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.
kingdom, scientists set out to reconstruct the evolutionary story of the baculum, by tracing its appearance in mammals and primates throughout history.
They found that the penis bone evolved in mammals more than 95 million years ago and was present in the first primates that emerged about 50 million years ago. From that moment on, the baculum became larger in some animals and smaller in others. The stump-tailed macaque, an animal that weighs only 10kg, has an extremely long baculum for its size, with the bone extending for 5cm. The bone is five times the size of the baculum in the collared mangabey, which is a slightly larger monkey.
Kit Opie who led the study at University College London, said that penis bone length was longer in males that engaged in what he called “prolonged intromission.” In plain
In chimps, the penis bone is no longer than a human fingernail. The tininess of the bone correlates with the very short spell that the male spends mating, in the order of seven seconds. In chimpanzee groups, females mate with all the males, in what appears to be a strategy to reduce the risk of her children being killed by older males. “It gives each male an idea that they may have fathered the subsequent offspring, and it is in her interests to get that done quickly,” Opie said.