Historians in the 1970s and 1980s explored the ways in which Victorian science characterised and caricatured the female intellect. As a core element of debates on the extension of the franchise, and on women in higher education, the scientific literature on the mental differences between men and women has been thoroughly explored. A key part of this literature dealt with the relative weights of male and female brains, and the assertions of evolutionists and anatomists that fundamental physiological differences explained any observable differences in psychology by natural law. The paper revisits this material with a new set of questions. To what extent did scientific discourse not only subordinate women, but also serve to reinforce a social hierarchy of men? How was manliness, as a natural mental quality, defined, and who did it exclude? Exploring the ways in which scientific literature mirrored discourses of racial, political and citizenship exclusions, substantial revisions to the existing historiography are suggested. The paper concludes by proposing a turn towards the image of the ‘animal’ as a fundamental category of analysis in Victorian thought, upon which constructions of gender, race and social hierarchy were constructed.