When women are ovulating their behavior changes in several ways, all seemingly designed to attract a certain kind of man. For example, a recent study found that at their most fertile time of month women tend to be more flirtatious—but only with masculine and confident guys.

These changes in women’s behavior do not go unnoticed by men. As some evidence of this, a 2007 study of female lap dancers at a gentleman’s club found that ovulating performers earned more in tips from male customers compared to their non-ovulating counterparts.

Some psychologists have argued that there’s an evolutionary reason behind these effects: If women give cues about their fertility to men with good genes, and those men pick up on their cues, it maximizes the chances of reproductive success for everyone involved.

To the extent that this is true, women experiencing these ovulatory behavioral changes might represent a potential risk to other women, particularly those in relationships with desirable guys. If increased flirting and other such behaviors make ovulating women even slightly more inclined to poach or steal other women’s mates, one could argue that it would be adaptive for women to have evolved the ability to detect when other women are ovulating in order to identify this potential relationship threat.

What the research shows

A new set of studies published in the Journal of Personality and Social Psychology set out to determine whether there’s anything to this idea. That is, are women in relationships prompted to engage in more “mate-guarding” behavior when they’re around other women who are ovulating?

Jaimie Krems of Arizona State University led four experiments to explore this question. In each study, researchers recruited heterosexual women online who were either married or engaged and showed them a photo of a woman (“Sara”) who (unbeknownst to participants) was either ovulating or not.

Each of the studies was a little different, but most of them involved asking participants to imagine themselves at a housewarming party in which Sara was seen talking to participants’ own partner and “making an ambiguously flirtatious gesture toward him (i.e., laughing and touching his arm).”

Participants were then asked to rate how they felt about this other woman, how likely they would be to limit their own and their partner’s contact with her, and how sexy and desirable they thought their own partner was.

A pretty consistent pattern emerged. Across these studies, women were more concerned with keeping their partners away from Sara when she was ovulating. However, this effect depended upon how sexy and desirable participants rated their own partners as being.


Only women who thought their fiancés/husbands were sexy were more worried about guarding their partners from the ovulating stranger. Among women with less attractive partners, mate-guarding tendencies didn’t depend upon whether the other woman was ovulating or not.

The ovulating stranger’s attractiveness also mattered, though. One of the studies found that women with desirable mates only increased mate-guarding when the ovulating stranger was good-looking. If the other woman was unattractive, ovulation status made no difference.

Another interesting finding that emerged was that women with desirable mates were more interested in having sex with their partners after seeing a photo of an attractive ovulating woman. One interpretation of this result is that when people feel threatened, they show more sexual interest in their partners in the hope that their partners won’t be tempted to look elsewhere for sex.

What is it about ovulation that prompted women with sexy partners to guard them? The data pointed to changes in perceived trustworthiness, with ovulating women being rated as less trustworthy.


There are some important things these findings don’t tell us, such as how women were able to detect ovulation simply by looking at a photo. In addition, the effects reported in these studies were relatively small, which suggests that other women’s ovulation won’t lead to dramatic changes in mate-guarding behavior in most cases.

Women who are very concerned that their partner might stray will probably be on high alert no matter who’s around and how fertile they are.

It’s also important to note that these findings don’t tell us whether mate-guarding actually works as a way of “affair-proofing” a relationship. Indeed, it’s not hard to imagine that trying to control who your partner can and cannot see could very well backfire in some cases.

That said, these results are fascinating because they contribute to a growing body of research suggesting that both men and women may have evolved the ability to detect ovulation and, further, that this information might be playing a very primal role in how we approach our relationships.

Justin Lehmiller, PhD is a sex educator and researcher at Ball State University and author of the blog Sex and Psychology. Follow him on Twitter @JustinLehmiller.

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