
Physics Makes Aging Inevitable, Not Biology (2016) - dnetesn
http://nautil.us/issue/36/aging/physics-makes-aging-inevitable-not-biology
======
rowyourboat
The headline's premise does not square with the fact that there are organisms
that don't age and whose life span is only limited diseases, accidents and
predation.

[https://en.wikipedia.org/wiki/Negligible_senescence](https://en.wikipedia.org/wiki/Negligible_senescence)

That strongly points toward a biological reason for aging. I mean, sure, the
heat death of the universe is inevitable, but that is not even remotely on the
same time scale as the life span of complex organisms.

~~~
brlewis
That none of the longest-lived organisms are warm-blooded squares well with
the article's premise that physical heat damage causes aging.

~~~
ecpottinger
Then how do you account for mole-rats.

[http://experimentalbiology.org/getattachment/2014/About-
EB/P...](http://experimentalbiology.org/getattachment/2014/About-
EB/Press/Press-Releases/Rodriguez-Buffenstein-Release-FINAL.pdf.aspx)

~~~
atmanthedog
My best guess would be that they are so because they are eusocial.

As I posted in a comment below somewhere, I think it is the complexity of the
nervous system that drives a tradeoff with repairable bodies. A brain does not
want to have to retrain itself, but the history it stores makes it
entropically very energy intensive to maintain. I think this drives most of
what we see here: things without complex nervous systems (pyramidal neurons
and such) have no disincentive in persisting indefinitely, because their
relatively simple nervous system does not take increasing amounts of energy to
maintain, and thus they can budget their energy for growing and other
evolutionary benefits.

Most mammals have to budget their energy such that they can maintain the state
of their brain, and thus have a disincentive for eternal aging: we either need
to start forgetting earlier memories, which could potentially be bad, or we
have to start paying the energy price of maintaining a very complex system.
Energy usage tends to get optimized by evolution, so then, we end up trading
off longevity.

Mole rats, however, being eusocial, have a different evolutionary strategy
than most mammals. Since the entire colony effectively behaves as a single
metaorganism, losing its experienced members is particularly painful if they
have valuable institutional memory. Thus, there is stronger evolutionary
pressure to pay the cost of maintaining these systems.

(I realize that isn't really what you were commenting about, but it does give
a thermodynamic reason for their longevity, but not one simply based on
temperature.)

~~~
rowyourboat
> Thus, there is stronger evolutionary pressure to pay the cost of maintaining
> these systems.

... which implies that it is biologically possible to maintain them, which
implies in turn that aging is a biological trade-off and not a physical
inevitability.

~~~
atmanthedog
Yes, I agree. I guess the question is what is meant by inevitable. The
meanings of biological and physical in this instance aren't really all that
different, if the biological problem is a limitation of the underlying
physics. Ultimately, the scarcity of usable energy is driving this trade-off,
which is a physical limitation of the universe. It becomes 'possible' in the
sense that a O(n^100) algorithm is 'feasible' (see Arora and Barak, section
1.6.2). If maintaining a youthful state indefinitely increases our energy
consumption hundredfold entirely due to the cost of maintaining a low entropy
state in a highly complex system, is that really 'possible'? If we have to pay
an ever increasing energetic cost to maintain ourselves, it is both a
biological trade-off and a physical inevitability.

------
RobertoG
I'm not sure what is the message of the author here.

Entropy always increase in closed systems, but we are not talking about a
closed system here.

My understanding is that, from the point of view of physics, there is not a
reason for not being possible to decrease entropy in the body increasing
entropy outside (expending energy).

Also, this is untrue: "DNA can only be repaired when there is an intact
replica to copy".

If you have, for instance, three incorrect copies of a DNA sequence you can
compare them in order to get the original sequence. The probability that the
copies are damaged at the same point being very small.

~~~
amelius
There are also some theories on proton decay, which could be considered a
source of "physical" aging, but the timescales are extremely large.

~~~
rtkwe
Yeah, if we get to the point where humans (or whatever our evolutionary
progeny are can't imagine it'd be anything resembling humans today) are still
around when that starts happening at 10^28 years which is ~10^17 years from
now I'll consider that a job extremely well done as a species/civilization.

