Supported by a reading of the historical and ethnographical literature, this article addresses the political consequences of the adoption of remnants [remanescentes] as a legislative term describing indigenous groups and rural Afro-Brazilian populations, and discusses the analytic and theoretical limits of the current polarization of "race" and "ethnic group" in Brazilian social sciences. Proposing the concept of "plastic identity", it analyzes the thematic and conceptual convergence of recent studies based on these two classifiers and questions the stability of their separation through recourse to a number of documented social situations. This concept allows a reflection on the close relationship between scientific production, juridical training and political action. Finally, a proposal is made to rethink the lifeworlds of communities designated "remnants" in terms of ethnic emergence and cultural invention.