Just want to point out...
People will always point to someone like Alek Wek or a south Sudanese person and say "this is the one and only pure african" that is not the case, many light skinned people are even more "pure" than them, believe it or not.
The Nilotic people live the harshest conditions in Africa. There few trees in that region so they are exposed to direct sunlight everyday, the temperature is almost always above 100 degrees and there is barely any water. That is why they look the way they do.
People in other parts of Africa have adapted to their own particular climate. S.E Nigeria is heavily forested so there is enough shade for lighter skinned people to live normally.
Southern Africa is colder than other regions, thus the Khoisan have lighter skin. They also have epicanthal eye folds like the Asians because they live near the Kalahari desert region. Ethiopia is mountainous, so it is more temperate than other parts of the continent so the people are thinner noses, straighter hair, etc.
Also when I meant no one on this Earth is "pure" I meant every group of people on this Earth has foreign ancestry one way or the other. And also that some people are less admixed than the other. Its simply due constant gene flow around the globe, which is why I brought up "isolation". BUT...Just because some people have SLIGHT admixture does not mean it has a impact on there phenotype which is mostly due to climate, diet and other things. I never said everyone on this planet was mixed, but that everyone one has slight foreign ancestry going far back.
Just wanted to clear up somethings.