Heredity versus Environment. Among the many determining factors of health and disease there is, in the case of each individual, one factor which cannot be altered. This is the factor of heredity. We cannot choose our ancestors, nor, try as they will, can our parents change certain characteristics of mind and body which they hand down to us. Sex, racial and family peculiarities, the red skin of the Indian, the black skin of the Negro, the eye of the Oriental, the Hapsburg chin are all manifestly predetermined and beyond the reach of human influence.

We come into the world with certain mental and physical characteristics which, however much environment may tend to develop or suppress, are our birth-right to which or from which we cannot add or subtract. Some of the more potent of these characteristics will be evident and will play a dominant role in our lives, irrespective of the conditions of existence. Even the most potent, however, are probably susceptible to some modification through the influences which we characterize as environment. Not all of these characteristics will be manifested, either through lack of development or through training, under the conditions of life, of opposite acquired characteristics. Thus we can conceive of a great potential pianist who never knows a piano, or of the puny child of delicate parents, who may grow into vigorous manhood through intelligent care of his body, or of the person with an inheritance of placid temper which may become acrid and irritable through association in youth with persons of unbalanced nervous systems or through a multiplicity of adversities through life. But as we analyze the evidence for and against the inheritance of characteristics, we find a much smaller number which are immutable than is popularly and commonly supposed.

We know that nutrition and exercise have a pro-found influence on physique, and that education, training, and association have even a greater influence on the mind and character. All such post-natal influences we group together under the general term of environment. It is at once evident that as a child imitates the mode of life of the father, the child will tend to reflect the same results of the environment as the father. A child, for example, may imitate the outbursts of temper of the father and, subjected to the same exasperating environment, may become a man subject to fits of anger. This characteristic may be attributed to either heredity or environment. Likewise, the child of studious parents may, if studious, be said to have derived this characteristic from heredity or environment. But in the case of a child stolen by thieving gypsies, who grows up to be a thief, environment must be the determining factor, just as in the case of the adopted child of an intellectual couple, who turns out to be feeble-minded, heredity must be the determining factor.

Light on this most complicated relation between heredity and environment is extremely important, since, for the future of the race, it is highly desirable to know what characteristics of mind and body are transmissible by inheritance and what are dependent on environment. It is necessary to ascertain as minutely as possible what characteristics of mind and body are not only predetermined but fixed and unalterable, and what are not; how to accentuate, by the factors of heredity and environment, the good characteristics and how to obscure the bad, and what are the results in posterity of the mixture of predetermined and acquired characteristics in all sorts of possible combinations. While it is true that we cannot modify the traits of our ancestors, yet by environment we can modify profoundly our own lives and some of our characteristics and we can attempt to modify posterity by selection of the other half of our child's inheritance.

Our sources of information on the vast subject of heredity are two. In the first place we have the immense data of human experience from which to draw. Information from this source is haphazard and unscientific, since carefully controlled experiments in human breeding are not possible. Our second source of information is through experiments on plants and animals, and through such experiments some of the fundamental factors in heredity have been disclosed. Yet, while accurate observations can be made and final conclusions drawn which are true for plants and animals, it is not possible to transfer all the details to the peculiar and the more complicated problem of heredity in the human being.

The Accumulated Data of Human Heredity. From time immemorial the classic controversy over the relative influence which heredity and environment play in determining physical and mental characteristics has continued. The believers in the supreme importance of heredity have been represented by the aristocrats, while the contenders for environment have been represented by the common people. The Socialists of today, for instance, believe in the predominating influence of environment, while to the aristocrat heredity means everything. The aristocrat maintains that one can only be born a gentleman and that on birth depends a man's intellectual and social status. In his arrogance of birth he attributes to it many qualities which are definitely the product of aristocratic environment.

Our knowledge of heredity has consisted for a long time of a number of isolated facts. It has been well known that large people breed large children. The transmission of such family characteristics as light hair, blue eyes, and a general resemblance is well recognized. It is generally accepted that colored people will breed colored children, and that the mingling of colored and white people will produce a mixture of colors. Then we know that certain races are more immune or more susceptible to certain diseases than other races, while a few diseases are definitely inherited. It is known that some diseases, gout and hemophilia, for example, occur regularly in certain families. At one time the belief in heredity was carried so far that it was thought that such a disease as tuberculosis was entirely hereditary. We now know, of course, that none of the infectious diseases are hereditary, but are due to contact. This contact may occur in the womb, and we speak, rather inaccurately, of inherited syphilis.

