During his long and productive life, Sewall Wright achieved international standing in the disciplines of experimental physiological genetics, the study of heredity, as well as quantitative evolutionary biology. Wright made significant contributions to the fields of genetics, zoology, biometrics (the use of statistics to analyze biological data) and animal breeding, but is best known for his comprehensive theory of evolution, known as the shifting-balance theory. The shifting-balance theory accounts for the spread of certain gene combinations within a population. The shifting-balance theory took a mathematical and analytical approach to population genetics. Wright's work brought serious statistical analysis to the forefront of biological science and touched off a long-running debate about the nature of animal species development.

Wright, the oldest of three children, was born to Philip Green Wright, a college professor, and Elizabeth Quincy (Sewall) Wright. When Wright was seven years old, he wrote a small booklet he...