Part 5

Some changes of the former class are due to the more regular and more ample nutrition; other changes are due to modifications of the kinds of food which the domesticated animal uses when compared with the wild animal of the same species; still others are due to the different manner in which the muscular and the nervous systems are put into use. These changes are not quite the same among carnivorous and among herbivorous animals. The dog and the cat, for instance, are fairly regularly fed when they are found in domestication; but the food which is given to them is of a quite different character from the food which the wild dog and cat eat. Even among people whose diet consists almost entirely of meat, dogs are generally fed with boiled meat, or rather with the boiled, less nutritious parts of animals; while, among other tribes which utilize to a great extent vegetable food, dogs are often fed with mush and other vegetable material. The same is true of our cats, whose diet is not by any means entirely a meat diet. The exertions which wild carnivorous animals undergo to obtain food are incomparably greater than those of domesticated carnivorous animals; and it is obvious that for this reason the muscular system and the central nervous system may undergo considerable changes.

The muscular exertions of herbivorous animals, so far as they are fed on pastures, are not so materially changed. The grazing habits of cattle and sheep in domestication are about the same as the grazing habits of wild animals of the same class; but the rapid movements and the watchfulness required for protecting the herd against carnivorous animals have completely disappeared. Stable-fed animals live under highly artificial conditions, and material changes may occur in them.

I think the changes due to these causes may be observed in the oldest types of domesticated animals, such as are found in the neolithic villages of Europe, in which native European species appear in domesticated form (Keller). They may also be observed in the dogs of the various continents, which differ markedly from the wild species from which they are derived. Even the Eskimo dog, which is a descendant of the gray wolf and still interbreeds with the gray wolf, differs in bodily form from the wild animal (Beckmann). Modifications may also be observed in newly domesticated animals, like the Chukchee reindeer, which differs in type from the wild reindeer of the same area (Bogoras). I think it very unlikely, judging from our knowledge of the methods of domestication of tribes like the Eskimo and Chukchee, that any material amount of selection has contributed to the modifications of form which are found in these races of primitive domesticated animals. Their uniformity is still fairly well marked, although they have assumed types different from the wild species.

A more marked differentiation of domesticated forms does not seem to occur until man begins to select and to isolate, more or less consciously, particular breeds. Opportunity for such isolation has been the greater, the older the domestication of any particular species. We find, therefore, that the number of distinct breeds have come to be greatest in those animals which have been under domestication for the longest periods.

The number of varieties of domesticated species has also been increased by unintentional or intentional crossing of different species, from which are derived many breeds whose ancestry it is often so difficult to unravel.

It appears, therefore, that there are three distinct causes which bring about the development of different types in domesticated animals: first, the influence of change of nutrition and mode of life; secondly, conscious selection; and, thirdly, crossing.

Among these causes, the first and the third have been most strongly active in the development of the races of man. The condition of the tribes of man the world over is such, that there are only very few whose mode of nutrition is analogous to that of wild animals, and a consideration of the stages of human culture shows that similar conditions have prevailed for a long period. I think we may safely say that in all those cases in which man practises agriculture, when he is the owner of herds of domesticated animals which are used for food, the food-supply has become regular, and is obtained by an application of the muscular system in highly specialized directions. Examples of this condition are, for instance, the central African negroes, who have their gardens near their villages, the cultivation of the gardens being essentially the work of the women, while the men are engaged in various specialized industrial pursuits. Neither is the manner of the use of the body which is applied by wild animals for protection against enemies found among these tribes. The manner of combat is one in which muscular strength alone is not decisive, but where excellence of weapons and strategy count as much as mere strength and agility. The conditions among the American agricultural Indians of the Mississippi Valley or of those of the South American forests are similar in character.

As an example of a pastoral people among whom considerable regularity in nutrition obtains, we might mention the reindeer-breeders of Siberia or the cattle-breeders of Africa.

We know, of course, that among all these people, periods of starvation occur, due to a failure of the crops or to epidemics in the herds; but the normal condition is one of fairly regular and ample food-supply.

