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