Well, heres the concept;
You start off with a single celled organism doing a pac-man type game(eat smaller stuff avoid bigger stuff) evolving different parts as you go, like little hairs to make you go faster, bigger mouth, etc.. and then you eventually become a more complex creature evolving up till your a fish type thing.
At this point(or perhaps earlier not too sure when this really kicks in) you can start designing your body parts to look however they want as many fins, teeth, flippers, as you want wherever you want them and they use procedural generation to figure out the movement animations for that body. You continue to try to survive and to evolve you breed yourself and lay an egg, give birth, divide, or whatnot and then you eventually gain sentience at which point you gain a tribe of your little dudes that you have evolved.
They go about their business and you influence their development at that point by giving them say a spear to make them more warlike or a musical instrument to make them more creative, and you continue doing this till they get to a certain level of intelligence at which point you start a simcity/age of empires type game.
Here you start building big cities, researching, and that good stuff and start trying to take control of the planet. And then you start building space craft and exploring the solar system and galaxy terraforming and conquering worlds, breeding new species.
The exciting thing about it is that all the stuff you encounter out there is from other players, it seeds your universe with player created content, and procedurally generates everything(which makes stuff small enough to do all this seeding.)
In a nutshell thats what spore is supposed to be like.
