Evolutionary psychology: the adaptive significance of semen flavor

April 18, 2009 • 5:42 am

I have long been critical of many evolutionary psychologists for their over-the-top stories, but today I am forced — albeit briefly — to join their ranks. I have thought of a hypothesis that shares all the salient traits of the best ideas of evolutionary psychology: it is brilliant, makes evolutionary sense, and is untestable.

It is the conventional wisdom in human sexuality that semen tastes bad. Anyone with minimal sexual experience knows that although many women will perform fellatio on their partners, most bridle at the thought of swallowing the ejaculate. Its flavor is frequently characterized as revoltingly bitter or salty. The “swallow or spit” dilemma faces any woman who performs such an act, and whose partner regards swallowing as a gesture of love.

The universal distastefulness of semen is attested by the many internet sites that give advice about how to improve the taste of one’s ejaculate, for example, here, here, and here.

To get a better scientific handle on this idea, I took a poll, asking a woman friend, Dr. Fawzia Rasheed, to canvass her female acquaintances about their willingness to swallow after the act of fellatio. Twenty-four women were asked this question:

Sperm…would you spit or swallow? In other words, can you abide by or do you hate the taste?

There were sixteen responses, many including pungent asides that I cannot repeat on a family-oriented website. One answer was a non-response (“I should be so lucky”). The other fifteen included eleven “spits” and four “swallows”. But among the latter, two women commented that they did not like the taste: one, in fact, swallowed to get rid of the flavor as quickly as possible. Two others said “swallow” but did not comment on whether they enjoyed it. Therefore, 13/15, or 87% of informative respondents could not abide the taste of semen.

This near-unanimous response to a random poll demands an evolutionary explanation. Why does semen taste so foul? One answer, of course, is that the chemicals necessary to make an ejaculate effective have the side effect of tasting bad. Semen is only about 5% sperm, with the remainder of the fluid consisting of a complex mixture of compounds from the prostate gland and seminal vesicle. These compounds include sugars such as lactose [CORRECTION: fructose; see below ] (to provide energy for the swimming sperm), enzymes, amino acids, zinc, hormones, and various amines to counteract the acidic environment of the vagina (these are said to give sperm its characteristic smell and flavor). Some of these amines have the names putrescine and cadaverine, which give an idea of how they smell. The function of some of the compounds is unknown; they may help overcome female immune defenses or even function in male-male sperm competition when females are multiply inseminated.

But this proximate answer will not satisfy the diligent evolutionary psychologist. After all, natural selection could presumably add some sugars or good-tasting stuff to semen if it were advantageous to do so. Why does it not do so?

A moment’s reflection gives the answer.

Natural selection maintains the repugnant taste of semen so that a man’s sperm will wind up in the appropriate place: the vagina and not the stomach. So long as sperm tastes bad, women will not be tempted to swallow it, but will turn their male partner towards conventional intercourse, which of course is the only act that will produce children. In other words, any male with good-tasting sperm would have fewer offspring than his competitors. A man whose sperm tasted like honey would probably not have any children at all.

I can think of only two ways to test this hypothesis, both of them impractical or impossible:

1. If women gave birth through their stomachs, semen would taste great

2. Those males with genes giving them better-tasting semen will leave fewer offspring than other males.

This theory is offered as a modest proposal, only partly (excuse me) tongue in cheek. It may even be true.

Notes added post facto: Although light-hearted, the post is somewhat serious; it’s the kind of interesting speculation that evolutionists indulge in over a few beers. And everything in the post is true, including the survey of women.

And note to T.R. Gregory: I don’t think this idea is refuted by finding, say, primate species that don’t have oral sex but do have similar compounds in the semen. The whole idea rests on those compounds TASTING BAD to females, and we’d need to know something about the taste reactions of females in these other primates. The evolution, after all, might have been in the female taste receptors rather than in the semen.

Finally, apologies to readers who find the subject distasteful.

72 thoughts on “Evolutionary psychology: the adaptive significance of semen flavor

  1. Where is the rest of the article?

    Or did I misunderstand “The hypothesis is offered only partly tongue in cheek.”

