I'm not buying the Demographic Theory of Senescence.
> Aging is nature’s way of leveling out the death rate, assuring that we don’t all die at the same time. Aging puts our deaths on an individual schedule so we can die at different times; other causes of death tend to kill everyone or no one.
It's a magical "group selection" hand-wavy argument—it sounds nice and is kind of heart-warming, but when making an evolutionary argument, that's usually a bad sign. In this case, it doesn't provide an explanation of how purposeful aging could possibly increase an individual's probability of passing on their genes.
If not aging was an option, you would expect to see something more similar to the results of Michael J. Wade's 1976 experimental attempt to show group selection behavior in individuals of a species. He artificially induced resource constraints on a selected subpopulation of flour beetles to see if the beetles would restrain their reproduction for the benefit of the group. What happened? The adults started eating the young of the other adult beetles.
I don't have an explanation for aging, but I seriously doubt that it's a way for Nature to regulate population size to avoid resource depletion for the group.
I'm way out of my league here, but what if aging is just the way to evolve and adapt. If there were no natural deaths, beings with the same genes would be around forever, with no possibility for its species to adapt to a new environment.
Any reproduction would be just creating more competition for resources if one expect to live forever. So there would be no deaths, but also no births, no mutations.
If there was no death we still would be just - what is the first life form to age? protofishes? populating the oceans until the salinity (?) changes and we were all dead.
Hey, sorry for the delay on this. That's not quite how natural selection works, but it's a very common line of thinking. When making an evolutionary argument, you can't make "top down" arguments. You have to look at it from a "bottom up" perspective.
Lets analyze the scenario where individuals don't die by aging. So we have some members of the species from generation 1 who grow up, then reproduce. In generation 2, there are some that have mutations that make them more suitable for the environment and some that make them less suitable. The less suitable ones are outcompeted and don't survive, the normal ones mostly group up to survive, and the ones with beneficial mutations outcompete all the others, leading to the deaths of some of the ones with the "original" genes, and procreate. This then happens again and again with beneficial mutations and they eventually becoming ubiquitous in the population.
There's just no way that an individual member of the species with a mutation that gives it a definite lifespan has a fitness advantage over the others, all else being equal. What's more likely is that immortality is not necessary to pass on genes, so it simply never developed because it would involve many complex systems, the individual components of which would not have conferred enough of a fitness advantage on their own to become universal in a population. And since the natural environment is harsh and predatorial, most animals don't die of old age anyway, which again limits the usefulness of an unlimited potential lifespan.
Yea, coming from the background assumption of "everything comes from the same thing", it seems more interesting to me that we have consciousness to experience, rather than the curiosity that we age and die. Age and death are phenomena we observe of ourselves, a thing that is constantly changing yet fundamentally the same thing.
It's a philosophical quirk, but it really depends on your existential and universal (philosophies / beliefs / religions). Things you must assume, basically, in order to make meaning from what is otherwise, pure logic (structural arrangement) and pure state (instances of that structure).
The idea that aging and death are undesirable is a complex phenomena to begin with. A rock does not care that the water slowly washes it away to shape it into a new form, yet humans have very discerning opinions on the matter across all phenomena they observe. Every explanation humanity manufactures seems to have some bias.
>it seems more interesting to me that we have consciousness to experience,
Everything that is alive has some level of "consciousness" aka some ability to sense, detect, and adapt to it's environment. The idea that consciousness is "special" and "unqiue" is the big lie. If knowledge is unified, then that means the same is true for the universe, since what we call "knowledge" is in fact the universes structure directly. Like your hand, your car, etc. What we call "knowledge" is our representations (symbolic languages like math, english, etc). We confuse our symbols with reality.
It's not that knowledge is "provisional" (aka the structure of the universe is the truth, hence not provisional), it's that our current abstract representations of it is.
Yes, it is group selection, and group selection has been badly maligned for almost 50 years now. But a large body of literature confirms group selection. See David Wilson's book, Unto Others. Group selection is especially effective in the case of population dynamics. See Michael Gilpin's monograph, Group Selection in Predator-Prey Communities.
