This is one of my five FAQ ("Frequently-Asked Questions") pages: it covers concerns that defeating aging is a bad idea or a low priority. The other FAQ pages respond to:

- general challenges to the "credibility" of SENS,
- questions about how long people of what current age may live,
- criticisms of how I'm going about making SENS a reality, and
- queries about how one can help the SENS effort.

I work to cure aging, and I think you should too, because I feel that saving lives is the most valuable thing anyone can spend their time doing, and since over 100,000 people die every single day of causes that young people essentially never die of, you'll save more lives by helping to cure aging than in any other way. (See Lopez et al 2006, Lancet 367:1747-1757 for a recent breakdown of cause-specific death rates, especially its "webtable 2" - or, for a more immediate graphical summary, see the World Clock.) Some people can make more difference than others, sure, but don't underestimate how much difference you can make: look here first, and also think hard about what you might be able to do that I don't mention there.

I have bitten my tongue and given earnest, sympathetic answers here to the many concerns I encounter when the prospect of defeating aging is raised - but I don't pretend that it has been easy to do so. I make no secret, here or elsewhere, that I have a low opinion of the reasons people give for defending aging - and an even lower opinion of the fear that people seem to have of thinking about the topic even faintly rationally. I think that apologists for aging are in a "pro-aging trance" - that they are victims of a mutually-maintained collective hypnosis on the topic, a flight from normal rationality that resembles nothing so much as the behaviour of participants in a stage hypnotist show. When I'm feeling charitable I remind myself that this is a relatively defensible coping strategy for putting the horror of aging out of our minds and getting on with our miserably short lives free of a preoccupation with how they will end. But let's remember that this logic makes sense only so long as aging really is inevitable for the foreseeable future. Today, now that we're at last able to embark on the rational design of strategies that may truly defeat aging - strategies that may succeed within the lifetimes of many people alive today - that attitude is an enormous part of the problem.

If you aren't convinced that aging should be cured by the time you leave this page, I encourage you to email me with your reasons. If you are convinced, email me too -- that way we can work together to make the best use of your talents (including, perhaps, improving or adding to the arguments presented on this page). Which means that if you don't email me, you think it's OK not to work to cure aging and it's also OK not to be able and willing to say why it's OK. Don't forget that.

1) Societal arguments why curing aging would be bad
Curing aging would cause terrible overpopulation
Rejuvenation therapies would be available only to the rich
We'd never be able to retire
Tyrants would live forever - it would be like Brave New World

2) Biomedical arguments why curing aging would be bad
Who would want to spend any longer being frail and decrepit?
What's the point of a youthful body while the brain is still aging?
We need to sustain natural selection, e.g. for resistance to infection

3) Personal or philosophical arguments why curing aging would be bad
The young are the most creative, so multi-centenarians would be ossified
With so much time, we'd have no drive to excel
With so much life at stake, we'd have to give up everything that's fun but risky
Our existing life course is a key part of what it means to be human
It's not natural to escape aging, it's playing God
We'd be denying future generations the right to be born
This wouldn't be saving lives, it'd be extending lives
We'd forget so much about our youth that we wouldn't be the same person

4) Arguments why curing aging isn't important
I don't even want to live to 1000!
I'm too old to have any chance of benefiting
We should focus on curing disease and feeding the starving first
Let's become better people first - we don't deserve long lives
We should focus on postponing frailty, not death
Life is already long enough to do the full range of what life offers

1) Societal arguments why curing aging would be bad

There are two types of answer to reservations about curing aging based on possible social consequences. One is to examine each such reservation in depth and construct a detailed argument for how we might avoid the scenario in question. I think that's a valuable approach; I adopted it myself here and below, and many others have done the same, often better than me. But I also have a more general response, which among other things avoids objections of the form: "Well, yes, that's a strategy, but what if it fails?". Namely: pay attention, people -- we're talking about lives here, 100,000 lives a day. What do you do at the moment if you're bored? -- kill yourself? I didn't think so. Society has always had problems and doubtless always will, and it works to minimise and solve them, just like technological problems. Pretending that we will be so unable to cope with future problems that it's better to condemn indefinite billions to the puny lifespan of their ancestors is a sick joke anyway, but even sicker when we consider how implausible it is that such problems would be any worse or harder to tackle than those that we've tackled in the past. It's not as if the problems we have successfully tackled in the past seemed less daunting, either. For example, who would have thought in 1850 that society would be willing to submit to the indignity of wearing absurd rubber contraptions every time they had sex, just to arrest the population explosion that followed the near-elimination of infant mortality? Yet, that's just what happened throughout the industrialised world, with no coercion other than the simple fact that children who are still alive are very expensive.

Curing aging would cause terrible overpopulation

Perhaps you're expecting me to propose a solution that society should and thus "obviously will" adopt. Actually I'm not. I have two answers that say nothing about what specific steps society will take, one concerning past precedent and one concerning human rights. Then I'll survey some of the issues concerning what solutions we might choose, and possibly allay some concerns, but don't forget that I'm not saying what I think society will actually do.

First let's look at past precedent. Put yourself in the position of someone powerful -- the prime minister of France, for example -- in, say, 1870 or so, when Pasteur was going around saying that hygiene could almost entirely prevent infant deaths from infections and death in childbirth. In your position, you have some influence over how quickly this knowledge gets out -- and, thus, how quickly lives start being saved. But you realise that the sooner people start adhering to these principles and washing their hands and so on, the sooner the population will start exploding on account of all those children not dying. What would you have done? -- got the information out as soon as possible, or held it back as best you could in order to delay the population crisis? I have yet to meet anyone who says they would have done the latter. With curing aging, there is no difference. None. So, specifically: sure, there may well be some sort of population explosion, just as there was following the elimination of all those deaths -- and we may respond by reducing birth rate as quickly as we did then, or we may take longer -- but the first priority is to end the slaughter. Everything else is detail.

