On Polysexuality (2/5)

by Jason Stotts

Isn’t Polysexuality Unnatural?

Before we begin our moral analysis, we must address the claim that polysexuality is unnatural, as it is the most common objection to polysexuality and the foundation of most objections to it.  However, what is the evidence that humans are naturally monosexual?  That some cultures are?  Others are not.  That some of our closest species-relatives are?  Our very closest are not.  That it is the optimal way to have a relationship?  What if it is not?  Interestingly, the preponderance of the evidence seems to suggest that humans are naturally polysexual.

So, what do we mean by “natural”?  A characteristic or trait is called natural when it is part of a thing’s nature.  By it’s nature, we mean the things that make it an X instead of any non-X.  Today, we might understand this for living things in terms of genetics and we would call a thing “natural” if it comes from our genes and develops unimpeded and without corruption.  Thus, a natural hair color is the one specified in a person’s genes, as opposed to an artificial hair color that is the result of dying it.  For humans being polysexual, we mean that humans are disposed to this because of traits in our genes.  It does not follow, however, that all things that are possibilities from our genes are good or desirable (and this point should be kept in mind), but simply that they are natural and follow from human nature.

I will not give a complete account of all of the evidence that humans are naturally polysexual, since that would take far too long; nor will I analyze the evidence from other primates in great detail.  Instead, let me refer readers looking for such an account to the very well done new book Sex at Dawn: The Prehistoric Origins of Modern Sexuality in which the authors give the full evidence for the naturalness of polysexuality (although they do not use that term), as well as copious references to support their position.  Here, I will confine myself to only the most obvious signs that humans are naturally polysexual, those that come directly from our bodies.  But what evidence in our bodies could possibly point to the naturalness of polysexuality you ask?  Let’s look.

1. Breasts

Breasts are interesting things.  Their apparent function is to feed young, but clearly this is not their only function.  If it were, then there would be no way to explain their size.  The size of a breast whose only function is to nurse would be very small, much as it is in other mammals, and they would only show when they were full of milk. Their unnecessarily large (for nursing) size, points to the fact that breasts must have another very important function that influenced their current state.  This function is signaling fertility and reproductive availability.  If they did not serve this function, we should expect them to be smaller and/or less prominent.  Their size would be an evolutionary disadvantage if they simply were for nursing.

Furthermore, the sensitivity of the nipple is perplexing as well.  A breast that was only for nursing would be better if it had little to no sensitivity, since, as any woman who has nursed can tell you, nursing can be quite painful and this pain is a disincentive for a mother to nurse her young, thus potentially leading to her young being undernourished, underweight, less viable, and therefore less likely to carry on her genes.

2. The Vagina

In large primates where females only mate with one male, such as gorillas, gibbons, and orangutans, the female’s vagina is oriented towards the back, in order to facilitate rear-entry sexual intercourse (SAD, 221).  In the polysexual large primates, like the bonobo, the female’s vagina is oriented towards the front, facilitating front-entry sexual intercourse (missionary position).  Thus, the orientation and position of the vagina is strongly correlated with polysexuality or monosexuality in large primates (SAD, 224).  Since the human vagina is oriented towards the front and this is strongly correlated with polysexuality in primates, this is strong evidence of at least a polysexual human past, since humans are large primates.

More important than the vagina’s orientation is the fact that the human vagina actively attacks sperm with leucocytes in the vaginal tract (SAD, 264).  Not only that, but the complexity of the human female cervix acts to filter sperm (SAD, 265).  This would be completely unnecessary in a monosexual species, in which sperm competition would not exist and where there would never be different kinds of semen in the same vaginal tract at the same time.

3. The Penis

The human penis is enormous!  Adjusting for body mass, the human male penis is 0.163cm/kg.  Compare this to an orangutan (0.053) or a gorilla (0.018) and you can see just how big it is!  The only large primate with a larger relative penis is the very polysexual bonobo.  In absolute values, the human male penis is by far the biggest at 13-18cm, compared to the bonobo (7.5cm), the orangutan (4cm), or the gorilla (3cm) (SAD, 230).  This would be absolutely unnecessary from an evolutionary standpoint in a monosexual species where a male would not be competing to inseminate a female, since a longer penis deposits sperm closer to the cervix, helping to ensure that more sperm make it into the uterus to attempt to fertilize the egg.

