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
On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection of science on which they bear". Years later, Darwin could only recall one review; Professor Haughton of Dublin claimed that "all that was new in them was false, and what was true was old." Despite illness, Darwin pressed on with writing the "abstract" of his "big book" on "Natural Selection"; this condensed version was published in November 1859 as "On the Origin of Species". In a largely overlooked passage from Wallace's essay, he says of the evolutionary principle: The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any