Theodosius Dobzhansky (1900-1975) was a geneticist and zoologist who made important contributions to the field of genetics. He was born in Nemirov, Ukraine, and educated at the University of Kyyiv. In 1927 he went to the United States because of political interference with genetic studies in the former Union of Soviet Socialist Republics (USSR). He joined the American zoologist Thomas Hunt Morgan at Columbia University and moved with him in 1928 to the California Institute of Technology, where he became a professor of zoology in 1936.

Dobzhansky's studies in population genetics, performed mainly with the fruit fly, served as a basis for his explanation of how the evolution of races and species may have come about through adaptation. He held that human culture is conditioned by heredity but warned that exaggerating genetic factors over environmental factors in human affairs could lead to distorted theories of racism and class prejudice. Dobzhansky also found that members of a species carry some genes that do not appear to be useful to the organism in its present environment. He discovered that successful species tend to have a wide variety of these types of genes; they provide a species as a whole with a genetic diversity that enables the species to better adapt to changes in the surrounding environment. In addition to his classic text Genetics and the Origin of Species (1937), Dobzhansky's books include Evolution, Genetics, and Man (1955), and Mankind Evolving (1962).