Now for the "human rights" aspect. The Earth's population will probably grow quite rapidly in the period immediately after these treatments become available, and we'll be faced with a simple choice: either we use the treatments and live a long time and have very few children, or we carry on having children at the current rate and we avoid using the treatments, so that we carry on dying of old age just like now. I don't say that I know which choice society will make at that time. What I do say is that that era's population has the right to make that choice itself, and not to have it made for it by today's society. If we delay the development of rejuvenation therapies, we are condemning future society to die at the ages that we are dying at today, whether they like it or not. We have no right to do that; we have a duty to develop these therapies as fast as possible in order to give future society the choice. Just as parliament has no right (in the UK) to constrain the choices of subsequent parliaments, so society today has no right to constrain the choices of society in the future.

OK, now for some discussion of the concrete possibilities. There are four things to consider:

- worst-case rate of arrival of an overpopulation problem;
- chance that the problem will never arrive at all;
- options if and when it does;
- whose choice it should be to decide between those options.
(Yes, the last of these will be something of a repetition of what I've said above. I reckon it bears repeating.)

1) Worst-case rate of arrival -- three main points.

First, the maximal rate of population growth resulting from eliminating aging -- i.e., the growth rate we would cause presuming we had fully effective rejuvenation therapies, universally available -- is only one big city per year. The growth rate of the global population is already a problem, of course - don't get me wrong, I'm not denying that - but it's already slowing, as a result of global lifestyle changes (greater wealth, better education of women and many other factors). Therefore, eliminating death from aging would actually only be equivalent to a few years' delay in the slowdown of population growth that's already occurring.

The second good thing is that even as and when overpopulation does get serious (if it ever does -- see below), it'll do so very gradually by comparison with other logistical problems, such as training enough medical personnel to provide the therapies. We'll be able to experiment with a variety of solutions, see how well they work, try something else, etc.

The third point to bear in mind is that a remarkably high proportion of people seem to like living in cities. With the staggering amounts of wealth that will be freed up by not having any frail people around any more, it will become practical to build very high-quality urban accommodation for everyone, and the density of that accommodation is such that a population of at least 20 billion will hardly encroach at all on the amount of rural space that currently exists.

2) Will it happen at all?

We will only have a population crisis at all if birth rate actually exceeds death rate by a large amount for a sustained period. There are good statistics (such as here) showing that a sharply increasing number of women are choosing not to have any children at all -- the proportion of women who are voluntarily childless in the USA rose 2.75-fold in just 13 years between 1982 and 1995, for example -- and it seems likely that the reason is simply female emancipation: firstly women are finding it more and more possible to occupy themselves in ways that they find more fulfilling than having kids, and secondly they are breaking out of their upbringing that having kids is the one true way to live. (I personally find the bombardment of young girls with dolls and other assorted paraphernalia of motherhood to be every bit as outrageous as the bombardment of young boys with toy guns and other assorted paraphernalia of violence, and of both with ideology of other sorts.) There are also psychological arguments suggesting that even if we want kids we will tend to want them at ever-increasing intervals, because the continued mental growth that can occur with a longer period of youthful mental capacity will progressively redefine psychological maturity as being complete at greater and greater ages.

If the above is too abstract for you, here's another reason why the trends of recent decades point to no overpopulation problem. We all know that women in the developed world (including the really big countries, China and India) are having fewer and fewer kids anyway. Now, it's reasonable to be pessimistic that this trend will continue rapidly enough to offset a sudden, wiorldwide elimination of death from aging, because OK, people are satisfied with one of two kids as opposed to ten, but their desire for those one or two is really big. But things look very different if we take into account a second trend among women in the developed world: not only are they having fewer kids in total, they're having them later. In fact, there is an overwhelming trend to having kids only when it becomes now or never, as the menopause deadline approaches. So, suppose there were no such deadline? We will want to rejuvenate ovaries anyway, for important hormonal reasons such as reversing osteoporosis. And when we do, it seems very likely indeed (on the basis of the above evidence) that women will postpone childbirth even more. So, paradoxically, giving people the ability to have more children in their lives will actually result in a sharp decline in the birth rate! This seems likely to delay the overpopulation problem a great deal, maybe forever.

3) What are our options if it does?

Basically our options are extremely simple: either restrict the birth rate or raise the death rate. The death rate can be raised by many means -- restrict access to rejuvenation therapy (thus killing old people), restrict access to antibiotics (thus killing people in more infection-laden regions) or restrict access to medical care overall (thus killing poor people, presumably). The birth rate can be kept low by, er, people acting in their own enlightened self-interest and choosing not to have kids, in the same way that today we choose not to fill up the environment with greenhouse gases, ozone-depleting chemicals and other environmental pollutants. (I realise the US is not exactly spearheading those efforts, but you'll catch up soon, I think.) Hm... kill people or don't have kids ... not a terribly hard choice, is it? Put yourself in their shoes: which would you do? Have a child and kill someone? Yourself? One can even imagine vigilantes going around and shooting people who have had kids and thereby made everyone's lives more crowded. The enlightened self-interest would be rather starker then.... Alternatives that (because of the above- mentioned gradual onset of the problem) are altogether more likely include biasing these choices by taxation. It's probably not an accident that the European nation with the highest birth rate is the one (France) with the most generous child benefit arrangements.

It's worth briefly examining the option of mass emigration into space. This seems to have limited persuasive value in reassuring people (since most people's reaction is that living in a space station would not be much fun), but maybe that's shortsighted. However, it's important to note that even if we did emigrate in sufficient numbers to allow us to maintain today's birth rate (and hence proportion of people who are children) on Earth, we would not be able to maintain that proportion indefinitely throughout the whole of humanity (including space), because space would fill up. Seriously. Space as a whole wouldn't fill up, of course, but the only space that matters is the space that we can get to by the time we want to occupy it, and that's limited by the speed of light, so for practical purposes space it's much smaller (though it grows with time). You might think that that would be only of academic interest, but it turns out you'd be wrong. In order for the proportion of humanity that are under 18 (say) to remain constant, despite a death rate that is independent of age (and very low), the total size of humanity has to grow exponentially. But the size of the space we can get to only grows cubically -- the volume of a sphere of linearly increasing radius. So eventually, we'd end up hitting a speed-of-light barrier. Would you like to guess how soon? Incredibly, it turns out that this would happen after only a few thousand years (and that's with quite generous assumptions about population density). There's also the rather more prosaic problem that we'd run out of matter to build our space stations (or ourselves, for that matter) from; we would hit that problem sooner, probably around the time we finished populating the Solar system.

