Evidence for a limit to human lifespan

[Ron Put]

Evidence for a limit to human lifespan

Driven by technological progress, human life expectancy has increased greatly since the nineteenth century. Demographic evidence has revealed an ongoing reduction in old-age mortality and a rise of the maximum age at death, which may gradually extend human longevity1,2 . Together with observations that lifespan in various animal species is flexible and can be increased by genetic or pharmaceutical intervention, these results have led to suggestions that longevity may not be subject to strict, species-specific genetic constraints. Here, by analysing global demographic data, we show that improvements in survival with age tend to decline after age 100, and that the age at death of the world’s oldest person has not increased since the 1990s. Our results strongly suggest that the maximum lifespan of humans is fixed and subject to natural constraints....

Hence, in contrast to previous suggestions that human longevity can be extended ever further1 , our data strongly suggest that the duration of life is limited. In the past, others have suggested that human lifespan is limited. For example, in 1980 Fries argued that increased prevention of premature deaths would lead to a compression of morbidity owing to a finite lifespan10. However, his arguments for such a limit to life, that is, the lack of a detectable increase in centenarians or in the maximum reported age at death, while correct at that time, have been refuted since2,6 . Ten years later, Olshansky et al.11 estimated the upper limits to human longevity based on hypothetical reductions in mortality rates, concluding that life expectancy at birth would not exceed 85 years.

Like Fries, Olshansky et al. also suggested a biological limit to life based on the lack of an increase in the age of the verified longest-lived individual. However, as they mention, insufficient data prevented them from drawing definite conclusions. Now, more than two decades later, such data are becoming available. With the caveat that the ages at death of the supercentenarians in our present study are still noisy and made up of small samples, we feel that the observed trajectories in Fig. 2 are compelling and our results strongly suggest that human lifespan has a natural limit.

What could be the biological causes of this limit to human lifespan? The idea that ageing is a purposeful, programmed series of events that evolved under the direct force of natural selection to cause death has now been all but discredited12. Instead, what appears to be a ‘natural limit’ is an inadvertent byproduct of fixed genetic programs for early life events, such as development, growth and reproduction. Limits to the duration of life could well be determined by a set of species-specific, longevityassurance systems encoded in the genome that counteract these inadvertent byproducts, which are likely to include inherent imperfections in transferring genetic information into cellular function13,14. To further extend human lifespan beyond the limits set by these longevity-assurance systems would require interventions beyond improving health span, some of which are currently under investigation15. Although there is no scientific reason why such efforts could not be successful, the possibility is essentially constrained by the myriad of genetic variants that collectively determine species-specific lifespan16.