Men, do your wives or girlfriends think you’re hot? If not, you better watch out because your women will wander. Or at least they’ll think about it.

And they don’t have to be desperate housewives, either. Whether or not they act on the amorous impulse, a cheatin’ heart may be hard-wired in every female.

Conventional wisdom has it that men like lookers, but women want something more substantial in a mate, like wealth or stability. Two new studies from UCLA and the University of New Mexico, however, say that’s not necessarily so.

The findings, reported in the scholarly journals Hormones and Behavior and Evolution and Human Behavior, suggest that women may have evolved to want to stray during the most fertile part of their cycle — but only when they find their partners are less sexually attractive than other men. Those poor guys, meanwhile, seem to be aware on some level that their significant other might be eyeing the hunky neighbor or handsome co-worker and step up their mate-guarding strategies when their wives or girlfriends ovulate. What’s more, this happens even if neither partner is keeping track of the woman’s cycle.

We’re finding out that there’s a hidden side of female desire,” says Martie Haselton, the UCLA assistant professor of communication studies and psychology who authored the studies. “They are not necessarily monogamous. They may have a psychology that evolved that leads them to cheat on their mates. It’s been to women’s advantage to keep this under wraps, and interesting that it’s been revealed relatively late in sex research. It’s not something women talk about. If they do, it gets them into trouble.”

In one of the studies, Haselton recruited 38 female students from a large U.S. university (kept nameless so the women in question don’t get unmasked and subsequently grilled by mates who learn of the sensitive findings). They were asked to reveal information from which their date of ovulation could be deduced, and asked to rate their partner’s sexual attractiveness as measured by, among other things, his desirability as a fling. The subjects also filled out 35 diary-like entries in which they rated the strength of their attractions that day to men other than their mates, and the frequency and manner in which they flirted or otherwise acted out those attractions. Finally, the women daily rated their own sexual attractiveness, desires and sense of power in romantic relationships.

The second study included 43 normally ovulating women who also rated their partner’s attractiveness. These subjects added data on their own desires and their partner’s mate-retention behaviors at high and low fertility. This time, lab tests that could detect the signs of ovulation confirmed the women were fertile in one of their reporting sessions.

“One thing I hope women get out of this research is that it is quite natural for a woman to become attracted to another man, even if she is in a good, long-term relationship,” Haselton concludes. “These are ancient evolved strategies. Another way of thinking about it is if a woman knows that it is a biological stew of hormones toying with her desires, she may choose to ignore them.”