When, in the course of time, sexual reproduction eventuated in a mammalian type, with greater intimacy between mother and offspring and a longer period of dependence of offspring on the mother, the function of the male in assisting the female became social as well as biological; and this was pre-eminently so in the case of man, because of the pre-eminent helplessness of the human child.[256] The characteristic helplessness of the child, which at first thought appears to be a disadvantage, is in fact the source of human superiority, since the design of nature in providing this condition of helplessness is to afford a lapse of time sufficient for the growth of the very complex mechanism, the human brain, which, along with free hands, is the medium through which man begins that reaction on his environment--inventing, exterminating, cultivating, domesticating, organizing--which ends in his supremacy. It is plain, therefore, that species in which growth is slow are at an advantage, if to the care and nourishment of the female are added the providence and protection of the male; and this is especially true in mankind, where growth is not completed for a long period of years. In this connection we have an explanation of the alleged greater variability of the male. Instead of an insignificant addendum to the reproductive process, he becomes larger than the female, masterful, jealous, a fighting specialization--still an attaché of the female, but now a defender and provider. This is the general condition among mammals; and among mankind the longer dependence of children results in a correspondingly lengthened and intimate association of the parents, which we denominate marriage. For Westermarck is quite right in his view that children are not the result of marriage, but marriage is the result of children. From this point of view marriage is a union favored by the scheme of nature because it is favorable to the rearing and training of children, and the groups practicing marriage, or its animal analogue, have the best chance of survival.