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Darwin, CharlesRobert (1809–82)The English naturalist who is remembered mainly for his theory of evolution, which he based largely on observations made in 1832–6 during a voyage around the world on HMS Beagle, which was engaged on a mapping survey. In 1858, prompted by and published together with a paper by Alfred RusselWallace (who had reached similar conclusions independently), he published in the third volume of the Journal of the Linnean Society a short paper, ‘On the tendency of species to form varieties: and on the perpetuation of varieties and species by natural means of selection’, and in 1859 he published a longer account in his book, On the Origin of Species by Means of Natural Selection. In this he presented powerful evidence suggesting that change (evolution) has occurred among species, and proposed natural selection as the mechanism by which it occurs. The theory may be summarized as follows: (a)The individuals of a species show variation.(b)On average, more offspring are produced than are needed to replace their parents.(c)Populations cannot expand indefinitely and, on average, population sizes remain stable.(d)Therefore there must be competition for survival.(e)Therefore the best-adapted variants (the fittest) survive. Since environmental conditions change over long periods of time, a process of natural selection occurs which favours the emergence of different variants and ultimately of new species (the ‘origin of species’). This theory is known as Darwinism. The subsequent discovery of chromosomes and genes, and the development of the science of genetics, have led to a better understanding of the ways in which variation may be caused. Modified by this modern knowledge, Darwin's theory is sometimes called ‘neo-Darwinism’.