WASHINGTON - It has been called "the only true American art form." Over a century old, it's appreciated around the world — what else, but the music called jazz? A blend of religious and work songs, Spanish and French influences, ragtime and marching bands, all laid over African rhythms, the history of jazz is uniquely tied to the African-American experience. From Jelly Roll Morton to Louis Armstrong, Duke Ellington, Charlie Parker and Miles Davis on to Wynton Marsalis, African-Americans have kept jazz evolving through the decades. Nearly 8 percent of adults in the U.S. attend a live jazz performance at least once a year