THE NEXT BIOLO3* LIBRARY G THE NEXT GENERATION A STUDY IN THE PHYSIOLOGY OF INHERITANCE BY FRANCES GULICK JEWETT «» AUTHOR OF THE FOLLOWING BOOKS OF THE GULICK HYGIENE SERIES "GOOD HEALTH," "TOWN AND CITY," "THE BODY AT WORK," "THE BODY AND ITS DEFENSES," AND "CONTROL OF BODY AND MIND" GINN AND COMPANY BOSTON • NEW YORK • CHICAGO - LONDON ATLANTA • DALLAS • COLUMBUS • SAN FRANCISCO COPYRIGHT, 1914, BY FRANCES GULICK JEWETT ALL RIGHTS RESERVED 518.9 BIOLOGY LIBRARY 6 gfte GINN AND COMPANY • PRO- PRIETORS • BOSTON • U.S.A. TO BOYS AND GIRLS THE GUARDIANS OF THE NEXT GENERATION 518749 ACKNOWLEDGMENT In offering this small volume to those who may read it the author wishes to express her own indebtedness, not alone to the men and to the women whose books have supplied her with facts and with inspiration, but also to relatives and personal friends who have shared in her work as coun- selors, and to authorities of distinguished attainment who have given the manuscript careful reading. Among these should be mentioned Professor Irving Fisher of Yale Uni- versity, Professor W. L. Tower and Professor G. H. Mead of The • University of Chicago, Professor Thomas M. Balliet of New York University, Dr. Luther H. Gulick of New York City, and Professor Adolf Meyer of the Johns Hopkins Universitv. Acknowledgment is also made to authors and to publishers through whose kindness many of the illustrations of this book have become possible ; also to Mr. Victor David Brenner for permission to represent on the cover his medallion, " The Successors to the Fates." Having been designed for the Fifteenth International Congress of Hygiene and Demog- raphy, this emblem most appropriately shows that " the distaff from which is spun the thread of life is held to-day by the forces of modern hygiene." FRANCES GULICK JEWETT CONTENTS PAGE INTRODUCTION ix CHAPTER I. FATHERS, MOTHERS, AND CHILDREN i II. ANDALUSIAN FOWLS 7 III. WHEN CHARACTERS ARE COMBINED 12 IV. MENDEL AND HIS GARDEN PEAS 20 V. LAWS OF INHERITANCE PUT TO USE 26 VI. EVOLUTION OF THE HORSE 34 VII. A FEW OF DARWIN'S FACTS 43 VIII. DARWIN'S PROBLEM 49 IX. FIVE LINKS TO THE CHAIN . 56 X. EVIDENCES OF EVOLUTION 64 XL ACQUIRED CHARACTERS AND MUTATIONS .... 72 XII. ISOLATION, OR LAND SHELLS ON HAWAII .... 81 XIII. CHANGED ENVIRONMENT FOR LEPTINOTARSA ... 88 XIV. NEW SPECIES THROUGH CHANGED ENVIRONMENT . 95 XV. BEGINNINGS OF THE NEXT GENERATION . . . . 100 XVI. THE MARVEL OF GROWTH no XVII. GERM CELLS DAMAGED BY ALCOHOL 118 XVIII. FROM FOURTEEN TO TWENTY 126 XIX. NICOTINE AND ADOLESCENCE 136 XX. ALCOHOL AS A BEVERAGE 145 XXI. THE CROWN OF EVOLUTION 153 XXII. FAMILY RESPONSIBILITY 162 XXIII. PROTECT THE STREAM OF LIFE 165 vii Vlll THE NEXT GENERATION CHAPTER PAGE XXIV. PREVENTION OF BLINDNESS 173 XXV. SAFETY FROM FEEBLE-MINDEDNESS 181 XXVI. OVERWORK FOR CHILDREN ONE HUNDRED YEARS AGO AND Now . 189 XXVII. THREE STEPS IN RACE IMPROVEMENT 196 XXVIII. THE FINAL STEP, OR RACE REGENERATION . . . 201 QUESTIONS 205 A PARTIAL LIST OF BOOKS USED IN THE PREPARA- TION OF THIS VOLUME 229 INDEX 231 INTRODUCTION In the days of myths in ancient Greece men talked about three Fates who were sisters. And in Rome an artist1 painted these sis- ters as they were supposed to be — three old women in a group, con- trolling the des- tiny of every human being. As they stand together in the pic- ture they neither weep nor smile ; they show neither joy nor sorrow, neither hope nor despair. Each is working, watch- ing, waiting. Clotho is the youngest sister. She holds the distaff which carries the thread of life. This thread begins to lengthen when the baby is born. Lachesis, the second sister, 1 Supposed to have been Michelangelo. ix THE THREE FATES x THE NEXT GENERATION spins out the thread as the years, go by ; and Atropos, the third sister Fate, stands by with huge shears. She is the oldest, the most haggard, the most cruel of them all, and she threatens the thread from the moment the spinning begins until she decides to cut it. Sometimes she clips her shears together and cuts when the thread has lengthened no more than a hand's breadth. This means that the baby dies very young. Sometimes the thread grows longer and longer, until yards of it have been spun off by Lachesis. This means that, although Atropos continued to threaten with her shears, she did not actually bring them together until years had passed and the baby had grown to be a man. The teaching of the picture of the myth is that human beings of every age, in every generation, are but the play- things of the Fates — that life is longer or shorter as the Fates decide, and that no act of man can change either his own destiny or that of his descendants. Here, then, is the difference between ancient myth and modern science. Nowadays science declares that man is by no means altogether helpless concerning his own future — that only the fool believes he cannot help himself. And, laden with facts to prove each point, science goes on to show how man may shorten his life or lengthen it, how he may bless his life or curse it, how he may make his life or mar it, by what he knows and by the way he puts his knowledge to use. Science does not stop even here, but, with proofs in hand, shows that the destiny of future generations lies in the hands of the men and the women, the boys and the girls, who are alive to-day. This book deals with the same absorbing topic. It tries to show how it is that science has crippled those ancient Fates, INTRODUCTION xi and why it is that a man who understands the laws of growth and of inheritance may, in a very real way, drive the crippled Fates from the field and help shape the future of the race. Some one has suggested that the three Fates of modern life are 1. Heredity — what we receive from our ancestors by the road of inheritance. 2. Environment — all that surrounds us and influences us from the cradle to the grave. 3. Personal choice or will power — what we make of ourselves during life. The analogy is not altogether perfect, but the following pages take each of these modern Fates into account. To understand inheritance we must follow life from pre- historic ages until now. From small beginnings we must trace large results — must learn how it is and why it is that all life on the earth is joined as a unit, and must know how life is passed on from generation to generation. We must even study life cells in their development, and watch them as they grow from stage to stage, until at last they become well-developed beings. In other words, we must learn so many facts about life itself and about what controls it, that we shall be better prepared to face our own lives and the lives of future generations. Science says human beings will be safer when people know the facts and are influenced by them. Teachers say, " Give us the facts and we will pass them on to the boys and the girls whom we teach." Both scientist and teacher agree that the human race will be better able to escape certain kinds of peril if we let young people know what the perils are and how to avoid them. Such is the purpose of this book. Hitherto the development of our race has been uncon- scious, and we have been allowed no responsibility for its right course. Now, in the fullness of time, we are treated as children no more, and _the_cpnscious fashioning of the human race is given into our hands. Let us put away childish things, stand up with open eyes, and face our responsibilities. WHETHAM THE NEXT GENERATION CHAPTER I FATHERS, MOTHERS, AND CHILDREN * At our county fair recently the animal that drew the crowd and won the prize was a huge Poland-China pig. He weighed twelve hundred pounds, measured seven full feet in length, was coal black with white feet and a white face, and had ears that flapped low. He had a turned-up nose, a curled-up tail, legs barely long enough to hold his body from the ground, and he cost exactly three thousand dollars. "But why did you pay so much ? " we asked the owner. " For three reasons," he said. 1. " The pig has a fine line of ancestors. 2. "He shows it in every part of his body. 3. "His descendants are sure to be like him and to bring fancy prices." From this man's point of view it was indeed clear that for the sake of the next generation even pigs must have the right sort of ancestors. And what about human beings, we wondered — the people next door and the rest of us ? Does the law apply to us all ? We thought them over, one by one, — neighbors to the north and to the south, to the east and to the west of us, . — men, women, and children who are set apart in families, with each family quite different from all the others. THE NEXT GENERATION Yet we knew that if a student of the laws of inheritance should come to town, and if he should hear certain definite facts about the ancestors of these neighbors, even without a glance at the men and the women themselves, or at their children, he would be able to go from door to door and nail on most of them a few definite statements about the children in the house. One label might read : " Every child here has light hair and blue eyes." Another : " Every child in this family has dark hair and dark eyes." Another : " Most of the children unusually bright." Still another : " Children dark-skinned with curly hair." And then if the same student should go to the small house around the corner, and should know what the parents and the grandparents of the children have been, the paper nailed to the door would read : " Every child in this family is either idiotic or feeble-minded." It is true that in many cases even the closest students of inheritance would not be able to make definite statements about color of hair, eyes, etc. Nevertheless, when all the doors had been labeled, those who read the statements would see that most of them told the truth about the children. Later chapters will show how it comes about that men are able to speak so positively about persons whom they have JONATHAN EDWARDS FATHERS, MOTHERS, AND CHILDREN 3 never seen. We know this is done. Perhaps, however, we hardly appreciate the tremendous power of the laws which tie the generations together. Take, for example, the record of the family of Jonathan Edwards. He himself was born in 1703. He was noted for his strength of character, for his mental power, and for his fearless loyalty to duty. Such was the character stamp which he had when he began to be an ancestor. As to whether or not his own character made any difference with the character of his descendants, nothing but facts will show, and here are some of them.1 In 1900, of the descendants of Jonathan Edwards, 1 394 had been located, and the occupations of many were ascertained. The following facts are quoted. College presidents 13 College professors 65 Doctors 60 Clergymen, missionaries, etc 100 Officers in the army and navy 75 Eminent authors and writers 60 Lawyers over 100 Judges 30 Holders of public offices, one being Vice President of the \Jnited States . 80 United States senators 3 Managers of railroads, banks, insurance companies, etc. 1 5 College graduates 295 Several were governors and holders of important state offices. The claim is also made that " almost if not every depart- ment of social progress and of public weal has felt the impulse of this healthy and long-lived family." 1 Taken from Mr. Winship's account of the descendants of Jonathan Edwards. 4 THE NEXT GENERATION The following statement touches another point. "It is not known that any one of them was ever convicted of crime." Such, then, is the well-authenticated record of a single family, living in the United States of America. Clearly enough, the world is better off because Jonathan Edwards became an ancestor. Take another American family, with another kind of fame. The " Jukes family " J it is called. The first discovered an- cestor of this group was a shiftless fisherman born in New York state in 1720. He had five daughters, and in the five generations since then the family has numbered 1200 per- sons. This includes 200 outsiders who have married into the family. Follow the occupations of some of these people. The facts are quoted from the printed record. Convicted criminals 1 30 Habitual thieves 60 Murderers 7 Wrecked by diseased wickedness 440 Immoral women fully one half Professional paupers 310 Trades learned by twenty. Ten of these learned the trade in prison. Think also of this other fact which the report brings out : During the years of their lives not paupers alone but also those who had committed robbery and murder and broken every law of decency had to be supported at public expense. That is to say, law-abiding and efficient citizens — those who stayed out of prison and out of the workhouse, those who worked hard with honest purpose to support themselves — had to pay taxes for the support of these lawless and in- efficient people who spent their days in prison and in the workhouse. 1 Not the real family name. Ill8 103 100 95 90 85 80 75 |,0 @* i 3 «60 • fc55 0 « 50 § 345 §40 35 30 25 20 15 10 5 °1 YEAR 00 1810 1820 1830 1840 1850 I860 1870 1880 1890 19( w 110 105 100 95 90 85 80 75 70 g •I V 60 * O q 55 5 50 g 03 45 g ^ 40^ 35 30 25 20 15 10 5 0 00 , / /' /' / / /' / / 1 / ,^'' 1 ' 1 ••?) > x " f, P ^ x ^ ^,-- y> x'' & » ^%j?=* ^'. / ^ ^ ^...^ xT~ -^JCix*^ f^ ^,^- — -/' \t$£- ...