SPOILER WARNING!!!Okay, now that you have been warned, if you read the book, you will find out that an Alien race plants intelligent life in various places in the universe. Then, they put those monoliths around the solar system of the life forms they created. This is so that once the life form is advanced enough, they will explore their solar systems and unearth the monoliths. Once that happens, the alien race takes one member of the race (in this case, Dave Bowman) and turns him into a deity to watch over his planet. That fetus was that god, and when Dave was in the hotel room, he was actually in the possession of the aliens.Another point, in the beginning of the movie, when the ape is holding up a bone and the scene cuts to a spaceship, that craft is actually a nuclear weapon launcher, which is what Dave Bowman has to, in turn, prevent from destroying his race.I hope that cleared it up for a few of you out there, and I strongly recommend you read the book if you like the movie. It'll clear up so many things.