by Nigel Barber Ph.D.
Studies in animal behavior show that polygynous mating systems (i.e., one male mating with several females) have at least three possible advantages.
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 (1). 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 (2).
Having economic resources facilitates polygamy for humans consistent with resource-defense polygyny in birds (third reason for birds). Thus, there were more polygamous wives in countries where men could monopolize wealth whether in terms of earned income or farm land (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 under developed countries close to the equator and why it is so unpopular in developed countries (3, see map.)
1. Barber, N. (2008). Explaining cross-national differences in polygyny intensity. Cross- Cultural Research, 42, 103-117.
3. Barber, N. (2009). The wide world of polygamy: We hate it, others love it. Blog post. Psychology Today. http://www.psychologytoday.com/blog/the-human-beast/200902/the-wide-worl…