I'm sure by now everyone here has heard about the Penis Spine Story. The actual paper involved bigger brains as well as penis spines...but who cares about brains when PENIS SPINES are around?? Yeah I didn't think so.
When I read the coverage of the penis spines, and heard it was the technical term, I was really confused. I thought, isn't the technical term the baculum? The bone in the penis of animals like mice and chimps and dogs, which facilitates erections. Humans don't have them. Penis Spine, baculum, makes sense, right? I was completely mystified as to why people weren't just calling it the baculum and seemed to be talking like there was more than one!!! Surely they didn't mean something like THIS:
And lo and behold, they DID mean ACTUAL PENIS SPINES!!! BE STILL MY HEART. I still didn't believe it, until Eric Michael Johnson (who will be doing another post on the penis spine paper over at Zinjanthropus! Check it out!) mentioned a need for a paper. And the paper...was on penis spines. The actual spines!
Osman Hill. "Note on the male external genitalia of the chimpanzee" Proceedings of the Zoological Society of London, 1944.
Science. You couldn't MAKE this stuff up.
So basically, the author, Dr. Hill, got an opportunity to study a freshly dead chimpanzee. Unlike previous specimens which got preserved in bad solutions, this one was SO freshly dead that they were able to preserve the body in the kind of fluid usually used for human embalming (he doesn't specify, but seeing as it's 1944, I'd bet on some formaldehyde in there). Why Dr. Hill was particularly interested in examining the penis, I don't know. But he drew it VERY carefully.
Count yourself lucky, the original view is a LOT larger. What you're looking at here is the view looking up between the legs, like you're staring at the taint, which is toward the bottom of the picture. The penis sticks up at the top, and you can note the extremely large testicles of the chimp. Testicle size in primates has an inverse correlation with monogamy, so you can see that chimps are VERY NON-monogamous.
What Dr. Hill noted upon examination of the penis was a series of tiny BUMPS on the surface of the glans (the head) of the penis. He wanted to study this in more detail, and took a sample. Yeah, he skinned the penis. He was also able to compare his adult specimen with the specimens of a fetal chimp and two teenage chimps.
In describing the basic form of the penis, it seems just like...a penis. Unlike humans, chimp penises taper toward the end, but they do have a foreskin. Also, it's lightly hairy. But it's when he starts talking about the spines that the true poetry comes out.
The surface of the glans is beset, especially on its lateral surface, with
numerous low, horny elevations, of yellowish-brown colour, sharply distin-
guished from the pale rosy tint of the remainder of the epithelial covering.
These papillae are hard t o the touch and impart a roughness to the finger
You can see there the little dots meant to represent the penis spines. In comparison, the fetal and adolescent chimps had them too, though the fetal chimp penis spines were described as "gelatinous" and relatively clear.
In detail, the spines are on average about 0.35mm wide. He goes into the cellular structure, but it's nothing out of the ordinary, except that the spines are...hard. In comparison to the rest of the skin. He describes them as "cornified", and they appear to be composed kind of like callouses...only tiny spines. Tiny corny spines.
While the author is mostly concerned with the potential evolution of the spines, I'm more concerned with their function. What are they FOR?! Why are they THERE?! One hypothesis is that they are actually more stimulating for the male (ribbed for his pleasure, anyone?), and therefore promote quicker sex. This could be especially important in promiscuous species, where it's important to get it over and done as quickly as possible, and on to the next! This means that humans, who don't have penis spines (thank goodness), find sex LESS stimulating, and it takes them longer. This might be ideal for promoting social bonding in humans, while in chimps social bonding via sex is far less important. But there are other possibilities. It's possible that bumps and ridges on the penises of promiscuous species are good for scooping out the sperm of competitors.
I just wonder what the girl chimps think.
Hill (1944). Note on the male external genitalia of the chimpanzee Proceedings of the Zoological Society of London