It will thus be seen that marriage centres in the child, and has at the outset no reason for existence apart from the welfare of the offspring.  Among those animals of lowly organization which are able to provide for themselves from the beginning of existence there is no family and no need for marriage.  Among human races, when sexual unions are not followed by offspring, there may be other reasons for the continuance of the union but they are not reasons in which either Nature or society is in the slightest degree directly concerned.  The marriage which grew up among animals by heredity on the basis of natural selection, and which has been continued by the lower human races through custom and tradition, by the more civilized races through the superimposed regulative influence of legal institutions, has been marriage for the sake of the offspring.[312] Even in civilized races among whom the proportion of sterile marriages is large, marriage tends to be so constituted as always to assume the procreation of children and to involve the permanence required by such procreation.

Among birds, which from the point of view of erotic development stand at the head of the animal world, monogamy frequently prevails (according to some estimates among 90 per cent.), and unions tend to be permanent; there is an approximation to the same condition among some of the higher mammals, especially the anthropoid apes; thus among gorillas and oran-utans permanent monogamic marriages take place, the young sometimes remaining with the parents to the age of six, while any approach to loose behavior on the part of the wife is severely punished by the husband.  The variations that occur are often simply matters of adaptation to circumstances; thus, according to J.G.  Millais (Natural History of British Ducks, pp. 8, 63), the Shoveler duck, though normally monogamic, will become polyandric when males are in excess, the two males being in constant and amicable attendance on the female without signs of jealousy; among the monogamic mallards, similarly, polygyny and polyandry may also occur.  See also R.W.  Shufeldt, “Mating Among Birds,” American Naturalist, March, 1907; for mammal marriages, a valuable paper by Robert Mueller, “Saeugethierehen,” Sexual-Probleme, Jan., 1909, and as regards the general prevalence of monogamy, Woods Hutchinson, “Animal Marriage,” Contemporary Review, Oct., 1904, and Sept., 1905.

There has long been a dispute among the historians of marriage as to the first form of human marriage.  Some assume a primitive promiscuity gradually modified in the direction of monogamy; others argue that man began where the anthropoid apes left off, and that monogamy has prevailed, on the whole, throughout.  Both these opposed views, in an extreme form, seem untenable, and the truth appears to lie midway.  It has been shown by various writers, and notably Westermarck (History of Human Marriage, Chs.  IV-VI), that there