Well, Jon, Darwin came from a religious background. He was always careful not to confront religion but he was acutely aware of the contradictions within and among big religions and he saw no particular reason why Christianity should have been accorded any more credibility than any other. I suppose "agnostic" descibes him best. He was troubled by doubts about his theory (almost to the point of recanting bits of it at times) and was notoriously sensitive to criticism. What he needed was a few good modern atheists around him to fortify him. ;-)