The Baym lab will explore how bacteria evolve resistance to antibiotics. The rise of drug-resistant bacteria is a threat to public health and limits our options for treating infections. In the laboratory, bacteria readily evolve resistance to extreme levels of antibiotics. Yet outside the laboratory, drug-resistant microbes are less prevalent than would be expected by theory, often cropping up and then disappearing while rarely taking over bacterial populations. This implies that although human use does affect the evolution of resistance, there are other factors that affect resistance at least as strongly. Using techniques in computational biology, microbiology, and genetic engineering, my lab will explore potential other selective pressures and, critically, what serves to counterbalance selection for resistance in nature. Further, to gain insight into the dynamics of resistance in the absence of human intervention, I will also examine bacteria prior to their clinical use with a combination of ancient DNA analysis and strain collection archives. My work will enhance our understanding of the pressures that influence the evolution of drug resistance and could lead to novel methods for diagnosing and treating antibiotic resistance at a population scale.