Mutation Theory

Hugo de Vries put forward the mutation theory after studying the Evening Primrose plant, Oenothera lamarckiana, in which he observed sudden, striking variations appearing without any obvious environmental cause. Where Lamarck and Darwin both believed new species arose through the slow, gradual accumulation of small variations across many generations, de Vries argued instead that large, sudden, discontinuous changes — mutations — were directly responsible for the origin of new species. The salient features of his theory are: mutations (discontinuous variations) are transmitted to later generations; mutations occur spontaneously and repeatedly in naturally breeding populations; mutants appear as fully-formed new types with no intermediate forms bridging them to the parent type; and, once they arise, mutant individuals remain fully subject to natural selection like any other variant in the population. Although the specific mechanism de Vries observed in Oenothera later turned out to reflect chromosomal irregularities rather than 'true' ge …