Do some animals have bones in their penis

A. Yes they do. The penis bone, os penis, (os is Latin for 'bone'), or baculum, occurs sporadically in the animal kingdom. It is found in insectivores, bats, rodents, carnivores, and pinnipeds, and in primates except humans.

Q. What is the os penis for

A. This rather odd bony structure gives the penis extra rigidity to prolong copulation. Although it's not exactly known why some animals have this bone, it would certainly be advantageous for those species in which ovulation is induced by copulation.

Another explanation is that prolonged copulation gives the male a greater chance of passing on his genes, which is important in species that don't live in social groups. In this scenario, where fertile females mate with any males they come across, it's in the males interest to try to mate for as long as possible, maximising their chances of fathering the female's offspring.

Q. What does the os penis look like

A. Well, it varies according to the species, but generally speaking, as would be expected, it is elongate.

Q. But humans don't have one

A. No, but apes, out closest living relatives do, although they're very small compared to the bacula of some other species. Humans and apes last shared a common ancestor around 6 million years ago and so at some point after that the os penis must have disappeared from the anatomy our ancestors, presumably because it was no longer needed.

However humans do seem to be slightly put out that we don't have one and make up for it in other ways...

Q. What 'other ways'

A. By giving them as love tokens! In some parts of the world, notably the USA, boys give them to girls as a symbol of their affection. Apparently the proper way to prepare a penis bone is to boil it clean and tie a piece of red thread or string around it, the object of your affection is then supposed to wear it as a necklace.

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by Lisa Cardy