Mutationism
Mutationism is one of several alternatives to evolution by natural selection that have existed both before and after the publication of Charles Darwin's 1859 book On the Origin of Species. In the theory, mutation was the source of novelty, creating new forms and new species, potentially instantaneously, in sudden jumps. This was envisaged as driving evolution, which was thought to be limited by the supply of mutations.
Before Darwin, biologists commonly believed in saltationism, the possibility of large evolutionary jumps, including immediate speciation. For example, in 1822 Étienne Geoffroy Saint-Hilaire argued that species could be formed by sudden transformations, or what would later be called macromutation. Darwin opposed saltation, insisting on gradualism in evolution as geology's uniformitarianism. In 1864, Albert von Kölliker revived Geoffroy's theory. In 1901 the geneticist Hugo de Vries gave the name "mutation" to seemingly new forms that suddenly arose in his experiments on the evening primrose Oenothera lamarckiana. In the first decade of the 20th century, mutationism, or as de Vries named it mutationstheorie, became a rival to Darwinism supported for a while by geneticists including William Bateson, Thomas Hunt Morgan, and Reginald Punnett.
Understanding of mutationism is clouded by the mid-20th century portrayal of the early mutationists by supporters of the modern synthesis as opponents of Darwinian evolution and rivals of the biometrics school who argued that selection operated on continuous variation. In this portrayal, mutationism was defeated by a synthesis of genetics and natural selection that supposedly started later, around 1918, with work by the mathematician Ronald Fisher. However, the alignment of Mendelian genetics and natural selection began as early as 1902 with a paper by Udny Yule, and built up with theoretical and experimental work in Europe and America. Despite the controversy, the early mutationists had by 1918 already accepted natural selection and explained continuous variation as the result of multiple genes acting on the same characteristic, such as height.
Mutationism, along with other alternatives to Darwinism like Lamarckism and orthogenesis, was discarded by most biologists as they came to see that Mendelian genetics and natural selection could readily work together; mutation took its place as a source of the genetic variation essential for natural selection to work on. However, mutationism did not entirely vanish. In 1940, Richard Goldschmidt again argued for single-step speciation by macromutation, describing the organisms thus produced as "hopeful monsters", earning widespread ridicule. In 1987, Masatoshi Nei argued controversially that evolution was often mutation-limited. Modern biologists such as Douglas J. Futuyma conclude that essentially all claims of evolution driven by large mutations can be explained by Darwinian evolution.
Developments leading up to mutationism
Geoffroy's monstrosities, 1822
Prior to Charles Darwin, most naturalists were saltationists, believing that species evolved and that speciation took place in sudden jumps. Jean-Baptiste Lamarck was a gradualist but similar to other scientists of the period had written that saltational evolution was possible.In 1822, in the second volume of his Philosophie anatomique, Étienne Geoffroy Saint-Hilaire endorsed a theory of saltational evolution that "monstrosities could become the founding fathers of new species by instantaneous transition from one form to the next." Geoffroy wrote that environmental pressures could produce sudden transformations to establish new species instantaneously.
Darwin's anti-saltationist gradualism, 1859
In his 1859 book On the Origin of Species, Charles Darwin denied saltational evolution. He argued that evolutionary transformation always proceeds gradually, never in jumps: "natural selection acts solely by accumulating slight successive favourable variations, it can produce no great or sudden modification; it can act only by very short steps". Darwin continued in this belief throughout his life.File:Kölliker Rudolph Albert von 1818-1902.jpg|thumb|upright|Rudolph Albert von Kölliker revived Geoffroy's saltationist ideas, calling his theory heterogenesis. It depended on a nonmaterial directive force.
Thomas Henry Huxley warned Darwin that he had taken on "an unnecessary difficulty in adopting Natura non facit saltum so unreservedly." Huxley feared this assumption could discourage naturalists who believed that major leaps and cataclysms played a significant role in the history of life.
von Kölliker's heterogenesis, 1864
In 1864 Albert von Kölliker revived Geoffroy's theory that evolution proceeds by large steps, under the name of heterogenesis, but this time assuming the influence of a nonmaterial force to direct the course of evolution.Galton's "sports", 1892
Darwin's cousin, Francis Galton, considered Darwin's evidence for evolution, and came to an opposite conclusion about the type of variation on which natural selection must act. He carried out his own experiments and published a series of papers and books setting out his views. Already by 1869 when he published Hereditary Genius, he believed in evolution by saltation. In his 1889 book Natural Inheritance he argued that natural selection would benefit from accepting that the steps need not, as Darwin had stated, be minute. In his 1892 book Finger Prints, he stated directly that "The progress of evolution is not a smooth and uniform progression, but one that proceeds by jerks, through successive 'sports', some of them implying considerable organic changes; and each in its turn being favoured by Natural Selection".From 1860 to 1880 saltation had been a minority viewpoint, to the extent that Galton felt his writings were being universally ignored. By 1890 it became a widely held theory, and his views helped to launch a major controversy.
File:Bateson@72.jpg|thumb|upright|Drawing of William Bateson, 1909, by the biologist Dennis G. Lillie
Bateson's discontinuous variation, 1894
's 1894 book Materials for the Study of Variation, Treated with Especial Regard to Discontinuity in the Origin of Species marked the arrival of mutationist thinking, before the rediscovery of Mendel's laws. He examined discontinuous variation where it occurred naturally, following William Keith Brooks, Galton, Thomas Henry Huxley and St. George Jackson Mivart.Early 20th century mutationism
De Vries and Mendelian ''mutationstheorie'', 1901
's careful 1901 studies of wild variants of the evening primrose Oenothera lamarckiana showed that distinct new forms could arise suddenly in nature, apparently at random, and could be propagated for many generations without dissipation or blending. He gave such changes the name "mutation". By this, de Vries meant that a new form of the plant was created in a single step ; no long period of natural selection was required for speciation, and nor was reproductive isolation.In the view of the historian of science Peter J. Bowler, De Vries used the term to mean
The historian of science Betty Smocovitis described mutationism as:
De Vries set out his position, known as Mutationstheorie on the creative nature of mutation in his 1905 book Species and Varieties: their Origin by Mutation. In the view of the historian of science Edward Larson, de Vries was the person largely responsible for transforming Victorian era saltationism into early 20th century mutation theory, "and in doing so pushed Darwinism near the verge of extinction as a viable scientific theory".
Similar ideas were propounded in Imperial Russia, even before De Vries, by Sergey Korzhinsky.