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Female orgasm: why O why?

Women’s orgasms might be as useful as male nipples. ex animø/Flickr

Why do women have orgasms? That may seem like a strange question, but it’s one which has perplexed scientists for decades and provoked fiery academic debates along the way.

The real question is: what is the evolutionary function of the female orgasm? In men, orgasms have a fairly obvious evolutionary explanation, since they are tied to ejaculation. For women, it’s unclear what function they serve.

Most animal species don’t show any evidence of a female orgasm, although some do (certain monkeys and apes, for example).

As with many unsolved mysteries, plenty of theories have been put forward – some with evidence, some without.

Give it to me

One of the earliest theories – “pair bonding” – suggested female orgasms helped couples remain together. Children require a great deal of care, and so women who stayed “bonded” to a man long enough to have him provide care and resources for her child would have been at an evolutionary advantage.

The pair bonding theory of women’s orgasm is based on oxytocin (the brain’s love drug) being released in the brain during orgasm. Oxytocin increases feeling of tenderness and togetherness with a sexual partner, supposedly to the benefit of the woman’s child and the propagation of her genes into future generations.

Another explanation is the evocatively-named “upsuck theory”. This suggests that, when a woman orgasms, negative pressure is created in her uterus and this sucks sperm up into it, presumably aiding transmission to the egg. So under this theory, a woman’s orgasm serves to improve her fertility.

One clear problem with upsuck theory is that no-one has demonstrated any link between a woman’s “orgasmability” and her fertility. Also, the studies have substantial flaws – one, for example, was based mainly on data from one female.

Another problem with both of these theories is that not all women have orgasms. Some 13% of sexually active women have never had an orgasm in their life, and for another 22% of women they’re a very rare occurrence during sex with a partner (these women tend to be more successful going solo).

It’s just not working

If having orgasms during sex improved women’s pair bonding and/or fertility throughout evolution then, in theory, women who can’t have orgasms should be very rare (as is the case with men who can’t have orgasms).

Also, in a recent study of around 3,000 female twins, I found that women’s orgasmability was unrelated to whether they tended to have (or prefer) long-lasting relationships or many short-term casual relationships.

This would seem to contradict the pair-bonding theory. One could perhaps make a counter-argument that modern women’s orgasmability is disrupted by anxiety stemming from sexually restrictive societal values, such as certain religious ideas that sex should only be done within marriage and only for the purpose of having children.

But my study also found no correlation between orgasmability and neuroticism – that is, a predisposition to anxiety – nor with a woman holding sexually-restrictive values. Thus, it seems unlikely that society is to blame for women’s unreliable orgasms.

More, please

Another evolutionary theory holds the unreliability of women’s orgasms is central to their function. Under this theory, a woman’s orgasm tends only to happen with a high-quality partner (physicaly attractive, healthy, intelligent, attentive), allowing orgasm to serve as a mate selection tool.

The orgasm may motivate them to continue having sex with the high-quality partner, or perhaps make sure the sperm of the high quality partner is well “sucked up”.

Recent evidence suggests that women whose partners have more masculine faces (e.g. heavier and squarer jaw, heavier brow) are more likely to orgasm during sex. In that sense, a masculine face is thought to be associated with health and “good genetic quality”.

This theory has trouble explaining the many women who never orgasm during sex and the 20% of women who always, or almost always orgasm during sex (including those who are single and have had more than five different partners).

An intermediate rate (orgasming 40-60% of the time during sex) seems like it should be the best at discriminating between different quality partners, but this is actually the least common rate of orgasm reported. This poses a problem for the mate selection theory of female orgasm.

Oh, what’s the point?

One widely-held theory proposes that women’s orgasms serve no evolutionary function at all. The “byproduct theory” holds that female orgasms are an accident of the evolutionary, developmental and physiological processes that generate the functionally-important male orgasm.

In other words, women have orgasms because men do.

If that sounds like evolution being sexist, then think about male nipples – men have non-functional nipples purely because nipples are functional in women.

Despite decades of theoretical debate and a number of recent empirical studies, we still don’t know the evolutionary function of women’s orgasms, or if they have a function at all.

But rather than simply shrugging and rolling over to sleep, we scientists are collecting more data and thinking of new ways of investigating the mysterious female orgasm.

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