The team gave questionnaires to 169 pairs of identical twins
- 100% genetically identical - and 104 pairs of fraternal twins - 50%
genetically identical - born in Minnesota.
The twins, all male and in their early 30s, were asked how often they
currently went to religious services, prayed, and discussed religious
teachings. This was compared with when they were growing up and living with
their families. Then, each participant answered the same questions regarding
their mother, father, and their twin.
The twins believed that when they were younger, all of their family members
- including themselves - shared similar religious behaviour. But in
adulthood, however, only the identical twins reported maintaining that
similarity. In contrast, fraternal twins were about a third less similar
than they were as children.
"That would suggest genetic factors are becoming more important and growing
up together less important," says team member Matt McGue, a psychologist at
the University of Minnesota.
Michael McCullough, a psychologist at the University of Miami
in Coral Gables, Florida, US, agrees. "To a great extent, you can't be who
you are when you're living under your parents' roof. But once you leave the
nest, you can begin to let your own preferences and dispositions shape your
behaviour," he told New Scientist.
"Maybe, ultimately, we all decide what we're most comfortable with, and it
may have more to do with our own makeup than how we were treated when we
were adolescents," says McGue.
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.
But McGue says the new work suggests that being raised in a religious
household may affect a person's long-term psychological state less than
previously thought. But he says the influence from this early socialization
may re-emerge later on, when the twins have families of their own. He also
points out that the finding may not be universal because the research
focused on a single population of US men.
Journal reference: Journal of Personality (vol 73, p 471)