It's widely accepted conventional wisdom that when it comes to creative works—TV shows, films, music, books—consumers crave an optimal balance between novelty and familiarity. What we choose to consume and share with others, in turn, drives cultural evolution.
But what if that conventional wisdom is wrong? An analysis based on data from a massive online fan fiction (fanfic) archive contradicts this so-called "balance theory," according to a paper published in the journal Humanities and Social Sciences Communications. The fanfic community seems to overwhelmingly prefer more of the same, consistently choosing familiarity over novelty; however, they reported greater overall enjoyment when they took a chance and read something more novel. In short: "Sameness entices, but novelty enchants."
Strictly speaking, authors have always copied characters and plots from other works (cf. many of William Shakespeare's plays), although the advent of copyright law complicated matters. Modern fan fiction as we currently think of it arguably emerged with the 1967 publication of the first Star Trek fanzine (Spockanalia), which included spinoff fiction based on the series. Star Trek also spawned the subgenre of slash fiction, when writers began creating stories featuring Kirk and Spock (Kirk/Spock, or K/S) in a romantic (often sexual) relationship.
The advent of the World Wide Web brought fan fiction to the masses, starting with Usenet newsgroups and mailing lists and eventually the development of massive online archives where creators could upload their work to be read and commented upon by readers. The subculture has since exploded; there's fanfic based on everything from Sherlock Holmes to The X-Files, Buffy the Vampire Slayer, Game of Thrones, the Marvel Cinematic Universe, and Harry Potter. You name it, there's probably fanfic about it.