Many people, when confronted with the question of whether average IQ varies between races, ask, quite reasonably, "why would there be differences? Wouldn't intelligence be as much of an advantage for humans living anywhere?"
Well, the answer is no, not necessarily. Or at least, different types of intelligence might be more beneficial depending on where you live. (As Thomas Sowell, and then Steve Sailer has pointed out, blacks on average appear to have better improvisational skill than white people do; while this is certainly a form of intelligence, it is not the sort of intelligence that IQ tests measure).
If the African/European IQ gap turns out to be largely genetic, an immediate question would be, why would Europeans have higher IQs on average? Genetic drift or selective pressures?
My personal conjecture would be that places with variable climates, particularly those where certain times of year offer little opportunity to grow food, might have a higher selective pressure towards long-term thinking, as the people living in such an area would have to plan ahead for the times of scarcity year after year. Perhaps the loss of "real-time responsiveness" is a trade-off for that, or perhaps quick improvisational thinking is more useful for some reason in more steady climates than in variable ones.
That is... well, not all. There's a lot of research to be done in this area, isn't there?