The conditions among fishing tribes are not very different; and we find that, owing to methods of storing provisions, and to the superabundance of food-supply obtained in one season and sufficient to last for the rest of the year, the nutrition of these people is also fairly regular. In this case, also, the kind of muscular exertion required for obtaining food is specialized, and differs from that required from the simple pursuit of game.

The only modern tribes among which the effects of civilization on bodily activities are slight are those who, like the Bushmen of South Africa, the Australians, the Eskimo of Arctic America, the Veddahs of Ceylon, obtain their livelihood by the constant, daily-repeated pursuit of animals, or by the gathering of plants or small invertebrates which grow scattered over a wide area.

Connected with these conditions are also the characteristic selections of food-stuffs by different tribes, such as the exclusive meat diet of some tribes (perhaps most pronounced among the Eskimo) and the exclusive vegetable diet of others, well developed, for instance, in southern Asia. Both of these have, in all probability, a far-reaching effect upon the bodily form of these races.

The second group of causes which is most potent in developing distinct races of domesticated animals—namely, conscious selection—has probably never been very active in the races of man. We do not know of a single case in which it can be shown that intermarriage between distinct types of the same descent was prohibited; and whatever selection there may have been in the development of primitive society seems to have been rather that type of natural selection which encourages the mating of like with like, or such intricate selection as is due to the social laws of intermarriage, which prevented intermarriages of relatives of certain grades, and often also of members of different generations. Thus a very common form of marriage restriction brings it about that among certain tribes the children of brother and sister intermarry, while the children of brothers and the children of sisters are not allowed to intermarry. Similar restrictions are found in great number, and may possibly have had a certain selective effect, although their operation can hardly be assumed to have had very marked results upon the form of the human body (Pearson).

In some cases social laws have had the indirect effect of perpetuating distinctions between separate parts of a population, or at least of retarding their complete amalgamation. This is the case where laws of endogamy relate to groups of distinct descent, and may be observed, for instance, among the castes of Bengal, where the low castes are of the characteristic South Indian type, while the highest castes preserve the type of the tribes of northwestern India (Risley and Gait). The numerous intermediate castes show, however, that the laws of endogamy, even where they are as stringent as those of India, cannot prevent blood-mixture. Whether or not in extreme cases endogamy in small groups, as among the ancient Egyptians, has led to the development of well-defined types, is a question that cannot be answered; but it is certain that none of these types, when found in a large population, have survived.

The third element of domestication, on the other hand, has probably been very important in the development of the races of man. Crossings between distinct types are so markedly common in the history of primitive people, and so markedly rare in the history of wild animals, that in this case the analogy between domesticated animals and man becomes very clear. Cases of hybrid forms in nature are almost everywhere rare; while, as I have pointed out before, domesticated animals have been crossed and recrossed without end. Crossings between the most distinct types of man are also of very common occurrence. As an instance, I might mention the intermarriages between the Hamitic tribes of the Sahara and the negro tribes of the Soudan (Nachtigal); the mixtures between the Negritos and Malay, which are of such common occurrence in the Malay Peninsula (Martin), and which are probably to a great extent the cause of the peculiar distribution of types in the whole Malay Archipelago; the mixtures which have taken place in Fiji; that of the Ainu and Japanese in the northern part of Japan; of European and Mongol in eastern Europe; not to speak of the more recent mixtures between European and other races which were incident to the gradual distribution of the European race over the whole world.

This point of view—namely, the consideration of man as a domesticated being (with the sole exception, perhaps, of a few hunting tribes)—is also of great importance for a clear understanding of his mental activities. The behavior of primitive domesticated animals, like that of the Eskimo dog or of the Chukchee reindeer, is decidedly different from the behavior of wild animals. We might perhaps say that the range of mentality of the domesticated forms seems to be, on the whole, wider, and this condition increases with increasing degree of domestication. Cases in which the mental activities of domesticated animals are more deficient than those of the wild animals, do occur, but are not as frequent as the reverse cases. An example of this kind is furnished by sheep.

