The Evolution of Cortical Development

The cerebral cortex appears in stem amniotes and evolved in divergent manner in the two main amniote branches, namely the synapsids, that include premammals and mammals, and the sauropsids, now represented by reptiles and birds. Progress in our understanding of cortical neurogenesis, neuronal migration and layer formation allow to define common principles that are therefore presumably homologous and inherited from stem amniotes. On the other hand, critical features of mammalian cortex are absent in sauropsids and evolved after divergence of the two main radiations. Chief among those is the multilaminar organization of the mammalian cortex and its propensity to increase its surface by folding. Careful studies of human genetic disorders of cortical development and of animal models allow us to formulate mechanisms that can be tested using modern genetic and cellular technology. An integrated understanding of cortical development and evolution no longer seems an unattainable goal.