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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| The eclipse of Darwinism | 4/5 | https://en.wikipedia.org/wiki/The_eclipse_of_Darwinism | reference | science, encyclopedia | 2026-05-05T03:39:04.808782+00:00 | kb-cron |
Mutationism was the idea that new forms and species arose in a single step as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was popular with early geneticists such as Hugo de Vries, who along with Carl Correns helped rediscover Gregor Mendel's laws of inheritance in 1900, William Bateson a British zoologist who switched to genetics, and early in his career, Thomas Hunt Morgan. The 1901 mutation theory of evolution held that species went through periods of rapid mutation, possibly as a result of environmental stress, that could produce multiple mutations, and in some cases completely new species, in a single generation. Its originator was the Dutch botanist Hugo de Vries. De Vries looked for evidence of mutation extensive enough to produce a new species in a single generation and thought he found it with his work breeding the evening primrose of the genus Oenothera, which he started in 1886. The plants that de Vries worked with seemed to be constantly producing new varieties with striking variations in form and color, some of which appeared to be new species because plants of the new generation could only be crossed with one another, not with their parents. DeVries himself allowed a role for natural selection in determining which new species would survive, but some geneticists influenced by his work, including Morgan, felt that natural selection was not necessary at all. De Vries's ideas were influential in the first two decades of the 20th century, as some biologists felt that mutation theory could explain the sudden emergence of new forms in the fossil record; research on Oenothera spread across the world. However, critics including many field naturalists wondered why no other organism seemed to show the same kind of rapid mutation. Morgan was a supporter of de Vries's mutation theory and was hoping to gather evidence in favor of it when he started working with the fruit fly Drosophila melanogaster in his lab in 1907. However, it was a researcher in that lab, Hermann Joseph Muller, who determined in 1918 that the new varieties de Vries had observed while breeding Oenothera were the result of polyploid hybrids rather than rapid genetic mutation. While they were doubtful of the importance of natural selection, the work of geneticists like Morgan, Bateson, de Vries and others from 1900 to 1915 established Mendelian genetics linked to chromosomal inheritance, which validated August Weismann's criticism of neo-Lamarckian evolution by discounting the inheritance of acquired characteristics. The work in Morgan's lab with Drosophila also undermined the concept of orthogenesis by demonstrating the random nature of mutation.
== End of the eclipse ==
During the period 1916–1932, the discipline of population genetics developed largely through the work of the geneticists Ronald Fisher, J.B.S. Haldane, and Sewall Wright. Their work recognized that the vast majority of mutations produced small effects that served to increase the genetic variability of a population rather than creating new species in a single step as the mutationists assumed. They were able to produce statistical models of population genetics that included Darwin's concept of natural selection as the driving force of evolution. Developments in genetics persuaded field naturalists such as Bernhard Rensch and Ernst Mayr to abandon neo-Lamarckian ideas about evolution in the early 1930s. By the late 1930s, Mayr and Theodosius Dobzhansky had synthesized the ideas of population genetics with the knowledge of field naturalists about the amount of genetic diversity in wild populations, and the importance of genetically distinct subpopulations (especially when isolated from one another by geographical barriers) to create the early 20th century modern synthesis. In 1944 George Gaylord Simpson integrated paleontology into the synthesis by statistically analyzing the fossil record to show that it was consistent with the branching non-directional form of evolution predicted by the synthesis, and in particular that the linear trends cited by earlier paleontologists in support of Lamarckism and orthogenesis did not stand up to careful analysis. Mayr wrote that by the end of the synthesis natural selection together with chance mechanisms like genetic drift had become the universal explanation for evolutionary change.