--- -••-''" Hf? * *<£^- '"..,- 22 ^:. — -- o-o-o-o- -0-0-0-0 J-OO-O-O o-o-o-o-< -o-o-o-o- D-0-O-O-O 500 1810 1820 1830 1840 1850 1860 1870 1880 1890 19 YEAR RATE OF INCREASE OF POPULATION IN DIFFERENT COUNTRIES (From " Statistical Atlas," Twelfth Census of the Unite -1 States) 6 THE NEXT GENERATION It is estimated that already this single family of Jukes has cost the state of New York over $1,250,000; and the expense still goes on, for each generation of descendants continues to be what its ancestors were. In the United States as a whole those of us who are able- bodied, clear-headed, and diligent are taxed over $100,000,- ooo each year for the support of criminals, paupers, the insane, the feeble-minded, and the diseased. This does not include the enormous sums paid out by ourselves in private charities. More serious still, thousands of those who were cursed from birth by the quality of their ancestors and by the surroundings in which they grew up are themselves now a curse to their descendants and to the communities in which they live. No wonder, then, that the relation of cause to effect in life is being studied now as never before in the history of the world. The truth is that there was never such an array of facts to show what the trouble is and how to escape it. Examine the chart which shows the rate of increase in national populations. Notice what is happening in the dif- ferent countries of the world. See how the millions of the inhabitants piled themselves up between the years 1800 and 1900. Imagine this rate of increase as it goes on for the next hundred years ; then think of the difference it will make in the outcome of things whether one kind of family or the other kind multiplies faster on the earth. The next few chapters give facts which show what the laws of inheritance are — laws which apply not only to poultry and to guinea pigs but to all living creatures, including man. CHAPTER II ANDALUSIAN FOWLS Selected eggs were in the incubator, and the men who owned them waited to see what the chicks would look like. It seems there are two distinct kinds of Andalusian fowls, — one pure-bred black, the other pure-bred white with dashes of black here and there, — and the owners had selected one bird from each group to be parents of the next generation of chicks. The question was whether these chicks would be black like one parent or white like the other parent, or whether they would show a mixture of the two colors. BLUE ANDALUSIAN PULLET The chickens come in three colors : blue, black, and white ; the larger number being blue each was a queer mixture of The answer came after the little creatures were hatched. Not a black one or a white one appeared among them black and white which is technically called blue. Was this an accident, the breeders wondered, or would the same thing happen over again if other Andalusian parents were chosen ? So they made another test. In the first ex- periment the father was black, the mother white. Now they 7 8 THE NEXT GENERATION changed the order. They chose a pure-bred white father and a pure-bred black mother. Again they waited for results, and again the chicks told the same story. Not a black one or a white one was among them ; all were as blue as the first group. From then until now the same experiment has always produced the same result. Whenever a black Andalusian , . fowl and a white Anda- lusian fowl have become parents, their chicks in the first generation have always grown up to be blue Anda- lusian fowls. They are a mixture and not pure-bred like their parents. Such a mixture is always called hybrid. Remember this word and its meaning. It is the opposite of pure-bred. All animals are hybrid un- less both parents are pure- bred of the same kind. The next step in this investigation was to gather facts about the descendants of the hybrids. Would they be blue like their parents or black like one grandparent or white like the other grandparent ? In making this experiment two blue ones were chosen as ancestors. The illustration shows what happened in the next genera- tion. One chick was white like one grandparent ; one was black like the other grandparent; two were blue like their parents. BLUE ANDALUSIAN COCK ANDALUSIAN FOWLS 9 Follow the illustration on the next page and see what came to pass when the different members of that mixed group of chicks became ancestors. The black one was mated with a black one from another family — not shown in the picture. Eggs were laid. These hatched out in proper fashion, and behold, every chick of the next generation was as black as its parents ; not one was blue like its grandparents. The white one was also mated with another white one from another family, and here the chicks in the next generation were all as white as their parents, with not a blue one among them to remind themselves of their blue grandparents. But when the blue ones were mated with others like them- selves, their children turned out precisely as did the children of the hybrids of the previous generation. That is, out of every four, one chick was black, one was white, and two were blue. These experiments have been repeated over and over again in different parts of the world, and the results are always the same. Stated concisely, they are as follows : 1 . When a pure-bred black Andalusian fowl is mated with a pure-bred black, all the descendants are pure-bred black ; and so long as black is mated with black, no white one and no blue one will ever appear in any generation of the family. 2. When a pure-bred white Andalusian fowl is mated with a pure-bred white, all the descendants are white ; and if white continues to be mated with white, no black one and no blue one will ever appear in later generations of the family. 3. When a pure-bred white is mated with a pure-bred black, not a member of the next generation will be pure-bred ; not one will be either black or white ; each will be a hybrid and each will be blue. 10 THE NEXT GENERATION 4. When a blue Andalusian fowl is mated with another blue hybrid like itself, one quarter of the offspring will be white, another quarter will be black, while the remaining half will be hybrid and will show it by being blue.1 COLOR INHERITANCE IN ANDALUSIAN FOWLS Follow the descendants of the first two and notice what occurs in successive genera- tions when a pure-bred black Andalusian fowl and a pure-bred white Andalusian fowl become ancestors. In studying the illustration remember that, in the second genera- tion of offspring, the black one and the white one are mated with pure-breds like themselves, which are not shown in the drawing With Andalusian fowls these laws of color inheritance never vary. They can always be depended upon. They con- tinue from generation to generation, and by knowing who the 1 The number of individuals in the diagram for each generation does not mean that there are always just so many chicks in each family. Instead, the number is chosen for no other purpose than to show the proportion of black and white and blue that comes in each generation of descendants when a black Andalusian fowl is mated with a white Andalusian fowl. Moreover, it is not meant that every family of four has one white, one black, and two blue chicks, but only that this is true on the average. There is just one chance in four that an egg will hatch out a white chick, one chance in four that the chick will be black, and one chance in two that it will be blue. ANDALUSIAN FOWLS II Andalusian ancestors are one can always tell what the color of the descendants will be. But inheritance is not always such an easy affair to follow. On the contrary, Andalusian fowls simply help us by showing what the laws are in their simplest form. We shall soon see that these same laws are in control even when inheritance seems nothing more than a tangled skein of chances. Take the guinea pig, for example. Here combinations occur which would be pretty hard to understand if it were not for Andalusian fowls. The next chapter deals with these guinea pigs. CHAPTER III WHEN CHARACTERS1 ARE COMBINED Between 1900 and 1905 about three thousand guinea pigs and several hundred rabbits were reared and housed and studied in the Zoological Laboratory of Harvard University. Professor Castle kept them in this laboratory of living crea- tures for the sake of seeing what he could do for descendants when he himself chose ancestors for them. His main work was with guinea pigs, and he chose them because they are small, because they do not eat much, do not take up much room, are easily cared for, and multiply fast. Perhaps the last reason was really the most important of all. The truth is, small animals have so short a time from one generation to the next — that is, from parent to child — that it is easy to trace resemblances between far-away ancestors and present-day descendants.2 Rabbits have a new generation every eight months, and guinea pigs multiply at the rate of four generations a year. This means that guinea pigs can have children, grandchildren, great-grandchildren, and great-great-grandchildren all within the same year. Thus guinea pigs are particularly well fitted to serve as helpers in answering questions about inheritance, for within a very few years the descendants show just what their long lines of ancestors have done for them. In size these animals are about as large as well-developed rats. But instead of being all of one color, as are rats, the 1 As used in books of this kind the word character means " characteristic." 2 All children of the same parent belong to the same generation. WHEN CHARACTERS ARE COMBINED 13 coats of guinea pigs show black, white, chocolate, yellow, or a mixture of certain shades of these different colors. For instance, spots of yellow-red and of blue-black, also dashes of black and of white, often occur in different combinations. But no combination of colors taught Dr. Castle plainer lessons GUINEA PIGS AND THEIR DESCENDANTS A dark, smooth mother and a rough albino father are at the top. Below is their son. He is black because, in guinea-pig inheritance, black is dominant over white ; he is rough because rough coat is dominant over smooth coat. At the bottom is a smooth, white grandchild of the black and the white grandparents. (After Castle, 1905.) Publication 23, Carnegie Institution of inheritance than those which he learned from guinea pigs that were plain black and plain white. Still, even these were more or less interesting according to another character of the coat that covered them. For some the coat was rough as a rug, with spots here and there that looked like " cowlicks " 14 THE NEXT GENERATION or rosettes ; others, both the long-haired and the short-haired, had coats smooth like silk. Some had fur so short that each separate hair stayed in place without being brushed ; others had hair so long that it could be combed and parted and brushed from side to side. Indeed, the length of hair for a full-grown guinea pig runs all the way from less than two inches on some to over six inches on others. But whatever the character of the fur, whether long or short, black or white, rough or smooth, Dr. Castle found that each one of these characters was transmitted from ancestor to descendant in accordance with definite laws, and that the laws themselves are quite like those which control the descendants of Andalusian fowls. At first sight this seems to be hardly true. Take, for exam- ple, his black guinea pigs mated with white albino1 guinea pigs. Judging by Andalusian fowls, we should expect to see a row of small blue guinea pigs in the next generation. But study the diagram and see what actually happened. One parent was pure-bred black, the other was pure-bred albino white, yet every child of theirs was as black as its black parent. Not a blue one or a white one was found anywhere among them. It looked as if each had inherited from its black parent alone — as if the white parent had not been taken into account at all. Still we know that every guinea pig in the row was bound to be hybrid ; we know there was no escape for them, because, one and all, they were the children of two different kinds of pure-bred parents. 2 "An albino is an animal with unpigmented eyes and with little or no pigment in its coat." — Castle. The eyes of an albino are pink because there is no pigment in the iris. The color of the blood vessels therefore shines through it. Albino guinea pigs always have pink eyes. There are white guinea pigs with black eyes. These are not albino. In this chapter it is the albino white that are mentioned. The other white ones are not pure-bred. WHEN CHARACTERS ARE COMBINED Why, then, were these hybrids black and not blue ? Simply because, with guinea pigs, black is the so-called dominant color. This means that when one parent is black and the other parent white, and when the two colors are therefore G? COLOR INHERITANCE IN GUINEA PIGS Although pure-bred black guinea pigs and hybrid black guinea pigs look alike, they are really different, and this difference appears in the color of their children. When a pair of black guinea pigs have only black children, we know the parents are pure- bred ; but when a pair of black guinea pigs have white children as well as black ones, we know their parents are hybrids. Study the illustration upwards from children to parents and decide which ancestors are pure, which hybrid. In doing this remember that in the second generation of offspring the black one and the white one are mated with pure-breds like themselves, which are not shown in the drawing. As you study the illustration keep the following facts in mind: i. Pure-bred black mated with white gives black in every member of the next generation. Still each is as distinctly hybrid as are the Andalusian fowls. 2. All are black and not blue, because, with guinea pigs, black is the dominant, white the recessive character. 3. Whenever a white guinea pig appears as the offspring of two black guinea pigs, we know that the parents were hybrids. (Find them in the illustration.) For this reason we can never tell whether a black guinea pig is pure or hybrid until we have seen its offspring. 4. Whenever all the children of two black guinea pigs are black, we know that at least one of the parents was pure. (Find them in the drawing.) 