Muller, Hermann Joseph (1890–1967)

US geneticist who was awarded a Nobel Prize for Physiology or Medicine in 1946 for his discovery, in 1926, that X-ray irradiation can cause mutation. This showed that mutations are nothing more than chemical changes.

Muller campaigned against the needless use of X-rays in diagnosis and treatment, and pressed for safety regulations to ensure that people who were regularly exposed to X-rays were adequately protected. He also opposed nuclear-bomb tests.

Muller was born in New York and studied at Columbia. In 1920 he joined the University of Texas, Austin, later becoming professor of zoology. The constraints on his freedom to express his socialist political views caused him to leave the USA in 1932, and from 1933 he worked at the Institute of Genetics in the USSR. When the false ideas of Trofim Lysenko began to dominate Soviet biological research, Muller was openly critical of ‘Lysenkoism’, and was forced to leave in 1937. After serving in the Spanish Civil War, he worked at the Institute of Animal Genetics in Edinburgh. In 1940 he returned to the USA, becoming professor at Indiana University in 1945.

In 1919 Muller found that the mutation rate was increased by heat, and that heat did not always affect both of the chromosomes in a chromosome pair. From this he concluded that mutations involved changes at the molecular or submolecular level. Next he experimented with X-rays as a means of inducing mutations, and by 1926 he had proved the method successful.

Muller's research convinced him that almost all mutations are deleterious. In the normal course of evolution, deleterious mutants die out and the few advantageous ones survive, but he believed that if the mutation rate is too high, the number of imperfect individuals may become too large for the species as a whole to survive.