Another test of the upsuck hypothesis

There’s an interesting argument that’s been raging for decades about women’s orgasms: are they useful or not? Normal people, especially women, are probably wondering how that can even be a question — you probably find them very nice — but that’s missing a deeper point, which is, do women’s orgasms increase their fertility? Which I would argue masks an even deeper question, which is about women’s Ultimate Purpose. And apparently, the ultimate purpose of having a woman orgasm is that it makes her cervix more likely to slurp up the manly ejaculate, a phenomenon called upsuck or insuck.

On to this paper by Robert King, Maria Dempsey, and Katherine Valentine. It’s a weak paper, but the authors, to their credit, acknowledge the weaknesses and submit it as primarily a method of testing one aspect contributing to potential fertility problems that individuals can test for themselves in their home. The procedure is simple. Six women (they also admit that their n was tiny) were each given a Mooncup, a rubbery device usually used as an alternative to tampons or pads, a supply of an artificial semen simulant, a 10ml syringe, a spoon, and a surgical glove, and sent home to masturbate. Their instructions were to first use the syringe to squirt 5ml of fake semen into their vaginas, and then flip a coin. Half the time they would masturbate to orgasm, and the other half they would masturbate for roughly the same amount of time, but then stop before orgasm, as a control. The next step was to place the mooncup over their cervix, and after an hour, remove it and measure how much of the fake semen had flowed back out of the upper reaches of their reproductive tract, which they were then to measure with the syringe.

Sounds romantic, I know.

The hypothesis was that muscle contractions during orgasm would propel semen deeper into their bodies, and that as they later relaxed, it would flow back into the mooncup, so they could compare the amount squirted up into the uterus/fallopian tubes/etc. in orgasmic vs. non-orgasmic situations. The prediction was that if orgasm were effective at increasing semen flow into relevant parts of the reproductive tract, they’d see more retention of semen after an orgasm. The answer is…they did.

I have a few problems with the study. As already mentioned, it has a minuscule number of participants, but also, it is not at all a blind study. The subjects knew what the expected result should be! I would not accuse them of outright cheating, but it’s very human to see an experiment that is purportedly testing the potency of your orgasms as a judgment, and that maybe a little fudging in one direction or another is acceptable. I’m also wondering why the contribution of the women’s fluids to the outcome wasn’t taken into account; they specifically excluded situations where the women produced female ejaculation, but as the investigators must know, women will produce more vaginal fluids with orgasm than without, which would have contributed to the volumes they measured.

One of the biggest problems of interpretation, though, is that nothing in this study actually tests fertility and the odds of conception. I would take it for granted that triggering vigorous contractions in a muscular, fluid-filled tube is going to move those fluids all over the place, but the question is whether this contributes significantly to successful fertilization. Maybe it does, maybe it doesn’t, nothing in these observations answers that question, or even whether this is a relatively significant factor compared to all the other variables in conception.

But that is the biggest problem of them all. If you’re trying to determine whether there is a selective advantage to a woman having an orgasm, why focus exclusively on the mechanical effectiveness of getting her pregnant? Humans are psychologically and sociologically complex, responsive to all kinds of subtle and not-so-subtle cues, and with a huge amount of individual variation. Looking at what is essentially the very last step in an elaborate courtship dance and declaring that that is the critical thing that evolution is looking at tends to kind of minimize an intricate behavioral complex that is also subject to evolutionary forces.

This reductive, narrow approach to a tiny aspect of a question is a common approach in some disciplines. Another subset tends to view programmed female responsiveness to male signals as the mechanistic goal of evolution. Evolutionary psychology, I’m looking at you.

King R, Dempsey M, Valentine KA (2016) Measuring sperm backflow following female orgasm: a new method. Socioaffect Neurosci Psychol. doi: 10.3402/snp.v6.31927


  1. says

    but that’s missing a deeper point, which is, do women’s orgasms increase their fertility?

    Yes, women’s orgasms increase their fertility, because a woman who cannot get any orgasms is unlikely to want sex. Which means she will have little (if any) sex. Which means she will have much fewer children. Which means a decreased fertility.


    Asking whether women’s orgasms are useful is inherently sexist and promotes an antiquated worldview that women aren’t supposed to enjoy sex.

  2. chrislawson says

    All good points, PZ. I’d also add that using a 5ml syringe to measure at 0.1 ml precision is a bit of a stretch.

  3. aziraphale says

    “Asking whether women’s orgasms are useful is inherently sexist…”
    That seems unduly woke. Surely we can ask of any biological feature whether it has a function, and is therefore likely to have been preserved by evolution, or not.

  4. ardipithecus says

    “Yes, women’s orgasms increase their fertility, because a woman who cannot get any orgasms is unlikely to want sex. Which means she will have little (if any) sex. Which means she will have much fewer children. Which means a decreased fertility.”

