This article provides insight into the entwinement of the allegedly neutral category of handedness with questions of sex/gender, reproduction, dis/ability, and scientific authority. In the 1860s, Paul Broca suggested that the speech centre sat in the left brain hemisphere in most humans, and that right-handedness stemmed from this asymmetry. One century later, British psychologists Marian Annett and Chris McManus proposed biologically unconfirmed theories of how handedness and brain asymmetry were passed on in families. Their idea to integrate chance into genetic (...) models of handedness was novel, and so was their use of computerized statistics to parse out the incidence of handedness genotypes and phenotypes. Notwithstanding significant conceptual and methodological overlaps, McManus and Annett did not collaborate and proposed competing theories. I analyse the sexed/gendered dimensions of their controversy by drawing on published literature, unpublished documents, and oral history interviews. I first attend to the epistemological importance of sex/gender. Both psychologists published several iterations of their models, which increasingly relied on questions of sex/gender and reproduction. Annett additionally linked handedness with stereotypically gendered cognitive abilities. Second, I argue that using masculine-coded computer technologies contributed to Annett’s professional marginalization whereas similar methods endowed McManus with surplus authority. Finally, I show that Annett’s complicity in stabilizing sociocultural hierarchies within her theory mirrored her personal experience of marginalization based on sex/gender, age, education, and lack of institutional affiliation. This analysis exemplifies the entanglement of cognitive and social factors in scientific controversies and adds to the literature on 20th-century British women psychologists. (shrink)