The Project Gutenberg EBook of Being Well-Born, by Michael F. Guyer This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org Title: Being Well-Born An Introduction to Eugenics Author: Michael F. Guyer Editor: M. V. O'Shea Release Date: May 21, 2012 [EBook #39751] Language: English Character set encoding: ISO-8859-1 *** START OF THIS PROJECT GUTENBERG EBOOK BEING WELL-BORN *** Produced by Bryan Ness and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive.) BEING WELL-BORN BEING WELL-BORN AN INTRODUCTION TO EUGENICS By MICHAEL F. GUYER, Ph. D. Professor of Zoology, The University of Wisconsin Childhood and Youth Series Edited by M. V. O’SHEA Professor of Education, The University of Wisconsin INDIANAPOLIS THE BOBBS-MERRILL COMPANY PUBLISHERS Copyright 1916 The Bobbs-Merrill Company PRESS OF BRAUNWORTH & CO. BOOKBINDERS AND PRINTERS BROOKLYN, N. Y. TO MY WIFE HELEN M. GUYER EDITOR’S INTRODUCTION The writer recalls that when he was a young boy, he heard the grown-up people in the community earnestly and incessantly debating the question: Does heredity play a greater part in shaping one’s mind and body than does his environment? From that day to this he has listened to men and women in every walk of life discussing the relation of heredity to environment in determining human traits. Teachers and parents are constantly asking: “Are such and such characteristics in my children due to their inheritance or to the way they have been trained?” Students of juvenile delinquency and of mental defect and deficiency are searching everywhere for light on this matter. It is not to be wondered at that practically all people are peculiarly interested in this problem, since it concerns intimately one’s personal traits, and it constantly confronts any one who is responsible for the care and culture of the young. It is suggestive to note how people differ in their views regarding the extent to which a child’s physical and mental qualities and capacities are fixed definitely by his inheritance. The writer has often heard students in university classes discuss the subject; and their handling of the problem has shown how superficially and even superstitiously most persons regard the mechanism and functions of heredity. It is significant also to observe what extreme views many people hold regarding the possibility of affecting a child’s traits and abilities by subjecting him to specific influences during his prenatal life. In any group of one hundred persons chosen at random, probably seventy-five will believe in specific prenatal influence. Many of them will believe in birthmarks due to peculiar experiences of the mother. A popular book recently published asserts among other things that if a mother will look upon beautiful pictures and listen to good music during the prenatal period of her child, the latter will possess esthetic traits and interests in high degree. On the other hand, people generally do not seem to think that degenerate parents beget only degenerate children. Alcoholics, feeble-minded persons and the like are permitted to bring children into the world. Very few people have any precise knowledge of the mechanism of heredity. The whole thing is inscrutable to them, and is shrouded in mystery. Superstition flourishes among even intelligent persons in respect to heredity, and errors due to education, and tragedies resulting from vicious social organization are all alike ascribed to its uncontrollable forces. Most people are none the wiser because they do not know to what extent the physical and mental defects and deviations of individuals are due to inheritance or to the malign influences of the individual’s environment and training. Professor Guyer, who has studied the whole problem in a thoroughgoing, scientific way, has prepared this book with a view to illuminating some of the mysteries that surround the subject of heredity, and to dispelling the illusions that persist regarding it. He shows the method which nature follows in the development of the individual. He presents the laws which have become established respecting the extent to which and the manner in which immediate and remote ancestors contribute to the child’s physical and mental organism. He answers many questions which those who are engaged in social work or in education in the home or the school are asking to- day. He discusses subjects upon which every serious-minded person wishes to be informed. He has thus made a book which is both of theoretical and of practical interest. He has written in a style which should make his book attractive to the parent and the teacher as well as to the student of the complicated mechanism of inheritance. Only a few special terms are used, and these should not give any reader trouble, because the treatment throughout is so concrete that the meaning of the terms will be easily grasped. Further, the book is illustrated, with many attractive and instructive illustrations which will show at a glance the working of the principles of inheritance which are developed in the text. This book may be heartily commended to all who are interested in questions of human nature, education and social reform. It should enable the parent, the teacher and the legislator to understand more clearly than most of them now do in how far children’s traits and possibilities are or can be fixed by inheritance as contrasted with environmental conditions and nurture in home, school, church and institutional life. M. V. O’Shea. Madison, Wisconsin. PREFACE One of the most significant processes at work in society to-day is the awakening of the civilized world to the rights of the child; and it is coming to be realized that its right of rights is that of being well-born. Any series of publications, therefore, dealing primarily with the problems of child nature may very fittingly be initiated by a discussion of the factor of well-nigh supreme importance in determining this nature, heredity. No principles have more direct bearing on the welfare of man than those of heredity, and yet on scarcely any subject does as wide-spread ignorance prevail. This is due in part to the complexity of the subject, but