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.

Discusses differences between Asa Gray’s view and his own on crossing. A common effect is the obliteration of incipient varieties. There is heavy evidence against new characters arising from crossing wild forms, "only intermediate races are then produced". Innate vital forces are somehow led to act differently as a result of direct effect of physical conditions. Astonished by JDH’s statement that every difference might have occurred without selection. CD agrees, but JDH’s manner of putting it astonished him. CD says, "think of each of a thousand seeds bringing forth its plant, and then each a thousand … I cannot even grapple with idea". Responds to JDH’s and Lyell’s feeling that he made too much of a deus ex machina out of natural selection. [Letter actually dated 20 Nov but is certainly after 3831.] [wrong field?]