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WHAT EVOLUTION IS 
 
LONDON : HUMPHREY MILFORD 
 OXFORD UNIVERSITY PRESS 
 
~ FEB? ry 1926. 
 
 
 
 
 WHAT EVOLUTI 
 
 BY | 
 GEORGE HOWARD PARKER 
 
 Professor of Zotlogy and Director of the Zoblogical 
 Laboratory, Harvard University 
 
 
 
 CAMBRIDGE 
 HARVARD UNIVERSITY PRESS 
 
 1926 
 
COPYRIGHT, 1925, 
 BY HARVARD UNIVERSITY PRESS 
 
 Second Printing. 
 
 PRINTED IN THE 
 UNITED STATES OF AMERICA 
 
PREFACE 
 
 THE growing popular interest in evo- 
 lution calls for a simple statement 
 concerning this doctrine. Such a 
 statement should be as brief as is con- 
 sistent with right understanding, and 
 should be to the point. In view of the 
 animated and heated discussions that 
 have been excited by the present situ- 
 ation, this statement should be free 
 from prejudice and partiality. It is 
 from this standpoint that the follow- 
 ing pages have been written. 
 
 No fundamental doctrine such as 
 that of evolution can be rightly con- 
 sidered without taking into account 
 its full bearings on the whole of or- 
 ganic nature. Plants and animals, 
 with all their intricate interrelations, 
 afford the materials for this theme. 
 Man as the most complex of animals 
 
vi PREFACE 
 
 must find his nature elucidated 
 through evolution if this doctrine is 
 to maintain itself. What its value is 
 in this respect must be judged by 
 each reader. 
 
 That the illustrative examples and 
 other like materials in the present vol- 
 ume are chiefly from zoological 
 sources is due to the fact that the 
 writer is a zoologist. It is scarcely 
 necessary to add that botanical ma- 
 terials afford the same kind of evi- 
 dence as that given in the body of 
 this text and might have been utilized 
 in the same way that the zoological 
 examples have been. 
 
 It is the object of this volume to 
 present a brief, readable account of 
 the main facts of evolution, that the 
 ordinary reader may acquaint him- 
 self with what may be called the ele- 
 ments of the subject. That so large a 
 topic as evolution can be adequately 
 
PREFACE Vii 
 
 treated in a volume of the size of the 
 present one is quite inconceivable, 
 and yet such an account as that which 
 follows may at least outline the sub- 
 ject and in this way prepare the 
 reader for further inquiry. 
 

 
WEE 
 
 IV. 
 
 VI. 
 
 CONTENTS 
 
 INTRODUCTORY . 
 
 ee LISTORICAL 
 
 EVIDENCE ON EVOLUTION 
 
 2 
 
 ee 
 
 6. 
 
 From Comparative Anat- 
 
 OLY eaten) aoe ile 
 From Embryology . 
 From Geology 
 From Zoogeography . 
 From Rudimentary Or- 
 
 gans . aeons 
 Conclusion 
 
 FACTORS IN EVOLUTION 
 
 Ls 
 
 SPSL C ee SS 
 
 Prefatory 
 
 Lamarckism 
 Lamarckism mitcieds 
 Darwinism ; 
 Darwinism eed 
 The Mutation Theory . 
 
 HuMAN APPLICATIONS 
 
 READING REFERENCES . 
 

 
 
 
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INTRODUCTORY 
 
 EVOLUTION is a term that has been 
 used in a great variety of ways. We 
 speak of the evolution of the stars, 
 meaning thereby the process by which 
 stars have grown from gaseous masses 
 to incandescent bodies, such as our 
 sun, and finally to the cold inert con- 
 ditions of stellar death. We speak of 
 the evolution of the earth, in that we 
 picture the growth of that body as a 
 part of the solar system whose central 
 element, the sun, yields the energy by 
 which the earth is moulded. Under 
 the varying heat of this luminary our 
 atmosphere is made to move as wind, 
 water is evaporated and condensed, 
 continents are eroded and dissected, 
 materials are disintegrated, trans- 
 ported, and deposited—in short, the 
 surface of the earth is put under con- 
 
4 WHAT EVOLUTION IS 
 
 tinual flux and change. Thus the 
 present configuration of oceans and 
 of continents, of mountains and of 
 abysses, is looked upon, not as some- 
 thing stationary, but as due to opera- 
 tions whose titanic energies have been 
 exerting themselves through untold 
 ages in the past and will continue so 
 to act far into the futures) these 
 happenings, and such as occur among 
 the stars, constitute what may be 
 called cosmic evolution, a body of 
 change which in the nature of things 
 preceded life and was, in a certain 
 sense, preparatory to it. It is the 
 plan of this book, not to deal with 
 this type of evolution, notwithstand- 
 ing the fact that cosmic evolution is 
 intimately bound up with the origin 
 of living things, but to consider ex- 
 clusively the kind of evolution that 
 has to do with organisms, with plants 
 and animals. Such a type of evolu- 
 
WHAT EVOLUTION IS 5 
 
 tion may be called organic, as con- 
 trasted with what has just been 
 spoken of as cosmic. 
 
 Organic evolution, dealing as it 
 does with living organisms, has a set 
 of problems quite its own. Although 
 the body of a plant or of an animal 
 contains no chemical element not 
 found in the earth, and the energy in 
 such living bodies is subject to the 
 same laws that govern the inorganic, 
 plants and animals have superim- 
 posed upon their fundamental cosmic 
 properties, other properties more or 
 less peculiar to themselves. Thus all 
 plants and animals, like other bodies 
 about us, are subject to the law of 
 gravitation and to other laws of a 
 purely physical and chemical nature; 
 yet these plants and animals grow, 
 reproduce, react, and respond in ways 
 which are not entirely consonant 
 with the chemistry and physics of the 
 
6 WHAT EVOLUTION IS 
 
 strictly inorganic. They have, in ad- 
 dition to the chemistry and physics 
 of lifeless nature, a chemistry and 
 physics more or less their own. It is 
 in this way that organic evolution 
 differs from simple cosmic evolution, 
 for organic evolution is a general op- 
 eration among plants and animals 
 some aspects of which are not to be 
 met with in the inorganic. 
 
 Organic evolution, though a well- 
 unified field in biology, can be profit- 
 ably treated under two heads. ‘The 
 first of these has to do with the doc- 
 trine of descent with modification — 
 the belief that plants and animals of 
 particular kinds have descended by 
 gradual modification from preéxist- 
 ing plants and animals of very dif- 
 ferent kinds. This belief, which is 
 often spoken of as if it were the 
 whole of evolution, is supplemented 
 by what may be treated under a sec- 
 
WHAT EVOLUTION IS 7 
 
 ond heading, a group of doctrines 
 that have to do with the way in which 
 descent with modification has been 
 accomplished. Granting that plants 
 and animals have arisen by the modi- 
 fication of earlier forms, what have 
 been the driving forces in nature that 
 have induced this modification? This 
 is a newer and much less certain field 
 of work than that which deals with 
 the simple fact of change or trans- 
 mutation in organisms. It includes 
 a consideration of Lamarckism, of 
 Darwinism or the theory of natural 
 selection and such subordinate theo- 
 ries as sexual selection, of orthogene- 
 sis, of the mutation theory, and of a 
 host of other views which from time 
 to time have been advanced as ex- 
 planations of descent with modifica- 
 tion. In the following pages, after 
 some brief historical comment, the 
 subject matter will be dealt with 
 
 WA 
 
8 WHAT EVOLUTION IS 
 
 under the two general headings just 
 mentioned: evolution as descent with 
 modification, and the explanations 
 that have been offered for this 
 process. 
 
II 
 HISTORICAL 
 
4 
 
 - 
 1 
 1 
 
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 —, 
 
 
 
HISTORICAL 
 
 THE idea of evolution is often looked 
 upon as a comparatively modern one. 
 As a matter of fact, it reaches back 
 into remote antiquity. Most races of 
 primitive man believed in some vague 
 way that they had kinship with the 
 lower animals. Many of the clans of 
 American Indians used animals as 
 their totems. Among the Indians of 
 the northwest coast the bear, the 
 raven, and the beaver were used in 
 this way, and in New England the 
 wildcat, the wolf, the muskrat, the 
 squirrel, the porcupine, and the frog 
 were similarly employed. Although 
 these totems were primarily signs of 
 the clan and were used as such, par- 
 ticularly in religious observances, 
 they were in many instances invested 
 with an ancestral aura, and the clan 
 
12 WHAT EVOLUTION IS 
 
 was supposed in some vague way to 
 have descended from the animal con- 
 cerned. Most primitive human be- 
 ings seem to have had some such 
 traditions as these about animals, but, 
 of course, in no case could these views 
 be said to have more than remotely 
 implied an evolutionary conception. 
 They merely show that in primitive 
 man kinship with animals was not an 
 unknown idea. 
 
 To certain Greeks organic evolu- 
 tion in the modern sense came nearer 
 to being a reality. Thus the great 
 physical philosopher of the Ionian 
 School, Anaximander (611-547 B.c.), 
 is credited with having held to a 
 form of general evolution in which 
 man was especially involved. Anaxi- 
 mander was apparently impressed 
 with the inability of man in his early 
 stages of life to care for himself, and 
 was thereby led to conclude that 
 
WHAT EVOLUTION IS 13 
 
 human beings in the beginning must 
 have been very different from what 
 they are at present. He is even be- 
 lieved to have assumed for them an 
 aquatic ancestry, perhaps fish-like 
 in character. Anaximander’s views 
 were often quoted, and thus classical 
 antiquity must have had some idea of 
 the evolutionary doctrine. 
 
 But the serious advances in this 
 body of opinion date from the last 
 two centuries. Throughout the early 
 part of this period uncertain rumors 
 of an evolutionary kind were contin- 
 ually heard; and as time went on, 
 these rumors ‘became more and more 
 distinct. With this growth in defi- 
 niteness opposition took on a more 
 final shape. Thus Linneus (1707- 
 1778), who may be said to have es- 
 tablished systematics by publishing 
 in his “Systema Naturz” a classifi- 
 cation and description of all plants 
 
14 WHAT EVOLUTION IS 
 
 and animals known in his time, be- 
 lieved firmly in the immutability of 
 species and declared in favor of the 
 biblical account of special creation. 
 According to him there are as many 
 different species of plants and of an- 
 imals on the earth as there were dif- 
 ferent forms created by the Supreme 
 Being in the beginning. This view, 
 based upon the account in Genesis, 
 was thus set in strong contrast with 
 that of the origin of species through 
 descent with modification. 
 
 The first radical exponent of mod- 
 ern organic evolution was Lamarck 
 (1744-1829) who published in 1809 
 his “Philosophie Zoologique.” In 
 this volume Lamarck set forth a plea 
 that the plants and animals of to-day 
 had arisen by the modification of pre- 
 existing forms, and he further ad- 
 vanced an hypothesis as to the way 
 in which this change had come about. 
 
WHAT EVOLUTION IS 15 
 
 His views were ably seconded by a 
 number of the most distinguished 
 savants of his time, among whom 
 may be numbered the great Goethe. 
 Of Lamarck’s confréres Geoffroy 
 Saint-Hilaire took up the subject in 
 public discussion with Cuvier, per- 
 haps the greatest naturalist of his 
 day. Cuvier, whose opinions were 
 anti-evolutionary, resisted with all his 
 strength and authority the rising tide 
 of new opinion and succeeded in 
 checking its flow, for it was generally 
 concluded at the end of the contest 
 that descent with modification must 
 be permanently abandoned. 
 
 For some decades the storm sub- 
 sided, for the appearance of the little 
 volume entitled “ Vestiges of the Nat- 
 ural History of Creation,” published 
 by Robert Chambers in 1844, was 
 only a ripple on the surface. Then 
 in 1859, with the publication of Dar- 
 
16 WHAT EVOLUTION IS 
 
 win’s “Origin of Species,” the storm 
 broke afresh, this time not to be 
 turned aside till it had swept the 
 shores clear of the wreckage of old 
 ideas. 
 
 Everyone knows the great public 
 upheaval that followed the appearance 
 of the “Origin of Species.” The 
 scientific world had been prepared for 
 it by a paper on the theory of natural 
 selection, published by Darwin and 
 Wallace in the preceding year; but 
 considering the long period of rela- 
 tive quiescence that had preceded 
 1859, even scientists must have been 
 startled at the uproar that broke 
 forth. Darwin and his able coadju- 
 tor, Huxley, had the double task of 
 showing to the world that, in contrast 
 with special creation, descent with 
 modification had taken place, and that 
 natural selection was the driving 
 force behind this process. In the 
 
WHAT EVOLUTION IS 17 
 
 days of Lamarck the chief question 
 was on the modifiability of species, 
 and on this first line of attack the 
 forces of evolution received for the 
 time being a serious setback. But 
 under Darwin and Huxley a new of- 
 fensive was launched, and after a 
 vigorous campaign both objectives 
 were attained. It is to the credit of 
 Charles Darwin, and his body of able 
 supporters, that the scientific world 
 was finally brought to accept the prin- 
 ciple of descent with modification, 
 and natural selection as the means 
 whereby it was accomplished. 
 
 The evidence that convinced the 
 world in Darwin’s day that descent 
 with modification, and not special 
 creation, was the means of peopling 
 the present globe with its variety of 
 living forms was meager in the ex- 
 treme as compared with what might 
 be drawn upon to-day, but it never- 
 
18 WHAT EVOLUTION IS 
 
 theless covered the ground and may 
 be profitably looked into now, since 
 it still affords the real support on 
 which the doctrine of evolution rests. 
 This body of evidence comes from five 
 important fields in biology: compara- 
 tive anatomy, embryology, the study 
 of fossils, zoogeography, and the 
 nature of rudimentary organs. 
 
Ill 
 EVIDENCE ON EVOLUTION 
 

 
EVIDENCE ON EVOLUTION 
 
 1. FROM COMPARATIVE 
 ANATOMY 
 
 AN important body of evidence that 
 bears on the evolutionary problem 
 comes from the field of comparative 
 anatomy. A little over a century ago 
 the school of comparative anatomy 
 was founded by Cuvier (1769-1832), 
 who, though an _ anti-evolutionist, 
 showed that animals in their structure 
 were not immensely diverse, but con- 
 formed to general plans or types of 
 organization. From this standpoint 
 each animal could be said to represent 
 its type, subject to such modifications 
 as its special mode of life called for. 
 Thus under the enormous diversity 
 of animal forms there was in reality 
 a more or less hidden uniformity. 
 This principle of type organization 
 
22 WHAT EVOLUTION IS 
 
 is abundantly illustrated by many 
 sets of organs. For instance, the 
 human arm is composed of parts that 
 recur in the corresponding organs in 
 other animals. The arm of man, as 
 shown on page 23, contains four sets 
 of bones: the single bone of the upper 
 arm, the pair of bones in the forearm, 
 the group of small wrist bones, and 
 the series of elongated bones in the 
 five digits. All these groups of bones 
 recur with great regularity in the 
 foreleg of the cat, of the turtle, and 
 of even so lowly organized an animal 
 as the frog. The wing of a bat, when 
 it is examined, is found not to be con- 
 structed upon a plan peculiar to itself, 
 but to be a modification of the type of 
 structure already described for man, 
 in that the single bone of the upper 
 arm is present, as are the pair of 
 forearm bones, the wrist bones, and, 
 enormously elongated to carry the 
 

 

 
WHAT EVOLUTION IS 25 
 
 web of the wing, the finger bones. In 
 the bird, unlike the bat, the expansion 
 of the wing is due to feathers but the 
 skeletal axis that supports the feath- 
 ers 1s formed from a set of bones 
 such as occur in the human arm, ex- 
 cept that the fingers are reduced in 
 number and bound together to serve 
 as a supporting axis for the larger 
 plumes. The flipper of a whale or 
 of a porpoise, superficially so unlike 
 the human arm, nevertheless shows 
 closely compacted within it the bone 
 of the upper arm, the two forearm 
 bones, wrist bones, and finger bones. 
 In the foreleg of the horse the bone 
 corresponding to that in the upper 
 arm of man is hidden in the flesh of 
 the animal. This bone is followed, 
 however, by the two bones of the 
 forearm, fused together, by the wrist 
 bones, which are situated at what is 
 popularly called the knee of the horse, 
 
26 WHAT EVOLUTION IS 
 
 and by a row of bones which repre- 
 sent the middle finger of man. These 
 bones in man are four in number, 
 counting the deep-seated long bone 
 in the palm, and this number is ex- 
 actly reproduced in the horse, in which 
 the last member of the series carries 
 the hoof corresponding to the human 
 nail. The front leg of the horse not 
 only rests on what is equivalent to 
 the enormously enlarged middle fin- 
 ger of man, but it contains, on either 
 side of this digit, relatively inconspic- 
 uous splint bones which represent our 
 index and our ring fingers. 
 
