Whatever be the cause of the variation, there is no doubt that there is a north and south swing of the wet and dry belts, so that there are on the west seven climatic zones : there is a narrow strip along the shores of the Mediterranean which has most rain in winter; then follows a broader belt, the Sahara, on which rain is rare, stretching from east to west across the continent with the northern tropic as axis ; this is succeeded by a somewhat narrower belt, the Sudan, with a wet summer but a dry winter; the equatorial regions have constant rain, greatest when the sun is overhead at midday; southwards the zones are repeated, but it must be noticed that it is " summer " in the North when it is " winter " in the South, and that the " zones " have little extent in longitude, partly because of the smaller area of land, and partly because there is an ocean to the east. The terms " winter " and " zone " are in this case somewhat misleading. The dry area in the south—the Kalahari—does have considerably more rain than the Sahara, and the area which has " winter " rains is only a small region in the extreme south-west. On the east, north of the equator, the influence of the great land mass to eastwards is such that the west coast zones are continued right across the continent. South of the equator the east coast has rains in summer.
The effect of this distribution of rainfall on the vegetation is very striking. Under the influence of the heavy rains and intense heat, great forests have grown on either side of the equator, occupying a large part of the Congo Basin and the shores of the Gulf of Guinea, and a similar though not so dense forest fringes the coast of the Indian Ocean from Zanzibar southwards ; where rain falls so seldom as to be extraordinary, stretches the great desert of the Sahara ; but elsewhere, owing to the lack of rain at some season, there is an extensive grassland, park-like in some parts, tending to desert in others, supplying food for animals which live on grass, especially all kinds of cattle and deer, which at the same time can stand considerable heat. This grass land stretches from the western Sudan right across Africa, and southwards almost to the Cape, filling almost the whole of the continent south of the equatorial forest.
Here, then, are the great geographical factors which have influenced man, civilized, semi-civilized, barbarian and savage. The great equatorial forest is no place where civilization may grow, but it must be remem bered that it is like all forest in that it hinders the movement of organized bands of men coming in peace or war. In Egypt, protected by the desert on either side, with a double water-supply from the equatorial region of constant rain and Abyssinia with summer rain, men might first find how to save energy on a great scale, and we have seen that they did so. On the great
flat expanse of grassland men could wander as do the steppe peoples of Euro-Asia, but while these are essential similarities, due to the similarities in the conditions, there are no less essential differences, because the differences in the conditions are great. In Africa it is never cold; no preparations need be made to withstand the cold; clothing, a necessity of the steppe-dweller, is by no means essential, and there is the less necessity to save. The grasslands, except along the borders of the desert, are not so dry as are the steppes of Asia, and even the dry lands are not so compact. The result, on the one hand, is that there is a greater possi bility of cultivating the soil and less need for living a purely pastoral life, and, on the other, the more purely pastoral tribes tend to dominate the agricultural as the wandering Arabs dominate those of the oases, and as the nomads of Central Asia dominated the farmers of the margin lands till a few centuries ago. There is thus less necessity to be hardy, and there is a greater possibility, almost amounting to a certainty, that the more powerful pastoral tribes, being the less civilized, will prevent the growth of any habits of saving among those whom they dominate.
Indeed, the history of Africa south of the Sahara, in so far as it may be said to have a history at all, consists in the story of the comparatively slow move ments of the different pastoral tribes over those grass lands, settling for a time in certain areas, undertaking a little agriculture, and establishing a military organiza tion by which they were able either to exact tribute from subject tribes or to exterminate them, but never founding anything resembling a civilized state. Even so, the existence of the ancient civilization to the north, and of peoples in touch with that civiliza tion, especially on either side of the Red Sea, seems always to have had an effect. The slow movements of these pastoral tribes appear to have originated almost invariably somewhere in the north-east, in touch to a greater or less extent with that civilization, and to have taken two main routes, westwards through the Sudan and southwards over the high plateau, driving the earlier peoples, such as Bushmen and Hottentots, still farther southwards to the Cape, or into the forest, and giving their names in more or less mutilated form to the lands in which Europeans found them. Zulu and Matabili, Mashona and Masai, have all moved southwards within the last thousand years or so into the regions now called after them.