Europe, except for its small sub-arctic area, has received immigrants, according to the testimony of history and ethnology, only from the temperate parts of Asia and Africa, with the one exception of the Saracens of Arabia, whose original home lay wholly within the hot climate belt of 20 deg.C. (68 deg.F.).  Saracen expansion, in covering Persia, Syria, and Egypt, still kept to this hot belt; only in the Barbary Coast of Africa and in Spain did it protrude into the temperate belt.  Though this last territory was extra-tropical, it was essentially semi-arid and sub-tropical in temperature, like the dry trade-wind belt whence the Saracens had sprung.

[Illustration:  ETHNOGRAPHICAL MAP OF AFRICA AND ARABIA.]

[Sidenote:  Range of movements in Africa.]

The Semitic folk of Arabia and the desert Hamites of northern Africa, bred by their hot, dry environment to a nomadic life, have been drawn southward over the Sahara across the Tropic into the grasslands of the Sudan, permeating a wide zone of negro folk with the political control, religion, civilization and blood of the Mediterranean north.  Here similar though better conditions of life, a climate hotter though less arid, attracted Hamitic invasion, while the relatively dense native population in a lower stage of economic development presented to the commercial Semites the attraction of lucrative trade.  South of the equator the native Bantu Kaffirs, essentially a tropical people, spread beyond their zonal border to the south coast of Africa at 33 deg.  S.L., and displaced the yellow Hottentots[199] before the arrival of the Dutch in 1602; while in the early nineteenth century we hear of the Makololo, a division of this same Kaffir stock, leaving their native seats near the southern sources of the Vaal River at 28 deg.  S.L. and moving some nine hundred miles northward to the Barotse territory on the upper Zambesi at 15 deg.  S.L.[200] This again was a movement of a pastoral people across a tropic to other grasslands, to climatic conditions scarcely different from those which they had left.

[Sidenote:  Colonization and latitude.]

The modern colonial movements which have been genuine race expansions have shown a tendency not only to adhere to their zone, but to follow parallels of latitude or isotherms.  The stratification of European peoples in the Americas, excepting Spanish and Portuguese, coincides with heat zones.  Internal colonization in the United States reveals the same principle.[201] Russian settlements in Asia stretch across Siberia chiefly between the fiftieth and fifty-fifth parallels; these same lines include the ancient Slav territory in Germany between the Vistula and Weser.  The great efflux of home-seekers, as opposed to the smaller contingent of mere conquerors and exploiters, which has poured forth from Europe since the fifteenth century, has found its destinations largely in the temperate parts of the Americas, Australia, New Zealand, and