The relationship between brain size and cognitive ability

Abstract

This review examines the relationship between brain size and human intelligence by integrating findings from neuroimaging studies, genetic analyses and large-scale population research. Early theories, such as Spearman’s concept of general intelligence (g), laid the foundation for understanding cognitive ability as a unified construct. Evidence from modern studies suggests that while brain size has a measurable and partly causal association with intelligence, its effect is modest. Research highlights that grey matter volume, specific brain regions and neural activity contribute more significantly than overall brain size alone. Additionally, the efficiency and connectivity of large-scale brain networks, particularly the frontoparietal system, play a central role in cognitive functioning. Overall, intelligence emerges from a complex interaction between brain structure, neural organization and functional connectivity rather than simply the size of the brain.