According to this article, a Danish professor of psychology (who’s about to retire) has found out that atheists on average have an IQ that is 5.8 points higher than that of believers.
I wonder whether Harry Turtledove realised this when he wrote Between the Rivers in which believers are depicted as extremely stupid compared to the free-thinkers. π
Anyway, if the article is correct, I wonder whether it’s believing that makes people less intelligent, or whether less intelligent people are more likely to believe in a god than more intelligent ones.