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The literature on human enhancement is awash with discussions about whether it really would be desirable to increase our lifespan, cognitive power, physical strength (etc.) above and beyond that which we currently consider to be healthy or normal. Almost all of these discussions hang on the question of whether it makes sense to draw a morally relevant distinction between those interventions that count as therapies and those that count as enhancements. Roughly, therapies are interventions that aim to restore health or normality to capacities or functions that are diseased or otherwise operating at a sub-normal level; enhancements aim to improve on the healthy or normal level of functioning.

Focusing on the case of lifespan enhancement, Andrea Sauchelli considers the desirability of enhancement from a perspective that is independent of the debate about the therapy/enhancement distinction. His starting point is an argument from Walter Glannon, who holds that ‘deep life-extending technologies’—Sauchelli’s term for ‘those technologies that purport to eliminate, in principle endlessly, the physically and/or mentally corrupting effects of the process of ageing’ (insert page ref. to Sauchelli’s article)—cannot coherently be desirable for beings like us, that is, persons. Glannon’s argument is, roughly, that any person X considering using deep life-extending technologies would be so psychologically dissimilar to the person Y whose mental life is a technologically-extended continuation of X’s mental life that X and Y cannot be said to be the same person. Glannon believes that a person literally cannot survive too large an increase in lifespan, where ‘too large an increase’ is one that renders the subject of the later stages of that lifespan so psychologically dissimilar to the subject of its earlier stages that the two subjects are not the same person. As Sauchelli notes, Glannon’s argument is premised on a psychological theory of personal identity of the sort associated with the 17^th century writings of John Locke, and more recently with Derek Parfit; along with the view that a necessary condition of being self-concerned for a future person is being identical with that person (as opposed, for example, to the view that our self-concern for a future person can be constitutive of our identity with that future person).

To resist Glannon’s conclusion that deep life-extending technologies cannot be desirable for beings like us, Sauchelli draws on narrative approaches to personal identity. While psychological theories of personal identity take persistence of persons through time to consist in the preservation of sufficiently many memories and other mental states (or of overlapping ‘strands’ of such preserved states), narrative approaches are concerned with the nature of those mental states. Specifically, what links our mental states over time—that is, what makes them ours—is their place in an ongoing narrative or story. Sauchelli notes that if we subscribe to a narrative account of personal identity rather than a psychological theory, Glannon’s claim that we cannot coherently desire to use deep life-extending technologies becomes unconvincing. This is because, even if it is true that a person X considering using deep life-extending technologies would be so psychologically dissimilar to the person Y whose mental life is a technologically-extended continuation of X’s mental life that X and Y cannot be said to be the same person based on a psychological theory of personal identity, X and Y may nevertheless count as the same person according to a narrative approach, since their respective mental states may feature appropriately in the right sort of narrative. As such, even accepting Glannon’s assumption that one’s identity with a future person is a necessary condition of being self-concerned for that person, it turns out that one can rationally desire to use deep life-extending technologies if we abandon the psychological theory in favour of a narrative approach.

One serious problem with this response to Glannon is that it is not clear that the narrative approach is robust enough to underpin a general account of what is involved in the persistence of persons through time. While philosophers like Marya Schechtman—the most prominent defender of the narrative approach—view the creation of a ‘(mostly implicit) autobiographical narrative’ (Schechtman, M. 2014: Staying Alive: Personal Identity, Practical Concerns, and the Unity of a Life (Oxford: Oxford University Press), p. 100) as constitutive of what it is to be a person, it is doubtful that everyone experiences their life in this way. Galen Strawson draws on the writings of various philosophers, artists, writers, and scientists including Mary Midgley, Paul Klee, W. Somerset Maugham, and Otto Frisch to demonstrate that, for plenty of people (Strawson counts himself among them), the experience of the self through time is far more disjointed and chaotic than Schechtman’s narrative approach allows. (Strawson, G. 2015: ‘The unstoried life’ in Leader, Z. (ed.) On Life Writing (Oxford: Oxford University Press)) Strawson argues that there is much that is valuable about living in this way, in which ‘the deliverances of memory are … hopelessly piecemeal and disordered’. That the likes of Schechtman take narrative to be so universally important to personhood is, he suggests, because they illicitly generalise from their own case. Quassim Cassam, too, gives us reason to be sceptical of narrative approaches. He has argued that we humans are prone to a variety of ‘epistemic vices’, which get in the way of our forming knowledge. In particular, we tend to create post-hoc rationalisations to explain why we believe what we believe and why we make the choices we make. (Cassam, Q. 2014: Self-Knowledge for Humans (Oxford: Oxford University Press); 2018: Vices of the Mind (Oxford: Oxford University Press)) If that is right, then the impression, had by many people, that one’s experiences form a narrative may be nothing more than an illusion.

