What’s So Smart About Unbelief?

Tom Rees

Intelligence is a bit of a slippery eel—it’s pretty tough to get it pinned down precisely. And yet, cognitive scientists do think there is something they call “general intelligence,” which describes an individual’s ability to perform well on a broad range of different kinds of intelligence tests. Put simply, someone who does well on one test is likely to do well on another.

What does this have to do with atheism? A number of studies have shown that atheists are more intelligent than believers. Actually, to be precise, these studies show that on average atheists are slightly more intelligent than believers. For example, Satoshi Kanazawa, a controversial psychologist based at the London School of Economics, found that the least religious adolescents in the United States have an IQ that’s around six points higher, on average, than that of the most religious.

That’s a narrow gap relative to the spread of IQ scores in the population, but it’s a finding that is typical of other studies. In one of the most thorough such studies, which used data from the MacArthur Foundation Survey of Midlife Development in the U.S., a group of psychologists at the University of Edinburgh in Scotland found that that lower IQ was significantly associated with every one of six different measures of religion. For the most part, this association still held even after adjusting for factors such as education, sex, age, and even personality—the only exception being spirituality, the weakest of all indicators of religion. Overall, the link between religion and IQ was strongest for the “fundamentalism” measure, although the team points out that even here the association was pretty weak.

So does this mean that atheists have shrugged off their religious beliefs because they are more intelligent? Maybe atheists are smart enough to figure out the truth. Well, maybe; but the problem with that theory is that intelligence and rational thinking are quite different beasts. A study by Keith Stanovich of the University of Toronto and Richard West of James Madison University in Harrisonburg, Virginia, has found there is no correlation between intelligence and a person’s ability to avoid some common traps of intuitive thinking. It seems that intelligence only helps overcome the cognitive biases that lead to poor judgment if you are the kind of person who uses it. It’s not so much about innate braininess; it’s about how you use it in your approach to the world.

Take a recent study by Sharon Bertsch (University of Pittsburgh) and Bryan Pesta (Cleveland State University). They flashed a series of straight lines in front of their test subjects and asked them to judge how long each line was. They also ran a test in which their subjects had to pick out a letter from a crowd of other letters. Their final test checked how prone their subjects were to “overclaim.” This is a fascinating test in which people are presented with facts (a famous person’s name or a scientific concept, for example), and they have to say how familiar they are with it. Some of the facts are false, and by using some clever processing the researchers can tease out how much the subjects are overclaiming their familiarity with the real facts.

Putting the results of these three tests together allowed Bertsch and Pesta to measure their subjects’ basic information-processing abilities. They found that those who were best able to process information were also the least religious. The effect was strongest in relation to sectarianism (by which they mean the belief that your particular religion is the only true religion), but they got similar results for scriptural acceptance and religious questioning (the most accurate in judging line length were least accepting of scriptural truth and the most willing to question beliefs). Bertsch and Pesta did find that IQs had a similar association, but when they analyzed the statistics they found that this was most likely simply because people with high IQ also tend to be speedy at information processing.

More evidence to support this idea comes from a research team lead by Amitai Shenhav, a psychologist at Harvard University. Shenhav and his colleagues were interested in whether people make snap decisions based on their gut feelings or whether they ponder things a bit more deeply. So they asked their subjects a seemingly simple question: “A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?” Now, if you don’t stop to think about it, you’d probably say the answer is ten cents. If you think about it a little, you’ll probably figure out the correct answer (five cents). So intuitive thinkers will tend to give the wrong answer.

What Shenhav discovered was that these intuitive thinkers were also more likely than deep thinkers to believe in God and immortal souls. Even more intriguingly, deep thinkers were more likely to say that they had lost their belief since childhood. Now, these atheists also had higher IQs. However, as with Bertsch and Pesta’s study, when Shenhav compared IQ and intuitive thinking statistically, he found that deep-thinker status was the most powerful explanation both for current atheism and for losing one’s religion.

These findings might help to explain the apparent link between atheism and high IQ. It might be that intelligence is not directly connected to atheism but is, instead, an innocent bystander. Instead of raw intelligence, it might be that your thinking style, and whether you take the time to ponder things thoroughly, is all that matters.

Tom Rees

Tom Rees is a medical writer and a lifelong humanist. His blog, Epiphenom, covers the latest research into the psychology and social science of religion and nonbelief.


Intelligence is a bit of a slippery eel—it’s pretty tough to get it pinned down precisely. And yet, cognitive scientists do think there is something they call “general intelligence,” which describes an individual’s ability to perform well on a broad range of different kinds of intelligence tests. Put simply, someone who does well on one …

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