They ruined the ending
Decent movie. If you ignore all the grunting by prehistoric man Charlie, the storyline develops fairly well up to near the end. Near the end of the movie, Shepard leaves Charlie's environmental area to enter the lab simply by pushing one button (oh, and Charlie is watching). So is it any surprise that Charlie does the "monkey see, monkey do" thing and escapes the compound (he is the find of all time and their security consists of a single button)?? From here on the movie makes no real sense, as if the writer got mental cramps and couldn't come up with a decent ending. If Charlie had gotten his teeth fixed and a decent haircut, I see him fitting nicely into society and getting his doctorate in Anthropology.
Mountain Man