in every generation tasks are carried out by intellectual athletes, toward which all the ordinary men in the world, uniting their efforts, could do nothing—absolutely nothing. § 4. PREY AND COMPETITORS If we suppose the differentiation of the _Hominidæ_ from the _Anthropoidea_ to have begun in the Upper Oligocene, and that the decisive change was initiated by some ape that adopted the life of a hunter, it is interesting to consider what the world was like in which he lived, what sort of animals surrounded him, what animals probably became his prey, and what were his rivals in the chase.[25] The surface of the planet was less mountainous than at present; in Europe the Pyrenees had risen, but the Alps were only beginning to rise; and in Asia the Himalayas began to dominate the world only in the middle of the next epoch, the Miocene. The distribution of land and water, too, was very different in the Oligocene from that which we now see: Europe was divided from Asia by a broad gulf stretching from the Indian Ocean to the Arctic Circle, and an arm of this gulf toward the west submerged a great part of Central Europe; Asia was broadly connected with North America, where now the sea penetrates between Siberia and Alaska; Africa had no connection with either Europe or Asia; North and South America were separated—perhaps at Panama. In the Miocene, Europe, Asia and Africa became united. These physiographic changes may have affected climate; for during the Eocene tropical conditions prevailed far to the north, and coal-beds were laid down in Alaska; but from the Oligocene onwards there was a gradual fall of temperature, slow at first, but ending (for the present) in the cataclysms of the Glacial Period. There was also a decrease in some regions of atmospheric moisture, which determines the density of vegetation. In its general character the vegetation was similar to that which now prevails in tropical, subtropical and temperate regions of the world. The species of plants now existing had not yet arrived; but of the same genera and families as those we see, conifers, palms and dicotyledonous flowering plants crowded the forests and overhung the rivers. The forests were more extensive and continuous than ours outside the tropics; for by degrees browsing animals, feeding down the young trees, check the renovation of forests and clear open spaces, where grasses grow; changes of temperature limit the northern or southern extension of certain kinds of plants, and a failure of humidity starves all the larger kinds; converting, at successive stages, forest into steppe and steppe into desert.