Why We Cheat


Sexual infidelity is one of humanity’s great obsessions, perhaps second only to violence. We abhor it, yet we want to hear all about it, and some can’t resist it. It’s what has kept Jerry Springer on TV for the past 14 years and Greek mythology alive in the retelling for the past 3,000.

In one story after another, mundane and epic, we are reminded of the emotional and social fallout of messing around. That’s in addition to the scowls it gets from the world’s biggest religions. Why, then, is monogamy so hard for so many?

Perhaps for humans, monogamy does not come naturally, and biology predisposes us to seek multiple partners. That’s what zoologist David Barash, PhD, and psychiatrist Judith Lipton, MD, argue in their book, The Myth of Monogamy: Fidelity and Infidelity in Animals and People. Virtually all animals, they say, are far from being 100% monogamous 100% of the time.

“The only completely, fatalistically monogamous animal we’ve been able to identify is a found in the intestines of fish,” Lipton tells WebMD. That’s because the male and female worms fuse together at the and never separate afterward.

Other animals, including humans, are motivated to ensure their reproductive success not only by picking the highest quality mate they can get but also by taking others on the side.

“>DNA testing and see who’s sleeping with whom,” Lipton says. She and Barash make a distinction between sexual fidelity and what they call “social monogamy.” Even in animals that mate for life, like many birds do, DNA tests reveal that the offspring are often not related to the male of the pair.

That is the case with people, too. Lipton says she was once contacted by a Canadian hospital, where doctors were running genetic tests to find out children’s risks for inherited diseases. In about 10% of the samples, the children were not genetically related to the supposed father.

But make no mistake: Lipton and Barash, who have been married to each other for 28 years, don’t say that sexual fidelity is impossible or wrong because it is not natural, only that it takes some effort. “We human beings spend a large part of our lives learning to do unnatural things, like play the violin or type on a computer,” Lipton says.


If fidelity is a matter of skill, then why are some talented and others terribly clumsy?

People who enter into long-term monogamous relationships, and who really keep their promises, “tend to be very healthy mentally,” Peter Kramer, MD, tells WebMD. Kramer, a psychiatrist, is the host of The Infinite Mind on NPR and author of Listening to Prozac, Should You Leave? and most recently, Against Depression.

“There are lots of things that they’re not, and that makes it possible for them to do this thing that may be in some ways difficult,” he says.

Don-David Lusterman, PhD, a marriage and family therapist and author of Infidelity: A Survival Guide, says he thinks some people who cheat are what he calls “pursuers,” who are also called womanizers when they are men. “They tend to require great numbers of conquests and they perceive them as conquests,” Lusterman tells WebMD. “I see that as a developmental flaw in an individual, as opposed to an affair frequently being a function of some disruption in the couplehood. They’re very different things.”

In clinical terms, he says, pursuers often have a . They crave and demand affection and attention but are not able to return it in kind.

Those who aren’t pursuers may be susceptible to an affair because they are not aware that something is amiss or lacking in the relationship. Given the attention of another man or woman, “>psychologist and expert moderator of WebMD’s Sex Matters® message boards. “They ceased to feel as special in their own first relationship.”

Others are well aware of their frustration and they actively seek what they want outside the relationship. “I do hear some variation of that quite frequently,” Priya Batra, PsyD, a women’s health psychologist in the Kaiser Permanente health care system, tells WebMD.

The proverbial midlife crisis can be another trigger for cheating, “And then you have the younger person who hasn’t tasted enough of everything who maybe committed prematurely,” Weston says.


A lot of the statistics on infidelity floating around are dubious. Some say that as many as 50% of women cheat on their husbands, and 70% of men step out on their wives.

More reliable and believable data come from the University of Chicago’s National Opinion Research Center. About 15% of women surveyed in 2002 said they’d ever had sex with someone besides their spouse while married, and 22% of men had. Roughly 2% of women and 4% of men had done so in the past year.

It’s clear that men are more prone to infidelity, and notably, the longer they live, the more likely they are to cheat. According to the 1992 National Health and Social Life Survey, 37% of men aged 50-59 had ever had an extramarital affair, compared with just 7% of men aged 18-29. The men’s percentages went up steadily in each age range, whereas for women, the most perfidious were the baby boomers, born between 1943 and 1952. About 20% of them reported ever having had an affair, but in all other age ranges, infidelity hovered between 11% and 15%.

What are not taken into account in these surveys are other kinds of infidelity besides having sex. Does a stolen kiss count? What about erotic chats with strangers online? A lap dance?

“Infidelity occurs when one member of a couple secretly violates the commitment to monogamy. That’s a very inclusive definition,” Lusterman says. If your partner considers it cheating, then it probably is. But what would mortify your partner might be a-OK, or at least tolerated, by mine.

“I think there probably is a bigger range of fidelity than we imagine,” Kramer says. Some couples enjoy bringing third parties into their bedroom, yet they would insist that they have never cheated.


Another problem with infidelity statistics is whether to read that the glass is 22% empty or 78% full. Certainly, many, many people cheat. But most people apparently do not, at least by the conventional definition.

Besides the great pressure from religious and cultural mores to stay faithful, and the threat of retribution, there are prizes for fidelity.

“There are more complex types of happiness to be found in behaving in an open and moral way, negotiating whatever problems there are,” Kramer says.

Monogamy is “essentially an arms treaty,” Lipton says. “Given the ubiquity of sexual jealousy, I will agree not to make my partner crazy with sexual jealousy by foreclosing some of my sexual options, if my partner agrees not to make me crazy by foreclosing his options.”

From an evolutionary standpoint, it also has advantages for men. First of all, it ensures that the child you’re working so hard to rear is biologically related to you, and secondly, to ensure that you get a mate, if you’re an average guy. In social groups that form harems, males at the top of the heap get all the women. “Monogamy equally distributes males and females in the culture, instead of Wilt Chamberlain getting 20,000 women, and somebody else getting zero,” Lipton says.

And there are warm, fuzzy reasons. “As I’m growing older and my husband’s growing older, and we’re monogamous, it’s so pleasant to have one other person that you trust completely,” Lipton says. “It’s a treasure.”