This seems obvious enough, and I might stop here if it were not for all the social theorists who have tried to imagine a time in history before there was a family. In fact, the evidence of anthropology reveals that there is no such animal. Nature, even without the support of divine revelation, can tell us a great deal about the family. The differences between males and females, we now know from researches into genetics and endocrinology, are fundamental to human nature and social life. The fact of life is that human males invest a great deal less in their offspring than mothers do.
Women produce few but large eggs in the course of a year, while men produce millions of gametes.
A woman can hardly conceive and bear one child a year, while a man might beget dozens without trying very hard. Once conception occurs, the mother not only carries the child for nine months, but she is the primary source of nourishment and care for many years. Fathers are, of course, important to the moral health of the child, but they are not so indispensable, and even in the best of all worlds, fathers cannot spend as much time with their children. Men and women are more distinct than male and female chimpanzees, and what is more, the higher civilizations of Greece, Rome, China, and medieval Europe all gave greater emphasis to sexual distinctions than are commonly found in more primitive cultures. They argue, for example, that until the 17th century, men did not love their wives or that sexual exploitation of children was normal.