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My last post, Why We Think Monogamy Is Normal, was about how monogamy came to supplant polygyny (one husband, multiple wives) as the socially accepted marriage system in Europe. My explanation focused on male interests, by suggesting that monogamy was imposed as a kind of reciprocal exchange between high status and low status men in ancient and medieval Europe: elite men allowed low status men to marry, in exchange for their tax contributions and military service. It's reasonable to suggest that the institutionalization of monogamy did mainly reflect male interests, as these societies were heavily male-dominated in fields that were highly relevant to this institutionalization, such as law, politics and religion. But it's also critical to consider what the interests of women would have been throughout this process. Could polygyny have been abolished in order to promote female interests?
Roman wedding on sarcophagus lid
People often think of polygyny as a system which benefits all men over all women, but from a Darwinian perspective, this is a big mistake. Polygyny actually advantages some men over other men, and some women over other women. Reproductively, polygyny is a higher stakes game for men than for women, with some men winning big and others losing big, but the stakes are pretty high for women as well. To illustrate these ideas, consider this simplified but useful thought experiment, adapted from Robert Wright's The Moral Animal [1].
Imagine that 5 men and 5 women live in a monogamous society, and that each person is ranked according to their mate value. (This value indicates how reproductively advantageous it would be to mate with that person, and is to some extent based on different criteria in each sex; among females, for example, it will have more to do with youth and fertility, whereas in males it will have more to do with status and resources; in both sexes it will have to do with genetic quality). Male 1 is the most desirable man, Female 1 is the most desirable woman, Male 2 is the second-most desirable man, etc. Each person pairs off with the best available mate, so that Male 1 marries Female 1 and so on, all the way down to Male 5 marrying Female 5. The marriage structure of the population would look like this:
Male 1 = Female 1
Male 2 = Female 2
Male 3 = Female 3
Male 4 = Female 4
Male 5 = Female 5
Now imagine that the same population lives in a polygynous society, and that Female 3 chooses to become Male 1's second wife, rather than Male 3's first wife. Male 1 has excellent genes and access to resources, and Female 3 perceives that becoming his second wife would be the best option for her and her future children. So Male 1 is now married to Females 1 and 3, and everyone else again pairs off with the best available mate. The marriage structure is now:
Male 1 = Females 1 and 3
Male 2 = Female 2
Male 3 = Female 4
Male 4 = Female 5
Male 5 = (no wife)
Who are the reproductive winners and losers as we shift from monogamy to polygyny? The biggest winner is Male 1, who can now have twice as many offspring, whereas the biggest loser is Male 5, who has been locked out of the mating pool entirely. A more moderate winner is Female 3, who has improved her reproductive prospects through her upward mobility, and a more moderate loser is Female 1, who now has to share her husband's attentions and resources with a co-wife. There are also some other relatively moderate winners and losers. Polygyny has made women scarcer among Males 2-5, and this scarcity benefits women at the expense of men. The women who rank below Female 3 (Females 4 and 5) have each moved up a notch in the mating market, and so are now slightly better off, just as their husbands (Males 3 and 4) are now each a little worse off.
This illustration shows how the reproductive effects of polygyny could be positive for the majority of women, and negative for the majority of men; it thus shows why it's a mistake, from an evolutionary perspective, to suggest that polygyny is worse than monogamy for women in general. (One might object that the illustration only focuses on the reproductive outcomes of sexual relationships, and that people in modern societies are often relatively unconcerned about these outcomes. This objection would overlook a fundamental tenet of evolutionary psychology, however, which is that the genetically-encoded adaptations that compose our modern minds evolved precisely because they positively influenced reproductive outcomes among our ancestors). This illustration also makes clear that women who are first wives (or who are likely to become first wives) have an interest in opposing polygyny, whereas women who have chosen to become later wives (or who are likely to so choose) have an interest in supporting polygyny [2].
Medieval wedding
This brings us back to the question of whether the interests of women could have played a role in the establishment of monogamy in ancient and medieval Europe. It seems plausible that the women who had the biggest interest in abolishing polygyny—first wives, or women who were likely to become first wives—could have been an important voice in favor of this establishment. This would be especially plausible if the likelihood of becoming a first wife, instead of a later wife, was positively correlated with social status. Perhaps especially influential women—for example, those of exceptional ability or beauty, or those from powerful families—tended to become first wives, and less socially powerful women tended to become later wives. If so, then the voices of women who stood to benefit from monogamy would have more likely drowned out the voices of women who stood to benefit from polygyny.
References
1. Wright, R. (1994). The Moral Animal. New York: Pantheon.
2. Kurzban, R. (2010). Why Everyone (Else) is a Hypocrite: Evolution and the Modular Mind. Princeton University Press.
Copyright Michael E. Price 2011. All rights reserved.
