Thus, in my opinion, we owe to Lombroso the recognition of a fact of enormous importance—namely, that many disturbances and also many advances in social life (crime, genius, and revolution) are brought about, not by economic or other social influences, but by the natural variability of the species, _homo sapiens_. (Be it noted that Lombroso contrasts with _homo sapiens_, _homo delinquens_; while he classes the latter with _homo neanderthalensis_.) To the sociologist it is a matter of indifference whether certain classes of varieties are termed degenerative or not. About this point it is for the biologists to come to an agreement, but in doing so they must not ignore Lombroso’s anthropological and morphological researches. No detailed exposition is requisite to show how remote this method of causal explanation of social phenomena is from the hypothesis that refers the whole past course of social evolution to the class war, or regards the class war as the sole factor of importance in the making of the future. From the standpoint of Lombroso, a moral organization which would transform its advocates from fighters for the interests of the community to fighters for the exclusive interests of a class would be condemned simply as moral insanity.[37] In his work on the anarchists he expresses himself in this sense (p. 16), here, indeed, with reference to the governments, which in their political activity are not concerned exclusively with the interests of a particular class. He has shown how nature produces socially important differentiations altogether apart from the co-operation of socially causative factors. The most important of these differentiations, that between the two sexes, was described by him exhaustively in the first part of his work on the female criminal and the prostitute; here, also, he discusses fully the significance of the natural organization of woman for social life in relation to motherhood. His description of the natural organization of woman is only one part of the important contributions of Lombroso to sociology. With regard to the natural differentiation of human beings, his work is summarized in the succeeding paragraphs (I do not think it necessary to refer here to the numerous passages in his works in which he elaborates, in greater or less detail, the views I am about to describe; for my account is based, in addition, more especially upon the direct exchange of ideas, by word of mouth and by correspondence, during an intimacy of many years’ duration): Human beings are differentiated—horizontally, as it were—into tribes and nations in consequence of original variability, in consequence of selective œcological factors (soil and climate), and in consequence of wars, expulsions, and migrations. This differentiation—greatly influenced by social factors, such as colonization, miscegenation, etc.—becomes organic, and this organic differentiation is of very great social importance.