Senescence in natural populations of animals: Widespread evidence and its implications for bio-gerontology

► That animals do not senesce in their natural environment is an oft-quoted fallacy. ► Reviewing studies of wild animals, we find evidence for senescence in 175 species. ► Recent field studies are shedding new light on key bio-gerontological questions. ► Ecological studies help establish the generality of findings from model organisms. ► Tests of evolutionary theories of ageing demand research in natural settings.