[HN Gopher] What is life? Its vast diversity defies easy definition
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What is life? Its vast diversity defies easy definition
Author : gHeadphone
Score : 64 points
Date : 2021-03-10 14:23 UTC (8 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| dukeofdoom wrote:
| I always wondered how does life pass information between
| generations. The many Behaviours that seem to be built into
| animals. For example like a dog barking at strangers. Or recent
| generations of Kangaroos that know to avoid crossing roads.
| Barrin92 wrote:
| I think Schrodinger in his book of the same name as the title of
| the article gave by far the clearest definition of life. Life is
| a local state of negative entropy. Which is to say that life
| orders matter and exports heat. There are other definitions
| mentioned here that are kind of equivalent, i.e life stores
| information, life as an out-of-equilibium state etc, but just
| expressing it in terms of entropy I think draws a clear line
| between living and non-living matter.
|
| I think the consequence of this is that quite a few systems can
| be considered alive that traditionally wouldn't, like crystals or
| DNA itself but I don't think that's that big of a deal.
| [deleted]
| millstone wrote:
| Life should be defined extremely narrowly, as in requires DNA or
| RNA. This frees us to consider equally complex non-living things
| (like AIs) on their own terms, without being hung up on whether
| they are alive or not.
| [deleted]
| ars wrote:
| Very interesting article, but if you are short on time I suggest
| stopping once it mentions Carol Cleland - it spends too much time
| talking about her, and not enough about the topic after that.
| ouid wrote:
| sustained chemical nonequilibrium.
| [deleted]
| readams wrote:
| I would say any process with differential replication and descent
| with modification is life. That is, any process that exhibits
| evolution through natural selection.
| ehPReth wrote:
| "too much for me, yet I must breathe anyways"
| xipho wrote:
| In trying to imagine ways to unify knowledge of the worlds
| phenotypes (not DNA/RNA) we ran various exercises to think of
| just one "standard" measurement that could be measured across all
| life. All failed at one scale or another. An individual clonal
| tree (poplar), good luck measuring its mass. A blob like radially
| symetrical single celled organism, "length" is meaningless. You
| get the idea ...
| ncmncm wrote:
| The definition of life is trivial: it is what biologists are
| interested in. If you want to know if something is alive, just
| count the biologists following it. Rabbits? Yes. Bugs? Yes.
| Viruses? Yes. Protons? No. Memes? Not really. Computer viruses?
| No. Prions? Borderline.
|
| Might the definition change, as biologists encounter new stuff
| and develop an interest? Sure. Does that make the old definition
| wrong? No.
|
| Dividing the world into life / non-life boxes is a purely human
| distinction. The universe totally doesn't care. Who does? People.
| Who cares most? _Biologists_.
| waserwill wrote:
| I would caution that we biologists study more than life, but
| also its environment! So, the abiotic conditions of soil, the
| function of enzymes (including proton pumps :D), and even the
| culture of humans (and dolphins and orangutans, etc.).
|
| It's true that life can't really be defined by some
| essentialist statement (i.e. it has properties that neatly
| divide X from not-X), and the family resemblance approach works
| better (things like rabbits and viruses and oaks and
| cyanobacteria), even though it's not as satisfying. Mind, it's
| OK to just tell kids in biology classes a more convenient
| definition.
| tsegratis wrote:
| A 'self' reproducing or 'self' continuing process, via some
| kind of recursion -- reproduction, cloning or otherwise
|
| Is that at all okay???
|
| Note, I say 'self', since just as a cloud is transitory, so
| too, we live on food and can't divide us from it
|
| Please note, I'm not saying this is right, I'm just having
| fun stabbing in the dark
| waserwill wrote:
| The definition I remember being taught early on includes
| that, so that's on the right track.
|
| From memory: 1. Reproduces itself/making things similar to
| itself (sort of; viruses are on the periphery, prions...).
