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As the number of our years increases, as we age in that simple chronological sense, we also age in a more important and profound sense. Gradually but progressively our bodies begin to function less effectively, and that increasing loss of function makes us more vulnerable to disease and death. Nevertheless, we should distinguish aging from disease. Unlike disease, aging is a normal stage of life that seems “built in.” It makes us more vulnerable to disease but is not itself pathology. No one dies because his hair turns gray, and the diseases often associated with old age can occur even apart from aging. Hence, to say that someone died “from old age” simply means, as the biologist Tom Kirkwood puts it, that his hold on life had “become so precarious that, had it not been this particular cause of death today, it would have been another tomorrow.”

Aging might be said to be natural for human beings in the sense that it happens to all of us (unless, of course, we die before getting a chance to age). And while few people seem to relish growing old, even fewer want to die young, without the opportunity to age. Nor is aging natural only for human beings. All mammals age, and, with only rare possible exceptions (such as the sea anemone), so do all living organisms. We grow, we experience puberty, we mature—and we age. That is the course of a normal, healthy life. If we do not think of the other, earlier stages of our development as problems to be overcome, and if aging itself is not a disease, then why think of it as a problem that needs solving?

One reason we hesitate to adopt such a benign view of aging is, of course, that it seems so inextricably connected to death. Thus, Lewis Thomas, imagining in one of his elegant essays that ours “will someday be a disease-free species,” is quite naturally driven to ask: How then will we die? And, by way of answer, he tries to picture how we might simply wear out without breaking down in any particular way—without, that is, falling prey to any disease. Aging then becomes “an orderly, drying up process, terminated by the most natural of events.”

The moral would seem to be: Aim to cure or ameliorate the diseases associated with old age but accept aging itself. Aim not at more years but at better, healthier years. To be sure, better health will probably mean a somewhat longer average life span, but it will not necessarily alter the maximum life span for human beings. The result will be platitudinous: adding life to years, not necessarily years to life.

Sensible as this seems in many ways, it may not “make sense.” If it is good to extend life by curing illness and relieving infirmity—knocking off age-associated diseases one by one in a way almost everyone seems to approve—why not also try to slow the aging process itself and extend life still further? Moreover, if we want to preserve health and overcome specific diseases, one way to do it would be to retard the process of aging, which is closely tied to increased vulnerability to illness. Indeed, doing that (were we really able) might be a more effective way of enhancing health than simply overcoming diseases one at a time.

Thus, even if aging—unlike disease—is natural, part of “the whole, the healthy, human life,” as the President’s Council on Bioethics put it in Beyond Therapy, as long as we cannot say the same of disease, we may find it hard to argue against work that retards aging and (in so doing) extends the maximum life span. Though theoretically separate, disease and aging are inextricably intertwined in our lives. We seem driven—sometimes, at least, for the best of reasons—to try to overcome even the limit of years imposed on us, as science writer Ronald Bailey thinks, “by our genes, our evolution, and our environment.” Whether doing so is, as Bailey puts it, “the highest expression of human dignity,” I doubt. But it is not easy to argue that we should entirely forgo the attempt.

From the start, we need to think about how to think about growing old—and, in particular, how to think not simply of aging but of human aging. This will require that we learn from but also move beyond what has become the standard way to think about aging. Scholars study both why we age and how we age. The first seems to invite talk about a purpose, the second a mechanism. The first is more germane to my inquiry here.

Why do we age? The dominant answer today is that of evolutionary biology. We age because nature has relatively little stake in keeping us alive beyond our reproductive years. Insofar as we may speak of our lives having a point, it is to be carriers of DNA. Having passed that on to the next generation, we are dispensable. Any genetic trait harmful enough to cause death before the reproductive years will have difficulty surviving the filter of natural selection. Those who have such traits are less likely to reproduce, less likely to be effective carriers and transmitters of DNA. And, by contrast, natural selection will have relatively little effect on harmful genes if those harms appear only in the post-reproductive years.