Here are a grab bag of overviews on evolutionary theories of aging, of which there are many, and these don't even cover some of the more recent epicycles, such as explanations for runaway longevity competition in some sessile species:
Group selection isn't as dead as you might think; I've seen it show up in a number of places in evolutionary considerations of aging over the years. But then the field of aging as a whole is very reluctant to let go of any of its hypotheses.
Insofar as there is any consensus on the evolutionary reasons for aging in multicellular organisms, it is along the lines of aging providing a necessary state of life history to provide a selection advantage in conditions of environmental change. Functionally immortal or at least negligibly senescent species clearly can exist, as there are some in the wild at present, but in near every niche that life history option has been outcompeted by aging species. Here is one expression of that idea, which again you'll see is veering into group selection:
"Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes."
which a) has nothing to do with Hiroshima or Nagasaki, and b) found that low dose radiation in fact increased cancer risk (shock!):
"The results suggest that prolonged low dose-rate radiation exposure appeared to increase risks of developing certain cancers in specific subgroups of this population in Taiwan."
"Paraquat is the chemical name for the active ingredient in Agent Orange."
In reality, paraquat is very different from the active ingredients in Agent Orange (2,4-D and 2,4,5-T).
For instance, a molecule of paraquat contains 2 nitrogen atoms and no oxygen atoms whereas a molecule of 2,4-D or 2,4,5-T contains no nitrogen and 3 oxygen atoms.
The only similarity between them that I know of is that they are both used as herbicides.
The author seems to be confusing the US government's use of agent orange in Vietnamese jungles, with their use of paraquat on marijuana farms in Mexico in the 70s.
Thank you for the correction. I was relying on my memory rather than looking up the chemistry. I regret that I'll have to remove the reference to the US atrocities in Vietnam, but I suppose I'll take that up another day...
Also if you look at the skin of older people from a sunny place compared to the skin of people from an overcast place, it's noticeably tougher and more wrinkled.
I'm an Australian who has lived the last ten years in the UK and my older Australian relatives definitely have older looking skin than my husband's UK-based family.
Plus the rate of skin cancer is definitely higher in Australia. It is a real public health issue there.
"Walking around with a 40-pound backpack has the opposite effect of carrying an extra 40 pounds of belly fat."
Actually walking around with a 40-pound backpack is a bad idea, as compared to carrying the weight at the level of your belly (all other things being equal) because the risk of back damage is much higher.
Right. Belly fat is stored there because a central location is best for the body (although it was sufficiently rare in our evolutionary ascent to afford 40 pounds of belly fat that our bodies didn't adapt well to it, which is why it's so bad for us). In terms of structural imposition on the body, the backpack is worse.
Incidentally, anyone who's hiked will tell you that the best position for heavy weight is at the very top of the pack. The reason is that this puts most of the weight on your hips rather than your back.
Women seem to prefer weight lower in the pack than men, even if equal height, because of a generally lower center of gravity. I nearly broke my nose carrying a male friend's pack briefly while hiking -- tripped on a tree root and was so unused to the high center of gravity that I smashed my face into the ground. My own pack was heavier (yay food!) but sized and packed very differently.
No, the bottom of the pack is completely outside (behind) the hips. If you put it at the top of the pack, you'll naturally bend forward slightly to an equilibrium between your torso and your backpack, the top of the pack will be roughly above the hips.
Completely different physics, because buoyancy cancels out gravity. The weight belt is distributed around your center of mass because it has different buoyancy (higher density) than you, but subject to the same gravity, and you don't want it affecting your orientation underwater.
Even if this was true it's ridiculous when taken as evidence for radiation lowering cancer risk:
Survivorship bias (or survivor bias) is a statistical artifact in applications outside finance, where studies on the remaining population are fallaciously compared with the historic average despite the survivors having unusual properties.
