Helen Joyce in The Economist:
It all began with “Star Trek”, or more precisely with James T. Kirk, the captain of the Enterprise, and his first officer, the half-human, half-Vulcan Spock. The show, which debuted in 1966, was no immediate hit: it was nearly cancelled twice before finally being taken off the air just three years later, after 79 episodes. But throughout the following decade, as it was endlessly repeated, a cult built up around it. Films and new series followed. Now, a half-century later, its influence on popular culture is clear. Its catchphrases (“Beam me up, Scotty”; “Live long and prosper”) have entered the language. Its adventures are entwined with real-life space exploration in the public’s mind. The show’s creators thought Kirk – handsome, outgoing, irresistible to curvaceous aliens – would draw female viewers. But many women found the slight, buttoned-up Spock at least as appealing. Some perhaps identified with the difficulty of being a Vulcan in a man’s world, or his struggle to repress his emotions (Vulcan hyper-rationality is actually a species-wide convention to suppress passions so turbulent they would otherwise tear society apart). But above all, female viewers were intrigued by the relationship between the two men. They risked their lives for each other, and stuck together through thick and thin. They were clearly more than colleagues. Were they, perhaps, more than friends?
For some female fans, the answer was clear. In “slash” fan-fiction, as it was known by the end of the 1970s (for the punctuation mark in Kirk/Spock, or K/S), they made explicit an erotic bond between the two men that the show’s creators had not intended to imply. They wrote slash in fan-produced magazines, or fanzines (the first, launched in 1967, was named Spockanalia) and shared their obsession at “Star Trek” conventions. Some soft-core, some highly explicit, these stories circulated via invitation-only mailing lists or could be bought from dealers who kept them under the counter at conventions. Even mildly suggestive slash was seen as more transgressive than the steamiest heterosexual pornography.