The expansion of the human brain during evolution, specifically of the neocortex, is linked to 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.

Researchers at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) in Dresden, together with colleagues at the Central Institute for Experimental Animals (CIEA) in Kawasaki and the Keio University in Tokyo, both located in Japan, now show that this human-specific gene, when expressed to physiological levels, causes an enlarged neocortex in the common marmoset, a New World monkey. This suggests that the ARHGAP11B gene may have caused neocortex expansion during human evolution. The researchers published their findings in the journal Science.

The human neocortex, the evolutionarily youngest part of the cerebral cortex, is about three times bigger than that of the closest human relatives, chimpanzees, and its folding into wrinkles increased during evolution to fit inside the restricted space of the skull. A key question for scientists is how the human neocortex became so big. In a 2015 study, the research group of Wieland Huttner, a founding director of the MPI-CBG, found that under the influence of the human-specific gene ARHGAP11B, mouse embryos produced many more neural progenitor cells and could even undergo folding of their normally unfolded neocortex. The results suggested that the gene ARHGAP11B plays a key role in the evolutionary expansion of the human neocortex.