Yes, thank you. Breast and thyroid cancer studies on Hiroshima survivors show HIGHER rates.
This was a blunder on my part. I've removed the paragraph on Hiroshima.
Mitteldorf has an interesting take on programmed aging, which is to say the collection of theories suggesting aging is a evolved program that acts to shorten life because there is some very global selection advantage in it. It is worth reading as a counterpoint to the more common viewpoints of that school (such as the hyperfunction theory of aging that is a modern take on antagonistic pleiotropy in the context of programmed aging) espoused by some of the Russian gerontology community. There's a link somewhere in the article linked above.
Programmed aging is, however, a minority view in the aging research community as a whole. The consensus view is that aging is caused by an accumulation of unrepaired damage, though there are many factions and a lot of debate within that tent. Programmed aging seems to be gaining some ground, but it's rather hard to tell from the sidelines as some of the advocates (e.g. Blagosklonny and his views on mTOR) are very prolific in their publications.
Hormesis as a phenomenon to be measured and evaluated can stand apart from either of these views on aging for the purposes of evaluation and investigation of molecular mechanisms. It is a robustly demonstrated thing in animal models, though as for all these things translating those findings into human health is ever a challenge. For things like calorie restriction, exercise, and intermittent fasting, where hormesis is thought to play an important role, the human and rodent responses in the short term are very similar. There is a small mountain of papers on this topic - just go look at PubMed and search for hormesis and longevity.
Hormesis works because some forms of damage - such as mild oxidative stress - trigger repair responses that last long enough and are proficient enough to produce a net benefit in cell health throughout tissues. There is a dose-response curve to all of this of course. This is may be how you get a variety longevity mutants in nematode worms wherein they live longer if you either reduce or increase the flux of reactive oxygen species emitted from the mitochondria. Less means less damage and more means less damage because it produces more aggressive repair.
There are plenty of ways to damage tissue that will cause incremental damage over time, but are not hormetic, and will not produce benefits. It all depends on how the repair mechanisms handle the specific case in question.
I'm sure your sources are correct but the view and sample data are biased. Cancer rates, as you note, go up with radiation and also withUV exposure. You make a dangerous point that some people who don't read carefully might buy into fast and make poor decision. A warning at the top of the post or another analysis of the effects of these exposures, on a large sample that also presents the downsides would be more balanced.
Hormesis as a general concept reeks of me of the "like cures like" of Homeopathy. This is mentioned in the article even. "A little snake venom is a cure to snake venom" is commonly used when explaining homeopathy. There may be some scenarios that exhibit this behavior but it still means your relaying on a fallacy of composition to turn it into something that can be sold as a life style.
Why do we have to simplify things and try to apply sweeping generalizations? The universe is complex. Things that apply one way to somethings do not apply that way to others.
Yeah but this concept isn't nearly as hard to stomach for me. "Fighting off disease makes you better at fighting off disease" is a little more believable than "these overpriced water molecules can learn the shape of toxins and help eliminate them in your body".
> Why do we have to simplify things and try to apply sweeping generalizations? The universe is complex. Things that apply one way to somethings do not apply that way to others.
The same reason we over complicate things. It's hard to select which direction to move in when both directions are ambiguously labeled.
Lab animals protected against stressors live longest of all. You get extremely long life spans in rats kept in sterile environments and fed plenty of very high quality food regularly. Aging is accumulated stress. It is not a genetic program.
“Every stress leaves an indelible scar, and the organism pays for its survival after a stressful situation by becoming a little older.”
--Dr. Hans Selye
The pro-hormesis claims I've seen are highly dubious. You constantly see caloric restriction and fasting brought up. It's bunkum. Within a species the animals that eat the most live longest. The restriction idea developed from two misunderstandings: 1) If you restrict feeding early in life the growth of the animal is stunted, and within a species smaller animals live longer. 2) Lab grade animal chow is loaded with mildly toxic things like soy oil and oxidized whey protein, so eating less of it rather than more is preferable.