 By the comparative method it is 
 thus possible to demonstrate that 
 such apparently diverse organs as the 
 arm of a man, the wing of a bat, and 
 the foreleg of a horse are similarly | 
 organized and are merely modifica- . 
 tions of one type of structure. 
 
 Animals and plants abound on 
 
WHAT EVOLUTION IS 27 
 
 every hand with series of parts in 
 which the elements are related, as in 
 the examples just described, and it is 
 one of the achievements of the com- 
 parative method that it has thus 
 yielded incomparably rich and signifi- 
 cant material for philosophical bi- 
 ology. By its means anatomy has 
 been lifted from a discipline of dead 
 description to a science rich in prob- 
 lems and resources. 
 
 This advance in method had an 
 immediate and decisive bearing on 
 the evolutionary question. If organ- 
 isms were separately created there 
 would be every reason to expect that 
 they would be constructed upon indi- 
 vidual plans, and not the least ground 
 to anticipate in them an underlying 
 common type of structure. If, how- 
 ever, they have evolved from a 
 common ancestry, precisely such un- 
 derlying similarities might be ex- 
 
28 WHAT EVOLUTION IS 
 
 pected. The human arm, the foreleg 
 of a quadruped, the wing ofa bird, and 
 the flipper of a whale have a common 
 plan of organization because these 
 animals have had a common ancestry. 
 Thus the science of comparative an- 
 atomy yields results that support 
 most completely the evolutionary 
 idea, and that give no ground for the 
 assumption of special creation. It is 
 a remarkable fact that Cuvier, who, 
 as already observed, was a strong 
 anti-evolutionist, should have been 
 instrumental in founding and in 
 partly developing a school that in the 
 end yielded such important evidence 
 in favor of descent with modification. 
 
WHAT EVOLUTION IS 29 
 
 2. FROM EMBRYOLOGY 
 
 THE science of embryology deals 
 with the growth of animals from the 
 ege to the adult, and this science, 
 though of comparatively recent ori- 
 gin, has had an important bearing on 
 evolutionary problems. It is a com- 
 monplace that, in the development of 
 any animal, the creature does not 
 start life as a miniature of what it is 
 finally to be and then slowly enlarge 
 until it reaches adult proportions, but 
 it begins life in a state very unlike its 
 adult condition and only gradually 
 assumes an outline that is associated 
 with its final form going through a 
 series of changes, often very pro- 
 found, till it finally arrives at its ma- 
 ture state. 
 
 Most common animals afford ex- 
 amples of this kind of growth. 
 
30 WHAT EVOLUTION IS 
 
 Frogs, for instance, lay eggs and 
 from these are hatched, not frogs, 
 but tadpoles which eventually, through 
 a series of rather complicated bodily 
 changes, reach the condition of an 
 adult frog. 
 
 The remarkable peculiarity of this 
 kind of growth is that, during the 
 steps in its progress, the young ani- 
 mal often shows striking resem- 
 blances to other animals. Thus, in 
 the instance just given, the tadpole of 
 the frog has unquestionably fish-like 
 characteristics. Instead of having 
 front and hind legs for locomotion as 
 in the adult frog, the tadpole moves 
 about by means of a flattened tail in 
 a way similar to that of a fish. More- 
 over, the tadpole has in its neck a 
 system of gills by which it breathes 
 precisely as a fish does. As develop- 
 ment goes on, these gills are gradu- 
 ally absorbed and are replaced by 
 
WHAT EVOLUTION IS 31 
 
 lungs when the tadpole approximates 
 the state of the frog. But before this 
 metamorphosis has taken place the 
 tadpole, in structure and in activities, 
 recalls in many important particulars 
 the state of a fish. 
 Examples of this kind may also be 
 found in the course of human develop- 
 ment. When the human embryo is a 
 small fraction of an inch in length a 
 definite number of narrow transverse 
 clefts appear on its neck as shown 
 in the uppermost figure on page 33. 
 These clefts lead into the throat and 
 correspond in position to the gill open- 
 ings of fishes. Moreover the sup- 
 ports between the clefts, the arches, 
 which are numbered in the figure, 
 carry large arteries resulting from 
 the division of the main blood-vessel 
 that emerges from the embryonic 
 heart, just as the gill arches of fishes 
 are supplied by large vessels from the 
 
32 WHAT EVOLUTION IS 
 
 heart of the fish. These embryonic 
 organs in man never serve for breath- 
 ing as the corresponding parts do in 
 fishes, but in gross structure the 
 human gill arches recall in a most 
 striking way the gill system of fishes. 
 As the development of the human 
 embryo proceeds, the gill clefts are 
 obliterated, excepting the first one 
 which is retained in forming the aper- 
 ture of the external ear. 
 
 Thus the frog and man and in fact 
 all the higher vertebrates show in a 
 temporary way gill clefts and gill 
 arches, both of which are the perma- 
 nent possessions of the fishes. 
 
 That higher animals should, in the 
 course of their individual develop- 
 ment, exhibit temporarily features 
 that are permanent in lower animals, 
 seems to be a rule of organic growth. 
 It certainly is abundantly exempli- 
 fied in many forms. Thus in all 
 
WHAT EVOLUTION IS 33 
 
 
 
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' WHAT EVOLUTION IS 35 
 
 true backboned animals a notochord, 
 or supporting rod, precedes in devel- 
 opment the real backbone of these 
 forms and is replaced by this bone, 
 except in the very lowest fishes where 
 the notocord is the permanent and 
 only organ of support. Another ex- 
 ample may be found in the embryonic 
 human being where small ribs occur 
 attached to the neck vertebrae. As 
 development advances these ribs fuse 
 with the vertebrae and are thus lost 
 to view, but in lower animals, like the 
 alligator, neck or cervical ribs are 
 persistent throughout life. Again 
 all animals that reproduce sexually 
 pass through an egg stage in which 
 they are, for the time being, a single 
 cell. This state is a permanent condi- 
 tion in the simplest animals, the pro- 
 tozoans, which are very usually only 
 single cells. Innumerable examples 
 such as these might easily be given. 
 
36 WHAT EVOLUTION IS 
 
 The peculiarity of development, 
 that higher animals pass in a tempo- 
 rary way through stages that are per- 
 manent in lower forms, has long been 
 recognized as a characteristic feature 
 of general growth. It has sometimes 
 been dignified as a law of develop- 
 ment and has been designated, in 
 honor of the father of modern em- 
 bryology, von Baer’s law. As such it 
 was strongly advocated by Louis 
 Agassiz. In a more descriptive way 
 it has been spoken of as the law of 
 recapitulation, for the reason that 
 such features in the development of 
 an animal as those already alluded to 
 recapitulate, in a rough way, the ra- 
 cial history of the animal concerned. 
 Thus the presence of gill slits in the 
 embryo of the human being indicates 
 that a gill-breathing animal is to be 
 included in our remote ancestry. As 
 Huxley facetiously remarked in dis- 
 
WHAT EVOLUTION IS 37 
 
 cussing this question years ago, each 
 animal in its development climbs its 
 own ancestral tree. 
 
 The facts associated with the law 
 of recapitulation are quite meaning- 
 less from the standpoint of special 
 creation, but from that of descent 
 with modification they receive a simple 
 and adequate interpretation. A de- 
 veloping animal shows temporary re- 
 semblances to lower forms, because 
 these forms represent steps in its 
 own racial history. 
 
38 WHAT EVOLUTION IS 
 
 3. FROM GEOLOGY 
 
 THE evidence on the evolutionary 
 problem to be drawn from geology 
 turns largely on the question of fos- 
 sils. A fossil is anything dug from 
 the earth. Specifically fossils are 
 bones, shells, or even delicate struc- 
 tures such as ferns and the like, that 
 have been more or less converted into 
 stone and have been exhumed from 
 their hiding places in the rocks. 
 
 The ancients were acquainted with 
 fossils, but they regarded them in a 
 light very different from that in 
 which the modern naturalist looks 
 upon them. Fossils were believed by 
 the ancients to have had something 
 to do with nature’s formative proc- 
 esses. These early observers were, 
 for the most part, believers in spon- 
 taneous generation. They accepted 
 
WHAT EVOLUTION IS 39 
 
 the view that new organisms, plants 
 and animals, were being continually 
 produced by nature, that fish, frogs, 
 worms, and the like were being 
 formed continually from the mud 
 and slime in the bottoms of ponds, 
 that maggots were being generated 
 spontaneously in decomposing meat, 
 and that parasitic worms were being 
 produced in the interior-of the ani- 
 mals whose bodies they inhabit; in 
 short that the process of spontaneous 
 generation pervaded nature gener- 
 ally. They were not conversant with 
 the modern idea, arrived at after 
 long experimentation, that all living 
 things come from preéxisting living 
 things and that none are formed de 
 novo. ‘Vhey held that mother earth 
 was continually producing new life 
 from her own substance. 
 
 With this doctrine in mind, their 
 interpretation of fossils was very 
 
40 WHAT EVOLUTION IS 
 
 different from that given by the mod- 
 ern naturalist. When they discov- 
 ered the impressions of shells in the 
 rocks of the mountainside they recog- 
 nized at once the inappropriateness 
 of the situation, and they believed 
 that they had before them evidence 
 of nature’s unsuccessful effort to 
 produce new life. She, in her prod- 
 igality of productiveness, had started 
 the formation of an aquatic animal 
 on a mountainside and, in conse- 
 quence of the unfavorableness of 
 the site, the process had failed of 
 completion and a mere trace of its 
 beginning was thus left stranded in 
 inhospitable surroundings. 
 
 This general view of the nature of 
 fossils was current for many gener- 
 ations, but as early as the fifteenth 
 century, Leonardo da Vinci (1452- 
 I519) recognized that shore lines 
 shifted, that the earth’s crust was ele- 
 
WHAT EVOLUTION IS 41 
 
 vated and depressed, and that what 
 was once sea bottom, with its myriads 
 of marine plants and animals, might 
 well become mountainside with its 
 contained fossils. Gradually the 
 opinion grew that all fossils were the 
 remains of once living organisms, 
 and this doctrine, advanced through 
 the efforts of such workers as Fra- 
 castoro, Steno, Hooke, and others, 
 had gained complete acceptance in 
 the days when Lamarck( 1744-1829) 
 and Cuvier (1769-1832) were found- 
 ing modern paleontology. 
 
 Concurrent with the growth of the 
 new ideas about fossils came the con- 
 ceptions of stratigraphic geology. 
 Rocks not only contain the fossil re- 
 mains of once living organisms, but 
 the underlying rocks hold remains of 
 an older date than do those above 
 them. Such a sequence of fossils, as 
 is implied by this view, was advocated 
 
42 WHAT EVOLUTION IS 
 
 by Woodward (1665-1728), Valis- 
 nieri (1661-1730), Smith (1769- 
 1829), and especially by Cuvier 
 (1769-1832). Cuvier further rec- 
 ognized that the older rocks con- 
 tained fossils of a simpler type than 
 the more recent ones did, and he ex- 
 plained this difference by assuming 
 that periods of cataclysmic destruc- 
 tion alternated with periods of special 
 creation. This doctrine was carried 
 to an extreme by d’Orbigny (1802- 
 1857) who claimed for the past some 
 twenty-seven such alternations. But 
 the idea of cataclysmic alternations 
 was defeated by the school of uni- 
 formitarians, whose advocates, like 
 Lyell (1797-1875 ), saw in the present 
 forces of nature an explanation of 
 the past and supported the idea of 
 continuity, not interruption, in the 
 organic series. By these steps the 
 modern conception of fossils and 
 
WHAT EVOLUTION IS 43 
 
 their significance was reached; they 
 are the remains of once living organ- 
 isms,and they discloseacontinuousand 
 real history of plant and animal life. 
 When this history is looked into, 
 it is found to have, as might be ex- 
 pected, a profound bearing on evolu- 
 tionary matters. It is by no means 
 easy to determine how long living 
 things have existed on the earth. 
 Estimates vary from a hundred-mil- 
 lion to two thousand-million years. 
 But from an evolutionary standpoint 
 such enormous periods, and even 
 such differences in the estimates, are 
 not so significant as the kinds of or- 
 ganisms that are shown to be present 
 at different periods in the earth’s 
 history and the sequences that this 
 history discloses. Sketched very 
 broadly, it may be said that during 
 about the first two-thirds of the period 
 in which life has been on the globe 
 
44 WHAT EVOLUTION IS 
 
 only invertebrates were present. 
 These include sponges, corals, star- 
 fish, worms, crustaceans, insects, 
 brachiopods, snails, clams, and other 
 shellfish. Vertebrates, or backboned 
 animals, first arose about the begin- 
 ning of the last third of the period 
 of life on the globe, and the earliest 
 fossil representatives of this group 
 were the fishes. These were followed, 
 near the opening of the last quarter, by 
 the amphibians which were succeeded 
 by the reptiles, the mammals, and the 
 birds in the order named. Man has 
 been present on the globe during some- 
 what less than the last hundredth of 
 the total period of living things. 
 When this sequence is reviewed it 
 is seen at once to present a reasonable 
 plan. Invertebrates precede verte- 
 brates, fishes antedate amphibians 
 and these in turn come before reptiles, 
 mammals, and birds. Man appears 
 
WHAT EVOLUTION IS 45 
 
 only near the very end, long after the 
 group of which he is a member, the 
 mammals, had established itself. 
 
 The sequence of forms that is here 
 portrayed is an orderly one and the 
 order is such as would be expected on 
 evolutionary grounds. Had special 
 creation been the rule of nature there 
 would have been no reason for inver- 
 tebrates to have preceded vertebrates 
 in their time of appearance, or for 
 fishes to have come before amphibians 
 and the like. But this order of ap- 
 pearance being such as it is, one must 
 conclude that this aspect of the fossil 
 series gives unequivocal support to 
 the evolutionary view. 
 
 Facts of the kind that have just 
 been narrated were well known in 
 Darwin’s day. Since that time the 
 study of fossils, and particularly of 
 vertebrate fossils, has enormously 
 expanded. Huxley in his time was 
 
46 WHAT EVOLUTION IS 
 
 much interested in the fossil series 
 illustrating the evolution of the horse. 
 As is well known, this animal can be 
 shown to have descended from a small 
 multi-toed creature of the approxi- 
 mate size of a fox. In the early days 
 of the evolutionary controversy this 
 was the one series of developing forms 
 that the paleontologist could point to 
 with assurance. To-day scores of 
 such series are known not only in the 
 vertebrates but in the invertebrates. 
 Even with man the call for the miss- 
 ing link seems to have subsided, for the 
 sequence in so many of the fossil series 
 is so nearly complete that it seems to 
 be only a matter of diligence and time 
 till the fossil record of any important 
 line can be brought to light. The imper- 
 fections inthe fossil seriesareno longer 
 interpreted as real and significant 
 breaks but as interruptions sooner or 
 later to be filled as science advances. 
 
