On the Origin of Species for Existence" Darwin includes "slow-breeding man" among other examples of Malthusian population growth. In his discussions on morphology, Darwin compares and comments on bone structures that are homologous between humans and other mammals. Darwin's early notebooks discussed how non-adaptive characteristics could be selected when animals or humans chose mates, with races of humans differing over ideas of beauty. In his 1856 notes responding to Robert Knox's "The Races of Man: A Fragment", he called this effect sexual selection. He added notes on sexual selection to his "big book on species", and in mid-1857 he added a section heading; "Theory applied
Reactions to On the Origin of Species to showing you the varieties of those species, or of any of those phenomena that would aid one in getting at that mystery of mysteries, the origin of species, our space does not permit; but surely there ought to be a space somewhere, and, if not in the British Museum, where is it to be obtained?" Huxley's April review in the "Westminster Review" included the first mention of the term "Darwinism" in the question, "What if the orbit of Darwinism should be a little too circular?" Darwin thought it a "brilliant review." Overflowing the narrow bounds of purely scientific circles,