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Nervous systems and scenarios for the invertebrate-to-vertebrate transition

TitleNervous systems and scenarios for the invertebrate-to-vertebrate transition
Publication TypeJournal Article
Year of Publication2015
AuthorsHolland N.D
JournalPhilosophical Transactions of the Royal Society B-Biological Sciences
Date Published2015/01
Type of ArticleReview
ISBN Number0962-8436
Accession NumberWOS:000365335500009
Keywordsanimals; Annelid scenario; brain; developing hemichordate; enteropneust; evolution; genes; insights; inversion; invertebrate-to-vertebrate transition; origin; phylogeny; saccoglossus-kowalevskii; scenario

Older evolutionary scenarios for the origin of vertebrates often gave nervous systems top billing in accordance with the notion that a big-brained Homo sapiens crowned a tree of life shaped mainly by progressive evolution. Now, however, tree thinking positions all extant organisms equidistant from the tree's root, and molecular phylogenies indicate that regressive evolution is more common than previously suspected. Even so, contemporary theories of vertebrate origin still focus on the nervous system because of its functional importance, its richness in characters for comparative biology, and its central position in the two currently prominent scenarios for the invertebrate-to-vertebrate transition, which grew out of the markedly neurocentric annelid and enteropneust theories of the nineteenth century. Both these scenarios compare phyla with diverse overall body plans. This diversity, exacerbated by the scarcity of relevant fossil data, makes it challenging to establish plausible homologies between component parts (e.g. nervous system regions). In addition, our current understanding of the relation between genotype and phenotype is too preliminary to permit us to convert gene network data into structural features in any simpleway. These issues are discussed here with special reference to the evolution of nervous systems during proposed transitions from invertebrates to vertebrates.

Short TitlePhilos. Trans. R. Soc. B-Biol. Sci.
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