9 Fascinating Things You May Not Know About the Penis
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Here on National Geographic, Yong also shares the weirdness that is the alligator penis. This member is eternally erect, “ghostly white,” doesn’t inflate at all, which makes it highly unusual, is filled with layer upon layer of collagen (even where blood would normally flow) and, as Yong notes, must have scared the bejesus out of this researcher when one appeared to rise from this dead reptile.
Then there’s the cute little echidna, a prehistoric, egg-laying hedgehog-like mammal whose penis has four heads. Click on the second picture and see how happy he looks (even though his name is Grumpy).
Lucy Cooke writes in Natinoal Geographic that, “The reason why the echidna’s penis has four heads is still up for grabs. The female echidna has two love canals and Stewart [Nicol, echidna researcher] believes that the penis works like a double double-barreled shotgun, firing out of the two heads on one side, and then again quite quickly on the other. Given the fact Mr. Echidna has no idea which side his lady’s egg will be released this might increase his chances of fertilization.”
And may be one reason why a species who walked with dinosaurs is still here to charm us with his ornate love machine.
7. Getting a big head.
So the elephant's penis is big, but the human male’s is huge among primates. Correcting for overall body size, it’s twice as big as the chimp’s, which may be why they’re always screaming.
How do I know? The wonderful Jesse Bering said so and he studied ape social cognition. Jesse Bering also knows why the human penis evolved to be the shape it is, hence his book Why Is the Penis is Shaped Like That? And Other Reflections on Being Human. This essay in Scientific American is nearly verbatim from his book, which you must buy to be both entertained and the life and soul of cocktail parties from now til the end of the world.
At any rate, the strong, straight shaft, large glans or head and coronal ridge look the way they do for a reason, and the reason is probably semen delivery and displacement -- delivery of one’s own and displacement of another male’s.
First let’s talk about length. Bering tells us that evolutionary psychologist Gordon Gallup and coauthor Rebecca Burch wrote a 2004 paper conjecturing that the lengths the penis can reach and the force of human ejaculate can delivery sperm into the uppermost part of the vagina and that a longer penis would be advantageous not only for reaching the vagina’s deeper recesses but to displace sperm that might have been left by another male. Interesting, especially since magnetic imaging of couples having sex is what tells us how the far the penis can go and how it expands inside the vagina.
But it gets way, way better.
The distinct arrow-like shape of the penis would be good for displacement, Gallup figured, because of the “upsuck,” (not kidding) caused by thrusting. If there was anyone else’s sperm in there, that ridge would effectively scoop it all out. To test this, Gallup and his researchers got some “prosthetic genitals from erotic novelty stores,” including a faux vagina and three faux penises, one with a coronal ridge extending .2 inches from the shaft, one extending out .12 inches and one with no glans at all, which was the control. They made a simulated semen solution of flour and water, put it inside the “vagina,” and the three dummy weiners were then inserted to see how much ersatz sperm they could displace.