The cerebellum may be our “little brain,” but a new study has found that it likely played a big role in human evolution. Although the neocortex of the brain has been given the majority of the credit for our unique cognitive abilities, new insights into the rate of evolutionary changes in human and ape lineages suggest that our expanding cerebellum may have also been crucial for technical intelligence. The work has been published in Current Biology.
The neocortex, which has been described as “the biological substrate of human mental prowess,” has previously received the majority of the attention with regards to human and ape evolution. Not only does it occupy around 85% of our brains, but it is also known to be critical for language, consciousness and spatial reasoning. The enlargement of this region during evolution was therefore believed to hold the secret to our cognitive abilities. However, it is becoming increasingly apparent that the role of the cerebellum may have been downplayed.
The cerebellum was previously believed to be primarily involved in the control of movement, but it is gradually emerging that its functions extend way beyond motor control. It may only make up around 10% of brain volume, but it contains four times more neurons than the neocortex, some 70 billion in total. Although it’s thought that many more functions remain to be elucidated, its importance is becoming increasingly recognized.
To find out whether it could have had a significant role in our evolution, Durham University and University of Reading researchers looked at evolutionary rate changes along primate lineages, including our own. They found that humans and other apes deviated from the tight correlation in size between the cerebellum and neocortex observed in other primates due to the rapid expansion of the cerebellum. Not only did the cerebellum increase in absolute size, but it also increased relative to the size of the neocortex.
It seems likely that the neocortex previously hogged all the attention because it is such a big structure. When comparing the size of various brain regions, the neocortex appears to have grown the most. However, when the size of the animal is also taken into consideration, the neocortex does not show the rate of expansion that was thought to have occurred. The cerebellum, on the other hand, grew much faster.
According to the researchers, since the cerebellum is known to be involved in sensory-motor control and in learning complex behavioral sequences, its growth may have been critical for the evolution of technical intelligence. This technical intelligence, such as tool making and use, was probably as important as social intelligence in human cognitive evolution.
The scientists are quick to point out that these brain regions are interlinked and that focus should not be moved from one to the other. “The broader part of the story is the way the cortex and cerebellum work together,” lead author Robert Barton told New Scientist. “It’s hard to damage one without affecting the other.”
[Via Cell Press, Current Biology, New Scientist and Examiner.com]
