This article discusses the work of some key players in the current debate on the construction of the notion of sexual difference in modernity, taking as the focus of analysis and illustration the theses submitted at the School of Medicine in Rio de Janeiro, Brazil, during the 19th century. The objective is to confront the argument that the difference between the sexes comes to be taken for granted and considered immutable by science. This emphasis on a natural difference between the sexes is related to transformations that occurred beginning in the late 18th century (growing industrialization and urbanization, more extensive participation by women in the labor market, the emergence of women's rights movements) that required changes in the established gender relations. Still, it is precisely through the attempts to prove that the difference was natural that one perceives how unstable and threatening it was. Interventions such as women's education and labor market participation were capable of altering and even "subverting" the difference. Thus, "natural" was not synonymous with definitive or guaranteed.
Gender; Sexuality; History of Medicine