The penis bone has been described as “the most diverse of all bones,” with variable width and shape across mammals – all except one, humans. The bone, known scientifically as the baculum, can be found in cats, dogs, rats, racoons as well as our cousins chimpanzees and gorillas – but humans have evolved not to have one.
This lack of baculum has been debated for decades and now a new research paper, published by the Royal Society, puts forward a reasoning for how humans evolved not to have one. The answer is likely to be monogamy.
Biological anthropologists from University College London traced the penis bone back through its 145 million-year-history and found the baculum is “significantly longer” in primate and carnivores where intromission is longer.
It can be as long as a finger in a monkey. In the walrus, it can be two feet long. But the human male has lost it completely. And researchers are a little stumped.
Known as the baculum to scientists with an interest, the penis bone is a marvel of evolution. It pops up in mammals and primates around the world, but varies so much in terms of length and whether it is present at all, that it is described as the most diverse bone ever to exist.
When human beings stopped swinging and settled down, the baculum went the way of the dodo bird, as it was no longer a necessary appendage for a guy to pass on his genes. (Chimpanzees, for comparison, have a baculum the size of your fingernail.)