Clear evidence of man's remote arboreal ancestry is offered by his stereoscopic or double-eyed vision. The great majority of ground animals, especially those living in the forest, have eyes on the sides of their heads; but in man's arboreal ancestors, by the recession of the intervening nasal and facial bones, the eyes were brought around to the front of the face. The resulting stereoptic vision enabled him to judge distance far more accurately than most mammals. Such power of determining distance is of course vital to an arboreal animal. Failure to judge accurately the length of a leap from branch to branch would be fatal.
One often hears it stated that man has lost his sense of smell; but this sense was probably never better developed within the human period than it is now. In the trees a sense of smell is not of much value. The monkey can sit on a branch and jabber with impunity at the leopard on the ground below. To forest animals, like the deer or boar, however, the sense of smell is the surest protection against attack and is much more highly developed than the sense of sight, which latter is often quite feeble. In fact, in the thick jungle it is almost useless (and at "black night" completely so).
Eurasia, where it is probable that mankind originated, was the greatest land mass on the globe in Tertiary times. Modern Europe and North Africa formed relatively small peninsulas in the extreme west of this Tertiary land mass. It is probably from Eurasia that man spread out to the uttermost parts of the habitable globe, carrying with him his language and such cultural features as had developed at the time of each successive migration. No race or language or cultural invention seems to have entered Eurasia from adjoining land areas. All went out. None came in. While the original center of dispersal of the Hominidæ or human family was probably Eurasia, it was at a later date also the center of the evolution of the higher types of man.
To the northeast of Eurasia lay the ancient land connection with North America via Alaska, over which various species of animals passed back and forth, some of them having their origin in Asia and others in western North America. It was undoubtedly over this land connection that man first entered America at a relatively recent period and probably he came in successive waves. The American Indians appear to have been derived from the Mongoloid tribes of northeastern Asia before the latter had developed some of those extreme specializations which characterize the typical Mongols of Central Asia and China proper today. Judging from the culture which these American Indians brought with them, this migration began before 10,000 B.C.
The existing races of mankind, and those either entirely extinct or now absorbed in other races, had their distinctive areas of differentiation and periods of radiation from Eurasia over the habitable globe. The most primitive types are now found farthest from this original centre of distribution in countries where through isolation they escaped competition with the higher types which evolved later.
The weight of evidence appears to show that Africa, or Ethiopia, lying far to the southwest of Eurasia, was peopled in earliest times, by way of Arabia, by a most primitive negroid type of mankind. While north of the Sahara migrations from Asia have continued until recent times, the south was left for a vast period in possession of the Negro. Even today, aside from the recent infiltration of Whites and Browns, Africa south of the Sahara belongs to three negroid groups; the Negroes proper, the Pigmies or Negrillos, and the Bushmen and Hottentots. These three human types are characterized by very dark or yellow skin, tightly curled hair, very scanty body hair, flaring nostrils, flattened noses and an absence of supraorbital ridges.
Again, Australia, Tasmania, and some of the adjoining islands are, or recently were, inhabited by what used to be considered one of the great divisions of mankind, the Australoids. These people have the black skin and certain features of the Negro; but differ from him in the possession of abundant body hair and of marked supraorbital ridges. Also the Australoid head hair is wavy, and not closely curled, a most important characteristic. The profound cleavage between the Negroes and the Australoids is now questioned in some quarters.
The differentiation of the human species into types so distinctly contrasted as Whites and Blacks and the problems of the evolution of higher types of man from original stocks bring us to a new classification of the genus Homo. Some anthropologists still maintain that all human beings are included in the species Homo sapiens; but this is an old-fashioned grouping. Sooner or later a new system must be formulated based on the same fundamental rules that are applied to the classification of other mammals. For instance, the physical differences between the Nordics and the Negroes, the Australoids and the Mongols, if found among the lower mammals, would be much more than sufficient to constitute not only separate species, but even subgenera, and they are now so regarded by some anthropologists.
Race is hard to define. It consists in the presence of a collection of hereditary characters common to the great majority of individuals in a given group. It lies in the preponderance of such characters as color of skin, hair, and eyes, facial and nasal contour, shape of skull, and even mental characteristics, which are more difficult to classify, but which are distinctly typical of specific human groups. Many individuals possess all the hereditary characters of a given race. But man is so ancient a being and intermixture has been so widespread that nearly every race shows signs of blending with others. This is especially true in Europe, where the intermingling of peoples has been extensive during the past twenty centuries.
Just as the classification of man according to race needs revision in the light of recent discoveries, so the definition of race must be understood anew in the light of genetics. Thirty years ago we talked glibly about the Aryan or Indo-European race, or the Caucasian or Germanic race. All these terms must be discarded. Aryan, Indo-European, and Germanic are only linguistic terms and Caucasian has no meaning except as used in America to distinguish between whites and colored.
Language or culture may spread quickly and widely among the peoples of the earth irrespective of race. For example, the bow and arrow may have originated with some specific race of mankind, yet we find this invention in use all over the globe and in the hands of the most diverse peoples. The use of firearms and of horses by the American Indians indicates nothing more than their contact with the Whites. It is unsafe to attribute the inception of any cultural feature to a given race.
Civilization itself, that is, agriculture and the domestication of animals, probably arose in West Central Asia, spreading east, south, southwest, and west. Although the earliest remains of the dog, the first animal tamed, are found in the Maglemose in Denmark approximately 8000 B.C., it may have been domesticated far earlier in Asia.
There were two centers of the development of civilization—two foci. The first was in southwestern Eurasia: the Valley of the Syr-Daria; Mesopotamia and its city states; Chaldea, Babylonia, Assyria; then Egypt, Crete, Greece, Rome, and modern Europe. There is the possibility, or even the probability, of finding in the unexplored portions of southern Arabia, connecting links of early culture between the Valley of the Euphrates and the Valley of the Nile. Recent discoveries indicate a very early civilization in the Valley of the Indus, which apparently had been brought down from the north. All these regions formed a single group and were the first center.
The second focus was an independent, but similar and parallel expansion of civilization in southeastern Asia, now China. There was apparently little intercourse until modern times between the Far East and the Far West of Eurasia, except by caravan routes across Central Asia. The Romans knew the silk of China and there was a certain amount of trade in jewels, precious metals, and spices down through the Middle Ages, but the extraordinary fact that these two cultures developed independently with slight mutual influence of the one on the other is little appreciated. Both cultures seem, as said, to have had their origin in West Central Asia and to have radiated southwest, south, and east.
One of the periodic cycles of drought desiccated the central area, and separated the Western and Eastern worlds by an almost impassable series of deserts, like the Gobi Desert of Mongolia. In the west, even as late as the time of Alexander the Great, Bactria and Sogdiana, northwest of India, were populous and flourishing states. Here it is that future exploration