Friday Weird Science: THIS JUST IN! Orgasms aren't an evolutionary by-product!

Sep 09 2011 Published by under Friday Weird Science, Uncategorized

Greg Laden pointed me to this paper the other day. He's got a write up of it on his blog from an anthropological point of view, and Wired and the Mary Sue both covered the story (though amusingly the Mary Sue reported that only 1 in 10 women COULD orgasm, when in fact it's the other way round or I imagine there'd be a lot less to talk about), but of course, it's orgasms. FEMALE orgasms, and this means that I have to give it my own special Scicurious treatment (the one from the...orgasmic...point of view??). Especially since I feel that the abstract and findings of this paper glossed over what I think is definitely the most important finding: sure, the female orgasm isn't an evolutionary byproduct, but it looks like there may be a genetic component.

Zietsch and Santtila. 'Genetic analysis of orgasmic function in twins and siblings does not support the by-product theory of female orgasm' Animal Behavior, 2011.

Also, their main point. Well. Yes, these findings do not SUPPORT the by-product theory of female orgasm...but they don't actually refute it either. Oops.

(You know what I'm talkin' about...)

People LOVE to debate female orgasm. We love to debate what it is (what really "counts" as orgasm, clitoral? Vaginal? Is there no difference?), we love to fight over how often it happens (Do you ejaculate or not?), and most importantly we wonder WHY. WHY female orgasm? Why does it happen? What purpose does it serve? For the 10% of women who have never had one, what are they missing? And why has it become some sort of sociological obsession for men in their 20s to make their partners achieve it more than 5 times per session?

In fact, people are so amazingly into the female orgasm that scientist have put forward over 20 theories as to why it occurs. Most of these fall into three categories: pair bonding (orgasms feel good, so it must make us like our mates more), mate selection (the best dudes evolutionarily speaking must bring the best skills to the sack, apparently. I'd love see that tested), and enhanced fertility (where orgasm produces "insuck" and makes it easier for the sperm to find the egg). All of these have their supporters, their detractors, their problems, etc. And then there's the FOURTH category: where female orgasm don't matter. Honey badger don't care.

That's right, there is a hypothesis that female orgasm serves no evolutionary purpose whatsoever. Instead, it's merely a by-product of male orgasm, where female bodies can orgasm...only because male bodies can.

Of course, this hypothesis is not very popular, but is it TRUE? The authors of this study wanted to test this, and figured that, if female orgasm really WERE a by-product of male orgasm, then genetically speaking, it would vary along with male orgasm. This means that people who are related will have similar...orgasmic abilities.

This is where you start asking many sets of twins some very personal questions. The authors gave a bunch of questionnaires to sets of Finnish siblings, fraternal twins, and non-fraternal twins. They asked the women how often they reached orgasm during sex, and how difficult it was, and asked the men how fast they ejaculated and whether they felt they came too early. From these they determined a score of "orgasmic function", and they thne looked for correlations among groups.

They found that the fraternal twins and the siblings had tiny, but significant correlations in orgasm function, but the fraternal twins were not different from normal siblings (as you might expect, given that they are related to the same degree). However, the male and female identical twin pairs had much higher rates of correlation.

From this the authors determined that female orgasm is not an evolutionary by-product.

Now, does this study PROVE that female orgasm is not an evolutionary by-product? Nope, not exactly. It proves that female orgasm does not co-vary or correlate with male orgasm in genetically close relatives. So, you know, your orgasms aren't correlated with your brother's. That probably made a whole bunch of you relax a little. But it doesn't completely prove that female orgasm is not an evolutionary by-product, either. In order to REALLY prove that, we would have to prove that female orgasm has NO FUNCTION. And this study did nothing to address that question at all. So, no disproof.

BUT. It did show something interesting, though it was something so glossed over by the authors that none of the mainstream coverage picked it up (though Greg certainly did). The biggest and best correlations here are those between the female identical twins and the male identical twins. This is not overwhelmingly surprising for the males, but I don't think it's been shown in females before. And it suggests that there's a genetic (and thus possibly a PHYSICAL) basis for the female orgasm. We do have some physical indicators for female orgasm (eletrodes will go all crazy when you orgasm and the electrodes are up in your business), but the correlation of genetics to the 'orgasm function' is a nice little finding.

But I gotta say these self-report studies, man, they get me DOWN. There are just too many issues at hand here.

1) Define orgasm. What kind? What do you MEAN?

2) Define sexual stimulation and whether it was self- or not. What if some of these women suffer from particularly bad partners?

3) SOCIOLOGICAL FACTORS. When women talk about having a tough time having an orgasm, or talk about having loads of them, it's not like we're talking about them like we'd talking about having our knee itch. Sex is very taboo in a lot of societies, certainly it's extremely thrilling, and so the sociological pressures going on just can't be underestimated.

