The evolution of human intelligence isn't just about the size of our brain.
Researchers from Australia and South Africa says while brain size has grown about 350 percent over millions of years, blood flow to the brain increased by a whopping 600 percent!
That's because the increasingly complex brain structure required more food and more oxygen to power it.
Scientists came upon the discovery after examining the two holes at the base of the skull that allow arteries to pump blood into our heads.
A University of Adelaide-led project looked at ancient fossil skulls from Africa and saw that over three million years - all the way up to modern humans - the size of those holes increased, getting larger to allow a bigger flow of blood in.
It appears that's because over the generations our brains demanded more and more nutrient-rich blood as our activities went from simple to complex.
So, although it seems counter-intutitive, the evolution of human intelligence isn't just about the size of our brains - but also the size of the holes in our head.