Dennis Mangan writes:
As anecdotal evidence for Steve's thesis, I'll just point out that while living in Sierra Leone for nearly two years, I encountered lots of people who were playing with much less than a full deck. Leaving aside the genetics, it's readily discerned that the environment played a huge role. Just about everyone is ill in some form or another just about all the time, and the reader will know how being ill affects mental wattage. A partial list of diseases that I personally dealt with there (I ran a hospital laboratory) would include: schistosomiasis; hookworm disease, which is the leading cause of iron deficiency anemia there; various other helminthic intestinal parasites; onchocerciasis, which causes "river blindness", the leading form of loss of sight in Africa; amoebic dysentery; malaria; tuberculosis; lymphatic filariasis, which can lead to elephantiasis; not to mention the ubiquitous skin and wound infections, diarrhea, etc., that people deal with daily.
On health grounds alone, IQ must be drastically affected, and with it the African economy.
I had lots of friends in Sierra Leone, and naturally I don't go around thinking of them as dumb as rocks. There were Africans in competent positions, for example as the lead nurse at the hospital. But facing the facts, most of them weren't so bright, and it's not a lack of education that makes them appear so.