Man as we know him from the study of modern races is descended from one or more species of a single genus, segregated out of a group of related Old World primate genera which had physically, and hence culturally, taken the first definite steps in a human direction. Members of a number of these genera found that they could cut with the sharp, glassy edge which is formed when flint is fractured, learned the use of fire, and discussed these and other matters with their fellows by means of speech. But all of them, including those destined to take part in the formation of the modern species Homo sapiens, remained, like less human primates and other animals, dependent on the natural occurrences of foodstuffs for their continued existence.

Man alone, of these parallel forms, succeeded in breaking loose from the natural limitations of food and climate, and he did this in a number of different ways. One of these was the invention of warm clothing which would permit him to hunt in comfort the numerous arctic and temperate mammals, whose flesh was richer in fats than the meat of his tropical prey; but this was not immediately a greater advantage than the development of a furry coat among the animals which he hunted. Another was the discovery of the principles of reproduction in animals and plants, and the knowledge of how to control this reproduction. This second step, which Childe calls the first revolution, produced of course agriculture and animal husbandry, and out of this dual economy have developed the civilizations of the ancient and modern worlds.

These two primary steps, which were in no sense consecutive, although the first was undoubtedly the earlier, and which had no necessary relationship one to the other, brought about different effects of far-reaching consequence. The first of them permitted the utilization by man of lands which could not otherwise have supported primate life, and also the ability to pass through the arctic barrier from the Old World into America; the second, the intense use of more favored regions, suited for farming and pasture, and the increase in population made possible by the consequent abundance of foodstuffs. These two steps, then, permitted the human species to multiply greatly, and to occupy all of the principal interconnecting areas of the earth, not covered by glaciers or waterless deserts, and not separated from the mainlands of the two hemispheres by wide expanses of sea.

Long before either of these two steps had been taken, most of the related primate genera and species, which had participated in the earlier discovery and utilization of speech, flint, and fire, had dropped out of the contest. Perhaps the last to disappear was Homo neanderthalensis, who became extinct as such in Europe, if not elsewhere, at the time of the last glaciation.

Homo sapiens, then, as we now know him, remained alone to deal with the results of the increasing control over nature which he himself had conjured. But all branches of the species did not participate in these results, while those which have participated have not shared them equally. In the far peripheries of the southern hemisphere, to which man in the earliest stages of culture could retire without encountering great cold, naked hunters and gatherers, such as the African Bushmen, the Tasmanians, the Australians, and the Vedda, have been able to survive in isolation until recent years. While only one, the Tasmanian, is extinct in the unmixed form,¹ the others promise soon to follow. Thus our species is repeating within its own ranks the selective process of elimination which effaced, in earlier times, its non-human competitors.

There is, actually, no real difference between these two cycles of extinction. In the first, although separate species were involved, we now know that at least one of those which disappeared was not pruned off the stem completely; for, as in the second cycle, its disappearance was consummated by absorption coincident with cultural changes, permitting the submerged genetic strain to survive in solution. Human genetic strains, however ancient and however primitive, are very hard if not impossible to eradicate completely, for the simple reason that all human racial stocks are mutually fertile, and men of all races are human.

Nevertheless these racial stocks possess, under varying conditions, very different rates of procreative value. It is a constant phenomenon of human history that a small group of people in a restricted area will, through some stimulus which is probably both environmental and cultural, increase rapidly, expand its boundaries, and inundate new segments of the earth’s surface with its progeny. For example, the numerical size of the white race has, since the time of the industrial revolution, increased vastly. The countries in which the new regime was initiated grew much more rapidly in population than did those yet to acquire these cultural innovations. In this manner, emigrants from Europe spread out into other Continents, previously occupied by less economical² populations, until they and their descendants had filled most of the available space suited to their powers of utilization. After this, their rate of increase fell. New conditions and new stimuli, provided that they are favorable, produce great increases in a species. Unfavorable ones produce absorption and extinction.

This phenomenon is not confined to human beings, but is a basic principle of biology, by which has been accomplished the spread of all plant and animal forms. Man, whose ancestors were a handful of precocious and biologically successful primates, has multiplied until his numbers are now reckoned in billions. The present numerical proportions of races and of nationalities has no reference to the former numbers of previously existing groups of people, to the importance of these various groups in the history of human racial development, nor furthermore, to their relative numerical values in the future. In the subsequent pages outlining the racial history of the white segment of mankind, this principle must not be forgotten.

This history is, on the basis of present knowledge, entirely confined to Pleistocene and Recent geological time. It is with the earlier of these two segments of the Cenozoic³ that the present chapter is concerned. In it, as in subsequent chapters, some attempt will be made to place the skeletal remains studied in their proper chronological horizons. With the Pleistocene specimens, this dating must be done primarily by geological means.

Since the primary diffusion of a zoological species is almost instantaneous, palaeontologists base their dating of geological horizons on the initial appearance of fossil genera and species. By this means they have divided the Pleistocene period into lower, middle, and upper levels.⁴ Glacial geologists, limited to the relatively small portion of the earth’s surface which was covered by one or more of the Pleistocene ice sheets, divide it by reference to the four or five successive glacial advances. Unglaciated regions were subjected, during the Pleistocene, to alternations of wet and dry climate, probably correlated with the vacillations of the ice. The pluvial and interpluvial periods so determined form a third means of dating Pleistocene remains. At the moment, a complete harmony between these three systems has not been achieved. Hence the relative dating of fossil human beings found in various parts of the world is not, as yet, wholly possible. For that reason we must proceed with reserve and caution.
 

Notes:

1 A few mixed survivors live on the islands between Australia and Tasmania, and in reservations on the Australian mainland.

2 In the sense of maximum utilization of the soil. No qualitative inference is intended.

3 The division between Pleistocene and Recent is here maintained purely for the sake of clarity. The possibility that we are now living in a Pleistocene interglacial is not, by the use of this. terminology, implicitly denied.

4 Hopwood, A. T., PGA, vol. 46, 1935, pp. 1, 46—60,