If you read the book by Pierre Boulle you might understand but in context of the film it makes no sense whatsoever. In the book the man travels from earth to a planet near beetlejuice, were he discovers a world populated by monkeys. He goes on a dig with some chimps and they discover artifacts which show man was once the dominent race, they the are able to read the wild mens brains and reveal supressed information about when man ruled the planet but Monkeys through mimicry learn to speak and take over and man goes back to the forset and loses all sense of intelligence. Anyway the man gets off the planet and goes back to earth and its 2000 years in the future (the book explains why basically due the Einsteins theory of relativity) and it ends the same as the film. But in the film none of these themes are explained in the same way.