Humans have a tendency to seek out their own kind, preferring others who have the same skin colour, the same culture and, yes, the same religion.
What’s more, there seems to be some sort of connection. People who are the most stridently religious also tend to be more racist, and to generally be more cautious about dealing with people from outside their own group.
Does this connection stem from some deep, common mechanism that drives people to be suspicious of non-group members (a “central affiliation mechanism”)? Or are do each of these prejudices derive from an independent mechanism. Does the brain have a pro-racism module, a pro ethno-centrism module, and a pro-religionism module (an “essentialism mechanism”)?
Gary Lewis and Timothy Bates, from the University of Edinburgh, set out to investigate the genetics behind this using data from the MacArthur Foundation Survey of Midlife Development (MIDUS) in the United States. They quizzed 957 identical and non-identical twins on their attitudes to people from outside their own group, using questions like “How much do you prefer to be with other people who are the same religion as you?”
Basically, the idea is that if identical twins score high on all three forms of prejudice, then it suggests a central affiliation mechanism. If particular identical twins tend to rate higher on one or other form of prejudice, than that suggests an “essentialism mechanism”.
So they cranked the numbers, and what they found was that both mechanisms are needed to explain the data!
Well, to be more precise, they found that the “central affiliation mechanism” accounts for 35%, 69%, and 21% of variation in religious, ethnic, and racial favouritism, respectively.
There does also seem to be a genetic trait that’s specific for religious prejudice. This predisposes for religious prejudice independently of racial and ethnic prejudice. However, according to Lewis and Bates’ data, it’s pretty weak – taking it out of the model didn’t much affect the results.
So it seems that religious prejudice is mostly driven by a general purpose prejudice module in the brain. Yes, religious prejudice is a kind of racism.
They found something else interesting. The shared environment – the family home, for example – didn’t have any effect on prejudice. That’s a surprise, and may simply indicate that their study sample wasn’t big enough to pick it up.
But they did find that the “unique environment” (all those environmental factors experienced by one of the twins but not the other) did have an effect, and in a surprising way. The more the unique environment favoured religious prejudice, the less it favoured ethnic prejudice – and vice versa.
According to Lewis and Bates, that’s because religion and ethnocentrism act in opposition:
This may reflect the influence of religious teachings, which may increase ethnic tolerance, or the possibility that religion became superordinate to coalitions based on ethnicity.
So although religious prejudice and ethnic prejudice stem in part from a common brain mechanism, they don’t seem to go together as traits. If your genes incline you to prejudice, that could form either into racial or ethnic prejudice, but not both (at least, not amongst this group of Americans).
That doesn’t seem to be the case for racism, however!
Lewis GJ, & Bates TC (2010). Genetic evidence for multiple biological mechanisms underlying in-group favoritism. Psychological science : a journal of the American Psychological Society / APS, 21 (11), 1623-8 PMID: 20974715