change in habit or conditions, once neglected or discon- tinued, that is, the organ is no longer used, any slight varia- DARWINISM DEFENDED. 147 tion toward reduction of the organ would be of advantage because of the saving in food which would be effected! But this is simply carrying the logic of the principle of advan- tage to an illogical extreme, an extreme impossible to accept. So Weismann devised the ingenious explanation of pan- mixia or cessation of selection to account for degeneration. ‘That is, a rigid and persistent selective activity is as neces- sary to maintain a specialisation as it was to produce it. But even Weismann has found this explanation inadequate and has, therefore, found a final and sufficient explanation in his new theory of germinal selection. This last theory, a refinement of Roux’s theory of the battle of the parts, is ingenious, suggestive, and thoroughly interesting, but un- fortunately it is founded on certain assumptions concerning the ultimate make-up of the germ-plasm and the behaviour of the unit parts of it, the truth of which simply cannot be tested. A strictly neo-Darwinian answer, that is, one based solely on selection, is therefore hard to give. Plate,”’ after an effective adverse criticism of the influence of the Weis- mannian panmixia as an explanation of the structural reduc- tion or atrophy of parts, concludes that such reduced or rudimentary organs are to be explained “through the inherited effects of disuse, the inherited effects of the influ- ences of external factors, the inherited effects of the influence of economy in nutrition, and, in a few cases, through re- versed selection. The first three principles are cnly admissi- ble under the assumption of the actuality of the inheritance of individually acquired characters, and the fourth principle has only a very subordinate importance.”” This is equivalent to saying that the strict selectionist has no sufficient answer to the objection under present consideration. One seems forced to rely on Lamarckian factors for anything like a satisfactory explanation of actual structural reduction of ‘useless organs. Tayler,”’ however, offers an explanation for both ontogenic and phyletic degeneration, based on the e 148 DARWINISM TO-DAY. “known facts of nutrition.” The interested reader may find this explanation in the appendix to this chapter. Doubt is expressed by some biologists of the reality and fierceness of the struggle for existence which is an essential part of the selection theory. De Vries ex- Answer to the . . : objectionsurged Presses the belief that the intra-specific strug- against therig- ole, that is, the struggle and competition among our ofselection. » |. . , individuals of the same species, has been much overrated. And a few observations ** have actually been made which indicate that for certain species this struggle is at least not rigorous enough to give to the slight Dar- Winian variations a determining value as to the character of the surviving individuals. Here again the proof for the Darwinian point of view is not one so much of observa- tion—although actual life-and-death combats between indi- viduals of a single species, and innumerable examples of the preying of one species on another are familiar—as it is a proof of reasoning. The fact of an over-production of eggs and embryos, that is, of reproduction by multiplica- tion, is undeniable. The lack of existing space and food for all individuals, if all should live the ordinary span of life peculiar to the species, is demonstrable by mathematics. The consequent conclusion of these two established premises is a struggle for existence. That is the sound Darwinian position. The principal answer of the Darwinians to the criticisms levelled at the theory of sexual selection is, that however ineffective the theory is to explain many of the Answer to the 8 ae objections to the Phenomena it is called on to cover, it is at least ae so much more reasonable and satisfying as an explanation of some of the phenomena, that is, some of the categories of secondary sexual characters, such as the ornamental plumes and colour-patterns of birds, the sound-making organs of insects, etc., than any alternative explanation that has been offered, that until a better expla- DARWINISM DEFENDED. 149 nation be presented the theory of sexual selection should not be discarded. That no other explanation of many, if not most, of the phenomena in question has anything at all convincing or satisfactory about it, or has met with any. general acceptance on the part of naturalists, is the plain truth. If we feel it imperative to give our adherence, with certain reservations, to any explanatory hypothesis of sec- ondary sexual characters, Darwin’s theory is the one to have first claim on us. As a matter of personal opinion I feel no necessity for any such attitude and am willing to look on most of the phenomena connected with the general problem of secondary sexual characters as quite inexplica- ble on the basis of our present knowledge of bionomics. The specific answer of Lloyd Morgan** and other Dar- winians to the objection that choice on the part of the female assumes an esthetic recognition and preference which it is doing violence to our knowledge of animal psychology to assume, should not be overlooked. This answer is, put summarily, that this so-called choice is one of impulse, not deliberation: it is an imperative reaction to a sufficient stimulus: and what determines that the stimulus from one male shall be sufficient while that from another 1s not, is the degree of pronouncedness or effectiveness of the ornament, or call, or behaviour. It is a choice “which is determined by the emotional meaning of the conscious mean- ing. And it is the reiterated revival of the associated emotional elements which generates an impulse sufficiently strong to overcome her instinctive coyness and reluctance. It is a perceptual choice arising from impulse rather than an ideational choice due to motive and volition.” Regarding Wolff’s argument that an explanation of these characters is very necessary to the acceptance of the theory of natural selection there is little to say in rebuttal. Natural selection confesses itself inadequate to explain those ex- traordinary characters and conditions by which the males 150 DARWINISM TO-DAY. of many species of mammals, birds, insects, spiders, etc., differ from the females. And if sexual selection does not explain them then some other explanation is necessary. But the lack of this explanation does not invalidate the general theory of natural selection as one of the factors in organic evolution and indeed one of the most important and far- reaching ones. The difficulty of a satisfactory discussion of the objection that natural selection rests too largely on an assumed likeness to artificial selection, while the differences in Consideration the two processes, especially in their results, are of the objection ; that natural se- too radical to allow us to rest any confidence ee on this apparent homology, is, that despite the assumed analogy Several thousand years through which artificial hiaertiuai selection has been followed and studied we still know too little of the real character of it, especially of its results. Most selectionists now admit that the argument for natural selection on the basis of its sim- ilarity to artificial selection has been given too great promi- nence and relied on too strongly, but that the observed processes of the one do teach us much of truth about the unobservable processes of the other the Darwinians firmly maintain. As Plate says, “The great value of artificial selection consists in this, that it shows first, that a gradual cumulation of characteristics in definite directions is actually possible through successive selections, and second, that it has afforded us a rich mass of data concerning variation, inheritance, and the influence of changing intrinsic condi- tions or influences. When Darwin showed what a high plasticity the domestic animals possess he built for his theoretical explanation of descent an indubitable necessary foundation, for the changes which a domestic animal passes through in the hands of man must of necessity be able to be called forth in similar manner in the feral animals by the creative force of nature, for the domestic animals cer- DARWINISM DEFENDED. 151 tainly have come from the wild ones. It is also true that man has made use of only natural factors, and whoever will compare the extraordinary creatures of the deep sea with even the most bizarre of our cultivated races, will see that the fluxing life-conditions of free nature can modify or reform the animal world in no less degree than the intelli- gence of man can do it... . “Recently de Vries,’* in his book on ‘Mutations,’ has tried to deny the worth of the selection principle, and although I fully recognise the high worth of his contribution to science based on such extensive series of experiments, yet I must oppose him in this position. In various places in the book he writes that nothing fixed can be produced by selection, and that therefore it can have no importance as a working factor in descent. For example, in the introduction (p. 6) he says: ‘Artificial selection never, as far as experience reaches, leads to the origin of new complete types.’ The reversion of modified domesticated races is indubitable, and de Vries himself has brought forward new illustrations of this fact which has been so long known. But convincing proof that natural selection cannot lead to constant forms cannot be deduced from these observations, because they refer in all cases to forms which have been highly modified in the course of a few years or decades, so that the pre- sumption lies close at hand that there has not been sufficient time really and lastingly to modify the original heredity established by centuries. Many facts indicate that the in- tensity of heredity depends upon the number of generations, that is, upon time. Long-inherited characters are difficult to eradicate; recent ones easy. We can, therefore, not expect to meet such a constancy in the products of a century as we find in Nature. Many gradually selected races of doves are now almost entirely constant, that is, no longer revert to the primitive race when they are inter-bred. The way in which the reversions appear shows that the duration 152 DARWINISM TO-DAY. — of time plays an important role in inheritance (heredity). Schubeler found in his studies of the translation of the northern boundary of the grain culture that the characters newly acquired (heavier and earlier ripening seeds) per- sisted for several generations when the forms were replanted in the original [more southerly] habitat. De Vries in six years selected corn which had an average of 20 rows of kernels instead of the original 12 to 14, and held the plants at this height of production through five years. When he then planted seed from a 16-rowed ear, the average of the ears gathered from this planting was in the first generation still at 20 rows, and sank only in the next two years again to 14 to 16. If he had continued his selection longer he would have arrived at a more nearly constant form. De Vries himself says: “When the selection ceases, the selected characteristics drop away and in practically the same length of time which was necessary for the production of the new race, that is within a few generations.’ From this it follows that a domestic race produced by slow persistent selection through many thousands of generations would show the same relative constancy or fixity as natural species, the majority of which also must have originated slowly, for otherwise the appearance of new species would be often observed. If one wishes to be very conservative in this matter one may declare: in the light of our present knowl- edge we cannot say that artificial selection gives us any safe means of judging just what degree of constancy [fixity] can be attained by its means; but it is not fair to say that be- cause up to the present only a partial constancy has been reached through artificial selection, natural selection cannot have led to the production of constant species. All culti- vated races have been relatively quickly, some indeed very quickly, selected ** and, therefore, they strike back very quickly. This, however, need not be assumed for the slowly arisen products of natural selection.” DARWINISM DEFENDED. 153 Tayler,’* making a general defence of the natural selection theory, says: “To realise how far the theory of selection is Resivecta: capable of explaining the facts of organic evo- eral defense of lution, it is necessary to bear in mind the natural selection. HoFor an excellent detailed critical account of these general, as well as the several accessory theories (amphimixis, polar bodies, etc.) of Weismann, see Romanes’s “An Examination of Weismann- ism,” 1893. *It is of interest to note that the strongest defenders of neo- Darwinism to-day are the English naturalists. Americans mostly lean toward neo-Lamarckism; the Germans are divided. * Plate, Ludwig, ‘““Uber die Bedeutung des Darwin’schen Selec- tionsprinzip und Probleme der Artbildung,” 2d ed., 1903. © Prof. Weldon, an English Darwinian, has recorded (Nature, — Sept. 22, 1898) an extremely interesting and much discussed statis- tical and experimental study of the presumable action of natural selection working on slight fluctuating quantitative variations. “I can only attempt to discuss,” says Prof. Weldon, “the importance of small variations, and the rate of organic change, in the one case which I happen to know. The particular case I have myself studied is the variation in the frontal breadth of Carcinus menas [a small shore-crab]. 158 DARWINISM TO-DAY. “During the last six years my friend, Mr. Herbert Thompson, and I have studied in some detail the state of this character in the Weldon’s ex- Small shore-crabs which swarm on the beach below periments on the laboratory of the Marine Biological Association, Carcinus. at Plymouth. “T will show you that in those crabs small changes in the size of the frontal breadth do, under certain circumstances, affect the death- rate, and that the mean frontal breadth among this race of crabs is,. in fact, changing at a rate sufficiently rapid for all the require- ments of a theory of evolution. “In Table IV [omitted], you see three determinations of the mean frontal breadth of these crabs, expressed in terms of the carapace-length, taken as 1,000. You see that the mean breadth varies very rapidly with the length of the crab, so that it was neces- sary to determine it separately in small groups of crabs, such that the length of no two crabs in a group differed by more than a fifth of a millimetre. The first column of the table shows you the mean frontal breadth of twenty-five such groups, between Io and 15 millimetres long, collected in 1893. These crabs were measured by Mr. Thompson. The second column shows you the mean frontal breadth in twenty-five similar groups of crabs, collected in 1895, and also measured by Mr. Thompson. You see that in every case the mean breadth in a group of crabs collected in 1895 is less than it was in crabs of the same size collected in 1893. The third column contains the result, so far as it is yet obtained, of my own measure- ment of crabs collected this year. It is very incomplete, because the 1895 crabs were collected in August and September, and I was anxious to compare them with crabs collected this year at the same season, so that there has not yet been time to measure the whole series. The measurements are sufficient. however, to show that the same kind of change has taken place during the last three years as that observed by Mr. Thompson in the interval between 1893 and 1895. Making every allowance for the smallness of the numbers so far measured this year, there is no doubt whatever that the mean frontal breadth of crabs from this piece of shore is considerably less now then it was .in 1895 among crabs of the same size.* “These results all relate to male crabs. The change in female *JT shall, of course, consider it my duty to justify this statement by more extensive measurement as soon as possible. In the mean- time I may say that I have measured other small groups of crabs, male and female, from the same place, at different seasons of the rt 1896-98, and the results agree with those recorded in the table DARWINISM DEFENDED. 159 crabs during this time has been less than the change in male crabs, but it is, so far as my measurements at present permit me to speak, going on in the same direction as the change in male crabs. “T think there can be no doubt, therefore, that the frontal breadth. of these crabs is diminishing year by year at a rate which is very rapid, compared with the rate at which animal evolution is com- monly supposed to progress. “T will ask your patience for a little while longer, that I may tell you why I feel confident that this change is due to a selective destruction, caused by certain rapidly changing conditions of Plymouth Sound. “On either side of Plymouth itself a considerable estuary opens. into the Sound, and each of these estuaries brings down water from the high granite moorlands, where there are rich deposits of china clay. Those of you who know Dartmoor will remember that in rainy weather a great deal of china clay is washed into the brooks and rivers, so that the water frequently looks white and. opaque, like milk. Much of this finely divided china clay is carried down to the sea; and one effect of the breakwater has been to increase the quantity of this fine silt which settles in the Sound itself, instead of being swept out by the scour of the tide and the waves of severe storms. ; “So that the quantity of fine mud on the shores and on the bot- tom of the Sound is greater than it used to be, and is constantly increasing. “But this is not all. During the forty or fifty years which have gone by since the breakwater was completed, the towns on the shores have largely increased their population; the great dockyard. at Devonport has increased in size and activity; and the ships. which visit the Sound are larger and more numerous than they were. Now the sewage and other refuse from these great and growing towns and dockyards, and from all these ships, is thrown into the Sound; so that while it is more difficult than it used to be for fine silt to be washed out of the Sound, the quantity thrown into. it is much greater than it was, and is becoming greater every day. “Tt is well known that these changes in the physical conditions. of the Sound have been accompanied by the disappearance of ani- mals which used to live in it, but which are now found only outside the area affected by the breakwater. “These considerations induced me to try the experiment of keeping crabs in water containing fine mud in suspension, in order to see whether a selective destruction occurred under these circumstances. or not. For this purpose, crabs were collected and placed in a large vessel of sea-water, in which a considerable quantity of very fine: 160 DARWINISM TO-DAY. china clay was suspended. The clay was prevented from settling by a slowly moving automatic agitator; and the crabs were kept under these conditions for various periods of time. At the end of each experiment the dead were separated from the living, and both were measured. “In every case in which this experiment was performed with china clay as fine as that brought down by the rivers, or nearly so, the crabs which died were on the whole distinctly broader than the crabs which lived through the experiment, so that a crab’s chance of survival could be measured by its frontal breadth. “When the experiment was performed with coarser clay than this, the death-rate was smaller, and was not selective. “T will rapidly show you the results of one or two experiments. The diagram [omitted] shows the distribution of frontal breadths, about the average proper to their length, in 248 male crabs treated in one experiment. Of these crabs, 154 died during the experiment, and 94 survived. The distribution of frontal breadths in the sur- vivors is shown by the lower curve in the diagram, and you see that the mean of the survivors is clearly below the mean of the original series, the mean of the dead being above the original mean. “Two other cases, which are only examples of a series in my possession, show precisely the same thing. “These experiments seemed to me to show that very finely divided china clay does kill crabs in such a way that those in which the frontal breadth is greatest die first, those in which it is less live longer. The destruction is selective, and tends to lower the mean frontal breadth of the crabs subjected to its action. It seemed to me that the finer the particles used in the experiments, that is to say, the more nearly they approached the fineness of the actual silt on the beach, the more selective their action was. “T therefore, went down to the beach, where the crabs live, and looked at the silt there. This beach is made of moderately small pieces of mountain limestone, which are angular and little worn by water. The pieces of limestone are covered at low tide with a thin layer of very fine mud, which is much finer than the china clay I had used in my experiments, and remains suspended in still water for some time. Under these stones the crabs live, and the least disturbance of these stones raises a cloud of very fine mud in the pools of water under them. By washing the stones of the beach in a bucket of sea-water, I collected a quantity of this very fine mud, and used it in a fresh series of experiments, precisely as I had before used china clay, and I obtained the same result. The mean frontal breadth of the survivors was always smaller than the mean frontal breadth of the dead. DARWINISM DEFENDED. 161 “T think, therefore, that Mr. Thompson’s work, and my own, have demonstrated two facts about these crabs; the first is that their mean frontal breadth is diminishing year by year at a measur- able rate, which is more rapid in males than in females; the second is that this diminution in the 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. “T see no shadow of reason for refusing to believe that the action of mud upon the beach is the same as that in an experimental aquarium; and if we believe this, I see no escape from the con- clusion 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.” These observations and conclusions of Professor Weldon have been the subject of much discussion. The adverse criticism has, on the whole, seemed to be successful in discrediting the case as an example of any such clear-cut action of natural selection, as Weldon seems to hold it to be. J. T. Cunningham (Natural Science, Vol. XIV, pp. 38-45, 1899) concludes, after a critical analysis of the work, that ‘““Weldon’s observations may be completely explained by variations in the amount or rate of growth. The difference in different years would be at once explained if the amount of change in frontal breadth was constant for each moult, while the amount of growth was variable. The fact is, that in 1893 crabs of a given frontal breadth were larger than in 1895 and 18098; and I have shown that the summer of 1893 was exceptionally fine and warm. Either the warmth alone, or warmth and food together, very prob- ably made the crabs grow more in that year for the same number of moults. On this view the broad-fronted crabs died in the expe- Timents with clay and mud because they were younger and weaker. In the same way the crabs that moulted in the bottles possibly grew more than those in the sea, because they were kept in warmer water and supplied with more food. Therefore they were, after the moult, larger than those in the sea of the same relative frontal breadth. “The change described is not, if terms are used correctly, a change in the character of the species, but merely a change in the rate of development. The variations investigated are not individual differ- ences, since each individual in the course of its growth passes through each one of the variations in its own person. It has not been shown that the change has gone on continuously for five years, or that it has taken place only in waters where there is much mud. If tadpoles of the same size were found to have shorter tails 162 DARWINISM TO-DAY. in one year than in another, few biologists would draw the con- clusion that the result was due to the selective destruction of those with the longest tails. The more probable explanation would be that those with the shorter tails were in a more advanced stage of their metamorphosis.”’ 7 Plate, L., “Uber die Bedeutung,” etc., pp. 31-32, 1903. ® Tayler, J. L., “The Scope of Natural Selection,” Nat. Science, Vol. XV, pp. 114-129, 1899. * Morgan, C. Lloyd, “Factors in the Evolution of the Mammalia,” Nat. Science, pp. 97-101, 1892. ° Plate, L., “Uber die Bedeutung,” etc., pp. 159-160, 1903. 1 Tayler, J. L., ‘The Scope of Natural Selection,” Nat. Science, Vol. XV, pp. 114-129, 1899. I quote as follows: ‘In the development Tayler's ex- of the individual we see a disappearance of structures, planation of dee which appear to become, with advancing development, generation by —useless, almost parallel to the gradual disappearance of natural selection. rudiments, etc., in the history of the species evolution. And a common explanation for both of these series of phenomena can, I believe, be satisfactorily found in the known facts of nutrition. Growth of any tissue would seem to depend on three conditions, a stimulus of the part adequate to promote functional activity, a proper food supply, and efficient removal of products produced by that particular tissue’s activity. There is abundant evidence to prove that a tissue tends to degenerate if its own excretory products are not removed; the evil effects produced by fatigue products in muscle and other tissues on the activity of the tissue itself, prove that this factor must be of great importance where- ever it is found to occur. Just as the growth and development of bacteria are interfered with, and finally altogether checked by the accumulation of products of their own activity, so a tissue in the higher organisms has its activity impaired and its power lessened when for some reason diminished elimination of its own metabolic products occurs. Now both in the development of the individual and the race we see an alteration of structure, a gradual transition from the less to the more specialised, and in this gradual transition there must be, as I endeavoured to prove in my answer to the last objection, an alteration in the line of functional activity of the parts, and that, owing to this fact, a tissue that was necessary in the earlier stages became less and less so as specialisation advanced, the whole tendency of the specialising organism being continually and increasingly against the earlier, less specialised, stages. It will thus happen that every structure which is becoming useless, owing to its deficient specialisation, whether in the history of the race or the individual, will have two adverse sets of conditions to contend DARWINISM DEFENDED. 163 _with—one, defective elimination of its own tissue products, owing to its becoming increasingly removed from the growing organismal specialisation of food products, while secondly, for this same reason, its own food supply will become less and less suitable. This theory would apply equally to germinal and somatic development and atrophy of structure; there would thus, through the alteration of functional activity of the whole organism, be brought about elimina- tion of all structures not in the line of evolution; and, therefore, organismal selection alone, if this theory is sound, would be able to explain the complete disappearance of rudiments, the various forms of development and atrophy, without calling to its aid climatic inheritance, panmixia, and ee or any other form of particular Scan * See the account of the observations of Kellogg and Bell in the appendix of chap. iv ** Morgan, C. Lloyd, “Animal Behaviour,” p. 2609. ““ De Vries, H., “Die Mutationstheorie,” 2 vols., 1901, 1003. ** Plate, in a later briefer treatment (‘“‘Darwinismus kontra Muta- tionstheorie,” Archiv f. Rassen- und Gesellschaft-Biologie, Vol. III, Plate's expla- PP- 183-200, 1906) of some of the offered objections to nation of charac- Natural selection refers to this matter from a slightly ter fixity indo- different angle. “So sehr der Ziichter danach streben mestic animals. muss, erblich konstante Formen zu erhalten, um der Muhe der bestandigen Auslese enthoben zu sein, so wenig spielt dieser Punkt in der freien Natur eine Rolle. Hier findet eine nie nachlas- sende Zuchtwahl statt, wodurch der betreffende Charakter auf einer gewissen Hohe erhalten und vor Riickschlag bewahrt wird. Welcher Grad von Konstanz nun auf diesem Wege im Laufe von Tau- senden von Generationen erzielt werden kann, ist eine zurzeit noch ungeloste Frage, die ihrer Natur nach wohl kaum mit Sicher- heit beantwortet werden kann. Jedoch lehrt die Tier- und Pflanzen- zucht, dass der Rtickschlag nach dem Aufhoren der Selektion um so spater und um so seltener eintritt, je langer und je intensiver der Zuchtungsprozess vorher betrieben worden ist. Daraus ist zu schliessen, dass die langandauernde Zuchtwahl, welche die Natur ausubt, jenen relativ hohen Grad von Erblichkeit zu erzeugen vermag, welcher den Spezies-Charakteren im allgemeinen zukommt, denn vollig konstant sind diese bekanntlich auch nicht.” ** Tayler, J. L., “The Scope of Natural Selection,” Nat. Science, Vol. XV, p. 119 ft, 1899. CHAPIER WIL DARWINISM DEFENDED (CONTINUED) : PLATE’S CONCILIATORY DEFENCE. THE foregoing consideration of the answers of the Dar- winians to the objections urged against the effectiveness of the selection theory as an explanation of evolution makes no pretence of having included, or even referred to, all the arguments offered by the defenders, and it is only fair to note that by no means all Darwinians and neo-Darwin- lans agree to making the concessions listed in the early part of the chapter. Some refuse a certain one or two of these concessions, some another or others, some indeed will make no admissions at all. With these last we are past arguing. The discussion assumes too much an “‘it is, it isn’t” character to be particularly illuminating or pro- gressive. But because of those who concede in considerable measure, and deny in some measure, the validity of those chief objections to the species-forming capacity of natural selection, the general character of the ground on which this last stand for the old flag is being made should at least be indicated. This half-surrendered but still not quite deserted position is perhaps most clearly to be seen through the smoke of Plate’s con- | battle by fixing one’s eyes on the representative sideration of the foure of Ludwig Plate, a strong Darwinian, objections to = © = selection, but one not blinded by prejudice or with ears wilfully closed to the calls of reason. In his recent elaborate discussion * of Darwinism, so often already referred to and quoted from in these present chapters, he groups under the head of wesentliche Einwdande (important objections) the 164 DARWINISM DEFENDED. 165 attacks on the species-forming capacity of natural selection, which are based on (1) the slightness and inutility of the fluctuating Darwinian variations, and (2) the improbability of the right variations appearing at the right time to make possible the development of specialisations of qualitative and coadaptive character. In a discussion of some length | (pp. 32-77), mostly quite fair and unprejudiced, he brings out the best and strongest arguments that the faithful Dar- winians have to offer to reduce the force of at least, if not to answer satisfactorily, even for themselves, the most effective attacks on the capacity of selection. In very condensed form I present in the following paragraphs the essential points in these defensive arguments. In regard to the first objection, namely, that the very slight or small differences in organs and functions which result from the fluctuating or Darwinian varia- The objection .. ‘ to the slightness tions cannot be sufficiently advantageous or of Darwinian = disadvantageous enough to afford “handles” variations, ; : ‘ for natural selection, that is, cannot be of life- and-death-determining value, Darwin devoted, in his “Origin of Species,’ a whole chapter of discussion and argument to show that in many cases even the slightest of differences may conceivably (it is of course a matter practically incapa- ble of proof by observation or experiment) be sufficient to turn the scale, in a rigorous competition, one way or the other. In many other cases such differences could not, even to Darwin, appear sufficient to be of a life-and-death advan- tage or disadvantage. But Darwin too often, Plate admits, confounded mere usefulness * with life-and-death-deciding usefulness (or non-usefulness). However, for many cases Plate maintains that the slight Darwinian variations can serve as handles for selection, particularly in periods of unusual rigour of competition or fierceness of struggle (either active or passive): ex- amples are, slight differences in the speed of preyed-on 166 DARWINISM TO-DAY. animals when pursued by an enemy, or slight differences in the length of neck of the giraffe in time of scarcity of foliage, or slight differences in the effectiveness of the organs of sense at times of approaching danger, or in endurance of cold, heat, hunger, dryness, etc., or in the clothing of hairs or feathers, the number of capil- laries in the skin, or richness of glandular secretion, and the like, in times of special stress of weather. ‘“Dodel- Port * has shown that microscopically fine hairs are capable of keeping plant-lice away from leaves or buds, and that very slight differences in the specific gravity of the seeds of water-plants may determine whether these seeds sink to the bottom and consequently germinate or not. For the long flights of migratory birds or for birds like our house-doves which protect themselves from birds of prey by swift flights upward to great heights, every smallest amount of advan- tage in the pneumaticity of the bones will be of worth and finally of vital advantage, just as every racing bicyclist knows by experience that for his record-breaking at- tempts he must have a machine in which every part is made as light as possible, for the effects of weight are cumu- lative in course of time.” And Plate fills a couple of pages with other similar cases. ‘‘Whoever scrutinises the life of nature and of man with biologically trained eye sees over and over again the coming of great effects from slight causes. The average of accidents in factories increases in proportion to the age of the workers, because muscular strength and keenness of the sense organs decrease with increasing age. In each age-class the difference is but slight, but in spite of that it demands its sacrifice. Nageli, in a paper concerning the abundance of tuberculosis, showed that among 500 dead human bodies examined 97 per cent. showed traces, at least, of tuberculosis. That is, practically every adult human is tainted by this disease. Now how often must slight differences in body structure, life habits, DARWINISM DEFENDED. 167 hygienic conditions, yes, even in temperament, determine whether there shall be healing or death? The iridescent colours of many male birds, butterflies, and certain parasitic copepods (Sappharina), are certainly of a nature to pro- duce a great effect on the eye, but these colour effects are not the result of special pigments but of microscopically minute structural conditions. In Africa the tsetse-fly * ex- tends over large regions, and only those cattle with a skin of a certain thickness, so that the tiny proboscis of the fly cannot penetrate it, can live in these regions immune from the fatal attacks of the pest. Many poisons work in almost infinitely weak dilution—a 1-200,000 solution of ricin, for example, is able to kill mice.” | Plate presents a second type of answer to the objection by calling on certain aids or auxiliary principles by whose in- fete fluence a difference at first unimportantly small may aidslight gradually comes to be transformed into one of ree: selective value, or may reach this stage sud- denly by means of a change in life habits. This may come about “through correlation,’ that is, through that unknown law of growth by which an indifferent organ may be so bound up with or related to a useful organ’ that it, the indifferent organ, is perfected along with the useful organ as this latter is developed or specialised through selection. All organs of an animal are intimately related to and influ- enced by one another: each is in relation to the other just as to the outer world. How close this inter-dependence is, is most easily appreciated by one in his own case when sick: a constipation causes headache, a slight diarrhoea affects the composition of the urine, etc. The correlation can be so intimate and important, as the case of the secondary sexual characters shows, that its origin and development depends directly on particular definite stages of the related organs.” In the case of many animals the appearance of various curi- ous and large modifications of legs, wings, skin, feathers, 168 DARWINISM TO-DAY. hair, etc., etc., depends on the various stages of development reached by the reproductive organs. Now these secondary organs or modifications thus produced through the influence of other organs may be for a while slight and indifferent in character, but yet safely maintained. When they reach a stage of utility or of positive disadvantage they will then be further perfected, or on the other hand be extinguished, by selection. The principle of the change of function (Functions- wechsel) first elaborated by Dohrn,’ is also called on by eee Plate to play an important part in explaining ciple of change how an organ of considerable specialisation can ac be shown to have been developed by selection, although the function it is now performing seems to be one that could have been useful only in a perfected state and hence could not have made the organ so constantly ad- vantageous in all the slow and gradual stages of its evolution as to be of selective value in its beginning stages. Dohrn’s principle is stated as follows: “An organ can, in its service of a certain definite useful function, be developed by natural selection to a certain stage. Simultaneously a second func- tion (Functionserweiterung) can have developed, due to some special peculiarity or condition of the position, struc- ture, or capacity for movement, which may have a value in another direction from that of the first function. Thus the appendages of crabs serve often special functions in rela- tion to respiration, copulation, and care of the eggs or young, while their original locomotory function may still be maintained or may be more and more surrendered in favour of the new functions.” Numerous other specific ex- amples are obvious enough to any student of biology. Now the new functions in many cases become the more import- ant so that there in time results a complete change of func- tion which wholly alters the physiological character of the organ, and in many cases it is difficult to see (if one does DARWINISM DEFENDED. 169 not know the phyletic history of the organ and the function) just how selection could have developed such an organ by slow degrees from slight beginnings. But the secret of the explanation, which is a perfectly consistent Darwinian explanation, lies in the Functionswechsel phe- nomenon. “Indifferent characters can suddenly become of selective value through change of environmental conditions or of life-habits. The cranial sutures are certainly of no vital importance with the reptiles and birds, but they can be of very great importance to the viviparous mammals as adapta- tions for passing the pelvis during birth. Lacerta vivipara has, perhaps, no advantage through its viviparousness over its nearly related species in our country, but in Scandinavia it has to thank this peculiarity alone for its success in life, because the development of its young is rendered inde- pendent of the sun by it. The nectaries were probably at first useless to the flowers; from that moment, however, when the insects learned to know them as food reservoirs and unwittingly insured cross-pollination by their visits to them, they became of the greatest importance and the indi- rect cause of the origin of the colour brilliance of the flowers. “There are organs of universal character which can be- come modified in most widely differing directions. Thus the tail of the mammals, originally a long, evenly-haired organ, can, without going through any very elaborate changes, be modified into a bushy steering-rudder of special use in climbing from branch to branch; or by the outgrowth of a terminal tuft be changed into a flying fan; or by the par- tial loss of the hair become a grasping organ, or a balancing organ, or an aid in leaping, a rudder in swimming, or a cover against rain and cold (Myrmecophaga jubata). The append- ages of crabs, the cirri of the annelids, and the teeth of mam- mals are further examples of a similar plasticity and capacity 170 DARWINISM TO-DAY. for modification in the most manifold ways, in which the first stages are often of immediate use.” Following these suggestions as to the aid that selection may have from various helping conditions to make its :; starts, Plate discusses as further similarly help- Fe soles ful conditions or auxiliary principles three most herited results important matters, namely, the effects of con- of use, from or- : 1a thogenesisand tinued use on parts, the principle of orthogen- oe esis, and the facts of sudden discontinuous variation. But as these three categories of biological phenomena and principles are exactly those, among others, which anti-Darwinians hold to be not aids to the selection theories, but to be the basis if not of actually replacing or substitutionary theories, at least of precisely those objections to the species-forming capacity of the strict Darwinian factors which have necessitated some of the principal concessions made by the Darwinists, it is obvious that Plate’s discussion of them is in itself simply the actual making of the concessions already noted as having been admitted by most Darwinians. Each of these categories of phenomena and principles is of course of much import- ance and interest, and they will all be found to be fairly fully set out in the chapters following this one. Plate’s answers to the second important objection, namely, that selection relies too much on chance and is therefore ae, improbable and inexact, may now be noted. He the objection | distinguishes two phases of this objection. The oe the first he expresses as follows: “It is highly im- ependence of selection on probable that for the progressive development erat or perfecting of an organ there will always appear just at the needed time the variation necessary for selection, that is, the exactly needed adaptive modification.” The second phase is: “It is highly improbable that in the development of a complicated organ, or body-part, or in the perfecting of a changing adaptation the numerous indis- . DARWINISM DEFENDED. 171 pensable modifications will appear in such a series that a harmonious correlation of the single variations will be possible.” : Referring especially to the first phase of the general ob- jection he says: “Thus this doubting query is, why do there always appear just the right variations at the right time? Or, somewhat differently expressed, in the words of Cope,’ ‘since the number of variations possible to the organism is very great, the probability of the admirably adaptive structures which characterise the latter having arisen by chance is extremely small.’ “Whoever expresses such doubts unwittingly hitches the wagon before the horse. Selection directs itself according to the variation, not variation according to Selection fol- , partes , ‘ lows variation, Selection. If the variability is large, selection not variatio has a large choice; if the variability is small, selection, : ; then there are but few lines of evolution open. Experience teaches that in general, the variability of organ- isms is very large, that it occurs both quantitatively and qualitatively in such pronounced manner in all individuals of a species that it can be readily recognised without re- course to complex methods of investigation, and that no characteristic (size, form, colour, numerical relation, consti- tutional vigour, instinct, life-habit) is free from it in any life stage from egg to last drawing of the breath. It is precisely to this variability expressing itself in the most manifold ways and combinations that is to be ascribed the condition that any individual as such is, usually, readily to be distinguished from other individuals of the same species. It results from this that the individual variation is indeterminate and undirected, or better expressed, universal and all sided, and that at any given moment the exactly needed modification will always appear in a number of indi- viduals of any species rich in individuals, provided that 172 DARWINISM TO-DAY. the needed variation can be produced through a slight ad- vance or progressive change. Naturally it is not sufficient if the variation appears in only a few isolated individuals, but it is necessary, for the modification of the species, that this variation occur in so many individuals that it will not be extinguished through interbreeding but on the contrary will be perpetuated. In other words selection works, except biiestiac wake in scattered cases where single or ics varia- with plural vari- tions are specially favoured by accidental iso- caine lation, not with single but with plural variations or varieties. Through this the host of variations is im- mensely reduced as far as they come into consideration as. handles for selection, and of course only in this sense is there any reason at all for the query as to whether we can assume that the right variation will always be present at the right time. The answer can only be, certainly not always: many promising beginnings must always be checked in the germ or at half-way, but in infinitely many cases the needed plural variation will appear, because the same external factors change a whole group of animals simultaneously so that progress is possible. But, it goes without saying, only a slow advance is conceivable on this basis. “One must not, for the rest, forget that the same condi- tion of selective worth may be reached simultaneously _ through combinations of different peculiarities, calyg may ead that the same effect may be attained by attained in dif’ various means, both of which facts render it ferent ways. ; : ‘ 5 importantly easier to get this selective worth. When pursued by an enemy one individual of the harassed species may save itself by a quick leap, a second through sharp ears, a third by sharp eyes. Wallace rightly explains that the necessity for a giraffe in times of famine is only to reach as high as possible in the trees, and that different means may avail for this, as a longer neck, long legs, or a long tongue, all of which may eventually come to be correl- DARWINISM DEFENDED. 773 atively increased. The individuals which survive by these aids may then later, through inter-crossing, exchange their advantages and so lead to the production of a mean type that shows a slight advance over earlier conditions in all three organs. Mammals can protect themselves from flies in various ways, either by a thick fur (bears), by reflexive twitchings of the skin muscles (horse), by tails with tufted ends (many hoofed animals), by a long neck which can bend sideways so that the animal can reach any part of its body as far as the hips (guanaco, stag) or finally by eyelids and long movable ears, which restrain the flies from the easily injured eyes. These means of protection from insects play an important role in determining the habitus of many mam- mals, and permit the conclusion that selection has been instrumental in producing this habitus. Here, also, it is possible for several of these means to be possessed at once by the same animal, as in the case of the guanaco with its long hair and elongate neck. It is absolutely necessary for molluscs that live between tide-lines to have some means of resisting the force of the surf. Many species possess this means in their small size which allows them to crawl into crevices and cracks in the rocks, but most of them have developed a strong pedal sucker and a low roof-like uncoiled shell which presses close to the rock surface and over which the water flows without exerting any strong lateral pres- sure. This is the case, for example, with Patella, Fissurella, ‘Chiton, Concholepas, Siphonaria, Gadinia, Calyptra, and others. All three of these means of safety can come into play simultaneously in selection, but it suffices when any given individual possesses any one of these means in suffi- cient degree of development. “T shall note here several other examples which show how related species reach the same advantage in the strug- gle through different means, for we can assume from these facts that also the individuals of the same species often 174 DARWINISM TO-DAY. escape the same dangers in the struggle for existence by means of different means. And by this the probability is made greater that the ‘needed variation’ appears at the right time. The differing characteristics of this sort will later lead, through crossing, to the formation of a mixed type, or, if the competition grows ever sharper with the course of time, they will produce a separation of the species into varieties (eventually species) with differing habits of life, or finally they may meet in direct competition or strug- gle with one another. The good flyers among the birds all have long wings, but in some it is the fore arm which is specially lengthened (cuckoo, goat-sucker, pigeon), in others the hand (terns, humming-birds, eave swallows), and in still others the upper arm (swan).—While Tapirus ameri- canus, like most mammals, drives the flies away from its eyes by throwing down the eyelids, Tapirus indicus accom- plishes the same thing by a strong rotation of the bulb of the eye. Elephas africanus seizes very small objects with its proboscis-fingers, while the Indian elephant lays the front end of the trunk laterally on the ground, grasps the object between the skin-folds, lifts it up high in this way, and only then allows it to fall into the tip of the proboscis.— Poulton has shown by several examples that in cases of mimicry the same effects may be got in very different ways. The glass-like transparency of the wings, for example, is got in the Heliconid genus Menthona by a considerable dimi- nution in size of the scales, in the Danaid /tuna thona through the absence of most of the scales, in Castnia linus var. heli- conoides, through the absence of pigment in the scales, which are as large and numerous as usual, in the Pierid Dismor- phia crise through the smallness of the scales, and finally in — the night moth Hyelosia heliconoides by the absence of pig- ment and lessened number of the scales.” Plate next offers a detailed explanation on strict Darwin- ian grounds of how such an extraordinary condition of DARWINISM DEFENDED. 175 mimicry can be brought about as the famous case of Kal- lima, the butterfly that simulates in colour, shape, and inti- mate details of pattern such as veins, flecks, ee of fungus spots, etc., a dead leaf with such fidelity as to make it the wonder of every one who sees. it and the classic example of the possibilities of such protect- ive resemblance. And he shows well that whatever diffi- culties selection may have in its necessary dependence on the chance occurrence of the proper numerous and neces- sarily simultaneously appearing variations to explain the gradual development of such a specialisation, the only other explanations so far offered are even more ludicrously de- pendent on “luck.” Piepers,’ the most active and polem- ically vigorous of all special opponents of the Darwinian explanation of protective resemblance and mimicry, says: “Chance alone can bring about such a correlation.” As Plate well says, “It is not without its comic aspect that a violent antagonist of the selection theory should be found clinging to the same safety-anchor ‘chance,’ that usually is the constant reproach of the Darwinian. . . . It would not be difficult,” continues Plate, “to refer to still other examples. to show that a needed selective value can often be attained at the same time by the individuals of a species through various means, by which the probability that this type of adaptations can arise is correspondingly increased. But one point should never be forgotten and that is it is always first the variability, and second the selection. If no varia- tions appear there can be no progress, and if the struggle for existence were too severe the [non-varying] species. would die out. Strictly speaking, the question, how is it possible that the right variations can be relied on to ap- pear at the right time? is really inverted and therefore incapable of receiving a correct answer. One can only say: If a complex adaptation has arisen through selec- tion, then it is certain that the necessary modifications. 176 DARWINISM TO-DAY. needed for success in the struggle for existence were not wanting.” We come now to the second phase of the general objec- tion, as analysed by Plate; viz., the assumed improbability that during the course of the development Caines (evolution) of a complicated organ or whole ability ofthe | body-part, or during the perfecting of a chan- ne fos al ging adaptation, the numerous necessary varia- tions neededin tions will occur in such a successive series as seaiieee el to make possible an harmonious correlation of structures, the various single variations. Plate writes as follows: “This objection has been, as is the case with the objection just discussed, raised by many students of evolu- tion as Spencer, Wigand, Nageli, and is in principle not different from the previous objection, but only presents an elaboration of it. It concerns, first, the numerous single variations which are necessary if a single complex organ (as an eye) or a whole body-part with its various organs and tissues (for example, the neck of the giraffe, the fore body of the elk) of a single individual is to be raised to a higher stage of adaptiveness; and, second, the perfecting of inter- dependent adaptations in different individuals. As example of the latter category I may mention the corolla of flowers and the proboscis of insects which cross-pollinate these flowers, the male and female copulating organs of many animals, as those of the Papilionide, the adaptations of myrmecophilous and termitophilous animals in relation to their hosts, also those of symbiotic (parasitic or mutualistic) species relative to their companions, and, in cases of mimicry, of the mimicking species relative to the protected species. When one of the species, party to such a mutual adaptation, changes, the other as a rule must also. There arises from this the query : how, in such cases, is there possible the neces- sary coadaptation (coordination), that is, the harmonious change of the parts which produce the interdependent physi- DARWINISM DEFENDED. © 177 \ ological or biological phenomena, whether these exist in a single individual or in two? How does it come that when the antlers of the giant stag become larger and larger, the skull bones become thicker and the neck tendons and the fore legs stronger (Spencer)? With the gradual lengthen- ing of the giraffe’s neck the skeletal system and with it numerous other closely-related internal organs have to be- come larger simultaneously. Hundreds of small modifica- tions are necessary. How does it happen that all come off exactly as is necessary? When the flowers’ cups for any reason become deeper the insects must develop longer proboscides in order to reach the nectaries in the bottom of the cup. Simultaneously the sucking apparatus of the cesophagus must change. How does it happen that these modifications in two different organisms, in an animal and a plant, occur pari passu? “In order to satisfy these questions of doubt Darwin and Wallace have referred to the domesticated animals as the best proofs that such coadaptations are possible. A grey- hound, a bulldog, a dachshund, a tumbler pigeon, a race- horse, have had to pass through a long series of numerous changes in the most various organs, in order to reach their present form, and yet all these variations have appeared one after the other in such a way as never to endanger the vital vigour, for man would never have chosen weakly ani- mals for breeding purposes. In artificial selection, there- fore, coadaptations are possible in almost infinite variety, and it can fairly be asked if such favourable conditions are not also possible in nature. This query must, a priori, be answered in the affirmative, for man is not able either to make more easy or to hasten the appearance of coadapta- tions: he can only hold on to those which once appear, and this can also be done by the struggle for existence in those cases in which the coadaptive variations are of vital import- ance. The real difference lies, therefore, in the fact that 178 DARWINISM TO-DAY. ’ man can make a beginning with ever so slight an advance; nature only with such simultaneous changes as are of suffi- cient grade or degree to be of selective value. And so far in this discussion nothing has been offered to show how this condition is to be reached.” . To attempt to get at an explanation of the actual means by which this necessary condition is attained, Plate believes it Plate's belief eCeSSary that one should make clear just what in the possibility standpoint he takes on the vexed problem of of the inheri- : : . ; tance of acquired the inheritance of acquired characters. With- characters: out going into Plate’s long discussion of this old subject, it is sufficient to say that he reaches the conclusion that the inheritance of acquired characters is not proved not to be possible, and hence that it may occur. And, for himself, he expresses the belief that acquired somatic char- acters can be and are inherited. From this point of view, he, consistently with Darwin’s own position, finds an answer to the objection touching the necessity of a repetitive cumulat- ing appearance of certain definite kinds of variation for the basis of the development of coadaptation, by invoking the Lamarckian factor of the inheritance of the effects of use and functional stimuli. Which refuge is of course not open to the modern strict selectionists, the neo-Darwinians. Now, as may be imagined, when the Darwinians them- selves are of various minds about the value of the answers to this objection, when these answers are based on a strict selection basis, they are not very convincing to anti-Darwin- ians. In general they rest on various observed facts and deduced assumptions which may be roughly classified into several groups. First, the facts of simultaneous correlative variation, or the fact that organs or parts which function together, very often vary in the same general direction. For example, if two leg or arm bones become longer the muscles attaching to these bones also become longer (since the attachments are not changed). The supplying blood-vessels ‘oi % DARWINISM DEFENDED. 179 and nerves also lengthen. Numerous observations by breeders show that in each organism there resides a capacity of self-regulation, up to a certain degree, which produces a harmonious growth and variation of inter-dependent parts. If a plant is removed to richly fertilised soil it will grow to great size, in the course of which growth all parts are pro- portionally changed so that the general habitus of the plant remains the same. If one allows insect larve to live on very short food rations, the adult insects will be unusually small but with all the organs of their usual relation to each other as to proportional size. Thus it seems that the single organs are definitely correlated with one another so that in their growth they maintain their relative characteristics. “I have,” says Plate, “called this form of organic Zweckmdassig- keit the unity of organisation.” If this quality or capacity is lacking in an individual then it develops into a cripple, a monster, and is killed out by selection. Therefore, if the neck of the giraffe varies so as to be longer, one may fairly assume that, in the case of many individuals, at least, all parts of the neck will share in this variation, although there will naturally be slight individual varyings inside of this general variation. And if the antlers of the stag vary towards a larger size there will simultaneously appear the necessary increase in calcareous materials for all parts of the skull, so that the whole skull will be correspondingly heavier and stronger. “The process of evolution may be assumed to be, as it was — by Darwin, very slow, so that plenty of time is allowed to selection to produce the necessary coadaptations which may be wanting in the earlier stages of the development. In the case of the enlarging of the stag’s antlers there may have been wanting at first the necessary congenital strengthen- ing of the neck muscles but this would come to exist through use. The effects of use would increase, however, only to a certain point, and there would finally come a time when the 180 DARWINISM TO-DAY. heavy antlers could be supported only by those individuals which had received a strengthening of the neck muscles through congenital variation. All others would be killed out. “The already discussed principle. of the attainment of selective value for a certain advantage by various means, comes also into play in this connection. In time of drouth it is important to the giraffe only that it can reach a certain height on the trees; whether this height be reached by the aid of a longer neck or higher shoulders or a specially elongate tongue is indifferent. Through inter-breeding these various advantages may be later united. There is always resulting, as Wallace *” has said, ‘Selection of the capacities or qualities resulting from the infinitely varied combination of variations that are always occurring.’ “Recently Weismann ‘’ has presented the principle of germinal selection as explaining coadaptive specialisations, Plate'sdis- SO that he is evidently not satisfied with the beliefin Weis- sufficiency of the three aiding explanations mann’s principle ; , ¢ 5 wees of germinal already given. I hold this germinal selection, selection. says Plate, ‘to be a false conception, and there- fore do not here refer to it further. It will be discussed in detail later.”’ (This later discussion of Plate’s is a detailed and effective destructive criticism of the theory.) “Weismann, in his ‘Lectures on the Theory of Descent, outlines in detail his theory, proposed several years before, Reena that amphimixis (bisexual parentage) is so principle of widely prevalent in both the plant and animal amphimixis, kingdoms, because it serves as the spring of individual variations. A considerable part of the chromo- somes of the egg-cell is removed by the discharge of the polar bodies, and the same results from the reduction divi- sions of the sperm-cells. By this the possibility is created of producing, through the fusion of the germ-cells, very various combinations of the hereditary tendencies and, there- fore, an actual high degree of variability in the offspring. 912 DARWINISM DEFENDED. 18t ‘Because in each reducing division of the germ-cells their ids are lessened by one-half, the possibility exists of gradu- ally removing from the germ-plasm of the species the ids of the disadvantageous variations, for in each generation the offspring of the disadvantageous id combinations are ex- tinguished [by selection], so that from generation to gen- eration the germ-plasm gradually becomes purified of the disadvantageous ids, while the favourable combinations which amphimixis produces are retained, and there finally remain only the advantageously varying combinations or, at any rate, those in which the advantageously varying deter- minants are in the majority and therefore have the most influence’ (Vol. II, p. 222). This conception of the sig- nificance of the reduction divisions of the maturing germ- cells and their fusion is very suggestive, and, theoretically, there is little to be objected to in the idea that the differences thus created can be used by personal selection for the pro- duction of harmonious coadaptations. Indeed, with this explanation in hand, it is obvious that the theory of germinal selection is superfluous for the explanation of coadaptations if we may assume that there is always a great mass of material in the individual variations, for the possibility of varying combinations of these requires no further expla- nation.” For the most part it is obvious that Plate, and with him other fair-minded Darwinians, recognise fully the Plate recog- COSeNcy of the objections against Darwinism nises the weight based on the inutility of slight variations, on of certain objec- ; 4 pia toe occurrence’ and persistence. of hosts of ism. trivial or indifferent species differences, and on the difficulties presented by the demands of a controlled appearance of variations necessary to the development of coadaptive structures and functions, so that they are inclined to make the concessions which I have referred to in the beginning (chapter vi) of this presentation of “Darwinism 182 DARWINISM TO-DAY. Defended.” With these concessions made it is necessary to call to the aid of the selection theory, if it is still to be con- sidered an important factor in species-forming—these con- cessions do not, of course, invalidate the claims of selection to be the all-important final factor in determining the general course of evolution, by encouraging or restraining the various general lines of descent—certain auxiliary and aiding theories or explanations. Such helps to selection are to be found especially in isolation, organic selection, and the Weismannian theories of panmixia and germinal selec- tion. The outlining of these theories will form the con- tents of our next chapter. APPENDIX. 1 Plate, Ludwig, “Uber die Bedeutung der Darwin’schen Selec- tionsprinzip,’ 1903. > The question, what is meant by “selective value,” has been dis- cussed by Conn (“Method of Evolution,” pp. 83-86, 1900), as fol- Conn’s discus- lows: “How useful must a character be to be of sion of selective selective value? Such a question it is, of course, im- value, possible to answer. The preservation of any particu- lar character is not an isolated matter. It is not single characters that are preserved, but a combination of many characters together. The survivor is the animal showing the best combination of char- acters. It may even have some harmful ones, provided the useful ones predominate. The rattle of the rattlesnake has at times doubt- less been of a disadvantage to its possessor, and has caused the death of hundreds of thousands of individuals. It is doubtless possible to show, as Darwin did, that it has also been of value to the animals. But how are we to decide whether its use or dis- advantage is the greater, except by the theoretical conclusion that it must on the whole be useful or it would have been eliminated? The whole study of utility is sure to result in an unsatisfactory circular logic, something as follows: The survival of the fittest. is a law. If an organ be not useful it could not have been developed by natural selection. Therefore, all organs and all characters must be useful. Since in such a problem no one can prove a negative, this position cannot be disproved; but it is certainly not very satis- factory. —— DARWINISM DEFENDED. 