Mutationism

Mutationism (also mutation theory or Mendelism ) is a theory of evolution, which emphasizes the creative and steering role of discontinuous mutations in evolution. The theory, among which several authors founder of modern genetics, was at the beginning of the 20th century, popular, than the Mendelian rules were rediscovered and the experimental results did not seem compatible with the Darwinian theory of evolution. After he had made it in the first decades of the 20th century to greater popularity, the Mutationism lost its importance and was considered obsolete after the synthetic theory of evolution had prevailed. Nevertheless, there are still scientists who represent mutationistische positions.

Problems with Darwin's theory of evolution

In Darwin's theory of evolution was natural selection the decisive factor of evolution. Starting from a continuous variation is in a natural population always, the selection of the driving creative element that allows the creation and alteration of species. Darwin himself could not satisfactorily explain the mechanism of variation, he relied on Lamarckian explanations and saw the continuous fluctuation in response to changing external conditions of life. The experimental confirmation of the heritability of variation in the sense of Darwin failed to materialize.

In the first decade of the 20th century, which was later referred to as a dark period of Darwinism ( Eclipse of Darwinism ), based on Darwin's natural selection theory of evolution was therefore by no means universally accepted. Competing theories, which included next to the Mutationism of Lamarckism and orthogenesis, also had a significant following. The rediscovery of Mendel's laws exacerbated the crisis of Darwinism even initially. The crossing experiments seemed to indicate that the majority of the visible variation is not hereditary. Those properties that were inherited were, however, inherited discontinuously according to Mendelian rules.

Mutationism as an alternative to Darwinism

Under the name Mutationism different explanations are out, all highlight the role of mutations to the selection, but differed in details.

The most common mutation theory derived from Hugo de Vries, who was an experimentally oriented biologist, trying to distinguish themselves from speculative explanation approaches. His mutation theory, which is based on research on evening primrose, states that the characteristics of organisms consist of separate and independent units. De Vries rejected Darwin's gradualism from and represented instead a saltationism, ie abrupt changes. To this end, he put Darwin's continuous variation against discontinuous (macro - ) mutations. Under mutations understood de Vries singular, compared to Darwin's ubiquitous fluctuation rare events that are the driving force of evolution. Despite these contradictions de Vries always tried to put his theory in the tradition of Darwin. He did not deny the importance of the selection, calling it even " The great principle, the evolution of organisms determined " In his theory selection but did not take a central role as in Darwin; creative element of evolution were spontaneous mutations.

Thomas Hunt Morgan took a more radical version of De Vries ' mutation theory. In his book Evolution and adaptation of 1903, he presented the Mutationism explicitly as the counterpart to Darwin's theory of evolution. For Morgan, the selection had a passive role only to prevent prevail deleterious mutations. Drifting element of evolution were mutations in the sense of de Vries '.

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

Transition to the synthetic theory of evolution

After the synthetic theory of evolution had prevailed, were brought in genetics, population genetics and evolution in line, the importance of Mutationism fell sharply. The synthetic theory of evolution recognizes the existence of mutations at though, does not see it as 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 in the Synthetic theory no central events since there is always an abundance of variation in the gene pool there, so that the selection of the dominant evolutionary factor. Ernst Mayr, one of the founders of this theory, this is expressed as follows:

"Evolution is not primarily a genetic event. Mutations provide the gene pool only with genetic variation; It is the selection of which causes evolutionary changes. "

Role in modern biology

Today the synthetic theory of evolution is still supported by a majority of evolutionary biologists. However, the weighting of the various factors of evolution is controversial, and there are researchers, the mutations and genetic drift assign greater weight than about Ernst Mayr did. Masatoshi Nei, the research in the field of molecular evolution, is the most famous proponents of this view. He demonstrates his thesis that mutations are the guiding force of evolution and selection occupies only the passive role to eliminate deleterious mutations and preserve good, specifically in the tradition of Morgan Mutationism.