The idea that there are more than two biological sexes is not as recent as you imply (Nature 518, 288–291; 2015). It emerged in the early 1990s after feminist critics of science joined forces with an intersex activist movement. Their aim was to prevent reinforcement of the artificial two-sex construct by reforming the practice of surgical intervention (see, for example, A. Fausto-Sterling The Sciences 33, 20–24 (1993) and S. J. Kessler Lessons from the Intersexed Rutgers Univ. Press, 1998).

These groups pointed out that science is not isolated from society: ideas that stimulate understanding travel into the lab from street activists, literature and varied scholarship, and move back out again. As a result of their efforts, research scientists were pushed into visualizing the previously invisible.