    1. I do not find the taste offensive.There are times usually that there is really nothing in the taste area of my mouth due to the the obvious layout of tastebuds on the tongue and the length of a penis. I do swallow and never mind the taste this preoccupation with taste would only ruin the moment.

    2. This article seems biased as
      1. I am a girl and like the taste and love swallowing
      2. My bf has three kids and his tastes great
      3. If everyone’s tastes different than how can one decide it has a “repugnant” taste intended to put people off swallowing.
      4. Spitting is digusting and messy.
      5. Spitters are quitters.

  2. It’s testable to some degree. Do other species that do not engage in oral sex, but which have similar vaginal conditions that challenge sperm success, have the same chemical constituents in their semen? If so, then those are probably not present in order to affect its flavour.

  3. The converse is probably equally true:

    Women’s vulvas look and smell disgusting to many men (myself included). That was even more true in primitive times when man first appeared, when there were no deodorants and bathing was infrequent.

    That is a deterrent to men wasting their time performing cunnilingus on women. Why bother wasting your time smelling that revolting odor. If you’re sexually aroused, just perform vaginal intercourse, get her pregnant, and then go back to your regular routine.

    1. “Women’s vulvas look and smell disgusting to many men”

      That doesn’t make this universally true. To be perfectly honest I, and many male friends I have known, find vulvas not only beautiful, but delicious as well. I’ve never understood men like you. Your opinion seems sexist and ignorant (maybe you just haven’t been with the right women). You have the right to your preferences, but I have the right to question the biases behind your preferences. Honestly, I think you are an outlier.

  4. When I was a grad student at Rutgers, the usually very low-key post-doc across the hall returned from a biochemistry lab section that he’d been teaching – that day on olfactory perception – and gleefully announced that he’d devised an assay for virgins. There’s apparently sexual dimorphism in the ability to detect at least one component of seminal fluid – I think it may be nonenal but this was a LONG time ago.

    Anyway, the lab apparently involved passing samples of various compounds around for all students to smell. As the nonenal (or whatever it was) was passed around, none of the men reacted. A fair number of the women marked comments as with any other compound, while the remaining women giggled the moment they smelled it.

    I sometimes wonder if they still run that lab.

  5. What a sin that Jerry didn’t think to submit this hypothesis to Evolution and Human Behavior. That’s the only way to see if evolutionary psychologists are as naive as he thinks.

    But strangely, we see that Jerry didn’t want to test his own hypothesis, which is exactly what he claims makes evolutionary psychology pseudoscientific.

    This is actually a “just-so story” about how evolutionary psychologists like to tell “just-so stories”.

    Hypocrite much, Jerry?

  6. The old joke was that the taste which made women give up oral sex was not semen but rather wedding cake.

    1. Renl67 doesn’t care. Vaginas are only good for one thing according to him…and cunnilingus is not one of them. He is basing his opinion on his own personal experience and the alleged experience of “many men.” Whatever that means. I.e., he’s not speaking from a position based on anything other than the most minimal anecdotal evidence.

  7. The question only approaches the issue form the viewpoint of one gender’s reaction to a particular (yucky) stimulus and is an overly simplified explanation for a complex set of behaviors. Did anybody ask gay men about this to find out if they have a similar response tot he taste? Do we know whether or not the taste affects them the same way as it does women?

  8. I second Mike’s curiosity: Why limit the inquiry to male-female couples? How do gay males feel about semen? (And how to gay women feel about lady juices?)

    Is semen flavor affected by the donor’s diet, or is that just an urban myth? My husband is a vegan, and his output tastes fine to me. Maybe our fruit-munching, infrequent-meat-eating ancestors had more pleasantly-flavored semen.

    1. I’m probably one of those rare women that actually enjoys the taste, but now I realize that many if not all of my samples were of men that were vegetarians and had healthy lifestyles. As a zoologist I have witnessed higher primates such as chimps and gorillas perform these acts and it appears that both genders, enjoy it – and considering that these particular primates live with a vegetarian diet, perhaps diet does play a significant role in satisfying the tastes of those who perform the act.

