Why do women have orgasms?


One of my favorite science books ever is Elisabeth Lloyd’s The Case of the Female Orgasm, which does a beautiful job of going case-by-case through postulated adaptive explanations for female orgasms and showing the deficiency of the existing body of work. It’s a beautiful example of the application of rigorous scientific logic; it does not disprove that female orgasms have an adaptive function, but does clearly show that the scientists who have proposed such functions have not done the work necessary to demonstrate that fact, and that some of the explanations are countered by the evidence. Her conclusion was that the likely explanation for the female orgasm was that it wasn’t directly adaptive: women have them because men are selected for having them, and that the women are just along for the happy ride, just as men have nipples because there has been selection for women to have them.

A lot of people detest the book, though. It does rather ruthlessly cut through many adaptive scenarios, and some people just seem to have a bias that if something exists, it must have a purpose. And for some reason, there is an odd preconception that purposeless features are counter to evolution (they aren’t).

Now there’s a new paper out by Zietsch and Santtila that purports to challenge the non-adaptive explanation. It fails. It fails pretty badly, actually. I’ll go further: I thought it was a terrible paper, especially in contrast to the clarity of Lloyd’s work. Here’s the abstract:

The evolutionary basis of human female orgasm has been subject to furious scientific debate, which has recently intensified. Many adaptive explanations have been proposed, invoking functions from pair bonding and mate selection to sucking up sperm, but these have been attacked as being based on flawed logic and/or evidence. The popular alternative theory is that female orgasm is not adaptive and is only evolutionarily maintained as a by-product of ongoing selection on the male orgasm-ejaculation system. This theory has not been adequately tested. We tested one of its central tenets: that selection pressure on the male orgasm is partially transmitted to the female via a positive cross-sex correlation in orgasmic function (susceptibility to orgasm in response to sexual stimulation). Using questionnaire data from over 10 000 Finnish twins and siblings, we found significant genetic variation in both male and female orgasmic function, but no significant correlation between opposite-sex twins and siblings. This suggests that different genetic factors underlie male and female orgasmic function and that selection pressures on male orgasmic function do not act substantively on female orgasmic function. These results challenge the by-product theory of female orgasm.

So their method was to survey twins and siblings about their sexual performance, and an absence of a correlation between different-sex siblings was interpreted to suggest an absence of a shared, heritable property between males and females. The logic of this experiment falls apart at every level.

First, they are relying on self-reporting of a trait that has strong psychological and cultural components, without making any effort to isolate any of the variables that would bias the subjects’ answers. I would be extremely cautious in interpreting the answers, yet the authors are making quantitative assessments of an inferred genetic network on the basis of some very mushy data.

Secondly, and this one drove me up the wall in trying to read this paper, they are comparing men and women…but asking the two sexes completely different questions. How can you even compare the answers? Men were asked, “How fast have you typically ejaculated after the intercourse (vaginal or anal) has commenced?” — a question about speed that assumes a 100% incidence of orgasm, and only considers intercourse. Women were asked, “Over the past four weeks, when you had sexual stimulation or intercourse, how often did you reach orgasm?” — so no constraint on how orgasm was achieved, or how long it took, but they do limit the interval. In order to compare a time to a frequency, the authors crunch the numbers down to a single value they call a measure of orgasmic function in males and females. But this is still bogus: they really are comparing apples and oranges at every step.

It seems to me that the relevant parameter to measure is whether the subject has any capacity to have an orgasm — do they have the physiological machinery to carry out this function? The question of how robustly this property is expressed is a different issue altogether. When you look at their data this way, it looks just as flawed, but with another twist. All of 1.9% of the male subjects reported never achieving orgasm through intercourse; 12% of the female subjects reported “rarely or never” having an orgasm in the last 4 weeks. This is actually a surprisingly good number; worldwide frequency of anorgasmia in women is typically around 20%, but the sample the authors are taking their data from is fairly homogeneous, consisting of Finns between 18 and 49. Again, though, the results highlight the cultural variability: the female response seems to be much more sensitive to environmental conditions, while the male response is strongly canalized. You can’t assess orgasm in women without taking a whole battery of social issues into account, while men are easy. The orgasmic response in men is locked in as a response to testosterone levels, which are reliably high in most men, while the same response in women relies on other, probably diverse, developmental cues to be switched on.

