Modeling effects of inter-group contact on links between population size and cultural complexity

Human populations rely on cultural artifacts and complex cumulative culture for their survival. Populations vary dramatically in the size of their tool repertoires, and the determinants of these cultural repertoire sizes have been the focus of extensive study in recent years. A prominent hypothesis, supported by computational models of cultural evolution, asserts that tool repertoire size increases with population size. However, not all empirical studies seeking to test this hypothesis have found such a correlation; this has led to a contentious and ongoing debate. As a possible resolution to this longstanding controversy, we suggest that accounting for even rare cultural migration events that allow sharing of knowledge between different-sized populations may help explain why a populations size might not always predict its cultural repertoire size. Using an agent-based model to explore different assumptions about the effects of population size and migration on tool repertoires, we find that connectivity of one population to others, particularly to large populations, may significantly boost its tool repertoire size when population interactions lead to cultural exchange. Thus, two populations of identical size may have drastically different tool repertoire sizes, hinging upon their access to other groups knowledge. Intermittent contact between populations boosts cultural repertoire size and still allows for the development of unique tool repertoires that have limited overlap between populations.