Twin studies, religiosity and the conservation of oddity

I’ve collaborated with my friend Martin on musical projects for several years, but we’ve not met for over forty, when we were both on the committee (and separately presidents) of Cambridge University Folk Club. He’s an atheist, but not a Gnu, since he uses a capital for “God”, and religion came up when he asked my news recently, and I told him about The Hump. We normally only talk saxophone solos and studio techniques.

Anyway, as he was just off to India on holiday it led to a rather bizarre e-mail exchange, with him sending me pictures of the ascetic rules in Gandhi’s ashram, and so on. Just before I persuaded him to get on with enjoying himself he mentioned – probably to account for why I’m religious and he’s not – that twin studies suggest that religion is genetically determined.

I reminded him that I’ve had my own identical-twin study going for 34 years (today!) since our girls were born, and that currently one is a (relatively recent) Christian and one isn’t, which suggests the genetics are not quite as clearcut as that.

The study he means is probably the one referred to here, in which adult monozygotic twins were compared on 7 measures of “religiosity”.

But in fact, they weren’t (compared on these measures) – the data was culled from one or more older studies, which opens up some of the critiques made of twin studies generally – statistical bias and post-hoc definitions of experimental aims. More severe detailed critiques have been made of the whole notion of twin studies, not least by Dr Jay Joseph, who has shown in a number of publications that their fundamental assumption – that the childhood environment of twins is near-enough identical – has been disproven, and that the attempts to remedy the situation actually involve circular reasoning.

Another major problem is what is called missing heritability. See here for an overview, and here for another detailed article by Joseph. The basic issue is that, for all the predictions of the twin studies (whose assumptions, arising originally from the eugenics movement, are based on an early 20th century conception of genes), very few actual genes have been found that are responsible for any condition or trait so identified. Which leads many to question if they exist at all.

The reasons are becoming increasingly obvious as it is realised that all phenotypic traits rely on the interaction of numerous genes – and that their expression and even makeup is influenced by many interacting epigenetic factors (acquired and inherited – Lamarck was right all along!) and by the local and global environment. We are not determined by our genes.

Ironically the paper alluded to, if I’m correct, by my friend Martin (who incidentally trained in zoology [woops, geology, he tells me] though I did the social psychology) was written by Dr Todd Vance, a practising Christian, who comments on it here. Though obviously persuaded that twin studies are not, as Jay Joseph argues, worse than useless, he does admit some methodological problems in studies of this type. One key one is that “beliefs that are identified as religious are defined at the social, not biological, level.” That seems a pretty fundamental flaw to me. Biology cannot determine non-biological entities – as is demonstrated pretty conclusively by another quotation from Vance’s article:

…interestingly, genetics have been reported to have a modest effect on church attendance in females.

Hullo? There is a sex-linked gene for church attendance? Would that be having separate Baptist and Methodist alleles? Can anyone seriously consider that with just 24,000 coding genes we can spare a few dozen to influence personal devotion, prayer and extrinsic religiosity, let alone churchgoing? Is it not far more likely that the methodology is barking up the wrong spire? Vance’s own conclusions are, in fact, pretty restricted:

Overall, the genetic effects on religiosity are likely modest and complex.

And he goes on to advocate evangelism as necessary for the expression of such genes – not quite what Martin had in mind, I’ll wager! An article in New Scientist entitled Genes contribute to religious inclination seems unconsciously to give the game away:

About a dozen studies have shown that religious people tend to share other personality traits, although it is not clear whether these arise from genetic or environmental factors. These include the ability to get along well with others and being conscientious, working hard, being punctual, and controlling one’s impulses.

One wonders why, if the associated general personality traits are only doubtfully genetic, something as specific as religion should be any different.

But leaving twin studies aside, in closing let me consider another factor. And that is that despite what was drilled into me in social psychology, genes and environment are not all there is to explain behaviour – they are just all that one particular materialistic set of theoretical spectacles can see. I’ve already mentioned the hitherto unsuspected epigenetics, but back in 1981 I wrote this article for World Medicine, in which I recount not only the case of the twin whose distant sister anticipated her pregnancy before my pregnancy test could detect it, but also my sister-in-law’s vivid precognitive dream of my wife’s twin (1:80 probability) female (1:3 probability) pregnancy. Rupert Sheldrake, all is forgiven.

My twins are too fiercely independent of each other now to admit to any telepathic connection (could that ever include religiosity?), but they do have an unusual tendency to find they’ve bought exactly the same articles and brand of clothing.

That would be the Gucci gene, I guess.

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About Jon Garvey

Training in medicine (which was my career), social psychology and theology. Interests in most things, but especially the science-faith interface. The rest of my time, though, is spent writing, playing and recording music.
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3 Responses to Twin studies, religiosity and the conservation of oddity

  1. Avatar photo Sy Garte says:


    Well, you pushed a couple of buttons with this one. Having done quite a bit of population genetics stuff, and much more on genetic correlates of disease susceptibility, I am very familiar with the weakness of twin studies, even for so called monogenic conditions (which probably don’t exist.). I have railed against genetic determinism for at least a decade, and now the science is starting to catch up with me. Surprise, surprise, there actually IS NOT a gene for violence, or a gene for good manners, or a gene for whether one is willing to take out the garbage (talk about sex linked!). Not only that, but there isn’t a gene for eye color or skin color or almost any actual phenotype. Turns out that Mendel got really lucky with those yellow peas. (and of course, he had to cheat a bit to make it all come out right).
    Anyway, I will stop ranting, but I blame you, Jon.
    The concept that there could be a gene for religiousness strikes as so funny that I am unable to see the humor in it.
    And if there is it would make me an interesting mutant, since I was born a homozygous atheist, going back several generations. I must have acquired a very recessive allele from some very distant ancestor.

    • Avatar photo Jon Garvey says:


      It did occur to me reading the Charney paper I cited, Behavior genetics and postgenomics, that the determinists could shift gear and say that some environmental factor prompted a change of gene expression. We have only to look at summer heat waves or flu to explain religion…

      In all seriousness that paper, whilst extremely long, gives a great overview of new trends in biology so is highly recommended for all biology-savvy readers.

  2. Avatar photo Jon Garvey says:

    As it happens, almost topically, the controversy is covered in the Independent today.

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