4) You're telling me that 39% of men ejaculated 10 minutes after penetrative intercourse has begun?! Someone's lying, and I think it's those dudes. Most other studies with more rigorous testing say the average is 5 minutes or less.

And you know, this is all so...self-reported. I think if you're really going to look at physical, genetic, what have you, bases for female orgasm, you gotta get IN there. You have to make sure those electrode readings are going nutso. You need a controlled setting without the influences of individual variation in partners. What you need here are related and non-related female volunteers, a large selection of vibrators, and some MEGs. And that still wouldn't really PROVE whether it's evolutionarily beneficial or not. But it would show more accurate readings. To me that's a good enough place to start.


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

31 responses so far

  • Bill Noble says:

    I've been wondering how much solid cross-cultural study has been done around female orgasm. Could the "10% don't" be a product of American or the larger European culture? And was it 10% in 1860 in England? What's the number in Vanuatu, or Tonga, or Saudi Arabia? Within the US, does it vary by social or economic class or by race or religion (given all we know about how sexual practices vary by class, might that not be a good first assumption?)?

  • Bill Noble says:

    Not to be obsessive, but some further thoughts after sticking my head back in your post:

    Orgasm as a reflex is controlled in the lower spine, not the brain. I know male paraplegics can have erection and ejaculation just fine, and I know both genders can be trained over quite brief time spans to have orgasm from ear lobes, lips, the wings of the nose, etc.

    So might a baseline be to see the stats on how sedated women responded (or didn't) to a Hitachi?

  • figleaf says:

    I still think people should be asking why men need to have such big orgasms. It's nice that we do. But all things considered I don't see why they're necessary either. Big ones I mean.

    I know it's not sexy thinking about stats on how sedated men respond isn't sexy to the 20-something men (or formerly 20-something men) who I think drive a lot of the hypotheses of "female" orgasms. But I still think until we get over the "well obviously men..." hand waving we're going to keep missing the big picture.

    Thank you, incidentally, for not saying "well obviously men..." at any point in your post.


  • [...] magari questi dati non supportano la teoria del byproduct, ma nemmeno la smontano. Come scrive Scicurious nel suo popolare blog (leggete il post, ve lo consiglio), lo studio prova che l’orgasmo [...]

  • CoR says:

    Nice, as always, Sci. I have a caveat to this statement:

    "But it doesn't completely prove that female orgasm is not an evolutionary by-product, either. In order to REALLY prove that, we would have to prove that female orgasm has NO FUNCTION."

    If was proven at some point that there is no function NOW for female orgasm, that doesn't mean there wasn't (dbl neg, aurgh!) a function in the past that we cannot currently assess. Ie, lack of current function does not mean female orgasm is an evolutionary byproduct. They should do a genetic mapping study with this data -- I just saw a paper showing a genetic basis of perm. teeth eruption in kids doing an association study. Who knew?! Not I, said the Rad.

    • Scicurious says:

      Oooh, good point. Yes, could have had a function in the past and doesn't have one now.

    • Greg Laden says:

      First it may be useful to identify the molecular pathway from gene to orgasm. It might prove difficult but until one can conceive of how do that any genetic theory of orgasmic function would involve mostly the waving of the arms.

      Things that have no function but did have a function in the past certainly can exist but if they retain a cost and no function they would be selected against if they are evolved traits. Meaning, simply, that it is a good idea to assess both costs and benefits.

      • CoR says:

        "Things that have no function but did have a function in the past certainly can exist but if they retain a cost and no function they would be selected against if they are evolved traits.

        If there was a cost and NO correlation or covariance to another trait then sure, they would be selected against and over time you would not expect to see said trait in the population. But where are we in time? Further, what if orgasm as a trait is correlated to say, the presence of a urethra? Might it be retained in the population?

        I am unclear as to why we need special genetic theory of orgasmic function -- I would suggest it can be modeled just as any trait, and as you have stated in your second paragraph.

  • Greg Laden says:

    Figleaf, if I understand you correctly I think you are approaching this exactly right. The female orgasm has for too long been considered in light of he male orgasm, and in light of an incorrect view of the male orgasm (which is one of the main points of my post)

    Sci: Excellent writeup! I'm spreading it around now. Thank's for covering this.

  • AK says:

    What I want to know is: Do female bonobos (Pan paniscus) have orgasms? Also, when was research first done on the question? Unfortunately, I don't have time right now to dig into the question, but I'm sure somebody here does.

