Hermann Joseph Muller (December 21, 1890 – April 5, 1967) was an American geneticist who was awarded the 1946 Nobel Prize in Physiology or Medicine, "for the discovery that mutations can be induced by X-rays".

From his first semester, he was interested in biology; he became an early convert of the Mendelian-chromosome theory of heredity—and the concept of genetic mutations and natural selection as the basis for evolution.

[6] Muller remained at Columbia (the pre-eminent American zoology program at the time, due to E. B. Wilson and his students) for graduate school.

He became interested in the Drosophila genetics work of Thomas Hunt Morgan's fly lab after undergraduate bottle washers Alfred Sturtevant and Calvin Bridges joined his biology club.

In the emerging collaborative culture of the drosophilists, however, credit was assigned based on results rather than ideas; Muller felt cheated when he was left out of major publications.

In 1918, he proposed an explanation for the dramatic discontinuous alterations in Oenothera lamarckiana that were the basis of Hugo de Vries's theory of mutationism: "balanced lethals" allowed the accumulation of recessive mutations, and rare crossing over events resulted in the sudden expression of these hidden traits.

In 1918, Morgan, short-handed because many of his students and assistants were drafted for the U.S. entry into World War I, convinced Muller to return to Columbia to teach and to expand his experimental program.

In 1920, Muller and Altenburg coauthored a seminal paper in Genetics on "modifier genes" that determine the size of mutant Drosophila wings.

In 1919, Muller made the important discovery of a mutant (later found to be a chromosomal inversion) that appeared to suppress crossing over, which opened up new avenues in mutation-rate studies.

In his early years at Texas, Muller's Drosophila work was slow going; the data from his mutation rate studies were difficult to interpret.

Meanwhile, the waning of the eugenics movement, ironically hastened by his own work pointing to the previously ignored connections between environment and genetics, meant that his ideas on the future of human evolution had reduced impact in the public sphere.

[17] Muller told the assembled that eugenic ideals could no longer be achieved, because the capitalistic system produces the wrong motives of individual action, and he disdained the natures of the dominant class, and the type of society they were creating.

[18] In September 1932, Muller moved to Berlin to work with the Russian expatriate geneticist Nikolay Timofeeff-Ressovsky; a trip intended as a limited sabbatical stretched into an eight-year, five-country journey.

The Nazi movement was precipitating the rapid emigration of scientific talent from Germany, and Muller was particularly opposed to the politics of National Socialism.

[20] By 1936, however, Joseph Stalin's repressive policies and the rise of Lysenkoism was making the USSR an increasingly problematic place to live and work.

Muller's publication rate decreased greatly in this period, from a combination of lack of lab workers and experimentally challenging projects.

Muller's appointment was ended after the 1944–1945 academic year, and despite difficulties stemming from his socialist political activities, he found a position as professor of zoology at Indiana University.

Genetics, and especially the physical and physiological nature of the gene, was becoming a central topic in biology, and X-ray mutagenesis was a key to many recent advances, among them George Beadle and Edward Tatum's work on Neurospora that established in 1941 the one gene-one enzyme hypothesis.

[citation needed] In 1955, Muller was one of 11 prominent intellectuals to sign the Russell–Einstein Manifesto, the upshot of which was the first 1957 Pugwash Conference on Science and World Affairs, which addressed the control of nuclear weapons.

[30][31] He was a signatory (with many other scientists) of the 1958 petition to the United Nations, calling for an end to nuclear weapons testing, which was initiated by the Nobel Prize-winning chemist Linus Pauling.

[29] He was also accused of suppressing opposing views, and that the US National Academy of Sciences Committee of which he was part of misrepresented research record to ensure continued funding and strengthen his influence on US health policy.

[47][48] As a result, for the first time in human history, a World Constituent Assembly convened to draft and adopt a Constitution for the Federation of Earth.