What is with the male fascination with heterosexual anal sex, anyway? Men seem to obsessively about it, hundreds of movies fetishize it, and while women everywhere debate whether they should or shouldn't have it with their boyfriend or husband, men discuss how to convince female partners to give it a try. When women do have anal sex, the overwhelming majority do so at the request of their male partner.

So, why? What does anal sex mean?

Heterosexual anal sex has been around for millennia. Paintings and etchings from Japan, China and Europe all depict men performing anal sex on women, as do ancient erotic drawings, sculpture and pottery from the Mediterranean and South America. In some Polynesian cultures, anal sex was practiced explicitly as a means of birth control. Today, some adolescents regard anal sex as a means to prevent conception, regardless of the increased risk for transmission of sexually transmitted diseases. Over the past decades, heterosexual anal sex rates have climbed. In the 1950s, anal sex experience was reported by fewer than 15 percent of the population. But current rates suggest that around a third of men have performed anal sex on a woman, and slightly fewer women report having received anal sex. The rates are even higher in sexually active adults in their twenties.

But for married and committed couples, for whom disease and may not be a significant concern, how can we explain the prevalence of the male fascination with anal sex? Men are sexually interested by variety, but aside from this, there is no relevant evolutionary argument, as anal sex of course produces no heirs.

Anal sex, and a desire for it, serves different purposes for men. The strongest and most common argument that men voice is that a woman who will engage in anal sex is inherently arousing. Such a woman embraces it with no intent or possible result of pregnancy: It is sex at its rawest. For a man, anal sex with a woman is her allowing him to play Star Trek, and venture into uncharted territory. Even if it is not a case of going where no man has gone before, it is still novel, uncommon, and even special in its rarity. A woman engaging in anal sex shows her desire and willingness to have sex in a purely physical way, with no thought of pregnancy. She is embracing, to some degree, a willingness to make her body a sexual object. Some research suggests that women who engage in anal sex report having more orgasms, not necessarily during anal sex alone, but in their overall levels of sexual activity. The overall conclusions are that women who are willing to engage in anal sex tend to be more adventurous, more sensual, more relaxed in bed, and thus, more orgasmic.

The degree of pain in anal sex is a mixed issue. In some relationships where bondage and discipline factors play a role, the pain a woman might experience in anal sex is part of the allure. In other couples, men and women work carefully to decrease any pain, using lubricants and preparation to increase comfort and pleasure for both parties. This special to preparation serves as an intense, extended form of foreplay, heightening excitement, extending the and sensuousness of the encounter, and, not incidentally, increasing the chances that the woman will have an .

In many relationships, anal sex is perceived as a type of "gift" from the woman, given out of love and regard, and a desire to give her partner something special and rare. When a woman is willing to engage in anal sex with a lover, it usually comes from a place of significant trust and love.

Some people perceive a man having anal sex with a woman as a form of dominance, in which the man is "having every part of her body." This "flavor" of dominance, and misogyny, plays out in the current (disturbing) porn phenomena of "Ass to Mouth," in which a man puts his penis in the mouth of a woman after performing anal sex on her. However, in most porn, female characters are portrayed as fantasy women who are always ready, always hot, always excited, and always willing. Another way of viewing this is that the actresses are expressing and displaying their willingness to violate any and all taboos, no matter how "distasteful," primarily because of how aroused they have become, rather than as an expression of female degradation.

Surprisingly large numbers of people don't regard anal sex as actual sex. Some studies suggest that as many as 19 percent of college students view anal sex as less intimate, less committed, and less important than vaginal sex.

Men overwhelmingly report positive experiences following performing anal sex on a female partner. But more than half of women who have had receptive anal sex describe it as an unpleasant experience they probably wouldn't repeat.

In the past, oral sex was taboo, as it was also unrelated to procreation, but today, it has become almost ubiquitous — although where it is still rare, it remains an intense fantasy. Anal sex is just another taboo being broken. Where couples have oral sex, and anal sex, is there yet another taboo on the horizon? And another after that? And after that? Is there a slippery slope of taboo, that once started on, you glide down an unstoppable slick of bedroom lubricant? Not necessarily. There is no evidence that once a couple fulfills one fantasy or desire, a burning desire emerges for another. In fact, substantial evidence suggests that most people with one or another fixate on that one and rarely expand. Even for those couples that have had anal sex, it usually remains a rarity, thus retaining its "specialness."

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