~~~
AnimalMuppet
10^28 years is ~10^17 years from now? I think you either typoed or your math
is faulty...

~~~
rtkwe
I just messed up the math. It should be 10^19. Either way it'd be an
unqualified success.

~~~
AnimalMuppet
I still think you're incorrect. If we're at 10^13 years, then 10^28 minus
10^13 is, essentially, 10^28 years from now.

> Either way it'd be an unqualified success.

Certainly. I'm just picking nits on the math.

~~~
rtkwe
Oh wow yeah. Well too late to edit the original now. My math mistake shall
live on.

------
antognini
This is outside my area of expertise, but it seems that the author may not
have presented Medawar's argument correctly. As I understand it, Medawar's
theory of aging was not so much based in physics as based in evolution. The
author presents it here as random DNA transcription errors building up
mutations which eventually cause the animal to die.

But I think that Medawar's argument was that all animals are subject to random
accidents, predation, disease, etc. This will produce an exponential
distribution of lifetimes. As a consequence, beyond a few half-lifes, there
will be exponentially few members of the species. So if there is some mutation
in the DNA which causes the animal to die beyond that time, there will be so
few members of the species around to exhibit it that there will be effectively
no selection pressure to keep this mutation out of the population. As a
consequence, even if you started out with a population that could in theory
live forever, it will very quickly become riddled with mutations which start
to kill the animals after a couple of half-lifes. From the outside, it would
appear as though the animals were "programmed" to die at a certain time.

George Williams presented a similar argument, but also claimed that some
mutations can increase an animal's fitness early in life at the expense of
decreased fitness much later in life. If the animal will likely have died of
some accident by that time anyway, this trait effectively has no downside and
will be selected for.

------
stochastic_monk
Senescence is a biological, not oxidative or thermodynamic, phenomenon.

More oxidation, more metabolism, and more turnover gives you more chances to
break down/accumulate mutations/shorten telomers, but that’s an artefact of
cells running out of their means for rapid growth. These can be modified.
Look, for example, at the countless immortalized cell cultures.

It is a biological problem with roots in statistical and biomolecular physics,
like literally everything else in biology.

------
justonepost
So how is it that green land sharks can live 400 years? Or the Great Basin
bristlecone pine is like 5K years? And what about
[https://en.wikipedia.org/wiki/Biological_immortality](https://en.wikipedia.org/wiki/Biological_immortality)

~~~
Numberwang
Land Sharks? Help!

~~~
EGreg
[https://i.ytimg.com/vi/sUOifHlxGiw/hqdefault.jpg](https://i.ytimg.com/vi/sUOifHlxGiw/hqdefault.jpg)

------
cornholio
> it is difficult to see how natural selection could have selected for
> senescence, because we don’t reproduce in our elderly years and natural
> selection is driven by differences in reproduction rates

That's an entirely backwards way to look at the problem: selection works with
living organism and the only reason an organism lives or performs a particular
function is that it was evolutionary useful to do so for it's genes. Aging
therefore is something natural selection can't discern on: at some point, the
number of additional offspring that can be produced becomes negligible
compared to the exponentially increasing probability of death from
environmental causes (just like the test tube example); so organisms that
quickly reproduce young are much more successful than long lived organisms.

It's easy to see then, why the long term accumulating damage, irrelevant for a
young organism, can't be evolved out of. We are essentially "single use" from
an evolutionary standpoint.

Therefore, advanced age (anything exceeding useful reproductive life) is
something outside evolution. Anything happening at senescence time is simply a
byproduct of the mechanism selected for ensuring success at young age, a
system that continues to work by momentum and not design or selection, up to
the inescapable moment when entropy catches up to it.

But there is no fundamental physical reason for it, and it stands to reason we
could create biological machines that maintain the power to self repair
indefinitely, given suficient outside energy. It's just enormously more
complex than "curing aging", it means artificially redoing billions of years
of evolutionary choices that were good enough for reproduction. It's a God
level task.

