PELELEEPESL Ee rceeeccter cater A ETH Pereeatacerr aH ' ety | ft Hen nth Hd tre aa44) HE THEE a ponte met eres tone tn we ns oe an ah Bes a rm et rt a av ae eee: eee rears eek ave een —— ie a ~ acne —— i oe AS Ssoasal HE HT A j WEEE eth Ha Oe ate Ul Lay trash F he ei hy nat vi Pa | } LS ap A Wea ie eS rae if i” wi a ys } he ‘ YX OF PRIVEE > Ny aN oo) Py , ye or agicat sews ees QUEER Section W Zz ri) sat 4 ah ie a. iy 1 the A (> gun cine ‘in 2022 with funding can Princeton Theological Saery ti Lik Wy Mila ee ay , Pom i ain a4 httos /Tarchive, org/detalls/evolutionforjohno J ‘ ' * i ia. j | 4 ‘es EVOLUTION FOR JOHN DOE apat OF Faia ie: Fr ee <1 Be OE fw4t* ¢ gf 4 “" OGi 20 1995 Evolution for John D By | HENSHAW WARD With Foreword by LORANDE LOSS WOODRUFF Illustrated INDIANAPOLIS THE BOBBS-MERRILL COMPANY PUBLISHERS CoprgicHt, 1925 By Tue Bosss-MerRiLL COMPANY Printed in the United States of America PRINTED AND BOUND BY BRAUNWORTH & CO., ING. BROOKLYN, NEW YORK FOREWORD by LORANDE Loss WoopRuFF Professor of Protozoology at Yale Unwwersity Mr. Ward has demonstrated in the present volume that it is possible for the layman to put in forceful, popular lan- guage a vivid, general view of what is meant by organic evo- lution. He gives just such a survey as a person unacquainted with biology needs for an introduction to some of the large problems of life—problems so large that they have burst the confines of the biological laboratory to trouble unnecessarily some politicians and theologians. The reader who has been curious about these questions will, I feel sure, find that his interest in the book grows as he proceeds, and will finish it with the desire to fill out the general picture he has obtained by turning to some of the eritical treatises which the author suggests. Mr. Ward opens the door, ACKNOWLEDGMENTS TO ALBERT GALLOWAY KELLER, CHESTER Ray LONGWELL AND LoRANDE Loss WoopRuFF. My dear Keller: If you would let me tell you in private how I feel about your share in this undertaking, I should not make you un- comfortable by displaying your name in such a public way. But since you will not listen, you must read. When you gave me the benefit of your twenty years of experience in teaching evolution without being a biologist, you showed the way through the maze; by giving criticism at every step you pre- vented a lot of blunders. I want you to know that I am grateful for making the path and trying to keep me in it. After you had been so tireless in helping me for two years, you went further. You persuaded Professor Longwell to eriticize the chapter on geology and to put me in his debt for some very useful comments. Then you enticed into my service a critic who could remove some technical mistakes, whose imagination was equal to sympathizing with this strange amateur enterprise, and whose kindness made him unsparing. I am sure you want to join me in thanking Professor Wood- ruff for this aid, of a sort that few biologists could give. No sensible scientist will find fault with him if he has not removed all the mistakes from this book, nor will readers blame you if my printed words are less racy than your spoken ones. You and he have done all that was possible, laboring with such generosity as I have never before seen in my struggle for existence. Henshaw Ward. CONTENTS Part OnE: A DESCRIPTION OF EVOLUTION WHat JOHN Dor THINKS ABOUT EVOLUTION . . THE MyriaAD Forms oF LIFE THe TANGLED WEB OF LIFE , THE VARIED MopES oF LIFE . THE JUNGLE OF ADAPTATIONS . THE STRUGGLE FOR EXISTENCE . VARIATION Pr cal Nele!, er ntt Mates Ul te HEREDITY ee he Reo NATURAL Sen ereeyate RNa Ween e Part Two: THE EVIDENCES OF EVOLUTION WHat ‘‘EvmpENcEs’’ ARE . . e ° ° THE EVIDENCE FROM THE RIVALRY OF Gaerne THE EVIDENCE FROM THE RockKS THE EVIDENCE FROM GEOGRAPHICAL Disa THE EVIDENCE FROM CLASSIFICATION THE EVIDENCE FROM ARTIFICIAL SELECTION THE EVIDENCE FROM THE STRUCTURES OF ANIMALS THe EVIDENCE FROM EMBRYOS THe EVMENCE FROM BLOOD . Part THREE: THE HISTORY OF LAMARCK St, RE Bl ain AONE DAT RULNGITN S et e BN oie hen ae RU ath WWI RLAN NS cr Uae Cini dann. Bog MENDELISM . . Sale une is DE VRIES’S te aa x How Evo.utrion Stanps To-DAY THE FospicK IDEA . BIBLAOGRATH Mons itis ca, ae tet ale InDEX PON tal oC CoO Oe eames 1 EVvoLurion 109 125 .167 169 178 204 216 231 236 252 260 267 271 286 292 301 304 332 339 345 oe: PART ONE A Descriprion or EVvoLutTIon Evolution for John Doe CHAPTER I WHAT JOHN DOE THINKS ABOUT EVOLUTION Joun Dor thinks evolution is ‘‘the doctrine that man is descended from monkeys,’’ and he is so amused or so offended at this theory that his whole mind is occupied with it. His conception is ridic- ulously false. Until John Doe discards that notion and takes a fresh start, he will never understand the subject. Therefore any one who tries to explain evo- lution to him will fail if he pays the least attention to the ‘‘monkey doctrine.’’ In this book there is no reference to any ape-like creature and no discussion of the descent of man. John Doe thinks that evolution explains the origin of life. But no scientist pretends to know anything about the origin, and in this book nothing is said of a subject which is far beyond the reach of present human knowledge. John Doe thinks evolution has something to do with ‘‘progress’’—that it announces some creed of an onward and upward movement toward perfection. Evolution is nothing of the sort; it does not venture into any speculation about the meaning of life or its final goal. In this book there is no doctrine of ‘‘prog- ress’? and no philosophical reasoning. 15 16 EVOLUTION FOR JOHN DOE To the mind of John Doe there is something mys- tical and awesome about ‘‘Evolution,’’ especially if it is printed with a large H. The evolution in this book is usually printed with a small e and means only the very plain scientific theory that every form of plant or animal that ever lived developed out of a previous form. John Doe guesses that evolution is true, but he rather wishes it were not. He has a vague fear that the theory is materialistic and tends to weaken reli- gious faith. If he reads the opinions of eminent divines in Part Three, he will find that there is no ground for his fear. Recently a young Presbyterian minister said to me, ‘‘All our theology is now based on evolution.’?’ He represents the thought of many divinity schools to-day. John Doe suspects from head-lines in his news- paper that evolution is a debatable theory, that it is being overthrown every six months, and that it may be discarded before long. When he has read section four of Chapter XXIV, he will understand that evolu- tion is here to stay; there is no more chance that the theory will be disproved than there is that men will some time give up their belief that the earth is round; every reputable modern scientist believes in it as a matter of course. It is now an integral part of all general education and culture. To suppose that it may some day be abandoned is to live in intellectual barbarism. To the common horse-sense of John Doe evolution appears probable. ‘‘But,’’ he says, ‘‘it is not to be seen at work here and now, and so it looks dubious to me.’’ When he has seen the ‘‘billion-year movie’’ in Chapter XII, he will feel relieved. Mr. Doe supposes that evolution is extremely diffi- cult, so that he has small chance of ever finding out WHAT JOHN DOE THINKS 17 about it. For this supposition he is excusable. It is true that most scientific books are highly technical, and that evolution is based on several branches of science at once, and that each is hard to learn about, and that the combination of several in one theory is excessively complicated. Also it is true that, to the best of my knowledge, no simple explanation has ever been put into a volume. For twenty years I have tried to find some book in a popular style that I could place in the hands of young men who were curious to read about evolution, and I have longed to find such a treatment for myself, which would give me in a few hours an outline of the information that is hidden in the forbid- ding tomes of science. I have examined several vol- umes that were said to be of this sort, but not one would serve my purpose. Librarians are constantly asked for ‘‘something simple about evolution,’’ but they have to shake their heads sadly. Apparently the biologists know so much of the details that they can not write a brief account of the whole theory. Not one of them has begun at the beginning of my ignor- ance and shown me, step by step, an outline of the whole. I see a lot of chapters about ‘‘Somatogen- esis’? and ‘‘Mendelism’’ and ‘‘Neo-Lamarckism,’’ but I am lost in a wilderness of big words, and I haven’t any sketch-map. Probably most intelligent people have tried during the last quarter-century to learn something about a theory that has remodeled all the world’s knowledge and profoundly affected its way of thinking. Last year I grew so desperate as to read a number of the standard works on evolution, and I was curious to see whether I could form a digest of the bewildering ar- ray of different branches of science to which all the authors have to appeal. I have written it out as if I were telling a friend about the knowledge that is so 18 EVOLUTION FOR JOHN DOE new and imperfect in my mind. It seems reckless to publish this. Yet the signs are that no professional scientist is ever going to attempt this job that so sore- ly needs to be done. Some amateur must try. Evolution for John Doe is not a proof of anything, because evolution has never been mathematically dem- onstrated. It is not an argument, because there is no sense in a layman’s arguing for or against the entire body of learned men whose business it is to study organic life. It is merely an outline of what this body of scholars conceives to be the explanation of how liv- ing forms have developed. It begins at the beginning, with sketches of the facts, and gives descriptions of how scientists look at nature. If you are not familiar with the history of scien- tific thought and not too eager to begin to read of evo- lution, spend a couple of minutes with the next para- graph, which is about the theory that the earth moves. It is an excellent preparation for the chapters that follow. The normal human brain, unfamiliar with the facts of astronomy, can not conceive that the earth goes around the sun. A thousand generations of the most observant minds that earth could breed never sus- pected such an idea. Men learned to build great cities and to write poetry and to predict eclipses long be- fore they ever questioned the apparent fact that the sun moves and the earth stands still. Twenty-five centuries ago Babylonian astronomers developed the notion that the earth might be a globe suspended in space, and a Greek philosopher, three centuries later, argued that the earth moved; but very few philos- ophers during the next twenty centuries could take this speculation seriously. They could not feel the earth move, and they could see the sun move. Yet the fantastic theory of the earth’s movement lingered on WHAT JOHN DOE THINKS 19 in philosophical writings and was considerably dis- cussed in Italy at the time when Columbus was pre- paring to sail west. Wild as this Pythagorean fancy seemed to most learned people, it appealed strongly to a Polish astronomer who was then studying in Italy. This genius, Copernicus, was equal to the su- perhuman task of fitting together facts and figures into a proof that the earth spins on its axis every day and travels around the sun every year. Yet because he made one wrong assumption, so that his explana- tion would not check with all the facts, most scholars continued to laugh at his topsy-turvy theory. Dur- ing the next two hundred years his proofs carried conviction to very few astronomers. The men who founded Yale and Harvard, like most of their con- temporaries in Oxford and Cambridge, believed that the earth was immovable and covered by an immov- able ‘‘firmament.’’ As late as 1800 there were many cultivated minds that believed it was irreligious to think of the earth’s rotating and revolving. Even down. almost to our own time the ancient belief was held by many in the United States; in 1880 a colored Baptist preacher of Richmond was still declaring that ‘ mirable Textbook of Botany for Colleges, 24 EVOLUTION FOR JOHN DOE Hiven so brief a glimpse as this at the wide expanse of life sets the mind to wondering, ‘‘How did it all come about? Why should there be so many different ways of living?’’ How many kinds of mosses have you ever heard of? If we had never seen but ten kinds, we could rest with the supposition that they were originally created so; but when we learn that there are sixteen thousand species of these inconspicuous growths and that the more common of the species have varieties that grade off insensibly into varieties of another species, then we can not be content with any such guess at the eause. The more a botanist becomes familiar with the countless varieties of plants, the more certain he feels that he is dealing with some sort of continuous growth of the whole system of organisms. A few dozen dif- ferent ferns would never have excited a Wallace or a Darwin to cudgel his brains for an interpretation of nature; but the four thousand five hundred species that botanists now know might well cause an inquisi- tive mind to he awake at night. All told there are about one hundred thousand spe- cies of this lower division of plants. Of the higher division, the flowering plants, there are more than one hundred and thirty thousand species. Some of the items that make up the total are five thousand grasses, one thousand palms, two thousand lilies, sev- en thousand orchids, one thousand two hundred eac- tuses. . More significant than mere numbers is the way in which plants unlike in appearance are found to be alike in their anatomy and way of growing, so that kinds which are very dissimilar in all outward ap- pearance are found to have inwardly a decided family resemblance. Thus elm trees, fig trees, nettles and hops are found to have such a similarity in their flow- THE MYRIAD FORMS OF LIFE 25 ers that they belong together. The figs include such apparently unlike plants as the rubber tree, the ban- yan and a vine-like parasite. In another great group the botanists have been obliged to lump together gera- niums, flax, oranges, mahogany and castor beans, because they are similar in their ways of propagating. The scientists have no desire to do queer things; they would much prefer to say that rubber trees and milk- weeds are alike because of their milky sap; simplicity has always been their aim. But nature has made it impossible for them to find any simple way of classi- fying. It is as if she had strung the most diverse forms on one thread of structure, and had then so looped and tangled the thread that the botanists are taxed to their wits’ ends to straighten it out in any- thing like orderly sequence. When a man has labored for thirty years at this effort to untangle related forms, he comes to think of plant life as a labyrinth, and he demands a clue. What will guide him? His work would be easier if he could discover that all the crisscrossing forms were originally created as distinct kinds of organisms, but the opposite conviction is con- tinually thrust upon him—namely, that these forms are a jungle of variation, that all plant life has for- ever been altering in character, putting out changes here, there and everywhere. The puzzle would not amount to much if a species were always a species—if, for example, a certain kind of pine tree were everywhere the same. But within any species there may be endless variations, some of them amounting to striking differences. A grizzly bear, for instance, would seem to be very different from a cinnamon bear; but grizzlies have been found that shade by slight degrees of color and size toward cinnamon bears, and a series of cinnamon bears could be arranged that shade off in color and size to meet 26 EVOLUTION FOR JOHN DOE the series of grizzlies. No sharp line can be drawn, and hence some scientists have called them all one species. Another illustration of the endless variegation within a species is a certain small grass, growing com- monly in the United States and Europe, Draba verna; when samples of this are gathered from different parts of the world, it is found that there are many distinct types—no less than two hundred have been counted, each of which will breed as true to itself as a Baldwin apple or a Boston Bull. Each of these types, the so-called ‘‘varieties,’’ might be called a species. And any naturalist who cares to cultivate the varieties can breed new ones; he can, as it were, watch the plant branching out into new forms. So with wheat: one acute observer counted in a field no less than twenty-three varieties which would, if separated and cultivated by themselves, continue to produce the twenty-three types of plants. A botanist in Amster- dam once counted seven hundred varieties of hya- cinths. It is estimated that American florists have caused fifty species of irises to branch out into one thousand five hundred distinct varieties; that they have developed as many forms of roses; and that there have been produced in the gardens of the world no less than eight thousand varieties of roses. So endless are these variations that botanists have no power to tabulate them; one of the most famous, the Dutchman de Vries, says of hawkweeds, ‘‘Thousands of forms may be cultivated side by side in botanical gardens, exhibiting undoubted differentiating fea- tures, and reproducing themselves truly by seed.”’ What shall a naturalist conclude after he has spent studious decades in watching these ceaseless fluctua- tions of countless forms of plant life? What shall he think when he takes stock of this medley of life, THE MYRIAD FORMS OF LIFE 27 this unmapped chaos of contradictions and relation- ships? He has no chart or compass until he adopts the evolution theory; with it he can always steer a course. The same remark applies to the zoologist. If men had never known of more than five hundred kinds of animals, they would not have realized that chaos ex- ists and would have laughed at evolution. Down to 1700 the knowledge of the diversity of life was so meager that naturalists did not recognize any mys- tery. Even after Linneus had been compiling data for thirty years—and no more industrious, capable classifier ever lived—he could learn of hardly more than four thousand* species; he would never have felt impelled to solve a mystery in 1758. But by 1858 the situation was entirely different; Agassiz then calculated that one hundred and thirty thousand spe- eies were listed, and many discerning zoologists began to fear that they were all at sea. Within thirty years from that date the count had more than doubled; and twenty-five years later had almost doubled again— that is, a conservative count had reached 522,000 spe- cies. If by that time (1912) the zoologists had not had the aid of the evolution theory, they would have been swamped by the mounting billows of species and sub-species. To say that in 1912 there were listed in scientific libraries 522,000 species of animals is like speaking of billions of dollars in a public debt—we can not com- prehend such a tremendous sum. No more can we have a comprehension of the numbers of animals un- til we dwell upon a few of the details. One of the smallest items illuminates the whole subject striking- ly: fifty years ago only thirty species of deep-sea _ *Most of the following figures are the estimates of Professor H, 8, Pratt of Haverford, in Science, March 22, 1912, 28 EVOLUTION FOR JOHN DOE fishes had been seen; now there have been dredged up and accurately described more than one thousand species. Linneus, the great father of classification, whose fame is still bright, could count only forty-one species of worms; there must be 8,000 known to-day. We now know of 2,500 kinds of sponges, 16,000 of spi- ders, 3,500 of reptiles, 61,000 of mollusks. Collectors have penetrated the wildest quarters of the globe, have braved the desert heat and the arctic ice, have searched the mountains above and the ocean below; everywhere they have discovered new species by doz- ens and hundreds. Whereas Linneus could count only 444 kinds of birds, we know of over 13,000. He listed only 183 mammals; at present we have accounts of some 3,000. These figures were compiled by Professor Pratt in 1911, and may be ten per cent. under the totals that could be reckoned to-day. If any of the figures are too high, we may be assured that before many years they will be too low; for they are being augmented almost daily. L. O. Howard, one of our greatest en- tomologists, has said that the number of insects now known may ultimately be multiplied by ten. Men who, like him, have spent a lifetime amid the rising tide of numbers would yawn at our little lists of the hun- dreds of thousands; for they do not think in terms of arithmetic, but in one term—of a flood of varied life. And this flood of life now in the world is only a small pool when compared with the ocean of forms that have, during the long history of the world, risen and flourished and become extinct.* The geologists are familiar with limitless reaches of changing life that stretch through the millions of years of the geo- *The long record of the prehistoric life of the earth, perhaps coy- ering five hundred million years, is outlined in Chapter XII. It furnishes stronger evidence than the study of the forms now living. THE MYRIAD FORMS OF LIFE 29 logic ages, glimpses of which may be seen in the fos- sils. Even the fragments of this ancient history, when pieced together in a list, reached, twenty years ago, the respectable aggregate of eighty thousand species of vanished life. The great naturalist Wallace believed that in the whole past history of extinct forms of animals there ‘‘must have been thirty or for- ty times as many species as are now living.’’ He euessed that probably there have been on the earth in all its different periods ‘‘many hundred times as many species of plants and animals as now exist.’’ So boundless, to the gaze of a scientist, is the realm of life which we amateurs have tried to skim over in one brief chapter. CHAPTER IIT THE TANGLED WEB OF LIFE THERE is nothing baffling about mere numbers of species. If the naturalists had never been confronted with any problem more puzzling than half a million or a hundred million species, they would never have been driven to seek out an evolution theory. The pre- vious chapter gave several indications of the real mystery: the tangle of forms. Only a lifetime of ex- perience would give a partial conception of the end- less series of kinds that shade gradually into other series of kinds. In this chapter we can do no more than view, as from an airplane, distantly, a few of the thousands of bewildering facts known intimately by scientists. In the previous chapter we got very little sugges- tion of any bewilderment. We saw neat packets of ‘fone thousand two hundred kinds,’’ of ‘‘three thou- sand five hundred kinds,’’ of ‘‘sixty-one thousand kinds.’’ The inference was that a biologist could tell two distinct species as easily as a stamp collector can decide that two bits of printed paper are not dupli- cates. The fact is just the contrary. Professors Pratt and Ganong would be the first to admit that no count of species can be made, that their lists represent only the roughest approximations to a set of balances of opinions. Until a reader understands that statement he is not on his way to a comprehension of evolution— 30 THE TANGLED WEB OF LIFE 31 any more than a detective could find a criminal before he knew what the crime was. What is life? The more we study it, the less able we are to give a definition. If an invisible bacterium is an individual plant, why is not a white corpuscle in our blood an independent animal? And if a white cor- puscle is a separate creature, how shall we draw the line between it and a cell in our muscles? If these self-propagating cells of our flesh are animals, why is each self-propagating cell of a leaf not a plant? We ean not tell where individual life begins. As soon as we pass upward from this doubtful region of cells at the basis of all life, we are at a loss to know the difference between the lowest plants (Protophyta) and the lowest animals (Protozoa). The voice of science can only admit that ‘‘no hard-and- fast line can be drawn around Protozoa to distinguish them from Protophyta.’’ It declares that ‘‘the for- mal distinctions between the animal and the vegetable kingdoms have vanished, and in their place we have an intimate, unbroken continuity.’’ So at the very beginning of any examination of the world of life it appears that all is confusion. The naturalists could never arrive at any understanding of this vast tangle until they found some one principle that would account for all the variety of the strands and for all the interweaving of them. All our obser- vation of nature shows that nothing ever happens by chance, that every object we see was fashioned by un- deviating law. Hence any naturalist in his senses must suppose that every least filament in the web, every variation of form, every continuous series of forms, became what it is by the operation of some fixed, unvarying forces. Just as our minds are obliged to think that there must be definite causes for rain- bows and wireless telegraphy and tides and fires, so 32 EVOLUTION FOR JOHN DOE we take it for granted that the various forms of life are not the result of a hodge-podge of unaccountable accidents. Much less can any reverent person nowa- days credit the idea that a whimsical Creator amused Himself and befooled His human children by devising a lawless welter of freaks. The devout and sensible scientists never tolerated such an idea. With one accord they have always as- sumed that there is some definite method of creation, and they have done their best to discover it. After 1700 their efforts were based on a certain assumption—a very natural one and very useful. This theory was that all animals were arranged on a ‘‘scale of nature,’’ from the low and simple forms to the high and complex. Hach degree on this scale was a small but sudden step upward from one kind—called a ‘“species’’—to the next higher kind. Thus each spe- cies was sharply marked off from the one below and the one above; it was a distinct type of life that had always been what it now is, and that would never be anything else. The ‘‘seale of nature’’ hypothesis stood the test of experience fairly well in the eighteenth century for classifying four thousand species; it still applies after a fashion; for the species that we observe in nature seem fixed. An account of what the word ‘‘species’’ signified in 1830, and of the controversy about it, is the easiest entrance to an understanding of the evolution theory. Some readers will wish, first, to see a display of the term in its setting in the system of classification that has been used for the last two centuries. For their convenience the following numbered paragraphs are inserted to show the graduated divisions, from large to small. This is not a review of technicalities, but is an approach to the heart of the subject. | 7 THE TANGLED WEB OF LIFE 33 The nature of classification. To begin with, what are the scientists about, what is their purpose, when they ‘‘elassify’’? They are only doing what we all have to do in our private affairs when we arrange or sort out a lot of articles that are in confusion. No business office can keep five thousand letters in the same order in which the postman brought them; they must be sorted—that is, classified—alphabetically or by their subject-matter. A carpenter must classify his tools and nails and screws, else he could never put his hand on what he needs; a college must classify its students as failing, passing, doing fairly, or doing excellently; if the people in a city were not classified by names and streets, all general business would come to a standstill. So the scientists would be all at sixes and sevens unless they carefully classified their huge stores of facts. One example will bring this home: thirty-five years ago the manuscript of the catalogue of plants kept at Kew Gardens in England weighed a ton. 1. Kingdom. A vast labor the classification has been, and is still very incomplete. A glimpse at the nature of it can be had most easily by noticing how the first ancient classifier went to work. He began, as any shrewd man would after some observing and meditating, by dividing all life into two ‘‘kingdoms,”’ vegetable and animal; and the scientists still follow this primary division. For the first subdivision of animals Aristotle found that he could make two great groups, according as they had or did not have a backbone. Among those with a backbone he naturally made sub-groups of those that walk on four legs, those that walk on two legs, and those that live in the water. Then his trou- bles began; for a man walks on two legs, but is unlike all the birds in not being covered with feathers. 34 EVOLUTION FOR JOHN DOH Classification is a task that demands the highest ana- lytical skill and patience. To this day the zoologists are agitated about the shortcomings and contradic- tions of their system of sorting into orderly groups all the known kinds of animals. 2. Phylum. With their elaborate details we have no concern, but we do need to know their principal terms. In beginning an arrangement of animal life they first try to put together in large groups those sorts that are similar in some general way—for ex- ample, all the backboned animals are grouped to- gether into a ‘‘phylum.’’ In another great phylum are lumped together all such ‘‘jointed’’ animals as insects and lobsters. 8 Class. Within each huge phylum many subdivi- sions must be made—for example all the lobsters and crabs and barnacles are put into one ‘‘class,’’ all the spiders into a second class, all the insects into a third. 4, Order. Insects are such a vast horde of dis- similar forms that they must be subdivided many times before there will be any practical classification ; they are sorted into twenty ‘‘orders.’’ One of these orders includes all the beetles. 5. Family. It is clear that classification has only begun. The order is divided into great groups called ‘‘families.’’ The largest family of the beetles, for ex- ample, is the snouted weevils. 6. Genus. This family, like every normal one in the plant or animal kingdoms is subdivided into groups, each of which is called a ‘‘genus”’ (plural genera.) One genus of weevils, named Anthonomus, includes many sorts that make a specialty of living in buds and pods; its members are spread over the whole globe. Classification is always that same op- eration of making narrower and narrower divisions of groups whose members are somewhat alike, sorting THE TANGLED WEB OF LIFE 30 out those that have closest resemblances into smaller and more homogeneous groups, and then again sort- ing each smaller group into sections that are most alike. | ) 7. Species. Such a subdivision of a genus is called a ‘‘species.’’? A species is the last complete stage of the sorting process; it is such a narrow division that all the members of it bear a close resemblance to one another and can usually mate together; whereas the members of two well-defined species can rarely pro- duce fertile offspring. Anthonomus contains one world-famous species, grandis, which has destroyed billions of dollars’ worth of property for the cotton- growers—the boll weevil. 8. Variety. It often happens that within one spe- cies there are many somewhat different forms, which ean be accurately defined and which breed as true to type as distinct species; these are called ‘‘varieties.’’ When we consider that such an exhibit of classifi- eation, though it extends through eight paragraphs, does not represent an outline of the scheme of even four thousand animals, we have a faint suggestion of the interminable maze of nature, and of the struggle which the eighteenth-century naturalists had. This struggle centered on one point—on the theory that species are unchangeable. The reader must cen- ter his attention on the same point, for it is the ap- proach to the whole subject. A species, as the eight- eenth-century classifiers conceived it, was a certain kind of plant or animal that never had been and never could be different. Linneus believed that a species was an unchanged and unchangeable unit of life. His own words were: ‘‘There are just so many species as in the beginning the Infinite Being ecreated.’’ If this had been true, the course of natural science would have been smooth. The zoologists would sim- 36 HVOLUTION FOR JOHN DOE ply have had to detect these eternal kinds of life and count them up as astronomers have counted the stars. Great was their amazement to discover, long before 1800, that they could not agree on how to distinguish. They all wanted to agree; they all took it for granted that agreement would be possible. But with the years the disputes increased. Even Linneus had qualms when he found how often a dividing line was difficult or even impossible to draw. By 1800 a Frenchman (La- marck) had denied that such divisions could ever be made successfully, because as the stores of facts rap- idly increased he saw the tangled web grow ever more tangled. He put the case thus in the very year of Darwin’s birth, 1809: ‘‘The supposition generally be- lieved—that organisms are arranged in ‘species’ that are always distinguishable by invariable character- istics, and that the existence of these species is as an- cient as nature itself—was established at a time when men had not observed enough and when the natural sciences as yet hardly existed. It is always belied in the eyes of those who have seen much, who have long attended to nature, and who have studied with profit the large and full collections of our Museum.’’ _Around the conception of species the battle raged. In France and Germany and England there were plenty of learned men ready to abandon the idea that a species was a fixed fact of nature. But if they had done so, where would they have found themselves? Floating in a fog of philosophy. It might be all very well for a reckless, imaginative Frenchman to aban- don facts and speculate about all life as a continuous stream of forms that changed into one another. But that was to deny their own senses, for they could see a multitude of fixed species, and Lamarck could not show them one that changed into something else. Why should they give the le to their own eyesight? They were like Romans who were asked to believe that the © THE TANGLED WEB OF LIFE 37 sun stood still and the earth moved. They decided— and quite sensibly—not to follow such vagaries of philosophy until some tangible evidence was forth- coming. It did not come. No one could find any proof for Lamarck’s fancy. By 1850 it was consid- ered unscientific and foolish to discuss any evolution theory. The fixity theory was more firmly established than ever. The scientists were, nevertheless, perpetually un- easy, at a loss, discordant among themselves. For they could not mark the limits of the species that they believed in. It was a curious dilemma. If a man be- lieved that species were variable, he was beyond the pale of realities; but if he believed that species were fixed, he could not lay his hand on the realities. Eith- er way he was lost and baffled in the tangled maze of hving forms. ‘“What is a species, anyhow?’’ was the constant query. Darwin often reveals in his letters what all scientists felt, but could not well give vent to in their formal publications. He wrote in 1849, when trying to classify the barnacles: ‘‘I can not at present tell the least which of two species all writers have meant by the common Anatifera levis. Literally, not one spe- cies is properly defined.’’ In the same year he wrote to a great botanist: ‘‘I often feel wearied with the work, and can not help sometimes asking myself what is the good of spending a week or a fortnight in ascertain- ing that certain just perceptible differences blend to- gether and constitute varieties and not species... . I have just finished two species which possess [1. e., in the different works of reference] seven generic and twenty-four specific names!’’ Seven years later he wrote again: ‘‘In some naturalists’ minds resem- blance is everything, and in some resemblance seems to go for nothing; in some sterility is an unfailing test, but with others it is not worth a farthing. It all 38 EVOLUTION FOR JOHN DOE comes, I believe, from trying to define the undefin- able.’’ Huxley thus describes a bit of the dialogue when, as a young man, he had his first interview with Dar- win: ‘‘I expressed my belief in the sharpness of the lines of demarcation between natural groups, with all the confidence of youth and imperfect knowledge. The humorous smile which accompanied his gentle answer, that ‘Such is not altogether my view,’ long haunted and puzzled me.’’ No wonder that Darwin smiled, for he was famil- iar with facts like these: ‘‘As soon as these three forms, which had previously been ranked as three dis- tinct genera, were known to be sometimes: produced on the same plant, they were immediately considered as varieties; and now I have been able to show that they are male, female, and hermaphrodite forms of the same species.”’ Wallace pictures the situation vividly in this sen- tence: ‘‘All students were so impressed with the be- lief in the reality and permanence of species, that endless labor was bestowed on the attempt to dis- tinguish them—a task whose hopelessness may be in- ferred from the fact that, even in the well-known British flora, one authority describes sixty-two spe- cies of brambles and roses, another of equal eminence only ten species of the same group.’’ The first authority had ‘‘split’’ the roses into six- ty-two species; the second had ‘‘lumped’’ them into only ten. This case is typical. The same tendency is as strong as ever to-day: if a naturalist is keenly in- terested in noting slight differences, he will find many species and be a ‘‘splitter,’? if his mind works on the other tack, he will be a ‘‘lumper.”’ In a recent study* of a genus of crickets the an- *F, E. Lutz, Carnegie Publication 101. THE TANGLED WEB OF LIFE 39 thor tells us that six species have been commonly de- scribed, that one man lumped these into two, that another man lumped them into two by a different grouping, and that the author thinks there is only one species. If we should search the ences of the ants, as made by all the splitters, we might count six thou- sand species; if we took the records of the lumpers and selected the lowest list from each, we might have no more than two thousand. Any amount of similar evidence could be cited to show that a species is essentially an opinion. If a very careful man makes a prolonged study of a cer- tain genus, and if succeeding students think well of his judgments, his opinions stand as named species; if his judgments do not stand the test, they are set aside by the next student. Illustrations like this from the Britannica article on wolves can be found very frequently in common books of reference: ‘‘These differences have given rise to a supposed multiplicity of species. . . . But it is doubtful whether these should be regarded as more than local varieties.’’ In- deed all the efforts of all the authorities to assort wolves and dogs and foxes and jackals have failed to produce any generally accepted scheme of species. A pretty demonstration of the whole species puzzle is exhibited in the American Museum of Natural His- tory. A cirele of fifteen tiger beetles is so arranged that the distinctive markings of one species, shown fully in the first specimen, are slightly different in the second, somewhat more different in the third, and so on, until when we have gone the round we find that the fifteenth specimen, next to the first, has the markings of another species. Truly the works of nature appear as cycles that merge into other cycles, and these loops are combined in a tangled web of life. CHAPTER IV THE VARIED MODES OF LIFE Wuen I, with my untrained eyes, pay any atten- tion to plants, they seem to be very regular, uniform things. A buttercup seems like all the other butter- cups; an acorn seems to produce the same kind of oak that it fell from; a housefly or a June-bug is always of the same size and has parents and children that are exactly like itself; a sea-gull never mates with a hawk; everywhere I go there are a lot of butterecups and flies and hawks and ants that are just the same as the ones I have seen before; an oyster is never an eel. So far as I ever noticed, all forms of life are well sep- arated, distinctive, uniform. I never see any puzzle or any need of worrying about classifying. And so long as I do not see any puzzling irregu- larity, I can not have any interest in evolution or take any stock mit. Every naturalist would have been as indifferent as I am if he had always remained as ignorant as | am. No person will see any sense in evolution until he knows at least a little bit of the end- less confusion and crisscrossing and interlacing of the kinds and modes of life of plants and animals. So it is time to describe a few of the puzzles that every biologist meets with. If you find this chapter somewhat bewildering, you are on the road to under- standing ; for you can then see, in some slight measure, what the scientist’s problem is. This chapter does not explain anything. It takes you to a maze of facts 40 This 12-inch African antelope (a dik-dik), only a foot high when full-grown, is a near relative of the 800-pound Eland antelope. The tropical leaf-hoppers are bugs whose heads have developed into great crests as long as the bodies. Two strange creatures from Australia. The green phalanger, above, is the only known animal that has greenish fur. The duckbill is the only species in its family; it has thick brown fur, a bill like a duck, and lays eggs like a reptile. THE VARIED MODES OF LIFE 41 and says, ‘‘Look at this, and this, and this. See what the scientist has had to explore and find a clue to. Notice that the facts are interlaced and perplexing.’’ In this and the following chapters we are going to take the course that Darwin’s mind covered in his twenty-five years of effort to solve the mystery. It is as if we, in an express train, whizzed at a mile a minute through the jungles where he had to hack his pioneer way foot by foot. As you glance at the few dozen illustrations in this chapter, try to imagine what they would be like if they were multiplied by a thou- sand and if your life depended on working out some theory that would bring them all into a neat and orderly arrangement. I. Groups Are Big and Inttle, Flourishing and Dying If I say to a man who has never pondered on the mystery of life, ‘‘This yellow-flowered weed belongs to a genus (Senecio) in which there are 2,300* spe- cies,’? he may think of a greenhouse where there are 2,300 flower-pots—or he may think of nothing. He does not feel that there is any puzzle about it. ‘‘Lots of kinds of weeds?’’ he replies. ‘‘I should say so. Weeds flourish everywhere.’’ But ask him to imagine how a botanist understands the statement. ‘To the botanist there is no such thing as the difference be- tween a ‘‘weed’’ and a cultivated plant. He knows them all alike as plants that have to fight for a living in the soil. When he hears of a genus of 2,300 species, he recognizes a group that is extraordinarily hardy, that has spread over wide reaches of territory, that has fought its way to victory in many climates, and *Gager, Heredity and Evolution in Plants. Most of the figures given in this chapter are taken from older works of reference; hence they are generally understated, though in a few instances they will be larger than those shown in some recent taxonomic arrangement, 42 EVOLUTION FOR JOHN DOL that has branched into 2,300 different ways of making conquests in battles against other plants. He admires it as a mighty and successful kind of organism. He sees it is an adaptable, ever-varying form that flour- ishes like a very fountain of changeable life. Show a botanist the opposite kind of picture: ‘‘Here is a Chinese tree (the gingko) which is a separate genus all by itself; there is only one species of it.’