Plot hole: The "video history" of the crashed USAF ship makes it very clear that the planet is uninhabited when they "landed". I can understand how a race of apes develops - they had a bunch of them on board. I can understand how a race of humans develops - they are descendants of the original crew. What I don't understand is...where the heck did all the horses come from?
Trivia: There are some lines in this movie that were famous lines from the old Planet of the Apes. They are "get your stinkin' hands off me you damn dirty human" (previously "Take your stinking paws off me you damn dirty Ape.") and "damn them, damn them, damn them all to hell" (previously "damn you, damn you, damn you all to hell").