Not that anyone who needs a job at the U would admit it:
Research published today by my colleagues and me in Frontiers in Ecology and Evolution indicates some of our earliest ancestors — which were likely still taking their first steps on land — had brains that only filled about half the space in their skulls.
Growing and maintaining brain tissue is energetically expensive for animals. The relative size of different regions of the brain is thought to be guided by a concept known as “the principle of proper mass”.
This states the more important a sense or brain region is to an animal, the more likely it is that region will be enlarged compared to others. After all, it’s pointless to spend lots of energy growing a visual processing centre if you’re a blind, cave-dwelling animal.Alice Clement, “When our evolutionary ancestors first crawled onto land, their brains only half-filled their skulls” at The Conversation
But why would skulls just happen to be so big all on their own if a greater need for capacity was not anticipated?
The paper is open access.