IMAGINE a world in which getting fitted with a new heart, liver or set of kidneys, all grown from your own body cells, was as commonplace as knee and hip replacements are now. Or one in which you celebrated your 94th birthday by running a marathon with your school friends. Imagine, in other words, a world in which ageing had been abolished.

That world is not yet on offer. But a semblance of it might be one day. Senescence, the general dwindling of prowess experienced by all as time takes its toll, is coming under scrutiny from doctors and biologists (see article). Suspending it is not yet on the cards. But slowing it probably is. Average lifespans have risen a lot over the past century, but that was thanks to better food, housing, public health and some medicines. The new increase would be brought about by specific anti-senescence drugs, some of which may already exist.

This, optimists claim, will extend life for many people to today’s ceiling of 120 or so. But it may be just the beginning. In the next phase not just average lifespans but maximum lifespans will rise. If a body part wears out, it will be repaired or replaced altogether. DNA will be optimised for long life. Add in anti-ageing drugs, and centenarians will become two a penny.

Man and superman

To this end, many hopeful repairmen are now setting up shop. Some of them want to upgrade worn-out tissues using stem cells (precursors to other sorts of cell). Such bio-renovation is the basis of an unproven, almost vampiric, treatment in vogue in some circles: transfusion into the old of the blood of the young (see article). The business of growing organs from scratch is also proceeding. At the moment, these “organoids” are small, imperfect and used mainly for drug testing. But that will surely change. Longevity is known to run in families, which suggests that particular varieties of genes prolong life. Some are investigating this, with the thought that modern gene-editing techniques might one day be used to make crucial, life-extending tweaks to the DNA of those who need them.

From an individual’s viewpoint, this all sounds very desirable. For society as a whole, though, it will have profound effects. Most of them will be good, but not all.

One concern is that long life will exacerbate existing social and economic problems. The most immediate challenge will be access to anti-senescence treatment. If longer life is expensive, who gets it first? Already, income is one of the best predictors of lifespan. Widening the gap with treatments inaccessible to the poor might deepen divisions that are already straining democracies.

Will older workers be discriminated against, as now, or will numbers give them the whip hand over the young? Will bosses cling on, stymying the careers of their underlings, or will they grow bored, quit and do something else entirely? And would all those old people cease to consider themselves elderly, retaining youthfully vigorous mental attitudes as well as physical ones—or instead make society more conservative (because old people tend to be)?

A reason for hoping that the elderly would turn out less hidebound is that life itself would be more a series of new beginnings than one single story. Mid-life crises might be not so much about recapturing lost youth as wondering how to make the most of the next half-century.

Retirement would become a more distant option for most, since pension pots would have to be enormous to support their extended lifespans. To this end, the portfolio career would become the rule and education would have to change accordingly. People might go back to school in their 50s to learn how to do something completely different. The physical labourer would surely need a rest. The accountant might become a doctor. The lawyer, a charity worker. Perhaps some will take long breaks between careers and party wildly, in the knowledge that medicine can offer them running repairs.

Boredom, and the need for variety, would alter family life, too. How many will tie the knot in their 20s in the expectation of being with the same person 80 years later? The one-partner life, already on the decline, could become rare, replaced by a series of relationships, each as long as what many today would consider a decent marital stretch. As for reproduction, men’s testes would presumably work indefinitely and, though women’s ovaries are believed to be loaded with a finite number of eggs, technology would surely be able to create new ones. Those who wished to could thus continue to procreate for decades. That, and serial marriage, will make it difficult to keep track of who is related to whom. Families will start to look more like labyrinthine networks. In the world where marriages do not last, women everywhere will be freer to divorce and aged patriarchs will finally lose their hold.

Such speculation is fun, and mostly optimistic. The promise of a longer life, well lived, would round a person out. But this vision of the future depends on one thing—that a long existence is also a healthy one. Humanity must avoid the trap fallen into by Tithonus, a mythical Trojan who was granted eternal life by the gods, but forgot to ask also for eternal youth. Eventually, he withered into a cicada.

Forward to Methuselah

The trap of Tithonus is sprung because bodies have evolved to be throwaway vessels for the carriage of genes from one generation to the next. Biologists have a phrase for it: the disposable soma. It explains not only general senescence, but also why dementia, cancer, cardiovascular problems, arthritis and many other things are guarded against in youth, but crammed into old age once reproduction is done with. These, too, must be treated if a long and healthy life is to become routine. Moreover, even a healthy brain may age badly. An organ evolved to accommodate 70 or 80 years of memories may be unable to cope when asked to store 150 years’ worth.

Yet biological understanding is advancing apace. Greater longevity is within reach—even if actual immortality may not be as close (or as interesting) as some fantasists would like to believe. Be sure to draw up a very long bucket list.