This is not quite the end of the matter, however. A scenario that some people have suggested as quite likely is that our desire to have kids will progressively decline in urgency, even if it doesn't decline in intensity. If so, it may turn out that we'll mostly be happy having kids on an exponentially stretching schedule -- for example, we have a child only when we get to be twice as old as when we had our last one. It turns out that that formula isn't enough to slow growth down to the cubic rate we would need so that the speed-of-light problem would never occur -- what is actually needed is something a bit more stringent, like a progressively increasing age at which people have their first child -- but you get the idea.

4) Whose choice should this be?

Most people's reaction, of course, is that such a world (no kids to speak of, and danger to one's own life, or at least one's wealth, if one dares to procreate) would not be one worth living in. But who are we to make that decision for future generations? How do we even know what decision we ourselves would make? I like to remind people how brief was the population explosion that resulted from the virtual elimination of infant mortality a century ago when we all discovered hygiene. What happened? Answer: we found that it was prohibitively expensive to have ten kids each, and we cheerfully submitted to the barbaric indignity of wearing absurd rubber contraptions every time we have sex in order to avoid this. What do you think people would have said in 1850 if you'd proposed this as a strategy to avoid the impending population explosion? Obviously they would have ridiculed you. We have no clue what we will choose when a requirement emerges to lower birth rate further.

The fact that we can't predict what those faced with this choice will choose is the ultimate reason why we have a duty to those people to work now to cure aging as soon as possible. The sooner we do that, the more people in the future will have the opportunity to make the choice of how to live their lives (including to refuse rejuvenation therapy and die as a result, if they really find a world with fewer and fewer kids not worth living in). The longer we prevaricate, the more people we will be denying that choice and condemning to death. It's as simple as that. Those people are people too, and they have the right to be given (by others -- us) that most basic choice of all, the choice of life.

One final point to be made here is that there's no reason to assume that the whole of humanity will need to make the same collective choice. You might be concerned that if most but not all people decide to choose indefinite youth rather than kids, those who make the opposite choice will have no option other than to go along with it (or to refuse the treatment -- effectively to commit suicide -- if they don't like it). But in fact, there's no reason why we shouldn't have some sectors of society make one choice and others make the other choice. That would be just like the situation today with the Amish, who reject most modern technology: we don't resent them for that, and nor do they resent us for choosing technology. They live in harmony with the rest of us. So it will be if it turns out that some people choose non-aging and others choose kids.

Rejuvenation therapies would be available only to the rich

There's not the faintest chance of these therapies being restricted by ability to pay for more than a few years after they arrive. There are many reasons why I'm so sure of this. Here I'll give four of them.

The first reason is a slightly dark one. When a cure for aging is developed, people will want it really quite badly -- more than they want cures for other things that can only extend their lives by a few years. The problem with democracy is that it only works well for issues that a lot of people really really care about, enough to determine whom they vote for. Contemporary medicine just doesn't quite achieve that -- the economy always beats it. But that won't be true of a cure for aging. As soon as a real cure becomes widely anticipated -- let alone actually developed -- it will become impossible to get elected other than on a platform incorporating a Manhattan project to expedite a cure, both in terms of its development and in terms of its dissemination. Patents that seem in danger of slowing down the push towards universal access will simply be subject to compulsory purchase by governments (at a very hefty price, of course, but compulsory nonetheless). All the laws that we currently see impeding such progress will be torn up as quickly as turns out to be necessary. This will happen not only because of the democratic process (which works only at a national level) but also of the global political process. Since 9/11 there is a good understanding that making a lot of people very angry is a bad idea for everyone, and it will therefore be seen to be in the enlightened self-interest of the industrialised world to make rejuvenation therapies available to all (at a price they can pay, even if that means free) as fast as possible, After all, the point of buying rejuvenation therapies is to live a long time, not to get blown up by someone from the other side of the world who resents you and your compatriots because they can't afford those therapies.

The second reason is less threatening. There will be a lead-time of at least a decade, which I call the War On Aging, starting with the achievement of results in mice impressive enough to shake society out of its current fatalism and make people really want to cure aging as soon as possible. At that point, mayhem will ensue -- society will be turned upside-down in a million ways, mostly revolving around increased risk-aversion when so many more years are at stake -- but the big thing of relevance here is that (as noted above) it will become politically mandatory to throw serious money, taxpayers' money, at hastening the end of age-related death. The phrase "War On Aging" is appropriate, unlike "War On Cancer", because people will want to make sacrifices on the scale normally only seen in wartime in order to end the slaughter as soon as possible. The main such sacrifice will be in simple taxation, to pay for training of a staggering number of medical personnel, to deliver these therapies ASAP when they arrive, and also to provide much more thorough traditional medical care in the interim so as to give people as much chance as possible of still being in a reasonably healthy state at that time. That means that by the time rejuvenation therapies actually arrive, society will already have done what was necessary to ensure that they will be free at the point of delivery to all who are aged enough to need them.

The third reason is really a reinforcement of the second one, in that it is a way to help you see that the development I've just described is not at all utopian - in fact, it's completely certain to occur. It's a purely hypothetical scenario, whose consequences in terms of society's reaction are obvious and whose similarity in all relevant respects to the War on Aging is equally obvious. Here goes.

HIV is a virus that we still don't know how to eliminate from the body, nor to vaccinate against (i.e., prevent uninfected people from becoming infected). What we do now have drugs to do is suppress HIV thoroughly enough that it never proceeds to full-blown AIDS, even though it stays in the body forever. But those drugs are pretty expensive, especially in wealthy nations where drug companies are allowed to charge extremely high markups to recoup the investment of developing and testing them.

So here's my scenario: HIV mutates to become as infectious as influenza, spreading by air. What would society do?

