Note 217 — Chapter IV · —The Movements Of Peoples In Their Geographical Significance

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