    As long as Christianity has held sway over western cultural mores, sex has been a ‘wifely duty’. Even though the sexual revolution began the acceptance of healthy female sexuality as something good and wonderful, there are still significant numbers of married women who have never had an orgasm with their husbands.

    Throughout western society where women are increasingly in command of their own sexuality, fertility rates are declining. I think that strongly suggests that simplistic, evo-psych type reasoning is not helpful.

  5. dma8751482 says

    Oh, they’re useful for much a simpler reason.

    Orgasms feel good, and people tend to do things that feel good more than once. Thus, orgasms encourage more sex and thus a greater chance of successful reproduction. Hell, I could apply the same logic to the male orgasm too- there’s nothing that inherently forces ejaculation to register as pleasurable for the underlying physiology to work.

  6. dma8751482 says


    Some biological features just come to be as accidents or byproducts of entirely unrelated processes and stay as they are because their presence does nothing to harm evolutionary fitness. My hastily thought up theory notwithstanding, this may be one of those cases.

  7. a_ray_in_dilbert_space says

    I tend to agree. Human sexuality is incredibly complicated. Others have pointed out that all other things being equal a woman’s pleasure could lead her to want sex more frequently. I would also suggest that it would reinforce sexual desire in the male partner(s). It could increase the strength of pair bonding…
    And these are just some of the competing effects that could also contribute to an evolutionary advantage for female orgasm. Evo-psych is just a bunch of Just-So stories designed to satiate curiosity rather than stimulate it. Evo-psych is anti-science, rather than science.

  8. PaulBC says

    I think it would be more interesting to try to understand why people seek out hot peppers (and I have heard some theories like masking spoiled food). It seems sort of obvious why sex should be pleasurable, so no more complicated explanation appears necessary.

  9. dma8751482 says

    That’s an easy one. Capsaicin, the stuff that makes peppers spicy, reacts with nerve cells that normally react to extreme heat (which is incidentally also why pepper spray causes a burning sensation, your body can’t tell it apart from actually being burned).

    Said nerve cells also trigger the release of endorphins and dopamine, which are interpreted as pleasurable. So all in all it’s a naturally occurring system that our body typically uses to suppress pain being activated in a matter where it is in no real danger.

  10. rrhain says

    One of the things I’ve never seen addressed in this hypothesis is the fact that this requires the woman to have the orgasm after the man has ejaculated. After all, if she has it before he does, there isn’t anything to suck up.

    But how often do we hear about women having to manage their own O because he has popped off before she got there herself? How many men continue to engage in after they have climaxed?

    Does this also explain the phenomenon of multiple orgasms in women? That perhaps the reason women have this response has to do with the idea of getting her cervix dipping and then he can release the semen.

    Surely we can see how ridiculous that sounds.

    But exactly how would this be a benefit from an evolutionary perspective given the issues of timing required to make it even possible as something that can happen? It would seem an odd thing to pin an evolutionary dependency upon where if the timing isn’t just so, it doesn’t happen. And I understand that so long as there isn’t a real downside to it, there’s no reason why it can’t drift into the population’s genome, but it just seems so ephemeral of a thing.

  11. robert79 says

    Indeed, n=6 is the least of their problems, as they’re measuring a crystal clear effect (a sign test would give a p-value of 1/2^6 or about 0.02 here as all measurements in group A are greater than those in group B.)

  12. lochaber says

    before worrying about a women’s orgasms affecting conception rates, wouldn’t it be more reasonable to try and address why human women’s reproductive cycles are effectively “hidden”? Don’t most other animals practically advertise when they are fertile?

    Personally, I think there is a lot to be said for sex having a much greater role than merely reproduction, and that those other roles, like pair-bonding and such, have superseded reproduction in importance. An orgasm, and pleasurable sexual encounters in general, would seem pretty important for both partners for pair-bonding to be effective, I would think…

  13. answersingenitals says

    Some time ago I read an explanation, probably quite speculative, for the orgasmic response, which, even in males, involves much more than the ejaculation of sperm. This theory suggested that orgasms had several endocrinological similarities to the fight/flight response with the release of adrenaline, strong muscle contractions all over the body, heightened blood pressure and flow, and most important, heightened immune response. The sex act is highly intrusive, and given the probable hygiene of our primitive ancestors, can be highly infective. So, orgasms could quite simply be a defensive survival mechanism. This could also explain the desire for kissing and oral sex, since saliva is very antiseptic (and why animals lick their wounds). It would be interesting to research what other animals (e. g., spiders) have orgasms and what hormones are released. This theory would also explain why masterbation is a thing, and why it is a very good thing.

  14. mountainbob says

    Testimony from one I love and have lived with for a long time was that an orgasm at the onset of the period reduced cramping. I have no additional information, no personal experience, and the N remains fixed at 1.