The natural world exercises its greatest influence in varying human society through the materials which it provides for man to appropriate or work upon. Where there are no available materials, as in the polar regions, on high mountains, in regions of excessive aridity, and on the deep sea, the earth remains a desert except as it may be necessary to pass through from one habitable locality to another. Amount and variety of food sets the limit to population; food depends on animal and vegetable life, the former in turn depending on the latter; then vegetable life depends on soil and climate. The food materials available determine directly or indirectly the occupations in which a large portion of the people must engage. The Germans have a pun to express the importance of food, Mann ist was Mann isst, "Man is what he eats," though it loses half its point in being translated.

Materials for clothing are perhaps next in importance. This is well illustrated by the fur-trade in the far north, which tempts white men into a life of semibarbarism, and offers the aborigines a larger reward for adhering to their old pursuits of hunting and trapping than they could obtain by the occupations of civilization. Materials for fuel and building, since they exist only in certain localities, fix the occupations of the peoples possessing them, especially in cold climates. Rich deposits of the metals do the same, provided the people have learned how to work them. Iron nowadays means a large manufacturing population, provided coal is within easy reach. The precise location of the iron works must be at some point where it is convenient to bring the coal and iron together and ship away the heavy products, as witness Pittsburgh, Philadelphia, the cities around the south end of Lake Michigan, Essen, and the two Birminghams.

Though commerce be subject to great revolutions, yet it is possible that certain physical causes, as the quality of the soil, or the climate, may fix its nature for ever.

In Europe there is a kind of balance between the southern and northern nations. The first have every convenience of life, and few of its wants: the last have many wants, and few conveniences. To one nature has given much, and demands little; to the other she has given but little, and demands a great deal. The equilibrium is maintained by the laziness of the southern nations, and by the industry and activities which she has given to those of the north. ...

. . . The trade of Europe is, at present, carried on principally from the north to the south; and the difference of climate is the cause that the several nations have great occasion for the merchandise of each other. - Montesquieu, op. cit., Book XXI, 1, 2, 3.