more to the fact that in the past no clear-cut methods of attacking the manifold problems involved had been devised. Happily this difficulty has at least in part been overcome. It is no exaggeration to say that during the last fifteen years we have made more progress in measuring the extent of inheritance and in determining its elemental factors than in all previous time. Instead of dealing wholly now with vague general impressions and speculations, certain definite principles of genetic transmission have been disclosed. And since it is becoming more and more apparent that these hold for man as well as for plants and animals in general, we can no longer ignore the social responsibilities which the new facts thrust upon us. Since what a child becomes is determined so largely by its inborn capacities it is of the greatest importance that teachers and parents realize something of the nature of such aptitudes before they begin to awaken them. For education consists in large measure in applying the stimuli necessary to set going these potentialities and of affording opportunity for their expression. Of the good propensities, some will require merely the start, others will need to be fostered and coaxed into permanence through the stereotyping effects of proper habits; of the dangerous or bad, some must be kept dormant by preventing improper stimulation, others repressed by the cultivation of inhibitive tendencies, and yet others smothered or excluded by filling their place with desirable traits before they themselves come into expression. We must see clearly, furthermore, that even the best of pedagogy and parental training has obvious limits. Once grasp the truth that a child’s fate in life is frequently decided long before birth, and that no amount of food or hospital service or culture or tears will ever wholly make good the deficiencies of bad “blood,” or in the language of the biologist, a faulty germ-plasm, and the conviction must surely be borne home to the intelligent members of society that one thing of superlative importance in life is the making of a wise choice of a marriage mate on the one hand, and the prevention of parenthood to the obviously unfit on the other. In the present volume it is intended to examine into the natural endowment of the child. And since full comprehension of it requires some understanding of the nature of the physical mechanism by which hereditary traits are handed on from generation to generation, a small amount of space is given to this phase. Then, that the reader may appreciate to their fullest extent the facts gathered concerning man, a review of the more significant principles of genetics as revealed through experiments in breeding plants and animals has been undertaken. The main applications of these principles to man is pointed out in a general discussion of human heredity. Finally, inasmuch as all available data indicate that the fate of our very civilization hangs on the issue, the work concludes with an account of the new science of eugenics which is striving for the betterment of the race by determining and promulgating the laws of human inheritance so that mankind may intelligently go about conserving good and repressing bad human stocks. In order to eliminate as many errors as possible and to avoid oversights I have submitted various chapters to certain of my colleagues and friends who are authorities in the special field treated therein. While these gentlemen are in no way responsible for the material of any chapter they have added greatly to the value of the whole by their suggestions and comments. Thus I am indebted to Professor Leon J. Cole for reading the entire manuscript; to Professors A. S. Pearse and F. C. Sharp for reading Chapter VII; to Professor C. R. Bardeen for reading special parts; to Doctor J. S. Evans for reading Chapter VI and part of V; to Doctor W. F. Lorenz, of the Mendota Hospital, for reading Chapter VIII; to Judge E. Ray Stevens for reading Chapter IX, and to Helen M. Guyer for several readings of the entire manuscript. Grateful acknowledgment is made to all of these readers, to various publishers and periodicals for the use of certain of the illustrations, to the authors of the numerous books and papers from which much of the material in such a work as this must necessarily be selected, and to my artist, Miss H. J. Wakeman, for her painstaking endeavors to make her work conform to my ideas of what each diagram should show. M. F. G. CONTENTS CHAPTER PAGE I Heredity 1 Blood heritage—Kind determined by origin—Ancestry a network—Ancestry in royalty— Offspring derived from one parent only—Dual ancestry an aid in studying heredity— Reversion—Telegony—Prenatal influences apart from heredity—Parent body and germ not identical—A hereditary character defined—Hereditary mingling a mosaic rather than a blend—Determiners of characters, not characters themselves, transmitted—Our knowledge of heredity derived along three lines—The method of experimental breeding— The statistical method—Galton’s law of regression—Correlations between parents and offspring—The biometrical method, statistical, not physiological—Mental as well as physical qualities inheritable. II The Bearers of the Heritage 20 The cell the unit of structure—Unicellular organisms—Importance of cell-theory— Heredity in unicellular forms—Reproduction and heredity in colonial protozoa— Conjugation—Specialization of sex-cells—The fertilized ovum—Advancement seen in the Volvox colony—Natural death—Specialization in higher organisms—Sexual phenomena in higher forms—Cell-division—Chromosomes constant in number and appearance— Significance of the chromosomes—Cleavage of the egg—Chief processes operative in building the body—The origin of the new germ-cells—Significance of the early setting apart of the germ-cells—Individuality of chromosomes—Pairs of chromosomes— Reduction of the number of chromosomes by one-half—Maturation of the sperm-cell— Maturation of the egg-cell—Parallel between the two processes—Fertilization— Significance of the behavior of the chromosomes—A single set of chromosomes sufficient for the production of an organism—The