With the rise of molecular genetics and the cornucopia of techniques it provides, a number of biomedical researchers in both the public and private sectors have turned to the human genome to search for variations among the world’s populations, with the purpose of tracing human evolution and migration patterns and predicting genetic disorders. The human genome also offers insight into an individual’s genealogy, which has never before been charted with such precision. Whereas 18th- and 19th-century scholars fetishized external characteristics in order to classify humans, more recent scholars have turned to the internal sequence of the genome. But how does one define populations? Should they be based on race? Can one speak of race at the molecular level? This essay explores the history of the biology of race with a view to compare and contrast modern molecular biological studies with the more pernicious actions of early-20th-century eugenicists. The key linking the two practices is the search for biological entities that do not overlap among the races. A critical difference is that modern studies use molecular biology to include previously excluded populations in the treatment of certain diseases. While the intentions are quite different, a number of scholars feel that genetic essentialism might be the end result.