We are reduced, therefore, to geological evidence, and this gives us nothing better than mere probabilities, or rather guesses, as to the original centre or centres of human existence upon the earth. The inference most generally drawn is in favour of the locality where the earliest traces of human remains have been found, and where the existence of the nearest allied species, the apes and monkeys, can be carried back furthest. This locality is undoubtedly Eur-Africa, that is the continent which existed when Europe and Africa were united by one or more land connections. And in this locality the preference must be assigned to Western Europe and to Africa north of the Atlas; in fact to the portion of this ancient continent facing the Atlantic, and Western Mediterranean, then an inland sea. Thus far Central and South-Western France, Spain, Portugal, Italy, and Algeria have afforded the oldest unequivocal proofs of the existence of man, and of the coexistence of anthropoid apes. Accordingly Darwin inclined to the view that North Africa was probably the scene of man's first appearance, and the latest authority on the subject, Brinton, in his Races and Peoples, gives at length reasons for assigning this to somewhere in Eur-Africa.
But it must be remembered that this inference rests entirely on the fact that the district in question has been more or less explored, while the rest of the earth can hardly be said to have been explored at all, for anything prior to those Quaternary paleolithic implements which prove the existence of man already spread over nearly the whole of the habitable globe. Nor would the origin of the white race in Eur-Africa, even if it were established, help us to account for the existence of the Negro race on the other side of the Atlas and the Sahara, or of the yellow race in Eastern Asia, or of the American race. Indeed America may fairly compete with Eur-Africa for the honour of being the original seat of the human race, for the geological conditions and the animal fauna of the auriferous gravels of California point to the Calaveras skull and other numerous human remains and implements found in them being of Tertiary age, and quite possibly as old or even older than anything which has been found in Europe.[17] The wide diffusion of the same peculiar racial type over the whole continent of America down to Cape Horn, and its capability of existing under such different conditions of climate and environment, also point to its being an extremely ancient and primitive race, and the generic distinction between the apes and monkeys of the Old and New Worlds is a remarkable circumstance which is not accounted for by any monogenist theory of the origin of the order of quadrumana.
It is to be observed also, that although all American races have a certain peculiar type in common, still there are differences which show that secondary types must have existed from a very early period, intercrossing between which must have given rise to numerous varieties. Thus, according to Morton, dolichocephaly was most prevalent among the tribes who inhabited the eastern side of the continent facing the Atlantic both in North and South America, while brachycephaly prevailed on the western, side facing the Pacific. Great differences of colour and stature are also found often among contiguous tribes, and irrespective of latitude. On the whole, however, the American type approximates in many important particulars, such as colour, hair, and anatomical structure, more nearly to the yellow races of Eastern Asia than to any other, though it is a fairly open question which of the two may have been the earliest to appear in the immensely remote ages of the Tertiary period.
Another theory is that man probably originated in some continent of the Arctic Circle, where, as we know from fossil remains of the Miocene and Eocene periods, Greenland and Spitzbergen enjoyed a mild climate and forest vegetation, admirably adapted for the evolution of a temperate mammalian fauna, including the human species. This is a very plausible theory, but at present it is a mere theory, like that of a lost Atlantis, or submerged continents in the Pacific or Indian Oceans. The only thing approaching to evidence to support it is, as far as I am aware, that Sir Joseph Hooker and other eminent botanists think that the diffusion of the forest trees and other flora of America can be traced along lines radiating from the extreme north, along the mountain chains and elevated plateaux which form the backbone of the continent from Alaska to Tierra del Fuego. There seems a probability also that the evolution of the human race, which turns mainly on the development of the erect stature, which is the basis of the larger brain and other anatomical differences between man and the other quadrumana, must have taken place not in tropical regions of dense forests, where climbing would have had a decided advantage over walking in the struggle for life, but rather in some region of wide plains and open forests, where it would be an advantage to see enemies or prey at a distance, or over tall grass or ferns.
