Sewall Wright

Sewall Wright was an American geneticist who, together with Ronald Fisher and J.B.S. Haldane, is regarded as one of the three founders of population genetics, the field that applies mathematical and statistical methods to understand how the frequency of genetic variants changes in populations over time. Wright developed the concept of genetic drift, the random change in how common a particular gene variant is within a population from one generation to the next, an effect that is especially pronounced in small populations and operates independently of natural selection, and which he argued could interact with selection in important ways that purely selection-focused models missed. He proposed the shifting balance theory of evolution, visualized through his influential metaphor of an adaptive landscape, a conceptual surface of peaks and valleys representing different combinations of genetic fitness, across which a population's genetic makeup might move under the combined influence of selection, drift and population structure. Wright, who spent most of his long career at the University of Chicago and later the University of Wisconsin, also invented path analysis, a statistical method for analyzing networks of cause and effect among correlated variables that had significant influence well beyond genetics, and he carried out extensive experimental breeding work on guinea pigs that informed his theoretical models of inbreeding and genetic variation.