Monogamy is under siege from our biology itself. Men are typically larger than women, have more muscle mass, are more inclined to violence and become sexually and socially mature later. These traits are characteristic of an animal species in which one male competes with other males to mate with multiple females.
For men, the underlying evolutionary calculus of polygamy is clear: the possibility for a larger number of offspring and thus enhanced evolutionary fitness. For women, the reasoning is more nuanced: the possibility of better genes for their children, improved access to material resources and social advancement. It can be argued that a woman would be better off as the 20th wife of a very wealthy man than as the only wife of a pauper.
But even though monogamy isn’t natural and therefore isn’t easy, it does offer the benefit of biparental care. It’s very rare for any species to engage in biparental care unless the males are guaranteed that they are genetically related to the offspring—confidence monogamy alone can provide. And because human children need so much parental assistance, protection and investment, humans, perhaps more than any other animal, especially benefit from monogamy.
It’s easy to do what comes naturally—animals do it all the time! Perhaps what makes human beings special is our ability to do things like monogamy that are socially imposed.
Barash is an evolutionary biologist, professor of psychology and co-author of The Myth of Monogamy