Darwin’s attitude to religion can be summarized as thoughtful but detached. There is no evidence that he ever had any strong religious feelings or a sudden crisis of faith. Although he gradually lost any belief in Christianity “as a divine revelation,” he described himself variously as a theist or agnostic but never as an atheist, drawing a careful distinction between the neutral “unbelief,” or lack of belief, of agnosticism and the positive “disbelief” of atheism. Toward the end of his life, Darwin wrote that disbelief in “Christianity as a divine revelation” had crept over him at a very slow rate “but was at last complete.” The rate was so slow that he felt “no distress,” and he had “never since doubted even for a single second” that his conclusion was “correct” (Recollections). Emma Darwin and Francis Darwin both referred to the importance to Darwin of the distinction between disbelief and unbelief in letters discussing publication of the Recollections written after his death; Emma Darwin considered that the use of the word “correct” was misleading and that Darwin intended to convey that he himself never “altered his opinion” rather than that he thought the position untenable (CUL DAR 210.8: 42 and 219.1: 179).

Darwin accepted that others found it possible to believe both in evolution and in a deity, and he respected that position. He had a profound respect for the views of others and was generally reticent about his own, both from a natural aversion to causing unnecessary distress and, more pragmatically, because he regarded conflict as counterproductive. Typical is this response to an inquiry as to whether natural selection was compatible with belief in a personal God: “My opinion is not worth more than that of any other man who has thought on such subjects … I thank you for your Judgement & honour you for it, that theology & science should each run its own course & that in the present case I am not responsible if their meeting point should still be far off” (Darwin 1985–, 14:423, letter to M. E. Boole, 14 December 1866).