The Advancing Frontier of Late Human Reproduction

Serena Vigezzi, Cpop - University of Southern Denmark
Annette Baudisch , Interdisciplinary Center on Population Dynamics (CPop)

As births and deaths happen at progressively older ages, further delays must increasingly face resistance from existing physiological constraints. These constraints coalesce into menopause, the well-known age limit for female fertility. Whether an analogous limit exists for survival, however, remains debated. Evidence indicates that reproductive and actuarial ageing share some physiological constraints. We hypothesize that these common constraints limit fertility and mortality postponement in similar ways and expect them to become particularly apparent as ages at birth and death shift upwards and physiological factors gain in importance. Hence, we propose to use the known limit to female fertility to shed light on the unknown limit to survival. We use percentile-based aggregate measures of mortality and fertility schedules to compare their trends since the 1940s in various low-mortality and low-fertility female populations. We show that for the last 30 years, the pace of mortality and fertility postponement has been surprisingly consistent, forming two parallel lines. This pace holds for almost the entire period of fertility postponement and therefore does not seem to hinge on proximity to an upper age-limit. These results support the hypothesis of common constraints of fertility and mortality delay and have deep implications for the nature of human ageing. Moreover, we highlight shortcomings of previous approaches to locate a limit to human lifespan using aggregate measures, informing future research on the subject.

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 Presented in Session P1. Families, Fertility, and the Life Course 1