A groundbreaking new study is challenging longstanding demographic wisdom by asserting that humanity’s current fertility rate is now too low to guarantee survival—even if average births per woman meet the historical “replacement” level. The research, led by a Japanese scientist and published in the journal PLOS One, argues that the global average of 2.1 children per woman simply isn’t enough. Instead, it suggests that a fertility rate of 2.7 is the true mark required to ensure humanity’s long-term prospects, a conclusion that carries serious implications for countries like Thailand, where the fertility rate is well below these thresholds.
For much of recent history, population experts and policymakers spoke anxiously about the risks of overpopulation. The global population soared from under 3 billion in 1960 to over 8 billion today, driven in part by high fertility rates in much of the post-war world. In response, family planning programs, wider access to contraception, and shifting social norms led to remarkable drops in fertility rates worldwide, from an average of 5.3 children per woman in the 1960s to just 2.3 in 2023 (Earth.com). This drop was long celebrated as a success story in development and environmental circles, particularly in densely populated Asian countries such as Thailand, where demographic transitions were especially rapid.
But the new study, conducted by researchers at Shizuoka University, warns that these gains may have inadvertently set humanity on a risky path. The current replacement rate of 2.1 assumes a “stable world”—one with consistently low child mortality, equal numbers of boys and girls, and a large, steady population. In mathematical models, this number keeps a population from shrinking or exploding. Yet, reality is far messier. Not everyone has children; some die young, and the randomness inherent in real-life birth and survival means that some family lines die out, even if the average number of children per woman appears “enough.” This random chance, known as demographic stochasticity, is often overlooked in traditional models.
To test these nuances, the Shizuoka University team created mathematical simulations that accounted for unpredictable variations in real-life populations. Using “branching process” models common in ecology, they tracked generational changes and concluded that unless the average number of children per woman reaches 2.7, the likelihood of family lines—and by extension, whole populations—disappearing climbs drastically. Notably, at 2.1, extinction through gradual attrition became the norm over centuries, barring a few exceptional cases. “Considering stochasticity in fertility and mortality rates, and sex ratios, a fertility rate higher than the standard replacement level is necessary to ensure sustainability of our population,” said a demographer quoted in the Earth.com report.
The impact of falling below the true replacement rate isn’t just academic. The study highlights that most family lineages in large countries will eventually vanish if this trend persists, eroding identity, heritage, and cultural memory. This loss isn’t dramatic extinction, but a “quiet fading away,” where surnames and traditions gradually disappear—a trend already observable in many societies grappling with aging populations and shrinking birth rates.
Globally, this trend is accelerating. As of 2023, two-thirds of the world’s people live in countries with fertility rates below the old replacement threshold of 2.1. For example, Japan’s fertility rate has fallen to 1.3, South Korea’s is now as low as 0.87, and the United States is at 1.66. Even in countries like France and Singapore, which offer generous incentives to encourage childbirth, results have been modest at best (The Bright Side News).
In Thailand, the National Statistical Office reported the fertility rate at just 1.3 in 2022 (World Bank), well below even the previously assumed replacement level. This demographic decline mirrors that of economic peers in East Asia, and raises profound questions about the future of Thai society, culture, and economy. Thailand’s aging population—a subject of worry for nearly two decades—brings increased social and economic pressures: fewer young people supporting growing ranks of elderly, rising public healthcare costs, and a potential loss of economic dynamism (Bangkok Post). The new research underscores the urgency of these challenges, suggesting that even aggressive pronatalist policies might not be enough unless they raise fertility rates above the 2.7 threshold.
The study’s analysis also presents a positive biological insight: populations with more female births have a better chance of persisting. In various species—including humans—stressful conditions (such as war or famine) have historically led to more girls being born, expanding the future pool of mothers and thus improving prospects for population survival. While not advocating for “social engineering,” the researchers note that a slight female bias in sex ratios at birth could be nature’s own subtle survival mechanism.
However, social and economic factors—especially in urbanized economies such as Thailand—remain formidable barriers. Educational attainment, delayed marriage, rising costs of living, limited access to affordable childcare, and changing gender roles all contribute to lower birth rates. Surveys among Thai urban middle classes routinely cite financial uncertainty, work-life balance, and housing as key reasons for having fewer children, despite increased government attention and policy incentives.
From a cultural perspective, Thailand’s extended family networks and traditions—historically a social safety net—are also under threat from declining fertility. The erosion of family lines could mean the loss of not only kinship but also language, rituals, and regional identities whose preservation depends on intergenerational transmission. This pattern is mirrored in the loss of global linguistic diversity, with at least 40% of the world’s approximately 6,700 languages predicted to disappear within a century, another drastic form of demographic extinction according to the study.
Future scenarios are concerning. The UN predicts the world’s population will peak around 2084 and then begin a slow but steady decline (Wikipedia). Without an increase in fertility rates, large economies like Japan and South Korea are expected to shrink by nearly a third per generation, with smaller countries like Thailand poised to face demographic crises sooner unless trends reverse rapidly. Policymakers are beginning to reconsider their population targets, with the new study suggesting that only a deliberate, multi-faceted approach—addressing economic, cultural, and gender equity issues—can hope to mitigate the risk of eventual extinction.
This recalibration of the replacement rate has specific implications for Thailand: it demands urgent national debate and innovative policies. Experts suggest that beyond just offering incentives for childbearing, governments need to create environments in which young Thais feel confident starting and raising families. This includes investing in affordable housing, quality childcare, parental leave, gender equality at work, and vibrant communities that support family life—policies already being experimented with in parts of Europe and East Asia, but with uneven success.
In conclusion, this research makes clear that the path forward is not just about staving off population decline but about preserving the continuation of Thai traditions, stories, and identities, and sustaining the vibrancy that has defined the nation for centuries. Policymakers, educators, and community leaders must work together to support families and create a Thailand where future generations are not just numbers, but active carriers of a living culture. For Thai readers and families, the take-home message is that the decision to have children now carries profound implications—not just for personal legacy, but for the collective resilience and richness of Thai society.
For those concerned about Thailand’s future, now is the time to engage in authentic public dialogues, support family-friendly reforms, and work collectively to raise awareness of the non-economic benefits of sustaining the nation’s diverse cultural heritage. Taking action today may ensure that future generations can carry Thailand’s stories and spirit forward in a world facing quiet, but profound, demographic change.
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