Planet of the Apes is a political allegory. From the beginning to the end of the film the viewer is shown a picture of a world ruled by a heavy handed government, and led by apes who represent the church and state alike. The main character that is an example of this is Dr. Zaius, "Chief Prosecutor and Defender of the Faith," who rules both nation and state with an equally closed mind. For most Americans, this is unheard of. One of the founding principles of the United States of America is a division of church and state. To us, having one individual controlling both seems not only preposterous, but dangerous. The American mind immediately concludes that a system such as this will lead to stagnation in science, and close-mindedness in religion.
In Planet of the Apes this stagnation does occur. When a young upstart scientist named Cornelius tries to attack the religiously based view of life in his society he is brought up on charges of heresy. Cornelius merely attempted to state that he had found evidence that apes had evolved from man. Defender of the faith Dr. Zaius then quickly ended the hearings and threatened Cornelius with charges of hearsay. This is a direct link to our own past. Charles Darwin challenged religions view on the origins of life in the 1800's, and frighteningly similar things occurred to him.
This is what Planet of the Apes attempts to do, and accomplishes so thoroughly. It mirrors things that have happened in out own world, yet portrays them in a way that makes humanity's own