In the area called "black public health" increases the interest about the African ancestry and the "racial diseases". Concomitantly, genetics mapping researches have been done with the purpose to disavow "race" through the affirmation of miscegenation as the "real identity" of Brazilian people. These issues will be discussed in view of how the legitimacy and authority of biology are being mobilized to justify political positions. "Geneticization" is not the case here. But a politics of representation that reproduces dichotomies - between science and politics, for example - in an intense movement of hierarchization of predicates and production of substances. A critical position about this politics is necessary as a political critic about the biological determination and his substancialistic and unveiling logic.131125136