5. Whenever a white guinea pig mates with a white one, all the offspring are sure to be white. Compare this illustration with that of the Andalusian fowls. Note the differences to be passed on by inheritance to later generations of guinea pigs, the black dominates in the immediate next generatitin. The white color, on the other hand, is recessive; that is, it recedes from, sight and does not appear in any member 1 6 THE NEXT GENERATION of that next generation. These two words, dominant and recessive, are to be remembered, because, as we shall see later, they help us understand why one character and not another makes its appearance in succeeding generations. As we already know, with Andalusian fowls neither black nor white is either dominant or recessive. As a result, when the two are mated, the color of the next generation is neither black nor white, but a mixture of the two, and every member of the young family is blue. With guinea pigs, however, black dominates in such high- handed fashion that white is crowded entirely out of sight in the next family of descendants. White is therefore called the recessive color. Even hybrids among them are black. Study the illustration to see what occurs in each successive generation. Notice that the children of black hybrid guinea pigs are of three sorts, even as are the children of blue hybrid Anda- lusian fowls. f One is pure-bred white, like its white grandparent ON THE AVERAGE, ~ . , , , , , ,., . , , , OUT OF EVERY FOUR! One 1S Pure-bred black' hke lts black grandparent. j^Two are hybrid black, like the parents. It is evident, then, that nature does not always label children so clearly as Andalusian fowls are labeled, Nevertheless, in both cases the same great laws hold true for ancestors and descendants alike. Now go a step further. Dr. Castle tells us that color is not the only character which moves along in definite fashion, by definite laws. He says that when he mates a rough- coated guinea pig with one that has a smooth coat, all the little guinea pigs of the next generation, whether they are white or black, brown or yellow, have rough coats ; not one among them is smooth-coated. This means that rough coat is the dominant character and smooth coat the recessive character. WHEN CHARACTERS ARE COMBINED Again, when he takes a pure-bred guinea pig with short hair and gives it a mate with long hair, each small guinea pig in the next generation, whatever its color may be, has short hair. -This means that short hair is dominant, long hair recessive. Thus it turns out that, with guinea pigs, as THREE GENERATIONS OF GUINEA PIGS The first row shows a white, smooth-coated father, a black, smooth-coated mother, and their children. Each one of these is black and has a smooth coat. The second row shows a pair of these black hybrid children. The third row shows grandchildren who were children of the hybrids. Notice the white one among them. It resem- bles its grandfather. (From photographs furnished by Professor W. E. Castle of Harvard University) he says, " black is dominant over white, rough coat over smooth coat, short coat over long coat." By knowing these facts Dr. Castle is able to mate his guinea pigs in such wise as to secure precisely the kind of descendants he wishes them to have. They will be black or white, with long coat or with short coat, with rough coat or 1 8 THE NEXT GENERATION with smooth coat, with spots or bands or dashes of color, in exact accord with the ancestors he chooses for them.1 In all this discussion, remember that there are many hybrid mixtures of every kind of guinea pig, that hybrids are always more abundant than pure-breds, and that when men hunt for laws of inheritance, they are as careful as possible to start with pure-bred ancestors. And because these laws of inheritance also affect human beings, we are interested in them. Science is teaching that each one of us is a bundle of combined characters. Shape of head, of hands, and feet ; length of arm, of leg, and backbone ; color of skin, of hair, of eyes ; turn of nose and of jaw ; quality of brain-stuff ; type of temperament — all these are combined in different ways in each generation, and some of the characters may be clearly traced back through generation after generation of our ancestors. Speaking of this matter, Dr. Forel says : " In my own face the two halves are distinctly different, one resembling my maternal ancestor, and the other, in a lesser degree, my paternal ancestor ; these points being seen distinctly in photographs taken in profile." 2 He adds : "A person may have his father's nose and his mother's eyes ; his paternal grandmother's humor, and the maternal grandfather's intelli- gence, and all with infinite degrees of variation, for it is only a matter of more or less accentuated variations." Much less is known of mental than of physical inheri- tance, nevertheless Dr. Forel shows how it may explain the children of many a distinguished man. He says that "a common woman will lower the level of the offspring of a 1 All this is called w breeding for points." Nothing of the kind has been done for human beings. 2 Doubtless an unusual case. WHEN CHARACTERS ARE COMBINED 19 distinguished husband, and inversely. . . . Moreover," as he adds, "the most deceptive point is the contrast of a man of genius with his children who do not rise to his standard because they represent a combination of ancestral energies with their other parent." We shall return to this subject later in the book. The next chapter goes back to the man who first dis- covered that color, shape, etc. are inherited through the working of definite laws. No name to-day ranks higher among students of biology than that of Gregor Mendel, the man who studied flowers for the sake of understanding inheritance. CHAPTER IV MENDEL AND HIS GARDEN PEAS Those who watched the man must have wondered what possessed him. Every day they saw him in the gardens of the cloister there in Briinn, Austria, and every day they noticed that, al- though he was a teacher of science, he worked like a trained gardener over his growing pea vines. Moreover, strange to say, he did not seem to care so much about the flowers on the vines as about the shape and the color of the seeds and the seed pods. In the course of time the neighbors learned that the teacher's name was Mendel,1 and that alto- gether he had twenty-two different kinds of peas under cultivation. Probably they did not know that he was searching day and night for laws of 1 Gregor Johann Mendel was born in Heinzendorf, Austria, in 1822. He was always a faithful student, and became a priest in Briinn, Austria, in 1847. In J868 he was appointed abbot of the Konigskloster, where he had been priest. 20 GREGOR JOHANN MENDEL MENDEL AND HIS GARDEN PEAS 21 inheritance, and that he expected to find these laws just as surely by studying peas and their descendants as by studying animals and their descendants. For the sake of getting clear results he studied characters in pairs or groups, as it were. 1. The form of the ripe seed — whether round and smooth or angular and deeply wrinkled. 2. The color of the cotyledon — whether yellow or green. 3. The color of the seed coat — whether white, gray, or brown. 4. The form of the ripe seed pod — whether inflated and smooth or constricted between the peas and wrinkled. 5. The color of the unripe pod — whether green or bright yellow. 6. The way the flowers grew — whether they were bunched together at the top or scattered along on the stem. COLOR INHERITANCE IN PEAS A, pod of yellow peas; B, pod of green peas; C, offspring of A and B ; Z), offspring of C. Notice that in C yellow is dominant and green recessive, and that green appears again in D, just as white guinea pigs appear among the offspring of hybrid black guinea pigs. (From " Mendel's Principles of Heredity," by W. Bateson) 22 THE NEXT GENERATION 7. The height of the plant. One kind had a stem seven feet long, while the stem of another was but a foot long. Mendel kept each kind absolutely separate from all the others ; that is, he never let the pollen of one kind reach the stamens of another kind unless he himself put it there. By being so careful he knew precisely which parents headed the list of each set of descendants. He could also tell which characters crowded the others out in the next generation. Tho.se that dominated he called dominant; those that receded out of sight he called recessive. In fact, Mendel was the first man who ever used these words in this way, but they explain the case so well that nowadays we all use them. Here are some of the dominant and recessive characters of Mendel's peas in two separate columns. DOMINANT RECESSIVE Tallness. Dwarfness. Round seeds. Wrinkled seeds. Colored seed coats. White seed coats. Yellow albumen in cotyledon. Green albumen in cotyledon. Purple flowers. White flowers. Sometimes characters were neither dominant nor recessive, so that the next generation was of necessity a mixture. Mendel kept on with his work of crossing pollen, watching results, and writing records until eight full years had passed. Then at last, in 1865 and again in 1869, he reviewed what he had done, put his statistics together, came to his conclu- sions, and wrote them down for the benefit of other people. In these papers he told how he had developed new kinds of peas, why he had done it, and what laws of inheritance he believed he had discovered. When he read his papers to the scientific society at Briinn, he himself was excited and enthusiastic, but he saw plainly MENDEL AND HIS GARDEN PEAS 23 enough that those who listened were neither excited nor enthusiastic. Indeed, they hardly seemed even interested, and when the reading was over, Mendel's own excitement was gone. His heart was heavy with disappointment. He had expected so much, yet nothing came of it. After that GREEN ROUND YELLOW WRINKLED ) YR YW GR YR YR GR. GW O D J J J !> GR YW YR YW YR YR INHERITANCE OF SEED CHARACTERS IN PEAS Y, yellow ; G, green ; W, wrinkled ; R, round. Notice that when green round peas are fertilized by pollen from yellow wrinkled peas, the offspring (only one is shown) in the first filial generation (7^) are all yellow and round. This means that yellow and round are dominant, while green and wrinkled are recessive. Also notice that in the second filial generation (F2) the recessive green and wrinkled appear again in differ- ent combinations with the dominant characters. (From " Mendel's Principles of Heredity," by W. Bateson) his papers were simply printed and packed away to gather dust in the Briinn library. And there they stayed, out of sight and out of mind, unheard-of and undreamed-of, for thirty-four years. Fortunately, however, during all these years the library had them in safe keeping. 24 THE NEXT GENERATION Mendel himself died in 1884, and it is reported that many times before he died he was heard to say, " Meine Zeit wird schon kommen " (" My time will yet come "). Then at last it did come for in 1900, sixteen years after he had been buried and apparently forgotten, his priceless papers were discovered by younger scientists, and news of the discovery was telegraphed to all parts of the world. To-day every book that discusses inheritance takes Mendel and his laws into account. Every breeder who studies in- heritance in rats, rabbits, mice, guinea pigs, and men builds on foundations which Mendel laid over fifty years ago in his Austrian gardens. Every intelligent man who raises plants and animals for the market improves his stock according to laws which Mendel discovered. Indeed, in these days the whole subject of inheritance is stamped with his name. We speak of " Mendel's laws of inheritance " and of " Mendelism," which means the same thing. The truth is, the laws given in the last two chapters are nothing but Mendel's laws as we see them working through families of fowls and guinea pigs. Study the following statements carefully. Compare them with the diagram of Andalusian fowls, and see how well they go together. MENDEL'S LAWS STATED IN SIMPLE TERMS 1. When pure-breds are mated with other pure-breds like themselves, every one of their offspring will be pure-bred. Moreover, so long as pure-bred continues to mate with pure- bred, the descendants of every generation will continue to be pure-bred. 2. When a pure-bred of one kind is mated with a pure-bred of another kind, every member of the next generation is hybrid. MENDEL AND HIS GARDEN PEAS 25 3. When hybrids are mated with each other, half of their offspring will be hybrid, one quarter will be pure-bred like the father, the other quarter will be pure-bred like the mother. These, then, are Mendel's great laws of inheritance. He discovered them by studying averages taken for multitudes of cases. They apply equally well to plants and to animals of every kind in every land.1 Mendel discovered his laws through the help of garden peas. Other scientists have proved them through the help of rats, rabbits, mice, guinea pigs, and other small animals. We ourselves should make use of them for the advantage of our own descendants. 1 In 1900, just before Mendel's work had been discovered, these same laws of inheritance were rediscovered by three different students, who inves- tigated independently in three different countries — De Vries in Holland, Correns in Germany, and Tschermak in Austria. CHAPTER V LAWS OF INHERITANCE PUT TO USE During the year 1900 the National Association of British and Irish Millers decided that the wheat yield of Great Britain was far too small — that a better grade must be grown, and VARIETY IN HEADS OF WHEAT The upper row shows two parents with their offspring between them. The second row shows six types that belong to the next generation of descendants. (Photo- graphed from specimens supplied by Professor Biffen.) (From « Mendel's Principles of Heredity," by W. Bateson) that they themselves must have the benefit of this new wheat as promptly as possible. Accordingly they raised money and asked certain scientists to do what they could to produce the wheat for them. 26 LAWS OF INHERITANCE PUT TO USE 27 Professor R. H. Biffen, of Cambridge, England, was chosen as chief investigator. His first act was to get samples of wheat, each one of which had some especially fine quality. One bore grain on a stout stalk, another had a full head of wheat, another was beardless, another yielded a great amount of grain to the acre, still another could not be injured by the wheat disease called rust — that is, it was immune to this particular disease. These and other varieties reached Dr. Biffen from different countries, and he kept them strictly apart except as he himself planted and paired them according to the descendants which he wished them to have. He did no guessing about his work ; neither did he wait for haphazard results. He had studied the laws of inheritance, and he knew perfectly well that by selecting ancestors carefully enough, and by keeping cause and effect ever in mind, he could travel a straight road toward his desired end. After a fashion he was really forcing a new variety of wheat into existence, and he was so successful that in the course of time he presented the National Association of Millers with precisely what they wished. This new wheat had a strong stalk and a full head of grain kernels. It was rich in gluten and beardless. It could resist all attacks of the dreaded rust, and it yielded large quantities of grain to the acre. Science had helped nature evolve a wheat which satisfied even the clamor of the millers. They pronounced it a great success. And what of corn, that other food stand-by ? In the state of Washington, in 1912, two fields of corn grew side by side. Each covered ten acres ; each grew in the same kind of soil ; but, strange to say, one of these fields yielded about half as much again as the other. I asked what made the difference, and the farmer who owned the rich field gave a broad smile. 