Genetic Factors and the Religious Life

It's getting late but for the record you can find a good study of genetics and religion in Do Genetic Factors Influence Religious Life? Findings from a Behavior Genetic Analysis of Twin Siblings. PSYDIR offers a good summary:


It's a fairly standard twin study. They took a sample of around 600 identical and non-identical twins from the National Survey of Midlife Development in the United States (MIDUS), and looked at a number of religious characteristics.

Basically, their analysis allows them to tease out the variations that are shared by identical twins but not by non-identical ones (genetic factors), by non-identical twins (family factors or shared environment), and that differed even among non-identical twins. This last factor was put down to the effects of external environment (i.e. things that happen in you life that aren't shared by your twin).

I've put the results in the graph. First off, look at childhood religiosity. The biggest factor is your family, and not your genetics. It's not until adulthood that the effects of genetics really start to shine through. No surprises there!

The 'salience', or importance of religion in your life is about one-quarter defined by genetics, as is your spirituality. The most important factor here, however, is the external environment. You get similar results for religious attendance.

When you get to more personal beliefs, the patterns start to shift. There are three factors that are about 40% driven by genetics, with your family upbringing having hardly any effect. These factors are: how often you turn to religion for guidance, whether or not you take the bible literally, and whether people should stick to one faith, or experiment with others (exclusivist beliefs).

It is true that there are tricky statistical issues with twin research and it is certainly possible that results like these will be overturned in the future. If that happens, however, it will be because of better twin/adoption and direct genetic studies. The type of evidence that Tyler cites is simply not capable of answering the fundamental questions that are being asked by this type of research. It is also true that these results are conditional on an environment, that is a time and place. (But that is the relevant measure for parenting today.)

I would also note that if you think the statistics get the numbers wrong you also have to deal with the fact that the patterns make sense. Parents have the biggest influence on childhood religiosity, non-shared environment has the biggest influence on attendance, genetics has the biggest influence on being "born-again." (Even the word suggests nature.) Bryan's book reviews a number of studies like this which are broadly similar.


The non-shared environment effects may just be the result of noise.

Could it be that twins have a closer connection with each other than non-twins, and as a result, if one twin becomes "born again," it spends all its energy persuading the other twin to accept jesus and whatnot? It seems like that could also be an explanation for the "genetic" factors.

"the fact that the statistics agree with preconceived notions is a reason to *distrust* the statistics"

The Rev. Bayes might disagree.

Most parents think they have a huge impact on their offspring's personality ... until they have a second child.

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What they label as "genetic" is not really genetic. It is something they measured. Nobody really knows what genes do what for the most part. "Genetic" is a conclusion based on their assumptions about what they think they controlled for.

And the relevant information is how do the other variables vary with 'childhood religiosity' as the controlled variable? In other words, as a parent what do I get from what I choose to expend effort doing. That is what is actually important to people outside of academia, not advocating for a pet theory one way or the other.

I think this type of interpretation gets ahead of itself. Until one can start tracing results to specific genetic patterns or specific genes this is just another ill-defined bucket that we're claiming some explanatory powers for.

Could there be a regression-towards-the-mean effect here? I bias my survey-answers asking "what will my twin brother say"? I'd trust it more if the parameters were external observations immune from self-reporting bias.

what on earth does "born again" mean outside of a Christian context? That's like claiming a genetic factor determines Theravada vs. Mahayana Buddhism.

Well, I don't know the details of specific sects of Buddhism, but if you substitute "influences" for "determines", it's not totally implausible. Some other studies have shown genetic components to authoritarian tendencies and while most religions are at least somewhat authoritarian, some religions are MUCH more authoritarian than others. Tendency either to flee those religions or to seek them out could depend on the person's innate (to some degree genetic) propensity for or against authoritarianism.

You could probably have similar explanations for other dimensions of personality, e.g. openness to new experience could have a lot to do with that exclusivity measure.

And the relevant information is how do the other variables vary with 'childhood religiosity' as the controlled variable?
That is a great question. It may already be included in the data, but I would love to see it broken down.

Also, one reason why I am suspicious of these results: Can someone please explain to me how genetic factors would have ANY influence at all on one's tendency toward biblical literalism? That just doesn't pass the smell test, to me.

From the abstract, this is probably a good summary for the whole debate:

"Specifically, genetic factors explain 19–65 percent of the variation, while environmental influences account for the remaining 35–81 percent..."

If anything this seems to underestimate the effect of genetics as they only define as genetic the variance associated with the difference between identical and non-identical twins. Non-identical twins still share much more genetic information than two random people, which means this is a lower bound estimate, which should mostly be taken from the family environment.

Also, I think there's a typo in the PsyDir breakdown. External Environment should be the variance between even identical twins, not between non-identical twins.

I think the bottom line is that Caplan's deemphasis of parenting is NOT supported by this document.

Genetics may be more important, but parenting and environmental effects that can be influenced by parents play a potentially large role.

I would LOVE to see this re-run with political ideology and other fervent beliefs included along with religion!

The history of my own maternal line for 4 generations:

Great-Grandmother: Doctorate in Divinity, Christian missionary in Korea most of her life, married to a fellow missionary (my great-grandfather).

Grandmother: Church choir director and married to a minister (my grandfather) for the first half of her life, followed by becoming *very* committed/active in Alcoholics Anonymous for the second half of her life.

Mother: Hardcore Trotskyite, high-level Teamsters Union organizer/activist throughout the 70s, married a man (my father) with an even more hardcore Socialist revolutionary ideology than her own. (Ah, to be a 10-year-old girl and have your father explain to you how important it is for you to be ready and willing to carry out assassinations and executions as necessary When The Revolution Comes. Good times!!!)

Me: Evangelical libertarian/objectivist and Libertarian Party hack, married a fellow Libertarian Party hack (but eventually divorced him and got remarried to a man who just likes my ass).

Although my mother is an agnostic and I'm a hard atheist, we both still not only became convinced that we knew the One True Answer but also felt compelled to Share The Good News with the world. (Each generation of my family also became deeply involved in the peace movement during at least one war and has been in the 95+th percentile of forward-thinking viewpoints on the civil rights issues of our respective times.)

So how much of that is environmental, and how much of it is genetic?

Given that *what* was/is believed changed so much over time while the overall level of fervor and ideologically driven activity remained roughly the same, I suspect that my maternal line is a carrier for the "born again" gene(s) -- each generation just found it's own thing (Christianity, AA, Socialism, Libertarianism) to feel "born again" over with the intensity of a religious belief regardless of whether that belief was in an actual religion.

(Each woman also chose a husband based on shared ideological commitment so there may have also been some contribution from the fathers' sides, but since each father was the first in his family to be so theologically/ideologically driven I don't think the "born again" gene(s) run as strongly in my paternal line.)

I hope that one day behavioral geneticists are able to isolate the genes that contribute to religious fervor. It would be fun to get tested and find out just how much of a genetic "born again" this atheist is deep down inside. :D

Science always give reasons to things that doesn't really need to be explained and discovered. There are just things we have to believe in without proofs.

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t that happens to everything, doesn't it?

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