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.
115 may be the current maximum for humans, but its clearly far, far from the maximum possible for biology. The oldest animal is apparently over 180 years old and the oldest tree over 5000 (first google results for those phrases). The only thing which decrepitude suggests is a poor housekeeper. When bits of a car fail, we can replace them, essentially indefinitely. Why not with humans? The neurons will be tricky, but otherwise?
That’s a large underestimate — koi can live over 200 years, a giant tortoise was estimated to have lived 255 years, some shark species are estimated to live up to 500 years, and corals and sponges can live for millennia.
And I too find the car analogy unconvincing, since a major feature of biological systems is that they are self-repairing. A priori arguments about physical limits on the longevity of such systems seem to miss the point (and the huge spread of lifespans of organisms, including many with spans far beyond our typical lifetime, seems to show that such base physical issues are not a real consideration).
However, there may indeed be specific biological limits for specific types of organisms — for example, as noted above, neural regeneration may be a problem for humans. But those are biological issues, and potential at least may have biological solutions.
I really, really hope that there actually is an upper bound and it’s not too far beyond those 115 years. Not that I enjoy the prospect of death, but I don’t want to live in a world with 500 year-old oligarchs.
PZ Myers says
The secret to longevity is to live very slowly, and be a poikilotherm or a sponge. Not very useful.
“Self-repair” is a glib answer. The self-repair mechanisms are also mechanisms that need to be repaired — what happens when they break? If you look at cancer, you can see all kinds of built-in self repair mechanisms in the cell, that go wrong, disastrously.
Ian King says
Humans are not soap bubbles, though. We’re arguably not even things, so much as large collections of smaller things, each of which can die and be replaced many times over the course of our lives.
I lack the high level education to be sure, but is it not the case that ‘degradation’ of the germ cells is otherwise known as evolution?
I appreciate the point about the inexorable flow of entropy, but life pushes back against that with every passing moment. Isn’t that one of its defining features?
To keep pushing it outward, you’d either have to figure out how to drastically increase our resilience to cancer and damage, gradually replace everything in the human body “Ship of Theseus” style – or both. Some mammals, like bowhead whales and naked mole rats, seem to have evolved with the former (they’re long-lived because of cancer resistance and low metabolisms). The latter just depends on where medical science ends up, particularly when it comes to cultivating tissue and replacing it.
Derek Vandivere says
I think it’s a bit like space travel – we might figure out how to drastically extend our lives, or travel to exoplanets, but certainly not in this form.
Pierce R. Butler says
The ceiling is probably hardwired into our biology.
All hail the power of Ceiling Cat!
I’m perfectly fine getting only 115 years—or even only 80 years for that matter (well, I’d like more than that)—provided they are high quality years. No point to living decades with dementia or in chronic, intractable pain, or other conditions that degrade quality of life below a certain threshold.
The women in my family live into their 90s, the men die around 70, but the one thing they all have in common is they remain mentally sound and functional for most of it, and then crash and burn at the end in relatively short order. I consider myself lucky.
The problem with the self-repairing idea is that the repair mechanism is also being repaired. Errors are going to creep in, and grow faster and faster.
I don’t doubt that there is a limit to natural age, but I do have doubts that they will remain important over time. I can easily see nano-repair bots working inside tissue to repair damaged cells, and transplants grown from placental cells (frozen and stored at birth) as an option for major organ failure.
I doubt I will live to see this, but the idea of returning aged cells to their youthful vigor I think is technically possible even if we don’t have the capability now.
The societal effects of this are terrifying.
The secret to longevity is to live very slowly, and be a poikilotherm or a sponge. Not very useful.
Or the way a mushroom lives faster than an elephant? The ‘rate of living’ hypothesis is based on a really noisy correlation.
It’s easy to declare that lifespan is limited by physics because we can’t falsify it yet. Nobody’s radically extended the life of any living thing, even things that have very slow metabolisms and short lives that *should* have a lot of margin to keep going.
As far as self repair goes, try this thought experiment:
1. When an animal is born, harvest a colony of stem cells and fully sequence the DNA of a subset of them.
2. Grow the colony to 16 times its original size, separate it into 16 groups, and fully sequence the DNA of a sample from each group.
3. Compare all groups with the original ‘master’ sequence, and keep only the colonies that completely match it. Throw away all the others.
4. Go to #2, and repeat.
So, why can’t you use Darwin to correct errors instead of just creating them? Cells undergo entropy, but the controlling data does not have to.
An article in Nature earlier this year described an experiment to induce cell death in senescent cells in mice. I don’t have a subscription to read the paper, but popular writeups of it (grain of salt goes without saying) say a 35% increase in lifespan as a result. Is that radical extension? A 35% increase in average lifespans in the U.S. would mean you could expect to live to about 107.
@7 Derek Vandevere
In fact, the two are probably related. I think achieving full cell replacement and functional immortality via nanobots is probably more achievable than warp drive. So if you solve the lifespan problem and start thinking in terms of centuries or millenia, then you can start thinking of space travel. Probably not before.
