Charlie Allnut (Humphrey Bogart): A man takes a drop too much once in a while, it’s only human nature.
Rose Sayer (Katherine Hepburn): Nature, Mr. Allnut, is what we are put in this world to rise above. ~ The African Queen (1951)
Which is more natural for human beings, monogamy1 or polygamy? If one is more natural, does that make it preferable?
Most documented human societies, about 85%, have been polygamous. This almost always involves polygyny, men having multiple wives. Polyandry, wives having multiple husbands and polyamory, having more than one consensual, intimate relationship at the same time, are far less common. Even in so-called monogamous cultures people have affairs, and they often engage in serial monogamy, the custom of having multiple, consecutive sexual relationships but not more than one at a time. Perhaps humans are naturally polygamous.
Yet there are examples in nature of mostly monogamous relationships: lar gibbons, mute swans, malagasy giant rats, waved albatrosses, california mouses, black vultures, shingleback skinks, sandhill cranes, prairie voles, convict chiclids, some African antelopes, and … humans. Humans are capable of long-term, happy, monogamous relationships, just as they are capable of having polygamous ones.
So it is hard to say whether monogamy or polygamy is more natural. It might be like asking whether it is more natural to speak English or German. Humans are wired to learn language just as they naturally crave contact with others, but culture largely determines the language they learn and the forms of their relationships. Nature doesn’t determine which language or relationship is best. And even if one is more natural than the other that doesn’t make it better. Some natural things are good, but some are bad—like smallpox!
Moreover humans have both long-term and short-term mating strategies. We associate long-term mating strategies with monogamy. These strategies value commitment, gene quality, economic prospects and parenting skills. We associate short-term mating strategies with polygamy. These strategies value physical attractiveness, sex appeal and sexual experience. But nature doesn’t decree which types of relationships are morally or biologically better.
Regarding the origins of monogamy the situation is straightforward:
The genetic evidence for the evolution of monogamy in humans is more complex but much more straightforward. While female effective population size (the number of individuals successfully producing offspring thus contributing to the gene pool), as indicated by mitochondrial-DNA evidence, increased around the time of human (not hominid) expansion out of Africa about 80,000–100,000 years ago, male effective population size, as indicated by Y-chromosome evidence, did not increase until the advent of agriculture 18,000 years ago. This means that before 18 000 years ago, many females would be reproducing with the same few males.
This strongly suggests that monogamy is a cultural imperative not a biological one. And the modern world favors monogamy—polygamy is illegal in the entire developed world. Why the transition from polygamy to monogamy? The main reason is that polygyny is detrimental to society. It creates an incentive for men to take many wives, leaving other men without wives—and men without mates cause problems. In polygynous societies levels of crime, violence, poverty and gender inequality are greater than in monogamous ones as a recent study at the University of British Columbia confirmed:
… monogamy’s main cultural evolutionary advantage over polygyny is the more egalitarian distribution of women, which reduces male competition and social problems. By shifting male efforts from seeking wives to paternal investment, institutionalized monogamy increases long-term planning, economic productivity, savings and child investment …
Monogamous marriage also results in significant improvements in child welfare, including lower rates of child neglect, abuse, accidental death, homicide and intra-household conflict, the study finds. These benefits result from greater levels of parental investment, smaller households and increased direct “blood relatedness” in monogamous family households …
… By decreasing competition for younger and younger brides, monogamous marriage increases the age of first marriage for females, decreases the spousal age gap and elevates female influence in household decisions which decreases total fertility and increases gender equality.
It seems that we should favor the wisdom of culture over our genetic lease. Still you might object. “Even if it’s in society’s interests to have stable monogamous unions that doesn’t mean it’s in mine. I like polygamous or polyandrous relationships.” It is hard to give a knockdown argument against this. If all involved parties are happier in such relationships, and the effects on society are limited, then so be it.
I can only speak for myself by echoing the words of that great freethinker Voltaire:
As I had now seen all that was beautiful on earth, I resolved for the future to see nothing but my own home; I took a wife, and soon suspected that she deceived me; but notwithstanding this doubt, I still found that of all conditions of life this was much the happiest.2
1. I am referring to marital monogamy, marriages of two people only, and social monogamy, two partners living together, having sex together, and cooperating in acquiring basic resources.
2. Voltaire, The Travels of Scarmentado.