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Edmund Beecher Wilson (October 19, 1856 – March 3, 1939) was a pioneering American zoologist and geneticist. He wrote one of the most influential textbooks in modern biology, The Cell, and is credited as America's first cell biologist. He discovered the chromosomal XY sex-determination system in 1905. This photograph shows Wilson at Bryn Mawr College c. 1890.Photograph credit: unknown; restored by Adam Cuerden