Darwin notes that "We need hardly say that Mr. Bates... is a zealous advocate of the hypothesis of the origin of species by derivation from a common stock", in other words that Bates was a staunch Darwinian. Darwin was happy to have the "Naturalist" on his side, and to use the book in the "Origin of Species" debate which was still heated in 1863. In particular, Darwin was struck by Bates's robust evidence of mimicry in "the Butterflies of the genus "Heliconius"". Here Darwin quotes nearly a whole page from Bates's conclusions, including Bates's view of his own findings that hint at speciation actually in progress: