Security Considerations in the Evolution of the Human Penis

Fascinating bit of evolutionary biology:

So how did natural selection equip men to solve the adaptive problem of other men impregnating their sexual partners? The answer, according to Gallup, is their penises were sculpted in such a way that the organ would effectively displace the semen of competitors from their partner’s vagina, a well-synchronized effect facilitated by the “upsuck” of thrusting during intercourse. Specifically, the coronal ridge offers a special removal service by expunging foreign sperm. According to this analysis, the effect of thrusting would be to draw other men’s sperm away from the cervix and back around the glans, thus “scooping out” the semen deposited by a sexual rival.

Evolution is the result of a struggle for survival, so you’d expect security considerations to be important.

Posted on May 5, 2009 at 1:39 PM45 Comments


mcb May 5, 2009 1:54 PM

“Change that to ‘Security Considerations in the Evolution of the Human Penis'”

I hear that. I’d like to think that if mine had been designed it would have been…uhh…different.

BF Skinner May 5, 2009 2:14 PM

April 1st already? Wow that was a fast year.

Just goes to show you there ain’t no intelligent design.

Craig May 5, 2009 2:18 PM

It would be interesting to try to validate this idea with a controlled experiment in which a large number of women have sex with several men one after another (with detailed records kept, of course), and for those that become pregnant, do paternity tests to see if there is a statistical correlation between successful impregnation and the sequence of partners. That is, would real-world experience verify that the first man in has less of a chance of fathering a child, as this theory suggests? Does the last man in have the best chance?

I’m sure there’s some reason that no reputable university would ever sponsor this study…

Some Guy May 5, 2009 2:26 PM

Trouble is, there’s also evolution that works the other way. Some of the sperm that get in don’t even try to fertilize the egg; they interlock tails to form a barrier, acting as a “rear guard” to slow down any new invader sperm from getting in. So the study would have to somehow control for such things.

All it proves is that, apparently, men are biologically programmed to assume their girlfriends are sluts.

HJohn May 5, 2009 2:40 PM

@Someone had to say it at May 5, 2009 2:32 PM

I don’t know which has right of way, but I think a tie would go to the sword.

@Craig at May 5, 2009 2:18 PM

It’s only a matter of time before there is a Clinton-U. 😉

Don’t I just crack you all up? Probably good I passed on the career as a comedian.

Fun topic, although I would hesistate to verify its success or failure in my life. My wife would, in those immortal words, “have some ‘splainin to do.”

Mackenzie May 5, 2009 3:05 PM

So uh…where’s the security aspect? I can kind of get that trust has broken down if one partner in the relationship has multiple partners without that being agreed to ahead of time, but what’s that got to do with dick shape?

rbtroj May 5, 2009 3:17 PM

Speaking from a strictly scientific perspective, in order to maintain this features usefulness women need to be putting out all the time.

Otherwise, I imagine it’s effectiveness shrinks rapidly (especially in cold water).

David Harper May 5, 2009 3:31 PM

I seem to recall that there are some species in which the male’s penis breaks off during copulation and remains lodged in the female’s reproductive tract, thereby preventing other males from mating with her.

Of course, the poor male only gets one shot, so to speak, but he’s pretty much guaranteed to be the daddy, and that’s all that matters in Nature.

Chris Hallgren May 5, 2009 3:33 PM

So, apparently what we need is the software equivalent of the “coronal ridge” for Windows – to “suck out” all the inferior code, viruses and hacks. Hrmm, interesting design approach.

Ralph May 5, 2009 3:46 PM

If that were true, then it would also seem to follow that, eh, viscosity and “gluiness” would also increase greatly to counteract the scooping out effect.

Another solution would be no loss of, er, firmness with multiple emissions over a longer time period in order to increase one’s chances and decrease the opportunities of others.

bethan May 5, 2009 4:23 PM

The third tenet of security is response, and one aspect of response is to repair. this is like evolutionary repair.

Trichinosis USA May 5, 2009 4:45 PM

@ Chris Hallgren:

What does that say about x86 architecture? And then there’s that whole Big Endian versus Little Endian aspect…

Andrew May 5, 2009 5:50 PM

Oh, dear. How low can we go? When the discussion is how men go about attempting to control the sexual behavior of women with other men, quite low indeed.

