Rapid Evolution of the Cerebellum in Humans and Other Great Apes

Humans’ unique cognitive abilities are usually attributed to a greatly expanded neocortex, which has been described as “the crowning achievement of evolution and the biological substrate of human mental prowess” [1]. The human cerebellum, however, contains four times more neurons than the neocortex [2] and is attracting increasing attention for its wide range of cognitive functions. Using a method for detecting evolutionary rate changes along the branches of phylogenetic trees, we show that the cerebellum underwent rapid size increase throughout the evolution of apes, including humans, expanding significantly faster than predicted by the change in neocortex size. As a result, humans and other apes deviated significantly from the general evolutionary trend for neocortex and cerebellum to change in tandem, having significantly larger cerebella relative to neocortex size than other anthropoid primates. These results suggest that cerebellar specialization was a far more important component of human brain evolution than hitherto recognized and that technical intelligence was likely to have been at least as important as social intelligence in human cognitive evolution. Given the role of the cerebellum in sensory-motor control and in learning complex action sequences, cerebellar specialization is likely to have underpinned the evolution of humans’ advanced technological capacities, which in turn may have been a preadaptation for language. •The cerebellum expanded rapidly in parallel lineages of apes, including humans•The cerebellum increased in absolute size and relative to neocortex size•This expansion began at the origin of apes but accelerated in the great ape clade•Cerebellar expansion may have been critical for technical intelligence Barton and Venditti show that the cerebellum underwent a marked acceleration in the rate of expansion during the evolution of apes, including humans, increasing faster than predicted by changes in neocortex size. These results suggest that cerebellar specialization was a key component of human brain evolution.