If you were under the impression that the human body had finished evolving, think again. It turns out that some people have a bone in their knee called a fabella. And while this particular little bone with an unknown purpose was once fading away, over the last century and a half, it's gotten more common. Back in 1875, nearly 18 percent of people examined had a fabella. That number dropped to 11 percent by 1918. However, by 2018, 39 percent of individuals had this mysterious bone.