Muller, Hermann Joseph (1890–1967), a United States geneticist. Experimenting with fruit flies, Muller found that mutations (changes in the structure of the genes) can be produced by X rays. This discovery, announced in 1927, led to further research demonstrating that mutations (and, therefore, new varieties of organisms) are produced by cosmic rays and other forms of radiation. Muller's work took on added significance after the introduction of nuclear weapons and the realization of the effects that nuclear explosions can have on human heredity. Muller was awarded the Nobel Prize in physiology or medicine in 1946.
Muller was born in New York City. He graduated from Columbia University in 1910, and began his research with fruit flies as a graduate student. In 1916, Muller received his Ph.D. from Columbia. He was professor of zoology at the University of Texas, 1920–36, and a research associate at the University of Edinburgh, 1937–40, and at Amherst College, 1940–42. He taught at Indiana University from 1945 until his retirement in 1964.