Darwin wrote to Asa Gray in 1860: “With respect to the theological view of the question; this is always painful to me.–I am bewildered.–I had no intention to write atheistically. But I own that I cannot see, as plainly as others do, & as I shd wish to do, evidence of design & beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice. Not believing this, I see no necessity in the belief that the eye was expressly designed. On the other hand I cannot anyhow be contented to view this wonderful universe & especially the nature of man, & to conclude that everything is the result of brute force. I am inclined to look at everything as resulting from designed laws, with the details, whether good or bad, left to the working out of what we may call chance. Not that this notion at all satisfies me …. But the more I think the more bewildered I become; as indeed I have probably shown by this letter.”

In a letter to Gray later in 1860 he added: “One word more on “designed laws” & “undesigned results.” I see a bird which I want for food, take my gun & kill it, I do this designedly.–An innocent & good man stands under tree & is killed by flash of lightning. Do you believe (& I really shd like to hear) that God designedly killed this man? Many or most person do believe this; I can’t & don’t.–If you believe so, do you believe that when a swallow snaps up a gnat that God designed that that particular swallow shd snap up that particular gnat at that particular instant? I believe that the man & the gnat are in same predicament.–If the death of neither man or gnat are designed, I see no good reason to believe that their first birth or production shd be necessarily designed. Yet, as I said before, I cannot persuade myself that electricity acts, that the tree grows, that man aspires to loftiest conceptions all from blind, brute force.”

I’ve just discovered, in looking for that first letter, that Cambridge makes what looks like all of Darwin’s letters through 1859 available online. That’s very nice of them. The project’s homepage is here.