duality of the body and the singleness of the germ —The cytoplasm in inheritance—Chromosomes possibly responsible for the distinctiveness of given characters—Sex and heredity—Many theories of sex determination—The sex-chromosome—Sex-linked characters in man—In lower forms. III Mendelism 67 New discoveries in the field of heredity—Mendel—Rediscovery of Mendelian principles —Independence of inheritable characters—Illustration in the Andalusian fowl—The cause of the ratio—Verification of the hypothesis—Dominant and recessive—Segregation in the next generation—Illustrated in guinea-pigs—Terminology—The theory of presence and absence—Additional terminology—Dominance not always complete—Modifications of dominance—Mendel’s own work—Dihybrids—Getting new combinations of characters —Segregations of the determiners—Four kinds of gametes in each sex—The 9:3:3:1 ratio —Phenotype and genotype—The question of blended inheritance—Nilsson-Ehle’s discoveries—Such cases easily mistaken for true blends—Skin-color in man— Questionable if real blends exist—The place of the Mendelian factors in the germ-cell— Parallel between the behavior of Mendelian factors and chromosomes—A single chromosome not restricted to carrying a single determiner. IV Mendelism in Man 97 Probably applicable to many characters in man—Difficult to get correct data—A generalized presence-absence formula—Indications of incomplete dominance—Why after the first generation only half the children may show the dominant character—Eye-color in man—Hair-color—Hair-shape—Irregularities—Digital malformations—Eye defects— Other defects inherited as dominants—Recessive conditions more difficult to deal with— Albinism—Other recessive conditions in man—Breeding out defects—Other inheritable conditions in man. V Are Modifications Acquired Directly by the Body Inherited? 121 Which new characters are inherited?—Examples of somatic modifications—Use and disuse—The problem stated—Special conditions in mammals—Three fundamental questions—External influences may directly affect the germ-cells—Such effects improbable in warm-blooded animals—Poisons may affect the germ-plasm—How can somatic modifications be registered in germ-cells?—Persistence of Mendelian factors argues against such a mode of inheritance—Experiments on insects—On plants—On vertebrates—Epilepsy in guinea-pigs—Effects of mutilations not inherited— Transplantation of gonads—Effects of body on germ, general not specific—Certain characters inexplicable as inherited somatic acquirements—Neuter insects—Origin of new characters in germinal variation—Sexual reproduction in relation to new characters— Many features of an organism characterized by utility—Germinal variation a simpler and more inclusive explanation—Analysis of cases—Effects of training—Instincts—Disease— Reappearance not necessarily inheritance—Prenatal infection not inheritance—Inheritance of a predisposition not inheritance of a disease—Tuberculosis—Two individuals of tubercular stock should not marry—Special susceptibility less of a factor in many diseases —Deaf-mutism—Gout—Nervous and mental diseases—Other disorders which have hereditary aspects—Induced immunity not inherited—Social, ethical and educational significance of non-inheritance of somatic modifications—No cause for discouragement— Improved environment will help conserve superior strains when they do appear. VI Prenatal Influences 159 All that a child possesses at birth not necessarily hereditary—The myth of maternal impressions—Injurious prenatal influences—Lead poisoning—The expectant mother should have rest—Too short intervals between children—Expectant mothers neglected— Alcoholism—Unreliability of most data—Alcohol a germinal and fetal poison—Various views of specialists on the effects of alcoholism on progeny—The affinity of alcohol for germinal tissue—Innate degeneracy versus the effects of alcohol—Experimental alcoholism in lower animals—Further remarks on the situation in man—Much inebriety in man due to defective nervous constitution—Factors to be reckoned with in the study of alcoholism—Venereal diseases—The seriousness of the situation—Infantile blindness— Syphilis—Some of the effects—A blood test—Many syphilitics married—Why permit existing conditions to continue?—Ante-nuptial medical inspection—The perils of venereal disease must be prevented at any cost—Bad environment can wreck good germ-plasm. VII Responsibility for Conduct 195 All mental process accompanied by neural process—Gradations in nervous response from lower organisms to man—Behavior of many animals often an automatic adjustment to simple external agents—Tropisms—Certain apparently complex volitions probably only tropisms—Complicating factors—Many tropic responses apparently purposeful— Tropisms grade into reflex actions and instincts—Adjustability of instincts opens the way for intelligent behavior—Modification of habits possible in lower animals—Some lower vertebrates profit by experience—Rational behavior—Conceptual thought probably an outgrowth of simpler psychic states—The capacity for alternative action in higher animals —The elemental units of the nervous system are the same in lower and higher animals— Neuron theory—Establishment of pathways through the nervous system—Characteristic arrangements of nerve cells subject to inheritance—Different parts of the cortex yield different reactions—Skill acquired in one branch of learning probably not transferred to another branch—Preponderance of cortex in highest animals—Special fiber tracts in the spinal cord of man and higher apes—Great complexity in associations and more neurons in the brain of man—The nervous system in the main already staged at the time of birth— Many pathways of conduction not yet established—The extent of the modifiable zone unknown—Various possibilities of reaction in the child—Probable origin of altruistic human conduct—Training in motive necessary—Actual practise in carrying out projects important—Interest and difficulty both essential—The realization of certain possibilities of the germ rather than others is subject to control—We must afford the opportunity and provide the proper stimuli for the