Even if we abandon the narrative approach, however, it is far from clear that we should default to Glannon’s view about the desirability of deep life-extending technologies. This is because it is far from clear that the most appropriate way for a psychological theorist to respond to the prospect of such technologies is the one chosen by Glannon. Psychological theories of personal identity work by considering the sort of beings that most of us are—which tends to involve, among other things, our living no longer than a handful of decades—and drawing inferences from this about the sort of relation that personal identity must be if we are to end up with the convenient truth that each of us will be the same person when we die that we were when we were born. As an output of this reasoning, it happens that over a period of 70-odd years we can undergo some very drastic changes, such as the changes involved in growing from a toddler into a middle-aged adult, without compromising our personal identity. There are, however, certain drastic changes that we have more trouble conceiving of within a single lifespan, such as the change from middle-aged psychopathic serial killer into benign, kindly, elderly neighbour. That we have trouble believing that some drastic transformations are possible stems from the fact that our knowledge of what humans are like involves the belief that there is a limit to the amount of psychological change that a person can undergo within her lifespan, given the sort of lifespan that humans typically have. So, what happens to our conception of persons if we encounter a scenario in which it might become possible for persons to undergo the sorts of psychological transformations that until now we have thought not to be possible—as could be the case were deep life-extending technologies available to us?

One possible response, which is the one made by Glannon, and which we also find in the work of Parfit and David Lewis, is to hold that we could not survive those changes. Were one to undergo them, one would emerge from them as literally a different person (less sloppily: one would not be the person to emerge from them at all). Implicit in this sort of response is the claim that what it is to be a person simpliciter is defined and constrained by what it is to be a person with roughly the sort of life expectancy we are used to; so, the sort of psychological changes that we could not expect to see within a lifespan of roughly 70 years are not the sort of psychological changes that any person can survive.

This is not the only possible response, however. The sorts of views held by psychological theorists about what personal identity consists in were originally shaped by observations about what sorts of beings persons in fact are, but even a psychological theorist might find it appropriate to revise these views in light of observations about what sorts of beings humans could become. In a world in which humans routinely lived for a couple of centuries, it is not obvious that it would be appropriate to cling to a view of personhood premised on an outdated lifespan expectancy. And indeed, there is reason to believe it more likely that, in such a world, we would adapt our views about what sorts of things persons are to accommodate very long lifespans. In her early work, Schechtman remarks that an important function of the concept of personal identity is to enable us to make sense of the idea that it is possible to identify and re-identify a single person at different times; and that for this purpose, we naturally use bodily identity as a proxy for personal identity. Since we already do this, and since we can expect bodily identity to persist throughout the sorts of deep life-extension that Glannon and Sauchelli focus on, we might reasonably expect even very long-lived humans to find it natural to continue to identify and re-identify each other over the centuries by identifying and re-identifying bodies. Without good reason to assume that bodily identity would cease to be viewed as a proxy for personal identity in such circumstances, we could expect very long-lived humans to embrace the idea that it is possible for persons to persist through several centuries, even through the sorts of psychological changes that we do not see within current lifespans.

Metaphysical concepts like personal identity lend a useful structure to a world that we often struggle to understand; but they are not immutable. Just as our concept of personal identity can help us make sense of what is likely to happen to us were we to embrace certain futuristic technologies, so the advent of those technologies might lead us to reconsider the sort of beings we are.