The expansion of the human brain during evolution, specifically of the neocortex, is linked to our cognitive abilities such as reasoning and language. A certain gene called ARHGAP11B that is only found in humans triggers brain stem cells to form more stem cells, a prerequisite for a bigger brain. Past studies have shown that ARHGAP11B, when expressed in mice and ferrets to unphysiologically high levels, causes an expanded neocortex, but its relevance for primate evolution has been unclear.
