You must have already read the tragic news: scientists have determined that I am doomed to die by 2072, when I turn 115, if not sooner. This was figured out by analyzing demographic data and seeing that people seem to hit a ceiling around age 115; the mean life expectancy keeps shifting upwards, but the maximum age seems to have reached a plateau. Carl Zimmer gives the clearest explanation of the methodology behind this conclusion, and Ed Yong gives a good description of the phenomenon of death in the very old.
The ceiling is probably hardwired into our biology. As we grow older, we slowly accumulate damage to our DNA and other molecules, which turns the intricate machinery of our cells into a creaky, dysfunctional mess. In most cases, that decline leads to diseases of old age, like cancer, heart disease, or Alzheimer’s. But if people live past their 80s or 90s, their odds of getting such illnesses actually start to fall—perhaps because they have protective genes. Supercentenarians don’t tend to die of major diseases—Jeanne Calment died of natural causes—and many of them are physically independent even at the end of their lives. But they still die, “simply because too many of their bodily functions fail,” says Vijg. “They can no longer continue to live.”
I agree with all that. I think there is an upper bound to how long meat can keep plodding about on Earth before it reaches a point of critical failure. But I’m going to disagree with Yong on one thing: he goes on to explain it in evolutionary terms, with the standard story that there hasn’t been selection for longevity genes, because all the selection has been for genes for vigor in youth, which may actually have the side effect of accelerating mortality.
This is true, as far as it goes. But I think it’s a different phenomenon, that we’re seeing a physico-chemical limitation that isn’t going to be avoided, no matter how refined and potent ‘longevity genes’ become.
When organized pieces of matter are stressed or experience wear, their level of organization decreases. You simply can’t avoid that. Expose a piece of metal in a car to prolonged periods of vibration and it will eventually fail, not because it was badly designed, but because its nature and the nature of its activity dictates that it will eventually, inevitably break.
Likewise a soap bubble is ephemeral by its nature. The same fluid properties that enable it to be blown doom it — the film will flow over time, it will tend to thin at the top, and eventually it will pop. There’s no way to suspend the physics of a soap bubble to let it last significantly longer, shy of freezing it and defeating the whole point of a soap bubble.
In people, we have a name for this wear and tear and stress: it’s called “living”. All these different things we do that make it worth existing are also fundamentally damaging — there’s no escaping the emergence of an ultimate point of failure.
115 years sounds like a reasonable best estimate from the current evidence. I’d also point out that this does not imply that we won’t find a common critical failure point, and find a way for medical science to push it up a year or five…but every such patch adds another layer of complexity to the system, and represents another potential point of failure. We’re just going to asymptotically approach the upper bound, whatever it is.
That’s OK. I’ll take 115 years. It also helps that it’s going to really piss off Aubrey de Grey and Ray Kurzweil.