The change from a fruit-eating to a hunting life subserved the great utility of opening fresh supplies of food; and, possibly, a failure of the normal supply of the old customary food was the direct cause of the new habit. If our ape lived near the northern limits of the tropical forest, and a fall of temperature there took place, such as to reduce (especially in winter) the yield of fruit and other nutritious vegetation on which he had subsisted, famine may have driven him to attack other animals;[1] whilst more southerly anthropoids, not suffering from the change of climate, continued in their ancient manner of life. A large anthropoid (Dryopithecus) inhabited Central Europe in the Miocene, for his bones have been found; there may have been others; and during that period the climate altered from sub-tropical to temperate, with corresponding changes in fauna and flora. Hence it formerly occurred to me that perhaps the decisive change in the life of our Family happened there and then. It seems, however, that good judges put the probable date of the great differentiation much earlier, in the Oligocene;[2] and since I cannot find that any extensive alteration of climate is known to have happened during that period, it seems necessary to fall back upon “spontaneous” variation (as one must in many other cases); that is to say, from causes which are at present beyond our vision, the fateful ape did, in fact, prefer animal food so decidedly as to begin a-hunting for it. That being granted, the rest of the history was inevitable. The new pursuit was of a nature to engross the animal’s whole attention and co-ordinate all his faculties; and to maintain and reinforce it, his structure in body and mind may reasonably be supposed to have undergone rapid modification by natural selection; because those individuals that were in any organ or faculty best adapted to the new life had an advantage, which was inherited and gradually intensified.[3]
§ 2. What the Hypothesis Explains
Let me run rapidly through the chief differences between Man and his nearest congeners: some of them are obvious and can be stated very briefly; others I shall return to in the next chapter. We shall see that they all follow naturally from the above hypothesis.
(1) The anthropoids are never found out of the tropical forests of Africa and Malaya (including Borneo and Sumatra). They feed chiefly on the fruits and other highly nutritious vegetable products that, all the year round, are only there obtainable. Although often coming to the ground, especially the chimpanzee and gorilla, they are adapted to living in the trees: that is their home. In contrast with their habits, Man is at home on the ground, with unlimited range over the whole planet from beyond the Arctic Circle to Tasmania and Tierra del Fuego; because on the ground (chiefly) he everywhere finds his food in the other animals whom he hunts and slays. This, then, is the condition of his emancipation from the tropical forest. It is, indeed, conceivable that a frugivorous animal, originally of the forest, should obtain a wider range by taking to a coarser diet of roots and herbage, such as suffices the Ungulates, browsing or grazing or digging with their snouts; but this would not have led to the upright gait, or the big brain, or any of the marks that distinguish Man. Not advance but retrogression must have followed such a change.
(2) That the earliest men of whose condition of life we have any knowledge were hunters agrees with the hypothesis. Any other view of Man’s origin must explain how and when he became a hunter. There seems to be no reason to put the change of habits (which certainly occurred at some time) anywhere nearer than the beginning of our differentiation. The further we put it back the better it explains other modifications.
(3) The erect attitude was reached by the apes in the course of adaptation to arboreal life;[4] but the erect gait as the normal mode of progression is (if we neglect the gibbons’ imperfect performance) peculiar to ourselves; and such a gait was attained because the most successful hunters followed their prey afoot upon the ground. The feeble ineffective shuffle of the anthropoids upon the ground, supporting themselves with their arms where there are no overhanging boughs to swing by and help themselves along, could not have served the hunter, especially if he was to leave the forest. We may, indeed, suppose that at first prey was sometimes attacked by leaping upon it from the branch of a tree, as leopards sometimes do; but the less our ancestor in his new career trusted to trees the better for him. Such simple strategy could not make him a dominant animal throughout the world; nothing could do this but the gradual attainment of erect gait adapted to running down his prey. Hence the numerous modifications of structure necessary to it, whenever from time to time they occurred, were preserved and accumulated by natural selection: namely, the curving of the vertebral column, the balancing of the head upon a relatively slender neck, changes in the joints, bones and muscles of the legs, the lengthening of the leg and the specialisation of the foot (in which the heel is developed more than in the gorilla, and the great toe is lengthened and lies parallel with the other toes).
(4) The specialisation of the legs and feet, as it proceeded, made possible the specialisation of the hands: being gradually rid of the task of assisting locomotion, whether in trees or on the ground, they were used in grappling with prey, seconded by massive jaws and powerful canine teeth. In course of time they brought cudgels and stones to the encounter, and after many ages began to alter such means of offence into weapons that might be called artefacts. These simple beginnings probably occupied an immense time, perhaps more than half of the total period down to the present. The utility and consequent selection of hands had been great throughout; but their final development may be referred to the making and using of weapons fashioned according to a mental pattern. Those who had the best hands were selected because they made the best weapons and used them best; but we know from remains of several palæolithic stages of the art of manufacturing implements how very slowly the art improved.
(5) Along with specialisation of the hands went a reduction in the length and massiveness of the arms; and this must have been disadvantageous in directly grappling with prey. But it was necessary to the runner in order to lessen the weight and cumbersomeness of the upper part of the body and to improve his balance and agility. The change may also have been beneficial by affording physiological compensation for the lengthening and strengthening of the legs. And as soon as unwrought stones and clubs came into use there was mechanical compensation for the shortening of the arms. The result is an adaptive co-ordination of the total structure to the life of a two-footed hunter.
(6) Darwin says: “The early male forefathers of Man were, as previously stated, probably furnished with great canine teeth; but as they gradually acquired the habit of using stones, clubs, or other weapons, for fighting with their enemies or rivals, they would use their jaws and teeth less and less. In this case the jaws, together with the teeth, would become reduced in size, as we may feel almost sure from numerous analogous cases.”
(7) Hence the profile began to approach the orthognathous type; and it progressed further in that direction on account of accompanying changes in the skull. The skull became less thick and rough, (a) because, as the hands (using weapons) superseded the teeth in fighting, jaws and neck grew less massive, and their muscles no longer needed such solid attachments; (b) because the head was less liable to injury when no longer used as the chief organ in combat. At the same time the skull slowly increased in capacity and became vaulted to make room for the brains of an animal, which (as we shall see) acquired much knowledge (parietal association area) and lived by the application of its knowledge to the co-ordination of increasingly complex and continuous activities (anterior association area).[5]
(8) Monkeys of most species, whether in the New World or in the Old, are social, living in bands of from ten to fifty or more, and may co-operate occasionally in mutual defence or in keeping watch. Baboons, indeed, are seen in herds of several hundreds; and they are credibly reported to co-operate in raiding plantations, and in defending themselves against leopards, other baboons and even human hunters.[6] Gibbons, again, are social, going in bands to the number of fifty. But the large anthropoids live only in families—the male orang being even of a somewhat solitary habit; three or four families of chimpanzees may for a time associate together. Man, however, is everywhere—with a few doubtful