had become accustomed in the Indo-Malaysian abode. Furthermore, upon the final retreat of the ice the people of the north became marked off from the inhabitants of the south by climate bounds. Regarded collectively, therefore, Mongols, Caucasians and Americans alike may be distinguished from the tropical Negroes as products of the temperate zone. The several stocks that migrated northward from the Indo-Malaysian abode were, however, separated from each other from the start by the mountain barriers and open seas that intervened between the different lines of march. Thus though subjected to somewhat the same climatic conditions during the period of dispersion, upon settling in their respective habitats, the geographic groups were influenced by different surroundings. As a result, ethnic diversity was established along the northern latitudes, and the three temperate races became separated from one another by topographic differences. Taking this as our clue we may go back again to the original point of departure and follow the several lines of northerly dispersion in detail.
As was indicated above, the Indo-Malaysian cradle-land is cut off from the Asiatic area by the Himalayan line. Passage was possible, however, between the longitudinal ranges of Cochin-China, and, judging from the remains that have recently been discovered in this mountainous region, it is probable that primeval man proceeded northward along these lines during the interglacial epochs. The effect of the Himalayan barrier was, therefore, not so much to prevent migration into the continental area, as to shut the Asiatic immigrants in, and separate them from the inhabitants of the south. Those that remained in this region—Mongols in the forming—must, accordingly, have been subjected for long ages to the influences of their own surroundings.
This Asiatic area is not characterized by any such uniformity as the eastern equatorial region, but as nature has operated here upon so stupendous a scale, there is still a certain sameness in the salient features of the environment. Speaking generally, Asia is a continental territory, made up for the most part of bleak plateaux and deforested steppes. Such at least were the prevailing conditions which impressed themselves upon the majority of the original inhabitants and constituted the basic type. The Mongolians may thus be regarded as the product of temperate plains, much as the Negroes were considered to be the children of the tropical forest.
Here as elsewhere, however, variations from the characteristic environment made for corresponding modifications of the normal ethnic type. Being of such enormous extent and cut off on two sides from the sea, the climate of the Asiatic section is predominantly continental. Nevertheless, as the region stretches from the Arctic circle to the tropic of Cancer, and rises in altitude from 100 feet below to 25,000 feet above sea-level, there is naturally a wide range of temperature within