Of course, we may continue to hang around for a while after we’ve produced the next generation, but as we do we inevitably begin to be affected by genes whose harmful effects manifest themselves only in those later years. Natural selection having less need to eliminate them, they accumulate and start to take a toll on us. We begin to experience the effects of a gradual and generalized physical deterioration. Because nature’s interest in us all along has been simply an interest in reproduction, in the transmitting of our genes, it has paid relatively less attention to maintaining us beyond the years crucial for that task. Focusing on reproduction rather than maintenance, nature has not bothered to weed out changes that make us more vulnerable to disease and death: a weakening immune system, increasingly brittle bones, a clogged cardiovascular system, deteriorating sensory systems. These are part of the natural process of aging, but, of course, they are also closely linked to a wide range of diseases—pneumonia, fractures, heart disease, hearing and vision loss.

Tom Kirkwood has labeled this account the “disposable soma” theory. The idea is that from the point of view of genes trying to transmit their DNA to the next generation the body is little more than a carrier and is not made to survive indefinitely. It will eventually die anyway, so not a lot should be invested in sustaining it beyond that reproductive task. “Disposable soma” is a label worth pondering. It may sound mechanistic, but it is pervasively marked by metaphors drawn from human experience. For example, it is human beings, not genes, who have a point of view. It is not genes but living organisms that have purposes and goals. It is human beings, not genes, who care about a “next generation.” And if the body seems from the perspective of this theory to be disposable, we should remember what body is being so characterized. It is our body—which is the place of our personal presence, through which we are linked to our world and to others, apart from which we can scarcely imagine our own continuing identity. Whatever the usefulness of this theory—and no doubt it is useful for many purposes—we may be led to wonder whether it is well suited to help us think about how long it is good for us to live.

It is also instructive to underscore the close connection this standard explanation discerns between aging and reproduction. “The rule, simply stated,” as molecular biologist John Medina puts it, “is this: If you have sex, you will eventually die.” From the perspective of the well-being of our species, there is little reason to devote the body’s energies to tasks of cell repair and maintenance aimed at sustaining any of us into an old age that extends well beyond our reproductive years. A favorite example of evolutionary biologists is the contrast between semelparous species (which reproduce only once) and iteoparous species (which may reproduce repeatedly). Semelparous organisms generally die after reproducing and, therefore, will not be around to provide care for their offspring. (They usually produce a large number of offspring, which compensates for the fact that they will not live to provide care.) If, however, they are prevented from reproducing, they will live much longer than their normal life span. Pondering that intriguing intertwining of reproduction with length of life, we may wonder: Would we too be less likely to produce offspring if we found a way to extend our maximum life span? Thus, science itself invites us to think about the relation between the generations.

The same lesson can be drawn from studies of caloric restriction in rodents (and, more recently, in rhesus monkeys). Indeed, a rather drastic reduction in calories seems to be the one certain method for retarding the aging process, even if we cannot say for certain how it works. Since the mid-1930s researchers have known that dietary restriction extends life. A diet containing normal healthy ingredients but with 30 to 40 percent fewer calories than usual has been shown to extend the life span of some mice and rats well beyond that of others whose food intake has not been so restricted. The usual explanation seems reasonable: If food is scarce, the body’s energy resources focus on cell maintenance rather than reproduction, increasing the animal’s chances of surviving longer and making time for it to reproduce when food becomes more readily available. Delaying reproduction extends the period of life when natural selection is effective. But, of course, a price is paid: Caloric restriction is closely tied to delayed puberty and reduced fertility. Moreover, it is not impossible that we might one day be able to manipulate the genome in ways that regulate reproduction in order to extend youthfulness and retard aging. At any rate, however we account for the connection, it indicates that aging affects not only individuals or a single generation; it has implications for the relation between the generations.

If, then, we take the standard account of why we age and try to derive moral advice from it, our first thought might be: Don’t have children, and I’ll live longer. But that would be to misunderstand, for nature is focused not on our well-being, but on that of our genes. So, instead, the moral advice that might seem to follow is: Have children, the more the better, the sooner the better. In that way we can be effective transmitters of our DNA and take our place in nature’s larger and grander undertaking. If this happens to make life burdensome for us, we can take comfort in knowing that we have played our part well. Indeed, anything—including living well into old age—that makes us less likely or less eager to have children seems contrary to nature’s ongoing project. “From an evolutionary point of view, the name of the game is,” as the biologist Robert Arking puts it, “to play again (i.e., the whole point of being a reproductive adult is to pass copies of your genes on to the next generation).”