  9. Interesting – I too would suggest that gay men may be an interesting way to study this. My experience is that more swallow than spit…


  10. Interesting. Count me in the spitter category.

    I think that the evolutionary point is not so much whether semen tastes bad, but *why* we dislike the taste. This is the flip-side of the question of why honey tastes good to us.

    After all, it is not the chemicals, but our *brain* that decides. Honey tastes good because it is good for us.

    Looking at fellatio from a different perspective, any female who much preferred the taste of sperm would be unlikely to conceive with *any* male. Since males typically do not say, “I’d prefer an act with greater procreative potential”, the reproductive onus is on the female.

    Those contented males could move on to impregnate a female who dislikes the taste of semen, whether or not he has wasted a little semen on the fact that he likes the taste of her.

    However, our theoretical “swallower” will not pass on her he-tastes-good genes.

  11. There’s another way to test this hypothesis: Feed a group of men some agent that improves the taste of their semen for a few months [assuming any of the many items reputed to have this effect actually work; that’s a whole other experiment]. Then compare that experimental group with a control group and see if the men with better-tasting semen in fact ejaculate more in mouths and less in vaginas.

    It wouldn’t answer the question once and for all, obviously, but it could support or argue against one important piece in the logical chain.

  12. As an evolutionary psychologist myself, I don’t see a problem with this. Adaptation is an onerous concept. There’s no need to posit an adaptation when there is no sign of evolutionary design, of complex design.

    I’d say semen tastes bad because is not meant to be eaten. It’s the same as broccoli, really 😉

    1. I love broccoli! Some people have a genetic tendency towards finding the taste of broccoli disgusting, that does not mean that it is universally disgusting. It is my favorite vegetable.

  13. My apologies for the busted link below. Click here for the correct page. I like that journalists are either feeling permission to be skeptical toward pop evo psych or that it was never taken as seriously as I have come to imagine that it was. See e.g. this recent Sharon Begley piece.

  14. I saw a study a while back (but can’t find the paper now) which said that swallowing semen made subsequent miscarriage less likely, perhaps by priming the woman’s immune system not to react against some protein present in her mate and any foetus fathered by him.

    In this situation, the ideal evolutionary strategy would be to for a woman to give her mate fellatio a few times before marrying him and then NEVER EVER again. You will notice that this is a shaky argument confirming a cultural stereotype; it is therefore, by evo-psych standards, 100% TRUEFACT.

  15. NOT THE FAAAAAAAAAAAAAAACE!!!!! unless you really want to get barfed on. (For realz.)

    Second option: spit… back in his face.

    Funny thing – I’ve never had anyone ask twice…..

  16. As a urologist, I should point out that fructose, not lactose is the sugar found on the seminal vesicles to support sperm nutrition and energy. Lactose of course, is the sugar found in milk, which would add more problems to those lactose- intolerant swallowers.

  17. I’m guessing it is a bonding thing. If semen tasted like chocolate it would be no big deal if a woman swallowed. Because it does taste unpleasant for most women it increases the bond between man and woman. It is usually quite big thing when the woman swallows.

  18. That’s interesting. I always found the taste inoffensive, but the texture repugnant. Then again, I’ve disliked swallowing thick liquids since I was a kid too young to know anything about sex. Don’t know whether it was too many doses of nasty and bitter liquid antibiotics, or miserable tooth sensitivity that made me hate even ice cream and milkshakes, but the stage was set for me long before sex became an issue.

  19. Okay – what am I missing? The whole premise seems non-sensical to me, since neither spitting nor swallowing is an effective way to avoid the taste.

  20. You have a point there, I agree with you. and also if it tasted good then females wouldve had to evolved also accordingly to enjoy the taste and bring forth their offspring due the fact that they want to have em too…..

    question would be, what type of semen flavour would grant you more offspring, sweet flavored,a more meaty flavour or what. What are the tastes that women prefer….

    great post, keep up the good thinking process going

  21. Good science, man. I’m a sucker for headlines like that. I’m surprised no one’s used the word ‘cannibal’ yet. Is that too far off? Ingesting semen is a form of cannibalism, and evolutionary forces tend not to encourage cannibalism. Sorry, Hannibal. As for leaving out the gay perspective on all this, well, there’s just no pleasing some people. I’ll email the Village Voice or the Stranger about it immediately.

