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Life extension and the burden of mortality: Leon Kass versus John Harris
  1. Andrea Sauchelli
  1. Correspondence to Dr Andrea Sauchelli, Department of Philosophy, Lingnan University, Castle Peak Road, Tuen Mun, New Territories, Hong Kong; andreasauchelli{at}


Some bioethicists have questioned the desirability of a line of biomedical research aimed at extending the length of our lives over what some think to be its natural limit. In particular, Leon Kass has argued that living longer is not such a great advantage, and that mortality is not a burden after all. In this essay, I evaluate his arguments in favour of such a counterintuitive view by elaborating upon some critical remarks advanced by John Harris. Ultimately, I argue that nothing substantial has been said by Kass to undermine the desirability of life-extending technologies.

  • Enhancement
  • Attitudes Toward Death
  • Research Ethics
  • Technology/Risk Assessment

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This paper is a contribution to the current debate on the moral permissibility of a certain subset of technological enhancements; in particular, those enhancements whose purpose is to prolong our lives over what is now perceived as its natural temporal limit.1

A moral theory that suggests that enhancements without qualifications are illicit is a non-starter when we realise that, for instance, even books, mobile phones and the internet are technological enhancements that greatly improve our capacities well beyond our biological limitations. In particular, these tools improve on our abilities of, respectively, remembering, communicating and sharing information to a degree that was barely imaginable, in the case of mobile phones and the internet, just few decades ago. If a theory turns out to imply that such technologies are immoral, it can be safely assumed that such neo-Luddism or primitivism should be rejected. Obviously, all technological advancements can be used for the worse. What is at issue here is rather whether certain enhancements are to be considered as undesirable in relation to the proper function for which they were designed.2

A contentious family of enhancements which have been seen by some critics as problematic are those aimed at prolonging the length of our lives, possibly, but not exclusively, by recurring to the modification of our genetic code, or of those other internal biological elements which can contribute to our phenotype.3 Opponents to life-extension enhancements, however, do not seem to argue solely against life-extension enhancements based on the modification of our nature, if such a term makes any sense at all, but also against the same idea of extending the length of our lives beyond what some philosophers think being its limit.4 In this paper, I will focus on Leon Kass’ attempt to undermine the desirability and legitimacy of such kinds of enhancements.5 In particular, I will elaborate his sketchy considerations aimed at showing that mortality, after all, is not a burden, and evaluate some of John Harris’ replies to these arguments.6 I will expand Harris’ criticisms and put forward new considerations to the effect that Kass’ arguments are not convincing.7

Kass on life-extending enhancements

Kass’ main reason to oppose life-extending technologies is that there are advantages in being mortals, and such advantages would justify the otherwise appealing idea of prolonging our lives indefinitely through appropriate technological means. Kass admits that some allegedly only therapeutic applications of biomedical science and biotechnology are morally acceptable. The problems, according to him, begin with the possibility (actual or merely in an unspecified future) of modifying and perfecting one of the contingent results of evolution, that is, what has been called our human nature. A corollary of the view that all modification to our nature, whatever this term may mean, would be that also life-extending enhancements are morally dubious. A first dubious point made by Kass is that techniques to enhance some of our inherited capacities, that is, memory, are at the same level of ‘instruments of bioterrorism’.8 One first argument to support this view is that these enhancements are not safe. In particular, Kass argues as follows.9