Evidence for a limit to human lifespan
Driven by technological progress, human life expectancy has increased greatly since the nineteenth century.
Arrgh! It would be nice if the authors managed to get the title and the first sentence to agree.
Life expectancy has definitely increased since the nineteenth century but that increase is more due to reduced infant and child mortality than an extension of lifespan.
I am just annoyed at the poor writing; the actual paper may be fine and but one is not encouraged by the mix-up between longevity and life expectancy in the first sentence.
It reminds me of my favourite “I am an idiot” first sentence in an otherwise very interesting article.
As late as the end of the 19th century, even a visionary like Jules Verne could not imagine a city with more than a million inhabitants. Jonas Rabinovitch and Josef Leitman Scientific American March 1996
Given that William Playfair reported that London in 1811 had a population of 1.1 million, I am not sure that Jules would have had much trouble.
Kimberly Dick says
I don’t know about that. It’s probably not possible to avoid it entirely, but there’s no physical limitation that prevents repair mechanisms from continuing to function for an extended period of time.
The main issue at hand here is entropy: yes, absent intervention, the entropy of the body will naturally tend to increase. But there are methods to lower the entropy of open systems. We lower the entropy of our bodies every time we ingest food, for example (the total food+body entropy always increases, of course, but we use the increased entropy from the breakdown of the food to lower our body’s entropy temporarily).
My guess is that the real problem here is that there won’t ever be one single advance which will lead to dramatically longer life. We might find a way to improve the cell’s repair mechanisms in one way, but then end up dealing with side effects on the other side, leading to minimal overall improvement. And then there are dozens of other cellular mechanisms to tweak. I’m sure that in the far future, we might even get to the point of using microscopic machines.
But no matter what steps we do take, no matter how outlandish or sci-fi-sounding, each additional year of additional longevity will likely be much harder to achieve than the last.
It seems to me that our time and money could be better-spent dealing with disease to get more people to live comfortably to be over a hundred than we would in increasing the maximal life expectancy from 115 to 118 or so.
That may be true for humans (all mammals, maybe?). But negligible senescence is a thing some fish and reptiles (alligators, yay!) have.
Gregory in Seattle says
The real problem to our life span is that Tree-Of-Life won’t grow on this planet, meaning that Human Breeders cannot fully advance to the Protector stage of life.
(Just want to see how many Larry Niven fans are here.)
chigau (違う) says
Gregory in Seattle #18
I am well advanced in that lumpy joint thing and the tooth loss.
Bring on the roots!
I have no desire to live to 115 until science and medicine figure out how to improve dementia-free survival after 100. I’d also rather see improvements in treating some of the problems that aren’t necessarily life threatening but seriously impact quality of life (hearing, vision, arthritis, osteoporosis etc.).
I don’t think that anyone is saying that thing don’t go wrong, I think the point of contention is your idea that they necessarily MUST go wrong in that way every time at approximately the same time for everyone.
Anders Kehlet says
@20 chris61: Aubrey’s argument is that we should do something about aging itself, thereby rendering geriatrics largely superfluous.
a 35% increase in lifespan as a result. Is that radical extension?
Definitely! I have been overtaken by events. In any case, it would cast doubt on the ‘hard limit because physics’ view of longevity.
To render geriatrics superfluous you’d have to increase the human lifespan indefinitely which is a horrifying prospect.
consciousness razor says
The paper in question described an increase in the median, which definitely does not imply anything about the maximum.
Also, thermodynamics is becoming the quantum woo of pessimists.
The 2nd law only talks about the amount of useable energy in a closed system, nothing else.
The words ‘information’ and ‘disorder’ aren’t in the official definition, and if they were it would be pretty suspicious, as those are very subjective qualities, each depending on the knowledge you have before you look at the system.
It seems odd to say 115 is a “ceiling”, when there are at least 16 well-documented cases of people living to 116 or more (one of them to 122). And i’m not in the least convinced by the “physico-chemical limitation”. Sure, nothing lasts forever. But where’s the evidence or argument implying that physics means people can’t live substantially longer than they now do?
Meg Thornton says
I’d put it this way: I’m from a long-lived family. Three out of four of my grandparents survived past ninety, both of my parents are now in their mid-seventies and still going strong. I’m likely to live out my threescore years and ten without too much trouble. On the other hand, this goes hand-in-hand with a tendency toward depression on both sides of the tree – so it’s basically swings and roundabouts. On the one hand, I’m likely to live to a respectable old age. On the other hand, I’m not likely to enjoy it all that much while I’m doing it.
I’m 45. I’ve lived with suicidal ideation since I was about 10. I’m fine with dying eventually – I have a corner of my brain which is constantly set to memento mori, and I’m fine with that. One day I will die, and the problems of life will be much reduced. I just hope I manage to achieve it before dementia sets in (both of my grandmothers had dementia when they died; neither of my grandfathers did). I do a lot of living in my head, and I don’t particularly fancy having to spend my declining years constantly bumping into the mental furniture.
Unless immortality comes with rejuvenation, I don’t want a bar of it.