Ultimate and proximate explanations for human cumulative culture and collective intelligence.

The controversy remains over whether chimpanzee culture is cumulative or why it may have remained incipient compared with human cumulative culture. In this perspective, we argue that many debates over cumulative culture and collective intelligence can be clarified by extending the parallels between genetic and cultural evolution. Inspired by Dobzhansky's formulation, we first argue that understanding cultural and cognitive differences between humans and chimpanzees requires evidence from the population-level distribution of evolved cultural traits, in addition to evidence for cultural reinvention or social learning at the individual level. Second, we propose that debates over the role of collective intelligence in cultural evolution can be solved if more attention is given to Tinbergen's differentiation between proximate and ultimate levels of explanation. Since cumulative cultural evolution implies that individuals become less likely to hold the totality of culture even with the assistance of social learning, we propose that hominin intelligence evolved to become at the same time more general, cultural and collective than in other African apes. Finally, we discuss our Foraging Niche Hypothesis, which points to increased fitness returns to tool making and spatial mobility as ultimate explanations, with the later evolution of increased general intelligence offering a proximate account for the cultural divergence between hominins and chimpanzees. This article is part of the theme issue 'The evolution of collective intelligence'.