Is it possible to slow the rate of ageing, or do biological constraints limit its plasticity? We test the ‘invariant rate of ageing’ hypothesis, which posits that the rate of ageing is relatively fixed within species, with a collection of 39 human and nonhuman primate datasets across seven genera. We first recapitulate, in nonhuman primates, the highly regular relationship between life expectancy and lifespan equality seen in humans. We next demonstrate that variation in the rate of ageing within genera is orders of magnitude smaller than variation in pre-adult and age-independent mortality. Finally, we demonstrate that changes in the rate of ageing, but not other mortality parameters, produce striking, species-atypical changes in mortality patterns. Our results support the invariant rate of ageing hypothesis, implying biological constraints on how much the human rate of ageing can be slowed.

We assembled a dataset on age-specific mortality rates in multiple populations of several different primate genera. Our combined dataset includes data from both wild and captive primate populations. The data from wild populations consist of individual-based birth and death data on males and females from 17 continuous long-term studies of wild primate populations representing 6 genera distributed across the order Primates, and include Old World monkeys (2 genera), New World monkeys (1 genus), great apes (2 genera, both African), and an indriid (1 genus, endemic to Madagascar). We also included data from 13 species in zoos using the Species360’s Zoological Information Management System (ZIMS), and from nine human datasets from populations that had not benefited from modern advances in public health, medicine and standards of living, which allowed us to carry out the most salient comparisons with nonhuman primates. We compared age-specific changes in the risk of death across multiple populations of each genus, and calculated Siler mortality parameters for each population. 

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