Last week, I tried to figure out why more women are having anal sex and why it correlates so highly with orgasms. Since 1992, the percentage of women aged 20-24 who say they’ve tried anal sex has doubled to 40 percent. The percentage of women aged 20-39 who say they’ve done it in the past year has doubled to more than 20 percent. And 94 percent of women who received anal sex in their last encounter said they reached orgasm—a higher rate of orgasm than was reported by women who had vaginal intercourse or received oral sex.

Why? For obvious reasons—anatomical, evolutionary, and aesthetic—anal sex should, on average, be less attractive and satisfying than vaginal or oral sex. In last week’s column, based on new survey data, I inferred that female orgasms caused anal sex rather than the other way around. The other acts reported by women who engaged in anal sex—vaginal intercourse, cunnilingus, partnered masturbation—delivered the orgasms. In turn, these women indulged their male partners’ requests for anal sex.

Well, shame on me. Not for talking about sodomy—that taboo seems to be fading fast—but for doubting that women love it. These women are now coming forward to affirm that they’re into it for their own pleasure, thank you very much. And they aren’t alone. Bloggers, blog readers, and Slate commenters are offering lots of other theories to explain the orgasm data.

I should start with a confession: I understated the mainstreaming of anal sex. I relied on data tables that reported how many women had done it at least once (around 40 percent), in the last year (around 20 percent), or in the last month (around 7 percent). I missed a different table (Table 4, page 284) that isolated women who were “partnered” and asked about their activities over a 90-day period. Among partnered women aged 18-24, 20 percent said they’d had anal sex in the preceding three months. Among those aged 30-39, 16 percent had done it. Among women aged 30-39 who were cohabiting but unmarried, 30 percent had done it. So we’re talking about something that a significant minority of partnered women does at least several times a year.

Why do they do it? And why do those who do it most often (women who reported anal intercourse in their last encounter) get the most orgasms? Here are some theories proposed by readers and bloggers.

1. Anal sex causes orgasms. At least 10 women have posted comments in Slate to say that they like anal sex. Five of them say they get orgasms from it. These women aren’t porn artifacts, nor are they trolling for sex. Many are explicitly partnered; most are using full names. Others who enjoy sodomy are raising their hands here, here, here, here, here, here, here, here, and here, with additional secondhand reports here and here. (All of these posts are from women; I’m setting aside the 20 or 30 secondhand reports I’ve seen from men.) I won’t try to convey their enthusiasm—you can read the testimonials yourself. Let’s just say that Tristan Taormino and Toni Bentley aren’t alone. And if you think is just male-imposed false consciousness, try reading a few lesbians on this subject.

Lots of women don’t like, want, or do anal sex (examples here, here, here, and here), and the data still suggest these women are the majority. But when I said female orgasms were causing anal sex, I shouldn’t have implied that the reverse wasn’t true. Sex is complicated. People vary. No single theory will explain the whole correlation.

2. Orgasms increase women’s willingness to try anal sex. Originally, I speculated that this effect was reciprocal: Women who got what they wanted were more likely to indulge their partners’ wishes. Some readers think my analysis was too transactional—women aren’t doing it just to please men—but they agree that the orgasm precedes the act. “I’ve had anal sex with multiple girlfriends but I don’t think it’s ever happened before she has orgasmed first,” says one man. “When we’ve been having a marathon session with serious orgasms, that’s when my wife is interested in exploring her adventurous side,” says another. These are just anecdotes, but the survey data back them up: Nearly all women who reported anal intercourse in their last encounter said they engaged in other sex acts, too.

3. Orgasms increase women’s willingness to try anal sex, which in turn causes orgasms. Theories 1 and 2 aren’t mutually exclusive. Some women cite both factors. Example:

Yup, once my boyfriend started going down on me 3+x/wk among other things, I was like, well… anal’s probably not that bad. I was more afraid of it because of scary porn. I’ve come to enjoy anal, perhaps even … prefer it? Makes my orgasm explosive. Course I want more.