A lot of this makes sense in the new deterministic model of aging.
It argues that aging is not a collection of mutations, the old/popular model, but instead a programmed outcome of our genes that never experienced selective pressure.
We are like a building, but the builders never know when they are done and eventually start doing counterproductive work that destroys us.
Kicking in a response to injury or pathogen may cause cells to run programs that are less detrimental to our continued survival.
Edit: Let me clarify that this in no way should be taken as an endorsement of the author's claims. I have proposed a possible model that would make the claims reasonable, but haven't examined them closely. There is a lot of quackery out there.
The only reason why we are here and not rotting are our immune systems. Take it away and we dissolve in matter of days.
Recently research on very old lady showed that all of her immune cells came from just a handful of stem cells.
It made me think that the only reason we live that long is because, that's how long our immune system lives. As we grow old it becomes less and less versatile as stem cells die out and less effective as the most effective randomly die out. Then the old age diseases kick in as there's less and less competence in cleaning up this pile of bio-matter that we are.
Excising and eating a little is not because it almost kills us and therefore it makes us stronger, just because our cleaning crew was optimized for much less food and much more movement.
Stress is not good for you. When you see pair of identical twins you can tell which one lived life of more stress. He/she looks older and by various measurements is older.
(I'm not endorsing this view - I believe aging is programmed, largely based on the fact that genes for aging have been conserved since the dawn of eukaryotic life, i.e., cells that have a cell nucleus.)
I think aging, in vertebrates, is mostly driven by the need to preserve what data has been encoded in the nervous system.
Ask yourself these questions. Would you rather have old bones or young bones? Would you rather have an old cardio-vascular system or a young cardio-vascular system? Would you rather have old muscles or young muscles?
In every case, the answer is "young".
But would you rather have an old nervous system or a young nervous system? The old nervous system is trained, the young one lacks all skills (skills range from the basics, like control of urination and defecation, to knowing how to hunt down an antelope).
Creatures that do not have a trainable nervous system (trees, coral, insects) experience a very different aging process.
Among vertebrates, those creatures that demonstrate negligible senescence (tortoises) also demonstrate a lack of learning. The price of immortality is perpetual immaturity of one's nervous system.
To quote Dobzhansky, this is all becomes obvious in the light of evolution. A challenging environment removes those cells that accumulate mutations. (i) In challenging or resource constrained environments mutated cells tend to behave more aberrantly and our immune system responds by attacking them (this is why radiation therapy works). (ii) Mutated cells will be more prone to pathogenic infection. In either case, we use the external world as a kind of extended immune system or to police our bodies against cellular mutiny.
There is no "natural selection" within an individual body, within an individual lifetime. Yes, there are some cells that continue to live and others that continue to die. But the cells are not competing, with the fittest winning out. Rather the whole scheme is orchestrated centrally for the good of the genome (which is the same in every cell).
Actually it's called somatic evolution. And there is no central orchestration. When cells start to mutate they no longer share the same genome and it's typically in the organism's interest to remove those cells because they can lead to mutation.
>If animals eat all the food that is available to them and reproduce as fast is they are physically capable, then the environment will be denuded, the next generation will starve, and the species will face extinction. All animal species are evolved to avoid this
Isn't this a Tragedy of the Commons? Won't genes that cause individuals to eat more and reproduce more quickly than fellow members of their species confer a relative advantage causing those genes to spread through the gene pool?
Tragedy of the Commons is exactly right.
Yes, the genes spread through the gene pool, but then the population goes extinct very quickly because there's a huge population and nothing to eat. This is the most powerful form of group selection, and it was first described by Michael Gilpin, http://press.princeton.edu/titles/663.html
This is all based on the ability of the organism to strongly adapt. In order to do this, they need enough energy (calories) and micronutrients. I assume the organisms studied in labs for the ability to adapt to these stressors, are (outside of calorie restriction or related studies) well-fed...
Humans are often not so well-fed, at least not nutritionally.
A very interesting concept, will definitely need to read more on this!
