Penis means power. The dominance of dicks and those who have them isn’t a coincidence, or the unavoidable consequence of Big Patriarchy keeping women down—rather, it’s a case of simple biology. In most mammalian embryos, the genital tubercle forms very early, later developing into either a penis or a clitoris, subject to a complex cocktail of influential hormones. Androgens like testosterone stimulate penile growth and are also associated with aggression, so the relationship between actual dicks (penises) and figurative dicks (aggressive jerks) is axiomatic. But amazingly, in the case of female-dominant spotted hyena societies, those boss bitches have actually evolved a sort of penis of their own.

It’s technically called a “pseudopenis,” and it’s an extreme example of clitoromegaly—essentially a very enlarged clitoris.

Clitoromegaly/pseudopenises have been documented in several species: I came across mentions of pseudopenises in binturongs (Arctictis binturong, a type of adorable Southeast Asian bearcat), fossas (Cryptoprocta ferox), and ringtailed lemurs (Lemura catta). (In each instance, the pseudopenis is an enlarged clit and isn’t linked with other masculine characteristics.) Clitoromegaly is also documented in humans; it’s considered a disorder of sexual development with a number of possible causes, including steroid usage or polycystic ovarian syndrome, with the most common cause being congenital adrenal hyperplasia. In humans, sometimes the enlarged clitoris can resemble a penis; more often, it just looks like a large clit.

The pseudopenises of female spotted hyenas (Crocuta crocuta), however, are different. They can be up to 90% as large as male penises and, at least from the outside, look almost exactly like actual penises, scrotum and all.

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(Image from IUCN Hyaena Specialist Group)

The illusion of a scrotum is created by two fleshy masses at the base of the pseudopenis, filled with fat and connective tissue. Where you’d expect to find a vagina, spotted hyena females instead have fused labia. (The anomolous female anatomy was first described by Morrison Watson for the Proceedings of the Zoological Society of London in 1877, but the first detailed illustration was done in 1949 by D. Dwight Davis and H. Elizabeth Story in Chicago and published in the Fieldiana journal of the Chicago Natural History Museum, now the inimitable Field Museum. Their observations included a number of facets: short spines covering the clitoris/pseudopenis; a well-defined glans of the clitoris, cylindrical with a prominent dimple in the center; fused labia and “scrotal swellings” containing only fat and connective tissue. In short, again, the whole situation looks almost exactly like a penis.)

For female hyenas, a lot happens through the clitoris—mating, urination, and even giving birth. Trying to put a penis inside a pseudopenis, or push a baby out a long, narrow clitoris, is unsurprisingly pretty challenging. Over 60 percent of cubs born to first-time spotted hyena mothers are stillborn, suffocating during their journey through the birth canal. (1) Giving birth causes the pseudopenis to rupture on one side, forming an open wound that takes weeks to heal and can become infected.

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But, on the other hand, this unique biology gives female hyenas complete control over mating. In order to permit penetration, females must voluntarily retract their pseudopenis up into itself, creating an opening for the males to enter. So yes, that means that it’s completely impossible for a male to rape a female hyena.

Considering the difficulties of giving birth through the pseudopenis, researchers have long wondered why it evolved in the first place, and what purpose it serves. Because the spotted hyena’s pseudopenis is so remarkably penis-like—much more so than any other instance of pseudopenises/clitoromegaly—it’s been heavily studied. But, when I tried to find out what role pseudopenises play for lemurs, binturongs, civets, European moles, platyrrhine monkeys, or any other species, sexism in science stopped my research short. Genital masculinization is very rare in female mammals, and the few studies I did come across were inconclusive and dull, with all reports suggesting that it’s not associated with female dominance. Even in ring-tailed lemurs (Lemur catta), which exhibit pseudopenises and some level of female dominance, results have been mostly inconclusive.

That’s not the case for spotted hyenas, who’ve managed to capture the hearts and minds of many scientists. In particular, Kay Holekamp at Michigan State University has been studying a population of wild spotted hyenas in Masai Mara for over 30 years. Thanks to her dedicated research team, much of the sociobiology of spotted hyenas has been demystified.

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Spotted hyena societies are nature’s truest matriarchies, and the rigid ranking order is well-known by each clan member, with males filling in the lowest social ranks. High ranking females pass their social power on to their female offspring, but male cubs must eventually leave their birth clans and attempt to join a new group. At that point, even juvenile females rank above the incoming males, who must tolerate any abuse hurled their way if they want to eventually mate with the ranking female or be accepted into a new clan. Females are generally larger than males, more aggressive than males, and socially dominant to them in almost every case.

