'I invented jazz in 1902, ' said Jelly Roll Morton. He was in the right place at the right time -- New Orleans at the turn of the century -- so in a sense his claim is as good as anyone else's; but jazz actually evolved from a complex variety of sources, in which French and Spanish influences are as vital as those of blues, ragtime, spiritual and the American popular song. Like its near-contemporary sibling cinema, jazz is both an art-form almost...