Australasian Science: Australia's authority on science since 1938

Smarter Brains Are Bloodthirsty

The evolution of human intelligence is not simply related to brain size; rather, the supply of blood to the brain has been more important according to research published in Royal Society Open Science. The study found that as the human brain became larger it also became more bloodthirsty and therefore more energetically costly.

The research team calculated how blood flowing to the brain of human ancestors changed over time, using the size of two holes at the base of the skull that allow arteries to pass to the brain. The findings allowed the researchers to track the increase in human intelligence across evolutionary time from 3 million-year-old Australopithecus to modern humans.

“Brain size has increased about 350% over human evolution, but we found that blood flow to the brain increased an amazing 600%,” says project leader Em/Prof Roger Seymour of The University of Adelaide. “We believe this is possibly related to the brain’s need to satisfy increasingly energetic connections between nerve cells that allowed the evolution of complex thinking and learning.

“To allow our brain to be so intelligent, it must be constantly fed oxygen and nutrients from the blood. The more metabolically active the brain is, the more blood it requires, so the supply arteries are larger. The holes in fossil skulls are accurate gauges of arterial size.”

Co-author Vanya Bosiocic of Flinders University added: “Throughout evolution, the advance in our brain function appears to be related to the longer time it takes for us to grow out of childhood. It is also connected to family cooperation in hunting, defending territory and looking after our young. The emergence of these traits seems to nicely follow the increase in the brain’s need for blood and energy.”