If another proof were necessary of the facility with which human groups intercross, it might be found in one of those testimonies the value of which is undisputed because they give the result of a daily experience. In 1861, the Californian legislature declared that any white person convicted of having cohabited with or married a Negro, Mulatto, Chinese or Indian, had forfeited all his rights, and became subject to all the constitutional incapacities imposed upon men of colour. The local press announced very plainly that the object of this measure was the prevention of the fusion and amalgamation of the races. The Californian legislature acted on this occasion like the proprietor of a flock of pure breed which he is anxious to keep free from all mixture. It was even more severe, ejecting from legal society, not only the offspring of the cross, but also the transgressing parents of the white race. Do not our breeders take similar precautions in the case of races only, and not in the case of species? Far from being sterile, unions between human groups apparently the most distinct are sometimes more fertile than those between individuals taken from the same group. “Hottentot women,” says Le Vaillant, “with husbands of their own race have three or four children. With Negroes this number is tripled, and it is still further increased with Whites.” M. Hombron, during four years which he spent in Brazil, Chili and Peru, studied this phenomenon in a large number of families. “I am able to state,” he says, “that unions of Whites with American women have given the highest average of births. Next come the Negro and Negress. And thirdly the Negro and the American woman.” Unions between Americans themselves gave the lowest average. Thus, the maximum of fertility is here presented in a case which would constitute a hybridism in the opinion of polygenists; the minimum is exhibited between individuals of the same group, and it is with the woman belonging to the latter, that, owing to the cross, the maximum is obtained. These facts are significant. In no case of crossing between species has fertility been observed to increase; on the contrary it is almost always diminished, and often, as we have seen above, in an immense proportion. Crossings between races have alone presented facts analogous to those mentioned by Hombron and Le Vaillant. III. Thus, in every case crossings between human groups exhibit the phenomena characteristic of mongrels and never those of hybrids. Therefore, these human groups, however different they may be, or appear to be, are only _races of one and the same species_ and not _distinct species_. Therefore, there is but _one human species_, taking this term species in the acceptation employed when speaking of animals and plants.