Many of the characteristics acquired in the old home still live on, or at best yield slowly to the new environment.

This is especially true of the direct physical and psychical effects.

But a country may work a prompt and radical change in the social organization of an immigrant people by the totally new conditions of economic life which it presents.

These may be either greater wealth or poverty of natural resources than the race has previously known, new stimulants or deterrents to commerce and intercourse, and new conditions of climate which affect the efficiency of the workman and the general character of production.

From these a whole complex mass of secondary effects may follow.
The Aryans and Mongols, leaving their homes in the cool barren highlands of Central Asia where nature dispensed her gifts with a miserly hand, and coming down to the hot, low, fertile plains of the Indian rivers, underwent several fundamental changes in the process of adaptation to their new environment.