Due to its complexity, the neuron as a specialized cell is assumed to have evolved only once in the history of life. However, the information from the newly sequenced genome of a comb jelly appears to suggest otherwise. Based on their DNA data these invertebrates were classified on a different, older branch of the tree of life from that of other organisms with complex nervous systems. As per Dr. Pennisi, this may suggest that nervous systems arose twice, particularly when taking into consideration the differences in the genome of these organisms (i.e. lack of genes for proteins considered essential to nervous system development and function) from that of other animals.
2013 Society for Integrative and Comparative Biology Annual Meeting. Nervous system may have evolved twice. Pennisi E. Science. 2013 Jan 25;339(6118):391. PMID: 23349266
posted by Yannis Trakadis, MD