development of good traits—Moral responsibility. VIII Mental and Nervous Defects 228 Prevalence of insanity—Imperfect adjustments of the brain mechanism inheritable—Many mental defectives married—Disproportionate increase in number of mental defectives— Protests voiced by alienists—Examples of hereditary feeble-mindedness—Difficult to secure accurate data—Feeble-mindedness and insanity not the same—Many types of insanity—Not all insanities of the same eugenical significance—Difficulties of getting genealogies of specific forms of insanity—Certain forms of insanity seem to behave as Mendelian recessives—Grades of feeble-mindedness—About two-thirds of feeble- mindedness inherited—Some results of non-restraint of the feeble-minded—Not all cases of mental deficiency inherited—Epileptics—Feeble-mindedness probably a recessive— Many apparently normal people are carriers of neuropathic defects—Tests for mental deficiency—The backward child in school—The exceptionally able child—Cost of caring for our mentally disordered—Importance of rigid segregation of the feeble-minded— Importance of early diagnosis of insanity—Opinion of competent psychiatrists essential— Some insanities not hereditary—Importance of heredity in insanity not appreciated. IX Crime and Delinquency 263 Heredity and environment in this field—Feeble-mindedness often a factor—Many delinquent girls mentally deficient—Institutional figures misleading—Many prisoners mentally subnormal—Inhibitions necessary to social welfare—The high-grade moron a difficult problem—Degenerate strains—Intensification of defects by inbreeding—Vicious surroundings not a sufficient explanation in degenerate stocks—Not all delinquents defectives—No special inheritable crime-factor—What is a born criminal?—Epileptic criminal especially dangerous—The mental disorders most frequently associated with crime—Bearing of immigration on crime and delinquency—Sexual vice—School instruction in sex-hygiene—Mere knowledge not the crux of the sex problem—Early training in self-restraint an important preventive of crime and delinquency—Multiplication of delinquent defectives must be prevented. X Race Betterment Through Heredity 289 Questionable charity—Past protests—An increasing flood of defectives—Natural elimination of defectives done away with—Why not prevent our social maladies?— Eugenics defined—Improved environment alone will not cure racial degeneracy— Heredity and environment—Inter-racial marriage—Human conservation—Kindness in the long run—The problem has two phases—Constructive eugenics must be based on education—Inferior increasing more rapidly than superior stocks—An unselected population may contain much valuable material—The lack of criteria for judging fitness— The college graduate—Native ability, independence and energy eugenically desirable— Four children to each marriage required to maintain a stock—Factors contributing to low birth-rate in desirable strains—The educated public must be made to realize the situation —Utilization of family pride as a basis for constructive eugenics—The tendency for like to marry like—Public opinion as an incentive to action—Choosing a marriage mate means choosing a parent—The best eugenic marriage also a love match—The elimination of the grossly unfit urgent—Suggested remedies—Inefficacy of laws which forbid marriage of mental defectives—Systems of mating impracticable in the main—Corrective mating presupposes knowledge of eugenics—Segregation has many advocates—Sterilization as a eugenic measure—To what conditions applicable—In insanity—In feeble-mindedness —In cases of epilepsy—Sterilization laws—Social dangers in vasectomy—Our present knowledge insufficient—Sterilization laws on trial—An educated public sentiment the most valuable eugenic agent—The question of personal liberty—Education of women in eugenics needed—Much yet to be done—A working program—Which shall it be? Glossary 343 References for Further Reading and Study 355 Index 361 BEING WELL-BORN CHAPTER I HEREDITY It is a commonplace fact that offspring tend to resemble their parents. So commonplace, indeed, that few stop to wonder at it. No one misunderstands us when we say that such and such a young man is “a chip off the old block,” for that is simply an emphatic way of stating that he resembles one or the other of his parents. The same is true of such familiar expressions as “what’s bred in the bone,” “blood will tell,” and kindred catch phrases. All are but recognitions of the same common fact that offspring exhibit various characteristics similar to those of their progenitors. Blood Heritage.—To this phenomenon of resemblance in successive generations based on ancestry the term heredity is applied. In man, for instance, there is a marked tendency toward the reappearance in offspring of structures, habits, features, and even personal mannerisms, minute physical defects, and intimate mental peculiarities like those possessed by their parents or more remote forebears. These personal characteristics based on descent from a common source are what we may call the blood heritage of the child to discriminate it from a wholly different kind of inheritance, namely, the passing on from one generation to the next of such material things as personal property or real estate. Kind Determined by Origin.