  1. Athletes who take steroids will suffer premature heart disease;

  2. College students who consume ecstasy will damage their brains;

  3. So, no biological enhancement will be completely safe.

In support of this conclusion, he maintains that something that is powerful enough to enhance A also has the power to destroy B, and that this consequence may ultimately be detrimental to A. For example, an organism can be seen as a functionally connected set of subsystems. Enhancing one of the subsystems, A, may lead to disastrous effects for another subsystem or for the organism as a whole. However, the previous generalisation is either an exaggeration in need of further evidence or a trivial and uncontroversial remark. More specifically, the above reasoning is trivial if we take (3) to mean that everything that can be used to enhance our capacities cannot be safe from a technical point of view. Thus, it is obvious that if an instrument can be used in a way that is not prescribed by competent people, or if not appropriately handled, this instrument can have dangerous effects. It is obvious that the improper use (in a technical sense) of a technique to improve our capacities may lead to dangerous results. For example, in the case of cars, one mechanical enhancement of our capacity of transportation, it is obvious that you may hurt yourself if you drive a car and you do not know how to use the brakes, but nobody is arguing that it is rational or morally acceptable to let incompetent people perform or do what is required in order to enhance people. Certainly, Kass means something different here. However, and this is the second horn of the dilemma, if he means that in the future, at all times, it will be always false that biological enhancements will be completely safe, this is unjustified given the sole two provided premises. It seems possible to have safe biological enhancements in the future if used by competent people. Eventual threats from biotechnological advancements are hard to assess, even with regard to current research focused on eradicating current or re-emerging diseases.10 Although regulations should certainly be enforced to control the eventual development of biological weapons based on life-extending technologies (ie, regenerating soldiers, or biological carriers immune to diseases that could be spread among a target population), the possible advantages to be gained suggest the need for precautions but certainly not complete abstinence. Therefore, Kass’ point seems to be better interpreted as a caution to be careful about research on biotechnological enhancements. Additionally, Harris noted that the possibility of risk is not a problem specific to biological enhancement but is rather an inherent feature of all human decision making, from fields of research, such as physics or security devices to more mundane activities such as road transportation.11 Changes to our genetic makeup may be considered to be a special case because of their alleged influence and irreversibility. In response to this, it should be noted that evolution already operates to modify our genetic nature, and nobody seems to object to that. Additionally, Allen Buchanan noted that not all biological enhancements involve irreversible modifications.12 For those modifications involving a transmittable alteration in the gene pool, Buchanan also suggests that genetic changes do not immediately amount to phenotypic changes. For instance, as certain genes have been found to be disruptive to other systems, drugs can be administered to prevent the expression of those faulty genes. In relation to this, it can be argued that by the time certain life-extending techniques have been made available, we may also have already developed techniques to revert their effects or control their influence. To conclude this series of reflections on the risks of genetic modification, it may well be the case that in the future, because of radical changes in the environment, it would be less risky to have well-developed technologies available and ready to modify our genetic nature due to eventual life-threatening menaces (ie, glaciations), than to be caught completely unprepared for these circumstances. Not having any biological enhancements may not be completely safe either.

Kass also advances more specific reasons to believe that life-extending enhancements should not be welcomed.13 Unfortunately, Kass does not always present his objections in the form of a precise argument, so it is not easy to state his thoughts in a completely straightforward way. In what follows, I will put his remarks more rigorously.

  1. Interest and engagement. Kass begins with the following question (presupposing a negative answer): If human life span were increased even by 20 years, would the pleasure be increased proportionately? The charge against life-extension technologies seems to be that even if we prolong our lives of, say, 20 more years (prolong relatively to what?), this additional time would not increase the total pleasure of a life had it been shorter. Therefore, after all, mortality is not as bad as it is depicted, for living for an undefined amount of time would not increase the amount of pleasure or happiness that can be experienced in a life. Kass claims that this reasoning is supported by the idea that even in the short time that we are allowed to live, our engagement to certain activities decreases and, as a result, extending our life span would not add up any pleasure to the total we may experience in our life.

  2. Seriousness and aspiration. According to Kass, it is a necessary condition for life to be meaningful that it be mortal. This claim seems to be supported by the anecdotal observation that many people need to feel to push off their mortality in order to pursue some (but not all) activities that would make life meaningful. As an example, Kass also claims that the Greek gods, as portrayed by Homer, led immortal but shallow and frivolous lives.

  3. Beauty and love. Kass seems to suggest, through various rhetorical questions, a series of disconnected and not argued views on the relationship between death and, first, beauty (both natural and artistic) and, second, love. The thoughts conflated here seem to be that artists are pushed to produce beautiful artefacts because they see their existence as limited. Therefore, extending life indefinitely would cause artists to not produce beautiful works anymore and, as a consequence, we should not develop technologies that extend life, given the importance of artistic beauty in our lives. Similarly, Kass hints at the idea that also our appreciation of natural beauty essentially involves awareness of its caducity. If an argument is to be extracted from his sketchy remarks, it would include the following: (i) the appreciation of natural beauty necessarily requires awareness of its transience, (ii) the appreciation of natural beauty (or of other kinds of beauty) is an essential component of a meaningful life, (iii) life-extending technologies will deprive us of our awareness of the transient dimension of our lives, (iv) thus, life-extending technologies deprive us of an essential component of a meaningful life, (v) given that living a meaningful life is desirable, it follows that (vi) such techniques are not desirable. A similar reasoning is applied to love: Kass says that also love (he probably means romantic love here) is somehow connected to the awareness of its transience.

  4. Virtue and moral excellence. The fact that we spend our limited time in certain activities ennobles them and, Kass argues, this is due to the fact that the time we have is indeed limited. As a consequence of this, he maintains that immortals cannot be noble, for their actions are not ennobled by the investment in them of something valuable and limited (in this case, time). Kass also claims that it is a necessary condition for doing virtuous acts to leave aside things related to our survival (ie, fear, bodily pleasure, or wealth) and thus to be vulnerable and mortal. Therefore, if we do not want to give up virtue and moral excellence, we should remain vulnerable and mortal.

