Does The "Seven Year Itch" Exist?
In the 1955 film that popularized this myth, a married man is tempted to cheat on his wife with his sexy new neighbor (played by Marilyn Monroe— who can blame him?).

But do marriages really fall apart after seven years? According to studies of couples worldwide, says Berman, divorce tends to occur during the fourth year of marriage.

"The anthropological explanation is that we evolved to be serial monogamists, not lifelong monogamists," she explains. Couples would stay together at least long enough to see the child to toddlerhood. After that— at least from an evolutionary standpoint—mom and dad were free to run off and find new mates, with genetic variety as the goal.

Do Men And Women Hit Their Sexual Prime At Different Ages?
Women are at the top of their game in their early 30s, when they are more confident and assertive, says Berman. But by the mid-to-late 30s, fertility—and libido—can decline. "Men are physiologically at their prime at 18," she adds. "Blood flows better, erections are harder. But they're at their emotional or social sexual peak in their mid-30s."

So the next time you're tempted to rob the cradle, it might be wise to keep your pants on. "People in their late teens are not good lovers," says Laumann. "The ability to form and maintain relationships comes later."

Do Men Have Stronger Sex Drives Than Women?
According to Berman, it's common for women to have lower libidos than men. But men, too, experience a loss of desire—"especially those in their mid-to-late 40s and beyond," she says.

Laumann adds that lower sex drives in women may be rooted in evolution: to protect themselves from predators, it was essential to avoid the vulnerable state of pregnancy. But for men, sex is less costly. "The majority of men think about sex every day. But only 25 percent of women think about it every day," he says. "Sex for men is less complicated. They tend to act on their urges."