Skull Study: Human Brains Grew by Drift, Not Selection
Get the Health newsletter
Daily health & science — research, biotech, public health, the studies worth knowing. Free.
- Katerina Harvati at the University of Tübingen and Mark Hubbe at the University of Tennessee, Knoxville analyzed 87 hominin skulls — 24 from Homo sapiens plus extinct relatives like Neanderthals, Homo erectus and Homo habilis — and found braincase changes were best explained by neutral evolution rather than selection for larger brains.
- The study, published in Nature Communications, tested six evolutionary scenarios and determined that random mutations accumulating without selective advantage, combined with periods of stasis constraining braincase size, best fit the 2-million-year fossil record.
- Human faces evolved along similar trajectories, but the pressure to stay roughly the same shape and size was even stronger than for the braincase, the researchers found.
- Amélie Beaudet of the French National Centre for Scientific Research called the work a valuable mechanistic deep-dive, but cautioned that skulls capture only overall size and shape — not internal reorganization, such as changes to Broca's area linked to language.
- Gerhard Weber at the University of Vienna said the 87-skull sample is too small for firm conclusions but agreed stasis likely held brains in check, suggesting prehistoric division of labor may have made exceptional intelligence less advantageous.
- Harvati proposed that the invention of cooking may have been the key release valve, since cooked food delivers more calories than raw food, potentially easing the energy constraint that limited brain growth.
Why it matters: The finding challenges the textbook narrative that human cognitive advantage drove brain expansion through natural selection. If brains grew mostly by random drift and were periodically released from constraint — possibly by cooking — then one of the defining features of our species may be less the product of adaptive pressure than decades of paleoanthropology have assumed, with significant implications for how researchers interpret fossils and model the evolution of cognition.
