It is this contrast that struck me when I first saw the original film as a kid and I'm sure that was the aim of the directors - apes acting like university professors and humans acting like primitive animals. Turning the creation vs. evolution debate around by having the apes unwilling to believe they were descended from humans. It is this aspect of the film that gives it its timeless quality and places it squarely into classic sci-fi film history. And the famous revelation at the end is probably one of the few of its kind that actually worked. This is precisely because the film's plot and content stands on its own, making the final scene a powerful commentary on it rather than a central device (a la Soylent Green). I also must hand it to the actors who managed to convey wonderfully convincing performances despite the stiff plastic over their faces.
Planet of the Apes has never been on my favorites list, and aside from the few points I just made, there's not much more that stands out. Several sequels were made due to its popular appeal at the time, and some of them had merit, but on the whole I think the original film pretty much said it all. And the modern remake in 2001 by Tim Burton is wholly forgettable. Still, any science fiction anthology would be remiss to leave it out, so consider this entry a tribute to a classic, and forgive me for including the closing scene below.