Development and evolution of the primate neocortex from a progenitor cell perspective

The generation of neurons in the developing neocortex is a major determinant of neocortex size. Crucially, the increase in cortical neuron numbers in the primate lineage, notably in the upper-layer neurons, contributes to increased cognitive abilities. Here, we review major evolutionary changes affecting the apical progenitors in the ventricular zone and focus on the key germinal zone constituting the foundation of neocortical neurogenesis in primates, the outer subventricular zone (OSVZ). We summarize characteristic features of the OSVZ and its key stem cell type, the basal (or outer) radial glia. Next, we concentrate on primate-specific and human-specific genes, expressed in OSVZ-progenitors, the ability of which to amplify these progenitors by targeting the regulation of the cell cycle ultimately underlies the evolutionary increase in upper-layer neurons. Finally, we address likely differences in neocortical development between present-day humans and Neanderthals that are based on human-specific amino acid substitutions in proteins operating in cortical progenitors.