The situation is that when you examine orgasm in men, you find a heritability that’s near zero — what that means is that there are almost no phenotypic differences in the population that can be accounted for by genetic variation. There could be hidden variation that is swamped out by a robust environmental effect (like testosterone!), but you can’t measure it. One interesting way to look at women, though, is they have the same genetic variations as men, but those variations are unmasked and exposed phenotypically by the absence of the canalizing effect of testosterone, and that’s one mildly suggestive result of this paper — they found a correlation in the frequency of orgasmic response in monozygotic female twins that was stronger than that between dizygotic female twins. Similarly, they found a correlation in the rapidity of orgasmic response between male monozygotic twins, which suggests there could be some genetic component there, as well.

But you can’t compare the male and female measures! They’re different things! Men and women could be sharing the very same genetic circuitry behind orgasm, supporting the by-product hypothesis, but the different endocrine regimes of male and female embryos could be activating entirely different auxiliary genetic circuitry that contributes to the response. In fact, I’d consider it extremely unlikely that female orgasm doesn’t use exactly the same genetic apparatus as male orgasm. If anyone wants to really show that the byproduct hypothesis is false, a demonstration that the female orgasm is produced by pathways that are independent of, and evolved in parallel to, the male machinery would be more than sufficient. A study that is built around subjective reporting of the experience of orgasm isn’t going to do it, though.


A few other sites have looked at this paper.

Greg Laden has more on the behavioral biology of primates, but I’m afraid he doesn’t really get the byproduct theory at all — he keeps talking about the adaptive value of female orgasm, but they’re all post-hoc rationalizations. That culture adapts to the existence of female orgasms does not imply that female orgasms evolved as an adaptive phenomenon. I can show that orgasms make women happy; the question is, does the happiness of women contribute to the evolutionary success of the species? And I’m sorry, evolution doesn’t care.

Scicurious rightly concludes that the paper does not demonstrate what the authors claim it does, but I get the impression that she hasn’t read Lloyd — she has a brief summary of the adaptive alternatives that is fairly casual. Really, Lloyd demolishes them all. She doesn’t necessarily prove that they’re wrong, nor does she claim to do so, but she does show that most of the hypotheses are little more than wishful thinking.


Zietsch B, Santtila P (2011). Genetic analysis of orgasmic function in twins and siblings does not support the by-product theory of female orgasm Animal Behaviour DOI: 10.1016/j.anbehav.2011.08.002

(Also on Sb)

Comments

  1. tsig says

    The idea that if women enjoy sex they’ll have more sex and therefor more babies seems reasonable.

  2. Carlie says

    Secondly, and this one drove me up the wall in trying to read this paper, they are comparing men and women…but asking the two sexes completely different questions.

    What the…how did this ever pass peer-review????

  3. Physicalist says

    It’s a beautiful example of the application of rigorous scientific logic

    *ahem* You mean philosophical reasoning. Lisa’s a philosopher

  4. Lyra says

    I went to a discussion where we talked about this very subject, and one of the things we also talked about is why some people really want the female orgasm to have a purpose. In some circles, people believe that if a trait has no purpose, then that trait isn’t important. To go with your male nipples example, these people would believe that male nipples aren’t important (because they have no function). Women are really, really nervous about having their orgasms labeled as “unimportant.” So there is the inclination to shout, “No, no, my orgasm is just as purposeful (important) as your orgasm is!”

    Now, I’m of the opinion that orgasms aren’t evolutionarily adaptive. There are many reasons, but one reason that I haven’t seen this is thread yet is that most women cannot orgasm from intercourse (penis in vagina) stimulation alone. A lot of us can’t come without direct, focused clitoral stimulation, and a chunk of us require this stimulation to be more intense than can be found in nature (vibrators, not just fingers/tongues). It doesn’t make a lot of sense that female orgasms would have an important evolutionary function in orgasm like men and yet miss as often as we do. To me, the whole thing practically screams “biproduct!”

