From his early transmutation notebooks in the late 1830s onwards, Darwin considered human evolution as part of the natural processes he was investigating, and rejected divine intervention. In 1856, his "big book on species" titled "Natural Selection" was to include a "note on Man", but when Wallace enquired in December 1857, Darwin replied; "You ask whether I shall discuss 'man';—I think I shall avoid whole subject, as so surrounded with prejudices, though I fully admit that it is the highest & most interesting problem for the naturalist."</ref>