183 “But with all this criticism of utility it must be recognised that the agency of utility as determining survival is becoming more significant as discussion proceeds. We have seen that it must be admitted that all characters to be affected by the principle of survival, must have selective value: 7. ¢., must affect the matter of life and death. But this demand does not prove to be so serious when we recognise that natural selection works upon general averages rather than individuals. Those who find the selection principle such a great factor insist that all characters have selective value if they have any value at all. If a character has the value of even rendering its possessor a little more comfortable, they tell us it will eventually be subject to the principle of survival at the expense of non-favoured animals. The substitution of old types by new ones is not a matter of a single generation, but many generations. In such a long history there must be innumerable conditions where any character, even the slightest, may have been of use enough to give its possessors an advantage over others. It is not necessary to believe that a character should preserve its possessor, while all non-favoured individuals perish, in order to consider that the character has selective value. Considering that the origin of species is a matter extending over hundreds of years and many generations, even little things will count in the long run. If an animal has a slight advantage over another, which simply gives it more comfort and enables it to obtain its food with a little less exertion, this may tell permanently in the struggle, since such an individual will have more energy to put into reproduction, and hence may leave a larger number of offspring. The other non- favoured individuals may not, indeed, be exterminated without off- spring, but may simply produce less offspring. In this struggle for permanency, the individuals which have the largest number of offspring, other things being equal, will inevitably come out ahead, and the others in time disappear. “An example will make this clearer. A difference of an inch or two in the length of a cow’s tail seems a matter decidedly too small to base the selection principle upon. Can it be imagined that the lengthening of the tail by a couple of inches can be of selective value? Can we honestly believe that these two inches will determine that the longer-tailed cow will live and produce off- spring, while the shorter-tailed individuals will die? Only thus, however, can we assume that the tail has been developed by natural selection. Now this example, which seems to be an extreme case of slight utility, may show us how it is possible, upon the principle of the selection of averages, to conceive that characters of slight use may be preserved by natural selection. It is not necessary to 184 DARWINISM TO-DAY. suppose that the long-tailed individuals are preserved by this extra couple of inches at the expense of the shorter-tailed individuals in order that the character may be within the reach of natural selection. If the animals are troubled by insect pests, it is cer- tainly a matter of convenience to them to have a tail long enough to brush off the flies, and the longer tail, within certain limits, will be more useful than a shorter one. It is not likely that this will preserve the life of a single individual, but it will follow that the animals with longer tails will be less irritated by insects than those with shorter tails. Now, although this would not affect the matter of life and death, a nervous irritation would pretty surely interfere with the reproductive efficiency. An animal that is con- stantly bothered by insects will have less nervous energy to devote to reproduction, and, therefore, such a constantly irritated animal would be likely to be somewhat less prolific than one less irritated. From this it would follow that the half of the animals with tails a little longer than the average, would be pretty sure to leave a some- what larger number of offspring than the half whose tails were below the average. But a slightly increased fertility of this sort would, in the course of a few generations, see the long-tailed animals becoming more and more numerous, until they would eventually replace the others.” * Dodel-Port, A., ‘“Wesen und Begriindung der Abstammungs- und Zuchtwahl-Theorie in zwei gemeinverstandlichen Vortragen,” 1877. *The tsetse-fly (Glossina sp.), long notorious as a terrible pest of cattle in Africa, produces its ravages by disseminating (through biting, % ¢., puncturing the skin) the specific causes (certain minute blood-inhabiting parasitic one-celled animals known as trypanosomes) of the plague called Nagana (fly dis- ease). ° For an elaborate discussion of the principle of correlation (not bearing perhaps except in a general way on the point just at issue, References to but of much general interest) see Radl, Em., “Uber papers on corre- die Bedeutung des Prinzips von der Korrelation in lation, der Biologie,’ Biol. Centralbl., Vol. XXI, pp. 4or- 416, 490-496, 550-560, 605-621, 1901. See also Webber, H. J., ‘“Cor- relation of Characters in Plant-Breeding,” Proc. Amer. Breeders’ Assoc., Vol. II, pp. 73-83, 1906. * For examples see R. Meldola, “The Utility of Specific Char- acters and Physiological Correlation,’ Proc. Ent. Soc., London, pp. 62-92, 1896; also A. R. Wallace, “The Problem of Utility; are specific characters always or generally useful?” Jour. Linn. Soc., Vol. XXV, pp. 481-496, 1894. DARWINISM DEFENDED. 185 * Dohrn, Anton, “Der Ursprung der Wirbeltiere umd das Princip des Functionswechsel,” 1875. ®*Cope, E. D., “The Energy of Evolution,’ Amer. Nat., Vol. XXVIII, p. 205, 1894. I quote the following: ‘In considering the rials proct dynamics of organic evolution, it will be convenient chat diataral to commence by considering the claims of natural selection cannot selection to include the energy which underlies the make new char- process. That natural selection cannot be the cause — of the origin of new characters, or variation, was asserted by Darwin,* and this opinion is supported by the following weighty considerations. “(1) A selection cannot be the cause of those alternatives from which it selects. The alternatives must be presented before the selection can commence. ““(2) Since the number of variations possible to organisms is very great, the probability of the admirably adaptive structures which characterise the latter having arisen by chance is extremely small. “(3) In order that a variation of structure shall survive, it is necessary that it shall appear simultaneously in two individuals of opposite sex. But if the chance of its appearing in one individual is very small, the chance of its appearing in two individuals is very much smaller. But even this concurrence of chances would not be sufficient to secure its survival, since it would be immediately bred out by the immensely preponderant number of individuals which should not possess the variation. “(q4) Finally, the characters which define the organic types, so far as they are disclosed by paleontology, have commenced as minute buds or rudiments, of no value whatsoever in the struggle for existence. Natural selection can only effect the survival of characters when they have attained some functional value. “In order to secure the survival of a new character. that is, of a new type of organism, it is necessary that the variation should appear in a large number of individuals coincidentally and_ suc- cessively. It is exceedingly probable that that is what has occurred in past geologic ages. We are thus led to look for a cause which affects equally many individuals at the same time, and continuously. Such causes are found in the changing physical conditions that have succeeded each other in the past history of our planet, and the changes of organic function necessarily produced thereby.” ° Piepers, M. C., ““Thesen tiber Mimikry,” Verh. Internat. Zool. Cong., p. 350, 1902. * “Origin of Species,” ed. 1872, p. 65. 186 DARWINISM TO-DAY. * Wallace, A. R., “Are Individually Acquired Characters Inher- ited?” Fortnightly Review, Vol. LIII, pp. 490-498, 1893. 11 Weismann, A., “Uber Germinal-Selection,’ Verh. Internat. Zool. Cong., 1896. *? Weismann, A., ‘““Vortrage tiber Descendenztheorie,” 2 vols., 1902. ya 1 ay oy dx oe ( CHAPTER VIII. OTHER THEORIES OF SPECIES-FORMING AND DESCENT: THEORIES AUXILIARY TO SELEC- TION. To be considered now are two categories of (mostly) post-Darwinian theories, viz., those which have been offered Classification 29 alternative theories intended to replace more of other theories or less nearly entirely the selection theories, aie and those other theories intended to serve as selection. auxiliary and supporting theories for Darwin- ism. Obviously these two kinds of theories * emanate from the two opposing biological camps. Several of these alter- native and auxiliary theories of species-forming have been referred to incidentally in the preceding two chapters, for the replacing theories constitute part of the strength of the anti-Darwinians, while the supporting theories are dis- tinctly relied on to help maintain the Darwinian front. The present chapter, then, is mostly a continuation of the pres- entation of “Darwinism Attacked” and “Darwinism De- fended,” which is given a separate place because of the special character of the argument with which it has directly to do, namely, the synthetic or theory-building side, instead of the analytic or theory-destroying side, and because of the probable advantage to the student and general reader wishing to understand and compare the general character and significance of the various new theories of species- forming with whose names, such as heterogenesis, ortho- genesis, metakinesis, geographic isolation, biologic isolation, organic selection, or orthoplasy, he occasionally meets in his 187 188 DARWINISM TO-DAY. general reading. As directly continuing the last chapter we may consider first those theories put forward, chiefly by Darwinians, as auxiliaries or supports of the selection theory. Then we may briefly take up those theories that have been advanced, mostly in recent years, as more or less nearly completely prepared to replace Darwinism as a suff- cient scientific causo-mechanical explanation of species- . forming and descent. The Weismannian Theories of Panmixia and Germinal Selection..—Weismann has for years been the most con- Weismann's im. SPCUOUS of the neo-Darwinians, that is, of portant contribu. those who would free Darwinism from all taint tions to biclogy. Gf Tamarckism—it should always be remem- bered that Darwin was inclined to attribute some degree of influence in species-forming to the Lamarckian factor of the inheritance of individually acquired adaptive charac- ters—and to make selection the all-sufficient and, indeed, sole factor in species-forming. His great services to biology in general and to the clearer understanding of the problems of heredity and descent in particular, are unquestioned and unquestionable. His careful investigation and illumination of the vexed question of the inheritance of acquired charac- ters, his definitive exposition of that point of view which distinguishes sharply in the individual between the germ- plasm (that particular protoplasm in the body from which the germ-cells, eventually new individuals, arise) and the soma-plasm (that which develops into, or gives rise to, the rest of the body), his development of the interesting and suggestive combinations of fact and theory designated by the phrase names “continuity of the germ-plasm” and “im- mortality of the Infusoria,’—these products of his investi- gating and philosophising mind prove him one of the ablest of modern biological scholars. They also make him the principal present-day champion of the selection theory. For all these expositions of fact and theory are of a nature to “: OTHER THEORIES OF SPECIES-FORMING. 189 enhance the credit of selection and to discredit certain other species-forming theories, in particular the only one, namely, ee Lamarckism, which, until recently, has been in champion of any real sense a rival of Darwinism. Against eaeceians Weismann then and against Weismann’s re- modelled kind of Darwinism, against his propaganda of the Allmacht of selection, the adherents of Lamarckism and the critics of selection have turned their sharpest weapons. The result of the struggle has been to compel Weismann himself to say: “Although the principle of selection appears to solve in simplest manner the riddle of the fitness (Zweckmassig- keit) of all arising organisms (alles Entstehenden), yet it appears ever more clearly in the course of the further inves- tigation of the problem, that one cannot explain all with it, at least in its original limitations (dass man mut ihm, in seimer wurspriingliche Beschrankung, wenigstens, micht ausreicht).” To support the selection theory in two of its weakest and most criticised places, Weismann has proposed two striking auxiliary theories, namely, the Theory of Panmixia, to explain the degeneration of functions and organs, and the more recent Theory of Germinal Selection, to account for the now practically generally admitted existence of orthogenesis or determinate variation and evolutionary progress along fixed lines even to the possible final dis- advantage of the organisms involved, and to account for the beginnings of variation and their maintenance until sufficiently developed to serve as handles for selection. The proposal by Weismann of the second theory, that of germinal selection, was the practical admission on his part of the impotence of selection to initiate new lines of develop- ment or descent. It was a concesston on Weismann’s part of the justness of the demand for ati evolutionary factor to explain the beginnings of lines of development, whether of new organs or new species. And there is no doubt that it is \ 190 DARWINISM TO-DAY. the most ingenious mechanical explanation yet offered of the workings of such a factor. Indeed, Weismann, with characteristic ingenuity and capacity, has offered the be- lievers in orthogenesis that which they so far had not been able to get for themselves, namely, a possible causo-mechan- ical explanation of it. It should be noted that Roux’s theory of the battle of the parts (explained later) was a forerunner of, and undoubtedly the suggestion for, the theory of germinal selection. Familiar to all students of biology, and certainly not wholly unfamiliar to laymen, are those structures or parts in the body known variously as vestigial struc- Riis _ tures, rudimentary or degenerate organs. The plain vestigial vermiform appendix in man is one; the eye of oor the mole is another; the functionless wing of the ostrich, the useless fore-feet of a milk-weed butterfly, and the splint bones of the horse, are others. Almost every animal kind possesses vestigial organs, and some kinds possess very many. Those in the human body make an amazingly long list. All these are organs, which have once— that is, in ancestors of the present particular organism —been well-developed and probably useful. But these organs now are useless or even harmful. The human appendix vermiformis is harmful; the tiny fore-feet of the milk-weed butterfly are useless. Why do animals have such vestigial organs? Because they derive them by hered- ity from ancestors. But in these ancestors the organs were well developed and useful. How is it that the present organisms do not need the same organs? They have adopted new habits, or live in a new environment, or have developed other means of supplying the old want; in a word the organs are superfluous. How is it that the organs have become thus degenerate or vestigial? This is the question that selection has difficulty in answering satisfactorily. Selec- tion can develop and specialise organs of use and advantage; OTHER THEORIES OF SPECIES-FORMING. Igt but how can it cause organs no longer useful and advan- tageous to degenerate? It is possible, perhaps, to explain the eradication of positively harmful organs by a process of negative or reversed selection. If an organ becomes actually harm- ful because of a change in life conditions, individuals. with the organ in poorest, least energetically functioning condition might be conceived to have an advantage and be preserved by selection to pass on to their offspring this less developed, i. e., rudimentary or vestigial, character of the particular organ in question. But when the organ is simply only rendered useless by the change in life condi- tions, as when a species of fish or insect gradually comes to: inhabit. deep dark caves and thus has no more use for its eyes, how does selection explain the degeneration? It really doesn’t, satisfactorily. So Weismann offers the theory of panmixia to account for it. This is, simply, that owing to. the cessation of selection in regard to the particular organ whose function is rendered no longer advantageous or necessary under the new life conditions—that this cessation of selection is an obvious result of such a state of affairs was recognised by Darwin himself, and by other biologists— individuals born with this organ defective or in a condition below the average, would not be necessarily killed by the rigours of the intra-specific struggle, and would therefore be as likely to mate and keep on producing offspring as the ones with the organ in average or above average conditions. This general participation of all kinds of individuals (all kinds, that is, as regards the state of the particular organ) in producing the next generation, and the continued repeti- tion of this general mixing, panmixia, would obviously lead to a reduction of the earlier high condition of development of the organ. Weismann thinks, or thought, it would lead to a steady degeneration of the organ. But few other biol- ogists, even those ardent selectionists anxious to find in 192 DARWINISM TO-DAY. panmixia an explanation not involving the admission of any new organ-modifying factor, have been able to see how panmixia can do more than simply reduce the organ to a certain stage below the original state of greatest effective- ness. By resorting to mathematics several writers have determined the exact—unfortunately for their convincing character—several degrees of reduction or degeneration that will result from panmixia. The difficulty of explaining degeneration (to the degree in which it is manifest in thou- sands of known cases) on the basis of panmixia alone, is that there is included no factor or influence that would sum up or cumulate variations in a retrogressive direction any more than in any other. The Darwinian variations of the use- less organ would, by the law of error, simply keep the organ, thus abandoned by selection, swinging about a mean but little below the condition possessed by the organ at the time of its abandonment. If the organ were large enough, or of a character whereby it would entail a constant considerable disadvantageous expense of food material to maintain it, then selection might, on a basis of an advantageous economy of living, tend to reduce it to a non-disadvantageous size or character. But this disadvantage, although easily presumed by carrying out the rigour of the struggle to a logical ex- treme, cannot, in fact,—and biologists on the whole admit this——in common serse be assumed. Lamarckism offers a perfectly simple and perfectly effect- ive and satisfactory explanation of vestigial organs and the modus of their degeneration. But to accept this fea pee means to accept the basic principle of Lamarck- of vestigial ism, namely, the inheritance of acquired char- pila acters. And it is one of Weismann’s most con- spicuous positive achievements that he has demonstrated the unproved character of this theory. Lamarckism says that the first fishes to go into the dark cave suffered a partial individual degeneration of their eyes through disuse and OTHER THEORIES OF SPECIES-FORMING. 193 that this eye degeneration was inherited by their young, whose eyes, already bad, suffered further degeneration in their life-time through disuse, and that after comparatively few generations this cumulative actual morphologic degen- eration through disuse—and we know that unused active organs, as muscles, stimulus-perceiving parts, etc., do actu- ally degenerate in an individual’s life-time through disuse— would reduce the eyes to a very degenerate condition. Other cases of degeneration, especially of passive organs (1. @., where the organ’s condition was not so wholly a function of use or disuse, but of the direct moulding influence of extrinsic influences), are explained by Lamarckism on the basis of the inheritance of the results of the direct action or influence of environment on the organ. For example, the gradual disappearance of pigment (blanching) charac- teristic of many cave animals, would be explained by the absence of the extrinsic factor, light, which is necessary to stimulate pigment production. In necessarily closing this all too brief reference* to panmixia, it may be said that Weismann himself has in recent years recognised its unconvincing character ; and that Plate, a strong upholder of selection, in a most careful weighing of panmixia, finds it capable of explaining func- tional degeneration but not any actual considerable mor- phological rudimentation. The Theory of Germinal Selection was proposed by Weis- mann in 1895, more definitively in 1896. Plate introduces Wejsmann's [iS discussion of this theory as follows: “Its theory ofger- aim is the rehabilitation of the selection princi- ee ple. It shall overcome all objections and doubts which have been raised against the selection theory and shall act as the magician’s wand to clear all difficulties from its way. Its strength shall avail in four directions. First, it shall explain how not only degeneration (physiological) but rudimentation (morphological) occurs in panmixia; second, 194 DARWINISM TO-DAY. 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 defi- nite line, without depending on the necessity of a personal selection raising them step by step.” Weismann himself refers to the theory as ‘“‘a spring of definitively determined variation.” In 1902, Weismann further applied the theory to the explanation of monsters, and other cases of terato- genesis, of “sports” (sudden or large discontinuous varia- tions), of suddenly appearing sex-characters, of specific talents, and still other heretofore unsatisfactorily explained phenomena. In defining the theory of germinal selection we come at the very start to a difficulty based on the fact that little or no reference has heretofore been made in this The physical 450k to certain various theories or speculations and chemical 4 structure of as to the ultimate structure of protoplasm, espe- protoplasm. . cially the protoplasm of the germ-cells. In recognising protoplasm as the “physical basis of life’ (Hux- . ley’s phrase), biologists have naturally tried to find in its actual physical make-up some clue to its marvellous capacities. The highest powers of our best microscopes, however, reveal little more of this intimate physical struc- ture than does our unaided eye. Probably the colloidal char- acter of protoplasm, that is, its amorphous, non-crystalline, viscous condition, is the most important physical fact about it revealed by our closest examination. But this apparent simplicity of physical structure is very unsatisfying to most biologists, and they demand the assumption of an extremely complex structure; a subdivision of germinal protoplasm into structural units and groups of units, just as the chemist assumes, in his atomic theory, a subdivision of substances into molecules and atoms. These protoplasmic units are, of course, invisible; like the atoms, they are beyond the see- OTHER THEORIES OF SPECIES-FORMING. 195 ing of our microscopes. This nearly unanimous demand on the part of biologists for a complex physical structure of protoplasm, depends largely on the fact that our present knowledge of the chemical constitution of protoplasm offers absolutely no explanation of its capacities. We know that protoplasm is composed of certain familiar elements, pres- ent in certain proportions. But beyond that nothing; the actual chemical relations of these component elements are too complex for analysis. Besides, certain observations of the processes of protoplasmic behaviour suggest strongly the workings of a machine whose effectiveness lies in its physical make-up. Finally, the phenomena of heredity seem to admit of no other explanation than the assumption of a composition of the germinal protoplasm out of myriads of structural units actually representing the myriads of cells, or groups of cells, of the fully developed body. Ever since protoplasm has been recognised as the physical basis of life, therefore, and ever since the germ-cells have been recognised not to be miniature men and women, but, as far as the eye and microscope go, masses of primitive protoplasm differentiated only into cell-plasm, nucleus, and nuclear parts (chromosomes, centrosomes, nucleoli, etc.), there have been “atomic” theories of protoplasmic struc- ture. Unfortunately for the standing of any one of these theories, each working biologist seems to have made one for himself, so that instead of one universally accepted, hence usable and useful, atomic or unit theory such as the chemists have—and the modern physical chemists seem to be rebelling even against that,—biology has had a host of protoplasmic unit theories of which the one we have here specially to refer to is known as Weismann’s theory of biophors and determinants. Several of the better known or more ingenious of these theories are outlined in very sum- mary fashion in the appendix‘ of this chapter. What we need now to know of biophors and determinants in order to 196 DARWINISM TO-DAY. understand the theory of germinal selection, is this: Weis- mann conceives the protoplasm of the cell nucleus to be composed of units called biophors—these biophors can also migrate out into the cytoplasm surrounding the nucleus— which are the bearers of the individual characters of the cell. The total character of any cell, its form, make-up, and spe- cial properties, is determined by the totality of its biophors. These biophors are not, however, such simple structures as the atoms of the chemist ; indeed, they are to be Icoked on as super-molecules, as complex groups of chemical molecules, of determined character and arrangement. Moreover, as these biophors are life-units, they possess the essential char- acteristics of life, that 1s, the capacity to assimilate food, to grow, and to reproduce themselves by division. The num- ber of different biophors is almost inconceivably enormous; for it must equal the possibilities of variety in character exhibited by, or capable of being exhibited by, all the cells of the body. But as each biophor is made of many complex molecules which may vary among themselves, and also vary in their structural relation to each other inside the biophor, it is not difficult, perhaps, to imagine the possible variety of biophors to be equal to the possible variety of cell char- acters. These biophors are conceived to be united into fixed, indissoluble groups called determinants, each de- terminant containing all the biophors necessary to deter- mine the whole character of any one kind of cell. Like the biophors the determinants can assimilate food, grow and multiply by division. While in each specialised body- cell there needs to be but a single determinant, namely, one of the special kind conforming to the special kind of cell, in the germ-cells there must be conceived to be every kind of determinant which may be found in all the body-cells taken together. But, fortunately, by virtue of the determinants’ capacity for multiplication it is not necessary to assume that there exists in the germ a OTHER THEORIES OF SPECIES-FORMING. 197 determinant for every cell that is to develop in the body, but only one for every different kind of cell; all cells exactly alike can be supplied with similar determinants by the multi- plication of the proper kind. Now Weismann’s theory of germinal selection rests upon the assumption of a competi- tion or “struggle” of the determinants in the germ-plasm for food and hence for opportunity to grow, to be vigorous, and to multiply. The germ-cells derive their food, as do the other cells and tissues of the body, from the general food streams circulating around and through the cells. Weismann, recognising the absolute principle of slight varia- tion everywhere in Nature,—it is practically impossible to conceive of identity,—believes that the initially slightly stronger or more capable determinants will be able to take up larger supplies of food, even to the extent of lessening the supply for neighbouring determinants, perhaps to the degree of starvation. Indeed he suggests a reason for the initial slight variations in vigour of the determinants in the probability that the food will reach the various determinants in slightly, purely fortuitously, variable quantity, so that the first inequality in vigour of the determinants will depend on the fortuitous variability of food supply, while there- after the variability in the determinants thus produced will enable the stronger ones to draw to themselves or take up more food and thus accumulate determinately the initial fortuitous inequality. Thus when the germ-cell begins its development into a new individual those kinds of cells, tissues, and organs will be best developed whose determinants were most suc- cessful in the struggle for food, while other parts of the body may be made smaller or even may not appear at all because of the starvation of the determinants re- sponsible for the cells which should compose them. Also these better-developed, larger, more vigorous determinants of one generation will hand on to the germ-plasm of the 198 DARWINISM TO-DAY. next generation strong and extra-vigorous daughter deter- minants. For any determinant in the germ-plasm of a fer- tilised egg-cell has not alone to furnish determinants which shall control the development of body-tissues and organs of the individual which develops from this cell, but also to furnish daughter determinants for the new germ-plasm of this individual. This will result in a repetition of the extra-development in the next generation of the same organs as were strongly developed in the first generation, and the under-development of the same organs as were weak or wanting in the first generation. Which process continued is simply determinate variation, that is, variation along fixed lines without reference to personal selec- Dtagucts tion. Now when this variation becomes so indeterminate marked that it is of life-and-death advantage variation, . ‘ : 9 ge A : or disadvantage in the life of the individual, it will immediately become subject to the control of personal natural selection, and under the influence of this dominant factor in determining adaptation, either be further fostered and fixed or be extinguished. If the increasing organ or part due to germinal selection be one whose increase is advantageous to the individuals possessing it, then natural selection will preserve those individuals and the germinal advantage of the determinants of this part will be steadily increased, as the size and power of assimilation of the determinants correspond to the size and vigour of the part. By this theory Weismann believes that he has explained away one of the most patent objections to natural selection, viz., that it is necessary to assume, for the effective work of selection, the timely appearance of the proper variations necessary for the continued advantageous modification of a part. “Knowing this factor, we remove, it seems to me,” writes Weismann,’ “the patent contradiction of the assump- tion that the general fitness of organisms or the adaptations necessary to their existence, are produced by accidental OTHER THEORIES OF SPECIES-FORMING. 199 variations—a contradiction which formed a serious stum- bling-block to the theory of selection. Though still assum- ing that primary variations are ‘accidental,’ I yet hope to have demonstrated that an interior mechanism exists which compels them to go on increasing in a definite direction, the moment selection intervenes. Definitely directed variation exists, but not predestined variation running on independ- ently of the life conditions of the organism as Nageli, to mention the position that the most extreme advocate of this doctrine has assumed: on the contrary, the variation is such as is elicited and controlled by those conditions them- selves, though indirectly.” Obviously Weismann in his theory of germinal selection has preserved the actuality of a struggle and a selection, but with a “rehabilitation” of natural selection in the real Dar- Winian meaning and only fair application of the phrase the new theory has nothing to do. It is, much more, a distinct admission of the inadequacy of natural selection to do what has long been claimed for it. It is the first serious attempt at a causo-mechanical explanation of a theory of ortho- genesis, that is, variation along determined lines. As to our acceptance or non-acceptance of such a theory we need say little. It consists of two purely speculative basic assumptions: First, Weismann’s particular theory of the ultimate structure of the germ-plasm, namely, the theory of biophors and determinants; and secondly, the assumption , that there is a struggle for food among the determinants. There is no proof of pure observation or experiment for the theory, and there is some proof directly against it. And yet the great need of a working hypothesis for the causo- © mechanical explanation of determinate variation makes us : give such a pure speculation more attention than it might © otherwise get. Unfortuna the attention thus given to | this particular theory seems tofhave resulted in the bringing ~ forward of some rather serigus objections to the possibility ear v2 Sra. IGP TOTS ‘ ed 200 DARWINISM TO-DAY. of the truth of the theory. A few of these objections * may be briefly stated. According to the theory there should be plainly exhibited in the variation of any species, decided tendencies in certain Objections to Specific directions. In all species, in all indi- is ea viduals, the struggle of the determinants must tion. result in the suppression or reduction of some, the extra-development of others. Thus variation should not reveal itself according to the law of error, that is, should not be distributed normally about a mean or mode. But that is exactly the condition of variation in a majority of those cases in which the variation of one or more organs in any species has been statistically studied. The plotted curve of any particular variation of this type is a symmetri- cal curve nearly coincident with the theoretical one express- ing the law of error for the same case. The constancy of species is just as marked and actual a condition as the condition of slight fluctuating variations inside the species. This constancy is steadfast for con- siderable time-periods. But with such an active orthogene- sis as the theory of germinal selection provides, there could be no such steadfast constancy. Weismann himself recog- nised the weight of this objection to the theory, and speaks of an attribute of “self-correction” pertaining to the germ- plasm, which shall regulate or check too rapid an ortho- genetic development. The actual change of the competitive determinants due to their obtaining an over cr under supply of food should be one simply quantitative in degree; such germinal selec- tion could thus lead to the change in size and strength of organs already present in the species, but could offer no explanation of qualitative changes, 1. e., the appearance of new kinds of structures. Moreover, even in cases of purely quantitative change, such familiar cases as the persistence through long time-periods of small, rudimentary organs, OTHER THEORIES OF SPECIES-FORMING. 20E without any indication of further reduction, indicate a pecu- liar cessation in the forthright working of germinal selec- tion. Why should not the weak determinants of these weak organs go completely to ground in the struggle? Actual experimentation on the influence of food-supply in development does not bear out the assumption on which the theory of germinal selection rests. Weismann himself gave the larve of flies, and I have given the larve of silk- worms through their whole life-time, an abnormally small food supply (in the case of the silkworms this supply was: from one-fourth to one-eighth the amount normally eaten by full-fed larve), with the only result that the mature individuals were dwarfed; that all their parts were reduced in size, but the actual size proportions of the various organs: and parts, and their relations to each other, were unchanged. The determinants seemed to share equally the hardships of short rations rather than a few of the stronger getting the better of the weaker. From the eggs of birds considerable quantities of yolk have been withdrawn without modifying appreciably the individuals developed from the eggs. If the struggle of the determinants is really an actual and severe one then only those of the large strong organs should survive, all the others being starved out. Such a condition would result in the exclusive development of monsters, 1. e..,. individuals lacking numerous organs (the small ones), and with the large ones all over-developed. Rousx’s Theory of Intra-selection or the Battle of the Parts.—Distinctly more likely to appeal to our reason is the theory of Roux,’ proposed in 1881, to explain how one or more organs may exhibit a progressive development or increase in size and capacity without reference to natural selection and also to account for the many remarkable adap- tations of slight and delicate but extremely precise character exhibited by various internal organs. Roux made, however, a too radical distinction between external or superficial: 202 DARWINISM TO-DAY. adaptations on the one hand, attributing these to the influ- ence of natural selection, and the adaptations of internal parts on the other, which he would attribute to the influ- ence of his functional stimuli and of his struggle among the inner parts of the body. This struggle, like that among Weismann’s hypothetical determinants, is one chiefly for food, but in Roux’s theory there is no assumption of hypo- thetical life units, nor any lack of clearness concerning the initiation of the actual struggle. The competing parts in Roux’s theory are the chemical molecules composing the Pi ona patlne cell, the cells themselves, groups or tissues of parts in Roux's cells, and even whole organs. The spurs to the theory are actu- ara : : ; ally recognised COMpetition for food are functional stimuli, structures, whose result is to set up a special demand and necessity for more food. Roux’s classic example will make this clear. It is a matter of fact that the fine plates and layers of bone in the “spongy tissue” of the long bones of the body, are so disposed as actually best to withstand the stresses most usually brought to bear on the bones. Thus they show a fine adaptation of arrangement, which one meets difficulties in trying to explain as due to natural selection. For, if we imagine the thin plates of the spongy tissue purely miscellaneously arranged, the possible slight varia- tions whereby a few plates at a time might fortuitously occur in a position or direction better fit to strengthen the whole bone, are so insignificant in proportion to the condi- tion throughout all the rest of the bone that we cannot possi- bly attribute to them a life-and-death value in the individual’s struggle for existence. Roux assumes that the stresses brought to bear on the bone during its development act as functional stimuli to all those plates in the forming spongy tissue, which lie in such places or at such an angle to the stress as to be affected by them, and in response to these stimuli, which in Roux’s belief are necessary to the normal structural development and maintenance of any part, these OTHER THEORIES OF SPECIES-FORMING. 203 forming bony plates will take up more food than the un- stimulated ones, and thus will be developed at the expense of these others. Similarly with all those other marvellously delicate inner adap- tations of fine and minute and oft-repeated structures to the special functions of the organs containing these structures. The stimulus of the function excites a trophic demand on the part of the struggle and an actual capacity for satisfying the demand, that soon leads to the extra-development of the stimulated parts at the expense of adjacent similar parts deriving food from the supply common to all. Thus Roux would explain the exquisite adaptation of the arrange- ment of the muscle-fibres in the walls of the blood-vessels, the tenidia or spiral threads in the trachez of insects, the little barbs on the feathers of birds which hold these feathers together in almost air-tight continuity, the numerous protect- ive hairs covering the spiracles of many insects, etc., etc. It will be noted that the competition of the parts is really twofold; thus, while for successful development it is neces- Piteccagele sary for parts tO“ be successful in food-getting, ofthe partsis this sticcess in food-getting seems to depend ees upon the prerequisite of receiving a needed functional stimulus. Thus there may be said to exist a com- petition for functional stimuli. But obviously success in this competition depends chiefly on the hazard of position. Those plates in the forming spongy tissue of a long bone which happen to lie where the stress comes, and in a special direction to be affecied by it, are the winners in the compe- tition for stimuli. Roux’s theory has appealed strongly to many biologists, but others have rejected it wholly, or at least as an explana- Caen tion of fine inner adaptations. Plate takes this cism of Roux’s latter position, but finds a great service in the Buoy: _ theory in that “Roux has given in it a profound analysis of the well-known fact that use strengthens and The struggle is for food. 204 DARWINISM TO-DAY. disuse weakens. His is the great merit of having clearly explained the extraordinary importance (Tragweite), in the building of new forms and adaptive structures, of this ele- mentary attribute of organisms. We have to thank him for the best putting together of all those observations which permit of but the one conclusion, that the functional stimuli exercise a trophic activity, that is, that each organ by the constant exercise of its function becomes stimulated to stronger assimilation and increased multiplication of its elementary parts, and that out of this there results a height- ened functional capacity.” However, as Plate points out, Thelawof this “law of functional adaptation” does not functional adap- apply to all organs and tissues; “the teeth of tation does not ' 5 apply to all many mammals become impaired through con- bi et stant use, and most of the sense-organs are apparently not bettered through use in regard to their per- ceiving elements but only in regard to their carrying ele- ments. Every exercise is followed by a certain fatigue which, in cases of exhaustion, is greater than the aimed at (ersielte) increase of functional capacity. Also the trophic stimulation can, in certain cases, lead to hypertrophy and other unadaptive results.” But as regards the actual “strug- gle of the parts,’ and especially as regards the claim that such a struggle is to account for inner adaptations, Plate, as a consistent natural selectionist, is wholly sceptical. He offers five objections to any usurpation of the functions of natural selection by this intra-selection theory. First, he holds, with Wolff, that it is impossible to place the inner adaptations in any sharp contrast with outer adaptations. They are contrasted only in that the former stand in a more indirect relation to the conditions of life. Indeed a single organ, as a claw for example, can show an external adaptive- ness in that it might be especially well arranged to scratch hard dry ground, and at the same time be distinctly adap- tively constructed as regards its fine inner structure. “If in ontogeny OTHER THEORIES OF SPECIES-FORMING. 205 natural selection,” says Plate, “is capable of producing outer adaptations such as making the fur of a mammal thicker and thicker as a protection against the cold, why can it not increase, or if advantage lies the other way, decrease, the number of bony plates in the spongy tissue of the long bones ?” Second, the capacity of living substance to be stimulated to increased food-getting is an elementary attribute of organ- Ty ahisaen: isms just as the capacities to assimilate, to be lation notex- irritable, and to breathe are. This special ee capacity is not explained by the theory of intra- selection; it is, indeed, just now wholly inexplicable. One might perhaps fairly assume that it is the result of a gradual development from the Protozoa onward, through the influ- ence of individual selection. But this is no explanation of its origin. Roux, himself, indeed, expressly declares that he bases his theory on the proved but not explained fact of functional adaptiveness, but some of his followers often forget this and seem to claim that the distinctly advantage- ous peculiarity of most tissues to be able to increase in strength and size through use is a direct result of the battle of the parts. Third, Plate holds that the battle of the parts plays no role in ontogeny. The cleavage and embryonal develop- Battle ofthe ment are wholly controlled by heredity, so that parts not evident there is nothing left for the battle of the parts. There occurs a peaceful and regular split- ting apart of the single cells and a separation of them according to their different qualities, and it does not at all occur that the strongest cells get all the food and the weak- est none, but on the contrary each receives as much as it needs for its growth. In a blastula of thirty-two cells it is not the capacity on the part of certain cells which results in the stronger growth of some and the weaker growth of others, or the more rapid multiplication of some and the 206 DARWINISM TO-DAY. less rapid of others, but, on the contrary, for each species there is a definite law of growth which we may only explain as the expression of a force of heredity, not capable yet of analysis. Matters certainly do not go on in an embryo as in an agar culture containing several kinds of bacteria of which only that one with the greatest life force remains. Were the development of the embryo determined by the food-zeal of the cleavage cells, it would happen that in a short time a few cells specially capable of assimilation would get the upper hand, and as a consequence only a few quali- ties be left to the embryo; a real differentiation into thou- sands of different cell-sorts would not be possible. All the facts of symmetry and auto-regulation in embryonic develop- ment speak against any considerable influence of a battle of the parts during development. Fourth, Plate declares that in the acquirement of new characters no selective intra-struggle takes place, or at least in only most insignificant manner, but that the No battle of ‘ ‘ , the parts inthe NeW structures arise either through the direct aoquirement of influence of new stimuli or by natural selection new characters, ; er as of new germinal variations of unknown origin. In the first place it is simply the matter of position, not at all that of quality, that decides whether the certain cells shall be changed or not. Think, for example, of a vessel in whose walls the connective tissue fibres cross and recross in all directions wholly without order, and conceive that a constant or repeated stress in both longitudinal and trans- verse directions is exerted on this vessel. It would result that all those fibres lying in the absolute or approximate directions of these stresses would be most stretched and | would in consequence of their trophic irritability most rapidly enlarge and increase with special rapidity. Now by the repetition and inheritance of this result of use it would finally come about in the course of generations that all the fibres situated in other directions to the stresses would die out, OTHER THEORIES OF SPECIES-FORMING. 207 and thus a definite longitudinal and transverse arrangement of fibres in the walls of the vessel result. Without doubt, holds Plate, much advance is won in this way, but this specialisation of structure is not a result of intra-struggle but rests on the elementary attribute of trophic irritability. Not the best-qualified but the best-situated fibres have van- quished the others by robbing them of food and thus finally destroying them. In the second place, “many inner struc- tures belong to the great category of passive adaptations ; they function only through their presence and cannot thus be further developed by use or disuse, that is, by functional stimuli, but only by natural selection. Here belong, for example, the stratification of the lens in the human eye, the apodemes (inner projections of the chitinised cuticula) which protect the ventral nerve-cord of the crabs, the chitin hooks which hold together the fore and hind wings of many insects, and the similar structures which bind together the secondary branches of the feather vanes of birds. These inner adaptations cannot have resulted through the influence of light or of nervous function or flight. There is but one explanation possible; namely, that natural selection has seized on and developed fortuitously appearing germinal variations. But if natural selection can produce such inner adaptations why can it not then produce all the others?” Fifth, Plate points out that Roux’s theory is based on the inheritance of those special body characters which are “ee acquired through the battle of the parts—more Rour’s theory tightly, Plate holds, through functional adapta- er tion,—so that to accept the theory, one has to acquired char- declare, to that degree, a belief in the inherit- pevert: ance of acquired characters. Thus from the start, the neo-Darwinians cannot accept the theory. After all what is this theory of Roux’s but a refinement, a special case, of the broader and more general long-known Lamarckian theory of the modifying and formative influ- 208 DARWINISM TO-DAY. ence of use and disuse, accumulated through inheritance? That is, if we accept Plate’s analysis that the theory is really not one of a battle of the parts, but of The battle of : : : the parts theory the effects of functional stimuli. And however ri oer the proposer of the theory may protest against such an apparent violent setting over of it from the category of selection (Darwinian) theories into that of the inheritance of use (Lamarckian) theories, I believe that most of us will see the justness of Plate’s analysis. I do not believe that Roux’s theory in any way strengthens the selection conception. To my mind, indeed, it is simply a concession of the inadequacy of selection to initiate adapta- tion, and a welcome and satisfying explanation of how such an initiation may occur in many cases, in certain cases, that is, Of active adaptations. Plate’s argument that natural selection must be the only explanation for the cases of passive adaptations and hence may be held capable for accounting for the active ones, has no conviction for me, for I do not believe that natural selection is the only possible explanation of the passive cases. In fact, I cannot conceive it to be a possible explanation of the initiation of these cases. And I am glad to find in Roux’s theory—even if it be not exactly applied in Roux’s own sense—a mechanical expla- nation of the possibility of initiating certain fine and delicate inner adaptations. Organic Selection.—An interesting attempt to escape from the difnctlties“which are imposed on one by an absolute adherence to Weismann’s doctrine of the impos- Organic selec- _., .,. ; ; : tion, orthoplasy, Sibility of the inheritance of acquired characters or ontogenetic § coupled with a belief in the inadequacy of the selection. ; ; . ae slight fluctuating germinal variations to afford handles for the action of natural selection, is the theory va- riously called organic selection, or orthoplasy, proposed by Baldwin * and Osborn® in America, and Lloyd Morgan” in England. This theory, which might also be called one of OTHER THEORIES OF SPECIES-FORMING. 209 “ontogenetic selection,” or of “coincident selection,” is that the personal selection, or individual survival, among’ indi- viduals of a species does not necessarily depend solely upon congenital variation but may, must, indeed, depend on any ontogenetically acquired adaptations as well. As in many cases these ontogenetic adaptations are considerable, they will often carry individuals through very critical periods in their lives. But the individuals showing these ontogenetic adaptations in best degree will be those which actually pos- sess certain slight congenital variations, especially of the nervous system or coérdinating nerve centres, “which lend’ themselves to intelligent initiative, adaptive, or mechanical modification during the lifetime of the creatures which have them.” The ontogenetic adaptations may occur regularly in the lives of successive generations of individuals if the environment remains fairly constant. During these suc- cessive generations the congenital variations of brain, say, which make the successful ontogenetic adaptations possible, will by selection of the best ontogenetically varying individ- uals be themselves selected, and the species thus gradually be modified in a determinate direction. Also congenital varia- tions of nearly the same nature as the ontogenetic variations, or of a nature to supply the same need, will have time (that is, more chance, because of the longer time and repeated generations) to appear. In this case these advantageous variations can be transmitted directly by heredity, and thus a permanent adaptation be effected which will seem to be the result of the inheritance of an acquired character (2. e., the similar ontogenetic modifications) but which in reality is only the normal inheritance of a congenital variation. In the language of all the sponsors for this theory there seems to be a suggestion of the piling up or adding together of congenital variations, not simply those of brain or other control centre which make the ontogenetic modifications possible, but also of these modifications themselves during the crt ate 210 = DARWINISM TO-DAY. successive generations through which the species is safely carried by the temporary regularly appearing ontogenetic adaptations. But there is nothing in strict neo-Darwinism to permit of any such idea of increase. Such moving for- ward without the aid of selection can. only beeen td the adoption of some theory of orthogenesis. Either the con- genital variations are of such a character that the resulting ontogenetic modifications are not fairly to be distinguished from them, in which case they are assumed to be large enough from the start to afford handles for natural selection (which the proposers of the theory are not claiming), or they depend for their preservation on a kind of happy coinci- dence in occurrence with similar more effective ontogenetic modifications which are really large enough to save the life of the organism and hence the slight congenital variations along the same line. But in this latter case organic selection cannot demand much discussion until it explains away a Delageand radical failing pointed out clearly by Delage eae and Plate. This is simply that, in the face of tion, the large character which ontogenetic adapta- tion may and often does possess, those individuals in which the slight congenital variations in the right direction finally appear will have no special advantage over those in which they do not appear; the large and effective character of the ontogenetic adaptations, which are common to both kinds of individuals, being quite sufficient to determine the result of personal selection. The congenital variations will be too small in comparison with the ontogenetic variations to cut any figure in the fate of the individuals, and there is no reason at all to believe that individuals showing the slight congenital variations in the right direction will be the only ones to show the saving large ontogenetic adaptations. Plate suggests the following case to show the inutility of this theory : Suppose an antelope species to have a leg muscle averaging seven cm, in thickness, and several individuals to OTHER THEORIES OF SPECIES-FORMING. 211 show a congenital variation bringing the leg muscle up to eight cm. of thickness. Now if it requires a leg muscle of eight cm. for safety, as a matter of fact almost all the indi- viduals of the species will quickly bring their leg muscles up to that size by use. But suppose the actual need for safety was a leg muscle of fourteen cm., then only those individuals specially capable of that ontogenetic adaptation, 1. e. (modi- fication of the leg muscle by use and trophic irritability), up to fourteen cm., would be saved; and undoubtedly among these the original eight cm. individuals ought to stand in_ slightly higher numerical proportion (in regard to their original numerical standing in the species) than the origi- nally seven cm. individuals. Since, however, these eight cm. individuals originally existed only in comparatively small number, and since they possess no special means of recognis- ing each other and distinguishing each other from the original seven cm. individuals, mixed mating will inevitably soon swamp the original congenital increase of one cm. in muscle thickness. In connection with the explanation of this theory it will certainly occur to some of my readers, as it has to me, to ask Banviek of if it is not a dangerous proposal to give to assuming too = ontogenetic adaptations a greater worth in great import- ee eae Oe : aucee iets. ceciding the fate of individuals durime the genetic selection. strygole for existence than the congenital varia- tions. Is this not proposing to take away from the fluctuat- ing, individiual, so-called Darwinian variations practically all worth and capacity except as they are of immediate use to the just-born individuals, 7. e., before the ontogenetic adaptations have been able to develop? Indeed, why is it not a perfectly legitimate and a serious criticism of congenital fluctuating variations that they must be overshadowed, hid- den, and overwhelmed by the quick and large ontogenetic or individual modification of which practically all organisms are capable? Why will not those individuals born with the 212 DARWINISM TO-DAY. better and larger capacity to adapt themselves during their ontogeny to their needs win in the struggle for existence rather than those born with predetermined slightly larger leg, slightly stronger muscle, etc.? What is needed is capacity to develop by use and functional stimulus a much stronger muscle, a much swifter flight than the average. Those individuals that are capable of such considerable and really worth while ontogenetic adaptation will win in the struggle for existence; and while they may not hand down by inheritance their actwatty acquired characters, will they not hand down their inherited congenital capacity for con- siderable and effective ontogenetic adaptation? APPENDIX. *For a fairly complete bibliography, with abstracts, of all the important discussions of species-forming theories published since 1895, see L’Année Biologique (ed. Y. Delage). For bibliography and abstracts, also see Zoologischer Jahresbericht, issued annually by the Naples Zoological Station. See also discussions and notes in various biological journals, as Biologisches Centralblatt, Natural Science (now discontinued), Nature, Science, American Naturalist, etc. * For a careful account and discussion of Weismann’s work and theories as far as developed up to 1893, see Romanes, “An Exami- List of Weise mation of Weismannism,” 1803. Weismann’s pres- mann’s evolution ent-day position and his arguments for the selection Papes®: theories are set out in his ‘“Vortrage tiber die De- scendenztheorie,” 2 vols., 1902, which we may look on as consti- tuting a manual of neo-Darwinism, treating all the more familiar bionomic phenomena and conditions as explained by selection. The following is a chronological list of the more important of Weismann’s publications: “Uber die Berechtigung der Darwin’schen Theorie,” 1868. “Uber den Einfluss der Isolirung auf die Artbildung,” 1872. “Studien zur Descendenztheorie: I, Uber den Saison-Dimorphis- mus der Schmetterlinge,” 1875. “Uber die Dauer des Lebens,” 1882. “Uber die Vererbung,” 1883. ii OTHER THEORIES OF SPECIES-FORMING. 213 “Uber Leben und Tod,” 1884. “Die Continuitat des Keimplasmas als Grundlage einer Theorie der Vererbung,” 1885. “Uber den Riickschritt in der Natur,” 1886. “Uber die Bedeutung der Sexuellen Fortpflanzung fiir die Selec- tionstheorie,”’ 1887. “Uber die Zahl der Richtungskérper und iiber ihre Bedeutung fiir die Vererbung,” 1887. “Botanische Beweise fur eine Vererbung erworbener Eigenschaf- ben, 1888, “Uber die Hypothese einer Vererbung von Verletzungen,” 1880. “Bemerkungen zu einigen Tages Probleme,” 1890. “Gedanken tber Musik bei Tieren und beim Menschen.” 1890. “Aufsatze uber Vererbung und verwandte Biologie,” 1892. (This includes the eleven preceding papers now published in book- form. These essays have also been translated into French, by H. de Varigny, and published under the title: ‘““Essais sur lHérédité et la Sélection Naturelle,” 1892; and also in Eng- lish as ‘““Essays upon Heredity and Kindred Biological Prob- lems,” trans. and ed. by Poulton, Shoneland, and Shipley, 2 vols., 1891 and 1893. “Amphimixis oder die Vermischung der Individuen,” 1891. “Das Keimplasma; eine Theorie der Vererbung,” 1892; Eng. trans. by Parker and Ronnfeldt, as “The Germ-plasm; a Theory of Heredity,” 1893. “Die Allmacht der Naturztichtung, eine Erwiderung an H. Spen- cer,” 1893; also in English as “‘The All-sufficiency of Natural Selection,” in the Contemp. Review, Vol. LXIV, pp. 309-338, 596-610, 1893. “The Effects of External Influences upon Development,” Romanes Lectures, 1894; also in German as “Aussere Einfliisse als Entwicklungsreize,” 1894. “Neue Gedanken zur Vererbungsfrage,” 1804. “Uber Germinal-Selection,” in Compt. Rendus, 3d Congress In- ternat. Zool., 1896; also, in English, trans. and ed. by Mc- Cormack, as “On Germinal Selection as a Source of Definite Variation,” 1806. “Thatsachen u. Auslegungen in Bezug auf Regeneration, ” Anat. Anzeig., Vol. XV, 1890. “Vortrage tiber Descendenztheorie,”’ 2 vols., 1902; also in Eng.,, trans. by J. A. Thomson as “Lectures on the Theory of Descent.” 2 vols., 1904. * For a detailed critical discussion of panmixia, see Wolff, “Der gegenwartige Stand des Darwinismus,” 1806. 9 214 DARWINISM TO-DAY. * Various theories of ultimate protoplasmic structure have been proposed to explain what is not really known about this substance. Theories of ul- hese theories refer almost exclusively to the physi- timate protoplas- cal, rather than the chemical, make-up of protoplasm, micstructuree and for the most part have been proposed with special attention to the germ-plasm, 7. e., the protoplasm of the sperm- and egg-cells. The spur to the formation of these theories is the necessity that biologists have felt imposed on them from the be- ginning of the study of heredity and development of offering some rational explanation of those phenomena. That from a single germ- cell formed by the fusion of a sperm-cell and an egg-cell from different parents, a complete new organism composed of millions of cells of manifold variety of specialisation and arrangement can develop, is wonder enough; but that this new organism shall repeat in all its parts with extraordinary fidelity the structure and physi- cal idiosyncrasies of one, or show a combination of the character- istics of both, of the individuals from which came the original single sperm- and single egg-cell, adds wonder to wonder. What physical or structural basis is there in the fertilised egg-cell that it can represent in its tiny self the whole of a giant body, like that of an elephant, whose every detail it can, by a process of development under suitable extrinsic conditions of temperature, food-supply, etc., repeat in a new creature. The answers to this, all purely specula- tive, or more fairly theoretical, because some of the answers at least have been guarded in their forming by all the care which a rigorous scientific attitude toward hypothesis demands, are many and various, and date from the days of the Greek philosophers to the present hour. It would take too much space and carry us too far afield to attempt anything like an explanatory list of even all of the better known of these general theories of the invisible ulti- mate structure of the germ-plasm here, but by selecting seven or eight types of the principal categories or kinds of these theories, and briefly explaining them, we.may have at least some conception of the attitude that biologists take toward this great problem. The reader who has a fancy for following this subject further is re- ferred to the admirably full and lucid treatment of it in Delage’s great work, “L’Hérédité” (2d ed., pp. 431-772, 1903). Most of these theories include much more in them than a santa speculation as to the ultimate structure of the life-substance; they attempt to explain all the phenomena of life, motion, nutrition, growth, reproduction, development, heredity, variation, etc., with reference to some assumed ultimate make-up of the primitive life- substance, and the relation of this structure to the known physico- chemical forces and conditions of Nature. Most of the older OTHER THEORIES OF SPECIES-FORMING. 215 theories assumed a peculiar vital force, which is not assumed in the later ones, although exception must be made.to this statement in favour of the point of view held by the recent so-called neo-Vitalists, those present-day workers who admit the hopelessness of trying to reduce all vital phenomena to a physico-chemical basis. An old type of theory of heredity and structure of the germ-. plasm, widely held in the seventeenth and eighteenth centuries, is Encasement that of the “encasement of the germ” in one of the theory. germ-cells, either the spermatozoid or the egg. The essential part of this theory is that the new organism is assumed actually to exist in miniature, with all its parts present, in one of the germ-cells, and in this miniature body must exist, by repeated encase- ment, all its future progeny. Whether the believer in this theory con- sidered the tiny new creature, only needing to swell and grow to be complete, to be encased in the sperm-cell or the egg-cell, ranked him respectively with the spermatists or the ovalists. A vigorous strife raged between these two factions among the upholders of this simple and effective explanation of heredity which led to cer- tain interesting compromises. A commonly held one was that the sperm-cell furnished the spiritual element, the egg-cell the material and mechanical elements of the new creature. Another, held by Linnzus, the great botanist and father of biological classification, was that, in plants, the egg (ovule) furnished the internal and re- productive organs, while the sperm-cell (pollen) furnished the exter- nal and vegetative parts. De Candolle, another great botanist, held just the reverse of this view. All these theories of an actual encasement in the germ-cells of a whole or part of a new organism were not mere guesses, but were based on what men thought they saw through their microscopes. The long reign of these theories, now shown to be utterly absurd, illustrates well the constant dan- ger which attends our attempts in all biological study to interpret what we see when working at the limits of visibility. With our much-improved microscopes we laugh at the fantasies which the microscopic vision of our eighteenth-century co-workers raised up. Who may say that our own interpretations of plasm-structure may not seem as absurd to the biologists of the next century? By far the great majority of theories of ultimate protoplasmic structure belong to what Delage calls the category of theories of Micromeric micromerism. Which means simply that all these theories. theories assume a composition of the plasm out of minute ultra-microscopic units of structure, which are also units of life, for all these units are presumed to be endowed with the essential life-attributes. These units may be looked on, as they were by Buffon, as universal, indestructible, hence immortal, parti- 216 DARWINISM TO-DAY. cles, or, as they are in most of the micromeric theories, as living particles which are destroyed with the death of the organism which they compose. In this latter type of assumption the units are, according to some theories, all of the same nature, all exer- cising an equal influence in determining the character of a devel- oping organism (Spencer, Haacke, His, Cope); or they are, as assumed in other theories, of various character and charged with various functions. This latter kind of unit is held by some authors. to be actually representative either of ancestral plasmas (Weismann) or of the actual body-cells of the parent (Darwin, Galton, Brooks, Hallez), or of elementary characteristics and functions of the organism (Nageli, Kolliker, de Vries, O. Hertwig), or at the same time of both body-parts and elementary characteristics (Weismann’s. latest theory). Buffon’s theory assumed that ‘the substance of which organisms are composed differs essentially from that which composes the Buffon’s inorganic bodies. Organisms are composed of special theory. particles, the organic molecules. These molecules are universal and indestructible: universal in that they exist everywhere where life has access, indestructible in that death and the dissolution which follows destroy the organisms, break down the molecular com- binations which constitute them, but do not reach the molecules themselves. These are only separated, put at liberty, but remain ready to enter into new groupings. While they cannot be de- stroyed, neither do they increase in numbers. They form nothing actually new, either spontaneously, or by means of old ones, so that, measured by these organic molecules, the total quantity of life in the universe is invariable’ (Delage). Nearly a hundred years. later Bechamp (1883) proposed a theory similar to Buffon’s in which he assumed the composition of organisms out of minute elementary living particles called microzymes. Like Buffon’s organic molecules they are indestructible, and they are strewed in innumerable numbers through earth, air, and water. They owe their origin to special creation by God. Of the non-immortal kind of micromeres Spencer’s physiological units represent a general type favoured by numerous theorists: namely, living units all of the same nature and active because of their polarity, their form and molecular forces, or their vibratory motion. Spencer’s physiological units are active because of their polarity, but the annular atoms of Dolbear’s theory and the plastidules of the slightly varying theories of Haeckel, His, Cope, and others, owe their active properties to their vibratory motion. According to Spencer (1864). there exist between the cells (morphological life-units) and the molecules which compose them OTHER THEORIES OF SPECIES-FORMING. 