We are thus led to the conclusion that environment has an important effect upon the anatomical structure and physiological functions of man; and that for this reason differences of type and action between primitive and civilized groups of the same race must be expected. It seems plausible that one of the most potent causes of these modifications must be looked for in the progressive domestication of man incident to the advance of civilization.

III. INFLUENCE OF HEREDITY UPON HUMAN TYPES

WE will now turn to the consideration of another element which determines the physical type of man. Although we have seen that environment, particularly domestication, has a far-reaching influence upon the bodily form of the races of man, these influences are of a quite secondary character when compared to the far-reaching influence of heredity. Even granting the greatest possible amount of influence to environment, it is readily seen that all the essential traits of man are due primarily to heredity. The descendants of the negro will always be negroes; the descendants of the whites, whites; and we may go even considerably further, and may recognize that the essential detailed characteristics of a type will always be reproduced in the descendants, although they may be modified to a considerable extent by the influence of environment. I am inclined to believe that the influence of environment is of such a character, that, although the same race may assume a different type when removed from one environment to another, it will revert to its old type when replaced in its old environment. This point has not been proved by actual anthropological evidence; but it seems reasonable to make this assumption by analogy with what we know of the behavior of plants and animals. It would, of course, be highly desirable to clear up this question by appropriate investigations.

In order to obtain a clearer understanding of the racial problem, it seems necessary to describe more definitely the characteristics of heredity. In the discussion of modern anthropology, two theories have been advocated relating to the manner in which parental traits are inherited by children. Francis Galton and his adherents have assumed that the form of the body of an individual is determined by the racial type to which the parents belong, modified, however, by the tendency of reversion to a type intermediate between the special variations presented by the parents. When, for instance, the father of an individual is unusually tall, his mother somewhat taller than the average, it is assumed that the tendency of the children would be to develop a stature which is somewhat near the general type, but at the same time dependent upon the intermediate value located between the stature of the mother and that of the father. On the other hand, the development of the Mendelian doctrine (Lock, Bateson) of heredity has led other investigators to assume that the offspring of two distinct types may be a mixed type, but that his descendants will tend to revert either to one parental type or to the other, or that one of the parental types may dominate over the influence of the other parental type. Investigations relating to this problem are not very numerous; but, on the whole, it would appear that the results so far obtained are in favor rather of a modified form of Mendelian inheritance than of an inheritance characterized by reversion of the children to a middle type between the parents, or to a type dependent upon such a middle type.

A number of years ago I had an opportunity to investigate a considerable number of Indian half-bloods; that is to say, of descendants of Indian mothers and white fathers. The most characteristic difference between the American Indian race and the European race, so far as these differences can be expressed in metrical form, is found in the width of the face. An extensive series of measurements of width of face made among half-bloods showed conclusively that the width of face does not tend to range around a certain intermediate value located between the width of face of the white race and that of the Indian race, but there was a decided tendency in the children to resemble either the Indian race or the white race; in other words, that feature of Mendelian inheritance which brings about the occurrence of mixed characteristics in the first hybrid generation was not found, but instead of this a decided tendency of reversion to either type, and to comparative rarity of intermediate forms. The results seem also to indicate that the Indian form in this mixture seems to dominate over the white form, but not in the Mendelian sense, which would require the presence of dominant features in a certain definite number of individuals, but only in the sense that the Indian type was a little more frequent than the European type, with the effect that the average width of face of the whole series was a little nearer to the Indian group than to the white group.

While this single observation is not by any means sufficient to determine fully the characteristic traits of heredity which govern the phenomenon in question, they indicate decidedly and beyond cavil that, in this case at least, we find what has been called by Karl Pearson “alternating inheritance.” It is worth remarking that not all the features of the body of the half-blood Indian exhibit the same tendency; that, for instance, in the case of stature, a general increase in the stature of the mixed people over that of the pure races may be observed.

Attention has been called by Felix von Luschan to a similar phenomenon which occurs in the mixed population of southern Asia Minor, where he believes to have found an alternating inheritance of the head-form, particularly of the proportions between width and length of head; some of the people retaining the short, high head-forms of the Armenoid type of the interior of Asia Minor, while the others have the long, low head of the Semites of Syria.