WHAT EVOLUTION IS 47 
 
 4. FROM ZOOGEOGRAPHY 
 
 THE past and present distribution of 
 animals on the surface of the globe 
 has important bearings on the evolu- 
 tionary problem. Animals are not 
 scattered in a haphazard fashion over 
 the earth, but show a marked regular- 
 ity in their occurrence. This can be 
 well illustrated by what is known of 
 the mammals. The group of mam- 
 mals is made up chiefly of the common 
 beasts of the field and forest, but it 
 includes also such exceptional forms 
 as the bats, among aérial creatures, 
 and the whales and porpoises of the 
 sea. Mammals have warm blood, 
 they produce milk with which they 
 nourish their young, and they are pro- 
 vided with more or less hair. 
 
 Almost all the mammals bring forth 
 their young in a highly developed, 
 
48 WHAT EVOLUTION IS 
 
 active state. Two of them, however, 
 the Australian porcupine and the 
 duckbill, lay eggs. These two mam- 
 mals, in addition to the habit of 
 laying eggs, have many primitive char- 
 acteristics. They constitute the low- 
 est group of this class of animals. 
 They are commonly designated as 
 monotremes. The remarkable feature 
 about them, from the standpoint of 
 the present discussion, is that they are 
 not found broadcast over the earth 
 but are limited to a very distinct zoo- 
 geographical area, the Australian 
 region. Thus the total representation 
 of this striking group of forms is re- 
 stricted to a small part of the globe. 
 The Australian region is not only 
 the habitation of the monotremes; it 
 is also the home of the marsupials. 
 These are mammals, such as the pha- 
 langers, the wombats, and the kan- 
 garoos, the females of which are 
 
WHAT EVOLUTION IS 49 
 
 commonly characterized by the pres- 
 ence of a pouch on the abdomen. This 
 pouch, which contains the milk glands, 
 serves as a receptacle for the young 
 after their birth. Most persons have 
 seen in our zoological gardens the 
 female kangaroo with her offspring 
 and have noticed how the young, when 
 alarmed, run to the pouch, enter it, 
 and are carried off by the mother. 
 The marsupials, like the monotremes, 
 are very primitive mammals. Ex- 
 cepting the American opossums and 
 one other pouched mammal in South 
 America, all marsupials are limited 
 to the Australian region. No mar- 
 supial occurs in Eur-Asia or in Africa. 
 Thus the marsupials, like the mono- 
 tremes, illustrate a common peculiar- 
 ity of animal distribution, namely, that 
 many large and important groups are 
 limited to well circumscribed and often 
 relatively small areas of the earth. 
 
so WHAT EVOLUTION IS 
 
 This topic is still better illustrated 
 if we take into consideration the 
 distribution of fossil, as well as of 
 living forms. Again the mammals 
 may serve as illustrations. Sloths and 
 armadillos constitute a group of mam- 
 mals very striking in their distribu- 
 tion. 
 
 The modern sloths are arboreal 
 creatures of moderate size; they feed 
 upon the succulent stems and leaves 
 of tropical trees. By means of their 
 curved claws, they hook themselves 
 through the tangle of branches in the 
 forest jungle. They are almost in- 
 capable of locomotion on the ground 
 and when by accident they fall, they 
 move about in a most awkward fash- 
 ion in regaining their haunts. 
 
 The modern armadillo is a burrow- 
 ing animal chiefly active at night. Its 
 covering of segmented shelly pieces 
 gives it more the appearance of a 
 
WHAT EVOLUTION IS 51 
 
 reptile than of a mammal, but its 
 warm blood, its mammary glands, and 
 the hair that projects outward be- 
 tween the segments of its shell pro- 
 claim it a true mammal. 
 
 Modern sloths and armadillos are 
 limited to the new world particularly 
 to South and Central America though 
 the armadillos extend northward 
 through Mexico into the southern 
 borders of the United States. None 
 of these forms occur in the old world 
 or in fact elsewhere than in the region 
 just described. 
 
 Fossil sloths and armadillos are 
 known in considerable numbers. Some 
 of these are of huge size. Fossil 
 eround sloths have been discovered 
 whose skeletons justify the belief that 
 the living animal must have been as 
 large as a rhinoceros. Armadillo- 
 like animals, the glyptodons, have been 
 found whose skeletons are almost as 
 
32. WHAT EVOLUTION IS 
 
 large as those of oxen. The fossil re- 
 mains of all these sloths and armadil- 
 los are found exclusively in the new 
 world and in that part south of the 
 central United States. It is a remark- 
 able fact that, notwithstanding the 
 great difference between these fossil 
 sloths and armadillos and their mod- 
 ern representatives, the living and the 
 fossil forms should agree almost 
 exactly in the regions where they 
 occur. One is forced to conclude from 
 facts of this kind, as well as from the 
 circumstance, that most well-defined 
 groups of modern animals, like the 
 monotremes and the marsupials, oc- 
 cupy definitely restricted areas, that 
 members of the same great group have 
 had a common origin, for had they 
 been specially created their distribu- 
 tion on the earth’s surface would have 
 called for no particular regularity. 
 
WHAT EVOLUTION IS _ 53 
 
 5. FROM RUDIMENTARY 
 ORGANS 
 
 THE last biological topic to be con- 
 sidered in the present account as bear- 
 ing on the problem of evolution has 
 to do with rudimentary organs. Rudi- 
 mentary organs are those organs that 
 are without use or function. They 
 are like the buttons on the sleeve of a 
 man’s coat; they are essentially use- 
 less and sometimes worse than useless. 
 A well-known rudimentary organ, 
 from the human body, is the vermi- 
 form appendix of the large intestine. 
 This organ is a blind tube several 
 inches in length and attached to the 
 large intestine near its beginning. It 
 is shown to the right in the figure on 
 page 55. It is easily subject to in- 
 flammation and forms a danger center 
 in the intestinal tract. In diseased 
 * states it is regularly removed by the 
 
54 WHAT EVOLUTION IS 
 
 surgeon and even in normal condi- 
 tions it is frequently excised as a pre- 
 cautionary measure. No one is known 
 to suffer any inconvenience from its 
 loss; in fact a person is commonly re- 
 garded as better off without it than 
 with it. In consequence of its com- 
 plete lack of function, it is a thor- 
 oughly good example of a rudimentary 
 organ. 
 
 The condition of the vermiform 
 appendix in man is by no means 
 typical of this organ in other mam- 
 mals. Cats show no sign of it, but in 
 rabbits it is a highly developed struc- 
 ture and is intimately concerned in this 
 animal with the regular activities of 
 the large intestine. 
 
 Other rudimentary organs in man 
 are easily pointed out. The external 
 ear of the human being has attached 
 to it three thin muscles, one above the 
 ear, a second behind that organ, and a 
 
WHAT EVOLUTION IS 55 
 
 Cat 
 
 Rabbit 
 

 
WHAT EVOLUTION IS 57 
 
 third in front of it. Most persons 
 have no power of motion in these 
 muscles and, in such instances, the 
 muscles may be looked upon as purely 
 rudimentary, but occasionally an in- 
 dividual will be found who can con- 
 trol them to a slight degree and who 
 can thereby move his external ear. 
 Even in such instances, however, the 
 amount of motion is extremely slight 
 compared with that seen in such 
 animals as the horse and the dog, 
 where the tube of the outer ear is 
 directed with great freedom in a 
 variety of ways and is used asa means 
 of discovering the direction of sound. 
 From the standpoint of actual useful- 
 ness, the three muscles attached to the 
 human ear are quite as rudimentary 
 as is the human vermiform appendix. 
 
 Well within the angle of the human 
 eye next the nose is a slight fold of 
 whitish membrane, the so-called plica 
 
58 WHAT EVOLUTION IS 
 
 semilunaris. No use is known for this 
 organ in man but in the cat, as one can 
 readily see by direct inspection, in 
 place of this fold there is a nictitating 
 membrane, or third eyelid, which by 
 its free movement back and forth 
 across the eyeball serves as a means 
 of protecting and cleansing that or- 
 gan. The plica semilunaris in man 
 is a completely useless remnant of this 
 third eyelid. 
 
 In an enumeration of the rudimen- 
 tary organs in man made some years 
 ago by Wiedersheim approximately 
 ninety such parts were noted. This 
 seems like a considerable list for one 
 species, but it is probably by no means 
 exhaustive. Most higher animals, like 
 man, abound in a great variety of such 
 useless parts. 
 
 From the standpoint of special 
 creation, it is by no means easy to 
 explain the presence of such function- 
 
WHAT EVOLUTION IS 59 
 
 less organs. If animals were spe- 
 cially created why should they contain 
 scores of parts that are without use 
 and that in some instances, like the 
 vermiform appendix, are positively 
 deleterious? A satisfactory answer 
 to this question has never been given. 
 From the standpoint of evolution, 
 however, rudimentary organs are 
 structures in process of disappear- 
 ance, organs that are just dropping 
 below the horizon of serviceableness. 
 Their presence in a given form in- 
 dicates that they were: functional in 
 some ancestor of that form, and that 
 as evolution proceeded and the species 
 changed, it dropped this particular 
 part from the level of functional sig- 
 nificance to that of uselessness. Such 
 an explanation of the presence of these 
 organs accords completely with what 
 is known of them from all points of 
 view. 
 
60 WHAT EVOLUTION IS 
 
 6. CONCLUSION 
 
 WE have now completed a brief sur- 
 vey of some of the more important 
 fields of evidence concerning descent 
 with modification. We have examined 
 this question in the light of compara- 
 tive anatomy, of embryology, of geol- 
 ogy, of zoogeography, and of the study 
 of rudimentary organs. In none of 
 these aspects of the problem has there 
 appeared reason for assuming that 
 special creation has been the method 
 by which the diversity of plants and 
 of animals at present on the globe has 
 been produced and in all of them there 
 has been shown either strong evidence 
 in favor of descent with modification 
 or a state of affairs open to ready in- 
 terpretation from this standpoint. 
 The several lines of evidence that 
 have been considered in this connec- 
 
WHAT EVOLUTION IS 61 
 
 tion could scarcely be said to have 
 been available in the time of Lamarck, 
 for most of them have been the result 
 of the scientific endeavor of the last 
 hundred years. It is therefore not 
 surprising that in his day evolution 
 received a serious setback, for at that 
 time not enough was known to give 
 the question a fair hearing. 
 
 Even when Darwin wrote, knowl- 
 edge on many important points was 
 very incomplete compared with what 
 it is to-day. It is, however, a sig- 
 nificant fact that practically all the 
 lines of evidence cited by Darwin as 
 confirmatory of evolution are signifi- 
 cant to-day and much more exten- 
 sively supported than they were in his 
 time. The confirmation thus received 
 is the result of the discovery and im- 
 partial accumulation of new facts on 
 lines that bear on the question at hand. 
 If to the naturalist of Darwin’s time 
 
62 WHAT EVOLUTION IS 
 
 the evidence in favor of evolution 
 seemed persuasive, that which can be 
 brought forward now would have been 
 overpowering. It is this strength of 
 the modern position that has placed 
 every biologist of any standing what- 
 soever on the side of evolution. In 
 other words, practically all biologists 
 to-day accept without any reserva- — 
 tions descent with modification as a 
 process of nature. They no longer 
 question this view. This statement 
 cannot be emphasized too strongly. 
 At the same time that these biolo- 
 gists accept descent with modification 
 as anactual occurrence in nature, they 
 are most skeptical and reserved about 
 what may be called the driving force 
 behind descent. What is there in 
 nature that has kept in motion this 
 incredible capacity to produce new 
 species? How is it that from age to 
 age large and ever larger floods of 
 
WHAT EVOLUTION IS 63 
 
 new forms have burst forth? To this 
 question no biologist has a clear and 
 unequivocal answer. It is this uncer- 
 tainty that has been seized upon by a 
 few thoughtless critics who have at- 
 tempted to discredit in the eyes of the 
 general public the well established fact 
 of descent with modification by con- 
 fusing it with the explanations of de- 
 scent. This confusion, commonly due 
 to ignorance, is the source of most of 
 the contentions now met with in evo- 
 lutionary controversies. It does not 
 characterize the clear thinker. Be- 
 cause biologists have not as yet dis- 
 covered how evolution takes place is 
 no reason for denying evolution itself. 
 
 The explanations of the evolution- 
 ary process thus far offered are large 
 in number. They include, to mention 
 only some of the most important, 
 Lamarck’s hypothesis, Darwin’s nat- 
 ural selection, Naegeli’s idioplasmic 
 
64 WHAT EVOLUTION IS 
 
 hypothesis, Eimer’s orthogenesis, De 
 Vries’s mutation theory and the like. 
 In so brief a survey as this volume 
 offers it will be profitable to consider 
 only the more noteworthy of these 
 views and in conformity with this plan 
 the next chapter will contain brief 
 critical accounts of Lamarck’s hypoth- 
 esis, of Darwinism or the theory of 
 natural selection, and of the mutation 
 theory of De Vries. 
 
OL, 
 FACTORS IN EVOLUTION 
 

 
 
 
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 i 
 
 i < " " av? As 
 dia eA ek 
 Pra aa’ | aT) Per hd 
 ae ee. WO CY ee 
 
 
 
 tn 
 
FACTORS IN EVOLUTION 
 PAPER EPEAT ORY 
 
 In the early discussions on evolution 
 it soon became apparent that, com- 
 pared with the biblical account of 
 creation, descent with modification re- 
 quired a relatively enormous length 
 of time. This contrast between the 
 two views was used by Cuvier in his 
 opposition to Lamarck. Cuvier had 
 careful measurements made of the 
 skeletons of mummified Egyptian 
 animals and of their recent represen- 
 tatives. No significant differences 
 could be detected on comparing these 
 two sets of measurements and Cuvier, 
 therefore, concluded that if no meas- 
 ureable changes had overtaken ani- 
 mals in the three thousand years that 
 separated the mummified from the 
 modern forms, it was useless to con- 
 
68 WHAT EVOLUTION IS 
 
 sider the possibilities of a process 
 which, if it occurred at all, was almost 
 inconceivably slow. Although Cuvier 
 has since been shown to be wrong in 
 his general deductions, the results of 
 such speculations as this led trans- 
 _ formists in the early days to assume a 
 very long period for the evolution of 
 life on the earth, a conception quite in 
 line with the growing uniformitarian 
 geology of the day. The assumption 
 of a relatively great age for the earth 
 and its inhabitants has been entirely 
 justified by subsequent scientific in- 
 quiry, but in the days of Cuvier and 
 Lamarck and even in the time of Dar- 
 win it was based on much less con- 
 vincing evidence than at present. 
 To-day it is beyond dispute that the 
 age of the earth as the abode of life is 
 to be reckoned in hundreds if not 
 thousands of millions of years. 
 
 In consequence of these growing 
 
WHAT EVOLUTION IS 69 
 
 opinions, there arose a belief among 
 naturalists of the transformist school 
 that evolution was so slow and grad- 
 ual a process that no direct observa- 
 tion of it could ever be made. The 
 life of man was not long enough to 
 admit of even a glimpse at evolution- 
 ary change. This view was current 
 in Darwin’s day and prevailed more 
 or less to the end of the nineteenth 
 century. It served as a most unfor- 
 tunate deterrent to scientific research, 
 for it discouraged investigators from 
 attempting any direct study of a proc- 
 ess whose operations seemed to be so 
 infinitely slow. 
 
 With the advent of the twentieth 
 century a new phase in evolutionary 
 investigation appeared. Through the 
 work of Tschermak, of Correns, and 
 particularly of De Vries the subject 
 passed from the observational and 
 speculative stage to the experimental 
 
70 WHAT EVOLUTION IS 
 
 one, and instead of looking upon evo- 
 lution as a process so slow as to be 
 imperceptible, it was soon believed, as 
 a result of experimental test, to be 
 relatively rapid at least in particular 
 instances. In fact it was declared 
 that species might be created almost 
 over night. Such a radical change of 
 view had a profound effect on the 
 growth of the subject and though the 
 new programme may not have real- 
 ized all that was expected of it, it 
 brought the science into a vastly more 
 wholesome state and led to positive 
 growth of a most encouraging kind. 
 In this revival of activity all the 
 older explanations of evolution were 
 brought to the test with the result that 
 such ideas as Eimer’s orthogenesis, 
 in which variation was supposed to 
 occur in definite and predetermined 
 directions, and Naegeli’s idioplasm 
 theory, in which an internal perfect- 
 
WHAT EVOLUTION IS 71 
 
 ing principle was assumed, lost ground 
 and the field was left almost ex- 
 clusively to Lamarckism, Darwinism 
 and the mutation theory. A consid- 
 eration of these views will now follow. 
 
