To the Editor: We were struck by the high level of genetic loading of church attendance in adulthood (58% of variance) reported by Kenneth S. Kendler, M.D., and John Myers, M.S., in the October 2009 issue of the Journal (1). Church attendance was a factor associated with less alcohol and nicotine consumption in the study. A simple, easily defined behavior, church attendance could be interpreted as a proxy of religiosity, which is a much more complex, multidimensional construct (2). In fact, church attendance belongs to the social religiosity dimension, one of the seven religiosity dimensions derived from a factor analysis the authors performed for their questionnaire data in a previous study (2). The other six religiosity dimensions were general religiosity, involved God, forgiveness, God as a judge, unvengefulness, and thankfulness.

Religiosity as a whole has been shown to be heritable (3) and has been hypothesized to be an adaptation or by-product of our evolution (4). Specific neural correlates to religiosity (i.e., God's perceived level of involvement, God's perceived emotion, and doctrinal/experiential religious knowledge) have been demonstrated (5). For such complex phenotypes, it is very difficult to demonstrate that there is no intermediate factor that more clearly explains the role of genes. Indeed, in the study by Kendler and Myers (1), subjects were all Caucasian male twins born in Virginia, 85% of whom were Protestant, mostly fundamentalist or Baptist. It is not clear that one would find similar results in subjects from another sociocultural context, since regular attendance at religious services can vary widely, from 1.7% (Estonia) to 62.3% (Turkey) in a recent European cross-cultural survey (6). It could then be speculated that the heritable trait captured by church attendance could rather be defined as the disposition to perform socially meaningful rituals in order to reinforce coalitional affiliation, as proposed by Boyer (4). Although this hypothesis is also difficult to prove, the selection (throughout generations) of people with high capacity to reinforce group coalition makes sense, at least regarding breeding potential and surviving in social groups.