Exploring the Limits of Human Lifespan: Insights from Ageing Research and Philosophy
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One of the biggest questions in ageing research is whether there is a ceiling on how long human beings can live. A recent study, published in Science, suggests there isn’t. The study measured the survival probabilities of 3,896 people in Italy aged 105 and older. It found that, while we are much more likely to die at 75 than at 55, once we reach about 105, the odds of death remain about the same each year of life. This effect is often referred to as a “mortality plateau”. If it were impossible to live past a certain age, we would expect mortality rates to continue rising as people age, rather than plateau. The fact that the odds of dying don’t appear to increase past 105 suggests that we have not yet approached our maximum lifespan as a species. But is potentially living for over a century something we ought to look forward to? Here, philosophy can offer some important insights.
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Of course, we still don’t know for sure that there is no ceiling. Some researchers argue that there is a natural “expiration date” for human beings, at about 125 years. Chiyo Miyako is currently the oldest known person in the world, at 117 years old. Jeanne Calment, who died in 1997, had the longest recorded lifespan, at 122 years.
In the UK, the number of people over the age of 100 has more than doubled since 2002, and could reach 36,000 by 2030. If there is a mortality plateau, by the year 2300 the oldest person alive could be about 150 years old. Would a maximum lifespan of 150 make our lives better or just longer? One way of thinking about this is in terms of pleasure and pain: the more pleasure (and the less pain) we have over the course of our lives, the better our lives are. Other things being equal, a life which lasts 100 years is better than one that lasts 80 years, as long as the extra 20 years contain more pleasure than they do pain.
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How likely an outcome is this? As people age, they are much more likely to develop degenerative conditions that could lead to a lower quality of life. But these conditions can be mitigated by a healthy lifestyle and adequate support services. While elderly life may be restricted in some ways, there is no reason that it cannot be, on balance, pleasurable. The late philosopher Ronald Dworkin distinguished between “experiential interests” and “critical interests” to shed light on how people may view their life goals. Experiential interests are for things like pleasure – anything we enjoy. Critical interests are those that we value becoming a reality – essential to what we think constitutes a good life. This could be a parent’s interest in the happiness of their child, for example. We can imagine a person having a critical interest in avoiding the perceived indignity of dementia, which may accompany extreme old age. We might think it would be better for this person, taking the whole of their life into account, if they had died prior to this period of decline.
