National Bureau of Economic Research, Cambridge, MA, USA.
Population Wellbeing Initiative, The University of Texas at Austin, Austin, TX, USA.
Demography. 2022 Dec 1;59(6):2003-2012. doi: 10.1215/00703370-10290429.
All leading long-term global population projections agree on continuing fertility decline, resulting in a rate of population size growth that will continue to decline toward zero and would eventually turn negative. However, scholarly and popular arguments have suggested that because fertility transmits intergenerationally (i.e., higher fertility parents tend to have higher fertility children) and is heterogeneous within a population, long-term population growth must eventually be positive, as high-fertility groups come to dominate the population. In this research note, we show that intergenerational transmission of fertility is not sufficient for positive long-term population growth, for empirical and theoretical reasons. First, because transmission is imperfect, the combination of transmission rates and fertility rates may be quantitatively insufficient for long-term population growth: higher fertility parents may nevertheless produce too few children who retain higher fertility preferences. Second, today even higher fertility subpopulations show declining fertility rates, which may eventually fall below replacement (and in some populations already are). Therefore, although different models of fertility transmission across generations reach different conclusions, depopulation is likely under any model if, in the future, even higher fertility subpopulations prefer and achieve below-replacement fertility. These results highlight the plausibility of long-term global depopulation and the importance of understanding the possible consequences of depopulation.
所有主要的长期全球人口预测都同意生育率持续下降，导致人口规模增长率将继续下降趋近于零，并最终转为负数。然而，学术和大众的争论表明，由于生育率具有代际传递性（即，高生育率的父母往往有更高生育率的子女），并且在人口内部存在异质性，长期人口增长最终必须是正的，因为高生育率群体将逐渐占据主导地位。在这篇研究说明中，我们表明，由于代际传递性的原因，生育率的代际传递不足以实现长期的人口正增长，这既有实证方面的原因，也有理论方面的原因。首先，由于传递并不完美，传递率和生育率的组合可能在数量上不足以实现长期人口增长：尽管如此，高生育率的父母可能仍然生育的子女数量太少，而这些子女保留了更高的生育偏好。其次，即使是今天的高生育率亚群体也显示出生育率下降的趋势，这最终可能会降至更替水平以下（在某些人群中已经如此）。因此，尽管不同的代际生育率传递模型得出了不同的结论，如果未来即使是高生育率的亚群体也偏好并实现低于更替水平的生育率，那么人口减少就很可能发生。这些结果凸显了长期全球人口减少的可能性，以及理解人口减少可能带来的后果的重要性。