    But it’s going to be hard to get people on board with this when they hear “There is no evolutionary purpose” as “It isn’t important.”

  5. jasondick says

    I somewhat wonder if the sexual sensitivity of the male prostate might have something to say about this, considering the fact that it is entirely hidden within the body and doesn’t appear to be stimulated much at all during “normal” intercourse. The sensitivity of the prostate gland *might* be a side effect of its normal sexual function, but I wonder if it might instead be a side effect of the female orgasm.

  6. Hershele Ostropoler says

    I wonder if people jump all over the non-adaptive explanation because it sounds sexist against women.

    On the one hand, it’s not denying the existence of female orgasms, and “no evolutionary purpose” isn’t the same as “no purpose,” but on the other “just a byproduct” is a bit dismissive. Since the female orgasm used to be pathologized (source: comment someone left on another blog, but it sounds right) I can understand why people are resistant to the notion that it’s an extra or even a bonus.

  7. jose says

    Is science sure male orgasms are adaptive, too, and not a side effect of some other thing? Since we’re here, I’m fairly sure our ancestors did fine without orgasms.

    You may say males who don’t enjoy sex are less likely to want it and therefore to have descendants. But so are women. If a woman doesn’t enjoy sex, why would she have it at all? She too would be less likely to have descendants, wouldn’t she?

    We know the most sexually active female chimpanzees are the most desired by the males. We also know those less interested in sex are more likely to do the role of “aunts”, belonging to a family core and taking care of their sister’s kids, helping the mothers. So the disposition of the females towards sex influences the outcome of reproduction, too.

  8. DLC says

    I agree on the paper. it shouldn’t have got past peer review.
    As for the orgasms. . . there I shrug my shoulders and move on.
    not enough data.

  9. Riptide says

    At first brush, it might indeed seem sexist to “dismiss” the female orgasm as “merely a byproduct” of the male orgasm. But at root here is the inherent *similarity* of the sexes, that when one reproductive gender has certain adaptations, these adaptations are often reflected in phenotypical expressions in all the other genders.

    I’m sorry, but nature doesn’t care about personal and cultural relations within the human population. And while I think it’s a bit more complex than “just a byproduct”, it is evident that a lot of male/female genitalia are (slightly) different expressions of the same kinds of organs. That is probably why it’s difficult for many women to orgasm without direct clitoral contact–how many men can orgasm from testicular and lower-shaft stimulation alone? Quite a few, but probably not a majority. It makes sense that similar mechanisms would be used, and ultimately points to the *unity* of the sexes (along with the non-cisgendered individuals of the species) at the genetic level. The rationalizations we wish to lay upon the facts at hand serve little point, either for or against a specific psychosexual point of view.

  10. Myti says

    Why does evolution ‘not care’ about happiness? I thought happy people had less chance of committing suicide while still young (thus increasing chances of their children getting to puberty), remained healthier, made better parents (ok this one I haven’t seen a study on, anyone have one?), and would be doing whatever made them happy more often.

    There seems to be a pretty straightforward link between their being happy doing something and doing it more often… This is in the case of animals that are capable of actually avoiding things they don’t want to do, of course – but humans fall into that category, I would think…

    So wouldn’t the trait of actually enjoying the act that gets you kids get passed on more often?

  11. tim Rowledge says

    Given the amount of effort that goes into making the clitoris and associated nerves it doesn’t seem that it should count as ‘unimportant’. There’s a lot of nerve tissue there – an article referred to some time ago (I’m fairly sure via PZ, possibly boingboing? Quick google returns way too many unrelated things to be sure) claimed that the clitoral nerve complex wrapped around a lot of the vulva, vagina and even the inner thighs and anal area. When I showed it to my wife she just laughed and said they should have asked her. Dim memories suggest that most of the women that have been generous enough to share intimacy with me would agree; a couple could orgasm multiple times without stimulation directly to vulva or clitoris.
    Either there is some evolutionary benefit or it’s a wonderful side effect of some other bit.

