Monogamy doesn’t seem to be the natural way for humans to live. Very few species mate with a single partner for life, and while humans in most parts of the world do, it is often not done well. Romantic affairs are the driving plot device in more books and movies than any of us can count. In the real world, we know plenty of people who have cheated on spouses or significant others, or been on the other side of the cheating. Numerous TV show hosts have made a living by revealing the results of paternity tests.
Yuval Noah Harari makes a suggestion in his book Sapiens that monogamy is so hard for humans today because most of human evolution was not focused on monogamous relationships. Nuclear families are a relatively recent invention. For most of human history, we lived in small social tribes, and raising a child wasn’t the responsibility of two parents who who married and stayed together for the rest of their lives. In some instances, tribes actively practiced fatherhood rituals that were the direct opposite of monogamy. Harari writes,
“The proponents of this ancient commune theory argue that frequent infidelities that characterize modern marriages, and the high rates of divorce, not to mention the cornucopia of psychological complexes from which both children and adults suffer, all result from forcing humans to live in nuclear families and monogamous relationships that are incompatible with our biological software.” Harari describes the ancient commune theory mentioned in the quote as a theory that people in small tribes didn’t understand that a single man’s sperm fertilized an egg. It was not clearly understood that only one person sired a child, and in some tribes women would actively haved sex with multiple men, even throughout a pregnancy, so that her child would gain the qualities of all the men.
When I first read this quote from Harari it made me question whether modern monogamous marriages were really the best thing for humans. If it contradicted our biology so much, I wondered why we kept it around, especially if it caused so many psychological, social, and emotional problems for so many people.
Joseph Henrich’s book The WEIRDest People in the World, helped me understand why monogamous institutions have become so useful in our modern world, despite the costs that Harari mentions and the incompatibility of monogamy with our evolutionary psychology. When societies do not have a system of single pair bonding, the highest status men tend to accumulate more females to exclusively marry. Regardless as to whether the women want to have sex with many men and partner with them, they often find that it is best for them to stick with just the one highest status man (possibly the wealthiest, strongest, or most politically connected man) for the best chance to raise their children. Pairing with a high status man who already has two or three other wives can often be more advantageous for a woman than pairing with the fourth most high status man, especially as women are pushed toward men further down the status ladder – as happens in strict monogamous societies.
As high status men accumulate more women who exclusively partner with them, even though the man doesn’t exclusively partner with the women, then lower status men do not find a partner. Single men who cannot get a partner are more likely to take large risks and gambles to try to move up the social ladder. They have more testosterone, because married men have a decrease in testosterone, and they have less reason to invest in the future. Henrich argues that policies which pushed monogamy and broke up polygamy were a driving factor in what made the West WEIRD – Western, Educated, Industrialized, Rich, and Democratic. Monogamous societies help ensure more men are able to find a partner, decreasing the number of single men without prospects for getting married or having children. This gave more men a reason to invest in the future and improve their behavior and cooperation with others.
Our monogamous relationships may not be in line with our biology, but they have encouraged a more even distribution of male and female partners, and have helped create more stable societies. The relationships are hard, but at least recently have been a driving force toward WEIRD progress and development. The cost of monogamy that stem from a reproductive and sexual system mismatched to our evolution and biology don’t outweigh the benefits of a more stable, peaceful, and fruitful society.