TWO PHASES OF EVOLUTION. “These and many other cases of reductive evolution are consistent with a general model composed of two distinct evolutionary phases: the short, explosive, innovation phase that leads to an abrupt increase in genome complexity, followed by a much longer reductive phase, which encompasses either a neutral ratchet of genetic material loss or adaptive genome streamlining.”
http://onlinelibrary.wiley.com/doi/10.1002/bies.201300037/full