Growing up in the 1980s, Evan Urquhart was seen as a girl, but began to feel a profound difference with the girls at school. Studying the “Sweet Valley High” series seemed to offer clues on how to behave like a regular teenage girl.

But in sixth grade, Urquhart got a library card and almost at random selected Isaac Asimov’s sci-fi novel “The Robots of Dawn” from the shelf. It had a relatable male protagonist … and an eye-opening sex scene. “If I wasn’t transgender before I started that book,” he says, “I was by the time I finished it.”

Evan Urquhart is a regular contributor to Slate, where a version of this article originally appeared as part of its Spark Notes series about lightbulb moments in sexual development.