Sex & Relationships

Did Monogamy Kill the Penis Bone?

New research suggests a shift in human mating habits sparked a major change in human anatomy.

Photo Credit: Amankris / Shutterstock

Because sex is responsible for the creation of new life, we don’t often associate it with loss. But our mating habits may be to blame for the disappearance of something inside ourselves, leading some to ask, what was the human penis bone, and where did it go?

The baculum, as it's more formally known, has been described as the “most diverse bone” ever to exist, or certainly the most individualized. Believed to have "evolved in mammals more than 95 million years ago," according to the Guardian, the size of the penis bone changes from owner to owner. In chimpanzees, the penis bone is roughly the size of a human fingernail. In walruses, it measures upward of two feet. In humans, it simply doesn’t exist. Or doesn't exist anymore.

A new study published in the Proceedings of the Royal Society might finally be able to explain why. According to Kit Opie, a postdoctoral research fellow at University College London who led the study, the penis bone grew larger in males who engaged in something called “prolonged intromission,” a fancy phrase that refers to sex lasting more than three minutes. While these days, lengthy sex sessions are linked to pleasure and stamina, evolution offers a more practical reason for shagging so long. A male who spends more time penetrating a female has a better chance of impregnating her. At the same time, a long romp helps keep her away from the competition. It’s believed that males with longer penis bones are armed with more structural support to accomplish that task.

But somewhere around 1.9 million years ago, something changed in human mating habits. We started pairing off. We started to practice monogamy. Males no longer had to worry so much about competing figures impregnating their female partners, and it was no longer necessary for sex to last more than, say, three minutes. (Though many would say it's preferable.)

“We think that is when the human baculum would have disappeared because the mating system changed at that point,” Opie explained to the Guardian. “This may have been the final nail in the coffin for the already diminished baculum, which was then lost in ancestral humans.”

“With the reduced competition for mates, you are less likely to need a baculum,” he 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.”

So we might have monogamy to thank for the boneless boner. But who knows, maybe in a million more years, things will change again. Polyamory is trending.

h/t The Guardian

Carrie Weisman is a writer focusing on sex, relationships and culture.