Functional evolution in the ancestral lineage of vertebrates or when genomic complexity was wagging its morphological tail.

Early vertebrate evolution is characterized by a significant increase of organismal complexity over a relatively short time span. We present quantitative evidence for a high rate of increase in morphological complexity during early vertebrate evolution. Possible molecular evolutionary mechanisms that underlie this increase in complexity fall into a small number of categories, one of which is gene duplication and subsequent structural or regulatory neofunctionalization. We discuss analyses of two gene families whose regulatory and structural evolution shed light on the connection between gene duplication and increases in organismal complexity.