This thread name is actually the title of a fascinating documentary I just watched. It tells the story of Dina Epstein, a music librarian who, after decades of painstaking research, mostly in obscure source material, was able to prove that the banjo was an African instrument brought over by slaves, placing her at odds with the established music academia of the day. Today, her work, the book "Sinful Tunes and Spirituals" and several articles, is considered groundbreaking by academics and musicians alike, and primarily responsible for a black string band revival.
I enthusiastically recommend this film as informative and inspirational. You can rent it from Amazon for a couple bucks. I would also be interested in comments from Catters who are familiar with Dina's work. Some here may have even known her. She worked for the University of Chicago and may have had some connection to the Old Town School of Folk Music. At least one scene from the film, where Dina meets with the Carolina Chocolate Drops, was shot there.