In 1951, Joshua Lederberg began studying for a doctor of medicine degree at Columbia College and working in the lab of Francis Ryan, and in 1946 the lab of Edward Tatum. Lederberg quickly showed that some bacteria can conjugate or come together and exchange part of themselves with one another. He called the material exchanged the plasmid. Lederbergﾒs 1947 GENETICS paper, an abstract of his PhD thesis, established that ﾓthe segregational behavior of mutant factors seems to be closely analogous to that of higher forms, and seems to compel their admission into the same arena as the genes of Drosophila.

At the age of 22, Lederberg was awarded a faculty position at the University of Wisconsin, and in 1958 shared the Nobel Prize in Physiology or Medicine with George Beadle and Tatum. He never received his MD degree because he was unwilling to abandon such exciting research.