Sewall Green Wright ForMemRS (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. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. Evolutionary biologists argue as
to whether Fisher or Wright made the greater contribution. He is the discoverer of the inbreeding coefficient and of methods of computing it in pedigrees. He extended this work to
populations, computing the amount of inbreeding of members of populations as a result of random genetic drift, and he and Fisher 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. The work
of Fisher, Wright, and Haldane on theoretical population genetics was a major step in the development of the modern evolutionary synthesis of genetics with evolution. Wright also made major
contributions to mammalian genetics and biochemical genetics.
Biography
Sewall Wright was born in Melrose, Massachusetts to Philip Green and Elizabeth Quincy Sewall Wright. He was the youngest of three gifted
brothers – the elder two 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, where he graduated
in 1906 to enroll in Lombard College, where his father taught a number of subjects, 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 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, the
Balzan Prize, and the Darwin Medal of the
Royal Society. He was a member of the National Academy of Science and a Foreign Member of the Royal Society.
Wright married Louise Lane Williams (1895-1975) in 1921, with whom he had three children: Richard, Robert, and Elizabeth.
Scientific achievements and credits
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, cumulative stochastic changes in gene frequencies that arise from random births, deaths, and Mendelian segregations in reproduction.
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 fitness landscapes. On
these landscapes 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.
Wright's explanation for stasis was that organisms come to occupy adaptive peaks. In order to
evolve to another, higher peak, the species would first have to pass through a valley of maladaptive intermediate stages. This
could happen by genetic drift if the population is small enough. If a species was divided
into small populations, some could find higher peaks. If there was some gene flow between the
populations, these adaptations could spread to the rest of the species. This was Wright's shifting balance theory of evolution. There has been much skepticism among evolutionary
biologists as to whether these rather delicate conditions hold often in natural populations. Wright had a long standing and
bitter debate about this with R. A. Fisher, who felt that most populations in nature were
too large for these effects of genetic drift to be important.
Wright strongly influenced Jay Lush, who was the most influential figure in introducing
quantitative genetics into animal and
plant breeding. 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.
He did major work on the genetics of guinea pigs, and many of his students became
influential in the development of mammalian genetics. He appreciated as early as 1917 that genes acted by controlling enzymes.
Wright and philosophy
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 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.
Legacy
Wright and Fisher were the key figures in the neodarwinian synthesis
that brought genetics and evolution together. Their work was essential to the contributions of Dobzhansky, Mayr, Simpson, Julian Huxley, and Stebbins. The neodarwinian synthesis was the most important development in evolutionary biology
after Darwin. Wright also had a major effect on the development of mammalian genetics and
biochemical genetics.
Trivia
Since Wright developed the methods used for assessing the degree of inbreeding and its effects, it is notable that his own
parents were first cousins. As a child he helped his father and brother print and publish an early book of poems by his father's
student Carl Sandburg.
References
External links
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