| 2. Metabolizes chemicals for energy 3. to grow, and as a
| result, 4. produces waste. 5. Reacts to stimuli in the
| environment. 6. Maintains homeostasis (reacts to stimuli in
| itself and keeps 1-5 going).
|
| I'm probably forgetting some and there are exceptions to
| all of these. Notably, in interesting cases like at the
| inception of life, or at the periphery of life: viruses,
| parasites, potential extraterrestrial chemical systems, and
| arguably cultural systems. But those criteria are still
| convenient.
| antattack wrote:
| Life is a process of getting to the minimum energy state.
| captaincrowbar wrote:
| What is life?
|
| A forkbomb implemented in hardware.
| [deleted]
| dota_fanatic wrote:
| After being introduced to Christopher Alexander's conception of
| life* through his _The Nature of Order_ textbooks (so
| verbose...), it 's brought a clarity to existence I've found
| otherwise lacking from other quarters.
|
| Simply put, every thing (and grouping of things up and down the
| scale of size) is more or less alive depending on the order /
| configuration within itself and in relation to the things
| surrounding it. So a door can be more or less alive, taken by
| itself or taken in context of the wall, floor, and ceiling around
| it (and so on). Or compare a city with no sidewalks, completely
| paved with concrete, all buildings identical, square grid
| streets, no plant life whatsoever to some of the great cities in
| Europe which organically grew according to the needs of the
| populace over time. Can't you say one is literally more alive
| than the other, both the physical city itself as well as its
| inhabitants?
|
| Since adopting this perspective, I've been able to make great
| strides in improving the order of my home which has resulted in
| an increase in well-being and mental health. The house is more
| alive and so I'm more alive for it, and vice versa, and so the
| positive feedback cycle continues.
|
| He goes into great depth identifying principles we see occurring
| in nature to help define this gradient of liveliness and analyzes
| countless examples of great works of art from human history. He
| also shows how to bring such life to the world around you and in
| the things you make. Check it out. :)
|
| * https://en.wikipedia.org/wiki/Christopher_Alexander
| svachalek wrote:
| I like this. I've always held a similar view of consciousness,
| it's not a binary condition but just another scale.
| bediger4000 wrote:
| "A computer virus performs self-reproduction with variations. It
| is not alive," declared the biochemist Uwe Meierhenrich.
|
| Eugene Spafford got an article published in 1994 arguing just the
| opposite:
| https://www.mitpressjournals.org/doi/abs/10.1162/artl.1994.1...
| johndoe42377 wrote:
| How so? A process which is capable of reproduction.
|
| Single cells and above quality, viruses and other molecular
| patterns don't.
|
| Life is a process. This is definition.
| jl6 wrote:
| A handy reminder that just because it's hard to define something
| doesn't mean it doesn't exist.
| Frost1x wrote:
| I've always found it amusing how in our day-to-day lives we speak
| with such completely assured confidence of highly complex
| interactions, problems, phenomena, etc. that we _know_ something
| is or isn 't, yet we still struggle with far more
| basic/fundamental questions like "what is life?"
|
| The thing I've always loved about pure science is that the best
| work is approached with much humility. We do _not_ know what
| something is or why something is. We have a lot of data, may be
| able to predict a secondary behavior or predict a primary
| behavior fairly consistently, but that 's a bandaid at best--we
| know it (hehe) and try to dig deeper. Outside of science, we tend
| to just "know" and brush off deviations from what we know as
| mysticism or something else.
|
| Sometimes I wish I wasn't aware of how little I really know
| compared to what I'd like to know. When you peel away the facade
| of certainty in a lot of aspects of life, it's a bit
| disheartening to see how people treat each other based on the
| assumptions they often make of such falsely placed certainty.
| bulleyashah wrote:
| I get what you're saying but I wouldn't discount all other
| forms of knowledge besides science.
|
| For example, mathematics is not mystical. Philosophy is also
| well argued.
|
| And secondly, not everything might be definable with data. For
| example, how should one treat others is not a purely scientific
| question.