28 THE NEXT GENERATION " Well," he said, " I simply took corn ancestors into account, and my neighbor over there did n't pay any attention to them." " In what way ? " I asked. " The only possible way," came the answer. " I was care- ful where the seed came from. Last year most of my corn had one ear to the stalk, just as his has now ; but I noticed that some of my stalks had two ears to the stalk. So you see, that was my clue. Those ^vere the ones I saved for seed corn." How he smiled ! " Besides that," he went on, " even when there were two ears to the stalk, I never kept seed that grew on weak stalks. All that corn of mine"-— and he waved his hand triumphantly toward his ten acres — -u came from seed that grew on strong stalks ; each one of those stalks bore two ears apiece. And look at it now. More than half that corn has two ears to the stalk. Some of it carries three ears. Good investment, wasn't it ? " And he smiled again. Had this farmer owned Luther Burbank's seed corn, he might have done better yet, for Mr. Burbank has raised corn that grows sixteen feet into the air and bears thirty-two ears AN EAR OF CORN IN ITS HUSK LAWS OF INHERITANCE PUT TO USE 29 to the stalk. He has also grown a potato so fine that the United States Department of Agriculture says it is ''adding seventeen and a half million dollars a year to the farm incomes of America alone." There is no question about wheat and corn and potatoes ; man has changed them all for the better. And the list might be made many times longer, for nowadays the same laws of in- heritance are being used to improve tomatoes, watermelons, apples, grapes, beans, peaches, and other edible things. Then, too, there is the case of cotton to be rescued from the weevil. In the southern states of America the boll weevil is the pest of the cotton crop. It is a flying insect that punctures the flower buds and the bolls of cotton and lays its eggs within. Here these eggs hatch out into small worms which feed on the heart of the bud. This so damages the growing flower that it loses its vitality and falls to the ground before the cotton is formed. At last, however, a variety of cotton plant has been developed which not only bears cotton that is long and silky, but which flowers so early in the season that the cotton itself is ready to be picked before the boll weevil has harmed it. This single discovery will save thousands of bales of cotton every year. Laws of inheritance have certainly been pressed into prac- tical use in all sorts of directions. And now steps in Luther Burbank to show what can be done in securing beauty. He took the plant amaryllis, with its slender stem and its blossom two or three inches across, and from this he helped nature evolve a new amaryllis with low, sturdy trunk about eighteen inches high, and a blossom nearly a foot in diameter. He took the common, everyday poppy, multiplied its hybrids by tens of thousands, made careful selection of ancestors, kept THE NEXT GENERATION close watch of descendants, continued the selecting, the re- jecting, and the multiplying for several years, and to-day it is as if the flower had been glorified. Each blossom is from eight to ten inches in diameter. When one is placed above another in a column, seven of them will stand as high as a man. With a dozen of these blossoms in front of him, even VARIATION OF HYBRID POPPY LEAVES Out of two thousand plants no two were alike. (From " New Creations in Plant Life," by W. S. Harwood. Published by The Macmillan Company) a large man would be hidden out of sight. Mr. Burbank is even able to take " a single one of these new poppy-seed capsules, divide it into four sections, and, by pollinating each section, produce from one section an annual plant, from an- other a perennial, from the third quarter crimson poppies, from the fourth, white ones." He has also produced a blue poppy, unknown to the world before, and has changed the color of the native poppy of California from gold to crimson. LAWS OF INHERITANCE PUT TO USE 31 In addition he has transformed the plum and has made a combined fruit from the plum and the apricot. He has taken the old-fashioned wild daisy of New England, has combined it with daisies from Japan and England, and has secured the lovely Shasta daisy, .which has no rival. He has taken dif- ferent species of cacti, has crossed them carefully, and has secured varieties so free from thorns that they are a boon to THE DEVELOPMENT OF THE PLUM The two larger ones are seedlings of the other two. (From " New Creations in Plant Life," by W. S. Harwood. Published by The Macmillan Company) man and beast alike. Other so-called " spineless " cacti were already in existence, but government reports tell us that these are " all more or less spiny." Mr. Burbank's varieties, however, are so free from spines that, according to Dr. D. S. Jordan, he had " upwards of 500 kinds of edible cactus in 1908." Each one was the result of laws of nature guided by man. The same is true of changes brought about in animal life. Take sheep, for example. Some are liked because they are hornless, some for. the quality of mutton they supply, some for the long, soft wool they grow. Knowing what was THE NEXT GENERATION desired, and knowing how to secure results through inheri- tance, certain breeders in England claim to have produced a final and best variety of sheep. , Here all the wished-for characters have been so happily brought together that to-day breeders proudly show the result — a sheep which bears fine wool, is hornless, and yields the sort of mut- ton that meat-eaters like the best. Practical breeders have secured its evolution by con- trolling its ancestors. We may take cattle for another example. Shorthorns have been developed in England during the past hun- dred and fifty years. They are profitable for their beef and some- times for their milking qualities. Then there is the Jersey, famous for its rich cream. In 1904, at the World's Fair in St. Louis, a Jersey cow took the prize. And no wonder, for within seven and a half months her cream yielded over 547 pounds of butter. Holstein cattle are bred for the quantity of milk they give ; Hereford for the quality of their beef. Some are chosen for color, for shape, or for size ; others for their combination of characters. THE CACTUS In the foreground is the ordinary thorny kind ; those in the rear are the thornless ones of the same species, secured by Mr. Burbank. (From " New Creations in Plant Life," by W. S. Harwood. Published by The Macmillan Company) LAWS OF INHERITANCE PUT TO USE 33 Horses are bred not for quality of meat, not for texture of wool, but for the work they can do, for the speed they can make in running, for their shape, their color, and their general good looks. But all this is about modern changes in plants and animals. It is an account of forced evolution, as it were. It shows what takes place when man uses the laws of inheritance in this ~ • - JERSEY Cow, FIGGIS 76106 Property of C. I. Hood & Company, Lowell, Massachusetts. Champion and Grand Champion, World's Fair, St. Louis, 1904. Made 547 pounds 6 ounces of butter in seven and a half months. Such a cow is worth perhaps a dozen of the ordinary kind that make 125 pounds in a year direction or that, as he wishes to get something different in the next generation, and in the next, for indefinite periods of time. As we know, the whole era of this modern experiment lies within the memory of the human race.. There were, however, other eras and generations unnumbered, in ages before man began his reckoning, when evolution made the same resistless headway, yet moved at slower pace and without the aid of man. The horse best illustrates this prehistoric, slower evolution. CHAPTER VI EVOLUTION OF THE HORSE Hieroglyphics on ancient tombs show that, even so long as thirty-five hundred years ago, royal Egyptians went to war in chariots drawn by horses. Other records tell us that wher- ever man has gone since then in the development of civili- zation, he has taken the horse with him. To-day, therefore, we find this animal in all lands where man lives and can use him. And this use takes different forms. Horses are bred for strength, for speed, for gait, for looks, for size, for the ability to perform tricks, and for several other special pur- poses ; but no development of any sort changes them beyond recognition. By their looks, their acts, and their anatomy we decide without question that all modern horses are related to each other. Bear these facts in mind as you go to the American Museum of Natural History in New York City, and think about them as you visit what is called the Department of Vertebrate Paleontology. This is where many fossil bones1 are kept. 1 A fossil bone is one that has been gradually turned into stone during past ages. Little by little, through chemical action, mineral matter takes the place of the bone, and when the exchange is fully made, the bone it- self has really become rock. Thousands of years are needed for the change, but, once made, the fossilized bone is brittle and heavy and able to en- dure as long as the rocks themselves shall last. It is to this bone petri- faction that scientists owe their knowledge of animals whose skeletons have been preserved unchanged for millions of years. 34 EVOLUTION OF THE HORSE 35 When you reach the place, hunt for the horse bones. You will find them grouped together — skull bones here, leg bones there, jaw bones in a row by themselves. Each set is in its own glass case ; each is carefully mounted and labeled ; each is protected from meddlesome hands and from fire. Notice that all are arranged according to size, and that they show progress from smaller to larger. Courtesy of the American Museum of Natural History HORSE SKELETONS COMPARED The larger skeleton is of a horse of modern times. The smaller one (set in plaster) is of a primitive horse that lived three million years or more ago. (After Osborn) Give special attention to the skeletons — one sixteen inches high and about as large as a good-sized cat, another a giant that towers as high as the largest dray horse in a modern city. If both these skeletons were wrapped in flesh again, if they were alive and could move about and meet each other to-day, neither creature would whinny to the other, for neither would recognize the other as a flesh-and-blood relation. 36 THE NEXT GENERATION Nevertheless, science tells us that thousands of other bones have been found, that these are graded all the way between the smaller and the larger skeleton, and that they prove the following remarkable fact : The huge dray horse is as truly related to the small, catlike creature as we ourselves arc related to our own distant ancestors of prehistoric times. To be sure, the smaller animal lived as much as three mil- lion years before his big relative was born, and it was during this time that legs and jaw and skull bones went through their tremendous transformations. The diagram shows what these transformations were. Follow the foot as it changes into a hoof. Notice the middle toe. See it grow larger and larger, until the side toes are entirely crowded out of service. They do not so much as touch the ground. They hang in mid-air as the animal walks. It took lengthened ages for nature to bring this change about. Then, in course of time, all but the middle toe had vanished from sight. Gradually also the toenail part of the middle toe had turned itself into a pounding hoof. And to-day, as Dr. Matthew1 says, "the horse may be said to be an animal that walks on its middle finger nail, all the other fingers having disappeared." The nail itself has indeed become a hoof so broad and so strong that it is able to support the entire weight of the animal that travels through life upon it. Examine the legs of any modern horse and you may find traces of two earlier toes. These so-called splint bones are four or five inches above the hoof, and they are so far out of sight and out of the way that they do not hinder the animal either in walking or in running. Neither do they in any wise help the horse as he walks and runs. i Author of " Evolution of the Horse." Q 2 5 a « w S^ 37 38 THE NEXT GENERATION § See by the diagram that while toe bones were changing in this way, jaw bones and teeth were changing, too. Notice that the small jaw of the smallest horse had teeth close together all the way from back to front. Now trace the change. See the jaws stretch out in front little by little from generation to generation. Notice that even though the jaws grew longer, the num- ber of the teeth stayed the same. Not a new one arrived to fill up the gap. The front teeth stayed in front, the rest stayed on the back of the jaw, a growing gap separated the two sets, and that gap grew wider and wider, until our own kind of horse appeared. And it is because this modern horse has several inches of stretched-out jaw which carry no teeth whatever, that a twentieth-century man can guide a twentieth- century horse with bit and bridle. When you find a friendly horse some day, examine his mouth and make discoveries for yourself. At the same time think of his ancestors and try to imagine what men thought when they first found fossil bones of that most ancient, smallest horse. Dr. Matthew says that when its bones first came to light years ago, even students of such subjects did not so much as suspect that the little creature was a horse. Instead they called him Hyracotherium, meaning "the coneylike beast." But afterwards so many other bones were found in Nebraska, Arizona, Oregon, and elsewhere, that these same students were able to construct the bone pedigree of our modern horse. At the same time they named the different types, as the chart shows. They traced connections from smaller horse to larger, from four toes to one toe, from foot to hoof, from short jaw to long jaw, and as they did all this they saw that every bone, EVOLUTION OF THE HORSE 39 every tooth, and every part of the skeleton had been changed by slow degrees during unmeasured periods of past time. Moreover, with this knowledge as their basis, they knew they had in hand a key which would help unlock the mys- tery of all change in all animals, both ancient and modern. Head Fore Foot HindFoot Teeth OneToe. Splints of 2nd and 4th digits OneToe Splints of 2nd and 4th digits Protohippus Mesohippus ThreeToes SidTtoes not touching the ground ThreeToes Side~toes not touching the ground Long- Crowned, Cement- covered ra ThreeToes Side toes Aft touching the ground; Splint of Sthdigit Protorohippus ThreeToes Side toes touching the ground Four Toes Short- Crowned, without Cement Hyrac other ium (Eohippus) FourToes Splint of 1st digit ThreeToes Splint of 5th digit DRAWING OF SKULLS, FEET, AND TEETH OF PREHISTORIC HORSES, GROUPED FOR COMPARISON They show the development of the horse by evolution. (Reproduced, by permission, from " Origin and History of the Horse," by H. F. Osborn) As might be supposed, it takes two sets of scientists to make out the truth about buried bones. i. There is the geologist. He studies the earth itself, knows which parts of it were formed first, which later, and by knowing just where the bones came from, he tells us which 40 THE NEXT GENERATION animals lived earlier, which later. He assures us that the smallest horse bones are the oldest horse bones ever found. 