Why do we age?

Ageing is driven by many overlapping processes rather than a single cause. Each time a cell divides, protective caps on the chromosomes called telomeres get shorter, and once they become too short the cell stops dividing or dies. DNA also accumulates mutations from radiation, chemicals, and copying errors, while proteins and cellular machinery become damaged and less efficient. Over the years, damaged senescent cells build up and release inflammatory signals, and mitochondria that power cells become less productive. Scientists group these causes into hallmarks of ageing, and research into slowing them is one of the fastest-growing areas of biology. Ageing is not the same in all species: some animals, like certain jellyfish and tortoises, age extremely slowly.