Why do some mammals have a bone in their penises?

PENILE stiffness is the stuff of smutty jokes. In Darwinian terms, though, it is no laughing matter. Intromission, the meeting of penis and vagina, is crucial to reproduction. With insufficient stiffness, intromission will not happen and the genes of the male will fail to make it into the next generation.

It is no surprise, therefore, that many male mammals have a bone, known as a baculum, in their penises to add to stiffness. What is surprising is that many others—men included—do not. What causes a baculum to evolve is not clear. But a study just published in the Proceedings of the Royal Society, by Matilda Brindle and Christopher Opie of University College London, has shed some light on the matter.

Ms Brindle and Dr Opie have reviewed what data there are about mammalian bacula, particularly those of primates and carnivores, and compared these with what is known about different species’ sex lives. They picked the primates and the carnivores in particular because both groups contain some species whose males have a baculum and others whose males do not. (The picture above is of a skeleton of an extinct wolf species, in…Continue reading
Source: Economist