  He clearly recognizes that Herschel is here providing a philosophical justification for the project upon which Darwin was secretly working. And, in the very first paragraph of On the Origin of Species, Darwin looks back to this ‘Hurrah’, attributing the idea that the origin of species is ‘that mystery of mysteries’ to ‘one of our greatest philosophers’, without mentioning Herschel by name. The first mention of the possibility of an evolutionary solution to this problem is in his Ornithological Notebooks, in a note written shortly after departing Cape  Town.[6] 