Introduction
Advanced countries have experienced prolonged below-replacement fertility, leading to population aging and, in many cases, decline [1,2]. A key consequence is the contraction of childbearing-age cohorts, raising the question of whether restoring fertility to replacement level can stabilize population size [3].
Methods
This study adopts a theoretical cohort–component projection approach grounded in stable population theory and the concept of population momentum [3,4]. Starting from low-fertility-age structures, projections assume an immediate shift to replacement fertility, constant mortality, and zero migration. Population trajectories are assessed through cohort evolution, focusing on reproductive-age groups and momentum effects [5].
Results
The analysis demonstrates that populations shaped by sustained below-replacement fertility exhibit negative population momentum [3]. While replacement-level fertility slows decline, it does not stabilize population size. The extent of decline depends on past fertility suppression, leading to smaller reproductive cohorts and increased population aging [6].
Conclusions
The findings indicate that fertility restoration alone is insufficient to reverse population decline in advanced low-fertility societies. Age structure and demographic inertia strongly shape outcomes [3,4]. Policies must address long-term aging and structural decline beyond fertility measures [2].
References:
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- Spears, D.; Vyas, S.; Weston, G.; Geruso, M. Long-Term Population Projections: Scenarios of Low or Rebounding Fertility. PLoS ONE 2024, 19, e0298190.
- Sobotka, T. Post-Transitional Fertility: Childbearing Postponement and Low Fertility. Popul. Dev. Rev. 2017, 43, 641–680.