We proceed from security design (penis shape, sperm conflict and motility, ovulation and female orgasm) to engineering controls (such as clitoridectomy, infibulation and circumcision) and work practice controls (missionary position, monogamy, adultery and fornication punishable by death), as well as prohibitive signage (burqa, veil, wedding ring, chadri, Mormon temple garments, etc.)

See also Sperm Wars among other texts.

The real security issue here in my arrogant opinion is the emerging field of “human security,” or the radical idea that a people-centered (rather than state-centered or organization-centered) view of security issues is essential for human liberty and global stability.

Andrew May 5, 2009 5:51 PM

Is it really necessary to eat URLs nowadays? I posted the Amazon link to that book and it burped.

John Moore May 5, 2009 6:16 PM

Rampant speculation likely based on little empirical evidence. Considering how taboo the subject is and the scantiness of current and past studies and their limitations due to these taboos, this field could be considered to still be in its infancy. We don’t even have reliable stats on the numbers of illegitimate children born within a given human population, so we don’t even know if this security feature even works. Since STDs are prevalent, likely it doesn’t work.

paul May 5, 2009 6:47 PM

Of course, you’d have to examine the penes of lots of primates and mammals to see whether this actually has anything to do with human beings or instead is something that’s been conserved more or less by accident from some distant ancestor. In security, as in other fields, it’s important to know the history of legacy systems before speculating on the purpose of particular features.

Brad Templeton May 5, 2009 7:21 PM

It’s rather amusing reading the comments of the guys who say “this assumes she has just recently had another male.” Of course she has, if you’re talking about humans in our natural state while we (and our ancestor species) were evolving. Read the book “female promiscuity” and you’ll learn that this is by far the norm in nature, and all sorts of approaches to counter it (and enhance it) have evolved.

To shock you more, studies show that a woman is more likely to have sex with a man who is not her partner when she is at her most fertile, just before ovulating. Her strategy is to bind a partner to help her raise the children, but to try not to give all her eggs to one male. Better to give her offspring a more diverse set of fathers to improve the chances her line will continue.

If you didn’t do things to make your line continue, then… it probably didn’t, and so you are not relevant to our genome.

supersaurus May 5, 2009 7:23 PM

ok, now explain why the testicles hang down there where every passing hazard can attempt to knock them off? and please…don’t give me the “because they need to be a little cooler than body temp” argument, evolution could have just as well made them hidden way back in the pelvis.

Beta May 5, 2009 7:26 PM

@Some Guy: “All it proves is that, apparently, men are biologically programmed to assume their girlfriends are sluts.”

No, it has nothing to do with male opinions or consciousness. IF this feature (or the “rear guard” feature you mention) is real, then it shows that human females have in fact always been sluts, at least often enough to, er, shape male evolution.

Greg May 5, 2009 9:25 PM

@Some Guy:

Well, you know what they say: “men want Jackie O at dinner parties, June Cleaver in the kitchen, and Linda Lovelace in the bedroom”

Blackbart May 5, 2009 9:48 PM

Aahrr, with this subject, young Mr ‘awkins,
yer kin now spill yers secret beans.

Penis Haver May 5, 2009 11:08 PM

It’s a cute theory and shows that some people get to do nice stuff at work, but it’s a bit biologically unfeasible.

Sperm cells are feisty little racers, swimming at around 1-4 millimeters a minute. Also, the egg cell isn’t waiting in the vagina – impregnation happens a bit further up. So, nice idea, but I’d put that down in the “give me more research grants because I said penis” bin.

tensor May 6, 2009 12:34 AM

As other commenters have noted, our society’s hangups on this topic make this area of research an, um, new and fertile field. (Dodges thrown tomatoes.)

If I recall my history properly, then monogamy is a relatively new construct for our species; humans lived in tribes, not nuclear families, for most of our history; children were raised communally. Furthermore, in a pre-industrial society, most children were either stillborn, or died young; the (ignorant) assumption of conception = child was even worse in those days; even now, most conceptions do not survive to term. (Recalling college biology from memory here.)

In sum, this “research” tells us a lot more about our cultural norms than it does about the hydrodynamics of vaginal fluids, or evolutionary responses thereto.

