He goes on to show, however, that the initiation of progress does not require only that the men concerned in it should inhabit a region in which the production of necessaries is easy and leaves them abundant leisure. It is equally essential that the men themselves should possess an energetic {30} temperament, which will not suffer them to devote their leisure to idleness, but will make it the starting-point for some further activity. Now this energetic temperament is the special gift of climate. So, to a great extent, is the ease with which necessaries are obtained from the soil; but whilst the fertility of the soil is dependent on the climate being hot, the requisite energetic temperament is dependent on the climate being dry. “_The evidence_,” says Mr. Spencer, “_justifies this inference. . . . On glancing over a general rain-map of the world, there will be seen an almost continuous area, marked ‘rainless district,’ extending across North Africa, Arabia, Persia, and all through Thibet and Mongolia; and from within, or from the borders of this district, have come all the conquering races of the Old World._” But the full operation of climate on human progress is not intelligible till a further climatic fact is considered. Though in hot and dry climates the production of necessaries is easy, in climates that are hot and moist their production is still easier. It is these last that are really the gardens of the world, and that offered to primeval man the easiest and most attractive homes. The original inhabitants, however, of these favoured localities not only profited by their conditions, but also ultimately suffered from them. Whilst the fertility of their habitat pampered them, its moisture destroyed their energy; and in process of time they were subjugated by other races, who, cradled in drier climates, {31} retained their energy unimpaired. In this natural descent of the stronger races on “_the richer and more varied habitats_” of the weaker, and the consequent super-position of one race over another, we see the origin of slavery, and of all the ancient civilisations that reposed upon it. We have here the three essential elements to the union of which primarily all human progress has been due: firstly, a race remarkable for its active energy; secondly, the appropriation by this race of some richer habitat than its own; and thirdly, the possession by it of an inferior race, as subjects, who are ready to work for its benefit, and are capable, when coerced and directed by it, of producing wealth indefinitely greater and more varied than they would or could have produced had they been left to their own devices.