Max Delbruck

Max Delbruck was a German-American biophysicist who turned the study of bacteriophage, viruses that infect bacteria, into a rigorous quantitative branch of biology and became one of the founding figures of molecular biology. With Salvador Luria, Delbruck carried out the Luria-Delbruck experiment of 1943, known as the fluctuation test, which showed statistically that bacterial resistance to viral infection arises from random spontaneous mutations that exist before the virus is ever introduced, rather than being induced by exposure to the virus itself, providing strong experimental evidence for Darwinian natural selection acting at the microbial level. In 1945 Delbruck co-founded the Phage Group with Luria and Alfred Hershey, an informal but highly influential research network centered on bacteriophage that trained a generation of molecular biologists and helped establish Cold Spring Harbor Laboratory as a hub for that research. He shared the 1969 Nobel Prize in Physiology or Medicine with Luria and Hershey for discoveries concerning the replication mechanism and genetic structure of viruses. Delbruck fled Nazi Germany in 1937, became a United States citizen in 1945, and spent most of his career at the California Institute of Technology.