C'mon, you know you want to to read its tables! For instance, those snotty French who think they are so smart? How do they really score? Or, if you've been wondering why so many people in so many Arab countries believe in so much dumb stuff, Lynn's book offers the most direct explanation: generally speaking, they ain't rocket scientists. Not surprisingly, the Northeast Asian tigers lead the world in average national IQ. (Lynn's mediocre score for Israel seems open to question.)
For the correlation between national IQ and per capita GDP, Lynn reports the kind of high number that social scientists normally only dream about finding. If all you know about a country is its average IQ and whether it has a free market economy, you can predict its income level with a surprising degree of accuracy. Of course, this doesn't solve the chicken or egg question. Are they rich because they are smart or smart because they are rich? From what I've seen so far out of the book, it looks to me like both are true.
Culture also plays a role. Lynn lists underachievers with high IQs and low incomes (e.g., perennial screw-up Argentina) and overachievers (e.g., Barbados, with its veddy, veddy English cricket-centric culture that makes it the best-run black country in the world.).