|
| Having said that, what would you like to know?
| jimbokun wrote:
| I think it's more an issue of how language and human brains
| work, than features of the world around us.
|
| The concepts behind words in human languages are extremely
| fuzzy and ambiguous. That is why progress on computational
| linguistics was stuck for a long time, until researchers
| started using statistical models.
|
| This fuzzy and ambiguous way of modeling the world seems to
| better fit whatever it is our brains do. The definition of what
| is or isn't "life" is fuzzy and ambiguous, because however the
| concept is encoded in our brains is fuzzy and ambiguous.
| kiba wrote:
| I don't think struggling to define the definition of life is a
| matter of not knowing or knowing. It's simply us attempting to
| impose our invented taxonomy on nature and reality.
| vishnugupta wrote:
| Indeed. I really like the way Feynman explained how nature
| doesn't care about what models or descriptions we come up
| with. Nature just is. This made me look at physics and
| science in a whole new perspective.
|
| There are so many phenomena that are beyond human intellect,
| intuition, and language that the best we can do is to observe
| and marvel. It doesn't mean that we should give up trying to
| seek explanation or modeling of observed reality, just that
| don't be dogmatic about it.
| lawpoop wrote:
| There was a definition I encountered in high school, which I
| never found a source for, but seems to be pretty robust and
| address many of the non-living things other definitions include.
|
| This definition is a rubric of several qualities:
|
| 1. Metabolizes energy
|
| 2. Stores Information
|
| 3. Self-replicates
|
| #1 rules out crystals; they are formed by outside forces, they
| don't metabolize themselves. It also rules out viruses and
| prions; they don't ingest any "food" to perform metabolic
| activity. #2 rules out fire; it doesn't store information in a
| DNA-like molecule or anything simliar. It's purely a chemical
| reaction. #3 is the obvious thing that differentiates non-living
| things like rocks from plants and animals.
| HPsquared wrote:
| As is typical for them, viruses are debatable under this
| definition (and how about computer viruses?)
| jimbokun wrote:
| "(and how about computer viruses?)"
|
| They don't metabolize energy.
| wruza wrote:
| Until you turn on the computer and receive electricity
| bill?
| tachyonbeam wrote:
| I would definitely say biological viruses are a life form.
| They use as a substrate. However, you need the ability to
| mutate in order to evolve. Computer viruses can't do that at
| the moment, they are dumb machines/tools that just keep doing
| the same thing over and over until we wipe them out.
|
| IMO, self-replication is the most fundamental characteristic,
| and the ability to mutate/evolve is key as well. The rest is
| all details.
| teraflop wrote:
| The "metabolism" requirement is an important one, though.
| If you remove it, and you allow for "self-replication"
| that's entirely dependent on an external agent, then it
| seems like you would have to consider all kinds of things
| as "alive" that would fall outside any common-sense
| definition of the term. For example, works of literature.
| [deleted]
| viklove wrote:
| So if humans stopped mutating/evolving (due to gene therapy
| or some drug), we would stop being life?
| wruza wrote:
| Many species "stopped being life" because they took a
| wrong turn at evolution crossroads. But that may become
| irrelevant for us in few centuries.
| [deleted]
| lawpoop wrote:
| Viruses rely entirely on the host cell's proteins for all
| of their replication. They don't metabolize anything
| themselves, nor do they create their own copies of
| themselves. The host cell creates copies of the virus.
| TheAdamAndChe wrote:
| Perhaps exploiting an entropy gradient would be more
| accurate.
| lawpoop wrote:
| > viruses are debatable under this definition
|
| I think it's a thin pro-argument. Viruses are completely
| dependant on the host cell and the host cell's metabolism.
| The host cell's protein unwraps the jacket, and the host
| cells' proteins replicate the viral DNA/RNA payload. The
| virus does not reproduce itself, and it does not metabolize
| anything. There are no inputs to a virus.