We are disinclined to draw such moral lessons from the account evolutionary biologists give of why we age—and with good reason. That account may be able to tell us about changes that have occurred during our natural history, but it cannot tell us whether these are improvements . The fact that we can and do appeal to “nature” to support quite different versions of moral advice should, as Stephen Jay Gould once wrote, “teach us two lessons: first, that we have a remarkable capacity for self-delusion in projecting our hopes and fears on nature and re-deriving them as ‘fact,’ and second, that nature is sufficiently rich and multifarious to say yes (in part) to any human vision.”

In a remembrance of his friend and colleague C. S. Lewis, Nevill Coghill recounted a conversation that took place once when he and Lewis were dining with Rector Marett of Exeter College.

Marett was a man of abundant geniality and intelligence, always ready with friendly freshets of conversation and new gambits of gossip to entertain a guest. Presently he turned to Lewis and said: “I saw in the papers this morning that there is some scientist-fellah in Vienna, called Voronoff—some name like that—who has invented a way of splicing the glands of young apes onto old gentlemen, thereby renewing their generative powers! Remarkable, isn’t it?”
Lewis thought.
“I would say, ‘unnatural.’”
“Come, come! ‘Unnatural’! What do you mean, ‘unnatural’? Voronoff is a part of Nature, isn’t he? What happens in Nature must surely be natural? Speaking as a philosopher, don’t you know”—(Marett taught philosophy)—“I can attach no meaning to your objection; I don’t understand you!”
“I am sorry, rector; but I think any philosopher from Aristotle to—say—Jeremy Bentham, would have understood me.”
“Oh, well, we’ve got beyond Bentham by now, I hope. If Aristotle or he had known about Voronoff, they might have changed their ideas. Think of the possibilities he opens up! You’ll be an old man yourself, one day.”
I would rather be an old man than a young monkey.

This anecdote, which refers, in fact, to a well-known episode in early attempts to develop anti-aging therapies, is not only amusing; it is also philosophically to the point.

We cannot read ethical principles off the accounts given us by evolutionary biologists, because moral reasoning requires something more complicated. What we need, as Alasdair MacIntyre once put it, is not only a description of human nature in its “untutored” condition but also at least some sense of what it would mean for that nature to be fully realized. The principles that obligate us and the virtues that shape us provide the guidance and direction we need to move from our natural condition in that first (untutored) sense to our natural condition in the second (fulfilled and flourishing) sense.

This teleological conception of ethics—in which the imperative makes possible growth from the descriptive to the attractive—bears similarity to the physician’s work of medical diagnosis. The physician begins with the patient’s symptoms and illness but also with a conception of health toward which the patient needs to be helped and directed. And the physician’s prescription mediates that movement toward health. When we think normatively about our nature, we cannot avoid something like this threefold scheme.

The account given by evolutionary biologists tells us what is “natural” only in the sense that it happens all around us, and that sense will give us little traction when normative questions are our concern. “We must,” as the great nineteenth-century philosopher Henry Sidgwick once wrote, “give a special precision to the meaning of ‘natural’; since in a sense . . . any impulse is natural, but it is manifestly idle to bid us to follow Nature in this sense.” Ethics would then become, as T. H. Huxley (Darwin’s bulldog!) himself put it, merely “applied Natural History,” in which theft and murder may be as natural as philanthropy. But we are looking for something different, for the natural in the sense of a completion or fulfillment of our inborn possibilities in ways that contribute to human well-being.

Although talking about “why” we age seems to invite us to think teleologically about the point or purpose of this natural process, the account given by evolutionary biology actually eschews all such talk of fulfillment and prescribes nothing. DNA has no aims or purposes, but we—who are not just collections of DNA—do. Hence, this account is insufficient as a guide to human aging. It cannot illumine what is natural for us in the distinctively moral sense: how we ought to live in order to flourish as human beings. What is natural for us in this sense is not what happens to us all the time but what is appropriate to beings of the sort we are. And, therefore, if we want to think about whether an indefinite prolongation of life is in accord with or contrary to our nature, we will need to reflect in ways that are normative from the outset. Rather than disposing of the soma, we will need to consider the goods to which our embodied human nature itself inclines.

