the oversized naughty bits of female spotted hyenas

By Alison Campbell 24/02/2010

When I visited Pharyngula today I saw that PZ had posted a video about spotted hyenas. Female spotted hyenas. And that reminded me of one of the late Stephen Jay Gould’s wonderful essays on the same subject. (Gould remains one of my favourite science writers -although, having said that, I do find some of his later work rather overblown – and you can find examples of his work at The Unofficial Stephen Jay Gould Archive.)

If you watch that video you’ll find out that female spotted hyenas look rather like males, especially when they’re aroused. They have a greatly enlarged clitoris that looks just like a penis. (Apparently early European observers didn’t recognise them as female at all.) The females are also large, heavily muscled, highly aggressive & dominant over any males they encounter. A group of spotted hyenas consists largely of females, with a few males hanging around at the periphery. The clan leader is the dominant female, who will pass on her rank to her pups. Females lead the hunt, & once the prey’s been caught, it’s the females who eat first. Social interactions involve much sniffing – and licking – of the dangling appendages.

All of this – the size, aggression, dominance & enormous clitoris – can be put down to the fact that hyenas are exposed to very high levels of testosterone while in the womb. The clitoral enlargement may be a secondary side effect; the heavily muscled bodies & bone-crushing jaws that result from the high doses of testosterone could well have been selected for, carrying the clitoris along with them. (I have to object to the slant – & the possible explanations – put on this by the video’s narrator, who asks why the females ‘put themselves through this’ – of course, they don’t! What we see is the outcome of a long series of selecction events over thousands of years, not a process driven by the needs or desires of female hyenas.) Giving artifically-high doses of testosterone to pre-natal rat & dog female foetuses has the same masculinising effect: larger size & muscle mass, higher aggression – & external genitals that look like those of the males.

The female hyena’s masculine appearance doesn’t stop at the faux penis: at the base of this structure she has a swollen ‘scrotal’ sac filled with fat. The apparent penis incorporates not only the clitoris but also the joined labia – and this has what must be an extremely painful consequence for all female spotteds: they urinate, mate, & give birth through a single small opening on the underside of this structure. I remember my eyes watering when I first read Gould’s essay, & they watered again on seeing this video! Apparently up to 20% of females die giving birth to their first pups – this also suggests that there’s some strong adaptive significance to the high levels of testosterone that produced the apparently maladaptive clitoris in the first place.

And the effects of the testosterone exposure extend to the behaviour of the pups themselves. These are no blind, helpless, mewling little softies. Spotted hyena pups come into the world with their eyes open, teeth in their jaws, & a heap of aggression of their own, sorting out their own dominance hierarchy by fighting. Apparently, while they don’t often kill their sibling directly, the subordinate is so scared of the dominant pup that it hides away in the birth tunnel (taken over from other burrowing animals), too scared to approach its mother to feed while the other pup is present – and eventually starves to death.

Disney Planet this isn’t.