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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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? |
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| Glossary | 343 |
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| References for Further Reading and Study | 355 |
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| Index | 361 |
BEING WELL-BORN
