Saturday, May 30, 2009

The Availability Heuristic and the Inborn Aging Process

Two weeks ago I gave a new paper entitled "Why Aging Research? The Moral Imperative to Retard Human Aging" to a group of scientists who work on biomedical gerontology at this conference in Quebec.

This talk was a unique experience for me as it was the first time I gave a talk to an audience where most people believe that (a) aging is a serious health problem, and (b) it is a problem we can actually do something about.

Why is it the case that this particular audience, unlike most audiences I address, hold beliefs (a) and (b)? The answer is simple- because this audience was composed of scientists who spend their lives studying and manipulating the biological processes of aging. So they are well aware of what happens to the biology of different species as they age, and the different kinds of interventions (e.g. dietary restriction, genetic manipulation, etc.) that can modulate the rate of aging.

Over the 3 days of the conference I met many interesting people, listened to some fascinating talks about experiments on worms, mice, and flies, and also had fascinating philosophical debates about aging and the "good life". In fact this conference was among one of the most enjoyable and rewarding conferences I have ever attended.

While at the conference I met people involved with the LifeStar Institute, and was invited to join their list of advisors. I was happy to accept, and urge you to watch the compelling and moving video on their web site.

Over the past few weeks I have also been busy making revisions to the paper that this talk is based on. And in this post I would like to bring together many of the thoughts I have been pondering. So, down to the details....

Here is a thought experiment:

Rank, from the most probable to the least probable, the following list of risks of mortality:

1. You and your loved ones will die from climate change.
2. You and your loved ones will die from a terrorist attack.
3. You and your loved ones will die from cancer.
4. You and your loved ones will die from a stroke.
5. You and your loved ones will die from Alzheimer's Disease.
6. You and your loved ones will die in a car accidence.
7. You and your loved ones will die from homicide.
8. You and your loved ones will die from pollution.
9. You and your loved ones will die from a poor diet.
10. You and your loved ones will die from the inborn aging process.

Once you have come up with your rankings, do the ranking again, but this time change the content of the first part of each sentence so it reads:

"Most people living in the world today will die from...."

These two tests do many things. Firstly, they test how accurate (or rather inaccurate) our intuitions about the major risks of mortality that we and our loved ones face are with the facts. Secondly, they test how accurate our intuitions are about the risks that face humanity as a whole.

One risk factor on this list is by far the greatest risk factor to your health, the health of your children and loved ones, and the health of the world's population-- aging (which is also implicated in risks 3,4, and 5).

I know, I know, many are sceptical about this claim. "If aging kills so many people, how come the Centre for Disease Control doesn't list aging as the leading cause of death?", you might reasonably ask. My short reply: "Because the current classifications for death, as is explicit in the title of the CDC, focuses exclusively on the proximate (e.g. specific diseases) rather than ultimate causes of mortality".

Most deaths in the world today (see here and here) are caused by chronic disease (like cancer, heart disease and stroke). And most chronic diseases afflict people in late life (over age 60). Why is this the case? Why do most cancer deaths, strokes, heart attacks, etc. occur after the sixth decade?

Evolutionary biology provides the answer. Most people alive today will die from the chronic diseases of aging. And the ultimate cause of this situation is evolutionary neglect. The inevitability of death due to hazardous external environments (e.g. predation, starvation, etc.) means that reproduction is made a higher biological priority than is indefinite maintenance. Natural selection does not influence the post-reproductive period of the human lifespan, hence why our bodies and minds begin to fall apart when they do.

But there is another problem. Because evolutionary neglect is not something we can directly observe (unlike melting polar ice caps and 9/11 terrorist attacks), few perceive the current rate of aging for the problem that is really is. No one walks into a nursing home and says: "Well, it is evident that evolutionary neglect has really left the human species vulnerable to frailty and disease in late life, let's do something about this!". The media does not report gripping stories on the impact evolutionary neglect has on scarce health care resources. Nor do politicians get elected by promising to combat the effects of evolutionary neglect. This is a problem, a big problem. It means we end up neglecting the leading cause of disease and death in the world. That's a perverse situation. Indeed, it's harder to think of a more perverse situation! And this is why I have dedicated so much of my research and energies into trying to help raise greater awareness about these issues.