  22. At least the idea merits good laughter. I mean, seriously, who thinks “Hey, that stuff tastes terrible! From now on, release it in my vagina!” *eye-roll*

    Wait a minute… I watch the Maury show… Perhaps you’re on to something here! As we evolve, clearly we become more stupid!
    Now spray it in me!

  23. Yes, the lack of comparative data of the gay male population was surprising, but not surprising.

    Speaking for myself, I love the taste and texture of spunk. From my non-scientist point of view, George @ #32 is correct, diet affects the taste, which is one reason I’ve discouraged boyfriends/partners from eating fish.

    As the Bronski Beat song says:

    The sweetest taste of all
    Is a man loving a man

  24. I am an evolutionary psychologist and I must say I’m quite puzzled at this post. While the intention behind it is not entirely clear to me, it has been cited and linked on the internet as a mockery of evolutionary psychology; however, it appears to betray a lack of familiarity with the way actual research in EP is done.

    Prof. Coyne implicitly conveys three messages about EP, all of them inaccurate or misleading: (a) EPs draw hypotheses from thin air, perhaps “on a moment’s reflection” – with no connection with previous theory or evidence, or to biological theory at large; (b) they are easily satisfied with untestable hypotheses, and do not try to derive new and testable predictions or to evaluate alternative hypotheses; and (c) the only way to support an evolutionary hypothesis is through direct observation of non-existent counterfactuals (“If women gave birth through their stomachs, semen would taste great”) or demonstration of present effects on reproductive success (“Those males with genes giving them better-tasting semen will leave fewer offspring than other males”).

    What would an actual evolutionary psychologist do? A serious way to start investigating this topic would be to frame it in a broader theoretical context, e.g., the evolution and function of non-reproductive sexual behaviors (which abound in humans). This is not my field of expertise, but I’m pretty sure there is some good literature available (on both humans and nonhuman animals). Oral sex is just a specific example of this class of behaviors, and it may turn out that the present hypothesis needs substantial revision in the light of previous research.

    Then, alternative hypotheses should be entertained and detailed: is the postulated aversive effect an adaptation on the part of males, females, or both? Is it a necessary byproduct of other adaptations (e.g., substances that counteract the acidic environment of the vagina)? At this point, an actual EP would -strive- to derive new and testable predictions from the various hypotheses, and to test them empirically if feasible. It turns out that several informative questions can be asked (depending on the specific hypothesis). For example, is the taste only aversive to females? Do taste preferences shift at different phases of the ovulatory cycle (e.g., more aversive feelings when fertility is high)? How does such variability relate with other forms of taste/smell aversion? How does oral sex covary with other non-reproductive behaviors? And then, what happens when a woman finds the taste aversive – does this actually increase the likelihood of penile-vaginal intercourse? Do males and/or females find oral sex less pleasurable when the woman is fertile? Are there meaningful correlates of individual differences in taste preferences? Are the same molecules found in species that do not practice oral sex? Are they only found in humans? And so on.

    Answers to these questions may indicate special design, and provide convergent support (if not definitive proof) for an evolutionary hypothesis without “counting babies” (which has problems in itself, not just with humans) or performing unethical manipulations. In the end, one of the hypotheses may actually become so plausible compared with the alternatives that we would have good reasons to endorse it. Or it may turn out that the hypothesis does not make sense after all, or that it just makes the wrong predictions. Or there may be equivalent support for two (or more) hypotheses, thus leaving the question open for future investigation (e.g., future biochemical studies may conclude that some of the substances contained in semen do not seem to have -any- plausible function, except for tasting bad). Just standard science, after all.

    Note 1: The idea that EP hypotheses are unfalsifiable (I know this is not what prof. Coyne is arguing here, but many seem to believe it) is discussed at length in [Ketelaar, T. & Ellis, B.J. (2000). Are evolutionary explanations unfalsifiable? Evolutionary psychology and the Lakatosian philosophy of science. Psychological Inquiry, 11, 1-21]. A good introductory discussion of evidential support in EP can be found in [Schmitt, D. P. & Pilcher, J. J. (2004)Evaluating Evidence of Psychological Adaptation. How Do We Know One When We See One? Psychological Science, 15, 643-649].

