At the turn of the twentieth century, comparative studies of human culture (ethnology) gave way to studies of the details of individual societies (ethnography). While many writers have noticed a political sub-text to this paradigm shift, they have regarded political interests as extrinsic to the change. The central historical issue is why anthropologinsts stopped asking global, comparative questions and started asking local questions about features of particular societies. The change in questions cannot be explained by empirical factors clone, and following Jarvie, this essay argues that political factors motivate the change. Jarvie's understanding of the role played by egalitarian politics is criticized, and the esay develops a new model of how political or moral values can become constitutive of scientific enquiry. On the erotetic view of explanation, whether one proposition explains another depends on the choice of contrast clas and relevance criterion. Since political or moral values can motivate these choices, explanation can depend on non-epistemic values. The essay argues that the comparative questions of nineteenth-century ethnology presupposed that Europeans were superior to other races. It closes by arguing that Fanz Boas recognized the political values implicit in nineteenth-century ethnology and rejected its questions on those grounds.