Anon May 6, 2009 2:17 AM

So, if women would practice polygamy or some other kind of multiple sexual relationships, then men should evolve larger penises…

Pedant May 6, 2009 3:51 AM

@Some Guy and @Beta:
A woman who has a lot of sexual partners is not a “slut”. A slut is a slovenly woman. If anything, a slovenly woman is less likely to attract a lot of men than a woman who keeps herself looking attractive.

Benty May 6, 2009 4:38 AM

Are you going to use this as an analogy for why penetrative testing of firewalls is a good idea? 😉

Bruce Barnett May 6, 2009 5:56 AM

Besides replacing competitor’s sperm, it can also replace old sperm from the same donor.

Tom May 6, 2009 6:01 AM

Other species have much more impressive (and much more obvious, to counter Urani Dot’s claim that these are ‘fairy tales’) modifications for much the same purpose. Steve Jones’s book Y: The Descent Of Man goes through them nicely.

David Teesdale May 6, 2009 8:37 AM

Excellent work here Bruce; on a more humorous note, there could be a euphemism somewhere…

Adrian May 6, 2009 12:14 PM

I thought the main security consideration for the human penis was protecting it from damage. As human beings are tool-using animals, the most effective development for penis security would seem to be the invention of the jockstrap (or possibly the rigid cup.) If a man has sex with a woman but doesn’t conceive a child with her, that’s not a security failure. If some large animal he’s hunting claws him between the legs, or a horse kicks him wrong, that’s a serious security failure.

I appreciate the SUNY researchers’ delight in applying for a grant to play with sex toys. But the research itself looks incredibly shoddy, even before the anthropological speculation. A few minutes of sex deposits a lot of semen in the vagina, some in the cervical mucus, and some beyond the cervix. Sperm can survive for several days in the cervical mucus. Therefore?!?! they conclude removing some of the semen from the outer part of the vagina makes a woman less likely to conceive. Do they also think douching with Coke the morning after sex will prevent pregnancy?

I used to expect better of Scientific American. sigh

havvok May 6, 2009 12:38 PM

Amazing how quickly the usually intelligent discourse on this blog quickly degenerates into thinly veiled locker-room jokes when the word “penis” is mentioned.

Andrew W May 6, 2009 12:45 PM

@mackenzie Evolution has little to do with trust. Penis shape presumably evolved back when our ape forerunners (or earlier I guess) did sleep with multiple partners.

El Snarko May 6, 2009 2:08 PM

“Use contraceptives at every conceivable opportunity”…

Regardless, human reproductive biology differs from just about all other mammals on this planet by “hidden estrus”… and that would have broken the back of the “Alpha Male”. Humans had to learn to communicate in order to keep a female occupied until a male’s seminal vesicles re-charged.

So all of civilization can be blamed on the refractory time in males.

“If someone ever publishes a unified theory of human personality it will consist entirely of exceptions” – someone else

Andrew Yeomans May 7, 2009 1:00 AM

This research seems to have a lot in common with information security. Let’s take a complex hypothesis (c.f. some fancy box of tricks will make you more secure), demonstrate that it could work, and then deduce that it must be true (and you must need the box). Unfortunately a lot of “evolutionary science” seems much like this, designed to “prove” some vested interest, and with little chance of being falsifiable.

What about alternative hypotheses (or alternative means of security)? In this case a more obvious hypothesis is that it makes sex more pleasurable, hence more likely to produce offspring.

Pauli’s comment of “not even wrong” seems appropriate here. And in much information security too?

Sai Emrys May 7, 2009 5:40 AM

Come on; this is purely magical thinking.

What the ridge does or does not do is a just so story. There is no evidence that it evolved for that purpose: claiming that it did is as bad a teleological fallacy as committed by Creationists.

I’m surprised you’d fall for this.

Clive Robinson May 7, 2009 10:39 AM

Oh dear are you lot outside of Europe so poorly educated due t religeous hang ups?

A little History on evolution and why Darwin published when he did might open a few eyes (he sat on it for around fifty years scared of how society would treat him and only published when he found out another person was in the process of publishing the same idea). Oh and incidently Darwin was not the first on evolution nor to step upto the plate against the slings and arrows of public opinion he was the one who survived proving yet again that being just behind the bleeding edge is a sound evolutionary stratagie 😉

Some basic facts,

The Bee has an unusual sex life go look it up you will cross your legs. Likewise with the spiders and mantisi and other “two brained” creatures.

