The Real Science Fiction


  The Last Lethal Disease

Over the past 500 years, the average length of a human life in the developed world has more than doubled while the maximum has remained essentially unchanged. We have eliminated or greatly reduced most of the traditional causes of mortality, including mass killers such as smallpox, measles, influenza, and complications of childbirth. But old age remains incurable and always lethal.

Why? On the face of it, aging looks like poor design. We have been selected by evolution for reproductive success; the longer you live without serious aging, the longer you can keep producing babies. Even if you are no longer fertile, staying alive and healthy allows you to help protect and feed your descendants.1

The obvious answer is that if nobody got old and died there would be no place for our descendants to live and nothing left for them to eat. But that confuses individual interest with group interest; although group selection may have played some role in evolution,2 it is generally agreed that the major driving force was individual selection. If I stay alive, all of my resources go to help my descendants; insofar as I am competing for resources, I am competing mostly with other people’s descendants. Besides, we evolved in an environment in which we had not yet dealt with other sources of mortality, so even if people did not age they would still die, and on average almost as young. In traditional societies, only a minority lived long enough for aging to matter.

A second possible answer is that immortality would indeed be useful, but there is no way of producing it. Over time our bodies wear out, random mutation corrupts our genes, until at last the remaining blueprint is too badly flawed to continue to produce cells to replace those that have died. This answer too cannot be right. A human being is, genetically speaking, massively redundant – every cell in my body contains the same instructions. It is as if I were a library with trillions of copies of the same book. If some of them had misprints or missing pages, I could always reconstruct the text from others. If two volumes disagree, check a third, a fourth, a millionth.3 Besides, there are organisms that are immortal. Amoebas reproduce by division – where there was one amoeba, there are now two. There is no such thing as a young amoeba.

A variety of more plausible explanations for aging have been proposed. One I find persuasive starts with the observation that, while the cells in my body are massively redundant, the single fertilized cell from which I grew was not. Any error in that cell ended up in every cell of my adult body.

Suppose one of those mutations had the effect of killing the individual carrying it before he got old enough to reproduce. Obviously, that mutation would vanish in the first generation. Suppose instead that it killed its carrier, on average, at age thirty. Now the mutation would to some degree be weeded out by selection – but some of my children, perhaps even some of my grandchildren, could still inherit it.

Consider next a mutation that kills at age sixty – in a world where aging does not yet exist, but death via childbirth, measles, and saber-toothed tigers does, with the result that hardly anyone makes it to sixty. Possession of that mutation is only a very slight reproductive disadvantage, so it gets filtered out only very slowly. Following this line of argument, we would expect lethal mutations that acted late in life to accumulate, with new ones appearing as old ones are gradually eliminated. The process reinforces itself. Once mutations that kill you at sixty are common, mutations that kill you at seventy do not matter very much – you can only die once. Aging may simply be the working out of a large collection of accumulated late-acting lethal genes.4

A slightly different version of this explanation starts with the observation that in designing an organism – or anything else – there are trade-offs. We can give cars better gas mileage by making them lighter, at the cost of making them more vulnerable to damage. We can build cars that are invulnerable to anything short of high explosives – we call them tanks – but their mileage figures are not impressive.

Similar trade-offs must exist in our design. Suppose there is some design feature, encoded in genes, which can provide benefits in survival probability or fertility early in life at the cost of causing increased breakdown after age sixty. Unless the benefits are tiny relative to the costs, the net effect will be increased reproductive success, since most people in the environment we evolved in didn’t make it to sixty anyway. So such a feature will be selected for by evolution. Putting the argument more generally, the evolutionary advantages to extending the maximum life span were small in the environment we evolved in, since in that environment very few people lived long enough to die of old age. So it is not surprising if the short-term costs outweighed the long-term benefits. My genes made the correct calculations in designing me for reproductive success in the environment of 50,000 years ago but I, living now and with objectives that go beyond reproductive success, would prefer they hadn’t.5

One reason to figure out why we age is in order to do something about it, a subject with which I become increasingly concerned as the years pass. If there is some single flaw in our design, if aging is due to shrinking telomeres or a shortage of vitamin Z, then once we discover the flaw we may be able to fix it. If aging is the combined effect of 1,000 flaws, the problem will be harder. But even in that case, there might be solutions, either the slow solution of identifying and fixing all 1,0006 or a fast solution such as a microscopic cell repair machine that can go through our bodies fixing whatever damage all 1,000 causes have produced.

