A new analysis of fossil skulls suggests that human brains grew larger over the past 2 million years without strong pressure from natural selection.
Researchers Katerina Harvati at the University of Tübingen and Mark Hubbe at the University of Tennessee examined 87 hominin skulls from species including Homo sapiens, Neanderthals, Homo erectus and Homo habilis.
They found that braincases expanded and faces flattened over time. Mathematical models showed these changes best matched neutral evolution driven by random mutations rather than selection for greater cognitive ability.
The study also identified periods of stasis where braincase size remained stable. Experts noted that cooking may have supplied extra calories to support larger brains but that social structures could have reduced advantages for exceptional intelligence.
The findings appear in Nature Communications.