The Idea of “Bad Blood”

In this wide-ranging opening lecture of an eight-part series, Ken Gemes introduces his course 'The Biology of Evil,' a project refined over thirty years of teaching at Yale and the University of London. Gemes argues that Western culture has repeatedly translated moral categories into biological ones, turning evil from a spiritual or intellectual error into something carried in the body. He traces this transformation through ancient Greek thought, where Pythagorean and Aristotelian frameworks established gendered and racialized hierarchies rooted in biology. He then moves through medieval theology, contrasting Manichean and Gnostic models of evil, and examines how biological metaphors fueled anti-Semitism and misogyny. Drawing on Borges, Freud, and Hegel, Gemes shows how the language we inherit shapes how we think, and why the genealogy of our concepts matters. The lecture builds toward the nineteenth century fear of infection: the terrifying idea that evil is contagious and that anyone might be corrupted. Gemes makes the case that these old metaphors remain dangerously alive today.