—It is inheritance in the sense of community of origin that determines whether a given living creature shall be man, beast, bird, fish, or what not. A given individual is human because his ancestors were human. In addition to this stock supply of human qualities he has certain well-marked features which we recognize as characteristics of race. That is, if he is of Anglo-Saxon or Italian or Mongolian parentage, naturally his various qualities will be Anglo-Saxon, Italian, or Mongolian. Still further, he has many distinctive features of mind and body that we recognize as family traits and lastly, his personal characteristics such as designate him to us as Tom, Harry, or James must be added. The latter would include such minutiæ as size and shape of ears, nose or [Pg 1] [Pg 2] hands; complexion; perhaps even certain defects; voice; color of eyes; and a thousand other particulars. Although we designate these manifold items as individual, they are in reality largely more or less duplicates of similar features that occur in one or the other of his progenitors, features which he would not have in their existing form but for the hereditary relation between him and them. “O Damsel Dorothy! Dorothy Q.! Strange is the gift that I owe to you; · · · · · What if a hundred years ago Those close-shut lips had answered ‘No,’ · · · · · Should I be I, or would it be One-tenth another, to nine-tenths me?” “Soft is the breath of a maiden’s yes; Not the light gossamer stirs with less; But never a cable that holds so fast Through all the battles of wave and blast, And never an echo of speech or song That lives in the babbling air so long! There were tones in the voice that whispered then You may hear to-day in a hundred men.” When life steps into the world of matter there comes with it a sort of physical immortality, so to speak; not of the individual, it is true, but of the race. But the important thing to note is that the race is made up, not of a succession of wholly unrelated forms, but a continuation of the same kind of living organisms, and this sameness is due to the actual physical descent of each new individual from a predecessor. In other words, any living organism is the kind of organism it is in virtue of its hereditary relation to its ancestors. It is part of the biologist’s task to seek a material basis, a continuity of actual substance, for this continuity of life and form between an organism and its offspring. Moreover, inasmuch as the offspring is never precisely similar to its progenitors he must determine also what qualities are susceptible of transmission and in what measure. Ancestry a Network.—From the fact that each child has all of the ancestors of its mother as well as of its father, arises the great complications which are met with in determining the lineage of an individual. A person has two parents, four grandparents, eight great grandparents, and thus following out pedigree it is plain to be seen that through this process of doubling in each generation, in the course of a few centuries one’s ancestry is apparently enormous. By actual computation, according to Professor D. S. Jordan, if we count thirty generations back to the Norman invasion of England in 1066, at this ratio of duplication, the child of to-day would have had at that time an ancestry of 8,598,094,592 persons. But we know that the total number of inhabitants in England during the time of William the Conqueror was but a small fraction of this enormous aggregate. This means that we shall have to modify our inference that a child has twice as many ancestors as its parents; a condition which at first sight seems evident, but which is not literally true. The fact is that the parents of the child, in all probability, have many ancestors in common—a state of affairs which is brought about through the intermarriage of relatives, and this is especially frequent among remoter descendants of common progenitors. Time after time in genealogy strains of blood have crossed and recrossed until it is not improbable that a man of to-day who is of English origin has the blood in his veins from every inhabitant of England who lived during the time of William the Conqueror and left fruitful descendants. Instead of conceiving of ancestry as an ever branching and widening tree-like system as it recedes into the past, it is more accurate, therefore, to regard it in the light of an elaborate meshwork. The “family tree” in reality becomes the family net. Ancestry in Royalty.—The pedigrees of royal families have proved to be of much importance in the study of human inheritance, not that royal traits are any more heritable than any other, but simply because the records have been carefully kept so that they are the most comprehensive and easily followed pedigrees available. The netlike weave of ancestry is particularly well exemplified in some of these families because of much close intermarriage. Their heritage typifies on an intensified scale the heritage of the mass of mankind. For example, if we go six generations back in the ancestry of Frederick the Great instead of the expected sixty-four individual ancestors we find only forty; or in a still more closely woven stock, in the Spanish royal line of Don Carlos we find in six generations instead of sixty-four individual ancestors, only twenty-eight. While the present German emperor might have had four thousand ninety-six ancestors in the twelfth generation back, it is estimated that owing to intermarriage he probably had only five hundred thirty-three. Offspring Derived from One Parent Only.—So far in our reckoning of heredity we have counted elements from both father and mother, and the complications which arise from such a double ancestry are manifestly very perplexing ones. If we could do away with the elements of sex and find offspring that are derived from one parent only, it would seemingly simplify our problem very much for we should thus have a direct line of descent, free from intermingling. This, in fact, occurs to a greater or less extent among lower animals in a number of instances. [Pg 3] [Pg 4] [Pg 5] [Pg 6] There may be only female forms for a number of generations and the eggs which they produce develop directly into new individuals. Moreover, many of the simpler organisms have the power of dividing their bodies into two and thus giving rise to two new forms, each of which resembles the parent. This shows plainly that we may have inheritance without the appearance of any male ancestor at all, hence sex is not always a necessary factor in reproduction or heredity. The development of eggs asexually, that is, without uniting first with a male cognate, is termed parthenogenesis. The ordinary plant louse or aphid which is frequently found upon geraniums is a familiar example of an animal which reproduces largely in this way. During the summer only the females exist and they are so astonishingly fertile that one such aphid and her progeny, supposing none dies, will produce one hundred million in the course of five generations. In the last broods of the fall, males and females appear and fertile eggs are produced which lie dormant through the winter to start the cycle of the next year. Again, the eggs of some kinds of animals which normally have to unite with a male germ before they develop, can be made to develop by merely treating them with chemical solutions. The difference between an offspring derived in such a manner, and one which has developed from an egg fertilized by the male is that it is made up of characteristics from only one source, the maternal. Dual Ancestry an Aid in Studying Heredity.