For decades, demographers told a tidy story: as countries got richer, women got more educated, and birth rates settled gently somewhere near the replacement level of 2.1 children per woman. That story is now falling apart. According to a Financial Times analysis by John Burn-Murdoch, the average number of children born per woman has dropped below 2.1 in 195 countries, meaning most of humanity now lives in places where the next generation will be smaller than the last — barring immigration.
What makes the new data so unsettling is not just the depth of the decline but its breadth and pace. South Korea's fertility rate has collapsed so fast that UN projections from just five years ago overestimated 2025 births by roughly 50%. Mexico's 2025 figure already sits below where the United States was a decade ago. And the trend is no longer confined to rich nations: Tunisia, Iran and Sri Lanka have all slipped below replacement, alongside high-income countries in Northern Europe and East Asia. Almost everywhere economists look, ultra-low and rapidly falling birth rates show up — in wealthy countries, but also in middle-income ones where, on the old theory, families should still be growing.
Because economic explanations cannot account for a slump that spans such different societies, researchers are widening their search. One striking pattern: across the US, UK, Australia, Indonesia, Mexico and others, birth-rate charts bend sharply downward at roughly the moment smartphones take off. Time spent socialising in person has fallen steeply in the US, UK and South Korea since the early 2010s, and the share of under-35s in long-term relationships — especially those without a college degree — has dropped along with it. Melissa Kearney, an economist at the University of Notre Dame, has argued that the mirror image of a smartphone-usage chart looks suspiciously like a fertility chart. The argument is not that phones reduce biological fertility, but that they crowd out the everyday socialising that historically led to partnerships, marriages and, eventually, children.
But here's the catch: governments have tried the obvious fixes and mostly failed. Pronatalist cash incentives in France and Poland produced only short-lived bumps. South Korea has spent enormous sums and watched its total fertility rate fall below 1 — a level at which a population roughly halves every 60 years. If the problem were purely about affordability, money would work better than it has. That is why a growing camp of demographers now frames fertility less as a household budget decision and more as a behavioural ecosystem: pull out one input (in-person time, partnering, home ownership), and the output (children) shrinks even when wages rise.
The stakes are enormous. Shrinking populations mean fewer workers supporting more retirees, slower innovation (Japan's three-decade stagnation is the cautionary tale), and political battles over immigration as the only fast lever. The compounding effect is brutal: each year of delayed partnership shaves a little off lifetime fertility, and fifteen years of small delays add up to a demographic cliff. Peak humanity, long expected near 10 billion, may now arrive sooner — and from there, decline. Whether the cause is cultural, digital, or some tangle of both, the world is heading into territory no modern society has navigated before, and the policies built for an ever-growing population will have to be rebuilt for one that, quietly, has started to shrink.
Across nearly every country on Earth, people are having far fewer babies than demographers predicted just a decade ago — and the usual economic explanations no longer fit the data.
In 195 countries, the average number of children born per woman has fallen below 2.1 — the so-called replacement rate needed to keep a population stable without immigration. South Korea's fertility rate has collapsed so fast that the FT estimates a 50% overestimate just five years ago in UN projections; Mexico's 2025 rate sits below that of the US a decade earlier.
What's strange is the breadth. High-income, middle-income and low-income countries are all sliding at once, including places like Tunisia, Iran and Sri Lanka. That universality is why researchers are now looking past purely economic explanations and toward something cultural — and digital.
Forget the old story that babies are just an affordability problem. The article treats fertility more like a behavioural ecosystem — when the inputs (socialising, dating, partnering, home-owning) shrink, the output (kids) shrinks too.
If you're 16 today, this is the world you'll inherit: fewer workers funding more retirees, strained pensions and healthcare, slower innovation (Japan's stagnation since the 1990s is the warning shot), and political fights about immigration as the only quick fix. It also reframes the smartphone debate you've already heard about mental health — the same device may be reshaping who pairs up, when, and whether they ever have kids.
Demographers used to assume population would keep climbing toward 10 billion. The new data suggests peak humanity may arrive sooner — and from there, decline. Watch for second-order effects: housing markets recalibrating, universities consolidating, AI being pushed as a substitute for missing workers, and a wave of policy experiments (from Hungary to South Korea) trying to engineer a baby boom that economics alone can't deliver.