217 (chemical units), units of a third order (physiological units) com- Spencer's posed of groups of molecules. These units are very theory. small but very complex, and are the smallest masses in which living substance can occur. Most of the micromeric theories, which come after Spencer’s, adopt this conception of a life-unit, very small, but composed of an aggregate of molecules, and therefore very complex. To his physiological units Spencer attributed a polarity, wholly analogous with that possessed by the molecules of crystalline substances. It is owing to this delicate, precise polarity, varying of course with the varying molecular consti- tution of the units, that they possess the capacity of actively arranging themselves in the varied groupings normal to the parts of the organisms. “Thus the resemblance is perfect between the chemical polarity which causes crystallisation and that of the physiological units which produces the form of organisms. In one case the chemical molecules group themselves in a manner to form an aggregate of definite but simple form, cubical, prismatic, rhomboidal, with their parts arranged en tremies, aiguilles, croix de Saint André, boules épineuses, etc. In the other the units group themselves in a body of a form less rigorously defined but which may be very complicated: such as a plant or an animal.” ( Delage.) Of the theories in which the living units are assumed to be of different kinds, and endowed with different functions, some assume the units to be not directly representative of different cells or parts of the body, while others assume this truly representative condition. Of the first sort are a number of theories like those of Berthold, Geddes, and others, in which the units are taken to be actual chemical molecules, endowed with activity through special physico- chemical properties or through purely chemical ones, while still others keep to the more usual type of a unit of a higher order than a molecule, in which case also this unit is looked on as spe- cially active because of particular electrical (Fol) or chemical (Altmann and Maggi) or vital (Wiesner) endowment. But all of these theories are much like each other and are much like Spencer’s theory in regard at least to the assumed units. Different, how- ever, is the type of theory which introduces the assumption that the fundamental life-units are directly representative of either the specific cells, parts, or elementary characteristics of the organ- ism. This is the kind of unit especially favoured by the men who had, in their formation of a theory, a special eye to the problem of heredity. How is the single germ-cell to be the bearer of the “heredity” of the organism from which it comes? what more simple to assume than that this cell shall be composed of minute particles gathered from all the cells or groups of similar aes 2 oo: DARWINISM TO-DAY. cells of the body of the parent? And that is precisely the charac- teristic assumption, dressed up in an ingenious variety of form, which charac-erises the theories of life-units most favoured at present: such theories are those of Darwin, Galton, Brooks, Nageli, de Vries, Hertwig, and Weismann. In some of these, interesting attempts are introduced to connect the assumed structure with the actually observed finer structure of the nuclear protoplasm, by introducing combinations of the fundamental units, in one or two, or even three, successive degrees until an aggregation is reached which corresponds with those microscopic structures, the chromo-. somes, or chromatin granules or threads, which are actually visible to the microscope-aided eye. The most recent one of the theories of this general type is that of Weismann’s biophors and determi- nants structure of the germ-plasm, already explained in connection with the presentation of his theory of germinal selection (see pp. 193 ff.). As other examples we may note especially Darwin’s, called the theory of the pangenesis of gemmules; and Nageli’s, ‘called the theory of micelle and idioplasm. Darwin’s gemmules are extremely minute particles, which are formed in all the various cells of the body and are capable of repro- Darwin's ducing themselves rapidly and in great numbers by theory. repeated division, and which, by virtue of their minute size and an innate activity due to a sort of affinity or attraction exist- ing between them and other substances, move about freely in the body, penetrating any membranes, and arranging themselves with a deli- cate precision just where they are most needed. When a gemmule enters an undifferentiated or developing cell as yet containing no other gemmules, it controls the development of that cell so that it becomes a cell of the type from which the gemmule had birth, each gemmule representing thus exactly the characteristics and the type of its mother cell. Thanks to the delicate and precise adjustment of affinities, migrating gemmules only enter those cells which they really should enter in order that a normal development of all the cells of the body should go on. But those few cells of the body which are destined to become germ-cells, that is the spermatozoids and eggs in animals, the pollen grains and ovules in plants, receive during their formation gemmules from all the other cells of the body. Not only from all the cells of the fully developed body, but from all those ephemeral cells which arise and live for a while during the ontogeny of the parent, performing certain special func- tions and then making way for the definitive cells of the mature organism. Thus in the germ-cells are stored actual physical repre- sentatives of all the cells which have existed during the whole life of the parent body. These innumerable gemmules remain inactive -—5 —— OTHER THEORIES OF SPECIES-FORMING. 219 jn the germ-cells until, after fertilisation, the egg-cell begins its development. Then as the cells of the new organism begin to be produced, the gemmules become active and each one moves into the cell it should control and there directs its further development into precisely the kind of cell it should be at precisely the time it should be this kind of cell, until there results from this gemmule- controlled development a photographic reproduction of the parent body. Nageli’s conception is that when the complex life-characterising al- buminous substances took their birth in an aqueous liquid, they would Nageli’s be precipitated, as they are not soluble in water. This theory, precipitate is formed of small masses, a sort of organic crystals, which may be called micelle. And just as an inorganic crystal deposited in a saturated saline solution of the same nature ‘determines the deposit on its surface of the dissolved molecules in the form of little crystals, and by this means grows, so wherever any micellz are formed they facilitate within their sphere of influ- ence the precipitation of others, so that this production of micelle instead of taking place miscellaneously through the liquid will be localised at certain points. Thus arise aggregates of albuminous substance, in the condition of micelle, forming the primitive protoplasm. The micelle, although insoluble in water, have a great affinity for it, and each one at the time of its precipitation fixes around itself a thin layer of water, at least as thick as a water molecule. Thus, all the micelle grouped together in a bit of primi- tive protoplasm are separated from each other, and also held to- gether by a layer of water as thick as two water molecules. This water forms an integral part of the protoplasm. By virtue of it, an aggregate of albuminous micelle can increase by intercalcation as well as by the addition of new micelle on the outer surface. By admitting more or less water the protoplasmic mass may become more or less nearly fluid. Thus are accounted for the various densities always met with in the different parts of a protoplasmic cell. . . A further essential part of Nageli’s theory is an arrangement of the primitive protoplasm in two ways, resulting in two kinds of it, which are called nutritive plasm and idioplasm respectively. This arrangement depends on the molecular forces pertaining to the micelle, and the difference, resulting in two kinds of plasm, depends upon the relative situation of the micelle composing the mass, just how this affects them differently, however, not being made very clear. But the differentiation is very important, for it is the idioplasm alone which contains the essential life-properties and which really Zives rise to life with all its variety and complexity. This idioplasm 220 DARWINISM TO-DAY. is formed at first in scattered bits in the nutritive plasm mass, but as these bits increase they join and become united into a network surrounded by and containing in its meshes the nutritive plasm. And one of the most interesting parts of Nageli’s hypothesis is that he conceives this network of idioplasm not to be limited by cell boundaries but to penetrate from one cell into adjacent cells and thus to spread through and unite in a most significant and important way all the cells and tissues of the body. It is just this sort of a ramifying, stimulus-carrying, protoplasmic network connect- ing all the parts of the body that the believers in the inheritance of acquired characters seem to need as a mechanism to transmit from soma to germ-cells the effects of external and functional stimuli. Next, the theory of intra-cellular pangenesis of de Vries may be briefly stated. This theory has become the more important be- cause of the great interest aroused by and the large appreciation given to the mutations theory of species-forming of the same biologist. De Vries’s theory of intra-cellular pangenesis has much in common with Darwin’s theory of the pangenesis of gemmules, but it is able to do away with that particularly weak part of Dar- win’s theory, which postulated the circulation of the gemmules. throughout the organism in order that they should meet in the germ-cells and modify these cells in a parallel way with the modi- fications occurring in the peripheral organs. Darwin had to postu- late this circulation of the gemmules through the organism in order to explain the phenomena of regeneration, and the heredity of acquired characters. Now that the heredity of acquired characters has been shown to be at best an extremely doubtful phenomenon, and that regeneration is explicable by other means, de Vries has. been able to drop this weakest part of the Darwinian conception. So that in the theory of the later biologist, the circulation of gem- mules does not extend from one cell to another throughout the body of the organism, but limits itself to that particular cell in which it is created and circulates only between the nucleus and cytoplasm, from which comes the name, “intra-cellular pangenesis,”’ as distinguished from Darwinian pangenesis. De Vries’ theory may be abstracted as follows (following Delage) : The form and properties of cells result from their protoplasmic composition just as the properties of the inorganic bodies result De Vries’s from their chemical composition. Is it necessary, then, theory, to admit that there are as many kinds of protoplasm as there are different sorts of cells in the organised beings? When one recalls how many different cells there are in a single organism, and that the homologous cells are not identical in different species, one. 1 a aie Te OTHER THEORIES OF SPECIES-FORMING. 221 realises the incalculable number of these cells and despite the rich- ness in variety of proteid substances, it will be impossible to con- ceive that each kind of cell should have its own kind of proto- plasm. There is here, apparently, an insurmountable difficulty, but one which it is easy to do away with by a very simple concep- tion. This conception consists in distributing the complex charac- ters and properties, innumerable in living beings, into elementary characters and properties much less numerous, which, by varying combinations, produce the almost infinite variety that we observe in the inorganic world. Just as with a score and a half of letters one may form all of the words of the human language, so with the elementary properties of which the actual number is still very con- siderable, one may reproduce all the characters of living beings in all their variety and complexity. It suffices, then, to admit that these elementary characters and properties are represented by as many material particles, and the problem is solved. These particles are the pangenes. The pangenes, then, are small, organic particles, invisible to the microscope, formed of an enormous number of chemical mole- cules and differing from the most complex chemical substances by three properties which are common to all of them and which are characteristic of living matter; they nourish themselves, in- crease in size, and multiply themselves by division. Beside these three general properties which make living molecules of them, the pangenes possess particular properties depending upon their chemical constitution, differing for each of them, and which are bound to them indissolubly in such a manner that, wherever a pangene finds itself, the elementary property or character special to it will show itself if internal and external conditions permit of this manifestation. Latent or patent, potentially or evidently, the char- acter is always there where is the corresponding pangene. Each cell contains a great number of pangenes in activity, and its charac- ters and properties in sum are the resultant of the elementary characters and properties of the pangenes composing it: just as the anatomical and physiological characters and properties of the living individual are resultant of the anatomical and physiological charac- ters of the cells composing it. It is necessary to conceive of the cellular protoplasm as formed of innumerable pangenes bathed in a liquid in which are dissolved substances purely chemical: albumen, glucose, salts, etc. Perhaps similar substances penetrate the pangenes themselves, but we do not know this. The nucleus contains in general all the kinds of pangenes that compose the individual. But these pangenes are there in a sort g2e DARWINISM TO-DAY. of inactivity, in reserve, in order to be transmitted to the daughter nucleus when the cell divides. They can divide themselves, and it is indeed necessary that this be so in order that the two daughter nuclei can each receive a complete lot of the representative pan- genes; but they do not manifest in the nucleus their special proper- ties, which remain in a latent state. There is no exception to this except in the case of those certain pangenes which control the division of the nucleus. These enter into activity at the necessary moment in order to determine the characters of the division and in particular the position of the plane of segmentation. The cytoplasm is also composed of pangenes; but these pangenes, with the exception of those which come from the cytoplasm of the egg, come from the nucleus. From the nucleus there come, in fact, pangenes which distribute themselves in the cytoplasm and multiply there abundantly. These pangenes are exclusively those of which the cytoplasm has need in order to manifest characters and proper- ties which belong to the cell, and it is by delivering to it such and such pangenes and no others that the nucleus rules the cytoplasm, which would remain inert were it not for this infusion of living and active particles. There is, then, a great difference between the nucleus and the cytoplasm from the point of view of the pangenetic constitution. Each nucleus contains in general all the pangenes of the individual united undoubtedly into groups more or less considerable, which lie in the chromatic filaments, and these groups, analogous to the gemmules of Darwin’s theory, probably form those little grains arranged in rows, which are revealed under a great microscopic magnification of the chromatic threads. But there are one, two, or, at most, a small number of pangenes of each kind; all are inactive save at the moment of division, those which rule this phenomenon; they can multiply themselves but slightly, and in general they do not divide except to replace those which emigrate into the cyto- plasm and to furnish at the moment of division to each daughter nucleus the complete lot which it ought to receive. In the cyto- plasm, on the contrary, there is but a small number of kinds of pangenes immigrated from the nucleus in the quantity exactly necessary, but there these pangenes are enormously multiplying, so that there is a very great number of each kind, and they are almost always in a state of activity. B. Hatschek has recently proposed (‘““Hypothese der Organischen Vererbung,” 1905) a new micromeric theory which postulates that Hatschek’s the protoplasm is composed of two different kinds cf theory. biomolecules; one called ergatules, which function as- similatively, that is, take up food-stuff and excrete waste, but do not OTHER THEORIES OF SPECIES-FORMING. 223: possess a capacity for growth or self-reproduction; second, the gen- eratules, which have no particular functional work to perform but can grow and reproduce themselves and can carry over this capacity of. reproduction to the ergatules, because they can fuse with them or attach themselves to them and thus carry over to them their char-- acteristic peculiarities. These generatules are looked on as the chemical radical of the ergatules, and become therefore the directly determining agents for all peculiarities of the body. The ergatules: sit chiefly in the cytoplasm of the cell, while the generatules lie in the cell nucleus, especially in the chromosomes, and therefore render these the bearers of hereditary characteristics. Thus baldly and wholly incompletely stated these theories of ultimate plasm structure which shall be of a sort to agree with all the varied phenomena of life, and particularly those of heredity, show, unfortunately, only their fantastic face. For as it is pre- cisely in showing how the postulated structure and properties are: perfectly consonant with all the known phenomena of life that these theories have their actual interest and strength, a fantastic: and improbable face shown as to this robs them of all interest. But,. perhaps, it is well that the fantastic aspect of them should be first recognised. For it is only fair to say that the ingenuity and plausi-. bility, the precise and exhaustive development of detail, of some of these theories, are really dangerous to the layman who first happens: to read a full and well-stated account of one of them by an enthu- siastic upholder. One’s eyes become closed to, the. fact..that.all.the structure and performancé that seem SO natural, and fit in so exactly with all” that’ “we” acttially “know” of the’ ‘phenomena “of. ‘life, havénot béen seen, only imagined. ‘One needs an introduction to these theories which insists above all on their wholly hypothetical! character. Otherwise one is surprisingly readily hypnotised into accepting one or the other of them as a statement of fact. These general theories are the atomic theories of biology without one-- tenth the probability of truth or one-tenth the actual acceptance in science that the atomic theory of the chemists has. And even: that 1s beginning to be discarded in modern chemistry. These: theories are, as Weismann has said, the outcome of the fact that “the deeper one studies into the phenomena of heredity, the more: one is convinced that something of this kind of a condition [of a composition of the fundamental life substance out of ultra-micro- scopic units bearing a certain spatial relation, and one of attractions -and repulsions to each other] must really’ exist: for it is impossible .to explain the observed phenomena in any other way, that is, by -any much simpler assumption.” But on the other hand a sufficient reason against accepting any one of these highly developed theories: 224 DARWINISM TO-DAY. of the structure and functional capacity of invisible life-units, is the sagacious one of Delage when he says that simply by the law Delage’s of probabilities it will be impossible by pure imagining criticisms. to explain correctly in detail the ultimate structure of protoplasm. Has any one, asks Delage, guessed in advance, with the least truth, structures which the microscope has later been able to reveal to us? Has any one guessed the cross-striation of muscles, the cilia of vibratile epithelium, the prolongations of the nerve- cells, the make-up of the retina, or the organ of Corti, the chromo- somes, the centrosome? Distinctly not. Delage points out that the chemists had a much better chance to hit the truth in supposing atomic structure, for they had a much less complex condition to perceive, and they had approached in their positive knowledge very much nearer the hypothetical element which they adopted. Le Dantec criticises the micromeric theories of protoplasmic structure by saying that all these theories seek to make mysteries Le Dantec’s Clearer, complex things simpler, by reducing large criticisms, things to small ones. A man, for example (he says) is composed of 60 trillions of cells and is nevertheless produced by sexual elements of very small size; here is a phenomenon to ex- plain. The micromerist says that the difficulty of this explanation would be less (or at least not so sharply defined!) if one divided the problem into 60 trillions of parts; that is, 1f one replaced the reproduction of man by 60 trillions of partial reproduction. One has therefore imagined particles infinitely small which are to the cells what the sexual cells are to the man. And this comparison has been, consciously or not, claims Le Dantec, the point of departure of all the systems of particulate representation in the germ- plasm. We have simply substituted for a single heredity, continues the critic, 60 trillions of partial heredities, each exactly as mysterious as the first. Thus these 60 trillions of gemmules gathered in the egg and distributed in a precise manner are in reality only a dis- guising of the homunculus of the ovalists. Perhaps we have no reason to suppose that these gemmules design by their agglomeration this invisible homunculus, but at least it is certain that they are disposed in a manner which is in relation to the form of the man to be determined, since in fact each of them represents not alone a cell of the man, but a cell with the place it is to occupy. One sees thus how complex is this system which has for its aim the simplifying of the question of heredity: it is more logical to consider simply the egg as having the power to produce a man than to attribute a power as mysterious to 60 trillions of gemmules to which it is necessary to accord, in addition, a determinative capacity OTHER THEORIES OF SPECIES-FORMING. 225 which results in conducting each cell to exactly that place which it ought to occupy. In addition to the theories of an ultimate micromeric structure of protoplasm, certain other recent hypothetical explanations of Verworn’s bio- the special properties of protoplasm should be noted. gen hypothesis. One is the biogen hypothesis of Verworn, the physiol- ogist of Gottingen, one the chemism theory of Le Dantec, one the physical machine theory of Delage, and another is the general vital principle hypothesis of the neo-Vitalists. Verworn’s hypoth- esis to account for the physiological activities of protoplasm, 7. e., the special life attributes, as assimilation, disassimilation, growth, irritability, etc., consists in the postulation of a complex chemical compound of unknown structure called biogen, but with the special capacities of an enzyme. This biogen is assumed to be constantly labile, 7. e., breaking down and rebuilding itself and by this per- formance acting as a go-between (enzyme or perhaps katalysator) between the atmospheric oxygen brought to the cell by the blood and the oxidisable (food) products (also brought by the blood). Not only can the biogen rebuild itself, but by polymerisation it can grow, that is, increase the size of its molecules by adding side- chains of atoms. ‘This, according to Verworn, constitutes cell growth. This growth is not indefinite, as the atoms tend to break away again and thus there is a limit to the size of the biogen mole- cules. The author only presents his conception of biogen as a good working hypothesis. Delage has also offered a tentative physico-chemical explanation of certain of the properties of protoplasm, as its movements, its Delage’s ma- nutrition, and even its reducing division, on the basis chine theory. of osmotic effects due to the constant interchange of substance from the outer layers of the cell protoplasm to the inner through fine membranes or special protoplasmic layers which he assumes to enclose each cell part, 7. e., nucleus, chromosomes, etc. Nutrition, for example, is effected according to Delage, by constant selective osmotic exchanges between the liquid and_ semi-liquid parts of the cell, the blood-plasm of course constantly bringing food and carrying off excreta to and from the periphery of each cell. Cell division is the result of mutual pulls and pushes, its essential feature always being the actual sundering of parts; but how this mechanical process is guided or controlled as it is, or even initiated, is left unexplained. Le Dantec holds that life is a chemical phenomenon. “La vie est Le Dantec’sthe- un phénomeéene chimique, c’est-a-dire que les seuls ory of chemism. caractéres essentiels par lesquels une action vitale differe d’une manifestation de l’activité de la matiére brute sont rela- 7 ad j 226 DARWINISM TO-DAY. tifs a des destructions et des constructions d’édifices moléculaires. Cette vérité, toute la biologie nous la prouvera de mille maniéres; il vaut donc mieux l’énoncer en commengcant, de maniere a ce qu'elle prenne la premiére place dans l’esprit de ceux qui se livreront a étude des €tres vivants. “Mais une réaction chimique n’est pas quelque chose d’isolé et ne se produit que dans certaines conditions dont la réalisation peut étre liée a des particularités d’ordre physique (chaleur, é€lectricité, lumiére, etc.) ; de plus, elle s'accompagne toujours de phénoménes accessoires qui sortent également du domaine de la chimie (chaleur, mouvement, etc.). Ceci est vrai surtout pour les réactions des matiéres vivantes, a cause de l'état trés spécial de ce qui représente la solution de ces matiéres dans l’eau. La vie est aquatique, mais les mati€res vivantes ne se dissolvent pas comme du sel marin” (‘“‘Traité de Biologie,” pp. 43-44, 1903). He goes on to discuss, with keen analysis and ingenious but uncon- vincing synthesis, the various primary conditions and activities of life, explaining each vital phenomenon separately on a basis of chemism. He even proposes a chemical notion of species. Such a chemical species can of course take no primary account of form, but as conditions of chemical identity will usually involve identity of form, the various individuals composing a chemical species will possess a similar or identical form. An author, undertaking what Le Dantec undertakes, must necessarily be a bold thinker and a bold writer. The present author is both. And he is nowhere unin- teresting or unsuggestive, but also is he nowhere wholly con- vincing. The position of the neo-Vitalists is perhaps best to be taken from that of Driesch, an extremely able present-day biologist, whose first belief was in a radical mechanical explanation of all life phenomena, and whose brilliant experimental work has furnished many of the examples referred to in all text-books of the modern study of the mechanics of development. But Driesch’s present position 1s an uncompromising belief in the impossibility of explaining life-forms and life-functions on the basis of ever so complex a combination of purely physico-chemical and mechanical conditions and factors. Put positively, neo-Vitalism demands the assumption of an extra-physico-chemical factor (called ‘“‘psychoid,” according to Driesch’s nomenclature), which is an_ attribute of, or essential kind of potentiality pertaining to, organised living substance, and not found in nor influencing inorganic bodies. Butschli has well pointed out that neo-Vitalism is really only a return to the old “vital principle” belief, and that we are now, Neo- Vitalism. OTHER THEORIES OF SPECIES-FORMING. 227 and have beep ever since our practical giving up of the vital prin- ciple notion, making steady progress in the explanation of life- forms and life-functions on strictly mechanical and physico-chemical grounds. While we have by no means explained all life attributes in this way, Biitschli holds that our progress has been such as to make no demand for the introduction as yet of a new vital principle under a pseudo-scientific guise. Other neo-Vitalists, of whom _G, Wolff_is a type, lay chief stress on the inexplicableness of the Zweckmdssigkcit in organisms by any of the known biological facts and factors, and see in the deter- mination or very existence of this Zweckmdssigkeit the chief revela- tion of a vital factor, wholly distinct from anything found in the inorganic world. Wolff's argument is clever and suggestive, and brings home to one strongly the indissoluble relationship between living matter and its adaptivity. In its fundamental character life is adaptivity: the indispensable relation between living matter and the rest of nature is the pliability, the adaptiveness of the living matter. “Die sweckmdssige Anpassung ist das, was den Organis- mus gum Organismus macht, was sich uns als das eigentlichste Wesen des Lebendigen darstellt. Wir kinnen uns keinen Organis- mus denken ohne dieses Charakteristikum. ... Und wir erkennen dass jede Erklarung, welche das Leben voraussetzt, jede postvi- tale Erklarung der organischen Zweckmassigkeit, in jedem Falle voraussetzt was sie erklaren will; wir erkennen dass die Erklarung der Zweckmassigkeit mit der Erklarung des Lebens zusammenfallen muss.” But perhaps there is a difference between the plastic response of protoplasm to the varying conditions of oxygen, food, temperature, etc., about it, so that within certain limits of external versatility it still lives, and that extraordinary specialisation of fitness which we see exhibited by a parasitic Sacculina with relation to its crab host. And believers in natural selection hold that it is exactly one of the chief glories of selection that it does explain this highly specialised fitness. More than that, closer examination of the phenomena of organic Nature reveals many examples of an unfit- ness, which certainly ought not to exist if there is a special vital principle responsible for fitness throughout the organic kingdom. There is a moth common with us here in California, by name Phryganidia californica, whose larve live on the leaves of the oak- trees. Two generations appear each year. The eggs for the first brood of caterpillars are laid in spring by the moths on the leaves of the live-oaks and also of the white-oaks. The larve soon hatch, feed through the summer on the leaves, and in September pupate, the moths appearing in October. These moths now proceed to lay 228 DARWINISM TO-DAY. the eggs for the second generation, which eggs are also deposited on the leaves of both live- and white-oaks. But while the live-oak is an evergreen tree, the white-oak is deciduous, and sheds its leaves soon after these October eggs are laid on them, which means that one-half of this second generation is doomed to die of starva- tion immediately after hatching. This is repeated regularly each year, and is certainly a distinctly unfit habit in this moth’s life economy. Plate refers to a similar instance of Unsweckmdassigkeit as follows: “As I once was landing on Santa Maria Island in the Gulf of Aranco, the whole shore swarmed with thousands of giant cuttlefishes (Ommatastrephes gigas) which partly lay dead on the beach and partly were swimming around in the shallow water. These latter instead of trying to get back into deeper water, con- stantly swam towards the land until a breaker threw them up high and dry. Reflexes and instincts often make mistakes, that is, they result in actions which result in actual harm, and nothing is more mistaken than the declaration that an organism reacts under normal circumstances always in a way to serve the preservation of its life. That organisms under new circumstances or in abnormal condi- tion very often react unfitly, requires no elaboration; every light- house against which thousands of birds and insects are killed, the toxicological phenomena, the incomplete regeneration, every club- foot, and every Wasserkopf prove this. The countless harmful re- actions and incompletenesses in structure make it impossible to speak, in the vitalistic sense, of an inherent Zweckmdssigkeit of organisms, of a tendency always to change in the direction of use- fulness. An organism is exactly as definitely ruled by chemico- physical laws as every dead body. Let an organism happen in any set of conditions: it has no longer the choice among a useful, a harmful, or an indifferent reaction, but the causal chain determines for a definite direction and this is, as a thousandfold observations show, not a life-preserving one, in other words is not sweckmdssig. If now in spite of this organisms have become, in the course of earth-history, even more complex and more capable and have acquired the most wonderful adaptation, there must obtain some regulatory principle in Nature, which we, with Darwin, recognise as actually existing in the struggle for existence and the con- sequent selection of fit variations. If organisms actually had the capacity to direct their vital activities always toward the side of utility, then the workings of the natural forces would be over- come and Mysticism again be introduced in natural philosophy. Both actual observation and the theoretical basis of natural science give no basis for any hypothesis of the existence in organisms of an immanent capacity for adaptive reactions.” OTHER THEORIES OF SPECIES-FORMING. 229 5 Weismann, A., “On Germinal Selection as a Source of Definite Variation,” trans. McCormack, p. 3, 1896. *T quote from Morgan, “Evolution and Adaptation,” pp. 165-166, 1903, the following special protest against the means of escape from Morgan’s criti- 2 tight place which Weismann has taken advantage of cism of Weis- in his dilemma: ‘Thus Weismann has piled up one mann’s method hypothesis on another as though he could save the of argument. 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 verifica- tion, 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 philosophisers 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 the selection of fluctuating germs has led one of the most widely known disciples of the Dar- winian theory. “The worst feature of the situation is not so much that Weismann has advanced new hypotheses unsupported by experimental evi- dence, but that the speculation is of such a kind that it 1s, from its very nature, unverifiable, and therefore useless. Weismann is mis- taken 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 observa- tion or by experiment.” 7 Roux, W., “Der Kampf der Theile im Organismus,” 1881. ® Baldwin, J. Mark, ‘““A New Factor in Evolution,” Amer. Nat., Vol. XXX, pp. 441 ff., 1896; see also the same author’s ‘‘Develop- References to ment and Evolution,” chap. viii, 1902; in the appen- discussions of dices of this book is given a detailed history of the orthoplasy. independent formulation of the theory of “Organic Selection or Orthoplasy,” by Baldwin, Osborn, and Morgan. ° Osborn, H. F., “A Mode of Evolution requiring neither Natural Selection nor the Inheritance of Acquired Characters,” Trans. New York Acad. Sci., pp. 141-148, 1896; also Science, April 3, 1896; also Amer. Nat., Nov., 1897. From this last reference I quote the following concise statement of the theory: “This hypothesis as it appears to myself is, briefly, that ontogenic adaptation is of a very profound character; it enables animals and plants to survive very critical changes in their environment. Thus all the individuals of a race are similarly modified over such long periods of time that, very gradually, congenital variations which happen to coincide with 230 DARWINISM TO-DAY. the ontogenic adaptive modifications are collected and become phylogenic. Thus there would result an apparent but not real transmission of acquired characters.” *°? Morgan, C. L., “Habit and Instinct,” pp. 312 ff., 1896; see also Science, pp. 793 ff., Nov., 1896. In Appendix C of Baldwin’s ‘‘De- velopment and Evolution,’ p. 347, 1902, is the following clear statement (in letter to Baldwin) of Morgan’s conception of organic selection: “7. On the Lamarckian hypothesis, racial progress is due to the inheritance of individually acquired modifications of bodily struct- ure, leading to the accommodation of the organism or race to the conditions of its existence. “2. This proposition is divisible into three: (a) Individual prog- ress is due to fresh modifications of bodily structure in accommo- dation to the conditions of life. (b) Racial progress is due to the inheritance of such newly acquired modifications. (c) The evolu- tion of species is the result of the cumulative series— “a>b+a'>b’+a">b"’+a'">b'"" etc, etc., where a, a’, a”, a’ are the acquisitions, and b, b’, b”, b’” the cumulative inherited results. “3. Anti-Lamarckians do not accept (b) and (c). But they accept (a) in terms of survival. No one denies that individual survival is partially due to fresh modifications of bodily structure in accommodation to the conditions of life. “4. It logically follows from 3 that individual accommodation is a factor in survival which cooperates with adaptation through ger- minal variation. “Weismann, following the lead of Roux, interpreted individual modification in terms of intra-selection. He clearly saw the impli- cation given in 4 above. Speaking of ‘the well-known instance of the gradual increase in the development of deers’ antlers,’ he says (Romanes Lecture, 1894, p. 18): ‘It is by no means necessary that all the parts concerned should simultaneously adapt them- selves by variation of the germ to the increase in size of the antlers; for in each separate individual the necessary adaptation [accommo- dation] will be temporarily accomplished by intra-selection—by the struggle of parts—under the trophic influence of functional stimulus.’ “6. So far there is no direct relation between specific modifications and specific variations. Individual accommodation, as a factor in survival, affords time (Weismann, op. cit., p. 19) for the occur- rence of any variations of an adaptive nature. “7, My own modest contribution to the further elucidation of the subject is the suggestion (1) that where adaptive variation v is similar in direction to individual modification m, the organism OTHER THEORIES OF SPECIES-FORMING. 23U has an added chance of survival from the coincidence m+v; (2) that where the variation is antagonistic in direction to the modifica- tion, there is a diminished chance of survival from the opposition m—v; and hence (3) that coincident variations will be fostered while opposing variations will be eliminated. “8 If this be so, many of the facts adduced by Lamarckians > may be interpreted in terms of the survival and gradual establish- ment of coincident variations by natural selection under the favourable environing conditions of somatic modifications. “9. It is clear that there is nothing in this suggestion of a direct relation between specific accommodation and coincident variation which can be antagonistic to the indirect relation indicated above in 6. “to. Correlated and coexistent variations would have the same relations to coincident variations as obtain in other cases of natural selection.” CHAPTER IX. OTHER THEORIES OF SPECIES-FORMING AND DESCENT (CONTINUED): AUXILIARY THE- ORIES (CONTINUED). Isolation Theories —The varying importance attributed by different biologists to the theories explaining means and results of isolation is notable. While by Importance of . . . . : the jsclation SOMe the species-forming influence of isolation factor in species- is held to be as effective as selection itself,— forming. : ; some deem it more effective,—others attach but little importance to it, indeed see no effects of consequence. These latter men are likely to be morphologists, cytologists, and laboratory men generally; the former are systematists, students of distribution, and so-called field naturalists. Thus Delage, who gives much attention in his general discussion of the theories of heredity, variation, and species-forming to many purely speculative theories of the ultimate structure and behaviour of protoplasm, and of the mechanism of heredity, dismisses the whole subject of geographic and topographic isolation with a couple of superficial para- graphs, in which he presents a singularly fallacious state- ment of what the effects of isolation should be. On the other hand the veteran German world-voyager and exploring naturalist, Moritz Wagner, established long ago, on the basis of his observations and deductions, a “law”’ of species-form- ing by migration and consequent isolation, which in his mind makes the natural selection theory superfluous. And Henry Seebohm in a discussion of Romanes’s* formulation of the principle of physiological selection, says: “So far as is 232 OTHER THEORIES OF SPECIES-FORMING. 233, known, no species (of birds) has ever been differentiated. without the aid of geographical isolation, though evolution. may have gone on to an unknown extent; and, so far as we: can judge, geographical isolation must always, sooner or later, be followed by differentiation.” And Romanes, him- self, conspicuous as the only pupil and disciple of Darwin personally advised and aided by the master himself, and one of the most brilliznt upholders and expositors of Darwin- ism, says:’ “Indeed I believe with Mr. Gulick, that in the principle of isolation we have a principle so fundamental and so universal, that even the great principle of natural selection lies less deep and pervades a region of smaller extent. Equalled only in its importance by the two basal principles of heredity and variation, this principle of isola- tion constitutes the third pillar of a tripod on which is reared the whole superstructure of organic evolution.” Thus the most ardent believers in the effects of isolation find it, inde-: pendent of selection and alone, sufficient to explain species- forming, while the most ardent neglecters of isolation theo- ries find them too slight to be of any consequence at all. We shall take middle ground and find in isolation a factor of great effectiveness and one wide-spread in its influence in helping to produce the present-day status of the animal kingdom, but yet a factor which shall most fairly be looked on as an auxiliary or helping-theory of natural selection. In fact, to my mind, the proof of the species-establishing effects of isolation, and of the actual existence of isolation (proof of means or modes of isolation), is something much needed by the general natural selection theory for its own sup- port. Selection needs help from isolation. To my mind, also, these means of isolation actually exist, and the result- ing isolation is actually a very potent factor in species-form- ing. The proofs seem to me obvious. The name isolation fairly well defines the condition that we are to discuss; (the term segregation has also been used. 234 DARWINISM TO-DAY. by some authors to name the same condition). 11, in a species, a number of individuals show a certain congenital variation, this variation will probably be lost by cross-breeding with individuals not having it, unless the individuals having it are in the ma- jority or unless they become in some way isolated from the others and segregated so that they will breed among them- selves. By such isolation and such in-and-in breeding the newly appearing congenital variations might soon become established, and if advantageous be so considerably developed as soon to distinguish as a variety or incipient species the members of the isolated colony. With time a distinct new species might result. Are there means to produce such isola- tion of groups of individuals belonging to a common species? The answer to this is certainly an affirmative one. There seem to be, indeed, several means of producing isolation, a and the isolation may be variously named ac- of effecting iso- cordingly. Undoubtedly the most important of meio these kinds of isolation, at least in the light of our present knowledge, is that known as geographical or topographical isolation. Isolation produced in other ways may be called biologic or physiologic or sexual isolation. In the case of geographic or topographic isolation the iso- lated group or groups of individuals are actually in another region or locality from the rest of the species, this being the result of migration, voluntary or involuntary. In bio- logic isolation the individuals of the species all inhabit the same territory but become separated into groups by struc- tural or physiological characters which prevent Weick aa ae miscellaneous inter-breeding. The real founder theory of species- and most insistent upholder of the theory of mast oe. species-forming by isolation (geographic and topographic isolation), was Moritz Wagner * (1813-1887), a traveller and naturalist, whose wanderings and observations brought to him the conviction that while What is meant by isolation. OTHER THEORIES OF SPECIES-FORMING. 235 natural selection might modify species and even produce continuous evolution it could never differentiate species, that is, produce new species. It could never, in Wagner’s belief, produce the actual condition which we know to exist in the present-day and past (now extinct) animal kingdom, this condition being the existence of hosts of distinct, though related, animal species or kinds. Wagner’s travels included journeys to North, Central, and South America, West Asia, and North Africa. His first clear enunciation of his theory, in which pronouncement he took definite stand against the claimed capacity of Darwinian selection to produce new species, was in 1868, in a paper read in Munich, entitled “Die Darwinische Theorie und das Migrationsgesetz der Organismen.” From the time of the appearance of this first paper until within a year or two of his death, Wagner steadily wrote and fought for his theory, but without gain- ing for it any such wide or authoritative acceptance as he hoped. In a letter dated August 30, 1884, Wagner pathet- ically writes, “Ich sterbe mit der Uberzeugung, dass man dies wenigstens nach meinem Tode anerkennen wird.” Wagner’s theory included not only the characteristics already pointed out as the basis of all theories of the influ- ence of isolation in species-forming, but the assumption that all species of animals have a strong tendency, or are con- stantly attempting, to “spread out’’; that is, have a driving instinct of migration and dispersal. The basis of this tendency is undoubtedly the overcrowding in the immature stages and in times of short food-supply or untoward exter- nal conditions of temperature, humidity, etc. This tendency to movement is Wagner’s “Migrationsgesetz,” and the out- come of it is to bring about conditions of topographic and geographic isolation among all kinds of animals. While in his first papers Wagner looked on his theory as a sort of supporting or auxiliary theory to that of natural selection, he soon began to see in it, calling it now by the name of 236 DARWINISM TO-DAY. “Separationstheorie,” an independent and alternative expla- nation of species-forming. In 1870, he wrote:* “Um den Unterschied beider Theorien moglichst kurz auszudrticken : nach der Darwin’schen Selectionstheorie ziichtet die Natur in Folge des Kampfes ums Dasein rastlos neue typische Formen der Organismen durch Auslese ntitzlicher Varieta- ten, gleichviel ob inner- oder ausserhalb des Verbreitungs- gebietes der Stammart, und kann diesen Prozess der Bil- dung einer neuen Art nur innerhalb eines sehr ees Zeitraumes vollziehen. “Nach der Separationstheorie ziichtet die Natur nur periodisch neue Formen stets ausserhalb des Wohngebietes: der Stammart durch geographische Isolierung und Kolo- nienbildung, ohne welche bei allen héheren Tieren getrenn- ten Geschlechts keine konstante Varietat oder neue Art. entstehen kann. Der Gestaltungsprozess einer neuen Form. kann nicht von langer Dauer sein.” Or in still more condensed form: . . . “Nach der Selek- tionstheorie ist der Kampf ums Dasein, nach der Separa- tionstheorie die ratumliche Absonderung, die nachste zwing- ende Ursache der Artbildung.” Wagner's latest, most definitive, cleanest cut, single formulation of the Separationstheorie is that contained in two paragraphs in his essay entitled, “Leopold von Buch und Charles Darwin” (Kosmos, 1883). These paragraphs are the following: “1. Jede dauernde ratimliche Absonderung einzelner oder weniger Emigranten von einer Stammart, welche noch im Stadium der Variationsfahigkeit steht, erzwingt auf Grund der Variabilitat und der Vererbung eine konstante Diffe- renzierung, indem sie unter Mitwirkung veranderter Le- bensbedingungen, die jeden Standortswechsel begleiten, auch die minimalsten individuellen Merkmale der ersten Kolonisten bei blutsverwandter Fortpflanzung fortbildet und _ befestigt. OTHER THEORIES OF SPECIES-FORMING. 237. “2. Keine konstante Varietat oder Art entsteht ohne Ausscheidung einzelner oder weniger Individuen von der Stammart und ohne Ansiedelung an einem neuen Standort, weil Massenkreuzung und Gleichheit der Lebensbedin- ‘gungen in einem zusammenhangenden Wohngebiet immer absorbierend und nivellierend wirken mussen und indivi- duelle Variationen stets wieder in die Stammform zurtck- drangen.” Wagner’s ° long series of interesting papers and addresses are crammed with facts of plant and animal geography, taxonomy and paleontology, and with keen interpretation of these facts, and clear and incisive formulations of his few generalisations, One of the most ardent present-day upholders of the ‘species-forming potency of geographical isolation is David Starr Jordan, the foremost American student of the classi- fication and distribution of fishes. From a recent paper’ I abstract the following brief statements of his beliefs con- ‘cerning the character and results of the influence of geo- graphical isolation. “It is now,” writes Jordan, “nearly forty years since Moritz Wagner (1868) first made it clear that geographical isolation (raumliche Sonderung) was a factor Jordan on geographic or condition in the formation of every species, aBUIRHGR: 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 even attacked, so far as the present writer remembers, 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 favourable variations would enable 238 DARWINISM TO-DAY. their possessors little by little to gain on the parent stock, so that a new species would be established side by side with the old, or on whether a wide fluctuation or mutation would give rise to a new species which would hold its own in com- petition with its parent. In theory, either of these condi- tions might exist. In fact, both of them are virtually un- known. In nature a closely related distinct species is not often quite side by side with the old. It is simply next to it, geographically 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 prob- lem of the origin of species by the study of the probable actual origin of species with which we may be familiar, or of which the actual history or the actual ramifications may in some degree be traced.” Dr. Jordan then proceeds to relate and analyse our pres- ent actual knowledge of the make-up of certain local faune,. of the migrations and distribution of certain well-known animal species (especially in the phyla of birds and fishes, in which groups our knowledge of the present status in North America of species and varieties and their distribu- tion is nearly exhaustive), and of the climatic, topographic, and general geographic barriers ° which determine this dis- tribution, in a way most convincing to unprejudiced minds. _ He brings to the support of his own statements of fact and opinion the testimony (contained in personal letters an- swering direct queries from himself) of many well-known American students of systematic and faunistic zoology. Jordan sums up the results of his display of North Ameri- can faunal conditions in various paragraphs, from among which the following are quoted: “In regions broken by few barriers, migration and inter- breeding being allowed, we find widely distributed species, OTHER THEORIES OF SPECIES-FORMING. 239 homogeneous in their character, the members showing indi- vidual fluctuation and climatic effects, but remaining uni- form 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 neighbouring 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 continued and intensified to form new species or races. Any horticulturist will illustrate this. “In these and in all 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. “In the animal kingdom, generally, we may say: When- ever a barrier is to some extent traversable, the forms separated by it are liable to cross from one side to the other, thus producing intergradations, or forms more or less intermediate between the one and the other. For every subspecies, where the nature of the variation has been care- fully studied, there is always a geographical basis. This 240 DARWINISM TO-DAY. basis is defined by the presence of some sort of a physical barrier. It is extremely rare to find two subspecies inhabit- ing or breeding in exactly the same region. When such appears to be the case, there is really some difference in habit or in habitat ; the one form lives on the hills, the other in the valleys; the one feeds on one plant, the other on another; the one lives in deep water, the other along the shore. There can be no possible doubt that subspecies are nascent species, and that the accident of intergradation in the one case and not in the other implies no real difference in origins. “To the general rule that closely allied species do not live together there exist partial exceptions. It may be well to glance at some of these, for no rule is established until its exceptions are brought into harmony with the phenomena which illustrate the rule.’ (Here Dr. Jordan details the facts of distribution in three cases from among the fishes, which apparently form exceptions to his general rule). As an example of the effects of an unusual and interesting phase of isolation I may refer to the conditions noted con- See cerning the distribution and species distinction isolation inthe Of the Mallophaga, a group of small wingless Mallophaga. = insect parasites on birds and mammals. These parasites live for their whole lives among the feathers or hair of their hosts, and while able to run swiftly are unable to fly and thus to migrate freely from bird to bird. “There are to be noted various results of the influence on the taxonomy of the Mallophaga of the peculiar conditions of their parasitic life. While the uniformity and persistence of the conditions under which the life of the parasites is passed tend to preserve with little change the species types, the peculiar isolation, often pretty complete, of groups of individuals of a parasite species on individual birds of the host species and the consequent close breeding, tend to foster and fix those inevitable slight variations always mani- isolation studied OTHER THEORIES OF SPECIES-FORMING. 241 fest in a comparison of offspring and parents, but under normal conditions held in check or lost (unless directly advantageous) by crossing among less closely related indi- viduals. For example, the individuals of a parasite species on a bird of long life and non-gregarious and monogamous habits, like an eagle, live very much the life of an isolated community. There must be many years of in-and-in breed- ing. It is like island life. The result is certain: the members of this isolated group will soon differ from the specific type in noticeable particulars. On the other hand, the con- ditions of life on this ‘island’ are practically identical with the conditions on other similar ‘islands’—other eagles—in- habited by other individuals of the same parasite species, so there is no influence working to produce a wide divergence of the members of these various isolated groups of indi- viduals of the same species. Now this isolation of groups of individuals is in some degree an incident of the life of all Mallophaga ; in some instances it is considerable; in others, inconsiderable, but taken altogether a condition in the life of the whole order exerting an influence which has the readily recognisable result of creating a great number of small variations within species limits. “The results, manifest to any student of the group, of these two opposing influences are to render difficult the divi- sion of the order into distinct genera on account of the gen- eral similarity of structure, and to make difficult the defini- tion of species on account of the many slight variations among the individuals from different bird individuals.” * The study of geographic distribution and its influences on species-forming has not been limited, of course, to living Geographic Organisms alone. In fact, the geologic study igh eat of distribution and migration of both animals animals, and plants has given us some of our most important facts touching the problem of the influence of isolation on species-transformation. In an interesting paper 242 DARWINISM TO-DAY. on the “geological study of the migration of marine inverte- brates,” Smith *° has pointed out the general principles and conditions upon which the interpretation of the geographic distribution of the marine invertebrates of the earlier geo- logic ages must be based. In closing this consideration of the status of geographic isolation as a factor in species-forming, I should not omit to Isolation not Call attention to the fact, which should be obvi- ee. ous enough to any reader, that isolation in itself forming. cannot be the basic and all-sufficient cause for the production of specific differentiation, any more than any selective factor can. The prerequisite in both cases is the occurrence of variation. What are the variations, and how are they produced: these are the fundamental questions in species-forming. Isolation is a tremendously favouring con- dition but not a primary cause of species-forming. It tends to help along, to hurry up species disintegration, not to initiate it. It is a biological catalytic agent. — In this present connection the pertinent question is, is the influence of geographical isolation in the cumulation of variation or intra-specific differentiation due to its com- pelling in-and-in breeding and hence the fostering and cumu- lation of fortuitous Darwinian variations occurring in the comparatively few individuals of the isolated group, or is there a spur to variation, or even actual production of it along determinate lines, in the new environmental conditions com- mon to all the isolated group but inevitably different from the conditions to which the parent type is exposed? Is there a gradual accumulation of differences between the split-off group and the parent group due to environmental influence plus in-and-in breeding? If we could reply yes to this question, we should have a sufficient explanation of how the isolated group splits rapidly away in many small, and in a few large, characteristics from the parent. stock. 17 OTHER THEORIES OF SPECIES-FORMING. 243 From the foregoing it is obvious that geographical isola- tion is a proved, effective, and widely applied species-form- ing factor. So much cannot be said for biologic and sexual isolation.” The actual existence of such isolation is not proved by any mass of evi- dence based on observation, although the theory is by no means pure speculation; nor are the results of such isola- tion clearly indicated, although a certain amount of observa- tion and experimental evidence can be adduced to show them. The different phases of isolation, not geographic, called by different names, as biologic, physiologic, sexual, and morphologic isolation, all have reference to some sort of segregation of individuals of the same species into groups inside of each of which mating takes place, and among which little or no cross-breeding occurs, because of varying habits, or unusual sexual aversion or attraction, or physio- logical or morphological variation affecting mating. For ' example, to take first a sort of combination of geographic and biologic isolation, Plate*” points out that there are twelve species of albatrosses in the southern hemisphere, of which nine or ten belong to the Australian zoo-geographical realm and intermingle throughout most of their range. At breeding time, however, these different species become segregated in restricted and separate localities so that mating is alwayS accomplished among different individuals of the same species, although hybridisation could doubtless obtain successfully among these closely related albatross forms. Thus the species characters are kept pure; the species dis- tinct. An example of pure biological isolation and one within a single species (which is the sort of isolation we are more Anexampleof interested in) might be produced in the follow- Aaa ing way. We know of numerous species of work, butterflies which appear in different seasons of the year in different colour-pattern. This is not a colour Biologic isolation. 244 DARWINISM TO-DAY. change in individuals but results from an earlier or later hatching of eggs laid in the autumn or summer before. These eggs may, indeed, be all of one batch or lot, laid by a single female. Some of these eggs hatch in the spring; the butterflies that come from these spring larve are of one col- our-pattern ; some of the eggs, however, delay hatching until summer; from these larve come butterflies of another colour-pattern; some of the eggs even go over until fall before hatching; these latest butterfly individuals may be of a third colour-pattern. The colour-pattern here must have some fixed relation to the time or season of hatching of the eggs; it is not a result of isolation. But the condition well illustrates the actual existence of a biological isolation within a species: the spring butterflies must mate among them- selves, the summer individuals among themselves, and the fall butterflies among themselves. Within the one species are three biologically isolated groups of individuals re- strained from inter-breeding. Suppose the individuals of a bird species show among themselves a tendency to vary in their breeding time; some are ready to breed early, others delay mating. Roughly segregated into two groups, early breeders and late, the individuals of the two groups would obviously tend to breed each inside its own group. Hut- ton ** actually records the occurrence of two varieties of the shore-bird, Céstrelata neglecta, in the Kermadec Islands, which live together but breed at different times. A pelagic crustacean living near the shore increases rapidly in num- bers; some individuals find themselves able to live on the shore in pools between tide-lines. The pool dwellers breed together: the pelagic individuals breed together; a biologic isolation—in truth an isolation partly topographic—might soon come to exist. Any variation in habits of life among individuals living in the same locality, which tends to deter- mine that breeding shall be roughly restricted within cer- tain groups produces biologic isolation ; such variation might OTHER THEORIES OF SPECIES-FORMING. 245 be a variance in sexual maturity, a change in breeding time for that or any other reason, a tendency on the part of cer- tain individuals to live more or less concealed in holes, under stones, etc., changes in food-habits, as the gradual going over of some individuals of a plant-feeding insect species from the old food-plant to a new one, or the tendency within an omnivorous species for groups to restrict themselves to certain specific foods: all such variations might lead to pos- sible biological isolation. By sexual isolation authors usually refer to the influ- ence of some variation tending to make difficult or impossi- Seenal ble wholly free and miscellaneous mating or isolation. breeding inside of a species. This variation may be of purely physiological character or may be a struc- tural one: that is, the hindrance to mating may be one of instinctive feeling, a “race-feeling’’ depending on an antipa- thy to odour, to age, to appearance, etc., or may be a slight modification of the copulatory organs making such mating difficult, or even a modification of the egg or the spermato- zoids making fertilisation difficult. It is a well-known fact that numerous varieties of domesticated animal species rarely breed together, although quite able to, and provided with full opportunity. On the other hand, animals of differ- ent species which in Nature rarely or never breed together may, if kept long in confinement, as in zoological gardens, mate ** and produce young. In each case there seems to be question of a “race-feeling”:; in the first case a sexual aversion keeping apart individuals of the same species, in the second the breaking down of race-feeling that in Nature has sufficed to prevent hybridising. This might be termed physiological isolation, or, indeed, physiological selection, as it has been called, and given much credit for species-forming by Romanes’** and_ others. Romanes and Hutton believe that a progressive infertility results in this way (and also by the way referred Physiological selection, 246 DARWINISM TO-DAY. to in the next paragraph) which can soon result in complete infertility, hence specific distinctness on the part of the mutually infertile groups. Mutual infertility due to morphological variations has been called “mechanical selection” by Karl Jordan,” and may rest on slight variations in germ-cells or copulatory structures. Such morphological variations of the reproductive organs have been believed to be shown for butterflies and spiders, while the delicate tropismic responses of the active spermatozoids to the attracting chemical substances in the egg-cells of echino- derms, ccelenterates, molluscs, and fishes have been thought to be conditions in which a slight chemical or physical varia- Mechanical selection. tion might have a large influence in preventing or insuring fertilisation. Indeed, when one examines comparatively the curiously various complex accessory reproductive organs (claspers, gonapophyses, intromittent organs, etc.) of almost any group of insects, one’s first thought is that this variety must practically effectually exclude all possibility of hybri- dising. But the interesting detailed comparative studies by Snodgrass ** of the accessory genitalia in various families of Diptera make this confidence less certain. In the large family Tipulidae, for example, he finds great complexity and remarkable variety (among the different closely allied species) in this complexity in the genitalia of the males, but almost no variation at all in the corresponding (complement- ary) parts of the females. “Throughout the entire family the females present one type of structure, of which there is but little modification, and certainly none to correspond with the great variety of specific differences found in the genitalia of the males.” Now while the great variety of the copula- tory parts would be extremely significant if shared by both sexes so that only one kind of key could fit one kind of lock, we have the inexplicable condition actually existing of the keys being extremely various and complex, but the locks all OTHER THEORIES OF SPECIES-FORMING. 247 © being so similar and simple that any bent nail is able to pick them. Seebohm ** criticises Romanes’s theory of physiological selection, which should better be called physiological Seebohm’s isolation, as demanding an almost impossible oes coincidence of conditions to make it work. physiologic se- : ; A lection. Formulated as nearly as it can be in a single sentence, Romanes has defined physiological selection as follows: “Wherever, among all the possible variations of the highly variable reproductive system there arises toward any parent form any degree of sterility which does not extend to the varietal form, there a new species must neces- sarily take its origin.’”’ Seebohm points out that this is exactly a condition that can rarely, if ever, occur, for to bring it about we must presuppose :— “tst. The special variation of the reproductive organs must occur in two individuals, otherwise the possible an- cestor of the new species would leave no descendants. “ad. It must occur at the same time in both. “2d. It must occur at the same place. “ath. The two individuals must be of opposite sexes. “sth. They must each of them possess some other varia- tion, or their progeny would not differ from that of the rest of the species. “6th. The variation must be the same in both or appear simultaneously in the majority of their children, otherwise it would be swamped by interbreeding within the physio- logically isolated family.” Romanes’s theory has also been strongly criticised by Wallace ** and by Karl Jordan.** Wallace contends that Biles Apa DO form of infertility or sterility between the ofRomanes’s individuals of a species can be increased by as natural selection unless correlated with some useful variation, while all unfertility not so correlated has a constant tendency to effect its own elimination. But the 248 DARWINISM TO-DAY. opposite property, fertility, is of vital importance to every species, and gives the offspring of the individuals which possess it, in consequence of their superior numbers, a greater chance of survival in the battle of life. It is, there- fore, indirectly under the control of natural selection, which acts both for the self-preservation of fertile and the self- destruction of unfertile stocks—except always, as correlated above, when they become useful and therefore subject to be increased by natural selection.” Jordan maintains that the outcome of physiological selection can be at best only dimorphism, not specific distinctness. Vernon ** has formulated a theory which he calls that of “reproductive divergence,” in the following words: “Sup- Vernon's posing that among the members of any species theory ofrepTo- those individuals more alike in respect to any ductive diver- gence. different characteristic, such as colour, form, or size, are slightly more fertile inter se than less similar indi- viduals, it necessarily follows that in the course of succeed- ing generations the members of this species will diverge more and more in respect to the characteristic in question, whereby ultimately the original species may be split up into two or more fresh species.” As a concrete example, Vernon supposes that in the Lepidopterous Jthania urolina, a certain insect found in the Amazon Valley, small individuals were slightly more fertile with other small individuals than with large individuals, while these were also more fertile inter se; “then it would follow that fewer individuals of intermediate size would be produced, and in course of time the species would be split up into a small and large variety. These varieties would continue to diverge as long as the process of ‘reproductive divergence’ was acting, till at length they might become differentiated in the two mutually sterile species. Supposing on the other hand this variation in fertility were correlated with slight differences of colour, then in course of time varieties differing in respect of colour OTHER THEORIES OF SPECIES-FORMING. 