  12. ChasCPeterson says

    Is science sure male orgasms are adaptive, too, and not a side effect of some other thing?

    like what?

    Since we’re here, I’m fairly sure our ancestors did fine without orgasms.

    of course, we also have ancestors without hair, fingers, pancreases, eyes, collagen, and endoplasmic reticula…what’s your point?

  13. Algernon says

    But it’s going to be hard to get people on board with this when they hear “There is no evolutionary purpose” as “It isn’t important.”

    Yeah, this. You’re dealing with the backlash of people who we can still read about having their genitals cauterized with irons to “cure” their orgasms.

    It’s unfortunate that people are so ignorant of science, but that’s really what you’re dealing with right there…

    People have fought long and hard just to get female orgasm recognized and to have sex with females brought out of the duck-sex arena.

    Unfortunately, people can’t seem to grasp the idea that just because something isn’t biologically essential it doesn’t mean it’s not worthwhile. While, at the same time you still have a large contingent of people who are eager to have scientific evidence that it’s ok to take a 12 year old girl, keep her in a basement, and stick your dick in her to get a baby and then move on to the next kid.

    People suck.

    What was the point?

    Oh yeah, that.

  14. says

    I thought happy people had less chance of committing suicide while still young

    Suicide seems to be pretty uncommon in people who are constantly fighting for their survival anyway ;)

    As somebody who hasn’t invested much time into studying this, would this:

    . In fact, I’d consider it extremely unlikely that female orgasm doesn’t use exactly the same genetic apparatus as male orgasm. If anyone wants to really show that the byproduct hypothesis is false, a demonstration that the female orgasm is produced by pathways that are independent of, and evolved in parallel to, the male machinery would be more than sufficient.

    mean that they haven’t demonstrated the first liklier scenario either?
    So, well yes, finding a different independent pathway would demolish the byproduct hypothesis, but doesn’t this meant that it is not supported by demonstrating that it does use the same pathways either?

    I would also think that self-reporting about female orgasms is rather difficult, unless you go very much into detail to control for different behaviour.
    Or test it. Volunteers forward, you get paid a handsome compensation for trying differnt methods of stimulation over a course of 4 weeks.
    If one woman answers “yes, lots of wonderful orgasms” because she’s found that perfect 1200 volt vibrator while another woman reports “never ever” because she or her partner never bothered about stimulating her, how can they think those answers to tell anything about their actual physiological abilities?

  15. says

    I think, “because it’s fun,” and “because it relieves stress” are good enough reasons. Even sounds evolutionarily sound.

    Whatever. The paper sucks and should be soundly slammed.

    Mormon women have orgasms too, but in some circumstances they add a shitload of guilt, and that’s got to be bad for their psychological health. The mormon women on the “Baby Center” are having a discussion today about masturbation.

    One of the women wrote about her problem and asked for advice. Excerpt:

    I’m struggling with masturbation. AHHH! I just said that! This is something that started after I was married a few years. I never did it when young or single and didn’t have the desire then.
    My dh [dear husband] and I have a pretty active sex life of at least 4 times a week. In my late 20s I craved sex A LOT. I mean at least 2 a day and my dh liked it at first and then tired of doing it too much. That is when I started to masturbate. I did it almost every day for several months. After a few more babies I haven’t been doing it as much. Now I do it at least once a week on stressful days. It seems I do it just to get that “release” to relax and feel better. Whenever I’m stressed I feel like taking a bath and doing it.
    My dh doesn’t know anything about it and I have never mentioned this to anyone.
    I’m trying to stop and don’t know if I need to talk to the bishop about it. Is this something I need to let anyone know of? Can I just stop and repent on my own?

