The Blues: Back to the Source
Born in the South, the blues is an African American-derived music form that recognized the pain of lost love and injustice and gave expression to the victory of outlasting a broken heart and facing down adversity. The blues evolved from hymns, work songs, and field hollers — music used to accompany spiritual, work and social functions. Blues is the foundation of jazz as well as the prime source of rhythm and blues, rock 'n' roll, and country music. The blues is still evolving and is still widely played today.
http://teacher.scholastic.com/activities/bhistory/history_of_jazz.htm