The arrival of DNA paternity testing in the 1980s was met with great enthusiasm in the Brazilian courts. Yet, over the past two decades, Brazilian legal doctrine and jurisprudence have increasingly rejected DNA proof as the sine qua non for paternity cases. Instead, DNA paternity testing has generated mountains of litigation, as biological proof has been challenged by the argument that paternity is primarily "socio-affective". Leading family law specialists describe this new conception of paternity as an outcome of the "revolutionary" provisions of the 1988 Constitution, which recognizes the "pluralism" of family forms in modern society and guarantees equal family rights for all children. Without denying the significance of the constitution's dignitary framework, we show that new legal understandings of paternity represent less a paradigm shift than a continuation of longstanding historical tensions between biological and socio-cultural understandings of family and identity. In this article, we explore the development of biological and eventually genetic typing in Brazil, both of which had ties to the fields of criminology and race science. Our review suggests that techniques of biological identification, no matter how sophisticated or precise, were ineffective means for establishing identity, whether of individual personhood, as in the case of paternity, or national make-up. Instead, they became incorporated as supplemental methods into complex legal, social, and cultural decision-making around families.