Race as an Evolutionary Episode

Abstract

BY THE middle of the Pleistocene period, we have certain evidence that mankind had spread from the Pacific to the Atlantic in the Old World. The presence of manufactured artifacts, as well as human fossil remains, attests to the existence of our ancestors both in tropical and temperate climatic zones. From the tools, of course, we dare not infer much more than that a toolmaker was present. From the fossil remains, on the other hand, we gain some information concerning the physique and appearance of the toolmaker. For the earliest times, to be sure, our data are woefully meager, but fortunately we have a frame of reference from which to examine them; a frame of reference provided by our knowledge of other species and of living human groups. It is quite clear, for instance, that any species of creature which occupies an extended range will be subject to various forces which will tend to divide it into different segments. The conditions of life are not the same in a tropical savannah as they are in temperate parkland; nor do temperate forests provide the same opportunites and hazards as do tropical jungles. Adaptation to purely local circumstances may well be necessary, so that the pressure of natural selection is likely to promote the retention of certain characteristics in one area, but their alteration in another. Simple geographic distance acts as a check to completely random mating, and consequently to gene-flow. Among animals which live in any sort of social groupings, no matter how naturally and unconsciously these groupings may be organized, social as well as geographical barriers to intermating exist. Mutations occurring in one group do not automatically spread throughout an entire species, even though they be potentially useful. We might well anticipate then, that as a species spreads over a range extending from Peking to Ternifine, and from Heidelberg to Java and Olduvai, it might begin to differentiate. Indeed, under such circumstances most animal species are known to divide, to come apart at the seams, as it were, and evolve into a number of separate species. An examination of living human groups shows that we have not been exempt from the normal processes of local evolutionary change. It would be difficult to mistake a Chinese for a Dane, or a Hottentot for a Sioux. Genetic differences between these groups have accumulated throughout the thousands of generations during which they have shared only a minute portion of their ancestry. Certain constellations of characteristics have become typical of the peoples of East Asia, others have become just as typical of Europeans. It is a matter of interest and importance that evolutionary diversification has not proceeded still further among humans, and that, by all biological criteria, we remain members of a single species.