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Paper: Monophyletic Origin of the Metazoan Nervous System: Characterizing
Volume: 213, Bioastronomy '99: A New Era in Bioastronomy
Page: 421
Authors: Watkins, Russell; Beckenbach, Andrew
Abstract: In the absence of additional cases to be studied, our understanding of the likelihood of intelligent life evolving elsewhere in the universe must be framed within the context of the evolution of intelligence on this planet. Towards this end a valid model of the evolution of animal life, and in particular of the nervous system, is key. Models which describe the development of complexity within the nervous system can be positively misleading if they are not grounded in an accurate model of the true relationships of the animal phyla. If fact the evolution of animal life at its earliest stages, from protists to the sponges, Cnidaria, and Ctenophora and onward to the bilateral animal phyla is poorly characterized. Recently numerous phylogenies of the early animal radiation have been published based upon DNA sequence data, with conflicting and poorly supported results. A polyphyletic origin for the animal nervous system has been implied by the results of several studies, which would lead to the conclusion that some characteristics of the nervous systems of higher and lower animals could be convergent. We show that an equally parsimonious interpretation of the molecular sequence data published thus far is that it reflects rapid speciation events early in animal evolution among the classical ``diploblast'' phyla, as well as accelerated DNA sequence divergence among the higher animals. This could be interpreted as support for a classical phylogeny of the animal kingdom, and thus of a strictly monophyletic origin for the nervous system.
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