Thus the races, though alike in their physical response to climate, may possibly be different in their mental response because they have approached America by different paths.
The evidence points to central Asia as man's original home, for the general movement of human migrations has been outward from that region and not inward.
Man could not stay there forever. He was bound to spread to new regions, partly because of his innate migratory tendency and partly because of Nature's stern urgency.
It seems strange that almost no other traces of the strong vikings are found in America.
Today, no less than in the past, the tetrahedral form of the earth and the relation of the tetrahedron to the poles and to the equator preserve the conditions that favor rapid evolution.
Although mountains may guide migrations, the plains are the regions where people dwell in greatest numbers.
Year by year we are learning that in this restless, strenuous American life of ours vacations are essential.
In America the most widespread type of forest is the evergreen coniferous woodland of the north.
Except on their southern borders the great northern forests are not good as a permanent home for man.
Nevertheless most of the evergreen forests of the north must always remain the home of wild animals and trappers, a backward region in which it is easy for a great fur company to maintain a practical monopoly.
As a matter of fact, an ordinary desert supports a much greater variety of plants than does either a forest or a prairie.
The coast of British Columbia was one of the three chief centers of aboriginal America.
Although farming of any sort was almost as impossible in the plains as in the dry regions of winter rains farther west, the abundance of buffaloes made life much easier in many respects.
From first to last the civilization of America has been bound up with its physical environment.
