I'm a 34-year-old woman seeking a relationship. Last week, I went to dinner with a man. We had an instantaneous connection and ended up having sex. I haven't heard from him since. I've always believed sex on a first date doesn't matter if there's a connection. Now I'm worried I moved too quickly. I'm tempted to call him. Any advice on what to say?

--Disappointed

Chasing a man into wanting you is usually about as successful as trying to split atoms with small household tools.

You may believe sex on the first date "doesn't matter," but our genes (the source of our psychology) have not heard of the women's movement and do not drink out of an ''ovaries before brovaries!" coffee mug. Women and men are more alike than different, physically and psychologically, but the physical differences we do have (like how only women get pregnant) led to the evolution of psychological sex differences. For example, evolutionary psychologists Martie Haselton and David Buss find that heterosexual men and women having sex with someone for the first time experience differing "affective shifts" -- shifts in feelings -- afterward.

In the afterglow, women felt more emotionally attached and more attracted to their partner (a "positive affective shift"). These commitment-fostering feelings align with how, for a woman, sex "signals the possibility of pregnancy" (and daddy shoes in need of filling).

On the male side, immediately after the first sexperience with a new woman, men who've had a lot of sex partners (six-plus as college undergrads, suggesting a short-term sexual strategy) experienced a "negative affective shift": finding a woman "less physically attractive and sexy." (This effect didn't show up in men with fewer sex partners or in women, no matter how many sex partners they'd had.) Haselton speculates that for hookupmeister men, the negative affective shift signals game over -- sex goal achieved -- and pushes them to move on lest they get "entangled in an unwanted long-term relationship."

If this guy wanted to see you again, he'd be blowing up your phone. To help yourself accept that, recycle him from a current goal to an ongoing reminder: Whenever you might want more than a hookup with a particular guy, wait till he's emotionally attached before having sex with him. How many dates, calls, and texts this takes will vary, but basically, a man needs to care about you enough to weather how your sex face makes you look like a mortally wounded hamster.

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.