query: When was Darwin's theory first published?
passage: Publication of Darwin's theory
Darwin made attempts to open discussions about his theory with his close scientific colleagues. In January 1842 Darwin sent a tentative description of his ideas in a letter to Lyell, then prepared a "Pencil Sketch" of his theory. He worked up his "Sketch" into an "Essay" in 1844, and eventually persuaded Hooker to read a copy in January 1847. His geology books and publication of Beagle findings were completed in 1846, when he began what became eight years of research into classification of barnacle species, exploring the immense amount of variation in nature.
passage: Sebright chicken
Charles Darwin read Sir John's 1809 pamphlet, and was impressed with a passage that elaborated on how "the weak and the unhealthy do not live to propagate their infirmities". These writings, along with Darwin's correspondence via their mutual friend William Yarrell, aided Darwin in the inception of Darwin's theory of natural selection. Darwin's seminal work "On the Origin of Species", first published in 1859, cited Sir John's experiments in pigeon breeding, and recalled "That most skilful breeder, Sir John Sebright, used to say, with respect to pigeons, that 'he would produce any given feather in three years, but it would take him six years to obtain head and beak.'" Darwin also cited Sir John extensively regarding the Sebright bantam, as well as pigeon and dog breeding, in his 1868 work "Variation of Plants and Animals Under Domestication", his 1871 "The Descent of Man, and Selection in Relation to Sex", and his book on "Natural Selection" (which was not published in his lifetime).