Demographic perspectives on the rise of longevity

Abstract

This article reviews some key strands of demographic research on past trends in human longevity and explores possible future trends in life expectancy at birth. Demographic data on age-specific mortality are used to estimate life expectancy, and validated data on exceptional life spans are used to study the maximum length of life. In the countries doing best each year, life expectancy started to increase around 1840 at a pace of almost 2.5 y per decade. This trend has continued until the present. Contrary to classical evolutionary theories of senescence and contrary to the predictions of many experts, the frontier of survival is advancing to higher ages. Furthermore, individual life spans are becoming more equal, reducing inequalities, with octogenarians and nonagenarians accounting for most deaths in countries with the highest life expectancy. If the current pace of progress in life expectancy continues, most children born this millennium will celebrate their 100th birthday. Considerable uncertainty, however, clouds forecasts: Life expectancy and maximum life span might increase very little if at all, or longevity might rise much faster than in the past. Substantial progress has been made over the past three decades in deepening understanding of how long humans have lived and how long they might live. The social, economic, health, cultural, and political consequences of further increases in longevity are so significant that the development of more powerful methods of forecasting is a priority.

Keywords: forecasts; life expectancy; life span equality; maximum life span; mortality.

Fig. 1.

Average rates of mortality improvement (RMI) in the preceding 10 y at ages 80–100: French, Japanese, Swedish, and US females, 1980–2017. Calculations by method in ref. using data from the HMD (26).

Fig. 2.

Best-practice life expectancy at birth, 1840–2017. Adapted from ref. using the most recent data from the HMD (26). In all cases, the values pertain to female life expectancy. Since 2013, Hong Kong females have a higher life expectancy than Japanese females in the HMD, but Hong Kong is not a country.

Fig. 3.

The continuum of life expectancy at birth and life span equality in human populations. Adapted from the original figure by Fernando Colchero in ref. to more recent data in refs. and . Life span equality is measured by the logarithm of the inverse of life table entropy (–49) and defined as $\text{ln}(e_o/e^{†})$, where $e_o$ is life expectancy at birth, and $e^{†}$ is an indicator of life span disparity (46, 50). The lengths of the tadpoles represent the difference between females and males in the population, with the head being the females and the tale the males.

Fig. 4.

Linearly increasing age of the world’s oldest person. Adapted from a figure by Jonas Schöley—inspired by a graph by Robert D. Young (https://grg.org/sc/graphs/wop2.png)—using data from ref. . Additional studies of supercentenarians and the world´s oldest persons are found in ref. .

Fig. 5.

Female life expectancy at birth, historical levels, and forecasts 2018–2070, with lowest and highest value in 2070 and their difference indicated. The linear trend in best-practice life expectancy is shown as a dashed line. The best-practice estimates for 2018–2070 are extrapolations of the 1840–2017 linear trend. Forecasts for the period 2018–2070 with time-series data for 1960–2017 from the HMD (26). Forecasts and prediction intervals (Table 2) are computed using six models (84, 85, 89, 90) or extracted from official national forecast (–99).