A report from the Pew Center is the latest to document America’s rapidly declining religiosity. Pew’s numbers show a 12-point decrease in the percentage of Americans calling themselves Christians between 2009 and 2019, while those describing themselves as atheists, agnostics, or “nothing in particular” have risen from 17% to 26%.
These findings are mirrored in the General Social Survey, which has been asking respondents about their religious affiliation since 1972.
The demographic surge of the religiously unaffiliated is a story of treatment effects triumphing over selection effects. A little context will help explain.
Natural selection seems to decidedly favor the religious. As the social psychologist Ara Norenzayan details in Big Gods (an excellent if at times slow book), religious societies, specifically those that follow omnipotent, moralizing “Big Gods,” have historically been able to outcompete others. To summarize Norenzayan’s findings, this is due to three factors, the first two of which are increased trust and greater social stability, both made possible by supernatural monitors (gods) that have allowed societies to scale by “building moral communities of strangers.”
In recent history, some societies (think Scandinavia and Japan) have been able to “kick away the ladder” of religion, replicating the monitoring effects of Big Gods through trusted civic institutions—police, courts, and others that allow for anonymous actors to cooperate in the same way religion used to. But there’s one other important advantage of religious societies that secular societies haven‘t been able to engineer: above-replacement fertility rates.
The religiously unaffiliated reproduce at notably lower rates—so much so that, even as I’m writing a blog post about their astronomical demographic growth in America, the Pew Center projects they will decline as a share of the global population, from 16% to 13% between 2010 and 2050.
Followers of Big Gods, especially those of fundamentalist branches of religion, tend to have more children. Note: this is mirrored by the liberal-conservative fertility gap, and both are fueled in part by divergent views on reproduction.
To give you a sloppy illustration, consider the graph below, which I constructed using national-level data from 55 countries that appear in the 2012 Win-Gallup International Global Index of Religiosity and Atheism and Gapminder total fertility rate data from the same year. Nearly every country with an above-replacement fertility rate has a majority-religious population by quite a large margin.
In a personal email quoted by Norenzayan in Big Gods, a colleague confides that despite reviewing all available data and case studies back to early Greece and India, he was unable to find a single example of a secular society maintaining a birth rate higher than two children per women for even a century. France, Germany, Japan, and quite a few other countries are trying—and failing—to address this problem with a variety of subsidies. Thus far, there is no secular substitute for religion’s fertility premium.
So with forces of nature solidly in support of religion, why is it rapidly losing ground across the rich world? It turns out there are countervailing secularizing forces that, it feels safe to say, have grown powerful enough to chip away at the natural demographic advantage of the religious. Unlike the selection effects that propel religiosity, these are treatment effects, meaning they’re driven by exposure to certain conditions. In addition to the aforementioned creation of secular civic institutions, those conditions include education, rising incomes, and the general removal of existential threat (of the “where is my food coming from” variety, anyway).
Notably, somewhere around 78% of all “religious nones” are “converts,” if you will, meaning they were born into a religion and ceased to identify with it over time.
While there is some observable increase of religious unaffiliation within generations, the flight from religiosity is largely driven by generational replacement. In other words, it’s not like longtime worshipers have suddenly lost faith en masse—it’s that their grandchildren aren’t interested, and older generations are losing ground demographically. This fits the pattern of other paradigmatic shifts in public opinion, and to me, suggests there’s an element of timing involved, that conditional secularization may be contingent upon one’s formative environment.
The question that remains to be seen is whether or not the secularizing rich world can support itself. Our economies, infrastructure, and social welfare systems are reliant on people, and a large population that doesn’t reproduce will age with dramatic consequences (see Baby Boomers). In the long run, this is probably one of the most consequential political issues out there.