? Then he is struck as by a sight of a dying race. He is puzzled as he contrasts it with a group of 2,300 species. Why should it remain so stolid and meager while another. race goes victoriously forth in a myriad of guises? One genus seems to sport in lavish, youthful strength ; the other appears to be dying. In an orderly universe what should make races come and go? A zoologist meets the same mysteries of the big and the little groups, the flourishing and the dying. A genus of squirrels in Borneo and another in India have only one species each; of the genus of pigmy squirrels there are a few species; of the striped ground-squirrels there are more; and of the tree- squirrels there are dozens—large and small, gaudy and plain—all over the world. Similar contrasts could be cited without end. The genus of rabbits is everywhere—in the foggy north of Scotland, in Brazil, in the Himalayas—overrunning all countries with its thirty species; whereas the genus of camels is domes- ticated in a small region and has only two species. The same contrast of numbers and strength is seen in the ‘‘families’”’ of plants and animals. Ordinarily a family is a large group embracing several or several dozen genera. In the sunflower family there are one hundred and fifty genera, and in the great families of animals there may be as many. But some forms of life are so peculiar that they must be made a family THE VARIED MODES OF LIFE 43 all by themselves; thus there is now living on the earth only one genus of the rhinoceros family. Those words ‘‘now living on the earth”’ give a hint of the depth of the mystery. The study of fossils shows that forms have waxed and waned through the millions of years of the geologic ages. There used to be many genera in the rhinoceros family. A long ac- quaintance with this flow and ebb of life arouses a suspicion that a large and a small family, a large and a small genus, are not permanencies, but temporary fluctuations; and such a thought is exciting to any scientist who is trying to discover nature’s secret. The California genus of sequoias is now limited to two species on one strip of coast, though some millions of years ago it flourished in many species from ocean to ocean. Why should this ancient group have dwindled almost to extinction while the genus of pines was in- creasing to seventy species that triumphantly made their way to every part of the north temperate zone? Nor is the mere fact of large and small, flourish- ing and dying, the most striking feature of what nat- uralists learn. Their curiosity is more aroused when they find that a chart of their classifications resembles a tree. If a certain order of animals branches into three families, two will probably be small side- branches and one will be like the continuation of the main trunk. If this dominant form divides into twelve genera, one genus will be very small, ten will be moderate in size, and the twelfth will be the large and typical group. It is this dominant twelfth genus that will ramify into a hundred species, and most of the hundred will show more vitality, be more numer- ous, and tend more to split into varieties, than the species of the eleven small genera. And of those hun- dred more lusty species there will probably be three that are decidedly more numerous and common, At EVOLUTION FOR JOHN DOH spreading into more varieties, than any of the others. A botanist expects a map of an order to look like the trunk of a tree, which grows upward in a main stem, the principal family ; this family continues in the larg- est branch, the principal genus; and this genus con- tinues upward in a few sub-branches, the principal species. II, Varied Sizes in One Group Among the rattlesnakes there is a species of which a full-sized adult is only eighteen inches long; another species furnishes specimens four times that length. Among the frogs, of the one genus Rana, there is a species (goliath, from western Africa) which weighs ten times as much as any frog that I ever caught for bait. In India there is a rat with a body that is over two feet long. The paleontologists have found in the family of horses a genus that was only a foot high. In a systematic, man-made world the clams would all be about three inches long; in the world as it is clams range in size from under that standard all the way up to gigas, which may be forty-three inches long and weigh nearly six hundred pounds. There is a parasitic animal so small that it is bare- ly visible when shown in a good light against a con- trasting background, and another that is two inches long, armed and armored in a terrific manner for the capture of tarantulas; yet both are wasps. A similar case is the pigmy deer, the dikdik of Hast Africa, which is only a foot high; it is quite unlike the little mouse deer of Asia, but is closely related to the great Eland deer which may weigh more than half a ton. When a visitor has strolled through a menagerie and a museum, he 1s impressed by these freakish vari- ations of size; he wonders why nature has sprouted out into all these deviations from a standard. THE VARIED MODES OF LIFE 45 III. Varied Developments The boy Darwin, like the rest of us, thought that a frog was just a frog; it was a leaping land-and- water animal that lived and looked like all the other frogs. Not until he was dead had the collectors found any species that was larger than our American bull- frog. How many readers of this book know that some frogs never enter the water except to breed; that one species burrows for its home; that another lives in trees and has a membrane with which it becomes a kind of flying frog; that another species builds nests among the bushes above the water; that another is hairy; that most species have teeth only in the upper jaw, while some have teeth in both jaws, and others have no teeth; that one species in the Solomon Islands has a horn? We stay-at-homes, who spend our time with bridge and business and novels, never know how, in the most uniform and monotonous genus, nature has modeled surprising species. She is perfectly varied in the most contradictory ways. No person can credit evo- lution until he sees something of what naturalists are involved in. No uniformity can ever be expected; no rule can ever be guaranteed. It is a rule, for instance, that animals eat plants and that plants draw food from the soil; and that rule holds for a hundred thousand species, and the next hundred thousand, and the next, and the next. But there is an exception. There are one hundred and fifty species of plants that eat animals. One, in Geor- gia, has hinged leaves that close on a fly, digest him, and open for the next fly. Another, in Australia, de- velops some of its leaves into cups that entrap insects. Our American pitcher-plant, of an entirely different order, makes for itself a much more elaborate trap, that is always open for insects and digests them by 46 HVOLUTION FOR JOHN DOK dozens. In the Malay Islands there are species of still another order that put a lid on their pitchers. Rather bewildering, all this, when we consider that these similar and very peculiar devices are found in different orders of plants on all the continents. A fanciful naturalist might guess that since the young- est rocks were made, several very different sorts of plants had learned to eat meat; for no such fossil plant has ever been found. It was a mere fancy, an utterly wild and unwelcome one to any steady mind in 18380. We human beings are apt to suppose that agricul- ture and slavery are a pride and a shame peculiar to the human race. But go to the ant. There is a tropi- eal species which cultivates the fibrous growths of a kind of toadstool; they have learned to cut off the spore-bearing branches, so as not to let the plant breed and destroy itself. Many kinds of ants keep plant lice, as a sort of cattle, for their sweet juices. Some ants have grown so used to being served by enslaved ants that they are powerless to feed them- selves and would perish without the servants. The more we see of animals, the greater grows our wonder at their varied developments. IV. Varied Relationships Most of us remember the mental shock we received when we first learned that whales and porpoises are not fishes, but warm-blooded, air-breathing mammals that suckle their young on the cold ocean waves and that would drown as surely as an elephant if they could not breathe air. So we all learned with a little start that tree-toads are not toads and that horned toads are lizards. Similar contradictions in classifi- cation, of a more striking kind, are the stock in trade of every zoologist. THE VARIED MODES OF LIFE 47 There is an opossum-like creature in Australia, not a foot long, which has a decidedly greenish color —the only mammal known which has fur thus tinged. In Tasmania there is a creature that looks like a wolf, that seems as different from an opossum as a tiger does from a rabbit; yet it is allied to the opossums and is not a wolf at all. The duckbill, which looks like a beaver and is covered with thick fur, has a horny bill like a duck and lays eggs. Plants furnish many examples of crisscross rela- tionships. Staid old peach trees, with only peach-tree ancestors, have more than a few times been known to send out a sporting branch that bore nectarines. The botanist can not draw any boundary line between peaches and almonds; for a small, hard, seedling peach is very like a green almond in appearance and structure; from these inferior peaches ‘‘we may pass by small transitions, through clingstones of poor qual- ity, to our best and most melting kinds.’’ On the other hand an apricot, which seems so like a peach, is by some botanists classed in a different genus, is com- monly grown on the stocks of plum trees, and—quite unlike the peach—will grow true from seeds. No matter-of-fact human brain could ever invent the freakish relationships that are to be found in plant life. Who would have thought of a partnership between two classes? A botanist who had dreamed that plants ‘‘learned’’ to catch insects might believe that his dream was confirmed when he investigated lichens: here are four thousand kinds which are com- pounds of two different classes of plants, fungi and alge. The fungi and alge enter into a very close partnership and provide nourishment for each other. The truths of botany are stranger than any fiction could be. 48 EVOLUTION FOR JOHN DOH V. Varied Ways of Propagating Occasionally there is an intelligent person, with opinions about evolution, who supposes that winged moths eat clothes; he does not know that the moth has for a mouth only a delicate tube with which she could not injure a cobweb. Yet this same intelligent person knows in a general way that there are voracious cat- erpillars, with powerful jaws, which spin cocoons, in which they become dead-looking pupx, and from which they emerge as moths with a slender, sucking proboscis in place of the former jaws. Most insects go through these three stages of life. A moth or a fly comes into its third stage full-sized and usually leads a life that is entirely different from its first stage. The double life is common among smaller animals, in the most extraordinary ways. Many disease-caus- ing parasites live their first stage in one animal and their second in another. They may live rather harm- lessly in spiders or mosquitos or squirrels or pigs; then when, by most diverse and remarkable means, they reach a second victim—a cow or a person—their second stage causes a virulent disease like bubonic plague or sleeping-sickness or malaria. Barnacles, after living as free-swimming, soft-bodied creatures, spend the second and longer part of their life-cycle dwelling quietly in a shell. Some animals reproduce by throwing off buds; some have male and female parts in one organism; in some cases the male individual is a mere minute parasite; some marine species seem to be male or female according to the accidents of their life. Plant lice breed for a long series of generations as females only, without any pairing; then comes a generation that contains males, and there is pairing of the sexes. Among the plants are to be seen all manner of com- binations: one sex only, two sexes in one plant that THE VARIED MODES OF LIFE 49 mate in that plant, two sexes in each plant that can mate only with the sexes of another plant, only one sex in each plant. | Why should nature, that stern and steadfast moth- er, thus toy with ways of propagating that seem so wantonly varied? VI. Varied Heredity We have been taught that like breeds like. We know that a grain of mustard seed will produce a mustard plant, that an eagle’s egg will yield an eagle. Surely, if there is any way in which we might suppose that nature is unvaried, it is in this matter of like producing like. If I walk through a patch of wild roses, they look alike to me; the ones I see in Maine seem like the ones in Iowa and California. But a florist, who has eyes to see, detects the dif- ferences. He knows that roses are very unlike, fluc- tuating in size and tint and odor. Put him into a field, and he will cull you out a dozen unlike ones, will plant their seeds, will cull again from the second generation those that are more unlike, will continue for several generations, and will then show you a ‘‘new’’ rose, such as the sun probably never looked on before. To my dull eyes the sheep in a flock are very much alike, but a shepherd knows them individually and calls them by name. Probably I could not tell one ant from another if I studied them under a micro- scope, but an Huber knows them apart as if they were children of the neighborhood; he names them and recognizes their mental peculiarities. Like never does beget precisely its like. And yet it is obviously the rule of nature that like tends to produce like; ordinarily an animal is like its parents, as they resembled theirs, and so on back through ten generations; we know by specimens in 50 EVOLUTION FOR JOHN DOE our museums that potato-beetles of a hundred genera- tions ago are like those that we spray to-day. If Huber had lived a thousand years earlier, he would have seen similar ants with the same individualities. Indeed the tendency to produce similarity seems strongly preponderant; for if the florist’s artificially selected roses were put back into a state of nature, they would soon recur to the ancient type. If cross- ings are made between two of our artificial domestic breeds of fowl, the offspring may show a strong tendency to revert toward the natural form that they had several thousand years ago when they were wild on the slopes of the Himalayas. Like does tend to produce like. This contradiction in heredity is an illustration of all the paradoxes woven into a web that hid the secret of nature from the prying eyes of science. It was this woof of contradiction and variation that young Darwin had before his eyes when, like Siegfried before the wall of flame, he girded himself to pene- trate the veil. He indulged in no such heroics about matching his intellect against the secret of the ages; but, after he had been around the world observing the varied forms of life, dedicated himself to the struggle in these simple words: ‘‘It occurred to me that some- thing might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts. which could possibly have any bearing on it.’’ Not till he had spent twenty-two years in accumulat- ing did he allow himself to publish. Then his Origin of Species opened a wide gate to knowledge, through which all men might walk and view a most remark- able revelation. CHAPTER V, THE JUNGLE OF ADAPTATIONS In THE last three chapters we have been taking glimpses at the mazes of life, and in this chapter we shall continue to do the same. There is no explana- tion here. We are going to look at a mystery, one at which men have always marveled and for which they have spun various theories out of their imaginations —the devices that enable living creatures to obtain a living. Every plant and animal has its own way of suc- ceeding in its struggle to live, is fitted for getting food and competing with its rivals by a peculiar anatomy and a particular set of instincts. All such adjustments for the fight of life are called ‘‘adaptations.’’? Their enormous number and variety, in an endless luxuri- ance of competing series of devices, are only feebly indicated when likened to a tropical jungle. The woodpecker is adapted for preying upon in- sects that live under the bark of trees: two of its long sharp toes grow backward and two forward, thus forming an instrument for grappling the surface of a tree; its tail-feathers are spiked to give a purchase for the toes and are like a spring to help the hammer- ing operations; the bill is a beautiful chisel; the skull is, unlike that of any other bird, so contrived that the rapid succession of resounding blows on the wood can be delivered without racking the head to pieces. This bird is adapted for its life-work. It could not ol O2 EVOLUTION FOR JOHN DOB live by wading or by searching for carrion or by div- ing in water, but is contrived to be a highly successful hammerer. Even a heedless mind is struck by this arrangement. Hiven a dull mind naturally asks, ‘How did it all come about?’’ Every child knows of the adaptations of animals for fighting and for defense: the rhinoceros is armed with terrific horns; the wasp has a most elaborate sting and poison gland; a Brazilian eel is equipped with an electric battery that can give powerful shocks; the skunk and the pinacate beetle emit offensive odors; the sword-fish is armed with a combination — battering-ram and spear that can pierce the planking ~ of ships. Whence came these adaptations? Nature-books picture the adaptations of the camel, which is fitted for its desert life by the thick soft cushions on its feet, by the hump where food is stored, by the tanks in its body where water is stored, by its power to digest dry shrubs, by its power to close its nose when a sandstorm is raging. So complete is the adjustment of these parts of his body that the beast can carry a rider two hundred and fifty miles across the sand in five days without a drink. How were all these devices assembled in such a partnership for enabling camels to live in the desert? The equipment of some animals is so extraordinary that a description sounds like a fairy story. There is a small fish, living in the utter darkness two miles below the surface of the ocean, which makes its own light that shines out through port-holes along its sides, and which sees through eyes that are perched on the end of long stiff tentacles. There are birds that hatch out eggs when the temperature is twenty below zero. There is a Malay plant with a blossom three feet wide which, when it is ready to be fertilized, makes an odor like tainted meat, and thus attracts the The Tasmanian ‘‘wolf’’ is not a wolf at all, but a marsupial, like the kangaroos. The Panda, which looks like a bear, is related to the raccoons. The Koala, one of the manv kinds of Australian marsupials, looks like a bear and has grasping toes for its life in eucalyptus trees. THE JUNGLE OF ADAPTATIONS 53 flies that will bring the needed pollen from other similar plants. These examples are not extreme. Stranger ones can be found in books that treat of. the wonders of nature—for example Fabre’s accounts of insects. If you ask a Malay savage why the big red blos- som has this queer power of making a bad odor, he may tell you a myth of how some angry spirit de- signed it. Ask an American business man, who has spent his life in trolley-cars and Pullmans, and he will say that the blossom was designed that way— that’s all there is to it. But ask a man who has long been curious about the odors of flowers, who knows all about these adaptations, and he will shake his head and talk like this: ‘‘It’s too much for me. If there were in the world only thirty-four odors of flowers, and if each were an adaptation peculiar in itself, I could let it go at that and bother my head no more about it. But the longer a man trains his nose in this study of mine, the more he finds out that there is no sharp distinc- tion between one smell and the next. No flower has any special adaptation of odor, but every one blends into its place in the whole long array of all the odors. ‘It’s like a spectrum of colors—you know, the rainbow band that is made when a beam of sunlight goes through a prism. If I stick a pin here in the band and another pin half an inch farther up, I can see the difference between the orange and the yellow colors. But if I start at the first pin and move my eye along only one thirty-second of an inch at a time, I’m not sure whether I can see any difference; the change is so gradual and blended. ‘ arin ieee 2 ‘ Nee h oy ef ~~ meh Ye 8) ~~ @___-- care Wore Se Vie ‘ Cet Fannie ares / 2 ="? = gS ¢ . i i g \ \w , hit eee ieee ey F bi Oe § Vid Wy ey N=, oa Vi mit se vis 7 w ¢ “ty SR eh cueotaa maT? nde, =\ WV Ps 4 ui a) £7 ? ad De Weed ‘ pee 7) , 7 NL Xy i. gr as o i 4 ie =? x\\ 7 rat ~ pel x SN gs we Ign = c b on StS 4 { % oe cso 7! ae te he } seh ~ Ss ‘He ~, 4 ‘ hb. Ye U4 ‘, he VD) vile Pe a aN | Pi ef Sd WA YV 7 Diagram, from Goodrich’s Living Organisms, to illus- trate the growth and death of species. The extinct an- cestors in the fossil record are shown by dotted lines; species still living are, shown in black. unfailing. The coiled ‘‘ammonite’’ shells became an alphabet of the earth’s history, as unmistakable as if they were the letters MES O2ZOZTIOC. In each decade since 1850 the knowledge has broadened and deepened, and grown in detail. If any single exception to the order of the fossil record had ever appeared, it would have blighted the whole science of geology—= 188 EVOLUTION FOR JOHN DOB just as surely as the proof that there was once a king of the United States would upset all our school histories. And fame has always awaited the geologist who could prove such an upset of the fossil record. But no man has been able to discover the exception. A geologist no more questions the story of the rocks than a boy who reads about yesterday’s league base- ball thinks the games are a myth. Yet the geologists of 1859 were in the dark. By their flash-lights here and there they saw the unmis- takable record; they pieced it together; they knew it as surely as they knew that they had eyes, but they knew it as a patchwork of incomprehensible frag- ments. The greatest of them all during a whole generation, Sir Charles Lyell, had no faith that there was any general progression of forms from the earliest times to the latest. His clear-headed judgment on all the facts that men had piled up was simply this: ‘‘We have not proved any progression of forms, from sim- ple ones to complicated ones, through succeeding ages. We may yet discover the bones of a mastodon among the Cambrian shells.’’ Imagine what the Evolution Theory would have meant to you if you had been Sir Charles Lyell in 1859. ‘‘If Darwin is right,’? you would have said, ‘‘then his idea is like the glint of sunshine to a person who has been lost in the mazes of a cavern; if I follow his theory, I shall be in the daylight henceforth. But if it is wrong, it will be only the flicker of a candle in the hands of another man as lost as 1am. Is Darwin right or wrong?’’ That was the question that Lyell faced when, early in September, he unwrapped a bun- dle of some of the page proofs of the Origin of Species that had been sent by a London publisher. And imagine how you would have felt if you had been Dar- win. After twenty-five years of constant labor and THE EVIDENCE FROM THE ROCKS 189 thought you have put your conclusions into the thrash- ing-machine. Are they wheat or chaff? Will this greatest student of rocks and fossils accept my theory? He is sixty-two years old; can he, at such an age, alter his whole view of the nature of life? ‘“‘Tho not be in a hurry in committing yourself,’’ wrote Darwin to Lyell on September second. ‘‘Re- member that your verdict will probably have more influence than my book at present; in the future I can not doubt about the admittance of my views, and our posterity will marvel about the current belief.’’ On the twentieth he wrote again: ‘‘As I regard your verdict as far more important than that of any other dozen men, I am naturally very anxious about it.’’ On October fifteenth he wrote to Hooker, the foremost botanist of England: ‘‘Lyell seems staggered by the lengths to which I go... .. . L entertain hopes that he will be converted, or perverted, as he calls it.’’ On October twenty-third, again to Hooker: ‘‘I had not in- ferred from Lyell’s letters that he had come so much round. J remember thinking, above a year ago, that if ever I lived to see Lyell, yourself, and Huxley come round, I should feel that the subject is safe.’’ He had only a month to wait. Then came a note from Hooker which spoke of ‘‘your glorious book’’ which will be ‘‘very successful’’ and of how ‘‘Lyell is perfectly enchanted and is gloating over it.’’ Lyell had already determined to admit the new theory to a revision of his Geology, and Darwin wrote to him: ‘‘T’o have maintained, in the position of a master, one side of a question for thirty years, and then delib- erately give it up, is a fact to which the records of science offer no parallel. I rejoice profoundly.’’ Huxley wrote a favorable review and girded on the whole armor of his intellect to fight the good fight for evolution—or, as he put it on November twenty-third, ‘‘T am sharpening up my beak and claws.’’ 190 EVOLUTION FOR JOHN DOE The whole meaning of the Evolution Theory to geology was thus summarized by a correspond- ent who wrote on the same day as Hooker: ‘‘How could Sir Charles Lyell, for thirty years, think on the subject of species and their succession, and yet constantly look down the wrong road!’’ Ever since 1860 geologists have been able to look down the right road. Read any text-book or encyclopedia article, and you will find testimony similar to this from the Britan- mca: “‘The Origin of Species produced an extraor- dinary revolution in geological opinion. The older schools of thought rapidly died out, and evolution be- came the recognized creed of geologists all over the world.’’ In the light of the knowledge of evolution they have read a record of vast eras, a record which is all consistent, intelligible, indisputable. They could no more continue their researches without evolution than a historian could read if you took away his theory that lines of print begin at the left-hand side of the page. Hundreds of geologists are mapping rocks in all quar- ters of the globe. If they assume that all species of ani- mals developed from previous species, they can make sense of the fossil record; if they should assume any other explanation, all geology would become a heap of meaningless curiosities. No achievement of the human mind is more credit- able than the building up of a connected narrative of the changes in the earth’s crust. I offer a brief sketch of the result as an example of what the Evolution Theory produced when it was applied to this stupen- dous riddle and was found to be an unfailing guide. The first four paragraphs have nothing to do with evolution and do not tell of a proved theory, but I include them in order to furnish a beginning of the story. It is based on The Origin of the Earth (Uni- versity of Chicago Press), by Professor T, Q, THE EVIDENCE FROM THE ROCKS 191 Chamberlin, a little book which is quoted with respect in recent scientific works. A billion years ago or more, as one of the stars, our sun, was soaring along calmly, another star came near. This meeting was quite in the ordinary course of things, for by the law of chances there must be now and then such encounters in the wide spaces of the heavens. It would appear that the star was larger than our sun and that its course happened to swing it very near the sun, though not producing a collision, and then to speed it away. Perhaps the meeting was only for a few days, or a part of a day. The bulk of the star almost disrupted the sun, for its attraction was so great that the matter of the sun began to stream out toward it; and if it had come a little nearer, it would have drawn the whole sun to itself. So adjusted did its course happen to be that during its approach it caused four bolts of sun-stuff to shoot forth, four more as it receded, and then sped away without doing more damage. (Such results are not an astronomer’s dream; cold figures show that just these effects would be produced by a meeting of a kind very likely to occur.) In such a sudden and spectacular way was the sun set upon and almost annihilated. Yet it had not been much diminished—no more than if you should draw off from a molten mass the size of a baseball enough material to make a small marble. The wreckage of the encounter was strewn about the sun in eight irreg- ular bunches of molten minerals and gases, which rapidly cooled, spread out as they were in a tempera- ture of four hundred fifty degrees below zero. They had darted toward the star, bending after it as it raced away, but it had been too fast for them. So they were left within the range of the sun’s attraction, yet 192 EVOLUTION FOR JOHN DOE unable to return to their warm home. ‘There was nothing they could do but continue to whirl in orbits around the sun. And there they have whirled ever since—eight planets, of which the third from the sun is our earth. Hach of these shapeless baby planets began to set itself in order. Its core rounded into a globe, to which - the outlying fragments were attracted. As it went along its orbit, it was continually drawing to itself the wreckage that lay there. As the centuries went by it continued to mop up its path, to gather the debris to itself, and so to increase in size. Countless tiny plan- ets, the ‘‘planetesimals,’’ pursuing their private courses around the sun, were daily drawn into the major planets. That is the picture that the ‘‘Planetesimal Hy- pothesis’’ offers us of the origin of the earth. It isa conjecture so carefully calculated that it seems highly probable. According to this theory there was a period early in the earth’s infancy when it was not half so large as now, cooled from its original heat, already surrounded by some air, and having on its surface the beginnings of an ocean. It grew gradually and uni- formly, as cool at the surface as it is now, by picking up the bits of sun-stuff that it encountered. Since that earliest and briefest period of infancy it has never been molten, never even hot on the surface, never the scene of violent changes, never more dis- turbed by volcanos and earthquakes than it is at pres- ent. The history of our earth has been a placid one. ‘‘Gradually, calmly, uniformly’? is what the his- tory of the rocks is forever repeating to us. Most of us have been familiar with the contrary idea. ‘‘There were tremendous doings here once,’’? I have heard passengers remark as they look at the Rocky Moun- tains from a train; they think of the past as a violent The Diatryma, from Wyoming, has to be called a bird, though it was unlike any ancient or modern bird and conld not flv. ' was a queer, unsuccessful twig of the tree of life. STAGE 7 UPPER GHADRON STAGE § LOWER CHADRON sea ND RIVER |e CG IDGER ses These rhinoceros-like Titanotheres developed in Wyoming. Each skull is known, by the stratum in which it was found, to be older than the one placed above it, to the right. THE EVIDENCE FROM THE ROCKS — 1938 voleanic age, which was in contrast to our slow and peaceful era. We are familiar with the description of the earth as a fiery mass that cooled enough for a crust to form, though it was still molten inside, that finally cooled enough after an age of frightful dis- order to allow coal to form, that continued to cool and to thin its atmosphere until some animals could live on it, that cooled to an ice age, that will grow colder still, and that will at length freeze into a dead mass like the moon. Recent geology knows of no such process. Ge- ology tells us that as it was in the beginning it is now and, so far as can be foreseen, ever will be. No mak- ing of mountains in the past was ever much more spectacular than what is going on now right before our eyes. There have been ice-ages as far back as any record can be read in the rocks. Where the oceans and continents are now, there they have always been. The land masses have come and gone and come again, but always in the same general locations. Since its roman- tic beginning the earth has had a quiet history, almost monotonous. The modern geologist pictures the earth as made of a dense core, rich in heavy metals, kept hot by the work of its own gravity and by chemical action, and covered with a crust of lighter rock some fifty miles thick. Some form of adjustment is always taking place within this crust—not that it is ‘‘wrinkling like the skin of a drying apple,’’ but that parts of it are con- tracting and expanding as they adjust themselves to the shifting loads on the surface. Some heaving ap- pears to lift up masses of stratified rock—very gradu- ally, through long ages—on certain fixed lines of adjustment in the crust, and so to make mountain ranges. Then may come a compression which slides rocks for fifty or even a hundred miles from their first location, and tilts them as we see them in the 194 EVOLUTION FOR JOHN DOE Alleghanies or the Alps. Recently geologists have learned that the material under a mountain chain is lighter than the material which underlies the regions on either side of the chain: the mountains seem to be counterpoised by denser portions of crust. In the be- ginning there were certain lines of adjustment—about where the greatest mountain chains now are—and there the mountains have usually been made. There were certain regions of depression—and there the deep oceans have always been. The changes in the earth’s surface have been a routine, a slow pulsing in certain regions. Though the alterations seem large to us, they are slight compared with the total bulk of the earth. The top of the tallest mountain is only six miles above sea level, a height which would be represented on a twelve-inch globe by no more than the thickness of a sheet of note-paper. As soon as a mountain range begins to rise, it is attacked by the water—worn down by friction, chipped by ice, decomposed chemically. Though it rises ever so high and is ever so hard, though the ac- tion of water seems ever so slight, the water will con- quer in the end; for water has as many millions of years as it needs to complete its destructive work. Slowly it carries away the pulverized rock, carries it as silt to the sea, and deposits it. As the thousands of years pass, the top of the mountain is being laid down in the bottom of the ocean. There it is subject to great pressure from later deposits, and to a ce- menting process. It is converted back into rock. Layer is formed upon layer. Thus an increasing burden is laid upon the shifty foundation of semi- fluid rock several miles below. Some time the strain will become too great to be borne, and then this new- made rocky bottom of the sea will be slowly crumpled THE EVIDENCE FROM THE ROCKS 195 and lifted, perhaps only a fraction of an inch a year, into a new mountain chain—to be again worn down, and again raised up. Suppose that half a billion years is a correct esti- mate* of the time since the first animal left a record of itself in the rocks. Suppose that an angel had been commissioned to take a photograph of the North American continent, as it appeared at that time, from an altitude of several thousand miles, where a lens could command a view of the whole expanse. Suppose that every five thousand years thereafter the angel had taken another view of the same part of the earth from the same point. If the one hundred thousand negatives thus far taken could be put together in a single reel, they could be shown on a screen in an hour. Watching such a picture would be heaven for a geologist. What would he see? Imagine that a map of North America is traced in dotted lines on the screen, so that as we see the views of the ancient land masses we can tell where they were. Understand that the reel which we are to see begins when half of the rock-forming history of the earth had already passed. Of all the previous half- billion years of the continual heaving up and wearing down of land we can have small knowledge. But we do know that before our motion picture began thirty- two miles of sedimentary rock had been laid down in the ocean and raised above it, and that during the *Barrell’s estimate, on a uranium basis, of the time since lower Cambrian is seven hundred million years, and Schuchert thinks ‘‘this is excessive by fifty per cent.’’ (The Evolution of the Earth, Yale University Press, 1918.) The figures will seem excessive to most readers, because they are five times as great as those given in most recent books of reference; if they are too high, they will be the first estimate that ever erred in that way. See the 1922 Britannica, article Palaeontology. The data for the sketch of the configurations of North America since Cambrian time are in Grabau’s Teaztbook of Geology, Part II. 196 EVOLUTION FOR JOHN DOE time of the picture only twenty-one miles of rock were made. 7 As a prelude to the main reel comes a one-minute picture which gives two glimpses of the era before the Cambrian and indicates that we are plunging into the middle of the total history. It is a close-up of the Great Lakes region. A sheet of ice stretches down from the north to the American border, its ragged southern edge quivering back and forth; after ten sec- onds we can see that it is retreating, as the tide goes out with a series of advances that are farther and ~ farther down the beach. The ice disappears to the north. There is a heaving up of land. Then near where Lake Superior now is a volcano pours out smoke; another appears to the north of Lake Huron; great sheets of lava, hundreds of feet thick, cover wide areas. In them, if we could but see, are the cop-- per and silver that are now being mined in those regions. The picture closes and there is an interval. Then the main reel begins with some blocks of land that we should never recognize as our continent if the dotted lines of the map did not guide us. There are three of them: the largest stretches from north of the Hudson Bay region, tapering to a point in southern Mexico; the second is at the left, a block corresponding to Alas- ka and stretching southeast where the Canadian Rockies now are; at the bottom is the third block, where the West Indies now are, stretching in a slender northeasterly neck across to England. Long arms of the sea separate the two smaller land masses from the large continental one. You watch the lower end of the great central con- tinent slowly disappear, and the channels on either side of it widen slightly; the sea encroaches* some- *So it appears on the screen and so the geologists speak of it. What actually happened, of course, was that the land sank. THE EVIDENCE FROM THE ROCKS 197 what on all the land for two minutes. Then for two minutes you observe that the sea is retreating and the land extending. During the following two minutes the changes are greater, for the whole southern third of the central continent is eaten away, and the other two blocks alter their shapes, becoming somewhat smaller in area. You do not find this entertaining. In seven minutes of the monotony you do not see as much change as an animated cartoon ought to show in three seconds. You shift in your seat and wonder whether anything worth while is going to happen dur- ing the next seven minutes. The learned lecturer tells you that you have now seen the whole of the great Cambrian period and are well into the still greater Ordovician. You are not thrilled. Still there is more doing on the screen. You see the central continent creep farther and farther south, widening as it goes, filling the arms of the ocean on the east and west, taking on an almost familiar ap- pearance: you can see a Gulf of California, a San Francisco Bay, a Puget Sound, and a Mississippi River. But the Gulf of Mexico opens toward the southwest, and a river twice as long as that ancient Mississippi runs from the state of Washington through Oregon and Nevada and Arizona. Now the ocean begins again to eat the land away, opening up the arms on either side of the continent and washing out a large gulf through Illinois and on through Iowa and Nebraska. At length it cuts clear across to the Pacific Coast, and runs a wide arm north through Wyoming to the Arctic Ocean. The continent be- comes a set of islands. So for a minute it remains. Then the land begins to grow, until a fairly respecta- ble continent emerges, stretching unbroken from northern Alaska to a tapering point in southern Mex- ico. ‘‘The close of the Ordovician,’’ the lecturer an- 198 EVOLUTION FOR JOHN DOE nounces; ‘‘now note how the sea begins to wear down the continent and carve a north-and-south channel through it at the opening of the Silurian. The 8i- lurian will last four minutes.’’ As a movie, this sort of display on a screen would not draw crowded houses. Yet any one with imagina- tion has spent an extraordinary quarter-hour, watch- ing the rocks come and go with the slow lapse of millions upon millions of years. Every second of this picture represents one hundred forty thousand years —ten times as long as the whole recorded history of man. A minute of these motions on the screen is longer than the mind can conceive—more than eight million years. Our quarter of an hour has meant fifteen times those eight million years, and yet that whole inconceivable extent of periods is but one chap- ter in the whole volume of the ages of the world. We have seen on the screen nothing but the com- ing and going of land. What about life? When the reel opened, life was already far advanced; there were beautiful scallop shells and jelly-fish and complicated erab-like animals. For aught we know these forms had been developing from simple one-celled animals during a whole half-billion of years. In the quarter of the motion-picture that we have seen the corals developed, and the chambered nautilus, and a kind of fish. So much advance to show in one hundred thirty million years! Somehow, when we realize what this picture means, the remaining minutes of Silurian time will not utterly bore us. It represents twenty-five million years, during which the ocean three times reduces the size of our continent, and three times is slowly driven back by the rivers that pile sediment along the shore. There is a fascination in seeing this portion of the earth’s crust pulsing back and forth, never entirely THE EVIDENCE FROM THE ROCKS ~— 199 consumed in the waters of ocean, always returning to that shape that tapers off at the south in the famil- iar Mexican outline, always showing some sort of Alaskan and Canadian and West Indian land, always showing a tendency to gulfs where gulfs are now. And there should be wonder in our hearts as we recall that this history was never revealed to geologists by an angel. No, they had to pack burros and wield ham- mers and draw maps and study specimens and com- pare notes and show up each other’s mistakes for a century before they could piece together the frag- ments that we are seeing by the grace of heaven. ‘‘If in this shale there is such a species of fish, and if this sandstone underneath it is of so coarse a texture, then’’—by comparing thousands of such inferences they slowly built up the knowledge of where the ocean was at different periods. Fishes are not adapted to desert life, and ferns never grew in the sea; each fossil of such an adaptation as a fish or a fern shows what the environment must have been for that form of life at that time. There is no more mystery in reading the geological record than there is in reason- ing that an old oriole’s nest was made by an oriole. All that is required is infinite care and patience, driv- en by curiosity. The records of the Silurian, and of the Devonian that occupies the next four minutes, show only one marked advance in organic life: cerae fishes devel- oped lungs, and so could live on the land. Plants also adapted themselves for living on land. At the times when the ocean was driven back there were likely to be certain bays that were filled across the mouth; the water-dwelling plants and animals that were thus cut off from the ocean would perish as the water grew brackish and finally evaporated. But if any organism varied in such a way that water became 200 EVOLUTION FOR JOHN DOR less and less necessary to it, and if these variations were inherited and increased, that species could in time become adapted to live altogether on land. It would survive, while all the others would become ex- tinct. Such development came about some time dur- ing the last two periods that we have seen on the screen. It was momentous. Life then escaped from the sea and began its career on land. Now for eleven minutes you may watch the sea eat out the top of North America in a great gulf that reaches down to Mississippi and east into Pennsyl- vania, and then retreat again. A close-up of this new land left by the retreating sea shows that it is covered with a strange forest, composed of forms like our modern ferns and horse-tails and ground pine, but maenified to large trees. It is a riotous growth of the plants that have learned to live on land and that have waxed gigantic in the rich, new, low, swampy soil. As the trees die, the trunks and leaves form a kind of peat-bog that is transformed and compressed into