I'm a 31-year-old woman, and I recently started dating a guy about my age. We've gone on five dates, but we haven't had sex, as I wanted to take things slowly. He's been okay with that, but I'm quite certain he's sleeping around elsewhere. I hate the idea of him having sex with other women. Still, we aren't at the level of being committed, and I'm not comfortable having sex with him yet. What do you recommend I do?

As you see it, the free-range penis should be more like those factory-farmed chickens.

The "hate" you describe feeling at the idea of him having sex with other women is actually jealousy -- specifically, "sexual jealousy": a stew of dark emotions (including humiliation, rage, despondency, and grief) that gets activated by the perception that a romantic relationship is at risk. Jealousy gets sneered at as some sort of pathetic emotional immaturity that's to be avoided, a la "C'mon...be bigger than that." That advice is like telling the police to ignore alarms going off in banks, which, sure, are sometimes false, but can be a sign there's a cash transfer in progress -- to the duffle bags of three gun-brandishing dudes in Richard Nixon masks.

Like bank alarms, sexual jealousy has a vital function. It triggers "mate-guarding" behavior: tactics to fend off threats "to a valued romantic relationship" that could lead to "infidelity or abandonment," explains evolutionary psychologist David Buss. Mate-guarding tactics frequently used by women include "monopolization" (like bolting oneself to a partner at a party), "appearance enhancement" (hotting up to outdo any lurking competition), and "sexual inducement" (performing "sexual favors" to keep a partner around).

In other words, the discomfort you feel is a call to action loaded into you by evolution. But evolved motivations aren't behavioral mandates. Resolving to just suck up and ride out the discomfort seems the best way to avoid responding in ways potentially damaging to your long-term interests. Letting fear of loss drive you to have sex before you're ready could tag you with an air of desperation and/or cause you to confuse lust with love. Being gnawed by curiosity about the competition sometimes spins even normally stable and levelheaded women into crazycakes stalkers. Tempting as it might be to know whom you're up against, it's best a new fir tree doesn't suddenly appear outside the guy's apartment wearing the same go-go boots you do.

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.