From all this we see how fully justified is J. W. Powell's remark that the natural history of early man becomes more and more a geological, and not merely an ethnological problem[63]. We also begin to understand how it is that, after an existence of some five score millenniums, the first specialised human varieties have diverged greatly from the original types, which have thus become almost "ideal quantities," the subjects rather of palaeontological than of strictly anthropological studies. And here another consideration of great moment presents itself. During these long ages some of the groups--most African negroes south of the equator, most Oceanic negroes (Negritoes and Papuans), and Australian and American aborigines--have remained in their original habitats ever since what may be called the first settlement of the earth by man. Others again, the more restless or enterprising peoples, such as the Mongols, Manchus, Turks, Ugro-Finns, Arabs, and most Europeans, have no doubt moved about somewhat freely; but these later migrations, whether hostile or peaceable, have for the most part been confined to regions presenting the same or like physical and climatic conditions. Wherever different climatic zones have been invaded, the intruders have failed to secure a permanent footing, either perishing outright, or disappearing by absorption or more or less complete assimilation to the aboriginal elements. Such are some "black Arabs" in Egyptian Sudan, other Semites and Hamites in Abyssinia and West Sudan (Himyarites, Fulahs and others), Finns and Turks in Hungary and the Balkan Peninsula (Magyars, Bulgars, Osmanli), Portuguese and Netherlanders in Malaysia, English in tropical or sub-tropical lands, such as India, where Eurasian half-breeds alone are capable of founding family groups. The human varieties are thus seen to be, like all other zoological species, the outcome of their several environments. They are what climate, soil, diet, pursuits and inherited characters have made them, so that all sudden transitions are usually followed by disastrous results[64]. "To urge the emigration of women and children, or of any save those of the most robust health, to the tropics, may not be to murder in the first degree, but it should be classed, to put it mildly, as incitement to it[65]." Acclimatisation may not be impossible but in all extreme cases it can be effected only at great sacrifice of life, and by slow processes, the most effective of which is perhaps Natural Selection. By this means we may indeed suppose the world to have been first peopled.