Prolonging life might, of course, take several different forms or have several different meanings. All things, even inorganic materials that are not alive, get older in one sense as years pass. But they do not age in the way living organisms do. We could perhaps prolong the life of many inorganic objects by taking great care to preserve them, but it would make no sense to talk about retarding their aging process. For living organisms, however, and certainly for human beings, life-prolongation and age-retardation are closely connected, yet not identical. Hence, prolonging life for more years—getting older in that simple sense—is not quite the same as retarding aging.

If the upshot of anti-aging research were that more and more of us—like Swift’s Struldbrugs—lived in a condition of indefinitely prolonged senescence, what Francis Fukuyama has called “the national nursing home scenario,” few would regard that as a successful outcome. Alas, that upshot is for us no longer entirely a matter for the subjunctive mood, as if it were still a condition contrary to fact. For many in our society it has already become the other side—the down side—of our remarkable medical progress.

But well before the marvels of modern medicine, our ancestors recognized the ambivalence of our thirst for longer life. The author of the sayings in Ecclesiastes—whoever precisely “Qoheleth” may have been—had no trouble picturing an old man dragging himself along like a grasshopper, taking no pleasure in his continuing days and years. No wonder Qoheleth famously said that there is “a time to be born, and a time to die.”

Equally powerful is the figure in Greek myth of Tithonus—a mortal man beloved of Aurora, goddess of the Dawn. She asked Zeus to make Tithonus immortal but neglected to ask in addition that he remain forever young. He became, therefore, an old man—unable to move, babbling endlessly, but unable to die. “I wither slowly in thine arms,” he says in Tennyson’s famous poem, and is driven finally to say “Take back thy gift.” If such an indefinitely extended life were the fruit of anti-aging research, no doubt many would likewise pray, “Take back thy gift.” One of the dangers of this form of life-prolongation is, in fact, that it may tempt many not merely to utter such a prayer but—deciding that if we cannot live well we should not live at all—to reject the gift entirely. In any case, life-prolongation that is not also age-retardation is unlikely to offer what we really want.

If, therefore, our present circumstance—in which many people will experience prolonged and progressive senescence—is undesirable, and if it tempts us to love life less than we ought, we do well to think about other conditions at which we might aim under the rubrics of life-prolongation or age-retardation. Without taking as our goal any increase in the maximum life span possible for human beings, we might, for instance, aim at what is often called “compressed morbidity.” The target here is primarily disease and, only indirectly, aging itself. The goal is that for (almost) as long as we live, we should live largely free of disease and disability. Then, it seems, after a (presumably) somewhat longer life than the current average life span, we would die—suddenly and rather quickly.

Something like this, it should be apparent, is what many in our society hope for. Live as long as we can at the peak of our powers—and then just fall off the cliff. We might idealize it less, however, if we thought about it more. If the idea is that we live—almost up till the end—a life that is vigorous and relatively free of disease or disability, why would we want it to end? The decline that aging involves is, in a way, a gradual and (at least sometimes) gentle preparation for the cliff toward which we move. Even now we are especially distressed when someone dies at—or near—the peak of his powers. If we all died that way, would that be an improvement?

Moreover, it is not clear—or, at least, not clear to me—that we can coherently think through the image of compressed morbidity. The idea is that we live a somewhat longer and (until the very end) disease-free life, and then we die suddenly. But we must ask: Die of what? That is not easy to say. The answer cannot simply be: of old age. To be old is merely to be increasingly vulnerable to a variety of diseases. If one or another of these is to relieve us quickly of this mortal coil, we will still have had to age. Bones must still have become brittle, sensory systems needed for vision and hearing must have deteriorated, our immune system must have weakened. (Must plaques and tangles have built up in the brain? But then we may have difficulty distinguishing this vision of life-prolongation from the first, prolonged senescence.) In short, compressed morbidity as an approach to age-retardation begins to look rather like standard geriatric medicine.

