It turns out that the thing that separates us from the animals may be our cerebellums, a new study shows. Scientists previously thought that the neocortex was the part of the brain that was most different from our primate predecessors, but a new study shows that the cerebellum may have played a previously unappreciated role in human evolution.
The study was published yesterday, October 2, in the Cell Press journal Current Biology.
"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 involved with the study.
At first, when monkeys were evolving, the neocortex and cerebellum grew at the same rate. However, this new study shows that around 25 million years ago, the cerebellum began to grow at an accelerated rate. Apes and humans have this accelerated cerebellum growth, meaning that our cerebellums have far more capacity for brain activity in the cerebellar region than a monkey. There are many more neurons by volume in a human or ape cerebellum than in a monkey.
Barton said that this extra cerebellar growth may have begun when the first apes learned how to swing on trees, because the cerebellum is tied to motor function. However, other research shows that the cerebellum is not only involved with motor function, but may have other uses that we are only beginning to understand.
"In humans, the cerebellum contains about 70 billion neurons - four times more than in the neocortex. Nobody really knows what all these neurons are for, but they must be doing something important," Barton said.
Barton and his partner, Chris Venditti, said that the cerebellum may also play a part in our understanding of language, time and sequences of behaviors.
Another misleading fact is that the neocortex is physically larger than the cerebellum. However, the size may not actually mean all that much. The neocortex of a sperm whale is proportionally larger than that of a human, for example.
Barton and Venditti called this development a new frontier in the study of the human mind.
