History in its broadest aspect is a record of man's migrations from one environment to another.
The human organism inherits so delicate an adjustment to climate that, in spite of man's boasted ability to live anywhere, the strain of the frozen North eliminates the more nervous and active types of mind.
For the source of any characteristic so widespread and uniform as this adaptation to environment we must go back to the very beginning of the human race.
Except on their southern borders the great northern forests are not good as a permanent home for man.
Curiously enough man's body and his mind appear to differ in their climatic adaptations.
Fertile soil, level plains, easy passage across the mountains, coal, iron, and other metals imbedded in the rocks, and a stimulating climate, all shower their blessings upon man.
In fact, the history of North America has been perhaps more profoundly influenced by man's inheritance from his past homes than by the physical features of his present home.
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.