From Phys.org:
The international collaboration between Australia and South Africa showed that the human brain evolved to become not only larger, but more energetically costly and blood thirsty than previously believed.
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, published in the Royal Society Open Science journal, allowed the researchers to track the increase in human intelligence across evolutionary time.
“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 Professor Emeritus Roger Seymour, from 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.”
More here.