evolution of a human brain

[siegfriedandroy]

as i was dozing off last night, i began pondering how something as complicated as the human brain could evolve by chance apart from God. to all you math majors out there, what is the probability of a human brain evolving from a 'singularity' w/i 17 billion years apart from any supernatural intervention?

I will concede that this singularity somehow simply appeared 17 billion years ago (for no reason, w/o God, etc.; a difficult, if not impossible proposition for the atheist to explain in itself).

If we could somehow conduct an experiment 1 billion times, starting w/ nothing but a singularity (and no Intelligence to guide it), how many times out of this billion will a human brain evolve w/i 20 billion years?