Overlooked brain area explains evolution

A brain area formerly relegated to controlling only a few functions might underpin the evolution of human intelligence, new research has revealed...

Relative to our body sizes, humans have very large brains. In particular, the cerebral cortex - which is the outer surface of the brain - is very well developed in man compared with other animals. Traditionally, scientists have concluded that this is what sets us apart from other animals.

But now a new study from Durham scientist Robert Barton has revealed that the contribution of another brain area, called the cerebellum, which sits behind and below the main part of the brain and originally thought to be concerned mainly with controlling movements, may have been overlooked.

By comparing the sizes of different brain regions among members of the ape - and ultimately human - evolutionary family tree, a surprising trend jumped out. Among primates, rather than just increasing in size in tandem with the rest of the brain, the cerebellum has become proportionally larger. And this might be the key to us learning to talk and becoming the highly successful social animals that we are.

According to Barton, the demands placed on a large animal trying to negotiate a safe route, swinging from branch to branch through trees, may have selected for a progrssively larger cerebellum.

But because this brain area plays a crucial role in performing fine, highly-coordinated movements, having a larger one would have made animals more dextrous, also endowing them with superior tool-making skills.

In the case of humans the impact may have been even more pronounced. The improved coordination provided by an enlarged cerebellum would also have influenced the ability to master the fine movements required for speech.

"The cortex has previously received all the glory as the reason why humans are so intelligent," says Barton, who thinks that this recognition of the evolutionary role played by the cerebellum, published this week in Current Biology, could be a game-changer.

"The development of this brain area could have endowed our early ancestors with the potential to speak, and, increasingly, we're realising that the cerebellum is also involved in a range of other cognitive roles too."

However, the observed expansion of the cerebellum over evolution might merely be a response to the increased demands of a more powerful cortex, so which came first is impossible to say. "We want to explore this further," says Barton.