Let's first explore what this would mean in terms of disease and mortality if society didn't do very much at all. Many viruses are as infectious as flu, but they fall into two categories: either (a) they make the infected person only briefly infectious, because the person either dies or their immune system eliminates the infectious agent from their body, or (b) they infect the body permanently but with no significant symptoms. The diseases you know most about are in category (a) -- influenza is one. A few things are in category (b) -- the most important is cytomegalovirus (CMV). And I'm sure you know, from the news stories about avian flu and its potential to cause a pandemic, that viruses mutate unpredictably to much more dangerous forms. So the scenario I'm asking you to consider is not ridiculously implausible. (Well, luckily it actually is, because HIV is "the wrong sort of virus" to be able to mutate in this way -- but that shouldn't stop you from considering this scenario and seeing what it means for how people would react to the announcement of successful "robust mouse rejuvenation".)

If this happened, we can be quite sure that virtually everyone in the world would have HIV in only a few years. Most people have CMV, and it's not as transmissible as flu, so this is not a controversial suggestion.

So, time to answer the question: what would we do? Well, one possibility is that we might ramp up the production and administration of anti-HIV drugs so that everyone got them. Is this financially plausible? Well, I've done the arithmetic for you, and it turns out that the cost in the USA would be just about the same as the cost of the war in Iraq. Quite manageable, in other words. The calculations for the rest of the world are not much different; don't forget that the fact that in sub-Saharan Africa far more people have HIV is irrelevant here, because in this scenario everyone everywhere has it.

I contend that it's perfectly clear that the world would respond to the scenario of universal HIV by ploughing the necessary funds into giving everyone effective anti-HIV drugs. Now, let's return to aging: what is the difference? Remember that I'm considering here the point where we've obtained results in mice that convince the scientific community that it's only a matter of time before we can fix aging in humans, and that it could be only a decade or two.

Well, are there any relevant differences? I suggest not. The fact that the anti-aging therapies don't yet exist won't do, because the ability to manufacture enough drugs also doesn't exist in my HIV scenario. I conclude, therefore, that society will not hesitate at all to spend the money (i.e., to elect governments who will levy the taxes to obtain the money) to make aging optional for everyone, irrespective of ability to pay.

Finally, here's my fourth reason for rejecting the "inequality of access" argument against developing anti-aging therapies. This one is a rather dry academic argument, but hey, some of those reading this may think of themselves as philosophers and prefer arguments like this.

The question before us is: even supposing that the above economic and sociological arguments are wrong, and that these therapies (if and when developed) will for many years (or possibly even forever) be available only to a subset of humanity, is it better to develop them and put up with that inequality of access, or is it better to avoid doing so in order to avoid such a divisive situation?

In order to answer this question, I'm going to introduce a third scenario. This third scenario is not a realistic one, but it doesn't need to be for my purposes, because my purpose is to use it as an intermediate between the two alternative realistic scenarios between which we wish to discriminate. In other words, I'm going to present a scenario that is unequivocally better than the scenario of never developing these therapies, and that is also unequivocally worse than the scenario of developing them and making them available to as many people as possible even though, for some time or possibly forever, we can't provide them to everyone. Since merit is transitive, that will suffice to show that developing the therapies to defeat aging is better than not doing so even if those therapies will temporarily (or possibly forever) be available only to the rich.

It's very simple: the scenario is that we develop these therapies as fast as we can, but we don't actually let anyone use them until we've made them cheap enough that we can give them to everyone old enough to need them.

Need I elaborate? I don't think so. The comparison between this scenario and the one of not developing the therapies at all eliminates the issue of unequal access, because in both scenarios access is equal. Thus, it's clear that this hypothetical scenario is better than not developing the therapies at all. Similarly, the comparison between the delayed-access scenario and the option of giving people access as soon as we can despite inequality is also clear: to delay access would be to condemn people to an unnecessarily early death.

We'd never be able to retire -- the retirement benefits would be unaffordable

No: they would be unaffordable only if we retired at a particular age and stayed retired forever thereafter. What will actually happen is that retirement will become periodic. There will be a huge demand for adult education and retraining, so that after a decade of playing golf you can go into a new career for the next 40 years. Golf all day forever won't be so attractive when we have the vigour of young adults. This applies to benefits too, including healthcare as well as living expenses: these are onerous today not because there are a lot of old people around but because there are lot of frail people, and there won't be any frail people. This is one of the most tangible and unambiguous benefits of curing aging: far from being increasingly consumed by the elderly (as is happening with the welfare situation today), wealth will be actually contributed to society by all people, of whatever age.

Tyrants would live forever - it would be like Brave New World

Tyrants who aren't aging can be assassinated just as easily as tyrants who are aging, and most tyrants these days don't die of old age, so this one doesn't bother me much. Also, just spreading democracy seems to work pretty well pre-emptively: I can't think of a single example in post-Roman history (can you?) of a state that was a democracy for more than 15 years and then ceased to be one by any method other than being conquered by another nation. [Note added after this paragraph had come online: a few examples do in fact exist, but not very persuasive ones. Chile was a dictatorship from 1973 after 40 years of democracy, but it only stayed that way for 17 years, or arguably only seven.] Another rather powerful rebuttal of the "tyrants" argument is that the majority of dictatorships last for more than one dictator. This means that one must take into account the possibility that the successor of a tyrannical dictator will be even worse. Given the choice, and with suitable hindsight, would the population of the Soviet Union of the 1920s have chosen an immortal Lenin over what they actually got? I rather suspect they would.

2) Biomedical arguments why curing aging would be bad

Who would want to spend any longer being frail and decrepit?