~~~
perlgeek
There are second-level effects where longevity can increase gene frequency: In
a social species like humans or some whale species, the presence of parents
and even grandparents can have positive effects on the survival of offspring,
long after the older generation has stopped producing offspring.

I don't know evolutionary biology enough to estimate how big of a selection
pressure that is, though. Maybe much lower than first-order effects, maybe not
so much.

> But there is no fundamental physical reason for it, and it stands to reason
> we could create biological machines that maintain the power to self repair
> indefinitely, given suficient outside energy.

Agreed.

~~~
cornholio
I agree, I would say there is a strong second order effect for parents to see
their siblings to reproductive age. As more generations stack up, any
longevity effects quickly become negligible, maybe with the exception of
hiper-social species with a learned culture like ourselves. Since this
development is very recent, I don't think it could affect such a fundamental
thing like aging.

Per Google, our closest living relatives, chimps and gorillas, very rarely
display grandparenting behavior and have comparable lifespans.

------
wmnwmn
Totally wrong from the get go. Cells do not use thermal energy to "ratchet"
order out of chaos. That would violate the 2nd law of thermodynamics. Cells
create order by using energy from an already-ordered source, namely the food
you eat. This source is in turn ordered ultimately by exploiting a very high
temperature differential, namely between the sun and earth temperatures.
Usable energy can be extracted from differentials; it cannot be extracted from
a heat bath at one temperature. But since we do have the virtually unlimited
energy from the sun, and some other sources, we can lower entropy in a fixed
region as much as we like. There is no physics barrier to repairing every
single atom of aging damage in a human body.

------
sytelus
Each cell in our body is derived from a cell that existed 3 billion years ago.
It seems twisted argument that some how cell in an individual body must die
but can renerate for billions of years if it only met with other damaged cell.
There are fair amount of examples such as a-sexual bacterial reproduction
where cell essentially survives for ever. There are many species known to live
on for multiple of 100 years.

------
matte_black
We can worry about physics based aging when we've gotten biological aging
under control.

~~~
contravariant
This article argues they are one and the same.

~~~
jcadam
Well, you know, peel away enough layers of abstraction and everything is "just
physics."

~~~
davidkuhta
FTFY: ...everything is "just mathematics." ;)
[https://xkcd.com/435/](https://xkcd.com/435/)

~~~
matte_black
Math makes aging inevitable, because every moment that passes increments the
amount of total time we’ve been in existence.

------
stareatgoats
> "If this interpretation of the data is correct, then aging is a natural
> process that can be reduced to nanoscale thermal physics—and _not a
> disease_. " (my italics).

To me this is the main problem with this article. The (ever more common)
notion that aging is a disease should be combated with philosophical
arguments, not shaky physics such.

~~~
vanderZwan
Half-serious, half-joking, but I think that procreation and death are nature's
way using the _" have you tried turning it off and on again?"_ approach to
evolving multicellular life. It's probably the most cost-efficient, all things
considered.

~~~
fwdpropaganda
Most cost-efficient for what purpose?

~~~
vanderZwan
For change and adaptation to new contexts. Unless you know of a way to turn an
elephant into a fly and back. I mean that literally.

For battling decay. It can be easier to grow a new body from a single cell,
than to keep patching up a running one.

A desire for immortality is the individual point of view. In the big picture
of things, there is little to no selection pressure for immortality. There is
plenty of selection pressure for adaptation and change, and death and rebirth
are effective tools for that.

~~~
majewsky
> For battling decay. It can be easier to grow a new body from a single cell,
> than to keep patching up a running one.

And we do the same in IT. Sometimes the old system has piled on so many
hotfixes and customizations that in order to upgrade, you can only build up a
new system next to it and transfer your data to it. Then you shutdown the new
system. That's procreation, learning, and death.

