Sexological ideas about gender similarity and difference have changed dramatically over the course of the last one hundred years. In the nineteenth century, sexologists, like other scientists, focused on the differences between women and men. This perspective is typified by researchers like Havelock Ellis, who considered female sexuality to be weaker, less fulfilling, and more passive than that of the male. Modern sexology since the Kinsey era has shifted to the ideology of similarity. Sexual scientists, most notably Masters and Johnson, emphasize how alike men and women are in sexual response and functioning. This change in emphasis was related to both socio‐political influences and to the quest by sexual scientists for cultural legitimacy. In addition, the ideology of similarity raises complex questions about scientific methodology and political considerations.