ARHGAP11B is a human-specific gene that amplifies basal progenitors, controls neural progenitor proliferation, and contributes to neocortex folding. It is capable of causing neocortex folding in mice. This likely reflects a role for ARHGAP11B in development and evolutionary expansion of the human neocortex, a conclusion consistent with the finding that the gene duplication that created ARHGAP11B occurred on the human lineage after the divergence from the chimpanzee lineage but before the divergence from Neanderthals.