The last great ice age was approaching, and where once the forest had grown thickly, the trees were becoming scant. The forest-belt receded before the advancing world of ice, which came out of those parts which are now Scandinavia, and its place was taken gradually by barren tundras or steppes. In the forest had dwelt a strange race, common stock of ourselves and the apes. These beings had lived in the trees, an arboreal life, far above the ground, more or less secure from the terrible beasts that stalked those parts of the world. When in a slow process of many hundreds of years the tree-belt receded, a large proportion of the tree-dwelling race went with it into the south, maintaining by migration the ease and safety of their old conditions. These migrants were the ancestors of the African monkey, born in the freedom and comparative security of the jungle, faithful to the old conditions and the old environment, to which they became more and more perfectly adapted in succeeding generations. But what of those who remained behind? From tree-dwellers they had become earth-dwellers. They must painfully adapt themselves to an entirely new environment, and learn new ways of feeding, moving, living, at bitter cost to the individual and to the race. They were no longer safe from marauding beasts, the giant mammoths and buffaloes and elks that preyed over the steppes. It would seem as if they had made an evil choice, and would have been wiser had they done as others of their race and clung to their old conditions, following the tree-belt southward. Nothing but destruction could come of this defiance of their environment, this painful adoption of new ways. Those who remained after the trees were gone must surely perish. But this first race of men (that yet were not quite men) had not acted entirely without light. Descending from the trees to the ground, their hands and arms, used hitherto for climbing, were now set free for enterprise. At last man stood upright. The ages went by, and his hands, no longer needed for mere balance and locomotion, learned skill. He picked up objects, used them, shaped them, and with using the power and scope of using grew. At the same time, the dangers with which he was beset sharpened his brain into resource and constructive planning. His reason came to have a definite survival value in the scheme of things. At first it had been by strength alone that living things survived. Those were the days when the ichthyosaurus and the giant iguanodon roamed the earth. Then the survival factor changed, and the battle was to the swift—instead of the ichthyosaurus and the iguanodon flourished the reindeer and the hare. But now at last mind became dominant, and mankind triumphed by virtue of his better brain development, both over the swift and over the strong. His brain taught him stratagem to atone for his lack of swiftness, it gave him skill to make weapons so that his weakness was a match for the strength of his enemies.