Hermann Muller

Geneticist 1890-1967

Hermann Joseph Muller was one of the founding members of the "fly lab" that was initiated by Thomas Hunt Morgan. In the early part of the twentieth century, this lab was the center of important research into the role of chromosomes in inheritance, using the fruit fly Drosophila as a model organism in experiments. The major members included Morgan, Alfred Henry Sturtevant, Calvin Blackman Bridges, and Muller, all working at Columbia University around 1910 to 1915, when their major contributions to classical genetics were carried out. Muller was the only one of Morgan's students to also win a Nobel Prize.

Muller's career was unusual in that he worked in several countries. He was a third-generation American, but he left the United States in 1932 to work in Germany, the Soviet Union, and Edinburgh, Scotland, before returning to his homeland. He had a productive career as an experimental and theoretical geneticist, but he also had a life-long interest in seeing genetics applied to society. This made him controversial and sometimes put his life in jeopardy.

The first phase of Muller's career was spent at Columbia, where the fly lab was established, and at Rice University, where he held his first tenured position from 1915 to 1922. During this phase he did work that contributed to the understanding of crossing over and gene mapping (discovered by Morgan and Sturtevant). Muller also clarified the meaning of genetic mutation by limiting the concept to variations in the individual gene. He proposed the gene as the basis of life, arguing that only genes had the property of replicating their errors, essential for the evolution of life. He was the first to measure mutation rates, and he designed stocks of Drosophila to detect them.

Muller's second phase was the decade he spent at the University of Texas, from 1922 to 1932. During this time he was heavily committed to the study of mutation, culminating in his Nobel Prize work on the induction of mutations by radiation. Muller rapidly followed up his initial reports and founded a new field of radiation genetics. He also used X rays as a tool to delete chromosomes, and used these small deleted chromosomes to reveal the mechanism of genetic functions such as dosage compensation, a phenomenon he was first to interpret. Muller showed that mutations are produced in proportion to radiation dosage and that chromosome rearrangements (such as translocations) were induced at higher dosages.

In his third phase, which ran from 1932 to 1940 and which he spent working in Berlin, the Soviet Union, and Scotland, Muller studied chromosome structure, gene structure, and changes in gene function when genes were moved from their normal chromosome location. He also introduced the idea that genes arise from preexisting genes, when he discovered that a fly mutation called Bar eyes arose from a physical duplication of genes. In his last phase, Muller was back in the United States (from 1940 to 1967), working mainly at Indiana University, where he worked out the mechanism of cell death from radiation exposure and calculated the amount of mutation normally occurring in humans (genetic load) each generation. He became a critic of the Cold War policies of the United States, favoring a strong nuclear defense as a protection against Stalinism but also calling for mutual treaties to limit nuclear arms. He also fought hard against the misuse of radiation by health practitioners and industry.

In addition to his fundamental work on fly genetics, Muller contributed to human genetics through studies of twins that he conducted in the 1920s. He argued that the relation of observable character traits to genes is very complex, a problem he had first studied in detail in Drosophila, when he investigated the verifiability of shape and size in the "truncate" and "beaded" wing mutations. Muller stressed that an observable trait such as intelligence or longevity will be influenced by many genes as well as by the environment, and that simple one-gene/one-trait relationships were the exception rather than the rule in complex organisms.

Muller felt that advocates of eugenics programs ignored environmental modifiers and the complex residual heredity that he called modifier genes. He denounced the American eugenics movement in 1932 at the Third (and last) International Congress of Eugenics. Yet he remained an idealist about eugenics, favoring a positive eugenics based on "germinal choice," a non-coercive way for educated people to choose the genetic character of their own children.