Returns Asa Gray letter. Gray has made a great blunder in his criticism of Oliver: he mistakes perpetuation of a variety for "propagation of variation". Confusion between "action of physical causes" and "effects of physical causes". Neither crossing nor natural selection has made so many divergent individuals, but simply variation. "If once you hold that natural selection can create a character your whole doctrine tumbles to the ground." CD’s failure to convey this, and the false doctrine that "like produces like" is at bottom of half the scientific infidelity to CD’s doctrine. There is something to the objection that CD has made a deus ex machina of natural selection since he neglects to dwell on the facts of infinite incessant variations.