~~~
vanderZwan
That's my line of thought too: look closely and see indirect empirical
evidence of this happening in all kinds of other systems. Life is no
different.

------
pipio21
While it is obvious that everything decays, it is equally obvious that you can
repair it.

For me eternal youth will happen sooner or later, probably 100 years in the
future,50 years,200, but it will happen when we understand biology and could
repair tissues, something that we could not do today. Today we don't heal a
bone fracture, we let nature do it, because we really do not control or
understand the process deeply. The body knows how to kill viruses, we do not.
Only bacteria after copying nature with antibiotics is under our control but
we do not control or understand the process again.

This is not being immortal, people will die in wars, or accidents, or being
killed, but they will be young all our lives.

For this people will probably have to go to a place that resembles the uterus
and spend some time there as the body repairs itself:

[https://pm1.narvii.com/6320/0940afb810563b4c4b67c4efb773adc0...](https://pm1.narvii.com/6320/0940afb810563b4c4b67c4efb773adc00b0de312_hq.jpg)

After that you will be 20 years younger. Not different from repairing a car.

~~~
FooBarWidget
We can't even repair our own machines to the point that they last forever. I
doubt we'll reach eternal youth any time soon, so I do think that we can
lengthen life span quite a bit (low-hanging fruits) before we hit a wall that
take even longer to surpass.

------
didgeoridoo
> Many researchers studying specific diseases, cellular systems, or molecular
> components would like to see their favorite research subject take the mantle
> of “the cause” of aging. But the sheer number of possibilities being put
> forward refutes the very possibility. They can’t all be the cause of aging.

[https://en.wikipedia.org/wiki/Fallacy_of_the_single_cause](https://en.wikipedia.org/wiki/Fallacy_of_the_single_cause)

------
subroutine
I think if one is to pose this as an acceptable theory on aging they must
explain why it doesnt apply to germ cells. The germline of an organism manages
to escape these fundamental laws of physics to achieve 'immortality' simply by
having more efficient DNA repair mechanisms than somatic cells. And so, imo,
we are back to a biological explaination of aging.

------
razorunreal
I think they've got the evolutionary argument backwards. Rather than the older
generation aging and dying because there is some evolutionary reason why they
should, I think there is simply not a strong enough reason why they shouldn't.
Why fix the remaining aging bugs when you already live long enough to
reproduce and pass on knowledge?

~~~
klmr
Both arguments exist, although I don’t think the “ageing was actively evolved”
argument has ever gained a lot of mainstream traction: it’s not very
parsimonious (all the available evidence can also be explained by the simpler
model).

------
rweba
Two points:

(1) I haven't seen this article mentioned here:

[https://gravityandlevity.wordpress.com/2009/07/08/your-
body-...](https://gravityandlevity.wordpress.com/2009/07/08/your-body-wasnt-
built-to-last-a-lesson-from-human-mortality-rates/)

I am not sure if the article addressed this model in particular, but I found
it compelling.

(2) It occurred to me that most of us don't fear death as much as becoming
increasingly useless as we become older due to ill health and physical
weakness.

It would be not much fun living to be 200 if the last 120 years were spent in
a bed or wheelchair.

So what we want is not to increase the lifespan but to prolong the amount of
time we can spend in relatively physically prime condition. I am sure this is
not an original thought, but something worth mentioning.

~~~
JoshTriplett
> It would be not much fun living to be 200 if the last 120 years were spent
> in a bed or wheelchair.

While I agree (and while I additionally think any plausible advancement of
that degree would necessarily need to increase _healthy_ lifespan), I'd also
say that it'd be inherently preferable to dying, and it would give 120 more
years to solve those problems. We can come up with a lot of medical
advancements in 120 years.

------
frlnBorg
Thermodynamics and entropy, while causing decay in the long-term, have nothing
to do with human decay over the span of 80-90 years. Arguing that entropy is
THE fundamental cause of death just shuts down the conversation.

