Do men and women cheat for different reasons?

The problem with studying adultery, of course, is that cheating is shrouded in secrecy, and philanderers are no more eager to discuss their discretions with a researcher than they are with their spouses. Further complicating the issue is what exactly constitutes cheating in this day and age -- is it just sex? Emotional betrayal? A stolen kiss?

According to data from the American Association for Marriage and Family Therapy, about 15 percent of wives and 25 percent of husbands have had sex with someone who's not their spouse [source: Jayson]. When actions other than sex are considered, the numbers rise: Marriage counselor M. Gary Neuman claims one in 2.7 men will cheat at some point [source: CNN]. While we may not have exact numbers, it appears that men cheat more than women, but the ladies have been cheating more frequently in recent years [source: Bryner].

As for why men and women cheat, the conventional wisdom for years has been that men seek quantity and women seek quality; in other words, men will cheat to have more sex, and women will cheat because they seek an emotional quality that is missing in their marriage [source: Bryner]. More and more marriage counselors and psychologists are saying that women aren't the only ones who cheat because they seek intimacy and attention after they've been neglected by their spouses. According to M. Gary Neuman, 92 percent of cheating men say it's not about the sex, it's about feeling underappreciated. Furthermore, Neuman's work shows men don't cheat because they find someone more attractive than their spouse; 88 percent of the men claim the other woman wasn't better looking than their wives [source: CNN].

Of course, such results again highlight the problem of studying infidelity. Are men claiming emotional neglect because they know that's what a psychologist or marriage counselor would like to hear? It's possible that such a claim engenders more support and sympathy. And to some extent, it pins the blame on the wife who created such a neglectful situation. In 2008, Dr. Laura Schlessinger garnered headlines when she claimed that women were somewhat responsible for their husbands' affairs [source: Celizic]. It's a woman's job, according to Dr. Laura, to make a man feel like a successful superhero stud; anything short of that, and you can't blame a man's wandering eye.

But some other studies show that no matter how great a marriage is, men and women may find themselves in another's arms.

When we learn of an affair, we may ask, "What went wrong?" The answer, according to some researchers, could be "nothing." In a study published in 2008 in the Journal of Marriage and Family, couples were asked to define their marriages as "very happy," "pretty happy" or "not too happy." Those in not too happy marriages were three times more likely than those in very happy marriages to report an affair, but surprisingly, couples in pretty happy marriages were twice as likely as those in very happy marriages to have had an affair [source: Jayson]. How happy is happy enough? Researchers and therapists wonder if we put too much pressure on the institution of marriage, if we expect a relationship to always be at its peak in terms of romance and companionship, despite developments such as children or a rough economy. When men and women perceive a dip or feel bored, they immediately throw a "pretty happy" relationship away.

There are a few studies which indicate that women are more attuned to small problems within the relationship that spell doom, and that's why they pursue affairs. A 2008 study found that half of women reported marital problems before an affair, while only a quarter of men reported problems [source: Jayson]. And a 2007 study published in the journal Sex Roles found that women are much more likely than men to begin a new relationship with the person they cheated with, perhaps indicating that women use affairs as a way to end stagnant relationships and find new, better mates [source: Brand et al.]. Men, the study reports, were more likely to cite "saw an opportunity and took it" as a reason for committing adultery than women were, while the women cited reasons that had to do with the demise of the relationship.

That opportunity that men cite, as opposed to happiness, may be the key factor to whether infidelity takes place. The rates of women committing adultery has been on the rise in recent years, a phenomenon researchers attribute to their increased presence in the workplace and in jobs that require them to travel. One University of Maryland professor believes that certain powerful professionals will always have the opportunity, because they have the status and wealth that attracts attention; according to him, infidelity magnets include athlete, pilot, lawyer, doctor and anyone with a measure of fame [source: Stoller].

And married men may always get a larger share of opportunity from single women, if a 2009 study from the Journal of Experimental Social Psychology is any indication. In that study, single women were shown a picture of a man and were told that a computer had rendered him a compatible match. When the women were told that the man was single, 59 percent of the single women were interested in meeting the man. The other half of the single subjects were told that the man was in a committed relationship; 90 percent of those women were interested in pursuing the man [source: Tierney]. Researchers theorize that the men in relationships have been pre-screened and deemed acceptable as a mate, while the unattached men are greater unknowns. For men in the study, a status of single or attached made no difference in whether they wanted to pursue their computer-generated match.

Using evolutionary psychology to explain human behavior can be somewhat controversial, but the field provides some interesting reasons as to why men and women may cheat. From an evolutionary standpoint, men cheat because they feel an imperative to spread their genetic code as much as possible, to ensure they have heirs. Men would also be upset by a woman's infidelity from a purely sexual point of view, because they don't want to waste hard-earned resources raising another man's children.

Women, on the other hand, might be more upset by their lover's emotional infidelity, because it threatens those resources she needs for her children. But because women are so invested in receiving those resources, researchers weren't sure at first why women would threaten them by cheating at all. As it turns out, even after women choose a partner that they deem worthwhile to father their children, researchers believe they still seek out a better one in a competition that we'll deem "Sperm Wars."

Here's how Sperm Wars works: According to a 2006 study published in Hormones and Behavior, women tend to be unfaithful at the most fertile part of their menstrual cycle, even if they're not trying to get pregnant. And the men they tend to cheat with are by and large better looking than their own partners. Even if their own spouse is a hardworking, high-earning, compassionate man, the study revealed, women would cheat if they didn't find the man attractive, perhaps because of some old instinct that good genes are synonymous with good looks [source: Jayson]. If women sleep with several men at their most fertile point, the Sperm Wars are underway: the best sperm wins, and the woman is ensured the best child she can get. From an evolutionary standpoint, that's important, as a woman spends nine months producing a child (a man, of course, may spend only a few seconds), so she wants to get the most bang for her buck, genetics-wise. She may also risk losing her partner's resources if she believes she can get better resources from another male. In other words, women are not likely to go slumming when they cheat; they'll always look for the best deal possible.

Researchers at Florida Atlantic University have found that men are somewhat affected by the Sperm Wars phenomenon. If a couple is separated a long time, time in which the woman could have been unfaithful, the man will produce more sperm the next time they have sex, which gives him better odds of impregnating his partner. Furthermore, the researchers noted that artificial penises have the ability to remove substances from artificial vaginas, so men may be able to handicap their sexual rivals. Certain sexual positions are best for removing another man's sperm -- most notably, deep thrusting. The FAU researchers claim that sexual relations following accusations of female infidelity often feature deep thrusting, as if the man is trying to become the ultimate victor in Sperm Wars [source: Association for Psychological Science].

For more on Sperm Wars' players, see the links on the next page.