Asa Gray, Darwiniana, 1876.

While Darwin and Gray both believed in evolution, they had radically diverging opinions about what those facts ultimately meant: Darwin was convinced that a God who would watch the sparrow’s fall with perfect indifference also had no real interest in the lives of people. The Presbyterian Gray, however, felt that the very complexity of Darwin’s theory proved, rather than denied, the existence of a benevolent, designing God. It was in conversation with Gray, too, that Darwin offered what I think is the most moving justification of his position: “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,” Darwin wrote to Gray on May 22, 1860. “There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice.” But Gray was undeterred—in his reviews and essays, collected in Darwiniana, he both defended and disagreed with Darwin, maintaining his view that evolution was proof of divine design rather than its opposite: “Difficult as it may be to conceive and impossible to demonstrate design in a whole of which the series of part appears to be contingent, the alternative may yet be more difficult and less satisfactory.”