2. The paleontologist comes next. He puts fossil bones together and tells us what kind of creature each animal was. It is the paleontologist who describes horse bones in the museum. He lets us see for ourselves that they are linked together from generation to generation, and that they make up an unbroken chain of ancestors and descendants. Other fossil bones tell tales of monster creatures that lived and changed and vanished from the earth long before man appeared. Each separate one yields its own separate story, but no set of bones is easier to study, none gives quite such a straight-ahead history, as the bones of the horse. These have been found in North and South America, in Europe, Asia, and Africa. Of all these places, however, Dr. Matthew says the best series comes from what is called the Tertiary Bad Lands of the Western United States. As you bear these bones in mind, turn to the finest horse you know and think of his pedigree. Also observe his present size and shape, his powerful muscles, his long and slender legs, his neck just long enough to carry his mouth to the ground for grazing. Look at his strong, broad hoof (he is the only single-hoofed animal in the world) and try to realize that it was the ancestors of this horse that made him what he is to-day. Many a man points proudly back to an ancestry more noble than himself. The horse might point backwards, too, not to show that once upon a time he had ancestors bigger, braver, more glorious than he himself is now, but simply to show that from small beginnings big results have come — to make it plain that, quite without conscious purpose, his early an- cestors improved their opportunities, adjusted themselves to Courtesy of the American Museum of Natural History COMPARATIVE SIZE OF THE ANCIENT AND THE MODERN HORSE The upper figure shows the skull of a large modern horse. The lower figure shows a prehistoric five-toed horse restored and placed here for comparison. (After Osborn) 41 42 THE NEXT GENERATION circumstances, and thereby so influenced their descendants that each generation passed a better inheritance on to the next. To-day if horses had the brain power of man, if they could study the past and talk about it as man is apt to do, each would have the right to say, " Through the struggle of my ancestors I am what I am." Since the laws of inheritance do not affect the horse alone, since they mold all other animals (including man), since they cover generations of time that sweep back beyond the reach of our reckoning, we understand why it is that scientists study the subject from year to year with an interest that never flags. They are determined to find out all they can about the laws which control and gradually change living beings as the ages go by. No one has spoken more clearly on this subject than Charles Darwin. For this reason the next chapter will give some of his facts. CHAPTER VII A FEW OF DARWIN'S FACTS Night after night Charles Darwin, already an aged man and famous, watched the actions of his angleworms. He kept them in his study in flowerpots, for he wished to find out for himself how ^ much mental power they had. He knew they could not see, for they had no eyes ; that they could not hear, for they had no ears ; that they could feel, for he had seen them shrink from the touch of any sharp thing. But the ques- tion was, Did they think as well as feel ? Did they guide their actions consciously ? This Charles Darwin wished to know. It happens that angleworms can only be studied at night, because by daylight they hide themselves underground, out of sight, but at night they stretch themselves out of their burrows and face the 43 CHARLES DARWIN 44 THE NEXT GENERATION world and run the risk of being captured. By night, there- fore, Darwin not only watched their operation in his flower- pots, but he also took his lantern and went into the fields to find them. Sometimes they raised themselves on their taper- ing, bent-over ends and seemed to be giving strict attention ; sometimes they shrank back into their burrows as if the light on their bodies gave unpleasant sensations. Darwin watched them as they seized leaves and drew them down to stop up the mouths of their burrows. He saw how they saved their lives and lost them ; how they did their burrowing ; how they gathered food and used it ; how they survived the winter rolled up in balls underground. For years the study went on, and no doubt it had really begun years earlier, when Darwin went a-fishing as a boy, for he writes : " I had a strong taste for angling, and would sit for any number of hours on the bank of a river or pond watching the float. I was told that I could kill worms with salt and water, and from that day I never spitted a live worm, though at the expense, probably, of some loss of success." This, then, is our introduction to the boy who was to become one of the world's most famous naturalists — the man who was to change certain beliefs of men for all future generations. No student of inheritance consents to be ignorant about Darwin. The work of his life lies between the time when, as a boy, he salted angleworms to save them from pain on his fish- hook by day, and when, as an aged man, he studied angle- worms by night for knowledge of their habits. It also appears that from the beginning of his life until it ended, Darwin's work knit itself together as two parts. A FEW OF DARWIN'S FACTS 45 1. He gathered facts. 2. He drew conclusions from his facts. Even before he was eight years old he collected shells and compared them with each other. Next he began beetle col- lecting. He was now a university student in Cambridge, England, and wherever he went in his walks, he was ready to see beetles and to seize them. This brought him to grief one day, for, as he says, " on tearing off some old bark, I saw two rare beetles, and seized one in each hand ; then I saw a third and new kind, which I could not bear to lose, so I popped the one which I held in my right hand into my mouth. Alas, it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as was the third one." And this is but. a sample of Darwin's enthusiasm from youth to old age ; he never lost it. On every side he gathered facts, and when he had facts enough, he began to draw con- clusions. No doubt his largest field for facts was South America. When he was twenty-two years old, he was asked to go as naturalist on board the Beagle^ He accepted the invitation ; spent five years in sailing from one country to another ; made collections everywhere ; and when he reached home again in 1836, he was laden with treasures and with the memory of his experiences. While in South America he came upon unnumbered fossil bones of buried monsters — creatures that had lived there and 1 This was a sailing vessel of 235 tons displacement. It was sent out on a voyage of scientific investigation by the English government, and Darwin went as naturalist for the expedition. As he himself states it, " The real object of the expedition was' to complete the survey of Patagonia and Tierra del Fuego, to survey the shores of Chile, Peru, and some islands of the Pacific, and to carry a chain of chronometrical measurements around the world." 46 THE NEXT GENERATION had died there before man had so much as appeared on the scene. He found head bones of some, leg bones of others, numberless huge teeth, and a few skeletons that were com- plete in every detail. Darwin named one of these the toxodon. He said it was as large as an elephant, and one of the strangest animals ever discovered. By its teeth he knew it had gnawed its food, just as rats and rabbits also gnaw when they eat ; and from THE BEAGLE LAID ASHORE FOR REPAIRS the position of its eyes and ears and nose he knew it was an animal that lived in the water. In one place he came upon what he calls " a perfect catacomb of monsters of extinct races." Keep the giants themselves in mind, then note these other facts : Within the memory of man no such creatures have been alive in South America ; all were extinct and turned to fossils when man first found himself in the land which had belonged to those earlier huge inhabitants. So true is this that in South America to-day the only wild living creatures are A FEW OF DARWIN'S FACTS 47 comparatively small — the tapir, the deer, the monkey, etc. Darwin says that ten specimens of the largest kinds weigh an average of but 250 pounds apiece. It is interesting to compare the size of these animals with the size of those in South Africa. There the elephant, the hippopotamus, the giraffe, eland, rhinoceros, and others are so large that ten members of the large kinds of animals weigh an average of 6040 pounds apiece. The strange fact about all this is that ages ago South American animals were quite as large as the present-day monsters of South Africa. Darwin says that at the very time when the animals of South America were becoming extinct, those of South Africa stayed alive through their descendants. Another set of Darwin's facts had to do with the horse. History tells us that when Columbus and his Spaniards came to America, not a horse was to be found in the land. They were, in fact, so unknown and unheard-of that when, years afterwards, a few were brought over from Europe, the native Indians looked at them with curiosity and fright. Im- agine, then, the surprise of Darwin and other naturalists when they found fossil horse bones in different places from the northern extremity of North America to the southern ex- tremity of South America. Clearly enough, horses were among the oldest inhabitants of the land ; yet, quite as clearly, not one had survived to receive Columbus. All had died and vanished from sight long before man arrived in modern times. Now it is interesting to know that while the largest early animals were dying off in South America they were also meeting the same fate everywhere else in the world except in Africa. The following statements bear on this point. I . Fossil remains which have been found in Europe, Asia, North America, and South America prove that ages ago 48 THE NEXT GENERATION animals of the same general kinds were alive in all three continents during the same era of the world's history. 2. The theory which explains this is that in early times there was land connection between Siberia and North America, and that the joining place was where Bering's Strait now separates the two continents. It is supposed that in those days this land connection was a well-traveled road, across which animals of every sort and size came as immigrants from the Old World to the New. " It seems most probable," writes Darwin, " that the North Ameri- can elephants, mastodons, horses, and the hollow-horned rumi- nants migrated on land since submerged near Behring's Straits, from Siberia into North America, and thence on land since submerged in the West Indies, into South America, where for a time they mingled with the forms characteristic of that southern continent, and have since become extinct." From first to last, Darwin was searching for facts which might connect one set of living creatures with all others. He wished, if possible, to relate the life of the past — even its monsters — to the life of the present. More than this, he wished to relate the life of the present to the life of the fu- ture. He hoped to find laws which would make it easier to understand why there are such countless varieties of living creatures on the earth to-day, and what their exact relation to each other is. In other words, the reason why Darwin gathered facts was because he was determined to find out as much as possible about the progress of life on the earth from generation to generation, through the ages of the past. This was the burden of his ambition, and facts were pil- ing up as the Beagle continued its voyage to the Galapagos Islands. CHAPTER VIII DARWIN'S PROBLEM The Galapagos Islands lie on the equator, six hundred miles from the western coast of South America. There are ten islands in the group, and here Darwin found animals unheard-of elsewhere in the world — tortoises by the Culpepper I. WenmanL 60 Miles ^Abinadon I. Bindloes I. Tower I. Narbcrouah I. Albermarle I. James I. ejatiaa Mel. Barrinytonl. Chatham I. Charles /. Hood's 1. THE GALAPAGOS ISLANDS thousand, that weighed one hundred pounds apiece and over. " I frequently got on their backs," he writes, " and then giv- ing a few raps on the hinder part of their shells, they would rise up and walk away ; but I found it very difficult to keep 49 SO THE NEXT GENERATION my balance." Here were lizards two and three feet long, one "terrestrial," the other "aquatic" -"the latter," says Darwin, " a hideous looking creature of a dirty black color, stupid and sluggish in .its movements." Sometimes these lizards weighed twenty pounds apiece or more. They went off on swimming parties a hundred yards from shore. As a certain sea captain said, " They go to sea in herds a-fishing, and sun themselves on the rocks, and may be called alliga- tors in miniature." In this surprising place Darwin found and named new species x of plants and animals by the dozen and the hundred. On every side he saw new birds, new reptiles, new shells, new insects ; and yet, as he himself says, " by innumerable trifling details of structure, and even by the tones of voice and plumage of the birds," these various creatures reminded him of those other creatures, similar yet so different, that had lived on 'the "temperate plains of Patagonia or the hot, dry deserts of northern Chile. . . . What is the explana- tion?" he asks. "Why were they created on American types of organization ? " 1 A species is a group of plants or animals in which the individuals are very much alike. For example, one species of violet has white blossoms, another has blue blossoms ; one has round leaves, another has leaves of lancet shape. Each is a different species, but all are violets. Then there are the humming birds. One species is almost as large as an English spar- row, other species are no larger than huge butterflies. One species has bright feathers on its neck that give it the name mbythroat, another has half a dozen stiff red feathers that stand above the others on its throat. All these are humming birds, but each is a different species. All other animals and plants are divided into species in the same way. Scien- tists do this for the sake of studying the life of the earth. They also put different species together to make a larger group, called a genus. They put genera together to make a family, and families together to make an order. Then come classes, divisions, and finally the animal and vegetable kingdoms. DARWIN'S PROBLEM 51 He had gone no farther than this with his questions when the Beagle returned to England in I836.1 And now began a new epoch in his life. He had his collection of fossils from South America. He also had his collection of modern skeletons from the same country, from the Galapagos Islands, from England itself ; and he wished to find some laws of life which would explain the differences between them, and which would, at the same time, show that all forms of life are connected. He asked himself whether or not the earlier kinds became extinct before the later ones were created ; why they became extinct ; why present-day creatures on the Galapagos Islands are more like the buried giants of South America than like modern animals in Africa ; why there are so many species of different plants and animals in the world, etc. The list of his questions was very long when he reached England, and he saw that he must have still more facts before he could even try to draw conclusions. To get these facts he turned his attention to pigeons, com- paring them with each other. Among them he found the Carrier pigeon, with its large nostrils, its wide mouth, its lengthened eyelids, its long, steady flight over land and water ; also the Tumbler, with its way of flying high up and tumbling down, heels over head, at unexpected moments. Then there was the Pouter, with its stretched-out body, wings, and legs, and its enormous crop, which it proudly inflates to prodigious size ; the Jacobin, with feathers that grow 1 During this voyage the Beagle visited the following places, in the order in which they are mentioned : Cape de Verde Islands, St. Paul's Rocks, Fernando, Noronha, South America, Galapagos Islands, Falkland Islands, Tierra del Fuego, Tahiti, New Zealand, Australia, Tasmania, Helena, As- cension. The Beagle did not go around the world, as at first intended. THE NEXT GENERATION backward down the back of the neck and stand up like a hood ; and, as conspicuous as any, the Fantail, with so many feathers in its tail (thirty or forty instead of twelve or fourteen) that it hardly looks like a pigeon at all. Darwin studied each kind, and he came to the conclusion that each had been secured through man's careful selection of pigeon ancestors — that not one had been created pre- cisely as he himself found it. He even went so far as to say he was sure " that the com- mon opinion of naturalists is correct, namely, that all have descended from the Rock pigeon. ... At least a score of pigeons might be chosen," he said, " which, if shown to an ornithologist and he was told that they were wild birds, would certainly, I think, be ranked by him as well-defined species." He talked the matter over with every intelligent bird breeder whom he met, and each assured him that the one essential thing was to select ancestors according to what was wanted in the next genera- tion. All acknowledged that the process took time. One told Darwin that " he could produce any given feather in three years, but that it would take six years to produce head and neck." In every case this selecting was done by the breeder himself. He knew precisely what he wanted. THE WILD PARENT OF NUMEROUS DOMESTICATED PIGEONS THAT HAVE BEEN DEVELOPED BY SELECTION (From " Domesticated Animals and Plants," by E. Davenport) DARWIN'S PROBLEM 53 The same was true of sheep breeders, and Darwin talked with them too. " In Saxony," he says, "the importance of TYPES OF PIGEON DEVELOPED BY SELECTION AND BREEDING i, Jacobins; 2, English Carrier ; 3, Duchess ; 4, Fantails ; 5, Birmingham Tumblers ; 6, English Pouter. (From " Domesticated Animals and Plants," by E. Davenport) the principle of selection in regard to merino sheep is so fully recognized that men follow it as a trade ; the sheep are placed on the table and are studied like a picture by the' 54 THE NEXT GENERATION connoisseur ; this is done three times, at intervals of months, and the sheep are each time marked and classed, so that the very best may ultimately be selected for breeding. . . . And," he continues, " not one man in a thousand has accuracy of eye and judgment sufficient to become a good breeder." Lord Sommerville speaks of their success : " It would seem as if they had marked out upon a wall a form perfect in itself, and then had given it existence." Do not forget that all this was before even the best breeders had heard of Mendel's laws and before Darwin himself had come to any conclusion about the power that controls the changing forms of life. Remember that even before Mendel and Darwin lived, breeders knew the following facts : 1. By choosing ancestors they could get the desired type of descendants. 2. Only by preventing cross mating could these new types be preserved. Darwin saw how easy it is to explain the beginning of any species when man is behind, controlling ancestors. But he wished to know how it comes about that wild animals have changed, too. He wondered if there might not be other laws which control descendants even when man has nothing to do with choosing ancestors for them. He believed there were such laws, and he hoped to find them. Darwin puzzled himself with this problem for twenty-three years, and at last he did what he could to answer it, in his book " On the Origin of Species by means of Natural Selection." The volume itself was published in 1859. Twelve hundred and fifty copies were printed for the first edition, and every one was sold on the day of publication. Three thousand more were printed. These went fast, too, and by 1876 sixteen DARWIN'S PROBLEM 55 thousand copies of the book had been printed and sold. It was translated into every European language and was dis- cussed by scientific papers in every scientific center of the world. It was a topic of talk for individual scientists as they met on the street, in the lecture hall, in the drawing-room, and everywhere else. Indeed, the excitement was so great that college students talked about the book in club and class- room. They sat up late at night in mighty discussion over Darwin's problem and over his solution of it. Certain mer- chants and preachers took up the subject and waxed eloquent about it over the counter and from the pulpit. And, as might have been expected, in every case those who knew most about the facts of life were usually most inclined to accept Darwin's theory about the origin of species. At the same time also, then as now, numberless persons lived in ignorance of Darwin's book and of what it taught. Until he died, in 1882, Darwin continued to gather facts, to draw conclusions, and to write about them for the benefit of those who were younger and more ignorant than he was. When he died he was seventy-five years old, honored and loved by thinkers the world over. His fame came through the success he had in studying certain problems of life, for his theory of evolution had turned upside down some of the cherished beliefs of the centuries. It was he who joined facts together in what we shall call the " five-linked chain." CHAPTER IX FIVE LINKS TO THE CHAIN I. THE PRODIGALITY OF NATURE At ten o'clock this morning I sat on the veranda and watched flying objects that traveled through the air ready for planting and for growing. Dandelion seeds, by scores and by hundreds, sailed across my vision like small parachutes bearing a precious burden. Maple seeds, thousands upon thousands of them, whirred by in zigzag fashion, steered without hands, guided by their delicate paddle rudders. They too bore their treasure of life and were ready for growing. Elm-tree seeds by the hundred thousand showered down like brown snowflakes in the sunshine, and rolled over each other as if in a panic of haste to find a lodging place for the elm trees of the next generation.1 As I watched all this I thought about the wasteful extrava- gance of nature. At the same time I stepped out to do some counting. Within one square inch of space I found twenty-five 1 These different kinds of seeds are not all in their prime at the same time, but in Ohio their seasons overlap each other. 56 DANDELION SEEDS READY FOR FLIGHT FIVE LINKS TO THE CHAIN 57 MAPLE SEEDS elm seeds crowded together in a heap. Near by, in another heap, on another inch of ground, were fifteen maple seeds piled upon each other, and there were many square yards of surface almost as thickly covered. One dainty dandelion stalk carried one hundred and fifty-four tiny parachutes in full sail, ready to fly off when the next carrier breeze came that way. All this was on my own lawn one bright spring morning. I then thought of the wooded groves just outside of town. I remembered the trees, the shrubs, the weeds, and the wild flowers — some in full bloom, others already gone to seed. I knew that millions of seeds were under the trees and on the shrubs in every forest during every spring season. I also knew that no more than tens or hundreds of these seeds ever take root and grow. I thought of the rivers too, and of the lakes, the ponds, and the ocean, with their millions of fish e£gs laid in every breeding spot — multitudes never to be hatched, other multitudes to be devoured by bigger fish as soon as hatched, and very few to live long enough to pass life on to the next generation. " Prodigality, prodigality, on every side ! " was my exclamation. Next I turned to printed records and looked for added facts of the same sort. Dr. Thompson says that a cod is reported to have two million eggs, and that " if these all developed into cods, there would soon be no more fishing." This means that the ocean would be so full of swarming, struggling, dying cod, that ELM SEED 58 THE NEXT GENERATION immigrants and emigrants alike would be able to walk across a slippery cod pathway between Europe and America. Dr. Thompson also says that " if all the progeny of one oyster survived and multiplied, its great-great-grandchildren would number sixty-six with thirty-three noughts after it (66,000,000, 000,000, 000,000,000, 000,000,000,000), and the heap of shells would be eight times the size of the world." No human mind can grasp such figures as these. They are indeed extreme examples of the first law of Darwin's famous five-linked chain. II. THE STRUGGLE FOR EXISTENCE The second law follows as a matter of course. Indeed, there is no escaping it, for with creatures of every kind multiplying at this rate, — with each of them obliged to find food or die, — the competition grows terrific. It becomes a struggle merely to keep alive. This, then, is the second link of Darwin's chain. It seems a peaceful world as I glance out of my window at the present moment. But, without seeing it done, I know that all forms of life are struggling not merely for food but for very existence too. Large insects are living on those that are smaller ; small birds are living on large insects ; birds are killing worms ; cats are killing birds ; dogs are killing rabbits ; man is killing and eating birds and beasts of many different kinds ; microbes are killing millions of creatures both large and small ; and man is killing microbes. The slaughter is universal ; the conflict is colossal. It con- tinues on every side every day, and it is inevitable. For if the supply of plants and animals were not limited in some way, — if all eggs were allowed to hatch and if all young animals lived on to good old age, — there would soon be such a battle FIVE LINKS TO THE CHAIN 59 on the earth as has never been dreamed of heretofore. Swarm- ing millions of creatures would, within a few days, crowd out of sight even the standing space of the earth. Soon after- ward the food supply of the world would be used up, and starvation would face all save those who found it possible to support their own lives by taking other lives. This is no fancy picture. It would be the inevitable state of things if the prodigality of nature were not checked some- how. Fortunately there are checks on every side. Wind and weather, flood and fire; take part in limiting the numbers of those that are to survive for a next generation. For the struggle is not simply between the individuals themselves but also between each individual and its surroundings. Clearly enough, then, the maimed, the weak, and the inefficient gen- erally have the poorest chance to live and become ancestors. And it is just because they do not live long enough to be- come ancestors that the race escapes deterioration. On