IntroductionThe culture industry may strive constantly for the latest hit ("The culture industry: Enlightenment as mass deception”, 2007), but even with extensive research and strong financial incentives, it remains difficult to predict the success of a film, book, or television series (De Vany, 2003). A widely adopted hypothesis suggests that successful creative works are a combination of, or balance between, convention and innovation. According to this theory, popular works are different from previous works and their peers, but not too different. For example, songs with a non-zero, but non-extreme, level of differentiation are more likely to be on the top of the Billboard’s Hot 100 charts (Askin and Mauskapf, 2017; Hargreaves, 1984), movies balancing familiarity and novelty have higher revenues (Sreenivasan, 2013), and visual metaphors in ads work best when they have mild incongruity (Mohanty and Ratneshwar, 2016). In scientific publications, the highest-cited papers are argued to be grounded on mostly conventional, but partly novel combinations of previous works (Uzzi et al. 2013). However, a significant amount of this research deals with cultural products in environments where their reception is strongly influenced by factors beyond intrinsic ones such as content, style, subject, genre, or length. In this work, we identify an unusually rich dataset of fanfiction that allows us to isolate the effect of novelty, and test the balance theory while controlling for external effects.Fanfiction draws on plots and characters from prior narratives to create new stories and alternate timelines. Generally considered to originate from zines created by Star Trek fans in the 1960s (Helmke Library, 2024), it is nowadays usually created by fans and published on the Internet (Merriam-Webster Dictionary, 2024). Fanfiction serves as a mediator for participatory sense-making within the bounds of a canon (the original work from which characters and plots are drawn) (Jaegher and Paolo, 2007). This participatory sense-making engenders a dynamic co-creative relationship between fans and transforms narratives in ways that reflect diverse interpretations, desires, and cultural or experiential contexts (Cheng and Frens, 2022; Popova, 2019; Thomas, 2011). Despite being based on a canonical work, fanfiction is one of the most innovative practices in contemporary culture, turning people who would, ordinarily, only be consumers, into creators (Thomas, 2011). It is playful, transformative, and transgressive (Barnes, 2015; Tosenberger, 2008). An enthusiast of the Harry Potter series may write a new adventure for Hermione and Harry; a fan of the television show Buffy the Vampire Slayer may write a story in which Willow’s girlfriend has a different fate. Fans of Sherlock Holmes, for example, have written stories in which Holmes and Dr. Watson fall in love, and Watson, by magical means, gestates the couple’s baby. Examples like these abound, and fanfiction communities (“fandoms”) are far from conservative, often subverting, as well as extending a canonical work. This production goes along with the interchangeability of the creator and consumer roles: an author also reads and comments on other fanfiction (Eiji and Steinberg, 2010). These interactions happen on time scales of hours, even minutes, and the rapidity of the feedback process allows for rapid change and selection, making them ideal laboratories for the study of cultural evolution.The practice of fanfiction writing is global and brings together individuals from multiple countries and cultures (Vazquez-Calvo et al. 2019). People write fanfiction to express their passion for the canon, to find erotic engagement (Busse, 2017), to transform hetero-normative narratives (Floegel,