If you want to know which sex is in the driving seat go look up the button might and what a femail does if she is not mated.

Talk to people who keep ferets or other of the pole cat species. Then find out why the domesticated cat has barbes on it’s penis and why religion used to burn them, despite theit proven utility to man.

And guess what the big cats have sexual distinctions that we humans males just cannot compeat with. Forinstance the male lion will mate over fifty times a day for various reasons (go look them up) but avarages just over six seconds a time.

The flea has a penis length of around a third of it’s body length, the sea urchine tops the scale with a length that would be around sixty feet in humans.

Now onto primate studies the females behaviour dictates not just the size and shape ot the penis but also the testies.

Size for size the most faithfull species has the smallest of both, the least faithfull the largest testicals.

There is a particular type of monkey that has sex all the time just for pleasure and social coheision often the female virtualy continuously and certainly whilst eating groming her offspring and others.

Guess what the size of testies and social norms in humans is well documented. The smalest by race is in oriental societies the largest in North western Europe. However the stronger the religeious norms or where polygamy has been practiced for over 200years reduces the size against racial norms by around 25%. Oddly the same shrinkage is found in the brains of domesticated-v-wild creatures particularly mamals after a similar number of generations.

On avarage the US collage male testical is 15% smaller than the western European male (oh and you are something like 40% less fertile acording to one or two studies). Then there is the size of the penis in the US you are again around 3-4cm shorter in lenght and around 2cm less in circumfrance on raicial norms. This is so well known it is written into standards for condom manufacturing…

Now humans are diferent than other primates in certain repects when it comes to sex organs and size shape and colour…

I won’t go into all the details go look them up yourself. But,

Woman select the size of the male penis and the ability he has to keep her on her back for the first few minutes after sex. Go look up the expected fertility rates for various sexual positions and you will find out why the “missionary position” is so called. In primarily Roman Catholic Countries where “girls on top” is practiced the fertility rate is down almost to that of IUD and other contraceptives even where sexual promiscuity is known to be excedingly high. Oh and the Churches thing with marage only started after VD became prevalent.

Now for another bit of bad news for us men.

During a study in the UK in the early days of genetic/DNA testing it was found that as many as 30% of men tested where not the genetic fathers of the child. It is one of the main (but unspoken) reasons that the UK has laws to stop the father of having paternaty tests without either a court order or the mothers written consent. It is also why the Child Support Agency tries to prevent alleged fathers having independent paternaty tests and makes them pay well over the odds for it and delays the process as long as possible whilst also taking money for child support directly out of the wages. And when it is proven the man is not the father find every excuse imaginable not to give the money back or in drips and drabs, loses test results etc. But importantly the CSA pretends it will use DNA testing to stop males appealing charging orders etc.

Oh and judjing by other studies male on the health benifits of circumcision, we are obviously dirty by habit, cervical cancer is virtualy unknown in races where circumcision is practiced and their are strong racial predudices in place (again look it up).

Oh and just by coincidence in the flat above me the woman is at home her husband is out at work and due to the thin ceiling between the flats I know she is engaged in pleasurable sexual activities right now as she does around 3 out of 5 weekday afternoons before her children come home from school, and if I was female and had her looks and stamina I think I would do the same 😉 oh and altleast two of the partners know each other as they live in the flat opposit her and double up and she is not unknown to other men and women in the block either. And yes I think her husband knows because he is often there as well as known to bring other women and couples back to the flat for a “swinging time” and jokes quite sugestivly and knowingly with those known to his wife…

Michael May 14, 2009 6:05 AM

I like the analogy between evolution and developing security strategies (although it doesn’t necessarily have to do with reproduction).
BTW the warthog also developed an effective strategy when it comes to reproduction:
a part of the male semen thickens and forms a “plug” to seal the vagina against insemination of rivals.
Rgds, MiKa

Leave a comment


Allowed HTML <a href="URL"> • <em> <cite> <i> • <strong> <b> • <sub> <sup> • <ul> <ol> <li> • <blockquote> <pre> Markdown Extra syntax via

Sidebar photo of Bruce Schneier by Joe MacInnis.