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They are talking about cells, but must every form of life be built from cells? It seems like all life on earth descended from one species, that was a cell. So
by andix 3y ago
They are talking about cells, but must every form of life be built from cells?
It seems like all life on earth descended from one species, that was a cell. So all our life on earth is made out of cells. But couldn't life be completely different somewhere else?
- timacles 3y agoA cell is just literally an organic unit. It’s something organized that is alive. Any living thing would have to have cell’s otherwise it’s just not organized in any way which doesn’t make sense in the context of our universe
- etskinner 3y agoThis is very close-minded thinking, it's very possible life doesn't require cells
- adrian_b 3y agoIt is very likely that some kind of life that doesn't require cells must be possible, because it must have existed before the appearance of cells. Cells are much too complex to appear spontaneously, without evolving from an acellular form of life. Cell membranes can form spontaneously from fatty substances, but no cell can live without complex molecular pumps that are embedded in the cell membrane and which bring in some substances from outside and which expel some other substances from inside. Such pumps must be the result of a long evolution that preceded the first cells. Nevertheless, any form of life that is not made of cells cannot live free in a fluid like water, but it must be attached to the surface of some suitable rocks, where a flow of nutrients must exist. The most plausible hypotheses about the appearance of life on Earth suppose that before the appearance of cells, life was restricted to pores inside rocks from hydrothermal vents, where a flow of dihydrogen and of alkaline ions could provide the energy, and metallic sulfide minerals could provide the catalysts for organic syntheses.
- notaustinpowers 3y agoThe biggest issue is that life has to perform some sort of chemical process. Any lacking any clear delineation of an inside the life in question and the outside, would make continuous chemical processes impossible. A stray breeze blowing away chemicals would effectively kill life. A "cell" having a barrier would allow that chemical process to happen. Life may not require cells in the way cells on Earth evolved, but they'll require cells of some sort.
- saltcured 3y agoI'm trying to imagine some wacky living polymer or protein that wiggles around and grabs whatever molecules it needs to force localized reactions without a protected cell environment. But then I start to wonder if evolutionary pressure would encourage ones that form colonies and eventually closed topologies and cells. And then others might specialize to hijack those colonies...
- wolverine876 3y agoMaybe the planet, or locality on the planet, has resources that permit continuous chemical processes to happen without cell (maybe no breeze). Maybe it doesn't need to be continuous.
- 0xBA5ED 3y agoOr... Life requires a closed system which requires a boundary. The boundary and its contents is considered a cell?
- IggleSniggle 3y agoTIL the Earth is a single cell
- 0xBA5ED 3y agoNot from me, since I didn't claim that all closed systems are cells.
- polishdude20 3y agoI mean, define "life" then.
- derekp7 3y agoI think that no matter what definition one comes up with, it is possible to have counter examples (i.e., is fire alive, seeing as how it reproduces, consumes food (fuel), etc). One of the indicators of life I like to use, that seems to be useful in the general sense is that life is good at decreasing (fighting against) entropy at a local level. So fire for example increases entropy. A living being takes in raw materials plus energy, and produces a lower entropy (higher organization) of those inputs. Like plants making sugar, and pulling apart CO2 to make free oxygen. Or animals taking in sugar and oxygen, the output is higher entropy (CO2) but you have higher organization of material (lower entropy) locally within that organism. This also means that life doesn't necessarily need to reproduce (although that is how life that we know of works). You could theoretically have a living being that kept evolving its own form but never developed the ability to copy itself. It just keeps consuming energy and environmental items, and maintaining its own internal complex structures.
- arrosenberg 3y agoFire is not alive, it cannot maintain homeostasis for any period of time. Your bit about entropy is actually looking for the concept of homeostasis.
- asdff 3y agoFire can maintain homeostasis if it is fed and is able to respire, same as us humans. Take away food and air and we flame out too.
- arrosenberg 3y agoNo, it actually can't. Fire will burn as hot and quickly as it has fuel and oxygen to sustain, because it's a chemical reaction, it doesn't maintain any kind of steady-state in order to extend it's survival. If you take away my food, I will still have energy to find more. If you take away my air, I will still have air (albeit quite time-limited) to find more. That gradient is how we understand something to be alive.
