What Happened to the Bone in Our Boners? Monogamy, Research Suggests

Ah, the mystery of the penis bone.

Sure, we call erections "boners," and it is indeed possible to break your penis, but anyone who's ever seen a penis knows very well that there's no actual bone in there. However, plenty of mammals have a penis bone, and researchers think our ancestors did at one point. So why did nature's Viagra disappear? What happened to the bone in our boners? A new study published in Proceedings of the Royal Society suggests that monogamy is to blame.

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Scientists first set out to study the differences in penis bone (bacula) length amongst animals and found "a clear [relationship] between the bone's length and a species' promiscuity: more promiscuous species had longer bacula," according to The Economist.

The researchers found that several links. First of all, the more promiscuous a species, the more risk that "a female will be inseminated by another male before the first male's spermatozoa have had a chance to fertilize the female's eggs," according to The Economist. Secondly, species that had specific seasons for mating had longer bacula. Thirdly, the longer the sex, the longer the penis bone—specifically, because males that had longer penis bones engaged in "prolonged intromission," meaning sex that lasts longer than three minutes, so that the competition stays away while the deed is being done.

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In chimps, the baculum is about the length of a human fingernail. In humans, it's gone entirely.

"We think that is when the human baculum would have disappeared because the mating system changed at that point," Kit Opie, a co-author of the study at University College London, told The Guardian. "This may have been the final nail in the coffin for the already diminished baculum, which was then lost in ancestral humans."

When monogamy became the primary means of reproduction among humans 1.9 million years ago, researchers believe humans may have lost their penis bones, because there was no need for competition anymore.

"We defined prolonged intromission as that which continued for longer than three minutes," co-author Matilda Brindle told Seeker. "Short intromission was that which continued for less than three minutes. When all cultural aspects of sex are stripped away and a male's aim is solely to ejaculate, human intromission is classified as short."


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