Hermann Joseph Muller

In 1926, a series of major breakthroughs began. In November, Muller carried out two experiments with varied doses of X-rays, the second of which used the crossing over suppressor stock ("ClB") he had found in 1919. A clear, quantitative connection between radiation and lethal mutations quickly emerged. Muller's discovery created a media sensation after he delivered a paper entitled "The Problem of Genetic Modification" at the Fifth International Congress of Genetics in Berlin; it would make him one of the better-known public intellectuals of the early 20th century. By 1928, others had replicated his dramatic results, expanding them to other model organisms, such as wasps and maize. In the following years, he began publicizing the likely dangers of radiation exposure in humans (such as physicians who frequently operate X-ray equipment or shoe sellers who radiated their customers' feet).[15]

His lab grew quickly, but it shrank again following the onset of the Great Depression. Especially after the stock market crash, Muller was increasingly pessimistic about the prospects of capitalism. Some of his visiting lab members were from the USSR, and he helped edit and distribute an illegal leftist student newspaper, The Spark. It was a difficult period for Muller both scientifically and personally; his marriage was falling apart, and he was increasingly dissatisfied with his life in Texas. 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.[16] Muller's speech before the Third International Eugenics Conference in New York has been credited with marking the end of Galtonism, and perhaps even eugenics itself, as a popular movement in the sciences. H. Bentley Glass, a contemporary observer and Ph.D. student of Muller's, would say Muller's speech "just about finished the activity of the Eugenics Society".[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. In Berlin, he met two physicists who would later be significant to the biology community: Niels Bohr and Max Delbrück. The Nazi movement was precipitating the rapid emigration of scientific talent from Germany, and Muller was particularly opposed to the politics of National Socialism. The FBI was investigating Muller because of his involvement with The Spark, so he chose instead to go to the Soviet Union (an environment better suited to his political beliefs). In 1933, Muller and his wife reconciled, and their son David E. Muller and she moved with Hermann to Leningrad. There, at the Institute of Genetics, he imported the basic equipment for a Drosophila lab—including the flies—and set up shop. The institute was moved to Moscow in 1934, and Muller and his wife were divorced in 1935.[19]

In the USSR, Muller supervised a large and productive lab, and organized work on medical genetics. Most of his work involved further explorations of genetics and radiation. There he completed his eugenics book, Out of the Night, the main ideas of which dated to 1910.[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 and many of the Russian genetics community did what they could to oppose Trofim Lysenko and his Larmarckian evolutionary theory, but Muller was soon forced to leave the Soviet Union after Stalin read a translation of his eugenics book and was "displeased by it, and...ordered an attack prepared against it."[21] By this time, Muller had already asked for a leave of absence. News of the Lysenko trials had reached the United States, and his son David was being raised there, after his divorce.[22] In the official declaration by the Institute, biological determinism was rejected: "The development of society is subject not to biological laws but to higher social laws. Attempts to spread to humanity the laws of the animal kingdom are an attempt to lower the human being to the level of beasts."[23]

Muller, with about 250 strains of Drosophila, moved to University of Edinburgh in September 1937, after brief stays in Madrid and Paris. In 1938, with war on the horizon, he began looking for a permanent position back in the United States. He also began courting Dorothea "Thea" Kantorowicz, a German refugee; they were married in May 1939. The Seventh International Congress on Genetics was held in Edinburgh later that year; Muller wrote a "Geneticists' Manifesto"[24] in response to the question: "How could the world's population be improved most effectively genetically?" He also engaged in a debate with the perennial genetics gadfly Richard Goldschmidt over the existence of the gene, for which little direct physical evidence existed at the time.[25]

Muller's house in Bloomington, Indiana

When Muller returned to the United States in 1940, he took an untenured research position at Amherst College, in the department of Otto C. Glaser. After the U.S. entry into World War II, his position was extended indefinitely and expanded to include teaching. His Drosophila work in this period focused on measuring the rate of spontaneous (as opposed to radiation-induced) mutations. Muller's publication rate decreased greatly in this period, from a combination of lack of lab workers and experimentally challenging projects. However, he also worked as an adviser in the Manhattan Project (though he did not know that was what it was), as well as a study of the mutational effects of radar. 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.[26] Here, he lived in a Dutch Colonial Revival house in Bloomington's Vinegar Hill neighborhood.[27]

In 1946, Muller was awarded the Nobel Prize in Physiology or Medicine, "for the discovery that mutations can be induced by X-rays". 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.[28] In Muller's Nobel Prize lecture, he argued that no threshold dose of radiation existed that did not produce mutagenesis, which led to the adoption of the linear no-threshold model of radiation on cancer risks.[29]

The Nobel Prize, in the wake of the atomic bombings of Hiroshima and Nagasaki, focused public attention on a subject Muller had been publicizing for two decades - the dangers of radiation. In 1952, nuclear fallout became a public issue; since Operation Crossroads, more and more evidence had been leaking out about radiation sickness and death caused by nuclear testing. Muller and many other scientists pursued an array of political activities to defuse the threat of nuclear war. With the Castle Bravo fallout controversy in 1954, the issue became even more urgent. 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.[30]

Muller's opinions on the effect of radiation on mutagenesis were used by Rachel Carson in her book Silent Spring,[32] however, his opinions have been criticized by some scientists; geneticist James F. Crow called Muller's view "alarmist" and wrote that it created in the public "an irrational fear of low-level radiation relative to other risks".[33][34] It has been argued that Muller's opinion was not supported by studies on the survivors of the atomic bombings, or by research on mice,[35] and that he ignored another study that contradicted the linear no-threshold model he supported, thereby affecting the formulation of policy that favored this model.[29]

Muller was elected to the American Academy of Arts and Sciences in 1942 and the American Philosophical Society in 1947[36][37] Muller was awarded the Linnean Society of London's Darwin-Wallace Medal in 1958 and the Kimber Genetics Award of the U.S. National Academy of Sciences, of which he was a member, in 1955.[38][39] He served as president of the American Humanist Association from 1956 to 1958.[40] The American Mathematical Society selected him as its Gibbs Lecturer for 1958.[41] He retired in 1964.[42] The Drosophila basic units of inheritance, their chromosomal arms, are named "Muller elements" in Muller's honor.[43]

H. J. Muller and science fiction writer Ursula K. Le Guin were first cousins once removed; his father (Hermann J. Muller Sr.) and her father's mother (Johanna Muller Kroeber) were siblings, the children of Nicholas Müller, who immigrated to the United States in 1848, and at that time dropped the umlaut from his name. Another cousin was Herbert J. Muller, whose grandfather Otto was another son of Nicholas and a sibling of Hermann Sr. and Johanna.[44]

In a recent retrospective article about Muller's contribution, James Haber[45] wrote as follows:

Drosophila geneticist, Hermann Muller, envisioned the fundamental principles that such a molecule must have: to be auto-assembling and to be mutable but then again stable. He followed his prescient review of these properties with a remarkable prediction: learning about the hereditary material and its properties would not come from studying Drosophila, but from studying bacteria and their bacteriophages.