§ 4. Prey and Competitors
If we suppose the differentiation of the Hominidæ from the Anthropoidea to have begun in the Upper Oligocene, and that the decisive change was initiated by some ape that adopted the life of a hunter, it is interesting to consider what the world was like in which he lived, what sort of animals surrounded him, what animals probably became his prey, and what were his rivals in the chase.[25]
The surface of the planet was less mountainous than at present; in Europe the Pyrenees had risen, but the Alps were only beginning to rise; and in Asia the Himalayas began to dominate the world only in the middle of the next epoch, the Miocene. The distribution of land and water, too, was very different in the Oligocene from that which we now see: Europe was divided from Asia by a broad gulf stretching from the Indian Ocean to the Arctic Circle, and an arm of this gulf toward the west submerged a great part of Central Europe; Asia was broadly connected with North America, where now the sea penetrates between Siberia and Alaska; Africa had no connection with either Europe or Asia; North and South America were separated—perhaps at Panama. In the Miocene, Europe, Asia and Africa became united. These physiographic changes may have affected climate; for during the Eocene tropical conditions prevailed far to the north, and coal-beds were laid down in Alaska; but from the Oligocene onwards there was a gradual fall of temperature, slow at first, but ending (for the present) in the cataclysms of the Glacial Period. There was also a decrease in some regions of atmospheric moisture, which determines the density of vegetation. In its general character the vegetation was similar to that which now prevails in tropical, subtropical and temperate regions of the world. The species of plants now existing had not yet arrived; but of the same genera and families as those we see, conifers, palms and dicotyledonous flowering plants crowded the forests and overhung the rivers. The forests were more extensive and continuous than ours outside the tropics; for by degrees browsing animals, feeding down the young trees, check the renovation of forests and clear open spaces, where grasses grow; changes of temperature limit the northern or southern extension of certain kinds of plants, and a failure of humidity starves all the larger kinds; converting, at successive stages, forest into steppe and steppe into desert.
Animals, especially mammalia, with which chiefly we are concerned, were, at the close of the Oligocene, very different from any that now roam the lands; all the species, most genera, many families and some whole orders have since disappeared. But there were plenty to eat and a good many to dread. Until we know the neighbourhood in which our ape’s adventures began, nothing precise can be said of his circumstances. Probably it was somewhere in the Old World, and probably it was in Asia. Unfortunately, we know nothing of the zoological antiquities of Asia until the early Miocene, and even then a very small selection of what must have existed, because geologists have hitherto explored a very small part of the continent—a few beds in north-western and northern India and in Burmah. But there is so much evidence of the migrations of animals in successive ages of the Tertiary Period, that any remains from the Oligocene and Miocene will help us to understand what sort of neighbours our remote ancestors had to live amongst.
For prey there was great variety of birds and reptiles (everywhere eaten by savages) and fishes; but we are most concerned with the mammalia, which he may be supposed to have pursued afoot. Of these the most important are the hoofed animals, which fall into two great groups, perhaps not closely connected—the odd-toed (Perissodactyls) and the even-toed (Artiodactyls). During the Oligocene there lived in Europe, or in North America, or in both—and, therefore, probably in Asia—numbers of the odd-toed group: tapirs; rhinoceroses of several species, some without horns, some with, some amphibious (Amynodonts), all smaller than their modern representatives; chalicotheres, strange beasts something like horses, but instead of hoofs they had claws on their toes—perhaps survived in China into the Pleistocene; small predecessors of the horse with three toes on each foot; titanotheres, hugest animals of their age, extinct in the middle of it—something like the rhinoceros and nearly as big as an elephant (Brontotherium). Of the even-toed group, pig-like animals abounded, and some true pigs appeared; entelodonts, or giant-pigs, were common; anthracotheres, somewhat pig-like in size and shape; ancestral camels about the size of sheep were to be had in North America; oreodonts, unfinished-looking creatures of many species; primitive deer and other ruminants, small in size and not having yet grown any horns. In Europe, during the Upper Oligocene, cœnotheres, small and graceful animals, lived in large herds around the lakes. There were also primitive proboscidia about half the size of modern elephants; many insectivores; and, amongst rodents, beavers and tailless hares. Generally, animals of this age that have left descendants were smaller than their modern representatives; and notably their brains were smaller.
In the Lower and Middle Miocene there appeared also horned cervuline deer, chevrotaines, and horned antelopes; dinotheres and mastodons, probably from Africa; primitive hedgehogs, moles and shrews; and in the Upper Miocene, hipparion, true hares, several varieties of hornless giraffe, true deer, and ancestral sheep. True horses and cattle are first known from Pliocene beds; but it is needless to follow the story further: the fauna becomes more and more modern in its character, and uncouth forms die out.
Anthropoids are first met with in the Miocene and in Europe: pliopithecus, allied to the gibbons, in the Lower; and dryopithecus, related to the chimpanzee, in the Middle Miocene; but they are believed to have come from Asia. There, in Pliocene beds of the Siwaliks (southern foot-hills of the Himalayas), occur the orang and chimpanzee, besides macaques, langurs and baboons. Since the orang is now found only in Borneo and Sumatra, and the chimpanzee only in Africa, southern Asia seems to have been the centre from which the anthropoids dispersed; and this seems to be the chief positive ground for believing that the human stock began to be differentiated in that region. Since, again, by the Middle Miocene a chimpanzee form had already migrated into Europe, it may be assumed that the orang was already distinct from it (and perhaps had spread eastward): the differentiation of these genera must, therefore, have happened earlier; and, therefore, also the differentiation of the human stock; so that this event cannot be put later than some time in the Oligocene.
How big was Lycopithecus to begin with? The answer to this question must affect our view of his relations both to prey and to enemies. Inasmuch as the three extant anthropoids and Man are all of about the same size, there is a presumption that their common ancestor was in stature superior to the gibbons and to the largest monkeys—in fact, a “giant” ape (to borrow a term from Dr. Keith). Dryopithecus “was smaller than the chimpanzee, but much larger than the gibbon.”[26] Awaiting further evidence of fossils, which is much to be desired, it is probable, on the whole, that Lycopithecus weighed less on the average than modern man, but more than the wolf.
As to competitors and aggressive enemies, there were snakes and crocodiles; but, confining our attention to carnivorous mammals, the time seems to have been favourable to the enterprise of a new hunter. By the middle of the Oligocene, the ancient Creodonts (primitive flesh-eaters which had flourished in the Eocene) were nearly extinct, represented in the deposits by their last surviving family, the Hyœnodonts. Ancestors of the modern carnivores, such as may be called by anticipation dogs and cats, derived (according to Prof. Scott) from the Creodont Family of the Miacidæ, were becoming numerous, but for the most part were still of small size. Apparently, the primitive dogs and their allies must, for some time, have been more formidable adversaries than the primitive cats, especially if we suppose them to have already begun to hunt in pack; and this is not improbable, both on account