When people fall in love, initially, they can't keep their hands off each other. But six months to a year later, the hot-and-heavy period subsides and sexual frequency declines. This is no problem if both people experience the exact same decrease in libido. But typically, one person wants sex more often than the other, and desire differences become a sore point in many relationships. In fact, today, desire differences are a leading reasons why couples consult sex therapists.

When desire differences emerge, who wants sex more? That's a no-brainer, right? The man. Perhaps you've heard the old joke: What's foreplay to a man married for 10 years? An hour of pleading.

There are plausible biological reasons why, in general, men would want more sex than women. Male sex hormones (testosterone in men and a slightly different hormone in women) fuel libido in both genders, and men have much higher levels. Studies of transsexuals show that when men become women and take female sex hormones, they typically report a mellowing of sexual desire, but when women become men and take testosterone, they usually say, "As a woman, I liked sex but didn't feel driven to have it. Now I do."

An evolutionary argument corroborates this. The biological purpose of life is to reproduce life, to send one's genes into future generations. Women are most likely to do this by having a few children and nurturing them until they, too, reproduce. That works for men, too, but men can also pursue another strategy—sex with as many women as possible to impregnate as many as possible.

These explanations sound neat and compelling, but if they truly explained desire differences between the genders, we would expect the overwhelming majority of men to want sex more often than the overwhelming majority of women. That does not appear to be the case.

Over the past 20 years, I've informally polled dozens of sex therapists asking about the gender break-down of desire differences. I don't pretend that my findings represent anything beyond a seat-of-the-pants inquiry, but therapists' replies have been remarkably consistent: Two-thirds of the time, the man wants sex more, but in one-third of cases, it's the woman. Now, this is a two-to-one margin, so partisans of the conventional wisdom can say, "See? Men clearly want sex more than women." All right. But if that's the case, why do somewhere around one-third of women want it more than men?

A fascinating recent book, Sex At Dawn: The Prehistoric Origins of Modern Sexuality takes a stab at an explanation. Co-authors Christopher Ryan and Cacilda Jetha marshall a great deal of psychological and anthropological research to support their view that if we remove the shackles of so-called civilization, women are just as libidinous as men and maybe more so. But for better or worse, we live in the world we inhabit, and the apparent enthusiastic promiscuity of prehistoric women doesn't alter our sexual norms today.

Any chronic desire difference can drive people crazy. But in our culture, when the woman wants sex more, the couple descends into a special circle of hell, the place reserved for those caught in culturally unexpected circumstances. It's bad enough to have a chronic desire difference, but when the situation contradicts the highly prevelant assumption that women—all women!—are erotically coy, while men—all men!—are insatiable horn dogs who can never get enough, desire differences feel even more distressing.

I sympathize, and I'm here to say that if, in your relationship, the woman is more libinous than the man, you're by no means alone. Whatever the reason, if women want sex more in one-third of couples who consult sex therapists, then after men say "good-night," the number of women who grit their teeth, or cry, or reach for a vibrator has to be in the millions.

Ladies, don't let the weirdness of wanting sex more than your man deter you from working to change things. The sex therapy program that resolves desire differences is remarkably effective, and it works no matter who wants sex more. To implement the program, start by visiting my site (GreatSexAfter40.com) and reading: "You're Insatiable!" You Never Want To!" The Sex Therapy Program for Resolving Desire Differences. And if my summary doesn't provide sufficient relief, consider finding a sex therapists near you by visiting the American Association of Sex Educators, Counselors, and Therapists, the Society for Sex Therapy and Research, or the American Board of Sexology.

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