249 would be produced; or if it were correlated with both size and colour, varieties differing in respect of both characters might be produced. As a matter of fact, this insect does actually occur as four distinct varieties differing in colour, form, and size, though whether in consequence of the oper- ation of reproductive divergence it is of course impossible to say.” But this theory has been strongly criticised by Karl Jordan,** who believes himself able to show that re- productive divergence would not work in the way conceived by Vernon, but actually in such a way as to establish an intermediate form. Karl Pearson ** has formulated a theory called “reproduc- tive selection” which he believes to be distinct from both the Peta Romanes and the Vernon theories, and to which theory of repro- he attributes an importance in evolution “equi- ductive selection. tent to natural selection, if indeed it be not prepotent.”’ The theory is based on correlations which seem to exist between the variation in some particular organ and fertility. From studies of variation of height in 4,000 Anglo- Saxon families and 1,182 Danish families, Pearson finds that there exists a distinct correlation between fertility and height in the mothers of daughters in these families. The effect of this correlation is to render women less variable and to raise their mean height. The quantities are small, but are sufficient, if unchecked by natural selection, to raise the mean height of women in forty generations by 3 1-4 inches. “A factor which would alter stature by about three inches in I,000 years is clearly capable of producing very considerable results in the long periods during which evolu- tion may be supposed to have been at work.” Of large importance in any consideration of the relations. Gulick’sim- Of isolation to species-forming are the observa- portant observa tions and conclusions of Gulick. Derived origi- sions. nally from an exhaustive study of the variation and life-conditions of certain land shells (Achatinellidz) 250 DARWINISM TO-DAY. in the Hawaiian Islands, he formulated, in 1872, an im- portant principle concerning the species-differentiating ef- fects of indiscriminate isolation. As Romanes ** well points out, isolation may not only admit of degrees, that is, may be either total or partial, and, if partial, may occur in numberless grades of efficiency, but it may be either dis- criminate or indiscriminate. If it be discriminate, the isola- tion has reference to the resemblance of the separated indi- viduals to one another ; if it be indiscriminate, it has no such reference. For example, if a shepherd divides a flock of sheep without regard to their characters, he is isolating one section from the other indiscriminately ; but if he places all the white sheep in one field and all the black sheep in another field, he is isolating one section from the other discriminately. Or, if geological subsidence divides a species into two parts, the isolation will be indiscriminate; but if the separation be due to one of the sections developing, for example, a change of instinct determining migration to another area, or occu- pation of a different habitat on the same area, then the isola- tion will be discriminate, so far as the resemblance of instinct is concerned. Discriminate isolation has been called by Gulick segregate breeding, and indiscriminate isolation sepa- rate breeding. Now the effectiveness of discriminate isolation or segre- gate breeding, however effected, to produce species-differ- entiation is of course obvious. In fact, as Romanes points out, it is only when assisted by some form of discriminate isolation which determines the exclusive breeding of like with like, that heredity can make in favour of change of type or lead to what we understand by organic evolution. But what about indiscriminate isolation? Does it not seem, at first sight at least, that this kind of isolation must count for nothing in the process of evolution? Is it not apparently self-evident that the farmer who separated his stock into two or more parts indiscriminately, would not effect any more OTHER THEORIES OF SPECIES-FORMING.,. 25f change in his stock than if he had left them all to breed together ? “Well,” says Romanes, “although at first sight this seems self-evident, it is in fact untrue. For, unless the individuals which are indiscriminately isolated happen to be a very large number, sooner or later their progeny will come to differ from that of the parent type, or unisolated portion of the previous stock. And, of course, as soon as this change of type begins, the isolation ceases to be indiscriminate: the previous apogamy [indiscriminate isolation] has been con- verted into homogamy [discriminate isolation], with the usual result of causing a divergence of type. The reason why progeny of an indiscriminately isolated section of an originally uniform stock—e. g., of a species—will eventually deviate from the original type is, to quote Mr. Gulick,”’ as follows: “No two portions of a species possess exactly the same average character, and, therefore, the initial differ- ences are for ever reacting on the environment and on each other in such a way as to ensure increasing divergence as long as the individuals of the two groups are kept from intergenerating.”’ Gulick was led to his recognition of the principle in ques- tion, not by any deductive reasoning from general principles, Belin sad: but by his own particular and detailed observa- iesof Hawaiian tions of the land mollusca of the Sandwich land-snails, = Tslands. Here there is an immense number of varieties belonging to several genera; but every variety is restricted, not merely to the same island, but actually to the same valley. Moreover, on tracing this fauna from valley to valley, it is apparent that a slight varia- tion in the occupants of valley 2 as compared with those of the adjacent valley 1, becomes more pronounced in the Wext valley. 2, “still more so: in 4,etc,,ete. Thusit was possible, as Mr. Gulick says, roughly to estimate the amount of divergence between the occupants of any 252 DARWINISM TO-DAY. two given valleys by measuring the number of miles be- tween them. On the basis of his detailed observations, Gulick’® has proposed the following three general propositions as to the relations of isolation to species-forming: “rt. A species exposed to different conditions in the differ- ent parts of the area over which it is distributed, is not represented by divergent forms when free inter-breeding exists between the inhabitants of the different districts. In other words, diversity of natural selection without separation does not produce divergent evolution. “2. We find many cases in which areas, corresponding in the character of the environment, but separated from each other by important barriers, are the homes of divergent forms of the same or allied species. ‘3. In cases where the separation has been long continued, and the external conditions are the most diverse in points that involve diversity of adaptation, there we find the most decided divergences in the organic forms. That is, where separation and divergent selection have long acted, the re- sults are found to be the greatest. “The first and second of these propositions will probably be disputed by few, if by any. The proof of the second is found wherever a set of closely allied organisms is so dis- tributed over territory that each species and variety occu- pies its own narrow district, within which it is shut by bar- riers that restrain its distribution, while each species of the environing types is distributed over the whole territory. The distribution of terrestrial molluscs on the Sandwich Islands presents a great body of facts of this kind.” Finally in a recent exhaustive discussion of the subject *’ of the relation of isolation to evolution Gulick declares that “the whole process of bionomic evolution, whether progres- sive or retrogressive, whether increasingly ramified and divergent, or increasingly convergent through amalgama- OTHER THEORIES OF SPECIES-FORMING. 253 tion, is a process by which the limitations of segregate breed- ing are either set up and established or cast down and obliterated.” APPENDIX. * Seebohm, Henry, “Physiological Selection,” p. 12, 1886. 2 Romanes, G. J., “Darwin and After Darwin,” Vol. III. p. 1, 1897. ® Wagner, Moritz, “Die Entstehung der Arten durch Raumliche Referencesto onderung,” 1889. This book is made up of the discussions of collected papers of Wagner, printed originally in the isolation. time from 1868-1886, mostly in the journal Kosmos. * Wagner, Moritz, “Uber den Einfluss der geographischen Isolie- rung und Kolonienbildung auf die morphologischen Veranderungen der Organismen,” July, 1870. ° Wagner, Moritz, “Uber die Entstehung der Arten durch Abson- derung,” Kosmos, 1880. ®Haacke in his “Grundriss der Entwicklungsmechanik,”’ 1897, gives, on pp. 335-336, an excellent summary statement of Wagner’s position, as follows: “Wenn wir eine Tierart bis an die Grenze ihres Verbreitungs- gebietes verfolgen und diese Grenze wberschreiten, so stossen wir Haacke’s sum- gewOhnlich sehr bald, und oft schon, ehe wir die mary of Wag- Verbreitungsgrenze der betreffenden Art erreicht ner’s theory. haben, auf eine andere, und zwar auf eine mit der ersteren nachstverwandte Tierart, die aber ein anderes Verbreitungs- areal inne hat. Gehen wir auch tiber das Gebiet dieser letzteren Art hinaus, so konnen wir auf eine dritte, vierte und ftinfte Art stossen, von denen jede den beiden ersten verwandt sein kann und ein besonderes Verbreitungsgebiet bewohnt. Im allgemeinen kon- nen wir den Satz aufstellen, dass es keine zwei nachstverwandten Tierarten giebt, deren Verbreitungsgebiete sich vollkommen decken. Vielfach kann der Fall festgestellt werden, dass die Verbreitungsge- biete zweier nachstverwandter Tierarten sich teilweise decken; aber eine vollkommene Deckung ist noch in keinem Fall bei zwei oder mehr nachstverwandten Tierarten festgestellt worden. ‘Es kann auch vorkommen, dass das Verbreitungsgebiet der einen Art voll- standig innerhalb desjenigen der andern Art liegt, das also, soweit der Wohnkreis der ersten Art reicht, ein Zusammenfallen mit dem Verbreitungsgebiet der zweiten Art stattfindet; aber in solchen Fallen dehnt sich eben die Heimat der einen Art tber die der zweiten aus, so dass von Kongruenz der beiderseitigen Wohnge- biete nicht die Rede sein kann. Nachtsverwandte Tierarten sind 254 DARWINISM TO-DAY. ketten- oder, besser gesagt, netzfOrmig tiber die Erde verbreitet. Wie die Maschen eines Netzes reihen sich die Wohngebiete der Arten einer Gattung aneinander, und wenn auch, wie schon hervor- gehoben, mancherlei teilweise Deckungen vorkommen, so hat sich noch in allen Fallen, wo man die Grenzen der Verbreitungsgebiete nachstverwandter Arten festgestellt hat, die Thatsache ergeben, dass keine vollkommene Deckung § stattfindet. Aus dieser Thatsache konnen wir den Schluss ziehen, dass in einem und demselben Gebiete, soweit wenigstens alle Individuen unter denselben Ver- haltnissen leben, aus einer Art nicht zwei oder mehr neue Arten werden koOnnen. Wagner meinte zuerst, dass hierbei die Moglich- keit einer allseitigen Kreuzung, wie sie nach ihm innerhalb eines und desselben Wohnkreises einer Art moglich sein soll, eine grosse Rolle spielt. Er hat ubrigens seine Ansichten im Laufe der Zeit geandert und es ist deshalb notwendig, auf die Entwickelungs- geschichte seiner Ideen etwas naher einzugehen. Ursprtinglich suchte Wagner seine Theorie mit der Darwin’schen zu vereinigen. Nach der letzteren entsteht eine neue Art dadurch aus einer vorhandenen, dass die Lebensbeeinflussungen andere werden, und dass nunmehr diejenigen Individuen seitens der ztichtenden Natur ausgewahlt werden, die den neuen Lebensbeeinflussungen am besten entsprechen. Wagner nahm nun an, dass dies zunachst nur einzelne Individuen sein konnen, und dass nicht bloss sie, sondern noch eine grosse Anzahl anderer leben bleiben. so dass nicht allein die Moglichkeit, sondern auch die hohe Wahrscheinlichkeit gegeben ist, dass die den neuen Lebensbeeinflussungen am _ besten ent- sprechenden, von den ubrigen Individuen der betreffenden Organis- menart abweichenden Vertreter der letzteren sich mit denjenigen geschlechtlich mischen, die nicht in zweckentsprechender Weise abgeandert sind. wodurch die neuen Errungenschaften wieder verloren gehen sollten. Wagner suchte also den Nachweis zu fiihren, dass die Darwinische Selektionstheorie nicht geeignet sei, eine Ziichtung neuer Tier- und Pflanzenarten ohne eine Hiilfslehre, die er in seiner ‘Migrationstheorie’ gefunden zu haben glaubte, nachzuweisen. Er meinte, dass die vorteilhaft abgeanderten Individuen, wenn nicht in allen, so doch in manchen Fallen auswan- dern wtirden in eine Gegend, wo die Art, der sie angehoren, nicht vertreten, wo also die Moglichkeit einer Kreuzung mit unabgean- derten Individuen ausgeschlossen ist. Spater hat Wagner seine Migrationstheorie durch die der Separation oder der raumlichen Sonderung ersetzt, indem er zugleich die Verquickung seiner Anschauungen mit denen des Darwinismus zurticknahm. Nach Wagners Separationstheorie bilden sich neue Arten dadurch, dass auf die eine oder andere Weise etliche Individuen einer Art in ein OTHER THEORIES OF SPECIES-FORMING. 255 Gebiet gelangen, das vorher nicht von dieser Art bewohnt war. Die Entstehung neuer Arten erklart sich dann nach Wagner dadurch, dass, da die Individuen einer Art ja alle mehr oder minder voneinander abweichen, die wenigen Grtinder der neuen Art ihre Besonderheiten bewahren und nicht durch Kreuzung mit anderen Individuen wieder einbussen wtrden. Die Anpassung lasst Wagner aber im Sinne Lamarcks zustande kommen, und: neben Einrichtungen, die den Organismen von Nutzen_ sind,. erkennt er andere an, die lediglich der Ausdruck eigenttmlicher Struktur sind. Die klimatischen Verhaltnisse sind nach Wagner von sehr untergeordneter, die Verhinderung der Kreuzung ist von ausschlaggebender Bedeutung. Wagner huldigte ferner der Anschauung, dass die weisse Farbe der Polar- und die gelbe der Wiistentiere dadurch zustande gekommen ist, dass entsprechend gefarbte Individuen von Arten, die andere Gegenden bewohnten,. nach den Polarlandern und den Wiisten auswanderten.” ‘Jordan, D. S., “The Origin of Species through Isolation,” Scrence, N.>., Vol. XXII,: pp. 545-562. 19005. * An excellent example of the careful study of the relation of a group of recognised varieties, or sub-species of a species, to the Grinnell’s study “limatic differences of their various geographic of geographic ranges, is presented by Jos. Grinnell in ‘The Origin differences in the and Distribution of the Chestnut-backed Chickadee,” chickadee. Auk, Vol. II, pp. 364-382, 1904. I quote from this paper the following: “The chestnut-backed chickadee (Parus rufescens) is a boreal species of peculiarly limited distribution. It is almost exclusively confined to the humid Pacific Coast region of North America, within which it is the most abundant, and in many places the only member of the genus Parus present. We find it characteris- tically at home within the densest coniferous forests, or along their edges, where there is much shade and an even temperature. “The range of the chestnut-backed chickadee is nearly two thousand miles long, north and south, extending from a little north of Sitka, Alaska, to some forty miles below Monterey, California. But its width is very narrow, only within the confines of Oregon and Washington exceeding one hundred miles, and elsewhere usually much less, save for one or two isolated interior colonies to be mentioned later. “The influences determining this queer-shaped distribution area may be safely assumed to be atmospheric humidity, with associated floral conditions. For this habitat coincides quite accurately with the narrow coastal belt of excessive cloudy weather and rainfall. “The specific character distinguishing Parus rufescens from all 256 DARWINISM TO-DAY. other American chickadees is the colour of the back, which is an intense rusty-brown, approaching chestnut. It is of common note that the most evident effects of similar climatic conditions on other animals is a corresponding intensification of browns, especially dorsally. We may, therefore, consider the chestnut-backed chicka- dee, as indicated by its chief specific character, to be a product exclusively of the peculiar isohumic area to which we find it confined. “Parus rufescens, from Sitka to Monterey, has a chestnut-coloured back. And from Sitka to Point Arena, between which we find the extremest humidity, another conspicuous character is uniform,— the colour of the sides, which are also deep rusty brown. But from Point Arena south to San Francisco Bay (Marin District), these lateral-brown areas suddenly weaken to pale-rusty; while from San Francisco south past Monterey (Santa Cruz District), adult birds have the sides pure smoke-gray without a trace of rusty. “The species thus presents geographic variation within itself, and three distinguishable forms have been named, respectively, the chest- nut-sided chickadee (Parus rufescens rufescens), the Marin chick- adee (Parus rufescens neglectus), and the Santa Cruz chickadee (Parus rufescens barlowi). But all three sub-species are unmis- takably the chestnut-backed chickadee (Parus rufescens).... ‘““As has already been asserted, Parus rufescens doubtless arose as a geographical race of Parus pre-hudsonicus [the hypothetical common ancestor of the present species, Parus hudsonicus, occupy- ing the interior of Alaska and British Columbia east to Labrador and Nova Scotia, and Parus rufescens]. It is now called a ‘species’ because intermediates have dropped out; in other words, the divarication is now wholly complete and there are two separate twigs. The area of intermediate faunal conditions between the humid coast belt and the arid interior region of British Columbia and Alaska is very narrow, consisting, in places personally traversed by me, of but a few miles over a mountain ridge. This very narrowness of the area of faunal mergence probably accounts for the lack of intermediates at the present day between hudsonicus and rufescens. “In the case of Parus rufescens and Parus hudsonicus, there seems to be now a narrow hiatus between the two. At least I can find no record of the two species having been found in the same locality. The narrowness of the region of intermediate faunal conditions may therefore be considered as the reason why we do not find connecting links between hudsonicus and rufescens at the present time. For the amount of difference between these two chickadees does not strike me as any greater than, for instance, OTHER THEORIES OF SPECIES-FORMING. 257 between Melospiza cinerea montana and Melospiza cinerea rufina, between which there is continuous distribution and free interoscula- tion. But we cannot expect any two species of birds or other animals to present the same degrees of differentiation in the same length of time or under the same conditions, much less under different conditions. For in no two animals is the physical organ- isation, in all respects, exactly the same. “In a given aggregation of individuals constituting a new colony, a certain amount of time is necessary for the set of environmental factors to become operative in bringing about new _ inheritable characters to a degree perceptible to us. Then the inherited effects of invasion and cross-breeding from season to season from the adjacent parent centre of differentiation will be evidenced less and less, as time elapses, as the distance from this centre increases. The offspring of successively further removed unions will, of course, inherit to a less and less degree the distinctive characters of the ancestral stock on one side and more and more of the incipient ones on the other. “If, now, the distance is great enough to permit of the time required for adaptive manifestations to become innate, then we would find new characters making their appearance distally nearest the new centre of differentiation. If the distance were too short we would not find new characters showing themselves because they would be constantly crowded down by the influx of the old. The time factor may, therefore, be reduced by the intervention of an impassable barrier. As an instance, we find three (and there are probably two other) insular forms of the song sparrow within a limited distance among the Santa Barbara Islands, while through the same distance on the adjacent mainland there is but one. Or, in the case of continuous distribution, the time element may be comparatively lessened by the great distance between the range limits, and it may be still further decreased as these limits lie in faunal areas of more emphatically different nature. The horned larks, as well as song sparrows, furnish us several good examples of the latter two rules. “It is isolation, either by barriers or by sufficient distance to more than counterbalance inheritance from the opposite type, that seems to me to be the absolutely essential condition for the differ- entiation of two species, at least in birds. “A strong argument in support of this conviction is that we never find two ‘sub-species’ breeding in the same faunal area, and no two closely similar species, except as can be plainly accounted for by the invasion of one of them from a separate centre of differentiation in an adjacent faunal area. An appropriate instance 258 DARWINISM TO-DAY. in illustration of the latter is the occurrence together, in the Siski- you Mountains of northern California, of the brown Parus rufescens of the wet coastal fauna and the gray Parus gambeli of the arid Sierran fauna. (See Anderson and Grinnell, Proc. Ac. Nat. Sc., Phila., 1903, p. 13.) The Siskiyou Mountains occupy a line of mergence between the two faune, and the two respectively repre- sentative chickadees have evidently extended their ranges toward each other until now over this one small area they occupy com- mon ground. Several parallel cases could be cited; their signifi- cance seems obvious. “We come now to consider the origin of the races of Parus rufescens. In a species of recent arrival into a new region (by invasion from a neighbouring faunal area), as it adapts itself better and better to its new surroundings, granted the absence of closely- related or sharply-competing forms, its numbers will rapidly increase. This means that there will be increased competition within the species itself, on account of limited food supply. The alterna- tive results are either starvation for less vigorous individuals during recurring seasons of unusual food scarcity, or dissemination over a large area. In a way the first might be considered as bene- ficial in the long run, as doubtless leading to the elimination of the weaker; such a process evidently does take place to a greater or less degree all the time. and is important for the betterment of the race. But as a matter of observation Nature first resorts to all sorts of devices to ensure the spreading of individuals over all inhabitable regions; in other words, the extremest intra-competi- tion does not ensue until after further dissemination is impossible. In birds we find a trait evidently developed on purpose to bring about scattering of individuals. This is the autumnal ‘mad im- pulse’ which occurs just after the complete annual moult, when both birds-of-the-year and adults are in the best physical condition, and just before the stress of winter food shortage. Even in the most sedentary of birds, in which no other trace of a migratory instinct is discernible, this fall season of unrest is plainly in evi- dence. I may suggest, not unreasonably, that autumnal migration may have had its origin in such a trait as this, the return move- ment in the spring becoming a necessary sequence. (See Loomis, Proc. Cal. Acad. Sc., 3d series, Zodlogy, II, Dec., 1900, 352.) It is a matter of abundant observation that autumn is the season when we find the most unlooked-for stragglers far out of their normal range and when sober, stay-at-home birds, like Pipilo crissalis and the chickadees, wander far from the native haunts where they so closely confine themselves the rest of the year. It is also the expe- rience of collectors that the greatest number of these stragglers OTHER THEORIES OF SPECIES-FORMING. 25y are birds-of-the-year, which thus, obeying the ‘mad impulse,’ are ’ led away from their birthplace into new country, where they may take up their permanent abode, and be less likely to compete with their parents or others of their kind. Then, too, cross-breeding of distinctly related individuals is more likely. The records of the Santa Cruz chickadee outside of its regular breeding range, are all of August to October dates (Haywards, Gilroy, San José, etc.). “Thus, as above indicated, by the occupancy of new territory the number of individuals which can be supported will corre- spondingly grow. Hence a vigorous colony will spread out along lines of least resistance, being hindered by slight faunal changes, but completely checked only by topographic or abrupt climatic barriers. Parus hudsonicus and its near relative Parus rufescens are boreal species, the former inhabiting the Hudsonian Zone and the latter a certain portion of the Canadian. It seems reasonable to suppose that rufescens differentiated in the northern part of the humid coast belt, which has been called the Sitkan District. This is a faunal subdivision of the Canadian Zone, and its northern part approximates more closely Hudsonian conditions than south- erly. Granting that the early centre of differentiation and distri- bution of Parus pre-hudsonicus rufescens was in the northern part of the Sitkan District, then the route of emigration would be con- fined to the narrow southward extension of that faunal area. The habitat of Parus rufescens thus gradually acquired the long north and south linear appearance, as shown at this day. But when the pioneer invaders at the south reached the vicinity of Point Arena, they met with somewhat changed temperature and consequent’ floral conditions, but not so abrupt as to constitute a permanent barrier. Doubtless the progress of invasion was retarded until adaptive modifications evolved, which correlatively allowed of further invasion, until the abrupt limits of the Santa Cruz Dis- trict were reached. “San Francisco Bay and the Golden Gate seem to now form a pretty effectual barrier between neglectus on the north and barlowt on the south. At least, among the large number of skins examined by me with this point in view, I can find none from one side that can be confidently determined as being identical with the race on the other. Neither chickadee has been found east of the bay, nor anywhere nearly so far from the coast belt, except for one record of a specimen taken in the fall at Haywards. This has been reéx- ‘amined and proved to be barlowi, as was to be expected from its contiguity. However, the Golden Gate is so narrow that an occa- sional crossing may take place. This was more probable formerly, when the redwood timber grew up to the Gate on both sides. 260 DARWINISM TO-DAY. Heermann, in 1853, recorded the species from ‘San Francisco.’ But now, I think, the bird is unknown for several miles on either side of the Gate. Doubtless this barrier accounts in part for the origin of the distinct form barlowi within so short a distance. ... “As has become a generally accepted idea, the young plumages of birds, if different at all from those of the adults, present a gener- alised type of coloration; or, to express it in another way, the young more nearly resemble recent ancestral conditions. The familiar examples of the spotted, thrush-like plumage of the young robin and the streaked, sparrow-like plumage of young towhees and juncos are cases in point. Accepting this phylogenetic signifi- cance of ontogeny, we find the chickadees giving some interesting illustrations. “Although the adult of barlow: has the sides pure smoke-gray, the juvenal plumage possesses pale-rusty sides. This points towards a rusty-sided ancestor like neglectus. This also agrees perfectly with the distributional evidence of origin. The adult of neglectus has pale-rusty sides; the young also has rusty sides, but somewhat darker than in the corresponding age of barlow:, and moreover is more nearly like the juvenal plumage of rufescens. But the sides in adult rufescens are deep brown, almost chestnut, while the young has much paler, merely dark-rusty sides. And what is most significant is that the young of rufescens and hud- sontcus are much nearer alike than are the adults, the former hav- ing only very slightly darker rusty on the flanks. The young of hudsonicus in respect to intensity of browns almost exactly equal the adults of the same species, showing that the present coloration is of very long standing, and offering further evidence that hudson- icus is nearest the common stock form of all the chickadees under consideration. Juvenal characters, resembling ancestral conditions, lag behind the newer acquired adult characters. “To repeat: The young of barlowi has the sides paler rusty than neglectus, neglectus slightly paler than rufescens, but rufescens has the sides slightly more rusty than hudsonicus, a sequence which accords well with the present theories of origin.” ° Kellogg, V. L., ““New Mallophaga, I,’’ Contrib. to Biol. from the Hopkins Seaside Laboratory of Leland Stanford Jr. University, 1896. *° Smith, Jas. P., “Studies for Students: Geological Study of Migration of Marine Invertebrates,” Journal of Geology, Vol. III, Pp. 481-495, 1895. ** Any selective breeding or segregation produced by other means than the separation of groups of individuals by actual topographic, or geographic barriers may be called biologic or sexual isolation. OTHER THEORIES OF SPECIES-FORMING. 261 72 Plate, L., “Uber die Bedeutung des Darwin’schen Selections- prinzip,” p. 193, 1903. ** Hutton, F. W., “The Place of Isolation in Or- Further refer- ganic Evolution,” Nat. Science, Vol. XI, pp. 240-246, ences to discus- g sions of isolation, 1°97: : ; . ** The not uncommon mating, in zoological gardens, of lions and tigers, with the production of healthy cubs, is a case in point. ** This principle, strongly advocated by Romanes, seems first to have been presented by Eimer in connection with his theory of orthogenetic evolution. At least it enters into the make-up of the Eimerian theory. See account of Eimer’s theory in chapter x of this book. ** Jordan, Karl, “Mechanische Selection,” 1896; see also Peter- sen, Wilh., “Entstehung der Arten durch Physiologische Isolirung,” Biol. Centralbl., Vol. XXII, pp. 468 ff., 1902; also Vol. XXIV, pp. 423-431, 467-473, 1904. Author describes cases of marked differ- ence in reproductive organs (includes primary and accessory parts) of closely allied species of Lepidoptera. *T Snodgrass, R. E., ‘The Terminal Abdominal Segments of Female lipulids, Jour. N.Y. Ent..Soc., Vol. X1, pp.-177-183, 1003: “The Hypopygium of the Tipulide,” Trans. Amer. Ent. Soc., Vol. XXX, pp. 179-235, 1904; ‘““The Hypopygium of the Dolichopodide,”’ Proce. Cal. Acad. Sci., Ser. 3, Zool, Vol. Til, pp.273-285; 1004. *® Seebohm, H., ‘‘Physiological Selection,” 1886. *° Wallace, A. R., “Darwinism,” p. 180, 1891. *° Jordan, Karl, ‘““Novitates Zoologice,” pp. 426 ff., 1896. ** Vernon, H. N., “Reproductive Divergence: An Additional Factor in Evolution,” Natural Science, Vol. XI, pp. 181-189, 1897. ** Jordan, Karl, ‘“‘Reproductive Divergence: A Factor in Evolu- tion?” Natural Science, Vol. II, pp. 317-320, 1897. ** Pearson, Karl, “Reproductive Selection,” Natural Science, Vol. VIII, pp. 321-325, 1806. ** Romanes, G. J., ‘Isolation in Organic Evolution,” Monist, Vol. VIII, pp. 19-38, 1807. *’ Gulick, J. T., “Divergent Evolution through Cumulative Segre- gation,” Jour. Linn. Soc., Zool., Vol. XX, pp. 189-274, 1888. *° Gulick, J. T., Jour. Linn. Soc., Zool., Vol. XX, pp. 202-211, 1888. *7 Gulick, J. T., “Evolution, Racial and Habitudinal,” Pub. No. 25, Carnegie Institution of Washington, 1905. In this large paper are to be found references to all of the author’s important papers. Some of these papers are reprinted (some completely, some in part) in this monograph. CHAPTER X; OTHER THEORIES OF SPECIES-FORMING AND DESCENT (CONTINUED): THEORIES ALTER- NALIVE TO SELECTION. WE come now to the brief consideration of three general theories, or groups of theories, which are offered more as alternative or substitutionary theories for natural selection than as auxiliary or supporting theories. These groups of theories are the Lamarckian one, based on the inheritance of characters acquired individually (ontogenetically) during the lifetime of the organism due to the effects of use and disuse and functional stimuli; the general conception of orthogenesis variously provided for by Nagel, Eimer, Jaeckel (metakinesis), and others, and finally the theory of heterogenesis, suggested by von Kolliker, definitely formu- lated by Korschinsky, and most recently, and importantly, developed by de Vries. Few biologists would hold any of these theories to be exclusively alternative with natural selection; de Vries himself would restrict natural selection but little in its large and effective control or determination of the general course of descent. But all of these theories offer distinctly substitutional methods of species-forming, and one of them includes certainly the most favoured expla- nation, next to selection, of adaptation, while the authors or later up-holders of some of them actually deny any con- structive, that is, adaptational, species-forming or descent- controlling, influence of natural selection. The Lamarckian Theory.—It is a great presumption to attempt to offer in so small a book as this any exposition of a theory so long known and elaborately developed as the ex- 262 OTHER THEORIES OF SPECIES-FORMING. 263 planation of adaptation and species-forming known as La- marckism. Lamarck* proposed his theory at a time most inopportune; it met with no gen- eral acceptance, but in later years, post-Darwinian years, fair-minded biologists have turned back to the books and papers of this pioneer French exponent of the evolution principle and have given his theory the careful attention and scrutiny it deserves—but which it failed to get from Lamarck’s contemporaries. This reéxamination of the La- marckian theory or theories has given rise to most radically — divergent opinion and belief concerning its worth: many . biologists account it of great value, others reject it prac- tically in toto. But this acceptance or rejection depends almost entirely on one’s attitude toward a single funda- mental part of it, namely, the assumption that variations, modifications, or characteristics acquired during the life- time of an individual, these modifications usually being due to use, disuse, or other functional stimulation of organs and parts, can be transmitted by this individual to its offspring. If such newly-acquired, non-inherited characteristics can be transmitted in full and in detail, or even approximately so, from the parent to the young, then Lamarckism obviously offers the simplest of all the explanations so far presented, of nearly all active and of many passive adaptations. If such characters cannot be so transmitted, then Lamarckism, as plausible, as reasonable, as simple and effective as it seems to be, is practically without validity. Now this matter of the inheritance of acquired charac- ters, apparently easily susceptible of definite proof or refuta- The fehectianse ON by observation and experiment, has been of acquired char- for years and is to-day one of the burning prob- one lems of biology. There is no general agree- ment about it, no consensus of authority even. Just at pres- ent the weight of evidence inclines strongly against such an inheritance, chiefly because of Weismann’s successfully Lamarckism. 264 DARWINISM TO-DAY. destructive criticism of about all the evidence of observa- tion which has been offered in behalf of it. And yet just at the present time do biologists recognise more keenly than ever the need and relief the actuality of such inheritance would give them in their attempts to solve the great problems of adaptation and species-forming? I cannot undertake to say whether more reputable biologists disbelieve in than believe in the existence of such inheritance, but it is obvious that the disbelievers have the present prestige of apparent vic- tory: they call for convincing evidence of such inheritance, and it is not produced. On the other hand, there are many reputable, thoughtful, honest, actively working biologists and paleontologists (particularly many paleontologists in pro- portion to the total number of palzontological students) who say, although not loudly and even a bit shamefacedly, per- haps, that they must believe in the possibility and the actu- ality of this inheritance; there is no getting forward with- out it. In taking up our brief exposition of Lamarckism, let me say first that only in post-Darwinian years has Lamarckism been put so strongly in contrast with Darwinism as it has. Darwin himself included part of Lamarckism as a minor factor or influence in his explanation of adaptation and species-forming, and Plate, in the recent most notable criti- cal discussion of Darwinism, takes nearly exactly the old ground of Darwin, namely, an acceptance of the inheritance, in some degree and under some conditions, of acquired characters, and the consequent possibility of a certain amount of Lamarckian orthogenesis, 1. e., an orthogenesis due to the inheritance of the results of use, disuse, and func- tional stimuli. It is only neo-Darwinism (of Weismann, Wallace, and others) and neo-Lamarckism (of Spencer, Packard, and others) that are so radically opposed, so mutu- ally exclusive. That an animal in its lifetime, and especially during its OTHER THEORIES OF SPECIES-FORMING, 265 immature life can effect very considerable changes in some The concep- Of its body-parts by special use or disuse of worl haleeaian these parts, or that certain parts may be modi- Lamarok. fied through the influence of external stimuli, is familiar knowledge. Let one recall the increase of the blacksmith’s biceps and inversely the degeneration of un- used muscles, and the thickening or callousing of palms or other parts of the skin exposed to repeated rough contact. Bones have ridges developed on them by repeated muscle- pulls, the hands and eyes can be trained to special functional skill which involves important although perhaps slight physi-. cal changes, the heart and lungs can be enlarged by special use; in short, almost any of the organs of the body, which are actively used, can be modified either by unusual or extra use, or by unusual lack of use. Now this use is, in Nature, almost always of the character of a better aiding in success- ful living; that is, it is adaptive use. Animals often chased by enemies become fleeter by practice; animals that must _ dig for roots or climb trees for leaves and fruits, or dive for fishes, or leap over obstacles, come by repeated digging, climb- ing, diving, or leaping to do these things better ; the muscles and tendons and bones work together better and better, become physically modified in accordance with these endeav- ours. If such betterment of organs and their functions acquired by individuals could be inherited by their young, it 1s obvious that general adaptations of this sort could be rapidly developed in the course of generations, and new species, new, that is, because of the adaptive changes thus effected, be formed. This is the essential thought in Lamarck’s theory of the method of adaptation and species- forming. In almost all criticisms of Lamarckism one reads much contemptuous reference to the expected results of the organism’s “willing” to vary or change in this or that direc- tion. As a matter of fact the critics of Lamarckism give that rather absurd feature of alleged Lamarckism much 266 DARWINISM TO-DAY. more conspicuousness than Lamarck did. He did, indeed, make some reference to the possible volitional effort of the organism to change along certain desirable lines, but it is evident that Lamarck had more in mind the animal’s desires and needs to stretch up higher for leaves or to dig better or run faster, leading to actual attempts to do these things, than to any expected results of mere mental wishing or willing. The essential principle of Lamarckism is an orthogenetic evolutionary progress toward better and finer adaptation and adjustment resulting from the inherited effects of actual use, disuse, and functional stimulation of parts. It is a great thought and a clear one, and only needs the proof of the actuality of the inheritance of individually acquired char- acters to make it one of the principal causal explanations of adaptation and species change. However, it is exactly this proof that is wanting. At any rate, proof of the character and extent necessary to con- iui all or even a majority of biologists is successful attack Wanting. The examples or cases brought for- on Lamarckism. ard by Lamarckians of the alleged inheritance of mutilations, of the results of disease, and of use and disuse, are not convincing. It is one of Weismann’s posi- tive contributions to biology to have analysed case after case of alleged inheritance of acquired characters, and shown its falseness or at least uncertainty. Many of these cases he has been able to explain as a result of selection; others remain inexplicable; a few,” only, are insisted on by the Lamarckian champions as indisputable examples of such inheritance. But this very paucity of so-called proved cases, where there should be thousands of obvious ex- amples if the principle were really sound, is argument against Lamarckism. Our knowledge, too, of the mechanism of heredity makes strongly against the theory of the inheritance of acquired characters. Another of Weismann’s positive contributions es i ahy ee bell. BCE Siting? ; OTHER THEORIES OF SPECIES-FORMING. 267 to biology is his generally sound distinction between the germ-plasm and the soma-plasm and parts of the many- celled body. At maturity the animal body is composed of a small mass of germ-plasm (germ-cells) situated in the ovaries or testes, and a great mass of somatic tissues and organs, all the rest of the body, in fact. Now what is the condition that exists in the body after a somatic part is modified by use or disuse or by other functional stimulus, as when a muscle is enlarged by exercise, the sole of the foot calloused by going barefoot, an ear more finely attuned by training? We have a definite physical change in a definite organ, but is the germ-plasm in any way changed or affected by this superficial or specific somatic modification, or if changed is it changed so that it will reproduce in its future development a similar change in the same organ of the future new individual? What possible mechanism have we in the body to produce or insure such an effect on the germ-plasm? The answer is obvious and flat; we certainly know of no such mechanism; in fact what we do know of the relation of the germ-cells to the rest of the body makes any satisfactory conception of such a mechanism as yet impossible. Not that certain external conditions may not directly affect the germ-cells, imbedded and concealed as they are Reh (alist in the body. me arying conditions of tempera- the way of ture,* of humidity, and of magnetism, perhaps, ee, certainly anything influencing the food supply acquiredchar- and nutrition, can influence the germ-cells at a the same time as it affects all the rest of the body. But will this influence photograph on these un- differentiated cells the same picture that it impresses on the * While temperature may be looked on as an extrinsic influence affecting germ-cells as well as all other parts of the body, it must be kept in mind that warm-blooded animals (birds and mammals) regulate the inner temperature of the body. So changes in external temperature would but slightly, or not at all, affect the germ-cells. 268 DARWINISM TO-DAY. affected somatic parts. A high temperature or a moist at- mosphere may modify the colour of the skin, change the pat- tern of the body superficies, but will overheated germ-cells produce new individuals showing the same changes of skin colour and pattern if the same conditions of environment of the soma are not repeated? How much less conceivable, then, is the influencing of the germ-cells so as to compel them to reproduce on daughter body-parts specific effects produced on special parental body-parts by such specific and localised influences as vigorous use of an arm, disuse of a leg muscle, repeated contact of the palm of the hand with hard bodies. Indeed, this lack of means of relating the germ-plasm to the soma, the rest of the body, has stood much in the way of any satisfactory conception of the phe- nomena of heredity, that is, the reproduction by the germ- cells of new individuals resembling the parental, and kas led to constant and thoughtful attention and speculation ever since the time of Darwin; indeed, from long before Dar- win’s time. One of the most favoured ways of attempting to explain how the germ-cells can represent in their make-up, and possess the capacity to develop into, the whole complex body, has been to conceive of the giving off of small representa- tive particles from all the cells of the body which should be carried by the blood to the germ-plasm and deposited in the germ-cells. The germ-cells in their development would then, by virtue of this manifold representation, be able to expand into the whole body during a shorter or longer course of development and growth. This notion of the com- position of the germ-plasm of micromeres collected from all the somatic cells, is the conception at the basis of Buffon’s theory of “organic molecules,’ of Spencer’s “physiological units,” Maggi’s “plastidules,’ Altmann’s ‘‘bioblasts,” Wies- ner’s ‘“‘plasomes,” Darwin’s ‘“gemmules,” Galton’s “stirps,” Nageli’s “micelle,’ Weismann’s “biophors and determi- OTHER THEORIES OF SPECIES-FORMING. 269 9? nants,’ and of numerous other micromeric theories.* But the facts of budding, especially as exemplified in plants, and of regeneration among animals, both of these kinds of phenomena seeming to show that germ-plasm is not neces- sarily limited to the germ-cells, strictly so-called, have pre- vented the acceptance of a too rigorous interpretation of Weismann’s distinction between the germ-plasm and the soma, and have led to some theories of germ-plasm make-up and disposition differing from the ones proposing a rigid restriction of germ-plasm to thé germ-cells. The facts that in many plants any part, as a bit of a twig, say, if cut off, can reproduce the whole plant just as effectively as a seed (germ-cell) can, and that many animals can reproduce con- siderable and complex parts, if lost by accident or self- mutilation, show that there often resides in somatic cells of much specialisation the capacity to reproduce not only cells of their own kind but others of much variety and different specialisation. So some biologists believe that there is either a net-work of primitive germ-plasm extending throughout the soma cells (Nageli’s idioplasm theory for example), or that each somatic cell (at least those with the capacity of regeneration or reproduction by budding, cuttings, etc.) con- tains a little primitive germ-plasm stuff besides its own soma-plasm. And some authors have seen in such theories of a widely diffused germ-plasm a mechanism for the trans- mission from the soma to the central germ-cells of the effects of use, disuse, and functional stimuli derived from external sources. But does even this conception of a diffuse and connected germ-plasm, after all, clear up in any way our difficulty? It makes it easier to see how germ-plasm may be affected by external and superficial influences, but does it explain in any degree how these effects can be car- ried to the germ-cells and so stamped on them as to compel them to reproduce photographically in their later develop- ment into new individuals, the specific effects that use, dis- 270 DARWINISM TO-DAY. use, and external stimuli may have had on specific soma parts of the parent? Indeed, Haacke * well points out that many or most cases of apparently direct working of extrinsic influences on the body are really indirect, in that these influences do not actually directly modify the structure, as a blacksmith’s hammer modifies the shape of a piece of red-hot iron, or a seal shapes the drop of melted wax, but that they do it indirectly as stimuli inducing chemi- cal processes, nervous impulses, etc. The adaptive re- arrangement of spongy tissue in broken and poorly reset long bones, apparently a direct reaction, is really only in- direct, occurring through complex chemical processes, 1. é., the bringing of special bone-forming materials to certain places, etc. The outer influences are all stimuli, not actual sufficient causes or manipulations. Haacke makes a proposal of much ingenuity, after a keen and suggestive discussion of the inheritance of acquired characters problem, to explain how such an inheritance may be effected. It is based on the fact that no characters are directly acquired; that is, that any change is only the result of some external stimulus and not of a directly and imme- diately moulding cause, and that, therefore, in any phenom- enon of stimulus and effect much more of the body substance than that composing the exact part or region modified is influenced. From this Haacke sees the possibility, even the necessity, of a modification of the whole constitution, includ- ing the germ-plasm (or perhaps the germ-plasm is modified as a result of the modification of the whole constitution or body in which the germ-plasm is being developed and formed). Thus every acquirement of a new character or change in an old one must or may affect the germ-plasm. With regard to passive organs such as the chitin skeletal parts of insects and crabs, Haacke points out that they are only the product of active organs, 1. e., the secreting skin- Haacke’s discussion, OTHER THEORIES OF SPECIES-FORMING. 271 cells, etc. Use and disuse are equivalent simply to much or little metabolism, and metabolism is as necessary to produce passive organs or to change them, as use is to make muscles larger. However, despite the successful destructive criticism by Weismann and the neo-Darwinians of the alleged cases of Maty natu UC inheritance of acquired characters adduced ists believe in. by the Lamarckians, and in spite of our lack of the inheritance A Ake : of acquired knowledge, and indeed, difficulty of conception ohatactert: of any mechanism in the body capable of im- pressing on the germ-plasm the effects of use, disuse, and external stimuli in such a way as to compel a photographic reproduction in the young of these effects as manifest in the soma of the parent, numerous biologists do not hesitate to avow their conviction of the actuality of such inheritance. Now these biologists must have some basis of observation or scientific fact for their belief. What is this basis? They rest their belief largely upon a kind of proof by indirection, a certain necessity of consequence of other facts, and a logical argument by elimination. The actual observed status of animal life to-day and, as revealed by fossils, in past ages, which is that of the existence of certain lines of descent or evolution obviously following lines of modification based on use and disuse; the inadequacy of natural selection to explain the cumulation of adaptive modification until such modification shall have reached a life-and-death determin- ing selective value; the apparent impossibility of explaining the continued degeneration of vestigial organs by natural selection; the great difficulty of explaining correlative or coadaptive modifications by selection alone; the possibility that our lack of knowledge of a mechanism for ensuring the hereditary transmission of acquired characters may be over- come with further knowledge of the ultimate structure and capacity of the germ-plasm; the great reasonableness and logical plausibility of the whole Lamarckian conception; 272 DARWINISM TO-DAY. these and other similarly not wholly convincing reasons are the sort of not very admirable scientific evidence that the believers in Lamarckism have to stand on. Two groups of scientific men are especially well represented among the Lamarckians: namely, paleontologists and pathologists. (Not all palzontologists and pathologists believe in the inheritance of acquired characters.) Both of these groups are familiar with facts that are unfamiliar to biologists gen- erally. And to my mind it is important that biologists should recognise the fact that familiarity with the facts of histor- ical geology on the one hand and with teratogenesis and human disease on the other, seems to lead to a belief in Lamarckism.* It should lead the general biologist to be less positive in his sureness of the invalidity of Lamarckism. But even were the inheritance of acquired characters now an established fact, or if it should come to be one, it must Lamarckism be kept in mind that Lamarckism could be sub- unable toex-— ctituted only partly for Darwinism. There are plain all adapta- ene ; : tions. many adaptations and much species-forming that Lamarckism might explain, but also there are hosts of adaptations that Lamarckism cannot explain. Plate,’ who defends natural selection but accepts some part of Lamarck- ism, has pointed this out clearly. He asks how the so-called “passive adaptations” could be explained by Lamarckism. “The salivary glands of a non-poisonous snake could pro- duce ever so much saliva, but it would not become poison- ous by this, just as little as simple teeth could change by use to grooved teeth and these to tubular ones. The tusks of Babiriussa could not be led to grow through the skin of the cheeks through use, for they would have to be actually * A scientific man representing another phase of biologic activity, and a man who has enjoyed an extraordinary opportunity for the observation and testing of modes of inheritance, also believes strongly in Lamarckism. This is Luther Burbank, the famous Cali- fornia plant-breeder. For some account ° of the scientific aspects of Burbank’s work, see the appendix of this chapter. OTHER THEORIES OF SPECIES-FORMING. 273 covered by the flesh for awhile in this process, and during this time be incapable of use. With Fierasfer, the fish that lives in sea-cucumbers ( Holothurians), the anus lies far for- ward in the throat so that the fish has only to thrust its head through the anus of the sea-cucumber in order to void its feces. How can use of the intestine or its peristaltic move- ment have produced such a remarkable change in position of the anus?” Plate‘ offers other similar examples of adap- tations inexplicable by Lamarckism, and justly says that hundreds of others could be adduced. He presents suc- cinctly the possibilities of Lamarckism, the inheritance of acquired characters being granted, as follows: Lamarckism could explain (1) many indifferent characters: example, changes of temperature produce proportional changes in the colour-pattern of butterflies’ wings; {2) many simple adaptations of active organs: example, a muscle becomes stronger through use, and creates a crest on a bone through pulls; (3) some simple adaptations of passive organs (so-called direct adaptations): example, in the whales, the water might directly affect the skin and sub-cutane- ous tissue and thus produce the loss of hair and the layer of fat; Lamarckism could not explain (1) many characters of active adaptation, even though of simple kind: example, the penetrating of the lung- sacs of birds through hair-fine holes into all the bones ; (2) many complicated adaptations of active organs: ex- amples, light-making organs, eyes, smelling-organs, auditory organs ; (3) all complicated passive adaptations: example, mim- icry. Even if we are ready to admit the possibility or actuality 274 DARWINISM TO-DAY. of the inheritance of acquired characters in some degree or under certain conditions—and this partial acceptance has. always seemed to me no more justified than the flat accept- ance of the principle in its entirety; it has seemed a weak sort of attempt at compromise with no real basis in reason and effecting no advantage in clearing up the problem— there can be no acceptance of the all-sufficiency of Lamarck- ism as an explanation of adaptation, species-forming, and descent, any more than there can be such an acceptance of the all-sufficiency of natural selection. Adaptation and spe- cies-forming are not, to my mind, one and the same problem: adaptation can and does lead to species-forming, but species. are formed that are not the results of adaptive modifica- tion; whose specific characteristics are indifferent; that are, in a word, non-adaptive species. De Vries’s new species of evening primroses have a cause not associated with adapta- tion. Now Lamarckism certainly cannot explain non- adaptive species any better than selection can. Both selec- tion and the inheritance of the effects of use, disuse, and external stimuli are primarily explanations of adaptations and of adaptive species-forming. Lamarckism is, perhaps, through its inclusion of the perpetuation of the direct influ- ence of external stimuli, in better condition to explain non- adaptive species, but both of these genius-offered explana- tions of organic evolution need the aid of another or other factors: the unknown factors of evolution, to speak with Osborn. Orthogenesis—One of the principal criticisms of the natural selection theory is that of the impossibility of ex- cane plaining the beginnings of advantageous modi- dence for ortho- fication and the beginnings of new organs, by genetic evolution. +6 selection of fluctuating individual variation, and of explaining the apparent cases of the existence of determinate variation and the admitted cases of forthright development along fixed lines not apparently advantageous, OTHER THEORIES OF SPECIES-FORMING. 275 and finally of explaining the definite cases of ultra-develop- ment of parts and species beyond the point of advantage even to such unfavourable degrees as lead to death and extinction. Paleontology * reveals to us the one-time existence of ani- mals, of groups of animals, and of lines of descent, which have had characteristics which led to extinction. The un- wieldiness of the giant Cretaceous reptiles, the fixed habit of life of the crinoids, the coiling of the ammonites and nautili, the gigantic antlers of the Irish stag—all these are examples of development along disadvantageous lines, or to disadvantageous degrees. ace statistical studies of varia- tion have made known numerous cases ° where the slight, as yet non-significant (in a life-and-death struggle) variation in pattern of insects, in dimension of parts, in relative pro- portions of superficial non-active structures, are not for- tuitous, that is, do not occur scattered evenly about a mean or mode according to the law of error, but show an obvious and consistent tendency to occur along certain lines, to accumulate in certain directions. Many biologists see in variation and in species-forming certain determinate char- acteristics exhibited by, or lines or paths being followed by all or most of the individuals of successive generations ; and see in descent certain phenomena of forthright progressive movement which they find selection based on utility unable to explain. Various theories to account for this apparent orthogenetic, but not ortho-selective, development have therefore been proposed by biologists, most of which theories and most of which biologists are to be looked on as antagonistic to the selection theory. For if a theory of ortho-— genesis is sufficient to explain those lines of variation and development not explicable by selection, it usually seems to its maker to be sufficient to explain other lines of evolution. It may very likely occur to some that in speaking of ortho- genetic development as contrasted with descent governed by selection we are making a distinction without a difference, 276 DARWINISM TO-DAY. in that it is obvious that selection also produces ortho- genetic evolution, that is, evolution along definite lines; that in fact it can produce no other kind of Orthogenesis evolution. To attribute orthogenetic results to contrasted with gcteeh is ; ; orthoselection, Natural selection is quite right,and some one has proposed the name orthoselection to distinguish orthogenetic evolution as produced by selection from such results produced independently, or at least partly inde- pendently of selection, that is produced in accordance with any one or more of the so-called theories of orthogenesis. All this latter kind of orthogenesis is distinguished from orthoselection in that it presumes all or most of the indi- viduals of successive generations to be modified, to vary, that is, in a similar manner as a result of factors, intrinsic or extrinsic, producing determinate variation. This is plainly different from orthoselection, in which definite lines of development are produced by the eradication, through the rigour of selective struggle, of all other lines. Variation may be wholly fortuitous, miscellaneous, indeterminate; but selection permits only certain kinds of variation to persist, to accumulate. In true orthogenesis the variation, and hence the lines of modification, are predetermined. It seems obvious, however, to any believer in natural selection that sooner or later the fate of these lines of development will come into the hands of selection. And most orthogenesists do indeed admit this. But it is precisely in the making of a start in modification that orthogenesis fills a long-felt want, and if capable of proof, should be gladly received by Darwinians as an important auxiliary theory in the ex- planation of modification, species-forming, and descent. The first of these theories of orthogenesis has just been explained, for Lamarckism may be looked on as an expla- nation of orthogenetic evolution based on the perpetuation and accumulation of the effects of use, disuse, and the direct effects of functional stimuli. Roux’s battle of the OTHER THEORIES OF SPECIES-FORMING. 277 parts theory, and Weismann’s theory of germinal selection are also in a way theories of orthogenesis: they explain how variations begin and continue along fixed lines, but they both soon surrender control of descent to natural selection. | There are, however, two or three theories of Different types orthogenesis which have been developed by of theories of orthogenesis, their proposers to the degree where they are boldly offered as substitutes for natural selec- tion. Two especially notable theories of this character are those proposed and defended respectively by Nageli and by Eimer. These two are not only the most notable and most completely elaborated of orthogenetic theories but they represent two radically different points of view among the orthogenesists themselves, in that Nageli found his ortho- genesis-producing factor or cause in a_somewhat mystical vitalistic inner force, or so-called V ervollkomnungsprinsip, in the organism, while E imer finds orthogenesis produced and controlled by the directly working external factors of climate, food supply, and environment generally. Similar conceptions or beliefs regarding the direct and accumulating effect of environmental factors have been presented by Dar- win, Haeckel, Cope, Henslow, Emery, Piepers, Lloyd Morgan, and numerous others. In fact probably a majority of biologists entertain a conviction,—often not clearly de- fined and generally unaccompanied by any satisfactory con- ception of a mechanism for achieving what they believe to exist,—of the actuality of an influence on organic modifi- cation and descent directly exerted by those various external factors or conditions of organic life which we call, collec- tively, environment. Nageli’s *” theory of orthogenesis depends upon the as- sumption of his so-called principle of progressive develop- Nigeli's theory Ment (Vervollkomnungsprinzip), a something of orthogenesis. inherent in the organic world which makes each organism in itself a force or factor making towards Pema OL 278 DARWINISM TO-DAY. specialisation, adaptation, that is, towards progressive evo- lution. Other authors who accept such a theory of an inher- ent driving force in organisms speak of this factor variously as an “inner directive force,’ an “inner law of development,” or an “intrinsic tendency towards progress,” etc. Nageli believes that animals and plants would have developed about as they have even had no struggle for existence taken place and the climatic and geologic conditions and changes been quite different from what they actually have been. Kor- schinsky ** says: “In order to explain the origin of higher forms out of lower it is necessary to assume in the organism a special tendency towards progress.”” That is, to the be- lievers in this kind of a theory of orthogenesis organic evolution has been and is now ruled by unknown inner forces inherent in organisfns, and has been independent of the influence of the outer world. The lines of evolution are immanent, unchangeable, and ever slowly stretch toward some ideal goal. It is needless to say that but few biologists confess to such a belief. However much in the dark we may be regarding the whole great secret of bionomics, how- ever partial and fragmentary our knowledge of the processes and mechanism of evolution, such an assumption of a mystic, essentially teleologic force wholly independent of and dominating all the physico-chemical forces and influences that we do know and the reactions and behaviour of living matter to these influences which we are beginning to recognise and understand with some clearness and fulness— such a surrender of all our hardly won actual scientific knowledge in favour of an unknown, unproved, mystic vital force we are not prepared to make. As Plate well says, such a theory of orthogenesis ** is opposed, in sharpest contrast, to the very spirit of science. On the contrary, the theories of orthogenesis of the general type exemplified by Eimer’s * are directly in line with the spirit of modern biological methods and investiga- OTHER THEORIES OF SPECIES-FORMING. 279 | tions; they rest on the assumption that physico-chemical factors produce direct effects on the plastic organism, and Mcelce type that such effects, repeated and intensified, re- of orthogenetic sult in a certain degree of modification or con- roach trol of variation and evolution. To be sure, there is not yet proposed a very satisfactory mechanism for conveying the environmental influence to, and trans- lating it into definite effect on the course of development, but the obvious fact that environment does strongly affect and modify individual function and structure and the rea- sonable belief that the modification of the race must ulti- mately rest on and proceed from the modification of the individual, make the theories of orthogenesis based on en- vironmental influence very suggestive and of distinct scientific value. In addition, too, there is a certain amount of actual evidence of observation for orthogenesis: an evidence of two categories, namely, positive affirmative evidence,’ and negative evidence drawn from the inade- quacy of other theories, notably natural selection, to explain certain observed phenomena which can be explained on the assumption of an orthogenesis. The general character of this evidence is indicated in our first paragraph treating of orthogenesis. To this may be added an ab- eae ton stract of Plate’s’® résumé of the facts or to prove ortho- phenomena which may be looked on as positive iil evidence for orthogenesis (although Plate cau- tiously notes that some of these may be only phenomena of orthoselection). These phenomena pointing toward ortho- genesis tay be grouped into six categories: 1. The “analogous or parallel variations” which have been recognised ever since Darwin’s time, he, himself, list- ing many examples of them. These are varia- tions of unmistakably similar character, which often appear in different branches of the same large group. “Comparative anatomy reveals many ex- Parallelisms in ‘variation. 280 DARWINISM TO-DAY. amples to show that a definite or determinate direction of modification may be noted in all the sub-groups of a large family, although appearing in unequal degree in different species. Examples are the reduction of the hind toes among the Artiodactyls which has continued in several genera (giraffe, camel, llama) up to a complete disappearance, and the modification of the originally single genital duct into a double and finally triple one, as occurs in both the Pul- monata and the Opisthobranchiata. Often a progressive development can, on mechanical or physical grounds, come about by a modification in but one direction, and may lead thus to convergent changes, as the development of a lens in a pigment fleck in the case of many unrelated lower animals, the similarity of the heart in crocodiles, birds, and mammals, the appearance of a placenta with Permales among the Marsupials and also among the Placentalia.” 