INTRODUCTION TO SOCIOLOGY 389
birth to fertile offspring. The Darwinists, however, cite some cases of fertile unions among different species, vegetable as well as animal. But the question whether the human species is the result of a natural selection, without being indifferent to soci- ology, is connected with it only very indirectly. Sociology has for its object only the human societies, comprehending their environments in so far as forming a special superorganic whole. The action of natural selection upon the formation of species and races is, according to Darwin, also favored by isolation, and this accords with our previous observations. This factor is especially important when it is a question of the formation of distinct social groups, but of a single species, such as the human species.
In South America, in going from north to south and from east to west, it is evident that the alterations in the conditions of life have modified the organisms in the several regions in such a way that they now form different races and even different species. It is further clear that in the isolated dis- tricts, however small they may be, the animals are modified almost always slowly. I am not able to decide how far this differentiation is due to the nature of the different conditions, however slight, to which the organisms are exposed, or at least unable to decide to what extent it depends upon intermixture Very slight differences, considered by the systematists as having no impor- tance in the structure, are found to be continually important from the func- tional standpoint. 1
Let us notice the prudent reserve of Darwin upon the ques- tion whether these variations are due to the conditions of environ- ment or to the conditions of intermixture, /. e., relative to the very nature of the individuals. Here is the point of departure of a partly new theory, that of Weismann the theory which will permit us finally to reduce the problem, in its purely relative and positive conditions, to the simplest terms. Let us point out and note further that if, as it is certain, isolation produces human varieties and races, the inverse phenomenon that is to say, the continued transformation, with the progress of civilization, of the greater part of the natural barriers of communication in equally natural ways, and the gradual lowering, at least relatively, of the social energy of those barriers which do not undergo this
1 CHARLES DARWIN, Life and Correspondence, Vol. II, p. 492 (French translation).
