In this article we explain why a tradition of instructions issued for the proper conduct of natural history and founded in the eighteenth century became such an influential source for pervasive notions of race in the nineteenth century. In particular, we locate the transnational influence of this tradition in the work of James Cowles Prichard (1786–1848) between his time as a student of medicine at the University of Edinburgh and the posthumous publication of his own instructions for “ethnology” in John Herschel’s A Manual of Scientific Enquiry in 1849. By locating Prichard in this intellectual context, we connect the transnational Enlightenment tradition of instructing natural history travel (section one), to the practice of collecting both artifacts and human remains (section two), and the role of both ideas and collected items that transformed people into specimens by the turn of the century (section three). We argue that this little-known but profoundly influential pan-European tradition of instructed natural history activated a set of ideas and knowledge practices in a wide range of colonial settings, regularly marked by violence and enslavement, that transformed human beings into specimens to be compiled in quest of a science of race.