When he came to review Origin of Species in 1859, Huxley identified this same method of forming sound beliefs as characteristic of Darwin: "so outspoken [is] his conviction, so honest and fair the candid expression of his doubts." Huxley urged that Darwin's readers adopt the same frame of mind: a state of "doubt which so loves truth that it neither dares rest in doubting, nor extinguish itself by unjustified belief."

In support of his claim, Huxley referred to the many passages in Origin in which Darwin raised objections to his own theory, or discussed the limits of scientific knowledge on particular questions. One can indeed find numerous examples of this in Darwin's publications: his devotion of a whole chapter in Origin to the difficulties of the theory of descent; his mode of assembling evidence favourable and unfavourable, circling around a position from all sides for dozens of pages, as in his writing on hybrid sterility in Variation in animals and plants under domestication (1868); or on the origin of human races in Descent of man (1871).
Photograph of Alfred Russel Wallace

Magnifying glass icon. Alfred Russel Wallace

Some leading Darwinians found this approach frustrating. Alfred Russel Wallace repeatedly urged Darwin to place more emphasis on the facts favourable to natural selection, and worried that Darwin gave leverage to his critics by calling attention to the difficulties of his theory. Indeed, Huxley's own style of debate, often aggressive and confrontational, hardly followed the Darwin role model.