The human brain is a fuel hog, and that, it turns out, is key to how our intelligence evolved. It has long been believed that the evolution of human intelligence was simply related to increasing brain size, but a team of researchers from South Africa and Australia have overturned that assumption.

By calculating how blood supply to the brains of human ancestors changed over time, the researchers were able to show that the human brain not only evolved to become larger, but also more blood-thirsty. And the need for blood outpaced the volume increase of the brain itself.

"Brain size has increased about 350% over human evolution, but we found that blood flow to the brain increased an amazing 600%," project leader Roger Seymour, from the University of Adelaide, said in a statement. "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."