Sigh. The reason I find this particular objection among the most frustrating of all is that it's been answered not only by me, but by everyone working on the biology of aging, for well over half a century. It's so old that it even has a name - "the Tithonus error" - deriving from its similarity to a Greek myth, in which a goddess (Eos) fell in love with a warrior (Tithonus) and asked her father (Zeus) to make Tithonus immortal. In the myth, Zeus agreed to this, but it all ended in tears, because Eos had forgotten to ask Zeus to make Tithonus permanently youthful. Tithonus thus became frailer and frailer, until eventually Eos had to turn him into a grasshopper. The survival of this myth indicates that people find it comforting to pretend that life extension would not be such a good thing after all - what I call "the pro-aging trance." But it's a myth! As you can discover on my science pages (start here), the only way we'll ever be able to extend lifespan is by extending youthful, healthy, vigorous life. And my colleagues have been saying this since the dawn of biogerontology. The first issue of the oldest biogerontology journal, the Journal of Gerontology, had emblazoned on its cover the slogan "Adding life to years, not just years to life".

Actually it's even better than that. As you can read on my timeframes page, the rate at which we will improve our rejuvenation therapies once we make the first real breakthroughs will very probably exceed what I've called "longevity escape velocity" - which means that we'll be pushing the frail end of life further and further into the future as time passes. That means we won't actually have any frail time at the end of life.

What's the point of a youthful body while the brain is still aging?

This concern is an increasingly pervasive followup expressed by those who finally understand that the Tithonus error is an error. But it's just as misguided as the Tithonus error itself. It probably arises because we are currently seeing a huge rise in the prevalence of dementia as people live longer. The reasons we're seeing that are (a) that current medicine has made much less progress in delaying the average age of onset of dementia (in particular Alzheimer's disease) than it has for the major causes of death, i.e. cardiovascular disease and cancer, and (b) that Alzheimer's doesn't kill people quickly, so sufferers tend to spend a long time demented before they die.

But Alzheimer's disease will not be similarly resistant to the rejuvenation therapies that I work on. Just like all other diseases of old age, Alzheimer's is a consequence of accumulated molecular and cellular changes in the body (specifically in the brain in this case). We don't yet know for sure which of the changes that occur throughout life in the brain are the main cause of Alzheimer's - but, as you'll understand from my science pages, we don't need to know that: all we need to do is revert all those changes back to a more youthful state and we'll definitely revert the disease too. (Really advanced Alzheimer's is a different matter -- when lots of our memories and personality have disintegrated, there's no getting them back -- but I'm talking here about earlier stages.) In particular, there are three major things that happen -- accumulation of junk ("plaques") between cells, accumulation of a different type of junk ("tangles") inside cells, and death and non-replacement of cells. All of these things are on the list of SENS targets, and really good progress is being made on all of them.

We need to sustain natural selection, e.g. for resistance to infection

There are three holes in this concern - two logical ones and a technological one. The first logical one is that any increased vulnerability to pandemics will be self-limiting, as any large loss of life from such a pandemic will be followed by a period in which population can grow again -- in essence, simply replicating what we have today except that the deaths happen in short bursts rather than at a uniform rate, and that of course they are mostly not preceded by a long period of debilitation as occurs with aging. The second logical error is that increased susceptibility to infection should not occur anyway, because it only results from a reduction in the genetic variety in the population, and a big reduction in birth and death rates will simply keep that variety constant. And the technological rebuttal of this worry is that one of the main prerequisites for SENS is effective and safe gene therapy, which will allow us to accelerate evolution by introducing genetic changes that we identify as protective into people who are already alive.

Interestingly, there's evidence that resistance to infections is already declining because modern hygiene and antibiotics are saving the lives of so many people whose natural immune systems are relatively weak, thereby stopping natural selection from maintaining the population at a high level of immune response. But no one is suggesting banning antibiotics in order to restore the population's imune response: rather, we carry on improving our medical defences against infections, so as to save even more lives.)

One can imagine reasons other than resistance to pandemics that would be addressed over evolutionary time natural selection: for example, better resistance to ultraviolet light in response to the diminished ozone layer. But again, we will be able to address such things far faster by technology (either changing ourselves or solving the environmental problem).

3) Personal or philosophical arguments why curing aging would be bad

The young are the most creative, so multi-centenarians would be ossified

How do you know? What is it about young and old brains that generally (not universally, let's remember) makes old people less creative? I see three possibilities: it's something about the biological aging of the brain, it's a consequence of the amount of information in the brain, or it's an artefact of social pressures (older people have less time to do the rumination and daydreaming that are so intrinsic to creativity). In all cases, we are in the clear. if it's because the older brain has lost cells and synaptic connections, or the interstitial fluid is more oxidised, etc.: well, the idea is to fix all that. If it's the amount we know: no problem, because by middle age we're already pretty much at steady state in terms of forgetting things as fast as we learn them, and we'll stay that way. If it's social, even better -- when age doesn't mean anything about ability, it won't mean anything about time either. In fact, it is eminently possible that the greater range of experience that very old people wil have, when combined with the avoidance of biological aging of the brain, will actually result in people with more cognitive flexibility and creativity than anyone (young or old) has today.

With so much time, we'd have no drive to excel

This is just silly. How much does our presumption of the inevitability of aging stop young adults from striving to excel today? It doesn't stop them at all -- rather, they're driven by self-esteem, i.e. by the desire to perform as well as or better than their peers. In fact, the chances are that people will have more desire to excel in a post-aging world, because there are things that no one attempts today because they feel they'll never get them done in a lifetime, and if a lifetime is a lot longer they'll try them.

With so much life at stake, we'd have to give up everything that's fun but risky

Some years ago I agreed with this and was genuinely concerned by it: we might become reluctant to leave our houses for fear of being hit by a falling rock, that sort of thing. In the book I published in 1999 about mitochondrial mutations and aging, which had just a few pages at the end about the social context of extreme life extension, I actually predicted that driving would be outlawed because it unacceptably risks the lives of people other than the driver. But now my feeling is that we will address this very real problem in just the same way as we will have addressed aging -- by technology. We will simply make risky activities less risky, rather than avoiding them. For example: cars with very sophisticated long-range sensors and automatic override are already quite within our capabiities to build and would reduce the risk of road accidents many-fold even in the context of severe human error. The only reason we don't build them already is that at present too low a proportion of deaths are from road accidents to make it a priority. But more than half of all accidental deaths are from road accidents, so when deaths from aging are eliminated they will comprise a much higher proportion of all deaths. We will have very different spending priorities as a result.

