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.