Africa is fairly linguistically diverse. I think the comparison would be to Papua New Guinea where you often have totally new languages every few miles because steep mountains and ravines keep ethnic groups separated. However, the geography of Africa is much flatter, and single ethnic groups have settled wide swathes of area. For example, the vast majority of all people in southern Africa are the descendants of Bantu language speakers. I'd also be careful of keeping linguistic and genetic diversity separate. The first language in many urban areas in Africa is often English, Portuguese and other colonizing language. Substantial language change can occur with only limited genetic change.

Maybe a better question for r/AskAnthropology/ ???