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The Three Reasons for Polygamy

Why the Obamas and the Romneys had multiple wives.

Both candidates for the presidency owe their very existence to polygamy (1). President Obama’s father belonged to the polygamous Luo tribe. Mitt Romney’s paternal great grandfathers moved to Mexico to continue the Mormon practice of polygamy then outlawed in the U.S. So the time is ripe to ask what advantages polygamy has over monogamy.

Although plural marriage is banned in developed countries, it is surprisingly common, and popular, elsewhere with 55 percent of women sharing their husbands in Benin and an average of 16 percent of women doing so in less developed nations (2). Polygamy may be detested in developed countries but it is practiced to some degree in most societies studied by anthropologists. What did polygamy do for the Obamas and the Romneys that they could not accomplish with monogamy?

Studies in animal behavior show that polygynous mating systems (i.e., one male mating with several females) have at least three possible advantages.

Polygamy: A bird’s eye view

There are three basic reasons for polygyny in birds. First, there may be a scarcity of adult males. Second, some males may have much better genes than others which is particularly important for populations where there is a heavy load of diseases and parasites to which resistance is genetically heritable. Third, females do better by sharing a mate who defends a good territory (with plenty of food and cover) than they would by opting to be the single mate in a bad territory.

So much for birds! Do humans choose polygamy for similar reasons?

My research on 32 countries where polygamy is practiced by at least five percent of married women yielded answers (2). Polygamy increased where there was a scarcity of males in the population (first reason for birds).

Countries having a heavy infectious disease load had many more polygamous marriages (second reason for birds.) Women in disease-prone countries may prefer highly disease-resistant (i.e., physically attractive) men to father their offspring leaving less desirable men without mates. There is independent evidence that women care more about physical attractiveness in these countries and have a higher sex drive (3).

Having economic resources facilitates polygamy for humans consistent with resource-defense polygyny in birds (reason number 3). Thus, there were more polygamous wives in countries where men could monopolize wealth whether in terms of earned income or farmland (analogous to animal territories.) My findings were not new: they corroborated earlier research but used better data.

So humans turn to multiple marriage for the same three basic reasons that birds do (scarcity of males, selection for disease-resistant genes, and defense of breeding territory and its economic equivalents.)

In my study, I also evaluated a number of “explanations” for polygamy that are routinely trotted out by social scientists and other observers in developed countries who find polygamy repulsive.

Contrary to popular assumptions, multiple marriage had nothing to do with poverty, backwardness, or oppression of women (e.g., acceptance of wife-beating) in my study. Of course, that begs the question as to why polygamy survives mostly in underdeveloped countries close to the equator and why it is so unpopular in developed countries (4, see map.)

Why the developed world hates polygamy

At least three factors are critical. First, instead of a scarcity of males, developed countries have an excess, thanks to better public health that saves more males than females. Second, colder winters made it impossible historically for mothers to raise children without substantial help from their husbands.

The most important reason that polygamy is out of place in the modern world is that it works best in agricultural societies where children contribute to farm labor and care of livestock (4).

Developed countries are highly urbanized and it is very difficult to raise large families in cities because children are a huge drain on finances that lasts for two decades thanks to the extent of modern education. In agricultural societies, by contrast, children defray the expense of raising them by contributing productive labor to the household economy.

Neither Romney nor Obama has any desire to discuss their polygamous background. Both are religious but they conveniently forgot the beloved patriarchs of the Old Testament like David, Solomon, and Abraham and their many wives (which neighbors were told not to covet).

Romney’s Mormon ancestors practiced polygamy but it was mainly confined to members of the church hierarchy who were wealthier than others in terms of land holdings and could maintain multiple households (bird reason number three).

Obama’s Luo ancestors likely practiced polygamy for all three bird reasons. There was a scarcity of males, local diseases were a major issue and powerful men could monopolize wealth.

The fact that both candidates are descended from recent polygamous ancestors (1) when no other Presidental candidate ever was is a remarkable instance of American diversity. It should be cherished rather than otherwise.


1. Maraniss, D. (2012, April 12). The polygamists in Obama and Romney’s family trees. The Washington Post.…

2. Barber, N. (2008). Explaining cross-national differences in polygyny intensity. Cross- Cultural Research, 42, 103-117.

3. Barber, N. (2008). Cross-cultural variation in the motivation for uncommitted sex: The role of disease and social risks. Evolutionary Psychology, 6(2): 217-228.

4. Barber, N. (2009). The wide world of polygamy: We hate it, others love it. Blog post. Psychology Today.…