10 ms·
What is life? Its vast diversity defies easy definition
- ncmncm 6y agoThe 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 6y agoI 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 6y agoA '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 6y agoThe 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.
- tsegratis 6y agoNice list!
- ncmncm 6y ago> "tell kids in biology classes a more convenient definition" That is where you get conflict. Too simple? Too inclusive? Too not? But it's the only place where you need one that doesn't mention biologists. "Life is a process that uses energy obtained from outside a boundary to reduce entropy inside it." You have define entropy, then, which kids might not like much.
- waserwill 6y agoThese are good questions. I care most about these sorts of definitions when teaching, since they can orient students and describe what it is you are talking about. Some criteria I was taught about life: > 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 really like these, because while they are wrong on some level, they are pedagogically useful: they orient students to what life does, what we can learn about it, and what sorts of data we can collect. Plus, it points towards both ecology and evolution. Your definition is more encompassing in a way, so it better describes any life-form, but so encompassing that it also describes crystalization! (The parallels between life and crystals are admittedly interesting, especially when thinking about abiogenesis.) Just from a practical perspective, I would rather start from those criteria than from physical chemistry and physics. Then, come exceptions and complications, which are great! Even when learning physics, I recall every other lecture beginning with, "Those assumptions we made were wrong. Instead, ..."
- ars 6y agoVery 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.
- ehPReth 6y ago“too much for me, yet I must breathe anyways”
- xipho 6y agoIn 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 ...
- deleted 6y ago[deleted]
- johndoe42377 6y agoHow 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.
- Frost1x 6y agoI'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 6y agoI 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?
- kiba 6y agoI 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 6y agoIndeed. 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.
- andagainagain 6y agoThe 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.
- k__ 6y agoYes. Sounds like a simple inductive problem to me.
- m12k 6y agoInterestingly, 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 6y agoFire is "alive" by many of the same definitions, that's what makes it so difficult.
- wtetzner 6y agoYeah, 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.
- ouid 6y agosustained chemical nonequilibrium.
- bgroat 6y agoA 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 6y agoWait 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 6y agoOr ring species [0] which is the extension to your example. [0] https://en.m.wikipedia.org/wiki/Ring_species https://en.m.wikipedia.org/wiki/Ring_species
- czzr 6y agoI would say - Plants produce their own food and don’t move. No doubt there are edge cases.
- machiaweliczny 6y agoCrazy idea but what if plants are actually higher lvl beings? They are more self-sustainable and helpful to ecosystem than humans. Actually they probably aren't because I guess otherwise all different planets would have them (but hey we are also only here so far). There's interesting question what would god-like(unlimited power over mater and limitless knowledge) entity do? I guess killing oneself and recreating with sprinkle of rng makes some sense after such event as you probably get bored thus I'm speculating that universe could be god itself (if it's bound by same laws of physics - if not then IDK). Don't ask me what I'm smoking :p
- deleted 6y ago[deleted]
- antattack 6y agoLife is a process of getting to the minimum energy state.
- bediger4000 6y ago“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.1994.1.3.249 https://www.mitpressjournals.org/doi/abs/10.1162/artl.1994.1...
- lawpoop 6y agoThere 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 6y agoAs is typical for them, viruses are debatable under this definition (and how about computer viruses?)
- tachyonbeam 6y agoI 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 6y agoThe "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.
- tachyonbeam 6y agoIt seems to me literature doesn't self-replicate, we replicate it... And apart from the bible and such, literature usually dies out fairly quickly in the grand scheme of things.
- jl6 6y agoA handy reminder that just because it’s hard to define something doesn’t mean it doesn’t exist.
- Barrin92 6y agoI think Schrödinger 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.
- dmm10 6y agoMy favorite statement of this idea is that, "life is that which reverses entropy."
- patcon 6y agoAnd maybe viruses, books... languages? Books seems to me a little like tardigrades sometimes, if you squint. Information stored indefinitely (hibernating?), which can be rehydrated and spring back to life within human minds. We talk about tardigrades like they're really weird, but maybe we just can't see how truly weird a form of life WE are :)
- deleted 6y ago[deleted]
- readams 6y agoI would say any process with differential replication and descent with modification is life. That is, any process that exhibits evolution through natural selection.
- a_band 6y ago"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?"
- deleted 6y ago[deleted]
- dota_fanatic 6y agoAfter 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 https://en.wikipedia.org/wiki/Christopher_Alexander
- svachalek 6y agoI like this. I've always held a similar view of consciousness, it's not a binary condition but just another scale.
- motohagiography 6y agoThis 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 https://news.ycombinator.com/item?id=22825048 [2] https://alexdanco.com/2020/04/09/life-is-made-of-unfair-coin-flips/ https://alexdanco.com/2020/04/09/life-is-made-of-unfair-coin... [3] https://mems.duke.edu/research/energy/bejan-constructal-law https://mems.duke.edu/research/energy/bejan-constructal-law
- millstone 6y agoLife 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.
- patcon 6y agoDoesn't that make us willfully blind to when they might arrive on our terms. This sort of "let's put it aside" thinking led to some dark places in the past, and we'll eventually come to them again with non-biological complex systems of emergence. I'd personally define it more widely, as I think that's more aligned with reality. It's much more of a gradient than we usually take it for, imho disclaimer: biochemist in a past life
- dukeofdoom 6y agoI 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.
- captaincrowbar 6y agoWhat is life? A forkbomb implemented in hardware.
- basicplus2 6y agoWhat was that about hats again?
- ianai 6y ago“Exogenous change.” Exogenous to any physical or chemical process-like seemingly reversing entropy locally.
- bionhoward 6y agoEasy: life is a fractal of systems generated by a recursive process: stay alive and copy yourself.
- patcon 6y agoSara Imari Walker has some REALLY interesting things to say about life and information: https://complexity.simplecast.com/episodes/40 https://complexity.simplecast.com/episodes/40 > if you want to understand the laws of gravitation, then you go and study black holes because you have a very intense gravitational field there. And you can understand and probe gravity very well there. > If you want to understand the laws of information and how information operates in the physical world, then you should go and study a living thing. Because that's where information actually is at its most dense or most intense.