The Eclipse of Darwinism - Saltationism and Mutation Theory

Saltationism and Mutation Theory

See also: Saltation (biology) and Mutation theory

Saltationism was the idea that new species arise 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. Some of these geneticists developed it into the mutation theory of evolution.

The 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 primroses de Vries worked with seemed to be constantly producing new vareties 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 of those influenced by his work, including Morgan, felt that natural selection was not necessary at all. DeVries's ideas were very influential in the first two decades of the 20th century as some felt mutation theory could explain the sudden emergence of new forms in the fossil record and research on Oenothera spread all over the world. Though some of his critics, which included 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, DeVries and others from 1900-1915 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 Drosphila also undermined the concept of orthogenesis by demonstrating the random nature of mutation.