I think Piltdown Man was a famous hoax ACD (and Teilhard de Chardin) fell for, rather than perpetrated. ACD was a real flake in a lot of ways. He’s a recurring character in the “Murdoch” mystery series.
Wiki lists Arthur Conan Doyle as one of the suspected hoaxers. Charles Dawson (an in-law) is listed as the most likely hoaxer. I doubt ACD fell for it because (I think) he did not believe in evolution.
Quote from ACD’s bio on Wiki:
“Richard Milner, an American historian of science, has presented a case that Conan Doyle may have been the perpetrator of the Piltdown Man hoax of 1912, creating the counterfeit hominid fossil that fooled the scientific world for over 40 years. Milner says that Conan Doyle had a motive—namely, revenge on the scientific establishment for debunking one of his favourite psychics—and that The Lost World contains several encrypted clues regarding his involvement in the hoax.”
http://en.wikipedia.org/wiki/Arthur_Conan_Doyle