Carel P. van Schaik, Zitan Song, Carolline Schuppli, Szymon Marian Drobniak, Sandra A Heldstab, Michael Griesser

Our understanding of the considerable variation in vertebrate brain size remains incomplete. Large brains are adaptive but brains require unusually high, near-constant energy inputs, and are prioritized energy targets. This trade-off also has understudied developmental consequences: immatures must develop a fully functional brain without already having one. We here propose that energy subsidies through parental provisioning solved this bootstrapping problem, and find strong empirical support. Parental provisioning also improves immature survival and facilitates evolutionary increases in brain size. We call for better integration of costs and benefits of brains, and reevaluation of the cognitive abilities used in comparative tests.