Page:The Outline of History Vol 1.djvu/91

 human-looking jaw. In the Siwalik Hills of northern India remains of some very interesting apes have been found, of which Sivapithecus and Palæopithecus were possibly related closely to the human ancestor. Possibly these animals already used implements. Charles Darwin represents baboons as opening nuts by breaking them with stones, using stakes to prize up rocks in the hunt for insects, and striking blows with sticks and stones. The chimpanzee makes itself a sort of tree hut by intertwining branches. Stones apparently chipped for use have been found in strata of Oligocene Age at Boncelles in Belgium. Possibly the implement-using disposition was already present in the Mesozoic ancestry from which we are descended. In Conquest for February, 1920, Mr. R. I. Pocock published a very useful criticism of this section as it stood in the first version of the Outline. It has been carefully modified in accordance with his views. In addition, we take the liberty of quoting the following: "It was formerly held, I believe, that, so far as habits are concerned, the transitional steps in man's descent were to be traced from an active arboreal monkey to the equally active arboreal gibbon, and thence to the less active, but still mainly arboreal, orang-utang; from the latter to the half arboreal, half terrestrial chimpanzee, thence, through the mainly terrestrial gorilla, to wholly terrestrial man. In other words, the stages of man's evolution were a series of structural modifications resulting from the gradual dropping of the ancestral habit of living in trees in favour of life on the ground. But such a conception leaves unexplained the great differences between monkeys and gibbons in arboreal and terrestrial activity. Were it correct, we should expect the gibbons to show a transition between monkeys and other apes in their method of moving through trees and on the ground. They show no such transition. It is necessary, therefore, to formulate another theory. "Since all the active climbing monkeys have well-developed tails, and since the tail tends to shorten or disappear in species of less active habits which live, like the monkey of Gibraltar, on rocky hillsides, the absence of the tail in apes suggests very forcibly that their ancestor had to a great extent given up living in trees. Moreover, the short broad foot of the apes, their ability to stand and walk erect, their peculiar way of climbing, all point to the conclusion that they are descended, not from a truly arboreal ape, but from an ape which had already taken to terrestrial life, with partly bipedal, partly quadrupedal progression; an ape which, while still retaining the power to ascend trees for purposes of feeding and escaping from carnivorous foes, was, at best, probably a slow, inactive climber, certainly not an arboreal leaper like a monkey. A large ape of that mode of life, with hands and feet not very different from those of a chimpanzee or gorilla, but with stronger legs and shorter arms, is my conception of the ancestor of existing apes and of man. And the progenitor of that hypothetical ancestor was probably a big ground monkey."