~~~
ordu
A "causation" is an illusion. We can think, for example, that cause of ageing
is in the evolution: those species who lives longer have slower evolving rate,
and they lose a competition with other species who have shorter lives. But
this causation does not contradict to the thermodynamic one, it just make
thermodynamic not the "fundamental cause" but the mechanism of ageing.

A causation is the way to describe reality, not the fundamental feature of the
reality. And so, the causation should follow the goals of researchers. While
searching for ways to live forever, we will not benefit from evolutionary
explanation (we cannot fix evolution to get longer lives), but thermodynamics
explanation could be useful (if its true, of course). So, thermodynamics is a
good candidate for the role of "fundamental cause".

------
fwdpropaganda
Complete bollocks. Molecules don't age and everything in your body is
molecules. If a molecule breaks down, in some cases the body has mechanisms to
replace it with a shiny new one. Those mechanisms are themselves made of
molecules. And if those mechanisms to stop working, in some cases those
mechanisms can also be replaced. Nothing in fundamental physics makes aging
inevitable.

From what I can tell, the reason why aging is so prevalent is that most
species haven't had time to evolve the mechanisms that solve the problems that
appear later in life. If there's some truth to this, you'd expect that the
species that are better at this also tend to be the simpler ones, since for
those simplicity also means smaller diversity of things going wrong.

~~~
sametmax
> If there's some truth to this, you'd expect that the species that are better
> at this also tend to be the simpler ones, since for those simplicity also
> means smaller diversity of things going wrong.

I doubt it.

IMO, aging is just a way to ensure that dying occurs.

And dying is necessary for evolution, as it's easier to replace the old with a
new generation that understand better the reality than changing the current
generation.

Old habits literally die hard.

~~~
prawks
Interesting. So by that line of thought, aging would be an evolved trait
giving certain species an evolutionary advantage over others without aging.

~~~
Tepix
Looks like evolution has decided that death is the winning strategy for long-
term survival.

All species that didn't die of old age (if there were any) have disappeared
regardless.

~~~
malnourish
That's untrue, there are a number of biologically immortal creatures[0]. Most
recently found being the naked mole rat.

[0]
[https://en.wikipedia.org/wiki/Biological_immortality](https://en.wikipedia.org/wiki/Biological_immortality)

~~~
52-6F-62
Exactly. Some tortoises as well can live a few hundred years, as well as
wales, urchins, sharks, quahog clams, and as someone else mentioned–
jellyfish.

Though you won't see any of them developing rockets and space-stations. To
what extent that is an evolutionary advantage on our part I'll leave to
general consensus.

------
scythe
A friend did his PhD in the thermodynamics of open systems -- the sort of
thing that describes, say, the long-term evolution of a "thing" that
occasionally consumes and rejects energy. One thing he mentioned to me was
being contacted by lots of crackpots, each with their own new idea wrt what
open system thermo means about living organisms. It's a very new and very
difficult field and there aren't hard results yet. I would take this article
with a shaker of salt, and perhaps some tequila, lime juice, and Grand
Marnier.

------
tomq
This is an interesting article, but the core argument that aging is an
inevitable result of physics and not biology has a counterexample. It’s the
biologically immortal hydra:
[https://en.m.wikipedia.org/wiki/Hydra_(genus)](https://en.m.wikipedia.org/wiki/Hydra_\(genus\))

------
rossdavidh
Sometimes, you can improve the software best by patching, sometimes by
reefactoring. And eventually, as it gets older and bad traits accumulate, it
becomes easier to do The Big Rewrite. That doesn't mean that it is impossible
to fix the legacy code, just that at some point you're better off starting
from scratch, but with the old one as a pattern to go off of.

Aging and reproduction feels like the same pattern. Sure, you may be attached
to the legacy code, but sometimes it makes more sense to do the big rewrite
instead. Legacy code performed well for its time, now it is time to retire it.

------
peterjlee
One thought I had was that species evolved to maximize the survival of the
species, not the individual organism. Once an organism is too old to reproduce
or contribute to the survival of the species, it's probably better to die than
becoming a burden to the rest of the members of your species. It sounds cold
hearted and brutal but that's just how nature works. Maybe it is possible for
an individual organism to reproduce and live forever someday but that would be
very hard to achieve and we're probably stuck in a local maxima.

