Origin and Evolution of the Vertebrate Telencephalon, with Special Reference to the Mammalian Neocortex (Advances in Anatomy, Embryology and Cell Biology Book 193)

How could a structure as complex as the vertebrate brain develop from the simplest multicellular animals? Natural selection offers an impeccable mechanism for the gradual transformation of species, but even Darwin sometimes expressed doubts about the origin of highly complex structures. Following an approach that has been termed "developmental evolutionary genetics," this book seeks to establish a correspondence between embryological processes and the phylogenetic history of an organism. "In this volume, we provide an overview of the origin of the vertebrate telencephalon and its evolution toward the origin of the mammalian neocortex. We start from the origin of the vertebrate central nervous system from an ancestral subepidermal network, considering new evidence indicating that this process occurred separately in different animal groups. The hypothesis of the origin of vertebrates based on the differentiation of the placodal and neural crest tissues is critically reviewed. In the different vertebrate radiations, the cerebral hemispheres have undergone a strong morphological divergence, while the genetic patterning mechanisms and the early embryological mechanisms seem to be highly conserved. Mammals are characterized by the emergence of a six-layered; neocortex in the dorsal pallium. We suggest that the neocortex arose as an expansion of a field in the dorsal pallium, which took place as a consequence of the interaction of different morphogenetic fields. Other theories propose homology of some neocortical areas with ventral pallial structures of reptiles and birds. We also propose a hypothesis for the origin of cortical lamination based on the expansion of the proliferating subventricular zone, and a tentative explanation for the origin of the inside-out gradient of cortical lamination. Finally, we briefly review the expansion and diversification of neocortical areas in mid-and late mammalian evolution."--Jacket