Sexual selection is probably not a source of variation (i. e., of type); its rôle is, on the contrary, to keep the specie in statu quo. The causes of variation are probably changes of climate, the nature of the soil, the general milieu, and also disease, the troubles of blood and nerve circulation--perhaps certain sexual aberrations. I say, "perhaps," for the cross-breeding between individuals of different species, living in liberty, seems difficult, as soon as the species is really something different from a variety in evolution, a form still seeking itself. At that stage anything is possible; but one is speaking of species (i.e., set species). Mules, bardots, leporides are artificial products; one has never found them in free nature. It is very difficult to obtain the copulation of a hare and she-rabbit; the she-rabbit is refractory and the hare lacking enthusiasm. The mare very often refuses the ass; if she turns her head at the moment of his mounting, one has to bandage her eyes to overcome her disgust; it is the same with the she-ass whom one offers a stallion for producing the bardot. As for the product of bull and mare, the celebrated jumart is a chimæra: comparison of the meagre prong of the bull to the massive one of the stallion is enough to convince one that such dissimilar instruments can not replace each other. Nevertheless it would be imprudent wholly to rule out this form of sexual aberration from the causes of variability of species. That is perhaps one of its justifications. Of all sexual aberrations perhaps the most curious is chastity. Not that it is anti-natural, nothing is anti-natural, but because of the pretexts it obeys. Bees, ants, termites, present examples of perfect chastity, but of chastity that is utilized, social chastity. Involuntary, congenital, the neuter state among insects is a state de facto, equivalent to the sexual state, and the origin of a characterized activity. In humans it is a state, often only apparent or transitory, obtained voluntarily or demanded by necessity, a precarious condition, so difficult to maintain that people have heaped up about it all sorts of moral and religious walls, and even real walls made of stones and mortar. Permanent and voluntary chastity is nearly always a religious practice. Men, in all ages, have been persuaded that perfection of being was only obtainable by such renunciation. This seems absurd; it is, on the contrary, very direct logic. The only means of not being an animal is to abstain from the act to which all animals without exception deliver themselves. It is the same motive that has made people imagine abstinence, fasting; but as one can not live without eating, and as one can live without making love, this second method of perfectionment has remained in the state of outline.