~~~
antognini
That doesn't really answer the question, though, of why animals get too old to
reproduce. Surely it would be evolutionarily advantageous for an animal to be
able to reproduce for its entire life.

------
foo101
Note this relevant comment from the author of the article:

'My original title was: "Aging: where physics meets biology". Nautilus changed
the title to the above more provocative version, which seemed to have worked -
judging from the number of responses!'

Comment URL: [http://nautil.us/issue/36/aging/physics-makes-aging-
inevitab...](http://nautil.us/issue/36/aging/physics-makes-aging-inevitable-
not-biology#comment-2682776102)

------
civilian
We don't violate the 2nd law of thermodynamics. We're still increasing
entropy, but we're processing so much fuel that the equations are still
balanced when we locally increase order.

Comparing lifespan to the bonds of a molecule is also pretty cringey. :-/

Obligatory link to Aubrey de Grey:
[https://www.ted.com/talks/aubrey_de_grey_says_we_can_avoid_a...](https://www.ted.com/talks/aubrey_de_grey_says_we_can_avoid_aging)

------
dang
Discussed at the time:
[https://news.ycombinator.com/item?id=11684718](https://news.ycombinator.com/item?id=11684718)

------
thefounder
Nobody wants to live forever...just until the universe ends. I would gladly
give the physics gods back my particles so that they can start a new big-bang!

------
Pica_soO
I never dared to ask- but- do cancer cells age? How does a tumor behave if he
gets to live longer then its own behaviour would allow to expect?

~~~
Balgair
Cancer is a _strange_ beast. Some types of tumors do not 'age' like usual,
some are 'hyper aged', some die off at incredible rates, but reproduce at even
higher rates.

Really, cancer cells are so wracked with errors and DNA damage, typically,
that they really aren't the species that they grew up in anymore.

For one instance, some tumor metabolisms are _radically_ different than what
is 'normal', more different than even what is seen in even prokaryotes:
[https://en.wikipedia.org/wiki/Warburg_effect](https://en.wikipedia.org/wiki/Warburg_effect)

------
saalweachter
I think this is a subject that is ripe for appeals to consequence.

People concerned about aging would really, really prefer there was a
biological cause for aging. If it's biological, there's a chance there's a
trivial fix (gene therapy, supplements, ...) for it, or at least a trivial
incremental fix that will get you an extra ten or twenty years while you wait
for the next incremental fix to be developed for the next problem down the
line.

If the problem is physical, caused by the wear and tear of your metabolism,
the problem becomes significantly harder. Not _impossible_ (after all, cell
_lines_ can be immortal, trivially, we have an unbroken line of single celled
organisms dating back billions of years), but you are potentially looking at
rebuilding mammalian life from the ground up before you make even incremental
progress. And the only maybe-possible-but-the-animal-models-are-mixed
incremental fix we have is to lower your metabolism by living your entire life
on a calorie-restricted diet, or maybe by being just a _little_ too cold all
the time.

I'm all for still devoting a healthy amount of resources to trying to find
easy biological fixes to aging, because I'm old enough now that probably
nothing else would happen fast enough to keep me, personally, alive, but if it
