Mutation Theory

The mutation theory was proposed by the Dutch botanist Hugo de Vries in 1901, shortly after the rediscovery of Gregor Mendel's work in 1900. De Vries based his theory on careful observations made across seven generations of the evening primrose, Oenothera lamarckiana. He found that although most offspring closely resembled their parents in the majority of their characters, some offspring showed the sudden, spontaneous appearance of a variation that was clearly and sharply different from the parent's phenotype. De Vries called these sudden changes mutations, or discontinuous variations. Importantly, plants that showed such a variant trait went on to produce further variant offspring rather than reverting to the normal parental form — that is, the changes proved to be genuinely heritable — and de Vries further observed that some of these variant lines went on to produce still more variation of their own. From these observations he proposed the mutation theory, whose main features are:

• Mutations are large, sudden, random and discontinuous variations appearing within a population.
• These changes are inheritable, and their direction may not be predictable (i.e. they need not point consistently in one useful direction).
• Mutations supply the raw material on which organic evolution acts.
• A mutation may turn out to be useful or harmful; useful mutations tend to be favoured (selected) by nature.
• The gradual accumulation of such mutations over long periods of time leads to the origin and eventual establishment of new species.
• A harmful mutation may either persist at low frequency or be eliminated from the population by nature.

Objections to the Mutation Theory. : …