Human intelligence cannot be explained by the size of the brain’s frontal lobes, say researchers. Many theories have considered that the expansion of the frontal lobe of our human brain was especially crucial to the development of modern human behavior, thought and language. A new study suggest this is not the case.

Research by Durham and Reading universities into the comparative size of the frontal lobes in humans and other species has determined that they are not – as previously thought – disproportionately large relative to other areas of the brain.

The study suggests that supposedly more ‘primitive’ areas, such as the cerebellum, were equally important in the expansion of the human brain. These areas may therefore play unexpectedly important roles in human cognition and its disorders, such as autism and dyslexia, say the researchers.

The frontal lobes are an area in the brain of mammals located at the front of each cerebral hemisphere, and are thought to be critical for advanced intelligence.

Lead author Professor Robert Barton, the study’s lead author, said:

Probably the most widespread assumption about how the human brain evolved is that size increase was concentrated in the frontal lobes. It has been thought that frontal lobe expansion was particularly crucial to the development of modern human behavior, thought and language, and that it is our bulging frontal lobes that truly make us human. 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. In fact there is already some evidence that damage to the cerebellum, for example, is a factor in disorders such as autism and dyslexia.

The scientists argue that many of our high-level abilities are carried out by more extensive brain networks linking many different areas of the brain. They suggest it may be the structure of these extended networks more than the size of any isolated brain region that is critical for cognitive functioning.

The study was published in the Proceedings of the National Academy of Sciences on May 13, 2013.

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