19.2 Explain the near-universality of marriage across cultures.
We said earlier that humans can survive and reproduce without marriage, but saying that does not mean that marriage isn’t advantageous. In fact, because virtually all societies practice female-male marriage as we have defined it, we can assume that the custom is adaptive. But saying that does not specify exactly how it may be adaptive. Several interpretations have traditionally been offered to explain why all human societies have the custom of marriage. Each suggests that marriage solves problems found in all societies—how to share the products of a gender division of labor; how to care for infants, who are dependent for a long time; and how to minimize sexual competition. To evaluate the plausibility of these interpretations, we must ask whether marriage provides the best or the only reasonable solution to each problem. After all, we are trying to explain a custom that is virtually universal. The comparative study of other animals, some of which have something like marriage, may help us to evaluate these explanations.