At the close of his arboreal life the ape had inherited or acquired the following assets: His vertebrate and mammalian structure had given him a large, vigorous, compact, athletic, adaptable body. The mammalian care of the young had insured their survival, but only at the expense of great strain and risk of the mother. Something at least approaching family life was already attained. Arboreal life with its gymnastic training had moulded the body, differentiated hand and foot, given the possibility of erect posture, emancipating the hand from the work of locomotion and setting it free to become a tool-fashioning and tool-using organ. The ape has keen sense-organs, an eye for distances, and other conditions; and the use of these powers has given him a brain far superior to that of any of his humbler fellows. These are full of great possibilities and opportunities, if he will only use them. But why did our ancestor descend from his place of safety in the trees and live on the ground, exposed to the attacks of fierce, swift, and well-armed enemies? Very few of the Primates, except the rock and cliff-inhabiting baboons, ever made this great venture. There must have been some quite compelling argument to induce him to take so great a risk. The change took place probably at some time during the latter half of the Cenozoic or Tertiary period, the last great division of geological time, the Age of mammals.[5] The earliest Tertiary Epoch, the Eocene, was a time of warm and equable climate, when apes lived far north in Europe, and doubtless in Asia also. Some of these apes were of fair or large size, showing that conditions were favorable and food abundant. The next epoch, the Oligocene, was similar but somewhat cooler. The third, the Miocene, was cooler still and dryer. Palms now forsook northern Europe, being gradually driven farther and farther south. Life became more difficult, food scarcer. Apes could not longer survive in northern Europe, but had to seek a warmer, more favorable, environment farther south, for many of the fruit and food trees had been crowded out and famine threatened.[6] But insects and other small and toothsome animals remained on the ground, and were abundant along the shores of rivers and lakes. There, too, were fruits and berries, roots and tubers. There the food supply was still more than sufficient.