Today I learnt the following fascinating fact about female spotted hyenas: They have no vagina. Where it should be they have a sort of small scrotum with a pad of fat inside where the testicles would be in a male. They have a long clitoris, the size of the male of the species' penis, with a small opening on the end. This opening is used for copulation and birthing. It is so small that during birth 60% of hyena babies suffocate inside the clitoris, and 9% of mothers die.
This is an evolutionary adaption of a pathological mutation, caused by a deficiency of an enzyme called aromatase in the placenta. Normally aromatase converts testosterone into estrogens, therefore in its absence the developing foetus is exposed to huge levels of male sex hormone. This creates a female pseudohermaphrodite; internally female, yet externally resembling males. In humans it is an incredibly rare mutation; in hyenas it is perfectly normal.
That fascinating fact about female hyenas was brought to you from the book Mutants: On the Form, Varieties and Errors of the Human Body by Armand Marie Leroi. Do with that information what your will. I'd always suspected there was something different about those hyenas. But never mind that; it's a great book with detailed historical accounts of mutation in humans explained using cutting edge genetic research and sympathetic writing. It's one of those great Christmas presents, the sort that Jesus would have asked for if he had known any better.
It's a proper exploration of the physical causes of mutation, and what they can tell us about the human body in its healthy and unhealthy states. It's not a freak show by any means, there is no look at this funny looking guy playing the piano, go on, look. It's a good book. One that I only own by mistake of accidentally adding it to my partner's Amazon wish list instead of my own. It was then bought, confusedly, as a Christmas gift for her, which she promptly passed on to me with a questioning eyebrow. Good tactic that, accidentally discovered. You can use it yourself.
Happy new year.