We have learned to appreciate and to disbelieve in the transfer of gross bodily mutilations. If a man has a leg cut off, for example, there is not the slightest chance that any of his children will lack a leg. We have also learned that it is impossible to pass on by inheritance the results of any training of the mind or body.

Many people have believed in the so-called prenatal impressions, a favorite device of writers of fiction. It was supposed, and is still supposed by some, that the mother, when carrying a child, could impress certain things on the child. This is absolutely impossible, at least to a physical extent. Hereditary influences are consummated once and for all in the union of the spermatozoon and the ovum.

The Jukes and "Kallikak" Families. We have learned a great deal about heredity through the study of families of abnormal individuals. The study of the Jukes and so-called Kallikak families has furnished us with a large amount of data which has permitted us to draw valuable conclusions. The Jukes family was descended from a lazy and irresponsible backwoodsman. As his descendants have lived in New York state since 1720, it has been possible to study the family with considerable care. In five generations the Jukes' descendants numbered approximately 1,200 people, and the histories of over a thousand of them have been worked out. Some three hundred died in infancy. Of the remaining, 310 were paupers living in almshouses; 440 were physical wrecks due to gross irregularities of life; more than half the women were prostitutes; 130 were convicted criminals; sixty were habitual thieves, and seven were murderers. None of the Jukes ever got a common school education; only twenty ever learned a trade, and ten of these learned it when in prison, where they had no alternative.

The so-called Kallikak family is, perhaps, even more suggestive. Kallikak was descended from good English stock and served as a soldier in the War of the Revolution. He had sexual relations with a feeble-minded girl, and she bore him a son who was also feeble-minded. This son married a normal woman. They, in turn, produced five feeble-minded and two normal children. From these children have come 480 descendants. Thirty-six of these were illegitimate; thirty-three sexually immoral; twenty-four confirmed alcoholics; and three epileptics. Eighty-two died in infancy, three were criminals, and 143 were distinctly feeble-minded. Only forty-six who were apparently normal have been found.

After Kallikak had started this degenerate line, he married a normal girl of good ancestry. From this union with a normal woman there have been 496 descendants. Only two of this number showed anything but a normal mentality. Both exceptions were insane, probably due to marriage with an outside stock of insane tendency. Not a case of feeble-mindedness appeared among the 496; on the contrary, all occupied positions in the upper walks of life, and there were no criminals among them.

From this evidence it becomes obvious that feeble-mindedness is not a question of environment, but largely, if not entirely, a matter of heredity. The law of heredity is that feeble-minded, who marry, will have feeble-minded children. Every child of two feeble-minded parents will be feeble-minded.

Feeble-mindedness. Feeble-mindedness is of varying degree. In the lowest scale is the idiot; next comes the imbecile, and then the high grade mental defective, who is classified under the term, moron. The degree of mental development which constitutes feeble-mindedness has been arbitrarily fixed, for an adult, as that of a child of twelve. By the use of tests based on the principles first advocated by Binet and often called the Binet-Simon scale of intelligence, it is reasonably simple to approximate the mental development of the feeble-minded person in terms of years up to twelve. These tests merely consist of simple questions and exercises appropriate for a child of a given age. The idiot is able to do the tests up to the level of the normal child of two; the imbecile the tests for a child between two and seven years, and the moron those of a child between seven and twelve. It is now believed that such tests are not applicable to mentalities corresponding to children over twelve. While it is thus impossible to designate by examination as feeble-minded persons of manifest low mentality (that is above twelve years of age), such persons, called normal, are frequent in feeble-minded families, and are often a menace to the community.

It should be borne in mind that feeble-mindedness is entirely a mental characteristic, for the body of the feeble-minded person is normal and often unusually well developed. But despite the bodies and physical ability of men and women, the feeble-minded are children,—they have the minds of children and are controlled by the emotions of children. The anger of a child is impotent of physical harm through the lack of physical strength; not so the anger of the feeble-minded with the powerful adult frame. Hence we read of murders for trivial causes, which are inexplicable to the adult mind and often to the laws of justice. No less inexplicable is the absence of any attempt at concealment and the absence of remorse. The culprit, adult in body, views the affair with the mental vision of perhaps eight years. Stupid petty burglary and arson are the crimes to which the feeble-minded are prone, but the criminal bent of the feeble-minded is determined entirely by environment.