    The poor women is receiving all kinds of terrible advice, including this:

    I do think you need to go to your Bishop. When in doubt, do see your bishop. Masturbation is a sexual sin. It is not something to be taken lightly. I do think that his gospel is WONDERFUL and TRUE. He has provided a way for us to repent and be clean again. How awesome! I know going to your bishop will be a really hard thing…. embrrassing to say the least. Please, do remember that this is a man of God. He has been called to be YOUR leader. He loves you, cares for you, and can recieve revelation for you. He can guide you in taking the right path and help you to take the correct steps. Just think…how wonderful it will to be clean and whole again. …

    http://community.babycenter.com/post/a29344591/tmi-_touching_oneself_repentance

  16. Physicalist says

    Scientific reasoning is a subset of philosophical reasoning. Lloyd’s book exemplifies the way I think scientists ought to think.

    I agree. My comment was made with toungue in cheek.

  17. jose says

    ChasCPeterson,

    I have no idea. Has the question been posed at all? Or science just took for granted it is an adaptation because it obviously can’t be anything else?

    Care to comment about the rest of my comment, where I talk about actual animals?

  18. Putting On The Foil says

    Choking the bishop is always a good way to blow off some stream, but a mormon woman who chokes her bishop might end up in hot water.

  19. Cheri says

    Orgasm would likely fall along a continuum for all people depending on what the fetus was exposed to during development, just like there is a continuum of physical sexual characteristics. When I was a teen (just barely at that) I had many sexual encounters that did not lead to orgasm. I still enjoyed those encounters, however. Now that I am older, I know how to reach orgasm and rather expect it.

    I talk to a lot of women who really don’t like sex because it is painful and they don’t have orgasm. Are they somehow that genetically different from me, or did their fetal development just occur differently from mine?

    The only way to really study this is to do physiological testing to determine the true variability. I am sure that every variation might somehow be evolutionarily beneficial, if not for the individual, then for the species.

  20. Jefrir says

    jose, it’s not just a matter of enjoying sex. It’s perfectly possible to enjoy sex without having an orgasm, and even possible to orgasm without enjoying sex. For men, orgasm includes ejaculation which is obviously necessary to reproduce. That physical requirement is not present for women.

  21. Lyra says

    @Jose

    Men cannot reproduce without orgasming. Women can and do reproduce without orgasming. There are lots of reasons that women can have sex for while excluding orgasm: her man wants to have it, it makes her feel attractive, it generates harmony, to convince a man to do something, to make money, to bond socially . . . the list goes on. Men can also have sex for these reasons, but orgasm almost always goes with it, which is not necessarily the case for women. And for both sexes, being interested in sex is not necessarily the same as being interested in orgasm; there’s a reason that we don’t just all masturbate.

    This ties into what I said in a different post: many women can’t orgasm from vaginal sex alone. The clitoris is where it’s at for women, not the vagina. If the goal of the female orgasm is to get women to put penises in vaginas, then evolution hasn’t done a very good job of providing proper motivation. It’s like evolution wanted us to put food in our mouths and swallow it, so it made looking at food the most foolproof way of satisfying hunger.

  22. says

    Could one function of orgasm be to help a woman feel closer to her mate? I believe oxytocin is released during and after orgasm. I’m certainly no biologist and I don’t believe this is about orgasm being adaptive. I do understand the problem a lay person like me would have with women’s orgasms being deemed “evolutionarily unnecessary”. That doesn’t mean “not important” but women’s sexuality has been dismissed and demeaned so much over time that this view can be quite threatening. It reminds me of fatherhood ideologues’ reactions to a paper about essentialism and parenting (in particular fathering). The paper referred to biological essentialism whereas the ideologues misrepresented what the authors meant, insisting they believed fathers were not important. That wasn’t what the paper was about at all.

  23. ChasCPeterson says

    Care to comment about the rest of my comment, where I talk about actual animals?

    The chimpanzee thing? I don’t really see the relevance.
    Are you suggesting that variation in orgasmicity might result from simultaneous direct selection for orgasmia (plausibly corelated to ‘sexual activity’) and kin selection for anorgasmia?

