Cheating Is in Our Genes: What Science Says about Monogamy


Everywhere you look in the world people are
adulterers, even where you can get your head chopped off for it or stoned. That means that
it probably has some biological predisposition. There’s all kinds of cultural reasons that
people are adulterers. If you ask a person why they’re adulterers they may say well
I get lonely when my partner is out of town. I want to solve a sex problem. I’d like
to have more sex. I’d like to get caught and patch up my marriage. I’d like to get
caught and end my marriage. I’d like to supplement my marriage. But scientists are
beginning to find out some biological predispositions. A predisposition doesn’t mean that you’re
necessarily going to be adulterers. I mean you can have a predisposition to alcohol and
give up drinking. And there’s some things about the brain
that seem to predispose some people to adultery. One of them is a set of genes or a gene, we’re
not quite sure which, in the vasopressin system. And there was a wonderful study out of Sweden.
They studied a gene in the vasopressin among 552 men. Some men had no copies of the gene,
some had one copy of the gene and some had two copies of the gene. And the more copies
of this gene you had the less stable your primary relationship was. They were not studying
adultery but they were studying the stability of a partnership which can certainly lead
to adultery that’s unstable. There’s also some genes in the immune system that seem
to play a role in adultery. We tend to be drawn to people who have a different set of
genes in this part of the immune system and, in fact, when the data show that when you
are with a partner who is very similar to you in this part of the immune system women
particularly are more likely to be adulterers and more likely to be adulterers when they’re
ovulating, when they’re more likely to get pregnant. I think we’ve evolved these three distinctly
different brain systems for mating and reproduction – sex drive, feelings of intense romantic
love and feelings of deep attachment. They’re often connected to each other. You can fall
in love with somebody, drives up the dopamine system, triggers the testosterone system and
all of a sudden they’re the sexiest person in the whole world. But they’re not always
well connected. You can lie in bed at night and feel deep attachment for one person and
then swing wildly into feelings of intense romantic love for somebody else and then swing
wildly into feeling the sex drive for somebody who you barely ever met. Which made me wonder whether millions of years
ago there was something adaptive about having a partnership with one person and raising
your babies and having extra relationships with other people. And it’s actually relatively
easy to explain. Let’s dial back a million years. You’ve got a man who’s got a wife,
a partnership, and two children. And he occasionally goes over the hill and sleeps with another
woman and has two children, extra children, with her. He’s doubled the amount of DNA
he has spread into the next generation. Those children will live and pass on whatever it
is in him, some of the genetics, some of the brain circuitry to be predisposed to adultery. But why would a woman be adulterous? A lot
of people think that they’re not as adulterous but every time there’s a man sleeping around
he’s generally sleeping around with a woman so you’ve got to explain women too. What
would a woman have gotten if she’s had a partner a million years ago and two children.
She slips over the hill and has sex with another man. Well she’ll get extra goods and resources
and extra meat, extra protection. If her husband gets injured and dies one of these extra lovers
might come in and help her with her children, even thing some of those children are his.
It’s an insurance policy. And she may even have an extra child and create more genetic
variety in her lineage. So the bottom line is for millions of years
there were some reproductive payoffs not only to forming a pair bond but also to adultery
leaving each one of us with a tremendous drive to fall in love and pair up but also some
susceptibility to cheating on the side.