Summary: New analyses of human and nonhuman primate populations provide fresh evidence supporting the invariant rate of ageing hypothesis and reinforce the conclusion that death remains inevitable.
Source: University of Southern Denmark
A multinational research team led by Fernando Colchero (University of Southern Denmark) and Susan Alberts (Duke University) analyzed extensive birth and death records from 39 primate populations to test the “invariant rate of ageing” hypothesis. The collaboration included researchers from 42 institutions across 14 countries and combined datasets from nine human populations and 30 nonhuman primate groups, including gorillas, chimpanzees and baboons in both wild and captive settings.
“Human death is inevitable. No matter how many vitamins we take, how healthy our environment is or how much we exercise, we will eventually age and die,” said Fernando Colchero, an associate professor in the Department of Mathematics and Computer Science at the University of Southern Denmark. Colchero specializes in applying statistical and mathematical methods to population biology.
To examine the invariant rate of ageing hypothesis, the researchers compared two demographic measures across species and populations: life expectancy (the average age at death) and lifespan equality (a measure of how concentrated deaths are at older ages). By combining an unprecedented breadth of data, the team traced how changes in mortality at different life stages shape population longevity patterns.
Their analysis found a consistent relationship between life expectancy and lifespan equality: as life expectancy rises, lifespan equality also increases. In populations where most individuals die at similar, older ages—such as modern Japan or Sweden—lifespan equality is high and deaths cluster around the 70s and 80s. In contrast, historical data from the 1800s for those same countries show low lifespan equality because earlier-age mortality was higher and deaths were spread across a wider range of ages, producing much lower average life expectancy.
Importantly, the researchers show that improvements in life expectancy across primates generally arise from reductions in infant and juvenile mortality rather than from large shifts in the biological rate of ageing itself. In other words, populations live longer primarily because more individuals survive early life, which raises the average age at death, not because ageing slows dramatically.
By applying rigorous statistical and mathematical analyses to the combined dataset, the team demonstrated that variation in the rate of ageing within genera is far smaller than variation in pre-adult and age-independent mortality. In practical terms, small changes to the intrinsic rate of ageing would be required to make the mortality profile of one species resemble that of another—for example, to make a baboon population display chimpanzee- or human-like demographic patterns. Those changes, however, appear limited when compared with the larger shifts possible by reducing early-life mortality.
“We observe that not only humans, but also other primate species living under different environmental conditions, succeed in living longer primarily by reducing infant and juvenile mortality. This relationship only holds when early mortality declines, not when the rate of ageing is slowed,” Colchero explained.
While the study’s results support the invariant rate of ageing hypothesis—implying biological constraints on how much the human rate of ageing can be modified—the authors also note that medical advances could still alter ageing in ways that natural selection has not. “Medical science has advanced at an unprecedented pace,” Colchero added. “It is possible that science may eventually achieve reductions in the rate of ageing that evolution did not.”
Funding: This research was supported by NIA P01AG031719, with additional assistance from the Max Planck Institute of Demographic Research and the Duke University Population Research Institute.
About this aging research news
Source: University of Southern Denmark
Contact: Press Office – University of Southern Denmark
Image: The image is in the public domain
Original Research: Open access. “The Long Lives of Primates and the ‘Invariant Rate of Ageing’ Hypothesis” by F. Colchero, J.M. Aburto, E.A. Archie, C. Boesch, T. Breuer, F.A. Campos, A. Collins, D.A. Conde, M. Cords, C. Crockford, M.E. Thompson, L.M. Fedigan, C. Fichtel, M. Groenenberg, C. Hobaiter, P.M. Kappeler, R.R. Lawler, R.J. Lewis, Z.P. Machanda, M.L. Manguette, M.N. Muller, C. Packer, R.J. Parnell, S. Perry, A.E. Pusey, M.M. Robbins, R.M. Seyfarth, J.B. Silk, J. Staerk, T.S. Stoinski, E.J. Stokes, K.B. Strier, S.C. Strum, J. Tung, F. Villavicencio, R.M. Wittig, R.W. Wrangham, K. Zuberbühler, J.W. Vaupel, S.C. Alberts. Published in Nature Communications.
Abstract
The Long Lives of Primates and the ‘Invariant Rate of Ageing’ Hypothesis
Is it possible to slow the rate of ageing, or do biological constraints limit its plasticity? This study tested the invariant rate of ageing hypothesis—which proposes that the ageing rate is relatively fixed within species—using 39 human and nonhuman primate datasets across seven genera.
The researchers first reproduced, in nonhuman primates, the strong and regular relationship between life expectancy and lifespan equality that has been observed in human populations. They then showed that variation in the rate of ageing within genera is orders of magnitude smaller than variation in pre-adult and age-independent mortality.
Finally, the analysis demonstrated that altering the rate of ageing, but not other mortality parameters, produces distinctive and species-atypical changes in mortality patterns.
Overall, the results support the invariant rate of ageing hypothesis and indicate biological constraints on how much the human rate of ageing can be slowed by natural processes. At the same time, they leave open the possibility that medical or technological interventions could influence ageing in ways evolution has not achieved.