Named after the English naturalist Charles Darwin (1809-92). Darwinism is the theory of evolution (or systematic change and adaptation) by means of natural selection. Those members of a species best suited to their environment survive and reproduce; those least suited die. Over very long time periods this produces new species. We now think of social evolution as an extension of biology but the idea of evolution was popular in a wide variety of intellectual fields in the mid-19th century and the phrase ‘the survival of the fittest’ was coined, not by Darwin but by Herbert Spencer, one of the founders of sociology, to explain the historical development of societies. One of the best known forms of social Darwinism is eugenics. Popular in Britain and the USA at the end of the 19th century, eugenics argued that the same deliberate selection that stockmen had for centuries applied to sheep and cattle, should be applied to people so that the best should be encouraged to breed and the weak, the criminal, and the stupid should be discouraged (or prevented) from breeding. Although periodically revived by racists who argued that certain peoples were superior to others (the Nazis in Germany in the 1930s, for example) eugenics fell from favour because it proved difficult to separate which human characteristics were genetic and which were a product of nurture and environment; few people would accept the ethics of preventing certain groups from producing: and no effective programme could be designed.