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

Human populations rely on cultural artefacts 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. A prominent hypothesis, supported by computational models of cultural evolution, asserts that tool repertoire size increases with population size. However, not all empirical studies have found such a correlation, leading 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 population's size might not always predict its cultural repertoire size. Using an agent-based model to test assumptions about the effects of population size and connectivity on tool repertoires, we find that cultural exchange between a focal population and others, particularly with large populations, may significantly boost its tool repertoire size. 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.

Cultural evolution and prehistoric demography.

One prominent feature of human culture is that different populations have different tools, technologies and cultural artefacts, and these unique toolkits can also differ in size and complexity. Over the past few decades, researchers in the fields of prehistoric demography and cultural evolution have addressed a number of questions regarding variation in toolkit size and complexity across prehistoric and modern populations. Several factors have been proposed as possible explanations for this variation: in particular, the mobility of a population, the resources it uses, the volatility of its environment and the number of individuals in the population. Using a variety of methods, including empirical and ethnographic research, computational models and laboratory-based experiments, researchers have found disparate results regarding each hypothesis. These discordant findings have led to debate over the factors that most significantly influence toolkit size and composition. For instance, several computational, empirical and laboratory studies of food-producing populations have found a positive correlation between the number of individuals in a population and toolkit size, whereas similar studies of hunter-gatherer populations have found little evidence of such a link. In this paper, we conduct a comprehensive review of the literature in this field of study and propose corollaries and interdisciplinary approaches with the goal of reconciling dissimilar findings into a more comprehensive view of cultural toolkit variation. This article is part of the theme issue 'Cross-disciplinary approaches to prehistoric demography'.