Over the last few decades, economists and psychologists have quietly documented the many ways in which a person's IQ matters. But, research suggests that a nation's IQ matters so much more.

As Garett Jones argues in Hive Mind, modest differences in national IQ can explain most cross-country inequalities. Whereas IQ scores do a moderately good job of predicting individual wages, information processing power, and brain size, a country's average score is a much stronger bellwether of its overall prosperity.