—Although we have the factors of heredity in a more simplified form in the case of asexual transmission, as a matter of fact most of our insight into the problems of heredity has been attained from a study of sexually reproducing forms, because the very existence of two sets of more or less parallel features offers a kind of checking up system by which we can follow a given characteristic. Reversion.—Occasionally, however, plants and animals do not develop the complete individuality we might expect, but stop short at or re-attain some ancestral stage along the line of descent, and thus come to resemble some progenitor perhaps many generations back of their own time. Thus it is well known that as regards one or more characteristics a child may resemble a grandparent or often some remote ancestor much more closely than it does its immediate parent. The reappearance of such ancestral traits the student of heredity designates as Reversion or Atavism. Reversion may occur apparently in any class of plants or animals. It is especially pronounced among domesticated forms, which through man’s selection have been produced under more or less artificial conditions. For example, among fancy breeds of pigeons, there may be an occasional return to the old slaty blue color of the ancestral rock-pigeon, with two dark cross-bars on the wings, from which all modern breeds have been derived. This is almost sure to happen if the fancy varieties are inter-crossed for two or three generations. Another example of reversion frequently cited is the occasional reappearance in domestic poultry of the reddish or brownish color pattern of the ancestral jungle-fowl to which, among modern forms, the Indian game seems most nearly related in color. Still another example is the cross-bars or stripes occasionally to be seen on the forelegs of colts, particularly mules, reminiscent of the extinct wild progenitors which were supposedly striped. Fig. 1, p. 9, is a picture of a hybrid between the common fowl and the guinea-fowl. The chevron-like markings on certain feathers show a reversion to a type of color pattern that is prevalent among both the primitive pheasants (the domestic chicken is a pheasant) and the primitive guinea-fowls. Although the common spotted guinea-fowl may be crossed with a black chicken which shows no trace of barring, nevertheless the hybrid offspring are likely to bear a chevron-like pattern such as that shown in the picture. There has been much quibbling over the relative meanings of reversion and atavism. The general idea, whichever term we use, is that there is a “throwing back” in a noticeable degree through inheritance to some ancestral condition beyond the immediate parents. A few recent authors have taken the term atavism in a restricted sense and use it to signify specifically those not uncommon cases in which a particular character of an offspring resembles the corresponding character of a grandparent instead of a parent. Such, for example, as the blue eye- color of a child with brown-eyed parents, each of whom in turn has had a blue-eyed parent. The tendency of other authors is to abandon the term entirely because of the diversity of meaning that has been attached to it in the past. Fig. 1 Hybrid between the guinea-fowl and the common fowl,showing in many feathers reversion to a primitive chevron-like barring. Certain classes of so-called reversions, such as the case of the eye-color just cited, are readily explicable on Mendelian principles as we shall see in a later chapter, but probably not all kinds of phenomena described as reversion can be so explained. For example, some seem to be cases of suppressed development. The word reversion, indeed, must be looked on as a convenient descriptive term rather than as the name of a single specific condition. [Pg 7] [Pg 8] [Pg 9] [Pg 10] Telegony.—There is yet a wide-spread belief in the supposed influence of an earlier sire on offspring born by the same mother to a later and different sire. This alleged phenomenon is termed telegony. For example, many dog- breeders assert that if a thoroughbred bitch has ever had pups by a mongrel father, her later offspring, although sired by a thoroughbred, will show taints of the former mongrel mating. In such cases the female is believed to be ruined for breeding purposes. Other supposed instances of such influences have been cited among horses, cattle, sheep, pigs, cats, birds, pets of various kinds and even men. The historic case most frequently quoted is that of Lord Morton’s mare which bore a hybrid colt when bred to a quagga, a striped zebra-like animal now extinct. In later years the same mare bore two colts, sired by a black Arabian horse. Both colts showed stripes on the neck and other parts of the body, particularly on the legs. It was inferred that this striping was a sort of after effect of the earlier breeding with the quagga. In recent times, however, Professor Ewart has repeated the experiment a number of times with different mares using a Burchell zebra as the test sire. Although his experiments have been devised so as to conduce in every way possible to telegony his results have been negative. Moreover, it has been pointed out that the stripes on the legs of the two foals alleged to show telegony could not have been derived from the quagga sire for, unlike zebras, quaggas did not have their legs striped. Furthermore it is known that the occurrence of dark brown stripes on the neck, withers and legs of ordinary colts is not uncommon, some cases of which have exhibited more zebra-like markings than those of the colts from Lord Morton’s mare. It seems much more probable, therefore, that the alleged instances are merely cases of ordinary reversion to the striped ancestral color pattern which probably characterized the wild progenitors of the domesticated horse. Various experiments on guinea-pigs, horses, mice and other forms, especially devised to test out this alleged after-influence of an earlier sire, have all proved negative and the general belief of the biologist to-day is that telegony is a myth. Prenatal Influences Apart from Heredity.