A Clear Voice: Genetic Influences on Religiousness

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March 17, 2005

Genetic Influences on Religiousness

Today Michael Williams had an entry about an article regarding a twin study that found that genes are responsible for about 40% of the variability in the religiousness of a person in adulthood, but are less important in childhood. I was interested to see what scale they were using in measuring religiousness. Obviously this could mean many things. They could be asking about belief in God or how much people go to church or whether they think they are spiritual, however that is defined, and so on. I went and looked the study up on my university’s electronic database (sorry, I can’t link to it) and it seems that the study asked nine questions of the subjects:

The first assessed external aspects of religiousness (the four items of attending religious services, discussing religious teachings, observing religious holidays, and membership in youth/study groups) that might be most susceptible to environmental influence; the second reflected internal aspects of religiousness (the five items of seeking help through prayer, reading scripture, deciding moral actions, having a friend with similar beliefs, and importance of faith) that may be most susceptible to heritable influence.

Obviously then, we are measuring certain aspects of religiousness, but these aren’t addressing particular religions or particular points that some religions would see as more important than these questions. For instance, I would be interested to see an analysis like this that compares different genetic and environmental effects among Christians and Muslims. The study admits that this is only one way to measure religiousness.

The concept of religiousness as defined in this study also deserves comment, as religiousness can be defined in many ways. While our measure formed one coherent scale, we lack the means to make the distinction between the different types of religiousness seen in the literature (e.g. intrinsic, extrinsic, quest), except for the rational parsing of items into internal and external aspects of religiousness.

I was interested to see that the study did a separate analysis on the internal and external questions.

Also, the analysis split up the influencing factors into genetic, shared environmental influences (which would include experiences with family, church, school, most influences in the womb, etc.), and non-shared environmental influences (which would include experiences not shared by twins, like different friends, along with everything else, like non-genetic personality traits and free-will, as well as error). Subjects answered the questions both with respect to themselves currently, and how they felt they were in childhood.

They also say

The assumption underlying twin models is that MZ twins share 100% of their genes while DZ twins share only 50%.

This means that the actual percentage of genetic material shared by the DZ twins introduces some error.

The paper makes some other conclusions that are interesting.

In fact, the heritability and shared environmental estimates for internal religiousness could be equated across the two ratings [retrospective and current] without significant loss in model fit, but they could not be equated for external ratings. These findings suggest that the increase in heritability in overall religiousness may reflect the increasing importance of individual dispositional factors and the decreasing importance of external forces.

This conclusion is pretty intuitive. Part of growing up is internalizing your values and opinions, such that it’s really you making your decisions rather than your family or culture.

This is something that parents really have to consider in regards to their children. They can teach them their religion and values, but ultimately the child is going to make a choice on their own. So many times people make the mistake of thinking that the behavior of a teenager or adult is completely dependant on how they were raised, but this isn't the case.

Twins were also asked to rate their parents religiousness.

The presence of a high correlation between parents for religiousness was consistent with the presence of high assortative mating for the trait.

Basically, then, people are more likely to be married to those who are similarly religious, which isn't a suprise.

There are some other interesting conclusions that can be drawn from looking at the internal vs. external data.

In adulthood, external religiousness is more affected by genetics than internal religiousness. This seems to fit with the theory that certain personality traits that are expressed more externally, such as the ability to get along with others, are what are accounting for the genetic factor in religiousness. In childhood, external religiousness is more affected by the shared environment than internal religiousness, whereas the effect is reversed in adulthood. This seems to fit with the theory that family environment is somewhat better at shaping behaviors than thoughts in a child, but will have more effect on the grown child’s thoughts than their behaviors (although the effect will be lessened overall). The effects of the un-shared environment remain pretty stable across childhood and adulthood and between internal and external religiousness.

There’s lots of good future work that could be done with sort of analysis. The subjects involved were all men from the same region who were the same age. Comparing people of different gender, religion, age, and culture would be a good idea. Age would be a particularly interesting variable to study. It may be that genetics is more important in your 30's, but it's effects lessen somewhat by age. I also wonder if there would be any difference in the effects of genetics and environment among a very religious group and a group that is not religious. Perhaps genetics pays a larger role in determining how religious a person is, but environment or other factors is more important in determining if a person is religious at all.

I find this study, and the one I talked about a few days ago on the issue of genetic effects on sexuality to be quite fascinating. As a Christian I believe that ultimately decisions are based on free will. I think this is a belief many people share. Every decision, though, is going to be influenced by some combination of genetic and environmental factors and it’s helpful to learn more about what they are. For instance, alcoholism has some strong genetic connections and knowing about them enables people who are predisposed to alcoholism to make decisions to lessen that risk. For instance, if I have no alcoholism in my family, I might choose to drink socially, but if I do, I might choose to not drink at all.

Future Pundit, who has a very interesting site by the way, also has an entry up on this. Uncorrelated does too, which is another site I ran across today. The blogosphere is cool like that.

Update: Gene Expression has more.

Posted by illuminaria at March 17, 2005 03:16 PM

Comments

Thanks for the link!

Posted by: Michael Williams at March 17, 2005 03:47 PM

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