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Sewall Green Wright (December 21, 1889 – March 3, 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. He was a founder of population genetics alongside Ronald Fisher and J. B. S. Haldane, which was a major step in the development of the modern synthesis combining genetics with evolution. He discovered the inbreeding coefficient and methods of computing it in pedigree animals. He extended this work to populations, computing the amount of inbreeding between members of populations as a result of random genetic drift, and along with Fisher he pioneered methods for computing the distribution of gene frequencies among populations as a result of the interaction of natural selection, mutation, migration and genetic drift. Wright also made major contributions to mammalian and biochemical genetics.[4][5][6]

Sewall Wright
Sewall Wright.jpg
Wright in 1954
Born(1889-12-21)December 21, 1889
DiedMarch 3, 1988(1988-03-03) (aged 98)
Alma materLombard College
University of Illinois
Harvard University
(Sc.D., 1915)[1]
Known forpopulation genetics
AwardsDaniel Giraud Elliot Medal (1945)
Weldon Memorial Prize (1947)
National Medal of Science (1966)
Darwin Medal (1980)
Thomas Hunt Morgan Medal (1982)
Balzan Prize (1984)
Foreign Member of the Royal Society (1963)[2]
Scientific career
InstitutionsUniversity of Chicago[3]
University of Wisconsin[3]
Doctoral advisorWilliam Ernest Castle



Sewall Wright was born in Melrose, Massachusetts to Philip Green Wright and Elizabeth Quincy Sewall Wright. His parents were first cousins,[7] an interesting fact in light of Wright's later research on inbreeding. The family moved three years later after Philip accepted a teaching job at Lombard College, a Universalist college in Galesburg, Illinois.

As a child, Wright helped his father and brother print and publish an early book of poems by his father's student Carl Sandburg.

He was the oldest of three gifted brothers—the others being the aeronautical engineer Theodore Paul Wright and the political scientist Quincy Wright. From an early age Wright had a love and talent for mathematics and biology. Wright attended Galesburg High School and graduated in 1906. He then enrolled in Lombard College where his father taught, to study mathematics. He was influenced greatly by Professor Wilhelmine Entemann Key, one of the first women to receive a Ph.D. in biology. Wright received his Ph.D. from Harvard University, where he worked at the Bussey Institute with the pioneering mammalian geneticist William Ernest Castle investigating the inheritance of coat colors in mammals. He worked for the U.S. Department of Agriculture until 1925, when he joined the Department of Zoology at the University of Chicago. He remained there until his retirement in 1955, when he moved to the University of Wisconsin–Madison. He received many honors in his long career, including the National Medal of Science (1966), the Balzan Prize (1984), and the Darwin Medal of the Royal Society (1980). He was a member of the National Academy of Sciences and a Foreign Member of the Royal Society.[2] The American Mathematical Society selected him as the Josiah Willards Gibbs lecturer for 1941.[8][9] For his work on genetics of evolutionary processes, Wright was awarded the Daniel Giraud Elliot Medal from the National Academy of Sciences in 1945.[10]

Wright married Louise Lane Williams (1895–1975) in 1921.[11][12] They had three children: Richard, Robert, and Elizabeth.[13][14]

Sewall Wright worshipped as a Unitarian.[15][16]

Scientific achievements and creditsEdit

Population geneticsEdit

Visualization of a fitness landscape. The X and Y axes represent continuous phenotypic traits, and the height at each point represents the corresponding organism's fitness. The arrows represent various mutational paths that the population could follow while evolving on the fitness landscape.

His papers on inbreeding, mating systems, and genetic drift make him a principal founder of theoretical population genetics, along with R. A. Fisher and J. B. S. Haldane. Their theoretical work is the origin of the modern evolutionary synthesis or neodarwinian synthesis. Wright was the inventor/discoverer of the inbreeding coefficient and F-statistics, standard tools in population genetics. He was the chief developer of the mathematical theory of genetic drift, which is sometimes known as the Sewall Wright effect,[17] cumulative stochastic changes in gene frequencies that arise from random births, deaths, and Mendelian segregations in reproduction. In this work he also introduced the concept of effective population size. Wright was convinced that the interaction of genetic drift and the other evolutionary forces was important in the process of adaptation. He described the relationship between genotype or phenotype and fitness as fitness surfaces or evolutionary landscapes. On these landscapes mean population fitness was the height, plotted against horizontal axes representing the allele frequencies or the average phenotypes of the population. Natural selection would lead to a population climbing the nearest peak, while genetic drift would cause random wandering.

Evolutionary theoryEdit


Path analysisEdit

Wright's statistical method of path analysis, which he invented in 1921 and which was one of the first methods using a graphical model, is still widely used in social science. He was a hugely influential reviewer of manuscripts, as one of the most frequent reviewers for Genetics. Such was his reputation that he was often credited with reviews that he did not write.

