It is natural to believe in God, so more intelligent individuals are more likely to be atheists.
Religion is a cultural universal, and its practice is observed in every known human society. However, as I explain in earlier posts (Why do we believe in God? Part I, Part II), recent evolutionary psychological theories suggest that religiosity may not be an adaptation in itself but may be a byproduct of other evolved psychological mechanisms variously called the “animistic bias” or the “agency-detector mechanisms.”
These theories contend that the human brain has been selected to overinfer agency – personal, animate, and intentional forces – behind otherwise natural phenomena whose exact causes cannot be known. This is because overinferring agency – and making a Type I error of false positive – makes you a bit paranoid, but being paranoid is often conducive to survival. In contrast, underinferring agency – and making a Type II error of false negative – can result in being killed and maimed by predators and enemies that were incorrectly assumed not to exist. So, evolutionarily speaking, it’s good to be a bit paranoid, because being paranoid can often save your life. Religiosity – belief in higher powers – may be a byproduct of such overinference of agency and intentional forces behind natural phenomena.
If these theories are correct, then it means that religiosity – belief in higher powers – may have an evolutionary origin. It is evolutionarily familiar and natural to believe in God, and evolutionarily novel not to be religious. Consistent with this reasoning, out of more than 1,500 distinct cultures throughout the world documented in The Encyclopedia of World Cultures, only 19 contain any reference to atheism. Not only do these 19 cultures exist far outside of our ancestral home in the African savanna, but all 19 of them without an exception are former Communist societies. There are no non-former-Communist cultures described in The Encyclopedia as containing any significant segment of atheists. Nor is there any reference to any individuals who do not subscribe to the local religion in any of the ethnographies of traditional societies.
It may therefore be reasonable to conclude that atheism may not be part of the universal human nature, and widespread practice of atheism may have been a recent product of Communism in the 20th century. So belief in higher powers is evolutionarily familiar and natural, and atheism is evolutionarily novel. The Hypothesis would therefore predict that more intelligent individuals are more likely to be atheist than less intelligent individuals.
Once again, analyses of large representative samples from both the United States and the United Kingdom support this prediction of the Hypothesis. Net of a large number of social and demographic factors, including education, more intelligent individuals are more likely to be atheistic than less intelligent individuals. For example, among the American sample, those who identify themselves as “not at all religious” in early adulthood have a mean childhood IQ of 103.09, whereas those who identify themselves as “very religious” in early adulthood have a mean childhood IQ of 97.14.
Even though past studies have shown that women are more religious than men, the analyses show that the effect of childhood intelligence on adult religiosity is twice as large as that of sex. Remarkably, childhood intelligence has a significant and large effect on adult religiosity even when religion itself is statistically controlled for. So it appears that more intelligent children are more likely to grow up to be atheists than less intelligent individuals, and the Hypothesis provides one explanation as to why.