The Social Direction of Evolution Part 4

III

HUMAN HEREDITY AND THE EUGENIC PROGRAM

"A breed whose proof is in time and deeds; What we are, we are--nativity is answer enough to objections."

A few years ago official recognition was taken of the disturbing fact that the annual wheat yield of Great Britain was grossly deficient in both quant.i.ty and quality. In 1900 The National a.s.sociation of British and Irish Millers, with almost unprecedented sagacity, raised a fund to provide for a series of experiments under the direction of a competent biologist, in order to discover if possible some means of restoring the former yield and quality of the native wheats. The story of the result reads like a romance. The experimenter--Prof. R. H.

Biffen--collected many different varieties of wheat, native and foreign, each of which had some desirable qualities, and studied their mode of inheritance. Now, after only a few years of experimentation a wheat has been produced and is being grown upon a large scale in which have been united this desirable character of one variety, that character of another. From each variety has been taken some valuable trait, and these have all been combined into one variety possessing the characteristics of a short full head, beardlessness, high gluten content, immunity to the devastating rust, a strong supporting straw, and a high yield per acre. A wheat made to order and fulfilling the "details and specifications" of the growers.

Manitoba and British Columbia opened up whole new lands of the finest wheat-growing capacity, but the season there is too short for the ripening of what were the finest varieties. This new specification was promptly met and the early ripening quality of some inferior variety was transferred to the varieties showing other highly desirable qualities, and these countries are now producing enormous quant.i.ties of the finest wheat in the world.

All of this has been made possible by the discovery, mentioned in the preceding chapter, that many characteristics of organisms are units and behave as such in heredity; they can be added to races or subtracted from them almost at will. Pure varieties breeding true can be established permanently by taking into account the Mendelian laws of heredity. Similar results have been accomplished in many other plants and in many animals. A cotton has been produced which combines early growth, by which it escapes the ravages of the boll weevil, with the long fiber of the finest Sea Island varieties. Corn of almost any desired percentage of sugar or starch, within limits, can be produced to order in a few seasons. The hornless character of certain varieties of cattle can be transferred to any chosen breed. Sheep have been produced combining the excellent mutton qualities of one breed with the hornlessness of another, and with the fine wool qualities of still a third. And so on from canary birds to draft horses. New races can be built up to meet almost any demand, with almost any desired combination of known characters, and these races remain stable.

Possibilities in this direction seem to be limited only by our present and rapidly lessening ignorance of the facts of Mendelian heredity in organisms--facts to be had for the looking.

What is man that we should not be mindful of him? Why should we utilize all this new knowledge, all these immense possibilities of control and of creation, only for our pigs and cabbages? In this era of conservation should not our profoundest concern be the conservation of human protoplasm? "The State has no material resources at all comparable with its citizens, and no hope of perpetuity except in the intelligence and integrity of its people." As Saleeby puts it: "There is no wealth but life; and if the inherent quality of life fails, neither battle-ships, nor libraries, nor symphonies, nor Free Trade, nor Tariff Reform, nor anything else will save a nation."

In this work of the creation and establishment of new and valuable varieties, two essential biological facts are made use of. The raw materials are furnished by variation--by the fact that there are individual and racial differences. The means of accomplishing results are furnished by heredity--the fact that offspring resemble the parents, not only in generalities, but even in particulars, and according to certain definite formulas.

And, further, in the formation and establishment of a new race of plant or animal a conscious and ideal process is involved. The will of some organism guides the process, carefully doing away with hit and miss methods, and proceeding as directly as may be possible to an end _desired_. The facts of variation and heredity are sufficiently demonstrated for all organisms other than man; are they true of man also? Have we available the possibilities for the improvement of the human breed? If not, Eugenics is merely an interesting speculation. We have mentioned already the facts of variation in man; we undoubtedly do have the raw materials. What about heredity, and what about the directive agency? Let us look now at some of the facts of human heredity and consider some of the possibilities in the way of directive agencies. Is it going to be possible to breed a stable human race permanently with or without definite characteristics which now appear only in certain groups, or sporadically as variations?