So, if immortality (or invulnerability which in Kass’ reasoning are not well distinguished) is, upon reflection, so undesirable, where does our desire to keep on living come from? Kass believes that such a longing is the manifestation of the aspiration of our souls to transcend and obtain something which cannot be achieved in our earthly life. Our aspiration to become immortals is the manifestation of a conflict between some unspecified transcendental longings and the finite and earthly body.

To sum up, Kass believes that if the technologies of life extension reach a level in which earthly immortality is finally achieved, the lives of these immortals would lack crucial and valuable features that make them meaningful. If a life is not meaningful, then it is not desirable. If something makes a life undesirable, then it should not be pursued. So, life-extending technologies should not be pursued.

Harris’ replies and additional criticisms

In his recent book, Enhancing Evolution, Harris provides an extensive criticism of Kass’ more general worries related to enhancements.14 However, as already specified, I will focus just on considerations about a specific kind of enhancement; in particular, those enhancements devised to extend the length of our lives to the point of immortality or, at least, to eliminate limitations in terms of duration due to our biological structure.15

One first crucial distinction to properly assess the whole debate is that between immortality and invulnerability: as Harris rightly points out, if an individual A's genetic code (or whatever other internal biological element is needed to achieve the intended result) is reprogrammed so as to interrupt the process of ageing and if, consequently, A could hypothetically live till the end of the universe, still it does not mean that A, for this sole reason, has also become invulnerable.16 Arguably, the process of extending the length of our lives will take place at a slow and irregular (in terms of distribution) rate among the population, and it is unlikely that death and finitude will be won completely (at least in a foreseeable future the features of which make sense to imagine from our particular historical moment). For accidents may still happen, along with new diseases, wars, violent crimes and so on.17 If this is the case, our aiming at immortality can be seen as asymptotic; that is, as an ideal to be reached but that cannot be secured beyond any reasonable worry. If this is the case, then finitude and transience would not completely disappear from the existence of future generations; on the contrary, finitude would appear even more dramatic, given the perspective of an easier to achieve prolonged life. As a consequence, premise (iii) of Kass’ previous argument (3—Beauty and love) is false: life-extending technologies by themselves do not deprive us of our awareness of finitude. What else can be said in relation to the same argument? In regard to the appreciation of natural beauty, recent works in environmental aesthetics do emphasise the cognitive dimension of the appreciation of nature, but this is not generally taken to imply that such awareness is essentially correlated to a sense of finitude.18 It can be also argued that premise (iii) contains a psychological assumption (our awareness of the transient dimension of life would be undermined) that would perhaps better be left to empirical sciences, such as psychology to test. Besides, Kass’ whole point about the appreciation of natural beauty relies on an equivocation: life-extending technologies are meant to preserve the lives of people and not, prima facie, mountains or landscapes. If we leave aside the fact that humans are also part of the natural realm, it can be argued that life-extending technologies would not affect the temporal finitude of a landscape, of a bright day of sun or of a stormy and dark night of December. So, even conceding for the sake of the argument that the appreciation of natural beauty (in the sense of the appreciation of landscapes and natural environments) requires awareness of their finitude, the adoption of life-extending technologies applied to humans does not interfere with such an aesthetic activity. For landscapes or other natural phenomena would still be contingent and finite, and thus, we will be able to appreciate their transient nature.

