Modelling provides clues to the evolution of human brain size.
Most organisms are brainless but thriving. Brains are expensive to produce and maintain, and in the human lineage they have grown so large as to incur a substantial metabolic burden as the brain develops1. A human brain stops growing by the age of ten, long before the body reaches physical maturity, and this costly and fast process of brain growth has been proposed to cause a delay in body growth1. Brain growth is not given priority in this way in other apes, and the human pattern is puzzling because it keeps our bodies smaller, more vulnerable and less productive for longer. The answer to this riddle must lie in how the human brain helped our ancestors to survive and reproduce. In a paper in Nature, González-Forero and Gardner2 investigate the role of different factors as possible drivers of our unusually large brains, and determine how well these factors might account for the pattern of changes in brain and body size that occur as humans develop.