2. The numerous “excessive structures” which are de- veloped far beyond the limits of usefulness. Examples, the tusks of the wild boar (Babirussa alfurus) ; the giant horns of many wild sheep and goats; the enormously elongated thread-like neck of several Rhynchophorous beetles, as Apoderus tenuissimus, etc.; the absurdly long eye-stalks of such crustaceans as Macrophthalmus laterillei and Podophthalmus vigil; Meso- plodon, whose mouth can be opened but a little when the animal is full grown because on each side an under tooth grows around the upper jaw. Such “excessive structures” have undoubtedly led to the dying out of many former species: examples, the tusks of the mammoth, the antlers of the Irish stag, the canines of Smuilodon neogeus. 3. “The constitution, or actual chemical composition of the body permits, in many cases, changes only in few directions. The animal or plant breeder may by no means produce any wished-for form or colour. No one has yet succeeded in producing a blue Maiblume, a grass with divided leaves, a Over-speciali- sations. OTHER THEORIES OF SPECIES-FORMING. 28% hen with a parrot’s beak. And we can declare with con- fidence that a chorda dorsalis can never appear in a beetle. Awan Through the very fact that an animal belongs limitationson to a group the possibilities of variation are agian distinctly delimited and in many special cases these possibilities may indeed be very narrow.” Plate does not mention in this connection the fact that some biologists have seen in this restriction of the range of varia- tion which inevitably accompanies specialisation in the development of animal groups an important factor in the determination of lines of descent. Cope gave much import- ance to this factor, and'very recently Rosa,’* in a most in- genious and suggestive paper, attributes to this “progressive reduction of variability” a large importance in the dying out of old species and the origin of new ones. 4. “By the correlations which bind each organ to others. the range of variation is also restricted.” 5. Many facts of paleontology seem to prove the existence of orthogenetic evolution. ‘Wherever a large supply of ma- Factsfrom terial permits the working out of a phyletic. Sine: series, we always see a limited number of lines thogenesis, of development, which despite occasional side- branching run essentially in straight lines, in steps which lead gradually one to another.” 6. The phyletic series (chains of forms) of recent species Single phy- also show, where we are able to trace them, letic lines. © distinctive single lines of development. Eimer’s particular theory of orthogenesis, which we have chosen aS a~representative Of the orthogenetic doc- trine in general (although few biologists who believe in the principle of orthogenesis accept this theory in detail), may be briefly stated as follows: Modifications of organisms, that is, lines of evolution, are not miscellaneous, but occur according to control along a few definite directions, these lines of change being deter- 282 DARWINISM TO-DAY. mined not at all, at least in their beginnings, by selection on a basis of utility, but as the result of the inheritance of ac- quired characters and according to the laws of organic growth (organophysis). The prin- cipal effects of these laws of organic growth are made manifest by the determinant evolution, or orthogenesis, which obtains, and which is in direct contrast to that kind of evolution which natural selection, if it really effected any- thing, would bring about. For evolution by natural selec- tion would occur along all sorts of heterogeneous and radiat- ing lines which is, according to Eimer, actually not the case. A few definite lines obtain from which occasional branches are given off, the whole building the familiar phyletic or genealogical tree. That these main lines and branches are not themselves the result of selection is proved by the fact that much evolution and modification of organ- isms is not directly useful, a majority, indeed, of the char- acters distinguishing different species not being characters of utility." Only when a character or line of evolution becomes of a life-and-death-determining disadvantage can selection interfere with evolution by orthogenesis. And this interference is always and only of the nature of a stamping out, never of the character of the creation of new characters or lines. Eimer believes in the inheritance of acquired characters, believes in a considerable species-forming influ- ence of geographical isolation, that is, finds such isolation very helpful to the general basic organic growth evolution principle and finds the actual causes of orthogenesis “‘to lie in the effects of external influences, climate, nutrition, on the given constitution of the organism.” “This is not Lamarckism,” Eimer points out, anxious to have his theory to his own credit, ‘““for Lamarck ascribed to the external in- fluences no effects on the animal body, and only very little on the plant body.” Eimer adds that the effects of external influences are usually considered a part of Lamarckism; Eimer’s theory of orthogenesis, Bi v ih OTHER THEORIES OF SPECIES-FORMING. 283 as a matter of fact Lamarck’s species-forming influences were, chiefly at least, the inherited results of actual use or disuse, or of other functional stimulation initiated or exer- cised actively by the organism itself. In the actual varia- tion of organisms Eimer sees none of that “oscillation” or equal variation around a median or modal point character- istic of the Darwinian conception, but sees always a deter- minate variation in a few definite lines. He denies positively any capacity on the part of natural selection to create species, finding it effective in breaking the continuous organic chain, that is, of separating it into species, only when aided by geographical isolation. The actual species-forming, that is, the breaking up into specific units of the orthogenetic lines of change instituted by his dynamic factors, he finds to de- pend on three chief moments, viz., a_standing still or cessa- tion _of development (Entwicklungsstillstand) : a sudden de- velopment by leaps, called halmatogenesis (which i: is almost exactly the fundamental idea in Korschinsky’ s and de Vries S men, nena culty in reproduction mee is the socal factor’ in Ro- manes’s theory of physiological selection proposed ten years later). It is of interest to note Eimer’s claim to the original conception of species-forming both by heterogenesis and through physiological selection, with which two theories the names of de Vries and Romanes, respectively, are com- monly associated as those of the original proposers. Of Eimer’s three species-forming factors he lays most stress on the one I have first mentioned viz., Entwicklungs- stillstand. “The origin of species depends essentially on Entwicklungsstillstand or Genepistase, that is, the standing still of certain forms at definite stages in the developmental line, while others go on.” This permits of the origin of numerous different species in the same locality or region, without any need of isolation. As orthogenesis modifies, that is, causes to vary in the same way, many individuals at — 284 DARWINISM TO-DAY. a time, it is easy to see that if some of these produce young which do not proceed farther along the orthogenetic line, that is, do not vary farther, while others produce progeny that tend to move on along the line or lines of determinate variation, new species can be dropped, as it were, out of the general course of the orthogenetic evolution all along. An if these persist we have a series of distinct organic forms all related chainwise although living simultaneously and in the same region. This cessation of development can lead to many added new forms when it occurs in the form of Heterepistase, that is, where only a few characteristics re- main fixed at some early developmental stage while others goon. By the fixing or cessation of development in differ- ent small groups of characteristics, and in different combina- tions of these groups many new species may result. All cases of so-called atavism are interpreted by Eimer simply as examples of his Entwicklungsstillstand, this cessation of development occurring in the atavistic organs at a very early stage. We should not omit mention, in connection with Eimer’s theory, of a point upon which he lays great stress, and that is that his theery is not the result of pure speculation, but is the unavoidable conclusien arrived at by long years of specific observations and study of the facts obtaining in the case of the relations, conditions, and course of evolution of certain groups of organisms. Eimer made careful and ex- tended studies of the wing-patterns of two large groups of butterflies, and of certain lizards and birds, and it is on the basis of these studies in particular that his theory was formulated. It is certainly to be admitted that his exhaust- ive and most suggestive account of the relations of species and patterns in the swallow-tailed and certain other butter- flies makes a very strong argument against the validity of natural selection as an explanation of these conditions. And the example of Eimer’s prolonged and minute study of OTHER THEORIES OF SPECIES-FORMING. 285 actual facts as a basis for his theory and hypothesis building is one which has not been always followed by biological generalisers. It is to be regretted that the polemical and personal character of much of Eimer’s writing has tended to make his whole work less regarded than it ought to be by biologists. That Eimer’s theory does not include in any degree the assumption 0 yn Of an inner ‘directive or. progressive. force the following quotation from Eimer himself shows: “Accord- ing to my investigations the chief cause of transformation [of species] is that determined definitive organic growth (organophysis) whose expression is a definite determined development (orthogenesis), which is imposed on the plasma by constant outer influences, climate, and nourish- ment. . . . Apart from the fact that the Nagelian assump- tion of a definite determined development is a hypothetical one, not proved by facts, the zoologist can hardly accept the existence of such a dominant inner factor ever pushing toward advance, when he recalls the host of regressive struc- tures which he has to see. This tendency to progress based on the assumption of ‘inner growth laws’ contradicts flatly the assumption of outer influences as causes of change. . . . And it is my belief that it is precisely these outer influences, and the physiological phenomena dependent on them, which are the determining factors in the phyletic development just as they are in individual development.” ** Among American biologists who have been believers, in some degree, in Lamarckism or some other form of ortho- genetic evolution, Cope is the one who has most definitely formulated his beliefs into a complete theory of the method of creating and guiding variation and descent lines. Cope’s theory may be called one of bathmism (growth- -force), Kinetogenesis (direct effect of use and disuse and environmental influence), and arch- Cope’s ortho- genetic theory, 286 DARWINISM TO-DAY. zsthetism (influence of primitive consciousness). In an essay’ first published by Cope in 1871 the following hypotheses were presented. (These hypotheses are stated here in Cope’s own words, quoted from the preface of his pook “The Origin of the Fittest,” 1887): “1. The law of repetitive addition, in which the structures of animals were shown to have originated from simple repetitions of identical elements. “2, The existence of an especial force which exhibits itself in the growth of organic beings, which was called growth-force, or bathmism. “3, That development consists in the location of this energy at certain parts of the organism. “4. That this location was accomplished by use or effort, modifying and being modified by the environment; or the doctrine of kinetogenesis. ‘“s. That the location of this energy at one point causes its abstraction from other points, producing ‘complementary diminution’ of force at the latter. “6. That the location of this energy, so as to produce the progressive change called evolution, is due to an influence called ‘grade influence.’ “7. That inheritance is a transmission of this form of energy, which builds in precise accord with the sources from which it is derived. “8. That this ‘grade influence’ is an expression of the in- telligence of the animal, which adapts the possessor to the environment by an ‘intelligent selection.’ “g. An attempt to account for the origin of “mimetic analogy’ by ‘maternal impressions.’ ” In later writings ** Cope subdivides his kinetogenesis prin- ciple, or the influence of use, disuse, and environment, into a physico-chemical influence affecting the organism through molecular effects, which he calls physiogenesis, and a me- chanical influence affecting the organism through molar OTHER THEORIES OF SPECIES-FORMING. 287 effects, for which the term kinetogenesis is retained. The modifications produced by these two classes of influences “are supposed to be the result of the action of the causes in question continued throughout geologic time.” These modifications are assumed to be inherited. In the animal kingdom kinetogenesis, or the modifying influence of mo- tion, is assumed to be the more potent efficient cause of evolution; in the plant kingdom, physiogenesis. The. gen- eral standpoint of Cope’s theory is thus strictly Lamarckian. But he adds to this reformulation of general Lamarckism a remarkable feature which he calls archesthetism. This 1s: the doctrine that ‘‘animal movements are primitively deter- mined by sensibility or consciousness” and that this “con- sciousness has been and is one of the primary factors in the evolution of animal forms.” That is, the kinetogenesis. which is the chief causo-mechanical factor of the evolution of the animal kingdom, from primitive single-cell type to most complex Metazoan, has for its own initiation conscious effort. Thus Cope is forced to assume, which he does, that “conscious states have preceded organisms in time and evolution.” The formal statement of this phenomenon, then, has to be the thesis that energy can be conscious. “If true,’ writes Cope, “this is an ultimate fact, neither more nor less difficult to comprehend than the nature of energy or matter in their ultimate analyses. But how is such a hypothesis to be reconciled with the facts of nature, where consciousness plays a part so infinitesimally small? The explanation lies close at hand, and has been already referred to. Energy become automatic is no longer conscious, or is. about to bécome-nnconseious:””*Cope’ holds then that “con- sciousness was coincident with the dawn of life,” and that “evolution is essentially.a process of mind. The source of the consciousness, which is back of it, is at present an un- See par eee 3 Cope was a palzontologist,** and his belief in the necessity 288 DARWINISM TO-DAY. of some factor or factors besides that of natural selection to explain evolution lines as revealed by paleontological study is shared by a large majority of the recognised American paleontologists. Osborn of Columbia, Williston of Chicago, Hyatt of Boston, Smith of Stanford, studying respectively the fossil mammals, the reptiles, and the molluscs, all voice their belief in the existence of evidence in the history of the evolution of these animal groups for orthogenetic variation and descent. Recently Whitman, the Nestor of American zoologists, has declared himself strongly as an adherent of the actuality of orthogenetic evolution. For many years Whitman’s ‘ ‘ ee expression in | Whitman has been studying the variations and favour of ortho- inheritance in pigeons, and through this work at in particular he has become convinced that species-forming variation does advance in a definite direc- tion as well as in various directions. He says,’ “natural selection, orthogenesis,* and mutation appear to present fundamental contradictions; but I believe that each stands for truth, and reconciliation is not distant. The so-called mutations of CEnothera are indubitable facts; but two lead- ing questions remain to be answered. First, are these muta- tions now appearing, as is agreed, independently of varia- tion, nevertheless a production of variations that took place at an earlier period in the history of these plants? Sec- ondly, if species can spring into existence at a single leap, without the assistance of cumulative variations, may they not also originate with such assistance? That variation does issue a new species, and that natural selection is a factor, though not the only factor, in determining results, is, in my opinion, as certain as that grass grows although we cannot see it grow. Furthermore, I believe I have found indubitable evidence of species-forming variation advancing in a definite direction (orthogenesis), and like- wise of variations in various directions (amphigenesis). If i OTHER THEORIES OF SPECIES-FORMING. 289 I am not mistaken in this, the reconciliation for natural selection and orthogenesis is at hand” (p. 4). In the category of determinate or orthogenetic variation should be included Delage’s ** not very clearly distinguished Denese variation générale. “We call by the name of ory ofgeneral general variation,” he says, “that which appears wanton at one time in all the individuals of a race or at least a large number of individuals and which affects, most often, several characteristics, if not all, in various degrees of strength. Variations of this sort must be due to modifications of the germ plasm produced either by the reducing division, or by fertilisation, or by accidental altera- tions which this plasm undergoes in its various divisions.” It is to these variations, according to Delage, that species- change is due. The inducing influences which result in the appearance of general variations are use and disuse and the ‘conditions of life’ (nutrition and climate). As forming a sort of link between the theories of ortho- genesis and those of heterogenesis (to be discussed in the ee next chapter), may be mentioned the rather theory of vague and unformed theory of Jaeckel,”’ the metakinesiss = Berlin paleontologist, called “metakinesis.” Jaeckel believes, from a study of fossil animal series, that there exists evidence of orthogenetic descent, but that while genera and families may show continuous phyletic series, specresappéa af sporadically, suddenly, and without special reference to the phyletic s series. He believes that many cases of epistasis occur: that is, that many sexually mature ani- mals show arrests of development in early ontogenetic stages, and have therefore given up a former further development. He finds numerous examples of this condi- tion among fossil crinoids and trilobites and living sela- chians. What his theory of metakinesis really seems to be is a combination of the sudden, definitive appearance of new species, which is the essential conception in the theories of 290 . DARWINISM TO-DAY. heterogenesis (explained in the next chapter), with the determinate lines of change or descent, which is the essential idea in orthogenesis. APPENDIX, * Lamarck, 1744-1828, the “founder of the complete modern theory of descent, is the most important figure [in the history of the References to theory of evolution] between Aristotle and Darwin” Lamarck’s (Osborn, ““From the Greeks to Darwin,” p. 156, 1899). writings. His theory of descent and the causes of descent was presented in his ‘‘Philosophie Zoologique,” a large work published in 1809. For a brief account of Lamarck’s life and work, see Osborn, “From the Greeks to Darwin,” pp. 156-181, 1899. For an exhaustive account with full quotations from Lamarck’s exposition of his the- ories, see Packard, ‘‘Lamarck, His Life and Work,” 1901. For ex- positions of the Lamarckian point of view compared with the Dar- winian position, see Haeckel, E., ““Die Naturanschauung von Darwin, Goethe, und Lamarck,” 1882; Lang, A., ‘Zur Characteristik der For- schungswege von Lamarck und Darwin,” 1889; Ward, L. F., ‘““Neo- Darwinism and Neo-Lamarckism,” Proc. Biol. Soc., Wash., Vol. VI, pp. 11-71, 1891; Hutton, F. W., “Darwinism and Lamarckism, Old and New,” 1899; Pauly, A., ““Darwinismus und Lamarckismus,” 1905. * Among the more conspicuous of these cases are Brown-Séquard’s epileptic guinea-pigs, Hyatt’s Planorbis shells, Cunningham’s flat- Brown Rs: fishes, and Fischer’s butterflies. Morgan, in “Evo- quard’s experi- lution and Adaptation,” gives the following account ments on guinea- and discussion of the Brown-Séquard experiments PIES. and results: ‘““The best direct evidence in favour of the Lamarckian argument is that furnished by the experiments of Brown- Séquard. He found, as the result of injury to the nervous system of guinea-pigs, that epilepsy appeared in the adult animal, and that young born from these epileptic parents became also epileptic. Still more important was his discovery that, after an operation on the nerves, as a result of which certain organs, the ear or the leg, for instance, are affected, the same affection appears in the young born from such parents. These results of Brown-Séquard have been vouched for by two of his assistants, and his results in regard to the inheri- tance of epilepsy have been confirmed by Obersteiner, and by Luciani on dogs. Equally important is their later confirmation, as far as the main facts go, by Romanes. “Brown-Séquard gives the following summary of his results. I follow Romanes’ translation in his book on ‘Darwin and After OTHER THEORIES OF SPECIES-FORMING. 291 Darwin, where there is also given a careful analysis of Brown- Séquard’s results, as well as the outcome of the experiments of Romanes himself. The summary is as follows :— “1. ‘Appearance of epilepsy in animals born of parents which had been rendered epileptic by an injury to the spinal-cord. “2. ‘Appearance of epilepsy also in animals born of parents which had been rendered epileptic by section of the sciatic nerve. “3. “A change in the shape of the ear in animals born of parents in which such a change was the effect of a division of the cervical sympathetic nerve. “a. ‘Partial closure of the eyelids in animals born of parents in which that state of the eyelids had been caused either by section of the cervical sympathetic nerve, or the removal of the superior cervical ganglion. “se ‘Exophthalmia in animals born of parents in which an injury to the restiform body had produced that protrusion of the eyeball. This interesting fact I have witnessed a good many times, and seen the transmission of the morbid state of the eye continue through four generations. In these animals modified by heredity, the two eyes generally protruded, although of the parents usually only one showed exophthalmia, the lesion having been made in most cases only on one of the corpora restiformia. “6. ‘Hematoma and dry gangrene of the ears in animals born of parents in which these ear alterations had been caused by an injury to the restiform body near the nib of the calamus. “7 “Absence of two toes out of the three of the hind-leg, and sometimes of the three, in animals whose parents had eaten up their hind-leg toes, which had become anesthetic from a section of the sciatic nerve alone, or of that nerve and also of the crural. Sometimes, instead of complete absence of the toes, only a part of one or two or three was missing in the young, although in the parent not only the toes, but the whole foot was absent (partly eaten off, partly destroyed by inflammation, ulceration, or gangrene). “8. ‘Appearance of various morbid states of the skin and hair of the neck and face in animals born of parents having had similar alterations in the same parts as effects of an injury to the sciatic nerve.’ “Romanes, who later went over the same ground, in part under the immediate direction of Brown-Séquard himself, has made some important observations in regard to these results, many of which he was able to confirm. “He did not repeat the experiment of cutting the cord, but he ‘found that, to produce epilepsy, it was only necessary to cut the 292 DARWINISM TO-DAY. sciatic nerve. The ‘epileptiform habit’ does not appear in the animal until some time after the operation; it lasts for some weeks or months, and then disappears. The attacks are not brought on spon- taneously, but by ‘irritating a small area of the skin behind the ear on the same side of the body as that on which the sciatic nerve had been divided.’ The attack lasts for only a few minutes, and during it the animal is convulsed and unconscious. Romanes thinks that the injury to the sciatic nerve, or to the spinal cord, produces some sort of a change in the cerebral centres, ‘and that it is this change—whatever it is, and in whatever part of the brain it takes place—which causes the remarkable phenomena in question.’ “In regard to Brown-Séquard’s statements, made in the 3d and the 4th paragraphs, in respect to the results of the operation of cutting the cervical sympathetic, Romanes had not confirmed the results when his manuscript went to press; but soon afterward, after Romanes’ death, a note was printed in Nature, by Dr. Hill, announcing that two guinea-pigs from Romanes’ experiment had been born, ‘both of which exhibited a well-marked droop of the upper eyelid. These guinea-pigs were the offspring of a male and female in both of which I had produced for Dr. Romanes, some months earlier, a droop of the left upper eyelid by division of the left cervical sympathetic nerve. This result is a corroboration of the series of Brown-Séquard experiments on the inheritance of acquired characters.’ ‘Romanes states that he also found that injury to a particular spot of the restiform bodies is quickly followed by a protrusion of the eye on the same side, and further, that he had ‘also had many cases in which some of the progeny of parents thus affected have shown considerable protrusion of the eyeballs of both sides, and this seemingly abnormal protrusion has occasionally been transmitted to the next generation. Nevertheless, I am far from satisfied that this latter fact is anything more than an accidental coincidence. This reservation is made on the ground that the protrusion in the young is never so great as in the parents, and also because there is amongst guinea-pigs a considerable amount of individual variation in the degree of prominence of the eye- balls. Romanes, while unwilling to deny that an ‘obviously abnor- mal amount of protrusion, due to the operation, may be inherited in lesser degree,’ is also unwilling to affirm so important a conclu- sion on the basis of these experiments alone. “In regard to Brown-Séquard’s 6th statement, Romanes found after injury to the restiform body that hematoma and dry gan- grene may supervene, either several weeks after the operation, or at any subsequent time, even many months afterward. The disease OTHER THEORIES OF SPECIES-FORMING. 293 usually affects the upper parts of both ears, and may then gradually extend downward until nearly the whole ear is involved. ‘As re- gards the progeny of animals thus affected in some cases, but by no means in all, a similarly morbid state of the ears may arise apparently at any time in the life history of the individual. But I have observed that in cases where two or more individuals of the same litter develop this diseased condition, they usually do so at about the same time, even though this may be months after birth, and therefore after the animals are fully grown.’ Moreover, the morbid process never extends so far in the young as it does in the parents, and ‘it almost always affects the middle third of the ear.’ Several of the progeny from this first generation, which had appa- rently inherited the disease, but had not themselves been directly operated upon, showed a portion of the ear consumed apparently by the same disease. Romanes then gives the following signifi- cant analysis of this result. Since a different part of the ear of the progeny is affected, and also a ‘very much less quantity thereof, it might seem that the result was due either to a mere coincidence, or to the transmission of microbes. But he goes on to say, that he fairly well excluded both of these possibilities, for, in the first place, he has never observed ‘the very peculiar process in the ears, or in any other parts of guinea-pigs which have neither themselves had the restiform bodies injured, nor been born of parents thus mutilated.’ In regard to microbes, Romanes tried to infect the ears of normal guinea-pigs by first scarifying these parts, and then rubbing them with the diseased surfaces of the ears of affected guinea-pigs. In not a single case was the disease produced. “Romanes concludes that these ‘results in large measure corrobo- rate the statements of Brown-Séquard; and it is only fair to add that he told me they were the results which he had himself obtained most frequently, but that he had also met with many cases where the diseased condition of the ears in parents affected the same parts in their progeny and also occurred in more equal degrees.’ “We come now to the remarkable conclusion given in Brown- Séquard’s 7th statement, in regard to the absence of toes in animals whose parents had eaten off their own hind toes and even parts of their legs. Romanes got neuroses in the animals operated upon, and found that the toes might be eaten off; but none of the young showed any defect in these parts. Furthermore, Romanes repeated the same operation upon the descendants through six successive generations, so as to produce, if possible, a cumulative effect, but no inheritance of the mutilation was observed. ‘On the other hand, Brown-Séquard informed me that he had observed this inherited absence of toes only in about one or two per cent. of cases.’ It is 294 DARWINISM TO-DAY. possible, therefore, Romanes adds, that his own experiments were not sufficiently numerous to have obtained such cases. “In this connection I may give an account of some observa- tions that I made while carrying out some experiments in telegony with mice. I found in one litter of mice that when the young came out of the nest they were tailless. The same thing happened again when the second litter was produced, but this time I made my observation sooner, and examined the young mice immediately after birth. I found that the mother had bitten off, and presumably eaten, the tails of her offspring at the time of birth. Had I been carrying on a series of experiments to see if, when the tails of the parents were cut off, the young inherit the defect, I might have been led into the error of supposing that I had found such a case in these mice. If this idiosyncrasy of the mother had reappeared in any of her descendants, the tails might have disappeared in suc- ceeding generations. This perversion of the maternal instincts is not difficult to understand, when we recall that the female mouse bites off the navel-string of each of her young as they are born, and at the same time eats the afterbirth. Her instinct was carried further in this case, and the projecting tail was also removed. “Is it not possible that something of this sort took place in Brown-Séquard’s experiment? The fact that the adults had eaten off their own feet might be brought forward to indicate the possi- bility of a perverted instinct in this case also. At least my obser- vation shows a possible source of error that must be guarded against in future work on this subject. “In regard to the 8th statement of Brown-Séquard, as to various morbid states of the skin, Romanes did not test this, because the facts which it alleges did not seem of a sufficiently definite character. “These experiments of Brown-Séquard, and of those who have repeated them, may appear to give a brilliant experimental confirma- tion of the Lamarckian position; yet I think, if I were a Lamarckian, I should feel very uncomfortable to have the best evidence in sup- port of the theory come from this source, because there are a number of facts in the results that make them appear as though they might, after all, be the outcome of a transmitted disease, as Weismann claims, rather than the inheritance of an acquired char- acter. Until we know more of the pathology of epilepsy, it may be well not to lay too great emphasis on these experiments. It should not be overlooked that during the long time that the embryo is nourished in the uterus of the mother, there is ample opportu- nity given for the transmission of material, or possibly even of bacteria. If it should prove true that epilepsy is due to some sub- stance present in the nervous system, such substances could get OTHER THEORIES OF SPECIES-FORMING. 295 there during the uterine life of the embryo. Even if this were the case, it may be claimed that it does not give an explanation of the local reappearance of the disease in the offspring. But here, also, we must be on our guard, for it is possible that only certain regions of the body are susceptible to a given disease; and it has by no means been shown that the local defect itself is inherited, but only the disease. Romanes insists that a very special operation is neces- sary to bring about certain forms of transmission.” The case of the Planorbis shells studied by Hyatt (Proc. Amer. Phil. Soc., Vol. XXXII, p. 615 ff.) has been interestingly dis- Hyatt’s studies cussed by Le Dantec (“Traité de Biologie,” pp. 296 of Planorbis. ff.. 1903) as follows: ‘On trouve, dans les terrains trés anciens, des coquilles de Céphalopodes qui ont la forme d’une corne de vache et dont la section transversale est 4 peu pres circu- laire; en suivant la série des fossiles de cette catégorie dans des terrains plus récents, on constate que ces coquilles, presque droites naguére, se sont enroulées de plus en plus a la maniere dune spirale d’Archiméde; nous ne connaissons pas la raison de cette transformation, mais la présence de certains caractéres communs permet de considérer comme démontré que les formes enroulées descendent des animaux a coquilles droites. Or, l’enroule- ment est tellement fort dans certains types que les tours de spire successifs s'impriment les uns dans les autres, donnant nais- sance a un sillon dorsal dont la genése mécanique est évidente, puisqu’il résulte sans conteste de la pression du tour de spire précédent sur le suivant. “Tant que les animaux en question restent aussi nettement enroulés, on peut admettre que ce caractére de l’existence d’un sillon dorsal est acquis individuellement par chaque Céphalopode pour des raisons mécaniques évidentes, le contact des tours de spires. “Mais voila qu’a une période plus récente de l’histoire du monde, les découvertes paléontologiques nous montrent que les descendants de ces Céphalopodes a coquille enroulée ont subi un commencement de déroulement et ont maintenant la forme d’une spirale d’Archi- mede a tours de spires plus écartés les uns des autres et ne se touchant plus; et notez bien que des caractéres communs permettent d’affrmer que ces Céphalopodes a moitié déroulés descendent de ceux dont l’enroulement était beaucoup plus serré. “Or, chose admirable, le sillon dorsal persiste chez ces étres a coque a moitié déroulée! Cependant il n’y a plus maintenant pression d’un tour de spire sur le tour de spire précédent; nous avons compris mécaniquement la genése de ce sillon dorsal, quand les tours de spire se touchaient et se pressaient l’un l’autre; et ce sillon persiste en dehors des conditions mécaniques ot il a été 296 DARWINISM TO-DAY. d’abord produit; il se transmet a des descendants dont la coquille est déroulée! C’est donc que le patrimoine héréditaire a été modifié sous Vinfluence de la production mécanique de ce sillon dorsal, au point de devenir adéquat a cette forme nouvelle d’équi- libre; il y a un nouveau patrimoine héréditaire, qui construisant un individu nouveau et son squelette, fera apparaitre, sans pression, le sillon dorsal!” The results of the experiments of Cunningham on flatfishes are stated by the author, in a paper on “The Problem of Variation,” Nat. Sci., Vol. III, p. 285, 1893. Cunningham put the very young fish, while still bilaterally symmetrical (in which stage the pigment is equally developed on both sides of the body), into aquaria lighted from below. He found that when the young fish begins to undergo its metamorphosis, the pigment gradually disappears on one side, as it would have done under normal conditions, 7. e., when they are lighted from above. If, however, the fish are kept for a short time longer, lighted from below, the pigment begins to come back again. “The first fact,” says Cunningham, “proves that the disappearance of the pigment-cells from the lower side in the metamorphosis is a hereditary character, and not a change produced in each individual by the withdrawal of the lower side from the action of the light. On the other hand, the experiments show that the absence of pig- ment-cells from the lower side throughout life is due to the fact that light does not act upon that side, for, when it is allowed to act, pigment-cells appear. It seems to me that the only reasonable con- clusion from these facts is that the disappearance of the pigment- cells was originally due to the absence of light, and that the change has now become hereditary. The pigment-cells produced by the action of light on the lower side are in all respects similar to those normally present on the upper side of the fish. If the dis- appearance of the pigment-cells was due entirely to the variation of the germ-plasm, no external influences could cause them to re- appear; and if there were no hereditary tendency, the coloration of the lower side of the flatfish would be rapid and complete.” Concerning Fischer’s highly interesting experimental work, I quote the following paragraph from Fuchs, H. (Biol. Centralbl., Fischer’sex- Vol. XXI, pp. 591-592, 1901; Fischer’s own papers periments with have been published in various biological journals, butterflies. the particular one recounting the results obtained with Arctia caja in the Allg. Zeitschr. fir Entomologie, Vol. VI, 1902): “Experimentelle Untersuchungen, ob es moglich sei, durch will- kurliche, geeignet gewahlte Veranderungen der ‘ausseren Lebens- bedingungen,’ besonders der Temperaturverhaltnisse, im Tierreiche OTHER THEORIES OF SPECIES-FORMING. 207 Variationen bei den Arten hervorzurufen, wurden in den letzten. Decennien wiederholt angestellt; mit Vorliebe hat man sich dabei als Versuchsobjekte die Schmetterlinge gewahlt: ich erinnere z.. B. an die schonen Versuche von Standfuss und E. Fischer. Das Resultat war—wie ja nach unseren heutigen Anschauungen wtber den ziichtenden Einfluss der Faktoren der Aussenwelt auf alle Organismen eigentlich kaum anders zu erwarten stand—positiv. Eine Frage allerdings, an welche bei diesen Untersuchungen wohl jeder der Forscher dachte, namlich: ob die auf solche Weise erworbenen Eigenschaften und Abanderungen auch auf die eventu-- ellen Nachkommen iibertragen, also vererbt wurden oder doch wenigstens werden konnten, blieb dabei einstweilen unentschieden. Erst kiirzlich gelang es E. Fischer, auch fiir dieses Postulat der modernen Biologie einen vollgiltigen Beweis beizubringen. F. expe- rimentierte mit Arctia caja, dem braunen Bar, der ja auch den meisten Laien—meist wohl unter dem Namen ‘deutscher Bar’— bekannt sein durfte, ein erfahrungsgemass fiir kunstliche Varia- tionsversuche besonders geeignetes Tier. Durch willktrlich ge- wahlte Temperaturveranderungen, und zwar durch intermittierende Abktthlungen bis auf—8° C., denen die Puppen wiederholt ausge- setzt wurden, erzielte F. stark aberrative Falter, und zwar aberrativ nicht nur beztiglich der ‘Farbe und Zeichnung’—wenn auch hier in erster Linie—sondern auch beztiglich der Form, z. B. der Flugel und der Beine. Dabei hebt F. ausdriicklich hervor, dass in letzterer Hinsicht es sich nicht etwa um Verkruppelungen handelte, sondern ‘die Fiisse waren kraftig und mit gut ausgebildeten Krallen versehen. Unter diesen Varietaten gelangen nun mehrfache Kreuzungen; die Puppen dieser Zucht wurden unter normalen Bedingungen erhalten. Und siehe! von den alsbald ausgeschlupften Tieren zeigte eine nicht unerhebliche Anzahl die Variationen der Eltern, und zwar im allgemeinen als Kombinationen aus den veranderten Eigenschaften beider Eltern, so dass einige mehr dem elterlichen Mannchen glichen, andere mehr dem elterlichen Weib- chen. Es ist dieses also, wie F. sagt, ein experimenteller Beweis, dass: “Tt. die Art durch die Faktoren der Aussenwelt Veranderungen. erfahrt, und dass “2. diese Veranderungen sich auf die Nachkommen wtbertragen. “Die Thatsache der Vererbung erworbener Eigenschaften steht. mithin fest, wenn wir auch tiber das Wesen der ratselhaften dabei stattfindenden Vorgange, auf Grund dieser Untersuchungen, natiir- lich absolut noch nichts sagen k6nnen.” To the above cases of the alleged inheritance of acquired charac- ters I may add some account of certain éxperiments with the mul- 298 DARWINISM TO-DAY. berry silkworm carried on by R. G. Bell and myself. (For detailed ac- count of this work see Science, N. S., Vol. XVIII, pp. 741-748, 1903.) “One of the races of the mulberry silkworm, Bombyx mori, has been the subject of experiments directed toward a determination of the exact quantitative relation which quantity and quality of food bear to the development and variations of the individual insect and its progeny. ... “The insect, Bombyx mori, has a complete metamorphosis, tak- ing no food as an adult, so that the experimental control of the Experiments feeding has been necessary only during the larval or with silkworms. ‘silkworm’ stage. The larval life is subdivided into five stages clearly set off from one another by the intervening moults, of which there are normally four, and these substages have been useful when an alteration of food conditions during a sharply de- fined shorter time than the entire larval life was desirable... . The change in quantity of food has consisted in altering the amount of mulberry leaf served to the larve, the control of which has been secured as follows: It has been determined through experience with normal larve that each will consume a certain amount of food in a certain number of hours (increasing in amount with the increas- ing age and size of the larva), this amount representing the optimum amount of food for the normal individual and necessitating as many daily meals as are required to keep any but the moulting larva constantly supplied with fresh food. This amount determined, a tolerably definite small proportion of the optimum amount has been allotted the individuals which were sentenced to short rations, which, roughly speaking, might be listed as one-quarter the optimum amount during earlier stages and one-eighth during the late larval stages. This one-fourth, one-eighth, or whatever it may have been numerically, was, at any rate, as small an amount of food as was compatible with mere life. ... “These experiments have extended over a period of three years, covering as many generations of the insect. The data gathered (being the measurements, weight, and duration of each larva in each of its five states; the time of spinning, weight of silk and weight and duration of each pupa; and the weight, size, pattern, and fertility of female of each imago) furnish material, then, for a study of the effects of under-feeding upon individuals during a single generation (the 1903 generation or that of 1902 or Igor), during two successive generations (1901-02 or 1902-03), and two alternating generations (1g0I-1903) and during three generations (1901-03), a control lot having been carried for each experimental lot so that what is ee may confidently be distinguished from what is normal. OTHER THEORIES OF SPECIES-FORMING. 299 \ “In these variously-fed worms there exists a very definite and constant relation between amount of food and size as indicated by weight, the starveling individuals being consistently smaller than the well-nourished, the lingering effects of this dwarfing being handed down even unto the third generation, although the progeny of the famine generation be fed the optimum amount of food; in case the diminished nourishment is imposed upon three, or even two successive generations, there is produced a diminutive, but still fertile, race of Lilliputian silkworms, whose moths, as regards wing expanse, might join the ranks of the micro-Lepidoptera almost unremarked. “In illustration may be quoted the typical or modal larval weights for each of the lots of 1903 at the time of readiness to spin, which marks the completion of the feeding and is, therefore, an advan- tageous point for a summary of the results of the three years’ experimental feeding. “The history of the eight lots referred to may be gathered from an examination of the accompanying table, in which ‘O’ means optimum amount of food and ‘S’ means short rations. The column to the right indicates the relative rank of the various lots as judged by the modes of frequency polygons erected to include all the individual weights for each lot at spinning time. HISTORY OF LOTs. Lot Number. Modal Rank. Igor. 1902. soo" Grandparents.|Grandparents. Paeo eee ee ee eee! O O O I aR 5 ee ne O O S) 6 de aey a pig hin'S) 4&4. O S O 3 LEYS oe ee rae O S S 7 eS aie ahs eile\e4 5. Ss O O 2 [2 Ry uee at oar are eR Ss O Ss 5 “a RT te or ee S) S O 4 SRO Ser Sone noe ee Ss S Ss 8 “We find that control lot 1, consisting of normally-fed indi- viduals of normal ancestry, holds first rank in weight, as was to be expected. Second comes lot 5, whose grandparents experienced a famine but whose parents as well as themselves enjoyed years of plenty. Lots 2 and 3 have likewise had one ancestral generation on Short rations, and the fact that they are lighter in weight than lot 300 DARWINISM TO-DAY. 5 illustrates a general rule which obtains throughout the entire company of experimental worms, namely, that the effects of famine grow less evident the further removed the individuals are from its. occurrence in their ancestral history. Thus lot 5 is two generations. removed from the famine of 1901, while lot 3 has had but one generation in which to recover its ancestral loss. Lot 2, which has had a total of but one famine year—the current year—neverthe- less ranks below lot 7, which has had two famine years in its ancestry succeeded by plenty during the current year. Lot 2 also ranks below lot 6, a fact which appears strange, considering that lot 6 has suffered two generations of famine, including the current year, which is the only famine year experienced by lot 2. In explanation of this anomalous condition it is suggested that possibly the larve of lot 6 were better fitted for enduring and making the best of hard conditions than were the individuals of lot 2, the ancestors of the former lot having been selected two years ago on a food-scarcity basis. This suggestion gathers support from an inspection of the mortality notes, from which it appears that the number of deaths—for which the famine was probably a contributing and not a primary cause—in each lot which is for the first time subjected to short rations is almost doubly greater than the num- ber of deaths in lots which are descended from starved ancestors, whether these ancestral famines occurred in successive or alternate years. The figures indicate that a reduction of food is almost twice as destructive upon the first generation which is subjected to it as it is when visited on a second generation. Lot 4 follows lot 2 as the seventh in rank and its position is in accord with the rule above noted, its latest ancestral generation which enjoyed an optimum amount of food during 1902 or 1903. Lot 8 holds lowest rank, it and its ancestors having been subject to trying conditions through- out the entire three years, during some one or two of which all the other lots have enjoyed the best of food conditions. Thus it appears that a generation of famine leaves its impression upon at least the three generations which succeed it, yet the power of recovery through generous feeding exhibited by the progeny of individuals subjected to famine, is so extensive (witness lot 5) that it appears probable that every trace left by the famine upon the race would eventually disappear. It is even conceivable that the ultimate result of the famine would be a strengthening of the race, the famine having acted the part of a selective agent, preserving only the strong. “But although there is a large difference between the well fed and the poorly fed, there persists, more obviously in late than in early life, a very considerable discrepancy as to size among the OTHER THEORIES OF SPECIES-FORMING. 301 individuals of each single lot whose environment, in so far as food, temperature, room, humidity, etc., constitute it, is identical. “For example, referring again to the weights at spinning time of the larve of 1903, it is true that, although each lot has a modal class of weights to which the majority of its individuals belong and about which the rest of the lot distributes itself rather symmetrically, the extremes are surprisingly distant from one another. Thus in lot 1 (the normal control lot) the extremes are 1,540 and 2,530 mg.; in lot 2,* 800 and 1,402 mg.; in lot 3, 1,180 and 2,170 mg.; in lot 4, 690 and 1,204 mg.; in lot 5, 1,370 and 2,100 mg. “That is to say, identical feeding has not made identical full- ‘grown larve out of individuals which undoubtedly varied congent- tally at the start, those variations—in embryo—standing at birth in the same relation to one another that they stand in the adults, hav- ing merely been smaller and less readily discernible in early life, although manifestly present in delicately measurable degree in the earliest records made upon normal individuals. For example, weight measurements taken immediately after the second moult, range in one lot from 21 to 39 mg., or 60 per cent. of the modal weight, while the weights in this same lot at spinning time, some five weeks later, range from 534 to 2,080 mg., or 85 per cent. of the mode for the lot. These embryonic but potentially large varia- tions have simply ‘grown up’ along with the insect and are as truly congenital in the adult as they were in the newly hatched larva. This would seem to place quite conclusively in the category of congenital variations some part of those variations (in size and pro- portions of parts) which are commonly, and properly to some degree, called acquired. “That conditions of alimentation bear a directive relation to func- tional activity, may be demonstrated by reference to the records of the physiological functions of moulting, spinning, pupating, and emerging, of the individuals of the experimental lots. “An abnormal extension of the time needed for the metamor- phosis follows upon a reduction of the food supply. The degree of extension depends with the utmost nicety upon the amount of food given the larve. For example, among the Igor generation of ‘silkworms, one control lot of twenty larve was given the optimum amount of food, a second lot of twenty larve one-half this amount, and a third lot of twenty larve one-quarter of the amount. To take the time of the fourth moulting as an illustration, the moulting was begun by the first lot, which led the way by two and a half days, at the end of which the second lot began to moult, while * See table, next page, for the history of each lot. 302 _ DARWINISM TO-DAY. the third lot was twenty-four hours behind the second. All the individuals of the first lot had finished moulting on April 20, all of the second on April 24, while the moulting in the third lot con- tinued until April 29. “As in the matter of weight, this retarding of the functions, by means of a reduced food supply, affects not only the immediate generation which is subjected to the famine, but the lingering effects of it may be traced in the progeny of the dwarfed individuals at least unto the third generation, even though two years of plenty follow the one year of famine. The conditions which obtain in each lot of individuals of the 1903 generation at spinning time are shown in the accompanying table, which is based upon polygons erected to include all the individuals in each lot. RANK OF 1903 LOTS AS TO PROMPTNESS IN SPINNING. HISTORY OF LOTS. Lot When Two-thirds of Each Lot Num- were Spinning. ber, P Earliest ree Spinner. a ee nee 1902. n Order ates Bee Parents.| 19°93 Date. | of Rank. Spinner. Micke O O O I May 12 I I ae O O S 5 9m 4 4 a O S O 2 pe 4 2 3 Pee O Ss SS) 4 a) ae 5 5 Coes Ss O O 3 lle 2 2 ti S O S 6 ‘> ae 6 | ee S) Ss O 6 “22 3 5 Roxx cas S S 7 te: 90 7 6 “This period in the life of the silkworms is particularly advan- tageous for consideration here, because it marks the completion of the feeding, so that the individuals of under-fed ancestry have been given the best chance to recover, while those subject to altered food conditions, had had the benefit of the alteration during the entire food-taking period of life. “In the table, ‘O’ means optimum amount of food, and ‘S’ means. short rations. To the right of the history of the lots is a section showing the rank of the lots as to the extreme time limits of the spinning time (emphasised congenital differences again), with a safer criterion, as to their relative promptness, in the column be- tween the extremes—a column of figures intended to show the rela- tive promptness with which a two-thirds majority of the larve OTHER THEORIES OF SPECIES-FORMING. 303 in each lot arrives at the spinning time, this proportion being taken to represent the typical condition for the lot. The order in which the lots are arranged in this column corresponds in a general way with that prevalent for the weights at spinning time, and the generalisations indulged in there may, with few exceptions, be applied here. The lots which were well fed during the 1903 generation are ahead of all of those given short rations in 1903, whatever ancestry they may have had. Lot 1 leads here as in the matter of weight. Lots 3 and 5 tie for second place, having held second and third places in weight. Lots 2 and q stand in the same relation to one another that they held as to weight. Con- trary to the weight relation, lot 6 follows lot 2 at the spinning—a fact which illustrates again the general rule that two generations of famine are more disastrous than one, but does not lend support to the notion of natural selection on a food scarcity basis as pre- viously suggested. Lot 8, which has had no relief from famine during the entire three years, brings up the rear at the spinning, as might be expected. “This check upon functional activity exercised by diminished nour- ishment affects the moulting, the time for the commencement of spinning, and the issuing time for the adults, but the time spent in the spinning of the cocoon, from its beginnings in the threads of the supporting net to its apparent completion when the cocoon becomes opaque, is practically identical for under-fed and well- fed individuals. A reason for this exception to the tardy habits. of the under-fed is to be found in the fact that the under-fed larve produce less silk (less in size, thickness, and weight) than the well-fed, thus accomplishing more meager results in the same amount of time. That the individuals sentenced to short rations. should produce less silk than their well-fed neighbours is certainly to be expected, silk not being made without leaves any more readily than bricks without straw. “Not only do short rations protract the time appointed for the spinning, moulting, etc., but they appear to have a more striking effect upon the actual occurrence of the moulting. The normal number of moults for the silkworm larva is four. Five moults have occurred for most of the individuals belonging to the under- fed lots of 1902 and 1903, whereas none of the well-fed individuals has undergone a fifth moult. It would seem, therefore, that the occurrence of a fifth moult may be fairly ascribed to a reduction of food; at least a fifth moult very frequently accompanies it and has suggested the possibility that the enforced fasting of the under- fed larva—in the intervals between meals—may have the same physiological effect as the normal fasting which precedes the normal 304 DARWINISM TO-DAY. moulting, during which time the so-called ‘moulting fluid’ is secreted. That this effect may accumulate throughout the life- time of the larva until the larva is actually forced to indulge in the extravagance (of strength, feeding time, and body wall material) of an additional moult is conceivable and will justify a further “Lest, “As to the life-and-death selection due to famine, it may be said, in addition to the previous discussion of mortality among the experimental silkworms, that while lots subjected to two years of famine (themselves in one year, their parents in the year before) were fertile in so far as number of young hatched is concerned, it was found to be exceedingly difficult to rear from them a 1903 generation. Indeed, at the time of the second moulting there were but nineteen individuals (and tolerably vigorous larve they were) alive in the lot which had experienced two years of famine, al- though every individual of the 149 hatched was carefully preserved and royally fed—a fact which goes to prove that the equipment at birth of many of these larve was inadequate. “The fact that some larve of starved ancestry have exhibited a superiority over their fellows, in surviving and recovering from hard conditions, is testimony for the existence of individual varia- tions which cannot be defined anatomically, and yet which serve as ‘handles’ for natural selective agents. Such variations might be called physiological variations, since it seems that the surviving larve must be those which are in best trim physiologically. These larve are able to make the most of the food offered to them. If competition were allowed, they would probably be the individuals which would cover the area most rapidly, securing whatever food there might be. But under our experimental conditions there was no competition allowed and yet certain precocious individuals made more grams of flesh and more yards of silk, than other larve furnished with the same amount of raw material under like con- ditions; that this was due to the possession by the former of certain congenital qualities of adaptability can scarcely be doubted. “As to the fertility of the variously fed lots, in so far as number of eggs produced is a measure of fertility, our records already demonstrate the fact that the better nourished are the more fertile. Furthermore, the economy in this matter practised by the starve- lings is not merely numerical, quality as well as quantity of eggs being affected. In witness of this point may be recalled the story of the dying 1903 generation, produced from eggs of the starvelings of 1901 and 1902, which would seem to offer conclusive evidence that a famine suffered by the parents works its way into the germ- cells so that most of their progeny have but a poor birthright.” “2 . m + ie ge ae | re OTHER THEORIES OF SPECIES-FORMING. 3°95 For special discussions of the inheritance of acquired characters, see the following: Roth, E., “Die Thatsachen der Vererbung,” 1885 ; Ziegler, E., “Konnen erworbene pathologische Eigenschaften ver- erbt werden und. wie entstehen erbliche Krankheiten und Missbil- dungen,” 1886; Rohde, F., “Uber den gegenwirtigen Stand der Frage nach der Entstehung und Vererbung individuellen Eigen- schaften und Krankheiten,” 1896; Osborn, H. F., “Are Acquired Variations Inherited,’ 1890; Elliott, D. G., “The Inheritance of Acquired Characters,” Auk, Vol. IX, pp. 77-104, 1892; Packard, A. S., “On the Inheritance of Acquired Characters in Animals with Complete Metamorphosis,” Proc. Amer. Acad. Science, pp. 331- 370, 1894; Ritter, W. E. “On the Nature of Heredity and Acquired Characters, and the Question of the Transmissibility of these Characters,’ 1900; Wettstein, R. von, ‘Der Neo-Lamarckis- mus und seine Beziehungen zum Darwinismus,” 1903; Detto, Carl, “Theorie der direkten Anpassung,’ 1904 (good bibliography of papers on plant adaptations); Lendenfeld, R. V., “Variation and Selection,” Biol. Centralbl., Vol. XXIII, p. 480 ff., and p. 563 ff., 1903; Pauly A., ‘“Darwinismus und Lamarckismus,” 1905; Lotsy, J. P., “Vorlesungen tiber Descendenztheorien,’ Vol. I, chap. xii, 1906; Wheeler, W. M., “The Polymorphism of Ants,” Bull. of Amer. Mus. Nat. Hist., Vol. XXIII, pp. 1-93, Plate I-VI, January, 1907 (see especially pp. 50-90). Certain writers of sociologic and philosophic interests, have discussed especially the possibility of the inheritance of acquired mental capacities or qualities in man; ex- pressing a belief in such inheritance are Biichner, “Die Macht der Vererbung und ihr Einfluss auf der moralischen und geistigen Fortschritt der Menschheit,’ 1882, and Hartmann, E. V., ‘“Philo- sophie des Unbewussten,” roth ed.; against such an inheritance is Rawitz, B., “Urgeschichte, Geschichte, und Politik,” 1903. Most important of all the discussions of the inheritance of acquired char- acters are those of Weismann, Spencer, and Eimer. A recent American champion of Lamarckism is Caspar L. Red- field, in whose writings (‘‘Control of Heredity,’ 1903, “Evolution Redfield’s of the Setter,” in American Field, 1904 and 1905, and position. “Breeding of the Trotter,’ in The Horseman, 1905) is urged the doctrine that acquired mental and dynamic qualities are inherited. On a host of data, derived from the pedigrees and records of trotting horses and setter dogs, Redfield keenly works out his inductions regarding the inheritance by young of the special qualities due to training and practice (acquirement) of the parents; that is, the best offspring (from the sportsman breeder’s point of view) come from the best trained parents. There is a great deal of ammunition for the advocates of Lamarckism in Redfield’s 306 DARWINISM TO-DAY. records, although his too sharp distinction between structural and functional (so-called “dynamic’’) characters is not at all helpful. The most recent serious treatment of the problem from the neo- Lamarckian side, and one of great interest and real force, is that Montgomery's of Montgomery in his book on “The Analysis of explanation of Racial Descent in Animals” (1906). Montgomery inheritance of contends that there can be no congenital variation Variation, without external stimuli (or hybridisation) to initiate it, because germ-plasm cannot be assumed to set up change inde- pendently and automatically, as this would be almost like the assumption of spontaneous generation. Montgomery says, “When the process of heredity proceeds unchanged the ontogeny of one individual is just like that of its parent. When a change of the ontogeny occurs, so that the offspring comes to be different from its parent, we say that a variation has appeared in the offspring. This variation, it is thinkable, may have been produced: (1) by internal growth energies, (2) by external environmental influences, or (3) by a combination of both; and it is necessary to discuss which one of these is the most probable. “There is clearly, in the process of production of variation and mutation, some modification of the normal process of heredity. Since in a number of species it has been shown that all the adult individuals from one locality are not exactly alike, but show meas- urable differences in dimensions, colour, or some other character, it follows that the hereditary process of each such individual must. vary correspondingly, even though the variation does not become: perceptible until the stage of maturity. The origin of inherited variation or mutation is then a question of the origin of modifica- tion of the hereditary process. “The regularity of the process of heredity is quite comprehensi- ble on the basis of the direct transmission of definite chromosomes in number, form, and quality constant for the species. From cell to cell, from individual to individual, these chromosomes are regu- larly transmitted in a continuous progress, therefore a succession of similar individuals is quite understandable. One germ-cell comes from a preceding one, to our knowledge is never formed from a specialised tissue-cell, so that there is an uninterrupted passage of the germ-plasm through the race. This is Weismann’s idea of the continuity of the germ-plasm, which we will paraphrase as the continuity of the chromosomes. “A variation to become inherited must then be referable to a modification of the energies of this germ-plasm. The germ-plasm is living substance of proved great importance in the metabolism of the cell. Though in a sense it appears, from microchemical re-- OTHER THEORIES OF SPECIES-FORMING. 307 searches, to be the chief agent in constructive processes of the cell, it equally appears to be incapable of life, or unable to act in a normal manner, when removed from the influence of other cell substances. The food required by a germ-cell for its growth is obtained from without the cell, and must pass through the cytoplasm, in more or less changed condition, to reach the chromatin within the nucleus and there be elaborated into living substance and passed over to the cytoplasm in other form. This conclusion is drawn from both experimental and microchemical studies. So the oxygen required by the cell, and the water, must be obtained from without the cell. This is simply in agreement with the general principle that no body can increase in mass, circumambient condi- tions remaining unchanged, without accretions from _ outside. Therefore, the germ-plasm does not so much create new substances as it changes substances brought to it. It and the other cell con- stituents are harmoniously and mutually interdependent, and the ultimate source of energies of these substances, all connected with the elaboration of living matter, is referable to external agencies because referable to food. “This being the case, the energies of the hereditable substance, the germ-plasm, are clearly dependent upon influences of the envi- ronment. This conclusion is not at all in contradiction with the idea of the continuity of the chromosomes, as we pointed out in the preceding chapter. Therefore, Weismann was in error when, to support his idea of the continuity of the germ-plasm, he at first argued the energies of the germ-plasm to be independent of body cells and of the environment generally. His supposition was both unnecessary for the view of the continuity, and also out of agree- ment with the phenomena. The ovum cannot elaborate its yolk substance except out of food substance received from without; the amount of its food substance will depend upon the state of nutritive metabolism of the individual carrying the egg-cell; starva- tion of that individual will cause cessation of energy in the germ- cell, and ligaturing of the blood-vessels supplying the ovary will produce death of the egg-cells. The results of observational expe- rience teach that the germ-plasm is not a little god, capable of self- existence without respect to external agencies, but is very intimately bonded to the latter. Whether the germ-cell, as in the sponges, be an amoeboid cell which wanders about in the body tissues, or whether it is immovably held in place by tissue-cells, it is impossi- ble that it can live and grow without receiving and reacting to stimuli from these tissue-cells. The egg-cells of many animals are set free in water before they commence to cleave into embryonic cells; how can we say, then, that the conditions in the water do 308 DARWINISM TO-DAY. not influence them? They will die if removed from the water, and develop abnormally if certain substances be added to or subtracted from the water. But the embryonic differentiation is a result of chromosomal activities, as we have seen; therefore, changes in the medium must influence the germ-plasm. Is not a well-recognised characteristic of living matter, response to external stimuli? How can any living cell be acted upon by stimuli and yet not react to them? There is not a single observation to show that any germ- cell, or its germ-plasm, is in any way guarded or protected from external stimuli, either by the structure of its cell wall or peripheral cytoplasm, or by the nature of the living tissue that encloses it. And whatever affects the cell body must indirectly affect the chromosomes, because of the physiological connection of the two. “From such considerations it would seem practically certain that the energies of the chromosomes are to some extent respondent to environmental stimuli. And since observation shows that living matter responds differently, if not always according to the nature of the stimulus at least to its degree, it would follow that change in the nature or degree of the environmental agencies would indirectly engender change in the activities of the germ-plasm. Not to admit this would be to deny to the germ-plasm, without empirical reason, properties proven for all other living substances. “This thought had long ago been expressed clearly, though from a different line of reasoning, by Spencer (1865). We may state it in another way. Tissue-cells are granted by experimental physiolo- gists the ability of different response, or different intensity of response, to stimuli of different kind or degree. But a tissue-cell is a lineal descendant of a germ-cell, and receives germ-plasm from the latter. Now since the germ-plasm has been transmitted continuously to the tissue-cell, must not the energies of the germ- plasms of the two be alike at least in their general response activity? Again, a Protozoan may be considered as a cell not exactly correspondent to a germ-cell of a Metazoan, but as some- thing more, as a unit with properties of both a germ-cell and a tissue-cell, for its cytoplasmic differentiations (cilia, contractile vacuoles, cytopharynx, etc.) are comparable to the soma of a Meta- zoan. In the case of the Protozoan Paramecium, Calkins (1904) has shown that the reproductive activity is increased or diminished according to the amount and kind of food stimuli. Here, then, a Protozoan has its reproductive activities, therefore the energies of its germ-plasm, profoundly influenced by environmental changes; and it is primarily what we may term the germ-cell constituent of the Protozoan that becomes influenced, that part which has to do with reproduction of the individual. Weismann considered the OTHER THEORIES OF SPECIES-FORMING. 