I'm actually going to toss all my previous theories to the wind for this one. Ramuh said that in the age before man, light and darkness were as one. Think about it: if that's true, that split can't have created man, because it came after.

Mankind split the mothercrystal. Possibly even the Twelve themselves.

Too sleepy to follow this train of thought coherently at this time, but I think I might be on to something.