from the alien race to the pre hominids on Earth. That is why the monkey grabbed a bone and beat another to death, it had never occurred to him (until the monolith told him) that he could overpower the other pack of monkeys to get what he wanted.
At the end of the movie, the astronaut travels through the portal orbiting Jupiter and is brought into the other realm/dimension created by the alien race.
At least that is what I remember. 2001 is an incredible movie in opinion.