Why Women Have Sex

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You co-authored a famous 2007 study "Why Humans Have Sex." Why focus on women this time around?
We discovered that women's sexual psychology turned out to be far more complex than we envisioned. [It] deserved an entire book-length treatment.

What differences between men and women did you notice?
There are important gender differences in sexuality, but these must be interpreted within the context of a high level of similarity. Both women and men have sex because they are physically attracted to the person, for pure pleasure, because they are in love, or simply because they are horny. But within the overall similarity, I'd say women's sexuality tends to be more linked with love and emotional bonding. Women, more than men, like sex when there's some kind of emotional connection. Men were more likely to have sex simply because the opportunity presented itself. Women tend to be pickier, especially for short-term sexual encounters. And men are more motivated to have sex to boost their status among their peers, although some women in our study also had sex for precisely this reason.

What are the main reasons why women have sex?

Other important reasons are to boost their self-esteem or sexual esteem, to get revenge, to secure "mate insurance" in case a partner dumps them, to relieve pain, to achieve health benefits such as getting rid of a headache — yes, it works — to decrease stress, to lose weight and as a sleep aid. We devote one chapter to "sexual economics," which focuses on all the ways in which women have sex as an exchange for other benefits, such as getting her partner to take out the garbage, securing free dinners or getting expensive gifts. We also devote one chapter to what we call "the dark side" of women's sexuality — when women have sex because they were deceived, coerced or forced into it.

Any particularly surprising findings?

How does evolution explain some of these complexities?

On the competition side, evolution by selection is an inherently competitive process. It's a cliché that "the good men are all taken, permanent bachelors or gay." And there's some truth to this. The number of truly desirable and available men is limited. So women are in sexual competition with other women for access to the most desirable men. Modern women are the descendants of ancestral mothers who succeeded in besting other women in these sexual competitions.


What advice could you give to the men out there not blessed with Michael Phelps' torso and George Clooney's face? What can they do to stay in the game?

Have good hygiene. Sense of smell is critical. A man who smells bad, or who has bad breath — that can be a sexual kill switch for women. Interestingly, women have a keener sense of smell than men, so men are sometimes oblivious to how bad they smell to women. A man's scent conveys critical information to women about a man's health status.
