The Scientific Fundamentalist

A look at the hard truths about human nature.

The paradox of polygamy I: Why most Americans are polygamous

Why most Americans are polygamous

Polygyny has been in the public eye and many Americans’ water-cooler conversations lately, from the success of the HBO series Big Love to the trial of the Mormon sect leader Warren Jeffs. Most Americans consider polygynous marriage to be exotic, unusual, bizarre, and even morally wrong, hence the attraction of Big Love or the titillation of the Jeffs’ trial. But polygyny is not that exotic; many -- even most -- Americans are already in polygynous marriages.

First, let’s get our terms straight. Polygyny is the scientific term for a marriage of one man to more than one woman. Polygamy refers to both polygyny and polyandry -- marriage of one woman to more than one man. Polygamy is often used synonymously with polygyny because there are very few polyandrous societies in the world.

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Of course, simultaneous polygyny, of the kind depicted in Big Love and practiced by Jeffs, is illegal in all 50 states. However, many Americans (and others) practice serial polygyny, through a series of marriage, divorce, and remarriage. For all practical purposes, the consequences of serial polygyny are exactly the same as those of simultaneous polygyny.

When a man like Bill Henrickson -- the fictional polygynist on Big Love -- has three wives simultaneously, the mathematical consequence, given a roughly 50-50 sex ratio, is that he is depriving two other men of their reproductive opportunities. Two other men cannot have a wife and children because Henrickson has three wives. When Donald Trump has had three wives sequentially, he too deprived two other men of their reproductive opportunities, because by the time he divorced his previous wives, they were past their reproductive age. The strongest predictor of remarriage after divorce is sex; men typically remarry, women typically don’t. Neither Ivana Trump nor Marla Maples remarried after divorce from Trump (although Ivana was briefly married without children before Trump).

Extramarital affairs are another means of polygynous mating, and married men are more likely to engage in affairs than married women. When a monogamously married man has two unmarried mistresses or girlfriends, the consequence is essentially the same; he is depriving two other men of their mating opportunities. So any man who’s ever divorced and remarried, any woman who’s ever married a divorced man, any married man who’s ever had long-term affairs, or any woman who’s ever had affairs with married men, are all practicing polygyny at some level, with the same consequences as simultaneous polygyny of Henrickson and Jeffs.

Whether simultaneous or serial, polygyny is common because humans are naturally polygynous. Scientists agree that anthropological and archeological evidence shows conclusively that humans have been mildly polygynous throughout evolutionary history. (But remember the danger of the naturalistic fallacy -- deriving moral implications from scientific facts. “Natural” means neither “good” nor “desirable.” Nor does it mean “inevitable.”) Humans are not as polygynous as gorillas, whose silverback males keep a harem of several females, but not strictly monogamous like gibbons, whose male and female mate for life.

In the next post, I’ll address the question of who benefits from polygynous society: men or women? The answer might surprise you.

Satoshi Kanazawa is an evolutionary psychologist at LSE and the coauthor (with the late Alan S. Miller) of Why Beautiful People Have More Daughters.

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