Almost all the apes found their old environment and continued their arboreal life by migrating far southward through India or into Africa. But at the rear of the retreating host were forms from the cooler northern regions. They were hardy and vigorous, and probably larger than most of their fellows. Possibly some of them were caught in isolated decreasing areas of forest surrounded by steppe or plain. Some of them, at least, began to descend from the trees, to seek the new food supplies of riversides, glades, and thickets, and thus gradually to become accustomed to life on the ground. It was a very hazardous experiment; only the most hardy and wary and the quickest in perception, wit, and movement survived. Among these were our ancestors, driven like all their forebears by the spur of necessity into a new mode of life under trying conditions. They were still only apes, with long arms and short legs, and probably scrambled mostly on all fours. They had heavy brows, retreating foreheads, projecting jaws, and a brutal physiognomy. Of the mental life of the man who was to be descended from them there were few signs. They were bundles of very slight possibilities. But let us not "despise the day of small things." They were still far from the invisible line between apedom and manhood. Physically they resembled man quite closely. They had hand and foot, and a fair-sized brain, though they had scarcely begun to realize the possibilities of these structures. Arboreal life could teach them little more; continuance in that school would have meant a very comfortable stagnation. They were now promoted to a new school of vastly more difficult problems, greater risks and dangers, and more severe and trying discipline. They had had an excellent course of manual and sensory training; now they must continue this and add to it the use of whatever wits they had, under peril of death. Nature was still compelling them to "move on." This descent to the ground probably was accomplished either in India or on the Iranian plateau, or somewhat farther to the northeast, somewhere in the great horseshoe of parkland which curved around the western buttress of the great central Asiatic plateau of Thibet. Can we locate it somewhat more definitely?[10]