ARHGAP11B and microcephaly: In this review, we discuss human-specific genes preferentially expressed in NPCs of the developing neocortex that can promote NPC proliferation, with a focus on ARHGAP11B and NOTCH2NL. We also discuss the potential involvement of the deletion or mutation of these genes in primary microcephaly (for the sake of simplicity from now on, referred to merely as “microcephaly”).