What, then, are the social advantages of monogamy which favor the development of a higher type of culture? These advantages are numerous, but perhaps the most important of them can be grouped under six heads. (1) The number of the two sexes, as we have already seen, is everywhere approximately equal. This means that monogamy is in harmony with the biological conditions that exist in the human species. The equal number of the two sexes has probably been brought about through natural selection. Why nature should favor this proportion of the sexes can perhaps be in part understood when we reflect that with such proportion there can be the largest number of family groups, and hence the best possible conditions for the rearing of offspring. (2) Monogamy secures the superior care of children in at least two respects. First, it very greatly decreases mortality in children, because under monogamy both husband and wife unite in their care. Again, monogamy secures the superior upbringing and, therefore, the superior socialization of the child. In the monogamous family much greater attention can be given to the training of children by both parents. In other forms of the family not only is the death rate higher among children, but from the point of view of modern civilization, at least, they are inferiorly socialized. (3) The monogamic family alone produces affections and emotions of the higher type. It is only in the monogamic family that the highest type of altruistic affection can be cultivated. It is difficult to understand, for example, how anything like unselfish affection between husband and wife can exist under polygyny. Under monogamy, husband and wife are called upon to sacrifice selfish desires in the mutual care of children. Monogamy is, therefore, fitted as a form of the family to foster altruism in the highest degree, and, as we have seen, the higher the type of altruism produced by the family life, the higher the type of the social life generally, other things being equal. It is especially to the credit of monogamy that it has created fatherhood in the fullest sense of the term, and therefore taught the male element in human society the value of service and self-sacrifice. Under polygynous conditions the father cannot devote himself to any extent to his children or to any one wife, since he is really the head of several households, and therefore, as we have already noted, fatherhood in the fullest sense scarcely exists under polygyny.