Identifying the necessary conditions for large populations to enhance cumulative culture.

Large populations have the potential to enhance cumulative cultural evolution (CCE) by increasing access to better-adapted solutions and providing more diverse inputs for recombination. However, evidence for this population size hypothesis is mixed: some studies find that large populations facilitate CCE, while others report the opposite. We present two large-scale experiments (combined N = 941) that identify the conditions under which larger populations reliably enhance CCE. In both experiments, participants were randomly assigned to different-sized groups and tasked with developing and improving a virtual arrowhead technology. Experiment 1 resolves the mixed findings in the literature by showing that the effect of population size depends on attention filtering—the ability to selectively attend to high-payoff solutions while avoiding low-payoff solutions. Experiment 2 introduces a novel mechanism: the use of external representations (e.g., diagrams, notes) to offload cognitive demands, support payoff-based comparisons, and create opportunities for solution recombination. In this context, CCE was enhanced in larger populations when participants could use an external record to support learning and innovation. Together, the experiments identify two conditions that enable large populations to enhance CCE.