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Sex Ed: The Cheat Sheet

There are many paths to unfaithfulness.

In a classic experiment, researchers asked men and women in committed, monogamous relationships how likely they'd be to cheat on their significant others. Men reported being much more willing to cheat. But when they were later offered the chance to go on a date with a stranger, the gender gap closed. Women in relationships were just as likely as men to seize the opportunity.

What affects someone's willingness to cheat? Women are most likely to cheat when they're ovulating, according to psychologist Martie Haselton and anthropologist Elizabeth Pillsworth at UCLA. During the "fertile window," they become more attracted to masculine men— muscular, symmetrical, socially dominant guys with pronounced brows and strong jawlines—providing their current mates don't already have those characteristics. Women pursue a "dual mating strategy," says Pillsworth, settling down with a partner who'll invest resources in her and her children but seeking out prime genes by having sex outside the relationship. Tall women also cheat more—possibly be cause testosterone may influence height and infidelity.

Among both men and women, personality plays a role, as does self-esteem. Men with high self-esteem cheat more, maybe be cause they think they're entitled. Wealth magnifies the effect. Women with low self-esteem are more unfaithful, maybe be cause they're seeking affirmation outside the relationship.

Very attractive women are more likely to cheat, reports Kristina Durante, a research er at the University of Minnesota. The real culprit is the hormone estradiol, an indicator of fertility. Fertile women tend to be very attractive, and estrogen tells their brains they have options.

And there's no getting around it: Cheating depends on your environment. Encouraging women to think they have options—say, by reading a fake news story announcing a surplus of single men in town—makes them less satisfied with their partners, which in turn leads to cheating. The same holds for men. As comedian Chris Rock put it, "You're only as faithful as your options."

Who's Likely To Cheat*

Personality factor: Extroversion Effect: Sensation-seeking and assertive, extroverts are driven to satisfy their sexual desires

Personality factor: Emotional Stability Effect: The less emotionally stable are prone to cheat, possibly because insecure people question the durability of their current relationships.

Personality factor: Openness Effect: The open-minded cheat more: They're more willing to try new things and tuned in to their inner desires.

Personality factor: Agreeableness Effect: People low in agreeableness are liable to cheat because they care less about hurting a partner.

Personality factor: Conscientiousness Effect: Less conscientious people cheat more—they're unable to control impulses and care less about morals

*Personality data courtesy of David Schmidt, a psychologist at BradleyUniversity.