However good such medicine is, the thirst for anti-aging remedies is, I think, a desire for something more. It is an aspiration for methods that—without entirely eliminating the aging process—slow its pace considerably and thereby extend even the maximum life span. Or, more far-reaching still, it is an aspiration for means that will continuously overcome the biological processes of aging by finding ways to reverse the kinds of change and loss that for now mark our post-reproductive years. The first of these aspirations would leave intact a kind of life cycle, simply stretching it out over a more extended period. The second, more thoroughgoing, would not only extend the maximum life span but would do so in a way that no longer seemed to leave place for stages of life. Each, at any rate, has in mind an indefinite prolongation of life through retardation of aging.

Why not aggressively pursue such strategies for retarding aging?

Once we are clear that evolutionary biology, which discerns no point or purpose in natural processes, cannot answer this question, we are free to learn what we can from more modest, less far-reaching reflection on human nature. Normative thinking cannot, after all, proceed in complete isolation from what we think we know about the sort of creature we are. Human beings are characterized by tendencies, by desires, and by limits. If these provide no ready-made ethical principles, we must at least keep them in mind when we think about what it would mean for us to flourish. And even if we bracket entirely talk about cosmic purposes, we may be able to discern something about the natural ends of human life and what will or will not fulfill those ends. “Although,” as political scientist Larry Arnhart puts it, “the evolutionary process does not serve goals, the organisms emerging from that process do.”

Moreover, as Arnhart notes, although evolutionary biology thinks in terms of a natural selection that has no purposes, in many other ways modern biology is shot through with such purposive language. For example, the ability of living organisms to maintain a stable body temperature and balance of bodily fluids”homeostasis”is a teleological concept. We examine not only how this takes place but also why—to what ends—the living body works to sustain this balance. Likewise, if we ask what the acorn is made for, the answer is in terms of a natural end: to develop into an oak tree. Or, put more fully, to fulfill its nature by developing into a thing appropriate to its kind.

To be sure, we find ourselves less confident—and less in agreement—when we ask a question such as What is a human being made for? But this is the sort of question that can begin to push us to think about the meaning of human aging. Thus, for example, when Arnhart lists “twenty natural desires” that are, he says, “so deeply rooted in human nature that they will manifest themselves in some manner across history in every human society,” first on his list is the desire for “a complete life.”

Human beings generally desire life. Like other animals, they pass through a life cycle from birth to maturity to death. Every human society is organized to manage the changing desires associated with this life cycle, which passes through distinct stages such as infancy, juvenility, adolescence, adulthood, and old age. . . . Although human beings will risk their lives for a good cause, they generally agree that to be fully happy one must live out one’s natural life span.

We may notice that two somewhat different claims are closely united here. Human beings desire life. And they desire a complete life (understood in terms of the full life cycle). These do not quite come to the same thing. An indefinitely extended life might not be a life still shaped by stages culminating in old age.

Among the twenty natural desires Arnhart thinks we can identify in human beings is the desire to give and receive parental care. “Parent-child bonding is naturally good for human beings.” This way of rearing the next generation has characterized almost all human communities and has been remarkably difficult to efface even in small communities that have intentionally sought to do so. The parent-child bond as a way of rearing the next generation seems to conform better to our nature than other possible ways. Under very special circumstances (such as in the kibbutzim) it may be possible for a time to set aside this bond. Even then, however, as Arnhart notes, the evidence suggests that doing so is generally experienced as a considerable sacrifice.

Once we begin to attend to the parent-child bond, to the relation between generations, we have begun to think not just of life but of a “complete life”—a life marked in some way by stages and movement, a life that has shape and not just duration, a life whose moments are not identical but take their specific character from their place in the whole. Moreover, it is difficult to imagine a “relation between the generations” that does not include aging—coming into being and going out of being. This may stand in some tension with the thirst for indefinitely more life that most of us sometimes experience, but it is hard to imagine a characteristically human life without it. And from this perspective, a simple thirst for more (and more) life might seem to carry an unmistakable whiff of narcissism, for it is hard to imagine how we can act responsibly toward the generations that succeed us if we cling firmly (and desperately?) to our own continued youthfulness.