For a clear understanding of the laws of heredity, it seems important to know whether a similar alternating inheritance occurs in marriages of members of the same type. I have been enabled to investigate this question by a study of the East European Hebrews living in New York. A simple consideration shows, that, if the children tend to follow a type intermediate between the type of their parents, then the children of one family will show the same degree of resemblance among themselves, no matter how great the difference between the parents; for, if they simply tend to reproduce a middle type, it would not make any difference whether the mother is excessively short and the father excessively tall, or whether both parents are of middle stature. In both of these cases the intermediate value would be the same, and we should therefore expect that the effect upon the children would be the same. If, on the other hand, there is any kind of alternation in inheritance, the effect upon the family would be quite different. We should expect, in a family of which both parents are near the typical average, to find the children also to be near this average. On the other hand, if the mother is excessively short and the father excessively tall, we should expect some of the children to follow the mother in regard to shortness of stature, others to follow the father in regard to tallness. It will therefore be seen that in the case of alternating inheritance, we must expect an increased variability among the children. The compilation of material obtained from several thousand families shows very definitely that the variability among children both of whose parents belong to the same racial type, even to the same local type, increases quite considerably with the increased difference of the parents; so that we may assume a decided tendency to alternating inheritance in these cases. There is, however, no evidence whatever of the dominance of one type over another.

Quite a number of investigations have been made in relation to the intensity of heredity of parents and of grandparents; and, notwithstanding the uncertainty of the quantitative result, it seems reasonably certain that the intensity of heredity for each parent may be expressed by the value of about one-third (Pearson, Boas). It is somewhat difficult to explain clearly the significance of this value. I may, however, briefly indicate it in the following manner. Provided the mother differs in her stature by an amount of 9 cm. from the racial norm,—for instance, if she is 9 cm. taller than the average individual,—then we may expect the child to be one-third of 9 cm., or 3 cm., above the average. It will thus be seen that if both parents differ in the same direction from the average, the effect of both will be cumulative; and if both differ from the average of their people by the same amount, the joint effect of the two parents may be expressed by the coefficient of about two-thirds. In case, for instance, both father and mother should be 9 cm. above the type average, we should expect the child to be about two-thirds of 9 cm., or 6 cm., above the average.

Although definite information on the amount of heredity of previous generations is not yet available, the probability seems to be that the grandparents have jointly an influence of about two-ninths, the great-grandparents jointly of about two twenty-sevenths, etc., upon the offspring.

When we study these problems according to statistical theories, and take into consideration the observations on the resemblance of brothers and sisters, it can be shown that the theory of alternating inheritance cannot be taken too literally; for, if there were an absolute reversion of any one trait to pure ancestral types, we might say that the probability would be very small that two brothers should happen to repeat the bodily form of the same ancestor, because the number of ancestors in remote generations is very large. In other words, there must be an additional cause of resemblance between brothers and sisters. It is possible to show, that in case the inheritance has the strength denoted before, and if bodily form of a certain generation were due only to alternating inheritance acting from parents, grandparents, great-grandparents, and so on, and directly upon the generation in question, and without an occurrence of the same individuals in various places in the line of ancestors, then the resemblance between brothers and sisters, or, as we say, between the members of a fraternity, would result in a degree of resemblance which is much lower than the one actually observed. When the total number of ancestors is small, the recurrence of the same forms would become more probable, and the similarity of the series would increase. On the whole, the data seem to be best explained if we assume that there is not only alternating inheritance, but also a direct dependence upon the combination of the two parental types.

I should like to repeat here that these results have not been obtained with absolute certainty, and that it seems improbable that the laws of heredity in regard to various ancestral traits are the same. I do not enter into a discussion of the question of in how far these traits follow the laws of Mendelian inheritance,—a question that cannot be answered definitely at the present time (Davenport).

These problems have a fundamental importance for a clearer interpretation of the conditions which prevail in the form of local types of man.