Mutationism

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Mutationism (also mutation theory or Mendelism ) is a theory of evolution that emphasizes the creative and directing role of discontinuous mutations in evolution . The theory, which was coined by several founders of modern genetics , became popular in the early 20th century when Mendel's rules were rediscovered and the experimental results seemed inconsistent with Darwin's theory of evolution. After becoming more popular in the first decades of the 20th century, mutationism lost its importance and was considered obsolete after the synthetic theory of evolution took hold. However, there are still scientists today who hold mutationist positions.

Problems with Darwin's theory of evolution

In Darwin's theory of evolution, natural selection was the decisive factor in evolution . Based on the continuous variation that always exists in a natural population, selection is the driving, creative element that enables species to emerge and change. Darwin himself could not explain the mechanism of the variation satisfactorily, he relied on Lamarckist explanations and saw the continuous fluctuation as a reaction to changed external living conditions. However, there was no experimental confirmation of the hereditary nature of the variation in the sense of Darwin.

In the first decade of the 20th century, later as a dark period of Darwinism ( Eclipse of Darwinism was called), Darwin was therefore not generally accepted in natural selection based theory of evolution. Competing theories, which included neolamarckism and orthogenesis in addition to mutationism , also had significant following. The rediscovery of Mendel's rules initially even exacerbated the crisis of Darwinism. The crossbreeding experiments appeared to indicate that most of the visible variation is not hereditary. Those traits that were inheritable, however, were inherited discontinuously according to Mendel's rules.

Mutationism as an alternative to Darwinism

Various explanations are given under the name of mutationism, all of which emphasize the role of mutations in relation to selection, but differ in details.

The best-known mutation theory comes from Hugo de Vries , who was an experimentally oriented biologist and tried to differentiate himself from speculative explanations. His mutation theory, based on research on evening primrose , states that the characteristics of organisms are made up of separate and independent units. De Vries rejected Darwin's gradualism and instead advocated saltationism, i.e. abrupt changes. To this end, he countered Darwin's continuous variation with discontinuous (macro) mutations. De Vries understood mutations to be singular events that are rare compared to Darwin's ubiquitous fluctuation and that are the driving force of evolution. Despite these contradictions, de Vries always tried to place his theory in the Darwinian tradition. He did not deny the importance of selection and even called it “The great principle that determines the evolution of organisms” In his theory, selection did not play the central role as it did with Darwin; spontaneous mutations were the creative element of evolution.

Thomas Hunt Morgan advocated a more radical version of De Vries' mutation theory. In his 1903 paper Evolution and Adaptation , he explicitly presented mutationism as a counter-image to Darwin's theory of evolution. For Morgan, selection only had the passive role of preventing harmful mutations from taking hold. The driving element of evolution was mutations in the sense of de Vries.

Other important geneticists who are counted among the mutationists are William Bateson , Wilhelm Johannsen and Reginald Punnett .

Transition to the synthetic theory of evolution

After the synthetic theory of evolution became established, in which genetics , population genetics and evolution were reconciled, the importance of mutationism declined sharply. The synthetic theory of evolution recognizes the existence of mutations, but does not see them as a driving or even creative force of evolution. The key concept was now the gene pool , which always provides a rich reservoir of continuous variation in which selection can act. Individual mutations are not central events in synthetic theory, because there is always an abundance of variation in the gene pool, so that selection is the dominant evolutionary factor. Ernst Mayr , one of the founders of this theory, put it this way:

"Evolution is not primarily a genetic event. Mutation merely supplies the gene pool with genetic variation; it is selection that induces evolutionary change. "

“Evolution is not primarily a genetic event. Mutations only provide the gene pool with genetic variation; it is selection that brings about evolutionary changes. "

- Ernst Mayr

Role in today's biology

Today, the synthetic theory of evolution continues to be supported by a majority of evolutionary biologists. However, the weighting of the various evolutionary factors is controversial, and there are researchers who assign greater weight to mutations and genetic drift than Ernst Mayr, for example. Masatoshi Nei , who conducts research in the field of molecular evolution , is the best known proponent of this view. His thesis that mutations represent the guiding force of evolution and selection only takes on the passive role of eliminating harmful mutations and preserving good ones, expressly in the tradition of Morgan's mutationism.

literature

  • Garland E. Allen: Hugo de Vries and the reception of the "mutation theory" . Journal of the History of Biology 2: 1, pp. 56-86 (1969)
  • Peter J. Bowler: Hugo de Vries and Thomas Hunt Morgan: The mutation theory and the spirit of Darwinism . Annals of Science 35: 1 pp. 55-73 (1978)
  • Masatoshi Nei: Selectionism and Neutralism in Molecular Evolution . Mol. Biol. Evol. 22:12 pp. 2318-2342 (2005)
  • Masatoshi Nei: The new mutation theory of phenotypic evolution . Proc. Natl. Acad. Sci. 104: 30, pp. 12235-12242 (2007)
  • Arlin Stoltzfus: Mutationism and the dual causation of evolutionary change . Evolution & Development 8: 3, pp. 304-317 (2006)
  • Arlin Stoltzfus & Kele Cable: Mendelian-Mutationism: The Forgotten Evolutionary Synthesis. Journal of the History of Biology (2014) 47: 501-546.
  • Naoyuki Takahata: Molecular clock: An anti-neo-Darwinian legacy . Genetics 176, pp. 1-6 (2007)

Web links

Individual evidence

  1. ↑ Julian Huxley : Evolution: the modern synthesis. London: Allen and Unwin. (1942) OCLC 900758272 .
  2. ^ Garland E. Allen: Hugo de Vries and the reception of the "mutation theory" . Journal of the History of Biology 2: 1 (1969) p. 58, doi: 10.1007 / BF00137268 .
  3. ^ Peter J. Bowler: Hugo de Vries and Thomas Hunt Morgan: The mutation theory and the spirit of Darwinism . Annals of Science 35: 1 (1978) p. 60, doi: 10.1080 / 00033797800200141 .
  4. ^ "The great principle which rules the evolution of organism". Quoted from Peter J. Bowler: Hugo de Vries and Thomas Hunt Morgan: The mutation theory and the spirit of Darwinism . Annals of Science 35: 1 (1978), p. 61
  5. ^ Peter J. Bowler: Hugo de Vries and Thomas Hunt Morgan: The mutation theory and the spirit of Darwinism . Annals of Science 35: 1 (1978) p. 65
  6. ^ Ernst Mayr: Animal species and evolution . Harvard University Press, Cambridge, MA. 1963, OCLC 318164950 .
  7. ↑ Masatoshi Nei et al. : Darwin 200: Great expectations . Nature 456, pp. 317-318. (2008), doi: 10.1038 / 456317a .
  8. ^ Masatoshi Nei: The new mutation theory of phenotypic evolution . Proc. Natl. Acad. Sci. 104: 30, pp. 12235-12242 (2007), doi: 10.1073 / pnas.0703349104 .
  9. ↑ Masatoshi Nei: Selectionism and Neutralism in Molecular Evolution . Mol. Biol. Evol. 22:12 pp. 2318-2342 (2005), doi: 10.1093 / molbev / msi242 .