For most of human history ageing has been seen as a natural and inevitable fact of life. Medical advances meant that we could prevent disease and mitigate some of the worst effects of ageing, but the brute fact that our body changes irrevocably as we get older has always seemed beyond the scope of science to tackle. Reversing ageing was at most the stuff of legends like the Fountain of Youth, not a realistic scientific proposition. Now, though, medical science has advanced far enough that some are seriously considering the possibility that ageing could be reversed – in fact, our own founder, Tej Kohli, maintains we will make significant enough progress against ageing that his son will live to between 125 and 150. But is this really true – and if so, will the benefits be distributed equally, or only to a few high net worth individuals who can afford it? One recent study found that an innovative new technique is able to reverse ageing in mice, extending their lifespan by up to 35%. To understand how scientists were able to achieve this startling result, we first have to understand a fundamental part of ageing: senescence. Senescence is a natural part of how the body functions, causing certain cells to cease reproducing themselves once they’ve gone through a particular number of generations – so after a normal cell has split itself a fixed number of times, senescence will mean it won’t split again. The particular cells that senescence affects are diploid cells. Diploid cells are cells with two sets of chromosomes – in humans, and indeed in most mammals, that’s every cell except the gametes (sex cells), so senescence has a very wide effect. Everyone carries senescent cells (cells which senescence prevents from reproducing) somewhere in their body, but when you’re younger your body will remove them over time. However, as we age our bodies stop being able to get rid of them – leading some to hypothesise that senescent cells may help to cause ageing. Researchers used this knowledge of senescence to get the headline-grabbing result above, actually reversing ageing in mice. By using a special compound, they were able to remove senescent cells in the mice, cells which would otherwise not have been cleared out naturally (since, as the mice get older, they stop getting rid of senescent cells). This meant that mice who received the treatment lived 35% longer and, importantly, were healthier and stronger than those that aged without the compound. Of course, the application to humans will pose tricky problems. It should be noted as well that the treatment didn’t tackle everything we associate with ageing – for example, it didn’t help the mobility of the mice. So this treatment really reverses certain facets of ageing. But even if we were able to transfer this result to humans, who would get to benefit? If only the very wealthy could afford the treatment, that would have a profound societal impact. That we all age together is a great leveller – but when ageing is something that only happens to the marginalised, it will have the opposite effect, increasing divisiveness. That’s why we need a more egalitarian approach to medical advances – it will take the work of philanthropists, charities and governments to make sure that these exciting new developments are to the benefit, not the detriment, of society.