Mutationism

Mutationism is an evolutionary theory that gives discrete mutations a leading role in producing evolutionary change, rather than treating gradual natural selection on small variations as its chief source.

Hugo de Vries: Dutch botanist whose mutation theory proposed that new species could arise through sudden, heritable changes. His studies of evening primrose helped establish mutationism as an alternative to Darwinian gradualism.
Mutation: A change in an organism’s genetic material that can be inherited if it occurs in the germ line. Mutationism assigns evolutionary novelty to discrete heritable changes.
Phyletic gradualism: A model of evolution in which species transform through the steady accumulation of small changes. It is the gradualist alternative that mutationism most directly opposes.
Biometrician–Mendelian controversy: An early twentieth-century dispute over whether continuous variation and Mendelian inheritance could be reconciled. The controversy framed the disagreement between gradualist selection and mutation-centered explanations.
Evening primrose: A flowering plant genus, Oenothera, whose unusual heredity and visible variants shaped early mutation research. De Vries drew his mutation theory from variants he observed in evening primrose populations.
Natural selection: Differential survival and reproduction that change the frequencies of heritable traits in a population. Mutationists differed over whether selection creates adaptive direction or mainly filters mutations.
Modern synthesis: A twentieth-century framework uniting Mendelian genetics with natural selection and population biology. The synthesis reconciled mutation as a source of variation with selection as a major evolutionary process.
Thomas Hunt Morgan: American geneticist whose fruit-fly experiments established chromosome-based inheritance and studied mutations. His work showed mutations could arise without immediately producing new species.
Mutation theory: Hugo de Vries’s proposal that new species can originate through sudden, heritable mutations. This named formulation gave mutationism its best-known early expression.
Saltationism: The view that major evolutionary changes can occur through large, discontinuous steps. Its emphasis on large changes overlaps with mutationism, though the terms are not identical.

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