University of Rochester analysis of 63 scientific studies spanning several decades suggests that the more intelligent a person is, the less likely they are to be religious.
The first systematic meta-analysis of the 63 studies conducted in between 1928 and 2012, led by Professor Miron Zuckerman, revealed "a reliable negative relation between intelligence and religiosity" in 53 out of 63 studies.
Only two studies showed significant positive correlations between intelligence and religiosity, while significant negative correlations were seen in a total of 35 studies.
Children with high intelligence were more likely to turn away from religion as they got older. In old age, those with high intelligence were more likely to be atheist.
One of the studies used in Zuckerman's paper -- begun in 1921 and still going today -- was a life-long analysis of the beliefs of 1,500 gifted children with with IQs over 135.
"Most extant explanations (of a negative relation) share one central theme -- the premise that religious beliefs are irrational, not anchored in science, not testable and, therefore, unappealing to intelligent people who 'know better,'" the authors write.
The study, published in the Personality and Social Psychology Review, defines intelligence as the "ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience." Religiosity is defined as involvement in at least some facets of religion.
Critics of the paper's conclusions note this is the definition of analytic intelligence, and more recently described creative intelligence and emotional intelligence are ignored in older studies.
Seemingly aware of the controversial nature of their conclusion -- that atheists are more intelligent than believers -- the authors suggest that intelligent people may simply value "personal control" over their lives.
"Intelligent people typically spend more time in school -- a form of self-regulation that may yield long-term benefits," the researchers wrote. "More intelligent people get higher level jobs (and better employment (and higher salary) may lead to higher self-esteem, and encourage personal control beliefs."