Sewall Wright

from Wikipedia, the free encyclopedia

Sewall Green Wright (born December 21, 1889 in Melrose (Massachusetts), † March 3, 1988 in Madison (Wisconsin) ) was an American theoretical biologist and geneticist who founded population genetics in the 1920s with Ronald Fisher and JBS Haldane . In doing so, he made a significant contribution to the theory of genetic drift and the inbreeding coefficient . Wright also invented statistical path analysis and the " fitness landscapes ".


Sewall Green Wright's father Philip Green Wright was a teacher, his mother's name was Elisabeth Quincy Sewall Wright and was a cousin of his father. Sewall had two younger brothers: the future political scientist Quincy Wright and Theodore Paul Wright, who became an aerospace engineer . From Sewall's third year of life, the family lived in Galesburg (Illinois).

Sewall Wright studied natural sciences with a major in zoology at the University of Illinois , where he received his Master of Science degree in 1912 . He then worked with the geneticist William Ernest Castle at Harvard University and received his doctorate there in 1915 with a thesis on the inheritance of fur colors in guinea pigs . In 1921 he married Louise Lane Williams (1895-1975), with whom he had three children.

After receiving his doctorate, Wright first worked at the United States Department of Agriculture (USDA) in Washington, DC During this time, he developed and published some of his most important ideas. In 1926 he was appointed professor at the University of Chicago , and remained there until he retired in 1955 at the age of 65. He then taught at the University of Wisconsin – Madison for another 5 years .

Wright was very active physically and mentally well into old age. He died in Madison in 1988 at the age of 98 from the effects of a pelvic fracture sustained in a fall while hiking.


In his dissertation , published in 1916 , Wright expressed the view that interactions of genetic factors within populations were much more important than the changes ( mutations ) of individual genes , which his teacher Castle and other eminent geneticists had so far mainly looked at. From 1917 he used "as a self-evident principle" (Jahn) the Hardy-Weinberg law formulated in 1908 by Wilhelm Weinberg and Godfrey Harold Hardy , without being aware of the publications of these predecessors. This law describes a state of equilibrium in which the relative frequencies of alleles in a population remain constant if no selection is made.

Sketch of a fitness landscape. The arrows indicate the preferred path of a population in the landscape through selection. Points A, B and C are local optima. The red ball represents a population that is moving from a very low fitness value towards a local peak.

In the early 1920s, Wright published the concept of the inbreeding coefficient , the newly developed method of path analysis for interpreting correlations in complex causal systems, and the theory that gradual genetic changes in populations are caused by the interaction of inbreeding , crossing and selection. Later he added the concept of genetic drift , which he had largely developed himself . Wright is one of the founders of theoretical population genetics alongside Ronald Fisher and JBS Haldane .

Another invention of Wright is the “fitness landscapes”. These are graphic representations of the fitness (reproductive success) of different gene combinations, which can represent both a certain phenotypic characteristic (e.g. eye, gills, exoskeleton) as well as the entire phenotype. Valleys in these landscapes mean less reproductive success of the gene combinations, hills represent more favorable gene combinations. Natural selection shifts the trait or phenotype to the top of the hill as an evolutionary adaptation . There the feature is adapted to its environment. Random movements in other directions in the fitness landscape are known as genetic drift . An adaptation, starting from a local summit on the way downhill and then uphill again to another, higher summit, is usually not evolutionarily possible. For example, a whale can no longer develop gills that it once had in a phylogenetically earlier phase.

Honors and Membership

In 1932 Wright was elected to the American Philosophical Society , 1934 to the National Academy of Sciences, and 1948 to the American Academy of Arts and Sciences .

In 1950 he received the John Frederick Lewis Award from the American Philosophical Society. In 1951 he became an Honorary Fellow of the Royal Society of Edinburgh . Wright was elected as a "Foreign Member" in the Royal Society in 1963 , which in 1980 awarded him the Darwin Medal . He received ten honorary doctorates. Other awards:

In his honor, the American Society of Naturalists presents the Sewall Wright Award for Biology.


  • An Intensive Study of the Inheritance of Color and Other Coat Characters in Guinea-pigs, with Especial Reference to Graded Variations (1916)
  • On the Nature of Size Factors (1917)
  • Color Inheritance in Mammals (1917/1918)
  • Correlation and Causation (1921)
  • Systems of Mating (1921)
  • The Effects of Inbreeding and Crossbreeding on Guineapigs (1922)
  • Coefficients of Inbreeding and Relationship (1922)
  • The Genetical Theory of Natural Selection - A Review (1930)
  • Evolution in Mendelian Populations (1931)
  • The Roles of Mutation, Inbreeding, Crossbreeding and Selection in Evolution (1932)
  • Evolution and the Genetics of Populations , four volumes (1968–1978)


Web links

Individual evidence

  1. Ilse Jahn et al .: History of Biology . 2nd edition Jena 1985, p. 483
  2. ^ S. Wright: The roles of mutation, inbreeding, crossbreeding, and selection in evolution . In: Proceedings of the Sixth International Congress on Genetics 1932, pp. 355-366.
  3. Richard Dawkins : Summit of the Improbable: Miracles of Evolution . rororo, 2008. p. 85 ff.
  4. ^ Member History: Sewall Wright. American Philosophical Society, accessed December 11, 2018 .
  5. ^ Members of the American Academy. Listed by election year, 1900-1949 . (PDF) Retrieved October 11, 2015
  6. John Frederick Lewis Award: Awards ( Memento of the original from December 29, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot /
  7. ^ Fellows Directory. Biographical Index: Former RSE Fellows 1783–2002. (PDF file) Royal Society of Edinburgh, accessed April 26, 2020 .