Why Men Don’t Have Penis Bones, According To Science

“Getting a boner” has never been a literal statement for one reason: men don’t have bones in their penises. Other mammals, such as chimpanzees, raccoons, and walruses, have them, but the modern human male doesn’t. For many years, scientists have been stumped on the reason why.

The answer lies in our mating habits, according to a study conducted by researchers at the University College London.

Animals with long penis bones practice what scientists called “prolonged intromission,” which means that sexual penetration lasts for longer than three minutes. The penis bone helps with this because it means that things “hold up” longer because it attaches at the tip of the penis instead of the base. Prolonged intromission allows the male more time to impregnate the female and keep her away from other males in the group who also want to mate with her.

But since human beings tend to be monogamous, a human male typically doesn’t have to worry about other horny males taking his mate and impregnating her before he can. As a result, penetration doesn’t have to take that long. Scientists surmise that this is the reason our evolutionary ancestors lost their penis bones.

A baby male chimpanzee is nursed by his mother 'Kuma' (L) at Taronga Zoo in Sydney, Australia. (Photo by Cameron Spencer/Getty Images)

“We think that is when the human baculum (penis bone) would have disappeared because the mating system changed at that point,” researcher Kit Opie said in an interview with the Guardian. “This may have been the final nail in the coffin for the already diminished baculum, which was then lost in ancestral humans.”

A full article on the results of their study can be found in the Proceedings of the Royal Society.

As Science Mag reports, the penis bone evolved in animals around 145 million to 95 million years ago. This means that the most recent shared ancestor between primates and carnivores would have had one. Monogamy became the dominant mating practice during the time of Homo erectus around 1.9 million years ago.

Prehistoric skulls on display side by side
The skulls of our prehistoric ancestors. Monogamy developed during the time of Homo Erectus, [Photo by Creativemarc/Thinkstock]

“With the reduced competition for mates, you are less likely to need a baculum,” Opie added. “Despite what we might want to think, we are actually one of the species that comes in below the three minute cut-off where these things come in handy.”

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