Dan poses an interesting question:
Have you looked at they effect of religiosity on fertility when intelligence is held constant?
This strikes me as a very important question. It is well-established, I think, that religiosity is positively correlated with fertility. But what is the specific impact of religiosity on the fertility of the really smarts, averages and dumb specifically?The significance of intelligence in predicting fecundity vanishes when education is controlled for. In the US, high IQ people have fewer children than those of more modest intelligence do, but it's a consequence of the fact that more intelligent people spend more time in school than less intelligent people do. Smart people who don't go to college have nearly the same fertility rates as dull people who don't, and low IQ folks who pursue post-secondary education don't have more children than high IQ people who do so end up having.
What, though, of the relationship between fecundity and religiosity when educational attainment is taken into account? Before delving into the data, it needs to be noted that the measure of religiosity I'm employing is frequency of attendance at a house of worship, which doesn't necessarily shed light on how fervently or literally respondents adhere to the precepts of their religions or the levels of credulity they display towards their faiths.
Marx's famous labeling of religion as the "opiate of the masses" aside, as Charles Murray points out in Coming Apart, the more intelligent and well-educated people are, the more likely they are to go to church (an assertion that the GSS affirms). At first blush, this may appear to present a conundrum: Religious worship and educational attainment are positively correlated, religious worship and fertility rates are also positively correlated, but educational attainment and fertility rates are negatively correlated. For those of some acquaintance with statistics, of course, we'd only necessarily be trying to square a circle here if all three of the aforementioned correlations were perfect, which they are not.
The following graph shows how religiosity and fecundity are related among those with similar levels of educational attainment. For purposes of contemporary relevance, avoiding racial confounding, and allowing time for family formation to occur, data are from 1990 onward, the respondent pool is limited to whites, and those under the age of 35 are excluded:
At each level of education, the trend is one of religiosity and fecundity moving in the same direction, even as fecundity drops among all cohorts as educational attainment increases. The only irreligious people out-procreating the Russ Johnsons and Inductivists of the world are high school dropouts.
From eyeballing the graph, it is difficult to ascertain whether education or religiosity is the stronger predictor of fertility rates. That's because they're about equally predictive. When it comes to predicting fecundity, the OLS standardized regression coefficients (with IQ included for purposes of reiteration) are as follows:
Educational attainment -- (.19)*
Worship attendance -- .15*
Wordsum score -- .00
* Statistically significant
As far as I'm aware, it appears that educational attainment and religiosity are the two strongest predictors of fecundity in the US (and the rest of the Western world?) today.
GSS variables used: CHILDS, EDUC(0-11)(12)(13-15)(16-17)(18-20), YEAR(1990-2010), BORN(1), RACE(1), AGE(35-89), WORDSUM, ATTEND(0)(1-3)(4-6)(7-8)6370726
++Addition++A reader asks:
What happens to the relationship between church attendance and fertility when you hold wordsum constant instead of education?
That would give the clearest picture of all as to whether religious attendance is eugenic...Here's the graph:
It looks pretty similar to what we get with the education graph in the body of the post, but the association between fecundity and and religiosity is less pronounced, as the regression coefficients mentioned above predict to be the case.