—In discussing the problems of heredity it is necessary to consider also the possibilities of external influences apart from lineage which may affect offspring through either parent. Although modifications derived directly by the parent, and prenatal influences in general, are of extremely doubtful value as of permanent inheritable significance, nevertheless they must be reckoned with in any inventory of a child’s endowment at birth. Impaired vitality on the part of the mother, bad nutrition and physical vicissitudes of various kinds all enter as factors in the birthright of the child, who, moreover, may bear in its veins slumbering poisons from some progenitor who has handed on blood taints not properly attributable to heredity. Of such importance is this kind of influence to the welfare of the immediate child that it will be necessary to discuss it in considerable detail in a later chapter. Parent Body and Germ Not Identical.—Inasmuch as each new individual appears to arise from material derived from its parent, taking the evidence at its face value one might suppose that any peculiarity of organization called forth in the living substance of the parent would naturally be repeated in the offspring, but a closer study of the developing organism from its first inception to maturity shows this to be probably a wrong conclusion. The parent-body and the reproductive substance contained in that body are by no means identical. It becomes an important question to decide, in fact, how much effect, if any, either permanent or temporary, the parent-body really has on the germ. A given fertile germ (Fig. 2, p. 13) gives rise by a succession of divisions to a body which we call the individual, but such a germ also gives rise to a series of new germ-cells which reside in that individual, and it is these germ- cells, not something derived from the body, that pass on the determiners of distinguishing features or qualities from generation to generation. It is only by grasping the significance of this fact that we can understand how in certain cases a totally different set of characters may appear in an offspring than those manifested in either parent. An Hereditary Character Defined.—By a character, in discussions in heredity, is meant simply a trait, feature or other characteristic of an organism. Where we can pick out a single definable characteristic which acts as a unit in heredity, for greater accuracy we term it a unit-character. Many traits are known to be inherited on a unit basis or are capable of being analyzed into factors which are so inherited. These unit-characters are in large measure inherited independently of one another apparently, although cases of characters inherited as a unit along with other characters are known. Hereditary Mingling a Mosaic Rather Than a Blend.—The independence of unit-characters in inheritance leads us to the important conclusion that the mingling of two lines of ancestry into a new individual is in no sense bringing them into the “melting pot,” as it has been picturesquely expressed, but it is rather to be regarded as the mingling of two mosaics, each particle of which retains its own individuality, and which, even if overshadowed in a given generation, may nevertheless manifest its qualities undimmed in later generations when conditions favorable to its expression transpire. Fig. 2 Diagram illustrating germinal continuity. Through a series of divisions a germ-cell gives rise to a body or a soma [Pg 11] [Pg 12] [Pg 13] and to new germ-cells. The latter, not the body, give rise in turn to the next generation. Determiners of Characters, Not Characters Themselves, Transmitted.—The fact should be thoroughly understood that the actual thing which is transmitted by means of the germ in inheritance is not the character itself, but something which will determine the character in the offspring. It is important to remember this, for often these determiners, as they are called, may lie unexpressed for one or more generations and may become manifest only in later descendants. The truth of the matter is, the child does not inherit its characters from corresponding characters in the parent-body, but parent and child are alike because they are both products of the same line of germ-plasm, both are chips from the same old block. METHODS OF STUDYING HEREDITY Before entering into details it will be well to get some idea of the methods which are commonly employed in arriving at conclusions in the field of heredity. Some of these are extremely complex and all that we can do in an elementary presentation is to get a glimpse of the procedures. Our Knowledge of Heredity Derived Along Three Lines.—Our modern conceptions of heredity have been derived mainly from three distinct lines of investigation: First, from the study of embryology, in which the biologist concerns himself with the genesis of the various parts of the individual, and the mechanism of the germs which convey the actual materials from which these parts spring; second, through experimental breeding of plants and animals to compare particular traits or features in successive generations; and third, through the statistical treatment of observations or measurements of a large number of parents and their offspring with reference to a given characteristic in order to determine the average extent of resemblance between parents and children in that particular respect. The Method of Experimental Breeding.