Contrasted environments effect a natural selection in another way and thereby greatly stimulate differentiation, whenever an intruding people contest the ownership of the territory with the inhabitants. The struggle for land means a struggle also for the best land, which therefore falls to the share of the strongest peoples. Weaklings must content themselves with poor soils, inaccessible regions of mountain, swamp or desert. There they deteriorate, or at best strike a slower pace of increase or progress. The difference between the people of the highlands and plains of Great Britain or of France is therefore in part a distinction of race due to this geographical selection,[214] in part a distinction of economic development and culture due to geographic influences. Therefore the piedmont belts of the world, except in arid lands, are cultural, ethnic and often political lines of cleavage, showing marked differentiation on either side. Isotherms are other such cleavage lines, marking the limits beyond which an aggressive people did not desire to expand because of an uncongenial climate. The distinction between Anglo-Saxon and Latin America is one of zone as well as race. Everywhere in North America the English stock has dominated or displaced French and Spanish competitors down to the Mexican frontier.
As the great process of European colonization has permeated the earth and multiplied its population, not only the best land but the amount of this has commenced to differentiate the history of various European nations, and that in a way whose end cannot yet be definitely predicted. The best lands have fallen to the first-comers strong enough to hold them. People who early develop powers of expansion, like the English, or who, like the French and Russians, formulate and execute vast territorial policies, secure for their future growth a wide base which will for all time distinguish them from late-comers into the colonial field, like Germany and Italy. These countries see the fecundity of their people redounding to the benefit of alien colonial lands, which have been acquired by enterprising rivals in the choice sections of the temperate zone. German and Italian colonies in torrid, unhealthy, or barren tropical lands, fail to attract emigrants from the mother country, and therefore to enhance national growth.
Two-type populations.
When colonizers or conquerors appropriate the land of a lower race, we find a territory occupied at least for a time by two types of population, constituting an ethnic, social and often economic differentiation. The separation may be made geographical also. The Indians in the United States have been confined to reservations, like the Hottentots to the twenty or more "locations" in Cape Colony. This is the simplest arrangement. Whether the second or lower type survives depends upon their economic and social utility, into which again geographic conditions enter. The Indians of Canada are a distinct economic factor in that country as trappers for the Hudson Bay Company, and they will so remain till the hunting grounds of the far north are exhausted. The native agriculturists in the Tropics are indispensable to the unacclimated whites. The negroes of the South, introduced for an economic purpose, find their natural habitat in the Black Belt. Here we have an ethnic division of labor for geographical reasons. Castes or social classes, often distinguished by shades of color as in Brahman India, survive as differentiations indicating old lines of race cleavage. There is abundant evidence that the upper classes in Germany, France, Austria, and the British Isles are distinctly lighter of hair and eyes than the peasantry.[215] The high-class Japanese are taller and fairer than the masses. Nearly all the African tribes of the Sudan and bordering Sahara include two distinct classes, one of lighter and one of darker shade. Many Fulbe tribes distinguish these classes by the names of "Blacks" and "Whites."[216] The two-type people are the result of historical movements.
Differentiation and isolation.
Differentiation results not only from contrasted geographic conditions, but also from segregation. A moving or expanding throng in search of more and better lands drops off one group to occupy a fertile valley or plain, while the main body goes on its way, till it reaches a satisfactory destination or destinations. The tendency to split and divide, characteristic of primitive peoples, is thus stimulated by migration and expansion. Each offshoot, detached from the main body, tends to diverge from the stock type. If it reaches a naturally isolated region, where its contact without is practically cut off, it grows from its own loins, emphasizes its group characteristic by close in-breeding, and tends to show a development related to biological divergence under conditions of isolation. Since man is essentially a gregarious animal, the size of every such migrating band will always prevent the evolution of any sharply defined variety, according to the standard of biology. Nevertheless, the divergent types of men and societies developed in segregated regions are an echo of the formation of new species under conditions of isolation which is now generally acknowledged by biological science. Isolation was recognized by Darwin as an occasional factor in the origin of species and especially of divergence; in combination with migration it was made the basis of a theory of evolution by Moritz Wagner in 1873;[217] and in recent years has come to be regarded as an essential in the explanation of divergence of types, as opposed to differentiation.[218]
Differentiation and digression.