Ageing and senescence

Ageing is the process of becoming older. As people age, they also senesce, which means their bodies slowly start to fail as they approach the end of their lives.  This is why older people usually become weaker, their hearing and sight is less good, they stop producing children, and their hair turns grey.

For a long time people thought that senescence happened to all living things, but scientists have shown this is not true. Some species show no change in performance with age, and some even improve! How they manage to escape from senescence is a great puzzle in biology.