One of the biggest television audiences ever was drawn to Roots, the saga of an American slave family: The impact on American life was immense. The book, by black ex-US coastguard ALEX HALEY , on which it was based, promises to join the all-time best-sellers. What has the phenomenon meant to Haley, who spent 12 years of his life tracing his family history back to its African origins, and has the impact of Roots survived its first shockwaves?