•Transcription factors and morphogens establish early pallial subdivisions.•Foxg1 and Lhx2 function cooperatively and independently to establish the neocortex.•Neocortical neurogenesis balances the output of functionally distinct subtypes.•Differential timing of gene expression underlies species-specific brain formation.The functional integrity of the neocortical circuit relies on the precise production of diverse neuron populations and their assembly during development. In recent years, extensive progress has been made in the understanding of the mechanisms that control differentiation of each neuronal type within the neocortex. In this review, we address how the elaborate neocortical cytoarchitecture is established from a simple neuroepithelium based on recent studies examining the spatiotemporal mechanisms of neuronal subtype specification. We further discuss the critical events that underlie the conversion of the stem amniotes cerebrum to a mammalian-type neocortex, and extend these key findings in the light of mammalian evolution to understand how the neocortex in humans evolved from common ancestral mammals.

The precise stereotypic projections of pyramidal neurons within the six-layered cortex of mammals are key in allowing this structure to attain its high level of function. Recent studies have provided the first indications that postmitotic transcription factors are required for the formation and maintenance of both corticofugal and intracortical pyramidal cell populations. Here, we discuss these new findings in the context of our present understanding of cortical cell specification.