Move on to anal sex, and the pattern gets even stranger. Again, women attracted mostly to men are more likely to say they've had anal sex with a man than are women attracted only to men. And in the case of anal sex, the gap is huge: While 30 percent of the totally straight women say they've had anal sex, 55 percent of the mostly straight women say they've done it. But get this: Among women who say they're attracted equally, mostly, or exclusively to women, the figure is 41 percent. Lesbian and bisexual women are more likely than totally straight women to say they've had anal sex with a man.
If you find this number hard to believe, check it against a related finding in the same table: 48 percent of women who self-identify as gay or bisexual report having had anal sex with a man, compared with 33 percent of women who self-identify as straight. This gap is true of anal sex, but not of vaginal or oral sex.
What could explain this?
The last time I wrote about anal sex, I learned not to generalize too much. In some cases, the key factor might be how much pleasure a woman gets from vaginal sex. That factor could correlate with female heterosexuality and, at the same time, make a woman less likely to try anal sex. In other cases, a history of inconsiderate male partners might correlate both with anal sex and with a woman's statement that she's more attracted to women than to men. Or maybe calling yourself fully heterosexual is simply the default answer of women who have limited or no sexual experience. But each of these theories has trouble accounting for the data on vaginal and oral sex.
Here's my best guess: In many if not most cases, openness to experimentation is driving everything else. Adventurousness makes a woman more likely to try various sex acts with men. And at the same time, it makes her more likely to express interest in other women. This factor would have to be strong enough in bisexual women, on average, to overcome the statistical effects of clear-cut lesbians who do nothing sexual with men.
The unkind way of putting this, from a liberal point of view, is that women who claim to be exclusively heterosexual are, on average, more conventional or uptight than women who report having some interest in other women. These "exclusively" straight women might not even be exclusively straight. They're just obtuse to their wayward feelings, or afraid to admit them. The equally unkind view, from a conservative perspective, is that sexual mores are collapsing in all directions.
To me, this theory does the best job of explaining why the experience gap between mostly and exclusively straight women increases as you go from vaginal to oral to anal sex—and why lesbian and bisexual women exceed exclusively straight women only in the case of anal sex. The kinkier the deed, the more it correlates with a woman's lesbian interest, her awareness of that interest, or her willingness to admit it.
But that's just my guess. Let's hear yours.