Christopher Ehret, an expert on African linguistics, who I have have referenced in the preceeding post, Locating early Nilo-Saharan societies (Link), was a speaker at the recent African Genetics International Conference (Link). Ehret was also a coauthor on the important paper The genetic structure and history of Africans and African Americans (Link). In this talk, available by youtube above, some of the questions he asks and attempts to answer are:
When can we give credence to linguistic claims about the past?
How do demographic processes and language history intertwine?
How does linguistic change actually proceed?
Are there historical linguistic tools and techniques that allow us to formulate testable hypothesis about demic and genetic change and the nature of different eras of demographic encounter in the past?
These questions are important in understanding past demic expansions in Africa. Their answer may also be relevant to the relation of genetics and linguistics in the broader context.
The slide that Ehret presents of the Nilo-Saharan language tree is also in the supplementary material of the paper Tishkoff et al, The genetic structure and history of Africans and African Americans, referenced above. Here is an expandable version of the slide: