Looks like they are becoming more public about polydactyly humans.

From the article: They recently set out to understand whether the human brain can control more than the usual body (the answer, they would discover, is yes), whether this could lead to richer behaviour (yes again) and whether, instead of sharing the same muscles as the other fingers, the additional fingers have their own dedicated muscles, nerves and brain resources (they do).

In fact, the formidable supernumerary finger on each right hand of the two subjects Burdet and colleagues recently studied gave them “exceptional manipulation abilities” compared to the normal-bodied — so much so that the researchers mused whether there might be some benefit to augmenting normal five-fingered hands with an artificial finger.

“Naively, one could imagine that in X-number of years, the six-fingered hands would provide an evolutionary advantage, and so be spread genetically,” Burdet, a professor of robotics at Imperial College London, said in an email. “However, it is likely that some ‘genetic pressure’ would keep the five-fingers design.”

https://calgaryherald.com/life/leap-day-how-six-fingered-humans-use-their-extra-digit/wcm/340a3d9a-8020-4d91-9bc8-c9e256b14cc5