At the outset we should say that the knowledge of human heredity is as yet largely of the statistical sort. We know how a great many characters are inherited, on the average. The subject of Mendelian heredity is so new that there has been hardly time to investigate more than a few human characteristics from this point of view. Certain conditions add to the difficulties here. First, many, probably most, of the more important human traits are complexes, not units, and it is a long and difficult process to a.n.a.lyze them into their units, with which alone Mendelism deals. Second, in human society we cannot carry on definite experiments under controlled conditions, directed toward the solution of some concrete problem in heredity. It is true that Nature herself is making such experiments constantly, but at random, and rarely under ideal conditions of what the experimenter calls control or check. We have first to seek and find them out, and when they are found we often discover that there are lacking many of the facts essential to a complete or satisfactory a.n.a.lysis of the facts displayed. The comparatively small size of the human family sometimes makes it difficult to get data sufficiently extensive to be really significant. And the long period that elapses between successive human generations adds to the difficulty of getting precise information, for in dealing with the heredity of some traits comparisons must be made with individuals of the same ages, and the period of observation of a single observer seldom exceeds the duration of a single generation.

Yet in spite of all these difficulties we have a fairly broad and exact knowledge of human heredity in respect to some characteristics.

Human heredity involves both physical and psychical characters--both the body and the mind are concerned. Among other animals little if anything is known regarding psychic inheritance, but the physical traits of men are inherited in just the same ways and to the same degrees as in animals. This degree or intensity of inheritance may be expressed in coefficients of heredity between the groups of relatives being compared. To mention a few examples of coefficients for physical traits we have the following:

CHARACTER OBSERVED PARENTAL FRATERNAL COEFFICIENT COEFFICIENT Stature .49-.51 } .51-.55 } Span .45 } .55 } Fore Arm .42 } .47 .49 } .53 Eye Color .55 } .52 } Hair Color .57 - Average Hair Curliness .52 Head Measurements-three .55 - "

Cephalic Index (Ratio between breadth and length of cranium) .49

We might give many others, but it is unnecessary. Notice that these parental and fraternal coefficients group about an average value of about .50 or slightly less. Similar coefficients have been worked out for other degrees of relationship; thus grandparental coefficients are about .25.

Stated briefly, in less exact terms, these coefficients mean that, with respect to such traits as deviate from the group average, the resemblance of brothers and sisters to each other or of children to their parents is, on the whole, approximately mid-way between being complete in its deviation from the average and in not deviating at all from the average in the direction of the fraternal or parental characteristic. Grandchildren tend to deviate from the group average only about one fourth as far as their grandparents. It should be remembered that these are statistical and not individual statements, and that as many "exceptions" will be found in the direction of greater resemblance as in that of lesser resemblance.

One of the present objects of the student of heredity, perhaps his chief object, is to be able to state the facts of human heredity in Mendelian terms, reducing many of the complex human traits to their simpler elements. Some of the chief objections to the use of the statistical formula of heredity are that apparently it is applicable only to the fluctuating variabilities of organisms; that it rarely takes into account the presence of (and therefore the heredity of) true variations or mutations--and we have seen that it is just these characters that are of the greatest value in evolution; and that heredity is after all fundamentally an individual relation which loses much of its definiteness and significance when we merge the individual in with a crowd. To some these seem fatal objections to any use of the statistical formula and it is certainly true that they greatly limit its value. But for the present at least the statistical statement of certain facts of heredity is still useful in this bio-social field. We may therefore use the statistical formulas of heredity as a kind of temporary expedient, enabling us to make statements regarding inheritance of certain characters in the group or cla.s.s, pending the time when we shall be able to give the facts a more precise and more "final" expression in Mendelian formulas. Many human traits are indeed already known to Mendelize. Most of these are, however, "abnormal"

traits or pathological conditions; we are still in the dark regarding the actually Mendelian or non-Mendelian inheritance of most of man's normal characteristics. We might enumerate the following Mendelizing human characters--eye color, color blindness, hair color and curliness, albinism (absence of pigment), brachydactylism (two joints instead of three in fingers and toes), syndactylism (union of certain fingers and toes), polydactylism (one or more additional fingers or toes in each hand or foot), keratosis (unusually thick and h.o.r.n.y skin), haemophilia (lack of clotting property in the blood), nightblindness (ability to see only in strong light--a retinal defect usually), certain forms of deaf mutism and cataract, imbecility, Huntington's ch.o.r.ea (a form of dementia).