My own guess is that the problem of aging will be solved, although not necessarily in time to do me any good. That guess is based on two observations. The first is that our knowledge of biology has increased at an enormous rate over the past century or so and continues to do so. So if the problem is not for some reason inherently insoluble – I cannot think of any plausible reasons why it should be – it seems likely that scientific progress during the next century will make a solution possible. The second is that solving the problem is of enormous, indeed vital, importance to old people, and old people control very large resources, both economic and political.

If I am right, one implication is that the payoff to slowing aging a little may be large, since that might result in my surviving long enough to benefit by more substantial breakthroughs. There are currently a variety of things one can do that there is some reason to believe will slow aging. It is only “some reason” because the combined effect of the long human life span and the difficulty of arranging to do experiments on human beings mean that our information on the subject is very imperfect. Most of the relevant information consists of the observation that doing particular things to particular strains of mice or fruit flies, experimental subjects with short generations and no legal rights, results in substantial increases in their life span.

Thus, for example, it turns out that transgenic fruit flies provided with a particular human gene have a life expectancy up to 40% longer than those without the extra gene. Modifying the diet of some strains of mice – by, for example, providing them a high level of antioxidant vitamins – can have similar effects. When I was investigating the arguments for and against consuming lots of antioxidants, one persuasive piece of evidence came from an article in Consumer Reports.7 It quoted a researcher in the field as saying that taking antioxidant supplements was “banking on an aging mechanism that hasn’t been proven,” but added that “like several scientists we contacted, he takes a supplement regimen that includes vitamins C and E, beta-carotene, and a multiple-vitamin tablet.” As an economist, I believe that what people do is frequently better evidence than what they say.

One of the most effective ways of extending the life span of mice turns out to be caloric deprivation, feeding them a diet at the low end of the number of calories needed to stay alive but otherwise adequate in nutrients. The result is to produce mice with very long life expectancies. Whether it will work on humans is not yet known – or, a question of more immediate interest to some of us, whether it would work on humans who only started late in life. A parent who chose to almost starve his children would risk being found guilty of child abuse but could argue, on the basis of existing evidence, that he was actually the only parent who wasn’t.


Suppose my guess is correct; at some point in the not too distant future, hopefully at some point in my future, we find the cure for aging. What are the consequences? On the individual level they are large and positive; one of the worst features of human life has just vanished. People who prefer mortality can still die. Those of us with unfinished business can get on with it.

But while I am unambiguously in favor of stopping my aging, it does not follow that I must be in favor of stopping yours. One reason not to be is concern with population growth. As it happens, I do not share that concern, having concluded long ago that, at anything close to current population levels, mere number of people is not a serious problem.8 That conclusion was reinforced over the years as leading preachers of population doom proceeded to rack up a string of failed prophecies unmatched outside of the nuttier religious sects. Readers who disagree, as many do, may want to look at the works of the late Julian Simon, possibly the ablest and certainly the most energetic critic of the thesis that increasing population leads to catastrophe.9 I prefer to move on to what I regard as more interesting issues.

  “Senator” Means “Old Man”

ext An absolute monarchy is one in which the sovereign does as he pleases so long as he pleases the assassins.

ES Ambrose Bierce, The Devil’s Dictionary

One is the problem of gerontocracy, rule by the old. Under our political system incumbents have an enormous advantage; at the congressional level they almost always win reelection.10 If aging stops and nothing else changes, our representatives will grow steadily older. An incumbent who is guaranteed reelection is free to do what he wants within a fairly large, although not unlimited, range. So one result would be to make democratic control over democratic governments even weaker than it now is. Another might be to create societies dominated by the attitudes of the old: bossy, cautious, conservative.11

The effect on undemocratic systems might be even worse. In a world without aging it seems likely that Salazar would still rule Portugal and Franco Spain. It would have been Stalin, equipped with an arsenal of thermonuclear missiles, who presided over, and did his best to prevent, the final disintegration of the Soviet Union. With the aging problem solved, dictatorship could become a permanent condition. Provided, of course, that dictators took sufficient precautions against other sources of mortality.

The problem is not limited to the world of politics. It has been argued that scientific progress consists of young scientists adopting new ideas and old scientists dying.12 It is frightening to imagine the universities our system of academic tenure might produce without either compulsory retirement, now illegal in the United States, or mortality.

