In The Blind Watchmaker Richard Dawkins says he and a philosopher friend disagreed about whether a godless universe would require special explanation. "I said I could not imagine being an atheist at any time before 1859, when Darwin's Origin of Species was published." The philosopher mentioned David Hume and asked "Why does the universe need any special explanation?"
I don't know about a "special explanation," but Dawkins should read the history of Doubt. Rational atheism doesn't seem to have been that hard for countless pre-Darwinians. Margaret Rose, for instance, may or may not have read her Darwin but she spoke for centuries of faithless skeptics when she disputed a fundamentalist's insistence that the discovery of "an eyeless fish living in a cave in Kentucky proved that there was a creator":
He forgot the demonstrable fact that the element of light is indispensable in the formation of the organ of sight, without which it could not be formed.Jennifer Hecht remarks: "Rose had a notion of how some doubters have always understood the world... nature suffices as explanation."