- timacles 3y agoIts very easy to say something like that, but impossible to provide any sort of examples, even in a fantasy context. Like what a gas cloud with intelligence? We live in a universe with distinct rules, saying life doesnt have to have cells is basically fantasizing about other dimensions where we're made out of hot dogs or something. Saying life doesn't require cells is just redefining what words mean, since a cell literally means the smallest functional unit of life.
- shkkmo 3y ago> We live in a universe with distinct rules, saying life doesnt have to have cells is basically fantasizing about other dimensions where we're made out of hot dogs or something. That comparison is ridiculous. We live in a universe for which many of the rules are unclear and we have only grasped some small subset of the possibility space dor emergent structures those rules enable. We have a hard enough time coming up with a clear definition of which of the emergent structures that we do know about qualify as "life". You seem to accept it as settled that viruses are not alive and are mere chemistry but it seems to me like drawing a line in the sand between two similar processes. When we're talking about cells, that seems like an easier thing to define, but I would posit that is another definition that could prove to be slippery if an alien biology without a common ancestor is discovered. We have to be careful about how we define life and cells in relation to each other to avoid just creating tautologies rather than useful definitions. For example, how sure can we be that by defining life to exclude viruses, we haven't defined life in such a way that we have excluded processes that can support consciousness? I think it is pretty easy to imagine life which has "cells" that we fail to recognize as such because they serve a similar function but with a sufficiently different form that we would fail to see or recognize them in a microscope. Now, many of those imaginings may be scientifically impossible but that doesn't justify comparing all of them to "a dimension where we are made of hotdogs."
- dekhn 3y agoTechnically yes, but I think many people would say it seems likely that all life would have some sort of "exterior layer" like a cell membrane. Realistically this falls into the "unknown unknown" category of knowledge, where we have to speculate with very little concrete evidence.
- andix 3y agoIt makes sense to think about an organisms like that. But it would be really interesting, if there were other possibilities too we could think of. A hundred years ago nobody thought something like quantum entanglement could be possible. Maybe there will be a similar eye opening surprise in extra terrestrial life. But off course it’s reasonable to start looking for all the things we can already imagine, and make observations in a way we already know of.
- dekhn 3y agoSure, I'd love to learn that some sort of inscrutable aliens on the surface of a neutron star (https://gwern.net/doc/science/1973-drake.pdf https://gwern.net/doc/science/1973-drake.pdf) or gasbags on Jupiter (1. Sagan, C., and Salpeter, E. E. "Particles, Environments and Possible Ecologies in the Jovian Atmosphere," Astrophysical Journal Supplement, 32, 737 (1976).) to creatures that leave in witch space. We simply don't have a framework other than basic physics and chemistry to speculate in this area. The possibility space is too large and we don't know the fitness function.
- notaurus 3y agoAlso Dragons Egg by Robert L. Forward
- cmrdporcupine 3y agoIt's not like there's a definition of life people universally agree on. But the only life we know... is cells. Unless you count viruses. Which most biologists don't.
- spelunker 3y agoYeah but what about the really big viruses??
- bjourne 3y agoSome microbiologists think they are alive: https://www.nature.com/articles/454677a https://www.nature.com/articles/454677a Others don't think so: https://virology.ws/2020/12/03/pandoraviruses-are-not-alive/ https://virology.ws/2020/12/03/pandoraviruses-are-not-alive/
- afiori 3y agoI find that these conversations are almost always backwards, as "is X alive" actually handled as "should we consider X as alive". That is we are not trying to discover whether a thing is alive or not, we are trying to decide what Alive means. This confusion creates the illusion that terms like Life, consciousness, emotions, reflexes, etc. are well defined while they in practice are not.
- mseepgood 3y agoThere is no such thing as alive, the word is a human invention. We can decide what the word means.
- afiori 3y agoThat was my the point, these conversations are linguistically phrased as trying to estabilish if something is alive but are actually structured as a debate on what "alive" means
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- Aachen 3y agoMaybe not, but let's do the science to rule that out?
- mensetmanusman 3y agoThe universe is a cell of sorts with interior bits that appear alive.