turns out most of the problems are physical, we shouldn't shy away from
acknowledging that just because it makes the work of beating death harder. We
aren't trying to beat aging because it seemed like an easy thing to do.

------
reasonattlm
Entropy arguments for the primacy of aging are fairly silly. For one, there
are actually species that appear to be essentially immortal. Secondly, the
germline. Cellular systems are clearly capable in principle of indefinitely
maintaining themselves against entropy by either asymmetric division in which
molecular waste is partitioned into one child cell (single cell life) or
leveraging asymmetric division to replace worn parts with good parts
(multicellular life). To explain why aging exists and is so prevalent in
biology one has to look at the level above physics, and that debate largely
takes place in the overlap between evolutionary biology and molecular
biochemistry.

The germline and hydra must be brought forward every time someone says that
aging is an inevitable, universal consequence of thermodynamics:

[http://www.demogr.mpg.de/en/news_press/press_releases_1916/f...](http://www.demogr.mpg.de/en/news_press/press_releases_1916/forever_young_4396.htm)

The common perception that the bodies of all living beings age, is wrong. This
has now been proved by a long-term experiment with the freshwater polyp Hydra,
a microscopic animal. In a unique long-term experiment researchers created
artificial conditions for the tiny water animals with their flimsy tentacles,
which were free of fatal natural threats like predators. For almost ten years
they have cared for of about 1,800 of the Hydras. Overall, the team has
counted 3.9 million observation days of individual Hydra. The number of
natural deaths per year, however, can be counted on one hand. On average there
have been only five. When a Hydra passed away it was mostly due to laboratory
accidents, such as a polyp sticking to the lid of its bowl and then drying up
or simply having been dropped on the floor. From of the few natural deaths
that remained researchers calculated Hydra's mortality. It is so low that even
several lifetimes of researchers would not suffice to observe the end of the
lifecycle of the polyps. Even after 500 years five percent of a cohort will
still be alive. For two out of twelve of the Hydra cohorts under
investigation, the risk of death was actually so small, that it will take
3,000 years until only five percent of the polyps remained. "Hydra apparently
manages to keep its body young because it does not senesce by accumulating
damages and mutations, as most other living beings do. Hydra are probably able
to follow a special self-preservation strategy, as its body and cellular
processes are rather simple." For instance, Hydra are capable of completely
replacing parts of the body that are damaged or are somehow lost. It can even
fully regenerate if its body is destroyed almost completely thanks to a high
number of stem cells. Stem cells are capable of developing into any part of
the body at any time. Additionally, as Hydra replaces all of their cells
within only four weeks, it regularly and quickly expels all cells that have
been changed genetically by mutations. Thus, damages have little chance to
accumulate.

Current thinking on why near all species fail to behave like hydra looks
somewhat like this:

[http://arxiv.org/abs/1103.4649](http://arxiv.org/abs/1103.4649)

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.

