This lecture discusses the Luria-Delbrück experiment, which demonstrated that mutations in bacteria occur randomly, not in response to a challenge. It explores the implications of this experiment on evolutionary mechanisms, emphasizing the importance of probabilities in understanding biological data. The lecture also touches on the significance of mutation rates computation in labs and the role of randomness in biological processes. Additionally, it outlines the course content, covering topics such as random variables, thermal fluctuations, and random walks in biological systems.