Answer
Theodosius Dobzhansky emigrated to the United States in 1927, after receiving his doctorate from the University of Leningrad. He quickly became one of the leading geneticists in the country, and his work on the genetics of natural populations helped to establish the field of population genetics. Dobzhansky also played a major role in the development of the Modern Synthesis, which integrated Darwinian natural selection with Mendelian genetics.