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Why don’t humans have a penis bone? © Getty Images

Why don’t humans have a penis bone?

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The penis bone, otherwise known as the 'baculum', is present in all primates aside from humans.

Asked by: Claire Russell, Leicester


The penis bone or ‘baculum’ is common to lots of placental mammals but by no means all of them. It seems to have evolved independently nine times in different mammal lineages but it has also subsequently been lost in many cases. Among primates, humans are the only ones without a baculum, although it is tiny in gorillas and chimpanzees.

The baculum allows prolonged penetration and it is normally only present in animals that mate for longer than three minutes. Lengthy sex sessions are an adaptation to maximise the male’s chance of impregnating the female. Humans evolved monogamy as a reproductive strategy, which – along with other social rules – reduces the risk of females mating with rival males. Men can therefore get away with shorter copulation times.


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luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.


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