This will really make you think about sex

Who thinks about sex more, men or women?

Many men and many women will tell you the answer is obvious — they think about sex more. There's a certain amount of male and female posturing behind this. We tend to turn this into a contest.

One "study" quoted on various blogs and Web sites but impossible to track down in its original form allegedly found that men think about sex about 150 minutes a day, women 180. How do they get anything done?

Does this reflect sexuality, or is it more a measure of how bored you are at work? And what constitutes thinking about sex? Does it count if you think "he looks nice" when a well-muscled cyclist rides by? Or do you have to imagine the whole act with him?

Last month, it seemed some relatively concrete science might reveal the answer. Neuropsychiatrist Louann Brizendine, of the University of California, San Francisco, determined that men think about sex a lot more that women do. This she lays out in her recently released book, "The Female Brain."

Here's what she told the San Francisco Chronicle about male/female brain difference: "Women have an eight-lane superhighway for processing emotion, while men have a small country road. ... Men, however, have O'Hare Airport as a hub for processing thought about sex, where women have the airfield nearby that lands small and private planes."

When I called Brizendine, she admitted to a bit of poetic license here. While there have been a few studies on sexual thoughts, it's hard to make direct comparisons, because men and women tend to think about sex differently. "The honest scientific thing to say is, on average, males have visual thoughts and fantasies more times a day," she says. And they're more likely to pursue a partner based on nothing but a sighting.

But scientists often focus on something more straightforward — sex drive. And that, she says, is controlled by the hormone testosterone. Men have 10 to 50 times as much testosterone as women. But the relationship to sex drive isn't that linear, she says. It takes much less testosterone to trigger a woman's circuits.

Several studies, she says, show that on average, men want sex more than women. A recent study out of Germany showed that men and women desire sex at the start of a long-term relationship, but after 20 years, 60 percent to 80 percent of men still report wanting sex regularly, while only 20 percent of women still do.

Brizendine said a much more interesting male/female difference is how we approach sex and love. Men, she says, feel secure in a relationship if they're having sex. As a very general rule, if they're getting sex, they assume they're wanted and loved. But women need verbal reassurance. We need pillow talk. "Women read emotion in words," Brizendine says.

If this difference indeed exists, it could have less to do with wiring than with rationality. For a woman, it's important for practical reasons to know whether a partner is committed.

Sex for men is often a penny-ante game; for women the stakes get higher. A man who doesn't love a woman can get her pregnant and abandon her, boast to others and hurt her reputation, give her a disease (most sexually transmitted diseases are more harmful to women) or eat up her precious time as her biological clock ticks away.

Being careful to check a man's emotional commitment isn't mushy girly stuff — it's common sense.

Other studies show men are more likely to want to engage in casual sex. So the only way you can answer who thinks about sex more is to define the question more sharply. If "thinking" entails more than just idle fantasy, but instead implies an active, critical weighing of risks and benefits, then women, on average, probably do it more — though maybe not for 180 minutes a day.

Faye Flam's Carnal Knowledge column appears Sundays in The Seattle Times.