The pentagenists occupied themselves at first chiefly with the intermixture of the five chief races; but even from this point of view, and taking the term race in a general sense, their negation, though, it must be admitted, far from being justifiable, is still founded upon a more solid basis, and less removed from the truth than the opposed affirmation. Hence it was considered valuable _ad interim_. But the principle of non-intermixture of races being once promulgated, the confusion of terms soon became apparent. The negation which was at first applied merely to the artificial groups formed by the reunion of races of the same type was applied to natural races, and thus arose that frightful proposition, that _no mixed races can subsist in humanity_. It is noteworthy how this excessive and exclusive theory differs from the first, which it has displaced. There is such a gap between the starting point and the conclusion, that it could never have been cleared had not the ambiguous term _race_ concealed the distance. The fact is established that affinities of organisation may exercise some influence on the results of crossing. In studying the phenomena of hybridity in quadrupeds and birds, we have already stated that homœogenesis, without being _always_ proportionate to the degree of the proximity of species, decreases _ordinarily_ in comparison with more removed animals, and that probability induces us to expect similar phenomena in the intermixture of human beings. But what have been the bases of the monogenists and of the pentagenists in forming the five ethnological groups, which constitute the five fundamental races? Why have all Caucasian races been united by them in one family, and called by them _the white_ or the Caucasian race? It has been already stated because the races with a skin more or less white possess between themselves a greater affinity than with any of the other races. In other terms, the zoological distance is less between Celts, Germans, Kimris, etc., compared with that existing between them and the Negroes, Caffres, Lapps, Australians, Malays, etc.