+1
We can't effectively evaluate intelligence within closely similar population. Standardized intelligence testing has been used for years even though its ability to give a true picture of an individual's intelligence is far from accurate or reliable.
As far as Africa is concerned, how do researchers even begin? The continent of Africa is huge and contains a very diverse population. In very poor regions of the world, I think physiologically, the difference in intelligence is probably negligible at most, and is more likely a difference in the rate of intellectual development due to physical and cultural impediments. Those impediments (lack of education, limited social interaction outside of their community, and limited exposure to advanced technology, etc.) would slow the rate of the learning process for many affected individuals, but it does not indicate a lesser intelligence, nor does it indicate a limited capacity to learn.
The funny thing is that in Africa, the most "uneducated" peasant usually speaks a minimum of three languages. In South Africa, for example, it is very common for Black South Africans to speak ten languages very well. The languages being all the major Bantu languages, Afrikaans, and English. Africans have been known to fix cars literally with sticks and strings. They can recycle and repair darn near anything also. In short, they function well in an environment that most Westerners cannot begin to handle.
