The higher the IQ, the less likely a person is to be religious, a US study has found.
Researchers at the University of Rochester looked at 63 scientific studies on religion and intelligence going as far back as 1928 and as recently as last year.
Intelligence was defined by the researchers as the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience.
Just 10 studies found a positive relationship between intelligence and religiosity, while 53 showed a "reliable negative relation between intelligence and religiosity".
The trend was the same among children and older people.
The researchers said people with higher IQs were more likely to have a higher self-esteem and notion of controlling their own life.
"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 researchers concluded.
"Intelligent people typically spend more time in school - a form of self-regulation that may yield long-term benefits.
"More intelligent people getting higher level jobs and better employment and higher salary may lead to higher self-esteem, and encourage personal control beliefs."
Study co-author Jordan Silberman said: "Intelligence may lead to greater self-control ability, self-esteem, perceived control over life events, and supportive relationships, obviating some of the benefits that religion sometimes provides."