Chapter 1 argues that, like liberalism and mestizaje, human population genetics has been characterized by a tension between purity and mixture, which has run through its attempts to understand human diversity. In the genetic study of Latin American populations, that tension is especially evident and is part of what constitutes Latin America as an interesting site for global genomic science. It then addresses the issue of the “relation” between “science” and “society,” outlining a perspective that avoids this dualism and sees scientific and political practices and ideas as elements in a complex assemblage, rather than being two interacting domains; the chapter then explores the concept of topology as a way to characterize the networks involved in the assemblage.