The guy that that made Spore (Will Wright) is the same guy that made "Sim City" and "The Sims" he's a genius, so much so that he made it on TED.com where they only have smart people ex: Steven Hawking. I encourage you to read and watch the video on his profile because it tells you how detailed the game is and how complex the system is, it is literally a world that has no limitations and I mean NONE. You've probably heard about all of this but this vid is filled with the details.
http://www.ted.com/speakers/view/id/128