That question has not been answered. But being a rational person and not a close minded fundy - I will not follow it up with the all purpose catchphrase.... so "god did it"
Rational Person : I don't know, we need to study it further
Fundy Nutjob : I don't know... therefore god did it.
One approach results in intellectual advances, the other in ignorance and mental stagnation. I know which you prefer.