Pew continues to do good research on religious growth trends. The indication is that Islam is growing and will continue to grow rapidly through 2060, although it is not expected to overtake Christianity in terms of world population share.
You may have heard that eastern religion, such as Buddhism, and the religiously unaffiliated are on the up-and-up. You heard wrong. Over the period of prediction those populations are expected to decline as a share of world population. The world will become more educated, wealthier, healthier, and more Christian. These things go well together, contra the incorrect popular notion that atheism and education or intelligence move together.
This would make Christianity a comparatively more durable institution. Durable institutions are efficient organizations, and efficiency is achieved in a competitive market largely due to constitution of superior technology. Technology is isomorphic to truth. Being able to build a better plane, for example, holding constant resource constraints, is simply a matter of knowing a bit more physics, or a bit more objective truth.
My view is that the comparative durability of a worldview is evidence of a net higher truth value of that worldview, or belief system. Truth value might be defined as the sum of the market value of each belief in a belief system, plus any interaction effects. Productivity gains from a workplace comprised of relatively fewer lies and liars would be one way to realize gains from a worldview on a market. Then there are also more trivial routes including supply and demand for religious services and books. By using the generic notion of a belief system, we can similarly compare gains from physics, biology, psychology, and various religions.
In the current news we hear about a resurgence of Roman Catholic sexual abuse cases. Surely sexual abuse isn’t a quality of an economically efficient or morally desirable institution. On an economic view alone, billions have been spent on court cases and cover ups. How could any organization expect to grow market share while enduring such massive direct costs, plus reputation and other associated costs, when faced with competitors without such issues? In addition there may be inefficiency built in to the structure of large, hierarchical institutions and organizations.
The answer is that the Roman Catholic church hasn’t been growing. Christianity has been becoming less Roman Catholic, indeed less like any of the mainstream denominations, and more Evangelical, non-denominational, and Protestant. These denominations tend away from hierarchical and toward distributed polity, consistent with certain economic theories about the efficiency of markets and crowds over hierarchies as an optimal structure.
So the theory that correct or optimal information and beliefs flourish or emerge in relatively free markets over time is not falsified by the durability of Christianity. Instead, the truth and effectiveness of certain Christian kinds are proved, and Roman Catholic-like practices (RC, Anglican, Episcopalian, etc) are shown to be comparatively non-robust. This may be seen as evidence of those denominations holding comparatively inferior theology and/or practice.
This indicates a trend hidden in the Pew religion data. Christianity is growing, but it is also improving. Likewise, what sort of Islam is growing? If the story about institutional durability is to be believed then Islam is set to stagnate. Economic incentives would tend to foster liberal Islam, because liberal Islam is relatively peaceful and peace moves with strong markets. However, liberal Islam is not theologically tenable. These incentives move in opposite directions, driving stagnation. Western Islam is certainly becoming more liberal, but the trend is less clear globally.
In regions where violent Islam is already institutionalized, those regions have relatively weak free market incentives and therefore incentives to move away from a belief system like Islam will be reduced. Notice that the growth in Islam which Pew predicts is mostly explained by population growth effects, not conversion. Wealth effects in general work to reduce conflict, however, so there is some possibility that enriching third world countries, which is driving up Muslim population growth through better healthcare, will also facilitate broader market conditions enabling free flow of information and so on, causing Islam to liberalize or altogether deteriorate at faster-than-expected rates.
Perhaps Pew is already modelling the endogeneity of wealth and nonviolence, albeit implicitly, through their modelling of population growth. We know higher wealth and literacy drive down population growth and Pew is modeling high-but-marginally-decreasing population growth for Muslims already. In order to argue lower-than-predicted population share for Islam we would need to find a threshold effect or a higher interaction effect for literacy on Muslim birth or deconversion compared to literacy on other religions, but I haven’t seen any data like that. It remains speculative.
To the contrary, it seems Western Muslims in the US are leaving Islam at nearly the same rate as Christians are leaving Christianity. However, if Christianity is able to improve as an institution through the purging of weaker denominations, practices, and theological variants, it may gain a comparative advantage.
(*Sarcastic voice*) Who knows? Maybe the longer term success of Christianity does relate to minutia like self-identified Christians ceasing sexual abuse.
- May 2013, Pew, Among Muslims, Internet Use Goes Hand-in-Hand With More Open Views Toward Western Culture
- January 2018, Pew, The share of Americans who leave Islam is offset by those who become Muslim