
Source: On the Origin of Species (1859), chapter VII: "Instinct", page 207 http://darwin-online.org.uk/content/frameset?pageseq=225&itemID=F373&viewtype=side
Context: I must premise, that I have nothing to do with the origin of the primary mental powers, any more than I have with that of life itself. We are concerned only with the diversities of instinct and of the other mental qualities of animals within the same class.