Understanding how active and healthy ageing can be achieved is one of the most relevant global problems. In this review, I use the "Four questions" framework of Tinbergen to investigate how ageing works, how it might contribute to the survival of species, how it develops during the lifetime of (human) individuals and how it evolved. The focus of ageing research is usually on losses, although trajectories in later life show heterogeneity and many individuals experience healthy ageing. In humans, mild changes in cognition might be a typical part of ageing, but deficits are a sign of pathology. The ageing of the world's populations, and relatedly, the growing number of pathologically ageing people, is one of the major global problems. Animal models can help to understand the intrinsic and extrinsic factors contributing to ageing.
Keywords: Adaptation; Ageing; Animal models; Dementia; Evolution; Mechanism; Ontogeny; Post-fertility lifespan.
© 2022. The Author(s).