I suppose they are related, but isn't this on general evolution, not the big bang theory?
As for the Big Bang, I believe it is the most accurate and reasoned scientific approximation of the start of the known universe available to man today. It's probably wrong, but it's as close as we're going to get right now. For as much scientific grounds as there are for supporting the big bang, there is even more supporting evolution. Evolution, at least to a certain extent, is pretty darn close to scientific fact.
For the God argument, as I stated before, the Big Bang is the most accurate and reasoned scientific approximation of the known universe. Even if it's wrong and we discover a new, better explanation for the universe's origin, there will still be the initial, unexplainable - but what caused it, or where did it come from. My answer to that is God.
Assuming an omnipotent God, when He first set the universe in motion, it began to play out like an elaborate rube-goldberg device. One thing leading to another, one species evolving to another. He might need to make a minor adjustment here or there, but nothing too out of the ordinary of the series of events that make up our known universe.