Plant and animal breedingEdit

Wright strongly influenced Jay Lush, who was the most influential figure in introducing quantitative genetics into animal and plant breeding. From 1915 to 1925 Wright was employed by the Animal Husbandry Division of the U.S. Bureau of Animal Husbandry. His main project was to investigate the inbreeding that had occurred in the artificial selection that resulted in the leading breeds of livestock used in American beef production. He also performed experiments with 80,000 guinea pigs in the study of physiological genetics. Further more he analyzed characters of some 40,000 guinea pigs in 23 strains of brother-sister matings against a random-bred stock. (Wright 1922a-c). The concentrated study of these two groups of mammals eventually led to the Shifting Balance Theory and the concept of "surfaces of selective value" in 1932. (Wright 1988 Pg 122 American Naturalist)


Wright and philosophyEdit

Wright was one of the few geneticists of his time to venture into philosophy. He found a union of concept in Charles Hartshorne, who became a lifelong friend and philosophical collaborator. Wright endorsed a form of panpsychism. He believed that the birth of the consciousness was not due to a mysterious property of increasing complexity, but rather an inherent property, therefore implying these properties were in the most elementary particles.[18]



An interesting anecdote about Sewall Wright and Barbara McClintock is linked here:[19]

"The Book of Why" by Judea Pearl and Mackenzie (2018) describes the contribution of Wright's work on path analysis and delays in its acceptance by several technical disciplines (specifically statistics and formal causal analysis).

OpenMx has as its icon a representation of Wright's Piebald Guinea Pig.


  • Wright, Sewall (1984). Evolution and the Genetics of Populations: Genetics and Biometric Foundations New Edition. University of Chicago Press.


  1. ^ "Sewall Wright - American geneticist". Retrieved 21 March 2018.
  2. ^ a b Hill, W. G. (1990). "Sewall Wright. 21 December 1889-3 March 1988". Biographical Memoirs of Fellows of the Royal Society. 36: 568–579. doi:10.1098/rsbm.1990.0044.
  3. ^ a b FOWLER, GLENN. "Sewall Wright, 98, Who Formed Mathematical Basis for Evolution". The New York Times. New York Times. Retrieved 6 September 2015.
  4. ^ Crow, J. F. (1988). "Sewall Wright (1889-1988)". Genetics. 119 (1): 1–4. PMC 1203328. PMID 3294096.
  5. ^ Crow, J. F.; Dove, W. F. (1987). "Sewall Wright and physiological genetics". Genetics. 115 (1): 1–2. PMC 1203043. PMID 3549442.
  6. ^ Hill, W. G. (1996). "Sewall Wright's "Systems of Mating"". Genetics. 143 (4): 1499–1506. PMC 1207415. PMID 8844140.
  7. ^ Allendorf, Fred W.; Luikart, Gordon H.; Aitken, Sally N. (2012). Conservation and the Genetics of Populations. John Wiley. p. 548. ISBN 978-1-118-40857-5.. So were Darwin and his wife Emma (Wedgwood).
  8. ^ "American Mathematical Society". Retrieved 21 March 2018.
  9. ^ Wright, Sewall (1942). "Statistical genetics and evolution". Bull. Amer. Math. Soc. 48 (4): 223–246. doi:10.1090/S0002-9904-1942-07641-5. MR 0006700.
  10. ^ "Daniel Giraud Elliot Medal". Retrieved 7 January 2018.
  11. ^ "Ohio Marriages, 1800-1958," database, FamilySearch ( : 8 December 2014), Sewall Wright and Louise Lane Williams, 10 Sep 1921; citing Licking, Ohio, reference 508B; FHL microfilm 384,312.
  12. ^ Provine, William B. (1989). Wright and Evolutionary Biology. University of Chicago Press. p. 106. ISBN 9780226684734. Retrieved 7 January 2018. They were married in Granville on September 10, 1921... The Wrights had two boys, Richard and Robert, during the remaining four years in Washington.
  13. ^ "United States Census, 1930," database with images, FamilySearch ( : accessed 7 January 2018), Sewall Wright, Chicago (Districts 0001-0250), Cook, Illinois, United States; citing enumeration district (ED) ED 208, sheet 11A, line 50, family 226, NARA microfilm publication T626 (Washington D.C.: National Archives and Records Administration, 2002), roll 423; FHL microfilm 2,340,158.
  14. ^ "Sewall Wright Profile".
  15. ^ Ruse, Michael (Jun 30, 2009). Monad to Man: The Concept of Progress in Evolutionary Biology. Harvard University Press. p. 376. ISBN 9780674042995. Archived from the original on January 7, 2018. Retrieved 7 January 2018. Wright worshipped as a Unitarian
  16. ^ Provine, William B. (1989). Sewall Wright and Evolutionary Biology. University of Chicago Press. pp. 460, 497. ISBN 9780226684734. Archived from the original on January 7, 2018. Retrieved 7 January 2018.
  17. ^ The Structure of Evolutionary Theory (2002) by Stephen Jay Gould, Chapter 7, sectionn "Synthesis as Hardening"
  18. ^ Steffes, David M (2007). "Panpsychic Organicism: Sewall Wright's Philosophy for Understanding Complex Genetic Systems". Journal of the History of Biology. 40 (2): 327–361.
  19. ^; see anecdote #25

Further readingEdit

External linksEdit