every side they are crowded out in the struggle. III. VARIATION This fact brings us face to face with the third link in Dar- win's chain. He noticed that while some animals of a species, are large, others of the same species are small ; where some are strong, others are weak ; where some have keen intelli- gence, others are slow of understanding. He saw that always and everywhere, among all kinds of plants and animals, there are contrasts, differences, and variations. On this fact he based what he called the law of variation. It is the third link in Darwin's chain. Follow it now somewhat in detail. When rain was withheld for some months in South Amer- ica, Darwin saw thousands of animals die for lack of water ; yet there is such variety in the power of animals to endure 60 THE NEXT GENERATION thirst, that some did not die. When food failed for birds in snow-covered Ohio during the winter of 1913, farmers found many of them dead in the frozen fields ; yet there is such difference in the power of birds to endure hunger for longer or shorter periods, and such variety in their ability to hunt for food, that many of them did not die. In 1885, when typhoid microbes found their way into the water supply of Plymouth, Pennsylvania, noo men, women, and children had the fever and were threatened with death ; but there is such a difference in the power of individuals to resist disease that, although 114 persons died, 986 of those who were ill did not die, and hundreds of others who had used the same contaminated water were not even affected by it.1 When seven men offered themselves for the yellow-fever tests in Cuba in 1900, all were bitten by mosquitoes loaded with blood from yellow-fever victims. But even against this disease there is a difference in the power of the body to pro- tect itself. One man escaped with no touch of the fever whatever, six were ill. with it, and one man died.2 Many other cases might be cited of persons who, overtaken by calamity, have escaped death because they had some power pf endurance which those who died lacked. IV. SURVIVAL OF THE FITTEST 3 We are now within sight of the fourth link of Darwin's chain. He says that, because of the universal law of variation, 1 Described in "Town and City," of the Gulick Hygiene Series, p. 107. 2 Described in " Town and City," pp. 234-235. 3 Darwin first called this the law of natural selection, meaning that the selecting was done without man's help ; but some people misunderstood his meaning, so he adopted the phrase survival of the fittest, which Herbert Spencer used. It means precisely the same thing as natural selection, is easy to understand, and is the term in common use to-day. FIVE LINKS TO THE CHAIN 6 1 some members of each species are different enough from the others to survive in spite of threatened destruction. In other words, he tells us that it is the fit who survive. This, then, is the fourth link to the growing chain. See how this law works itself out. Some creatures have longer legs and are- therefore better fitted than their mates to run away when danger threatens. Some have stronger claws with which to kill the foe before being killed themselves. Some have keener eyesight with which to discover danger or to sight it from a distance and to escape it. Some have keener scent with which to trace both food and danger. Some can live longer than others when deprived of water. Some can survive a famine where others die in the midst of it. Thus, in one way and another, in every group of animals, when the critical moment comes, certain individuals are better fitted to survive than are their neighbors. This does on no account mean that the fittest are always the largest, the tallest, the keenest-eyed, the bravest, the strongest, or the longest-legged. Certainly not. The huge animals of South America were bigger than any of those that crowded them out ; English sparrows of the United States are smaller than bluebirds, swallows, robins, the purple martin, and other birds that please us ; but the smaller sparrow attacks the larger birds, takes up their nesting places, destroys their eggs, and finally succeeds in driving them from our villages. During heavy storms it is the birds with small bodies and strong legs and wings that survive, while birds with large bodies and small wings die in greatest numbers. Judging by appearance, certain animals — the donkey, for example — were better fitted to survive when their ears were large. It was different with moles. Living and working underground as they did, ears were a nuisance ; they got in 62 THE NEXT GENERATION the way. For this reason those with the smallest ears were best fitted to survive, and now we have the modern mole with ears so small that they are not worthy of mention. The change has come about gradually, step by step, through the laws of variation, the struggle for existence, and the survival of the fittest. Nevertheless, none of these laws would be of the slightest value from one generation to the next without that supreme law which forms the fifth and final link to Darwin's chain. V. HEREDITY The mere mention of this word carries us back to the first chapters of the book. It calls to mind Andalusian fowls and guinea pigs. It reminds us of all that inheritance does for the next generation and the next, when man selects ancestors and decides to bring about definite changes in animal de- scendants. But remember that Darwin was searching for laws which control the destiny of all descendants, whether their ancestors are selected by man or not. No human power ever chose the ancestors of the wild animals of to-day. Nevertheless, Darwin believed that these same ancestors were selected relentlessly by the five laws which controlled their fate — prodigality, the struggle for existence, variation, survival of the fittest, heredity. He be- lieved that all creatures that live to-day are what they are because the laws of nature chose their ancestors for them. Now connect the five links and apply the chain to last year's codfish. By the law of prodigality, thousands upon thousands of eggs were laid. Most of these were destroyed before hatching time came. After hatching, the struggle for existence began. By the law of variation these young cod- fish differed from one another as they continued the struggle. By the law of survival of the fittest only those who were FIVE LINKS TO THE CHAIN 63 most fit to survive were able to hold to life long enough to become ancestors. . By the law of heredity the characters of those that did survive were passed on to their codfish descendants. Scientists are still discussing Darwin's chain. Some put the emphasis on this link, some on that, but all agree in his claim that, even as all kinds of pigeons are descended from the same original ancestor, so too are all kinds of fish descended from their original ancestor, all kinds of birds from theirs, all mammals from theirs, and so on through the entire list. With one accord, indeed, scientists of to-day accept Dar- win's conclusion that, from the beginning of time until now, laws of nature have controlled the changing forms of life ; that each living creature of to-day is joined by close connec- tion to its ancestors of the past ; that living creatures both of the past and of the present move through the ages as a procession marching in lock step, and that every form of life is linked to distant ancestors by an endless chain of cause and effect. Through Darwin's discoveries we see that creative power has raised a structure of life on the earth which is welded together from foundation to summit. The evidences of this evolution are about us on every hand, and the next chapter points out a few of them. CHAPTER X EVIDENCES OF EVOLUTION Watch swimming fish in any pond or. aquarium ; even goldfish in a glass jar will answer the purpose. Notice those two small flaps, one on each side of the head. See them open and shut, and open and shut again, with never-failing regu- larity. They cover what are known as the gill-slits. These DOGFISH WITH GILL-SLITS WHERE THE ARROWS POINT slits open out from the gills, and gills are the breathing apparatus of the fish.1 Notice also that the mouth of the fish is open, too, and that, although he seems to be swallowing mouthful after mouthful of water, he really gets nothing to eat. The truth is, he is simply breathing with his mouth open. If he should shut his mouth and keep it shut, he would die of suffocation. To keep alive he needs oxygen as much as we do, and the only way he can get it is by taking water into his mouth and sending 1 Blood which circulates in the membranes of the gills takes oxygen from water which passes over them, just as blood which circulates in the mem- branes of lung cells takes oxygen from the air which enters the lungs. 64 EVIDENCES OF EVOLUTION 65 it out again through his gills within his gill-slits. As the water passes along, the red-blood corpuscles in the gills take out all the oxygen they need. When fish are drawn out of water and left on land, they die because they cannot get oxygen from the water in their usual way, through their gills. When we are held under water, we die because we cannot get oxygen from the air in our usual way, through the lungs. Since this is the case, zoologists1 expected to find gill- slits in embryo2 fish, and lungs in the embryos of animals that take their oxygen directly from the air. Imagine, then, the surprise of these men when they found gill-slits and lungs too in the embryo of all vertebrates, whether they were fish or not. Birds that are to live in trees and never swim, mice and men, monkeys and elephants, snakes and bats and vertebrate beasts of every sort — all these have gill-slits in the neck during the embryo stage. At the same time those that are to breathe air after birth have embryo lungs too. And this is not all. Even in Darwin's day the bodies of animals held other mysteries which no man could explain. It was well known that full-grown whales have rudiments 3 of hind legs concealed under the flesh ; that all embryo whales have rudimentary teeth, although after birth some kinds never have any teeth in their jaws ; that the python and the boa have rudiments of legs never used, never desired ; that calves before they are born have beginnings of front teeth in the upper jaw which never cut through the gums after birth. Notice that no cow has front teeth on the upper jaw. 1 A zoologist is a student of animal life. 2 Before birth a creature is called an embryo. 8 A rudiment is the beginning or foundation of any part or organ. 66 THE NEXT GENERATION The list might be made still longer. But no one explained these rudiments of legs, teeth, gill-slits, etc. until Darwin came with his five-linked chain and his proofs. He said that through millions of years unused parts of the body become more and more inefficient, until, in course of time, they have no power left. To prove this, think of the ancestral horse and his useless toes. Think of the fish in the dark recesses of Mammoth Cave, Kentucky. They are blind, but they have rudiments of eyes. Parasites in particular show the same degeneration from lack of use. One of the most extraordinary among these is the sacculina, as described by Dr. David Starr Jordan. It begins life by looking very much like a young crab. Both creatures have feelers, swimming apparatus, eyes, heart, brain, etc. But soon a change sets in. The crab, on the one hand, goes on developing. Feelers grow longer, brain grows bigger, eyes continue active, the heart never stops beating. In other words, the crab keeps active in every part and grows as it should. Not so with the sacculina. Soon after birth it fastens itself to the body of any conven- ient crab and stays there the rest of its life. It first sends a slender feeler down into the blood stream of the crab. This feeler lengthens each day like a ramifying root. At the same time branches of the root grow in this direction and that until they have entered the entire system of crab blood vessels. And as they ramify, they draw up from the blood of the crab all the nourishment the sacculina needs. Feelers have there- fore no work to do in hunting for food. Eyes are needed no longer. Heart and brain cease to serve. As a result they disappear, one after the other, until the sacculina finds itself nothing but a sac fastened to the body -of the crab — a sac EVIDENCES OF EVOLUTION 67 with root processes and reproductive organs. Everything else is gone, and, as the illustration shows, the parasite finally looks more like a growth of the crab itself than like a sepa- rate creature. The sacculina lives as long as the crab lives, and when the crab dies, it must die too. Now this record is simply an illustration of the result of disuse. Somewhat the same thing happens in other animals. SACCULINA ON THE ABDOMEN OF A CRAB Notice how the root processes of this parasite ramify through the legs and the body of the crab. (Adapted from Parker and Haswell) In many cases, however, unused parts remain as mere rudi- ments through later generations. Darwin makes three state- ments concerning this whole matter, which may be condensed as follows : 1 . All organs degenerate by disuse. 2. As any race of animals grows more and more success- ful in the struggle for existence, it develops new organs and 68 THE NEXT GENERATION may stop using old ones. If it stops using any part of its body, that part may be inherited as a rudiment. 