Diversity of ageing across the tree of life

Evolution drives, and is driven by, demography. A genotype moulds its phenotype’s age patterns of mortality and fertility in an environment; these two patterns in turn determine the genotype’s fitness in that environment. Hence, to understand the evolution of ageing, age patterns of mortality and reproduction need to be compared for species across the tree of life. However, few studies have done so and only for a limited range of taxa. Here we contrast standardized patterns over age for 11 mammals, 12 other vertebrates, 10 invertebrates, 12 vascular plants and a green alga. Although it has been predicted that evolution should inevitably lead to increasing mortality and declining fertility with age after maturity, there is great variation among these species, including increasing, constant, decreasing, humped and bowed trajectories for both long- and short-lived species. This diversity challenges theoreticians to develop broader perspectives on the evolution of ageing and empiricists to study the demography of more species. Examination of demographic age trajectories for species from a wide range of taxonomic groups shows that these species have very diverse life-history patterns; mortality and reproduction vary greatly with age for both long- and short-lived species, and the relationships between ageing, mortality and reproduction are clearly complex. Multiple approaches to growing old It is usually assumed that ageing is accompanied by decreasing reproductive potential and increasing mortality. But such assumptions might be parochial, as Owen Jones et al . show in this wide-ranging survey of life-history patterns in a variety of animals and plants. It turns out that mortality and fertility rates vary enormously with age, in short- and long-lived species alike. No single pattern fits all. The relationships between ageing, mortality and reproduction are clearly complex, and more work is required to achieve a more general understanding. Theoreticians need to develop models that can more adequately capture the diversity of ageing, and experiments could usefully be carried out on a more diverse set of species.