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  • Writer's pictureAmos Gdalyahu

Hyena, clitoris and intersex

Updated: Feb 27

Look at the picture of a this female hyena. Hmmm... Yup, what you're seeing is a female and this is her clitoris.

??!! What's going on here? There's a certain species of painted hyena in which the clitoris grows to the size of a penis. It's not just the size, (which BTW is about 20 cm!), this clitoris, just like a penis, has an opening that leads to the urinary tract. In other words, she urinates from the clitoris. In addition, that same tract leads to an internal vagina that continues to the womb. In other words - and this is the painful part - she gives birth through the clitoris. ..?! I don't even want to imagine her labor pains. In about 60% of first-time births, the pup gets stuck on the way and dies inside the clitoris. Sometimes the mother dies too. Although people talk about the painted hyena's laughter, it's not funny. The pain that nature has caused these hyenas continues: since it's the only opening that leads to the womb, in mating... well, the male penetrates the clitoris. To allow this, the clitoris is elastic and expands. By the way, in female mole, too, the urinary tract exits through the clitoris (!) but only in the spotted hyena, one of the four species of hyenas, the urinary tract continues to the uterus. Why is it good? Actually, it is unknown. It is possible that it is not good, but rather that it was not that bad as to cause the extinction of hyenas with this trait. Because human-based knowledge - (I will write about humans in the last section of this post) - it was thought that having high levels of testosterone in females would confer an evolutionary advantage, and a side product of that high level of testosterone would be hugh clitoris. Indeed, in hyenas, the female is dominant, she's larger than males, much more aggressive than them, and has a very high level of testosterone. But recent research showed that the development of sexual organs in hyenas is largely genetically determined and not dependent on the level of testosterone (1): It was found that reducing the level of testosterone in the developing fetus hyena slightly reduces the clitoris but it remains relatively large and still serves as a urinary duct, mating opening, and birth canal (2). Such treatment, of lowering testosterone levels during pregnancy, was done when the fetus was male or female. It was found that when it was female, then when she grew up and reached the age of giving birth, the success rate of giving birth increased (normally it's about 40% because fetuses get stuck in the way). That is, the minor changes in clitoris size caused by the treatment when she was an embryo were sufficient to prevent fewer fetuses from getting stuck and dying when she matured and gave birth. But in the case where the fetus was male, lowering testosterone levels during pregnancy caused infertility in adulthood. The conclusion, therefore, is that today, biology forces hyenas to maintain an environment with a high level of testosterone. Otherwise, males will be infertile (2). But why is it like this? and why did the female clitoris developed into a sort of a penis that serves for urination, reproduction, and birth? It's actually still unknown and being researched. In the end, I do not know of an evolutionary explanation that gives an advantage to a reproductive system that is designed like this, and in fact, this is a unique example in nature of such development. So, it may belong to the drawer of 'unsuccessful experiments' that cause us to see how things that seem obvious are not really so. This is an extreme example of how the penis and the clitoris are originally created from the same tissue exactly (genital tubercle). In humans, testosterone does cause the development of sexual organs and determines whether the genital tubercle will develop into a clitoris or a penis. Similarly, the covering of the clitoris, also known as the clitoral hood, develops from the same tissue as the foreskin of the penis. The labia majora comes from the same tissue that creates the scrotum, while the skin of the penis (as opposed to the penis itself) comes from the same tissue as the inner labia (6). It's crazy! The development of sexual organs occurs in a complex path and sometimes there are malfunctions. Some malfunctions cause intermediate conditions in which there is not a full match between the biological sex (chromosomally speaking) and the external appearance. Such conditions are now called intersex. Intersex conditions occur in about 1/5000 people, meaning they are relatively rare but not very rare (7). My brain sexuality lectures Many of you can stop now, and for those who want to delve a little deeper into biology I'm adding the following, as mentioned, it is complex: In humans, testosterone (or more precisely, the DHT that is formed from testosterone with the 5-alpha-reductase enzyme) does cause the initial development of the penis and excess testosterone during pregnancy leads to excess DHT, causing an enlarged clitoris in females. Excess testosterone during pregnancy can occur, for example, due to growth in the mother's adrenal gland (adrenal produces testosterone). Sometimes, in humans, there is a condition that causes a mismatch between the biological sex (in terms of chromosomes) and appearance. When there is a mutation in the 5-alpha-reductase enzyme that I mentioned earlier, DHT is not formed from testosterone, and therefore the penis does not develop. In this case, there are internal testes, and therefore there is testosterone, but it does not turn into DHT. From the outside, the genetically male baby appears female. However, at puberty, secondary sex characteristics require testosterone and not DHT. As mentioned, there is testosterone from the internal testes, and thus the girl suddenly becomes a boy. In fact, most penile growth occurs during puberty under the influence of testosterone, and therefore the clitoris will grow and a state of intersex is created. There is a city in the Dominican Republic where the mutation in the 5-alpha-reductase enzyme is present in about 1% of men! There are many other mutations that cause intersex conditions besides those I mentioned. If a baby girl grows up to be an athlete without knowing that biologically she is male but due to a mutation in the 5-alpha-reductase enzyme, her external sex organs appear female, does she have to compete with men? With women? To what extent do sex hormones like testosterone shape our brain and behavior? This is a fascinating question, and it will be addressed in a separate post, so if you are interested, keep following! Back to the clitoris - do you know that in many animals there's a bone in the clitoris? and in the penis. Read my post about it here. Sources and more information 1. Development of the external genitalia: Perspectives from the spotted hyena ( Crocuta crocuta ) Gerald R.Cunha, Differentiation (2014) 2. Spotted hyaenas and the sexual spectrum: reproductive endocrinology and development, Place, Ned J, Glickman, Steve EThe Journal of endocrinology, (2020) 3. A short movie from National Geographic 4. Rare footage of spotted female hyena giving birth 5. Pictures of the embryonic genitals at stage they look the same in females and males and here too in a more scientific way 6. Wikipedia on the embryonic development of the sexual organs 7. How common is intersex? a response to Anne Fausto-Sterling2002

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