Ageing is not one process but many running together. A central one involves telomeres, protective caps of repeated DNA at the ends of chromosomes that shorten a little each time a cell divides. When they grow too short the cell stops dividing and becomes senescent, neither working properly nor dying. An enzyme called telomerase can rebuild them, and it is active in embryos — living things at their earliest stage — and in some stem cells, but switching it on everywhere is dangerous: unlimited division is close to a definition of cancer. Other mechanisms add up alongside it, including accumulated damage to proteins and declining repair. Biologists studying species that barely age, such as certain jellyfish and the naked mole-rat, find no single trick but several defences layered together. The picture that emerges is that ageing is the price of a body built from cells that must keep dividing.

Visual AidAn animal that hardly ages

The idea of water that restores youth appears across unconnected cultures. Herodotus recorded a report of a spring in Ethiopia said to give long life; Alexander romances sent the conqueror searching for a water of life; medieval Europe placed such a fountain in the imagined kingdom of Prester John. The version most familiar in English attaches to the Spanish explorer Ponce de León and Florida, and historians are confident it is a later invention: no contemporary account of his expedition mentions it, and the story appears in print decades after his death. Folklorists treat this as a classic migratory legend, a portable tale that attaches itself to whichever traveler a culture finds convenient. The persistence tells us less about geography than about desire. Every version places the water somewhere just beyond the known world, which is exactly where a wish has to live to remain believable.

A symbol is a concrete thing that stands for something abstract while remaining fully itself. That double life is the whole craft. A wheel in a story is a real wheel and can also mean the turning of time; if the author insists too hard on the second meaning, the wheel stops being a wheel and the writing turns into a lecture. Critics distinguish inherited symbols, which arrive with meanings a culture already agrees on, from private ones a book builds through repetition. Water is a strong example of the first kind, connected to birth, cleansing and death across many literatures. Novelists usually let a symbol accumulate quietly and then place it in one scene where a character interacts with it physically, so the idea is felt through an action rather than explained. That physical contact is the test of a working symbol: if a character can pick the object up, refuse it, break it or give it away, the abstraction has been converted into something a story can actually dramatize.

Philosophers ask what makes a life go well, and answers fall into three families. Hedonism says a good life contains the most pleasure and least pain. Desire theories say it consists of getting what you actually want, whether or not it feels good. Objective-list theories name goods that count regardless of preference — friendship, knowledge, achievement, health. The debate matters here because the three disagree sharply about duration. Bernard Williams argued in a famous essay that an endless life would eventually exhaust every project that gives a person reasons to act, leaving boredom no amount of time could cure. Others reply that new interests keep arriving indefinitely, and that boredom is a failure of imagination rather than of arithmetic. What both sides accept is that a life is assessed by its shape as well as its length, and that a story with no possible ending is also a story with nothing at stake.