But what about the kind of research that talks about the dangers of living in cities... like "living in a polluted city is like smoking X cigarettes a day"?
In reality it's the other way around: Antifragile sounds like a lot of principles in nature, or rather: observations about nature that have been made a long time ago. However, this article sounds scientific but really isn't, as others in this thread have already pointed out.
I would be very, VERY sceptical - the moment he brought in evolution, he argued a theory based on (and nigh-identical to) group selectionism. Except group selectionism has been thoroughly debunked, to the point where he might as well have been spouting Lamarckism - read "The Selfish Gene", by Richard Dawkins.
Put simply, you can't just jump from looking at individual survival to looking at a group's survival, because any individual could just be a free-rider. More importantly, what's actually been observed is that group selectionism simply doesn't happen in the real world.
So while anything I said about the rest would be mere opinion, there is at least one multi-paragraph section of his argument that is a GIANT heap of shit.
The Selfish Gene was a phase in our understanding of evolution. The mainstream now agrees that evolution is a whole lot more complicated than that. It's still true that "group selection" is a dirty word to a majority of evolutionary scientists, but this is shifting pretty fast - much less true than it was 10 years ago. Take a look at the works of David Sloan Wilson. I recommend his book, Unto Others. http://www.hup.harvard.edu/catalog.php?isbn=9780674930476
Well, the main advice is eating less and exercising more, the author stops short of recommending a radiation source in the home. So, it's not really controversial and is not considered harmful.
Yeah... what about bacteriocidal antibiotics that cause mitochondrial DNA damage? The people affected by that stuff don't seem to just like recover and get stronger.
Mitochondrial damaged human speaking (genetic cause, not antibiotics)
Hormesis is about dose. In these cases, the dose is just too high and our body is unable to cope with it.
In my case the damage is just below this threshold and my body has created a powerful antioxidant machinery [1] that is keeping me alive. In other cases of my disease, the burden - % of mutant mitochondria - is just too high [2] and sadly, the kids die when they are 3-4 years old.
Aging isn't there because our genes "need" it. It's there because our genes don't need long lifespans. The gain in reproductive viability that we'd get with a >60 year natural lifespan just isn't enough to justify the constraint that a much longer (or indefinite) lifespan would impose on our genetic "search space". We can live forever and be simple, or we can be complex and get a job done and die.
There probably is some anti-fragility in us. I don't buy the LNT threshold of radiation, for example. All that said, I'm not sure that hormesis is useful as a general concept. There are mild stressors (such as cold, when prepared and for short duration) that turn out to have positive effects, but there are a great number of stressors that seem to have no positive effects, whether you're talking about biological agents (e.g. cadmium, lead) or psychological experiences (e.g. rape, war).
Natural selection only molds us up to the point where we procreate and ensure the survival of our offspring. After that (say age 50), we're winging it.
Mild stressors that would occur naturally - physical exertion, exposure, hunger; it is perfectly logical that natural selection would favour those who handle these circumstances well.
I like that ... "winging it" after 50. :-) Made me chuckle. I agree with it.
I have a (an emotional) problem with that number though, being acutely aware and sensitive to ageism or age-related relegation of human functions and roles in society. I have a problem with any number for that matter. 50 is too low, and any number will always be too low, the way I see it if you incorporate Dawkins' idea of the Selfish Gene into the mix. I would argue that sticking around "to ensure the survival of our offspring" (as you put it) for the human species is significantly more important than any other species on the planet.
Turtles don't need this survival strategy. Lay eggs (procreate) and chuck - that form of hormesis aggressively weeds out the weak members of the species from the ones laying eggs for the next generation. While chimps, elephants and whales may also need to "stick around longer" for their young - relatively, the human is by far an incredible outlier in this regard. Not only do adults have to stick around for their kids well into the young's teen years, but elders too have to stick around for the group or for the clan. This last point is important to understand the relationship between the survival success of the species and an imagined age cutoff for "usefulness" (that contributes to the success of the species) of any one member of the species. The individual has extended roles beyond just his/her offspring. His/her role in the clan's survival success mattered too.