Incidentally, this quasi-misandrist social structure has the distinct advantage of reducing genetic bottlenecks when resources are scarce and populations plummet. (2) Spotted hyenas are the most abundant large carnivores in Africa—personally, I like to think their success is largely due to the subjugation of males, but the intellect and prefrontal cortex development required to support such a complicated social hierarchy is probably a contributing factor. In fact, some studies have shown that spotted hyenas have social cognition and recognition on par with that of primates. (3)

Pseudopenises play an important role in the social order as well. In addition to looking just like a penis, they act like a penis too—erections are common among females, and licking or inspecting erect female penises is an important greeting behavior within spotted hyena society. Presenting an erect penis or pseudopenis is actually an indicator of submission, and a behavior that’s unique to spotted hyenas. (4) High-ranking females rarely present their pseudopenises for inspection, and in greetings between males and females, males nearly always lift their legs first.

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Since social rank largely determines access to resources like food, and thus heavily influences reproductive success, high-ranking females enjoy many privileges within the clan. Their teeth are usually better than the rest of the clan, because they’re granted access to the choicest hunks of fresh kills, while lower-ranking clan members are left to feast by crushing bones with their powerful jaws. (And yes, contrary to most pop-culture representations, hyenas are excellent hunters, not just scavengers. They have incredible immune systems and can eat pretty much any rotting carcass, but they seem to prefer fresh meat and are particularly fond of zebra.)

In a 2008 Smithsonian piece, Holekamp postulated that this premium food access might hold the key to the evolutionary mystery of the pseudopenis. Spotted hyena feeding is intensely competitive, with adults consuming 30 to 40 pounds of meat in one feeding, vying with up to 30 other hyenas for access. Since hyena cubs don’t have the jaw strength to crunch bones, mothers must be dominant enough to ensure that their cubs get preferential access to food. Social rank is so strongly related to food access that in one photograph of two six-month-old cubs sitting side by side, the cub born to the clan’s alpha female is twice as large as the other, who was born to a female ranked #19.

But even if feeding cubs was the driving force behind the evolution of female dominance and aggression, the pseudopenis is still an outlier—and unfortunately, one that remains a complete mystery. Body size and aggressiveness do seem to be linked to pseudopenis development. A common misconception is that female spotted hyenas have higher levels of testosterone than males. They don’t, but studies have shown that, during pregnancy, high-ranking females have higher levels of androgens than those who are lower in rank. Rates of aggression and mounting behavior in cubs were also positively related to their mothers’ relative gestational androgen levels. So aggression is adaptive, and pseudopenis development is linked to aggression, (5) but the mechanism for that link is still unknown. (6)

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I set out to find an answer to the seemingly simple question, “What’s a pseudopenis, and why do they develop?” I ended up down a k-hole of endocrinology, evolutionary biology and sociobiology. I read at least 60 scientific articles about hyenas, lemurs, vivverids, and more. But still, I’m no closer to knowing the answer than I was when I started.

I’ll admit to being pretty disappointed with the lack of conclusive evidence on the evolution and purpose of such a fascinating edge case of female genital morphology. But animals are endlessly fascinating; it’s not always possible to shoehorn evolutionary idiosyncracies into a neat, tidy narrative. Frequently, any attempt to do so is a disappointing oversimplification. We may not be able to explain the female hyena’s pseudopenis, but we can marvel at it—all seven inches.


Kaitlyn Tierney (@krtierney) is a former librarian for the San Diego Zoo. She’s now a London-based writer-for-hire.

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Illustration by Bobby Finger, source image via National Geographic/screengrab


1. Frank LG, Weldele ME, Glickman SE. 1995. Masculinization costs in hyaenas. Nature 377: 584-585.

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2. If you’d like to nerd out over population genetics, check out: Watts HE, Scribner KT, Garcia HA, Holekamp KE. 2011. Genetic diversity and structure in two spotted hyena populations reflects social organization and male dispersal. Journal of Zoology 285: 281-291.

3. For more, see Holekamp KE, Sakai ST, Lundrigan BL. 2007. The spotted hyena (Crocuta crocuta) as a model system for study of the evolution of intelligence. Journal of Mammalogy 88(3):545-554.

4. East ML, Hofer H, Wickler W. 1993. The erect ‘penis’ is a flag of submission in a female-dominated society: greetings in Serengeti spotted hyenas. Behavioral Ecology and Sociobiology 33:355-370.

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5. Dloniak SM, French JA, Holekamp KE. 2006. Rank-related maternal effects of androgens on behaviour in wild spotted hyaenas. Nature 440:1190-1193.

6. According to research performed on a population of hyenas at UC Berkeley, suppressing gestational androgen levels did not impact pseudopenis development.

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