Penis Bone
The Penis Bone or "bacula" is a bone found in the penis of several mammals. Despite slang terms that imply otherwise, the human penis contains no bones.
Why???
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.
History
The Penis Bone first showed up in mammals around 95 million years ago. Most researchers think that it became a thing for reproductive strategy. See, most mammals back then had sex for like seven seconds. Wham, Bam, Thank you ma'am.
This shortness of sexual happy time was a poor strategy as such short time periods allowed for other mates to jump on for a ride, making it so that the previous mate's DNA would not be passed on. Slowly, but surely, mammals began evolving a bone that would keep the male member harder for a longer period of time, ensuring that other mates couldn't get in there and screw things up.
But Humans Don't Have One
Yep, humans don't have a penis bone. Chimps and other higher primates have them, but us guys don't. The reason? Another reproductive strategy. See, sometime around the time of the last ice age, about 1.9 million years ago, humans began to move towards monogamy.[1] Single mates, as a strategy, prevents some other potential mate from getting sloppy seconds.
With the reduced competition for mates, you are less likely to need a baculum,” he added. “Despite what we might want to think, we are actually one of the species that comes in below the three minute cut-off where these things come in handy.[2] 
While there are a ton of sluts and man-whores out there fucking everything that moves, the vast majority of us tend to just stick with one mate.[3] Whether this is out of laziness or out of loneliness, it still proved to be such an effective sexual strategy that we lost the bone to our boners.[4]
Effect
Because humans lost their Penis Bone, they needed to evolve a better system. This system was to make human schlongs bigger than most other great apes.
Humans have a much longer and wider penis than the other great apes. Even the largest of gorillas, more than twice as heavy as a human, will have a penis just two and half inches long when erect.[5]
Further Reading
- Penis bones shed light on sex life of ancient, extinct bears
- Penis Facts
- What Otters' Penis Shrinkage Could Mean for Humans
- Why does it seem like all these articles are written by women?
- It could have been a "sperm scoop"
References
- ↑ It is worth noting that hunter-gathers around the world practice only monogamy or serial-monogamy which suggests that our ancestors may have used this mating system.
- ↑ https://www.theguardian.com/science/2016/dec/14/why-dont-humans-have-a-penis-bone-scientists-may-now-know-baculum
- ↑ Three main theories have been put forward. First is the need for long-term parental care and teaching, as our children take a long time to mature. Second, males need to guard their female from other males. Third, our children are vulnerable for a long time and infanticide could be a risk from other males. So to ensure that children are able to reach maturity the male is likely to stay to protect them, both socially and physically. This may be why males have maintained their larger relative size.
- ↑ Human monogamy has long puzzled anthropologists, and lots of effort has gone in to working out what keeps males hanging around.
- ↑ https://theconversation.com/why-did-humans-evolve-big-penises-but-small-testicles-71652