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How long will you live?

The promise of ever-longer lifespans is a new phenomenon that probably won’t last.

For all but the last 10,000 of the 315,000 years Homo sapiens have existed, we were hunter gatherers. From the point of view of longevity, it seemed to suit us. Life expectancy for people in those apparently primitive societies was not equalled until well into the 20th century.

Recent research has debunked the notion that hunter-gatherer life was “solitary, poor, nasty, brutish and short”. A comprehensive study of those early peoples found that hunter-gatherer societies that had developed a strong and cohesive culture (such as Australia’s Aboriginal people), of every 100 people born, on average:

  • 67 reached the age of at least 15;
  • 53 lived to between 57 and 72;
  • Some lived even longer.

The shift from the nomadic hunter-gatherer lifestyle to village settlements may not have been the blessing it is often supposed to be.

The dig at Çatalhöyük
Archaeologists examining skeletons in a cemetery at Çatalhöyük, an agricultural settlement in Anatolia, showed how much life regressed with a settled existence. At that time – between 8,000 and 10,000 years ago – the trend towards living in settled farming communities had begun in the fertile crescent of Asia Minor.

The researchers estimated that the average age of death for men was 34 and 28 for women. None survived past 45.

Living in a crowd and close to domestic animals encouraged lethal outbreaks of infectious disease. It also led to interpersonal violence, especially against women. Many of the skeletons in that cemetery had had their skulls bashed in.

Densely populated cities, linked with busy trade routes, allowed pandemics to sweep regularly across continents. Plague outbreaks were frequent, with peaks that killed vast numbers. At the height of the Plague of Justinian in the 540s, 5,000 people died every day in Constantinople alone. The Black Death in the 14th century killed between 75 million and 200 million people throughout Europe and Asia.

AT LAST, LIVES LENGTHEN

It took over 8,000 years, but by the 1920s, people in industrialised countries were finally living as long as those palaeolithic hunter-gatherers.

But until the 1880s, the scourges of city life – cholera, typhoid, malnutrition – kept lifespans down to prehistoric levels. But with the understanding of disease transmission, improved sanitation and diet – basic elements of public health – the turnaround began.

By comparison, colonial Australia was a dangerous place to live.

When the deprivations of the convict period faded, Australia became a largely rural and agricultural nation. Today, living in the country equates to poorer access to healthcare and, often, shorter lives. But back then, medicine made little difference to survival, and any deficit was more than made up by a healthy, open-air lifestyle and plenty of good food.

By the middle of the 20th century, the rapid gains faded. For a decade in the 1960s, no progress was made at all in life expectancy. Progress resumed in the 1970s but on a slowing trajectory.

Much of that early, sharp increase in overall life expectancy came from an equally sharp decline in child mortality. As those gains slowed, so did the improvements in overall life expectancy.

The very high rates of childhood death in colonial Australia did not, fortunately, last. Once the convict era passed, a largely rural lifestyle sent these rates dramatically lower – and substantially lower than the rates in the Britain of the industrial revolution where much of the population lived in squalid and unhygienic cities.

But in both countries, the most significant long-term declines in child mortality dated from the turn of the 20th century.

The causes of this rapid decline are uncertain and hotly debated by academics. It’s likely that a large range of factors worked together to produce this result; but after 50 years of major improvement, the graph flattens out. In Britain and Australia, child mortality rates now stand at four for every 100,000 people. Further improvements are being made but, at these levels, will not greatly alter population-wide life expectancy.

But the survival of more children into adulthood is only part of the picture. Disease control was also of major importance.

Cardiovascular disease and cancer are by far the two biggest killers of modern-day Australians. The effect on cardiovascular death rates of blood-pressure medication, introduced in the 1960s, was dramatic.

 
Until 2010, these conditions – mostly heart attack and stroke – took far more lives than all cancers put together. But there have been no such decisive breakthroughs in the detection and treatment of cancer. Data from the Australian Bureau of Statistics show that in 2019, cancers accounted for 33% of all deaths; cardiovascular deaths had declined to 25%.

Continued improvement in life expectancy depends significantly on greatly improved prevention, detection and treatment of cancers. Progress so far has been slow and – at best – incremental. New cancer drugs are almost always expensive and come with serious side-effects. Their effect on survival, particularly in patients with metastatic disease, is usually minor. Further improvements in radiotherapy and surgery are unlikely to provide the level of benefit that would have a noticeable effect on population-wide lifespans.

Early detection may be the key, although many apparently promising tests have failed to deliver. There may, though, be more grounds for hope in a new blood test that is claimed to detect more than 50 cancers and which has so far performed well in human trials.

Data on deaths from lung cancer show how uncertain the link between prevention efforts and actual reductions in deaths can be. For Australian men, the link between reduced smoking and longer life is clear. For women, there is a paradox. Rates of daily smoking declined in a parallel trend with those of men – but lung cancer deaths rose.

The declines in respiratory and other infectious diseases, in Australia and elsewhere, were largely the result of the availability of antibiotics from the 1930s and 1940s. Vaccines have also been important but most were developed later and could not have had a major influence on mortality before the 1950s and 1960s.

