The evolution of human intelligence is something that tickles the imagination of anthropologists for years. How do we do this crucial step that has separated us from other primates and make us what we are today? For all we know, we know, thanks to archaeological remains found. But can discovered ancestor’s tools give us all the answers? Hardly. That’s why anthropologists take a look at the place where brain resided – fossil human’s skull. It sounded logical. But instead of watching and comparing the brain size, this time they focused on the blood flow. This changing course has brought us new interesting findings.

Hominin skull casts (L-R) Australopithecus afarensis, Homo habilis, Homo ergaster, Homo erectus, Homo neanderthalensis. Image credit: ger Seymour/South Australian Museum

The Rate Of The Blood Flow

It is a fact that our brain today is three and a half times larger than our 3 million years old ancestors. That’s why is the intelligence connected with brain size. The number of nerve cells, especially in the cortex, was the reference for cleverness for decades. However, scientists from the University of Adelaide have focused on the rate of blood flow in their research. Typically, the rate of a blood flow to the brain is 7ml per second, regardless what we do – sleep, learn or just having fun. How blood comes to the brain? Through left and right carotid arteries which size depends on the rate of blood flow.

The arrows on the human skull (right) show two internal carotid artery foramina, the size of which indicates the rate of blood flow to the cerebrum. Image credit: School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand

The most important moment was when the researchers realized that they could measure these carotid arteries through holes in the fossil skulls. After collecting fossils from museums in Australia and in South Africa, they calculate that the rate of blood flow in the ancestor’s brain was 1.2ml per second. Also, their brain was 3.5 times smaller than today’s brain.

Evolution of blood flow to the brains of human ancestors. The data reveal an increasing rate of blood flow among hominin species over 3 million years. Image credit: Royal Society Open Science/Roger Seymour, Vanya Bosiocic, Edward Snelling/Skull illustrations by Vivi Hu., CC BY

Comparing to other primates, size increasing of our brain and body is not only peculiar to us. What really makes the difference is that among other primate representatives body size developed faster. On the other hand, our brain has increased much faster, than the body. However, this development wasn’t only about the brain size, but in its usage as well.

The development of human brain and intelligence intrigues many scientists. While anthropologists claim that the answer is the rate of the blood flow to the brain, some biologist thinks the answer is cooking. After all, see one of the most inspiring TED speech on the development of primate brains.