Why Birthrates (And Not Beliefs) Are Shaping Global Faith
(ANALYSIS) We’ve been telling the story wrong. For years, the dominant narrative in the West has gone something like this: religion is fading, science is rising, and people everywhere are waking up from the fog of faith. A secular world is not only inevitable — it’s already on its way.
Look past the podcasts and opinion polls, and a very different picture emerges. If anything, the global religious map isn’t flattening. It’s tilting — dramatically. And it’s not belief that’s driving the change. It's birth rates.
Despite the sense that organized religion is withering, global numbers don’t reflect that. By 2050, Christianity will still be the world’s largest religion. Islam will be a very close second. In raw numbers, the unaffiliated — atheists, agnostics and “nones” — will grow in places like the U.S. and Europe, but globally, they’re not keeping up.
Not because their ideas are weaker, but because their fertility rates are. Globally, religious women tend to have more children than secular women. In countries with the highest fertility rates, belief in God is not just a cultural artifact. Rather, it’s a living, breathing part of daily life.
This is not a judgment. It’s a demographic reality. Faith isn’t being debated out of existence; it’s being outbred. Take Sub-Saharan Africa. The region is expected to add over a billion people by 2050. These are not children being raised in secular households with Spotify playlists of Sam Harris lectures. These are children born into Muslim and Christian homes, where belief in God, prayer and religious identity remain central. Nigeria alone is projected to surpass the United States in population by mid-century and is already home to some of the fastest-growing Christian movements in the world.
This single region will account for the bulk of global Christian growth in the next 25 years, transforming the face of Christianity itself. Forget the aging, mainline Protestant churches of the American Midwest. Tomorrow’s Christians will be Nigerian, Congolese, Ugandan — young, devout and growing.
Meanwhile, Europe’s population is in slow retreat. It will lose roughly 45 million people by mid-century. Aging populations, low fertility, and cultural fatigue have accelerated secularization. But this decline isn’t happening in a vacuum. It coincides with the steady growth of Islam across the continent, driven less by conversion than by immigration and birthrate gaps. French sociologists have been ringing alarm bells for years, not over a wave of sudden religious awakenings, but over the math: Muslim families in Europe tend to have more children.
Secular Europeans tend to have fewer, or none at all. This simple arithmetic is already reshaping neighborhoods, schools, and political discourse — especially in countries like France, Germany and Sweden.
In Iran, birth rates are dropping fast, and alongside them, religious intensity has waned. In Afghanistan, where families are still large, religiosity holds strong. Across the board, the pattern is clear: the more children being raised in a religious environment, the more that faith sustains itself over time. Religion, it turns out, doesn’t need to win intellectual debates — it just needs to survive from one generation to the next. Even religions that seem to be fading fast tell a deeper story. Buddhism, for instance, is in demographic decline.
In China, Japan, South Korea and Thailand, low fertility and aging populations are reducing the number of self-identified Buddhists. But again, this isn’t about philosophical rejection. It’s not a wave of people leaving temples for rationalist Reddit threads. It’s simple arithmetic: fewer Buddhists are being born, and those who are born aren’t having children of their own.
There are exceptions to the birthrate rule, but they’re few and far between. Religious conversion, often cited as a powerful force in shifting belief systems, turns out to have a surprisingly limited global impact. People don’t switch religions at scale. In the United States, where conversion rates are more dynamic, we’ve seen a noticeable rise in the “nones” — a mix of atheists, agnostics, and the spiritually indifferent. But even here, it’s not all gain: Many of the unaffiliated aren’t raising their children with a strong secular identity, leaving future generations open to spiritual exploration — or simply less anchored altogether.
Globally, religious populations are expanding while secular ones plateau. The future belongs to those who show up, and in demographic terms, that means those who have children.
Even “folk religions,” often ignored in these conversations, are holding their ground. In Vietnam and parts of East Asia, ancestral worship and local spiritual practices remain strong, not because of aggressive outreach or ideological persuasion, but because they are woven into family life and passed down organically. Their survival isn't about belief in the abstract. It’s about community, continuity, and childbirth.
In the United States, a very different trend offers a mirror image. Megachurches, long mocked for their theatricality and market-savvy theology, have proven remarkably durable. They operate like businesses — slick branding, customer retention strategies, and charismatic CEOs on stage every Sunday — but the growth is real. These churches often attract large, young families.
It’s tempting to read religious trends as reflections of intellectual history, for example, who’s winning the argument about God? But that’s not how history is playing out. The reality is far more biological. The future of religion is being written in maternity wards.
This may be unsettling to those who’ve invested in the idea of a steadily secularizing globe, but the numbers don’t lie. Ideas matter, yes. But people carry ideas. And in the long run, the groups that reproduce tend to shape the narrative. If religion continues to dominate global culture through the 21st century, it won’t be because it won a war of ideas. It’ll be because believers have more babies.
John Mac Ghlionn is a researcher and essayist. He covers psychology and social relations. His writing has appeared in places such as UnHerd, The US Sun and The Spectator World.