That's a very interesting idea but here is a question : is going to be a drama or action or what?
Since it goes this far into human history there should be a lot of room for you to deal religions and the way civilization developed..,again nice idea ,many possibilities .
PS. to the people that said it is like pokemon....DAMN YOU :P
now i didn't really mean that... but i hate everything that has to do with little pets that need a master to tell them : block the monster who is trying to kill you ...or, avoid the obviously painful attack you are going to get...(i apologize to any possible fun that is reading this thread )