Cerebellum’s growth spurt turned monkeys into humans

When we search for the seat of humanity, are we looking at the wrong part of the brain? Most neuroscientists assume that the neocortex, the brain’s distinctive folded outer layer, is the thing that makes us uniquely human. But a new study suggests that another part of the brain, the cerebellum, grew much faster in our ape ancestors.

“Contrary to traditional wisdom, in the human lineage the cerebellum was the part of the brain that accelerated its expansion most rapidly, rather than the neocortex,” says Rob Barton of Durham University in the UK.

With Chris Venditti of the University of Reading in the UK, Barton examined how the relative sizes of different parts of the brain changed as primates evolved.

During the evolution of monkeys, the neocortex and cerebellum grew in tandem, a change in one being swiftly followed by a change in the other. But starting with the first apes around 25 million years ago through to chimpanzees and humans, the cerebellum grew much faster.