The Origin of Species was a revolutionary book written and revised by Charles Darwin between the years 1859-1872. The Origin of Species included and described many of Darwin's original theories on Natural Selection, Variation,Survival of the fittest and Sexual Selection
"No one supposes that all the individuals of the same species are cast in the very same mould. These individual differences are highly important for us, as they afford materials for natural selection to accumulate, in the same manner as man can accumulate in any given direction individual differences in his domesticated productions"
Source: : John van Wyhe, ed. 2002- The Complete Work of Charles Darwin Online '(http://darwin-online.org.uk)