} 
 
 72 WHAT EVOLUTION IS 
 
 2, LAMARCKISM 
 
 LAMARCK’S hypothesis as to the means 
 by which evolution has been accom- 
 plished is best stated in his “ Philos- 
 ophie Zoologique”’ published in 1809, 
 a year which is noteworthy as the 
 birth year of Charles Darwin. La- 
 marck’s explanatory views excited 
 very little attention at the time of their 
 publication, for, so far as the scientific 
 world took any interest in evolution 
 at all, it was concerned with the ques- 
 tion of the validity of this doctrine 
 rather than withits explanation. Fifty 
 years later when Darwin advanced 
 natural selection the explanatory as- 
 pects of this question came much more 
 to the front. Then a contrast be- 
 tween Darwin’s views and Lamarck’s 
 views could be drawn. 
 
WHAT EVOLCUTIONZ IS 73 
 
 The explanation offered by La- 
 marck turned chiefly on the effect 
 upon organisms of the surroundings 
 or environment. Lamarck noted that 
 marsh plants, such as the aquatic 
 Ranunculus, which grew partly sub- 
 merged and partly out of water, had 
 leaves of different shapes in the two 
 situations. Under water the leaves 
 were finely divided, but in the air they 
 were simply lobed. This difference 
 he rightly conceived to be due to the 
 environment, one situation producing 
 the first type of leaf and the other the 
 second. He looked upon this as a 
 direct effect of the surroundings and 
 regarded it of great importance par- 
 ticularly with plants. A special plant 
 being thus directly dependent upon its 
 surroundings for its peculiar form, any 
 change in these surroundings would 
 be likely to be followed by a change 
 in the form of the plant, that is, an- 
 
74 WHAT EVOLUTION IS 
 
 other form would arise and evolution 
 could be said to have taken place. 
 
 Lamarck conceived the effect of en- 
 vironmental change on animals to be 
 carried out in a rather more complex 
 way than on plants. He illustrated 
 this by several examples such as the 
 webbed foot of water birds and the 
 long neck of the giraffe. 
 
 Lamarck rightly believed that land 
 birds were the ancestors of water 
 birds, and in thinking of the transi- 
 tion, he pictured land birds coming 
 more and more to frequent the shore, 
 to pass much of their time in shallow 
 water and to seek their food there. 
 Such newcomers would from time to 
 time get into deep water and naturally 
 attempt to propel themselves by kick- 
 ing with their legs. The muscular 
 exercise of kicking would induce an 
 extra flow of blood to the legs whose 
 bones, muscles, skin, and the like 
 
WHAT EVOLUTION IS 7s 
 
 would respond by extra growth. In 
 this way the skin between the toes 
 would become firmer, tougher, and 
 more extensively developed. These 
 effects would be increased in the de- 
 scendent stock, and as they accu- 
 mulated generation after generation, 
 the passage would be accomplished 
 from the webless foot of the land 
 bird to the webbed foot of the water 
 bird. 
 
 Lamarck conceived that the gi- 
 raffe’s neck, to take another of his 
 examples, was lengthened by a similar 
 process. These animals were sup- 
 posed to browse among the branches 
 of trees. In their endeavors to reach 
 the leafy food, they would naturally 
 exert the muscles of the neck and this 
 activity would induce an extra flow of 
 blood to that region. In consequence 
 the muscles, bones, and other parts of 
 the neck would increase in size, just 
 
76 WHAT EVOLUTION IS 
 
 as the arm of a man increases under 
 exercise. Asa result of this activity 
 continued through generation after 
 generation, the neck of the giraffe 
 would lengthen and eventually reach 
 the extreme condition seen to-day. 
 Both these instances involve a proc- 
 ess more complex than that in the 
 partly submerged plant, but in both 
 of them the environment is the fun- 
 damental factor. With the bird the 
 change from inland surroundings to 
 a shore environment is the important 
 element, and with the giraffe the 
 change from a region where browsing 
 was low to one where it was among 
 trees. Thus as with the plant, en- 
 vironmental differences play the chief 
 part in the evolution of these animals. 
 Put briefly, the Lamarckian scheme, 
 as applied to animals, is as follows: 
 a change in the environment is fol- 
 lowed by a change in habit, and a 
 
WHAT EVOLUTION IS 77 
 
 change in habit is followed by a 
 change in structure. Thus the condi- 
 tion of the animal is modified and 
 evolution is the result. 
 
 Such an application of the La- 
 marckian principle, as is involved in 
 the last two examples, requires what 
 may be called the indirect influence of 
 the environment in contrast with the 
 direct influence as seen in most plants, 
 but in both direct and indirect influ- 
 ences, the environment and its changes 
 are the paramount elements. 
 
 In addition to the general principle 
 that has just been illustrated, La- 
 marck also called attention to certain 
 subordinate principles that he believed 
 to be significant in evolution. First 
 of these was the principle of use and 
 disuse. Organs that are exercised 
 tend to increase in size, and organs 
 that are not exercised tend to shrink. 
 This is so obvious a matter in every- 
 
78 WHAT EVOLUTION IS 
 
 day life that it needs no special illus- 
 tration and no one denies it. 
 
 Another principle that Lamarck 
 advanced was the principle of effort, 
 that in order to accomplish an end an 
 animal must make an effort, must 
 exert itself. If it did not so do its 
 effective powers would diminish. This 
 is an element of a psychological na- 
 ture; it has a certain vague and in- 
 tangible side not involved in the 
 principle of use and disuse, for in- 
 stance. It nevertheless plays no un- 
 important part in Lamarck’s general 
 hypothesis. 
 
 The scheme advanced by Lamarck, 
 and briefly outlined in the preceding 
 paragraphs, carries with it the im- 
 pression of great naturalness. Every- 
 one knows that activity or lack of 
 activity modifies an organ and, grant- 
 ing that the changes thus produced 
 are handed on generation after gen- 
 
WHAT EVOLUTION IS 79 
 
 eration and emphasized, evolution 
 seems to be a natural consequence. Is 
 not this precisely the method by which 
 plants and animals are moulded to 
 their surroundings; is not this, in 
 other words, the driving force that 
 lies behind evolution? On the surface 
 it seems as though Lamarck’s hy- 
 pothesis must indeed offer the true 
 explanation. 
 
80 WHAT EVOLUTION IS 
 
 3. LAMARCKISM CRITICIZED 
 
 NOTWITHSTANDING the ease with 
 which Lamarckism appears to pro- 
 vide the necessary machinery for the 
 evolutionary process, this hypothesis 
 is not free from serious defects. Dar- 
 win considered it as a possible factor 
 in evolution but did not lay much 
 stress upon it. It was not until after 
 Darwin’s time that Lamarckism came 
 into prominence in consequence of the 
 contrast between it and natural selec- 
 tion. Half a century ago a new 
 school, chiefly paleontological, arose 
 which, under the name of neo-La- 
 marckian, attempted to establish and 
 expand the principles of Lamarck. 
 This school was opposed by the neo- 
 Darwinians who, under the leader- 
 ship of Weismann, made a vigorous 
 onslaught against Lamarckism and 
 
WHAT EVOLUTION IS 81 
 
 claimed natural selection as the all- 
 sufficient factor in evolution. 
 
 The objections that were raised 
 against Lamarckism by its opponents 
 were first of all as to its limitations. 
 As a process effective in evolution it 
 applies to those changes that are in- 
 duced either directly by the environ- 
 ment or indirectly through exercise, 
 lack of exercise, and the like. 
 
 Some conditions seen in organisms 
 do not easily fall under any of these 
 heads. ‘The protective coloration of 
 insects is an example of this kind. 
 Many insects exhibit colors, forms, 
 and activities that make them easily 
 mistaken for other objects in their 
 environment. Moths resemble the 
 bark of the trees on which they rest, 
 butterflies, on closing their wings, be- 
 come indistinguishable from leaves 
 or the earth and the walking-stick 
 insect gets its name from its resem- 
 
82 WHAT EVOLUTION IS 
 
 blance to twigs. Anyone who has 
 taken the trouble to acquaint himself 
 with examples of this kind must have 
 been struck with the perfection of the 
 resemblances and with the evident 
 protection that the creature enjoys 
 through being mistaken by its foes 
 for something other than it is. It 
 was this principle that toward the end 
 of the Great War led to the camou- 
 flaging of vessels, of artillery, and 
 even of men. The insects that are 
 camouflaged do not acquire this state 
 through individual activity, but are 
 hatched out in this condition. They 
 receive their protective markings 
 fully formed, in the nature of birth- 
 rights as it were, and no efforts on 
 their part make the camouflage more 
 or less complete. In this respect, the 
 insects are quite unlike the fishes, 
 the frogs and toads, and especially the 
 chameleons where the colors of the 
 
WHAT EVOLUTION IS 83 
 
 skin are under nervous control, with 
 the result, that the animals can mo- 
 mentarily change colors and patterns 
 and thus, so to speak, exercise this 
 system as muscles may be exercised. 
 In the insect the condition is fixed 
 once for all and the individual is in- 
 capable of modifying it. Fixed con- 
 ditions of this kind are beyond the 
 reach of the Lamarckian principles 
 and form a body of material the evo- 
 lutionary explanation of which must 
 be sought for in other directions. 
 Thus, granting the validity of La- 
 marck’s hypothesis, it, nevertheless, 
 falls short of an explanation of all 
 the evolutionary aspects of organic 
 nature and must be supplemented by 
 other factors to reach completion. 
 But not only does Lamarckism fail 
 to apply to all classes of instances 
 under organic evolution, it also in- , 
 volves, as one of its essentials, the 
 
84 WHAT EVOLUTION IS 
 
 assumption of the inheritance of ac- 
 quired characters. Acquired charac- 
 ters are those peculiarities that are 
 gained during the lifetime of an in- 
 dividual as contrasted with his inborn 
 traits. That Lamarckism shall be 
 effective, it is necessary that precisely 
 these characters be inherited. For a 
 long time biologists have attempted 
 to show that such characters are in- 
 herited, but thus far they have been 
 unable to get any conclusive evidence 
 that such is the case. 
 
 The chief opponent of the inherit- 
 ance of acquired characters was 
 Weismann (1834-1914) who pointed 
 out that the bodies of the higher ani- 
 mals were composed of two catego- 
 ries of cells, the body cells proper 
 such as muscle cells, nerve cells, skin 
 cells, and the like, and the reproduc- 
 tive cells, the egg cells and sperm 
 cells. He also showed that acquired 
 
WHAT EVOLUTION IS 85 
 
 characters were changes in the body 
 cells—muscle, nerve, skin and so 
 forth—and that there was no known 
 mechanism whereby the changes reg- 
 istered in these cells could be trans- 
 ferred to the reproductive cells in 
 order that such changes might be 
 handed on to the offspring. Ifa black- 
 smith through exercise increases the 
 muscles of his arm, how are these 
 muscles to modify his reproductive 
 cells that his offspring may have larger 
 arm muscles than they otherwise would 
 have had? This theoretic objection 
 to the inheritance of acquired char- 
 acters seems to many to be an insuper- 
 able one, It is, however, an objection 
 based on ignorance and may at any 
 time be set aside by new discovery. 
 Many of the older advocates of the 
 neo-Lamarckian school pointed to the 
 inheritance of mutilations as evidence 
 in favor of Lamarck’s views, and it 
 
86 WHAT EVOLUTION IS 
 
 was this that led Weismann and 
 others to experiment in this direction. 
 Colonies of mice and of rats were © 
 subjected to mutilation and were 
 then used for breeding with the view 
 of ascertaining whether such mu- 
 tilations were heritable. Thus the 
 lengths of the tails of a number of 
 adult white mice were measured, their 
 tails were then cut off, and they were 
 used as breeding individuals for a 
 new generation. When the second 
 generation had matured, their tails 
 were in turn measured and cut off 
 and a third generation was produced 
 from them. After the breeding of 
 approximately twenty such genera- 
 tions, all of which had been subjected 
 to the amputation of the tails at an 
 appropriate stage, the tails in the final 
 generation were found to be as long 
 as those in the first generation. Such 
 mutilations, then, gave no evidence 
 
WHAT EVOLUTION IS 87 
 
 of being inherited and this conclusion 
 was to have been expected at the out- 
 set, for it is well known that the 
 innumerable deformations of the hu- 
 man body as practiced by primitive 
 races whereby the ears, the lips, the 
 nose, and even the head become mis- 
 shapen, have had no inborn effect 
 upon the stocks concerned. The an- 
 cient religious rite of circumcision, 
 though practiced for very many gen- 
 erations by the Hebrews, has had no 
 effect in shortening the foreskin of 
 Hebrew male infants. If mutilations 
 were inherited man would be a mere 
 fragment of what he is as a result of 
 handing on from one generation to 
 another the injuries received from 
 wars and accidents. Mutilations evi- 
 dently are not inherited and the so- 
 called examples of this kind seem to 
 be nothing but old-wives tales or 
 coincidences. 
 
88 WHAT EVOLUTION IS 
 
 But even though mutilations have 
 no effective influence on the germ 
 cells of the animals suffering from 
 such defects, may not bodily activi- 
 ties, more normal in character than 
 mutilations, influence the germinal 
 elements? May not a normal but 
 novel and unusual condition of the 
 body cells influence the contained 
 germ cells? To test this Castle and 
 Phillips attempted the very ingenious 
 experiment of transferring germ cells 
 from one individual, with a given set 
 of bodily traits, to another individual, 
 with very different traits, and of test- 
 ing the results of such a transfer by 
 breeding. ‘They proceeded in the fol- 
 lowing way. The ovaries were re- 
 moved from a young guinea pig of 
 pure white stock and in their place 
 were set the ovaries from a pure 
 black individual. After recovery 
 from the operation, this white female 
 
WHAT EVOLUTION IS 8g 
 
 with “black” ovaries was paired 
 with a pure white male with the 
 result that between six to twelve 
 months after the operation she bore 
 two litters of young. These consisted 
 in all of six offspring every one of 
 which was black exactly as though a 
 black female had been paired with 
 the white male. This test shows that 
 after almost a year of residence in 
 the foster white body the ovaries 
 from the black female still retained 
 in full force their original potentialt- 
 ties and gave no evidence that the 
 new foster body had influenced them 
 in the least. This experiment sup- 
 ports Weismann’s contention that the 
 germ cells are essentially independent 
 of the body in which they reside. 
 
 But again it may be maintained 
 that the period over which such trials 
 extended was much too short for a 
 real test of the question and that, if 
 
90 WHAT EVOLUTION IS 
 
 experiments could be devised that 
 would of necessity last over a number 
 of generations, results of a very dif- 
 ferent kind might be obtained. 
 
