n :  a theory of the origin and perpetuation of new species of animals and plants that offspring of a given organism vary, that natural selection favors the survival of some of these variations over others, that new species have arisen and may continue to arise by these processes, and that widely divergent groups of plants and animals have arisen from the same ancestors : broadly  :  a theory of biological evolution Dar*win*ist n or adj 
 
 
 
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