3. The embryo of many vertebrates tells by its different parts what the history of the evolution of its ancestors has been. For example, when we find rudimentary teeth in the front upper jaw of an embryo calf, we know that once upon a time the ancestors of this calf had well-developed upper front teeth to aid them in their eating. When we find rudimentary legs hidden under the flesh of full-grown whales, we know that, in the ages of the past, whale ancestors used legs instead of fins for locomotion. So, too, with gill-slits. When we find rudiments of these in any embryo, we know that somewhere back in bygone ages the ancestors of this particular embryo lived in water and breathed through gill-slits. Evidently, then, each rudiment is nothing less than a signboard — a reminder of the road by which developing creatures have traveled from the past to the present. Each is a so-called ancestral reminiscence. Each declares that in the struggle for existence this organ or that had to be given up, and that other organs were developed instead. Our modern whale tells the story of a double change. To- day he is a queer combination — a mammal that lives in water and uses lungs for breathing. But his rudimentary legs and his rudimentary teeth prove that at some time in the past his ancestors were out-and-out land animals that roamed the fields on sturdy legs and used good-sized teeth for chewing. Also, by his embryonic gill-slits the same whale tells us that even before he was a land animal his ancestors were water animals with gill-slits for their breathing apparatus. EVIDENCES OF EVOLUTION 69 At the present time every whale in every ocean uses lungs and not gills when he breathes. Nevertheless, as a reminder of the ancient road which their ancestors traveled, every embryo of every whale has the double outfit — lungs and gill-slits too. Thus it is that rudiments repeat over and over again the long-drawn history of whale life. They show how the struggle for existence drove some early ancestors first from water to land, then back again from land to water. Scientists say that RORQUAL, THE GIANT OF THE ARCTIC SEAS One of these whales, captured on the British coast, measured 95 feet in length and weighed 249 tons by learning how to live in one environment after another, as they did, whales have shown that they were better fitted to survive than many of their fellow monsters who perished in the struggle. And all this lends a glow of romance to our modern whale, yet he himself is as indifferent as if no line of struggling ancestors had made him what he is. For the sake of studying the evidences of evolution in close relation to each other, they are now summarized in five separate statements. 70 THE NEXT GENERATION 1 . Structural evidence derived from the form and general make-up of animals. It is often found in rudimentary bones and organs — leg bones of the whale, for example, toe bones of the horse, etc. Darwin himself was thinking of structural evidence when he wrote, ''What can be more curious than that the hand of man, formed for grasping, the leg of the horse, the paddle of the porcupine, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones in the same relative position." 2. Embryological evidence. This includes such rudiments as are found in the embryo alone — gill-slits, for example. Without this important embryological evidence we should not so much as suspect that in early ages all vertebrates lived in the water. 3. Geological evidence gathered from fossil bones etc. This gives us the pedigree of the horse back to his five-toed ancestors, and shows what kind of creatures lived on the earth before man himself arrived. 4. Geographical evidence. This shows that creatures which are most alike are found nearest together. 5. Experimental evidence. Man gets this for himself when he chooses different varieties and breeds new species of animals. Taken all together, these five kinds of evidence prove that at some time in the past all vertebrates were very much more alike than their descendants are to-day ; and, as we have seen, these present differences are the result of the combined action of environment and heredity1. The two, working together, have caused such specialization along different lines that we now have many different types of vertebrates. Some of these 1 "By heredity we mean organic resemblance based on descent." - Castle. EVIDENCES OF EVOLUTION 71 live in the air, some live in the water, and some, as ourselves, live on land. And throughout the history of it all we see that in every case it was the fittest ancestors that were able to change their habits of life, able to save themselves from extinction when the THE LUNGFISH THAT LIVES BOTH ON LAND AND IN THE WATER In 1913 this fish was sent alive from the Gambia region of Africa to the American Museum of Natural History in New York City. It came "coiled up in a kind of cocoon, deeply sunken in a large clod of earth which months before had been the bottom of a stream." There was an opening through the clod so that air reached the fish. This kind of fish " breathes by means of gills when in the water, but with a lung during the summer drought, inhaling and exhaling air as if it were a land- living animal." In its degree of development it belongs with fossil fish that lived millions of years ago, because it is a transitional type — a water animal that is be- coming a land animal. The fish died soon after reaching New York, and its body is preserved in the Museum struggle was on, and able to pass certain kinds of characters on to the next generation. Thus it is that each generation takes its part in changing the history of later generations. But this is not all. The next chapter introduces another side of the subject. It shows what the difference is between characters that can be passed on and characters which can never be passed on by inheritance. CHAPTER XI ACQUIRED CHARACTERS AND MUTATIONS A young mother expressed the greatest disappointment over the fact that her daughter was not musical. " I simply cannot understand it," she exclaimed. " Before the child was born I spent hours every day practicing the piano, because I was determined to have at least one musical person in the family. Does n't science say that we can stamp our children this way or that before they are born ? I have proved that we can't." " Has she no musical ability whatever ? " I asked. " None at all," was the answer ; " neither have I ; neither has her father. That's precisely why I practiced so. I was trying to help the family out. I wanted to put musical power into it." "And you failed ? " I asked. " Absolutely," was the answer. "The trouble was with your own lack of information," I continued. She looked surprised, but I gave her no time to speak. "The process of evolution proves that we stamp our children according to what we are in ourselves, not accord- ing to what we make ourselves do. The doing is n't going to stamp children before they are born ; it is the being that does it. Is n't your daughter rather persistent ? " " Indeed she is," said the woman, looking at me in as- tonishment. " She's the most persistent thing you ever saw. But what gave you the idea? You haven't even seen her." 72 ACQUIRED CHARACTERS AND MUTATIONS 73 "No," I answered, "but from your story I see that you yourself are persistent, not musical. Where was her musical taste to come from if neither you nor her father had it ? You mustn't blame her. Laws of nature are responsible." This true story shows how it is that uninformed people often expect to secure what they desire without any reference to the laws of nature. For three hundred years and over, Chinese mothers bound the feet of CHINESE SHOES Two AND ONE HALF INCHES LONG The one on the left has been worn ; the one on the right shows how the foot was bandaged and cramped above the shoe their young daughters, and from generation to generation those feet were cramped from girlhood to middle age, old age, and death. Surely, if ever an acquired character1 was to be 1 An acquired character is secured by an individual during his own life, not by inheritance. Professor Weismann was the first scientist to give the words acquired character their present meaning. He says, " Acquired char- acters are those which result from external influence upon the organism, in contrast to such as spring from the constitution of the germ." 74 THE NEXT GENERATION inherited by oncoming generations of girls, this was the one. Mothers and grandmothers, great-grandmothers and great- great-grandmothers, back in direct line through all these generations, had done what they could to compel Chinese women to have small feet. And what success did they have ? Each baby born in each generation had as perfect feet as if no ancestral bones had ever been deformed. Moreover, when those feet were allowed to grow, they became as large and well shaped as if there never had been any foot-binding in China. This illustrates the fate of acquired characters. Facts show that they are not passed on. A woman may crimp her hair from the cradle to the grave, but unless she marries a man with curly hair, or unless there has been curly hair some- where back in the ancestry of the father or the mother, she will not succeed in giving curly hair to her children or to her children's children. Other characters are acquired, too. Eyes that have been weakened through overstrain ; hands calloused through rough work ; faces tanned through exposure ; firm or flabby muscles ; bent or straight backs; stiff or limber joints — these and many others are acquired characters. They can never teach the next generation through inheritance. In the flower gardens of Japan there are trees so dwarfed by human art that orange, pine, and plum are in full bloom and bearing fruit when they are no more than a foot high. Judging from appearances, these trees are a race by them- selves, and one would expect to find nothing but dwarfs among their descendants. But, strange to say, no seed of a tree that was dwarfed ever grows into a dwarfed descendant. Each successive generation has to be crippled and deformed and compelled to stay small by the aid of man. ACQUIRED CHARACTERS AND MUTATIONS 75 Dogs and sheep and horses in England have had their tails cut off for very many generations. Yet each pup, colt, and lamb born of these tail-docked ancestors has as normal a tail as if its ancestors had never endured any amputation. The acquired character of short tail has never been passed on and never will be. With such facts in mind we naturally ask how short-tailed cats came into existence, and how it is that such cats are able to pass on the short-tailed character. A series of rather star- tling facts points the way to a probable answer. They deal with what are called mutations. In more ordinary language a mutation is referred to as a sport, and a sport might be de- scribed as a living novelty which cannot be explained by its ancestors. To illustrate this : In Paraguay, in the midst of an ordinary herd of long-horned cattle there appeared one day a young bull destitute of horns. This was in 1 770. Not an ancestor of that small animal had been hornless, yet until he died he remained as hornless as when he was born. He was a mutation — a sport. An animal without horns is so easy to manage that this one pleased his owners, and they wished to have others like him. But as he was the only one of his kind, his pairing had FULL-GROWN JAPANESE PINE TREE Dwarfed by human skill 76 THE NEXT GENERATION to be done with ordinary horned mates. The results were unexpected certainly, and the owners were astonished. So many of his descendants had no horns that in the course of time there was established a race of hornless cattle from horned ancestors. Darwin tells us that short-legged Ancon sheep started in the same way —that in a herd of long- legged sheep there ap- peared one day this one little lamb with short legs ; that it lived to grow up and become an ancestor ; that among its own de- scendants there were sev- eral short-legged sheep. These could not jump fences and escape from the fold ; therefore sheep raisers selected them as ancestors of succeeding generations. As a result, short-legged sheep are A CASE OF POLYDACTYLISM The boy's father had twelve fingers and twelve toes, but the fingers were boneless. (Photo- graph by Professor Scott.) (From " Heredity in Relation to Eugenics," by C. B. Davenport) now the chosen type. They are found the world over, and appreciated everywhere. Mr. Poulton describes a family of cats with an extra toe. The first one came as a mutation. After this, for seven gen- erations of that family, the feet of all the kittens and cats were faithfully examined, and, by actual count, the majority of them were found to be supplied with one or two extra toes, making six or seven toes on each foot. ACQUIRED CHARACTERS AND MUTATIONS 77 From one point of view this is a calamity even for cats. Think, then, of the misfortune it is for human beings ! Yet such cases are on record. Professor Scott gives the photo- graph of a boy who began life with six fingers on each hand and six toes on each foot. His father had had the same num- ber. One of his brothers had extra toes, another brother had extra toes with one extra finger on his left hand, a sister had RADIOGRAPH OF NORMAL AND ABNORMAL HAND Notice that one hand has three joints to each finger, while the other has but two. (Photograph by Drinkwater.) (From " Mendel's Principles of Heredity," by W. Bateson) extra toes only, while five brothers and sisters had perfectly natural hands and feet. The condition of having too many fingers is called polydactylism. Besides this there is brachydactylism. The word itself means " short-fingeredness." All we know about the following case is that the woman had two joints instead of three joints to each finger. She married a man with perfectly normal, three- jointed fingers. They had eleven children, and facts are known 78 THE NEXT GENERATION about eight of them. Among these, as the diagram shows, four had short fingers and four had normal fingers. Study the diagram and see that in the next generation there were seven short-fingered persons and five that were normal. f ? Y f f : 98, 99 Toxodon (tok'so don), description of, 46 Treves, Sir Frederick, 146 University of Chicago, The, 96 Variation, Darwin's law of, 60 Vertebrates, evidences of similarity in, 70 ; individual life of, how started, 101 ; four statements in regard to, 113 INDEX 235 Vineland, as " a great human labora- tory," 183-185; methods adopted by, 183, 184, 1 88 Viviparous (vl vip'arus), 115 Watt, James, 1 57 Weismann, Professor, 73, 105 West Point, failure in entrance ex- aminations to, 141 Whale, its double change, 68 Wheat, variety in heads, 26 ; Pro- fessor Biffen's work with, 27 Wilson, Dr., 179 Wirthwein Hall, 149 Zoological Laboratory of Harvard University, 12 Zoologist, definition of, 65 Zygote (zi'got), definition of, 106 n. ANNOUNCEMENTS A NEW GULICK HYGIENE SERIES By FRANCES GULICK JEWETT THIS new series is built on the same principles that have made the original Gulick Hygiene Series the leader in its field. 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