 To try out this aspect of the prob- 
 lem numerous investigations have 
 been made or are still in progress. 
 Few workers have done more in this 
 direction than the Viennese experi- 
 mentalist, Kammerer. Of his num- 
 erous studies one may be chosen as 
 an example. The European spotted 
 salamander deposits either numerous 
 eges or young that have been hatched 
 in the mother’s body in ponds and - 
 pools in damp woods. All the young, 
 irrespective of their condition of 
 birth, are provided with gills and 
 live for several months in the water 
 after which they lose their gills and 
 become inhabitants of the land. The 
 European black salamander gives 
 birth only to active young, usually 
 
WHAT EVOLUTION IS gt 
 
 two in number, and these are born 
 without gills and in full readiness 
 for terrestrial life. By keeping the 
 spotted salamander away from water, 
 Kammerer attempted to change its 
 breeding habits in the direction of 
 those of the black salamander. Such 
 artificially restrained salamanders re- 
 tained their young in their bodies till 
 the young had lost their gills and 
 were in a condition for life on the 
 land. The young of such parents 
 were reduced in number, as compared 
 with the normal number produced, 
 and were mostly black. In both these 
 respects the stock approached the 
 European black salamander. Spotted 
 salamanders, whose parents had thus 
 been modified in habit by experimen- 
 tal conditions, on arriving at: sexual 
 maturity were, during their breeding 
 season, given access to water. They 
 deposited their young in the water at 
 
92 WHAT EVOLUTION IS 
 
 an advanced stage of growth, and 
 these young remained in the water 
 - only a few days instead of several 
 months. Thus the reproductive hab- 
 its of the spotted salamander, by a 
 change in the environment, were 
 modified in the direction of the black 
 salamander, and this modification 
 persisted more or less in their de- 
 scendants, even after these descend- 
 ants had been allowed to return to 
 the original environment. 
 
 Several lines of experimentation 
 such as the one described in the pre- 
 ceding paragraph have been carried 
 out by Kammerer within the last few 
 years and point to the inheritance of 
 acquired characters. How sound the 
 experimental evidence is in all such 
 cases remains to be seen. Is it not 
 possible that the peculiarities that 
 Kammerer believed he originated in 
 the spotted salamander, to take this 
 
WHAT EVOLUTION IS 93 
 
 as an instance, may have been inborn 
 traits in this animal which were 
 simply called into evidence by the 
 changed environment rather than 
 produced by it? Certainly such as- 
 pects of the problem should be tested 
 before a final conclusion can be ar- 
 rived at, and in so crucial an experi- 
 ment as the one described, it 1s 
 extremely desirable that independent 
 evidence on the same point from 
 other investigators should be at hand 
 before a final decision is reached. 
 Other students of this general 
 problem have also carried out ex- 
 tended series of experimental studies 
 reaching over many generations. 
 Thus the Americans Guyer and Smith 
 have advanced evidence to show 
 that eye defects produced in one 
 generation of rabbits are inherited 
 by the descendent stock. But here 
 the defects produced and those as- 
 
04 WHAT EVOLUTION IS 
 
 sumed to be inherited are often quite 
 different and the question, therefore, 
 of real inheritance remains open. 
 The same general criticism applies 
 to Griffith’s studies on the inheritance 
 of defects in the internal ear of the 
 rat. Both these lines of investiga- 
 tion, and especially those of Guyer 
 and Smith, are, however, extremely 
 near the point and are very sugges- 
 tive. 
 
 A novel and very remarkable test 
 of the inheritance of acquired char- 
 acters is one that has been advanced 
 by the celebrated Russian physiolo- 
 gist Pawlow. It is well known that 
 mice can be trained easily to come to 
 a particular place for food. If, dur- 
 ing this training, a bell is sounded 
 each time that the animals are fed, 
 they will learn after a while to come 
 for food at the sound of the bell even 
 when no other signal for the presence 
 
WHAT EVOLUTION IS 95 
 
 of the food is given. This kind of 
 response where a second form of 
 stimulus, such as the sound of a bell, 
 replaces the primary stimulus is called 
 by Pawlow a conditioned reflex. To 
 induce this state in untrained mice 
 required, according to him about 
 300 lessons. The descendants of this 
 trained stock, however, acquired this 
 capacity after only 100 lessons, the 
 third generation after 30 lessons, the 
 fourth after 10, and the fifth after 5 
 lessons. Pawlow expressed the hope 
 that in time a generation of mice 
 might be produced in which this con- 
 ditioned reflex would occur immedi- 
 ately and, so far as that generation 
 itself was concerned, without train- 
 ing at all. These statements were 
 published in a preliminary way in 
 1923 and, though in certain respects 
 they are very precise and final, it is 
 hardly possible to comment on them 
 
96 WHAT EVOLUTION IS 
 
 till the complete report is published. 
 They are nevertheless full of signifi- 
 cance. 
 
 The whole problem of the inherit- 
 ance of acquired characters has ar- 
 rived at a stage where the results are 
 coming to be of the first importance, 
 and it must be admitted even by those 
 who oppose Lamarckism that the re- 
 cent tests have come much nearer 
 yielding conclusive results than those 
 attempted in the early stages of the 
 controversy. Nevertheless lit is gen- 
 erally agreed by almost everyone 
 concerned that up to the present time 
 no entirely convincing instance of 
 the inheritance of acquired characters 
 has come to light and that from this 
 standpoint Lamarckism must be ad- 
 mitted to be without direct support 
 There are, however, those like Samuel 
 Butler and, more recently, George 
 Bernard Shaw, as disclosed in his 
 
WHAT EVOLUTION IS 97 
 
 preface in “Back to Methuselah,” 
 who cry out for Lamarckism, but 
 their cry is far-fetched and although 
 the Lamarckian doctrine may eventu- 
 ally prove true, the proof of it will 
 come from other sources than literary 
 intuition. 
 
 The conclusion that Lamarckism is 
 a possible but unproved factor in evo- 
 lution is a statement that represents, 
 I believe, the opinion of the majority 
 of modern biologists. That the criti- 
 cism upon which this statement rests 
 applies to animals only in so far as 
 they exhibit sexual reproduction is, I 
 suspect, generally appreciated though 
 not so commonly stated. In organ- 
 isms that reproduce in this way, as 
 Weismann clearly showed, the cells 
 that make up the creature are divisi- 
 ble into the two classes of body cells 
 and reproductive cells and, as already 
 noted, it is extremely difficult, if not 
 
98 WHAT EVOLUTION IS 
 
 impossible, to show how under such 
 circumstances the inheritance of ac- 
 quired characters can take place. In 
 those forms in which non-sexual re- 
 production is found the inheritance 
 of acquired characters must be a reg- 
 ular occurrence, for, in this method 
 of reproduction, the whole body of 
 the organism divides into two or 
 more masses, and the body cells of 
 the parent, with all the peculiarities 
 that the environment may have im- 
 pressed upon them, become the body 
 cells of the offspring. Here the 
 method of reproduction is as clearly 
 in favor of the inheritance of ac- 
 quired traits as in the other instance 
 it is opposed to this process. It must 
 be kept in mind, however, that non- 
 sexual reproduction is a characteris- 
 tic of the plants and the lower 
 animals and is absent from the higher 
 forms. It occurs on the animal side 
 
WHAT EVOLUTION IS 99 
 
 among protozoans, sponges, corals, 
 starfish, moss-animals, worms, and 
 the group of sea-squirts or tunicates, 
 but it is not known among: snails, 
 clams, crustaceans, insects, or the ver- 
 tebrates. If, therefore, the inherit- 
 ance of acquired characters is a 
 feature of non-sexual reproduction 
 and the Lamarckian principles may 
 apply where this occurs, it is after 
 all a limited application and _illus- 
 trates again what has already been 
 pointed out that Lamarckism at best 
 cannot be regarded as an all-inclusive 
 factor in evolution. From what has 
 been said it appears to be at best a 
 possible element in this process. 
 
100 WHAT EVOLUTION IS 
 
 4. DARWINISM 
 
 DARWINISM, or as it is often called 
 natural selection, is an explanation of 
 evolution that originated independ- 
 ently in the minds of Darwin and 
 of Wallace. It is best stated in Dar- 
 win’s memorable work “The Origin 
 of Species” (1859), without doubt 
 the most significant single publication 
 of the nineteenth century. As a re- 
 sult of the discussion called forth by 
 the appearance of this work, two 
 great steps in the progress of biology 
 were accomplished; first, the accept- 
 ance of descent with modification, 
 instead of special creation as the 
 order of organic nature, and, sec- 
 ondly, the establishment of natural 
 selection as a driving force in evolu- 
 tion. The first of these has already 
 
WHAT EVOLUTION IS io1 
 
 been taken up; the second remains to 
 be considered. 
 
 In seeking a clue as to the way in 
 which evolution takes place Darwin 
 first turned his attention to plant 
 and animal breeding. Domesticated 
 plants and animals, notwithstanding 
 their great diversity and variety, are 
 the products of comparatively few 
 wild species. Thus all the various 
 races of domesticated pigeons have 
 descended from the European rock- 
 pigeon. The original wild stock of 
 this bird is fairly well represented by 
 the common domesticated individuals 
 of slaty color, with two dark bars on 
 the wings and with a white rump. In 
 addition to this stock there are over 
 150 named varieties of pigeons that 
 breed true. These include such un- 
 usual forms as pouters, carriers, fan- 
 tails, tumblers, jacobins, trumpeters, 
 and a host of others whose forms and 
 
102 WHAT EVOLUTION IS 
 
 habits are most diverse. Were these 
 met with in nature, the zoologist 
 would unhesitatingly assign many of 
 them to separate species or even 
 distinct genera. What is true of 
 pigeons is also true of other domesti- 
 cated animals such as dogs, horses, 
 swine, cattle, and the like. 
 
 In considering evolution Darwin 
 first set for himself the task of ac- 
 counting for the origin of domesti- 
 cated stocks. He found that when 
 the breeder wished to develop a par- 
 ticular feature, such as an excessive 
 covering of feathers on the leg and . 
 foot of a pigeon, he watched his stock 
 closely and chose for breeding pur- 
 poses those individuals that showed 
 evidences of the trait he sought. By 
 this method of selection applied to 
 one generation after another, he 
 eradually arrived at a stock in which 
 the given feature was as pronounced 
 
WHAT OEVOLUTION- IS: ‘103 
 
 as he wished and thus attained his 
 end. Darwin called this process arti- 
 ficial selection and believed it to be 
 the method by which man had pro- 
 duced from comparatively few wild 
 sources the great variety of domesti- 
 cated forms with which he was sur- 
 rounded. 
 
 Darwin then raised the question, 
 Is there not a similar process going 
 on in nature as a means of producing 
 the limitless variety of life in the 
 open? This he believed to be so and, 
 in contrast with artificial selection, 
 he designated this process as natural 
 selection. The grounds for his belief 
 in natural selection as an actual proc- 
 ess in nature may be briefly stated in 
 the following way. _ 
 
 More organisms are produced than 
 can possibly continue to exist because 
 of the limitations of food, space, and 
 other essentials. This comes about 
 
104 ‘WHAT EVOLUTION IS 
 
 from the fact that each individual or 
 pair of individuals gives rise to sev- 
 eral offspring and often to many. It 
 is not always appreciated what this 
 method of increase means. 
 
 If a single plant produces at the 
 end of its life two seeds and these 
 grow to mature plants the next year 
 and produce each two seeds and so 
 on, in the twenty-first year the orig- 
 inal plant will be represented by over 
 a million descendants. Even an ani- 
 mal, such as the elephant which 
 breeds with extreme slowness, will 
 nevertheless in time populate the 
 elobe, if all its progeny live and re-. 
 produce. When rapidly reproducing 
 forms such as the insects are con- 
 sidered, the increase in numbers is 
 bound to be quickly prodigious so 
 that the swarms of locusts described 
 in the past seem as nothing to what 
 might have happened. All organisms 
 
WHAT EVOLUTION IS 105 
 
 are endowed with such powers of in- 
 crease that even the slowest would in 
 time overrun the earth. 
 
 Darwin further recognized the 
 fact that the offspring of all animals 
 and plants are more or less diverse, 
 and that no two are ever exactly 
 alike. This is apparent to everyone. 
 In a litter of puppies the individuals 
 are quickly and easily distinguished 
 by size, markings, vigor, disposition, 
 and the like, and we name them and 
 treat them as we do separate persons. 
 
 These slight individual differences 
 are, according to Darwin, either fa- 
 vorable or unfavorable for the con- 
 tinued life of the given organism and, 
 since more individuals come into the 
 world than can possibly survive, those 
 with unfavorable traits are less likely 
 to reach maturity and leave offspring J 
 than those with favorable traits. In 
 this way there is a continual elimi- 
 
106 = WHAT EVOLUTION IS 
 
 nation of the less fit with the result 
 that the fittest survive, leave off- 
 spring, and thus hand on to future 
 generations their peculiar qualities, 
 for the individual differences noted by 
 Darwin are the inborn traits of each 
 individual. Thus a form of natural 
 selection is continually in operation 
 ever moulding plants and animals 
 with great nicety to their fluctu- 
 ating surroundings. This, according 
 to Darwin, is the mainspring that 
 keeps evolution continually moving. 
 Survival of the fittest, struggle for 
 existence, and other like expressions 
 have been used as figures of speech 
 with which to make clear what is 
 meant by natural selection. And 
 these expressions do indicate what at 
 times occurs in nature, but anyone 
 who looks upon the world of plant 
 and animal life will not see a field of 
 battle, an arena of combat, with each 
 
WHAT EVOLUTION IS __ 107 
 
 living thing ranged against its neigh- 
 bor. In fact when we seek a figura- 
 tive expression for peace and quiet, 
 we are very likely to turn to that very 
 nature which, according to these 
 phrases, should be in deadly turmoil. 
 Nevertheless, natural selection is 
 probably running at full speed in 
 every quiet countryside. Four seeds 
 from a given plant fall on a small 
 plot of ground. All germinate and 
 produce growing plants, one a little 
 in advance of the other three. The 
 early one shades the others, reaches 
 maturity first and sets its seeds. Au- 
 tumn comes and the other three have 
 not yet flowered and in consequence 
 they fail to produce fruit. Natural 
 selection has taken place. The early 
 plant leaves offspring for the next 
 year; the other three are unrepre- 
 sented. All may have lived what is 
 essentially the same length of time 
 
1088 WHAT EVOLUTION IS 
 
 and all in perfect peace; there has 
 been no struggle, no conflict, but 
 natural selection has nevertheless 
 occurred. The essential act of re- 
 production has been completed by 
 only one and that one has thereby 
 handed on its inborn peculiarities to 
 the next generation. The same oper- 
 ation is true of animals. Any crea- 
 ture that fails to leave offspring 
 suffers elimination from the stand- 
 point of natural selection, yet such an 
 animal or plant may live individually 
 as long or even longer than many 
 another whose progeny will reach 
 into future generations. Hence na- 
 tural selection is not necessarily con- 
 cerned with the destruction of the 
 individual, as is often inferred by 
 the figurative expressions already al- 
 luded to, but is a process that has to 
 do with the way in which plants and 
 animals succeed or fail in leaving off- 
 
WHAT EVOLUTIONS IS "109 
 
 spring. In most instances it is a 
 quiet, unobtrusive natural phenome- 
 non that permeates nature in every 
 direction and is more truthfully rep- 
 resented by the quiet countryside than 
 by the turmoil of battle. 
 
 Having reached some idea of what 
 is meant by natural selection or Dar- 
 Wwinism and having seen how it may 
 be an active force in moulding plants 
 and animals, we may pause a moment 
 to compare it with what Lamarck be- 
 lieved to be the energizing factor in 
 evolution. Natural selection first of 
 all does not suffer from limitations 
 to the extent that Lamarckism does. 
 Natural selection not only applies to 
 all that Lamarckism reaches but it 
 meets with success such conditions as 
 the protective coloration of insects, 
 which, it will be remembered, were 
 hardly within the range of Lamarck’s 
 principle. Insects, that have only an. 
 
IO es WHATSE VOL TIGNaIS 
 
 imperfect resemblance to the bark of 
 the tree on which they rest, are much 
 more likely to be espied and carried 
 off as prey, than those that have a 
 closer resemblance. Natural selec- 
 tion may in this case be expected 
 to act with full efficiency whereas 
 Lamarck’s principle, as already indi- 
 cated, is apparently entirely inappli- 
 cable. From this standpoint, natural 
 selection is not subject to the limita- 
 tions that characterize Lamarck’s 
 hypothesis. 
 