Our existing life course is a key part of what it means to be human

I tend to answer this statement with a few questions:

1) Do you think modern medicine has made us no longer human?

2) If you think modern medicine is a good thing (e.g., because it relieves pain and suffering, plus it has only extended lifespan a rather small amount if we ignore infant mortality) then do you consider longer lifespans to be an acceptable side-effect of the alleviation of pain and suffering that modern medicine increasingly provides? If so, is future medicine that extends lifespans a great deal more not also acceptable given that it will certainly also alleviate the suffering that is an intrinsic corollary of frailty and age-related debilitation?

3) Supposing that indefinite lifespans are indeed so transformative that possession of them would make us non-human: would the availability of such technology make us non-human in your view even if we chose not to use it? For example, supposing it were developed and you chose not to use it, would you nevertheless be rendered no longer human by its arrival? I ask this because if the availability is not a problem, only the use, then there is always the option for some (or indeed all) of society to preserve, or indeed reclaim, its humanity by turning its back on such therapies.

4) Many people dispute the view that rapid medical or other technological progress endangers our humanity. Would they be rendered non-human by the cure of aging, or is one's humanity a personal thing, something to be determined by each individual for themselves? The scenario that I foresee is that those who embrace this technology when it arrives will in fact regard those who reject it as not genuinely human, even more emphatically than the rejecters will similarly regard the adopters, simply because it has demonstrably been human nature to press forward with technology ever since we invented fire. Thus, if you are sure that you will reject such technology, those of us who feel otherwise may tend to regard you as already not really human. If you feel that human-ness is an objective characteristic, who are you to decide who has it and who doesn't?

It's not natural to escape aging, it's playing God

This type of "ethical" argument is possibly the most absurd of all -- a strong statement, I realise, given the stiffness of its competition -- because of the enormity of what it overlooks within its own scope. To stand back and (by one's inaction) cause someone to die sooner, when one could act to let them live a lot longer at no (or even at some modest) cost to oneself or anyone else, is arguably the second most unnatural thing a human can do, second only (and then by a very small margin) to causing someone's death by an explicit action. (Of course, there is plenty of departure from these ethics in the world, but that's not the point -- rejection of "the law of the jungle" is what most fundamentally defines humanity, and also what defines civilisation.) Thus, to ask humanity to accept the "naturalness" argument against life extension, and on that basis to delay the development of a cure for aging, is thus to ask it to transform itself into something as un-human as can be imagined. Even if such concerns were to turn out to be valid, it is for those who experience this diminution of their existence to act to restore it (e.g., by rejecting rejuvenation therapies that are on offer), not for us to make their choice for them.

One can also put this in terms of technology, rather than civilisation. It's clearly unnatural for us to accept the world as we find it: ever since we invented fire and the wheel, we've been demonstrating both our natural ability and our equally natural inherent desire to fix things that we don't like about ourselves and our environment. We would be going against that most fundamental aspect of what it is to be human if we decided that something so horrible as everyone getting frail and decrepit and dependent was something we should live with forever. And if you believe God put us here, presumably you also believe that God made us the way we are on purpose. Thus, if changing our world is playing God, it's just one more way in which God made us in His image.

The above points are, as any philosophers reading this will notice, examples of why it's logically tempting but wrong to equate what is with what should be. Philosophers call this "the naturalistic fallacy" and lots has been written about it - not because there's any argument that it's a fallacy, but because people who haven't thought about it make the "natural = good" mistake so often. Note that the naturalistic fallacy is distinct from the idea that one can reliably discern what is good or bad by inspecting one's own gut feelings - what Leon Kass has called "the wisdom of repugnance". I take the view that the wisdom of repugnance is actually correct in some ways (though not in others) and I've explained my reasons here.

We'd be denying future generations the right to be born

This argument suggests that hypothetical individuals - people who have not yet been conceived - have rights that we should take into account in making decisions affeecting them. (Note that this bears not at all on the question of whether abortion is morally acceptable - something that I'm certainly not going to comment on.) It's an interesting idea, so let's look at it a bit more closely. There are two huge holes in it.

First of all, it's generally hard to argue that activities in which we currently all engage, and of which no major religious or philosophical school of thought disapproves, is in fact wrong. And that's what this would be - because we deny hypothetical people the right to life every day. Think about it. How old are you? How many kids do you have? And how many could you have had, if you had put your mind to it? Let's be fair and recognise that the limiting factor is the number a woman can have; it's still clear that we could raise the birth rate by at least a factor of 10 if we chose. Why don't we? Because we feel that the quality, and indeed the probable length, of those lives would be poor, and we feel that giving those who are born a respectable quality and length of life is morally better than maximising the number of births. So humanity's position on this matter is already quite clear. And all we'd be doing by eliminating aging would be adding at most 10% to the rate at which we're denying hypothetical people the right to life.

Secondly, even if we were to conclude that hypothetical people had some right to be born, that wouldn't be enough. What we're asking here is, do such people have so fundamental a right to be born that those who are already alive should lay down their lives in order to allow those people to be born? You can fill in the rest yourself: it's just as above. We have already voted with our actions; the elimination of aging would not herald a new dilemma in this regard.

This wouldn't be saving lives, it'd be extending lives

There's no difference between extending lives and saving lives. When we save someone's life, we give them the opportunity to live longer than they would otherwise have had the opportunity to live. Period. If you think you can state a clear-cut distinction between saving and extending someone's life, send me it. And don't forget that the life that rejuvenation therapies will allow is not one with extended frailty at the end of it, but one with no frailty, even at the end. Putting it another way: to say that we shouldn't cure aging is ageism, saying that old people are unworthy of medical care. That's not true: old people are people too.

One could, of course. come up with a concrete terminological distinction between extending lives and saving lives that might be useful for simple purposes of communication. But the point is that there is no moral difference between extending lives and saving lives. If it's good to cure ten-year-olds of leukemia and thereby give them the chance of another 70 years of healthy life, then it's also good to cure 80-year-olds of aging and give them that same chance. To deny this is to say that old people are worthless. I fully agree with Leon Kass and other bioconservatives that there is a concept of the "wisdom of repugnance" -- that ultimately, what is good and bad is defined by what feels natural and unnatural. But here what that means is that we should cure aging as soon as possible. I consider that saving lives is natural, and conversely that standing by and not doing life-saving research as quickly as possible is repugnant. It's not natural to condemn people to an unnecessarily early death.

