You should define your idea of original. Ive done some reading on the movie business, and "original" has NEVER been their first priority. Going all the way back to beginning of film making, the majority of films have and always will be adaptations of literature and other movies. You would probably be amazed at how many of your favorite films were based on another movie.
The Godfather, Schindler's List, One flew over the cuckoo's nest, Star Wars, Jaws, Raider's of the Lost Ark, Silence of the Lambs, Forest Gump, Dr. Strangelove, Citizen Kane, Alien, Lawerence of Arabis, etc., etc., etc.