In observing Mendelian heredity we should bear in mind that a given character may be due either to the presence or to the absence of a "determiner" in the germ. Long hair such as is characteristic of many "Angora" varieties of the guinea pig and cat, for example, is believed to be due to the absence of a determiner which stops its growth. Blue eyes are due to the absence of a brown pigment determiner, _et cetera_. The presence or absence in the offspring of such characters as we know do Mendelize can be predicted when we know the parental history for two generations.

Turning now to the inheritance of mental traits and including, of course, moral traits here as well, we find that we are almost entirely limited to the statistical statement of results. Pearson found upon examining data from a large number of school children, brothers and sisters, that the coefficients of heredity between them were the same as for their physical traits. His results are summarized in Figure 12.

The physical traits measured were, in the order plotted in the figure--health, eye color, hair color, hair curliness, cephalic index (ratio between breadth and length of cranium), head length, head breadth, head height. These gave an average of .54 in brothers, .53 in sisters, and .51 in brothers and sisters. The psychical traits in order were--vivacity, a.s.sertiveness, introspection, popularity, conscientiousness, temper, ability, handwriting. The corresponding averages were .52, .51, .52.

[Ill.u.s.tration: FIG. 12.--Coefficients of heredity of physical and psychical characters in school children. Characters enumerated in text. (From Pearson.)]

Galton's pioneer works on "Hereditary Genius," "English Men of Science," and "Natural Inheritance" showed with great clearness the fact of mental and moral heredity. Wood's recent extensive study of "Mental and Moral Heredity in Royalty" shows the same thing, although not all the results of these investigations are given in mathematical form. Little can be said regarding Mendelian heredity of mental traits because the psychologist has not yet told us how to a.n.a.lyze even the common and simpler psychic characters into their fundamental units; since we do not know what the mental hereditary units are, obviously we cannot work with them. Much of our knowledge in this field does not permit of very accurate summary, though pointing indisputably to the fact of mental inheritance in spite of the very great influences of training and education, environment and tradition, in moulding the mental and moral characteristics--influences with much greater effect here than in connection with physical characters.

Galton studied the parentage of 207 Fellows of the Royal Society, a Fellowship which is a real mark of distinction. He a.s.sumed that one per cent of the individuals represented by the cla.s.s from which his observations were drawn, that is the higher intellectual cla.s.ses, might be expected to be "noteworthy": among the general population the average is really about one in 4,000 or one fortieth of one per cent.

On the one per cent basis Galton found that Fellows of the Royal Society had noteworthy fathers with 24 times the frequency to be expected in the absence of heredity; noteworthy brothers with 31 times the expected frequency; noteworthy grandfathers 12 times; and so on through various grades of relationship.

Schuster examined the cla.s.s lists of Oxford covering a period of 92 years and found that first honor men had 36 per cent first or second honor fathers; second honor men had 32 per cent first or second honor fathers; ordinary degree men 14 per cent first or second honor fathers. These percentages are far in excess of that to be expected--perhaps 0.5 per cent--on the a.s.sumption that ability is not inherited. Schuster also determined the coefficients of heredity between fathers and sons as regards intellectual ability, the evidence being cla.s.s marks in Oxford and Harrow; these he found to be about .3 for the parental relation and .4 for the fraternal. The intensity of heredity in many forms of insanity has been determined and this runs up much higher--.57 parental and .50 fraternal.

It is clear I take it, that the fact of human heredity does not concern only physical traits but extends to psychical traits as well, and with about the same intensity. This fact has been found true also for still less a.n.a.lyzable characters such as length of life, fertility or infertility and the like, and again about the same intensity of resemblance is found.

Human heredity is a fact then just as human variability is a fact. We have truly the raw materials and the means for racial improvement. The ability to direct the evolution of the human race makes this our supremest duty.