399 Protozoan exactly comparable, in the sense of strict continuity of reproduction, to the germ-cell of a Metazoan, and yet failed to note that a Protozoan can be influenced by environmental change. “Accordingly, an environmental change may be capable of induc- ing change in the energies of the germ-plasm. The expression of the energies of this substance, as viewed in temporal succession, constitutes heredity. Therefore, the process of heredity may become modified by a change in the environmental conditions of the germ- plasm. And since we defined variation as a modification of heredity, a variation could be produced by external influences acting upon the germ-plasm, understanding by external influences influences of the tissue-cells upon the germ-cells, or, in case the germ-cells are not enclosed, influences of the non-living environment.” In a recent exhaustive paper by Tower, W. L., on “Evolution in Chrysomelid beetles of the genus Leptinotarsa,’ Publication No. 48 of the Carnegie Institution of Washington, 1907, the author, although on the whole a strong adherent of selection as the all-important factor in species-forming, states specifically his belief, on the basis of extensive observation and experiment, that external factors may and do influence the germ-plasm to the extent of compelling it to produce variations. These variations will not be photographic re- productions of modifications of the soma, but they will be the vari- ations which lie at the basis of species change. In other words, Tower holds that variations are epigenetic in their origin, although they are manifest as congenital differences. That is, acquired characters in the usual sense of the term are not heritable, but all variability is nevertheless due to the influence of environment. This paper by Tower is a distinctly valuable contribution to our knowl- edge of heredity and species change and it is based upon a large amount of actual close observation and experiment. In a recent paper by Jonathan Wright, “The Origin and Heredity of Matter,” in the St. Louis Medical Review, 1906, something of the same attitude is taken, although the author is much more inclined to the belief in the general heritability of acquired characteristics. This short paper is an admirable treatment, based on a full acquaint- anceship with the modern literature on the subject, of the problem of heredity. * See exposition of a number of these theories in appendix of chapter viii of this book. *Haacke, W., “Grundriss der Entwicklungsmechanik,” p. 289 fF. 1307. © Palate“ As., “Uber die Bedeutung der Darwin’schen Selections- prinzip,” p. 218, 1903. * The following account of the scientific aspects of Luther Bur- 310 DARWINISM TO-DAY. bank’s work, which has attracted so much attention from evolu- tionists and the world generally, was published by Kellogg, in the Pop. Sct., Mo., Vol. LXIX, pp. 363-374, 1906. “Mr. Burbank has so far not formulated any new or additional laws of species-change, nor do his observations and results justify Solentific any such formulation, and we may rest in the belief aspects of Bur- that he has no new fundamental laws to reveal. He bank's work, has indeed the right to formulate, if he cares to, some valuable and significant special conclusions touching certain already recognised evolution factors, in particular the influence on varia- bility of the two long-known variation-producing factors of hybridi- sation and modification of environment. Huis reliance on the marked increase in variability to be got after a crossing in the second and third generations over that obvious in the first, will come as a sur- prise to most men first getting acquainted with his work. He has got more starts for his new things from these generations than in any other way. He is wholly clear and convinced in his own mind as to the inheritance of acquired characters; ‘acquired characters are inherited or I know nothing of plant life,’ he says; and also con- vinced that the only unit in organic nature is the individual, not the species; that the so-called species are wholly mutable and de- pendent for their apparent fixity solely on the length of time through which their so-called phyletic characters have been ontogenetically repeated. He does not agree at all with de Vries that mutations in plants occur only at certain periodic times in the history of the species, but rather that, if they occur at all, they do so whenever the special stimulus derived from unusual nutrition or general environment can be brought to bear on them. He finds in his breeding work no prepotency of either sex as such in inheritance, though any character or group of characters may be prepotent in either sex. He believes that no sharp line can be drawn between the fluctuating or so-called Darwinian variations and those less usual, large, discontinuous ones called sports. Ordinary fluctuating varia- tion goes on under ordinary conditions of nutrition, but with ex- traordinary environmental conditions come about extraordinary variation results, namely, discontinuous, sport or mutational varia- tion. These variations are the effects of past environment also, having remained latent until opportunity for their development occurs. Starvation causes reversions, but reversions can also be produced by unusually rich nutrition. New variations are developed most often, as far as environmental influences go, by rich soil and generally favourable conditions. So-called new qualities are usually, if not always (the fact may sometimes not be obvious), simply new combinations of old qualities, both latent and obvious. To get OTHER THEORIES OF SPECIES-FORMING. git a new and pleasing odour it may often be sufficient simply to lose one bad element in an old odour. So one might go on for some pages with specific conclusions or deductions reached by Burbank on a basis of experience. But it is true that he has at his command the knowledge of no new fundamental scientific principles to give him advantage over us. And yet none of us has done what Burbank has been able to do, although many of us have tried. What then is it that Burbank brings to his work of modifying organisms swiftly and extremely and definitely that others do not? “To answer this it will be advisable to analyse in general terms, at least, the various processes which either singly, or in combina- tions of two or three, or all together, are used by Mr. Burbank in his work. We may roughly classify these processes and means. First, there is the importation from foreign countries, through many correspondents, of a host of various kinds of plants, some of economic value in their native land and some not, any of which grown under different conditions here may prove specially vigorous or prolific or hardy, or show other desirable changes or new quali- ties. Among these importations are often special kinds particularly sought for by Burbank to use in his multiple hybridisations; kinds closely related to our native or to already cultivated races which, despite many worthless characteristics, may possess one or more particular, valuable ones needed to be added to a race already useful to make it more useful. Such an addition makes a new race. “Second, the production of variations, abundant and extreme, by various methods, as (a) the growing under new and, usually, more favourable environment (food supply, water, temperature, light, space, etc.) of various wild or cultivated forms, and (b) by hybridi- sations between forms closely related, less closely related and, finally, as dissimilar as may be (not producing sterility), this hybridising being often immensely complicated by multiplying crosses, 7. ¢., the offspring from one cross being immediately crossed with a third form, and the offspring of this with still another form, and so on. These hybridisations are made sometimes with very little reference to the actual useful or non-useful characteristics of the crossed parents, with the primary intention of producing an unsettling or instability in the heredity, of causing, as Burbank sometimes says, ‘perturbations’ in the plants, so as to get just as wide and as large variation as possible. Other crosses are made, of course, in the deliberate attempt to blend, to mix, to add together, two desirable characteristics, each possessed by only one of the crossed forms. Some crosses are made in the attempt to extin- guish an undesirable characteristic. “Third, there is always immediately following the unusual produc- 312 DARWINISM TO-DAY. tion of variations, the recognition of desirable modifications and the intelligent and effective selection of them, 7. e., the saving of those plants to produce seed or cuttings which show the desirable varia- tions and the discarding of all the others. In Burbank’s gardens the few tenderly cared for little potted plants or carefully grafted seedlings represent the surviving fittest, and the great bonfires of scores of thousands of uprooted others, the unfit, in this close mimicry of Darwin and Spencer’s struggle and survival in nature. “It 1s precisely in this double process of the recognition and selec- tion of desirable variations that Burbank’s genius comes into particular play. Right here he brings something to bear on his work that few other men have been able to do. It is the extraordi- nary keenness of perception, the delicacy of recognition of desirable variations in their (usually) small and to most men imperceptible beginnings. Is it a fragrance that is sought? To Burbank in a bed of hundreds of seedling walnuts scores of the odours of the plant kingdom are arising and mingling from the fresh green leaves, but each, mind you, from a certain single seedling or perhaps from a similar pair or trio. But to me or to you, until the master prover points out two or three of the more dominant single odours. the -impression on the olfactories is simply (or confusedly) that of one soft elusive fragrance of fresh green leaves. Similarly Burbank is a master at seeing, and a master at feeling. And besides he has his own unique knowledge of correlations. Does this plum seed- ling with its scores of leaves on its thin stem have those leaves infinitesimally plumper, smoother or stronger, or with more even margins and stronger petiole, or what not else, than any other among a thousand similar childish trees? Then it is saved, for it will bear a larger, or a sweeter, or a firmer sort of plum, or more plums than the others. So to the bonfires with the others and to the company of the elect with this ‘fittest’ one. Now this recogni- tion, this knowledge of correlations in plant structure, born of the exercise of a genius for perceiving through thirty years of oppor- tunity for testing and perfecting it, 1s perhaps the most important single thing which Burbank brings to his work that other men do not (at least in such unusual degree of reliability). Enormous industry, utter concentration and single-mindedness, deftness in manipulation, fertility in practical resource, has Burbank—and so have numerous other breeders and experimenters. But in his per- ception of variability in its forming, his recognition of its possi- bilities of outcome, and in his scientific knowledge of correlations, a knowledge that is real, for it is one that is relied on and built on, and is at the very foundation of his success, Burbank has an advantage of true scientific character over his fellow workers, and OTHER THEORIES OF SPECIES-FORMING. 313 in it he makes a genuine contribution to scientific knowledge of plant biology, albeit this knowledge is so far only proved to be attainable and to exist. It is not yet exposed in its details and may never be, however unselfish be the owner of it. For the going to oblivion of scientific data of an extent and value equivalent, I may estimate roughly, to those now issuing from any half-dozen experimental laboratories of variation and heredity, is the crying regret of all evolution students acquainted with the situation. The recently assumed relations of Mr. Burbank to the Carnegie Insti- tution are our present chief hope for at least a lessening of this loss. “But let us follow our saved plum seedling. Have we now to wait the six or seven years before a plum tree comes into bearing to know by actual seeing and testing what new sort of plum we have? No; and here again is one of Burbank’s contributions (not wholly original to be sure, but original in the extent and perfection of its development) to the scientific aspects of plant-breeding. This. saved seedling and other similar saved ones (for from the exami- nation of 20,000 seedlings, say, Burbank will find a few tens or even scores in which he has faith of reward) will be taken from their plots and grafted on to the sturdy branches of some full-grown vigorous plum tree, so that in the next season or second next our seedling stem will bear its flowers and fruits. Here are years saved. Twenty, forty, sixty, different seedlings grafted on to one strong tree (in a particular instance Burbank had 600 plum grafts on a single tree!) ; and each seedling-stem certain to bear its own kind of leaf and flower and fruit. For we have long known that the scion is not materially influenced by the stock nor the stock by the scion; that is not modified radically, although grafting sometimes. increases or otherwise modifies the vigour of growth and the extent of the root system of the stock. “Tf now the fruit from our variant seedling is sufficiently desira- ble; if it produces earlier or later, sweeter or larger, firmer or more abundant, plums, we have a new race of plums, a ‘new creation’ to go into that thin catalogue of results. For by simply subdividing the wood of the new branch, 1. e., making new grafts from it, the new plum can be perpetuated and increased at will. Simple, is it not? No, it is anything but that in the reality of doing it; but in the scientific aspects of it, easily understandable. “Perhaps it may not be amiss to call attention to what must be the familar knowledge of most of us, and that is the fact that many (probably most) cultivated plants must be reproduced by division, that is by cuttings, buds, or grafts, and not by seeds, in order to grow ‘true. For a piece of a cultivated plant will grow out to be 314 DARWINISM TO-DAY. very much like the individual it was cut from, but the seeds will not, in most cases, reproduce faithfully the parents, but will pro- duce a very variable lot of individuals, most of them strongly reversionary in character. Grow peach trees from the stones of your favourite peach and see what manner of peaches you get; but if you want to be sure of more peaches like the ones you enjoy, graft scions from your tree on to other trees. Indeed one of the plant-breeder’s favourite methods of making a start for new things, of getting the requisite beginning wealth and eccentricity of varia- tion, is to grow seedlings, especially from cross-bred varieties. Burbank will give you a thousand dollars for a pinch of horseradish seed. Sugar-cane seed is needed. The amelioration of many kinds of fruit and flowers and vegetables is checked, because in our care- lessness we have allowed these kinds to get into that condition of seedlessness which almost all cultivated races tend toward when grown from cuttings. In our oranges and grape-fruit and in a score of other fruits, the elimination of seeds is exactly one of the modifi- cations we have bred and selected for, in order to make the fruits less troublesome in their eating. But when we lose the seeds entirely of a whole group of related plant kinds we may find our- selves, as we have found ourselves actually in many cases, at the end of our powers of amelioration of these plant sorts. Burbank believes that the very fact that plants when grown asexually always sooner or later lose their power to produce seeds is almost suff- cient proof (if such proof is needed) that acquired characters are transmitted. “Another of Burbank’s open secrets of success is the great range of his experimentation—nothing is too bold for him to attempt, the chances of failure are never too great to frighten him. And another secret is the great extent, as regards material used, of each experiment. His beds of seedlings contain hundreds, often thou- sands, of individuals where other men are content with hundreds. Another element in his work is his prodigality of time. Experi- ments begun twenty years ago are actually still under way. “In all that I have so far written, I have purposely kept to gen- eral statements applicable to Burbank’s work as a whole. My readers might be more interested. perhaps, to have some illustra- tions of the application of various processes of making new sorts of things, some analytical account of the history of various specific ‘new creations, but considerations of space practically forbid this. Just a few briefly described examples must suffice. More than is ‘generally imagined, perhaps, Burbank uses pure selection to get new things. From the famous golden orange coloured California poppy (Escholtzia) he has produced a fixed new crimson form by OTHER THEORIES OF SPECIES-FORMING. 315 selection alone. That is, noticing, somewhere, sometime, an Escholt- zia individual varying slightly redder, he promptly took posses- sion of it, raised young poppies from its seeds, selected from among them those varying in a similar direction, raised new generations from them and so on until now he who wishes may have his California poppies of a strange glowing crimson for the price of a little package of seed, where formerly he was perforce content with the golden orange. For me the golden orange suffices, but that does not detract from my eager interest in the flower-painting methods of Mr. Burbank. Even more striking a result is his blue Shirley poppy, produced also solely by repeated selection from the crimson field poppy of Europe. ‘We have long had various shades of black and crimson and white poppies, but no shade of blue. Out of 200,000 seedlings I found one showing a faintest trace of sky blue and planted the seed from it, and got next year one pretty blue one out of many thousand, and now I have one almost pure blue.’ “But another brilliant new poppy was made in a different way. The pollen of Papaver pilosum, a butter-coloured poppy, was put on the pistils of the Bride, a common pure white variety of Papaver somniferum (double), and in the progeny of this cross was got a fire-coloured single form. The character of singleness was common to the ancestors of both parents, the character of fire colour in the lineage of sommniferum only, although the red of the new form is brighter than ever before known in the somnifera series. Both characteristics were absent (or rather latent) in both parents. And yet the perturbing influence of the hybridisation brought to the fore again these ancestral characters. The foliage of this fire poppy is intermediate in type between that of the two parents. “The history of the stoneless and seedless plum, now being slowly developed by Burbanks, shows an interesting combination of selection, hybridisation, and reselecting. Mr. Burbank found a plum in a small wild plum species with only a part of a stone. He crossed this wild species with the French prune; in the first generation he got most individuals with whole stones, some with parts of a stone, and even some with no stone. Through three generations he has now carried his line by steadily selecting, and the percentage of no-stone fruits is slowly increasing, while quality, beauty, and productiveness are also increasing at the same time. “The plum-cot is the result of crossing the Japanese plum and the apricot. The plum-cot, however, has not yet become a fixed variety and may never be, as it tends to revert to the plum and apricot about equally, although with also a tendency to remain fixed, which ‘tendency may be made permanent. 316 DARWINISM TO-DAY. “Most of Burbank’s plums and prunes are the result of multiple crossings in which the Japanese plums have played an important part. Hundreds of thousands of seedlings have been grown and carefully worked over in the twenty years of experimenting with plums, and single trees have been made to carry as many as 600 varying seedling grafts. The Bartlett plum, cross of the bitter Chinese Simoni and the Delaware, itself a Simoni hybrid. has the exact fragrance and flavour of the Bartlett pear. The Climax, a successful shipping plum, is also a cross of the Simoni and the Japanese triflora. This Chinese Simoni produces almost no pollen, but few grains of it ever having been obtained. But these few grains have enabled Burbank to revolutionise the whole plum shipping industry. The sugar prune, which promises to supplant the French prune in California, is a selected product of a second or third generation variety of the Petite d’Agen, a somewhat variable French plum. “Next in extent probably to Burbank’s work with plums and prunes is his Jong and successful experimentation with berries. This has extended through twenty-five years of constant attention, has involved the use, in hybridisations, of forty different species of Rubus, and has resulted in the origination of a score of new com- mercial varieties, mostly obtained through various hybridisations of dewberries, blackberries, and raspberries. Among these may spe- cially be mentioned the Primus, a hybrid of the western dewberry (R. ursinus) and the Siberian raspberry (R. crategifolius), fixed in the first generation, which ripens its main crop before most of the standard varieties of raspberries and blackberries commence to bloom. In this Primus berry, we have the exceptional instance of a strong variation, due to hybridisation, breeding true from the time of its first appearance. It usually takes about six generations to fix a new variety, but like de Vries’s evening primrose mutations, the Primus berry is a fixed new form from the time of its beginning. An interesting feature of Mr. Burbank’s brief account, in his ‘New Creations’ catalogue of 1894, of the berry experimentation, is a re- production of a photograph showing ‘a sample pile of brush, 12 ft. wide, 14 ft. high, and 22 ft. long, containing 65,000 two- and three-year-old seedling berry bushes (40,000 blackberry \ rasp- berry hybrids and 25,000 Shaffer Gregg hybrids) all dug up- with their crop of ripening berries. The photograph is introduced to give the reader some idea of the work necessary to produce a satisfactory new race of berries. ‘Of the 40,000 blackberry \% rasp- berry hybrids of this kind, ““Phenomenal” is the only one now in existence. From the other 25,000 hybrids, two dozen bushes were reserved for further trial.’ OTHER THEORIES OF SPECIES-FORMING. 317 “An astonishing result of the hybridisation between the black walnut, Juglans nigra, used as the pistillate parent, and the Cali- fornia walnut, J. californica, staminate parent, are walnut trees which grow with such an amazing vigour and rapidity that they increase in size at least twice as fast as the combined growth of both parents. Many tremendous growers are got in the first gen- eration, but in the second there are included some of the most rapidly. growing trees, perhaps, in the world. This hybrid has clean-cut, glossy bright-green leaves from two to three feet long with a sweet odour like that of apples, but it produces few nuts. Curiously enough the result of hybridisation by using the pollen of nigra on pistils of californica produces in abundance large nuts of a quality superior to that possessed by either parent. “The famous Shasta daisy is the result of a multiple crossing between an American and a European species of field daisy and then between these hybrids and a Japanese form. The fragrant calla, known as ‘Fragrance,’ is descended from a single individual found by Burbank while critically examining a block of Little Gem calla seedlings. He was surprised in this examination by a fra- grance resembing that of violets or water-lilies; as he had long been seeking a fragrant calla, the individual giving this perfume was carefully hunted out. No farther selecting was done; this plant was the single ancestor of the fragrant new race. “And so one might go on for pages, but with slight variations in detail all these pages would tell only the same story: the stimulating or inducing of variability by environmental influences and by hybrid- isations; the search after, and keen recognition of, promising spe- cial variations; the selection of the plants showing these variations; rearing new generations from them, repeated selection, and new hybridisations to eliminate this characteristic or introduce that, and on until a desirable combination is found. Then the careful fixing of this form or type by repeated selection through several generations. “But an end must be made of this. Let us, in a paragraph, simply sum up the essential things in the scientific aspects of Burbank’s work. No new revelations to science of an overturning character; but the revelation of the possibilities of accomplishment, based on general principles already known, by an unusual man. No new laws of evolution, but new facts, new data, new canons for special cases. No new principle or process to substitute for selection, but a new proof of the possibilities of the effectiveness of the old principle. No new categories of variations, but an illuminating demonstration of the possibilities of stimulating variability and of the reality of this general variability as the fundamental transforming factor. 318 DARWINISM TO-DAY. No new evidence either to help the Darwinian factors to their death- bed, or to strengthen their lease on life; for the ‘man’ factor in all the selecting phenomena in Burbank’s gardens excludes all ‘natural’ factors. Here are some of Burbank’s own words, touching these matters that scientific men are particularly interested in, in his work: “All scientists have found that preconceived notions, dogmas, and all personal prejudice must be set aside, listening patiently, quietly, and reverently to the lessons one by one which mother nature has to teach, shedding light on that which before was a mystery, so that all who will may see and know. ““Crossing gives the raiser of new plants the only means of uniting the best qualities of each, but just as often the worst quali- ties of each are combined and transmitted, so that to be of any value it must be followed by rigid and persistent selection, and in crossing, as in budding and grafting, the affinities can only be demonstrated by actual test. “*All wild plants of any species are under almost identical envi- ronments, having their energies taxed to the utmost in the fierce struggle for existence. Any great variation under such circum- stances is not likely to occur, and is much more likely to be stamped out at once by its struggling competitors, unless the variation should be of special use in competition, in which case it will survive, and all others may be supplanted by it. Thus we see how new species are often produced by nature, but this is not her only mode. Crosses and hybrids are very often found growing wild where two some- what similar species grow contiguous, and if the combination hap- pens to be a useful one, as it often does, the new creation is encouraged by nature; then time and environment fix it, and man comes on the scene, perhaps ages later, and discovers it, and, not knowing all the facts, wonders where the connecting links have gone. It is botanically classified as a new species, which it is most certainly. “Tn cultivated plants the life struggle is removed, and here we find variation almost the rule rather than the exception. “ ‘Varieties are the product of fixed laws, never of chance, and with a knowledge of these laws we can improve the products of nature, by employing nature’s forces, in ameliorating old and produc- ing new species and varieties better adapted to our necessities and tastes. Better food, more sunshine, less arduous competition, will of themselves induce variation in individual plants which will be more or less transmitted to their seedlings, which, selected con- secutively through a certain number of generations, will become permanent. Environment here exerts an influence as in all chemical cosmical, and celestial movements. These small increments from OTHER THEORIES OF SPECIES-FORMING. 319 environmental forces may produce a gradual or sudden change according to circumstances. The combustion of food liberates the moving force, environment guides it as it does the planets. ““*When once the persistent type is broken up, old latent forces may be liberated and types buried in the dim past reappear. This, called atavism, is a concentration of ancestral forces—reverberating echoes—from varieties long since passed away, exhibiting them- selves when from some cause, for instance crossing, present forces are in a state of antagonism, division, perturbation, or weakness. These echoes, if collected by crossing and selection, produce com- binations of superlative importance and value.’ ” Pop late: 7b, ‘Uber die Bedeutung,” etc., p. 220. ® See Koken, Ernst, ‘‘Palzontologie und Descendenzlehre,” 1902. Koken (Professor of Geology and Palzontology in the University Orthogenetic Of Tubingen) is very explicit in the statements of his variation in belief that the paleontological records prove the exist- palzontology, ence of orthogenetic variation and hence evolution. “Das Darwin’sche Prinzip der Selektion ist nicht das einzige, das. in Betracht kommt und es scheint nicht das wichtigste zu sein. Vielfach vermissen wir in der palzeontologischen Geschichte den Hinweis auf ein Eingreifen des Kampfes ums Dasein und anderer-. seits heben sich Richtungen der Entwickelung heraus. welche nicht in Beziehung zu einem Nutzen stehen, in einigen Fallen zu einer Schadigung der socialen Bedingungen fuhren.” * For an account of the facts of one such case, see Kellogg, “‘Is. There Determinate Variation,” Science, N. S., Vol. XXIV, pp. 621I- 628, 1906. In this paper the gradual but obvious change from. Acase ofap- one dominant type of colour-pattern to another in parent determi- the leaf-eating beetle Diabrotica soror (on the campus: nate variation. of Stanford University, California) during the last. ten years, is shown by statistical variation studies. It is shown that such change is not explicable on a basis of intra-specific selection, nor can it be interpreted as a direct ontogenic reaction - in each succeeding generation to changing climatic conditions. The case is believed to be an example of definitive orthogenetic: variation. Certain examples of presumable determinate variation have been recorded by Henslow (‘The Origin of Species,” Natural Science, p. 250, 1894). ‘In 1847, Prof. J. Buckman sowed seed of wild parsnip in the garden of the Agricultural College, at Cirencester. The seedlings began to vary, but in the same way, though in differ-. ent degrees. By selecting seed from the best rooted plants, the acquired ‘somatic’ characters of an enlarged root, glabrous leaves, etc., became fixed and hereditary; and ‘The Student,’ as he called. 320 DARWINISM TO-DAY. it, having been ‘improved’ by Messrs. Sutton & Sons, is still regarded as ‘the best in the trade.’ This is definite variation, ac- cording to Darwin’s definition, for those weeded out did not differ from the selected, morphologically, except in degree, the variations towards TABS TGet not being quite fast enough to entitle them to survive. “M. Carriére raised the radish of cultivation, Raphanus sativus, L., from the wild species R. raphanistum, L., and moreover found that the turnip-rooted form resulted from growing it in a heavy soil, and the long-rooted one in a light soil.* Pliny records the same fact as practised in Greece in his day, saying that the ‘male’ (turnip form) could be produced from the ‘female’ (long form), by growing it in ‘a cloggy soil. Both forms are now, of course, hereditary by seed.” *? Nageli, C. von, “‘Mechanisch-physiologische Theorie der Ab- stammungslehre,” 1884. ** Korschinsky, S., “‘Heterogenesis und Evolution,” Naturwiss. Wochenschrift, Vol. XIV, pp. 273-278, 1890. *? Recently, Georg Pfeffer (“Die Entwicklung,” 1895) has pro- posed a theory of orthogenetic evolution not very different from the much earlier Nagelian one. Pfeffer postulates as ine inherent in living matter a capacity for change and for self-directing this change. The principle of change or progress he calls the conception of “‘developmental-screw” (Entwicklungsschraube), and for directing this progress the con- ception of “self-steering” (Selbststeuerung). Both these capacities of individualised living stuff are something over and beyond the mechanical and physico-chemical attributes of living matter. ‘On the contrary,” says Pfeffer, “life consists of the capacity (more exactly the exercise of this capacity) of consciously permitting and consciously influencing (that is, actually producing) through physico-chemical phenomena changes in the matter or form of the fundamental life-stuff.” From this curious, though keen, critical, and constructive essay, I quote as follows: “Der Begriff der Entwickelungsschraube deckt sich eigentlich vollig mit dem Begriff der Selbststeuerung der lebendigen Natur; ich halte aber mit gutem Grunde beide Ausdrticke aufrecht, weil sie einer verschiedenen Betrachtung entspringen, namlich die Selbststeuerung der mechanischen, die Entwickelungsschraube der historischen, entwickelungsgeschichtlichen Betrachtungsweise; die Selbststeuerung ist das Prinzip der Herstellung des Gleichgewichtes * This has been corroborated by M. Languet with the carrot. Soc. Roy. et Cent. d’Agricult., 2d ser., Vol. II, 1846-7, p. 539. OTHER THEORIES OF SPECIES-FORMING. 32! eines aus lebendigen Einheiten gebildeten Ganzen; die Entwickel- ungsschraube das Prinzip der veranderten Weiterfthrung dieser Gleichgewichtsverhaltnisse in der Zeit. Also ist, ebenso wie die Selbststeuerung, auch die Entwickelungsschraube selbstthatig (pp. 12and 13). “Es ist hier nicht der Ort, die physikalischen wie die Unzahl der chemischen Eigenschaften der lebendigen Grundsubstanz zu eror- tern; sie liegen freilich nicht auf der Hand, sind aber im Ganzen ziemlich leicht herzuleiten als das allen lebendigen protoplasmati- schen Substanzen Gemeinsame. Es fallt aber Niemandem ein, bez. sollte Niemandem einfallen, die physikalischen und chemischen Eigenschaften der lebendigen Substanz als Lebens-Eigenschaften zu betrachten; vielmehr besteht das Leben in der Fahigkeit (bez. der Austibung der Fahigkeit), die durch chemisch-physikalische Vorgange an dem Stoff oder der Form-Auspragung der Grund- substanz bewirkten Veranderungen bewusst zu erleiden und bewusst zu beeinflussen (bez. hervor zu bringen). Es hat also jeder kor- perliche Vorgang der lebendigen Substanz seinen von ihm untrenn- baren Bewusstseinsvorgang; oder anders ausgedruckt: jeder Vor- gang an lebendigen Wesen hat einen in chemisch-physikalische und einen anderen in Bewusstseins-Verhaltnisse zerlegbaren Anteil. Beide sind Gegenstande wissenschaftlicher Betrachtung, dagegen entzieht sich die Art und Weise des Zusammenhanges zwischen beiden unserm Anschauungsvermogen, liegt also ausserhalb der naturwissenschaftlichen Betrachtung und ist damit als gegeben hinzunehmen”’ (p. 17). A recent proposal of an orthogenetic theory of the general character of Nageli’s is that set out in O. F. Cook’s ‘Aspects of Kinetic Evolution,” Proc. Wash. Acad. Sct., Vol. VIII, pp. 197-403, 1907. ** Eimer, Th., “Die Entstehung der Arten auf Grund von Verer- bung erworbener Eigenschaften nach den Gesetzen organischen Wachsens,” I, 1888; trans. into English, as “Organic Evolution,” 1889; “Artbildung und Verwandschaft bei den Schmetterlingen,” I, 1889, II, 1895; “Ortho- genesis bei Schmetterlinge” (Part II of ‘Die Entstehung der Arten’”), 1898; ‘‘Orthogenesis,’ 3 Internat. Congress Zool., 1895; trans. in English as “On Orthogenesis and the Impotence of Natural Selection in Species-Formation,” 1898. This address, and Eimer’s other writings as well, are sadly marred by intemperate polemic and the indulgence of personal rancor. He deems himself and his views unfairly overlooked by biologists and seems to hold Weismann personally responsible for this. Apart from these unfortunate digressions his papers are extremely suggestive and logically and Eimer’s theory of orthogenesis, 322 DARWINISM TO-DAY. keenly composed. I believe that Eimer’s work and theories should have more attention from students of evolution then they now get. ** Dean, Bashford. ‘Evolution in a Determinate Line, as Illus- trated by the Egg-Cases of Chimeroid Fishes,” Biol. Bull., Vol. Apparent deter- VII, pp. 105-112, 1904. In this paper the author minate evolution. expresses his belief that the conditions existing in the curious inter-related adaptations between eggs and egg-cases of the shatk-like fish, Chimera, can be explained only on the basis of determinate or orthogenetic modifications, in which modifications neither natural selection nor the Lamarckian factors of use and disuse can have played any part. The capsule or egg-case, although “only indirectly connected with the egg, 1.e., as a secretion formed by the parent after the mechanism of heredity has already been established in the egg, nevertheless foresees with startling exact- ness the size and shape of the young fish when many months hence it comes to hatch out, and it provides a series of progressive multi- plications adapted to the physical needs of the young. It is evident, accordingly, that if natural selection be adduced to explain the present phenomena it encounters difficulties more numerous and complex than in usual instances. In the latter cases selection con- cerns itself with variations which affect the progeny directly; but in the present case variations must have occurred in the lines both of the progeny and, indirectly, of its far less indifferent capsule- forming capabilities—with result that a succession of closely corre- lated stages in variation must have coincided in both distinct con- ceptions.” * Plate, L., “Uber die Bedeutung,” etc., p. 190 ff. *® Rosa, Daniel. ‘“La Riduzione Progressiva della Variabilita 1 suoi Rapporti coll’ Estinzione e coll’ Origine della Specie,” 1899. Author believes that in animal life there is a gradual progressive reduction of variation (or modification) necessitated by the well- known fact that highly specialised forms have distinctly fewer lines of modification, 7. e. specialisation, left open to them than general- ised forms; and that all groups of animals are of the nature of series of more and more specialised forms. He bases this belief, as far as facts go, on the well-known cases of the dying out of spe- cialised species (Irish stag) and specialised groups (Cretaceous reptiles), and on the alleged facts (which the author devotes many pages to trying to show) that all present-day principal groups of animals are related to each other solely by derivation from com- mon very old and generalised ancestors. If there is less modifica- tion possible, then there occurs actually less and less variability, and the actually occurring variations will be only along certain lines, 1. e. there will be in this limited variability an actual basis for ortho- OTHER THEORIES OF SPECIES-FORMING, = 323 genesis. On the double basis of progressively less variation and of the thus produced orthogenesis the author sees a factor in phylogeny (organic evolution) which works, to some degree, independently of natural selection or of Lamarckian factors. Rosa thinks he has thus contributed to biology one of the always sought-for “unknown factors in evolution.” 17 Tn an interesting paper by Snodgrass, ‘“The Relation of the Food to the Size and Shape of the Bill in the Galapagos Genus Geospiza,” Snodgrass’s Auk, Vol. XIX, pp. 367-381, 1902, detailing the ex- observations on amination of the stomach contents of over 200 indi- billsof Gala-~ = viduals, representing 13 species and sub-species (taken pagos birds. from several of the Galapagos Islands) of the peculiar Galapagos Fringillid genus, Geospiza, remarkable for the great differences in size and shape of bill characterising the various species and sub-species, the author states that all the “evidence seems to be in favour of the general conclusion that there is no correlation between the food and the size and shape of the bill.” The following five propositions were established: (1) The same species at different localities may feed on different seeds; (2) different species at the same locality may feed on the same kinds of seeds; (3) different species at different localities may feed on the same kinds of seeds; (4) different species at the same or at different localities may feed on different seeds; and (5) birds with small bills eat only small seeds; birds with large bills eat both small and large seeds. The seeds taken from the stomachs varied in size from seeds of 1 cubic millimetre up to those 15 mm. long by 10 mm. thick. The bill of the different species and sub-species of Geospiza, varies from that of G. scandens scandens, 13 mm. long by 7 mm. high at base, to that of G. pachyrhyncha, 17 mm. long by 20 mm. high at base. ** Eimer, Th., “Orthogenesis der Schmetterlinge,”’ 1897. ** Cope, E. D., “The Method of Creation of Organic Types,” Proc. Amer. Phil. Soc., December, 1871. *° Cope, E. D., “The Energy of Life Evolution,” Pop. Sci. Mo., Vol. XXVII, pp. 789-800, October, 1885: “Primary Factors of Organic Evolution,” 1896. ** “Paleontologists, as a rule—and Prof. Cope is one of them,— are so profoundly impressed by the adaptive nature of the evolu- Cope’s belief | tionary process and by the definitiveness of its direc- in orthogenetic tion, that they cannot regard the restraining or evolution. selective action of the environment as enough to keep the breed true. They are so accustomed to seeing mutation after mutation, generation after generation, developing in apparent obe-. dience to obvious physico-chemical or mechanical conditions, that 324 DARWINISM TO-DAY. they incline to regard these conditions as causes. And if it be suggested to them that the results they see may have been achieved by the selection of adaptive variations from among a number of promiscuous variations that are not adaptive, they ask why it is that they do not find evidence of these numerous known adaptive variations in the organs, when one would suppose that, on any hypothesis, except that of definite variation, such forms must have been the more abundant of the two. It is useless to reply to them that the known adaptive variations in each generation were killed off when young, and so, even if fossilised, are practically undistinguish- able; because they will reply with abundant proof that the adaptive characters chiefly appear in the adult stages of the organism, possibly only in its senile stages, and so are incapable of coming under the action of natural selection during the early undifferentiated stages. How the conversation might continue does not much matter, for it 1s obvious that it has reached a point beyond which all must be speculation. The facts on which the paleontologist relies, the facts that Prof. Cope adduces with such wealth of knowl- edge, are strong presumptive evidence in favour of his second thesis, but they are not proof.” (Bather, F. A., Natural Science, Vol. X, pp. 40-41, 1897.) Prof. Scott, another American paleontologist, discusses the question of variation in an interesting paper in the American Journal of Science, Vol. XLVIII, pp. 335-374. 1894. The great point made by Prof. Scott is the clear distinction between individual and phylogenetic variation. Individual variation is irregular and not fixed, while ‘phylogenetic variation,” or mutation (in the sense of * Waagen) which is distinguished from individual variation, not by any character of quantity or quality, but by pursuing a deter- minate direction and thus, under control of natural selection, leading to the formation of new species. ‘‘Remembering that the signifi- cant fact in the history of a group is not so much the character of its variations at any one stage, as the gradually shifting positions successively occupied by the normal or centre of stability, we find that any mammalian series at all complete, such as that of the horses, is remarkably continuous, and that the progress of discovery is steadily filling up what few gaps remain. So closely do successive stages follow upon one another that it is sometimes extremely * The term “mutation” was first used in biology, probably, by Waagen, 1869, in a paper on the phylogeny of an ammonite. In this first use of the word its meaning was a change or modification accomplished during a considerable historic period. Indeed, it had much the meaning of evolution or descent as we use these terms nowadays. OTHER THEORIES OF SPECIES-FORMING. = 325 difficult to arrange them all in order and to distinguish clearly those members which belong in the main line of descent, and those which represent incipient branches. Some phylogenies actually suffer from an embarrassment of riches.” ?? Whitman, C. O., ‘The Problem of the Origin of Species,” Pro- ceedings of Congress of Arts and Science, Universal Exposition, St. Whitman's Louis, Vol. V, pp. 41-58, 1906. In this paper Whit- belief in deter- man takes strong ground for orthogenesis and recites minate variation. jn detail a number of interesting facts touching the evolution of pattern in pigeons to illustrate his belief. Touching the criticism of orthogenesis, that it involves a teleologic element in its make-up, Whitman says (p. 5): “I take exception here only to the implication that a definite variation-tendency must be con- sidered to be teleologic because it is not ‘orderless.’ I venture to assert that variation is sometimes orderly, and at other times rather disorderly, and that the one is just as free from teleology as the other. In our aversion to the old teleology so effectually banished from science by Darwin we should not forget that the world is full of order, the inorganic no less than the organic. Indeed, what is the whole development of an organism if not strictly and marvel- lously orderly? Is not every stage, from the primordial germ on- ward, and the whole sequence of stages, rigidly orthogenetic? If variations are deviations in the directions of the developmental processes, what wonder is there if in some directions there is less resistance to variation than in others? What wonder if the organ- ism is so balanced as to permit of both unifarious and multifarious variations? If a developmental process may run on throughout life (e. g., the life-long multiplication of the surface-pores of the lateral-line system in Amia), what wonder if we find the whole species gravitating slowly in one or a few directions? And if we find large groups of species, all affected by a light variation, moving in the same general direction, are we compelled to regard such ‘a definite variation-tendency’ as teleological, and hence out of the pale of science? If a designer sets limits to variation in order to reach a definite end, the direction of events is teleological ; but if organisation and the laws of development exclude some lines of variation and favour others, there is certainly nothing super- natural in this, and nothing which is incompatible with natural selection. Natural selection may enter at any stage of ortho- genetic variation, preserve and modify. in various directions the results over which it may have had no previous control.” ** Cunningham, an English neo-Lamarckian, expresses (‘Origin of Species Among Flatfishes,” Natural Science, Vol. VI, p. 2309, 1895) his belief in orthogenesis as follows: 326 ~ DARWINISM TO-DAY. “The only general view, as it seems to me, which can be held concerning the structural diversity of the animal kingdom, is to regard it as resultant of two more or less opposing Cunningham = general tendencies. On the one hand, there is uni- and orthogenesis. : é Ly versal evidence of a tendency to definite variation, or growth in different directions, leading to manifold variety of regu- lar definite symmetrical forms. This tendency can only be regarded as internal to the organism, as connected with a tendency to growth and multiplication inherent in organic units. On the other hand, there is the molding, limiting, constructing action of the external forces of the environment resulting in more or less complete adap- tation. Whatever be the process of adaptation, whether Darwinian selection or Lamarckian modification, adaptive structural combina- tions are mechanisms each working with the particular result which is important to the feeding, living, and breeding of the organism. Whatever the causes of non-adaptive variation, the resulting struct- ural features are the regular genetic forms and characters which the multitude of different organic forms present in such marvellous diversity. No one who, like Weismann, ignores everything except adaptation, or who, like Bateson, regards the study of adaptations as barren and profitless, can hope to produce a consistent and com- prehensive theory of organic evolution.” ** Delage, Yves, “L’Hérédité,” 2d ed. p. 849, and others, 1903. °° Taeckel, O., “‘Uber verschiedene Wege phylogenetischer Ent- wicklung,” 1902. CHAPTER XI. OTHER THEORIES OF SPECIES-FORMING AND DESCENT (CONTINUED): ALTERNATIVE THEORIES (CONTINUED). Heterogenesis—Under the name heterogenesis we have to consider a theory of species-forming which is more popu- larly and widely known under another name, viz., the muta- tions theory. This theory is commonly associated with the name of de Vries, the Amsterdam botanist. But this gen- eral conception of species-forming on a basis of the occur- rence of occasional, sudden, fixed, and often considerable changes or variations in the offspring of a plant or animal, isa ‘conception not of course new with de Vries, but one variously expressed by numerous biologists from Dar- win’s time on, especially by von Kolliker, Galton, Dall, Bateson, Emery, Scott, and Korschinsky. It is, however, chiefly due to the patient, persistent, well-planned, and ex- tensive experiments and observations of de Vries that this theory of species-forming by heterogenesis, or.as called by de Vries, by mutations, has recently received so much re- newed attention. With the observations of de Vries on the breeding of certain plant species, notably certain GEnotheras (evening primroses), there have been much associated in recent popular scientific literature accounts of the ear- lier observations of Gregor Mendel,” an Augustinian monk, who recorded, in 1865, in an obscure journal, some very valuable observations and logical conclusions concerning the phenomena of heredity in certain other plants (especially garden peas). Reference should also be made, in this con- 327 328 DARWINISM TO-DAY. nection, to observations and experiments carried on nearly simultaneously with those of de Vries by Correns* and Tschermak.? As a matter of fact the data on which de Vries bases his theory of species-forming by heterogenesis are, in part, nearly identical with those obtained by Mendel, Tschermak, and Correns, which, however, is concerned primarily with explaining the “laws” of heredity. The meaning of heterogenesis in connection with species- forming and descent is essentially this: whereas by the Darwinian theory species are transformed slowly and by slight changes in at first one or two or a few and only later in more parts, and all new species are derived from the old ones (which usually disappear as the new ones appear) by the gradual selection of the advantageous cnes among the regular slight, fluctuating, individual variations (known commonly as Darwinian variations and which mostly occur according to the law of error), by the theory of hetero- genesis new species appear suddenly, not by a selective choosing among the slight fluctuating Darwinian variations, but independently of selection, and largely independently of the so-called Darwinian variations, by the appearance in fixed definitive form of several to many slight to consider- able variations, which give the new species definite char- acteristics differentiating it often in many particulars from the old species, which differentiating characteristics are fully and faithfully transmitted to the succeeding generations of individuals derived from this suddenly born new species. In some theories or views of heterogenesis the suddenly appearing new variations—and none of these theories gives a satisfactory explanation of the cause of these Bra aie sudden variations—which give rise to new species, are those large, sometimes monstrous, variations known as “‘sports,” “monsters,” etc.; or, in Bate- son’s words, are “discontinuous variations,” 7. ¢., considerable variations not connectéd bya continuous: series of gradations. OTHER THEORIES OF SPECIES-FORMING. 329 with the parent type of the variable organ or individual. Darwinians have always been interested in such variations, for if they do occur in any considerable numbers they might offer a possible solution of that difficulty in the selection theory of explaining the origin of new structures and the needed degree of size and development sufficient to make these beginnings useful and hence available as handles for natural selection. But it has long been recognised that such sports or discontinuous variations are too few and occur too rarely to furnish the basis for a comprehensive theory of species-forming. Like the extremes of individuals in the series of fluctuating variations, their characters would be lost or swamped by crossing. Darwin himself made as full a list of such sports as any post-Darwinian writer, ex- cepting Bateson, has been able to do, and he recognised the fact that certain species, or races at least, of domesticated animals and cultivated plants undoubtedly had their begin- nings in these sports. His examples of such discontinuous or saltatory evolution as the Ancon and Mauchamp sheep, the Paraguay cattle,* etc., are the classic examples in ani- mal evolution, and to this day nearly the only ones! Bate- son” has, to be sure, gathered together in his “Materials. for the Study of Variation” a much larger list of sports or discontinuous variations than Darwin included in his knowl- edge (it should be borne in mind in referring to Bateson’s list that several, probably, indeed, many of his alleged ex- amples are cases of teratogenic regeneration)—but he has been able to add almost no new examples of the origin of a new species from such discontinuous variations. A few cases are known of the inheritance through a number of generations of suddenly appearing sports or discontinuous variations in human beings (cases of polydactyly, etc.) and cats. (Kennel’s stump-tailed cat, which produced in six litters four stump-tailed, twelve tailless, and twelve normal young, is an example of several similar cases which have. 330 DARWINISM TO-DAY. been recorded.) Species-forming by sports and discon- tinuous variations is obviously no theory to presume to offer itself as a species-forming substitute for natural selec- tion. But the de Vriesian mutations theory, the most recent development of the heterogenesis conception, has rehabilitated this conception to such an extent that a number of biologists see in it an actually satisfactory substitute for the natural selection theory. Before explaining the theory of de Vries let us first note two or three other prior formula- tions of theories of heterogenesis, one at least being nearly identical with that of de Vries. In 1864 the great zoologist von Kolliker,* in a paper under the title “Uber die darwinische SchSpfungstheorie,” took positive ground against the adequacy oractuality of natural selection as a species-forming factor, and proposed a theory of “heterogene Erzeu- gung” (heterogenesis) which he formulated, however, only in most general terms. He said that “under the influence of a general law of development (evolution) organisms bring forth other kinds differing from them out of the germs produced by them.” He included in his general theory of heterogenesis a basic plan of progressive evolution. Such a conception has in it too much autogenic orthogenesis ; it is too redolent of teleology for present-day biology. The Von Kolliker’s suggestion. variations, too, which are to serve as beginnings of new species are those too rare ones which we have referred to as sports and discontinuous variations. The American naturalist, Dall,” in a paper written in 1877, expresses his conviction that sudden changes of species-forming character do occur, and as- _ Dall’sbelief cribes such changes “to the action of the in sudden spe- , ; cies-change, law of development, which finds expression in the paradox that the same species may belong to different genera.” That sudden leaps may be due to the gradual accumulation of minute differences he OTHER THEORIES OF SPECIES-FORMING. 331 exemplifies as follows: “In a sloping gutter of a paved street not too cleanly swept every one will notice on a sudden shower how small particles of earth and other materials will sometimes act as a dam, producing a puddle which, relieved by partial draining, may for a time remain in statu quo. A time comes, however, when the gradually accumulated pressure suddenly sweeps the dam before it for a short distance, until another similar one is formed, the pool again appears for a time to remain unchanged, and so on indefinitely. Now the modern idea of a species may be stated to be a greater or lesser number of similar individual organisms in which for the time being the majority of characters are in a condition of more or less stable equi- librium, and which have the power to transmit these char- acters to their progeny with a tendency to maintain this equilibrium. This tendency may be, in some cases, sufficiently strong to resist for a considerable period the changes which a gradual modification of the environment may tend to bring about. When the latter has reached a pitch which renders the resistance no longer effectual, it is conceivable that a sudden change may take place in the arrangement of the constitution of the organism, adapting it once more to its surroundings, when the tendency to equilibrium may reassert itself in the minor characteristics, and they may, as it were, crystallise once more in a form not dissimilar in generic type. If among a certain assemblage of individuals con- stituting a species, the tendency to maintain the specific equilibrium be (as it should be a priori) transmitted to the progeny in different degrees of intensity, a gradual separa- tion might take place between those with a stronger tendency to equilibrium and those with less. Here natural selection would come in. Those yielding as above to the pressure of the environment would necessarily become better adapted to it (or perish) and with their changed generic structure might be able to persist. On the other hand, those ORE ee 332 DARWINISM TO-DAY. with the broader base, so to speak, with the inherited tendency to remain unshaken by the modifications of the environment, may be conceived as through this tendency to be and to remain less injuriously affected by adverse circumstances, and consequently might still endure. In short, natural selection in the one case would find its ful- crum in the tendency to easy adjustment of characters; and in the other case in the inherited persistency in equilibrium rendering its possessor more or less indifferent to the in- jurious elements of the environment. The intermediate individuals by the hypothesis would be those least-fitted to persist in any case and hence liable to be rapidly eliminated. Then we should have parallel series of species in two or even more genera existing simultaneously.” Francis Galton, the great student of heredity and, in most of his belief a thorough Darwinian, nevertheless held it to be probable that evolution might proceed not only Galton’s belief Hy minute steps but that decisive sudden changes in discontinuous steps. of the type may occur. “That the steps may be small and that they must be small are very different views; it is only to the latter that I object, and only when the indefinite word ‘small’ is used in the sense of ‘barely discernible’ or as small compared with such large sports as are known to have been the origin of new races.” * And his familiar analogy of organic stability to that of the polygon * with unequal sides, whose stability or r fixity de- presses well the basic ides in sc helerapeness or rnitaien - small but definitive and fairly stable changes. Galton also believed in the stability or fixity of sports; not that all trans- mit their character to their young but that many do and thus give rise to new types. Emery,’” in his suggestive paper called “Gedanken zur Descendenz- und Vererbungstheorie,” expresses his belief in the importance in species-forming of what he calls “pr OTHER THEORIES OF SPECIES-FORMING. 333 mary variations,” which are large and sudden as contrasted With “secondary variations,’ which are the usual small, Emery’ fluctuating or so-called Darwinian variations. ery’s the- ; ’ : ory ofprimary Emery bases his belief on the few cases like variations.” the Ancon sheep and the inherited six-fingered- ness of men, and also on an argument drawn from the dif- ficulty of explaining by the natural selection theory various existing conditions such as sexual polymorphism, and numer- ous cases of extremely complex structural and physiological specialisation. But there is little that is convincing in Emery’s presentation. A later exponent of heterogenesis of a different kind, and a more sharply-spoken antagonist of the selection theory, Eetuchincky's much more nearly anticipates de Vries’s muta- theory of hetero- tion theory. Indeed this biologist, the Russian geneets botanist Korschinsky, in his championship of heterogenesis goes much beyond de Vries in his denial of the influence of selection in species-forming and descent. De Vries, as we shall see, admits natural selection to be a factor, and perhaps a large one in the determination of descent, of organic evolution, but holds it to be wholly a restraining and cutting-back factor, not at all a formative one. Korschinsky | says plainly that the struggle for existence and selection have either no influence in species-forming and descent, or, if any, a hindering and antagonising influence, a retarding and nullifying influence. Korschinsky has published his theory in three papers, one a large work in Russian which I have not seen, the others shorter papers ** in German which are of the nature of vorlaiifige Mitteilungen. In these papers he formulates clearly and positively a theory of heterogenesis or species-forming by “mutations” and attacks sharply and positively the natural selection theory. A con- cise statement of his theory and at the same time of his position with regard to the selection theory is given by. him in a table of two columns in which the contrast between ee the two theories is graphically shown. DARWINISM TO-DAY. I translate here this “parallel columns” statement in full: ACCORDING TO THE TRANSMUTA- TION THEORY. 1. To all organisms there be- longs a capacity for variation which is called into play partly through inner, partly through outer causes, through use and disuse, etc. This capacity for variation regularly finds its ex- pression in the appearance of slight and unnoticeable individ- ual differences. 2. As a result of this strug- gle for existence and selection, those individual variations which prove themselves useful become fixed and accumulated, while the non-useful ones dis- appear. All characteristics and peculiarities of a species must, as a result of a prolonged selec- tion, stand in harmony with the outer conditions, and be useful to the organism. 3. Through prolonged selec- tion and accumulation of char- acteristics all species undergo a persistent change, whereby they are gradually transformed into new species without, how- ever, sacrificing their normal physiological relations. 4. This process can take place everywhere and under all cir- cumstances. The harder the outer conditions and the sharp- er the struggle for existence, the more energetically selection works, and therewith the quick- ACCORDING TO THE THEORY OF HETEROGENESIS. 1. To all organisms there be- longs a capacity for variation, which is a fundamental inner peculiarity independent of outer conditions, and which remains usually in latent condition, re- tained by heredity, but which now and then finds its expres- sion in sudden changes. 2. These sudden changes can, under favourable conditions, be the beginnings of persistent races. These new characteris- tics, having appeared independ- ently of outer conditions, are sometimes useful to the organ- ism, but they may also stand in no harmony with outer condi- tions. 3. All once-formed species re- main unchanged, although new forms occasionally split off from them by heterogenesis. Such newly-arisen forms have, as the result of a disturbed heredity, a deranged constitution, which re- veals itself in a lessened fertility and often in a generally weak- ened condition of the organism. The new forms, becoming con- stant races, gradually recover their constitution. 4. The origin of new forms can, however, occur only under favourable conditions of exist- ence for the species, and the more favourable these condi- tions, that is, the less severe the struggle for existence, the OTHER THEORIES OF SPECIES-FORMING. er the development of new forms. 5. The chief requisite for evo- lution is, therefore, the struggle for existence and the selection which results from it. 6. If there were no struggle for existence, no selection, no survival of the strongest, there would be no evolution and no specialisation, for adapted spe- cies would have no advantage over unadapted ones, and as a result of crossing with the lat- ter, they would sacrifice their useful characteristics. 7. The so-called advance in nature or the perfecting of or- ganisms, is nothing else than a more complex, more complete adaptation to outer conditions, and it is reached in a purely mechanical way through selec- tion and the accumulation of characteristics useful under the existent outer conditions. 335 more energetically can evolution go on. New forms do not arise under hard external conditions, or if any do, they go quickly to ground. 5. The struggle for existence, and the selection that goes hand in hand with it, constitute a fac- tor which limits new forms and hinders further variation and is, therefore, in no way favourable to the origin of new forms. It is a factor inimical to evolution. 6. If there were no struggle for existence, there would be -no killing out of newly arising or al- ready arisen forms. The world of organisms could then grow to a mighty tree, whose branches could all persist in blossoming condition, and the most aberrant, now isolated, species would be connected with all others through intermediate forms. 7. The adaptation which comes to exist through the struggle for existence is not at all identical with an advance, for higher, more specialised (voll- kommenere) forms are by no means alwavs better adapted to outer conditions than the lower ones. One cannot explain the evolution of organisms in a purely mechanical way. In or- der to explain the origin of higher forms out of lower it is necessary to admit a_ special tendency, in organisms, for ad- vance, which is nearly related to, or identical with the tend- ency to vary, and which com- pels organisms toward perfect- ness as far as external conditions allow. The theory of heterogenesis as formulated by Korschinsky (and also as held by de Vries, as we shall see) 1s not neces- 336 DARWINISM TO-DAY. sarily a theory of sudden large changes or variations, al- though it is of sudden and fixed ones. It is not based on any belief that sports or large variations are any more numerous, nor of any more worth as the beginnings of new species, than now generally recognised, but it assumes sudden radical changes in the organism which, if not visibly large as regards obvious quantitative conditions, are large or at least comprehensive as regards qualitative conditions. The mutation or variation assumed by the theory of hetero- genesis affects many organs and parts, structurally and physiologically ; it produces a radical change throughout the organism. And this change is the result of an influence wholly intrinsic, inherent, and has no reference to external conditions, except in that the stimulus for it may come partly or chiefly from specially favourable conditions of nutrition. This change is at once definitive and fixed: it is transmitted unimpaired to the offspring of the organism showing the mutation, only the capacity for the production of offspring, 1. ¢., the reproductive fertility, is often weakened. Korschinsky’s theory and declarations are not based on any very large amount of personal experimentation and observation—at least his references to new facts are few and meagre. He gives a short list of old and more or less familiar together with a few new examples of heterogenesis but he does not lend the theory of heterogenesis very much in the way of authority, except in so far as the evidently positive and clear conviction on the part of a biologist of experience and reputable standing of the necessity and truth of such a theory is authority. Korschinsky’s conviction is probably based on much observation and experience besides that which he definitely catalogued, but what is needed to carry conviction to others is direct reference to proved, and where possible verifiable, facts of observation and experi- ment. The supplying of this demand, to a degree which will OTHER THEORIES OF SPECIES-FORMING. 