The baculum, also known as the ‘os penis’, or the penis bone has always been a head-scratching issue for the scientists. Most of the placental mammals have this penis bone, but no two species are the same. Mice, bats, cats, dogs, and hedgehogs all sport structural reinforcement in their nether regions.
These bones vary widely in shape and size, some are spiked, some are even curved. Moreover, these bones are not proportional to an animal’s physical size. For example, Walruses posses a flabbergasting two foot long baculum which resembles a baseball bat. A gorilla’s baculum is only a few millimeters long, but a dog's can reach upto three inches.
Two foot long penis bone of a walrus (Source: By Didier Descouens - Museum of Toulouse, CC BY-SA 4.0)
Most primates, including our closest relatives, also have members in the baculum club, but humans, peculiarly, do not.
Over the years, many scientists have researched and came up with different hypothesis for why man’s manhood is boneless. But a new evolutionary study offers some plausible evidence. Analyzing anatomy and mating practices of thousands of mammals, anthropologists Matilda Brindle and Christopher Opie of University College London suggest that humans lost their baculum due to quick sex and relatively little competition.
During their research, Brindle and Opie found that the baculum appeared in the placental mammals after they split from non-placental mammals, about 145 million years ago. However, the bones were present before carnivores and primates evolved, around 95 million years ago. This suggests that more recently evolved species in these groups that lack a baculum, such as humans, lost the bony package.
Later, Brindle and Opie examined the mating practices of the species with and without the baculum, including polygamy or monogamy and also the duration of vaginal penetration, called intromission (yes, that's what it is called).
The presence of the baculum tightly hooked up with longer intromissions - those more than three minutes, over the course of primate evolution. The researchers also found that the longer the intercourse, the longer the bone. Moreover, long bacula were also linked with more competition for females.
Other researchers also speculate that this baculum allows for extended lovemaking sessions. But this isn’t a romantic gesture. The theory suggested that, prolonging intromission like this is a way for a male to prevent a female from sneaking off and mating with anyone else.
However, the theory isn’t perfect. Bonobo apes have maintained a baculum (a very small one though) and only have sex for about 15 seconds in one go. Brindle and Opie speculate that stiff competition between males keeps the bone around.
After our split from chimpanzees and bonobos and with monogamy becoming popular these days, the chances of keeping the penis bone reduced drastically.
Title image: mensjournal,