We'd forget so much about our youth that we wouldn't be the same person

This is a non-issue, because we already have revolving memories and it doesn't bother us. I can't remember the names of everyone in my school class when I was 13, for example, but I don't consider myself to have died in the meantime. A large part of the reason this doesn't bother us is that we don't lose memories in first-in-first-out sequence -- the process of memory recall intrinsically reinforces a memory, so the things that we find important enough to remember (which are the things that define our self-image and identity) are maintained indefinitely, even though more superficial things are forgotten. This would be just as true for a 5000-year lifespan as for a 50-year one.

A biology-centric answer may also be useful here. Our memories (and indeed everything else about our personalities etc.) are stored in the connections between cells in the brain, and when a cell dies those connections are obviously lost forever, because a replacement cell will not necessarily hook up with exactly the same other cells even if it's in exactly the same place as the dead one was. Actually it's even worse than this, because brain cells sometimes atrophy a lot, losing a lot of their connections with other cells, even before they actually die. So it looks pretty difficult. But we're in luck, because of the way that the brain stores memories and so on. There's a lot we don't know about how it does that, but what we know for sure is that it's "holographic" -- a given fact or opinion or whatever is stored not in a single cell or connection but in the whole network of connections in the relevant brain region. So when a cell dies, it's just like removing a chunk of a hologram: the memory is still present, just that it's in a slightly less multiply "backed-up" form. Now, another thing we know is that distant memories hang on better if they are frequently recalled: I can remember my mother's name without any problem, but not the names of half the people in my primary school class which I learnt more recently, because I use my mother's name rather often and I never use my schoolmates' names. This is the crux of how we can maintain brain function and memories. If cells are replaced in the brain roughly at the same rate that they naturally die, they will be used by our normal cognitive processes that reinforce memories, just as if the cells had been there (unused) all along.

4) Arguments why curing aging isn't important

I don't even want to live to 1000!

Let's take a look at what this assertion could possibly mean. In order to live to 1000, you must first live to 999, which you'll only do if you live to 998, and so on. So, honestly, isn't it a bit premature to be forming an opinion about whether you want to live to 1000? I would respectfully suggest that you actually haven't a clue whether you want to live to 1000 - and neither do I. In fact, I don't even know whether I want to live to 100. But I do want to be able to make that choice when I'm 99, rather than having my choice gradually taken away from me by my failing health.

Perhaps the best way to look at this is to prise the question apart a little. By and large, people's desire to avoid dying any time soon -- in the next year, say -- is pretty strong if their quality of life is good. And by and large, people's assessment of their own quality of life is heavily influenced by their health. Putting those together, most people who are in full, vibrant, youthful good health don't want to die any time soon. And that's true however old they are.

So I suspect that the main reason people intuitively feel that they're not interested in living longer than is currently normal is because they are imagining it as living in the same state that today's elderly live - in other words, in a state of diminished and ever more rapidly diminishing health. But why are you still clinging to that assumption, when gerontologists have been correcting it for 60 years or more?

No - if these therapies are developed in time for you, and you get them, you'll live one year at a time, just as now, except that each year you will be just as youthful as the previous year. So the thing you should be asking yourself in deciding whether you want these therapies is not whether you want to live a really long time -- it's whether you want to get frail and decrepit and dependent and diseased, as everyone does now who lives long enough. If you don't want that to happen to you, you're going to want these therapies -- and if you end up living a really long time as a side-effect, maybe you will find it more enjoyable than you currently expect. If you don't, no one is going to force you to keep getting rejuvenated -- but you'll have the choice.

Besides: even if you yourself are really sure that you yourself don't want to live very long, quite a lot of other people may want to. (Have you asked many people whether they would prefer to die of old age than stay youthful, even if there was the "side-effect" of long life?) It's not generally considered appropriate to deny life-saving treatments to people who want to carry on living, even if those people are in a very poor state of health, and in this case the people in question would be in the prime of health. Don't we have a duty to give people the choice to live as long as they want, even if sone (or even most) people would not make that choice?

I'm too old to have any chance of benefiting

So what? Are your children too old? All lives are valuable. Consider the passengers on flight 93, who overpowered the hijackers. They can't have thought they had much chance of saving their own lives. They must have acted as they did because they knew they were going to save a great many lives on the ground. Did they know whose lives? -- clearly not. And they didn't care.

I can tell you with my hand on my heart that that is really how I look at this crusade. Roughly two people die every second, worldwide, and more than half of those people die of causes that young people more or less never die of. So we're talking about the fact that aging kills one person a second, it kills a hundred thousand people a day, it kills thirty million people a year. This is a serious number of people. And saving lives is good. I don't actually think of it in terms of saving my own life as much as I used to. Of course, when I first got into this, I was thinking of my own prospects. One thinks selfishly by default. But the more I've been working on it, the more I appreciate the value of saving other people's lives as well. So at whatever level the science is, whether I feel there's any chance of saving my own life, or whether I feel that it goes without saying that I'll save my own life and it's only older people that I need to worry about, every day that I help to bring forward the true defeat of human aging is saving a hundred thousand lives, which is like, you know, thirty World Trade Centers. It's a serious business.

But OK, I know that people matter to themselves as well as to each other - and indeed I'm perpetually reminded of this by people's unabashed acknowledgement that that's their first thought when they think about life extension. So I also think it's important to encourage you to assess carefully whether you are indeed too old to have any chance of benefiting. First, please read my timeframes page to understand how soon I think we may make various degrees of progress and with what probability. Also, don't laugh off the possibility of cryonics eventually working -- it's really only a natural extension of the repair and maintenance idea that underpins SENS, and there's good reason (see the above link and references cited there, for details) to think that people who are cryopreserved with the best technology available today (let alone with the best available in ten or 20 years) may well be preserved well enough to be revivable by future medicine.

