Historians of crime have often borrowed theoretical perspectives from sociology, criminology, and anthropology. An influential body of scholarship produced by psychologists, however, offers a new and unusually intriguing interdisciplinary perspective for historians of violence. Emphasizing the ways in evolutionary adaptations condition human behavior, "evolutionary psychologists" have developed a complex model for understanding certain kinds of violent social interactions. Aggressiveness, risk taking, and related forms of violent behavior, these scholars argue, have biological and evolutionary roots. Analyzing patterns of male-on-male homicide from Chicago between 1875 and 1920, this essay tests the applicability of evolutionary psychology theory to historical data on violence. If the model helps to account for both patterns of lethal violence and shifts in such patterns, then perhaps historians of crime should expand their use of interdisciplinary theory to include models from evolutionary psychology.