During the filming of Planet of the Apes in 1967, Charlton Heston noted “an instinctive segregation on the set. Not only would the apes eat together, but the chimpanzees ate with the chimpanzees, the gorillas ate with the gorillas, the orangutans ate with the orangutans, and the humans would eat off by themselves. It was quite spooky.”
James Franciscus noticed the same thing filming Beneath the Planet of the Apes in 1969. “During lunch I looked up and realized, ‘My God, here is the universe,’ because at one table were all the orangutans eating, at another table were the apes, and at another table were the humans. The orangutan characters would not eat or mix with the ape characters, and the humans wouldn’t sit down and eat with any one of them.
“I remember saying, ‘Look around — do you realize what’s happening here? This is a little isolated microcosm of probably what’s bugging the whole world. Call it prejudice or whatever you want to call it. Whatever’s different is to be shunned or it’s frightening or so forth.’ Nobody was intermingling, even though they were all humans underneath the masks. The masks were enough to bring out our own little genetic natures of fear and prejudice. It was startling.”
(From Joe Russo and Larry Landsman, Planet of the Apes Revisited, 2001.)