Brain Structure, Not the Frontal Lobe, Responsible for Advanced Human Intelligence

The evolution of the human brain was as much about structure and interconnected parts as it was about increasing size, say researchers

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Using phylogenetic or 'evolutionary family tree' techniques, Professor Robert Barton from the Department of Anthropology at Durham University analyzed data developed from previous animal and human studies to examine the speed at which evolutionary biological change in the brain occurred. His results could be a game-changer when it comes to understanding how the brains of our distant ancient ancestors changed during the course of human evolution. He and his research colleagues at Durham and Reading universities have concluded that, contrary to popular scholarly conception, the frontal lobes of the brain did not evolve comparatively faster than their primate cousins after the human lineage split from the chimpanzee lineage about 5-7 million years ago. It was actually just as much, if not more, about the evolution of the overall brain structure.

"It has been thought that frontal lobe expansion was particularly crucial to the development of modern human behaviour, thought and language, and that it is our bulging frontal lobes that truly make us human", says Barton. "We show that this is untrue: human frontal lobes are exactly the size expected for a non-human brain scaled up to human size. This means that areas traditionally considered to be more primitive were just as important during our evolution. These other areas should now get more attention."

Barton and colleagues maintain that many of the advanced cognitive abilities that distinguish us from other animals are made possible by more extensive brain networks linking many different areas of the brain. They point to the structure of these extended networks more than the comparative size of any particular brain region as the key. 

The frontal lobes are an area located at the front of each cerebral hemisphere in all mammals, and have been traditionally thought to be critical for intelligence, or cognitive thinking. While this may be at least in part true, Barton and colleagues are now suggesting that scientists begin to focus on the evolution of other parts of the brain and how they are interconnected and contribute to the total functionality that defines human intelligence. 

A detailed report of the study is published in the Proceedings of the National Academy of Sciences(PNAS).