Max Delbrück

Max Delbrück shared the 1969 Nobel Prize in Physiology or Medicine with Alfred Hershey and Salvador Luria for his discoveries concerning the replication mechanism and genetic structure of viruses. His quantitative experiments with bacteriophages (viruses that infect bacteria) demonstrated that viruses reproduce in a predictable, stepwise manner, establishing bacteriophages as a powerful model system for molecular genetics.

The 'phage group' was an informal network of scientists organized by Max Delbrück, Salvador Luria, and Alfred Hershey in the 1940s to study bacteriophages as a way to understand fundamental genetic mechanisms. Delbrück hosted annual summer courses at Cold Spring Harbor Laboratory that trained a generation of molecular biologists and standardized phage research methods.

In 1943, Delbrück and Luria designed the fluctuation test, an experiment using Escherichia coli and bacteriophage infection to prove that bacterial resistance to viruses arises from random genetic mutations, not from adaptation to the phage. This was a landmark result because it demonstrated that bacteria undergo Darwinian selection, helping launch bacterial genetics as a field.

Delbrück was trained as a theoretical physicist in Germany, having studied under and collaborated with figures linked to the Niels Bohr circle, before he turned to biology in the late 1930s. His insistence on rigorous quantitative thinking and simple model systems—applying physics-style measurement to phage replication—pioneered the interdisciplinary approach that defined the early molecular biology movement.