Why are most africans dark skinned?

my name is Derick, and I use to be a racist that I told someone else on that other question. and I have a dark skinned wife, that I told someone about.but I don't think all dark skinned women or men come from Africa or south or north.I stop thinking racially when I first got with natasha(my wife)in a starting relationship(boyfriend/girlfriend)I don't think my wife natasha ever came from Africa,she's just dark,but not that dark,she's plain black.but not relly dark.