The unity of nature and of its processes is established more and more surely as the naturalist classifies the facts of structure, development, fossil history, and evolutionary method.  Our own species is not unique; it takes its high place among other organic forms whose lives are controlled in every way by the uniform consistent laws of the world.

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The physical evolution of human races is the next major division of the large subject before us.  Heretofore the obvious differences displayed by various races have been disregarded and the species has been treated as a unit, in order that its evolution from pre-human ancestors might be made clear.  Knowing now how the facts of structure show that the supreme position of our kind has been attained mainly as the result of the progressive elaboration of the higher portions of the brain, and not because new and unique structures have been developed, we are prepared to turn our attention to the diverse characteristics of human races; and during this inquiry anatomical matters will still be the only ones to be reviewed.  The intellectual and social characters of numerous races belong to the category of physiological or functional phenomena, which are to receive due consideration at a later time.  It is the meaning of the facts of racial diversity for which we are now to look.

For many reasons this subject is more difficult to describe in a concise outline than those taken up before.  It is true that every one is familiar with different types of human beings, such as the Negro and Japanese and Chinese, while furthermore the obvious differences between such races as the Norwegian and Italian are sufficiently marked to strike the attention of any one who looks about at his fellow-passengers in a crowded street car.  But few indeed have a comprehensive knowledge of the wider range of racial variation in which these familiar examples find their place.  Anthropology, or the science of mankind, is a large and well-organized department of knowledge, dealing with the entire array of structural and physiological characters of all men.  One of its subdivisions, anthropometry, is almost an independent discipline with methods of its own; it describes the characteristics of human races as these are determined by statistical methods of a somewhat technical nature.  There is still another science, ethnology, which deals more particularly with institutions, customs, beliefs, and languages rather than with physical matters, although it is clear that ethnology and anthropology cannot be sharply separated, and that each must employ the results of the other for its own particular purposes.