After Double Helix by Don Thomas, which you have already read (which also has a recommended reading list in the back), I would recommend African Twilight by Robert F. Jones, Safari by Walt Prothero, and my favorite of the year, Colors of Africa by James Kilgo. As I am headed to Africa this coming June, I have become something of an African literature junkie, and these three are at the top of the list, after Don's book, of course.