black people, the Australians, the Asiatic negroids and the negroes, derive from one origin, but only that they have lived for vast periods under similar conditions. We must not assume that human beings in the eastern Asiatic area were all differentiating in one direction and all the human beings in Africa in another. There were great currents of tendency, it is true, but there were also backwaters, eddies, admixtures, readmixtures, and leakages from one main area to the other. A coloured map of the world to show the races would not present just four great areas of colour; it would have to be dabbed over with a multitude of tints and intermediate shades, simple here, mixed and overlapping there.
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 classi-