Among the feeble-minded we see, perhaps, best illustrated the dual influences of heredity and environment. The childlike mind, free from evil influences and associations, may go through life and, possibly, only be regarded as somewhat simple. Complicated tasks and persistent endeavor, especially in the face of obstacles, are beyond the individual, but simple physical work, under supervision, is easy. But the chances favor childlike rebellion against the restraint of the laws and customs of society. So the fully developed physical instinct of sex plays an important role in the delinquencies of the feeble-minded. The sexual desires are not restrained, and the sexual immoralities of the feeble-minded are notorious. Feeble-minded women often have physical attraction and statistics show that they comprise between seventy-five and eighty per cent of the public prostitutes. So, too, the feeble-minded are frequently alcoholics and other drug habitues. In general they are industrial misfits, the ne'er-do-wells, the habitual loafers and "bums" of the community. They fill the almshouses as well as the jails, and even the insane asylums.

The high grade feeble-minded person, the moron, or the person just above that type, is a particular problem of the community. He transmits his defect and, as a potential criminal, is a constant menace to society. The trait of feeble-mindedness may be obscured by mating with a normal person, since normality is predominant over feeble-mindedness, but the trait still persists. Experience has shown that such persons cannot be allowed to roam at large. Sterilization, which has been suggested as a remedy for the problem, merely prevents propagation, but not crime. Communities are slowly beginning to realize that it is almost inevitable that such persons, depending on how their tendencies are developed by the peculiar environment, must eventually be supported in almshouses, hospitals, asylums, and jails. So it is probably wiser and more economical for the community, as has already been accomplished successfully in certain places, to support the feeble-minded in segregated colonies.

Other Hereditary Defects. Feeble-mindedness, as a purely hereditary characteristic, is the most important hereditary disease we know. While brain injury and brain disease may cause a deficient mentality, such a defect is not transmitted. Heredity plays an important role in the causation of other mental abnormalities, but in none, according to our present knowledge, is it the sole determining factor as is the case in feeble-mindedness. Nervous and mental instability of many varieties definitely run in certain families. Heredity, as well, is the most important factor in determining certain types of insanity.

Certain more obvious physical phenomena and conditions, such as short fingers, deafmutism, hemophilia, albinism, forms of chorea and ataxia, cleft palate, myopia, and the like, are peculiarly present in families and are handed on from generation to generation. We have, furthermore, the most interesting observation that hemophilia is transmitted only through females and only to males. Color-blindness is essentially a male inherited characteristic.

But it should not be supposed that only the bad traits are transmitted through inheritance. Fortunately for us the studies of families indicate as positively that the good traits are handed on with the same certainty as all the weaknesses. Marked musical talent, generosity, artistic bent, and similar qualities are essentially hereditary, as well as desirable physical attributes. A few notable families in which many of the descendants accomplished marked achievements show positively how even intellectual power is inherited. The family of Bach is an illustration of the inheritance of musical talent. This family produced twenty eminent composers and twice as many who possessed marked ability. The classical example of the inheritance of intellectual power is the family of Jonathan Edwards. The achievements of the 1394 descendants of this eminent philosopher have been tabulated by Kellicott in his book on "Social Direction of Human Evolution." The list includes "295 who were college graduates; 13 presidents of our greatest colleges; 65 professors in colleges, besides many principals of other important educational institutions; 60 physicians, many of them eminent; 100 and more clergymen, missionaries, or theological professors; 75 were officers in the army and navy; 60 prominent authors and writers, by whom 135 books of merit were written and published and 18 important periodicals edited; 33 American states and several foreign countries, and 92 American cities and many foreign cities have profited by the beneficent influences of their eminent activity; 100 and more were lawyers, of whom one was our most eminent professor of law; 30 were judges; 80 held public office, of whom one was vice-president of the United States; 3 were United States senators; several were governors, members of Congress, framers of state constitutions, mayors of cities, and ministers of foreign courts; one was president of the Pacific Mail Company; 15 railroads, many banks, insurance companies, and large industrial enterprises have been indebted to their management. . . . It is not known that any one of them was ever convicted of crime."