Implicit in some of these worries is a buried assumption – that we are curing the physical effects of aging but not all of the mental effects. Whether that assumption is reasonable depends on why it is that old people think differently than young people.13 One answer, popular with the old, is that it is because they know more. If so, perhaps gerontocracy is not such a bad thing. Another is that the brain has limited capacity.14 Having learned one system of ideas, there may be no place to put another, especially if they are mutually inconsistent. Humans, old and young, demonstrate a strong preference for the beliefs they already have; old people have more of them.15

One way of understanding aging is as a shift from fluid to crystallized intelligence.16 Fluid intelligence is what you use to solve a new problem. Crystallized intelligence consists of remembering the solution you found last time and using that. The older you are, the more problems you have already solved and the less the future payoff from finding new and possibly better solutions. The point was brought home to me in a striking fashion some years ago when I observed a highly intelligent man in his eighties ignoring evidence of what turned out to be an approaching forest fire – smells of smoke, reports from others who had seen it – until he saw the flames with his own eyes.

It is possible, of course, that if we ended aging – better yet, made it possible to reverse its effects – the result would be old people with the minds of the young. It is also possible that we would discover that the mental characteristics of the old, short of actual senility, were a consequence not of biological breakdown but of computer overload, the response of a limited mind to too much accumulation of experience.

  World Enough and Time

When contemplating an extra few centuries, one obvious question is what to do with them.17 Having raised one family, grown old, and then had my youth restored, would I decide to see if I could do even better a second time or conclude that that was something I had already done? Weak evidence for the former alternative is provided by the not uncommon pattern of grandparents raising their grandchildren when the children’s parents prove unable or unwilling to do the job.

The same question arises in other contexts. Having had one career as an economist, would I continue along the lines of my past work or decide that this time around I wanted to be a novelist, an entrepreneur, an arctic explorer? It is a familiar observation that, in many fields, scholars do their best and most original work when young. My father once suggested the project of funding successful scholars past their prime to re-train in some entirely unrelated field, in order to see if the result was a second burst of creativity.18 In a world without aging, that pattern might become a great deal more common. And a novelist or entrepreneur who had first been an academic economist or a Marine officer might bring some interesting background to her new profession.19

An alternative is leisure. We cannot all retire, since there has to be someone left to mow the lawn, grow the food, and do the rest of the world’s work. But it might be possible for most of us to retire or for all of us to mostly retire. Capital as well as labor is productive; more and better machinery, other forms of improved production, permit one person to do the work of 10 or 100. Consider the striking fall in the fraction of the U.S. workforce engaged in producing food, from almost everybody to almost nobody in the space of a century.20

How productive capital is at present is shown by the interest rate, the price people are willing to pay for the use of capital. The real interest rate, the rate after allowing for inflation, has typically been about 2%. If that pattern holds in the future, you could spend the first fifty years of adulthood earning (say) $80,000 a year, spending $50,000, saving the rest, accumulate about $2.54 million and then spend the rest of a very long life living on the interest: $50,800 a year for food, housing, and a good internet connection. You could, if you wished, continue working part-time, picking those activities that you liked to do and other people were willing to pay for.21 Good work if you can get it. One can easily enough imagine a future along these lines where a large fraction of the population, even a large majority, was at least semi-retired.22

While thinking about how to spend your second century, you might want to consider the social consequences of eliminating the markers of age. In a world where aging is entirely under our control, a young woman of 20 might be dating a young man 100 years older than she is – and he may or may not tell her. The same thing already happens online, where a flirtatious twelve-year-old girl may be almost anything, including a forty-year-old male FBI agent. If you, a grandfather with a retirement pension and a century behind you, could go back to college as a freshman, would you? Part-time? Lots of cute girls. The women of your own generation are just as cute, thanks to the same advanced biotech that makes you eighteen again, but the real thing has its charms. Perhaps.

  Life or a Hundred Years, Whichever is Shorter

Immortality also raises issues for our legal system. Consider a criminal sentenced to a life sentence. Do we interpret that as “what a life sentence used to be” – say to age 100? Or do we take it literally?

To answer that question, we start by asking why we would lock someone up for life in the first place. There are at least two plausible answers, associated with two different theories of criminal punishment. One is that we lock a murderer up for the same reason we lock a tiger up: He is dangerous to others, so we want to keep him where he cannot do much damage. That is the theory of criminal punishment sometimes described as incapacitation. The other is that we lock a murderer up in order to impose a cost on him, a cost high enough so that other people contemplating murder will choose not to incur it. That is the theory described as deterrence. In practice, of course, we may operate on both theories at once, believing that some criminals can be deterred, some only incapacitated, and we cannot always be sure which are which.

