Brain Evolution: Speedy Expansion of the Cerebellum May be Behind Evolving Apes

Scientists may have uncovered a different story when it comes to ape and human brain evolution. While in the past scientists believed that the neocortex of the brain was the "crowning achievement" of evolution, they've now found that the cerebellum expanded up to six times faster than anticipated throughout the evolution of apes.

"Our results highlight a previously unappreciated role of the cerebellum in ape and human brain evolution that has the potential to refocus researchers' thinking about how and why the brains in these species have become distinct and to shift attention away from an almost exclusive focus on the neocortex as the seat of our humanity," said Robert Barton, one of the researchers, in a news release.

The neocortex has gotten the most attention partly because it is such a large structure to begin with. By looking at variation in the size of various brain regions, in fact, the neocortex seems to show the most expansion. But much of this increase in size can be explained away by the size of the animal as a whole. In contrast, the cerebellum contains about 70 billion neurons, which is four times more than in the neocortex.

In order to better understand these brain regions, the scientists used a comparative method that controlled for differences in the way the two brain structures correlate. In the end, they found that both nonhuman apes and humans depart from the otherwise tight correlation in size between the cerebellum and neocortex found across other primates due to relatively rapid evolutionary expansion of the cerebellum.

So what does this mean? It looks as if the cerebellum has been critical for human evolution. Already, researchers have found that the cerebellum plays a critical role in language. The fact that this region of the brain has rapidly expanded shows that it may be responsible for higher cognitive thinking associated with apes, including humans.

The findings are published in the journal Current Biology.