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Miguel Jorge
WriterJournalist. I've spent more than half of my life writing about technology, science, and culture. Before landing here, I worked at Telefónica, Prisa, Globus Comunicación, Hipertextual, and Gizmodo. I'm part of Webedia's cross-section team.
Karen Alfaro
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A group of researchers in Japan studied how many children per woman would be needed to “avoid extinction”—not in terms of a civilizational apocalypse, but to prevent the statistical disappearance of lineages over time. They found two things: the previously assumed number was too low, and a large portion of the global population falls short.
Beyond the threshold. For decades, the magic number for maintaining a stable population has been 2.1. This is the average number of children per woman believed necessary to ensure generational replacement and prevent decline.
However, a new study warns that this threshold is outdated and insufficient. According to Japanese researchers, the actual fertility level needed to ensure the long-term survival of a population isn’t 2.1, but 2.7 children per woman.
Why? Because the traditional calculation doesn’t account for stochastic variability—randomness in factors such as individual fertility, mortality, sex ratios at birth, and the likelihood that some people never have children.
By including these real-world fluctuations in population models (via the Galton-Watson model), the authors concluded that a higher rate is necessary to prevent the gradual extinction of family lineages in future generations, especially in societies with persistently low birthrates.
Warning ignored. The finding is particularly alarming because, at the time of writing, two-thirds of the world’s population lives in countries with fertility rates below the old 2.1 benchmark and far below the new 2.7 estimate. Among the most affected—many of them highly developed—are South Korea (0.87), Italy (1.29), Japan (1.30), Canada (1.47), Germany (1.53), the UK (1.57), France (1.79), and the U.S., with only 1.66 children per woman.
These persistently low rates mean nearly all family lines in these countries are statistically on track to disappear over time. The study notes that a slight female-birth bias (a higher proportion of girls) could slightly reduce the risk by boosting future reproductive potential. Still, that alone can’t offset a chronically low birthrate.
Total fertility rate map.
Pronatalists. This insight reinforces concerns raised by certain pronatalist groups. One of the most visible figures is Tesla CEO Elon Musk, who has repeatedly warned that low birthrates will “end civilization” and whose large number of children (at least 11 known) is often framed as a personal response to this fear.
Pronatalists argue that raising the birthrate is an existential priority. However, the broader population doesn’t appear to share that urgency.
United Nations population projections by region, shown on a logarithmic vertical axis representing millions of people.
Social realism. According to Fortune, a Population Connection survey earlier this year found that most people don’t view the low birthrate as a critical problem.
Only 15% saw it as a top global challenge, while 45% expressed greater concern about overpopulation, fearing children would be born into poverty or a resource-depleted world.
More perceptions. A separate poll by Yahoo News and YouGov found only 8% of Americans were “very concerned” about the declining birthrate, and just 32% showed some concern.
Most people who have few or no children cite practical reasons: a lack of institutional support, high living and child-rearing costs, and the belief that today’s world isn’t suited for large families. There’s also a growing gap between expert projections and public priorities.
What will happen then? The Japanese researchers’ warning is clear: Without a course correction, demographic extinction will unfold slowly but inevitably across many regions.
While “extinction” sounds apocalyptic, scientists emphasize it refers not to humanity’s sudden disappearance but to the gradual erosion of family and cultural continuity. Future generations may become smaller, more isolated and, in some cases, nonexistent. From this angle, reproduction hinges more than ever on social, economic, and environmental conditions. The 2.7 figure may seem more like a demographic utopia than a realistic goal. We’re unlikely to face extinction in the short term—at least not due to fertility—but the study draws attention to a population decline that many regions are already experiencing.
Images | Joseph Chan (Unsplash) | Korakys | United Nations
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