|
| Whereas living cells, give them the proper inputs, and they
| metabolize energy, catalyze reactions, and create copies of
| themselves.
| SigmundA wrote:
| Self replication of information with mutation and evolution
| would be my definition, which would include viruses, but not
| crystals, AI could be included if it could evolve on its own.
|
| I think in reality like most things its not black and white,
| there is a continuum of life and some things are more alive
| than others.
|
| Edit: perhaps adapting to environment through
| mutation/evolution or learning or both might be better.
| n4r9 wrote:
| Evolution has _led_ to life but I 'm struggling to see why it
| should be a criterion. What if something happened that
| stopped humans evolving, and we maintained the same general
| genetic distribution for the next few millennia? Would we
| stop living?
| guerrilla wrote:
| A bee hive and a country fit this definition. Is that intended?
| I'm not against it.
| jimbokun wrote:
| This seems like a higher order definition.
|
| Bees and Humans fit the definition. Therefor, aggregations of
| bees and humans, like hives and countries, also fit the
| definition.
|
| "Countries" seem more of a stretch, as replicating would
| technically mean creating other countries like itself. Not
| just sustaining itself into the future.
|
| Do hives seed other hives? I suppose they would, so they
| better fit the definition.
| Scarblac wrote:
| Individual humans don't quite fit the definition, many
| don't reproduce at all, the ones that do only do in groups
| of two. Strictly speaking you'd have to wait and see
| whether a given human child eventually reproduces to decide
| it's alive...
|
| But with bees it's much worse -- in each hive, only the
| queen and some drones reproduce, most bees are worker bees
| that can't. So this definition fits bee hives _better_ than
| it does individual bees.
|
| Seems the definition would need to say something about the
| species as a whole reproducing. But that leads to the
| species definition problem. And what about that tortoise
| that was the last of its species?
| monkeydreams wrote:
| > "Countries" seem more of a stretch, as replicating would
| technically mean creating other countries like itself. Not
| just sustaining itself into the future.
|
| The world is full of countries, nations and so forth. At
| some time in the distant past there was no nations. After
| that there was one. Now there is over a hundred, with the
| corpses of many more lying in our past.
|
| All usable land on Earth has been claimed now so they have
| no space to grow in number without cannabilising one
| another. Their walls have grown hard and inflexible with
| the passage of time and laws and agreements, and the
| evolutionary pressures of conflict have subsided of late,
| as they cannot move against one another without incurring
| the wrath of alpha predators, and the alpha predators
| cannot attack one another without the assurity of mutual
| destruction.
|
| But countries live a long time, and their frame of
| reference is different from our own. Their moods encompass
| entire generations of the lives of mankind. They will
| eventually again fight among themselves unless ordered into
| cells within a higher organism. They will fight and devour
| one another, birthing new border states or vassal states.
| To any greater being it would appear like an almost
| peaceful dance, the ebb and flow of lines on a map, the
| respiration of civilisation.
|
| To us it would be every bit as savage and chaotic as it
| must be for the cells and bacteria which comprise us.
| lawpoop wrote:
| Well EO Wilson posited certain eusocial insect colonies,
| including bees, as a super-organism. I think the idea has
| some currency in biology. The idea is that Darwinian
| selection is acting upon the colony, so it is the unit of
| evolution. Remember that eukaryotic cells are a symbosis of
| two prokaryotic cells.
|
| Not sure how often or even if countries self-reproduce.
| benlivengood wrote:
| > Not sure how often or even if countries self-reproduce.
|
| Colonialism and independence.
| lawpoop wrote:
| I'm mulling this over... It's an interesting idea for
| sure. I'm not sure that it can't be reduced to human
| populations in general, which makes it more like the
| super-organism Wilson describes.
|
| OTOH, not all human populations are states, as in
| countries, and arguable that is the "organism" said to be
| reproducing itself....
| toddh wrote:
| #3 removes the whole class of AI based life forms that would
| not need to replicate. Our future AI citizens may not
| appreciate not being thought of as living.