coal. Insects swarm in the forest—some early ele- mentary kinds of bugs and beetles, cockroaches, and especially darning-needles, some of them thirty inches long. There is a reptile that reaches a length of eight feet. The semi-tropical growth fades away. The land rises, and the climate becomes cold. Those animals that have been well adapted to the warm moist condi- tions are in hard case to survive. Many must perish. Lucky are the animals that now have variations which fit them somewhat better for the struggle with a harsh environment. This five-minute period* causes rapid evolution of new types. A chart of the animals. through the ages widens out suddenly at this section into many kinds of short-legged, lizard-like reptiles. *The Permian, THE EVIDENCE FROM THE ROCKS ~~ 201 During the thirty-six minutes of this picture that we have seen—and during a whole previous reel that ge- ologists can never see—life has been developing; and has progressed only as far as a big lizard. It is the early stages of any development that require time. From now on* the changes of the land will be quicker and seem more significant. During the last six minutes it comes back to almost its present shape, and remains so. In the last quarter of a minute of the performance you see a spectacular ice-sheet come down jerkily almost to the Ohio and Platte Rivers, and then retire. It was this that left the hills of pebbles on the Nebraska farm. And man in this picture? He was on the globe during the last second or two; civil- ized man has been here a tenth of a second. A few views of the animals during those last twen- ty-four minutes would furnish entertainment.t For fourteen minutes we could watch the reptiles increase in size, till some achieve a length of a hundred feet; and some grow heavier than four big elephants. They walk principally on their massive hind legs, which are midway between the long neck and the tapering end of the long tail. There are many other types of these ‘‘dinosaurs,’’ and all varieties of other sorts of large and small, smooth or horned, lizard-like animals. It is the age of reptiles. From one species of these the birds developed, from another the earliest mammals. Other reptiles remained reptiles, and are with us to- day—crocodiles and horned toads and turtles and snakes. And all the other reptiles? They died out. There could be a picture of the progress, during the last six minutes of the reel, of a little animal only a foot high that walked on five toes. Its four side *That is, after the Paleozoic. tO. H. Ditmars has made, and shown to enthusiastic college audi- ences, a2 moving picture of animal evolution, 202 EVOLUTION FOR JOHN DOH toes grew smaller; its middle toe grew longer and longer; it increased in size until it was five feet tall, and became the modern horse. The paleontologist has been able to reconstruct other histories, quite as re- markable, of insignificant animals that developed dur- ing these same periods into the camel and the elephant. The stages of their growth are in the rocks, as surely labeled and dated by accompanying fossils as if they were classified for us in a museum. Yes, they are more reliably recorded; for naturalists make mistakes, but nature never does. When any man has learned the alphabet of the fossils and is familiar with its grammar and idiom, he reads with assurance the history that has been pre- served in the volumes of stone. It is written in the language of the Evolution Theory—more consistent and indubitable than any chronicles that come down to us in Latin or Greek characters. It reveals how every form of life descended from some earlier and simpler form. The whole of the evidence in the rocks is vast be- yond comprehension and makes bewildering demands on our mind. To any reader who knows no more of it than I can compress into this chapter it must seem somewhat unreal. As an indication of how actual and vivid it all is to men who spend their lives with it, I will give a description of a scene that has recently been uncovered in southern California. If you could drive west from Los Angeles over a boulevard, and step out of a car at Rancho La Brea, and walk through the dry fox-tail grass to look into a certain excavation in a bed of tar, you would feel the reality of geology. All along the coast there are these outcroppings of asphalt, that has seeped through the shale and in some places formed deep pools of an extremely sticky THE EVIDENCE FROM THE ROCKS ~— 203 substance, which can be dug out only by using heated shovels. The edge may be covered by soil and become hardened, while the center remains tarry. Shortly be- fore the World War an excavation was made in one of these pits, near Santa Monica, and there was discov- ered such a dramatic cluster of fossils as has never been seen elsewhere—saber-tooth tigers and elephants and mastodons that had been caught in this death- trap, mired in it, sunk, and been perfectly preserved. If I should find my horse dead in quicksand, I should not know more certainly how he died than I know when I look into this pit how these tigers died. The men who study oil shales know, as a matter of prac- tical business, in what geological period the asphalt was made. It is a certainty that during the last min- ute of our reel elephants mired down in the California tar and trumpeted their distress, and that they were heard by a kind of tiger that no longer lives on earth, and that the tigers were attracted, and mired down to their death. The contorted bodies tell their story as plainly as a charred corpse in a house of Pompeii, covered with volcanic ash, tells how the man died. The episodes of all the history of evolution in the rocks have come from scenes which, though not so romantic, are as unmistakable as that in the asphalt pit. CHAPTER XIII THE EVIDENCE FROM GEOGRAPHICAL DISTRIBUTION WHEN acertain entomologist had studied a genus of beetles from Colorado south into Mexico, he prepared a chart showing where the different species live. ‘The study of the chart,’’ he says, ‘‘gives clear ideas as to what the course of evolution has been.’’ This little example will illustrate the experience of all modern naturalists when they map the locations of animals. If you could remove from their minds all knowledge of how species originate from previous species, their charts would have no meaning; all the groupings of animals would be a disorderly jumble. But the combined labors of collectors fit together into an orderly whole of animal life when evolution is understood. To every modern naturalist the term ‘‘distribu- tion’’ is a pictorial way of saying ‘‘evolution.’’ If we eould look at the world of life through his eyes, we should see that any great class of animals, such as the insects, is everywhere over the globe; to make a chart of them would be simply to draw a complete map of the land surfaces of the earth, except for those few areas where there is no life of any kind. Even one division of this class, say the order of beetles, would be spread almost as widely. But any one family of this order, the leaf-beetles, for example, would be ab- sent from some desert areas where other families have found a way to live. Any one genus of this 204 GEOGRAPHICAL DISTRIBUTION 205 family flourishes chiefly on one continent; it is to be found in only a part of the region that the family covers. Any one species of this genus—for instance, the potato-beetle before it found potatoes to eat—is restricted to a part of the territory occupied by the whole genus. When the range of any one species is thoroughly known, and its varieties charted, it ap- pears that the species is most uniform and constant in the center of the range, and that the distinguishing characters fluctuate more and more in proportion as the specimens are gathered farther from that center. The chart of the range of the species of any large - genus of animals always shows a similar fact: there seems to be a center of the most typical forms, from which many species radiate; and each species radiates from its own center in varieties. If the naturalist assumes that each species is a group which developed from a preceding species, and that all the species of a genus branched out and pushed afield from some com- mon ancestor, he can understand the distribution of animals. If he tries to imagine any other explana- tion of the locations of the different groups, he comes to grief. All the facts of distribution point toward one fact —that the species of animals always develop by mi- grating continuously from their centers. Just as the evidence from the rocks shows that all organisms have developed continuously in time, from one age to an- other, so the evidence from distribution shows that they have spread by steady advance from a center where they originated. The chapters on classification and structure will show other phases of the evidence that life is always continuous in its lines of descent and location and classification and structure. The central truth of all the evidence in Part Two is that organic life, from whatever point of view we examine 206 EVOLUTION FOR JOHN DOE it, appears as a continuous whole. We can not explain such a many-sided truth except by the theory that every form descends from a previous form. If a zoologist finds some specimens of a certain species in Vermont and some specimens of the same species in Ohio, he can not conceive that they are un- connected. All the evidence of distribution declares that the species must live—or that eggs must have been transported, or that individuals must at some time have lived—continuously all the way from Ver- mont to Ohio. There is no evidence that the same species has ever originated in two places; it has only one origin, in one place, at one time; and from that origin it has spread out as far as it could go. And as a species spreads from its original center, it tends to alter, adapting itself to the new environments that it comes into. The whole theory of evolution would re- ceive a severe shock if the facts of distribution did not always indicate that development has been continuous in time and place. An illustration of the evidence that comes from distribution is seen in an exhibition of snail-shells in the American Museum of New York. They were col- lected in the island of Tahiti. The genus to which they belong has various species on many islands, but the five species in the exhibit are found only on Tahiti.* Hach of these appears as a pushing, branching, vary- ing group of forms. Number one has pushed into al- most every valley, and nowhere varies much in its *The New York Times of April 20, 1925, gave a striking account of what Professor H. E. Crampton, of Barnard College, had discovered about Partula on the island of Moorea, near Tahiti, ‘‘One of the three varieties found in 1909 had spread over the entire island. Its different valley colonies had become greatly diversified in size and color, pre- senting types unknown in 1909.’’ Professor Crampton’s earlier re- searches are in the splendidly illustrated Carnegie Publication No. 228, 1916; his later work is reported in The American Naturalist for Jan- uary, 1925. "90zZ osed 900 ‘£IOJLLIOY LAPUA THAO PBards ovavy Sotoods ouloOSs puB ‘padoaAdp IABY SOTOLMVA MoT SIBIOA AJUOMY JSBL OY} Surinqg ‘Tyyey, Jo puBsyT 9} UL S[IVUS JO SNUDS B JO SUOTIBIUBA JY} GUTMOYS ‘UNESNI UBIO YW oY} UL JIqtyxes uB Jo ydersojoyg Sona, S THE SALAP ASHE ESAS SOE THEA SNIMALS 2 Be ioaasnae Beem aon iba Nee socks 668 noo 6 ee UR FON ES oot co cases ooo mnonoonl on rs 88 ‘he Roms eepeck- Seg. ats, sete Ta A: Bae ee Sth: Sete a CRS MEAS Another American Museum exhibit of the evidence that com i nee es from geograph distribution—the finches in the Galapagos Islands, where Darwin aot a aati studies of evolution. See page 213. Z GEOGRAPHICAL DISTRIBUTION 207, white color; whereas number two is confined to one valley. Number three ‘‘has recently extended its range and differentiated into four varieties.’? Num- ber four ‘‘has recently migrated and differentiated into varieties.’’ Hight varieties of the wide-ranging number five have been found. If these descriptions of what the shells have been doing were the fancy of some one collector, we should pay no attention to them; they would mean nothing: But the same kind of description comes nowadays from all students of all kinds of animals everywhere. Another graphic display of distribution is a large map of the western half of the United States, on which are the skins of eleven species of striped ground squir- rels that range from Oregon to Wisconsin. The great family which embraces all the squirrels is world-wide, though it is strongest in North America. This genus on the map (Hutamias) ranges over only part of the United States. Hach species is limited to a part of the whole area of the genus. When a scientist sees the large dark pelt of one species change through a series of species across the map to one that is light- colored and small, he reads a record of branching out from a parent stock and of altering to adapt to the new environments that were met as the genus spread. Every chart of every successful genus always reveals the same fact. When specimens are arranged accord- ing to where they live, they present a series of graded forms, as if their genus were a source of variant life that was forever trying to propel itself farther away, and that altered as it moved. ‘‘Harther south,’’ says one naturalist’s report, ‘“‘the species degenerates in size and is obscurer in color.’?’ That matter-of-fact statement would have been queer jargon to Darwin in his boyhood, for it represents a group of forms as a fluid, fluctuating 208 EVOLUTION FOR JOHN DOE mass that changes while it grows toward a new habi- tat. But to the Darwin of middle life it would have sounded like a perfectly natural description, because a species at one end of a wide range is bound to be different from what it is at the other end. ‘‘In dif- ferent localities,’? says the naturalist, speaking of another species, ‘‘it tends to the development of dis- tinct local forms.’’? Every study of distribution, of any plant or animal, shows the same tendency. We have been attending to some petty examples. Take a very large one, as stated by Professor H. F. Osborn in 1900: ‘‘The fact that the same kinds of mammals and reptiles appear simultaneously [1. e., during the same geological periods] in Hurope and in the Rocky Mountain region is strong evidence that the dispersal-point is half-way between.’’ He pre- dicted that such an origin would ‘be found in Asia, and he named the fossils that must some day be searched for there. In the spring of 1922* the Amer- ican Museum expedition to Mongolia began to find them, and in generous measure. When any theory of distribution has produced such successful prophecy as that, it is well tested. The greatest test of the theory is on the islands. Some of these are very close to a mainland, and some are very remote; some have been separated very re- cently, and some for several geological periods, and some never were connected with other land; some could be reached by immigrant animals of certain sorts, but not by other sorts; they might preserve old species with little change, or they might force old species to develop new adaptations. Thus they are like experiment-stations established in the ocean to give proofs of whether or not all species develop by continuous descent and in continuous lines of migra- *Still more striking discoveries have been reported in 1924 and 1925. GEOGRAPHICAL DISTRIBUTION 209 tion. If evolution were not true, its falsity would be sure to appear in some of the facts of animal life on islands. If it is true, then the following conditions would have to be found: 1. There would never be upon an island an ani- mal whose ancestors had not reached the island. 2. In proportion as islands are farther from a mainland, or have been longer separated from it, the animals on them should be more different from those of the mainland. 3. But in some cases (for example, if some fierce competition of the mainland were removed on the island) we should expect to find that species had al- tered less on islands than on the mainland. 4, The kinds of animals would, in a general way, be numerous in proportion to the ease with which they could reach the island—for example, by flying, swim- ming, being borne in currents, being drifted by gales. The facts of the distribution of animals on islands are in accordance with those conditions, as the fol- lowing descriptions will show. Long Island is detached from the mainland by only half a mile of water, and the separation was made in very recent times. Hence we should expect that the animals and plants on it would be only very slightly different from those on the mainland. That is the fact. When it became an island, it was stocked with the same species that were on the New York shore; and it has been so close to that shore that there could be much migration. There has been little time for new varieties to develop, and there has been only partial isolation from the life that swarms on the mainland. If you go eight hundred miles southeast in the Atlantic, you come to the Bermuda Islands, twenty square miles of low-lying limestone hills surrounded 210 HVOLUTION FOR JOHN DOE by coral reefs, a small remote bit of land that has long been separated by hundreds of miles of water from the nearest Bahamas. Here we should expect to find the animals very different from those of our nearest Atlantic coast and somewhat different from those of the Bahamas. Such is the case. There is only one backboned animal which is native, a lizard that is found nowhere else in the world. Yet among the birds there are no peculiarities—no species that is not found on the mainland. Among the shell ani- mals and insects, however, there are extraordinary dif- ferences—a great array of peculiar species. Class a. order b. order TT Class 1. Grade a. order b. order c order 2. Grade (or this division may belong under Grade 1 as the d order) 3. Grade a Order b. order IV. Class EVIDENCE FROM CLASSIFICATION 227 We have seen the tree-like appearance of the largest divisions of a great phylum. If we should take the next step down in classification, and should chart, for example, the b order of one of the grades, we should produce just the same kind of diagram of branchings; the big bare limbs of orders would each have clumps of branches—the families. And each of these families would send out clumps of smaller branches—the genera. Each genus, if it was pros- perous, would fork into many twigs—the species. And each flourishing species would have several leaves—the varieties. And the leaves might be send- ing forth buds—some sub-varieties. The diagram on page 228 pictures one man’s class- ifying of a sub-genus of the big, black Eleodes beetles of the Southwest. This man would have been lost in the mazes if he had not known how to look for the course of development of each species and variety that he found. Suppose that you had encountered Mr. Blaisdell as he returned from his six-month collecting trip over the sage-brush plains and up the bouldery bar- rancas of the Mojave Desert, and suppose that you had asked him what a species is. Perhaps he would have sent you a copy of his bulletin, with this passage of the definitions marked: ‘‘Heterotype=an indi- vidual that forms an extreme of a specific or varietal series. Mesotypes=individuals connecting the ex- tremes of a series. Amphitypes=individuals that simulate another species. Monotype’’—and so on through polytype, sexitype, and others. So abso- lutely non-perfect were the species and varieties that they can not be conceived or in any way classified except by paying attention to that greatest truth of nature, that a species is a fluid form of life. Pause a minute to take stock of the labor that Mr. 228 EVOLUTION FOR JOHN DOE Porc ie Obsoleta 2 Knausii Omissa Carb i Pygmwa inn I Een Dewdisn Lustransa nthracina Quadricollis Cuneaticollis Humeralis Li X Pedinoides es. Rileyi / Neomexicana Ampla Carbon- Quadricollis /-—~ Tricosta ia LE Section Section cae Subgeneric Trunk Chart of one section of a genus of large, black beetles, after Blaisdell in the United States National Museum Bulletin 63. It shows the same sort of branching that is seen in the chart of the whole vast phylum of sponges on page 225. Blaisdell put into determining the twelve species and eight varieties of this one part of a genus of beetles. And his labor was only a portion of the whole; for six specialists had worked in the genus before him. Mul- tiply the total labor of these seven men by eight thou- sand, in order to know how much effort it took to classify all the beetles. Multiply the product by some large factor, in order to have the sum of expert toil that has been spent upon classifying all animals. Double the product, so as to include all the classifying of plants. Then—and not till then—you will appreci- EVIDENCE FROM CLASSIFICATION = 229 ate slightly the amount of evidence that is furnished by classification. A classifier never can find a sharp line of demar- eation between different groups. Between most species there are varieties that bridge the gap; be- tween genera there are interlocking species; between families there are dove-tailing genera; to separate orders so clearly that no family will bridge the gap is usually impossible. Classification always indicates that if our knowledge could ever be complete we should see that there never had been any gap any- where, but that all transitions have been continuous, over bridges of variation that dropped out and dis- appeared from the record. ‘‘At this point,’’ we are told by botany, ‘‘the distinction between flowering and flowerless plants breaks down.’’ So deep a rift as that is well bridged over. The more men learn of fossil plants and animals, the more they are taught that in past times there have been bridges between forms that to-day seem wide asunder. Life has been a whole, and there has never been any such thing as a separate species that was not attached through its branching ancestry to every other form that ever lived and branched upward from the beginning of life. A modern classifier can no more conceive of a species without ancestry than a biologist can conceive of an animal that had no parent. I will close the chapter by a comment on the men who classify. So far as a rough count of the different sorts of sponges can be made, there are about two thousand five hundred species—only two thou- sand five hundred. It is well for us amateurs to try to stretch our imaginations to the classifying of the sixteen thousand species of spiders. Perhaps we had better excuse ourselves from trying to imagine the extent of the intricate labors of classifying the 230 EVOLUTION FOR JOHN DOE sixty-one thousand species of mollusks. Even if we were willing to strain our minds to the breaking-point, we could not conceive the total of patient work that has gone to the making of a chart of all the animals or all the plants. Of this vast domain of classifica- tion no modern scholar can know thoroughly more than one corner. The botanists and zoologists are a great corps of tireless and clever campaigners against the mysteries of nature. No one can command them; there is no discipline. Some delve in coal mines for ancient ferns, some spend the years viewing grass- hopper eggs under a microscope, and others dredge the depths of ocean or thread the tropical forests or study agricultural pests at home. No horde of self- willed barbarians were ever so free to spread where they like and think what they choose. Yet they all think one way and—whether they will or not—contrib- ute to one fund of ever-increasing knowledge of one subject. Whenever they classify truly, they extend the kingdom of evolution. CHAPTER XV THE EVIDENCE FROM ARTIFICIAL SELECTION THE kind of evidence that comes from artificial selection has been outlined in Chapter IX—that is, the ways in which breeders select the variations pro- _ vided by nature through a series of generations, pil- ing them up as they occur in a desired direction, until they gradually develop a race that is widely different from the one with which they started. In this way many plants and animals have been slowly changed into forms so unlike their ancestors that they appear as different as a new species or even a new genus. Kixamples were given of two ways in which new va- rieties arise: (a) by selecting a series of slight varia- tions,* as in producing new kinds of pigeons or changing a small single daisy into a large double chrysanthemum; (b) by the sudden appearance of a new breed, as in the case of the hornless cattle or a new kind of peach. This sort of evidence has always been persuasive; it can be seen in operation; it indi- eates that all kinds of life, wild as well as cultivated, are variable and are prone to change to very different forms. There is no need here to add pages of further illus- tration, but there is need of showing in Part Two that the facts of artificial selection are an important kind of evidence for evolution. I will give a few examples *For variations that can not be cumulated see Chapter XXIV, Section ITI. 231 232 EVOLUTION FOR JOHN DOE which supplement Chapter IX, and will then explain why this line of evidence is, if taken by itself, incom- plete. Darwin founded much of his reasoning on his knowledge of the breeding of animals and plants. In- deed the evidence was so important to his theory that in 1868 he published two large volumes, The Varia- tion of Animals and Plants under Domestication, as a sort of ‘‘case-book’’ for the Origin of Species, a storehouse of evidence that was too bulky to go into the Origin. So exhaustive was this great collection of facts that it is still cited as the principal source of information about artificial selection. I give below five quotations from the book, which show how dif- ferences brought about by artificial selection may be very great, very firmly established, and sometimes fitted to succeed in wild life. 1. The Japan pig is so distinct in appearance from all common pigs that it stretches one’s belief to the utmost to admit that it is simply a domestic va- riety. . . . The modification of the skull in the most highly cultivated races is wonderful. The whole of the exterior in all its parts has been altered: the hind- er surface, instead of sloping backwards, is directed forwards, entailing many changes in other parts; the front of the head is deeply concave; the orbits have a different shape; the canines of the upper jaw stand in front of those of the lower jaw, and this is a re- markable anomaly; the knobs at the base of the skull are so greatly changed in shape that no naturalist, seeing this important part of the skull by itself, would suppose that it belonged to the genus of pigs. 2. The Niata cattle of South America have a fore- head that is very short and broad, with the nasal end of the skull curved upwards. The lower jaw projects beyond the upper. Even the connection of some of the bones is changed. Scarcely a single bone presents ARTIFICIAL SELECTION 233 the same shape as that of the common ox, and the whole skull has a wonderfully different appearance. 3. In the genus Auchenia there are four forms— the Guanaco and Vicufa, found wild and undoubtedly distinct species; the Llama and Alpaca, known only in a domesticated condition. These four animals appear so different that most naturalists, especially those who have studied these animals in their native coun- try, maintain that they are distinct species... . Now that we know that the domesticated species were systematically bred and selected many centuries ago, there is nothing surprising in the great amount of change which they have undergone. 4, The humped cattle of India have run wild in certain parts of Oude and Rohileund, and can maintain themselves in a region infested by tigers. They have given rise to many races differing greatly in size, in the presence of one or two humps, in length of horns, and other respects. . . . There are magnificent wild bulls on the bleak Falkland Islands in the southern hemisphere. o. We must not overrate the amount of differ- ence between natural species and domestic races; the most experienced naturalists have often disputed whether the races are descended from one or from several aboriginal stocks, and this clearly shows that there is no palpable difference between species and races. The statement that ‘‘there is no palpable differ- ence’’ between the results of artificial selection and of natural selection may be misleading. For it is a fact that no artificial species has been produced which ean not breed with other species descended from the same stock; and that means that in the brief time of man’s selection no such deep and wide separation of types has been made as nature has created. Artificial selection is by no means a proof of natural selection; it is only an index to a strong probability. 234: EVOLUTION FOR JOHN DOE Yet some of our domestic races are so ancient, as human history goes, and so thoroughly distinguished from any other forms existent in the world, that they seem to justify Darwin’s emphasis. No one has ever seen a wild llama; we know that it has been domesti- cated in Peru for four centuries and that it was prob- ably derived from the wild guanaco, but it exists now as a separate species. The Arabian camel has never been seen except as an animal domesticated by man. Our Indian corn has never been seen wild, and no an- cestry is known for it. The same is true of wheat. The differences between these results of artificial se- lection are certainly not ‘‘palpably different’’ from the species in nature. Certainly none of the hundreds of practical men who work in our agricultural colleges know how to tell the difference between artificial and natural species, nor are they much interested in the difference. They all work on the supposition that the variations and sports in nurseries are of the same kind as those that occur in nature, and that the new varieties they produce are not palpably different from what nature has produced through all the ages. If sports from buds of sugar- cane and potatoes are so important in artificial chang- ing of species, presumably the same sort of sporting has been a factor in nature’s evolution. If the Seneca cherry of 1923 sprang into existence with new quali- ties—ripening early and having a spicy flavor—pre- sumably such sporting seeds have had their share in causing nature’s results. When Pennsylvania State College gradually develops a tobacco leaf that has only half the ordinary percentage of nicotine, the ex- perimenters suppose that they are dealing with the same sort of mechanism which has caused tobacco and potatoes to branch from the common ancestry that every botanist knows about in nature. Of course the \ ARTIFICIAL SELECTION 230 experimenters may be wrong; but thus far no one has made any progress in discovering a difference between their results and nature’s results. All men who collect and direct the variations of plants and animals sup- pose that their work is evidence for the Hvolution Theory. The strongest part of the evidence will bear re- statement in this chapter. If all artificial selection dealt only with domestic plants and animals, the evi- dence would be weak. The fact is that all artificial selection begins with a wild species. In recent years many experiments have been made with plants that were never domesticated, and it appears certain that, if an experimenter is patient enough and has enough time, he can always discover variations to work with. It is believed that every wild plant, and presumably every wild animal, could be developed gradually by artificial selection, into a form that is very unlike its present form. It would seem that artificial selection, however violent and abnormal it may be, is simply a use of the machinery of natural selection. Artificial selection may pull the wrong levers and may spoil the engine, but it indicates that the engine of natural se- lection is there. CHAPTER XVI THE EVIDENCE FROM THE STRUCTURES OF ANIMALS In tHe American Museum of Natural History there is a chart of the supposed course of development of animal life, from one-celled creatures to mammals. The makers of the chart would wish us to emphasize ‘‘supposed’’ while we study the branching lines of their exhibit; for they know better than we how mazy and back-tracking the paths of evolution have some- times been and how puzzling is some of the scanty evidence. On the other hand, they would wish us to know that in many ways the evidence is copious and that it is extremely probable that their exhibit represents the main lines of evolution correctly. The principal parts of it were known fifty years ago, have been subjected to the severest criticism, and have stood the test. It is likely that the improved chart which can be made fifty years hence will differ only in some details. And the men who planned this diagram of life would wish us to understand something of the vast labor that has been necessary, by thousands of scientists in many de- partments, to secure the knowledge which made their chart possible. There is no guesswork in it. It rep- resents keen observation and close reasoning. The principal value of this graphie exhibit is to show us that the different sorts of animals do not have other sorts for ‘‘ancestors.’’ The worms, for example, which are placed higher in the chart than the 236 The chart in the American Museum which shows the course of evolution of animals, by the special kindness of Dr. F. A. Lucas. The lines do not indicate that animals ‘‘descended from’’ others, but that each sort branched from a common stem. Sec page 237. ‘MoTTod ‘aITYM ‘YABP sS1O[O ody} FO ooURpIOYUT PoXttu ot} St 4st oyd VW ‘ayIyM “YrVp :sxofoo Fo aed vB st 4yFop oyy FY ‘“dnois yovo Ut SUOTZBIOUS 991} SUTMOYS ‘S}BL UL OOUBPIIOYUL UBITOPUo IW STRUCTURES OF ANIMALS 237 jelly-fish, are not ‘‘descended from’? jelly-fish. The fact seems to have been, as the chart shows, that the different forms of life have kept budding off into branches, which have divided into further branches. The squirrel, perched at the top, did not ‘‘descend from’’ some fishes that are below him; he is one of the latest twigs that come from a branch that came from a limb that grew from the common trunk. If human beings were to be placed in the chart, they could not be shown as descendants of any animals now living, but only as a twig from the ‘‘primate’’ limb of that common branch from which all mammals spring. All animals must have a common ancestry, but seldom is one kind known to have sprung from another kind. Though it is commonly said that birds developed from reptiles, it might be truer to say that birds and rep- tiles have descended from some common stock. The bottom of the trunk is labeled ‘‘Protozoa’’— that is, one-celled animals. Science does not know anything about the roots of this tree—the origin of life—and probably never will know anything. It does not know, with mathematical assurance, that the earli- est form of life was one-celled. But it finds all the evidence pointing in that direction and makes the sup- position until some contrary evidence appears. Sci- ence does not know positively that the first step of evolution was when two cells varied in such a way that they could live to better advantage in partnership; but science finds indications that such was probably the first step. Science supposes that, by a series of variations, many cells came to live in a partnership, forming a sort of colony. It is likely that these cells varied in diverse ways so that some became better adapted for obtaining food, some for digesting it, some for distributing it. When these several sorts of cells had become much differentiated, they were 238 HVOLUTION FOR JOHN DOE no longer able to live separate lives; each sort was dependent on all the other sorts; and thus the earliest many-celled animals are supposed to have evolved. That sounds somewhat fanciful. Perhaps the idea would have remained a pure speculation if we had never known anything about sponges; but among these Wwe can see many stages of just such a process. There are sponges which seem to be mere colonies of similar and independent cells; other sponges in which the cells are highly differentiated and utterly dependent. In this case, as in every other part of the evolution chart, the biologists have not built upon their imaginations, but have always laid foundations upon facts now ob- servable in nature. Above the sponges the chart shows a branch of such salt-water animals as jelly-fish and sea-anemo- nes. At this point the needs of saving space and avoiding complexity have made the diagram mislead- ing; for the jelly-fish have continued to prosper ever since their ancient beginnings, and their line deserves to be extended to the same height where birds and frogs are displayed. A complete chart of evolution would show, from bottom to top, in what geologic period each type of animal arose, and would continue its line upward till it became extinct or reached the height of the present time. ‘This chart, more con- venient and graphic, indicates only how each type branched from the stem. Two main branches of many-celled animals are shown. The one at the right has ramified into a far greater number of types than the other—from several sorts of animalcules and mollusks to crabs, spiders, and insects. Most of these are small animals; but one, the giant squid, is large enough to give a whale a tough fight. At the base of the left branch are certain worms, STRUCTURES OF ANIMALS 239 and just above these some ‘‘radiating’’ forms, like starfish. From here up all the types tend to a ‘‘ver- tebrate’’ form—that is, having a backbone. They did not descend from worms or starfish, but from the same parent stock that gave rise to worms and star- fish. So, as we look higher up, we are not informed that reptiles descended from fishes, but only that rep- tiles and fishes grew out of a common stem. it staggers imagination to see the results of ages of the evolution of structures put thus abruptly be- fore us in a disjointed series. We can not see how the gaps could be bridged. When we learn that the schol- ars themselves disagree about particulars, and that sometimes they imagine linking forms which they have never seen, we are excusable if we give a verdict of ‘‘not proved. di Indeed such an exhibit of successive fe ices through a long development may misrepresent evolu- tion to us amateurs, for it implies that scientists have relied on a lot of clever conjectures. The truth is just the opposite. The unfilled spaces in the chart of evolution have always seemed more incredible to a biologist than they do to us. He knows how imitative nature always is and how the origin of a new bone is a prodigious work for her mechanism; he marvels at the ease with which college students can take it all on trust and repeat offhand, ‘‘Oh, yes, the leg evolved from a fin.’’ It is the scientist who sees that the gaps are extraordinarily hard to fill. It has always been the keenest scholar who has felt most dubious about the successive steps of the evolution of a limb or other organ. He has never accepted sur- mises and guesses. He has had to be convinced by an unanswerable array of facts. The study of structures is called anatomy, and the study of the similarities in the anatomy of different 240 HVOLUTION FOR JOHN DOE animals is called comparative anatomy. The more science learns about comparative anatomy, the more it discovers those same continuous serves that are so striking in the geological record and in classification. The student of anatomy knows of finely graded forms from the limb of a lizard to the wing of a swallow, from the fin of a shark to the leg of a lion, from the smooth skin of a whale to the shaggy coat of a bear. The two ends of any such series of structures seem incredibly remote from each other. Every sci- entist of the nineteenth century, confronted with the extremes and asked to believe that one evolved from the other, was infinitely more skeptical than you and I can be; for he knew how distinct they are in the de- partments of nature’s workshop. Until he saw a dem- onstration of many actual steps in an anatomical series, he never credited the evolution of one from another. : Imagine that in 1855 Darwin had said to some young man who was beginning the study of zoology, ‘“The hoof of a horse must have developed by gradual continuous stages from the fin of a fish.’’ Imagine the amazement of the young man. If he had lived till 1920, keeping himself abreast of the times and following each advance in zoology, he would slowly have learned—always against his will and his strong- est prejudice—that there is no escaping Darwin’s conclusion. It is now impossible for the comparative anatomist not to believe it. An outline of what the young man would have learned begins in the rocks. In the geological period before the coal began to form a lizard-like amphibian one day walked on the hard mud of a river delta where western Pennsylvania now is. His foot, about three inches long, was divided into two principal parts, but there was a bunchy third toe and a slight swelling STRUCTURES OF ANIMALS 241 corresponding to a fourth toe. One of his tracks was covered in such a way that it was preserved while the mud was transformed to sandstone; and after Darwin died it was discovered by an American geologist and placed in the Yale museum. It is obviously the print of an amphibian’s foot, padded and creased and un- mistakable. It is the most ancient record ever dis- covered of any animal that went on feet. Above this stratum of rock there are, in all parts of the world, animals with five toes.* When these are classified in time order, they are found to branch into many kinds, which can be charted in different lines of de- scent. One line comes down unbroken to modern tur- tles, another to lizards and snakes, another to croco- diles. Two other lines can be traced to queer species that are all but extinct to-day, one of which is the duck- billed Ornithorhynchus of Australia. Many of the lines have completely died out. One developed into birds, and one into mammals. The young zoologist would have had small trouble in believing that all modern reptiles descended from ancient reptiles; a small part of the evidence would have convinced him completely. But birds! That would have been beyond belief for some years. Yet if he examined the structure of the winged reptiles that were found, and if he did not think that nature was making game of human beings, he would have had to believe that birds evolved from reptiles. The facts are patent in the museums of London and Berlin, where he could see animals the size of a crow that are as much like our feathered fliers as they are like the oldest lizards. Photographs can be faked, but these remais in the rocks can not be deceptive—unless Satan has played a practical joke on the geologists. *For the explanation of this great gap im the evolution of the foot see the next chapter. 242 EVOLUTION FOR JOHN DOE The wing of the most ancient bird was, in part, a mem- brane stretched along the side of the body, like the gliding-planes of the extinct flying reptiles; and it was also like the true wing of a modern bird, sup- ported from the fore limbs and covered with feathers. Yet there were claws on the outer joint; and the head, skeleton and teeth were reptilian. No naturalist would have dared to imagine such a beast; nature made it and preserved two specimens for us to see. ‘‘But what about the feathers?’’ the skeptic would have asked. ‘‘I can see that here really is a form midway between reptile and bird, but how could the scales change? You don’t show me any steps in the evolution of such an extraordinary structure as a feather. Am I asked to guess that in some vague way each scale grew longer and frayed itself out into tens of thousands of perfectly adapted barbules?’’ That is what he was asked to believe. Surely he might well have refused, since he had been taught to think of a seale as a fixed kind of structure, and of a feather as another kind of structure. But if we de- voted a year to the study of each, we should find that some fish have scales that are ‘‘like hair or feathers,’’* that the feathers of the cassowary are very simple structures compared with what we know as feathers, and that in young birds there is a coming and going of feathers such as we never see in any adult bird. We should learn that there is nowhere any hard-and- fast line to be drawn among all the forms that the cov- erings of vertebrates take: nails, skin, hoofs, scales, shells, plates, plumes, hair, down. We may go all the way along a series of structures from microscopic scales to the horny sections that make up a turtle-shell. Long famiharity with this blending of the different *Press report of William Beebe’s expedition to the Sargasso Sea, March 7, 1925. STRUCTURES OF ANIMALS 248 structures that grow from the skins of animals would make it hard for any one to believe that they had sep- arate origins; for they seem all related and essentially similar. Thus the young zoologist would have grown to believe that undoubtedly birds evolved from reptiles. Not that the few indications here given would teach him—far from it—but that in his studious life he would encounter the hundreds of similar links in the chains of evidence that scientists are forever discov- ering. Bare logic would not be effective; a few dozen probabilities would not persuade him. But the multi- plied examples as the years went by would create an unshakable conviction. As for the descent of mammals from reptiles, it is just a repetition of similar evidence from many series of structures: the order of the fossils and the rare animals still surviving in some corners of the earth give an indication that is irresistible. A student of comparative anatomy learns that there is no hard-and- fast line between reptiles and mammals—not even among the animals that now live. Perhaps to me in my ignorance there seems to be an unbridgeable dif- ference between laying eggs and bringing forth young alive. But the biologist knows of a gradation from one kind of bearing young to the other kind: an egg may be hatched outside of the body, or it may remain with- in the mother till it is hatched, or it may remain at- tached to the mother till 1t has partly developed. Some fishes and snakes bring forth their young alive. The biologist gives the same name to the egg of a snake and to the egg of a sparrow and to the egg of a rabbit; he can not distinguish sharply between the different kinds; he can not conceive that they come from different sources; all his evidence shows that each mode of bearing young was developed from some preceding mode. 244. EVOLUTION FOR JOHN DOE The early mammals were small. Apparently they developed in many races through long ages, picking a living as best they could by keeping out of the way of the huge reptiles that dominated the life of the world. If our zoologist kept pace with the fossil dis- coveries, he might have been convinced of this before 1880. But if any of his early doubts then remained he might have said, ‘‘It is too much to ask me to sup- pose that from a five-toed animal a few inches high there should develop an animal five feet high that walks on a solid hoof. There is no evidence for such profound alterations.’’ Yet most geologists of that time believed that such had been the history of the horse, and they confidently expected that the proof would some day come out of the rocks. It came. There was a find of a small three-toed horse; and another that was smaller, with the side toes longer; and an- other that was smaller still. One day the news flashed over the wires that a four-toed horse a foot high had been found. Now a series of horses has been set up in a museum,” showing graphically the actual prog- ress of teeth and limbs as they changed and enlarged and took different proportions, from little twelve-inch Eohippus to a racing thoroughbred. Similar series are now known for camels and elephants. The experience of this one zoologist represents the course of scientific opinion since 1860. Then evo- lution was seen at once to be a shrewd and likely hy- pothesis, but the gaps in the series of structures were so many and so great that few geologists could expect them to be accurately filled. Every decade has made some remarkable contribution to the evidence, and this steady accumulation which has always fulfilled proph- *The original series, which Huxley viewed with so much delight, re sores for the Peabody Museum at Yale by Professor O. Q, arsh. STRUCTURES OF ANIMALS 245 ecies and never disappointed them, has converted the hypothesis into an axiom of zoology. You may be wondering why a chapter on structure keeps talking about the geologic record. ‘‘Why,’’ you ask, ‘‘must geology and anatomy be mingled in this way?’’ The answer is that the subjects are insep- arable, as can be illustrated from the life of Huxley. He took a medical degree at the age of twenty, studied marine zoology till he was twenty-five, and at the age of twenty-seven, when he first met Darwin, had small faith in evolution. To him, as a student of structures, the gaps between the different classes of animals were too great to be bridged by any theory of common descent. He believed that even species were unchangeable forms of life. If he had never en- countered any evidence outside his own field, it is probable that he never would have accepted Darwin’s theory. But the fossil record was pointed out to him, and then he realized that the most incredible links of succession were actually to be seen in nature’s mu- seum. His judgment of structures had to yield to the knowledge that paleontology put before him. When he based his anatomy on these facts, he found that baffling mysteries were cleared up, and that his study of structures could safely be built on the new foundation. And this, mind you, was long before the discovery of the reptile-like bird or the series of fossil horses. Huxley expressed his debt to geology thus: ‘‘The primary and direct evidence in favor of evolution can be furnished only by the fossil record.’’ I suspect that even the combination of paleontology and anatomy would not have been absolutely convinc- ing to the young zoologist whose career we have been tracing. I can guess that, if he was at all like me, he would not have surrendered till he had learned of the entirely different line of evidence that is explained in 246 HVOLUTION FOR JOHN DOE the next chapter. The structures of animals, taken by themselves, might not have seemed a proof; they link together and complete the evidence that is in the rocks and the evidence that is in embryos. As you read the rest of this chapter about structures, bear in mind that it is going to be supplemented in an extra- ordinary way. Consider one of the simplest cases of evidence from structure. If we make a list of all the animals that — have five digits at the ends of their limbs, we have reason to suspect that they are all related. The way those five fingers or five toes appear in so many guises among the vertebrates, but nowhere else in the animal kingdom, is remarkable. How could it happen —as a set of unrelated accidents—that a panther and a mouse and a frog should have their feet built on the same five-toed plan? The front limb of a bat looks like a five-fingered hand with enormously long bones, one of which extends beyond the wing as a claw. A seal has no apparent use for bones in its flipper—for fish swim faster with no bones in their fins, and seven bones or seventeen bones would make as good a frame for a flipper. But, no—the seal has the same five fingers. The structure of a whale’s fin is utterly unlike that of any fish; it is an arm—for there is a big bone at the top, then a pair of bones, then a wrist, and then five digits, one of which is shorter, like a thumb. It can hardly be an accident that so many backboned animals have at the ends of their limbs a hand-like structure—no matter whether they live on land or sea—while no other phylum of animals has anything of the sort in its anatomy. If this five-finger structure is studied, it is found to be wonderfully prevalent, though in all sorts of disguises and concealments. In the wing of a bird, though the limb structure has been modified almost ‘OFZ 90Rq “MOTJIMGODAL PUOKS JSOW[B poaytpowu wseq SBY aInjont}s Sty spitq FO SoUIM OY} UT * * * ‘s}PUOUTTBIDTOD PUB SASINOSIP JO $}LOS [[B UL Yonoyy “yuoTBaAoid AT[NJLapUOM oq OF PUNOF St Yt ‘potpNys st aiNjon.tys AVvsuy-9AY oy} FY] é a B J _ f : me or ae 9 iY ine we SaG WE e, The five-finger structure in the wing of a fruit-bat, above. Compare this modern apparatus with one of the earliest of Nature’s efforts to make a wing. From Seeley’s Dragons of the Air. STRUCTURES OF ANIMALS 247 beyond recognition, there still remain three little bones of the five of the original foot; and a rudimentary fourth one has been seen in embryos. In the bird’s foot there are three prominent bones (the ‘‘metatar- sals’’), one small one, and the stunted remnant of a fifth. | Here we have opened up a whole new realm of structure. We wonder to what extent these remnants of bones could be found elsewhere among the ver- tebrates. They are a regular element of anatomy; so that if we know how to detect them, we can add vastly to the number of five-fingered animals. In fact the student comes to feel that any number smaller than five is abnormal and must be the result of a loss at some time in the history of any modern species. He calls these undeveloped parts ‘‘vestigial,’’? for they are vestiges or slight remains of what was once full- grown. A whale is an exhibit of many remnants of struc- tures that are of no use whatever to it, though they are highly important to the land-living mammals in which they are fully developed. Buried in the body of some species of whales, detached from the backbone, floating in the flesh, are some small remains of legs. They are at the point where a pair of hind paddles would naturally be. And in some snakes the same vestiges of legs appear. Jn the seal’s body the cor- responding bones have a strong development—into a regular leg-like series of thigh, lower leg, ankle, foot, and toes—to form the frame of the hind paddle. The only vestiges of hair on a whale are a few bristles near the mouth; the fur seal has the finest coat of hair in nature. The bones of the head of a whale are not the bones of a fish, but strictly those of the land-dwelling mammals; the skull of a seal is still nearer to the land- dwelling type. One kind of whale has true mammalian 248 HVOLUTION FOR JOHN DOE teeth, but so vestigial that they never come through the gum; the seal’s teeth are strong and useful. An ingenious naturalist who speculated on seals and whales could note that a seal, which spends much of its time on the land, is more land-like in structure (as shown in a dozen ways other than the hind limbs and teeth and eyes and ears), though it has much of the fish-like form. He could note that a whale, which never lives on the land, has almost entirely a fish-like appearance. Then he could hazard a guess that in some past age certain four-footed mammals found good hunting in the ocean, that every slight variation in structure which fitted them to move better in the water and to stay in it longer was useful and was se- lected to survive, and that thus there was a gradual adaptation to sea life. He could guess that the seals had gone one-fourth of the way toward complete sea life, and the whales about ninety per cent.—for the whales must still come to the surface to breathe air. If such a supposition about structures stood all alone in the world, it would be no more than a probability till other series of structures had been studied. Some wings form such a series. It begins with squirrels which can make longer leaps because they — are helped by an expanse of skin stretched along the — body and held out as a gliding-plane between the legs. Many animals of very different kinds—from squirrels to fish—are helped in their motion by a similar device. Such a membrane is most completely developed among — the bats, where it is supported on the excessively long — fingers and is like a webbed hand. The extreme of — the series is the feathered wing stretched along the © whole arm. Other wings form a series that is an en- © tirely different piece of architecture—a membrane ~ supported on extended ribs. A third type of architec- ture is the wing of all the insects, which is not sup- _ f { STRUCTURES OF ANIMALS 249 ported on limbs, but is an entirely different kind of outgrowth from a different element of the body. When all the wings of animals are thus assorted into three groups of structure, it appears that the second is rarely seen. The first is the one that has been developed in two lines: the feathered arm-wing of the birds, the hand-and-leg membrane of the bats. The third has branched in the most extraordinary and successful ways among the wasps and flies and moths and bugs. Each type of wing shows a series. Each type of structure appears, when all are charted, to be a well-defined pattern which goes off at an angle from the other types. As we trace them back in time, we can see the similarity of their origins—that is, as outgrowths of the body-covering that were somewhat useful for aiding motion. We can see how each sort radiated farther from the other sorts in the course of ages, like the spokes of a wheel. But we never dis- cover, in wings or in any part of anatomy, that the lines ever come together again. If all the structures for seeing are classified and charted, they fall into three distinct types: the eyes of vertebrates; the eyes of mollusks; the eyes of in- sects. The first type of structure is found among all fishes and reptiles and mammals; every form is only a slight variation of the one architectural type. Nothing like the first type is ever found in insects or erabs or lobsters; nothing of the third type is ever to be seen in squids or snails. It appears that eyes, like wings, can be arranged in lines of structure that had similar origins—that is, in spots of the body that were sensitive to hight. We can see how each type passed through a series of changes in a long course of devel- opment. This fact of series of structures is observed in every phase of animal life. An armored snail and a pulpy slug appear unlike and unrelated; but the student 250 HVOLUTION FOR JOHN DOH finds an unbroken series between the two extremes, through smaller and smaller shells, to a mere vestige, to a rudiment under the skin, to no trace at all. The heart of an ox is unlike the heart of a shark; yet, though they are such different structures now, we must suppose that there is a line of descent to a com- mon origin. So we could fill page after page—and great volumes have been filled—with these examples of the series that comparative anatomy has discov- ered. A dozen series would prove nothing; a hundred would make us suspect; a thousand would suggest a strong probability. When the students of anatomy find that in every respect the structures of all animals are always arranged in such ways that they could have been developed by inheriting variations, they feel al- most persuaded. After they have searched a hundred years for some other reasonable explanation of the structures and have found none, then they are con- vineced. The whole study of structures fits in with the results of classification. An example is the eye of a hawk and the eye of an octopus. These animals had to be classified in entirely different phyla—that is, in the most widely separated groups, profoundly unlike in organization. Yet their eyes were remarkably similar: each had cornea and lens and retina. This was perplexing; it seemed as if the evidence from structure was at odds with the evidence from classifi- eation, and the early skeptics about evolution made much of the argument. But their own reasoning proved that they were wrong: the eye of an octopus, for all its similarity in appearance, is built by a dif- ferent portion of the body, and is, in its origin, very different from the hawk’s eye. As in this case, so in all others: the two kinds of evidence never have failed to support each other. The evidences of struc- STRUCTURES OF ANIMALS 251 ture have never been made doubtful by the facts of the fossil record, but have in the most complete manner always been vindicated by the fossils. The three kinds of evidence, which are quite independent of each other, check perfectly. . The evidence from structure is the kind that is least understood by general readers. The ordinary way of thinking about evolution is shown im the ques- tion, ‘‘How could a snake be changed into a turkey?”’ Each of these animals is at the end of an extremely long line of development. It is like a topmost twig of a branch on which some lower limbs have died and some have branched into varied forms. The evolu- tion of forms never leaps across from the end of one twig to the end of another. Evolution is always a branching from below. If the student of structure follows back, down the tree of life, from the twig of snakes, he will come to a certain reptile stock; and if he follows down from the twig of turkeys through the branch of modern birds to the limb of ancient birds, he will come to the reptile stock that gave rise to snakes. He does not want to do this; he has no ‘‘will to believe’? it; he knows full well that many a part of the tree of life is undiscovered. But when he is thoroughly acquainted with all the lines of develop- ment of structure—from the short and obvious ones to the far-reaching and baffling ones—he has no option but to believe that every species of animal which ex- ists came originally from a common ancestry in a very simple form of life. Or perhaps it would be more correct to say that he suspends judgment until he learns about the evi- dence that is seen in the development of eggs, and then has no option but to believe. CHAPTER XVII THE EVIDENCE FROM EMBRYOS A criticaL reader of the previous chapter may have noticed one point at which I seemed to slip hastily over a dubious description—the account of the earliest fos- sil footprint: ‘‘His foot was divided into two prin- cipal parts, but there was a bunchy third toe and a slight swelling corresponding to a fourth toe.’’? The description passed quickly on to the five-toed reptiles, and then to the wide development of the five-toed foot among mammals. Thus it implied that reptilian feet were evolved through a three-toed and a four-toed form. No evidence was offered of any knowledge that this actually was the course of evolution. No evidence could be offered in the previous chap- ter, because none has been found in the rocks. Yet no student of fossils doubts that there was such a course of evolution. If he had nothing to rely on outside of his own field, he would be assured. But he has, from an entirely different source, a confirmation of a most impressive sort. It is a form of evidence that clinches all the other probabilities so completely as to seem almost uncanny when any person first hears of it. It is furnished by the microscope, from observations of what takes place in eggs while they are hatching. If you could look through a biologist’s microscope at the developing egg of a mud-puppy (alittle, smooth- skinned, lizard-like salamander), this is what you 252 THE EVIDENCE FROM EMBRYOS — 2538 would see. The single cell divides into two; each of these two divides into two others; and the process con- tinues until there is a globule composed of a great num- ber of cells. Inits next stage the egg becomes a hollow globe. During the third stage one half of this globe bends inward, while the other extends itself around the bent-in part, and there results another globe with an inner and an outer layer. Now the embryo seems to be really under way. What follows has been described by Huxley in words of almost po- etic enthusiasm: ‘‘The plastic matter undergoes changes so rapid, and yet so steady and purpose-like in their succession, that one can only compare them to those operated by a skilled modeler upon a formless lump of clay. As with an invisible trowel, the mass is divided and subdivided into smaller and smaller por- tions, until it is reduced to an aggregation of granules not too large to build the finest fabrics of the organ- ism. And then it is as if a delicate finger traced out the line to be occupied by the spinal column, and moulded the contour of the body, pinching up the head at one end, the tail at the other, and fashioning flank and limb into due salamandrine proportions, in so artistic a way that, after watching the process hour by hour, one is almost involuntarily possessed by the notion that some more subtle aid to vision than a lens would show the hidden artist, with his plan be- fore him, striving with skilful manipulation to perfect his work.’’ The embryo that Huxley described has at first only one toe. After a few hours this has swelled and shows three slight protuberances. These grow stead- ily more distinct, until the one at the end and the one at the right look almost like pulpy toes. Now the third toe (the one at the left) protrudes more and more, and later there is at its lower left side a fourth 954 EVOLUTION FOR JOHN DOE swelling; this becomes a well-extended fourth toe. Finally from the lower left side of this fourth toe grows the fifth stubby toe. By this time the second and third ones have doubled their length, and there is your salamander foot with its five digits.* The steps that were conjectured from the order of the fossils are here visibly reproduced in nature’s moving pic- ture, the development of an egg. A record in the rocks, which extended over millions of years of slow evolution from species to species, is here rehearsedt before our astonished eyes in a few hours. It is as hard to believe that the two records are not related as it would be to believe that the White House and a photograph of it were accidental similarities. What was conjectured about the evolution of the parts of animals, as this was judged simply from the comparison of their structures, can be seen as the minutes go by while we gaze at the building of a body in an egg. It was hard to see how an extra toe could ‘Just somehow sprout’’ from a three-toed foot; and, indeed, we may never know how it could. Yet in the making of every individual salamander the fourth toe, and then the fifth toe, do sprout. The fact of millions of years of evolution of a race is written for our skeptical eyes whenever we watch the ‘‘inyisible trowel’’ form a foot in an embryo. More difficult still is it to imagine how in the evo- lution of such a complicated creature as a lobster the claws and feelers and legs were ever derived from a *Description after Lull, from Rabl. tThis ‘‘recapitulation theory’’ was much overworked previous to 1910, and was extended with enthusiasm to help in the harder parts of classifying. Hence some distrust of it arose. This was put very strongly in the old Britannica article by Driesch, and echoes of the caution are heard in recent texts. ‘‘But,’’ says Professor W. B. Scott, ‘none of the criticisms denies, and many strongly affirm that em-: bryology affords some of the strongest and most convincing evidence in favor of the evolutionary theory.’’ THE EVIDENCE FROM EMBRYOS — 255 set of those simple and similar segments into which the primitive body of its ancestors was divided. Per- haps we shall never learn how. The fact that there must have been such evolution through long ages is brought home to the observer of the shaping of any embryo lobster. Let Huxley tell in his vivacious style what he once saw under his microscope: Our lobster has not always been what we see it; it was once an egg, a semi-fluid mass of yolk, not so big as a pin’s head, contained in a transparent mem- brane, and exhibiting not the least trace of any one of those organs whose multiplicity and complexity in the adult are so surprising. After a time a delicate patch of cellular membrane appeared upon one face of this yolk, and that patch was the foundation of the whole creature, the clay out of which it would be molded. Gradually investing the yolk, it became subdivided into segments, the forerunners of the rings of the body. Upon the surface of each of the rings thus sketched out a pair of bud-like prominences made their appearance—the rudiments of the appen- dages of the ring. At first all the appendages were alike, but, as they grew, most of them became distin- guished into a stem and two terminal divisions, to which, in the middle part of the body, was added a third outer division; and it was only at a later period that, by modification, the limbs acquired their perfect form. Thus the study of development proves that the doctrine of unity of plan is not merely a fancy, that it is not merely one way of looking at the matter, but that it is the expression of deep-seated natural facts. The legs and jaws of the lobster may not merely be regarded as modification of a common type; in fact and in nature they are so, the leg and the jaw of the young animal being at first indistinguishable. These are wonderful truths, the more so because the zoologist finds them to be of universal applica- 206 HVOLUTION FOR JOHN DOE tion. The investigation of a polyp, of a snail, of a fish, of a horse, or of a man, would have led us to exactly the same point. Unity of plan everywhere lies hidden under the mask of diversity of structure—the complex is everywhere evolved out of the simple. Every animal has at first the form of an egg, and every animal and every organic part, in reaching its adult state, passes through conditions common to other animals and other adult parts. It is impossible for Huxley, or for any man of mental keenness, to remain scientifically prosy when he states the fact that ‘‘every animal and every part passes through conditions common to other animals and other adult parts.’’ No creature, in its early stages, has the outward look of its species—no, not even of its great class or sub-kingdom of animals; it is, so far as human eyes can see, at first a single cell, then a colony of cells, then a folded creature within an inner and an outer layer. It is true, in a very gen- eral way, that the embryo of every animal progresses up the scale of lower phyla to that point of advance where its limit lies; it emerges from the embryo to be a lobster, or to be a fish, or a reptile, or a bird. It would appear as if nature could not originate any novel way of bringing an animal to maturity, but always had to follow the ancient process that she learned with great slowness in the course of long ages, while the higher races very slowly evolved. What she learned to do in the early eras of life she can now do with rapid ease, so that the lowest stage of any embryo is gone through with in comparatively short time; and as the limit of development of any embryo is reached, its processes take longer. It would seem, if we continue this comparison with an artisan, that nature has learned many short cuts in the steps that took her so long while she fashioned THE EVIDENCE FROM EMBRYOS ~— 257 the changing races. At any rate, our eyes can not see all the steps as we observe a developing egg. The early ones seem hurried and huddled together; there seem to be quick jumps over gaps; and there are com- binations of processes that probably never were in adults, but have been invented for use in embryos. Hence the history of all ancestors is not told fully and clearly in the egg. What can be seen, especially of the older parts of the line of descent, is a distorted and transformed history. But a history itis. Many of the chronicles of descent are there under some guise or other. The development of every individual is a partial and blurred ‘‘repetition’’ or ‘‘recapitula- tion’? of the long development of the race. Hence the facts of the development of embryos are ex- pressed by the name ‘‘Recapitulation Theory.’’ What happens when a hen sits on her eggs, as every encyclopedia now tells us, is this: a fish-like animal appears, with gills and a long tail; then legs bud at four points, and there is a lizard-like animal; the fore legs develop rapidly into wings; the hind legs become chicken legs. The record of tens of mil- lions of years in the rocks is rehearsed here in three weeks. When the ovum of a pig begins to develop, it is hardly to be distinguished from the early stage of a chick, for it looks like a fish; then its legs bud—not pig’s legs in appearance, with a cloven hoof, but legs that resemble a lizard’s; the fore limbs and the hind limbs develop into pig’s legs. The embryo of a rab- bit seems to be a fish and a reptile before it becomes a rabbit. Every mammal, in its own life, lives rap- idly through the stages that cover such stupendous ages in the rocks. If John Doe is curious about his own evolution, he should read an encyclopedia article that describes the stages through which he himself lived during the first months of his life. 258 EVOLUTION FOR JOHN DOE The revelation of race history that comes from embryos is of a kind that rivets attention. It is startling and romantic to the last degree. The nature of it may be put into graphic form thus: An English surveyor goes tapping about the hills with his ham- mer, never dreaming of evolution, and as he pieces together the facts in the rocks they spell out before his astonished eyes a history of an order in which animals succeeded one another while the different rocks were formed. In a laboratory of northeastern Prussia a Russian scholar works month after month with his microscope; through the lenses there swims into his ken, as the egg develops, the history of the same order of succession. The testimony of the rocks and the revelation from the egg coincide. Long before the Origin of Species appeared, the embryologists had seen the stages of development in eggs. One of the greatest of them used to exclaim as he showed his specimens, ‘‘I have here the embryos of lizards and pigs and rabbits, but I can not tell which is which. They are all alike.’’ Until 1859 there was no meaning to these facts. Then embryology took a fresh start, and it began to contribute to evolution. : The first actual demonstration that embryos and rocks tell the same truth was not made until 1869. In that year a German named Waagen published his observations of three species of coiled ammonite sfells—the kind that Holmes addresses in his Cham- bered Nautilus, Waagen found in three successive strata the three species arranged, of course, in the order of their evolution. Many of the specimens were of half-grown shells, and of shells only in infancy. A study of some of the ufideveloped shells in the top stratum showed that they resembled the mature shells of the earlier species in the stratum next be-« THE EVIDENCE FROM EMBRYOS = 259 low; and a study of shells still less developed proved that they resembled the oldest species in the lowest stratum. Nature had arranged in this series of rocks a display of embryology, a demonstration that every shell in its individual life had gone through just the changes that the race of shells had gone through in the three strata. No more precise or sensational sort of proof was ever known to science. The life histories of all sorts of animals have been studied with most painstaking scrutiny. There have been able embryologists who would have given all they owned to prove that the development of an egg does not parallel the fossil record, and they have argued and protested with vehemence. So startling a correspondence between two such different depart- ments of science is unique, and the reasoning about it has been subjected to a long and fierce test. The recapitulation theory has stood the test. No evidence from the microscope collides with any evidence from the fossils. In many striking and conclusive ways the microscope has shown zoologists how to classify; but it has never given evidence counter to the prin- ciples of classification. If the combination of the fos- sils and the embryos is not a proof, then the universe is a whirligig and man’s reason signifies nothing. It may perhaps be conceivable by some minds that the records of rocks and eggs merely happen to have a resemblance. Possibly some intellects can suppose that all nature was planned as a temptation, to deceive the minds of scientists by a coincidence that means nothing. We can not prove that a Creator might not have paralleled the embryos and rocks in a fit of humor, Evolution can not be demonstrated. But every modern scientist, aware of how serious and uniform nature always is, must reject any such eva- sion of evidence. There is nothing for any logical mind to do but to accept the Evolution Theory. CHAPTER XVIII THE EVIDENCE FROM BLOOD Tue chapter on the structures of animals was lim- ited to the large and noticeable features of the body, such as bones and organs. It could have been ex- tended to all the minute portions, like the fluids and cells that carry on the life processes. For just as na- ture follows one architectural pattern for limbs and eyes in each sub-kingdom of animals, so for each small matter of physiology she keeps to a general similarity throughout the whole of a group. Take the blood as an example. We should suppose that the warm blood of a bird was more like the warm blood of a mammal than the cold blood of a turtle. But this is not so. For birds are of the reptile stock, and every corpuscle that carries oxygen to their tissues is made on a reptilian pattern—that is, it has a nu- cleus, and is a true cell. The full-grown red corpuscle in a mammal’s blood has no nucleus. Hence a biol- ogist could tell by a glance through his microscope whether a sample of fresh blood came from a lower vertebrate or a mammal. The differences in the blood extend to very much finer matters than corpuscles. The chemical components are different. And they do not differ erratically, independently, but always in correspond- ence with the general structure of the phylum and class and order and family... If we had instruments fine enough to detect all these slight and orderly dif- 260 : THE EVIDENCE FROM BLOOD 261 ferences there is no doubt that a mere examination of a specimen of blood would show from what genus it came, and from what species. Every particle of blood is compounded by the recipe that fits its par- ticular species, a recipe that is unlike the formula for any other species. These distinct and precise differ- ences that must be in bloods was somewhat under- stood forty years ago. In 1904 an elaborate treatise on the subject was published in England, called Blood Immunity and Blood Relationship, which explained a most accurate and far-reaching method in physiology. The knowledge of blood relationships has fur- nished the latest kind of evidence for the detectives who seek the clues to evolution. It is evidence from an unexpected source, entirely independent of any knowledge that comes from other lines of research. The nature of these ‘‘blood tests’? and of what they show may be briefly outlined as follows: If some serum of the coagulated blood of a horse is injected into the veins of a rabbit, the rabbit’s blood forms a sort of anti-toxin against the chemicals of the invading serum from the horse. If, now, some serum from such prepared rabbit blood is put into a solution with horse blood, there is a chemical reaction that is well known and unmistakable. But if the pre- pared rabbit blood is put with ordinary rabbit blood, there is no reaction. In other words, the blood that has bred anti-toxin against the horse serum is a very sure and delicate test for horse blood. The evidence, it should be noted well, is not from living cells or tis- sues or any form of life: it is from a very different source—from the field of chemical reaction. The test works so perfectly for human blood’ that *In Science for May 8, 1925, is an article by Landsteiner and Mil- ler, of the Rockefeller institute, "confirming and extending the Nuttall tests in a remarkable way. 262 EVOLUTION FOR JOHN DOE it can safely be used in murder trials to determine whether or not a stain was made by blood from human veins. It indicates in a very detailed way that the re- lationship of man to other animals is what the evi- dence of anatomy and the embryo shows. A long series of experiments has been made with all sorts of combinations; the result is that ‘‘anti- blood tests’’ are found to be of varying intensity. For example: the rabbit’s blood that is ‘‘anti-horse’’ will react against the blood of a mule or a zebra, but less strongly; it will react less strongly still against the blood of a cow or a pig. It is found to be gener- ally true that in proportion as any animal is more’ nearly related to the horse in classification its blood gives a stronger reaction, and that as the relation- ships of different animals grow more and more dis- tant from the horse the reactions from their bloods grow weaker and weaker. The chemical evidence is in close correspondence with the evidence from classi- fication and structure. In fact the anti-blood tests are now well enough understood and tabulated to be used as evidence in clearing up some doubtful points of classification. Anti-pig serum,for instance, will act strongly against the blood of any member of the pig family; it will act much less strongly against the blood of camels and llamas (about equally for these nearly-related ani- mals); and much less still for a whale. Blood tests have shown that birds are more nearly related to turtles than they are to lizards, and thus confirm in a most curious way what the experts in fossils had conjectured. How to classify the horse-shoe crab has always been a puzzle. The study of embryos showed that it was more nearly related to the scorpions than to real crabs—an unexpected verdict. Hence the blood-test THE EVIDENCE FROM BLOOD 263 men must have felt some excitement when they had perfected their art enough to apply it to this peculiar puzzle. The blood test confirmed the embryos. What fame would have come to these workers with serums if they could have produced evidence against the rocks or the embryos! Their experiments would have been proclaimed in every scientific journal, and the newspapers would have written them up. They eould have sold one hundred thousand copies of a book entitled Darwin Overthrown by Blood. But there was no such fame or wealth in store for them. They could do no more than add to the list of evi- dences which always grow stronger, never infringe on one another, and multiply one another’s strength. EKivery one who has ever learned something new about the life of plants and animals has always—whether he would or not—brought fresh witness to the [vo- lution Theory. Yad Mehta N PART THREE Tue History or Evoitution tik ee AS ta) v, s ; LOU tH! , A RRS Ne fet Mille ay ah aCe He aA, 0 Vinee ay aed, CHAPTER XIX LAMARCK AristorLe inferred from his observations that all which now exists—the stars, the mountains, the trees, the animals—has developed into the present forms by a series of changes. This remarkable conception be- came material for the philosophers, but was never supported by observation; during the Middle Ages it was seldom defended or even mentioned. Up to 1700 it was no more than a general theory of causa- tion—that is, the idea that all changes in the physical world are due to natural causes, not to miracles. By 1760 this theory had been applied particularly to plants and animals by several writers—notably by Buffon. In 1794 Erasmus Darwin speculated about de- velopment in these terms: ‘‘Would it be too bold to imagine that all warm-blooded animals have arisen from one living filament, which the great First Cause endued with animality?’’ The general theory of de- velopment was in the air, but it remained a vague philosophical conjecture. In 1809 (the very year of Charles Darwin’s birth) a brilliant Frenchman, Lamarck, published his Zoo- logical Philosophy, in which he described a theory of evolution that he had been brooding on for sixteen years. Here for the first time evolution was brought down from philosophy to be applied in a particular way to animals and plants. Lamarck was a thorough scholar and a hard worker, who was so well ac- 267 268 EVOLUTION FOR JOHN DOE quainted with the difficulty of classifying species that he felt there could be no hard-and-fast line be- tween them. It seemed to him that somehow the whole series of animals was like a continuous stream of forms that had developed from previous forms. His quick fancy framed a theory to account for such development—briefly this: Persistent use of any part draws the fluids of the body there, ‘‘and in proportion as the fluids are quickened in their movements, they alter the tissues in which they move’’; such changes in the body are inherited and tend to accumulate in_ successive generations. | This theory is based on ‘‘the effects of use and disuse’? and on the supposition that such effects (‘‘the acquired characters’’) can be inherited. It was a brilliant bit of imagining, put forth in a small book that could have been written in a few weeks, and it contains few efforts to supply facts in support of the reasoning. Lamarck belonged mentally to the eighteenth century, when it was thought that science could be spun out of an ingenious brain. In his early efforts at science his speculations about chemistry were ‘‘of a chimerical kind,’’ and he made ‘‘fruitless meteorological predictions.’’ In his latest efforts, when he reasoned about fossils, he poured out from his teeming brain the extravagant guess that all the rocks were made from the remains of animals. From youth to old age his mind was primarily fanciful. Yet he was much more than a wild fancier. His eyes were sharp and his intuition quick. However flimsy his reasoning might be, he had keen powers of perception. What he thought out he could express in a cogent and lively style. His book set the scien- tific world allagog. Its influence was strong for half a century—yes, for almost a century—captivating many LAMARCK 269 trained minds. Its teaching could not be disproved by any facts that were then known to science, and it was so much in line with the natural suppositions about heredity that even Herbert Spencer espoused it and argued for it all during Darwin’s lifetime. In fact the teaching of Lamarck has not yet ceased its effect. The reason for this influence is not difficult to see. Lamarck had perceived a great fact that was hidden from all slow and conservative minds—to wit, that a species is not a fixed form of life, that there is no telling where one species ends and the next one begins. That is a great truth, and it is Lamarck’s glory that he saw it and put it vigorously before the world. What is more, no one could offer any sub- stitute to improve on Lamarck’s reasoning, His theory split the naturalists into three camps: those who followed him in believing that species changed by inheriting acquired characters; those who believed that species did not change by any process; those who thought that possibly species did change, but by some process that had not been discovered. If any intel- lectual man was imaginative and had no special knowledge of animals, he was likely to belong to the first Camp and be a Lamarckian; if a man was a hard- headed specialist familiar with facts, he was likely to belong to the second camp; if he was an exceptionally thoughtful naturalist, familiar witk the difficulties of classification, he would have leanings toward the third camp. The great majority of scientists be- longed to the second group—at least after 1840, when the spell of Lamarck had begun to wane. Two ex- amples will show this. Weismann says that when he was a young student in Germany during the late fif- ties it was bad form scientifically to take any stock in an evolution theory. When Huxley was a young 270 EVOLUTION FOR JOHN DOE ‘man and first met Darwin about 1850, he made the remark which he felt sure was the correct thing to say to a great scientist: ‘‘I believe that species are immutable.’? Thus Lamarckism was tried in the bal- ances for half a century and found wanting. Any sketch of the history of the Evolution Theory should at this point repeat in italics the prin- cipal feature of all discussions before 1859: No one disputed the possibility that acqured characters could be inherited. This was one phase of that ques- tion which has always been paramount and which ts not yet settled—‘What is variation???’ Lamarck assumed—all scientists assumed—that variation is the alteration produced in the body of an organism by use or disuse or by changed environment, and that such alteration is inherited. The eyes of all the dis- putants were turned to acquired characters. And to what else could they turn? There was nothing else in sight. CHAPTER XX DARWIN THE son of the Hrasmus Darwin mentioned in Chapter XIX settled in Shrewsbury, built up a large practice, and became well-to-do; but he inherited no acquired theory of evolution. He named his fourth child, born in 1809, Charles Robert, and hoped that the boy would continue the family tradition by enter- ing the medical profession. But Charles could not endure the horrors and the dullness of the Edinburgh school of medicine. So at the age of nineteen he was sent to Cambridge to be educated for the ministry. ‘‘I liked the thought of being a country clergyman,’’ he says in his autobiog- raphy, ‘‘and did not then doubt the strict and literal truth of every word in the Bible. Nor was this inten- tion ever formally given up, but died a natural death when, on leaving Cambridge, I joined the Beagle as a naturalist.’’ In the classics he had no interest, but in any sort of experimental science, or in the study of insects and birds and shells, in geometry, in Paley’s Natural Theology, he delighted.