Popular Science Monthly/Volume 77/December 1910/The Paleontologic Record VII: The Birthplace of Man
|THE PALEONTOLOGIC RECORD|
By Professor S. W. WILLISTON
THE UNIVERSITY OF CHICAGO
VARIOUS writers, from Le Conte to Smith Woodward, have spoken of critical or rhythmical periods in evolution, periods when evolutionary forces have acted more vigorously than at others, with intervals of relative quiescence. What these forces are and have been we are not yet sure, whether extrinsic, that is, environmental or Lamarckian, or intrinsic, that is, orthogenetic, teleological or what not. Perhaps we shall sometime be more certain of the basal causes of evolution, for the paleontologist at least is not satisfied with the crass ignorance of our Weismannian friends who impute the beginning of all things to mere chance. Perhaps when we do know these fundamental causes we shall understand better why evolution has been rhythmical, if such was really the case, as some of us believe with Woodward.
But, whether there have been internal forces which have had chiefly to do with the rhythm of evolution, or whether such critical periods in the evolution of organic life have been due solely to the larger cosmic forces, I think we shall all admit that there have been critical places of organic evolution, places upon the earth where evolution has advanced with more rapid pace than in others, places perhaps where environmental conditions have conspired to hasten the development of life, or of particular groups, classes or kingdoms of life.
Such a critical period, at least for the higher organisms, it seems to me, was the early Pliocene; such a critical place was central Asia; and both together resulted in the birth of man.
It is a curious fact that nearly all our domestic animals had their origin in Asia. It is also a curious fact that the domestic animals are, almost without exception, the crowning ends of their respective lines of descent, the most highly specialized of their kinds. The genus Bos, the most highly developed of the even-toed ungulates began, to the best of our present knowledge, in the Lower Pliocene of India. And its four distinctive types likewise first appeared there: the Bubalus group, including the domestic buffalo of India, and its untamable kin of Africa; the group that is represented by the domesticated humped oxen of India and their wild relatives of Africa; the bison strain which spread in Pleistocene times almost to the remote corners of the earth; and the true oxen, the most useful of all creatures to man, which spread to Europe as Bos primigenius, the ancestor of Bos taurus.
The sheep also found their expression point in India, and their home to-day is central Asia. So too the domestic goat yet lives wild in western Asia, a less plastic type, but purely Asiatic in origin. Indeed, of the whole family of Bovidæ, Asia was the origin and dispersal center, and it is a curious fact that it still remains the home of the higher types while others of lower degree have wandered afar to find their homes in Africa, Europe and America. The camelids after long ages of exclusive development in North America migrated to Asia to find their highest evolution in the true camels, the highest and probably final stage in the evolution of the family, while their kin, of lower degree, went southward to terminate in the llama and alpaca, the only mammals among all man's servants which we can say with tolerable certainty have been entirely beyond the influence, direct or indirect, of Asiatic environment. The reindeer, the highest of all the cervid family, doubtless arose in northern Asia; certainly its home is in part there, though some of its early kin migrated to America and have left their descendants in the caribous. And India was the birthplace, as it is the home, of the pig, whence came originally our domesticated swine. "Whether or not we give to Sus the highest place among the non-ruminant, even-toed ungulate mammals, or to the Babirussa, matters not, for both are of Asiatic origin.
Of the odd-toed ungulates our domestic horse, Equus caballus, stands on the very summit; and Equus caballus arose in Asia, where its ancestors yet have their wild progeny. And I believe that eventually we must give to Asia the honor of the birthplace of the genus itself. And the next lower type of the Equidæ, the asses, are of Asiatic ancestry, though our domestic species comes from Arabia and Africa, while the most primitive of the horses yet living found their refuge in Africa.
Southern or central Asia was the birthplace in early Pliocene times of the elephants, and was their dispersal center; and, in Elephas indicus, the only domesticated species, we have the last and highest stage in the evolution of the Proboscidea, and, as is the case with the cape buffalo, the zebras, wart hogs and others, we find in Africa their only living kin, of more primitive form and untamable.
