Early central nervous system evolution:

 BM&L was right


Since long time some Brain Mind & Life’s neuroscientists maintained the relevance of the Central Nervous System morphological evolution from an external site of the simplest animal body, or surface-nerve-net, to the interior of the skeleton as in the mammals, as connected to ectodermal differentiation, with the adaptation of the homologues of some skin-nerve genes as vertebrates genes like Emx-1. Nicholas D. Holland faces this problem in the interesting article that will appear in the next month number of Nature Review Neuroscience (Nicholas D. Holland, Early central nervous system evolution: an era of skin brains? Nature Review Neuroscience. Vol 4 No 8, August 2003). Until recently, it was assumed that the ancestral nerve net or surface-nerve-net became localized as all or part of the CNS in the basal groups of bilaterally symmetrical animals. However, in the enteropneust hemichordate Saccoglossus, expression of homologues of vertebrate CNS anteroposterior patterning genes is not limited to the nerve tracts, but extends widely throughout the ectoderm, implying that the CNS of this animal includes the entire basiepidermal nerve net. Holland discusses the implications of this discovery for CNS evolution.

BM&L-July 2003