Reddit reviews African Banjo Echoes In Appalachia: Study Folk Traditions (PUBLICATIONS OF THE AMERICAN FOLKLORE SOCIETY NEW SERIES)

For books a Google search will turn up some great stuff. I find the early evolution from an African instrument really fascinating - Google 'ankoting' for some great info.

This is a classic on that topic: http://www.amazon.com/African-Banjo-Echoes-Appalachia-Publications/dp/0870498932

I was once at a concert of some great African musician playing an native instrument. When I looked closer I realized he was playing with the backs of his fingernails like the clawhammer style - so very likely that style of playing, not just the instrument, has African origins as well.

You might want to watch Bela Fleck's video, Throw Down Your Heart. It's basically following Fleck around as he meets and plays with musicians around Africa. While I was a little disappointed by how it's much more about Fleck than it is about Africa, there are a couple sections that are wonderful. Watch for the explanation of what the title means.

There is of course more to the history of banjo than its African origins, but it's definitely an important aspect.

I have some excellent reading recommendations for you.

http://www.amazon.com/African-Banjo-Echoes-Appalachia-Publications/dp/0870498932

http://www.npr.org/templates/story/story.php?storyId=95607716

http://www.theworld.org/2012/03/stalking-the-african-banjo/

http://www.spinner.com/2009/02/24/bela-flecks-african-banjo-odyssey/

http://www.throwdownyourheart.com/

http://www.banjohangout.org/group/africanbanjoroots

http://www.amazon.com/African-Banjo-Echoes-Appalachia-Publications/dp/0870498932/ref=pd_sim_m_1

This book is amazingly interesting, if he likes history and Old Time music.