Why We Cheat (cont.)

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.

Infidelity by the Numbers

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.

Rewards for Fidelity

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."

Part 2: Overcoming Infidelity

Published April 25, 2005.

SOURCES: Judith Lipton, MD, author, The Myth of Monogamy: Fidelity and Infidelity in Animals and People. Peter Kramer, MD, host, The Infinite Mind, author, Listening to Prozac, Should You Leave?, and Against Depression. Don-David Lusterman, PhD, marriage and family therapist; author, Infidelity: A Survival Guide. Luanne Cole Weston, PhD, sex therapist; author, Sex Matters®. Priya Batra, PsyD, psychologist, Kaiser Permanente. "American Sexual Behavior: Trends, Socio-Demographic Differences, and Risk Behavior," General Social Survey Topical Report No. 25, National Opinion Research Center, University of Chicago, April 2003.

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