~~~
atmanthedog
If all of a hydra's cells are replaced every four weeks, I would say that the
hydra has a life span of about four weeks. Ship of Theseus and all that.

But even if you don't subscribe to that particular view of what constitutes a
consistent identity, the issue is still fundamentally thermodynamic. It is not
a task of just maintaining a particular dynamic system indefinitely, but
maintaining one with memory. If the hydra is storing absolutely no information
about its past states, then it isn't evolving, and it is completely at the
mercy of its environment. This makes it more akin to fire or a piece of iron
rusting than life: just a consumptive chemical process. This harmonizes
exactly with your last paragraph, things need to store some amount of memory
of past failure if they are to adapt. This storing process is exactly aging,
but how it manifests in different organisms can obviously be very different.
Landauer's principle, then, tells us that since information is thermodynamic,
so too must be aging. However, I don't really think the author of the original
article was arguing at that deep of a level. In humans, many of the processes
that we consider to be the detrimental effects of aging do occur because the
components that make us do have memory effects. One particular example would
be the cross-linking of elastin, causing degradation of vascular system
efficiency.

But aging truly is an inevitable consequence of thermodynamics, it's just that
since everything is a consequence of thermodynamics, it's not a particularly
illuminating argument.

~~~
grondilu
> If all of a hydra's cells are replaced every four weeks, I would say that
> the hydra has a life span of about four weeks. Ship of Theseus and all that.

Most of our cells in our bodies are renewed in a few months or something. Yet
people don't assimilate this to death.

Now, you may object that neurons don't follow this rule, so our subjective
identity is not concerned by this. To this I will say that when people are
concerned about ageing, they are indeed concerned about what happens to their
brain (that is, neuro-degenerative diseases), but certainly not _only_ that.
The state of all the other tissues is at stake : the heart, the bones, the
skin and so on. Yet all of these are renewed on a regular basis. That renewal
is not perfect though, and it's that imperfection they blame on ageing.

------
ecpottinger
Don't forget the latest research on mole rats.

[http://experimentalbiology.org/getattachment/2014/About-
EB/P...](http://experimentalbiology.org/getattachment/2014/About-
EB/Press/Press-Releases/Rodriguez-Buffenstein-Release-FINAL.pdf.aspx)

------
csomar
Maybe infinite aging is not the solution here. The probability that you die
from an accident or cancer when your age is infinite is 100%. Brain backup,
and brain uploading into a new body is a perfect solution.

It might be harder but it cuts through the issues of aging and accidents.

------
HugThem
It would be interesting to simulate a little world with species that evolve
via genetic crossover. And let them have an aging gene that is just a number:
The average lifespan.

Wonder what evolution in the simulation would come up with as the best
lifespan.

Could be a fun weekend project.

~~~
hans05
I think the main reason we haven't seen many life forms evolving long life
spans is that the biological cause of aging may be closely tied to other
important things. So it may be difficult to evolve long life without some
other disadvantage like slower growth.

------
sseth
We age for the same reason that code bases go bad over time - the accumulated
cruft of tech debt overwhelms the ability of different parts of the system to
work together well. This is a problem of any dynamic system, not something
related to physics.

------
jugg1es
Evolution has selected for tons of different mechanisms and strategies for
combating the decay and dissolution of organic molecules. This author doesn't
seem to have read a lot of literature on how powerful these DNA repair
proteins can be.

------
User23
We tend to think of parents having offspring, but in a very real sense
offspring use their parents as an entropy dump.

Feynman's Lectures on Computation are a great read that explores the physical
limits of computation and information.

------
JepZ
> Nanoscale thermal physics guarantees our decline, no matter how many
> diseases we cure.

If that is true, I wonder what the total live expectancy for our species is. I
mean shouldn't stem cells be affected by that too?

------
vectorEQ
its silly to seperate biology and physics, seems to me that biological systems
are also physical systems.

other then that, stress causes aging. people who reduce stress keep their mind
younger and often live longer and are less effected by diseases common among
aging biological systems.

ofcourse, stress then isn't the root cause of aging... as stress takes many
forms, what causes stress is. so the answer to what causes aging is probarbly
not a single point or item, but a combination of factors which all cause some
form of stress on the system.

------
jostmey
I wish I could download this because it is so wrong. There's been a lot of
amazing work in biology explaing why aging exists. It has nothing to do with
physics

------
Tepix
If we manage to reset the age of our biological cells, their DNA may change
over time but that doesn't mean it's infeasible or a dead end.

------
dade_
This article is very informative about the challenges that biology contends
with, but it doesn't convince me that the headline is true.

------
ilaksh
See [http://www.sens.org](http://www.sens.org)

------
daemonk
That's like saying: given a flowchart where A->B->C, A leads to C, not B.

------
markstos
Because sometimes systems need a start-from-scratch rewrite to progress.

------
neals
Well if you really want to talk hard-core Physics... isn't aging inevitable
because of the eventual heat death of the universe?

------
fizixer
This (headline) is the one of the most idiotic things I've ever read on HN,
regardless of the content of the article.

------
tanilama
Nautil.us seems to have a tendency to publish pesudo sciency article with
grand claim and irrelevant random thoughts.

------
saool
Physics Makes Flying Impossible, Not Biology

------
lawlessone
If this were true how would we reproduce?

------
c0nan69
Our life is an oxidation

------
stinos
I always considered biology, chemistry, ... to ultimately be applied physics.
So nothing new here :]

~~~
Koshkin
By the same logic economics is applied physics. This fallacy is called
"reductionism".

~~~
scrrr
Your comment prompted a web search and I ended up here:
[https://www.quora.com/Why-is-reductionism-a-logical-
fallacy](https://www.quora.com/Why-is-reductionism-a-logical-fallacy)