Recent discoveries of hominid fossils suggest that as early as Erectus, "humans" have been keeping their elders alive! :-) Evidence of a toothless skulls suggest that able members of the group may have been keeping the elder alive by chewing for her. But for what?? Could it be to access knowledge of poisoned berries to avoid, or hunting methods to teach or ... stay at home creche for the kids while able-bodied adults went out for hunting??
Again, I don't think I needed to respond to your point necessarily ... you're right for the most part.
> 50 is too low, and any number will always be too low, the way I see it if you incorporate Dawkins' idea of the Selfish Gene into the mix. I would argue that sticking around "to ensure the survival of our offspring" (as you put it) for the human species is significantly more important than any other species on the planet.
I see what you mean, but with every generation of your offspring, you're less and less vital to their survival - your children and grandchildren can care for your great-grandchildren as well; there's more redundancy there, so no individual is as crucial.
Of course, menopause needn't be an adaptation, but a side-effect of some other adaptation. (Even that is pushing it, since it is hard to talk about evolution without using language of agency.) The point is: if you do not have actual information about how and when this evolved, you have nothing to stand on.
Searching for articles with the keyword "hormesis" (a word I first learned in the latest book by Nassim Nicholas Taleb, who is not a person with medical training or experience) on the Science-Based Medicine website is instructive.[1] The concept of "hormesis" is not well thought out enough or well validated enough with careful measurements to be your guide to your personal health practices. There is better health advice in some of the earlier comments here.
Thank you to the several commenters who have already politely pointed out factual and logical mistakes in this submission. We can do better for reading matter to be submitted to Hacker News. "Essentially there are two rules here: don't post or upvote crap links, and don't be rude or dumb in comment threads."[2]
> Searching for articles with the keyword "hormesis" (a word I first learned in the latest book by Nassim Nicholas Taleb, who is not a person with medical training or experience) on the Science-Based Medicine website is instructive.
No it's not! 3 out of the 7 links relate to homeopathy, which the article explicitly states is problematic:
'Association with the problematic science of homeopathy. In the early 20th Century, people who promoted homeopathic medicine were prominent supporters of the concepts of hormesis.'
Your stance is based on an argumentum ab auctoritate. How about constructing an argument, rather than spewing meta-trash talk?
> a word I first learned in the latest book by Nassim Nicholas Taleb, who is not a person with medical training or experience
Ergo, hormesis does not exist? Non sequitur.
> The concept of "hormesis" is not well thought out enough or well validated enough with careful measurements to be your guide to your personal health practices. There is better health advice in some of the earlier comments here.
The only prescription of the article was to eat less & exercise more!
> Thank you to the several commenters who have already politely pointed out factual and logical mistakes in this submission.
Agreed. It's called 'discussion'.
> "Essentially there are two rules here: don't post or upvote crap links, and don't be rude or dumb in comment threads."
> Aging is nature’s way of leveling out the death rate, assuring that we don’t all die at the same time. Aging puts our deaths on an individual schedule so we can die at different times; other causes of death tend to kill everyone or no one.
It's a magical "group selection" hand-wavy argument—it sounds nice and is kind of heart-warming, but when making an evolutionary argument, that's usually a bad sign. In this case, it doesn't provide an explanation of how purposeful aging could possibly increase an individual's probability of passing on their genes.
If not aging was an option, you would expect to see something more similar to the results of Michael J. Wade's 1976 experimental attempt to show group selection behavior in individuals of a species. He artificially induced resource constraints on a selected subpopulation of flour beetles to see if the beetles would restrain their reproduction for the benefit of the group. What happened? The adults started eating the young of the other adult beetles.
http://www.pnas.org/content/73/12/4604.full.pdf
I don't have an explanation for aging, but I seriously doubt that it's a way for Nature to regulate population size to avoid resource depletion for the group.