In their piece, published in Nature Human Behaviour, IIASA Distinguished Emeritus Research Scholar Wolfgang Lutz and IIASA Senior Researcher Guillaume Marois , who is also an associate professor at the Asian Demographic Research Institute of the Shanghai University, respond to political and public concern over declining birth rates in highly developed countries. While low fertility is increasingly framed as a crisis, associated with population ageing, labor shortages, and fiscal pressure, the authors argue that this narrative is based on outdated assumptions that no longer reflect current demographic realities.A central motivation for the paper was the widespread belief based on earlier studies that fertility would recover as human development continues. However, using the most recent data up to 2023, the authors demonstrate that this pattern has reversed. Today, the global cross-sectional relationship is clearly negative: the higher a country's Human Development Index, the lower its fertility tends to be.
"This finding came as a surprise to much of the demographic community," says Marois. "Even countries once considered models for balancing work and family life, such as the Nordics, have experienced unexpectedly steep fertility declines. The idea that development alone will bring fertility back up simply doesn't hold anymore."
The commentary also questions the normative status of replacement-level fertility, often defined as 2.1 children per woman. This benchmark, the authors argue, is an artificial construct that only leads to long-term population stability under unrealistic assumptions, notably the absence of further mortality decline. More importantly, population stability does not automatically translate into economic or social wellbeing.
Instead, the authors emphasize that economic sustainability depends more on population structure than on population size. Higher levels of education, increased labor force participation, and rising productivity can offset – and even outweigh – the effects of having fewer births. Lower fertility can enable greater investment per child, strengthening human capital and innovation while reducing dependency burdens over the coming decades.
The policy implications are clear. While pro-natalist measures can improve family wellbeing, increasing fertility should not be their main objective, as their impact on fertility is typically modest and higher fertility does not necessarily improve economic wellbeing. Governments should instead adapt social security, labor market, and pension systems to the reality of sustained low fertility, while strengthening investments in education and productivity. This shift is particularly relevant for countries such as South Korea, China, and Japan, which currently record some of the world's lowest fertility rates and face especially intense political pressure to raise birth numbers.
"Our message is not that low fertility is inherently good or bad," concludes Lutz. "There is no single 'ideal' fertility level that guarantees prosperity. Instead of trying to push birth rates back to an arbitrary target, governments should focus on adapting social security systems to the changing demographic realities and invest strongly in education and productivity. Under those conditions, societies can thrive even with fewer births."
Reference
Marois, G., Lutz, W. (2026). Low fertility may persist and could be good for the economy. Nature Human Behaviour DOI: 10.1038/s41562-026-02423-6
