II. We know that among animals atavism often causes the reappearance of ancestral characters, even when a careful selection has acted upon hundreds of generations. The silkworms of the Cévennes which yield white cocoons, and the black sheep of Spain furnish examples. In man, where selection does not exist, such facts would be much more likely to be produced. Some characters of our first ancestors ought to appear in isolated cases or collectively in all human races; perhaps, there are some which have been preserved in one or more groups. Consequently, by searching for them, and classifying those which appear in a more or less erratic manner among races which are most dissimilar in all other respects, we shall probably be able to form a partial reproduction of the primitive human type. In this respect, it is difficult to avoid attaching a real importance to the prognathism of the upper jaw. This anatomical feature is very pronounced in almost all Negro races: it is also strongly marked in certain Yellow races. It is considerably diminished among Whites: but, nevertheless, it appears at times almost as strongly marked as in the two other groups: it existed in Quaternary man. Everything seems to indicate that it must have been as strongly developed in our first ancestors. Phenomena of atavism acting on the colouring are of frequent occurrence among animals. They are equally prevalent in the human species. This consideration causes me to attach real importance to the opinion of M. de Salles, who attributes red hair to the earliest men. In fact, among all human races, individuals have been noticed whose hair more or less approaches to this tint. The experiments of Darwin upon the effects of crossing between very different races of pigeons led to the same conclusion. He found that the crossings resulted in the reappearance of certain peculiarities of colour in the mongrels, which were peculiar to the original _species_, and which had disappeared in the two parent _races_. Now in our colonies the offspring of a Mulatto and a White frequently has red hair. In Europe also, M. Hamy has remarked that children are born with red hair, when one of the parents is decidedly dark and the other decidedly fair. In all cases of this nature, we should say that the primitive character reasserts itself, being accidentally acquired by the reciprocal neutralisation of opposed ethnical characters.