 Further, natural selection is not 
 concerned with the inheritance of ac- 
 quired characters. The slight indi- 
 vidual differences, upon which it is 
 believed to act, are not differences 
 due to the action of the environment 
 on the given organism but are inborn 
 traits which in consequence may be 
 handed on through the germ cells to 
 descendent offspring. In these two 
 
WHAT EVOLUTION IS 111 
 
 particulars natural selection has a 
 ereat advantage over Lamarckism. 
 It is of wider application and it 
 avoids the difficulty concerning the 
 inheritance of acquired characters. 
 It may not be amiss if at this point 
 we compare Lamarckism and Dar- 
 winism by attempting to show how 
 each may be made to apply to the 
 same example, and as an instance to 
 to be so treated, we may take the 
 webbed foot of the water fowl origin- 
 ally discussed by Lamarck. Accord- 
 ing to his hypothesis this structure 
 arose by the accumulation, in the 
 course of generations, of acquired 
 modifications which resulted from a 
 change of habit in consequence of the 
 bird’s removal from purely terrestrial 
 surroundings to an aquatic environ- 
 ment. From Darwin’s standpoint the 
 webbed foot resulted from selection, 
 among a diverse offspring, whereby 
 
112 WHAT EVOLUTION IS 
 
 those with favorable inborn traits 
 would be preserved and have off- 
 spring as contrasted with those whose 
 conditions were less favorable. Thus 
 Lamarckism deals with difference in- 
 duced by the environment, acquired 
 characters, and Darwinism with in- 
 born native differences. 
 
 Before leaving this comparison of 
 the two views it should be pointed out 
 that they are in no sense mutually ex- 
 clusive. It is sometimes implied that 
 if Darwinism could be shown to be 
 true Lamarckism must be false and 
 vice versa. It must be evident, how- 
 ever, that such is not the case. There 
 is not the least reason to assume that 
 one view is in any way incompatible 
 with the other. It is entirely possible 
 that both Lamarckism and Darwin- 
 ism may be acting at once and in per- 
 fect accord as mutually efficient 
 factors in evolution. 
 
WHat hVOCUTION IS. \113 
 
 5. DARWINISM CRITICIZED 
 
 In discussing Darwinism or natural 
 selection from a critical standpoint 
 we may begin by inquiring whether 
 there is any evidence that this process 
 is an actual occurrence in nature. To 
 answer such a question, one would 
 naturally turn to conditions where 
 organisms are subjected to severe 
 and unusual strain. Some years ago 
 Bumpus studied the effects of a 
 severe winter storm on sparrows. 
 As a result of a heavy sleet many 
 birds were brought close to death. A 
 large number of these spent birds 
 were collected, and of the total col- 
 lection, 64 died and 72 revived. Do 
 the members of these two groups 
 thus naturally established differ, or 
 are they essentially the same? A 
 statistical study of the two sets of 
 
114, WHAT. EVOLUTION IS 
 
 birds showed that the survivors were 
 less variable than those that perished. 
 The birds that died were, in many 
 cases, extreme individuals. For in- 
 stance, they more frequently had 
 large bodies combined with small 
 wings, or the reverse, than the sur- 
 vivors had. Hence they represented 
 conditions in which it might be said 
 that there was too much power or too 
 little power for the wing surface and 
 the like. This disadvantageous ten- 
 dency was in general the cause of 
 their death. One may therefore con- 
 clude that, under the severe circum- 
 stances mentioned, elimination was 
 not haphazard but rather, as would 
 be expected, that the least fitted birds 
 succumbed and the best fitted sur- 
 vived. In this rather crude way, evi- 
 dence of a selective capacity in nature 
 has been obtained, and from instances 
 of this kind, it is fair to conclude that 
 
WHAT EVOLUTION IS _ = 115 
 
 natural selection is a process that is in 
 actual operation in the world about us. 
 
 Natural selection, however, is not 
 without its limitations. It is an op- 
 eration that at best can lift organ- 
 isms only to the level of positive needs. 
 Nature, with a certain prodigality, 
 often goes much beyond this limit. 
 Examples are abundant enough. 
 Many crustaceans have the curious 
 habit of casting injured legs and 
 other appendages. When a crab loses 
 a part of one of its legs, it recovers 
 by a new growth, but this new growth 
 does not replace simply the lost part; 
 the old stump is thrown off from a 
 so-called casting joint at the base of 
 the leg and a wholly new leg is 
 formed. Most crabs, picked up on 
 the shore at random, are undergoing 
 this process on some one of their nu- 
 merous appendages. 
 
 Hermit crabs live with the pos- 
 
 / 
 
116 WHAT EVOLUTION IS 
 
 terior parts of their bodies tucked 
 away in some dead snail-shell appro- 
 priated by the crab for this purpose. 
 Their hind appendages are therefore 
 protected and, according to Morgan, 
 who recorded this case, these append- 
 ages are never found suffering from 
 injury as their front legs are. Never- 
 theless, if by experimental steps the 
 hind appendages are injured, they are 
 cast and recovered as the exposed 
 appendages are. Here then is an in- 
 stance where nature has stepped be- 
 yond the actually necessary, and 
 where it would be difficult to offer for 
 the condition an explanation based 
 purely upon natural selection. 
 Another instance of the same kind 
 occurs among certain almost micro- 
 scopic crustaceans, the copepods. 
 These small creatures are abundantly 
 represented inthe surface watersof the 
 sea. Copepods of different sexes are, as 
 
WHAT EVOLUTION IS 117 
 
 a rule, strikingly unlike. The females 
 are relatively inconspicuous and sim- 
 ple in their dress. The males, on the 
 other hand, are gaudy and ornamen- 
 tal in the extreme. In their colors 
 they are veritable microscopic pea- 
 cocks. In fact the comparison with 
 birds is quite appropriate, for just as 
 the male bird often has a conspicuous 
 plumage so is the male copepod com- 
 monly highly decked out, and one 
 would suppose for the same reason, 
 namely, to attract the females at the 
 breeding time. But the female cope- 
 pod, unlike the female bird, has eyes 
 that are quite incapable of taking in 
 all this beauty, and we meet again a 
 condition in which nature seems to 
 have gone so far in excess of what is 
 necessary that natural selection can- 
 not be offered as a means of explaining 
 the condition. This kind of excess, 
 which is an example of what has been 
 
118 WHAT EVOLUTION IS 
 
 called hypertely, is a common occur- 
 rence in nature and is beyond the 
 reach of natural selection. 
 
 The most serious objection that 
 has been raised against natural selec- 
 tion is its apparent inability to launch 
 any real change. When we consider 
 how very slight and insignificant the 
 individual differences are in any 
 group of plants or of animals, it is 
 almost inconceivable that these dif- 
 ferences can afford sufficient grip for 
 what natural selection is supposed to 
 do in producing a new species. Once 
 well established, it is easy to see how 
 a new and advantageous trait can be 
 fostered and developed by this proc- 
 ess, but at the inception, it would 
 seem impossible that natural selec- 
 tion could start a new feature forward 
 from such small beginnings. Indi- 
 vidual differences are not sufficiently 
 life and death differences to enable 
 
WHALE VOLUTION UES T19 
 
 natural selection to obtain an initial 
 hold. From the time of Darwin this 
 has been the great obstacle to his 
 theory, and no Darwinist has thus 
 far successfully met this objection. 
 When we view the face of organic 
 nature, we see such an array of mar- 
 velous adaptations and such a bewil- 
 derment of plant and animal species, 
 many of which are separated one 
 from another by differences of a very 
 slight kind, that we are forced to 
 admit that it is inconceivable that 
 natural selection, as understood by 
 Darwin at least, could have produced 
 what is before us. This conviction 
 has so impressed itself upon the minds 
 of most modern evolutionists, that 
 they have one by one come to the con- 
 clusion that natural selection, which 
 in Weismann’s time was declared to 
 be all-sufficient in evolution, may 
 after all be of little real significance. 
 
120 WHAT EVOLUTION IS 
 
 Opinions of this kind have been 
 frankly expressed by such eminent 
 authorities as Bateson in England 
 and Morgan in America, and they 
 reflect the view of the majority of 
 biologists the world over. 
 
 Although the statements of these, 
 and other authorities on this subject, 
 have been made with perfect clear- 
 ness and in full knowledge of what 
 the words imply, they have been 
 seized upon by many thoughtless per- 
 sons as evidence that biologists are 
 abandoning the doctrine of evolution. 
 What is really meant by these decla- 
 rations, as must be evident to any- 
 one who has read thus far, is that 
 descent with modification, or evolu- 
 tion, is not questioned, but that the 
 particular explanation of it, known 
 as natural selection, or Darwinism, is 
 seriously doubted. One often sees in 
 current literature lists of noted biolo- 
 
WHAT EVOLUTION IS 121 
 
 gists who are said by anti-evolution- 
 ists to be opposed to evolution, but, 
 when the ground for these statements 
 is scrutinized, it is commonly found 
 that the authority named questions 
 natural selection (Darwinism), but 
 not descent with modification, or evo- 
 lution, in the ordinary sense of the 
 word. Ina recent newspaper a prom- 
 inent Boston pastor names “some 
 scientists who at least call in question 
 the loudly asserted proof of evolu- 
 tion.” These names include those of 
 J. P. Lotsy and William Emerson 
 Ritter both of whom have criticized 
 Darwinism but, to the best of my 
 knowledge, are firm believers in 
 evolution. If by Paul Kamerer is 
 meant Paul Kammerer and by E. B. 
 McBride, E. W. McBride, the same 
 statement applies to these zoologists 
 as to the other two scholars named. 
 Hence this list includes several well 
 
122 WHAT EVOLUTION IS 
 
 reputed evolutionists. The confusion 
 whereby these names have been in- 
 cluded has probably arisen through 
 failure to distinguish Darwinism from 
 evolution. It is unclear thinking of 
 this kind that is responsible for many 
 of the present contentions. 
 
 In the opening portion of this sec- 
 tion, it was pointed out that natural 
 selection was without doubt a real 
 occurrence in nature, and as the dis- 
 cussion progressed, it was made clear 
 that this process, at least as under- 
 stood by Darwin, fell short, and per- 
 haps far short, of accomplishing 
 what it was originally believed to do. 
 This, 1n general, seems to be the 
 modern opinion concerning it. That 
 it is a real factor in evolution, there 
 is not the least doubt; but that it is a 
 subordinate factor, and perhaps even 
 a very subordinate one, is likewise 
 true. Biologists know that one spe- 
 
WHAT EVOLUTION IS 123 
 
 cies comes from another, but how this 
 is accomplished no one apparently 
 can yet explain. As a contributing 
 factor, natural selection doubtless had 
 a hand in this operation, but it is in 
 the rough-hewing of the species, and 
 not in the polishing of the final prod- 
 uct that itisconcerned. The polishing, 
 which after all is perhaps the most 
 essential aspect of the process, seems 
 still to be hidden from scientific gaze. 
 
1244 WHAT EVOLUTION JS 
 
 6. THE MUTATION , THEORY 
 
 For almost forty years after the pro- 
 mulgation of natural selection, biolo- 
 gists were content to speculate on the 
 way in which plants and animals 
 might be changed through this prin- 
 ciple. Only as the methods of zo- 
 ology and of botany changed, from 
 the more purely observational to the 
 experimental, did evolutionary inves- 
 tigation receive a new impulse. ‘This 
 change in evolutionary work may be 
 said to have been initiated, about the 
 beginning of the present century, in 
 the studies on heredity, carried out 
 more or less independently by Tscher- 
 mak, by Correns, and especially by 
 de Vries. One of the results of these 
 studies was the unearthing of the 
 long-neglected but highly important 
 publications of Mendel which had 
 
WHAT EVOLUTION IS | 125 
 
 appeared some thirty years previ- 
 ously. The principles, contained in 
 Mendel’s writings, were at once 
 made the basis of an extensive and 
 thorough-going experimental pro- 
 gramme and served, at the same time, 
 as ground on which de Vries erected 
 his mutation theory. 
 
 Those portions of Mendel’s work 
 that are directly concerned with 
 the mutation theory are easily and 
 quickly grasped. They can be illus- 
 trated by what occurs in animals as 
 well as in plants. If we breed a pure 
 _ black guinea pig to a pure white one, 
 the offspring are always black and if 
 these offspring are bred amongst 
 themselves, they produce young one- 
 fourth of which are pure white and 
 three-fourths are black. On testing 
 the black individuals, one-third of 
 them, or one-fourth of the total, can 
 be shown to be pure black and the 
 
126 WHAT EVOLUTION IS 
 
 other two-thirds, or one-half of the 
 total, can be shown to be mixed, in 
 that, like their parents, they will 
 when bred together produce both 
 black individuals and white individ- 
 uals. The remarkable feature of 
 such breeding series is the regularity 
 with which the proportions, just 
 stated, occur. The occasion of these 
 remarkable Mendelian proportions 
 can be seen when such a series, as 
 that described, is analyzed. 
 
 When opposing characters, such as 
 white and black, are combined in 
 breeding, as in the case of the guinea 
 pigs mentioned in the preceding para- 
 graph, only one of these characters 
 appears in the first generation of off- 
 spring, namely, in the particular in- 
 stance under consideration, black. 
 All guinea pigs in the first generation 
 after the cross white-black are black. 
 But these black individuals carry 
 
WHAT EVOLUTION HS: “127 
 
 hidden in their bodies the white trait, 
 for, when they are bred amongst 
 themselves, one-fourth of their off- 
 spring are white. Black, then, in 
 some way overcomes white; not that 
 it obliterates the white, but it holds 
 this traitinabeyance. In the language 
 of the modern breeder black is said, 
 in a case such as the guinea pig, to be 
 dominant over white and white is 
 said to be recessive to black. This 
 state of affairs, though not universal, 
 is common to many such pairs of 
 breeding characters. As a generali- 
 zation, it is often referred to as the 
 principle of dominance and was one 
 of the discoveries of Mendel. 
 
 A second and very much more im- 
 portant principle, that is illustrated 
 by the example under consideration, 
 is, what may be called, the principle 
 Oimthe = purity of, the céerm)It7is 
 briefly this: a given germ cell, be it 
 
128 WHAT EVOLUTION IS 
 
 sperm or egg, can carry the exciter 
 or gene of only one of two opposing 
 characters, such for instance as white 
 and black. No germ cell can carry a 
 gene for white and a gene for black 
 at the same time. In any pair of op- 
 posing traits, the gene of only one 
 can be present in any germ cell. In 
 other words the germ cells are in this 
 respect always individually pure. 
 This principle of the purity of the 
 germ cell makes clear the remarkable 
 proportions, already pointed out, in 
 the second generation of offspring. 
 It will be recalled in the example of 
 the guinea pigs that, in the second 
 descendent generation, there were one- 
 quarter or twenty-five per cent pure 
 whites, another quarter or twenty- 
 five per cent pure blacks, and a half 
 or fifty per cent black individuals 
 which, however, were really mixed, 
 for, on being bred amongst them- 
 
WHAT EVOLUTION IS __ 129 
 
 selves, they, like their parents, pro- 
 duced whites as well as blacks. 
 
 If, now, we examine the whole 
 breeding series from the standpoint 
 of the purity of the germ, we shall 
 find reason for the occurrence of the 
 
 proportions given. This can be done 
 best by reference to the diagram on 
 page 131. Here it will be seen that 
 the source of the descendent stock 
 is the pair of guinea pigs, one white 
 and the other black, represented in 
 outline at the top of the page. Which 
 of the two is male and which female 
 makes no difference so far as the final 
 outcome is concerned. The white one 
 is supposed to have been derived 
 from a pure white stock, that is, 
 from a stock which in all its pairings, 
 within its own bounds, produced 
 nothing but white individuals. Hence 
 the white pig must be assumed to 
 have come from an egg containing a 
 
130 WHAT EVOLUTION IS 
 
 white gene, fertilized by a sperm also 
 containing a white gene. This is rep- 
 resented in the diagram by the two 
 white circles above the white pig, one 
 for the egg and the other for the 
 sperm. Such an individual can pro- 
 duce only one class of germ cells, 
 namely those with white genes. As- 
 suming in this particular instance 
 that the white pig is the female, she 
 may then be described as an individ- 
 ual producing eggs all of which carry 
 the white gene. If the white member 
 of the pair is the female, the black one 
 must be the male and what has been 
 said of the white pig may be said of 
 her black mate, except that black gene 
 is to be used in place of white gene 
 and sperm cell in place of egg cell. 
 
