Aliens Exist...or do they?

I read The Host by Stephenie Meyer a long time ago, but I was just thinking about it the other day, because I'm hoping someone will make it into a movie soon. Anyways, in the book, souls are taking over human bodies and the humans are trying to survive. It was a really good book and I highly reccomend it. Another novel I read more recently, I am Number Four by Pittacus Lore, also deals with alternate life forms from other planet systems. Anyways, while I personally don't believe in aliens, to me it is still a very entertaining idea and makes for good novels. :)