IQ, trust/trustworthiness, and cooperation all seem to be positively related.
Garrett Jones blogs a description of his study showing a relation between IQ and trust/trustworthiness. He collected prisoner’s dilemma studies at different US universities, compared them to the schools’ SAT scores and found that students cooperate 5% to 8% more often for every 100 point increase in the school’s average SAT score.
Jones thinks this link between IQ and trust/trustworthiness probably holds among nations. He asks:
Why would high IQ groups be more cooperative anyway? Isn’t cynicism intelligent? Sure, sometimes, but the political entrepreneur who can find a way to sustain a truce can probably skim quite a lot of the resulting prosperity off for herself. And people who are better at solving the puzzles in an IQ test are probably better at solving the puzzles of human interaction.
The IQ-cooperation link probably holds on the longer time scale. Thinking about human evolution, we are both much higher IQ than chimps and bonobos as well as crucially much more cooperative.
Was higher IQ might a group adaptation for higher cooperation? Groups with higher IQ could cooperate better and increase at the expense of competitors.
There has been a long term trend to more cooperation (see Robert Wright, Nonzero; Matt Ridley, The Rational Optimist). Might a long-term Flynn Effect of rising IQ be behind the trend of growing cooperation?