In 1803, French physician Jacques-Louis Moreau argues against previous European understandings of the binary definition of men and women as different expressions of the same basic physical structure, stating that males and females are "different in every conceivable aspect of the body."

This new anatomy of "sex difference" distinguishes between organs previously understood as being equivalent (ovaries and testes) and emphasizes perceived differences between "male and female" nervous systems and other structures previously understood as the same across sexes.