John Allen Paulos writes a very good explanation about how the creationist probability argument doesn't work. That argument is that the probability of all the things happening to make a human eye (or other complex thing) evolve is so low that it just couldn't have happened that way. It's bunk. As Paulos writes, think of a dealing out a deck of 52 cards in a row. The probability that you got that particular ordering is miniscule. Extremely miniscule. So miniscule that there is no way it could have happened by dealing a deck of cards out. At least that's the creationist argument applied to a deck of cards. And yet, that's exactly what you got and how you got it.