If our objective is deterrence, centuries of incarceration may be overkill, which is an argument for eventually letting the convict out. If our objective is incapacitation, on the other hand, we may want to keep him in. Under current circumstances, a ninety-year-old murderer is unlikely to be of much danger to anyone but himself, but if we conquer aging that will no longer be the case.

A third justification offered for imprisonment is rehabilitation, changing criminals so that they no longer want to commit crimes. That is the theory that gave us “reformatories” to reform people and “penitentiaries” to make people repent. It is hard to see why, on that theory, we would have life sentences; perhaps one could argue that there are some people who take longer to be rehabilitated than they are likely to last. If so one might reinterpret “life” as “to age 100 or until rehabilitated, whichever takes longer.”23

So far in this chapter I have been considering the consequences of hypothetical solutions to the aging problem. Next we turn to one that is already here.


Thus, the appropriate clinical trials would be to:

  1. Select N subjects.

  2. Preserve them.

  3. Wait 100 years.

  4. See if the technology of 2100 can indeed revive them.

The reader might notice a problem: what do we tell the terminally ill patient prior to completion of the trials?

(Ralph Merkle, from a webbed defense of cryonics)

The idea of cryonic suspension – keeping people frozen in the hopes of someday thawing them, reviving them, and curing what killed them – has been around for some time. Critics view it as a fraud or a delusion, analogizing the problem of undoing the damage done to cells by ice crystals in the process of freezing to converting hamburger back into a living cow.24 Supporters point out that as the technology of freezing organs improves we are learning how to decrease the damage – among other things by replacing the body’s water with the equivalent of antifreeze during the cooling process. Nobody has turned a mouse kidney into hamburger and then back into a working kidney, but the equivalent has apparently been done successfully – once – with freezing. And they argue that as the technology needed to revive a frozen body improves – ultimately, perhaps, through the development of nanotechnology capable of doing repairs at the cellular level – it will become easier to undo the damage that we cannot prevent. Finally and most convincingly, they point out that however poor your chances are of being brought back from death if you have your body frozen, they can hardly be worse than the chances if you let it rot instead.25

Suppose we accept their arguments to the extent of regarding revival as at least a possibility. We are then faced with a variety of interesting problems, legal and social. Most come down to a simple question – what is the status of a corpsicle? Is it a corpse, a living person temporarily unable to act, or something else? If I am frozen, is my wife free to remarry? If I am then thawed, which of us is she married to? Do my heirs inherit, and if so can I reclaim my property when I rejoin the living?

Many of these are issues that can be – if suspension becomes common will be – dealt with by private arrangements. If the law regards my wife as a widow, she can still choose to regard herself as a wife; if the law considers me frozen but alive, she can apply for a divorce. I am in no position to contest it. If I am concerned about keeping my wealth to support me in the second half of my life, there are legal institutions, trusteeships and the like, that give dead people some degree of control over their assets.

Such institutions are not perfect – I may be revived in 100 years to discover that my savings have been stolen by a corrupt trustee, the IRS, or inflation – but they may be the best we can do. Their chief limitation is one that applies to almost all solutions, the fact that over a period of a century or more, legal and social institutions might change in ways that defeat even prudent attempts at planning for revival. One alternative is to transfer wealth in ways that do not depend on stable institutions, perhaps by burying a collection of valuable objects somewhere and preserving their location only in memory. That tactic faces risks as well – you may be revived, dig up your treasure, and discover that gold coins and rare stamps are no longer worth very much. If only you had known, you would have buried ten first editions of this book instead.

Other problems involve adapting existing legal rules to a world where a substantial number of people are neither quite dead nor quite alive. If I commit a crime and then get frozen, does the statute of limitations continue to run, providing me a get out of jail free card if I stay frozen long enough? If I have been sentenced to fifty years in jail and, after ten of them, “die” and am frozen, does my sentence continue to run? What about a life sentence?

A more immediate problem is faced by somebody who wants to get frozen a little before he dies instead of a little after. Whether or not freezing makes it impossible to revive me, dying surely makes it harder. And some illnesses – cancer is an obvious example – do massive damage well before the point of actual death. Once it looks as though death is certain, there is much to be said for getting frozen first. At the moment, though, that is not a legal option. The law against suicide cannot be enforced against the person most directly concerned – at least, not until he is revived, at which point it retroactively stops being suicide – but it can be enforced against the people who help him. Under current law, freezing someone before death, even ten minutes before, is murder.