A similar reasoning can be applied to the case of the appreciation of the finitude of our love. If life-extending technologies amount to the modification of our genetic code and have the effect of interrupting the process of ageing, this does not mean that the person in question will be invulnerable. So, after all, also our beloved would still be exposed to the possibility of death. There is still the theoretical possibility of applying a combination of technological enhancements through which a certain level of immunity from disasters may be achieved. For example, special armours or protective clothes may be devised to eliminate the risk of accidental deaths. It has to be noticed that such technologies would probably not spare their users from physical phenomena which are likely to remain for an indefinite time ahead beyond our control (black holes, explosion of stars, meteorites, powerful weapons, and so on). Let us grant for the sake of the argument that such life-protecting technologies may achieve a level of protection which can be surpassed solely by particularly catastrophic events. Would this scenario destroy our idea of romantic love? Again, it is not clear in which way these non-biological life-extension technologies would undermine our awareness of the finitude of love. In fact, Kass’ reasoning seems to be ambiguous also in this case. In particular, his point about the importance of our awareness of mortality for love can be interpreted as meaning that in order for A to love B, A must be aware (1) that B is mortal, or (2) that the relationship of love between A and B may come to an end. If (2) is what is meant, then foreseeable life-extending technologies would not undermine such awareness: biologically and non-biologically enhanced people may still change their minds, and their emotional life may take unexpected turns. From the fact that A is invulnerable or immortal, it does not conceptually follow that A cannot change her mind in matters of love. If this is the case, then A can also have the awareness that the love between her and B may end at some point. If, on the other hand, we intended (1), the point is too strong: it may be true that awareness of the finitude of somebody may make us appreciate the time that that person spends with us, but it is dubious that this is a necessary or sufficient condition for loving that person. For we may love someone for other features other than his or her mortality and, besides, there does not seem to be anything conceptually wrong with the idea of being immortal and being the object of love. There are Christians and other religious people who believe that they and their partners will keep on living forever as, perhaps, souls in the afterlife. So at least some Christians believe that we do actually are immortal, and that the death of our bodies represents just one passage to a different world. Now, it would be absurd to maintain that these people are not capable of loving each other because they think that, after all, they will meet also in the afterlife. So we should give up the premise that mortality is a necessary requirement for love. In conclusion, Kass’ argument (3) based on the idea that mortality is required to appreciate beauty and love is not sound.

Let us now examine argument 1—Interest and engagement. To explain his reasoning, Kass uses an example: 125 more women for a don Juan who has already had 1000, or 20 more years for somebody who has achieved something in life, would not add up to their total happiness. Adding years would make these lives less meaningful or not worth to be lived any further because they are less stimulating, or so Kass maintains. In reply, Harris claims that if many of the same does not add up to more happiness, there is still the opportunity of trying something different.19

A more effective way to prove that Kass is wrong is as follows. According to Anthony Wrigley and Roger Schofield, an Englishman could expect to live for approximately 40 years in 1570.20 That could have been considered the natural length of a lifetime for those living at that time. After all, people had enough time to grow up, procreate and achieve important results. Nowadays, an Englishman could expect, on average, to live more than 76 years. This change can be seen as the result of a combination of various improvements that have, de facto, added at least 30 years to the life of people in England. Now, it is clearly false that people in England, when they reach 40, stop to be engaged in meaningful activities, or that they do not enjoy what they do, despite the fact that they have achieved important results. A similar claim can be made for all the populations of those other countries in which the average life expectancy has increased. Therefore, it is false that adding 20–30 years would make a life less meaningful or less stimulating: if healthy, people do seem to enjoy these additional years.

Obviously, what is missing in Kass’ reasoning is more specificity in regard to what is the age limit above which meaningful activities stop to be such for the people who are engaged in them. Now, it is likely that such criteria are extremely variable and depend on singular cases. For example, Jonathan Glover, and with him a great number of people, would add a few million years to his lifetime and see how it goes.21 Leibniz enjoyed writing about philosophy till the very end of his life, and probably would have continued if he had lived 20 more years, while Rimbaud stopped composing poetry at an early age. Overblown generalisations about what people would or would not do if their lives had been longer than 70 or 80 years seem to be particularly difficult to be convincing or based on some sort of evidence. Probably the desirability of a 1000-year-old life depends not only on the increased length, but also on other factors such as the introduction of other technologies aimed at reducing the side effects of the process of aging. Be this as it may, Kass’ reasoning is not grounded on anything solid enough to justify the rejection of what, on the contrary, seems to be a well-entrenched desire of most people in normal health: to keep on living in good conditions as long as possible. Therefore, also this attempt to show that mortality is not a burden fails.

Kass’ argument 2—Seriousness and aspiration is based on the idea that mortality confers meaning to our lives because it is necessary to feel the push of the passage of time to begin certain meaningful activities. Also, this reasoning is difficult to assess due to its sketchy form. Bernard Williams, another philosopher who has expressed doubts regarding the desirability of immortality, discusses the role of desires in relation to those activities that may be taken as conferring meaning to our lives.22 Williams claims that we have desires that are contingent on one's being alive, and desires that are not conditioned by being alive or not. For example, we may desire to watch a football game the coming evening, and this is surely contingent on us being alive at the moment of the game. On the other hand, a desire such as saving and preserving human life on Earth may not be contingent on one's being alive (unless the person having this desire is the last of our species). Desires of this second kind can be called categorical. A plausible requirement for our lives to be meaningful over time is that of being used to achieve or strive to achieve certain projects that are desired. Categorical desires need not necessarily be of a large scale, such as saving humanity or travelling with a space ship. For instance, a categorical desire may simply be that of providing a decent and happy life to the loved one. These desires need not be fully explicit all the time, or always present in the mind of the person who has them. They can be taken as dispositions that somehow regulate more specific choices. Now, back to our discussion on life-extension, Kass seems to suggest that those desires and projects that make our lives meaningful require, to be carried out, awareness of our mortality. However, this does not seem to be true. As has been said, there can be categorical desires that are independent of the fact that we are alive or not. If A desires that life on Earth be preserved, and this is taken to make A's life meaningful, then even if life on Earth is preserved as a result of A's actions, then A's life would be meaningful whether A be mortal or immortal, and thus, independently of his condition in regard to mortality. If A desires that life on Earth be preserved, and this can happen only by making human beings immortals, then again, A's life would be meaningful precisely by virtue of introducing immortality. If the only way in which A's desire to maintain life on Earth were that of living forever, then, obviously, A's categorical desire is connected to immortality in a way that would make, at the same time, his life meaningful and indefinitely extended in time.

