Model Systems for Exploring the Evolutionary Origins of the Nervous System

Abstract

The development of nervous systems can be seen as one of the key transitions in animal evolution, allowing the efficient integration of sensory input and motor output and the expedient transmission of impulses over relatively long distances inside an organism. With the increased availability of genome sequences for animals at the base of the metazoan phylogenetic tree, two alternative hypotheses have been proposed regarding nervous system evolutionary origins, ultimately prompting a debate whether an enormously complicated system like the nervous system could have evolved more than once. This review summarizes what is currently known about nervous system origins, concentrating on the evolution of synapse components, with respect to phylogenetic knowledge of early diverging animal groups, comprising members of the Porifera, Ctenophora, Placozoa, and Cnidaria.