How did bathrooms get to be separated by gender in the first place?

Men and women have shared bathrooms through history. The idea of separat rooms for women is a rather new invention, dating back to the late 19th century.
Terry S. Kogan writes:
Rather, these laws were rooted in the so-called “separate spheres ideology” of the early 19th century – the idea that, in order to protect the virtue of women, they needed to stay in the home to take care of the children and household chores. (…)
By the middle of the [19th] century, scientists set their sights on reaffirming the ideology by undertaking research to prove that the female body was inherently weaker than the male body.
Armed with such “scientific” facts (now understood as merely bolstering political views against the emergent women’s rights movement), legislators and other policymakers began enacting laws aimed at protecting “weaker” women in the workplace. Examples included laws that limited women’s work hours, laws that required a rest period for women during the work day or seats at their work stations, and laws that prohibited women from taking certain jobs and assignments considered dangerous.
Kogan points out that opponents of trans rights have employed the slogan “No Men in Women’s Bathrooms”, which evokes visions of weak women being subject to attack by men if trans women are allowed to “invade” the public bathroom.
In fact, the only solid evidence of any such attacks in public restrooms are those directed at trans individuals, a significant percentage of whom report verbal and physical assault in such spaces.
Photo: Restroom, Sandsundvær, Herøy, Nordland, Norway Photo: Guttorm Raknes
