Sewall Wright (1889 - 1988) was an American geneticist who played a central part in the foundation of the modern synthesis, together with R.A. Fisher and J.B.S Haldane.
• Wright noticed that genes can disappear from a small population not because of selection, but because of chance - a phenomenon known as genetic drift.
• He invented the influencial concept of an adaptive topography - a graph of mean population fitness against gene frequency.
Wright attempted a comprehensive, realistic model of evolution, including complex interactions between genes, random effects, selection between and within populations, and migration.
He lived to a grand age, and published a four-volume treatise (1968 - 1978) at the end of his career.
This photograph of Sewall Wright was taken in 1928.