I’d like to begin today’s Friday Weird Science with a brief story about SciMom. SciMom is a brilliant mom. She’s encouraging and supportive and smart, and also really REALLY funny. Mostly because she’s prone to say really funny things. And begin telling jokes by saying the punchline. But one day we were with my college roommate over spring break (we went to each other’s houses over spring break. Way to geeky and poor to go to the beach, I can tell you. But it was still good times) and had to stop by the grocery store. I recall we were in the bean aisle, when suddenly my mom turns around and says “you know, penises are really funny looking”.
Now you know where I get it from.
(Inserting fold due to extensively NSFW pictures...)
And penises ARE funny looking. I mean, look at this!
And we cannot forget this.
And the human penis is funny looking as well. You probably don’t think so, but that’s just cause you’re used to it. After all, ducks think that is TOTALLY normal.
On a previous Friday Weird Science, we got into a discussion in the comments of testicle and penis size in humans in comparison to other primates. In many species, testicle size in particular correlates with how many partners the female of the species has. Thus, animals like rats and right whales have HUGE balls because the females tend to have many partners (sometimes more than one at a time!). It makes sense, if your lady is going to have multiple partners, to have large balls, and produce lots of SPERM, in the hopes that you’ll outcompete your fellow males to get to be the babydaddy.
In some species of primate, this follows too, gorillas have small balls, chimps have larger ones. But what about humans? It turns out that humans fall at the higher end of the primate spectrum in terms of testicle size, but they REALLY fall at the high end in terms of penis size, with thicker penises than other primates.
Now, is this just because the males of the species need to compete? Or is it something else? After all, ball size is one thing, but penis size is another. And what about SHAPE? What’s with that big bulbous glans?
Well, this guy has a theory.
EA Bowman. “An explanation for the shape of the human penis” Archives of Sexual Behavior, 2010.
So first, some basic penis anatomy.
The shaft is at the top, and at the bottom is the bulbous head that is surrounded by a thin membraneous and loose skin which is what gets removed in male circumcision. But the question is, why is the glans bigger? Why is it that bulbous kind of shape? Scientists have previously hypothesized that the glans is shaped this was in order to kind of scoop out the semen of other males. It’s not peculiar to humans, other animals like whales have it, too.
Bowman says that this is unlikely, due to the extremely acidic pH of the vagina, which he says would immediately destroy any sperm that didn’t make it up to the uterus. I’m not too sure about this, the pH of the vagina is between 3.8 and 4.2, and sperm are well capable of surviving in there for a little while, in fact, the mucosa favors sperm survival. Another hypothesis (which isn’t addressed here) is the bulbousness of the glans as a way to increase a pressure differential during intercourse, acting like a plunging mechanism to get their sperm out and your sperm in. But Bowman thinks that scooping or plunging isn’t the point at all.
He’s got a different theory. And he thinks it’s got to do with the foreskin. He points out that the foreskin is a very absorbent membrane (and cites for this the increased vulnerability to HIV infection in uncircumcised men, though there’s no ACTUAL citation, and I’ll have to look this up). If this membrane is absorbent, what’s it absorbent FOR? His hypothesis? Vaginal secretions. Women have secretions in the vagina (duh) containing various compounds including hormones like oxytocin and vasopressin. And so Bowman hypothesizes that women secrete these hormones in their vaginas, and men absorb them with the foreskin, to promote things like pair bonding and serve as a deep evolutionary level of communication. He also notes that this means the best position is “primate rear approach” (that’s doggy style) in order to hit the posterior wall of the vagina where he says a puddle of vaginal secretion is likely to be (would love to see the citation for that one).
Sci’s got to say I don’t really buy this. There are no references cited (though I can cite a few for some of them), and…where is the evidence? Does this mean that couples who have sex with a condom (thus covering the glans and preventing absorption) exhibit less pair bonding than those who have sex without? What about the effects of hormonal contraceptives (which drastically change the vaginal mucosa) on pair bonding? And what about the effects of, you know, having a relationship with someone? Wouldn’t that produce more pair bonding?
I don’t buy it til we test it. Going to have to have a condom and condomless condition, and a contraceptive and non-contraceptive condition (if we’re not dealing with couples trying to get pregnant, could use a cap or other contraceptive device). But now we run into a problem. Should we test already pair bonded couples, and ask the man about emotional closeness before and after sex? Or should we test totally random pairings (tough to get THAT past IRB approval) and see how people feel before and after sex? And before we even get THERE, is there any proof that the foreskin can absorb hormones at all? Anyone ever soaked a foreskin in vaginal mucosa to look at uptake? Perhaps we may want to begin in vitro.
So does a penis have a bulbous glans because of a plunging mechanism? Because of a scooping mechanism? Or because of a hormone mechanism? Or is it all three? Or none of the above?
Regardless, they’re still pretty funny looking.
Bowman EA (2010). An explanation for the shape of the human penis. Archives of sexual behavior, 39 (2) PMID: 19851854