Sewall Wright

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.

Sewall Wright (December 21, 1889 – March 3, 1988) was an American geneticist known for his influential work in evolutionary biology and population genetics. He is particularly famous for his concept of the adaptive landscape, which visualizes the relationship between genotypes and reproductive success. His work laid the foundation for the Modern Synthesis of genetics and evolution, integrating Darwin's theory of natural selection with Mendelian genetics.

Biography

Sewall Wright was born in Melrose, Massachusetts, to Philip Green Wright and Elizabeth Quincy Sewall Wright. He graduated from Lombard College in Galesburg, Illinois, where his father was a professor. Wright then went on to complete his Ph.D. in zoology at Harvard University in 1915, where he studied under William Ernest Castle, a prominent geneticist of the time. After completing his doctorate, Wright worked at the U.S. Department of Agriculture, where he conducted research on animal genetics, particularly in guinea pigs and cattle.

In 1926, Wright joined the faculty of the University of Chicago, where he spent much of his career. During his tenure at Chicago, he developed many of his most significant theories, including the concepts of the adaptive landscape, genetic drift, and the coefficient of inbreeding. In 1955, he moved to the University of Wisconsin-Madison, where he continued his research until his retirement.

Contributions to Genetics

Wright's contributions to genetics and evolutionary biology are vast. One of his most notable concepts is the adaptive landscape, which he used to describe how populations evolve. According to Wright, populations can move across the landscape, which is shaped by the fitness of different genotypes. This movement can lead to populations becoming stuck on local adaptive peaks, separated by valleys of lower fitness.

Another significant contribution is his work on genetic drift, also known as the Sewall Wright effect. Genetic drift describes how allele frequencies in a small population can change due to random sampling errors from one generation to the next. This concept is a key mechanism of evolution, particularly in small populations.

Wright also developed the coefficient of inbreeding, a measure of the probability that two alleles at a locus in an individual are identical by descent. This work has had profound implications for the study of population structure, mating systems, and conservation genetics.

Legacy

Sewall Wright's work has had a lasting impact on the fields of genetics and evolutionary biology. His theories and concepts are still taught in biology courses around the world. Wright received numerous awards and honors throughout his career, including the National Medal of Science in 1966.

Wright's legacy is also preserved through the Sewall Wright Award, given annually by the American Society of Naturalists to a senior investigator who has made significant contributions to the conceptual unification of the biological sciences.

Selected Publications

Wright authored hundreds of papers and several books throughout his career. Some of his most influential works include:

• Evolution: Selected Papers (1986)
• Evolution and the Genetics of Populations (a four-volume work published between 1968 and 1978)

See Also

• Population genetics
• Evolutionary biology
• Modern Synthesis
• Charles Darwin
• Genetic drift