When the physical unity of a group is perpetuated by the succession of parents and children, the racial temperament, including fundamental attitudes and values which rest in it, is preserved intact. When, however, society grows and is perpetuated by immigration and adaptation, there ensues, as a result of miscegenation, a breaking up of the complex of the biologically inherited qualities which constitute the temperament of the race. This again initiates changes in the mores, traditions, and eventually in the institutions of the community. The changes which proceed from modification in the racial temperament will, however, modify but slightly the external forms of the social traditions, but they will be likely to change profoundly their content and meaning. Of course other factors, individual competition, the formation of classes, and especially the increase of communication, all co-operate to complicate the whole situation and to modify the effects which would be produced by racial factors working in isolation. III. INVESTIGATIONS AND PROBLEMS 1. Conceptions of Human Nature Implicit in Religious and Political Doctrines Although the systematic study of it is recent, there has always been a certain amount of observation and a great deal of assumption in regard to human nature. The earliest systematic treatises in jurisprudence, history, theology, and politics necessarily proceeded from certain more or less naïve assumptions in regard to the nature of man. In the extension of Roman law over subject peoples the distinction was made between _jus gentium_ and _jus naturae_, i.e., the laws peculiar to a particular nation as contrasted with customs and laws common to all nations and derived from the nature of mankind. Macauley writes of the "principles of human nature" from which it is possible to deduce a theory of government. Theologians, in devising a logical system of thought concerning the ways of God to man, proceeded on the basis of certain notions of human nature. The doctrines of original sin, the innate depravity of man, the war of the natural man and the spiritual man had a setting in the dogmas of the fall of man, redemption through faith, and the probationary character of life on earth. In striking contrast with the pessimistic attitude of theologians toward human nature, social revolutionists like Rousseau have condemned social institutions as inherently vicious and optimistically placed reliance upon human nature as innately good. In all these treatises the assumptions about human nature are either preconceptions or rationalizations from experience incidental to the legal, moral, religious, or political system of thought. There is in these treatises consequently little or no analysis or detailed description of the traits attributed to men. Certainly, there is no evidence of an effort to arrive at an understanding of human behavior from an objective study of its nature.