By the middle of the 20th century it was widely supposed that infectious disease had been permanently controlled in developed countries and would no longer produce major threats to population health. But new epidemics and pandemics – HIV/AIDS, SARS, Covid-19, Ebola and the other haemorrhagic fevers – changed that view. Many are viral diseases, not treatable with antibiotics. Challenges include viral and bacterial resistance and the failure of the global pharmaceutical industry to develop new antibiotics to replace those which resistance has rendered no longer effective.

Infectious disease, even in developed countries, retains the potential to cause mass deaths

As people live longer, the diseases of old age become more significant. Sixty years ago, dementia was not a major killer: now it is. About half as many people die of dementia as from cancer. Apart from an apparent turndown in the first year of Covid, we can expect the death rates from Alzheimer’s and the other dementias to increase.

The mix, though, may change. Improvements in cardiovascular health should produce a decline in vascular dementia, the second most prevalent form.

Projections by the Australian Institute of Health and Welfare suggest the number of people living with dementia is likely to double by mid-century and then to keep on rising.

 But this is less scary than it looks. When we compare the prevalence estimates with the Australian Bureau of Statistics’ population projections, we can see that by about 2040, the rate of growth will slow. Even by 2058, only about 2.1% of the Australian population is likely to have any form of dementia and, of those, many will be less serious cases. And it doesn’t translate directly into death rates: most people with dementia will eventually die of something else.

THE LONGER YOU LIVE, THE LONGER YOU LIVE

If you’re old enough to read this, life expectancy at birth is not a good measure of how long you have left. These figures all work on averages: as time has passed, some people of your age have already died. As more and more die (and you survive) your average improves.

This is how it works, according to the current estimates. A baby now has a life expectancy of 81.2 or 85, depending on gender. But if you’ve made it to 85, you’re likely – again, on average – to reach 91.6 or 92.7.

Even here, you can still beat the odds. That average includes people who are well and those who are already seriously ill. If you’re well, you’ll go further into your 90s than the average.

There’s nothing very fair about these cold statistics. This chart again demonstrates that fact: your chance of a long life depends heavily on where you live and how much money you’ve got.

Between the poorest and richest areas of Australia, there’s a massive difference. The extreme results – outback Queensland and Northern Territory – reflect the early death rates of indigenous Australians. But look at the difference between the Latrobe Valley in Victoria and the inner suburbs of the major capitals.

Overall, though, Australia does pretty well. According to the Organisation for Economic Cooperation and Development, our life expectancy at birth puts us at number six on the list of the world’s 193 countries.

HOW MUCH LONGER CAN THIS GO ON?

More people are living longer lives but the rate at which this is happening seems to be slowing. What, then, are the limits?

The proportion of the population who are in their nineties is now six times the level of 50 years ago. That reveals the pattern of ageing: more and more people living into extreme old age.

Many more people are living into their eighties and nineties, but that trend is likely to come up against a hard boundary: the ultimate limit to human lifespan.

Only the most fervent optimists working in the science of ageing think there may be no limit at all – and even they concede that extending life indefinitely would depend on a fundamental and unlikely reboot of the human genome.

Other, more credible, research projects have tried to calculate how long humans could, in ideal circumstances, live. Most have come up with answers from 120 to 150 years. But there’s also a body of evidence that we may already be approaching the practical limits of human longevity. There will always be some rare outliers who live a few years longer, but those are irrelevant to the rest of humanity.

This chart shows the age of the oldest person to die each year in Australia and in the world. In the past half century, it has not moved – despite huge improvement in population-wide life expectancy over that time.

Here, then, is the probable hard limit on life. But these people are all outliers, the least typical of all humans. While it’s theoretically possible for large numbers of people to live until 110 or so, there are many reasons to believe this is unlikely.

All the main trends in life expectancy in developed countries like Australia are slowing. Child mortality can’t get much lower. Ditto for death rates from infectious disease. The downward curve for cardiovascular disease is beginning to slow. Cancer death rates have hardly shifted in a century.

One more chart: the pattern of death. This shows how far we still have to go, and how hard it will be to get there.

It is plainly unrealistic to expect that more than a few will live past 100. A more likely outcome is that most of us will eventually live into our nineties. For that to occur, two things must happen: dementia and the other diseases of old age must be successfully addressed; and we have to stop so many people dying in their sixties and seventies.

It may, of course, never happen. Perhaps a more cogent question is whether mere lifespan is more important than the quality of life. It may not be such a great bargain if the price of living on and on is  increasingly debilitating disease, enduring discomfort, disability, pain and indignity.

When she turned 110 in 1985, Jeanne Calment was in high spirits and joked with reporters: “I’ve only got one wrinkle,” she said, “and I’m sitting on it.”

She finally died, in 1997, at 122. Hers is believed to be the longest life ever recorded. Not long before, blind and ailing, she was asked if she wanted to see the end of the century. “No,” she replied. “I’ve had enough.”

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