Wright, Sewall Green (1889-1988), was an American geneticist who greatly influenced the fields of genetics (the study of heredity) and evolutionary biology. He became known as one of the fathers of population genetics, which focuses on processes that change the relative frequency of genes in a population through time.

Wright was born to Philip Green Wright and Elizabeth Quincy Sewall, in Melrose, Massachusetts, on Dec. 21, 1889. About three years later, when his father took a teaching job at Lombard College, a Universalist college, the family moved to Galesburg, Illinois. Wright did not attend school until he was 7, but he could read and write when he was quite young. At age 7, he wrote a pamphlet on the physical characteristics of certain animals.

Wright attended Galesburg High School, and, after graduating in 1906, he enrolled in Lombard College and received his bachelor's degree in 1911. In 1912, he graduated from the University of Illinois in Urbana-Champaign with a master's degree in biology. He received his doctorate from Harvard University in Cambridge, Massachusetts, in 1915.

At the beginning of his career, Wright served from 1915 to 1926 as senior animal husbandman in the United States Department of Agriculture (USDA) in Washington, D.C. Wright conducted a detailed study of animal breeding using guinea pigs as a breeding population. Much of modern animal and plant breeding is based on his pioneering work. In 1926, Wright became a professor of zoology at the University of Chicago,

In his research and writings, Wright described a synthetic theory of evolution. The synthetic theory of evolution synthesizes (combines) the principles of natural selection outlined by Charles Robert Darwin with the principles of genetics. Wright explained evolution in terms of changes in gene frequencies. According to this theory, a species evolves when gene frequencies change.

Much of Wright's work dealt with population genetics. A population is a group of individuals of the same species that live within the same area. Population genetics is the study of how mutations (changes in genes) and other processes of evolution, such as natural selection, interact with one another. Population geneticists try to understand how such interactions affect the frequency with which certain genes occur within a population. They believe that an understanding of the processes of evolution and genetic transmission helps explain the diversity of life on the earth—and within our own species.

Wright's best known contribution was the shifting balance theory, which explains how certain combinations of genes spread in a given population. The shifting-balance theory proposes that gene changes first occur within small groups. The favorable combinations of genes increase, and they are then dispersed through the whole population.

Oxford University in Oxford, England, awarded Wright its Weldon Memorial Prize for outstanding contributions to biometric science in 1947. Among the other awards received by Wright were the Medal of the Royal Society of London (1980), the National Medal of Science (1966), the Elliott and Kimber Awards from the National Academy of Sciences (1947 and 1956), and the Lewis Prize from the American Philosophical Society.

Wright retired from the University of Chicago in 1954, at age 65. He then joined the University of Wisconsin in Madison in 1955 as a professor of genetics. He retired in 1960, but remained active as a scientist, participating as professor emeritus and publishing scientific papers, until his death on March 3, 1988, at the age of 98. Wright's four-volume Evolution and the Genetics of Populations was published between 1968 and 1978. Many of his papers are maintained at the American Philosophical Society, of which he had been a member since 1932.

The American Society of Naturalists established the Sewall Wright Award in 1991 for a researcher who has made a major contribution to the unification of the biological sciences. The society works to advance knowledge of organic evolution and other broad biological principles.

The Sewall Wright Institute of Quantitative Biology & Evolution (SWI) was created by an informal group of scientists in 1995 at the University of Wisconsin-Madison to honor Wright and carry on the tradition he started. The institute is working to promote interdisciplinary programs in such areas of biology as animal breeding and genetics; statistical genetics; cellular and molecular biology; ecology, evolution and behavior; and plant breeding and plant genetics.