337 appear to various people insufficient or sufficient according to their respective ideas of what is needed in De Vriesand the way of fact material for the satisfactory the mutations ; peo we ; . theory. founding of a theory, it is the special vir- tue of de Vries to have attempted on behalf of heterogenesis. De Vries ** introduces his now classic two-volume pres- entation of his views on evolution and species-forming (“Die Mutationstheorie,” 1901-1903) with the following paragraph: “Als Mutationstheorie bezeichne ich den Satz, dass die Eigenschaften der Organismen aus scharf von einander unterschiedenen Einheiten aufgebaut sind. Diese Einheiten konnen zu Gruppen verbunden sein, und in verwandten Arten kehren dieselben Einheiten und Gruppen wieder. Ubergange, wie sie uns die ausseren Formen der Pflanzen und Thiere so zahlreich darbieten, giebt es aber zwischen diesen Einheiten ebensowenig, wie zwischen den Molekulen der Chemie.” And again in the first paragraph of the preface to his book ‘Species and Varieties” ** (an edited transcription of his American lectures on species-forming, delivered in California in 1904) he says: “. . . but the way in which one species originates from another has not been adequately explained. The current belief assumes that species are slowly changed into new types. In contradic- tion to this conception the theory of mutation assumes that new species and varieties are produced from existing forms by sudden leaps. The parent-type itself remains unchanged throughout this process, and may repeatedly give birth to new forms. These may arise simultaneously and in groups, or separately at more or less widely distributed periods.” Obviously there is no ambiguity here as to the relation of species-forming by mutation to species-forming by gradual modification through selection or fluctuating varia- tions. In the words of de Vries: “Species have not arisen 238 DARWINISM TO-DAY. through gradual selection continued for hundreds or thou- sands of years, but by jumps (stufenweise) through sudden, though small, transformations. In contrast with variations which are changes in a linear direction the transformations to be called mutations constitute divergence in new directions. They take place, so far as experience goes, without definite direction.” ** And even if transition forms exist between the species produced by mutations, they are no evidence against the mutations, “for,” says de Vries, “the transitions do not appear before the new species, at most only simul- taneously with this, and generally only after this is already in existence. The transitions are therefore no intermediates or preparations for the appearance of the new forms. The origin takes place, not through them, but wholly independ- ently of them.” *° Too often de Vries’s theory is said not to be alternative with Darwin’s, but auxiliary to it. As regards the forma- tion of new species, the two theories are directly De Vries's in opposition. But as regards the general nai course of organic evolution (which is another opposition to Darwin's as con- matter) the mutations theory is not in contra- rise diction to the theory of descent through selection. De Vries himself says: “Notwith- standing all these apparently unsurmountable difficulties, Darwin discovered the great principle which rules the evolu- tion of organisms. It is the principle of natural selection. It is the sifting out of all organisms of minor worth through the struggle for life. It is only a sieve, and not a force of nature, no direct cause of improvement, as many of Dar- win’s adversaries, and unfortunately many of his followers also, have so often asserted. It is only a sieve, which de- cides which is to live, and what is to die. But evolutionary lines are of great length, and the evolution of a flower or of an insectivorous plant.is a way with many side-paths. It is the sieve that keeps evolution on the main line, killing OTHER THEORIES OF SPECIES-FORMING. 339 all or nearly all that try to go in other directions. By this means natural selection is the one directing cause of the broad lines of evolution.” ** While de Vries admits that recorded mutations are few; “mutations under observation are as yet very rare; enough to indicate the possible and most probable ways but no more;” *” yet he strongly maintains that there is no scientific proof of the origin of species in any other way than by mutation and that there is such proof of their actual muta- tional origin. He says: “I intend to give a review of the facts obtained from plants which go to prove the assertion that species and varieties have originated by mutation and are, at present, not known to originate in another way.” But in any consideration of de Vries’s work and theories, one must have clearly in mind the distinctive meaning which de Vries attaches to the word species. However little biologists agree on any absolute definition of species, the term nevertheless is consistently used to refer to differ- entiated organic types between any two of which there is considerable obvious describable difference, either quali- tative or quantitative. If two types of such obvious differ- ence in one or several characteristics (usually external or at least externally noticeable differences are the ones used) are connected by a series of connecting gradatory forms existing either in the same territory or in other regions, the two forms are not referred to as distinct species but as varieties ; at least the form at one end of the series is called a variety of the form at the other end. But de Vries’s species and varieties are of different stuff. Specific dis- tinctions with him are based on differences in aggregation of the elementary units, the Einheiten, that go to compose the specific types. “Species is a word,’ says de Vries, “which always has had a double meaning. One of them is the systematic species, which is the unit of our system. But these units are not at all indivisible. Long ago Lin- 340 DARWINISM TO-DAY. nzus knew them to be compound ideas in a great number of instances, and increasing knowledge has shown that the same rule prevails in other instances. To-day the vast ma- jority of the old systematic species are known to consist of minor units. These minor entities are called varieties in sys- tematic works. However, there are many objections to this usage. First, the term variety is applied in horticulture and agriculture to things so widely divergent as to convey no clear idea at all. Secondly, the subdivisions of species are by no means all of the same nature, and the systematic varieties include units the real value of which is widely different in different cases. Some of these varieties are in reality as good as species, and have been ‘elevated,’ as it is called, by some writers, to this rank. This conception of the elementary species would be quite justifiable, and would at once get rid of all difficulties, were it not for one practical obstacle. The number of the species in all genera would be doubled and tripled, and as these numbers are already cumbersome in many cases, the distinction of the native species of any given country would lose most of its charm and interest. “In order to meet this difficulty we must recognise two sorts of species. The systematic species are the practical units of the systematists and florists, and all friends of wild nature should do their utmost to preserve them as Linnzeus has proposed them. These units, however, are not really existing entities; they have as little claim to be regarded as such as the genera and families have. The real units are the elementary species; their limits often apparently overlap and can only in rare cases be determined on the sole ground of field-observations. Pedigree-culture is the method required and any form which remains constant and distinct from its allies in the garden is to be considered as an elementary species.” *” With regard to varieties de Vries has the following to OTHER THEORIES OF SPECIES-FORMING. 34! say: “Linneus himself knew that in some cases all sub- divisions of a species are of equal rank, together constituting the group called species. No one of them outranks the others; it is not a species with varieties, but a group con- sisting only of varieties. A closer inquiry into the cases treated in this manner by the great master of systematic science shows that here his varieties were exactly what we now call’elementary species. “In other cases the varieties are of a derivative nature. The species constitutes a type that is pure in a race which ordinarily is still growing somewhere, though in some cases it may have died out. From this type the varieties are derived, and the way of this derivation is usually quite manifest to the botanist. It is ordinarily by the disappear- ance of some superficial character that a variety is dis- tinguished from its species, as by the lack of colour in the flowers, of hairs on stems and foliage, of the spines and thorns, etc. Such varieties are, strictly speaking, not to be treated in the same way as elementary species, though they often are. We shall designate them by the term of ‘retro- grade varieties,’ which clearly indicates the nature of their relationship to the species from which they are assumed to have sprung. In order to lay more stress on the contrast between elementary species and retrograde varieties, it should be stated at once, that the first are considered to have originated from their parent-form in a progressive way. They have succeeded in attaining something quite new for themselves, while retrograde varieties have only thrown off some peculiarity, previously acquired by their ancestors.” *° With regard to the facts and general evidence ** on which The facts at © VtIeS bases his beliefs and theory a few basis of de ‘words, too few, I regret, must suffice. Like Vries's theory. Darwin, de Vries only came to the full pub- lication of his theory after many years of assiduous obser- 342 - DARWINISM TO-DAY. vation, of persistent compilation of other men’s observing, and careful weighing and consideration of the data in hand. In de Vries’s case too there was added a large amount of experimental testing of his conclusions. This experimental study of the species-forming problem de Vries and his followers rather seem to claim as a distinct- ively new part of the basis for the mutations theory, but as a matter of fact Darwin himself, in much less degree per- haps, and in somewhat different manner, appealed to experi- ment to test many of his conclusions. The actual forming of new species by selection could not be experimentally tested or proven by Darwin. Whether biologists are ready to accept de Vries’s pedigree-culture work and results as of the same nature of rigid experimental test and proof as there exists in experimentation in chemistry and _ static physics (for that is the claim for the new “experimental method” in biology) remains, perhaps, a moot point. De Vries’s general statement of the character and the amount of the evidence on which he rests his belief in the formation of species by mutation is contained in the following para- graphs from his book “Species and Varieties” (p. 22). “Mutations are occurring from time to time in the wild state as well as in horticulture and agriculture. A-selec- tion of the most interesting instances will be given later. But in all such cases the experimental proof is wanting. The observations, as a rule, only began when the mutation made its appearance. A more or less vague remembrance about the previous state of the plants in question might be available, though even this is generally absent. But on doubtful points concerning possible crosses or possible intro- duction of foreign strains, mere recollection is insufficient. The fact of the mutation may be very probable, but the full proof is, of course, wanting. Such is the case with the mutative origin of Xanthium commune Wootom from New Mexico and of Cnothera biennis cruciata from Holland. Fs >. ** OTHER THEORIES OF SPECIES-FORMING. 343 The same doubt exists as to the origin of the Capsella Heegeri of Solms-Laubach, and of the oldest recorded muta- tion, that of Chelidonium laciniatum in Heidelberg about 1600.” | ~ Next, after introducing the necessity of experimental proof and explaining how one must go to work to acquire such proof he refers to his own well-known work with Lamarck’s evening primrose as follows (pp. 26-29) : “Complying with these conditions, the origin of species may be seen as easily as any other phenomenon. It is only necessary to have a plant in a mutable condi- The work with tion. Not all species are in such a state at Lamarck’s even- ing primrose, Present, and therefore I have begun by ascer- taining which were stable and which were not. These attempts, of course, had to be made in the experi- mental garden, and large quantities of seed had to be pro- cured and sown. Cultivated plants, of course, had only a small chance to exhibit new qualities, as they have been so strictly controlled during so many years. Moreover their purity of origin is in many cases doubtful. Among the wild plants only those could be expected to reward the investi- gator which were of easy cultivation. For this reason | have limited myself to the trial of wild plants of Holland, and have had the good fortune to find among them at least one species in a state of mutability. It was not really a native plant, but one probably introduced from America or at least belonging to an American genus. It was the great evening-primrose or the primrose of Lamarck. A strain of this beautiful species is growing on an abandoned field in the vicinity of Hilversum, at a short distance from Amsterdam. Here it has escaped from a park, and multi- plied. In doing so it has produced, and is still producing, quite a number of new types, some of which may be con- sidered as retrograde varieties, while others evidently are of the nature of progressive elementary species. 344 DARWINISM TO-DAY. “This interesting plant has afforded me the means of ob- serving directly how new species originate, and of studying the laws of these changes. My researches have followed a double line of inquiry. On one side, I have limited myself to direct field observations, and to trials of seed, collected from the wild plants in their native locality. Obviously the mutations are decided within the seed, and the culture of young plants from them had no other aim than that of ascertaining what had occurred in the field. But then the many chances of destruction that threaten young plants in a wild state could be avoided in the garden, where environ- mental factors can be controlled. “My second line of inquiry was an experimental repetition of the phenomena which were only partly discerned at the native locality. It was not my aim to intrude into the process, nor to try to bring out new features. My only ob- ject was to submit to the precepts just given concerning pure treatment, individual seed-gathering, exclusion of crosses, and accurate recording of all the facts. The result has been a pedigree which now permits of stating the rela- tion between all the descendants of my original introduced plant. This pedigree at once exhibits the laws followed by the mutating species. The main fact is, that it does not change itself gradually, but remains unaffected during all succeeding generations. It only throws off new forms, which are sharply contrasted with the parent, and which are from the very beginning as perfect and as constant, as narrowly defined, and as pure of type as might be expected of any species. “These new species are not produced once or in single individuals, but yearly and in large numbers. The whole phenomenon conveys the idea of a close group of mutations, all belonging to one single condition of mutability. Of course this mutable state must have had a beginning, as it must sometime come to an end. It is to be considered as a OTHER THEORIES OF SPECIES-FORMING. 345 period within the life-time of the species, and probably it is only a small part of it.” The following paragraphs and diagram quoted from Morgan * give an admirably concise statement of the actual details of the primrose mutations observed by de Vries. “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 Morgan’s : : account ofde Fiilversum, near Amsterdam, a locality where Meee experi a number of plants of the evening primrose, , CEnothera lamarckiana, grow in large numbers. This plant is an American form [native to the Southern United States] that has been imported into Europe. It often escapes from cultivation, as is the case at Hilversum, where for ten years it has been growing wild. Its rapid increase in numbers in the course of a few years may be one of the causes that have 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 thivee, years. “A year after the first finding of these plants de Vries observed two well-characterised forms, which he at once recognised as new elementary species. One of these was O. brevistylis, which occurred only as female plants. The other new species was a smooth-leafed form with a more beautiful foliage than O. lamarckiana. This is O. levtfolia. It was found that both of these new forms bred true from self-fertilised 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 O. la- marckiana, were collected, and from these plants there have 346 DARWINISM TO-DAY. arisen the three groups or 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 O. lamarckiana form. The accompanying table CENOTHERA LAMARCKIANA., ELEMENTARY SPECIES. GENERATION. Gigas Albida. Oblongata. Rubriner- vis ana. Nannella. Scintillans. | Lamarcki- Lata. is) ~ Lan ee © Daan te 8 Gener. 1,700 1899 ~- annual a ME eer egrie 7 Gener. 9 O 3,000 II 1898 - / annual WE os eeniea ee 6 Gener. II 29 4. Efe = 5 1897 o> yi J annual Vi adeeuesed ey 5 Gener. a5 135° 20 3,000 “46. S427 @ 1896 ' ~- 4 annual EN 2s euendees 4 Gener, I 45 1x76 S$ 34,000 *60.. 94 I 1895 a a J annual Rit as ane ek 3 Gener. tr 10,000 4 4 1890-91 ‘ ~ / biennial EO ER see mee 2 Gener. 15,000 5 5 1888-89 \ np / biennial aoe ys arr Fee 1 Gener. 9 1886-87 biennial tu ~ fe) - shows the mutations that arose between 1887 and 1899 from these plants. The seeds were selected in each case from self-fertilised plants of the /amarckiana form, so that the new plants appearing in each horizontal line are the descendants in each generation of /amarckiana parents. It will be observed that the species, O. oblongata, appeared again and again in considerable numbers, and the same is OTHER THEORIES OF SPECIES-FORMING. 347 true for several of the other forms also. Only the two species, O. gigas and QO. scintillans, appeared very rarely. “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 arti- ficially fertilised with pollen from the flowers on the same plant, or of the same kind of plant, they gave rise to forms like themselves, thus showing that they are true elementary species.* It is also a point of some interest to observe that all these forms differed from each other in a large number of particulars. “Only one form, O. scintillans, that appeared eight times, is not constant as are the other species. When self- fertilised its seeds produce always three other forms, O. scintillans, O. oblongata, and O. lamarckiana. It differs in this respect from all the other elementary species, which mutate not more than once in ten thousand individuals. “From the seeds of one of the new forms, O. levifolia, col- lected in the field, plants were reared, some of which were O. lamarckiana and others O. levifolia. They were allowed to grow together, and their descendants gave rise to the same forms found in the /amarckiana family, described above, namely, O. lata, elliptica, nannella, rubrinervis, and also two new species, O. spatulata and leptocarpa. “In the /ata family only female flowers are produced, and, therefore, in order to obtain seeds they were fertilised with pollen from other species. Here also appeared some of the new species already mentioned, namely, albida, nannella, lata, oblongata, rubrinervis, and also two new species, ellip- tica 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, * O. lata is always female, and cannot, therefore, be self-fertilised. When crossed with O. lamarckiana there is produced fifteen to twenty per cent. of pure Jata individuals. 348 DARWINISM TO-DAY. 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 culti- vation, and that they arise year after year from the seeds of the parent form, O. lamarckiana.” Since the publication of de Vries’s theory and the data and considerations on which it is based (these considera- tions including an unusually keen and effective Attitude of a pce i naturalists to- Criticism of the Darwinian factors of species- ward the muta- forming) a great deal of discussion of the tions theory. : ; theory has been indulged in. On the whole the theory has been warmly welcomed as the most promis- ing way yet presented ** out of the difficulties into which biologists had fallen in their attempts to explain satisfactorily the phenomena of the origin of species through Darwinian selection. And especially has been welcomed the fruitful idea of unit species characters, and of the indivisibility and the distinctness of such characters in inheritance. But with all the interest aroused by de Vries’s presentation of his theory, and with all the eager scrutiny of species and records of species-appearing an output of new evidence amazingly small (when one stops to consider the publicity gained for the theory itself and its obvious need of more confirmatory data of observation and experiment) has resulted. Even though the answer may be that experiment takes time, the lack of new observational evidence of the occurrence of mutations,’* and of the origin of new species through muta- tions in nature, is significant. It is my belief that a reaction against the curiously swift and widespread partial to com- plete acceptance of the mutation theory as the sufficient ‘“‘way out” of our troubles to explain the origin of new species will soon occur. (See notes 24, 25, and 26, the appendix of this chapter, for references to certain recent criticisms of the mutation theory.) OTHER THEORIES OF SPECIES-FORMING. 349 In closing this confessedly inadequate consideration of the important work and theorising of de Vries we should not fail to note that the mutations theory is Weeroe. in strong contrast to any theory of species- trasted with forming based on Lamarckian principles in that Lamarckism. : : : ; the newly appearing differences in organisms leading to the establishment of new species are purely con- genital: that is, the mutations arise in one or both of the sex cells and only later appear in the adult organism. There is no question of the transference to the germ-cells of changes induced in the soma by use or disuse or functional stimulus in such a way as to result in the photographic reappearance of these changes in the offspring. Mutations are true congenital or blastogenic variations. “The muta- tion theory,” well says Conklin,”’ “is a theory of the evolu- tion of organisms through the evolution of their germ-cells.” The mutations theory is also in sharp contrast to the theory of species-forming by geographical isolation (see chapter ix). According to de Vries many dis- Mutations : : ee : theory contrasted tinct species (de Vriesian elementary species) eee can and do exist side by side in the same range. In fact they “are found to be heaped up in the centre of their area of distribution, but are more scattered at the periphery.” ** Now according to Wagner, Gulick, and Jordan two closely allied species, 7. ¢., stock and off- shoot, are found practically never to inhabit the same range, except in those cases where a migration of one type into the territory of the other has taken place after the differ- entiation has been effected (by previous segregation). It would carry us into too extended a discussion to at- tempt to sum up here the pertinent criticism that has been directed against the mutations theory. As already indicated, there is plenty of it and of distinctly non-negligible char- acter. But just now it seems to me sufficient simply to call attention to the extreme meagreness in quantity of the real 350 DARWINISM TO-DAY. scientific evidence for the theory as a theory capable of ex- plaining species-forming as a whole. There is probably no gainsaying the actuality of the occurrence of certain muta- tions (in de Vries’s sense) nor of their establishment of certain apparently fixed new organic types (de Vries’s elementary species of CEnothera). But this is very far from accepting the mutations theory as a sufficient causal explanation of the origin of the hundreds of thousands of species of animals and plants that are now or were formerly existent. As for the help that the establishment of the mutations theory would give those biologists who reject the natural 1 ; : 29 Morgan's sufn- selection theory of species-forming, Morgan mation ofthe writes as follows, summing up the advantages advantages of am sonra ae of the theory: theory, “rt. 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 muta- tions 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 foot- hold. 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. “2. If the time of reaching maturity in the new form is different from that in the parent forms, then the new species will be kept from crossing with the parent form, and since this new character will be present from the beginning, the new form will have much better chances of surviving than if a difference in time of reaching maturity had to be gradu- ally acquired. = ‘OTHER THEORIES OF SPECIES-FORMING. 351 “4. The new species that appear may be in some cases already adapted to live in a different environment from that occupied by the parent form; and if so, it will be isolated from the beginning, which will be an advantage in avoiding the bad effects of intercrossing. “cs. 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.” Finally, the attention of students especially may be called to Bateson’s interesting suggestion that mutations mav be Beeontanae: simply pure Mendelian recessives appearing gestion that mu- atter a crossing. It would take us too far ret oa: afield to attempt to explain here to readers. cessives, unacquainted with the Mendelian principles of inheritance just how Bateson’s suggestion has a certain plausibility. It must suffice to say that Mendel, and after him a considerable number of present-day students of heredity, have shown that after a crossing between two individuals sharply contrasting in regard to some particular character, as colour of hair, all the offspring of the first generation may agree in showing but one of the two parental colours (the dominant), but that if these first generation offspring are bred to each other, or to similarly produced in- dividuals, the members of the second generation will split up as regards the character in question, some showing one of the grand-parental hair colours, and the rest showing the: other one. Now breeding likes together, it would be shown in third generation groups that one of these colours, and, namely, that one called the recessive, which did not appear: at all in the first generation, will always henceforth breed true while the other colour may or may not breed true (de-- 352 DARWINISM TO-DAY. pending on whether in making the matings pure dominants or cross-bred dominants happen to be used). Thus the sudden appearance in the second generation of the latent or recessive characteristic, and its breeding true, are occur- rences which might readily be interpreted as the appearance of a mutation or true-breeding sport by an observer unac- quainted with the ancestry of the individuals under his eye. Alternative Theories to Explain Secondary Sexual Char- acters.—Before closing this discussion of theories which have been proposed as substitutes for the Darwinian selec- tion theories to explain the actual conditions in the organic world as we see it to-day, and as we know it to have been in past ages, we should mention, at least, the few attempts to formulate a substitute explanation for the existence of secondary sexual characters. The discrediting of the sexual selection theory as such an explanation is certainly nearly complete. But it is interesting to note how lame and uncon- vincing are the proposed substitute explanations. The first, and most appealing one, is the explanation that the extra plumes, wattles, horns, the unusual display of bright colours, etc., of the males are simply the Extra growths manifestations of an extra growth-force or the result of ‘ oe ; : extravigour, Vigour exhibited by the male in the breeding season. The female also may be endowed with extra growth-vigour at this time, but it goes, in her case, to the formation of ova, to the storing up of food in or around the egg cells. The songs, the dances, the violent play and antics of the males common to many species of birds, insects, spiders, etc., are also attributed to this special or sexual vigour. Now while such secondary sexual characters as colour, plumes, wattles, etc., might perhaps well enough seem to be the outcome of an extra growth-vigour, what about such special male characters as the stridulating organs of male katydids and crickets, and other similar complex, highly OTHER THEORIES OF SPECIES-FORMING. 353 perfected, adaptive structures? A male cricket has the veins at the base of one wing-cover curiously and com- plexly modified in course and in superficial structure, while the veins of the other wing-cover are also modified in a way differing from but exactly correlated with the venation of the first wing, the whole specialisation resulting in a com- bination of file, scraper, and vibrating membrane to form the effective musical instrument of the insect. Can such an adaptive structural modification be conceived to be a sudden bursting forth or result of superabundant growth-force? And many of the secondary sexual characters are of this class of ¢omplex adaptive specialisations. The growth- force explanation can, at best, explain but few of the various categories of sexual dimorphism. Some explanation more directive in its character is needed for these others. Even more restricted in its application, and less con- vincing in the assumptions at its very base, is the curious replacement theory of Emery.’” This investi- Emery’s theory ' ‘ , of the origin of ator believes that sexual selection can explain oe but few if any cases of sexual dimorphism, and would explain these other cases largely by the sudden appearance (mutation or sport) of a second form of male or female, the persistence for a while of the two forms side by side, as now exemplified by numerous dimor- phic or polymorphic (or di- or polychromatic) species, and then the gradual or sudden dying out (killing out by selec- tion?) of the older original form (the one resembling the other sex), thus leaving the once dimorphic sex represented only by the newer aberrant form. While such an explana- tion may possibly explain a few cases of extreme sexual dimorphism or dichromatism, it certainly will not do for the many cases of secondary sexual difference constituted by the existence in one sex of some one or few particular adaptive specialisations for music-making, scent-producing, or weapon-forming, not possessed by the other sex. 354 DARWINISM TO-DAY. Cunningham ** (and also at about the same time Wigles- worth) in 1898 suggested, on a neo-Lamarckian basis, that . secondary sexual characters were due to the peas are stimulation of parts through use or external secondary sexual violence or irritation. Cunningham would ex- characters, ‘ : ‘ a plain all adaptations as derived from variations actually induced by responses or reactions to the environ- ment. His theory of the origin of secondary sexual char- acters would simply be the explanation of the adaptive dif- ferences between two individuals of a species on the same basis as the explanation of the adaptive differences between individuals of different species. His argument is summed up as follows: “Selection assumes the occurrence of varia- tions; the variations must either be similarly indefinite and promiscuous in all cases, or they must be different in differ- ent cases—that is, in different species, different sexes, dif- ferent stages of life. If they are different in different cases, then selection is a very unimportant matter, for the chief questions are evidently what are the differences and what made them differ. To deny that the variations have always been different in different cases is to deny the most evident facts; such denial might be possible when we consider only the difference between species, but it is impossible when we study the differences between the sexes in the same species and between different stages in the same individual. In all cases the variations correspond to differences in habits and mode of life, and in many cases are of the same kind as the changes known to be produced in the individual by special stimulation or special activity of organs; this is true of many and probably of all cases of adaptation. The gen- eral conclusion is that adaptation is not produced indirectly by the selection from indefinite variations, but directly by the influence of stimulation in modifying the growth of the parts or organs of the body.” Wallace * has suggested that the differences in color- rec OTHER THEORIES OF SPECIES-FORMING. = 355° ation between males and females are due largely to the necessity of the better protection of the young wataoe's producing and (in the case of birds and mam- suggestion, ‘ : mals) young protecting and caring for female, and hence the acquirement on her part of a dull incon- spicuous protective colour-pattern. Wallace’s large ac- quaintanceship with birds and butterflies enables him to illustrate his theory by many apparently confirmatory ex- amples, but as soon as one stops to consider the matter thoughtfully the impossibility of the general or even wide application of this explanation of secondary sexual char- acters is at once apparent. It is necessarily limited to one single category of sexual differences. Barrett-Hamilton ** has noted that both sexes of the sal- mon (Onchorhynchus) become markedly discoloured during the spawning season. The discoloration is accompanied by overgrowth or hypertrophy, especially of the jaws. “I can- not believe,” he says, “that this is of an esthetic nature, since these phenomena terminate in the death of the fish. They seem to be, in fact, merely the outward symptoms of what, as I have persuaded myself from personal observation in Kamschatka, is a pathological condition accompanying, and perhaps resulting from, the growth of the ova and milt. I regard the whole metamorphosis as a purely excretory phenomenon resulting from the upsetting of the metab- olism due to the concentration of the whole vital force on the effort to produce the greatest possible amount of spawn. “May not such a state of things be invoked to explain the nuptial changes of our own salmon so strangely assumed before and lost after the breeding-season? Is it not possible that in the phenomena displayed by the spawning Oncho- rhynchus we may have a clue to the origin of the hitherto inexplicable temporary and permanent sexual characters of the vertebrates and even of some invertebrates, of which 356 DARWINISM TO-DAY. it may be that the origin has been primarily excretory and only secondarily protective or zsthetic ?” The plain truth is that the satisfactory, all-explaining ex- planation of secondary sexual characters and sexual dimor- phism as a whole is yet to be formulated. APPENDIX. 1 At some time between 1855 and 18605, Gregor Johann Mendel, an Augustinian monk in the small Austrian village of Brunn, car- Mendel and ried on pedigree cultures of peas and some other his work. plants in the gardens of his cloister. From this work he derived data that he read, together with his interpretation of their significance, before meetings of the Natural History Society of Briinn, and which, in the same year of their reading, 1865, were published under the title “Experiments in Plant-hybridisation,” in the Abhandlungen (Vol. IV.) of the society. Mendel was the son of a peasant and had been educated in Augustinian foundations and ordained priest. For two or three years he studied physics and natural science in Vienna, and refers to himself as a student of Kollar. He became Abbot of his cloister, and was for a time president of the Brtinn Natural History Society. Such are the essential details of the education and situation of the man whose name will undoubtedly live forever in the annals of biological science. For the observations, experiments, and conclusions of Mendel on inheritance have taken their place already as matters of fundamental importance in the study of heredity. It would take us too far afield even to outline Mendel’s work and derived “princi- ples of heredity,” but the interested reader can find an admirable exposition and discussion of them (together with translations of Mendel’s own papers) in Bateson’s ‘““Mendel’s Principles of Hered- ity,’ 1902. For an excellent exposition of Mendel’s work and other similar work by botanists, see Lotsy, J. P., ‘““Vorlesungen tuber Descendenz- theorien,” Vol. I, chap. viii, 1906. Cuenot, in L’Année Biologique, Vol. VII. for 1902, pp. 58-77, gives an excellent review of the work of Mendel, de Vries, Cor- rens, and Tschermak; and a bibliography, relating to the so-called Mendelian laws of the principles of heredity. Bateson, in ““Progressus rei Botannicae,” Vol. I, pp. 368-468, 1907, gives a complete abstract of the nature of the work and its results which has been done on the Mendelian problem from the time of OTHER THEORIES OF SPECIES-FORMING. o57 Mendel to the present. The bibliography in connection with this paper is practically complete up to the date of its making. ? Correns, C. G., “Uber Levkoyen-Bastarde, zur Kenntniss der Grenzen der Mendel’schen Regeln,” Botan. Centralbl., LXXXIV, References to P- 97, 1900; “Uber Bastarde zwischen Rassen von recent workon Zea Mays,” Ber. Deut. Bot. Ges., XIX, 211 (1901) ; Mendelism. “Bastarde zwischen Maisrassen, Bibliotheca Bota- nica,’ Heft 53, 1001; “Uber Bastardirungs-Versuche mit Mirabilis- Sippen,” Ber. Deut. Bot. Ges., XX, 594-608, 1903. *T. E. Tschermak, “Uber kiinstliche Kreuzung bei Pisum sati- vum,” Zeitschr. f. d. Landwirthsch. Versuchswesen, III, 465-555, 1900; “Weitere Beitrage iiber Verschiedenswerthigkeit der Merkmale bei Kreuzung von Erbsen und Bohnen,” ibid. IV, 641 ff., 1901; “Uber Ztchtung neuer Getreiderassen mittelst kunstlicher Kreuzung,” ibid.. IV, 1902. ‘Die Theorie der Kryptomerie und des Kryptohybridismus,” Beihefte z. Bot. Centralbl., XVI, 25 pp., 1903; “Weitere Kreuzungsstudien an Erbsen,” Zeitschrift f. d. Landwirth- Versuchswesen in Oesterr., 106 pp., 1904. *See Darwin, “Animals and Plants Under Domestication,” Vol. I, chap. ili, p. 104. “In some few instances new breeds [of sheep] Darwih ov have suddenly originated; thus in 1791 a ram-lamb was race origin from born in Massachusetts, having short crooked legs and sports. a long back, like a turnspit dog. From this one lamb the otter, or ancon, a semi-monstrous breed, was raised; as these sheep could not leap over the fences it was thought that they would be valuable; but they have been supplanted by merinos, and thus exterminated. The sheep are remarkable from transmitting their character so truly that Colonel Humphreys never heard of ‘but one questionable case’ of an ancon ram and ewe not producing ancon offspring. When they are crossed with other breeds the offspring, with rare exceptions, instead of being intermediate in character, perfectly resemble either parent; even one of twins has resembled one parent and the second the other. Lastly, ‘the ancons have been observed to keep together, separating themselves from the rest of the flock when put into enclosures with other sheep.’ “A more interesting case has been recorded in the Report of the Juries for the Great Exhibition (1851), namely, the produc- tion of a merino ram-lamb on the Mauchamp farm, in 1828, which was remarkable for its long, smooth, straight, and silky wool. By the year 1833 M. Graux had raised rams enough to serve his whole flock, and after a few more years he was able to sell stock of his new breed. So peculiar and valuable is the wool, that it sells at 25 per cent. above the best merino wool: even the fleeces of half- bred animals are valuable, and are known in France as the 358 DARWINISM TO-DAY. ‘Mauchamp-merino. It is interesting, as showing how generally any marked deviation of structure is accompanied by other devia- tions, that the first ram and his immediate offspring were of small size, with large heads, long necks, narrow chests, and long flanks, but these blemishes were removed by judicious crosses and selec- tion. The long smooth wool was also correlated with smooth horns; and as horns and hair are homologous structures, we can under- stand the meaning of this correlation. If the Mauchamp and ancon breeds had originated a century or two ago, we should have no record of their birth; and many a naturalist would no doubt have insisted, especially in the case of the Mauchamp race, that they had each descended from, or been crossed with, some unknown aborig- inal form.” The Paraguay cattle are a hornless race which is composed of the descendants of a hornless bull which was born in Paraguay in 1770. A recent interesting case wholly parallel with those just recorded, is that of the Polled Herefords originating in 1889 in Kansas, U. S. A. (see Guthrie, W. W., “History of Polled Herefords,” in Proc. Am. Breeders’ Assoc., Vol. Il, pp. 93-95, 1906). “In the fall of 1889, W. W. Guthrie. Sr., of Atchison, Kansas, now deceased, discovered among the calves that had been weaned at his ranch in Chase County, Kansas, one with Here- A recent ex- : ; : ample of race ford markings which was perfectly polled. In his origin from a herd were purebred Shorthorn as well as purebred sport in cattle Hereford cows. Two purebred Hereford bulls were at the head of the herd. This calf was the product of a three- quarter Hereford and one-quarter Shorthorn cow by one of the two purebred Hereford bulls, Grateful 3d, No. 8,001, and Treasurer, No. 10,585. Discovery, as the calf was subsequently named, was a well-formed animal, with a good loin, and well-developed hind- quarters, and had the Hereford colour and markings, with body more on the type of the Shorthorn. At three years of age he weighed, without special feeding, 1,986 lbs. “It then occurred to Mr. Guthrie that by using this animal he might in time establish a herd of polled Herefords, and that the experiment was at least worth trying. Shortly afterwards, he happened to meet on the train Chancellor Snow, of the Kansas State University, on his way to lecture before the Atchison High School on evolution, and during their several hours conversation discussed with him the proposition of animal architecture. The Chancellor agreed that the proposition of establishing a polled Hereford herd was one worth considering, and Mr. Guthrie deter- mined to carry out his ideas along this line. eo ert OTHER THEORIES OF SPECIES-FORMING. 359 “When Discovery matured it was found that his calves from horned cows were all hornless. In 1893, a two-year-old bull and six heifers were selected and brought to Atchison County, where the experiment was carried on under the personal supervision of Mr. Guthrie and with very encouraging results. “On October 31, 1898, Mr. Guthrie purchased at the Kansas City Scott & Whitmann sale four purebred Hereford heifers. The calves from these horned heifers by a descendant of Discovery were found to be in every instance polled, only two showing scurs, scarcely noticeable, and loose in the skin. A number of purebred Hereford heifers were later obtained from the Funkhouser herd, and still later others from the Armour herd, and equally good results were obtained. ; “Eight head of polled Herefords were exhibited by Mr. Guthrie at the Omaha Exposition, and, while these animals did not present the finished appearance of modern show cattle, not having been forced from date of birth, they attracted such attention that articles on the herd were published in the newspapers and periodicals throughout this country, and even in such far-away lands as Aus- tralia and New Zealand. : “The desirability of Herefords without horns, the one objection which Hereford breeders had been willing to admit, becoming appa- rent, other Hereford breeders began to take notice of an occasional polled calf, freaks of nature as they were considered, appearing in their herds, and Soon a brisk demand for polled bulls developed, animals being shipped as far north as South Dakota, and Wiscon- sin, and as far south as Texas. Breeders in many instances have reported that in their horned herds, after several years’ breeding. not a single calf had come with horns, and only occasionally would slight scurs, loose in the skin, appear.” ... “In December, 1904, four head of polled Herefords from West Virginia were exhibited at the International Live Stock Show at Chicago in connection with horned Herefords, and during the past season a larger number from the same State were exhibited through- out the eastern circuit of fairs. At the American Royal Cattle Show at Kansas City, last October, seven head from the original herd were exhibited. As a result of these exhibits, many horned Hereford breeders are now turning their attention to the subject of breeding Herefords without horns, and so great has become the demand for animals with which to start polled herds that at the last meet of the National Polled Hereford Breeders’ Association it was found that the members were unable to supply enough young bulls to meet the demand. . “Quite a number of purebred Hereford calves, termed ‘freaks’ 360 DARWINISM TO-DAY. or ‘sports,’ have been dropped in this country, and some have been kept. The President of the National Polled Hereford Breeders’ Association has a perfectly polled cow, the produce of one of his purebred horned Hereford cows by a purebred horned Hereford bull, and has lately purchased a purebred polled Hereford bull. The original herd now contains two polled males and a number of polled females, descended direct from purebred Herefords. The above animals are registered in the American Hereford Record. “During a trip through England several years ago, Mr. Guthrie made inquiry among Hereford breeders and found that, while an occasional polled animal had been calved, they were considered as. freaks of nature by the owners and butchered.” °> Bateson, Wm., ‘Materials for the Study of Variation,” 1894. ° K6lliker, A. von, “Uber die Darwin’sche Schdpfungstheorie,” Zeitsch. f. wiss. Zool., Vol. XIV, pp. 174-186, 1864. Dall, Wil, 1s77. ® Galton, Francis, ‘“Natural Inheritance,” p. 32, 1889. ® Galton, Francis, loc. cit. p. 27, “‘The distinction between primary Galton's dis) and subordinate positions of stability will be made cussion of spe- clearer by the help of Fig. 1, which is drawn from a cific stability. model I made. The model has more sides, but Fig. 1 suffices for illustration. It is a polygonal slab that can be made to stand on any one of its edges when set upon a level table, and is B A Cc B D Cc FIG. I intended to illustrate the meaning of primary and _ subordinate stability in organic structures, although the conditions of these must be far more complex than anything we have wits to imagine. The model and the organic structure have the cardinal fact in com- mon, that if either is disturbed without transgressing the range of its stability, it will tend to reéstablish itself, but if the range is overpassed it will topple over into a new position; also that both of them are more likely to topple over towards the position of primary stability, than away from it. “The ultimate point to be illustrated is this. Though a long established race habitually breeds true to its kind, subject to small a OTHER THEORIES OF SPECIES-FORMING. 361 unstable deviations, yet every now and then the offspring of these deviations do not tend to revert, but possess some small stability of their own. They, therefore, have the character of sub-types, always, however, with a reserved tendency, under strained condi- tions, to revert to the earlier type. The model further illustrates. the fact that sometimes a sport may occur of such marked pecu- liarity and stability as to rank as a new type, capable of becoming the origin of a new race with very little assistance on the part of natural selection. Also, that a new type may be reached without any large single stride, but through a fortunate and rapid succession of many small ones. “The model is a polygonal slab, the polygon being one that might have been described within an oval, and it is so shaped as to stand on any one of its edges. When the slab rests, as in Fig 1, on the edge A B, corresponding to the shorter diameter of the oval, it stands in its most stable position, and in one from which it is. equally difficult to dislodge it by a tilt either forwards or back- wards. So long as it is merely tilted it will fall back on being left alone, and its position when merely tilted corresponds to a simple deviation. But when it is pushed with sufficient force, it will tumble on to the next edge, B C, into a new position of stability. It will rest there, but less securely than in its first position; moreover, its range of stability will no longer be disposed symmetrically. A com- paratively slight push from the front will suffice to make it tumble back, a comparatively heavy push from behind is needed to make it tumble forward. If it be tumbled over into a third position (not shown in the figure), the process just described may recur with exaggerated effect, and similarly for many subsequent ones. If, however, the slab is at length brought to rest on the edge C D, most nearly corresponding to its longest diameter, the next onward push, which may be very slight, will suffice to topple it over into an entirely new system of stability; in other words, a ‘sport’ comes suddenly into existence. Or the figure might have been drawn with its longest diameter passing into a projecting spur, so that a push of extreme strength would be required to topple it entirely over. “If the first position, A B, is taken to represent a type, the other portions will represent sub-types. All the stable positions on the same side of the longer diameter are subordinate to the first position. On whichever of them the polygon may stand, its principal tendency on being seriously disturbed will be to fall back towards the first position; yet each position is stable within certain limits. “Consequently, the model illustrates how the following cond:- tions may co-exist: (1) variability within narrow limits without prejudice to the purity of the breed; (2) partly stable sub-types ; 362 DARWINISM TO-DAY. (3) tendency, when much disturbed, to revert from a sub-type to an earlier form; (4) occasional sports which may give rise to new types.” *° Emery, C., “Gedanken zur Descendenz- und Vererbungstheorie,” Biolog. Centralbl., Vol. XIII, pp. 397-420, 1893. *? Korschinsky, S., ‘Heterogenesis und Evolution,” Naturw. Wochenscrift, Vol. XIV, pp. 273-278, 1899; also “‘Heterogenesis u. Evolution,” Flora, oder Alig. Bot. Zeit., Erganzungsbd. 89, pp. 240- 368, IQOI. 7? De Vries, H., ‘Die Mutationstheorie,” Vol. I, 1901, Vol. II, 1903. Blecaioss te at De Werres, H., “Species and Varieties, Their discussions by Origin by Mutation” (ed. by MacDougal), 1905. de Vries of spe- “De Vries, H., “Die Mutationstheorie,” Vol. I, cies-forming, p. 150, I90I. *® De Vries, H., “Die Mutationstheorie, Vol. I, p. 362, I9go1. *® De Vries. H., “Species and Varieties,” p. 6. *7 De Vries, H., ‘Species and Varieties,” pp. 8-9. *® De Vries, H., ‘Species and Varieties,” p. Io. *® De Vries, H., “Species and Varieties,” p. 13. *° For an excellent exposition and discussion of the de Vries muta- tion theory and mutations, see Lotsy, J. P., ““Vorlesungen uber De- scendenztheorien,” Vol. I, chaps. xiv and xv, 1906. ** Morgan, T. H., “Evolution and Adaptation,” pp. 294-295, 1903. ** As evidence of the interest and favour with which American biologists have received the theory, the six addresses on “the muta- pee yo tion theory of organic evolution” delivered before the opinion ofthe | American Society of Naturalists at Philadelphia, mutations December 28, 1904, may be especially referred to. theory, These addresses by naturalists distinguished for their work in different phases of biology, as systematic and cecologic botany, cytology, human anatomy, animal cecology, etc., are printed in Science, N. S., Vol. XXI, pp. 521-543 (April 7, 1905), and from them I quote various paragraphs indicating some of the points of view of the speakers and some of the arguments advanced in favour of the theory. “On the whole, it appears that the formation of new breeds be- gins with the discovery of an exceptional individual, or with the production of such an individual by means of cross-breeding. Such exceptional individuals are mutations” (Castle, p. 524). “Modification of character by selection, when sharply alternative conditions (2. e., mutations) are not present in the stock, is an exceeding difficult and slow process, and its results of questionable permanency. Even in so-called ‘improved’ breeds, which are sup- o OTHER THEORIES OF SPECIES-FORMING. 363 posed to have been produced by this process, it is more probable that the result obtained represents the summation of a series of mutations rather than of a series of ordinary fluctuating variations. For mutations are permanent: variations transitory” (Castle, p. 524). “Tt is to my mind impossible to find any support for a theory of evolution by minute changes from the study of anatomical varia- tions. I should not venture to say, on the other hand, that they give any direct support to the theory of mutation: but, at least, they are not in disaccord with it” (Dwight, p. 532). “Tt seemed necessary to discuss ethological characters at some length for the purpose of vindicating their importance. Having attempted this, I may say that these characters seem to me to offer even fewer difficulties than the morphological characters to the acceptance of the mutation theory, for the reason that the ethological and psychological processes are conceived primarily as qualities and not quantities. Thus the psychical elements, 7. ¢., the simple feelings, cravings, and sensations, are disparate qualitative processes which cannot be derived from one another or from some more undifferentiated process. This is still more evident in the case of the complex psychical phenomena. Similarly, instincts, with which ethology is most concerned, when resolved into their simplest com- ponents are seen to consist of discrete reactions which cannot be shown to arise from one another. Although, on the other hand, the measurable intensities and durations of the reactions are anal- ogous to the fluctuating structural variations, it is even more difficult for the psychologist to conceive of a particular feeling, craving, or sensation as arising from the greater or less intensity or dura- tion of some other psychic process, than it is for the morphologist to conceive of the origin of new characters from the fluctuating variations of structure’ (Wheeler, p. 539). “Mutation is even more urgently demanded for the explanation of many other instincts, especially those of symbiotic and parasitic species and of species with profound and sudden metamorphosis. In these cases, a particular activity, on which most often depends the life of the individual or of its progeny, has to be performed with a high degree of proficiency at its very phylogenetic incep- tion or it can be of no advantage to the individual or the race. Such cases, with which you are all familiar, have ever been the insurmountable obstacle to the evolution of instincts on the theory of fluctuating variations and natural selection. The theory of organic selection seems to me merely to conceal but not to over- come the difficulties. The mutation theory frankly avoids the diffi- culties even if it fails to throw any light on the origin of the muta- 364 DARWINISM TO-DAY. tions and bundles this into the germ-plasma. It is, of course, no objection to the theory that it leaves something under the heavens to be accounted for. This is rather to be regarded as one of its chief virtues. As working naturalists we have reason to be most sus- picious of the theories that explain everything’ (Wheeler, pp. 539- 540). “In view of the amount of orderly and- well-authenticated evi- dence now at hand, it may be regarded as demonstrated that char- acters, of appreciable physiological value, originate, appear in new combinations or become latent, in hereditary series of organisms, in such a manner as to constitute distinct breaks in descent” (Mac- Dougal, p. 540). 23 Some of de Vries’s experiments and observations on the La- marck primrose have been repeated (with naturally some variation) in the New York Botanic Garden, by MacDougal and assistants. See MacDougal, D. T., “Mutation in Plants,” Amer. Nat., Vol. XXXVII, pp. 737-770, 1903; also, “Mutants and Hybrids of the CEnotheras,’ by D. T. MacDougal, assisted by A. M. Vail, G. H. Shull, and J. K. Small, Pub. No. 24, Carnegie Inst. of Wash., 1905. I am aware of the rather sweeping statements made by some biologists touching the probability of the origin by mutation of many species, or at least, races of animals and plants. For example, Castle (Science, N. S., Vol. XXI, p. 522; 1905) says:—"So far, however, as these varicus sorts of evidence go, they indicate that the material used by breeders for the formation of new breeds con- sists almost exclusively of mutations.’ And Davenport (Science, N. S., Vol. XXII, p. 372, 1905) says: “Undoubtedly many, if not most, of the characteristics of the races of domesticated animals and probably feral species have arisen by mutation.” He then refers, as example, to the qualities that differentiate the races of poultry— feathered feet, rose comb, elongated tail, taillessness, silky feathers, frizzled feathers, cerebral hernia, polydactyl feet, albinism, and many others. But I have been assured by Luther Burbank, the most experienced and distinguished plant breeder in this country, that the many races of plants actually produced by him have not been derived from mutations. But on the contrary, that the selec- tion of small variations—a special abundance and variety of these variations usually being induced by hybridisation and by change of environment—has been his almost exclusively relied-on means for producing new forms of plants. As a matter of fact the cases. actually adduced by upholders of the de Vriesian theory as supports for it are astonishingly few. Castle (Science, N. S., Vol. XXI, pp. 522-523, 1905) calls attention to the sudden appearance of a super- oo. ie OTHER THEORIES OF SPECIES-FORMING. 365 numerary fourth digit on one of the hind feet of one of nine young produced by a certain pair of guinea-pigs. ‘Neither of the parents had such a digit, nor had I ever heard of the existence of such a character before, either in any of the wild Caviede or among domes- ticated cavies or guinea-pigs. Further, I have been able to find no reference to such a thing in the literature of the group, though I have several times simce found this same mutation in other herds of guinea-pigs. The mother of my four-toed pig never produced another similar individual, though she was the mother in all of thirty young. The father, however, who sired in all 139 young, had five other young with extra toes, but these were all by females descended from himself, so that it seems certain that the mutation had its origin in this particular male. By breeding together the four- toed young and selecting only the best of their offspring, I was able within three generations to establish a race with a well-developed fourth toe on either hind foot. This race was not created by selec- tion, though it was improved by that means.” Castle also had another mutation appear in a second family of guinea-pigs. “A few individuals were found to have hair about twice as long as that of their parents and grandparents. Intermediate conditions did not occur. Long-haired individuals mated together were found to produce only long-haired young, so that a new breed was already fully established without the exercise of any selection.” Casey (Science, N. S., Vol. XXII, p. 308, 1905) presents a number of facts touching the sudden appearance of certain molluscous genera in early Eocene strata, and in certain Lower Oligocene rocks, which seem to be evidence for the mutations theory. “At least, the mutation theory is evidently the best that has been advanced to account for these known facts.” Scott (Science, N. S., Vol. XXII. pp. 271-282) attempts to make out a case for the mutational origin of nine kinds of North American birds that, because of their rarity and the obscure character of the records of their occurrence, are mostly rather puzzling to ornithologists. (They are all included in the “hypothetical list” of the American Ornithologists’ Union Check-List.) But this attempt is robbed of much significance by Allen’s critical discussion of it (Science, N. S., Vol. XXII, pp. 431- 434, 1905). Morgan (Harper’s Monthly Mag., Vol. CVI, p. 478) refers to the “japanned” turkeys, a kind of bronze-shouldered aber- ration that appears occasionally in flocks of turkeys, as “mutations.” These turkeys are called attention to by Darwin (‘Variation of Animals and Plants Under Domestication,” Vol. I, p. 305). Indeed, more cases of such mutations are referred to and described by Darwin himself than by all those who have attempted recently to adduce examples, for the support of the mutations theory, of an 366 DARWINISM TO-DAY. alleged case of sudden appearances of modified animals or plants that seem to breed true. But these infrequent prepotent sports, or discontinuous variations, do little to furnish any convincing foundation for de Vries’s theory. Far better than all of them are de Vries’s own long and carefully observed primrose mutations. Here, besides a few single mutations, were several that appeared in considerable numbers, which is a condition almost imperatively necessary for the successful propagation of a new organic type. A recent record of an alleged case of mutation is Schaffner’s, “A Successful Mutant of Verbena without External Isolation,” in Ohio Naturalist, Vol. VII, pp. 31-34, December, 1906. As Davenport (“The Mutation Theory in Animal Evolution,” Science, N. S., Vol. XXIV, pp. 556-558, November, 1906) puts it: “The real argument for discontinuity in evolution is the occurrence of characteristics in nature that are discontinuous and which never show intergrades. The mere fact of discontinuity between species of the same genus is not sufficient to prove that they have arisen by mutation. It must be shown that the differential characters are in essence discontinuous. The practical way to get at the true nature of characteristics, whether continuous or discontinuous, is by their behaviour in inheritance. If, in cross-breeding, a char- acter tends to blend with the dissimilar character of its consort it must be concluded that the character can be fractionised and inter- grades are possible. If, on the contrary, the characteristic refuses to blend, but comes out of the cross intact, as it went in, the con- clusion seems justified that the characteristic is essentially integral and must have arisen completely formed, and hence discon- tinuously. “Using this criterion, I have of late been testing the application of the mutation theory to animals and have had an opportunity to examine the experiments of others. Some of the work has been done on the characteristics of domesticated ‘races,’ others on wild varieties. There seems to be no difference in the behaviour of characteristics of domesticated and wild varieties. The result is that most characteristics, but not all, fail to blend and are strictly alternative in inheritance. I interpret this to mean that the char- acteristic depends on a certain molecular condition that does not fractionise. The inference is that if the characteristic is incapable of gradations now it has always been so and hence must have arisen without gradations, 7. e., discontinuously. Examples of such discon- tinuous characteristics are the spots in the elytra of certain beetles, the crest on the canary, the form of the comb in poultry, extra toes, black plumage, and colour of iris. One who sees the striking failure of these characteristics and many others to be modified in OTHER THEORIES OF SPECIES-FORMING. 367 any important way will feel convinced that they are not capable of forming intergrades and hence could not have arisen gradu- ally.” 24C, B. Davenport (“Evolution Without Mutation,” Jour. of Exper. Zool., Vol. II, pp. 137-143, 1905), in a recent short paper, adduces facts concerning the variation and evolution Davenport's : : examples of spe- of Pectens, which lead him to conclude that the races cies-origin by of Pecten inhabiting different geographical regions slight continu- are connected so plainly by integrating variations ous change. that there can be no question of mutations in con- nection with their origin. They must have arisen through evolu- tion by trivial variation. Davenport concludes his paper with the following summary: “The process of evolution has taken place by various methods and not always in the same way. It is not more justifiable to maintain that all evolution is by mutation than that evolution has always proceeded by slow stages. The best evidence for slow evolution is found in wide-ranging species which, while differing greatly at the limits of their range, exhibit all gradations in intermediate localities (Melospiza, Pecten); also in fossil series (Pecten eboreus and P. trradians) where the change from one hori- zon to the next is of a quantitative order. Thus evolution may take place without mutation.” Naturalists whose special field of study is systematic and fau- nistic rather than morphologic or experimental, seem to be slow to Mesias find much good in the mutations theory. Indeed, criticism of the some of them seem to be quick to find much that is mutations theory: j]] in it. For example, Merriam and Allen, deans of American faunistic students of birds and mammals, are both strong antagonists of the mutations theory. Merriam, in an address as chairman of the zoological section at the 1905 meeting of the Ameri- can Association for the Advancement of Science (“Is Mutation the Factor in the Evolution of the Higher Vertebrates?” Science, N. S., Vol. XXIII, pp. 241-257, 1906), shows by the use of illustrations drawn from the distribution and taxonomy of American chipmunks and ground squirrels that the mutations theory cannot by any means explain all species-forming. ‘My argument,” says Merriam, “is not that species of plants may not in rare cases arise in perpetu- ation of sport characters, as de Vries believes they do, but admitting this, my contention is that the overwhelming majority of plants, and so far as known, all animals, originate in the generally recog- nised way by the gradual development of minute variations. The theory of origin of species by mutation, therefore, far from being a great principle in biology, as some seem to believe, appears to be one of a hundred minor factors to be considered in rare cases as a ’ 368 DARWINISM TO-DAY. possible explanation of the origin of particular species of plants, but so far as known, not applicable in the case of animals.” Certain naturalists even go so far as to express some doubt about the value of the mutations observed by de Vries in the primroses. This doubt touches two points. First, the possibility that the mutating primroses are not pure cultures, but are hybrids; second, that when an investigation of the wild primroses in their native locality (southern United States) is made it may be found that these primroses in true wild condition do not mutate. Touch- ing these two points, it should be said that de Vries has convinced himself that his cultures are pure, and has tried to discover the actual conditions existent among the primroses in their native habitat. As a matter of fact, the Lamarckian primrose seems to be practically extinct as a wild species. De Vries (“Uber die Dauer der Mutationsperiode bei Gnothera Lamarckiana,” Ber. Deutsch. Bot. Gesell., Vol. XXIII, pp. 382-387, 1905) found specimens of CEnothera Lamarckiana in three botanical collections in the United States. These specimens were collected in Florida and Kentucky. How- ever, since these specimens were taken (the Florida ones in 1860) the species has not been observed, perhaps on account of lack of close observation, perhaps because actually disappeared. There- fore the question whether the Lamarckian primrose mutates in wild condition remains undecided. *° The most considerable critical discussion and analysis of the mutations theory is that made by Plate in his review of Morgan’s Plate’s criti: | Evolution and Adaptation. (Plate, L., “Darwinismus cism ofthe mu- kontra Mutationstheorie,”’ Archiv f. Rassen- und Ge- tations theory. — se//schafts-Biologie, Vol. III, pp. 183-200, 1906.) In the course of his critical review of Morgan’s book (which book is at once an attack on Darwinism and an upholding of the muta- tions theory), Plate points out keenly and strongly the weak places in de Vries’s theory. As a general substitute for the natural selec- tion theory as an explanation of adaptation as well as species-form- ing, the mutations theory is open to many of the same objections as the Darwinian theories. Plate takes up, serially, Morgan’s claims for the mutation theory and readily shows their unconvincing char- acter. I quote some of this analysis, as follows: “Es ist von Interesse zu sehen, welche Grtinde Morgan bestim- men, der Mutationstheorie trotz ihrer fundamentalen Mangel den Vorzug zu geben vor der alten Darwin’schen Auffassung. Auf. S. 2908 zahlt er die ‘Vorztige’ dieser Theorie auf, die aber meines Erachtens alle vor der Kritik nicht standhalten. ““t. Da die Mutationen von Anfang an vollstandig ausgebildet auftreten, fallt die Schwierigkeit fort, die Anfangsstadien in der OTHER THEORIES OF SPECIES-FORMING. 369 Entwicklung eines Organs zu erklaren, und da das Organ sich erhalten kann, selbst wenn es keinen Wert fur die Rasse hat, kann es durch spatere Mutationen weiter entwickelt werden und schliess- lich eine wichtige Beziehung zum Leben des Individuums erlangen.’ “Die erwahnte Schwierigkeit, die Anfangsstadien niitzlicher Struk- turen und Organe nach der Darwin’schen Auffassung zu erklaren, lasst sich nicht leugnen, aber sie ist, wie ich in dem oben erwahnten * Buche gezeigt zu haben glaube (S. 34-51), zu tiberwinden, besonders dann, wenn man in der Vererbungsfrage Gegner von Weismann ist und annimmt, dass ein durch Generationen ausgetibter Reiz sich in seinem Effekt allmahlich steigert (Prinzip der Orthogenese) und wenn man sich dartiber klar ist—was Morgan vollstandig entgangen zu sein scheint—das der Konkurrenzkampf zwischen zwei Arten sehr oft nicht sofort, sondern im Laufe von Generationen bloss durch die grossere Fruchtbarkeit entschieden wird, diese aber kor- relativ durch geringfigige morphologische Unterschiede und unbe- deutende Anderungen in der Lebensweise wesentlich beeinflusst werden kann. Durch die Mutationstheorie wird aber jene Schwie- rigkeit in keiner Weise gehoben, denn erstens stellen die Mutationen, wie auch Morgan zugibt, meistens geringfiigige Abanderungen dar, welche die morphologische Breite der Fluktuationen nicht wber- treffen. Man kann also nicht annehmen, dass das Stadium der Nitzlichkeit mit einem Sprunge erreicht wird, dass etwa der Rollrtissel des Schmetterlings plotzlich aus kauenden Kiefern hervorging. Es mussten also eine Anzahl Mutationen in ganz bestimmter Weise aufeinander folgen, was, wie eben schon ange- deutet wurde, nach unsern jetzigen Kenntnissen von diesen regel- und richtungslosen Variationen unmoglich ist. “*2. Die neuen Mutationen konnen in zahlreichen Exemplaren auftreten und von ihren verschiedenen Sorten werden diejenigen sich erhalten, welche festen Fuss fassen konnen. Da dieselben Muta- tionen zu wiederholten malen auftreten konnen, wird die Gefahr, durch Kreuzung mit der Stammform vernichtet zu werden, im Ver- haltnis zu der Zahl der neu auftretenden Individuen geringer.’ Dass eine neue Mutation bei ihrem ersten Auftreten sofort in zahlreichen Exemplaren erscheint, ist ein ausserst seltenes Vorkommnis. Mir ist aus der Literatur nur der eine Fall der Whiteschen Washington- Tomate bekannt, welche sofort zu 100% aus der Varietat Acme zwei Jahre hintereinander auf derselben Lokalitat entstanden sein soll. Die Mutationen der Gartenpflanzen sind alle von einer oder einigen wenigen Stammexemplaren ausgegangen, waren also extreme *Plate, Li. “Uber die Bedeutung der Darwin’schen Selections- prinzip,” 1903. 370 DARWINISM TO-DAY. Singularvariationen, und erst durch Isolation und Selbstbefruchtung hat man grossere Mengen von Individuen erzielt. Die zoologischen Mutationen weisen, soweit ihr Ursprung bekannt ist, immer auf ein Stammtier: so das 1791 in Massachusetts entstandene Otterschaf, die 1770 von einem hornlosen Stier ausgegangene Rinderasse in Paraguay und die Rasse der Mauchampschafe, welche 1828 zuerst in einem Lamm, das von Merino-Eltern abstammte, auftrat. Schwanz- lose Katzen, Ziegen mit 4 Hornern, Menschen mit 6 Fingern sind weitere Belege dafuir, dass solche sprungartige Abanderungen grosste Seltenheiten sind. Da Selbstbefruchtung im Tierreich im allgemeinen als ausgeschlossen gelten kann, so konnen solche Falle nur durch grosste Inzucht und strengste Selektion zum Range einer Rasse erhoben werden. Correns,* der selbst grosse Verdienste um die Erkenntnis der Mutationen sich erworben hat, schreibt (S. 34) iiber die Notwendigkeit der Selbstbefruchtung: ‘Es genugt aber nicht, die Samen einer neu entstandenen Form zu sammeln und auszusaen; es muss auch dafur Sorge getragen werden, dass diese Samen ausschliesslich durch Selbstbefruchtung entstehen oder wenigstens, wenn mehrere abgeanderte Individuen verwendbar sind, durch Inzucht. Bei der Bestaubung der abgeanderten neuen Pflanzen mit dem Pollen einer zur alten unverandert. gebliebenen Form gehorenden Pflanze, die der Wind oder die Insekten ausftihren konnen, entsteht ein Bastard zwischen der neuen und der alten Form, indem die letztere fast immer die erstere zunachst so vollkommen unterdruckt, dass der Bastard genau wie die alte Form aussieht. Die neue Form kann dann zwar in der folgenden Generation des Bastards wieder zum Vor- schein kommen; in der Praxis beurteilt man aber die Erblichkeit nach der ersten Generation.’ Wenn also in der freien Natur eine einzelne Mutation auftritt, so wird sie als Regel mit der Stammform sich kreuzen und Bastarde erzeugen, die entweder nach dem Mendelschen Gesetz wie die Stammform aussehen oder den neuen Charakter in abgeschwachtem Grade besitzen. Die meisten von diesen Bastarden werden sich wieder mit der unveranderten Stammform kreuzen, da deren Individuen weitaus in der Majoritat sind, und so muss der neue Charakter in einigen Generationen wieder ausgelOscht werden, selbst wenn er in der ersten Zeit in einzelnen Individuen ab und zu zum Vorschein kommt.t Es gilt also meines Erachtens fiir die Mutationen dieselbe Regel wie fur die Fluktuationen: Singular- * Correns, C., ““Experimentelle Untersuchungen tiber die Entste- hung der Arten auf botan. Gebiet.” Diese Zeitschr., I, 1904, S. 27-52. Wie man sieht, vertritt Correns hier die Dominanz der phyletisch alteren Form. f Vgl. hierzu S. 185, Anm. OTHER THEORIES OF SPECIES-FORMING. 371 variationen spielen bei der Evolution keine Rolle, sondern nur Pluralvariationen, wenn wit absehen von jenen vereinzelten Fallen, in denen ein giinstiger Zufall fur die Isolation der Singularvariation sorgt. Wahrend aber bei den Fluktuationen sich leicht eine neue Rasse bilden kann, da immer viele Individuen nach dieser oder jener Richtung vom Durchschnitt abweichen oder durch die ausseren Faktoren in gleicher Weise verandert werden, liegen die Verhaltnisse fur die Mutationen sehr viel ungiinstiger. “3° Wenn die Zeit der Geschlechtsreife bei der neuen Form abweicht von der der Elternform, vermag sich die neue Ari nicht mit der Elternform zu kreuzen, und da dieser nette Charakter von Anfang an vorhanden ist, wird die neue Form bessere Aussichten haben am Leben zu bleiben als wenn der Zeitunterschied der Ge- schlechtsreife erst allmahlich erworben werden miusste.’ Morgan erwahnt hier eine ganz spezielle Form der sexuellen Isolation. Man braucht jedoch nicht anzunehmen, dass dieselbe von den Fluktua- tionen allmahlich erworben wird; sie ist entweder von vornherein da, d. h. die neue Varietat wird in der Mehrzahl ihrer Individuen friiher oder spater geschlechtsreif als die Stammform, oder diese Schranke tritt tiberhaupt nicht auf. In diesem Punkte verhalten sich also die Fluktuationen genau so wie die Mutationen. “‘a. Die neuien Arten, welche erscheinen, konnen in einigen Fallen schon an eine andere Umgebung angepasst sein als die von der Stammform bewohnte; in diesem Falle werden sie von Anfang an isolirt sein, was einen Vorzug bei der Vermeidung der schlechten Einfltisse der Kreuzung bedeutet.’ Auch diese biologische Isolation gilt natiirlich in demselben Masse fiir die Fluktuationen, ja sie muss bei ihnen eine weit grdssere Rolle spielen, denn nach der Darwin- ’schen Auffassung wandern gewisse Individuen allmahlich in ein. neues Wohngebiet ein und passen sich auf Grund ihrer Variabilitat an dieses im Laufe von Generationen an. Wenn aber unter den Exemplaren einer in der Ebene lebenden Art plotzlich einige muta- tive Individuen auftreten, welche fiir das Leben im Gebirge einge- richtet sind, so ist gar nicht zu verstehen, wie solche Mutationen sofort die ihnen zusagende Wohnstatte resp. Lebensweise auffinden. “5. Es ist wohl bekannt, dass die Unterschiede verwandter Arten zum grossen Teile Differenzen unwichtiger Organe sind, und dies steht in Harmonie mit der Mutationstheorie, bildet aber eine der wirklichen Schwierigkeiten der Selektionstheorie. “6. Nutzlose oder selbst leicht schadliche Charaktere k6nnen als Mutationen auftreten und sich erhalten, wenn sie die Fortdauer der Rasse nicht ernstlich beeinflussen.’ “Morgan muss sich wirklich sehr wenig in die Darwinischen Gedanken eingearbeitet haben, wenn er nicht einsieht, dass die a72 DARWINISM TO-DAY. Selektionstheorie ttber den Ursprung der Variationen tberhaupt nichts aussagt, sondern diese einfach als gegeben hinnimmt, mdgen sie nur durch aussere Faktoren oder unbekannte innere Ursachen hervorgerufen werden und mogen sie niutzlich, schadlich oder indifferent ausfallen. In dieser Hinsicht steht sie auf demselben Boden wie die Mutationstheorie, welche gleichfalls den Ursprung der Mutationen nicht aufklart, sondern diese als pl6tzlich vorhanden ansieht. Die Selektionstheorie sucht uns nur klar zu machen, wie durch den Kampf ums Dasein die komplizirten ntitzlichen Ein- richtungen, die Anpassungen, allmahlich entstehen konnten, und da nahverwandte Arten haufig in dem Grade der Ausbildung solcher Anpassungen—man denke z. B. an die Unterschiede zwischen dem indischen und afrikanischen Elefanten im Bau der Rtisselspitze und der Ohren—voneinander abweichen, macht sie bis zu einem ge- wissen Grade auch den ‘origin of species’ verstandlich.* Morgan wirft in seinem Buche immer und immer wieder ganz unberechtigter Weise dem Darwinismus vor, er behaupte ‘That adaptations have arisen because of their usefulness.’ Selbst die extremsten Anhanger Darwins haben immer nur gesagt: gewisse Variationen bleiben erhalten, weil sie nutzlich sind, und indem eine nttzliche Stufe zu der andern allmahlich addirt wird, entstehen schliesslich jene auffallenden Einrichtungen, die wir ‘Anpassungen’ nennen. Genau denselben Standpunkt nimmt die Mutationstheorie ein. Auch fur sie ist der Kampf ums Dasein—dieses Wort wie bei Darwin im weitesten Sinne genommen—das oberste regulatorische Prinzip der organischen Natur, welches die dauerfahigen Mutationen von den schadlichen sondert, dadurch die Evolutionen in ganz bestimmte Bahnen drangt und langsam die Entstehung der Anpassungen er- moglicht. Dadurch dass der Kampf ums Dasein das ‘Uberleben des Passendsten’ bedingt, schafft er etwas Positives und macht uns die mit dem Wechsel der Lebensweise und Umgebung stets wech- selnden Formen der Anpassungen verstandlich.” 7° Klebs, the eminent plant physiologist, keenly criticises the muta- tions theory in his paper on “Willktirliche Entwicklungsanderungen bei Pflanzen,” 1903. See also Copeland, E. B., ‘The Variation of Some California Plants,’ Botan. Gaz. Vol. XXXVIII, pp. 401-426, 1904. In this paper the author describes some striking aberrant forms of oak and fern leaves, but shows that between these mutation-like forms and the modal forms intergrading steps exist. Copeland * Es ist also nicht richtig, wenn Morgan (S. 454) von der Dar- win’schen Theorie behauptet, sie werfe die Frage des Ursprungs der Arten zusammen mit der des Ursprungs der Anpassungen. og Probleme konnen zusammenfallen, aber sie brauchen es nicht. OTHER THEORIES OF SPECIES-FORMING. 373 discusses keenly the mutations of de Vries and finds in them noth- ing radically different either in character or behaviour from the Darwinian fluctuating variations. ** Conklin, E. C., Science, N. S., Vol. XXI, p. 525, 1905. *° Morgan, “Evolution and Adaptation,” p. 292, 1903. *° Morgan, “Evolution and Adaptation,” pp. 298-299, 1903. Baoan ts °° Emery, C., “Gedanken zur Descendenz- und theories explain- Vererbungstheorie,” Biolog. Centralblatt, Vol. XLV, ing secondary PP. 397-420, 1893. sexual characters: 51 Cunningham, J. T., “The Species, the Sex, and ere Natural Science, Vol. XIII, pp. 184-192, 233-2390, 1808. *? Wallace, A. R., “Tropical Nature,” 1878. ** Barrett-Hamilton, G. E. H., “Note on a Possible Mode of Origin of some Nuptial and Sexual Characters in Vertebrates,” Anatom. Anzetg., Vol. XVIII, pp. 47-48, 1900. CHAPTER 21. DARWINISM’S PRESENT STANDING, A RIVER rises froma perennial spring on the mountain side ; gravitation compels the water to keep moving, and rock Natural selec Walls, intervening hills, and soft loam banks artis determine the course of the stream. The living descent. stream of descent finds its never-failing primal source in ever-appearing variations; the eternal flux of Nature, coupled with this inevitable primal variation, com- pels the stream to keep always in motion, and selection guides it along the ways of least resistance. Although there can be no modification, no evolution, without variation, yet neither can this variation, whatever its character and extent, whether slight and fluctuating, large and mutational, de- terminate or fortuitous, long compel descent to go contrary to adaptation. And the guardian of the course is natural selection. Selection will inexorably bar the forward move- ment, will certainly extinguish the direction of any ortho- genetic process, Nagelian, Eimerian, or de Vriesian, which is not fit, that is, not adaptive. Darwinism, then, as the natural selection of the fit, the final arbiter in descent control, stands unscathed, clear and high above the obscuring cloud of battle. At least, so it seems to me. But Darwinism, as. the all-sufficient or even most important causo-mechanical \ factor in species-forming and hence as the sufficient ex- © planation of descent, is discredited and cast down.’ At least, again, so it seems to me. But Darwin himself claimed no Allmacht for selection. Darwin may well cry to be saved from his friends! 374 DARWINISM’S PRESENT STANDING. + 235 The selection theories do not satisfy present-day biolo- gists* as efficient causal explanations of species-trans- ee formation. The fluctuating variations are not selection nota sufficient handles for natural selection; the marge hed hosts of trivial, indifferent species differences forming, are not the result of an adaptively selecting agent. On the other hand the declarations of Korschinsky, Wolff, Driesch, and others that natural selection is non- existent, is a vagary, a form of speech, or a negligible influ- ence in descent, are unconvincing; they are unproved. / And these bitter antagonists of selection are especially un- convincing when they come to offer a replacing theory, an ie eetiaue alternative explanation of transformation and of the replacing descent. To my mind every theory of hetero- SHEE: genesis, of orthogenesis, or of modification by the transmission of acquired characters, confesses itself ulti- mately subordinate to the natural selection theory. How- ever independent of selection and Darwinism may be the beginnings of modification, the incipiency of new species and of new lines of descent; even, indeed, however neces- sary to natural selection some auxiliary or supporting theory to account for the beginnings of change confessedly is, the working factor or influence postulated by any such auxiliary theory soon finds its independence lost, its influ- ence in evolution dominated and controlled by natural selec- tion. As soon as the new modifications, the new species characters, the new lines of descent, if they may come so far, attain that degree of development where they have to submit to the test of utility, of fitness, just there they are practically delivered over to the tender mercies of selection. No orthogenetic line of descent can persist in a direction not adaptive, that is, not fit, and certainly no present-day biologist is ready to fall back on the long deserted stand- point of teleology and ascribe to heterogenesis or ortho- genesis an auto-determination toward adaptiveness and 376 DARWINISM TO-DAY. fitness. Modification and development may have been proved to occur along determinate lines without the aid of natural selection. I believe they have. But such develop- ment cannot have an aim; it cannot be assumed to be directed toward advance; there is no independent progress upward, 7. e., toward higher specialisation. At least, there is no scientific proof of any such capacity in organisms. Natural selection * remains the one causo-mechanical ex- planation of the large and general progress toward fitness; the movement toward specialisation; that is, descent as we know it. But what Darwinism does not do is to explain the begin- nings of change, the modifications in indifferent characters An explanation and in indifferent directions. And all this 1s ele re tremendously important, for there are among ge is needed, animals and plants hosts of existent indifferent characters, and many apparently indifferent directions of specialisation. As to the obvious necessity of beginnings nothing need be said. What is needed, then, is a satisfactory explanation of the pre-useful and pre-hurtful stages in the modifications of organisms: an explanation to relieve Dar- winism of its necessity of asking natural selection to find in the fluctuating individual variations a handle for its action; an explanation of how there ever comes to be a handle of advantage or disadvantage of life-and-death- determining degree. With such an explanation in our possession—and whether any one or more of the various theories proposed to fill this need, such as Eimerian orthogenesis, de Vriesian heterogenesis, Rouxian battle of the parts, or Weismannian germinal selection, etc., give us this explanation, may be left for the moment undebated —with such a satisfactory explanation, I say, once in our hands, we may depend with confidence on natural selection to do the rest of the work called for by the great theory of descent. Among all the divergent lines of development DARWINISM’S PRESENT STANDING, 377 and change, instituted by this agent of beginnings, natural selection will choose those to persist by saying No to those that may not. And the result is organic evolution. But all this is equivalent to saying that there are other important factors in descent than selection, and that as to the beginnings of descent—and this is species- The causes of : . variation and the forming—these other factors are the more im- San hate portant ones. Which I behéve: is: true; Te factors inspe- Causes of variation and the means of segrega- oies-forming» ~~ tion or isolation are the chief factors in actual species-forming. Certainly the mutations theory is not yet ready to offer itself as an explanation of adaptation, how- ever confidently it may claim to be enrolled among species- forming factors. The very same objections that have served to topple down selection from its high seat of honour, can be directed immediately and effectively against this latest claim- ant for recognition as the Great Cause of descent. Nor can geographical isolation explain modification where adaptation is included. Nor can Lamarck’s beautiful explanation of adaptation claim validity, until the actuality of its funda- mental postulate, the carrying over of ontogenic acquire- ments into phylogeny, be proved. And so with Buffon and St. Hilaire’s influence of the ambient medium, and Eimer’s modifying factors. Nor can any Nagelian automatic per- fecting principle hold our suffrage for a moment unless we stand with theologists on the insecure basis of teleology. No, let no ambitious student hesitate to take up the search for the truth about evolution from the notion that, biology is a read book. The “Origin of Spe-} Theunknown | ; factors ofevolu- Cies’ was the first opening of the book—that wan: the world recognised at least; poor Lamarck opened the book but could not make the world read in it— and that time when it shall be closed because read through is too far away even to speculate about. With Osborn * let us join the believers in the “unknown factors in evolution.” 378 DARWINISM TO-DAY. Let us begin our motto with Jgnoramus, but never follow it with [gnoribimus. Now if we do not know, but want to know, and are willing to make an attempt toward knowing, where shall our energy Prime needs 01 €XPloration and discovery be first directed ? * of evolution To what particular points or aspects of the ama: causes-of-evolution problem shall we give our first attention, what fields of study first invade? What, in a word, is the principal desideratum in present-day investiga- tion of evolution? I should answer, the intensive study of variability, Not alone of the statics of variation but of its dynamics. Indeed, above all its dynamics. The experimental study of the stimuli, external and internal, the influences, extrinsic and intrinsic, which are the factors and causes of variation,—this is the great desideratum; this the crying call to the evolution student. Experiment in variation study includes controlled modification of ontogeny (experimental development) and controlled modification of phylogeny (pedigreed breeding). In the study of variation statics, biometry is the greatest advance in modern methods, and the essential basis of biometric study, namely, quantitative and statistical data, must have its part in the investigation of variation dynamics. But in entering the realm of the causal study of variability, “we must not,” as Roux has clearly pointed out, “conceal from ourselves the fact that the causal investigation of organism is one of the most difficult, if not the most difficult, problem which the human intellect has attempted to solve, and that this investigation, like every causal science, can never reach completeness, since every new cause ascertained only gives rise to fresh questions concerning the cause of this cause.” I believe that the neglect on the part of the selectionists to pay sufficient attention to the origin and causes of the varia- tion which is such an indispensable basis of their theory, has been one of the most obvious reasons for the present strong DARWINISM’S PRESENT STANDING. 379 reaction against the selection theories. Thankfully accept- ing the bricks and stones handed to them they have builded Neglectof a house of great beauty: but with stones of aun dg different shape a house of quite different ap- tion, pearance might have been built. Is it not a cause for wonder that the selection masons have not been more inquisitive concerning the whence and why of this magical supply of just the needed sort of material at just the right time? As a matter of fact, Darwin himself gave serious attention to the origin of his always-ready varia- tions, but his tremendous undertaking was too nearly super- human already to permit him to add to it an adequate attention to the problem of causes. But that same excuse does not attach to his followers. And it is, I repeat, largely | this neglect to strive to penetrate the so-far unrent veil of obscurity lying over the beginnings of species change that has contributed to the growing revolt against the Allmacht of the selection dogma. Who would in these days have a following for his explanation of species origin must include in his theory some fairly satisfying explanation of the first visible beginnings of modification. Then, after the explanation of the why and how of varia- bility, comes the necessity of explaining the cumulation of this variability along certain lines, the first visi- ble issuance of these lines being as species, and later becoming more and more pronounced as courses of descent. This explanation has got to begin lower down in phyletic history than natural selection can begin. Before ever there can be utility and advantage there must have come about a certain degree of heaping up, of cumu- lating, of intensifying variations. What are these factors? They are possibly only two: (1) orthogenetic or deter- minate variation as the outcome of plasm preformation or of epigenetic influences, and (2) the segregation of similar variations by physiologic or topographic conditions. Hence, How is varia- tion cumulated ? 380 DARWINISM TO-DAY. next to the cause or origin of variability the great desider- atum is a knowledge of the means of cumulating and direct- ing variability. And both these great fundamental needs of a satisfactory understanding of organic evolution seem to me to be wholly unreferred to in the theory of natural selection. To be sure the control and cumulation of such large differences among organisms and species as are posi- tively sufficient to determine the saving or the loss of life are explicable by selection. And this factor is sooner or later in any phyletic history bound to step in and probably be the dominant one. But a species, or a character, will always have a longer or shorter preselective existence and history, and it is precisely these days before the Inqui- sition of which we demand information. For of one thing we are now certain, and that is, that evolution and the origin of species have both their beginnings and a certain period of history before the day of the coming of the Grand Inquisitor, selection. Finally there is still another desideratum and one whose seeking will carry us into dangerous country. For while there may be and are selectionists who might allow us to fumble about in the darkness of preselective time for first causes, there is probably none who will allow us to ques- tion his right to explain that other element in evolution be- sides species transformation, namely, adaptation, or, as the Germans untranslatably put it, Zweckmdassigkeit. But by no means all biologists ° find in natural selection a sufficient explanation of adaptation. In the visible expression of organic evolution are two chief elements, one the variety of life kinds, the existence of tious species, the reality of lines of descent; and the need ofexplain- Other the adaptedness and adaptiveness of these ing adaptation. tife kinds. The varieties of organic kinds show themselves adapted in structure and function to the varie- ties of environment and life-conditions. Hence, the task DARWINISM’S PRESENT STANDING. 381 of an evolution explanation is a double one; it must explain not only diversity or variety in life, but adaptive diversity or variety. And there is no gainsaying to the selection explanation its claim to stand among all proposed explana- tions of adaptation as that one least shaken by the critical attack of its adversaries. However mightily the scientific imagination must exert itself to deliver certain difficult cases into the hands of selection, and however sophisticated and lawyer-like the argument from the selection side may be for any single refractory example, the fact remains that the selectionist seems to be able to stretch his explanation to fit all adaptations with less danger of finding it brought up against positive adverse facts than is possible to the champion of any other so far proposed explanation. The explanation of adaptation by natural selection steers wide of teleology on one hand and of unproved assumptions con- cerning heredity on the other. The protoplasmic conscious- ness of Cope and the automatic perfecting principle of Nageli and those of his manner of explanation, are only indirect ways of attributing to natural forces visions and anticipations of what does not yet exist; while the influence of the ambient medium of St. Hilaire and of the extrinsic factors of Eimer, and the impressing photographically on the species and the carrying over into phylogeny, with approximate identity, of characteristics and modifications acquired ontogenetically by the individual as a result of functional stimulation—all these are assumptions not only apparently unproved, but in the light of our present knowledge of the mechanism of heredity seemingly un- provable. Yet the explanation of species transformation and of adaptation by the introduction into phylogeny of modifica- tions (reaction effects) arising in the individual during its ontogeny, has to its credit a certain logical proof, or basis, which has great validity in my mind, and yet which 382 DARWINISM TO-DAY. has enjoyed little general recognition and almost no em- phasis from supporters of Lamarckism or neo-Lamarckism. As the great strength of the natural selection explanation of species-change and adaptation lies precisely in the logical nature of its premises and conclusions rather than on scien- tific observation and experiment,’ it certainly is not unfair to emphasise any similar kind of proof tending to support the Lamarckian type of explanation. The logical proof that I refer to is simply this: It is a universally admitted fact that environment and functional A logical proof stimulation can and do modify organisms dur- nine ing their lifetime, and that this modification ony of adaptive jis usually plainly adaptive. It is also an ontogenetic ; ; ix d changes. admitted fact that species differences or modi- fications are often identical with these cntogenetic modifica- tions. That is, that under similar environment or life conditions species modification often follows the same lines as ontogenetic or individual modification. Now when we recall the possibilities of the hosts of ways in which the necessities of adaptation to varying environment might be met by selection among nearly infinite fortuitous variations, and yet see that exactly that means or line or kind of adapt- ive change occurs, which in the case of the individual is plainly and confessedly a direct personal adaptive reaction to varying environment, is it not the logical conclusion that the species change and adaptation is derived, not by the chance appearance of the needed variation, but by the com- pelled or determined appearance of this variation? In other words when species differences and adaptations are identical with differences and modifications readily directly produci- ble in the individual by varying environment, are we not justified, on the basis of logical deduction, to assume the transmutation of ontogenetic acquirements into phyletic acquirements, even though we are-as yet ignorant of the physico-chemical or vital mechanism capable of effecting the DARWINISM’S PRESENT STANDING. 383, carrying over? Has natural selection’s claimed capacity to effect species change, unseen by observer, untested by exper- imenter, any better or even other proof of actuality than that just offered on behalf of species modification as a direct result of the stimulus of varying environment and func- tional exercise? I cannot see that it has. And this kind of argument, based half on observed facts and half on deduction, may be extended even farther on ee Or behalf of the theory that species change is the of proof fornon- direct reaction to environmental conditions. adaptive change. Tor there are many ontogenetic variations pro- duced directly in response to environment that are not plainly adaptive; many, indeed, between which and the environmental conditions that produce them no reasonable relation is apparent; no relation, that is, that would be ex- actly expected or could be foretold until empirically deter- mined. In other words, many apparently non-significant ontogenetic differences or variations appear as direct result of environmental influence or stimulus. For example, indi- viduals of certain species of the Crustacean phyllopod genus Artemia show marked structural differences when grown in salt water of varying density. These differences are in the size and shape of the plate-like lateral gills, the seg- mentation of the post-abdomen, the length of the caudal flaps (telson) and the hairiness of these flaps. The size of the whole body is also affected, individuals developing in water of higher density being markedly smaller than those. which have been grown in less dense water. Now of all these differences only two seem to have what I call a rea- sonable relation to the environmental differences. The in- creased proportional size of the gills shown by the Artemias. grown in denser water appears to be a regulatory change connected with the smaller amount of oxygen in the water,. and the decreased size of the body may similarly be con-: ceived by some to be an expected concomitant of the: 384 DARWINISM TO-DAY. denser water condition. -But what of the extra abdominal segment, the longer telson projections and their increased hairiness, all of which as shown by Schmankewitsch * (how- ever mistakenly this investigator may have interpreted his results as examples of actual species modification) and Anikin® for Artemia salina and by the writer’? for Artemia franciscanus, are the ontogenetic differences that varying density of salt water actually produces in individuals of a single Artemia species. These differences, these variations, are of the sort that I am calling non-significant, non-adapt- ive, non-reasonable. They would not be prophesied; they seem to have no reasonable correlation with the causes which produce them. But they are actually the results or effects of determined proximate causes which are extrinsic or environmental. If now the logical argument (based on identity of adaptive modification in individuals and in spe- cies) for the transmutation of ontogenetic changes into phyletic changes has any validity, then these non-adaptive, indifferent modifications may be transmuted as well as the adaptive ones, and thus hosts of trivial, non-adaptive indif- ferent species differences be explained on this Lamarcko- Eimerian basis as well as the obviously adaptive modifica- tions. But I am not insisting on this sort of argument too strongly. It is exactly the sort of argument upon which the theory of natural selection chiefly rests, and I have cer- tainly tried to make evident in this book my belief in the danger of the substitution of this sort of logical or meta- physical basis of belief in a theory for a scientific basis of observation and experiment. Finally, let us ask ourselves why we have adopted the common belief that our search for a cause of variability is a Asuggestion Search for some so far unknown, some quite 0s grea new factor or force in biology? May it not be tion. that the factor is already familiar to us; so familiar indeed perhaps that we are esteeming it too simple DARWINISM’S PRESENT STANDING. 385 and too obvious to play the rdle of the Great Desideratum, a causal factor of variability. When one attempts to picture the process of the making of a new individual, and follows the complex phenomena of fecundation, of embryology, and post-embryonic develop- ment, is it not impossible to conceive of the production of two identical individuals? In all the course of this develop- ment, from the first cleavage of the fertilised egg-cell on, it is practically impossible to repeat processes absolutely identically, hence to produce absolutely identical organs, parts, cells. Now the germ-cells have their very origin in a repeated complex process, mitotic cell division; they are produced as nearly alike as possible, but it is not possible to make them absolutely identical. Development, whether largely epigenetic or largely evo- lutionary, depends at least partly (probably largely) on the physical, 7. e., structural, character of the germ-cells. Slight differences in the germ-cells then would lead to considera- ble differences in the fully developed organ. If the differ- ences in the germ-cells happened, as would occasionally or rarely be the case, to be considerable, then the differences in the adults would be very considerable (mutations, sports, monsters, etc.). We know enough of the complex and epigenetic character of ontogeny to see plainly that identity among individuals, even of the same brood, is impossible. Variation, then, seems the necessary, the absolutely un- avoidable outcome of the conditions to which the developing individual is exposed. Indeed, all the individuals of a species might start (as fertilised eggs) exactly alike, and yet I cannot see how any two could come out alike. The inevitable slight differences in position, and hence in nutri- tion, in the results of the host of dividing and folding, in- vaginating and evaginating processes, the relations of each individual, whether in the mother’s body or out of it, to everything else outside of itself—all these are conditions 386 DARWINISM TO-DAY. bound to vary a little between any two individuals. And as we know from the facts of experimental embryology that development is, partly at least, epigenetic in character, 1.e., depends on and is influenced by external factors, this in- evitable variation in influencing conditions is bound to pro- duce variations in the individuals. Is there, indeed, any need at all for assuming (1) any mysterious “tendency” of the germ-plasm to vary? and (2) that the individual (continuous) variation depends wholly on germ-plasm structure? Why cannot the simple fluctuating or Darwinian variations be chiefly the result of the inevitable variation in the epigenetic factors, which, when not intruded on by exceptional disturbances, would themselves follow the “law of error” and hence produce “law of error’ variabil- ity? All normal swingings of the variation pendulum in any part or character, between long and short, large and small, round and angular, smooth and rough, etc., etc., would result from the normal variation of the processes; the larger (extremes of range) variations being the fewer be- cause the larger (extremes of range) variations in the ontogenetic processes would be the fewer. Exceptionally large epigenetic variations would produce exceptionally large variations in the individual—sports, mutations. Klebs,** as a result of his masterly experimental studies on modifications of plant development, comes to the conclusion that the only proved causes of variation are extrinsic influences stimulating, working through, or com- bined with, intrinsic conditions (not vitalistic, but physico- chemical). Similarly, Tower,’* from his protracted studies on the variations in certain insects, concludes that all these variations are caused by external stimuli working on the germ-plasm. . If variation is thus simply the wholly natural and un- avoidable effect ** of this inevitable non-identity of vital process and environmental condition, why does not evolution DARWINISM’S PRESENT STANDING. 387 possess in this state of affairs the much sought for, often postulated, all-necessary, automatic modifying principle an- See wiihviets tedating and preceding selection which must thongh not pur- effect change, determinate though not purpose- poseful change. F141? Nageli’s automatic perfecting principle is an impossibility to the thorough-going evolutionist seeking for a causo-mechanical explanation of change. But an automatic modifying principle which results in determinate or purposive change, that is, in the change needed as the indispensable basis for the upbuilding of the great fabric of species diversity and descent; is not that the very thing pro- vided by the simple physical or mechanical impossibility of perfect identity between process and environment in the case of one individual and process and environment in the case of any other? It seems so to me. But I do not know. Nor in the present state of our knowl- edge does any one know, nor will any one know until, as Brooks ** says of another problem, we find out. We are ignorant; terribly, immensely ignorant. And our work is, to learn. To observe, to experiment, to tabulate, to induce, to deduce. Biology was never a clearer or more inviting field for fascinating, joyful, hopeful work. To question life by new methods, from new angles, on closer terms, under more precise conditions of control; this is the requirement and the opportunity of the biologist of to-day. May his generation hear some whisper from the Sphinx! APPENDIX. *One of the most serious and detailed critical analyses of the selection theory, resulting in conclusions totally antagonistic to Dar- Wigand’s criti- winism, is that of the Marburg botanist, Prof. Albert cism of the selece Wigand, composing the three volumes entitled “Der tion theories’ =Darwinismus und die Naturforschung Newtons und Cuviers” (Vol. I, 1874; Vol. II, 1876; Vol. III, 1877). From the “Announcements” at the beginning of each volume I quote as follows: 388 DARWINISM TO-DAY. From Vol. I. “Die hier dargebotene Kritik der Darwin’schen Lehre weist zunachst durch eingehende Prufung der hierher ge- horigen naturhistorischen Thatsachen nach, dass weder die Voraus- setzungen, von denen die Theorie ausgeht, noch ihre Consequenzen mit der wirklichen Natur tibereinstimmen, dass sie demnach den Anforderungen an eine wissenschaftliche Hypothese nicht entspricht. Vielmehr erweist sich dieselbe als eine philosophische Speculation, welche nicht nur die unserer Naturerkenntniss vorgezeichneten Grenzen tiberschreitet, sondern vor Allem die wichtigsten Grundsatze der wahren Forschung, wie sie durch die grossen Meister aufgestellt und in der bisherigen Entwickelung der Naturwissenschaft allgemein anerkannt und unbedingt maassgebend gewesen sind, insbesondere die Principien der Causalitat und der organischen Entwickelung, aufs grobste verleugnet. Demnach erkennt das vorliegende Werk seine Hauptaufgabe gerade darin, der bis dahin befolgten Forschungsweise gegentiber jener neuesten Naturphilosophie ihr Recht zu wahren.” From Vol. II. ‘‘Vermittelst der hierdurch gewonnenen Kriterien gelangt die Untersuchung in Betreff des Darwinismus zu_ fol- gendem Ergebnis: Derselbe geht nicht bloss von falschen Voraus- setzungen aus, erweist sich nicht nur unfahig in Beziehung auf die versprochenen Leistungen, ist nicht nur verfehlt durch die princi- pielle Unmoglichkeit seiner Aufgabe, ist nicht nur eine der Natur- forschung fremdartige, rein speculative Operation, sondern indem derselbe das Princip der Causalitat und Entwickelung mit dem Zufall und der Teleologie als Erklarungsgrunde vertauscht, erscheint er als eine der Naturforschung in ihrer Fundamentalmaxime wider- sprechende, darum dieselbe geradezu gefahrdende Verirrung, um so mehr als er unter ihrer Maske auftritt. Der Darwinismus ist einer jener Versuche, welche im Namen der Naturforschung die Naturforschung verderben.” From Vol. III. “Der vorliegende dritte Band, mit welchem dieses Werk abschliesst, hat zum Gegenstand nicht die dem Darwinismus zu Grunde liegende Theorie, sondern die concrete Gestalt, in welcher derselbe als eine ftir unsere Zeit charakteristische culturhistorische Thatsache in die Erscheinung tritt. Insbesondere wird versucht, ein Bild von der Darwin’schen Schule als der Gesammtheit der die Transmutationstheorie vertretenden Auctoren und von der Art und Weise, wie sich die letztere im Lichte ihrer Bekenner darstellt, zu entwerfen. MHierbei ergibt sich, dass der Darwinismus mehr in einer ziellosen ZeitstrOmung und in einer wissenschaftlich nicht motivirten Stimmung der Geister als in einer bestimmt zu formulirenden Lehre besteht, und dass derselbe bereits in seinem eigenen Lager in allen wesentlichen Punkten wissenschaftlich ttbherwunden ist, und zwar in solcher Weise, dass in den widerstreitenden Ansichten der Darwin- » 2. 9 ae sg DARWINISM’S PRESENT STANDING. 389 ianer doch zugleich der Keim fiir die allein richtige Auffassung der organischen Natur, wenn auch grossentheils unklar und unbewusst, verborgen liegt.” A special answer to this exhaustive pleading of Wigand is offered by H. Spitzer in his “Beitrage zur Descendenztheorie und zur Metho- dologie der Naturwissenschaft,” 1886. * However, there still exist, especially in England, thorough- going Darwinians who see nothing serious in all this criticism of Lankesters their great compatriot’s explanation of the origin of upholding of species. Lankester, one of the most prominent of Darwinism. English naturalists, said at York, last August (1906), in his inaugural address as president of the British Association for the Advancement of Science: ‘Under the title ‘Darwinism’ it is con- venient to designate the various work of biologists tending to estab- lish, develop or modify Mr. Darwin’s great theory of the origin of species. In looking back over twenty-five years it seems to me that we must say that the conclusions of Darwin as to the origin of species by the survival of selected races in the struggle for exist- ence are more firmly established than ever. And this because there have been many attempts to gravely tamper with essential parts of the fabric as he left it, and even to substitute conceptions for those which he endeavoured to establish, at variance with his conclusions. These attempts must, I think, be considered as having failed.” * “Physiologic facts concerning the origin of species in nature were unknown in the time of Darwin. It was a happy idea to De Vries's dis- Choose the experience of the breeders in the produc- cussion of species- tion of new varieties, as a base on which to build an forming by explanation of the processes of nature. In my opinion oe Darwin was quite right, and he has succeeded in giv- ing the desired proof. But the basis was a frail one, and would not stand too close an examination. Of this Darwin was always well aware. He has been prudent to the utmost, leaving many points undecided, and among them especially the range of validity of his several arguments. Unfortunately this prudence has not been adopted by his followers. Without sufficient warrant they have laid stress on one phase of the problem, quite overlooking the others. Wallace has even gone so far in his zeal and ardent veneration for Darwin, as to describe as Darwinism some things, which, in my opinion, had never been a part of Darwin’s conceptions. “The experience of the breeders was quite inadequate to the use which Darwin made of it. It was neither scientific, nor critically accurate. Laws of variation were barely conjectured; the different types of variability were only imperfectly distinguished. The breed- ence mes 390 DARWINISM TO-DAY. ers’ conception was fairly sufficient for practical purposes, but science needed a clear understanding of the factors in the general process of variation. Repeatedly Darwin tried to formulate these causes, but the evidence available did not meet his requirements. “Quetelet’s law of variation had not yet been published. Mendel’s claim of hereditary units, for the explanation of certain laws of hybrids discovered by him, was not yet made. The clear distinction between spontaneous and sudden changes, as compared with the ever-present fluctuating variations, is only of late coming into recog- nition by agriculturists. Innumerable minor points which go to elu- cidate the breeders’ experience, were unknown in Darwin’s time. No wonder that he made mistakes, and laid stress on modes of descent which have since been proved to be of minor importance or even of doubtful validity. “Notwithstanding all these apparently unsurmountable difficulties, Darwin discovered the great principle which rules the evolution of organisms. It is the principle of natural selection. It is the sifting out of all organisms of minor worth through the struggle for life. It is only a sieve, and not a force of nature, no direct cause of improvement, as many of Darwin’s adversaries, and unfortunately many of his followers also, have so often asserted. It is only a sieve, which decides which is to live, and what is to die. But evo- lutionary lines are of great length, and the evolution of a flower, or of an insectivorous plant is a way with many side-paths. It is the sieve that keeps evolution on the main line. killing all, or nearly all that try to go in other directions. By this means natural selec- tion is the one directing cause of the broad lines of evolution. “Of course, with the single steps of evolution it has nothing to do. Only after the step has been taken, the sieve acts, eliminating the unfit. The problem, as to how the individual steps are brought about, is quite another side of the question’ (De Vries, “Species and Varieties,” pp. 4-7, 1905). The distinguished French zoologist (Professor in the University of Paris), Delage. leader among French morphologists and experi- Delage’s esti- menters, voices his position concerning Darwinism in mate of selection. the following concise phrases (‘‘L’Hérédité,” 2d ed., Pp. 397, 1903): ‘‘La sélection naturelle est un principe admirable et parfaitement juste. Tout le monde est d’accord aujourd’hui sur ce point. Mais ot l’on n’est pas d’accord, c’est sur la limite de sa puissance et sur la question de savoir si elle peut engendrer des formes spécifiques nouvelles. 11 semble bien demontrer aujourd’hui quelle ne le peut pas.” *“A study of the recent discussion in the Contemporary Review between Spencer and Weismann leads to the conclusion that neither DARWINISM’S PRESENT STANDING. 39t of these acknowledged leaders of biological thought supports his position upon inductive evidence. Each displays his main force Cctnrs's cham. 1 destructive criticism of his opponent; neither pre- pionship of the sents his case constructively in such a manner as to “anknown factors carry conviction either to his opponent or to others. In of evolution.” = short, beneath the surface of fine controversial style we discern these leaders respectively maintaining as finally estab- lished theories which are less grounded upon fact than upon the logical improbabilities of rival theories. Such a conclusion is deeply significant; to my mind it marks a turning point in the history of speculation, for certainly we shall not arrest research with any evolution factor grounded upon logic rather than upon inductive demonstration. A retrograde chapter in the history of science would open if we should do so and should accept as established laws which rest so largely upon negative reasoning... . “The first step then towards progress is the straightforward con- fession of the limits of our knowledge and of our present failure to base either Lamarckism or neo-Darwinism as universal princi- ples upon induction. The second is the recognition that all our thinking still centres around the five working hypotheses which have thus far been proposed; namely, those of Buffon, Lamarck, St. Hilaire, Darwin, and Nageli. Modern criticism has highly differ- entiated, but not essentially altered these hypothetical factors since they were originally conceived. Darwin’s ‘survival of the fittest’ we may alone regard as absolutely demonstrated as a real factor, without committing ourselves as to the ‘origin of fitness. The third step is to recognise that there may be an unknown factor or factors which will cause quite as great surprise as Darwin’s.” . “The general conclusion we reach from a survey of the whole field is, that for Buffon’s and Lamarck’s factors we have no theory of heredity, while the original Darwin factor, or neo-Darwinism, offers an inadequate explanation of evolution. If acquired varia- tions are transmitted, there must be, therefore, some unknown principle in heredity; if they are not transmitted, there must be some unknown factor in evolution.” (Osborn, H. F., “The Un- known Factors of Evolution,” in Wood’s Holl Biological Lectures, Pp. 79, 80, 81, 98, and 99, 1894.) ° Davenport, C. B., “Animal Morphology in its Relation to Other Sciences,” Congress of Arts and Sciences, Vol. V, pp. 244-257, 1900. In this paper are pointed out in admirable manner the present- moment problems, interests, and points of view of evolution biolo- gists. * Henry de Varigny, in “La Nature et La Vie,” 1905, says that for many adaptations “il n’y a pas a se dissimuler que, dans beaucoup ’ 392 DARWINISM TO-DAY. de cas, cette explication [of the adaptation] est purement verbale ; nous constatons un résultat. nous l’exprimons en essayant de 1’inter- préter ; mais le mécanisme reste obscur. . . . Dans beaucoup de cas, adaptation est un phénoméne que |!’on constate sans peine mais qui dans l’état actuel de nos connaissances, reste sans explication” (p. 184 and p. 185). Klebs, Georg, “Willkurliche Entwicklungsanderungen bei Pflan- zen,” 1903. An interesting, suggestive, and valuable account of Klebs’s conclu- €XPeriments, and their significance, on altering the sion from experi- developmental phenomena of plants. Although he is ments on plants: strongly opposed to any vitalistic theory which attrib- utes to life an independence of physico-chemical laws, Klebs does not accept the Darwinian explanation of adaptiveness. Darwin “betrachtet die Zweckmassigkeit selbst als den wesentlichsten Faktor der Artbildung, indem nach seiner Meinung die naturliche Zucht- wahl aus der Menge der richtungslos auftretenden variationen nur die zweckmassigkeiten Merkmale zur Ausbildung und weiteren Entfaltung bringt. Daher stammt die frither so verbreitete und heute uns sonderbar erscheinende Meinung, dass die Deutung eines Merkmales als eines zweckmassigen schon als eine Erklarung fiir sein Entstehen und seine Ausbildung angenommen wurde. Die Geltung der Darwin’schen Theorie muss seit den Arbeiten Nagelis,. de Vries, u. a. jedenfalls eingeschrankt werden. Das eigentliche Problem der Artbildung muss, wie wir spater sehen werden in anderer Weise, formuliert werden” (p. 3). Friedlander (‘““Entdeckung eines ‘Atlantischen Palolo,’” etc., Biol. Centralbl., Vol. XXI, pp. 352-366, i901) refers to the Darwinian explanation of Zweckmassigkeit as follows: “Der ganze Darwinismus im weiteren, also auch vordarwin’schen Sinne der Descendenzhypothese, mit oder ohne Betonung der Selek- Friedlinder’s tionstheorie, und samt den allseitig als fertig und discussion of sicher festgestellt gedachten Stammbaumen aller Or- adaptation, ganismen, wtirde, wenn auch alles damit sonst seine Richtigkeit hatte, unsere Gesamterkenntnis keineswegs in so tber- massigem Grade bereichern, wie man fruher wahnte und vor allem nicht in dem Masse, als dass es sich lohnte, auf die Herstellung der zudem immer problematischen Stammbaume sonderliche Zeit und Muhe zu verwenden. Zweitens aber haben die neueren Experimental- forschungen Arten der Zweckmassigkeit an den Tag gebracht, welche aus rein logischen Griinden durch die Selektionstheorie durchaus nicht, auch nicht einmal scheinbar, ‘erklart’ werden kénnen. Nun ist aber doch gerade die vermeintliche ‘Erklarung’ der organischen Zweckmassigkeit oder sogen. ‘Anpassungsvollkommenheit’ die. Hauptstarke des eigentlichen Darwinismus. Wie die Sache jetzt DARWINISM’S PRESENT STANDING. 393: liegt, miissten die Verteidiger des Darwinismus annehmen, dass die organische Zweckmassigkeit zwei vollkommen verschiedene Wurzeln habe. Die eine ware die alte Darwin’sche oder darwinistische—. da namlich, wo diese logischerweise moglich ist; obwohl ja auch hier die Erklarung die nicht recht befriedigende Form hat, dass. gesagt wird, die Zweckmassigkeit rithre daher, dass die weniger zweckmassigen Formen ausgestorben seien. Die zweite Wurzel der organischen Zweckmiassigkeit, wie sie sich namentlich in den Selbst- regulationserscheinungen aussert und zwar auch unter solchen Bedingungen, die in der freien Natur kaum jemals vorkommen und daher fiir das ‘Bestehender Art’ nicht von irgend welcher Bedeutung sein k6nnen—diese zweite Wurzel der Zweckmassigkeit ist der eigentliche Stein des Anstosses. Die Thatsachen sind hartnackig,. eine darwinistische Scheinerklarung ist hier unmodglich und die an sich doch so ausserst interessanten Erscheinungen, sowie die ganze experimentelle Forschungsmethode ist bei den eigentlichen Dar- winisten nicht in gutem Ansehen; aus dem sehr begreiflichen Grunde,. weil jene Thatsachen ftir die betreffende Richtung unbequem sind. Eine Reihe sicher festgestellter Thatsachen aus dem Gebiete der sogen. Selbstregulation beweist also, dass es organische Zweck- massigkeiten und obendrein typische Beispiele von solchen giebt,. welche dem Darwin’schen Erklarungsschema vollkommen trotzen. Nun aber hat die organische Zweckmassigkeit im ganzen ein so einheitliches Geprage, dass ein doppelter Ursprung von vorn herein ausserst unwahrscheinlich ist. Hieraus folgt dann weiter, dass die darwinistische Betrachtungsweise in der Wirklichkeit wahrscheinlich auch in den Fallen nicht zutrifft, wo sie logisch wenigstens die Moglichkeit einer Erklarung oder Quasierklarung darzubieten scheint. Endlich aber sollten auch diejenigen, denen die Bedenken gegen die darwinistischen Schlussfolgerungen nicht recht eingehen wollen, nachgerade doch wenigstens das einsehen, dass der Teil der Biologie, der sich allenfalls im darwinistischen Sinne behandeln liesse oder doch in Sinne jener Richtung nach Darwin’schen Prin- zipien behandelt werden kann,—dass dieser Teil nur ein kleines. und vergleichsweise auch unwichtiges Gebiet umfasst.” “Jacques Loeb, in a recent address (‘‘Recent Development of Biology,” Congress of Arts and Sciences, Vol. V, p. 17, 1906), takes this attitude toward the problem of species-forming: “The theory Loeb’s attitude Of heredity of Mendel and de Vries is in full har- toward the prob- Mony with the idea of evolution. The modern idea lem of species- of evolution originated, as is well known, with forming, Lamarck, and it is the great merit of Darwin to have revived this idea. It is, however, remarkable that none of the Darwinian authors seemed to consider it necessary that the trans- 394 DARWINISM TO-DAY. formation of species should be the object of direct observation. It is generally understood in the natural sciences either that direct observation should form the foundation of our conclusions or mathematical laws, which are derived from direct observations. This rule was evidently considered superfluous by those writing on the hypothesis of evolution. Their scientific conscience was quieted by the assumption that processes like that of evolution could not be directly observed, as they occurred too slowly, and that for this reason indirect observations must suffice. I believe that this lack of direct observation explains the polemical character of this liter- ature, for wherever we can base our conclusions upon direct obser- vations polemics become superfluous. It was, therefore, a decided progress when de Vries was able to show that the hereditary changes of forms, so-called ‘mutations,’ can be directly observed, at least in certain groups of organisms, and secondly, that these changes take place in harmony with the idea that for definite hereditary characteristics definite determinants, possibly in the form of chemical compounds, must be present in the sexual cells. It seems to me that the work of Mendel and de Vries and their successors marks the beginning of a real theory of heredity and evolution. If it is at all possible to produce new species artificially, I think that the discoveries of Mendel and de Vries must be the starting point.” * Schmankewitsch, A., Zeitschr. f. wiss. Zool., Vol. XXV, p. 103, 1875; also Zeitschr. f. wiss. Zool., Vol. XXIX, p. 429, 1877. ° Adelung, Zool-Centralbl., Vol. VI, p. 757, 1899. (A review of Anikin’s paper, which is in Russian.) 1 Kellogg, V. L, “A New Artemia, and Its Life-Conditions,” Science, N. S., Vol. XXIV, 594-596, 1906. 1 Klebs, G., “Willkiirliche Entwickelungsanderungen bei Pflan- zen,’ 1903. 12 Tower, W. L., “Evolution in Chrysomelid Beetles of the Genus Leptinotarsa,” Pub. No. 48, Carnegie Institution of Washington. “The phenomenon of variation primarily owes its existence to the fact that community of descent and heredity tends to produce the exact counterpart of the parent organisms; the process of develop- ment, however, is not carried out under absolutely constant or uni- form conditions, but in a world wherein there exist changing environ- mental states in endless proximity. This results in the turning aside in the line of development from the parental standard, per- haps ever so little or only in one character; but in this we have deviation or variation” (p. 208). “In the explanation of origin of variation in organisms the only assumption we need make is that the original unit of organic matter was possessed of the attributes which characterise organic matter DARWINISM’S PRESENT STANDING. 395 to-day—motion, sensation, growth, and reproduction. This assump- tion cannot meet with any serious objection unless we change our ideas and definition of organic units. Granted the existence of one single organic unit endowed as above, there is no reason for intro- ducing further complications by the explanation of phenomena through undemonstrable hypotheses, because the fact of variation in organic units can be explained solely through their existence in a natural world surrounded by varying conditions of existence” (p. 299). “In the third chapter, where colour characters are used as sub- jects, it is demonstrated that variation is directly produced by stimuli—that from relatively invariable parents, stimuli produce variable offspring; and again in the fifth chapter it is shown that variations arise in direct response to stimuli” (p. 300). “TI maintain, therefore, that all organic variations are responsive to stimuli, and are not due to inherent tendencies or latencies, or the product of mystic elements” (p. 300). 18 Montgomery, T. A., in a recent book of much interest (‘‘Anal- ysis of Racial Descent in Animals,” 1906), explains clearly his belief in the inevitable production of variation (even that called blastogenic or congenital), and the influence on heredity (through this varia- tion) by the influences of environment. 14 Brooks, W. K., “The Foundations of Zoology,” p. 43, 1899. A most thoughtful and keen discussion of many of the conspicuous problems of “philosophical biology,” written in lucid and epigram- matic style. In many ways Brooks stands at the head of American philosophical biologists. INDEX. Adaptation, complex and cor- related, not explicable by selection, 144; Friedlander’s discussion of, 392; lack of, in egg-laying habit of Phrygani- dia californica, 68; the great need of explaining, 380; not all explicable by Lamarckism, 272 Amphimixis, Weismann’s prin- ciple of, 180 Anosia, mimicry of, by Basi- larchia, 49 Anti-Darwinism, present-day, 4 Baldwin, J. M., theory of ortho- plasy, 208 Basilarchia, mimicry of Anosia by, 49 Bateson, W., records of discon- tinuous variation, 33; sugges- tion that mutations are Men- delian recessives, 351 Battle of the parts, theory of, 201 Biologists, many not satisfied with the selection theory, 89 Biophor, 195 Brown-Séquard, experiments on guinea pigs, 290 Buffon, theory of ultimate structure of protoplasm, 216 Bumpus, H., example of in- creased variability due to emancipation from selection, 56; references to papers by, 69 Burbank, Luther, belief in La- marckism, 272; scientific as- pects of work of, 310 Roux’s Callosamia promethea, Mayer’s experiments with, 120 Carcinus, Weldon’s _ selection experiments on, 158 Castle, W. S., discussion of mutations theory, 364 Chance, law of, variation accord- ing to, 32-59 Characters, numerous, useful only in highly perfected state, 49; species, of no utility, 38 Colour and pattern of insects, Piepers’ antagonism to selec- tion explanation of, Conn, H. W., discussion of the chances of death, 83; discus- sion of selective value, 182; statement of objection to se- lection, based on trivial char- acters, 40 Cope, E. D., belief in ortho- genetic evolution, 323; claim- ing that natural selection can- not make new characters, 185; theory of orthogenesis, 285 Correlation, references to papers on, 184 Crab, hermit and polyp, sym- biosis of, 23 a Weldon’s experiments on, 15 Cunningham, J. T., criticism of Weldon’s experiments on erabs, . 160i. discussion) (of orthogenesis, 326; experiments on flatfishes, 296; explanation of secondary sexual charac- ters, 354; theory to explain sec- ondary sexual differences, 124 Dall, W., belief in species-change, 330 Darwin, C., attitude toward de- terminate variation, 34; basis of theory of sexual selection, 112; explanation of descent, 13; On race origin from sports, 357; theory of sexual selec- tion, I11; theory of ultimate structure of protoplasm, 218 Darwinism attacked, 25; attack on, by Dennert, 7; concilia- sudden 397 398 tory defence of, 164; death-bed of, 1; defended, 129; defined, 2, 10; not synonymous with organic evolution, 2, 3; pres- ent standing of, 374; upheld by Lankester, 389 Davenport, C. B., discussion of mutations theory, 367 Death-bed of Darwinism, I Death indiscriminate, 80 Defence of Darwinism, 129 Degeneration, complete, not ex- plicable by selection, 77, 146; example of progressive, not explicable by natural selection, 100; explanation of, by pan- mixia, 190; Lamarckian ex- planation of, 192; Plate’s La- marckian explanation of, 147; Tayler’s Darwinian explana- tion of, 147; Weismann’s dis- cussion of, 77 Delage, Y., criticism of Del- boeuf’s law, 72; criticism of organic selection, 210; esti- mate of selection, 93, 390; ma- chine theory of protoplasm, 225; theory of general varia- tion, 289 Delbceuf’s law, cist of, 72 Dennert, E., attack on Darwin- ism, 7 Descent, Darwinian explanation of, 13; evidences for, 17; evi- dences of, references, 23; his- tory of theory of, references, 22; natural selection the final arbiter in, 374; relations to theology, references, 23; theo- ries of, 187; theory of, de- fined, 11; theory of, dis- tinguished from theory of nat- ural selection, 17; theory of, history, of. 11; theory, given validity by Darwin, 12; theory, relation to pedagogy, 21; theory, relation to sociology, 21; theory, relation to theology and philosophy, 20 Determinant, 95 DeVries, H., belief of, that artificial races are not fixed and constant forms, 87; dis- cussion of geologic time and Delage’s criti- INDEX. species-forming, 54; discus- sion of species-forming by selection, 389; objection to selection based on linear char- acter of variation, 139; refer- ences to discussions of muta- tions theory by, 362; summing up of discussion of compari- son of natural and _ artificial selection, 89; theory of muta- tions, 337; theory of the ulti- mate structure of protoplasm, 220 Dohrn, A., principle of change of function, 168 Douglass, N. G., observations on wall lizard, 123 Durigen, observations on_ liz- ards,. 123 Eimer, Th., theory of ortho- genesis, 282, 321 Emery, C., theory of primary variations, 332; theory of the origin of secondary sexual characters, 353; theory to ex- plain secondary sexual differ- ences, 124 Evolution, defined, 10; organic, not synonymous with Darwin- ism, 2, 3; Osborn’s champion- ship of the unknown factors of, 391; the unknown factors OF, 377 poe a study, prime needs of, 37 Fischer, experiments with but- terflies, 296 Fleischmann, A., opposed to evo- lution, 8 Friedlander, discussion of adap- tation, 392 Friedman, H., theory of the con- vergence of organisms, 8 Galton, F., belief in hetero- genesis, 332; discussion of specific stability, 359; discus- sion of variation according to the law of chance, 61; law of regression, 71; statement of the law of regression, 97 Germ-cells, theories of ultimate composition of, 268 INDEX. Grinnell, Jos. study of geo- graphic differences in the chickadee, 225 Gulick, J. T., studies of Ha- waiian land snails, 251; theo- ries of isolation influence, 249 Haacke, W., discussion of in- heritance of acquired char- acters, 270; summary of Wag- ner’s theory, 253 Haeckel, E., champion of evolu- tion, 130 Hatschek, B., theory of the ultimate structure of proto- plasm, 222 Henslow, G., experiment of sow- ing of wheat, 80; references to aoe antagonistic to selection, 7 Heterogenesis, 326; belief in, of Dall, 330; Emery’s theory of, 332; Korschinsky’s theory of, 333; proposed by von Kol- liker, 330 Hutton, F. W., argument for dualism, 23 Hyatt, A. experiments on Planorbis, 295 Inheritance of acquired char- acters, 263; Brown-Séquard’s experiments, 290; Cunning- ham’s experiments, 296; diff- _ culties in accepting, 267; ex- periments with = silkworms, 2908; Fischer’s experiments, 296; Haacke’s discussion of, 270; Hyatt’s experiments, 295; logical proof of, 382; Mont- gomery’s explanation of, 306; references to discussions of, 305 Insects, parthenogenetical varia- tion in, 58; variation in, 62 Interbreeding, swamping favour- able variations, 44 Intra-selection, Roux’s theory of, 201; Plate’s criticism of Roux’s theory of, 203 Isolation, biologic, 243; biologic, example of, 243; geographic, studied among past animals, 241; defined, 234; importance of, in species-forming, 232; 399: not an all-sufficient agent of species-forming, 242; physio- logical, 245; references to dis- cussions of, 253, 261; sexual,. 245; theories, 232; various. means of effecting, 234 Jaeckel, theory of metakinesis, 289 Johannsen, W., experiments. with beans bred in pure lines, 72 Jordan, Karl, criticism of Ver- non’s theory of reproductive divergence, 249; on mechanical selection, 246 Jordan, D. S,, isolation, 237 on geographic Kallima, case of, explained by Plate, 175; over-specialisation of, 53 Klebs, G., experiments on plants, 392 Korschinsky, H., radical anti- selection position of, 9QI; theory of heterogenesis, 333 Kramer, P., classification of sec- ondary sexual characters, 107 Lamarck, references to his life and writings, 290 Lamarckism, 263; Burbank’s be- lief in, 272; favoured by Red- field, 305; Plate’s discussion of, 273; unable to explain all adaptations, 272; Weismann’s. attack on, 266 Lankester, R., answer to objec- tion to selection, based on in- sufficient time, 55; upholding of Darwinism, 389 Law, Delbceuf’s, Delage’s criti- cisms of, 72; of chance, varia- tion. according to, 32, 50; of regression, Galton’s, 71; of regression, statement of Gal- ton, 97 Le Dantec, F., chemical theory of protoplasm, 225 Lizards, experiments on, 123 Loeb, J., attitude toward the problem of species-forming,. 393 400 Mallophaga, effects of isolation on, 240 Mayer, A. G., experiments on Promethea, 121; experiments on sexual selection, 120 Mendel, G., references to life and work, 356 Mendelism, references to discus- sions of, 357 Merriam, C.. Hi ‘criticrm of mutations theory, 367 Metakinesis, Jaeckel’s theory of, 289 Mimicry of Anosia by Basi- larchia, 49 Montgomery, Th., of inheritance characters, 306 Morgan, C. L., statement of con- ception of organic selection, 230; theory of orthoplasy, 145, 208; answer to objections to sexual selection theory, 149 Morgan, T. H., antagonism of species-forming by selection, 93; criticism of Weismann’s method of argument, 229; dis- cussion of de Vries’s theory, 345; objections to sexual se- lection theory, 118; summation of the advantages of the muta- tions theory. 350 Mutation, as used by Waagen, 324; de Vries’s theory of, 337 Mutations theory, American opinion of, 362; attitude of naturalists toward, 348; con- trasted with Lamarckism, 349; contrasted with the isolation factor, 349; discussion of, by Castle. 364; discussion of, by Davenport, 366, 367; Mer- riam’s criticism of, 367; Mor- gan’s summation of the ad- explanation of acquired vantages of, 350; Plate’s criticism of, 368; references to discussions of, by de Vries, 362 Nageli, Ch., seven objections to species-forming by selection, 62; theory of orthogenesis, 277; theory of ultimate struct- ure of protoplasm, 219 INDEX, Neo-Darwinians, concessions of,