Religion and Genetics
There are several twin studies showing, that the tendency to be religious has a genetic component. Not which religion you choose, because that is a cultural thing, but how serious you are abot it. I am lazy for a detailed report, but this blog can lead you to the studies: http://www.scilogs.eu/en/blog/biology-of-religion/2011-03-12/religiosity-genes-again-confirmed-by-another-twin-study

Also this article: http://www.popsci.com/science/article/2013-08/what-twins-reveal-about-god-gene

EDIT after a few years - I was informed one link is broken and the other contains no citation. So I checked for new material today and wikipedia has a cool passage how genes and environment affect religion. Wikipedia saves the old version, so this is from March 8 2018, article Religiosity.

"
The contributions of genes and environment to religiosity have been quantified in studies of twins (Bouchard et al., 1999; Kirk et al., 1999) and sociological studies of welfare, availability, and legal regulations [15] (state religions, etc.).

Koenig et al. (2005) report that the contribution of genes to variation in religiosity (called heritability) increases from 12% to 44% and the contribution of shared (family) effects decreases from 56% to 18% between adolescence and adulthood.[16] "

15 Nolan, P., &amp; Lenski, G. E. (2010). Human societies: Introduction to macrosociology. Boulder, CO: Paradigm Publisher.

16 L. B. Koenig, M. McGue, R. F. Krueger and T. J. Bouchard, Jr. (2005). Genetic and environmental influences on religiousness: findings for retrospective and current religiousness ratings. Journal of Personality, 73, 471-88

https://en.m.wikipedia.org/wiki/Religiosity#Genes_and_environment