Of all the great order of Carnivora the genus Felis admittedly occupies the highest place. The home of the cats is southern Asia and there doubtless was their birthplace and the center of their dispersal. The known paleontological record of the true cats is very meager indeed, and doubtless always will be till we know more of the Pliocene and Pleistocene faunas of Asia. Two of the domesticated cats, the Siamese and the cheetah, are of immediate Asiatic origin, and our fireside pet, while coming from northern Africa, doubtless arose from Asiatic forebears in Pliocene or Pleistocene times. What the origin of the various strains of dogs was we know not, though the wild forms most nearly allied are living in Asia to-day, and the greyhound and mastiff almost surely were domesticated in Africa thousands of years ago. I believe that we may safely give to Asia the honor of the birthplace of most of the domesticated species in Pliocene or Pleistocene times.
Nor does it seem that this remarkable evolutional acceleration during Pliocene times in central Asia was confined to the mammals alone. The ostrich, the highest type of ratite birds, arose in central Asia. The jungle fowl, the highest of the gallinaceous birds and the ancestral stock of our most valued domestic fowls, arose in India and is still at home there. The peacock is exclusively Asiatic; the gray goose, the parent of our domestic geese, has its home in part at least in Asia; and the same may be said of the ancestors of the domestic doves; while the domestic duck may have originated there for aught we yet know. The guinea fowls only are exclusively African, and the turkey American.
Of the reptiles I will venture to say less. But is it not a significant fact that the highest specialization of the reptilian class appeared during Pliocene times in the gigantic extinct gavials of central Asia? Certainly the cobra is entitled to a high but unenviable distinction among the snakes. And Megalobatrachus, the largest of all recent amphibians, lives in Japan and China. Finally, of the domestic plants by far the majority come directly or indirectly from the Asiatic flora.
Have all these and doubtless many other facts of their kind no significance? Has man been an exception among so many branches of vertebrate evolution? The common inference has been that so many of our domesticated animals and plants come from India because man first reached civilization there, but the inference is, I believe, quite unjustifiable. Man was born and attained elemental civilization in Asia because there was the place of all others upon the earth where evolution in general of organic life reached its highest development in late Cenozoic times. No mammals and few other creatures have been domesticated by man in thousands of years, for the simple reason that he had eliminated all but the most advanced and most adaptable long before, and none were left to compete with them.
That man originated in the western continent is quite impossible. There is not a particle of evidence in support of such an hypothesis, for there is no evidence that either man or any of his ancestry ever inhabited the western continent till late in Pleistocene times. Indeed, so far as North America is concerned, there is much to justify the assertion that the Pliocene and Pleistocene were a period of evolutional depression here, of relative quiescence when the rhinoceroses, tapirs, and later the camels and horses, found conditions uncongenial and migrated to Asia, a more favored region.
It has often been assumed that man must have originated in a warm or tropical climate, to account for the loss of his hairy covering. But I quite agree with Dr. Matthew, that the loss of hair is almost conclusive evidence of his origin in a temperate or cold climate where he found clothing necessary to protect himself from the inclemencies of the weather. We know of no mammals or birds losing their pelage or plumage because of tropical conditions, though some may have lost their hair because of vermin.
Taking all these facts and conclusions into consideration it seems to me that such evidence as paleontology can at the present time offer points toward central Asia as the birthplace of Homo, and that the time of his origin, as a family, was late Miocene or early Pliocene. If Pithecanthropus be really a true hominid, then we already have evidence of his origin in the Asiatic region. Be it as it may, I confidently believe that within a very few years the discovery of indubitable links in man's ancestry will be made in central Asia, in China or northern India. Perhaps to no region of the world does the paleontologist look with more eager expectation for the solution of many profound problems in the phylogenies and migrations of the mammals than to central and eastern Asia. That there are remains of many extinct vertebrates awaiting discovery there in the late Tertiary and Pleistocene deposits has been made evident by the many fragments brought to light by explorers and travelers.
A field second to none other in the importance and richness of the results to be expected awaits the paleontologist in Asia.