It must be admitted, however, that in our present state of knowledge all these theories of the place, time, and manner of human origins are speculations rather than science. We have proof positive that man was already spread over most parts of the world in the Quaternary period, and the irresistible inference that he must have existed long before, is confirmed by conclusive evidence as to the finding of his remains and implements in the earliest Quaternary and latest Pliocene periods, and very strong evidence for carrying them back into the Miocene. Anthropoid apes, which are so similar to man in physical structure, and in their ways are as highly specialized from any more general and primitive ancestral form as man himself, undoubtedly did exist in the Miocene period, and have come down to us with comparatively little change. It puzzles the best anatomists to find any clear distinction between the present Hylobates and the Hylobates of the Middle Miocene, while that between the white man and the Negro is clear and unmistakable. Why then should "Homo" not have existed as soon as "Hylobates," and why should any prepossession in favour of man's recent creation, based mainly on exploded beliefs in the scientific value of the myths and guesses of the earliest civilized nations of Asia, stand in the way of accepting the enormous and rapidly increasing accumulation of evidence, tracing back the evolution of the mammal man to the same course of development as other mammals?
As regards the course of this evolution, all we know with any certainty is, that as far as we can trace it back, the human species was already differentiated into distinct races, and that in all probability the present fundamental types were already formed. When and where the primitive stock or stocks may have originated, and the secondary ancestral races may have branched off from it, is at present unknown. All we can say is, that the more we examine the evidence, the more it points to extreme antiquity even for these secondary stocks, and makes it probable that we must go, as in the case of the horse and other existing mammals, at least as far back as into the Eocene to look for the primitive generalized type or types from which these secondary lines of quadrumanous and human evolution have taken their origin. As regards the secondary types themselves, there is no certainty as to the place or time of their origin, but the balance of evidence points rather in favour of polygeny, that is, of their having followed slightly different lines of evolution from the common starting-point, under different circumstances of environment and in different localities; so that when man, as we know him, first appeared, he was already differentiated into races distinct though not very far apart.
In conclusion, I may remark that these hotly-contested questions as to monogeny or polygeny, and as to the place of man's first appearance on earth, lose most of their importance when it is realized that human origins must be pushed back at least as far as the Miocene, and probably into the Eocene period. As long as it was held that no traces of man's existence could be found, as Cuvier held, until the Recent period; or even as some English geologists still contend, until the post-glacial, or at any rate the glacial or Quaternary periods, it was evident that the facts could only be explained by the theory of a series of supernatural interferences. Agassiz's theory, or some modification of it, must be adopted, of numerous special creations of life at special centres, as of the Esquimaux and polar bear in Arctic regions, the Negro and gorilla in the tropics, and so forth. This theory has been completely given up as regards animals, in favour of the Darwinian theory of evolution by natural causes, and no one now believes in a multiplicity of miracles to account for the existence of animal species. Is man alone an exception to this universal law, or is he like the rest of creation, a product of what Darwinians call "Evolution," and enlightened theologians "the original impress"?
The existing species of anthropoid apes, the orang, the chimpanzee, and the gorilla, do not differ more widely from one another than do many of the extreme types of the human species. In colour, hair, volume of brain, form of skull, stature, and a hundred other peculiarities, the Negro and the European stand further apart than those anthropoids do from one another, and no naturalist from Mars or Saturn, investigating the human family for the first time, and free from prepossession, would hesitate to class the white, black, yellow, red, and perhaps five or six other varieties, as different species.
In the case of these anthropoid apes no one supposes that they were miraculously created in recent times. On the contrary, we find their type already fully developed in the Miocene, and we infer, that like the horse, camel, and so many other existing mammals, their origin may be traced step by step backwards to some lower and generalized type in the Eocene. Who can doubt that physical man, an animal constructed almost exactly on the same anatomical ground-plan as the anthropoids, came into existence by a similar process? The only answer would be, if it could be proved, that his existence on earth had been so short as to make it impossible that so many and so great specific variations as now exist, and some of which have been proved to have existed early in the Quaternary period, could have been developed by natural means and by the slow processes of evolution. But this is just where the evidence fails, and is breaking down more and more every year and with every fresh discovery.
Recent man has given place to Quaternary man; post-glacial to inter-glacial and pre-glacial; and now the evidence for the existence of man or of some ancestral form of man, in the Tertiary period, has accumulated to such an extent that there are few competent anthropologists who any longer deny it.