| the_af wrote:
| That seems to me a form of begging the question: you assume
| "AI based life forms" will indeed be life forms, then argue
| the definition from the parent post fails to account for this
| new life form.
|
| But that such a thing as AI life forms will exist and be
| accepted as such by scientific consensus is not a given, at
| all.
| toddh wrote:
| Not really. There is no objectively true unarguable
| definition of life. When in silico life becomes reality and
| humans do their human thing of devaluing anything that's
| not like them, it won't matter what human consensus deems
| as life. I'm not worried about determining what "indeed
| will be life forms" no more than I worry about objectively
| defining what is a good meal or which is the most beautiful
| color. Humans have no standing it determining what true
| life is. What's important is developing an intentional
| stance towards whatever is not us.
| babygoat wrote:
| The human mind invented the concept of life. There's no
| objective definition other than what people decide that
| it means, because no other form of intelligence tries to
| make the distinction.
| wruza wrote:
| I'm pretty sure siliconers do pasteurize their silk and
| disilfect medical equipment as well. Life is too
| intrusive and too eager for food to not care about it.
| the_af wrote:
| > _When in silico life becomes reality and humans do
| their human thing of devaluing anything that 's not like
| them_
|
| That is, again, begging the question.
| n4r9 wrote:
| I'm not sure it is begging the question, at least not if
| framed properly.
|
| The question seems to be to be "what exact criteria
| categorises what is commonly meant when people talk about
| what is alive". I think you could interpret OP as claiming
| that there is an idea of artificial or alien life as
| presented in science fiction which people would commonly
| describe as life but may not replicate.
| benlivengood wrote:
| There are still some cool edge-cases. Is a sperm cell alive? An
| X-chromosome sperm (do X-chromosome sperm have a (probabilistic
| N)-stage lifecycle?) Are red blood cells alive? Is every
| molecule of an organism that's alive also considered alive, or
| just the ensemble? If only the ensemble, are mitochondria
| alive?
| dandanua wrote:
| Also, why we consider a single human as living organism, but
| not a society? Single human without society is a pitiful and
| helpless chunk of meat, who unable to replicate btw.
| ealloc wrote:
| Sperm cells can be seen as a haploid phase of many organisms'
| lifecycle, so are alive by pretty much any definition.
|
| In humans, the haploid phase of the lifecycle is single-
| celled, while the diploid phase is multicellular. In
| contrast, in mosses and fungi the haploid phase is
| multicellular while the diploid phase (sporophytes/zygote) is
| single-celled.
|
| Red blood cells are discussed in the article.
| selestify wrote:
| Are people who are sterile, and therefore incapable of #3, no
| longer alive?
| motohagiography wrote:
| This is similar to a previous HN thread [1] about a post about
| paper called the "information theory of individuality" [2] that
| talked about life as the ability to "cohere information forward
| in time."
|
| There is another related idea I stumbled on called the
| "constructal law," [3] which seems related.
|
| Where I think they are related to the question of what life can
| be defined as is that you could express this constructal force in
| terms of that information theory idea by summarizing it with a
| slight extension - as a bounded system is living based on its
| ability to _dynamically_ cohere information forward in time. The
| limits of this constructal theory will be defined in using
| information theory terms.
|
| When we discover stuff in the universe and ask, "is/was this
| life?" there might be some criteria in these ideas in terms of
| asking, does this thing take feedback from its environment and
| produce coherent information? Or, is this thing a source of neg-
| entropy in its environment? If we look at life as a temporary,
| dynamic whorl of neg-entropy, it might yield some useful
| criteria. Half-baked, but measuring information-in, information-
| out could tell us whether something other than classical physics
| is processing it. It suggests we could figure out whether
| something was created by life as well, since the internet is not
| "alive," but it is evidence of life. Sorting things based on
| whether it is evidence of life, seems testable.
|
| [1] https://news.ycombinator.com/item?id=22825048 [2]
| https://alexdanco.com/2020/04/09/life-is-made-of-unfair-coin...