The facts of human heredity can more easily be brought home to us by the examination of some actual pedigrees and family histories. We may look at a few representative cases which will serve to bring out some additional aspects of the significance to society of the demonstrated fact of heredity. In the examination of single family histories we should remember that a single pedigree may not accurately ill.u.s.trate a general law of heredity--again, an individual case may belong to a group of cases without representing them fairly. Even in observing ill.u.s.trations of Mendel's laws allowance has to be made for the variability due to "chance" meetings of germ cells. It is only when large numbers of individuals are observed that the typical Mendelian fractions and ratios can be strictly observed. It must be borne in mind then that the histories given below ill.u.s.trate the nature of the facts of heredity rather than the laws of heredity. Some special cautions in the interpretation of certain pedigrees will be suggested in particular cases. Many of the figures are taken from the extremely valuable "Treasury of Human Inheritance," now being published by the Eugenics Laboratory of the University of London. In these figures and some others a uniform series of symbols is used. Successive horizontal lines designated by Roman numerals indicate generations; within a single generation the individuals are numbered consecutively simply for purposes of reference. The meaning of the more common symbols is as shown in Table IV. We may first consider a few pedigrees showing the heredity of physical abnormalities or defects.

TABLE IV.

_Symbols used in Pedigrees. As adopted by the Galton Eugenics Laboratory._

[Symbol] Male and female respectively, not possessing the trait under consideration.

[Symbol] Male and female possessing the trait under consideration.

[Symbol] Unknown s.e.x--normal or affected.

[Symbol] Trait incompletely developed.

[Symbol] Neither presence nor absence of trait can be affirmed.

[Symbol] With a deformity or disease of special character which may possibly be a.s.sociated with that under consideration.

[Symbol] Twins.

[Symbol] Indicates number of children.

[Symbol] Marriage.

[Symbol] Number of children unknown.

[Symbol] Number and character of children unknown.

_S. P._ _Sine prole._ (No offspring.)

Fig. 13 ill.u.s.trates a family history where brachydactylism (an abnormality of the digits commonly called shortfingeredness, due to the lack of one joint in each digit) is present and frequently a.s.sociated with dwarfism. We may describe this case rather fully because it ill.u.s.trates nicely the heredity of a trait according to the Mendelian formula. The parentage of the affected female (II, 1) who started this line is uncertain. The marriage was with a normal male whose parentage is unknown but evidently normal. This pair produced 11 children, the character of 8 of whom is known; 4 were affected, 4 unaffected, a Mendelian ratio resulting from the mating of a normal with a hybrid individual, the observed character dominating (i. e., the abnormality appearing in the hybrid individuals). According to Mendelian laws, the normal offspring of affected hybrids when mated with normals should produce all normal offspring; this result is shown clearly through generations IV-VI, where no affected individuals are produced by two normal parents, although one or two of the grandparents were affected. Marriage of a normal person with one affected parent is fit because this individual is wholly without germinal determiners for this character. Marriage between a normal and an affected person is unfit (or it would be if the observed character were a serious defect) because approximately one half their offspring will be affected like the one parent. Thus in IV, 7-21, we see 12 children from one such marriage, 7 of whom are affected, 5 unaffected.

All of the 11 children of the 5 unaffected are normal, while of the 16 children of the affected persons, all of whom that married at all married normal individuals, 9 were affected, 7 unaffected. Similar relations are found in generation VI, where the 9 affected persons in V married normals, producing 33 children, 15 of whom were affected, 18 unaffected. Taking all the offspring of marriages between unaffected and affected (hybrid) persons through the four generations III-VI, we find 35 affected and 33 unaffected, with the condition of 3 unknown.

There is no instance in this pedigree of the marriage of two affected persons, but such a marriage would be highly unfit (again in the case of a serious defect) because we know that all their offspring would be affected. Mating of two unaffected persons, even though each had one affected parent, would be fit because the offspring would all be unaffected, barring the possibility of a new variation or mutation to this character, which would be extremely unlikely. Such a pedigree as this ill.u.s.trates very well how a knowledge of Mendelian heredity may be of the greatest value practically, in determining the fitness or unfitness of marriages in families where an abnormality or defect is known to occur. The course of the inheritance here ill.u.s.trates the simplest form of Mendelism. We have already indicated that there are many other forms which we have not described and which we cannot undertake to describe here on account of their complexity; in such cases, however, it is still possible to predict with fair accuracy the characters of the offspring of parents whose history is known for one or two generations.

