Population connectivity shapes cultural complexity in chimpanzees

Cultural complexity in chimpanzees depends on migration and interaction between groups, echoing early human patterns of cultural evolution, researchers report in a new study. The findings offer insight into the development of cumulative culture in early hominins. Culture, defined as a set of socially learned behaviors, has been increasingly documented across various animal species. However, human culture stands out for its complexity and cumulative nature, where cultural knowledge builds upon previous innovations. While chimpanzees – humans’ closest relatives – demonstrate a variety of cultural behaviors, such as using foraging tools, their culture lacks the depth of cumulative culture seen in humans. It's thought that this divergence may stem from our ancestors highly mobile foraging practices, which likely fostered broader social networks and enabled the sharing and preservation of diverse cultural knowledge. This contrasts with the limited population connectivity observed among chimpanzee subspecies, which may have restricted more complex cultural exchange. Here, Cassandra Gunasekaram and colleagues investigate the conditions that promoted the development of cumulative culture in the shared ancestor of humans and chimpanzees and why it remained nascent in chimpanzees. Gunasekaram et al. combined recent genetic data on chimpanzee migration with cultural records from the Pan African Program, focusing on the transmission of 15 distinct foraging behaviors among 35 populations across the four chimpanzee subspecies. By analyzing foraging behaviors – ranging from simple or tool-free strategies to those involving complex toolsets – the authors found that complex foraging behaviors were more closely tied to recent genetic markers of migration, suggesting that such behaviors likely require cultural transmission across groups. Moreover, populations at genetic intersections of three chimpanzee subspecies demonstrated the highest levels of cultural complexity, hinting at the role of intergroup connectivity in cultural accumulation. On the other hand, behaviors involving simple, or no tools show weak associations with genetic markers of recent migration, suggesting these simpler behaviors may be more likely to emerge independently across regions over evolutionary time. According to Gunasekaram et al., the findings suggest that cumulative culture may evolve faster in species with increased mobility and extensive social networks where broad foraging networks can facilitate the exchange of innovations. This heightened connectivity among our ancestors likely promoted cooperative behaviors, teaching, and shared learning, setting humans on a distinctive path of cultural coevolution.