Experimental Data. Approximately all the fundamental facts we know about heredity are contained in the so-called Mendel's law. Mendel was an Austrian monk who conducted extended experiments on peas. In 1866, he was able to state with definiteness some of the considerations which govern the transmission of characteristics. His conclusions, however, important as they were, did not receive the consideration which they merited until the publication of the work of DeVries, an investigator in Holland, in 1899. The essential factors in heredity, as stated by Mendel, are unit characteristics, dominance, and segregation. A unit characteristic is one that is transmitted from parent to offspring through successive generations. When parents with complementary unit characteristics mate, it is found that one characteristic pre-dominates in the offspring. This is dominance. Thus when Mendel crossed giant and dwarf peas, the giant peas predominated in the offspring, since the characteristic of giantism, in this illustration, is dominant and dwarfism is recessive. These unit characteristics from the separate parents usually remain separate and distinct,—segregation. We do not know just what is transmitted from parent to offspring, but it is only something which determines the development of the unit characteristic,—the determiner.

A good illustration of the Mendelian law is the inheritance of color in the Andalusian fowl as worked out by Bateson. There are two established varieties of this fowl,—one black and the other white. Each of these, by itself, breeds true to itself. Black mated with black produce black offspring; while white mated with white produce only white offspring. But if a white fowl mates with a black, the offspring will be neither white nor black, but a grayish color known as "blue." When these hybrids mate there are three colors among the offspring, blue, white, and black. Furthermore, the proportions of each color are fixed, for one-half will be blue, one-quarter black, and one-quarter white. In all generations, white from white or from blue will always breed true and so with the black. A pure race of blues cannot be established.

Guinea pigs well illustrate the law of dominant and recessive characteristics. If black and white guinea pigs are mated, the offspring will all be black. The black is the dominant characteristic and the white the recessive. These black guinea pigs are as true hybrids as the blue Andalusian fowl. If these hybrid guinea pigs are mated, all the offspring will not be black, but three-quarters will be black and one-quarter white. Some of the blacks will breed true, while others, apparently like their black brothers and sisters, nevertheless contain the white taint, and so will breed one-quarter white.

The same principles of heredity hold true for human beings, although it is difficult to work this out, as we can rarely get sufficient details concerning our ancestors. But we do see striking illustrations of Mendel's law in the transmission of disease. The difficulty in applying the law is to determine dominance. We know, however, that normality is dominant over feeble-mindedness and insanity, and that Huntington's chorea is dominant over normality, and black eyes over blue eyes.

A further complication presents itself in the fact that all characteristics are not unit characteristics. In other words, instead of maintaining the two original characteristics and one hybrid type, we get blending, as seen in the varying shades of color of the skin in the mixed negroes and whites. As we have seen, heredity simply governs the proportions of the ultimate descendants. So the studies of human heredity are complicated by a small number of children. While the chance for the appearance of a certain characteristic is fixed numerically, we may not be able to fix the status of the individual child until we have had an opportunity to study the progeny. We may see, therefore, in the single child the outcome of at least three possibilities, and this outcome may be happy or tragic in his person, or in his progeny.

Inbreeding. Inbreeding, or the mating of people with the same characteristics, is a hazardous experiment. This is illustrated by the problem of the marriage of cousins. The objection to such marriages rests entirely on this question of heredity. Any defect in the inheritance, such as a strain of insanity, will become intensified in the offspring by such a marriage. The intermarriage does not create the defects, but simply brings them to the light. Cross-breeding does not remove defects of inheritance; it only hides them. If an insane person is married to a person, apparently normal, but with a taint of insanity in the family, the probabilities are that some of the children will be insane. If, however, the person with a strain of insanity marries into a rugged stock, the defect will tend to be obscured, although there is a chance that the insanity may crop out again in a later generation.

The study of the results of inbreeding in many localities shows exactly what we should expect. Consanguinity on Martha's Vineyard shows eleven per cent deaf mutes; on Point Judith thirteen per cent idiots and seven per cent insane; in the Bahamas the result is idiocy and blindness; in a community on Chesapeake Bay dwarfness in stature, and on a Maine island stupidity.

The possibility of the inheritance of acquired characteristics, which are, of course, due to environment, is denied by present-day scientists, although the belief in such inheritance has existed from the earliest times. If any acquired characteristics are ever passed on, it is done very, very slowly.

In regulating our lives we should appreciate that heredity is a fundamental factor in our physical and mental makeup. The transmission of defects, excellences, and tendencies is fully recognized. Training and good habits can go far towards developing desirable traits and suppressing those that are undesirable. We should, therefore, so adjust our mode of living as to make the most effective use of our bodily and mental equipment. While as yet the knowledge of the complexities of human heredity is not sufficiently complete or positive to justify marriage on the sole basis of genetics, nevertheless the data at hand may well be an influencing factor for those who desire to hand down to the next generation a good inheritance of mind and body.

Roger I. Lee

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