The unique shape of the human penis is almost irrefutable evidence of a polysexual human past.  The uniqueness is in the shape of its head, or glans, and the coronal ridge, which has been demonstrated to create suction in the vagina during intercourse.  The function of this suction is to remove sperm from other males that might already be in the vaginal tract (SAD, 234-235).  This it does very effectively, with studies showing up to 90% displacement with a single thrust (SAD, 235).  In order to not remove his own sperm from the vaginal tract, the head of the penis shrinks immediately after orgasm, so that the final thrusts or removal of the penis will not displace any of the male’s own semen (SAD, 235).  If you combine the unique shape and function of the head, with the length and girth of the penis, then what you get is a very efficient tool for both removing the sperm of other men and replacing it with your own as close to the egg as possible.  Really, the human penis is an evolutionary masterpiece.

4. The Testes

Evidence from the testes alone is almost sufficient to prove the fact of a polysexual human past.  First, having external testes is a great disadvantage for a male, as any man can attest, and would not have been naturally selected if it did not have a very important function.  By having external testes, a man is risking an incapacitating attack on his testicles and injury to his most vital reproductive organ.  The very existence of external testicles is a great evolutionary disadvantage and would only have been selected for in order to achieve a very important end (this should not be taken as a purposive teleological claim).  In monosexual, or mostly monosexual, larger primates, like the gorilla, orangutan, or gibbon, the testes are safely housed inside the body.  This prevents them from being used to easily incapacitate or injure the male.  The reason that polysexual primates have external testes is to maintain them at a cooler temperature to facilitate the storage of semen (SAD, 237).  This allows the male to have larger quantities of viable semen available at all times.

Second, the size of human testes, combined with their productive capacity is way beyond what any monosexual primate might need.  In absolute size, human testes are not the largest at 35-50grams, compared with the bonobo (118-160g), but they are larger than both the orangutan (35g) and the gorilla (29g) (SAD, 230).  However, in terms of productive capacity, seminal volume per ejaculate, humans are by far the highest at 2-6.5mL, compared to even the bonobo (1.1mL), the orangutan (1.1mL), and especially the gorilla (0.3mL).  So, even though the human testes are not absolutely the largest, they are far more productive compared to other higher primates and dramatically more efficient at producing semen per gram of testicular tissue.  This evidence, while being compelling, is certainly not enough to prove a polysexual human past; in order to do that, we need to take a look at the function of sperm itself.

In a study where researchers captured the different spurts of male ejaculate, which comes out in a series of discreet spurts, they found something surprising: not all sperm have the same function.  For much of medical history, after it was understood that sperm fertilizes eggs, it was assumed that the function of all sperm was to fertilize eggs.  This, however, we now know that this not true.  Semen is made up of different types of sperm, in addition to those that fertilize the egg.

The first spurts [of human ejaculate] contain chemicals that protect against various kinds of chemical attack…[like] leukocytes and antigens present in a woman’s reproductive tract…[and] from the chemicals in the latter spurts of other men’s ejaculate [which] contain a spermicidal substance that slows the advance [of other men’s sperm].  In other words, competing sperm from other men seems to be anticipated in the chemistry of men’s semen, both in the early spurts (protective) and in the latter spurts (attacking).  (SAD, 228)

The fact that the very composition of human sperm has evolved to deal with the presence of other men’s sperm in the vagina of a woman points unflinchingly, and inarguably, to a polysexual past.  There is simply no other plausible explanation for this to exist in all human males at the current time.

5. Orgasmic Disparity

Most of us who are sexually active and experienced know all too well that there is a very large disparity between the male and female orgasm.  The male orgasm takes a comparatively short time to reach and requires a physiological refractory period between orgasms.  The female orgasm takes a comparatively longer time and requires no physiological refractory period.  Indeed, while most men orgasm fairly quickly and then cannot orgasm again for some time, women take longer to orgasm, but can repeatedly orgasm with no loss of tumescence (physical arousal) or desire.  This is a most unfortunate combination and leads to the common complaint in couples that the man orgasms “too quickly” and then is done or that the woman takes “too long” to orgasm and then might still be aroused and ready for more after her partner is already satisfied.  Indeed, there is a fundamental mismatch here, if we assume that humans are naturally monosexual.  However, if we do not make that assumption, then the origin of the problem becomes clear.

On a one male to one female basis, human orgasmic response makes no sense.  But, if we have a polysexual past that includes women having sex with multiple men, in order to get the best possible semen, then it’s obvious why men would need to orgasm quickly and women would need to take a long time.  If a man were to take too long to orgasm, he might not have time to finish and deposit his semen.  If a woman were to orgasm too quickly or lose interest in sex after orgasm, then she might not get the best sperm inside her, because she would stop being receptive.  Thus, the orgasmic disparity problem is a function of an unnatural monosexuality and is not a problem inherent in men or women themselves.

