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Atheists are more intelligent - but why?

When psychologists first studied the connection between religion and intelligence, in the 1920s and 30s, they came to the conclusion that atheists were more intelligent, on average, than their religious counterparts. But further research showed a murkier picture, and by the 1970s the general conclusion was that there was no difference between atheists and the religious.

More recent studies have started to shove opinion back. They seem to be showing that there is, after all, a difference - albeit with some caveats and nuances. Here's a couple of recent ones.

Miron Zuckerman, at the University of Rochester in New York State, USA, along with colleagues has conducted a meta-analysis of all the previously-published studies. A meta-analysis is a statistical tool used to pool together different studies, so that you can see the overall picture.

Altogether, Zuckerman dug up 63 studies, dating back to the 1920s. He found that, although there was a lot of variation, there was clear evidence that "the higher a person’s intelligence, the lower the person scored on the religiosity measures".

With this much data, Zuckerman was also able to dig a bit deeper into what factors affect the relationship. He found that the relationship is weakest in pre-college (i.e. young) individuals, and stronger for religious beliefs than for religious behaviour (i.e. church going).

Now, there are several theories on why intelligent people are less religious.

One idea is that religion is irrational, so intelligent, educated people simply 'know better'. It's also been suggested that intelligent people are more likely to be unorthodox. In a similar vein, Satoshi Kanazawa has suggested that religion is an evolutionary adaptation - and therefore instinctive. It takes intelligence, he suggests, to break free of our instincts. An alternative, more radical idea from Darren Sherkat is that the culture of religious fundamentalists actually impedes their intellectual development.

Zuckerman and colleagues looked at four so-called 'time-gap' studies, in which intelligence was measured at an early age and then religion was assessed later. Taken together, these suggest that intelligence can predict your religiosity in later life. 

They also looked at two studies of gifted children. These studies found that intelligent children were less likely to be religious later - but that the religiosity of their upbringing had little influence over their religion in later life.

Now, you should take these findings with a pinch of salt in light of other research which shows the powerful influence of upbringing on religious belief - and given that in the US (where these studies were conducted) people usually have a religious upbringing. That limits the possibilities for intelligent people to become more religious!

But the idea that intelligence turns people off religion fits nicely with the results of the second study.

Francisco Cribari-Neto and Tatiene Souza are statisticians at the Universidade Federal de Pernambuco and the Universidade Federal da ParaĆ­ba, respectively, in Brazil.

They've taken a look at a how the average IQ seen in different countries varies with average religiosity. The idea is to see whether religious culture is related generally to intellectual life. Now, this has been done before (by Richard Lynn in 2009), but Cribari-Neto and Souza have taken a rather more sophisticated approach.

They were able to show that the link is real, and that it is independent of economic development (both intelligence and loss of religion are independently linked to economic development, but there is something additional to that). What's more, the effect is strongest in nations at middling levels of average IQ - as shown in the figure.

The reason for this, they suggest, is that at low IQs there is little scope for critical reasoning. And at high IQs most of the potential effect of critical reasoning have already happened (as the nation transitioned from lower IQs. So it is the middle range of IQs that the effect of increasing IQ is most clearly seen.

Of course, because it's a correlation you can't rule out the reverse effect. But it does all seem to fit together nicely.
Zuckerman M, Silberman J, & Hall JA (2013). The Relation Between Intelligence and Religiosity: A Meta-Analysis and Some Proposed Explanations. Personality and social psychology review : an official journal of the Society for Personality and Social Psychology, Inc PMID: 23921675
Francisco Cribari-Neto, & Tatiene C. Souza (2013). Religious belief and intelligence: Worldwide evidence Intelligence, 482-489 DOI: 10.1016/j.intell.2013.06.011

Creative Commons License This article by Tom Rees was first published on Epiphenom. It is licensed under Creative Commons.


  1. 3rd paragraph, last sentence, typo "tat". Sorry can't help myself I'm an atheist (and 99th percentile lol). Lincoln.

  2. That's what you get for relying on computers to do your proofreading for you!

  3. Great article. Good to see there are actual experiments being done.

  4. Thanks for the article. Interesting debate. I think these findings should not be overstated, though. If you look at the result, what appears most striking is the overwhelming variation, not the miniscule mean differences in religiosity between people with higher and lower IQ.

    What will inevitably happen when media pick up such findings is that they will claim that religious people are idiots, to put it bluntly, and that truly intelligent people can't be religious. As if Augustine, Cusanus, Luther, and others of that ilk, were all dumb, and as if there was not a plethora of both anecdotal and statistical evidence pointing to exceptional abilities and achievements among certain religious groups (Nobel laureates among Jews, successful entrepreneurs among Latter Day Saints in the US, etc.). This blatant oversimplification is what disturbs me, though an agnostic, about such results.

    In addition, I am doubtful whether IQ - a very basic function of your central nervous system's ability to transmit and manipulate information quickly and error-freely - is really the driving force here. What about years of schooling as an alternative explanation? People with more years of schooling, especially university graduates, have a higher IQ as a result of schooling. They are also, on average, slightly less religious because a scientific worldview and critical stance towards religion, as taught at most schools in Western societies, instills religious doubts in them. Thus, it not IQ but socialization into a community of adherents of a secular worldview would be the driving force.

  5. Yes, I did see that one. It was a little hard to know what to make of it. It seems that worrying about money makes it harder to perform analytic tasks. And it also seems true that cognitive dysfunction does explain at least some religious tendencies (that's a study I'll cover in the next blog post).

    So it's plausible. Yet I'm thinking that the link cannot be all that strong, since I don't think that intelligence is very tightly linked to religion, or that religion is tightly linked to wealth. And religion may in fact cause financial problems.

    So my guess would be that it could be part of the mix - that financial anxiety has a lot of effects, that both turn people to religion and make it harder for them to correctly analyse their environment.

  6. Sorry to burst your bubble, but I'm a devout Christian and also happen to have a genius IQ, advanced degree, and am a member of MENSA- and there are many others like me.

    1. Mr. or Mrs. Genius,

      There has never been a bubble because this post is not about individual cases, but more about why atheists in general are more intelligent than theists. It does not say ALL theists are less intelligent than atheists or vice versa....

    2. The data does not preclude the possibility of an intelligent religious person, its funny that someone with a genius IQ can't see that. I think somebody might be lying about their IQ.

  7. I love this site. It's well-written and presents the arguments fairly. I also love the comedy of the comments. Amazing how the genius above chose to be anonymous, and didn't choose to elaborate on his advanced degree. My IQ is a little below genius level, so I guess that's why I fail to understand My Wile E Cyote's comment.

    Keep up the brilliant work and food for thought, Tomas.

    1. Thanks! It's been tough to find the time to keep this blog running recently, so really glad to hear that you like it.


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