388 THE AMERICAN JOURNAL OF SOCIOLOGY
All men are of the same species in so far as they present among themselves only quantitative differences, relatively secondary to their structure and to their essential qualities. They may be of different races by reason of certain variations equally quantitative, but always secondary, though transmissible through heredity.
It is to be observed, first of all, that the distribution of the human races within certain organic and geographic limits is less circumscribed than the distribution of animals in general. This fact results precisely from the principle that man, from the point of view of natural history, constitutes quite a unique zoological species, comprehending a great number of varieties. There is unity of constitution and unity of composition of this constitu- tion. All of the human varieties are capable of uniting among themselves and of producing offspring. Was there at first a single couple, one sole center of creation ? Of what importance is it to ask? What is certain is that the various conditions of civilization have engendered, and still engender for example, among the Anglo-Americans some variations just as among the domestic animals. Natural evolution has always followed the same laws. The differentiation is derived from the primitive homogeneity.
The monogenist's hypothesis and the formation of races are completely explained by Darwin and his school according to the simple play of natural laws. The factors in the formation of races, as the factors in the formation of species, are, first, varia- bility, which is a general phenomenon among all organic beings, together with heredity, no less general, which fixes and transmits the variations; and, lastly, natural selection, which assures con- tinually the survival of the fittest, i. e., those which are best able to adapt themselves, actively or passively, to the physical or social conditions of the environment.
This explanation appears so much more reasonable in refer- ence to the human species, that the objection raised by M. de Quatrefages against natural selection, which according to him can produce races, but not species, does evidently not apply to the human species, which exactly divides only into races and varie- ties entirely capable of uniting among themselves, and of giving