The simplest way of changing that is to interpret freezing not as death but as a risky medical procedure whose outcome will not be known for some time. It is both legal and ethical for a surgeon to conduct an operation that might kill me if the odds without the procedure are even worse. The probability of revival does not have to be very high to meet that requirement if the alternative is dying. Alternatively, one might change the law, as one state already has, to make assisted suicide legal.


1 For an intriguing fictional picture of a species where the old are no longer fertile but utterly devoted to the welfare of their descendants, see Niven, 1973, and other books of his set in the same universe.

2 An article on the history of the idea of group selection. Some software for simulating group selection.

3 I do not know who first made this point, but it goes back at least to Drexler, 1987.

4 Medawar, 1946. For simplicity, I am ignoring here the distinction between lethal dominants and lethal recessives.

5 A discussion of modern evidence supporting the idea that aging is not a bug but a feature in human design, some new empirical evidence, based on observed mortality in organisms ranging from yeast to human, and an explanation that links aging to an evolved device to protect against cancer.

6 A current project along these lines is DeGrey’s Strategies for Engineered Negligable Senescence.

7 Consumer Reports, January, 1992, p. 12. Some more recent studies have failed to detect any benefit from antioxidant supplements, however, and the question is still open.

8 Suppose everyone lives forever; how fast does population go up? Starting with what was a stable population of 10 billion, if each couple has 2 children and then stops we get about 15 billion in 30 years, 25 billion in a century; the growth pattern ends up linear. If every couple has 2 children every 40 years, on the other hand, we end up with an exponential growth pattern at 2.5% per year, giving about 21 billion in 30 years, 118 billion in a century, and over a trillion in two centuries.

9 Information on Julian Simon and on Bjorn Lomborg, another critic of popular views on population.
For an old discussion of some of the underlying issues, see David Friedman, “Laissez-Faire in Population: The Least Bad Solution.” An Occasional Paper of the Population Council, 1972, 43 pp.

10 In 1998, for example, of 401 incumbent congressional representatives who sought reelection, 395 won – a success rate of better than 98%. That somewhat exaggerates the advantage, since an incumbent who is confident of losing may decide not to run – but in that year there were a total of only 435 incumbents and presumably some of them decided to retire for other reasons.

11 For a fictional portrayal of such a society, see Sterling (1997).

12 Famously  by Karl Popper, whose views are described here and here.

13 An interesting discussion of the effects that life extension and the ability to alter one's personality might have on personalities.

14 Perhaps most famously stated by Sherlock Holmes, “A man should keep his little brain attic stocked with all the furniture that he is likely to need, and the rest he can put away in the lumber room of his library, where he can get it if he wants it.”

15 Neuroscientist Richard Sapolsky has written about people's disinclination to explore novelty as they age.

16 See Richard A. Posner, Aging & Old Age, University of Chicago Press, Chicago (1997)

17 For a fascinating fictional account of what a far future with immortality, VR, and much else might feel like, see Greg Egan, "Border Guards."

18 And I pointed out that, given how controversial his ideas were in his own field at the time, there should be no trouble finding people willing to pay him to switch to something, indeed anything, else.

19 Elizabeth Moon was a 1st Lieutenant with the US Marine corps before she retired to write science fiction and fantasy. For a more famous example, consider Conrad, first a sailor and later a novelist.

20 In 1900, half of the labor force were farmers; by the end of the century only 2 percent worked on farms.

21 This discussion ignores a variety of complications, such as the effect of such a pattern of saving and consumption on the market interest rate, which would carry us well beyond the limits of this book. See, for instance, Robin Hanson’s intriguing essay.

22 A discussion by Jeremy Siegel and Michael Milken of the results of life extension on the economy.

23 Arguably, “rehabilitation” may become much easier as a result of other technologies – VR immersion to show the criminal how the crime looked from the victim’s point of view or using advanced biology or nanotechnology to revise the criminal’s personality. Both pose the possibility of other and less defensible uses.

24 “Believing cryonics could reanimate somebody who has been frozen is like believing you can turn hamburger back into a cow.” (cryobiologist Arthur Rowe, quoted in “Frozen Future,” National Review, July 9, 2002). A webbed FAQ supporting cryonics points out in response that there are some vertebrates that can survive freezing but none that can survive grinding. Current procedures for cryonic suspension attempt to minimize the problem of damage from ice crystals by replacing body fluids with what is, in effect, antifreeze. A further step, currently available for head-only suspension, is to vitrify rather than freeze the body’s water – turning it solid without letting it crystallize.

25 An intelligent webbed piece by a proponent of cryonics.