SEEM Seminar - Carel van Schaik and Zitan Song

The expensive brain and the evolution of brain size

Vertebrate brains vary considerably in size, and this variation is often attributed to different cognitive demands. Here, we ask whether unusually high brain costs have acted as constraints on brain size evolution. We confirm that mammalian brains are smaller when animals face periods of reduced net food intake, but we also show that brain size coevolved with greater pre- or post-hatch provisioning in both endothermic and exothermic vertebrates. We conclude that the evolution of large brains was made possible by the lifting of the constraint on egg size or parental provisioning before or after birth, linked to the evolution of hard-shelled eggs and endothermy.