I seem to remember that the majority traits south of Sahara (black/very dark skin, and curly hair) can be traced back to something called the “great Bantu expansion”, which was essentially the result of a group of people with these traits developing agriculture and wiping out most other peoples south of Sahara, much like the Europeans did to the Americas.

Some cultures south of Sahara did survive, which can be seen both genetically, and in some languages that are completely from other languages in the area (I believe the family of languages with “clicking” sounds is an example).

I’m on my phone now, but I’ll have a double check and come back.