 In the first descendent generation 
 all offspring, in the present instance, 
 would be the product of a white egg 
 fertilized by a black sperm. This is 
 
WHAT EVOLUTION IS 
 
 Guinea-pig 
 e@ 00 
 
 Four-o'clock 
 ee foXe) 
 
 131 
 
, 
 
 GPa f 
 Aes Wat 
 Panty, inky ,) { 
 
 
 
WHAT: EVOLUTION IS 133 
 
 indicated by the white circle and the 
 black circle in the diagram over the 
 representative of this generation. In 
 consequence of the dominance of 
 black over white, all individuals, in 
 this generation, will have black coats. 
 But since they arise from a germinal 
 mixture, each of these individuals 
 will be able to produce two kinds of 
 germ cells, the males white sperm and 
 black sperm, and the females white 
 eges and black eggs. If, now, we 
 assume that the two kinds of eggs 
 are produced in equal numbers and 
 that the same is true of the sperm and 
 that the union of egg and of sperm is 
 purely fortuitous, the kinds of guinea 
 pigs and their proportionate num- 
 bers, as already stated for the second 
 descendent generation, will be ex- 
 ' actly realized. For with two kinds of 
 sperms and two kinds of eggs, there 
 will be four possible combinations in 
 
134 WHAT EVOLUTION IS 
 
 fertilization. Once in four chances 
 a white sperm will fertilize a white 
 egg, a process which will yield the 
 twenty-five per cent pure white guinea 
 pigs. Once in four a black sperm 
 will fertilize a black egg and thus will 
 arise the twenty-five per cent pure 
 black guinea pigs. Once in four a 
 white sperm will fertilize a black egg 
 and once in four a black sperm will 
 fertilize a white egg and these two 
 classes taken together will yield the 
 fifty per cent mixed stock which, like 
 their parents, can produce either 
 white or black offspring. Thus the 
 assumption of the purity of the germ 
 leads to a simple and illuminating 
 understanding of the proportionate 
 numbers of young in the several Men- 
 delian classes. 
 
 This assumption has been tested by 
 geneticists in many ways and has been 
 found to hold good. In fact, the 
 
WHAT EVOLUTION IS 135 
 
 whole set of Mendelian principles has 
 proved in the hands of the experi- 
 mentalist little short of marvelous in 
 their application. Exceptional cases 
 often occur, but when these are 
 worked out, they are commonly found 
 to be in essential agreement with the 
 general principles. Thus when the 
 red-flowered variety of the common 
 garden four o’clock is crossed with 
 the white-flowered form, as shown 
 on the lower half of page 131, the off- 
 spring are neither red-flowered nor 
 white-flowered but have flowers of an 
 intermediate tint, pink. If now these 
 offspring are bred amongst them- 
 selves three classes result: twenty- 
 five per cent pure whites, twenty-five 
 per cent pure reds, and fifty per cent 
 pinks, a state of affairs that may be 
 described as parallel to that of the 
 guinea pigs, so far at least as purity 
 of the germ is concerned but without 
 
1336 WHAT: EVOLUTION IS 
 
 dominance. In this way particular 
 examples may show individual dif- 
 ferences and thus illustrate the extent 
 to which the general principles are 
 open to readjustment. 
 
 De Vries, having discovered inde- 
 pendently much that was afterwards 
 found in the writings of Mendel and 
 having come to many of the same 
 conclusions that this writer had ar- 
 rived at, turned to the problem of 
 evolution in the hope that the new 
 ideas on heredity would be helpful in 
 understanding descent with modifi- 
 cation. In 1901 he published the first 
 general account of his mutation 
 theory. According to this theory, the 
 characters by which we distinguish 
 different plants and animals are made 
 up of units which are sharply sep- 
 arated from one another and are 
 without intergrades. They are repre- 
 sented by such features as black and 
 
WEA EVOLUTION IS) 137 
 
 white in the guinea pig’s coat. These 
 opposing traits were called unit or 
 elementary characters by de Vries 
 and, in describing them as elementary, 
 he meant that they partook in their 
 separateness of the nature of the 
 chemical elements. Every organism 
 is marked by a great array of these 
 unit characters. In the guinea pig, 
 for instance, there are coat colors, 
 white, black, piebald and the like, dif- 
 ferences in hair, long, short, rosetted, 
 or smooth, and a host of other features 
 all of which are inherited in accord- 
 ance with Mendelian principles. 
 Thus the pairs of traits in Mendelian 
 inheritance are the unit characters of 
 the mutation theory. 
 
 According to de Vriesa real species, 
 or as he called it an elementary species, 
 is to be described from its unit char- 
 acters and any new combination of 
 unit characters is a new species. A 
 
138 WHAT EVOLUTION IS 
 
 black guinea pig differs from a white 
 guinea pig in one unit character, and 
 yet this is sufficient to place these two 
 individuals in different elementary 
 species. This is certainly a novel 
 conception, for it implies that two 
 brothers may be of diverse species 
 provided they show a unit character 
 difference. In evolution, however, 
 we are not so much concerned with 
 this aspect of the subject as with 
 another. 
 
 As already stated, the unit char- 
 acters, by which elementary species 
 may be distinguished, show no inter- 
 erades; they are fixed characters. 
 Hence the difference between one ele- 
 mentary species and another is an 
 abrupt difference. These abrupt dif- 
 ferences are what de Vries calls muta- 
 tions, and he contrasts them with 
 the very slight individual differences 
 which are seen between members of 
 
WHAT EVOLUTION IS = 139 
 
 the same species and which are com- 
 monly designated as variations. Vari- 
 ations, according to de Vries, are 
 always very slight and insignificant. 
 They never even approximate the 
 magnitude of a mutation. Mutations 
 on the other hand are striking differ- 
 ences such as black or white in the 
 coat of a guinea pig and represent, 
 in this sense, considerable jumps or 
 breaks. Variations are like the slight 
 movements that a cube may be made 
 to execute when it is wabbled about 
 on one of its faces. Mutations are 
 like the changes that arise when 
 the cube is turned from one face to 
 another. 
 
 The mutation theory is to the effect 
 that evolution takes place not through 
 small differences or variations, as Dar- 
 win believed, but through large and 
 sudden changes, mutations. Just as 
 the cube does not progress when it 
 
140 WHAT EVOLUTION IS 
 
 merely wabbles back and forth on one 
 side, so evolution makes no progress 
 through variations. Only when mu- 
 tations occur, when the cube rolls over 
 on to a new face, is evolution taking 
 place. Darwin recognized mutations 
 as conditions in nature and used for 
 them the breeder’s common name of 
 sport. He was doubtful, however, 
 whether they had any significance in 
 evolution. To de Vries they are 
 the only real factor in evolutionary 
 progress. 
 
 No one can have bred plants or an- 
 imals for any length of time without 
 having noticed the frequency with 
 which mutations occur. Morgan, in 
 his exhaustive study of inheritance in 
 the fruit fly, has recorded many scores 
 of mutations, and there is no reason 
 to suppose that they do not occur as 
 frequently in open nature as in the 
 laboratory. 
 
WHAT EVOLUTION IS_ 141 
 
 Whether a mutation persists or not 
 depends upon its nature. If it is in 
 a favorable direction, the individual 
 possessing it is likely to be preserved 
 and finda mate. As such changes are 
 handed down undiminished by Men- 
 delian inheritance, the mutation would 
 be expected to reappear in many of 
 the descendants in full vigor. In this 
 way, it could establish itself in the 
 stock and help to modify that stock so 
 as to form a new species. As de Vries 
 rightly states, this process of preser- 
 vation involves natural selection, for 
 the retention of such a character de- 
 pends upon this principle. All muta- 
 tions must run the gantlet of natural 
 selection. In this sense, the mutation 
 theory and natural selection are 
 mutually dependent. The mutation 
 theory yields the grain for the natural 
 selection hopper. 
 
 It must be evident that the muta- 
 
 i 
 
142° (WHAT EVOLUTION] Ts 
 
 tion theory presents a means of avoid- | 
 ing the chief difficulty with which 
 Darwinian natural selection has to 
 contend. That difficulty, it will be 
 remembered, had to do with the first 
 steps in the origin of favorable traits. 
 These steps are not necessary in the 
 origin of mutations, for mutations 
 appear fully formed and are not built 
 up by slow degrees. This is the great 
 advantage that the mutation idea has 
 over Darwin’s view of the way in 
 which new traits are supposed to be 
 ushered in. As mutations they enter 
 fully formed. 
 
 Difficulties with the mutation the- 
 ory can be easily found. First of 
 all this theory depends upon Men- 
 delian inheritance and what that kind 
 of inheritance implies as to the sep- 
 arateness of characters. But char- 
 acters often blend, in fact there may 
 be such a condition as blended in- 
 
WHAT EVOLUTION IS)? (143 
 
 heritance, and such a condition, if at 
 all general, would be very restricting 
 to the mutation view. 
 
 Mutations further give the impres- 
 sion of laboratory and of garden 
 products, rather than of products of 
 the land and sea. Mutations certainly 
 occur in nature, witness albino ani- 
 mals, but the experimental product 
 seems to be far removed from what 
 is demanded by open nature. Many 
 workers have been so impressed with 
 this aspect of the question, that they 
 have come to look upon the great 
 biological advance of the last two 
 decades as illuminating, from the 
 standpoint of heredity, but as having 
 very little real bearing on the evolu- 
 tion problem. The truth is that the 
 mutation idea, and all its intricate 
 connections, are somewhat too novel 
 to admit of final judgment. 
 
 What the factors of evolution are, 
 
144. WHAT EVOLUTION IS 
 
 what the moving forces behind this 
 great natural process are, no one is 
 in a position to state. Lamarckism 
 may be one of these. Darwinism 
 alone, or supplemented by the muta- 
 tion idea, seems quite clearly another 
 though perhaps a subordinate one. 
 Others still are probably to be dis- 
 covered, for it is unlikely that a proc- 
 ess so intricate, so many-sided, and 
 so far-reaching as organic evolution 
 should depend for its energizing on 
 only one source. 
 
My 
 HUMAN APPLICATIONS 
 

 
HUMAN APPLICATIONS 
 
 MAN as an animal is a product of evo- 
 lution and is subject to its laws as all 
 other animals are. Such a statement, 
 however, does not mean that man with 
 all his complexities is at once under- 
 stood the moment this position is as- 
 sumed. The evolutionary standpoint, 
 like a mountain top, is a commanding 
 situation for a general survey, but it 
 does not do away with the intricacies 
 in the field of vision, it merely brings 
 them into more truthful relations with 
 the whole. 
 
 The derivation of civilized man 
 from a primitive human stock is a 
 subject that has grown so enormously, 
 in the last few decades, that its treat- 
 ment merits a volume. The new in- 
 formation on the subject, that has 
 come to us since Darwin’s time, is 
 
148 WHAT EVOLUTION IS 
 
 simply overwhelming in amount. Man 
 appears to have been on the earth for 
 nearly half a million years. His old- 
 est known representative is from Java, 
 the Trinil man or Pithecanthropus, 
 a restoration of whose head has been 
 made by McGregor. This is shown in 
 an outline sketch at the top of page 149. 
 For the use of this sketch and the 
 other outlines of heads on this page, 
 I am indebted to Professor R. S. Lull 
 and to the Yale University Press. 
 Pithecanthropus flourished about 
 500,000 years ago and is believed to 
 have made use of fire and simple flint 
 implements. — 
 
 Of later date is the dawn-man, 
 Eoanthropus, of Piltdown, England, 
 who lived about 250,000 years ago. 
 His bones seem to be the most ancient 
 remains of man in England and occur, 
 associated with crude stone imple- 
 ments and the remains of several 
 
WHAT EVOLUTION IS_ 149 
 
 
 
 Trinil man Piltdown man 
 
 
 
 Neandertal man Cré-Magnon man 
 
vo 
 ys ay 
 wh Py," 
 
 ACE 
 iP 
 
 Ho Cee 
 cone 
 
 J 
 
 vera 
 , Wee wh Viet 
 
 4? fe ¢ J 
 CPN ] Aq. 
 I i 
 
 
 
Viera y ORU TIONS Soro r 
 
 animals long since extinct. Another 
 ancient type of man is the Neandertal, 
 or Mousterian man, evidences of 
 whom have been found in many Euro- 
 pean localities. These remains date 
 from about 100,000 years or more 
 ago. Of still later time is the Cro- 
 Magnon man, believed to be of the 
 same species as ourselves. His period 
 may be set at some 25,000 years ago, 
 and his blood may still flow in the 
 veins of certain European peoples. 
 He was remarkable for his great 
 height, being commonly over six feet 
 tall. His stone implements were of 
 good workmanship, and his engrav- 
 ing, painting, and sculpture show him 
 possessed of esthetic traits and of 
 unusual powers of expression. His 
 remains have been found in Wales, 
 France, and Spain. These few ex- 
 amples show how rich and numerous 
 are the traces of primitive man. 
 
152 WHAT EVOLUTION IS 
 
 That man has descended from an 
 ape-like stock no reasonable person 
 can doubt. He shows this affiliation 
 in his body and in his activities in a 
 thousand ways, and yet more than 
 most animals, he has peculiarities of 
 his own. When we look at civiliza- 
 tion as represented in the complex life 
 of cities and of nations with all their 
 commercial interrelations, with their 
 humane institutions such as asylums 
 and hospitals, and with their oppor- 
 tunities for intellectual, esthetic, and 
 spiritual growth, it seems as if an 
 attempt to base this enormous struc- 
 ture on an evolutionary foundation, 
 with Lamarckism, Darwinism, and 
 the like as driving forces, is futility 
 in the extreme. Who for a moment 
 would attempt to account for the 
 Divine Comedy as a product of evolu- 
 tion? And yet, if evolution means 
 anything, it means exactly this. Some- 
 
WHAT EVOLUTION IS 153 
 
 where in the scope of its totality evo- 
 lution must finda place for the highest 
 achievements of the human soul, or the 
 general conception crumbles. Every 
 thorough-going evolutionist believes 
 this and looks to the natural history of 
 man, when viewed in its all-inclusive 
 light, as the real history of man. 
 
 But how is it that man holds such 
 an exceptional place in the world? 
 We are quite sure that never before 
 in the history of the earth has there 
 arisen an organism that has probed 
 the universe as man has, that has 
 developed art, poetry, religion, and 
 science as the human species has done 
 and is doing to-day. Not that these 
 accomplishments are in any sense 
 final or ultimate, for no one can tell 
 what the future has in store, but com- 
 pared with the efforts of the long 
 geologic past they are stupendous. 
 We look with admiration on the bee 
 
134 WHAT EVOLUTION IS 
 
 and the ant, and we are astounded at 
 the instinctive capabilities of many 
 animals, but, when we examine our- 
 selves closely, we find most of these 
 potentialities within us and a host 
 more of capacities of which no lower 
 creature seems ever to have dreamed. 
 
 In what respects has man lifted 
 himself so much above his neighbors? 
 Man 1s first of all a social organism. 
 He is banded together in families, 
 clans, and nations and, as thus organ- 
 ized, he resists the vicissitudes of life 
 vastly more successfully than he pos- 
 sibly could single handed. As an 
 organization, human society is in 
 many respects unique. Social life was 
 tried eons ago by the simpler animals 
 in a thousand different ways; proto- 
 zoan colonies out of which sexuality 
 grew, sponge colonies and coral col- 
 onies which have had a hand in mould- 
 ing the earth’s surface, insect colonies 
 
WHAT EVOLUTION IS 155 
 
 such as the ant hill and the bee swarm, 
 all these preceded human society by 
 untold ages. Wheeler informs us 
 that in the insects alone social states 
 have arisen no fewer than twenty- 
 four different times in as many dif- 
 ferent groups of these animals. Yet 
 none of these societies accomplished 
 what man, as a social organism, has 
 achieved. 
 
 They almost all differ from human 
 society in two fundamental aspects. 
 First of all, the members of most 
 animal societies are close-blood rela- 
 tives. In the ant hill the individuals 
 are commonly the offspring of one 
 queen; they are all sisters in one 
 household. In almost all animal col- 
 onies, except the human, this close- 
 blood relationship holds. Second, 
 among the colonies of lower animals 
 the division of labor is relatively 
 slight. In human society occupations 
 
156 WHAT EVOLUTION IS 
 
 mount into the tens of thousands at 
 the very least. Among the other co- 
 lonial animals the classes of perform- 
 ance are to be counted at most in 
 scores. In the beehive, the drones 
 have as their one duty the fertiliza- 
 tion of the queen, the queen is service- 
 able only in that she lays eggs, and 
 finally the worker performs the ordi- 
 nary duties of caring for the young, 
 procuring food, cleaning the hive and 
 the like. Compare for a moment the 
 relative simplicity of even so complex 
 a situation as that in the beehive with 
 the enormous intricacies of human 
 life and civilization, where blood- 
 relationship is most diverse and per- 
 formance is specialized to an almost 
 incredible degree. These aspects of 
 human society set it in strong contrast 
 with the social organizations of all 
 other animals. 
 
 Another feature, in which man 
 
WHAT EVOLUTION IS 157 
 
 differs from most animals, is in his 
 striking ability to use the environment 
 to his advantage. The primitive ac- 
 quisition of fire made available to 
 him such gigantic forces as we see in 
 steam, electricity, and their endless 
 applications. Who would have sus- 
 pected that the unclad savage, as he 
 warmed himself over the dying em- 
 bers, was nursing a form of energy 
 that was to do for man all that modern 
 machinery has done! Little do we 
 think as we look at a watch face that 
 shines in the dark that the changes 
 going on there foreshadow, in germ, 
 possible sources of energy for future 
 man that may be as much superior to 
 fire as fire was to ancient brawn. But 
 this may be so, and it is precisely this 
 capacity to discover and utilize to the 
 utmost such environmental changes 
 that makes man different from almost 
 all other organisms. 
 
158 WHAT EVOLUTION IS 
 
 In harnessing the energies of nature 
 man has discovered and perfected 
 tools. Few other animals use tools. 
 Monkeys and apes have their sticks 
 and stones, but it took man to fash- 
 ion them into serviceable shapes, 
 to discover metals, to build engines, 
 steamships, and airplanes. Man’s 
 tools were amongst his first posses- 
 sions and not till he acquired the habit 
 of preserving them and passing them 
 on to future generations did society 
 progress. The race that buries with 
 the primitive artisan the choice ob- 
 jects of his life’s work never goes 
 forward. Even the rude tools of one 
 generation must be put in the hands 
 of the next, if real progress is to be 
 made. In this sense the inheritance 
 of property separates man from most 
 other animals. 
 
 Another trait in which man is pe- 
 culiar is in the possession of a com- 
 
WHAT EVOLUTION IS __1s9 
 
 plex language. The lower creatures 
 have their cries as outlets for emo- 
 tional states, and these cries form 
 a simple kind of organic language. 
 Everyone knows the difference be- 
 tween the hum of a complacent and of 
 an angry bee. How diverse and in- 
 forming are the vocal sounds of a 
 dog. All these are types of primitive 
 language, but they are almost end- 
 lessly remote from human _ speech 
 which, as represented in written form, 
 is not only a means of communica- 
 tion between distant individuals but 
 the stabilizer of all past events, the 
 vehicle of history. From this stand- 
 point the simple organic language 
 of the lower animals fades into in- 
 significance. 
 
 Finally, though not last, for there 
 are many other points of contrast be- 
 tween man and other animals, the 
 human species has acquired the habit 
 
160 WHAT: EVOLUTIONS 
 
 of teaching, of passing on to a new 
 generation the practices and the wis- 
 dom of the older generations. This 
 is largely a human institution, for few 
 animals other than man possess the 
 least trace of it. Very many animals 
 learn. Beasts, birds, frogs, and fishes 
 learn; even an earthworm can learn 
 to find its way out of a simple maze. 
 Such animals learn by individual ex- 
 perience; they do not learn by ex- 
 ample. To learn by example is to have 
 a model and this is at once the worth 
 and the artificiality of the teacher. 
 Man learns not only by experience as 
 the lower animals do, but also by 
 being taught and the profession of 
 teacher is almost exclusively a human 
 profession. Contrary to the belief of 
 the commonalty, animals, other than 
 man, do very little teaching. In a 
 beehive worker bees, that have never 
 seen a queen reared, will make queen 
 
WHAT EVOLUTION IS 161 
 
 cells and hatch queens with as much 
 skill as the best. Their operations are 
 largely instinctive. Such perform- 
 ances are not taught, though bees like 
 most animals of their grade can learn. 
 
 Thus, man, though an animal, is 
 preeminent in a multitude of ways as 
 compared with his neighbors. He has 
 the most intricate and complicated 
 form of social life of which we have 
 any knowledge. He controls his en- 
 vironment, devises and uses tools, and 
 acquires property as no other organism 
 has ever done. He has developed a 
 most complex spoken and written lan- 
 guage which serves him for com- 
 munication and record, and he teaches 
 as wellas learns. No wonder with all 
 these exceptional traits that he ap- 
 pears so strikingly unlike other ant- 
 mals. It is therefore to be expected 
 that his evolutionary relations will be 
 far from usual. 
 
162 WHAT EVOLUTION IS 
 
 When we ask ourselves how im- 
 portant natural selection is in human 
 affairs, and whether man’s life pro- 
 gresseswithno showofthe inheritance 
 of acquired characters, we pass im- 
 mediately into a situation where every- 
 thing that the biologist has taught 
 seems to be contradicted. At every 
 step human society seems to have 
 gone forward by the inheritance of 
 daily acquisitions and all our humane 
 institutions, charities, and the like cry 
 out against such an ideal as natural 
 selection. ‘This reversal of affairs is, 
 however, merely apparent. 
 
 Every scheme in evolution, whether 
 it be Lamarckian or Darwinian in its 
 tendencies, turns on the transmission 
 of traits, on heredity, and when we 
 inquire what and how man inherits, 
 we find him as peculiar in this respect 
 as he is in others. A child may in- 
 herit, for instance, a book from its 
 
WHAT EVOLUTION IS _ 163 
 
 parent which means that this partic- 
 ular book is passed from the parent 
 dead to the child living. This is the 
 literal significance of the term inherit. 
 But less tangible things than a book 
 may be inherited; the child may in- 
 herit the parent’s habits of thrift and 
 frugality or of poor table-manners. 
 Such an inheritance involves learning 
 through example and applies to an 
 enormous number of social customs. 
 Finally the child may inherit the color 
 of the parent’s eyes or his stature or 
 the like, and this form of inheritance, 
 which involves a rather figurative use 
 of the term, we know to be germinal. 
 The eyes, unlike the book, are not 
 handed on from parent to child, but a 
 tendency is transmitted whereby the 
 child’s eyes develop the color of those 
 in the parent. This tendency, as we 
 know, is passed on by the egg or the 
 sperm. Almost no other animal than 
 
164 WHAT EVOLUTION IS 
 
 man inherits as we inherit a book, and 
 few animals inherit as we do thrift or 
 table-manners, but all animals inherit 
 as we inherit eye-colors and the like. 
 This type of inheritance has been 
 called germinal, or organic, and may 
 be contrasted with the other types of 
 inheritance which have been called 
 social, for they depend primarily on 
 man’s social condition. Human in- 
 heritance, then, like other human 
 capacities, is more complex than in- 
 heritance in lower animals, for it in- 
 cludes in addition to their type of 
 inheritance, social inheritance. 
 Organic or germinal inheritance 
 involves the physical traits of our 
 bodies, hair-color, eye-color, size, 
 tendencies and resistances to disease 
 and, less physical in character, tem- 
 perament and the like. Many of these 
 peculiarities are inherited in accord- 
 ance with Mendelian principles; they 
 
WHAT EVOLUTION IS 165 
 
 are subject to mutational change and 
 to natural selection. The part La- 
 marckism plays in their moulding is 
 as little known in man as in other 
 animals. 
 
 Social inheritance includes our so- 
 cial customs, our language and the 
 way we use it, our daily habits of 
 honesty or dishonesty, frugality or 
 wastefulness, and such minutiae as 
 eating food with a knife or using a 
 napkin. All these features are learned 
 either through experience or from a 
 teacher. None of them comes to us 
 through the sperm or the egg. Lan- 
 guage, one of the most fundamental, 
 never reaches us as a germinal con- 
 tribution, but must be learned by each 
 generation as it matures. To these 
 traits natural selection has no applica- 
 tion except in a figurative way, for 
 though an individual may gain a mate 
 and offspring in consequence of his 
 
166 WHAT EVOLUTION IS 
 
 table-manners, there 1s no certainty 
 that any of his descendants will show 
 these traits as they may his eye-color 
 or hair-color. Social inheritance is 
 accomplished on what may be de- 
 scribed as a Lamarckian model, for 
 the habits of one generation are modi- 
 fied and, as such, are handed on to the 
 next. But this, of course, is through 
 what one individual learns from an- 
 other and not through the germ, so 
 that when we speak of it as La- 
 marckian we are using that term in 
 a figurative way. 
 
 The methods of social inheritance, 
 then, are very different from those of 
 germinal inheritance. They have a 
 superficial resemblance to the La- 
 marckian conception, and probably it 
 is this resemblance coupled with our 
 great familiarity with them in daily 
 life that predisposes us to the La- 
 marckian doctrine. It is a strange 
 
WHAT EVOLUTION IS = 167 
 
 fact, but nevertheless true, that in the 
 estimation of character or in the for- 
 mation of friendships we are more 
 likely to be influenced by social than 
 by germinal inheritances. The color 
 of the hair or the color of the eye is 
 under such circumstances of less 1m- 
 portance to us than the speech or table- 
 manners. ‘Thus human inheritance 
 and in consequence human evolution 
 extend over a wider field than the 
 corresponding operations in lower an- 
 imals and man’s uniqueness again re- 
 asserts itself. 
 
 But though we are in this respect 
 above the rest of creation, we are still 
 subject to the common law. Not an 
 epidemic sweeps through a commu- 
 nity without leaving behind it, in the 
 young members of the population, a 
 selected race whose partial immunity 
 will have its effect on the coming gen- 
 eration. This is especially noticeable 
 
168 WHAT EVOLUTION IS 
 
 in the arrival of a new disease. The 
 first coming of Europeans to America 
 is said to have brought to the native 
 Indian a variety of entirely novel mal- 
 adies. Among these was smallpox. 
 This disease is said to have run like 
 wildfire among the natives and to have 
 reduced their numbers to an almost 
 incredible level. Measles is another 
 disorder of the same kind. To the 
 Aleut Indians, of the extreme North- 
 west, this is a disease of great severity 
 and has been known to have exter- 
 minated whole villages. Yet to Eu- 
 ropeans it is a mere bagatelle due 
 doubtless to the long exposure of this 
 race to it and to the partial immu- 
 nity acquired in the course of time 
 through selection. 
 
 The social habits of man have not 
 only had their influence on the kinds 
 of inheritance that he has developed, 
 but they have impressed his nature 
 
WHAT EVOLUTION IS: 169 
 
 and in fact that of every other social 
 organism, in a way too often over- 
 looked. All such organisms are of 
 necessity cooperative. It is inconceiv- 
 able that a social state should exist 
 otherwise; in every sound state there 
 must be cooperation between its mem- 
 bers. In fact the so-called solitary 
 animals show more or less coopera- 
 tion, and it is this primitive condition 
 that reaches a much higher level 
 of development in all social forms. 
 Wheeler has very justly emphasized 
 this feature in the life of the insects. 
 It is commonly overlooked that, among 
 most animals, cooperation is as usual 
 a form of response as competition, 
 and in social organisms, it is of neces- 
 sity a primary form of response. 
 
 In consequence of his social pro- 
 clivities, we find, in the evolution of 
 man, a large body of permanent al- 
 truistic action which in the form of 
 
170. WHAT: EVOLUTION MS 
 
 benevolent acts, charities, and the like, 
 is intended to extend the life of those 
 who otherwise might meet a speedy 
 end. Viewed from what might be 
 regarded as a biological level this 
 practice at first sight would seem to 
 demand condemnation. Why not fol- 
 low the example of the ant and destroy 
 all defectives? Surely this would give 
 added resources to those who are most 
 able to use them. But a wholesome 
 human society could not exist under 
 such circumstances. Such an act as 
 the destruction of the weak would be 
 so subversive of the cooperative prin- 
 ciple, not to mention the higher vir- 
 tues, that a state endorsing such a 
 practice would disintegrate and fall. 
 This principle is so clearly recognized 
 that civilized man has always striven, 
 and rightly striven, to succor the un- 
 fortunate. 
 
 Yet if one takes the trouble to look 
 
WHAT EVOLUTION IS 171 
 
 through any group of public hospitals 
 or asylums, he cannot help but be im- 
 pressed with the heavy burden of 
 wreckage there represented. In a 
 harsh world natural selection would 
 have removed much of this, but the 
 hand of public benevolence has inter- 
 vened and warded off the stroke. 
 _ Nevertheless, every one must see that 
 if such a weight as this be sufficiently 
 increased, society may be crushed by 
 it. The situation is not an academic 
 one, but has already begun to bear 
 heavily on legislatures and through 
 them on the public. What may be 
 done to meet, in a humane way, such 
 a situation? That the state should ar- 
 range for those who, in their weak- 
 ness, come upon it as public wards to 
 live the length of life that nature 
 allots them is indisputable. But that 
 such individuals should be restrained 
 from perpetuating their kind is like- 
 
1720 “WHAT EVOLUTIONS 
 
 wise reasonable. It will probably soon 
 come to be a recognized function of 
 the state to guard against offspring 
 from those of its wards who, because 
 of serious heritable incapacity, are on 
 its hands. How this is to be accom- 
 plished — through segregation, steril- 
 ization, or some other effective means 
 —is a practical question that com- 
 munities may sooner or later be called 
 upon to settle. In the performance of 
 this duty society, like natural selec- 
 tion, will concern itself not so much 
 with the life of the individual as with 
 what that life may transmit to future 
 generations. 
 
 Thus man’s nature though in many 
 respects apparently contradictory to 
 that of the animals below him is after 
 all grounded on the same basic prin- 
 ciples. He has evolved far beyond 
 the vast majority of creatures and 
 though he has reached a level where 
 
WHAT CEVOLUTION AS: 173 
 
 conduct is directed in new ways and 
 under novel conditions, he is never- 
 theless still subject to the old laws. 
 There is after all only one kind of life 
 in the universe. 
 
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VI 
 READING REFERENCES 
 

 
READING REFERENCES 
 
 Darwin, C. 
 The Origin of Species, 1859. 
 Many subsequent editions. 
 De Vries, H. 
 Die Mutationstheorie, 1901-1903. 
 De Vries, H. 
 Species and Varieties. Their Origin 
 by Mutation, 1905. 
 LAMARCK, J. B. 
 Philosophie Zoologique, 1809. 
 LaMARCK, J. B. 
 
 Zoological Philosophy. Translated by 
 H, Elliot, 1914. 
 
 Caste, W. E. 
 
 Genetics and Eugenics, 1924. 
 ConkKLIN, E. G. 
 
 Heredity and Environment, 1919. 
 Lu ti, R. S., H. B. Ferris and others. 
 
 The Evolution of Man, 1922. 
 Morcan, T. H. 
 
 A Critique of the Theory of Evolution, 
 1916. 
 

 
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