    Note 2: I encourage those interested in knowing more about actual EP research to have a look at the latest issues of journals such as Evolution and Human Behavior, Human Nature, and Evolutionary Psychology. Evolutionary Psychology is open-access, by the way (www.epjournal.net). I’ve found that all too often people form an opinion on EP research based on second-hand newspaper reports (often inaccurate or grossly misleading) and popular books (not all of them are of good quality).

    1. very interesting read. no one seems to put forward any reasoning for oral sex. I would suggest it has nothing to do with the quality or taste of sperm but the arousal to help reproduction.

  25. Why do you think semen tastes bad?

    My own tastes sweet the rare time I’ve tasted it, I guess the fructose content is higher than average?

    While it’s a minority, I read in Dan Savage’s sex advice column that there are some men (straight as well as gay) who regularly eat their own semen after masturbation (not me, but hey, whatever).

  26. This, of course, presupposes that mammalian sexual behavior is all about reproduction and nothing else. This ignores the very real role played by sex in creating and maintaining social bonds and generally catalyzing all manner of reciprocity behavior. Our near relatives the bonobos seem to spend a disproportionate amount of time doing this.

    Of course the ultimate roots of sexual behavior are reproductive, but is that all it has to be? Not if you take into account the role of preadaptation in evolution. Feathers, for example, had to predate flight and were probably originally had an insulation function. Later evolution “retrofitted” them for flight. It seems clear to me that sexual reproduction and its associated reward mechanisms have been similarly retooled through the course of mammalian evolution.

  27. Based on this research – I think the case could be made that only gay scientists semen tastes bad and therefore, a new, double blind study needs to be performed in college dorms across the country. And when I say double blind, I mean double blind folded. Any volunteers from the audience?

  28. Actually, for those really interested in the behavior of gay men…there are many, like women who don’t like the taste of any semen at all…. but I have notice a larger number of men who LOVE the taste of another man’s semen – but NOT their own! Its as if there is some natural sense that our bodies know that they want to accept someone else’s, but that there is no need or desire to ingest our own.

  29. I was wondering if anyone had an explanation based on Evolutionary Psychology for those rapes by females that are happening in Russia these days. They do not seem to have been directly addressed on the “a natural history of rape” hypothesis.

    Perhaps… hardcore alpha female instincts… sometimes… the environment triggers an alternative modular behavior in females, forcing them to be much more assertive than they usually are, in order to reproduce better somehow.

    Maybe somewhat like saigas, which, due to the hunt for male horns, are inverting the sexual selection typical behavior, with females guarding male harens from other competing females.

    That also should be an alternative behavior naturally selected, of course. There’s a brain switch, that is activated according with the perceived number of males, more or less like with the specialization on ant morphs.

    (Beware of Poe’s law)

  30. As a hypthesis doesn’t it leave things left to be proved right or wrong?

    Even so hypthesis being proved wrong and being recorrected.

    There are a lot of variables disregarded in these statements. Can you take 30 females/subjects that all dislike different things in taste and compare the results? If 15 dislike sardines (lets say) and the rest favor them could, this discount accuracy the of the results? I think that too many things could play into the actual outcome of whether or not semen can, just by taste, be disqusted. Things like age, sexual experience and interest, background, sense of taste, all of these and more can play into this. I’ve had partners that have disliked, liked and utterly enjoyed ejaculation in their mouths and swallowing it. All were completely different people with different ideas and opinions on what they enjoyed. Some had more sexual experience than I had while others were just newbies. You have to experiment to figure what it is actually truth and even then truth is left to be refreshed and changed. Some women may dislike the taste but that may not keep them from swallowing, primarily based on the fact that their sexual arousal was on a level where that was more arousing for them. Try to keep an open mind. Statements made without experience leave room to be torn apart and disregarded, and with experience I mean REAL hands on experience, not seconhand knowledge or opinionated study.

  31. The first book of the Losing My Transmission trilogy introduces college student Terry Johnson in 1992, just before the events that alter his already distorted view on life caused by a traumatic brain injury from a car wreck.

