In the book Guns Germs and Steel, What are the dates, methods, and locations of the Bantu Migrations? can you please name every date, every method, and every location the book states
Just to point you in the right direction, you need to read Chapter 19, entitled "How Africa Became Black." You have very specific questions and this will help you to gain the answers that you are looking for if you keep those questions in mind as you read this chapter. It is a very interesting book, so I recommend you read it for yourself.