How Long Could Humans Live If We Cured All Disease?

This article originally appeared on Motherboard. 

For a while now, the most common causes of death around the world have been relatively constant, albeit varied depending on place: heart disease and respiratory illness rank high in the list regardless of country, while in some parts of the developing world infectious diseases like malaria and HIV/AIDS take a larger toll.

But what if, in some as-yet undiscovered medical breakthrough, these conditions and all other causes of physical infirmity could be cured? How long would we live, if the only way we died was when an accident or injury befell us?

According to a calculation by statistics website Polstats.com the answer is a respectable 8,938 years on average: long enough that humans born in the Neolithic period would still be alive today.

To give a sense of what that looks like, the website uses an interactive simulation of a 100-strong population, who die off over time as accidents randomly occur. (Some of the Reddit discussion of the site has focused on the lone outliers who may survive 50,000 years or more.)

Of course, the website is mostly an example of how to have fun with statistics and doesn't pretend to be making any scientifically valid claims, but some of the methods used still do resemble professional epidemiology.

Dr Katherine Keyes, Associate Professor of Epidemiology at Columbia University's Mailman School of Public Health, confirmed that the basic technique—calculating the incidence of types of death in a population based on the statistical likelihood of accidents—is sound, even if the list of causes selected by Polstats are incomplete. But rather than asking what would happen if all diseases were eliminated, an epidemiologist is more often concerned with how the average life expectancy would change if just one cause of death could be reduced.

"There has been some interesting work that has shown that one of the central reasons the US lags behind a lot of similarly positioned nations [in life expectancy] is the burden of injury, which especially afflicts younger individuals: firearm related homicide and suicide for example, and drug poisoning," Keyes said in a phone call.

In this case "injury" refers to causes of death outside illness, what Polstats calls 'unnatural' although those who study mortality avoid the term. In fact, Keyes says that rather than imagine a drastically raised life expectancy all round, much of her work involves questioning why certain groups have worse outcomes than others.

"Trends in life expectancy are troubling right now in the US," she said. "The most recent analyses available indicate that for the first time we're seeing declines in life expectancy for some demographic groups, especially those at the lower end of the socioeconomic ladder. There have been gains in life expectancy, but those have been almost exclusively confined to high socioeconomic status groups, so there's a widening disparity between the haves and the have-nots."

While it's fun to imagine what might happen if injury became the only cause of death, the sad truth of the evidence we have is that there's a lot more work to be done before we're anywhere near.