  • Dan says:

    I think given that humans hide estrus, and that it usually takes quite a few sexual encounters to conceive, we are missing a possible explanation for female orgasm. An initial encounter could be a litmus test of the man. A good partner needs to have many socially desirable characteristics: the ability to delay gratification, reading social cues, and physical stamina. Runaway selection may also play a role. So if a man can give a woman an orgasm, she will be more likely to sleep with him again, increasing his chances of conceiving a child with her. An ultimate explanation for orgasm may be mate sorting, and a proximate explanation may be that a woman finds sex more pleasureable with a man she will have sex with him more.

  • Laden overstates some claims, like saying, without offering any proof or even a URL, that the "byproduct" school started in part in a belief that women don't have vaginal orgasms. (Stephanie Zvan was probably standing over his shoulder while he wrote.)

    The study may or may not prove much of anything, but to link to Greg as offering a great degree of insight? Meh.

    • Stephanie Z says:

      Remember, men. Never agree with a woman in public, especially if another man disagrees with you (to the point of ranting that you're a government shill or something else ridiculous). If you do, that woman will forever be used against you (somehow) to demonstrate that everything you say on your topic of expertise needs a specific citation, preferably to someone you've never worked with.

      Or to put it another way: Seriously, dude?

    • Might want to look up the Socratic method and rethink your name, or your strategy of suggesting things without first having eliminated every other possibility.

  • Brittany says:

    Well written as always! Both informative and enjoyable.

    Just wanted to give a little shout-out to one of my favorite books, "Bonk" by Mary Roach. I think that if anyone here is enjoying Sci's writing about the subject of sex you'd really like this book

  • pornalysis says:

    This was a good read, solid writing; a real mouthful of information 😉

    "you gotta get IN there. You have to make sure those electrode readings are going nutso. You need a controlled setting without the influences of individual variation in partners"

    Wouldn't this sort of skew the results a bit? I mean, isn't a woman's intimate and personal space with her partner a part of some type of orgasm too?

    And what about the connection between standard, and anal orgasm?

  • Occam says:

    Lets look for a reason for female orgasm. Lets say that it serves an evolutionary purpose, and then try for hypotheses. Well, how about as the most parsomoneous beginning: Sex is to motivate humans to breed, men need to orgasm to ejaculate- so a no brainer there- no male orgasm no offspring, so we are expecting a close to 100% 'goal' of evolutionary selection for male orgasm. For whatever reason (see e.g. 'investment differential' such as one egg and 5 years versus 5 million sperm every 24 hours) there is a different 'drive' to have immediate and indescriminate breeding sex asap and to whomever one can. This would be closer to the male position but not the female position. So females 'choose' more selectively because of, say, greater resource investment in getting the best genes - not that men dont also, but just LESS discriminating due to LESS investment. So, maybe orgasm in women functions as (a) a PART of the normal distribution of 'desire' per se . i.e. females must have SOMe sex drive, even if its just enough to 'allow' the male, but since such desire would be normally distributed, they dont need as high a base level as the male.BUT random factors will make some VERY excited and some not. Thus, orgasm is just a part of the GENERAL desire need to have sex at all. (b) orgasm selects as it 'rewards' females when they choose genetically better genes, so motivates them for mate selection.

  • kha says:

    That was a great article! I use to only read the mag but that was great. It made me ponder, grin and smile all at the same time. Ha!

    But I gotta wonder, could not the female mind's processing of the orgasm make it necessary or make the female 'yearn' to mate and produce offspring - evolutionarily speaking of course (if there is such a word)?

  • Magoonski says:

    Female orgasm is definitely not a by-product, if anything the male orgasm is. Think about the womb babies are all female until the genitals start 'migrating' into place. Also consider that women have more nerves in their clitoris then men in their penis. Not to mention that the "rest" period inbetween orgasm is much shorter in comparison to men's, and women can experience multiple orgasm.
    If we look back to the late 1800's and early 1900's, women were treated by doctors with special paddle devices, that were essentially the old-school version of a vibrator. Women often sought out this treatment for various "female ailments" which were probably caused by the various hormones that women have to deal with constantly. Point is, orgasms made these women feel better. I've even heard that having a few extra orgasms before a menstral cycle starts actually makes it easier to deal with. Therefore, if it is evolutionary, it's because women need orgasms. Plus, if we're more on the bonobos side of things then the chimp side, then it would also be beneficial for the females to enjoy sex if it is also a peacekeeping measure and not just a reproductive one.

  • Amoeba says:

    Obviously I haven't done the science so I'm probably missing something, but to me this doesn't seem like a big mystery. Humans who had more sex had more offspring. Females who derived pleasure from sex were more willing partners, and thus were more likely to have offspring.

    Am I way off base?

