There is, then, an absence of those conditions which just allowed of, and stimulated, the early development of civilizations so quickly as those of the Old World.
In North America, that land which is driest and most nearly desert stretched roughly from the north-west of the Gulf of Mexico, past the head of the Gulf of Cali fornia. Here it is warm at all seasons, and indeed hot in summer, so that life is comparatively easy where it is possible at all. Though rivers as a rule flow far below the general level of the land, yet here and there they may be used for irrigation by small communities. Farther south the plateau of Mexico is high, compara tively dry, difficult of approach across the dry land from the north, and difficult of approach through the dense forest that clothes the lower slopes to the east and south. Here is a warm land supplied with water by streams from the highlands to supplement a rainfall fairly abundant in summer but scanty in winter, and possessing a measure of protection. In the desert area to the north the water supply could support only a widely scattered population, but on the Mexican plateau there is a possibility that small communities might here and there come into contact with each other. There is neither the same measure of protection nor the same basis for a dense population as in Egypt, but at any rate it is the region most like Egypt in the New World north of the equator.
That the desert and the forest were by no means effective as barriers may be seen from what we know of Mexican history. Little, indeed, is known, but it seems probable that there has been a succession of waves of warlike peoples from this drier north, each of which first partly destroyed the more advanced form of civiliza tion which they found, and then made themselves the heirs of that civilization. Some may have come merely as nomadic hunters from the dry plains eastward of the Rocky Mountains; others may have brought some knowledge of arts of saving energy learned in the small isolated communities of the arid lands—of house-building with dried mud, " adobe," or of cultivation of maize for food and cotton for clothing. In any case, what we find in Mexico are small tribal communities living in permanent pueblos, or communal village houses of stone, clothed with cotton, and depending for food on grain stored in special granaries in these pueblos. Alliances of two or three pueblos for a time dominate those within a short distance, levy tribute of grain and cotton, and in turn are compelled to acknowledge the sway of other federations.
Here, on the one hand, there is considerable advance. Only by a settled life can great stores of energy be accumulated in a form other than that of flocks.. These people had settled to accumulate food energy of a kind which even now can be kept longer than any other, though it entails most trouble in preparation. The fruits eaten by the savage can be pulled and consumed at once; an advance has been made when he grubs up roots, for most of these require some treatment before they are eaten; but seeds of cereal grains, selected and improved by generations of farmers so that they become larger and larger, not only require care and attention when growing in order that the most may be made of them, but require much to be done to them after they are ripe before they are in the best form for food; think of the number of processes which wheat has to pass through before it is eaten, and compare them with those necessary to make apples and bananas or turnips and potatoes edible. Wheat the inhabitants of the New World did not know, but maize, the corn of the Indians, the cereal of the New World, was known. Requiring less attention than wheat when growing, and less need for preparation, it was in one form or another known all over the conti nent, It may be grown by a tribe who stay long enough in one place only to clear the ground of forest and plant the seeds, and who return when the crop is ripe to consume what has grown. In this case there is little saving. It may, however, be grown on the drier lands by irrigation, and part of the crop saved; this the early inhabitants of Mexico did. And not only had they enough stored energy from times of plenty to provide for scarcity, they were by this very accumulation of energy able to protect themselves ; the pueblos were practically fortresses within which the whole popula tion might withdraw, and living on their accumulated stores might be in a favourable position to withstand attack for a time. Further, their whole time was not taken up with an attempt to preserve life; they had sufficient energy to provide some of the ornaments of life, for simple sculpture, for the accumulation of pretty things of gold and silver which they had made.