Monogamy is no doubt an old and well-established phylogenetic heritage, while polygamy is on the whole rather an aberration produced by individual power and wealth. But phylogenetic monogamy is by no means identical with the religious or other formality of our present legal monogamy. It assumes first of all an early marriage immediately after puberty, while our civilization has placed between this and marriage, which it only allows later as a rule, the unhealthy swamp of prostitution, which so often sows in the individual the destructive seed for his future legal union, before this has taken place. Again, phylogenetic monogamy imposes no legal constraint; on the contrary, it assumes a free, natural and instinctive inclination in each of the conjoints, when it is not the result of the brute force of the male. Lastly, it by no means excludes a change after a certain time. We are speaking only of man, and not of birds and monkeys, who are more monogamous than ourselves. Monogamy without children has little reason for its existence and must be considered simply as a means to satisfy the sexual appetite or as a union for convenience. It is the same with certain marriages between individuals of very different ages, especially the marriage of a young man with a woman already old and sterile. As far as we can ascertain, the majority of sexual perversions, of which we shall speak in Chapter VIII, are a sad pathological acquisition of the human race. We observe, however, especially in the higher mammals, acts of pederasty between males when the female is wanting. The sexual repulsion which normally exists between animals of different species rests on a selective basis, the hereditary mneme of their reciprocal germs being unable to place itself in homophony, and their blood also having a mutual toxic action. In speaking of sodomy we shall see that this instinctive repulsion may disappear in pathological cases, both in man and in animals, owing to bad habits or unsatisfied sexual appetite. We cannot absolutely demonstrate the phylogenetic existence of an instinctive disgust for consanguineous sexual intercourse. The sexual advances made by women in civilized countries, show how easily we may be deceived in attributing to a phylogenetic or hereditary origin, certain details which are only due to external circumstances. In man, the bearer of the active germ, the instinct of sexual advance has deep phylogenetic roots. It is quite natural to him and is evident among savage races, where the man risks more by remaining single than the woman. Violent combats between rivals to obtain the woman, who remains passive like most animals, are evidence of this.