In the early Neolithic Period in Europe--it may be 10,000 or 12,000 years ago or so--man was differentiating all over the world, and he had already differentiated into a number of varieties, but he has never differentiated into different _species_. A “species,” we must remember, in biological language is distinguished from a “variety” by the fact that varieties can interbreed, while species either do not do so or produce offspring which, like mules, are sterile. All mankind can interbreed freely, can learn to understand the same speech, can adapt itself to co-operation. And in the present age, man is probably no longer undergoing differentiation at all. Readmixture is now a far stronger force than differentiation. Men mingle more and more. Mankind from the view of a biologist is an animal species in a state of arrested differentiation and possible readmixture. § 2 It is only in the last fifty or sixty years that the varieties of men came to be regarded in this light, as a tangle of differentiations recently arrested or still in progress. Before that time students of mankind, influenced, consciously or unconsciously, by the story of Noah and the Ark and his three sons, Shem, Ham, and Japhet, were inclined to classify men into three or four great races, and they were disposed to regard these races as having always been separate things, descended from originally separate ancestors. They ignored the great possibilities of blended races and of special local isolations and variations. The classification has varied considerably, but there has been rather too much readiness to assume that mankind _must_ be completely divisible into three or four main groups. Ethnologists (students of race) have fallen into grievous disputes about a multitude of minor peoples, as to whether they were of this or that primary race or “mixed,” or strayed early forms, or what not. But all races are more or less mixed. There are, no doubt, four main groups, but each is a miscellany, and there are little groups that will not go into any of the four main divisions. [Illustration: Bushwoman]