In 1876, Brazilian physical anthropologists De Lacerda and Peixoto published findings of detailed anatomical and osteometric investigation of the new human skull collection of Rio de Janeiro’s Museu Nacional. They argued not only that the Indigenous ‘Botocudo’ in Brazil might be autochthonous to the New World, but also that they shared analogic proximity to other geographically very distant human groups – the New Caledonians and Australians – equally attributed limited cranial capacity and resultant inferior intellect. Described by Blumenbach and Morton, (...) ‘Botocudo’ skulls were highly valued scientific specimens in 19th-century physical anthropology. A recent genomic study has again related ‘the Botocudo’ to Indigenous populations from the other side of the world by identifying ‘Polynesian ancestry’ in two of 14 Botocudo skulls held at the Museu Nacional. This article places the production of scientific knowledge in multidisciplinary, multiregional historical perspectives. We contextualize modern narratives in the biological sciences relating ‘Botocudo’ skulls and other cranial material from lowland South America to Polynesia, Melanesia, and Australia. With disturbing irony, such studies often unthinkingly reinscribe essentialized historic racial categories such as ‘the Botocudos’, ‘the Polynesians’, and ‘the Australo-Melanesians’. We conclude that the fertile alliance of intersecting sciences that is revolutionizing understandings of deep human pasts must be informed by sensitivity to the deep histories of terms, classification schemes, and the disciplines themselves. (shrink)