Tina Fey and scholar James Franco are some of the hottest names in Hollywood—and they're as smart as they are eye-catching. But for ordinary eggheads, the intellect that serves so well in the boardroom might need an assist in the bedroom.

" is negatively associated with frequency," says Rosemary Hopcroft, a sociologist at the University of North Carolina at Charlotte. "It's a bit dismaying."

And people with higher levels generally have lower numbers of sexual partners. The latest National Survey of Family Growth shows that, for example, men with college degrees are half as likely to have had four or more partners in the last year as men with a high school education alone. (Or at least, they're half as likely to admit it, points out Anjani Chandra, a health scientist and demographer at the Centers for Disease Control.)

Why? "It's hard to pick apart," Chandra says. But the sexual habits of teens might offer a clue. Carolyn Halpern, a professor at the UNC School of Public Health, found a high of virgins at the top of the intelligence scale. She thinks the smartest kids might hold off on sex because they're thinking through its potential consequences.

But that doesn't tell the whole story: The same bright teens are just as likely to postpone relatively innocuous activities like kissing. "It's hard to imagine a 15-year-old wouldn't kiss a boy because she's worried about getting ," she admits. "You have to ask: Are these choices or questions of opportunity?"

She's not implying that gifted kids are homely rejects—Halpern, along with other researchers analyzing the link between sex and intelligence, controls for , personal grooming, and affability, and the observed effect still holds. It might be a question of priorities: "Pursuing education takes up a lot of time," Chandra says.

That's fine for scholarly teens, but why are the brightest adults still getting the least action? Life history theory, which examines how species have evolved different reproductive strategies to survive, offers a possible explanation.

People with high —in judgment, , and impulse control—usually have what's called a slow life history strategy, notes Aurelio José Figueredo, an evolutionary psychologist at the University of Arizona: They tend to have fewer partners and less sex but more resources (such as money and status) to invest in potential offspring.

Geniuses hoping to lead lives of passion and promiscuity might be disappointed, but it's not all bad news—at least for men. "Money, not intelligence, helps men have more sex," Hopcroft says. "In and of itself, intellect won't do the trick. But intelligence helps them get money."

What does that tell us? "Don't be an academic!" she says with a laugh.