At least based on the popular imagination, you’d think having a big head would be an indication of greater intellect. Just look at the ultra-intelligent, bulbous-headed character Megamind (pictured above), from the movie of the same name.

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As with many neuromyths, there is a grain of truth to all this – among humans, brain size and intelligence (as measured by IQ tests) are correlated, albeit modestly (estimates place the correlation at around 0.3 to 0.4, where 1 would be a perfect correlation).

But of course, correlation does not imply causation and there are many reasons to be careful about how we interpret the link. For starters, the modest correlation is based on an average of many people, and head/brain size will tell you nothing about a particular individual’s intelligence (bear in mind that Albert Einstein’s brain size was unexceptional, perhaps even on the small side).

Consider too, that many animals have brains that are dramatically larger than human brains and yet we do not consider them anywhere near as smart as we are. For instance, elephants and whales have brains that are about six times as large as ours. At the other extreme, there are many animals capable of feats of intelligence in spite of having tiny brains – take the bumblebee, which can memorise the location of countless flowers over an area of several square miles.

Most experts agree that for intelligence, what’s more important than overall brain volume, is neuronal efficiency (how quickly and reliably neurons communicate with each other) and the nature and extent of the connectivity between key brain regions.

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Authors

Dr Christian Jarrett is a cognitive neuroscientist, science writer and author. He is the Deputy Editor of Psyche, the sister magazine to Aeon that illuminates the human condition through psychology, philosophy and the arts. Jarrett also created the British Psychological Society's Research Digest blog and was the first ever staff journalist on the Society's magazine, The Psychologist. He is author of Great Myths of The Brain and Be Who You Want: Unlocking the Science of Personality Change.

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