Is the World Entering an Era of Permanent Low Fertility and Depopulation?

Geruso and Spears (2026) ask whether persistently low global fertility is likely to continue and potentially lead to long-term population decline. They analyze United Nations fertility data, historical birth trends, and cohort fertility data from sources like the Human Fertility Database and Demographic and Health Surveys. They find that global fertility has fallen from about 4.85 in 1950 to roughly 2.25 today, with 67% of the world living below replacement levels. They show that no country has sustained a return to replacement fertility once below it, and that most fertility decline (about 63%) reflects smaller family sizes rather than rising childlessness.

Why This Article Was Selected for The Policy Scientist

This article addresses a policy issue with unusually broad implications: whether sustained sub-replacement fertility will reshape global population trajectories for generations. The topic is timely given that most of the world now lives below replacement fertility, raising questions about labor markets, fiscal sustainability, and long-run economic growth. Geruso and Spears have written extensively in this area, and this piece consolidates that agenda into a clear assessment of persistence. It contributes by integrating long-run demographic data with cohort analysis, extending foundational work on demographic transition and fertility decline. The data—UN estimates and Human Fertility Database—are high quality and broadly generalizable across contexts. The methods are primarily descriptive and comparative rather than causal; future work using quasi-experimental or experimental designs would strengthen inference.

Full Citation and Link to Article

Geruso, M., & Spears, D. (2026). The likelihood of persistently low global fertility. Journal of Economic Perspectives, 40(1), 3–26. https://doi.org/10.1257/jep.20251463 

Central Research Question

Geruso and Spears (2026) investigate whether the recent and widespread decline in global fertility is likely to persist and, if so, whether it will result in sustained global depopulation. The core question is not simply whether fertility has fallen—this is well established—but whether existing demographic, economic, and social dynamics make a reversal to replacement-level fertility plausible. The authors frame the issue in terms of long-run population trajectories, emphasizing the distinction between temporary fluctuations in fertility and durable shifts that would alter generational replacement. Implicit in this inquiry is a second-order question: whether existing policy tools or social changes have demonstrated the capacity to meaningfully increase completed fertility, rather than merely shifting the timing of births.

Previous Literature

The article builds on a long tradition of demographic and economic research on fertility transitions, including foundational work by Notestein (1945) on demographic transition theory and more recent contributions synthesized in the economics of fertility literature. The authors situate their analysis within a body of research that documents sustained declines in fertility across both developed and developing contexts, as well as scholarship examining the determinants of family size, including income, mortality, female labor force participation, and social norms. They engage selectively with studies of pro-natal policy interventions and historical fertility reversals, such as the mid-twentieth-century Baby Boom, while noting the absence of a clear, consensus explanation for such episodes. Their contribution is not to introduce a new causal mechanism, but to integrate existing empirical patterns—particularly the divergence between period and cohort fertility—and to assess the plausibility of reversal in light of that evidence. In doing so, they extend recent work, including their own, on childlessness and parity progression as components of fertility decline.

Data

The empirical foundation of the article relies on multiple high-quality, internationally recognized data sources. The authors use United Nations World Population Prospects data to track global total fertility rates (TFR) over time, capturing broad cross-national and temporal trends. They supplement this with data from the Human Fertility Database, which provides detailed cohort-based fertility measures for advanced economies, allowing for analysis of completed cohort fertility (CCF). Additional micro-level evidence is drawn from Demographic and Health Surveys, particularly for India, enabling examination of fertility patterns in a large, emerging, below-replacement population. The combination of these datasets allows the authors to compare period-based and cohort-based fertility measures, assess heterogeneity across regions, and decompose fertility trends into childlessness and parity among parents. The breadth and consistency of these data sources enhance the external validity of the findings, though limitations remain for low-income contexts where long-run cohort data are less complete.

Methods

The authors employ a descriptive and comparative empirical strategy rather than a causal identification framework. Their analysis emphasizes demographic accounting, graphical trend analysis, and decomposition techniques. A central methodological distinction is between period total fertility rates and completed cohort fertility, with the latter providing a more accurate measure of long-run reproductive behavior. To disentangle the drivers of fertility decline, the authors implement a Kitagawa-style decomposition, separating changes attributable to increased childlessness from those due to reduced fertility among women who have children. They also examine cross-country and within-country variation, including district-level comparisons in India, to assess the relative contribution of these components. The article further evaluates historical policy interventions, such as Romania’s Decree 770, to illustrate the divergence between short-run period effects and long-run cohort outcomes. While these approaches yield robust descriptive insights, the absence of quasi-experimental or randomized designs limits the ability to draw strong causal inferences about the effectiveness of specific policies in altering lifetime fertility.

Findings/Size Effects

The authors document a sustained and widespread decline in global fertility, with the total fertility rate falling from approximately 4.85 in 1950 to about 2.25 in 2023. They show that 67 percent of the world’s population now resides in countries with below-replacement fertility. Projections illustrate that if fertility stabilizes at levels such as 1.5, generational population size would decline by roughly 44 percent over two generations. Cohort-based evidence reinforces these trends: once fertility falls below replacement, no country in the available data has experienced a durable return to replacement-level fertility. In decomposing fertility decline, the authors find that approximately 63 percent of the reduction in completed cohort fertility is attributable to lower fertility among parents, while about 37 percent is due to increased childlessness. This pattern is even more pronounced in contexts such as India, where nearly all variation in fertility is explained by differences in births among the parous. The analysis of policy interventions indicates that many pro-natal policies produce only modest or temporary increases in period fertility, with limited evidence of sustained effects on completed fertility. The Romanian case illustrates that even large, coercive interventions can generate sharp short-term increases in birth rates without significantly altering lifetime fertility outcomes.

Conclusion

The article concludes that persistently low global fertility is a plausible and likely outcome given current trends and historical evidence. The absence of sustained reversals to replacement-level fertility, combined with limited evidence on the effectiveness of policy interventions, suggests that long-term population decline is a credible scenario. The authors emphasize that existing policy tools—primarily financial incentives and family support measures—have not demonstrated the capacity to substantially increase completed fertility. They also highlight the conceptual and empirical challenges in evaluating fertility policies, particularly the distinction between timing effects and lifetime reproductive behavior. While acknowledging the possibility of future social or institutional changes that could alter fertility patterns, the authors find no empirical basis for expecting such a reversal under current conditions. The analysis underscores the need for further research that can more precisely identify causal mechanisms and evaluate interventions capable of influencing long-run fertility decisions.