The recent introduction of lawsthat regulate whether transgender people can use the facilities that align with their gender identities has brought the issue of bathroom sex segregation to the forefront of national conversations. Some have proposed that the solution may lie in gender-neutral facilities, while others worry about what the consequences might be. But, while efforts to prohibit gender intermingling in restrooms have taken on a new focus, the roots of the debate date back over a century.

Though the first sex-segregated toilets were established in Paris in the 1700s, regulations requiring that American men and women use separate restrooms got their start in the late 1800s. The first regulation requiring separate toilet facilities for men and women was passed in 1887, when Massachusetts required the establishment of separate privies in businesses. “Wherever male and female persons are employed in the same factory or workshop, a significant number of separate and distinct water-closets, earth-closets, or privies shall be provided for the use of each sex and should be plainly designated,” the law reads. In the next line, mixed use of such facilities is prohibited. Over the course of the next three decades, nearly every state passed its own version of that law.

But the rules that govern who pees where in public spaces were not created simply because of physical differences between men and women that affect how bathrooms are used. “One might think that it makes perfect sense, that bathrooms are separated by sex because there are basic biological differences,” says Terry Kogan, a law professor at the University of Utah. “That’s completely wrong.”

Kogan, who has done extensive research on the history of sex-segregation in public restrooms, tells TIME that the policies came about as a result of social anxieties about women’s places in the world.