- ben_w 3y agoKinda? Cells (as in the bit that makes it a contained volume) are both a thing that forms spontaneously without biology, and very useful for isolating one blob of chemistry from others right next to it. There is however life on earth with huge cells and multiple nucleuses: https://en.wikipedia.org/wiki/Plasmodium_(life_cycle) https://en.wikipedia.org/wiki/Plasmodium_(life_cycle) But also, the Viking test was more general than "cells", it would have ben positive with anything that could, to simplify, eat the food it was given.
- adrian_b 3y agoAll the cells that can form spontaneously without biology are dead. More precisely, they are just cell membranes, not cells. Cell membranes form spontaneously from many fatty substances, the root cause being that oil and water do not mix, i.e. fatty substances are hydrophobic. A dead cell or cell membrane does not exchange chemical substances with the environment (except passively, i.e. when molecules or ions diffuse from high concentration towards low concentration). A living cell has not only a cell membrane that separates the interior from the exterior, but it also has molecular pumps and ionic pumps embedded in the membrane, which selectively pump some substances in and other substances out. Without this controlled exchange between interior and exterior, the growth and multiplication that define life are impossible. What is characteristic for life are the molecular pumps and ionic pumps. The cell membranes have only the passive role of preventing the substances that have been pumped in one direction to come back to the place from where they had been taken by the pump.
- rolph 3y agoi think your looking for this: https://en.wikipedia.org/wiki/Micelle https://en.wikipedia.org/wiki/Micelle
- opportune 3y agoIf extraterrestrial life were silicon-based, it may instead of cells have ceramic and metallic structures (like filaments) that grow via crystallization. I think that is what the parent is getting at - cells are part of our carbon/water based biology but maybe not all possible forms of life
- jszymborski 3y agoAnything is possible, obviously, but in the current way we understand life, it's not likely. I am unaware of any understanding of evolution or early life on Earth which supports an idea of some giant contiguous life-form. That said, Mars is not Earth, and our definition of life is ever evolving (is a virus alive? is fire alive?) so, again anything is possible, but not everything is likely.
- edgyquant 3y ago> I am unaware of any understanding of evolution or early life on Earth which supports an idea of some giant contiguous life-form Okay? People have no idea what pre-cellular life looked like so the entire earth being a giant cell is not out of the question.
- whalesalad 3y agoI recall hearing this explicitly stated by a member of the current rover team. They said that we need to begin imagining completely different forms of life from our own - like completely outside the box thinking.
- radicalbyte 3y agoThankfully plenty of hard sci-fi writers have done that for us. It's something that I've been very interested in for a long time, especially the idea of "scale of life" - could there be a brain the size of a solar system? How would we even understand it? What about life which operates on a different time scale (in the solar-system brain example, it would operate on a different scale on two axis - space and time).
- jrumbut 3y agoThe timescale issue is fun to think about. Even in my own life, there have been times that I've responded to a message within a second and other times that I've taken multiple years. Our lifespan also seems quite arbitrary. Some sophisticated animals live quite a bit longer than us and others live a tiny fraction of a percent as long. One would imagine that between solar systems there is a much greater degree of variance. It would be difficult to understand the time horizons of a collectively intelligent swarm of fruit flies or a serene pod of whales, but imagine if interstellar life has a geologic component to its life cycle?
- archargelod 3y agoI'd still consider all sci-fi stories and images quite inside the box thinking. The idea is that our brains are hard-wired to think the way they do. So we can't really think outside of our small subset of reality. I believe, In the slim chance we encounter some kind of 'life', it wouldn't be even considered as life by our standards. Just a simple quiz to exercise the brain: - should life move at all? - what's the maximum distance between molecules we can still consider as one entity? - can a state of matter be 'life'. Not a matter itself, but just a state of it?
- andix 3y ago
- ramblenode 3y agoA cell is fundamentally a structural division between an inside and an outside. This creates an energy gradient that does work. So a cell is simply a structure that maintains a gradient for the purpose of doing work. It's a very simple object--kind of a thermodynamic primitive for resisting entropy. The organelles within cells are themselves cells. I'm not sure what life would look like without cells but it would probably rely on some type of otherwise naturally occuring gradient like a tide pool or mineral formation.