  • Brachiator says:

    The whole search for a purpose driven reason for the female orgasm is bad science. Heck, it is not even science. This search to validate orgasms seems a holdover from a religious view that says that in the Deity's universe, everything fits together, and a pseudo-modernist philosophy that wants to insist that men and women are exactly alike, and everything that exists in the male must have a complementary function in females (except for lactation and reproductive organs). And lastly, apparently a lot of scientists know about as much about sex as Dungeon and Dragon nerds. Here, they want to fall back on some lazy notion that pair bonding monogamy is the default status for human beings, ignoring the variety of human societies.

    So, I don't know whether the female orgasm has a purpose. I DO know that for much of recorded history and across all human societies, "marriage" and its variants has been as much about tribal and family alliances, and the happiness and prospective pleasure of either the male or the female has been irrelevant. And we also know that women have often been the prizes of raiders, invaders, and slaveholders, and that this sad status does not impede reproduction. We know that in the days before reliable birth control, pregnancy was an occupational hazard of prostitutes.

    And self-reporting counts, too. There are numerous examples of journals and diaries in which men and women express dissatisfaction and a distinct absence of pleasure with their spouses, and the discovery of all kinds of pleasure with lovers. And yet, the number of children produced with lovers and spouses does not much vary.

    Put another way, the underlying assumption that there are processes that encourage monogamy is nonsense, or at least is greatly complicated by reality. The larger principle is that evolution drives humans, and other species, to reproduce without regard to fun, pleasure, loyalty or fidelity.

    As an aside, the "problem" of premature ejaculation is a modern issue, that is more related to a society which rightly equally values men and women. But one could make a strong case that selective pressures balanced any "desire" to derive maximum pleasure from sex and the need to get the deed done as quickly as possible so that neither the male nor the female would be exposed to danger.

    This is obviously not to say that orgasms are not important. It is only to say that it is not up to science to validate any particular view about the value of sex or relationships, or to look for a single, reductive evolutionary "purpose" to biological processes.

  • BeardedGirl says:

    I volunteer!

  • Matteo says:

    happyness is necessary to evolution , the research of pleasure is a good motivation to search partners, what was a byproduct can (in different environmental-social situations) became necessary. Too many science -philosophers actually don't understand what evolution is. Case dismissed.

  • Matteo says:


    You're totally wrong... and ignorant..
    Psychology and recently neuroscience are exactly doing what you 've said "is bad science".
    Moreover:"The larger principle is that evolution drives humans, and other species, to reproduce without regard to fun, pleasure, loyalty or fidelity." Another bullshit, I hope you're not a researcher or a scientist....
    Evolution drives human in the way you've said...till "memes" come into play. A lot of academic literature on depression , motivation and so on contradicts your view.

  • Mel says:

    Females achieve orgasm on there own more commonly than with males partners. Female orgasm is purly controlled by the females willingness to reach orgasm
    With the male. A female orgasm is completely voluntary and independent upon the female. Even when a male stimulated her she must be willing . A woman can decide if she would like to orgasm even choosing not to while being stimulated . It has nothing to
    Do with reproduction. Due to the fact that woman become pregnant without climax . It may play a part in enabling sex with a male as her climax could encourage sex . But as far as a female orgasm goes it
    Mostly represents pleasure and freedom of body and mind. And totally seperate from the male penis.

  • Mel says:

    Don't want to offend , but all those scientists need to seriously stop thinking that the female orgasm has anything to do with a Penis! Because Woman achieve most of there orgasms by themselves due to the complex nature of clitoral climax. Most woman fake it because it's easier and to boost there partners ego . Fact
    Females do not need orgasm to conceive , so there's that theory out the window . It's so amusing to me that the general conclusion regarding orgasm must be involving the male somehow or pregnancy . ! Bullshit theory's. most of female orgasms don't end up
    In pregnancy ! And most females achieve it on there own . Maybe we'd get a lot further by taking reproduction out of the equation ? And focusing on the chemical and hormonal impacts of orgasm in woman and the way it's useful to the female body in relation to stress hormoes ect.

  • Mary says:

    I have a different evolutionary theory on this topic.
    Consider the issue from a woman's point of view -
    women have strong sexual desires. If they could only
    find satisfaction with a man, they would be a lot less
    selective in who they have sex with. I believe the clitoris
    is there as a way for women to achieve orgasm on their
    own and relieve sexual frustration without need for a penis.
    To choose the best available partner for genetically fit children,
    they need to discriminate and not choose primarily based on
    unfulfilled sexual desire, but desire for a particular genetically
    fit man.

  • [...] of "insuck", as it were? The concept is this: over a long time now, people have wondered about the purpose of female orgasm. What is it for? Is it a byproduct because men can have orgasms? Is there a genetic basis? One [...]