No new types of races have been developed either by amalgamation or by transfer to new climatic and economic conditions in historic times. Contrasted geographic conditions long ago lost their power to work radical physical changes in the race type, because man even with the beginnings of civilization learned to protect himself against extremes of climate. He therefore preserved his race type, which consequently in the course of ages lost much of its plasticity and therewith its capacity to evolve new varieties.[233] Where ethnic amalgamations on a large scale have occurred as a result of the historical movement, as in Mexico, the Sudan and Central Africa, the local race, being numerically stronger than the intruders and better adapted to the environment, has succeeded in maintaining its type, though slightly modified, side by side with the intruders. The great historical movements of modern times, however, have been the expansion of European peoples over the retarded regions of the world. These peoples, coming into contact with inferior races, and armed generally with a race pride which was antagonistic to hybrid marriages, preserved their blood from extensive intermixture. Hybridism, where it existed, was an ephemeral feature restricted to pioneer days, when white women were scarce, or to regions of extreme heat or cold, where white women and children could with difficulty survive. Even in Spanish America, where ethnic blendings were most extensive, something of the old Spanish pride of race has reasserted itself. [Sidenote: Checks to differentiation.] Improved communication maintains or increases the ranks of the intruders from the home supply. The negroes in North America, imported as they were _en masse_, then steadily recruited by two centuries of the slave trade, while their race integrity was somewhat protected by social ostracism, have not been seriously modified physically by several generations of residence in a temperate land. Their changes have been chiefly cultural. The Englishman has altered only superficially in the various British colonial lands. Constant intercourse and the progress of inventions have enabled him to maintain in diverse regions approximate uniformity of physical well-being, similar social and political ideals. The changed environment modifies him in details of thought, manner, and speech, but not in fundamentals.