- eternityforest 3y agoWasn't there news of some kind of simulation showing there could be a self replicating dust pattern in space or something like that?
- Symmetry 3y agoSo, one the one hand all Earth life depends on proton gradients over membranes in some form or other for energy, as in the mitochondria powering us. But because prokaryotes and archea seem to share a common ancestor but use radically different cell membranes it looks like their common ancestor might not have generated its own membranes but used naturally occurring lipid membranes. And we'd probably want to call that common ancestor alive.
- zdragnar 3y agoProkaryotes are archaea. The nature of the difference between their cell walls and other single cell organisms is not fully explored, and whether they formed from convergent evolution or not is still up for debate: https://en.m.wikipedia.org/wiki/Pseudopeptidoglycan https://en.m.wikipedia.org/wiki/Pseudopeptidoglycan
- bigbillheck 3y agoArchaea are prokaryotes, but not all prokaryotes are archaea.
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- sircastor 3y agoThere's an interesting theory that suggests Martian and Earth life have a common ancestor, and have exchanged life through material kicked up out of atmosphere due to asteroid or meteor impact.
- red-iron-pine 3y agowhat martian life?
- cududa 3y agoNot sure why you're being downvoted. Martian is a phrase explicitly tied to life/ beings/ organisms on Mars. Martian isn't a broad synonym for alien or extraterrestrial. It just means life on mars
- SamBam 3y agoI think the implication was that it's kind of putting the cart before the horse. "Scientists hypothesize that Martian life and Earth life had a common ancestor" is pretty bizarre given that no Martian life has been found.
- wruza 3y agoYou have to separate low entropy volume from high entropy volume to do life. Btw cell internals are also full of membranes for the same reason. https://en.wikipedia.org/wiki/Organelle https://en.wikipedia.org/wiki/Organelle That doesn’t mean your idea is wrong, but if we assume regular cold chemistry (i.e. not stellar insides or other exotic states/physics), membranes are just the sane and obvious default. Which conditions could make them less effective than something else?
- ethbr1 3y agoExactly. Earth life requires organization (low entropy) to generate usable biological energy. Absent a division, that low entropy state reverts to the environmental mean. I'm struggling to imagine what usable energy generation in a high entropy environment would look like.
- astrobe_ 3y ago> You have to separate low entropy volume from high entropy volume to do life That's what I believed too, but I have doubts now after reading another comment that defines it as energy gradients. As far as I understand the concept, a crystal is low entropy as well. Or is it the same thing? Or the combination of the two (Use energy to keep entropy low)? > membranes are just the sane and obvious default The less sane one could be... Magnetic confinement fields I guess?
- klodolph 3y agoIf you want to understand crystals thermodynamically, in terms of entropy, you should be using a more rigorous notion of entropy. When crystal formation is thermodynamically favorable, the process causes entropy to increase, not decrease. So if you have a crystal which exists in-situ, in the conditions which caused it to form, you don’t increase entropy by un-creating it.
- jerf 3y agoThe main problem with crystals and solid-phase life in general is that, being solid, it tends to just sit there and be solid. It's why silicon life is nominally appealing if you just look at the periodic table, but when you look out into the real world and see what the characteristics of the compounds it actually forms look like, you see an awful lot of solids and it isn't really plausible as a basis for life. It helps to look at how biology actually works; we get these images of things like DNA copying where the next amino acid is just sitting there, all but busting in the door to be copied. It gives a very false image of how biology works. In reality it's an insane world down there with a whole bunch of the cell just jiggling around thermally all the time, and the mechanisms all work by waiting to be bashed into by the right thing. Everything is so fast and the rate of jiggling is such that it all ends up working out. But it's nothing like anything we'd design or even very easily wrap our head around. I've sometimes wondered if we were somehow otherwise the same, but not biological, how long it would take for us to ever invent biology. We are certainly nowhere near it now. Crystals and solid-phase in general doesn't have an obvious route to chemistry occurring anything like the way it does in biology, and indeed, it doesn't have an obvious route to chemistry occurring at all at any scale.