differences between Man and his nearest relatives are innumerable; but taking the chief of them, and assuming that the minor details are correlated with these, it is the hypothesis of this essay that they may all be traced to the influence of one variation operating amongst the original anthropoid conditions. That variation was the adoption of a flesh-diet and the habits of a hunter in order to obtain it. Without the adoption of a flesh-diet there could have been no hunting; but a flesh-diet obtained without hunting (supposing it possible) could have done nothing for the evolution of our stock. The adoption of the hunting-life, therefore, is the essential variation upon which everything else depends. We need not suppose that a whole ancestral species varied in this way: it is enough that a few, or even one, of the common anthropoid stock should have done so, and that the variation was advantageous and was inherited.

Such a variation must have occurred at some time, since Man is everywhere more or less carnivorous; the earliest known men were hunters; weapons are among the earliest known artefacts. And it is not improbable that the change began at the anthropoid level; because although extant anthropoids are mainly frugivorous, yet they occasionally eat birds’-eggs and young birds; the gorilla has been said to eat small mammals; and other Primates (cebidæ, macaques and baboons) eat insects, arachnids, crabs, worms, frogs, lizards, birds; and the crab-eating macaque collects a large portion of its food on the Malay littoral. Why, then, should not one ape have betaken itself to hunting?

We need not suppose that our ancestors were ever exclusively carnivorous: that is very unlikely. A mixed diet is the rule even amongst hunting tribes, and everywhere the women collect and consume fruits and roots. But if at first nearly omnivorous, our ancestor (it is assumed) soon preferred to attack mammals, and advanced at a remote date to the killing of the biggest game found in his habitat. Everywhere savage hunters do so now: the little Semang kills the tiger, rhinoceros, elephant and buffalo; and many thousands of years ago, in Europe men slew the reindeer and the mammoth, the horse and the bison, the hyæna and the cave-bear. It is true they had weapons and snares, whilst the first hunter had only hands and teeth.

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