Pictorial representation is a key human behaviour. Cultures around the world have made images to convey information about living kinds, objects and ideas for at least 75,000 years, in forms as diverse as cave paintings, religious icons and emojis. However, styles of pictorial representation vary greatly between cultures and historical periods. In particular, they can differ in figurativeness, i.e. varying from detailed depictions of subjects to stylised abstract forms. Here we show that pictorial styles can be shaped by intergroup contact. We use data from experimental micro-societies to show that drawings produced by groups in contact tended to become more figurative and transparent to outsiders, whereas in isolated groups drawings tended to become abstract and opaque. These results indicate that intergroup contact is likely to be an important factor in the cultural evolution of pictorial representation, because the need to communicate with outsiders ensures that some figurativeness is retained over time. We discuss the implications of this finding for understanding the history and anthropology of art, and the parallels with sociolinguistics and language evolution.
IntroductionPictorial representations are ubiquitous in human culture. We find them in visual art, pictographic writing systems, road signs, graphic design, book illustrations, comics, and animations, just to mention a few examples (Drucker & McVarish, 2009;Harthan, 1997;Hockney & Gayford, 2016;Sabin, 2001). Pictorial representations are tangible expressions of ideas, mental models, and ways of understanding the world. They are highly versatile: they can visualise simple physical objects as well as very complex and abstract concepts and situations; as such, at the individual level, they are external cognitive tools that help elaborate, manipulate, store and retrieve ideas that would be difficult for the mind alone to handle, such as beliefs about supernatural agents (Mithen, 1998(Mithen, , 2004(Mithen, , 2009). Pictorial representations are also effective attention-catching devices, especially when depictive and decorative techniques enhance their aesthetic appeal (Donald, 2009;Gell, 1992). They are sometimes easier to remember than words (Madigan, 2014;Scaife & Rogers, 1996) and, unlike spoken words, they are durable material objects that can reach different audiences in different times and places, and thereby influence minds and guide behaviours (Donald, 2006;Gell, 1998). At the 2 social level, pictorial representations are an effective tool of social coordination, a powerful means to disseminate ideas within a community, transmit them from generation to generation, and create shared worldviews; this makes them ideal vehicles to disseminate ideologies, both religious and secular (Collins, 2016;Donald, 2009;Mithen, 2009). Humans have made use of pictorial representations since before the Upper Palaeolithic (Bahn, 2016;Henshilwood et al., 2002), and image-making is likely to have played an important role in the evolution of human cognition an...