In most mammals, marriage (if we may give this name to their sexual union) is only of very short duration, depending on the time necessary for the procreation of a single brood of young. After copulation the male generally pays little attention to the female, beyond protecting her for a certain time. In the anthropoid apes (orang-utan, chimpanzee, gorilla and gibbon) however, we find monogamous marriage and the institution of family life. The male protects the female and the young, and the latter are often of different ages, showing the existence of conjugal fidelity extending beyond one birth. While the female and the young remain in their nest, perched on a tree, the male takes his place at the foot of the tree and watches over the safety of the family. According to Westermark this was probably the same in primitive man. Formed by the father, the mother and the children, the family was in primitive man a general institution, based on monogamy, polygamy or polyandry. The wife looked after the children, and the husband protected the family. No doubt, the husband was not particularly anxious for the welfare of his wife and children, but concerned himself chiefly in the satisfaction of his sexual appetite and his pride. He was useful, however, in building the nest, or hut, in procuring the necessary food, and in defending his family. Most legends relate that primitive man lived in promiscuity with women, without marriage, and that marriage was instituted by some god or by some law. But this opinion, which is still held by most modern authors, is quite erroneous, as Westermark has demonstrated in a masterly manner, by the aid of documents which are absolutely conclusive. The duty of the husband to provide food for the family is a general law among savage peoples. A confirmation of this law is found in the fact that most often in polygamous races the man has only the right to as many wives as he can support. Every man must give proof that he is capable of feeding his family. Even after divorce the husband's duties continue, and may even be transmitted to his heirs. For example, among certain peoples, his brother is obliged to marry his widow. The husband's duties appear to be inherited from the higher apes, among whom conjugal fidelity lasts longer than the sexual appetite. This fidelity has therefore deep phylogenetic roots in our nature, and we shall see later on that we cannot neglect it without compromising our social state (Chap. XIII). The following is the definition of marriage as given by Westermark: _Marriage is a sexual union of variable duration between men and women, a union which is continued after copulation, at least till the birth of the child._