December 21, 1889-March 3, 1988

BY JAMES F. CROW

THE MATHEMATICAL THEORY of evolution and the science of population genetics began with, and for a generation was almost totally dominated by, three men: R. A. Fisher, J. B. S. Haldane, and Sewall Wright. Wright's unique contribution was his "shifting balance theory," which holds that the best opportunity for evolutionary progress is afforded by a large population comprising many partially isolated local groups. Within each group a certain amount of trial and error experimentation can take place, and successful combinations can spread throughout the population. Although the theory remains controversial, it has been very popular and influential in the biological community.

Wright also developed much of the theory of inbreeding (his coefficient of inbreeding is standard material in elementary textbooks) and the genetics of quantitative traits. In addition, he was a pioneer in physiological genetics and was uniquely responsible for the developmental and coat-color genetics of guinea pigs. Wright's method of path analysis, originally used mainly by animal breeders, has become a standard statistical technique in the social sciences.

Wright was elected to the National Academy of Sciences in 1934.