Dar·win \ˈdär-wən\ , Charles Robert (1809–1882), British naturalist. Darwin is celebrated for his documentation of the theory of evolution and the development of the principle of natural selection. In 1831 he began a five-year voyage around the world, making stopovers in South America where he gained critical insight into the variation between populations of animals on the various islands and the mainland which played an important role in the development of his ideas on evolution. In 1859 he published On the Origin of Species by Means of Natural Selection. This landmark work brought about a revolution in biology and firmly established the study of evolution as part of the science of biology. The Descent of Man, 1871, was a follow-up work that contained his related theory of sexual selection. Darwin was not the first to question the immutability of species in nature or to conceive the notion of evolution, but he added to the theorizing of Lamarck and others the concept of natural selection and voluminous documentary evidence.