I'm listening to the audio commentary on 2001: A Space Odyssey. Gary Lockwood, who plays astronaut Frank Poole in the film, says something interesting about the famous sequence in which a prehistoric ape-man flings a bone into the air after using it to kill some rivals. As the bone falls to earth, Kubrick jump-cuts to a spaceship or satellite in freefall around the globe.
I always assumed that the sequence was illustrating the evolution of tools; crude club to sophisticated spacecraft. But according to Lockwood, the craft in the shot is a missle-carrying satellite, an orbital weapons platform. In his words, it's a "weapon-to-weapon shot."
Of course, just because Lockwood was in the movie doesn't mean that he's correct about Kubrick's intentions, but his insight is almost certainly more valid than mine. It certainly adds a more pessimistic flavour to the film.