Theodosius Dobzhansky
Dobzhansky emigrated to the United States in 1927. He worked with Thomas Hunt Morgan at Columbia University, who had pioneered the use of fruit flies (Drosophila melanogaster) in genetics experiments. He followed Morgan to the California Institute of Technology from 1930 to 1940. Dobzhansky took fruit fly research out of the laboratory and into the field. He discovered that regional varieties of flies were more similar to each other genetically than to flies from other regions.