Market forces affect patterns of polygyny in Uganda

Abstract

Polygynous marriage is generally more beneficial for men than it is for women, although women may choose to marry an alreadymarried man if he is the best alternative available. We use the theory of biological markets to predict that the likelihood of a man marrying polygynously will be a function of the level of resources that he has, the local sex ratio, and the resources that other men in the local population have. Using records of more than 1 million men in 56 districts from the 2002 Ugandan census, we show that polygynously married men are more likely to own land than monogamously married men, that polygynous marriages become more common as the district sex ratio becomes more female biased, that owning land is particularly important when men are abundant in the district, and that a man's owning land most increases the odds of polygyny in districts where few other men own land. Results are discussed with reference to models of the evolution of polygyny.biological markets ͉ mate choice ͉ operational sex ratio ͉ humans ͉ land ownership M ost human societies historically have allowed polygyny, or the marriage of more than 1 woman to 1 man (1, 2). However, within polygynous societies, many marriages are monogamous, and across polygynous societies there is variation both in the mean and in the variance of the number of wives per married man. What, then, explains how many wives men marry?The payoffs to polygyny are not symmetric across the 2 sexes. Men always increase their reproductive success by adding an extra wife. In African agriculturalist and pastoralist societies, for example, every extra wife a man has adds to his number of surviving offspring, and most of the variance in men's reproductive success is explained by variation in number of wives (3-6). For women, being polygynously married seems less beneficial because each additional wife subdivides household resources and male investment. Compared with monogamously married women, polygynously married women have lower fertility (7-9), increased child mortality (10), and poorer child growth and development (11,12). The latter 2 outcomes obviously affect the reproductive success of both parents but fall disproportionately on women, for whom they are not offset by the increased offspring number that men experience in polygynous marriages. The costs of polygyny seem to fall particularly on women of later rank in the union, and their children (6, 13). Thus, it seems that polygynous marriage in African societies is most beneficial to men and most costly to women, especially wives of lower rank.Situations whereby individuals receive asymmetric payoffs from collaboration and yet continue to collaborate can be conceptualized using the theory of biological markets (14-17). Biological markets operate wherever there are 2 classes of individual (e.g., male and female), with distinct commodities to exchange (e.g., resources and fertility), and where each has the possibility of partner choice. This leads to competition within each class to attract members of the other clas...

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