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. 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. Suspending it is not yet on the cards. 1 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. 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. 2 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. 3 Retirement would become a more distant option for most, since pension pots would have to be enormous to support their extended lifespans. 4 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? 5 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. A. 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. B. 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. C. 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. D. 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. E. 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. F. 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. G. 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.