Larger social groups require proportionally more brain tissue to manage

Evidence

Mutual cooperation has tremendous fitness benefits to individuals, but does not come for free. A considerable amount of brainpower is required to get along with one another, and the larger the number of social interactions one must track, the more cortical tissue one needs to navigate the ensuing complexity of the social world. Based on these considerations, the anthropologist Robin Dunbar conducted cross-species comparisons of brain size, and found that, among primates, the best predictor of neocortex volume relative to body size is group size. A wide range of intensely cooperative human behaviors begins to break down as groups get too large—unless additional cultural solutions are injected into the group dynamics. — Norenzayan, Ara, Big gods - how religion transformed…, 413

Categorization

• XREF: Dunbar’s number directly connects to the reader’s Big God/partner-choice framework — group size strains the cognitive machinery that surveillance-based cooperation (Norenzayan’s own thesis) is built to solve.