We should focus on curing disease and feeding the starving first

There are two types of error in this idea - logical ones based on a self-contradictory interpretation of the merits of equality, and practical ones based on short-termism.

First, let's look at the question in a purely utilitarian way: let's start from the assumption that all men were created equal. If that's true, it's a reasonable corollary that all men continue to be equal however old they are. This clarifies quite a few aspects of the whole issue. First there's a question each of us must ask ourselves -- how much difference we can make in different ways. Since the main problem with curing aging soon is getting the science done, the vast majority of people can make more difference to it than to starvation in the third world, simply because the latter involves overpowering enormous political and economic pressures to preserve the status quo. Second, even if there were a choice between feeding the starving and curing aging, the arithmetic of healthy years added to people's lives by the two policies argues that we should put most of our effort into curing aging. But the third error is the most decisive: the idea that curing aging isn't urgent is based on the fact that it'll definitely take a couple of decades at least, whereas feeding the starving saves lives immediately. This is not logical. Consider two ways that someone (A) might kill someone else (B): A might shoot B, or A might build a house for B and purposely make the roof unsound so that it falls in and crushes B in bed a year later. The interval between A's action and B's death in these cases is different by perhaps seven or eight orders of magnitude, but is A's culpability any different? No. It's not different if B sells the house in the interval and the person who dies is C, either (which is the equivalent of the difference between curing diseases today and curing aging in 20 years) -- nor if by a fluke the roof falls in when there's no one home. So long as there is a pretty good chance that an action today will bring the cure for aging closer, that action today is saving lives. Putting it another way: there is no difference between saving lives and extending lives, because in both cases we're giving people the chance of more life. To say that we shouldn't cure aging is ageism, saying that old people are unworthy of medical care. Old people are people too.

The second type of reasoning is perhaps more appealing, less cold and calculating. It's simply that a maximum rate of progress over the long term requires that not only those at the back of the line, but also those at the front, continue to move forward. I'm all for helping the disadvantaged in society - I'm overjoyed that people like Bill Gates and Warren Buffett are donating huge sums to such causes. But in the long run we must at the same time continue to push for improvements in the quality (whcih includes the quantity) of life for the luckiest of us too. If we neglect that, technological progress will be slowed and we'll eventually end up with everyone worse off than they could have been.

Let's become better people first - we don't deserve long lives

I, too, sometimes get depressed about how useless we are at giving each other or our environment the respect they deserve. But to use this as an objection to defeating aging is illogical. First, you're not giving a plan for improving people, you're just wringing your hands. And more than that, there's very good reason to think that defeating aging will actually do more than anything else to make people more altruistic and responsible. Here's why.

First, there's the environment - and here the argument is simple. We're damaging the environment all the time, and we know it - but unfortunately (in a way!) we're only damaging it rather slowly. That's unfortunate because it means the environment will still be just about liveable-in 50 years from now, by which time today's adults (i.e., decision-makers) will nearly all be dead - IF we don't defeat aging. If we do, maybe people in power will preserve the environment better our of simple enlightened self-interest.

Second, there's violence - and here I include wars, state violence such as capital punishment, and simple criminal violence. Anything that is a threat to other people's lives tends to become less popular as life expectancy rises. In Western Europe, deaths from all the above causes have fallen by large factors in the past century. The same goes for health and food for those unable to afford it, which are supplied in vastly greater quantities now than a century ago (and more equitably, mainly through taxation rather than charity).

And finally - and perhaps most importantly - there's enpowerment. The fact is, aging is a constant reminder of our inability to control nature. If we can't even preserve the thing we cherish most -- our own lives -- we are always going to have a tough time believing that we can preserve or enhance much else about the world, so our impetus to try to do so is weak - we become fatalistic. Conversely, when we bring aging under our control, we will raise our sights - and our game.

We should focus on postponing frailty, not death

Arguably the single most common misunderstanding about life extension -- one that I've dealt with earlier on this page -- is that it's about keeping people alive in a physically or mentally frail state. This is also the main problem that politicians have with life extension (on account of the expense, apart from anything else), and if there were the faintest shred of truth in it then it would indeed be a serious concern. But of course we're actually about extending or restoring physical and mental youthfulness and vitality. One of the things I often berate my colleagues for is that they pander to this: rather than take the bull by the horns and educate policy-makers and the public, they try to duck the issue by pretending that gerontology isn't about life extension at all, but rather about what's called "compression of morbidity" -- keeping us healthy until very soon before we die, without necessarily delaying death at all. This is really shameful, firstly because the science tells us quite clearly that anything which extends healthy lifespan is just about certain to extend total lifespan by the same amount, i.e. not to compress morbidity at all, and secondly because people who have only just ceased to be healthy will probably not be keen on dying just yet. Being scared to tell politicians the truth does nobody any good. There have been some minor compressions of morbidity in the past 20 years in the area of mild disability, but none whatever in severe disability, and this is why -- it's biologically impossible. Some people have much shorter morbidity before death than others, it's true, but they aren't in the state that they were 20 or 50 years previously.

Not only that, even the total elimination (compression to nothing) of morbidity is not so great if you think about it: dying tomorrow if you are still in the prime of health is no more attractive at 90 than at 40. (If you don't believe me, ask a truly healthy 90-year-old!)

Life is already long enough to do the full range of what life offers

Speak for yourself. I'm quite sure I'll never run out of new and exciting things to do. Now, I agree that that's largely because I have had a very good education that has taught me how to explore new avenues as and when I feel bored, and that those less lucky than me in that regard may have more limited horizons. But remember, when we cure aging we won't have many frail people any more, and frail people today are very, very expensive -- in terms of medical care, retirement benefits and also of course the fact that they're not contributing wealth to society the way youthful people are. A lot of this freed-up wealth will be spent on adult education and retraining to enhance the lives of those who have drawn the shorter straws in today's cash-strapped world. And on top of that, there will be time to do many things that we can't do now even if we dedicate our whole life, because they simply take too long -- visiting distant stars, for instance.