4. Orgasms cause relaxation, which facilitates anal sex. “Anal sex with a woman does seem, um … easier following her orgasm … or any other kind of deep relaxation, like a massage or hot bath or bourbon,” one man reports. (See this lesbian testimonial on the same theme.) This theory is psychological but also physical: If you haven’t had an orgasm, you’re less likely to be relaxed, so you can’t do anal sex. So when women are surveyed about their last sexual experience, the only women who say they had anal sex are the ones who had orgasms.

5. Adventurousness causes orgasms and anal sex. A male commenter puts it this way:

Couples who have consensual, playful and open-minded sex lives tend to do things that result in the women in these relationships having orgasms AND to experiment with (and possibly find they enjoy) anal sex. It’s not one causing the other, but a common cause that results in the two being correlated.

That’s an intuitively appealing theory. It fits the survey findings (“greater behavior diversity is related to ease of orgasm“) and the specific data on anal sex. While nearly all women who had anal intercourse in their last encounter reported other sex acts as well, nearly half the women who had vaginal intercourse reported no other sex acts.

But is this really a matter of adventurousness? Maybe vaginal sex is simply more satisfying, so women are less likely to need an additional act. A female Slate commenter proposes a way to test the hypothesis: “My guess would be that female orgasms are also highly correlated with bondage, role play, more varied sexual positions overall, and whatever other ‘kinks’ you can think of.” Perhaps the next survey will sort this out.

6. Women who orgasm easily are more likely to try anal sex. This turns the adventurousness theory upside down. The idea here is that a woman’s relative ease of orgasm (which could be largely anatomical) is a cause, not an effect, of trying new kinks. Orgasmic women are more willing to dabble in unconventional things, including anal sex, because compared with other women, sex is more fun for them, or orgasmic payoff is more likely.

7. Self-assurance causes orgasms and anal sex. Short version: “Women comfortable enough to enjoy anal sex are pretty much relaxed enough to orgasm. They’re women who get what they want.” Longer version:

Women who offer anal sex are typically those most comfortable with themselves, their bodies or with asking for what they want from their partner, and when a woman is comfortable with those things she’s more likely to reach orgasm. … a guy’s not getting back there unless the woman is very comfortable with you being there …

Another good hypothesis. The paradox to be explained is why an act widely considered icky or deviant correlates with orgasms. The self-assurance theory uses the ick factor to explain this. To overcome the ick and deviance, you have to be the kind of woman who’s good at getting satisfaction. To that extent, anal sex doesn’t create orgasmic women. It selects them.

8. Anal sex requires affirmative interest. This is a more direct version of the self-assurance theory. A commenter explains:

Women who go for anal sex are into having anal sex. It turns them on. More likely to have an orgasm. Vaginal sex is what every women does, even those who…. aren’t interested really, so the numbers are going to be lower.

Again, anal sets a higher bar. Women who don’t much feel like having vaginal sex often do it anyway. Women who don’t much feel like having anal sex don’t do it. So disinterested women dilute the orgasm rate for vaginal but not anal sex. The same could be said of orgasms: Women who don’t get orgasms from vaginal sex keep doing it, but women who don’t get orgasms from anal sex stop, thereby reducing the anal-sex population to women who really get off on it.

9. Love and trust cause orgasms and anal sex. One woman writes:

The more I love and trust someone, the more likely I am to have an orgasm while with him—and the more likely I am to be okay with pushing society’s “norms” with him. Similarly, the more he proves that he knows what he’s doing, the more likely I am to let him do something that could potentially really, really hurt me.

This is the most uplifting theory. It implies that the sample of women who report regular anal sex is heavily biased toward intimate relationships. The data (Table 4, page 284) strongly support this. Compared with women who are single and dating, women in a relationship are only about 50 percent more likely, at best, to report vaginal sex in the last 90 days. But they’re two to three times more likely to report anal sex. And women who live with their boyfriends are more likely to report anal sex—but not more likely to report vaginal sex—than women who don’t. Anal sex, more so than vaginal sex, seems to correlate with intimacy and commitment. (Did I mention you should use a condom especially if you don’t know your partner well? Use a condom.)