  32. The Great Sperm Race is an interesting documentary on the battles sperm face once inside the vaginal tract-quite a tragedy! You can find it on Youtube. Besides the documentary, I’m wondering if it is possible for sperm to evolve to outsmart the condom (I’m assuming this would take thousands of years)? I know the shape of the vaginal tract accounts for sperm variation.

  33. I’m a gay man. Some times I spit and some times I swallow, and it doesn’t depend upon the taste. For me, the difference depends upon how “horny” I feel at the time, also, ingesting semen affects my stomach, for some bizarre reason – leading to my hasty departure for the toilet…. Semen acts as a very strong laxative… I don’t know why….

    As an “aside”, in evolutionary terms – i.e. “survival of the fittest” – why do gay men and women still exist in society? Aren’t Genes supposed to “improve” after thousands of years? I can only guess that, in the absence of moral society, that the Alpha straight male would, ordinarily, have killed many gays (well – other men who are gay, leaving the gay women behind….)) and “don’t even get me started” about the irony that some str8 men are turned on by observing perceived lesbianism…..

  34. I was just at an event and a company was there that was marketing a strip (think Listerine) that you dissolved on your tongue prior to the act and it conceals the bad taste of semen. I was highly skeptical. However, I tried it on my husband and it works! Truly made it taste like chocolate. Masque.


  35. I have tasted several mens seman. Its like certain foods or a gag reflex, its not for everyone. My mans pre seman & seman is sweet like the taste of sweet nectar. I am not joking. It does not taste like a nectarine but to explain the sweet level. I taste no salt, no foul taste. It depends on how clean ur man is too.You can get the extra salty taste off his penis if he is sweating, or a metal taste if he has not bathed (gross, I hv not experienced the salt or metal taste with my current& hopefully life long man) othrs 8 hv.
    I love to swollow, I do not spit. I do it for him& I enjoy every minute of it, sometimes crave it!

    1. What type of diet does he have? This seems to play an important part on semen taste. My man tastes sweet one day and nasty the next so I need to figure out what is different about his diet. I want to crave him every day.

  36. I am a gay man who has been “oral only” all my life and write about it in my adult website. I love the taste of semen and always have. So, since I, along with millions of other gay males like me, love the taste….what singificance does that have to scientific evolutionists?

  37. ok, so studying porn ever since i saw it was significant to others my whole life. I along my crazy life path have tasted my own semen….it was exciting, partially because it felt good to lick my own penis as a teen. I’m not gay, just scientific. and open because I’m anonymous. if I was gay. I’d probably eat my own sperm all the time. It tastes great in peanut butter and honey btw. I don’t crave the flavor though, and I did date an Asian girl and performed oral sex on her… she started to have the beginning of an orgasm and it tasted like mine, but I really loved it. the first time I ever felt addicted, but its because I really loved her. here is an analogy, a friend gives you money and you thank him, an enemy gives you money and you want to throw it back in their face, if you give yourself money, its interesting but there’s no value assigned. so moral of the story.. sex=money why else would you work you ass off all week for a family if it was just torture. sex was the original form of payment, Children are interest and investment. orgasm is money, cum is evidence of the transaction. I thought about the flavor of my girlfriend, it was very provoacative, I would have puked if I was not attracted. but since I was attracted, I wanted all I could get. still do 😉

  38. i agree that diet affects taste as my girlfriend has often told me it varies and is unpleasant after lots of meat or even bacon. this leads to my agreement with the above comments on diet especially the one about primate diet. perhaps the semens taste is an indicator to the suitabilaty of the partner both in terms of health and genetics. this could be much like other markers of suitabilaty such as scent which is affected by both diet and genetics

  39. Hmmm all I know is I love giving my partner oral sex but I will jump on him and have full intercourse rather than let him orgasm in my mouth. We are having a baby soon……. Prof you are so right- I have always thought this is the case. I love sex, I love orgasms of both of us, but boy do I hate sperm. Taste and smell! I have also noticed that once it is in the vagina the smell changes and it becomes sweet.

Leave a Reply