I personally think that the question of whether polysexuality is natural is now a closed question: polysexuality is natural and monosexuality is unnatural.  This does not, however, mean that polysexuality is the ideal situation for all people or couples.  Furthermore, it does not mean that polysexuality is a moral ideal or even that it is morally permissible.  These questions are still open and we need to take a critical look at them.  However, we must keep in mind that polysexuality is natural and that all claims against it based on its non-naturalness are misplaced.


Big Brother Note: if you click on the Amazon.com link and purchase Sex at Dawn: The Prehistoric Origins of Modern Sexuality, then I will receive some small amount of money in compensation.  Thus, if you are going to buy the book, please do it via this link and help me out.

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8 Responses to “On Polysexuality (2/5)”

  1. Aaron

    While I generally agree with the conclusion about what is natural, I am not convinced most of the evidence here supports it.

    Larger testes and sperm storage definitely correlate with polysexual species, and I agree with that as significant evidence. Vaginal orientation comparison between species also seems strong.

    The orgasmic disparity claim is very specious, however. It would imply as the norm not merely polysexuality but outright ‘gang-bangs’. Further, there’s essentially no opportunity for similar cross-species comparisons due to lack of evidence of female orgasm in almost all species.

    Breast and penis size certainly suggest sexual selection at play in favoring large size. However, sexual selection could occur without regard for mono vs. poly.

  2. William

    How does the orgasmic disparity claim imply a rapid succession of sexual intercourse? “Pregnancy has been shown to result from intercourse as long as five days before ovulation” (http://humupd.oxfordjournals.org/content/12/1/23.full) so that means four days for other men to have a go.

  3. William

    My cursory search indicates evidence for non-human female orgasm is scanty. Indirect evidence exists for at least two species (Japanese macaque and brown greater galago):
    (references http://dx.doi.org/doi:10.1006/anbe.1998.0898)

  4. Kelly Elmore

    Kind of an unimportant note, but here it is. Breastfeeding, when done right, is painless after the first week or so. I suspect that if breasts were exposed to the elements as they would have been before clothing, even that initial desensitization might be avoided. But pain while nursing is not normal. It’s even conceivable that sensitive nipples that detect pain might indicate a bad latch, which would draw less milk and increase breast infection. Nipple pain might be the same kind of pain signal that we get from a cut or a burn or a muscle injury.

  5. JasonStotts

    Aaron and William,

    The orgasmic disparity doesn’t necessarily point to anything other than the fact that females stay sexually receptive longer than males and need more stimulation than the average male can give them (through intercourse alone) in order to orgasm. This seems to indicate that this is a relic of a polysexual past. Not necessarily “gang-bangs,” but perhaps two or three men in one sexual session. Interestingly, this is not abnormal behavior for bonobos, our closest primate relative. Also, the fact that semen can live in the vagina for up to five days is rather irrelevant to why females take more time and stimulation than do men.

    Part of the problem is that when we try to infer back to things that happened thousands of years ago, the evidence we have is often sketchy at best. Here, I want to suggest that the preponderance of the evidence points to a polysexual past, but not that every fact above is its own knock down case for polysexuality.


  6. JasonStotts


    That is a very good point and I’ll likely remove that for the final version of the essay.


  7. D. Bandler

    But, if we have a polysexual past that includes women having sex with multiple men, in order to get the best possible semen…

    This is the “Sexy Sons” hypothesis and it is very popular in evolutionary circles. Evolutionary psychologists will go from this to arguing that human females are “hypergamous”. Hypergamy means that women are biologically “wired” to mate with the highest ranking alpha male that she can get with her youth and beauty. This, by the way, is the entire basis for the cultural phenomenon which was formerly known as PickUp but which is now know as “Game” (think Mystery Method).

    It will be interesting to see how you deal with this. The evolutionary crowd approach all things genetics with a strong determinist bent. But as an Objectivist, I imagine you will stress volition. But it does raise some interesting questions that if our evolutionary past has “wired” us for polygamy and promiscuity, just how natural is it for monosexual relationships? And how realistic is the institution of marriage? Especially the “till death do us part” element?

    Fascinating subject. I’m glad you are trying to tackle it.

  8. Erosophia

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