Psychologist David Geary, author of The Origin of Mind (second edition underway), explains why human brains grew so large. His argument: technology-driven population growth set off between-group conflict, and male kin-based coalitions with weapons drove expansion, extinctions of rival Homo species, and later civilization-building.
Key evidence: a Y-chromosome diversity collapse 5,000-7,000 years ago, with 17 female ancestors per male, implies organized male-on-male violence. Reproductive skew among men rose from about 3x in hunter-gatherers to about 100x in early empires. Geary links the default mode and frontoparietal networks to future simulation, and says status anxiety and a drive for control are ancestral legacies. He also covers women's relational competition, the patriarchy and modern mismatch.