This is scientific, but possibly NSFW so I'll spoiler the details. I first heard about this on the Joe Rogan Podcast. Spoiler The Plunger Hypothesis (TPH). TPH is basically the idea that the bulbous shape of the glans in humans acts as a plunger which scoops a previous male’s sperm out of the vaginal canal, while at the same time delivering his own sperm to an optimal position for insemination. At least, until the next competitor’s plunger penis scoops it out. Some insects actually do exactly this. So, what should we expect from such a hypothesis? First and foremost, we have to have evolved in a society in which there is a lot of sperm competition. Chimpanzees have tons of it, and since their troops are primarily composed of related males, there is little to no outward signs of competition for females. They’re certainly not thumping their chests or doing other threat displays to get their brothers to lay off their female. Instead, they’re politely lining up and waiting their turn. So do humans fit this criteria? Maybe, maybe not. We should also expect that the shape of the “plunger” actually affects how much semen is scooped out. Males with better plungers should have more offspring, and there should be some variation in penis shape, glans to shaft ratio, all that stuff. Does this criterion apply? Maybe, but no one’s looked at it. All we have is the infamous dildo experiment. And now we have the Glans-as-Hormone-Sponge Hypothesis. The GHSH suggests that the human penis is plunger-shaped in order to scoop, but instead of scooping out the competitor’s sperm, it’s scooping up vaginal secretions filled with love-inducing hormones. The foreskin, he states, is particularly sponge-like, and will soak up her hormones, be absorbed into his blood stream, and induce the release of more hormones from his brain. Okay, that’s an interesting idea, too. And he’s not saying he has evidence for it; he’s just suggesting it. Here’s the problem with both of them, though: The glans begins life as the genital tubercle. In males, the base of the tubercle grows out to become the shaft of the penis, while the glans becomes demarcated from the shaft by the coronary sulcus- the ring around the plunger, if you will. The shaft of the penis gets a little groove down the middle of it which will eventually fold around itself to become the urethra. This groove does not extend into the glans. In the glans, a little pit develops at the tip and moves inward until it meets up with the future urethra. The two adult structures are distinct because they’re formed from from distinct embryonic structures. And here’s the part that will blow your mind: Females also have a coronary sulcus around their glans (of the clitoris). Her coronary sulcus separates the glans from the rest of the phallus. The main difference between the male glans and the female glans is that the male glans had to extend out from the body so it could get to the vagina, and did so by growing a larger phallus. So my question is, why do females have vaguely plunger-shaped clitorises? Or are we perhaps trying to ascribe function to a simple relict of an embryonic event? Do females have a coronary sulcus because males have a coronary sulcus, or might it be the other way around? Do males have a ledge around their glans for a reason, or is it simply because the clitoral glans is a distinct structure from the rest of it? http://zinjanthropus.wordpress.com/2011/02/04/adaptationism-in-the-human-penis/
Well this is a disappointment. I came here wanting to learn more about the plunger and the men who wield them in plumbers. The forgotten heroes of this world.
I've been hearing a lot of "weird" people talking about the Rogan podcast. What's the deal with it? Seems interesting? And by "weird" I mean what y'all consider "weird", I don't mind open minded thinking personally.
Maybe because I am a nerd but I found that an pretty interesting read. It seems to me that there is definitely something there to the Plunger Hypothesis since humans like Bonobos have sex all the time and multiple partners. It would make sense then that having an ability to scoop out rival sperm would be an evolutionary advantage that would get passed on. So if my ancestor had glans that were very good at removing a rivals genetic material it goes that that trait is the one that gets passed on. As far as glans for scooping and soaking up female hormones that would make sense also as it would make sex more pleasurable but there is an easy way of testing that since condoms would also block absorbtion of female hormones through the glans so then test could be conducted to see how much female hormones are present in males having sex with or without condoms. One thing pretty much all of us who have had sex with and without condoms know is that sex is less pleasurable with a condom so there might be something there to that theory. As for why women have structures similar to men that makes sense since biologically males are actually just a mutation of females, one reason why males still have nipples, so it makes sense there are similar structures.
SAY WHA??? Maybe perhaps the Male species, has a total different gene structure that encodes for the differences in the Human body between male and female. Its called the "Y" chromosome...
Eh, sort of. I wouldn't say a "total different gene structure" at all. The SRY region/gene of the Y chromosome is the only part that really matters. If SRY is present in a developing human at around 6 weeks then undifferentiated/indifferent gonads develop into testes. If there's no SRY present then another set of genes is activated and the indifferent gonads develop into ovaries. There's a bit more to it after that (testes secreting testosterone which has wide ranging effects) but if you have a Y chromosome with a broken SRY region you'll develop as a female.
Interesting stuff that I've heard somewhere before. If this sort of stuff fascinates you, and it should, then I highly recommend Dr. Tatiana's Sex Advice to All Creation by Olivia Judson. It's not focused on humans, but it's a really enjoyable and wonderful read.