Evolution has not only made human brains larger, but has also increased the supply of blood to the brain, a new study has found.
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 at allow arteries to pass to the brain.
The findings, published in the Royal Society journal Open Science
, allowed the researchers to track the increase in human intelligence across evolutionary time.
"Brain size has increased about 350 percent over human evolution, but we found that blood flow to the brain increased an amazing 600 percent. 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," said Roger Seymour, Professor at the University of Adelaide, in Australia.
The more metabolically active the brain is, the more blood it requires, so the supply arteries are larger and the holes in fossil skulls are accurate gauges of arterial size.
"The size of ancient fossil skull holes show how blood flow increased from three million-year-old Australopithecus to modern humans," said Edward Snelling, researcher at the University of the Witwatersrand, in South Africa.
"The intensity of brain activity was, before now, believed to have been taken to the grave with our ancestors," Snelling added.