Below I made a reference to the heritability of religiosity. In a chat with Christer Chris that the heritability for religiosity was 0.5, and he was surprised at the result. I decided to double-check, and here is the latest paper:
Estimates of the degree of genetic and environmental influences on religiousness have varied widely. This variation may, in part, be due to age differences in the samples under study. To investigate the heritability of religiousness and possible age changes in this estimate, both current and retrospective religiousness were assessed by self-report in a sample of adult male twins (169 MZ pairs and 104 DZ pairs, mean age of 33 years). Retrospective reports of religiousness showed little correlation difference between MZ (r=.69) and DZ (r=.59) twins. Reports of current religiousness, however, did show larger MZ (r=.62) than DZ (r=.42) similarity. Biometric analysis of the two religiousness ratings revealed that genetic factors were significantly weaker (12% vs. 44%) and shared environmental factors were significantly stronger (56% vs. 18%) in adolescence compared to adulthood. Analysis of internal and external religiousness subscales of the total score revealed similar results. These findings support the hypothesis that the heritability of religiousness increases from adolescence to adulthood.
In Bouchard's "twins raised apart" studies he found about a 0.5 heritability. In any case, remember what heritability is: The proportion of population level variance attributable to genetic variance. Why does environmental variance become so much less important once you leave adolescence? Take a guess....
Psalms 137:9 Happy shall he be, that taketh and dasheth thy little ones against the stones.
Do you know how those studies are defining "religiosity"? What exactly are they measuring and counting as religiosity before they ever set about trying to estimate its heritability? I'm a sociologist and I work in religion as a sub-specialty, so this is a really important question. Are they measuring the subjective "qualia" of religious experience, rates of practice, affiliation, etc.?
I think the correct reference for your apocalyptic hypograph is Psalms 137:9.
Why does environmental variance become so much less important once you leave adolescence? Take a guess....
Well it's measured environmental variance. Home environments typically. When we're younger our parents choose much more of our environment directly and indirectly (e.g. trying to influence which peer groups an adolescent hangs with by choosing neighborhood and simple parental pressure). As we grow older we're more able to choose our own environments - what we read, watch, whether we go to church, and who are friends are.
Similar dynamic as with IQ appearing to be more heritable when it's measured in older individuals. The somewhat naturally smarter are more likely to keep going to the "brain gym" in various ways, since they enjoy working out that muscle more than others, thus magnifying differences.
Do you know how those studies are defining "religiosity"
Good point. In our culture someone who doesn't go to church and has no regrets about that, but thinks there's sometime to astrology or even 'crystals' is likely to often get counted as 'not very religious', and in fact might well self report that way.
It's almost a dead certainty that a passionate follower of e.g. Greenpeace, who's also not done much if any research into the pros and cons of the environmental causes in question that they've come to feel passionately about, won't be thought thereby to have a 'religious' disposition. While I'd argue that such a person does have a strong natural desire for group solidarity and dogma - certainly a side of nearly all religions. (The marine biologist who supports a number of Greenpeace causes is another thing entirely and need not thereby be thought religious at all. The question is the degree of rationality behind the choice and identification.)
So the next question is, "Is the heritability the same in all cultures?" If selection is strong in some places (e.g., "Stone the non-believers!!!" The heritability might go down (i.e., only the truly religious alleles persist).