| [3] https://mems.duke.edu/research/energy/bejan-constructal-law
| bgroat wrote:
| A little naval-gazy, but I once tried to separate "plants" from
| "animals" from first principals and had a really hard time.
|
| - They both reproduce - They both eat - They both have some sort
| of a nervous system - They both breath - They both live and die
| waserwill wrote:
| Wait till you try to find the boundary between species!
|
| Many plants, and some animals such as birds, can produce
| fertile hybrids after being separated for millions of years.
| Especially true for organisms that have reproductive barriers
| besides genetic and physical incompatibility (different
| pollinators, geographic separation, birdsong differences, etc).
| Engineering-MD wrote:
| Or ring species [0] which is the extension to your example.
|
| [0] https://en.m.wikipedia.org/wiki/Ring_species
| andagainagain wrote:
| The problem isn't "we can't come up with a definition of life",
| it's "every time we define life, we don't like the results".
|
| We could make up any definition. The problem is that we instantly
| think "well, that's stupid, let's define it again". But I'll say
| it again, that wasn't ever the problem. The problem was when we
| thought we were talking about one thing, but we were really
| talking about something else - our own personal heuristic.
|
| And nature doesn't care about your heuristic. Hueristics make
| terrible definitions.
|
| Virus's are alive by a lot of heuristics. They act alive-ish.
| They're not alive by a lot of definitions. Bacteria are one
| species by definition. But since that's not useful, we make up
| heuristics that separate them into all sorts of species. Go
| through every situation, every time we are disappointed with the
| definition of life, and we find that the reason is that we just
| don't like it. We WANT something else to be called life, because
| it feels that way.
| titzer wrote:
| > The problem isn't "we can't come up with a definition of
| life", it's "every time we define life, we don't like the
| results".
|
| Well said. E.g., for almost any definition of life, we end up
| with superorganisms like ant colonies and bee hives being live
| things--not to mention cities and human societies being
| superorganisms too.
| k__ wrote:
| Yes.
|
| Sounds like a simple inductive problem to me.
| m12k wrote:
| Interestingly, most definitions of life that would characterize
| a virus as alive, would also characterize ideas and culture as
| living (unless you add some explicit requirements like "must
| have DNA" or "transmission between hosts must happen by
| transfer of matter"). It's easy to reject that out of hand, but
| if you think a bit about the Ship of Theseus, then it might not
| be so crazy to think that what is important is the replication
| and mutation of patterns rather than the specific matter
| carrying that pattern. Cf. also The Selfish Gene, where Dawkins
| coined the term "meme" as a mental analogue to a gene.
| minikites wrote:
| Fire is "alive" by many of the same definitions, that's what
| makes it so difficult.
| wtetzner wrote:
| Yeah, trying to fit the complexity of reality into a taxonomy
| is always going to run into problems. That doesn't mean it's
| not a useful exercise (sometimes), but we need to keep in mind
| that it's just us trying to mentally organize reality.
| jimbokun wrote:
| So in other words, it's more a question about human language,
| than a question about the empirically observed world around us.
| cortesoft wrote:
| This topic is covered quite well in a couple of essays:
| https://www.lesswrong.com/posts/aMHq4mA2PHSM2TMoH/the-catego...
| and https://www.lesswrong.com/posts/yA4gF5KrboK2m2Xu7/how-an-
| alg...
|
| Humans need to categorize things; it is how we are able to
| navigate our complex world, by recognizing patterns and acting
| on them. We get in trouble when we think our categorizations
| are objective fact, or that we can ever cleanly categorize
| things in a way that will satisfy all our categorizing needs.
| a_band wrote:
| "Your honor, Science shows us that life is vastly more
| complicated than antiquated ideas of 'alive' and 'dead'. I submit
| that my client cannot be guilty of murder as the very concept
| relies on binary categories that Science has discredited. Who are
| we to say if a murder has occurred?"
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