—A tremendous impetus was given to the method of experimental breeding when it was realized that we can itemize many of the parts or traits of an organism into entities which are inherited independently one of another. Such traits, or as we have already termed them, unit-characters, may be not only independently heritable but independently variable as well. The experimental method seeks to isolate and trace through successive generations the separate factors which determine the individual unit-characters of the organism. In this attempt cross-breeding is resorted to. Forms which differ in one or more respects are mated and the progeny studied. Next these offspring are mated with others of their own kind or mated back with the respective parent types. In this way the behavior of a particular character may often be followed and the germinal constitutions of the individuals concerned can be formulated with reference to it. Inasmuch as we shall give much consideration to this method in the chapter on Mendelism we need not consider it further here. The Statistical Method.—The statistical method seeks to obtain large bodies of facts and to deal with evidence as it appears through mathematical analysis of these facts. The attempt of its followers is to treat quantitatively all biological processes with which it is concerned. Historically Sir Francis Galton was the first to make any considerable application of statistical methods to the problems of heredity and variation. In his attempts to determine the extent of resemblance between relatives of different degree as regards bodily, mental and temperamental traits, he devised new methods of statistical analysis which constitute the basis of modern statistical biology, or biometry as it is termed by its votaries. Professor Karl Pearson in particular has extended and perfected the mathematical methods of this field and stands to-day as perhaps its most representative exponent. The system is in the main based on the calculus of probability. The methods often are highly specialized, requiring the use of higher mathematics, and are therefore only at the command of specially trained workers. Just as insurance companies can tell us the probable length of human life in a given social group, since although uncertain in any particular case, it is reducible in mass to a predictable constant, so the biometrician with even greater precision because of his improved methods can often, when a large number of cases are concerned, give us the intensity of ancestral influence with reference to particular characters. For example, it is clear that by measuring a large number of adult human beings one can compute the average height or determine the height which will fit the greatest number. There will be some individuals below and some above it, but the greater the divergence from this standard height the fewer will be the individuals concerned. Galton compared the heights of 204 normal English parents and their 928 adult offspring. In order to equalize the measurements of men and women he found he had to multiply each female height by 1.08. Then, to take both parents into account when comparing height of parents to that of children he added the height of the father to the proportionately augmented height of the mother and divided by two, thus securing the height of what he termed the “mid-parent.” He found that the mid-parental heights of his subjects ranged from 64.5 to 72.5 inches, and that the general mode was about 68.5 inches. It should be mentioned that the mode, in a given population, represents the group containing the largest number of individuals of one kind; it may or may not coincide with the average. The children of all mid-parents having a given height were measured next and tabulated with reference to these [Pg 14] [Pg 15] [Pg 16] [Pg 17] mid-parents. The results of Galton’s measurements may be expressed simply as follows: MODE Height of mid-parent in inches 64.5 65.5 66.5 67.5 68.5 69.5 70.5 71.5 72.5 Average height of offspring 65.8 66.7 67.2 67.6 68.3 68.9 69.5 69.9 72.2 The Law of Regression.—It is plain from this table that the offspring of short mid-parents tend to be under average or modal height though not so far below as their parents. Likewise children of tall parents tend to be tall but less tall than their parents. This fact illustrates what is known as Galton’s law of regression; namely, that if parents in a given population diverge a certain amount from the mode of the population as a whole, their children, while tending to resemble them, will diverge less from this mode. It is clear that the extent of regression is an inverse measure of the intensity of inheritance from the immediate parents; if the deviation of the offspring from the general mode were nearly as great as that of their parents then the intensity of the inheritance must be high; if but slight—that is, if the offspring regressed nearly to the mode—then the intensity of the inheritance must be ranked as low. In the example in question it must be ranked as relatively high. Computations show that as regards stature the fraction two-thirds represents approximately the amount of resemblance between the two generations where both parents are considered. Correlations Between Parents and Offspring.—In modern researches the conception of mid-parent and mid- grandparent as utilized by Galton has been largely abandoned. It has been found more convenient as well as more accurate to keep the measurements of the two parents separate and to deal with correlations between fathers and sons, fathers and daughters, mothers and sons, mothers and daughters, brother and brother, etc. Professor Pearson and his pupils have found for a number of characters that the correlation between either parent and children, whether sons or daughters, is relatively close. The correlation between brother and brother, sister and sister, and brother and sister, usually ranges a little higher than the corresponding relation between parents and children. The Biometrical Method, Statistical, Not Physiological.—While biometry may in certain cases go far toward showing us the average intensity of the inheritance of certain characters it can not replace the method of the experimental breeder which d...