Why We Choose Monogamy

A fossil discovery sheds new light on the history of human pairing  

By Helen Fisher

Among the traditional Cashinahua Indians of Brazil, marriage is a casual affair.  After a young woman gets her father’s permission, she asks her husband-to-be to visit her in her hammock after the family is asleep.  He must be gone by daylight.  But gradually he moves his possessions into her family home.  In the U.S. we spend months preparing for that one big moment of  “I do.”  And in India a formal wedding celebration can last for days.  Marriage customs vary.  But from the steppes of Asia to the coral atolls of the western Pacific, we share an ancient tradition: monogamy.  Volumes of data illustrate that monogamy—marrying one person at a time–is common around the world. Although polygyny, the custom of having more than one wife at a time, is permitted in 84 percent of human societies, in the vast majority of these cultures only a small percentage of men actually have several wives at once. Polyandry, the tradition of taking several husbands simultaneously, is even rarer—practiced in less than half of one percent of cultures.  Neither men nor women are always faithful to their partners.  Nor is monogamy always lifelong—divorce and remarriage are common around the world.  But when I analyzed United Nations data on 97 societies, I found that everywhere on earth the vast majority of men and women eventually wed one person at a time: monogamy. And forget what you’ve heard about men being commitment shy.  Studies show that men fall in love faster than women do; young men are more emotionally dependent on their partners because they have fewer intimate male friends; and today men are more likely than women to want a committed partnership.

 Monogamy is human.  And it probably evolved long ago.  Why?  Meet “Ardi” or Ardipithecus ramidus.  Ardi is a 4.4 million-year-old fossil recently discovered in East Africa, and evidence suggests that she reared her infants with a mate. (It sounds odd, but anthropologists determine this by analyzing characteristics of her teeth.)  Yet with all due respect to Ardi, I maintain that monogamy began even earlier—more than five million years ago—when our forebears first descended from the fast disappearing trees of Africa and began walking on two feet (instead of four) to carry sticks and stones and food.  How could an ancestral female carry her baby in one arm and supplies in the other and still protect herself? How could a single primordial male guard a harem of females when lions prowled? As our forebears began to walk upright, pair bonding became essential for survival. 

Will monogamy survive in our modern world?   I think it will, because scientists have recently discovered some of the genes, neurochemicals and brain circuits that spur us to settle with a mate.  These are deeply embedded in the brain.  Moreover, monogamy still brings prosperity.  Marriage is a source of essential social support.  Married men and women are also healthier.  They live longer, and have a lower risk of cardiovascular disease, cancer and other serious illnesses, fewer alterations in hormones related to stress and less risk of depression than do singles.  They also have a higher household income.  And a married couple can provide stability for their children and grandchildren—their genetic future.   

Partnerships aren’t always easy, that’s for sure.  And under some conditions, it’s necessary to reevaluate, even depart.  But the next time you’re ready to hit the ejection button on your relationship, remember that you’re a walking archive our common human heritage–and built to settle down.  With some earnest attention to your partnership, you might make it last.   Across millions of years, millions have.