 The field of molecular biology arose from the convergence of work by geneticists, physicists, and structural chemists on a common problem: the nature of inheritance. In the early twentieth century, although the nascent field of genetics was guided by Mendel’s laws of segregation and independent assortment, the actual mechanisms of gene reproduction, mutation and expression remained unknown. Thomas Hunt Morgan and his colleagues utilized the fruit fly, Drosophila melanogaster, as a model organism to study the relationship between the gene and the chromosomes in the hereditary process (Morgan 1926; discussed in Darden 1991; Darden and Maull 1977; Kohler 1994; Roll-Hanson 1978; Wimsatt 1992). A former student of Morgan’s, Hermann J. Muller, recognized the “gene as a basis of life”, and so set out to investigate its structure (Muller 1926). Muller discovered the mutagenic effect of x-rays on Drosophila, and utilized this phenomenon as a tool to explore the size and nature of the gene (Carlson 1966, 1971, 1981, 2011; Crow 1992; Muller 1927). But despite the power of mutagenesis, Muller recognized that, as a geneticist, he was limited in the extent to which he could explicate the more fundamental properties of genes and their actions. He concluded a 1936 essay: