The thing that has puzzled me for years is that if you look at distribution of population in Africa by language group for example or racially, Bushmen for example, is seems that people were coming into Africa rather than departing.
North Africans are what I call 'come-back' Africans, more like the rest of humans, who migrated back to North Africa after they went through many changes.
The Sub-Saharian Africans, I call them 'stay-at-home' Africans, are different than all other people on earth. Everyone else on earth are more closely related to themselves that they are to Sub-Saharian Africans. The 'stay-at-home' Africans missed out on all the changes that make most of us who we are today.