"Journey to the Microcosmos: The Complicated Legacy of Lynn Margulis" examines microbiologist Lynn Margulis’s influence on modern biology through her work on symbiosis and endosymbiotic theory. The video explains how interactions among microbes helped shape ideas about the evolution of eukaryotic cells, especially the origins of mitochondria and chloroplasts from ancient prokaryotes. It also explores scientific debate, evidence, hypothesis testing, and the importance of revising ideas when claims are not supported, including Margulis’s incorrect conclusions about flagella. With strong connections to life science curricula, evolution, cell biology, microbiology, and scientific practices, the episode offers a clear overview of how scientific knowledge develops through collaboration, criticism, and ongoing research. Part of the "Journey to the Microcosmos" series.