Trivia: Taylor's first name, George, is never mentioned in the film. He is referred to only as "Taylor."
Trivia: During breaks, the ape makeup couldn't be removed. It is interesting to note that the chimps naturally hung out with other chimps during breaks, the gorillas natually hung out with other gorillas, and the orangutans naturally hung out with other orangutans.
Trivia: This film holds the world record for highest makeup budget.
Trivia: During breaks, the ape makeup couldn't be removed, so almost all of the food eaten had to be fed through straws.
Trivia: Something that I found rather amusing. In the 1968 'Planet Of The Apes' film, its immediate sequels, and the spin-off television series, apes have acquired a high level of intelligence, but lack technology. They can construct simple houses and buildings, write books, cultivate the land for food, organise governmental systems, but they cannot make machines, or run factories. Yet the apes possess vast quantities of guns, and have an unlimited supply of ammunition, which they apply to keep humans under control. Like or loathe firearms, it requires a great level of technical skill and resource to make a gun. Soon many people began to ask: how can the apes have so many guns, when they have no factories in which to make them? It was not long before somebody found a simple answer to what seemed like an unanswerable conundrum. All the weapons were left over from World War III, and discovered by the apes after they evolved.
Trivia: Charlton Heston is shot in the throat and captured by the apes. During his healing in captivity, Dr. Zira nicknames him "Bright Eyes," because of his obvious intelligence. A year earlier, when Charlton Heston appeared in the western "Will Penny," Heston's pack-horse was also named "Bright Eyes" in the film.
Answer: I think that this is meant to be a mystery. Taylor/Charlton Heston, an astronaut, leaves a world set somewhat in the future after 1968 (when the movie was made) but still recognisable to cinema-goers at the time, to travel through a "time vortex" to arrive in a world in a distant future, which has changed beyond recognition. Taylor meets the orangutan Zaius/Maurice Evans, and Zaius hints that he has some idea of what had happened, but Zaius' knowledge is either limited, or else Zaius is not going to tell Taylor (or his fellow apes) the full story. At the end of the movie Taylor discovers that, at some point between his leaving his own time and arriving in the "Planet Of The Apes", the world had been devastated by a nuclear war, but I think that the exact time, causes of, and course of this nuclear war are deliberately left as a mystery. Sometimes I think a bit of unresolved mystery actually improves a story, and I think this is the case here.
Rob Halliday