In the twentieth century, biomedical researchers believed the study of Indigenous Amazonians could inform global histories of human biological diversity. This paper examines the similarities and differences of two approaches to this mid-century biomedical research, comparing the work of virologist and epidemiologist Francis Black with human geneticists James V. Neel and Francisco Salzano. While both groups were interested in Indigenous populations as representatives of the past, their perspectives on epidemics diverged. For Black, outbreaks of infectious diseases were central to his methodological and theoretical interests; for Neel and Salzano, epidemics could potentially compromise the epistemological value of their data.