To be sure, we ought to be able to appreciate the desire so to cling. “A living dog is better than a dead lion,” Qoheleth says, articulating succinctly the thirst for more life. He is not entirely wrong, since, after all, only the living can aim at anything more than living. Nevertheless, to take survival as our primary goal—however necessary at times in a seemingly Hobbesian world—does not express the full dignity of our humanity. A virtuous commitment to the indefinite prolongation of life cannot be founded merely on the narcissistic desire to survive. But perhaps—put more hopefully—it can take root in the virtue of love. Indeed, this is, I believe, the strongest argument for attempts to retard aging and prolong life indefinitely. Somewhat to my own surprise, I find that it makes me hesitant—and should make us hesitant—to dismiss too quickly the desire to retard aging. Even if there are deep problems with that desire, something more is at work here than mere narcissism.

How love might elicit from us a desire to extend life is captured beautifully in John Hall Wheelock’s “Song on Reaching Seventy.” “Shall not a man sing as the night comes on?” the poet asks. And, remembering how “at evening’s hush” he has heard “A belated thrush / Lift up his heart against the menacing night, / Till silence covered all,” he is moved to reflect on the sweetness of life.

Oh, now
Before the coming of a greater night
How bitterly sweet and dear
All things have grown! How shall we bear the
The fury and joy of every sound and sight,
Now almost cruelly fierce with all delight:

The delights of the natural world come unbidden to his mind: the sun making its way through the clouds of dawn and “the clouds that stand, / Raging with light,” around the sun’s burial; a pool of rain; the flight of a bat; the cock pheasant’s morning call. “Oh, every sight and sound has meaning now.”

Still more, he calls to mind those to whom he is closely tied in love.

Now, also, love has laid
Upon us her old chains of tenderness,
So that to think of the beloved one,
Love is so great, is to be half afraid— 
It is like looking at the sun,
That blinds the eye with truth.
Yet longing remains unstilled,
Age will look into the face of youth
With longing, over a gulf not to be crossed.
Oh, joy that is almost pain, pain that is joy,
Unimaginable to the younger man or boy— 
Nothing is quite fulfilled,
Nothing is lost;
But all is multiplied till the heart almost
Aches with its burden:

We might say, of course, that the “joy that is almost pain” and the “pain that is joy” could not be so rich, ambivalent, and deeply moving an experience were it not that life moves relentlessly through its stages toward its appointed end. We might say—and this is a profound truth not to be forgotten—that, were the poet magically to cross back over that “gulf not to be crossed,” his longing would remain “unstilled.” All true. Yet, we cannot deny the power of love.

To love another is to affirm that person’s being and well-being. Not just well-being, but the sheer goodness of the loved one’s existence. To love another is to say (in Josef Pieper’s phrase), “It’s good that you exist.” Anyone who has loved must therefore feel the force of the poet’s concluding plea.

Great night, hold back
A little longer yet your mountainous, black
Waters of darkness, from this shore,
This island garden, this paradisal spot,
The haunt of love and pain,
Which we must leave, whether we would or not,
And where we shall not come again.
More time—oh, but a little more,
Till, stretched to the limits of being, the taut heart
Bursting the bonds of breath,
Shattering the wall
Between us and our world, and we awake
Out of the dream of self into the truth of all,
The price for which is death.

And of course, for anyone who loves, for as long as he loves, it may continue to make sense to say, “More time—oh, but a little more.” We should, therefore, be able to understand the thirst that drives research aimed at retarding or, even, overcoming the aging process. If aging is, in one sense, built into our nature, the desire to live more (and more) is, in another sense, equally natural for beings formed by the virtue of love.

If, despite the power of such love, there is good reason not to aim at extending our life span indefinitely, it cannot be that the delights the poet mentions are unworthy of our deep affection. It must rather be that there is yet more to being human than the poet has discerned and that these delights—sweet as they are—cannot, as St. Augustine puts it, catch the heart and hold it still. In the end, “more time” would not quench the thirst that drives us to look for ways to retard aging. We need a fuller conception of our humanity and a deeper and richer understanding of love—one that is shaped by patience and hope in the struggle to understand what, really, is good for us.

Gilbert Meilaender is the 2010-2011 Remick Fellow at the Notre Dame Center for Ethics and Culture. The writing of this essay was supported by a grant from the John Templeton Foundation. The opinions expressed here are those of the author and do not necessarily reflect the views of the Templeton Foundation.

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