    Orgasm would likely fall along a continuum for all people depending on what the fetus was exposed to during development

    I suppose it’s possible, but afaict this is pure speculation.

    Are they somehow that genetically different from me, or did their fetal development just occur differently from mine?

    Far from the only two alternatives.

    I am sure that every variation might somehow be evolutionarily beneficial, if not for the individual, then for the species.

    oh…no…evolution can’t really work like that.

  24. Anri says

    The idea that if women enjoy sex they’ll have more sex and therefor more babies seems reasonable.

    The idea that if women enjoy childbirth they’ll have more sex and therefore more babies seems reasonable.

    …and yet…

  25. Lyra says

    Ok! I did a little digging on reasons men and women have sex, and I found a paper. I haven’t spent much time looking at it yet, so I’m not sure how good it is, but I thought I’d share it in case anyone was interested. This is a paragraph that I thought was particularly relevant.

    http://homepage.psy.utexas.edu/homepage/group/busslab/pdffiles/why%20humans%20have%20sex%202007.pdf

    Gender differences in reasons for having sex To examine gender differences at the item level, given that 237 t-tests would be conducted, we set the significance threshold at a conservative level of p < .005. Thus, roughly one difference that showed significance at this level would be attributable to chance alone. An astonishing 123 items, or 52% of the items, showed significant gender differences at or beyond the p < .005 level.
    Men showed significantly greater endorsement of having
    sex due to physical reasons, such as ‘‘The person had a
    desirable body’’; ‘‘The person was too ‘‘hot’’ (sexy) to resist,’’ and simply because the opportunity presented itself: ‘‘The person was available’’; ‘‘The person had too much to drink and I was able to take advantage of them.’’ Men exceeded women on many items that pertained to physical pleasure such as, ‘‘I wanted to achieve an orgasm,’’ and ‘‘It feels good.’’ Men more than women reported having sex as a way to improve their social status (e.g., ‘‘I wanted to enhance my reputation’’; ‘‘I wanted to brag to my friends about my conquests’’) and their sexual experience (e.g., ‘‘I needed another notch on my belt’’; ‘‘I wanted to improve
    my sexual skills’’). Finally, men exceeded women on
    endorsing a variety of utilitarian reasons for sex: ‘‘I wanted to change the topic of conversation’’; ‘‘I wanted to improve my sexual skills.’’

    Women exceeded men on only three of the 237 reasons
    (at p < .005): ‘‘I wanted to feel feminine’’; ‘‘I wanted to
    express my love for the person’’; ‘‘I realized that I was in
    love.’’ Means, SDs, and effect sizes calculated using Cohen’s
    d are reported for the 50 items showing the largest
    sex differences in Table 3.

    All very interesting, assuming there wasn’t something seriously wrong with the study.

  26. Peter says

    I don’t understand why it’s clear that the male orgasm is adaptive, but the female orgasm is up in the air.

    Also, if I assume that only the male orgasm is adaptive, then why isn’t that a satisfying explanation for why females have orgasms also? Surely, what would need explaining then is not so much why females have orgasms, but why they wouldn’t. Why would the default assumption be sexual dimorphism in orgasms?

  27. bananacat says

    The idea that if women enjoy sex they’ll have more sex and therefor more babies seems reasonable.

    Orgasm isn’t synonymous with sexual enjoyment. Sex and masturbation always felt really amazingly good for me, even though it took me years to have an orgasm. Even now I don’t have orgasms every time or even half the time, and I still enjoy sex a lot. I frequently don’t even orgasm when I’m masturbating but obviously feels great anyway so I keep doing it.

    Of course orgasms are awesome and I’m sure some people will find sex unfulfilling without them, but orgasm isn’t the ultimate goal of sex, and lacking them doesn’t mean sex isn’t enjoyable.

    So you boys (and girls) can relax a little and know that your partner probably enjoyed sex even if she didn’t have an orgasm and you didn’t “fail” to satisfy her. The same thing can be said to