The pre-cambrian flora have no explanation for the Cambrian. Red in tooth and claw arrives in the Cambrian. No claws or teeth in prior periods. Darwin has no explanation except a paucity of fossil record. That record is now well documented and precursors just ain't there. No Mt. Improbable to climb.-http://www.evolutionnews.org/2013/06/as_darwins_doub073571.html