This article examines the way in which genetic « ancestry » tests have been promoted and developed over the last two decades as a genealogical tool, ostensibly capable of finding the geographic and « ethnic » origins of diasporic groups in the US. We follow the case of the descendants of enslaved Africans, emphasizing the historical context and political discourses that led to the proposal of these tests as a means to repair the social and psychological harm done by the transatlantic slave trade. Furthermore, by analysing the theories and processes implicated in the creation of « ancestry » tests, we point out how they have led to the reproduction of a vision of the world as divided into « indigenous » and « mixed » populations, in which « true » human diversity is conceived of as quantifiable, mappable, and biological. Finally, we evaluate how these genetic concepts are being translated in the discourses and practices of social actors in the search of their ancestral « roots ».