canines have them
Canto: We'll give the global warming crisis a break for a while, and maybe return to the origins of life, or the origins of the universe, or the origins of Homo sapiens – whatever you'd like to focus on.
Jacinta: Thanks for the choice Canto. I'm currently reading The Link, by Colin Tudge, so if we're talking origins, it'll have to be Homo sapiens. It's a great book, it has taught me so much. Frankly, I'm woefully ignorant when it comes to palaeontology, so this has been like an introduction for me, in spite of reading a few Stephen Jay Gould essays.
Canto: So what specifically have you learned from The Link?
Jacinta: A lot of confusing stuff. That Homo sapiens is maybe 500,000 years old, but that Cro Magnon woman, someone as recognisable as ourselves, is maybe only 40,000 years old.
Canto: That is confusing. So there's a Homo sapiens that isn't Cro-Magnon? I thought Cro-Magnon and Homo sapiens were interchangeable, that they had found fossils – more than 40,000 years old though – that were just like us, and so they named them Cro-Magnon, presumably after some location...
Jacinta: We'll try to clarify all that later, but so many other things I've learned, such as that we're the only primate without an os penis – that's a bone in the penis. Every other male primate has one. And most mammals too. And there at least 250 species of living primates, by the way.
Canto: You mean, we human-type blokes have boners without having bones?
Canto: And chimps and bonobos, our nearest living relatives, have penis bones?
Jacinta: That's what I've read.
Canto: So when did it drop off, and why?
Jacinta: Qui sait? The fossil record with regard to our hominid ancestors is extremely patchy –bits of skull, jawbones, teeth. Nothing like the near-perfectly preserved fossil of Ida, the subject of The Link. Not too many penis bones either, not attached anyway. There are speculations as to why humans are penis-boneless though. Here's how Tudge summarises it:
For animals without an os penis, the only way to achieve a convincing erection is by hydrostatic pressure – which only a vigorous animal can generate. An erection achieved without obvious support may not tell a potential mate all she might want to know about her suitor's health, but it does tell her that he is not actually ill, at least in one important respect.
Canto: Yes, the only respect that counts for some women, eh Jass?
Canto: So maybe as we got smarter, we got to convince our females that being sexy was more about thinking sexy, especially when she was around, than about the size of bone in our boner.
Jacinta: Something like that. You could call it the romantic turn.
Canto: You know, I'm pretty sure that cats don't have an os penis. Have you seen a cat's dick? It's pretty teeny.
Jacinta: I'd have to look more closely at that one.
Canto: Don't excite yourself. Take my word for it. Let's get back to the Cro-Magnon issue, if you please.