To illustrate the previous point, consider a modern and revised version of the myth of Atlas: one man is in a situation in which his continuous presence is required for humanity to be preserved. Suppose that this person can become immortal by genetic manipulation, and that his categorical desires coincide with that of maintaining life on Earth. Call him the Guardian. Now, is the Guardian's life meaningless if made immortal and if he assumes his duties? His categorical desire to maintain life on Earth is formulated in a way that awareness of his mortality would lead the Guardian not to perform his duty, as he knows that if he dies, humanity would be doomed. The Guardian is thus pushed to perform his duties precisely because he can be immortal. Now, if our intuitions about the meaningfulness of the life of the Guardian are sound, it follows that there is potential to be moved to do something despite the fact that the person in question is immortal. It may be replied that such a situation is too far from reality to be evaluated. I think that this is a fair point; but it seems also that this same reasoning can be directed, in turn, to what Kass says about the fact that the immortal life would be essentially shallow. Although Kass’ reasoning is not (and so far, cannot be) supported by any psychological study that suggests its veridicity, further considerations may strengthen its plausibility. However, it remains an open question as to what kind of arguments can be used to support the idea that immortal lives would be shallow and meaningless.23 What I have tried to show is that there is nothing wrong with the idea of a categorical desire that gives meaning to life (the life of the Guardian) and that is grounded in the awareness of immortality (intended as a life not subject to ageing or, at least, without temporal limits). A variety of different scenarios can be imagined to stimulate our intuitions about this issue. For instance, if we suppose that the universe is in continuous expansion, imagine the possibility of space travel, and consider the possibility of discovering new galaxies and worlds as equally valuable and inspiring, it seems that we will not run out of possibilities to make our lives interesting, meaningful and not shallow.

Harris has a good reply to Kass’ argument 4—Virtue and moral excellence too. As has been said, Kass claims that immortals cannot be noble.19 If by ‘being noble’ it is simply meant ‘doing virtuous deeds’, as Kass seems to hold, then Harris suggests that the argument's conclusion is certainly too strong. There is nothing incoherent in a situation according to which immortals perform virtuous acts. Consider again the case of the Guardian. His duty is certainly a noble activity. Therefore, mortality is not a necessary requirement for doing noble acts. Harris also maintains that, keeping in mind that life-extending technologies do not imply in themselves invulnerability, if a person has been genetically altered so as to have no limits in the duration of her life, and if she sacrifices this for, say, saving the rest of humanity, we would certainly regard her act as noble seeing the great number of possibilities of happiness that she is giving up. In conclusion, also Kass’ last argument fails to show that mortality is, after all, not a burden, and should be preferred on balance to an immortal life.


Kass’ four arguments have revealed not to provide sufficient reasons to believe that immortality is undesirable because, by losing mortality, we would lose something that is much more valuable. Admittedly, I have not addressed all the possible objections against the desirability of life-extending technologies, and more work has to be done to clarify which features of a prolonged life are desirable.24

Before concluding this essay, here are some further considerations. The project of interrupting the process of aging and achieving some sort of immortality by removing the temporal limits that have burdened the existence of humans should not be challenged by simply sketchy remarks or conjectures drawn from poems. The stakes are too high to renounce the possible benefits of introducing innovative technologies only on the basis of political or literary sympathies. It is probable that for a considerable amount of time, immortality will likely be just a noble and, from my point of view, rational target of modern science. However, it is of the utmost importance that the process of approaching such an ideal be not obstructed by careless considerations. Even though certain arguments against modifying our biological makeup may have an intuitive rhetorical appeal, it should not be forgotten that we are placing on the balance an awe-inspiring number of possibilities that, in our given condition, would not be imaginable.


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  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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