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Artículo Humans lost their penis bone, and now scientists think they know why News

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Humans lost their penis bone, and now scientists think they know why

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Antonio J. Rodríguez

16 Diciembre 2016 08:41

Almost all mammals have it... so what about our species?

Among the most diverse bones in mammals is the penis bone. It can span from 5 centimetres in the stump-tailed macaque (which weighs only 10 kg) to 60 centimetres in the walrus. But what most intrigues scientists is the fact that humans have completely lost theirs.

Researchers at University College London have been asking why. And, after an extensive study, they believe they've found the key to explaining this strange phenomenon.

According to the study, the penis bone appeared in mammals 95 million years ago, and was already present in some primates that date back 50 million years. From then on, it adapted according to each species. But the species whose penis bones have completely disappeared are few.

Kit Opie, who ran the study, has explained that the length of the bone is always greater in species whose males practise so-called “prolonged intromission”. That is, when the act of penetration exceeds three minutes. This approach allows the male to impregnate the female and, at the same time, keep competition at bay. The bone, which is situated at the tip, rather than the base of the penis, serves as structural support for males that reproduce in this way.

In chimpanzees, for example, the bone is no longer than a nail, which corresponds with mating that lasts little more than seven seconds. In groups of chimpanzees, the females mate with all the males because the males kill baby chimpanzees that aren't theirs. In other words, if all the males believe that a baby is their own, none of them will kill it.

For a female to remain still while she mates – that is, not to run off and mate with another male – the chimpanzees use the bone as a method of restraint during penetration. In some species, such as pigs, it allows greater support, given that the act can exceed half an hour.

In humans, however, the appearance of monogamy has meant that it's no longer necessary for the male to restrain the female during penetration for fear that she might mate with another, rendering the bone useless.

This was some 1.9 million years ago, in the time of the Homo Erectus. In a monogamous relationship, the male doesn't have to spend so much time penetrating the female, as it's unlikely that she might run off to mate with a different male (at least in theory).

We think that is when the human penis bone would have disappeared because the mating system changed at that point,” Opie said. 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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