It is the task of the student of human evolution to unravel the tangled threads of human histories. The task is relatively simple when it is concerned with recent times where the aid of written history may be summoned but when the events of remote and prehistoric ages are to be placed in order, the difficulties seem well-nigh insuperable. All is not known, nor can it ever be known; but wherever facts can be established, science can deal with them. By a study of the present races of mankind, much of their earlier history can be worked out, for their genetic relations may be determined by employing the principle that likeness means consanguinity. Let us suppose an alien visitor to reach our planet from somewhere else; if he were endowed with only ordinary human common-sense, he would very soon ascertain the common origin of the English-speaking people in Canada, the United States, Australia and New Zealand, South Africa, and many other places. Even if he could not understand a word of the English language, he would be justified in regarding them all as the descendants of common ancestors because they agree in so many physical qualities. The anthropologist works according to the same common-sense principle, obtaining results that find no explanation other than evolution when the varying characters that are used to determine social relationship are properly classified and related. It is to these characters that we must now give some attention. * * * * * The average stature of adults varies in different races from four feet one inch in certain blacks to nearly six feet and seven inches, as among the Patagonians. These are the extreme values for normal averages, although dwarfs only fifteen inches high have been known, while "giants" sometimes occur with a height of nine feet and five inches. Such individuals are of course rare and abnormal, and are not to be taken into account in establishing the average stature of a race for use in comparison with that of another group. The color of the skin is another criterion of racial relationship, though it is more variable in races of common descent than we are wont to assume. We are familiar with the fair and florid skin of the northern European, the fair and pale skin in middle and southern Europe, the coppery red of the American Indian, the brown of the Malay, of the Polynesian and of the Moor, the yellowish cast of the Chinese and Japanese, and the deeper velvety black of the Zulu; but it has been found that many of the close relatives of the black are lighter in skin color than some of our Caucasian relatives, so that this character cannot be taken by itself as a single criterion of racial affinity.