1. They have.
2. Sub-Saharan Africa doesn't have the required plants & animals that are needed to jump from a hunter gather society to an agricultural one.
If you stuck stone age White people in Africa they would likely be in a similar state. 
When you can't argue you tell people to kill themselves multiple times. 
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Hey speaking of you being a reprehensible coward do you remember when you repeatedly told someone to kill themselves?
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