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The Kinky Reason Human Penises Are Mushroom-Shaped

We’ll give you a hint: rival semen

If you’ve ever wondered why your penis is shaped like that, you’re not alone. In fact, it’s all everyone’s Googling right now. Specifically, you’re asking: Why is the penis shaped like a mushroom? And, before you bring it up, yes we all remember that Stormy Daniels quote. But this isn’t about Trump’s “toadstool” dick — it’s about everyone’s toadstool dick. And, as it turns out, there’s a very logical reason for their universally shroomy shapes.

In 2004, psychologist Gordon Gallup and academic Rebecca Burch co-authored a paper about the evolution of the penis. Published in the Evolutionary Psychology journal, the study proposed the “semen displacement hypothesis,” suggesting that the human penis’ mushroom cap-shaped tip — or, as they call it, “pronounced coronal ridge” — exists to “scoop out” “rival” cum in the vagina, with the ultimate aim of making sure their semen wins the daddy race.

Gorg! So how does it work? Well, the authors say, the mushroom head forces the semen of the previous partner “back over/under” the tip of the penis, so “during intercourse, the effect of repeated thrusting would be to draw out and displace foreign semen away from the cervix.” This also explains why the human penis tends to be longer and girthier than other animals — as Gallup and Burch point out, it “needs to be of sufficient size to fill the vagina and supplant foreign semen.” Other animals do this too, but they use “penile barbs, hooks, combs or a textured” penis tip.

To test out their hypothesis, the researchers simulated sexual encounters using artificial models, with the aim of monitoring semen displacement, depth of thrusting and semen viscosity. Reflecting on their findings nearly 20 years on, Burch tells me, “We were very surprised when the penises with coronal ridges were extremely efficient at pulling fluid from the cervical end of the vagina to the entrance. One thrust (insertion and withdrawal) of a penis with a coronal ridge displaced 90 percent of the fluid in the vagina. We predicted there would be some displacement, but 90 percent was above and beyond.”

Unlike the more primitive days, when birth control didn’t exist and everyone was having gangbangs and orgies all the time (hence the plethora of “rival” semen), today — for better or worse — many people are monogamous or, at least, practice safe sex with a condom. So, will the penis soon evolve out of its mushroom shape and into something else?

Probably not, says Burch. “Even though monogamy is a common mating system, infidelity exists,” she tells me. “There has been extensive research on the incidence of infidelity, and even infidelity and then sleeping with a committed partner shortly after. This is still an important strategy, particularly in monogamy, as the male in the committed relationship would be expected to raise children with his partner. Men would use this strategy to help ensure that these children are theirs.”

“In fact, we have data that show that when the man is separated from his partner, or suspicious of her infidelity, he thrusts more (and more deeply), which increases displacement,” Burch continues. “We also see this in rough sex research — that rough sex triggered by male jealousy involves more displacement — and in cheating scenarios on the part of the ‘other man.’ Men who have sex with a woman and are aware that she’s in a relationship, engage in more displacement behaviors.”

Of course, Gallop and Burch’s theory isn’t universally accepted, and, when their study was published, it faced some criticisms. Speaking to BBC News in 2003, other scientists described the theory as “far fetched” and “flawed,” with one questioning: “If the man continues to thrust after ejaculation he would simply be scooping out his own semen. Also does the sexual position matter? I imagine gravity has some role here.” 

Another study proposed that men’s penises had simply evolved to be the size and shape they are because of women’s preferences for bigger dick. As National Geographic reported in 2013: “Since early humans didn’t wear clothes, male penises were obvious to women. So if women chose their mates based on the size of their genitalia, it’s possible that these decisions influenced the evolution of bigger penises.” Gallop himself criticized this theory, pointing out that women would just see men’s flaccid penises more often, which have less bearing on pleasure during sex. Also, as I’m sure you’ve noticed, this conversation is extremely heteronormative, meaning that even if these theories are true, they don’t adequately describe what’s happening for everyone. 

Without further research, it’s near-impossible to state with complete accuracy exactly why the penis is mushroom shaped. Still, with little examination out there, Gallop and Burch’s evolutionary theory does appear to make most sense. With this in mind, and thanks to men’s inherently competitive nature, it looks like the penis might just stay shroomy forever. 

So, maybe Trump is the ultimate dick after all.