[Ill.u.s.tration: FIG. 13.--Family history showing brachydactylism. Farabee's data. (From "Treasury of Human Inheritance.")]

The defect we have just been considering is dominant. Many defects are recessive, i. e., transmitted though not exhibited by a hybrid individual. Viewed from the standpoint of the character of the offspring, mating with such a person would be unfit only when both persons were similarly recessives. Such a chance similarity would be likely only in cases of blood relationship. Here lies the scientific basis for many of the legal restrictions against cousin marriage or the marriage of closer relatives, for here, although both persons may appear normal, the chances for latent ills appearing in the progeny in a pure and permanently fixed condition are greatly increased. Of course the same relation holds for characteristics which are not defects but really valuable traits. Marriage of cousins possessing valuable characters, whether apparent or not, might be allowed or encouraged as a means of rendering permanent a rare and valuable family trait which might otherwise be much less likely to become an established characteristic. Some discrimination should be exercised in the control, legal or otherwise, of such marriages.

[Ill.u.s.tration: FIG. 14.--Family history showing polydactylism. (From "Treasury of Human Inheritance.")]

Fig. 14 gives a brief pedigree of a family in which polydactylism occurs. This is a condition in which one or more additional or supernumerary fingers or toes are present in the extremities. The Mendelian character of the heredity of this defect is less clear than in the preceding, yet there are many indications that this is really an ill.u.s.tration of a complex Mendelian formula. Probably if the parentage of the individuals marrying into this family were known we should be able to give a complete formula. At any rate the pedigree ill.u.s.trates the unfit character of the matings with affected persons, for in no instance has such a marriage resulted in the production of fewer than one half affected offspring.

Fig. 15 ill.u.s.trates a form of what is known as "split hand" or "lobster claw," where certain digits may be absent in the hands and feet. In this case all the digits are absent except the fifth. This is frequently a.s.sociated with syndactylism or the fusion of the remaining digits into one or two groups. When present this usually affects all four extremities. Two pedigrees of this defect are ill.u.s.trated in Fig.

16. Here again we have a defect whose inheritance follows quite closely the Mendelian formula, although the character of the matings is not fully known; it is unnecessary to describe the details--the histories speak for themselves.

[Ill.u.s.tration: FIG. 15.--Mother and two daughters showing "split hand." (From Pearson.)]

Fig. 17 ill.u.s.trates a pedigree of congenital cataract. This history is less satisfactory because the matings are given in only three instances. It is known from other data that this defect follows simple Mendelian laws. Normal individuals produce only normals, while affected persons produce one half or all affected offspring according to the character of the mating.

Fig. 18 ill.u.s.trates the heredity of another defect of the eye called night blindness. This is a retinal defect, the affected being able to see only in strong illumination. The particular form of the disease in this family resulted in total blindness later in life. Little is known definitely concerning the character of the matings; no mating is known to have been with an affected person and some are known to have been with unaffected. Of the 42 descendants of the first affected person only 6 are known to have been unaffected. Can there be any doubt regarding the unfitness of these matings? In generation III a single mating led to a family of 10 children _all_ affected by this serious defect, rendering them dependents.

One of the most complete pedigrees of a defect on record is given in condensed form in Fig. 19. This summarizes the extraordinarily complete data of Nettleship covering nine, and in one branch ten, consecutive generations. The defect is another form of night blindness as it existed in a French family. The inheritance is obviously Mendelian: no affected persons are produced by unaffected parents, although their own brothers or sisters or one parent may have been affected. The pedigree gives the history of 2,040 persons, all descended from one affected individual. Of these 135 were known to have been affected, and all were children of affected parentage. Of the total number of progeny of affected persons mated with normals, 130 were reported as affected and 242 as unaffected.

[Ill.u.s.tration: FIG. 16.--Two family histories showing split foot. (From "Treasury of Human Inheritance.")]