Why are we Monogamous? A new study offers clues into the origins of monogamy.

The majority of Americans, and to a lesser degree the majority of humans, profess to be serially monogamous.

None of this polyamory, bigamy, open marriages, or cheating: you have one intimate partner with whom you are sexually exclusive until he or she dies or you get a divorce. Then you have another exclusive partner.

Seems normal, right?

It’s not.

It’s highly unusual, at least from a biological perspective.

For example, only 2 percent of mammals share monogamy’s strictures on sexual fidelity. And whereas a relatively high 15 percent of primate species are monogamous, they’re really just socially monogamous—meaning a pair may stick together, share most resources, and appear to enjoy one another’s company, but they’re far from sexually exclusive.  The same goes with birds: over 90 percent of avian species are faithful to their mates, but only up to a point, after which they’ll openly or slyly participate in cuckolding, rape, necrophilia, pedophilia, non-procreative sex, and homosexual behaviors.

The question, then, is how in the world did serial monogamy ever come about? How did the rampant infidelity of non-human animal sex become so narrow and confined in humans?

While this remains hotly-debated among paleoanthropologists and evolutionary biologists, a possible answer to this question was recently proposed by Sergey Gavrilets, a  biomathematician at the University of Tennessee in Knoxville.

In a paper published in the Proceedings of the National Academy of Sciences, Gavrilets posited that “monogamous coupling” evolved because low-ranking male humanoids who were too weak to fight off the dominant alpha males bought long-term sex from females.

It’s certainly a plausible theory. We’ve known for years that male chimpanzees bribe females with meat for sex; in fact, those males willing to share meat with females got laid twice as often as their stingy counterparts. The offering of food or other resources to a female in return for sexual favors is known as provisioning.

But Gavrilets hypothesized that provisioning became more than primate prostitution—it became the origin of serial monogamy.  For eventually females began to show preference for the roots and mastodon meat provided by low-ranked males—a form of child support, really—and, for males, provisioning became a more effective method of securing females than just beating the hell out of another male.

So there it is—evolutionary validation for all the studies that show that men prefer young, healthy women who can produce healthy babies, and women prefer wealthy men who can contribute resources to rear them.

But even Gavrilets admits that it might not be that simple. Besides, the “monogamous coupling” Gavrilets describes is still more social monogamy than serial monogamy. Provisioning and other good husbandly behavior is not, in and of itself, always enough to secure one’s mate’s unwavering fidelity.

Take, for example, the black-capped chickadee, by all appearances and general habits a serial monogamist.

Studies have shown that flocks of black-capped chickadees form strict dominance hierarchies, with every bird knowing its rank and place. In spring the flock breaks up into pairs, with each pair staking out its own territory for breeding. For the most part, the pair acts like a happily monogamous human couple: prepping their nest, foraging, chirping to one another, etc.

But here’s the catch—on occasion, a female paired with a low-ranking male will sneak out of the nest and slip into the territory of a nearby higher-ranking male. Her infidelity provides her with the best of both worlds: a stable mate helping raise the young and the possibility of passing on the superior genes of the dominant neighbor.

And that’s probably closer to the reality of most humans today: we’re not, actually, serially monogamous. .

We believe in serial monogamy; we aspire to serial monogamy, we often enjoy serial monogamy, but it’s a complicated sexual world out there. We struggle between the sexual worlds of pure biological impulses and our own unique human standards.

Like our provisioning ancestors, we settle into mutually beneficial patterns of reproductive convenience, but then, like the female chickadee, we’re dictated by primal sexual urges. Those primal urges may be dampened by morals, tradition, and laws, but then over time those morals and traditions and laws evolve, and many are discarded.

So while Gavrilets may be on to something with his hypothesis about the origins of monogamy, and while it’s all very interesting, it’s not entirely useful in deciphering modern humans’ complicated sexual relationships. His hypothesis certainly doesn’t apply to me—I’m in a serially monogamous marriage with a lovely and successful woman even though I lack both dominant fighting skills and a large bank account.

Perhaps, then, what we need is a study into the origins of love.


By Nathaniel Brodie