Declines in Religiosity Predict Increases in Violent Crime—but Not Among Countries With Relatively High Average IQ

Many scholars have argued that religion reduces violent behavior within human social groups. Here, we tested whether intelligence moderates this relationship. We hypothesized that religion would have greater utility for regulating violent behavior among societies with relatively lower average IQs than among societies with relatively more cognitively gifted citizens. Two studies supported this hypothesis. Study 1, a longitudinal analysis from 1945 to 2010 (with up to 176 countries and 1,046 observations), demonstrated that declines in religiosity were associated with increases in homicide rates—but only in countries with relatively low average IQs. Study 2, a multiverse analysis (171 models) using modern data (97–195 countries) and various controls, consistently confirmed that lower rates of religiosity were more strongly associated with higher homicide rates in countries with lower average IQ. These findings raise questions about how secularization might differentially affect groups of different mean cognitive ability.