After thus clearing away the racial prejudice, the most formidable obstacle to a clear understanding of our problem, we turned to an investigation of the question whether human types are stable, more particularly whether environment may change the anatomical structure of man, and thus of his mental make-up, and to the correlated question, what man owes to heredity. In treating the general question of the stability of human types, we described some rudimentary organs and some peculiar anatomical traits which prove a phylogenetic development of man, traces of which were found in all races. The influence of environment was demonstrated in all those cases in which changes in the rate of growth affected the final form of the body; and we saw particularly that early arrest of development does not necessarily mean unfavorable development, because in many cases the rapidity and short period of development seemed favorable elements. We saw that other changes in human types may be brought about by selection, and that environment itself seems to have a direct effect upon bodily form, as was proved by the changes of type due to the transfer from a rural environment to city life, and to the immigration of various nationalities from Europe to America. We saw, however, that there is no evidence at present to prove that these changes exceed certain definite limits. Special attention was directed to those features of the bodily form that characterize man as a domesticated animal, and which are due to the peculiarities of human nutrition, and which facilitate crossing of distinct types. The mentality of man appeared also to be influenced by the degree of his domestication. Turning to the influence of heredity, we recognized that by it are determined all the most fundamental features of each race and type of man, and that often the individual reverts to the traits of the one or the other of his parents, or of his remote ancestors, in such manner that one trait may belong to one ancestor, another to another. This tendency seemed to explain the development of local types, and we recognized the importance of the breaking of old fines of heredity, in cases of intermarriages of branches of the same race that had long been separated. By analogy we concluded that possibly, or probably, similar tendencies may exist in the mental life of man.