10. Male assertiveness causes orgasms and anal sex. This is a macho inversion of the love theory. A commenter at a misogynous Web site puts it this way:

Also, women are more likely to acquiesce to buttsex demands from the highest-quality men. Anal sex is associated with orgasms, but mostly because both anal sex and orgasms occur more frequently with alphas.

Flame away, ladies.

11. Anal includes manual. Several commenters at Slate and other venues report that in their experience, women got orgasms only with a bit of simultaneous Christine O’Donnell. One man writes:

My experience with women I asked and were willing to try is that 5 women loved it, 1 was accepting but it didn’t do anything for her, 3 disliked it. All of the ones that liked it had fairly intense orgasms (no surprise there) but only if their clitoris was stimulated at the same time. It could be that the pleasurable attraction for the women is due to it being a position that allows easy access for addition stimulation.

The survey backs this up: Of women who had anal sex in their last encounter, 31 percent said they also had “partnered masturbation” (Table 4, pages 355-6). To the extent that this factor explains the happy endings, the anal orgasm data are inflated.

12. Anal sex requires more foreplay and patience, which increases the odds of orgasm. One commenter observes that anal sex is “a more drawn out experience, what with prep work.” This is more complex than the manual-stimulation theory. The best way to understand it is to look at the data in negative terms: While only 6.5 percent of women who had anal sex in their last encounter didn’t report an orgasm, 30 percent of women who had vaginal sex didn’t report an orgasm. Maybe that’s because nature makes it easier to have vaginal sex even when the man is hasty and self-absorbed. Anal sex requires more attention to the woman’s mind and body.

13. Internet porn is spreading the idea. According to a male commenter,

the most recent increase in the prevalence of anal sex is mostly due to the near simultaneous rise in access to high-speed Internet … [When people] see these fetishes carried out frequently in pornography they may slowly begin to feel more comfortable about their suppressed fetishes and even muster up the courage to find someone who shares the same fetishes.

On its face, this theory would explain only the prevalence, not the orgasms. But prevalence could increase the rate of reported orgasms by boosting the number of couples who discover they like anal sex, thereby increasing the odds that a woman who had anal sex in her last encounter (i.e., the sample of women who provided the orgasm data) did so because she likes it, not just because her partner asked.

These are just a few of the answers people have come up with. I’m excluding the vicarious pleasure theory (which doesn’t explain why anal sex outscores vaginal sex and fellatio at delivering female orgasms) and the virginity preservation theory (which, given the ulterior motive, would predict a lower, not higher, orgasm rate). I also found a few amusing disputes between women and gay men over how to do anal sex and whether women can directly get orgasms from it. And I took some criticism from the pegging community for ignoring straight men who like to be penetrated. Sorry, gents. Some other time.

The most interesting thing I learned from reading dozens of testimonials is that many sodomy enthusiasts have a slight anal superiority complex. They don’t mean to boast. It’s just that they’re more adventurous, enlightened, and fulfilled than other folks are. They’re less uptight and more comfortable with themselves. They’re better lovers, or their lovers are better. And this attitude is starting to irk some anal virgins. “There are plenty of women who are in tune with their bodies and not sexually repressed and still don’t like anal sex,” protests one woman. She notes that in her Reddit community,

[P]eople who do not enjoy certain acts are really frowned upon, and it’s bugging me. If you’re not causing anyone harm, and you and your partner are happy and satisfied, then all should be well. … when one partner is not satisfied it’s a whole different story, but it still wouldn’t be up to us to judge the more vanilla partner.

So if anal sex goes mainstream, be nice to the vanilla holdouts. And don’t be surprised if the revolution is short-lived. As women embrace sodomy, it may lose its taboo appeal for men. Lots of men are coming forward to say they don’t like it (examples here, here, here, here, here, here, here, here, here, here, here, and here), and some seem to have been turned off to it by women who wanted it. With buggery on the daily menu, men might start begging for vaginal sex, or even kissing. Won’t that be something.