In a rational world, aging research would be at the forefront of a global collaborative initiative to improve the health and economic prospects of today's aging populations (and all future generations).

But humans are not rational. We suffer many cognitive biases. One prominent bias is the availability heuristic. Risks that are easily brought to mind are given a higher probability; and conversely, the less vivid a risk, the more likely we are to underestimate the probability of their occurring.

The two tests above reveal how prominent this heuristic is in your own comprehension of the risks facing yourself, your loved ones and humanity. Because death by aging is not something that is vivid is most people's minds (though it is in the minds of the scientists who study the biology of aging and thus know all too well how it affects a species functional capacities), odds are you probably underestimated it as a risk of mortality. When you attempt to picture the scenario of someone dying from aging you probably picture a peaceful, painless death- perhaps a centenarian who, while asleep, suffers heart failure and dies immediately. Sadly this is not the reality. Very few humans have the "longevity genes" that centenarians have. Most people have the genes typical of the adults who populate nursing homes. The only thing separating you from them is the number of years you have been alive. Normal aging entails a period of chronic disease, which means a prolonged period of painful, and expensive, existence.

The reality is that almost everyone you and I know will die from the chronic diseases caused by the inborn aging process. This means your children will probably die from the same diseases that killed your parents and grandparents.

If there was nothing we could do to alter this state of affairs then it would be depressing and pointless to go on about all this. But we now know that ageing is not immutable. Humans do not have to endure the disease and frailty that the current rate of aging imposes on us. Retarding aging would add more years of health and compress morbidity at the end of life. The goal of age retardation is thus among one of the greatest priorities for humanity this century.

Sadly, not only does the availability heuristic impair our ability to perceive the risks of the inborn aging process, but it also impairs our ability to accurately evaluate the magnitude of the benefits of age retardation.

Here is another thought experiment:

Imagine what would happen if a safe and effective drug was developed that could retard human aging (by mimicking calorie restriction), thus adding 20-30 years to the human healthspan. What would the consequences of this be?

Many people's intuitions immediately gravitate towards negative consequences that can easily be make vivid in their minds- like global overpopulation and growing health inequalities between the rich and poor. But these consequences, which come up a lot in discussions of these issues, are not premised on empirical evidence. They are based on the availability heuristic.

So what are the most likely consequences of a drug that retards human aging? Well, like immunizations- that have helped reduce early-life morbidity and mortality- the most obvious consequence would be a reduction in late-life morbidity and mortality. Fewer people would get cancer, have a stroke, suffer from arthritis, be frail, suffer from dementia, suffer bone fractures, burden their families by requiring constant care, etc. So the population would be healthier and economies would flourish. But these realities are much harder to make vivid in our minds than the imagined negative consequences. It is so much easier to imagine worst case scenarios, even if they have no basis in reality. And this impedes some of the most important scientific advancements of our time.

Thus two distinct legacies of our evolutionary history present formidable challenges. The first, the inborn aging process, causes most disease and death in the world. And given how many aged people there are in the world (600 million over age 60 today, and this will rise to 2 billion by 2050) the inborn aging process will kill, for the first time ever, more people this century than any other cause. Each year chronic disease kills more people than three centuries of the "Black Death" plague killed.

The second legacy of our evolutionary history are cognitive biases, like the availability heuristic. We have evolved to perceive risks through our five senses. So a charging tiger is easily perceived as a risk. But evolutionary neglect is not. To make serious headway against aging we must also make serious headway against the faulty heuristics we commonly premise our decision-making on.

If you really care about the future your children will inherit from us, then I urge you to join the battle against chronic disease and the battle against irrationality. And championing the cause of aging research is at the forefront of both of these battles. Our children do not have to suffer the same fate that our parents and grandparents suffered in late life. Please support the science that could help reduce most disease and death in the world. Please support aging research.