Psychologist, University of British Columbia; Author, Big Gods: How Religion Transformed Cooperation and Conflict

Theodiversity is to religion what biodiversity is to life.

There are, by some accounts, more than 10,000 religious traditions in the world. Every day, somewhere in the world, a new religious movement is in the making.

But this theodiversity—a term I borrow from Toby Lester—is not evenly distributed in human populations anymore than biodiversity is evenly distributed on the planet. The reasons for this aren’t very well understood, but the overwhelming majority of religious movements throughout history are failed social experiments. Most never take hold, and of those that do, don’t last for very long—not even for a few decades. Of those that last for a while, most stay small.

Then there are the “world religions.” Christianity, Hinduism, and Islam especially, have been growing at a brisk pace. Buddhism is much smaller and not growing much, but still a sizable presence on the world stage.

We are at a point in time when just a few religious traditions have gone global, making up the vast majority of believers in the world.

This fact is detailed in a landmark Pew Research Center report, released on April 2, 2015. It’s the most comprehensive and empirically derived set of projections based on data, age, fertility, mortality, migration, and religious conversion/de-conversion for multiple religious groups around the world. Barring unforeseen shocks, if current demographic and social trends keep up, by 2050:

  • Possibly for the first time in history, there will be as many Muslims as Christians in the world. Together, these two faiths will represent more than 60 percent of the world’s projected population of 9.5 billion.
  • 40 percent of Christians in the world will live in sub-Saharan Africa (the region that will have the largest share of Christians), compared to 15 percent living in Europe. This means that the epicenter of Christianity will finally shift from Europe to Africa.
  • India, while maintaining a Hindu majority, will have the largest Muslim population in the world, surpassing Indonesia and Pakistan.
  • All the folk religions of the world combined will comprise less than 5 percent of the world’s population.
  • 1.3 billion people, or 13.5 percent of the world’s population in 2050, will be non-religious.

One might think that religious denominations that have adapted to secular modernity the best are the ones that are thriving the most. But the evidence gleaned from the Pew report and other studies points in the exactly opposing direction. Moderate denominations are falling behind in the cultural marketplace. They are the losers caught between secular modernity and the fundamentalist strains of all major world religions, which are gaining steam as a result of conversion, higher fertility rates, or both.

There are different types, shades, and intensities of disbelief. That’s why the non-religious are another big ingredient of the world’s astonishing and dynamically changing theodiversity. Combined, they would be the fourth largest “world religion.” There are the atheists, but many nonbelievers instead are apatheists, who are indifferent towards but not opposed to religions. And there is the rising demographic tide of people who see themselves as “spiritual but not religious.” This do-it-yourself, custom-made spirituality is filling the void that the retreat of organized religion is leaving behind in the secularizing countries. You can find it in yoga studios, meditation centers, the holistic health movement, and eco-spirituality.

Theodiversity once was the exclusive subject matter of the humanities. But it is now a focal point of a budding science-humanities collaboration. The religious diversification of humankind in historical time poses fascinating questions and challenges for the new science of cultural evolution. Also, these are times of renewed anxieties about real or imagined cultural conflict between religions, and between religions and secular modernity. This is why quantifiable, evidence-based, and nuanced understanding of the complexities of theodiversity are important now more than ever.