{Note: This post was selected for inclusion in The Open Laboratory 2009, an anthology of the year’s best science blogging. You can read about the book, and where to buy it, here. Bloggers do not profit from their post being selected. Wolfgang Wickler kindly allowed us to reproduce his original sketch, left.}
Let’s just get straight to it. Spotted hyena’s have two kinds of erections: sexual erections for reproduction, and social erections for… well, socializing. (Um, yes. This is for real.) The females get them too, by way of an enlarged clitoris masquerading as a penis. I stumbled upon this interesting tidbit as an aside when interviewing a Duke University evolutionary anthropologist, Christine Drea. Before working on this project, I really didn’t know much at all about spotted hyenas or their behavior. But when she mentioned “female clitoral erections” in a group context, how could I have resisted following up on this quirky phenomenon?
In order to appreciate the full context of this behavior, it is important to know a little about the social structure of spotted hyenas. It starts and ends like this: Females Rule. Always. Obviously this is simplistic, but it is true that female spotted hyenas dominate males in the pack pecking order. They weigh up to 10 percent more, and they behave more aggressively too — keeping every animal in its place. And there can be a lot of animals… spotted hyenas differ from other hyena species because they are extremely social. They live in groups that can be as large as 90 individuals (or as small as five) and they hunt large prey cooperatively — going after wildebeest and zebras in organized forays.
Spotted hyena clans are led by a single dominating matriarch. Females tend to stay in their natal clan throughout their lives, but young males will disperse to new clan territories in search of mates. Hyenas inherit their social status from their birth mothers… that is, the clan learns to associate the social status of the mother with her pups because the fiesty mothers often intervene in clan interactions on the behalf of their offspring, and they will aggressively fight for food to give to their pups. This is key to the pups life, because spotted hyenas live and die according to their social status. Every aspect of their daily life is ruled by how high or low ranking they are. And most importantly for an obligate carnivore, how much food they eat is also dictated by their social status. Being born into a high-ranking status therefore has its privileges. (For more on their social structure and the use of aggression to sort of who rules, check out this Michigan State University web site” Establishing Dominance,” on the research of Kay Holekamp.) Spotted hyenas live only in Africa and they primarily inhabit the portions of the continent that lie below the Saharan desert, with the exception of deep jungles ecosystems. They are most closely related to a super family within the order Carnivora which includes cats, mongooses, and civets.
But perhaps the oddest twist of their story is that the female spotted hyena’s sexual organs are evolved to mimic that of a male spotted hyena’s. Their vagina was rendered useless because their outer labia fused to form an ersatz scrotum. Their clitoris elongated, and then developed an interior canal that became the main vesicle through which they urinate. They also have sex and birth their young through their sham “penises.” (As a writer, this pendulous clitoris is the sort of gnarly natural detail that makes me more fascinated with reality than with fiction.) For the casual observer — and even for some trained ones — it’s a hard task to discern a female spotted hyena’s elongated clitoris from a male spotted hyena’s penis. (If you are thinking ahead to the mechanics of how their copulation might work, visit Neurotopia’s recent entry on this.) Unfortunately, about 10 percent of the would-be mothers die in the process of birthing their first set of young through their pseudopenis, also called a “peniform clitoris.”
Another added danger is that pups may suffocate in the extra long birth canal and be stillborn. {1} (For more on the dangers of this odd reproductive system, visit here.) Some researchers call this sort of phenomenon the “masculinizing” of female genitalia, or genital mimicry. In the animal world, where most species main goal is to reproduce and multiply, genital mimicry is fairly rare. It would seem that anything which obfuscates the genitalia to the opposite sex would work against reproductive purposes of making new offspring. So why does the genital package of a female spotted hyena rival that of a males? Scientists aren’t entirely sure, but they have some ideas. One idea is that what we see as so odd — a clitoris masquerading as a penis — is really just a physical side-effect of prenatal exposure to lots of androgens. These hormones would produce more aggressive behavior in the females, but also change their genitalia. There appear to be a lot more behavioral benefits to this prenatal hormone bath than there are benefits to their revamped plumbing which, as we’ve noted, causes physical barriers to copulation and even death to the mother and her young. Aggressive behavior, allows the mothers to successfully raise her young in a very aggressive environment, and it allows them to garner more food for themselves and their young — all of which serves to reinforce selection for aggressive behavior in females. Feeding is a truly competitive event in the world of the spotted hyena. From an earlier article by Sean Henahan:
“When hyenas make a kill, everybody comes out of the woodwork. You see 30 animals arguing over a large kill. A zebra can be reduced to a dark patch on the ground in half an hour,” said Frank. “The whole key to high rank is that you get to eat first. These mothers make room for their cubs, but lower-ranking animals get pushed off.” – Excerpt from: “Female Hyenas and Male Hormones, A Strange Combination”
One researcher estimated that high-ranking females are 2.5 times more likely to reproduce sucessfully than low-ranking females. This more than offsets the 10 percent death rate from birthing, and reinforces the selection and propagation of ever-more aggressive females. {1} By this line of thinking, successive generations of females will be more and more aggressive, and as a side effect they will have larger and larger clitorises.
Now that we know why females might have a sham penis… what about those “social” erections?
Hans Kruuk was one of the first scientists to formally observe and describe how spotted hyenas greet each other with a genital sniffing routine when reunited after being separated. It’s kind of similar to how your dog always has to sniff the bum of your neighbor’s dog, even though they know each other well and see each other often. With spotted hyenas, the longer the separation, the more intense the sniffing scrutiny may be. Sometimes these moments of greeting involve licking and erections. Richard C. Francis describes it like this:
This erection clearly is not a signal of sexual interest, because it occurs without respect to the sex of the partner. Moreover, spotted hyena erections are not, as in most mammals, confined to males: females too can extend their phallus in greeting. In truth, female hyenas are somewhat less prone to experience a greeting erection, but only because of their higher social status. – Excerpt from: “Why men won’t ask for directions: the seductions of sociobiology”
Contrary to the value that we humans assign to an erect penis, in spotted hyenas an erect penis actually signals submission. {5} And so it is usually the lower-ranking individuals that wave a hello hard-on. The lower-ranking animal lifts its rear leg and allows the high-ranking animal a good sniff. And because the females Always Rule, it is the male spotted heyenas that are more submissive in these “greeting ceremonies.” But the females will voluntarily harden their pseudopenises when signaling submission to a higher-ranking clan member, which is typically a more dominant female. Sorry boys, but the girls keep it all to themselves.
NOTES and SOURCES:
{1} Henaha, Sean. “Female Hyenas and Male Hormones, A Strange Combination.” Access Excellence.
{2} Francis, Richard. “Why Men Won’t Ask For Directions: The Seduction of Sociobiology.”
{3} Meadows, Robin. 1995. “Sex and the Spotted Hyena.” Zoogoer.
{4} Uknown author. “Establishing Dominance.” Michigan State University.
{5} East, Marion L., Hofer, Heribert & Wickler, Wolfgang. 1993. The erect “penis” is a flag of submission in a female-dominated society: greetings in Serengeti spotted hyenas. Behavioral Ecology and Sociobiology (33) pg. 355-370
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