Odd neurons hint that nervous systems evolved twice

摘要

MARINE animals called comb jellies have nervous systems unlike those of any other known animal. Their neurons are oddly shaped and use chemicals not found in those of other animals. "These neurons are quite unique," says Pawel Burkhardt at the University of Bergen in Norway. The discovery adds to an ongoing debate about how the first animal brains evolved. In particular, there is controversy over whether brains evolved once in early animals, or several times in different groups.