Future births: A formal perspective on humanity's yet-to-be-born generations

Miguel Sanchez-Romero , TU Wien and IIASA
Tomas Sobotka, Vienna Institute of Demography
Gustav Feichtinger, Vienna Institute of Demography, Austrian Academy of Sciences
Alexia Fürnkranz-Prskawetz, TU Wien
Stefan Wrzaczek, International Institute for Applies Systems Analysis

The global fall in fertility led to concerns about the prospects of population decline. Many discussions of `depopulation' seem to imply that such a population collapse is imminent and presents a grave threat to humanity. Using data from the UN World Population Prospects we model future births over a very long-term period. We compute the total number and the relative fraction of births to be born in the future. We complement our analysis by considering different timing of births and computing the year when the global number of births would fall below one thousand. Our hypothetical exercise provides three key insights. First, indefinite scenarios of low fertility, with a net reproduction rate around 0.9 or lower imply that most people who would ever live on Earth had already been born. Second, the mean age at childbearing impacts population dynamics in the long run: longer inter-generational span slows down the pace of births and population decline. Third, even when assuming a permanent continuation of very low fertility humanity's final demise would occur very slowly, with a critical threshold of extinction---a number of births falling below a thousand per year globally---reached more than 1,400 years from now.

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 Presented in Session 99. Formal and Conceptual Approaches to Kinship, Generations and Social Change