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There is a concept call the minimum viable cell, where researchers attempt to splice almost all genes from a Mycoplasma mycoides except what is needed for survival. The genes that are necessary include metabolic proteins that handle essential functions like reproduction, fermentation, and amino acid synthesis.

"It has a smaller genome (531,490 bp) than that of any known organism that can be grown in axenic culture. There are only 438 protein-coding genes and 35 RNA-coding genes (Hutchison et al. 2016)."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5710109/#:~:text=A%20minimal%20cell%20is%20one,genes%20and%20components%20are%20understood.

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As far as I am aware, this is currently our best answer. I saw a talk by the Primary Investigator in 2015 - I recall that they were basically knocking out every gene. We had a brief conversation about an area they hadn't explored where they could potentially go even further, if there are genes sets where knocking out only single components was lethal, but knocking out the whole set was survivable, so there's potential to go even further.

OP, the virus mentioned doesn't really represent an organism because it requires the mechanisms of a cell to replicate. The organism that FrostRever mentions here exists in "axenic culture", which means there are no other species present at all.

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Would this be a likely candidate for what the first life on Earth looked like since the structure is so simple?

For this to work you need to have a cell will enzymes and ribosomes to be able to use the DNA to make proteins It's likely that the first living organisms were simpler and then built all this machinery.

The first cells could've been a couple strands of RNA in a micelle with a protein.

There's even a theory that proteins appeared later, since RNA can do a lot of stuff by itself and have enzymatic functions.

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There's actually viroids, Virus like "Organisms" that infect only flowering plants. They are basically free floating pieces of genetic material without a protein shell. Avsunviroid seems to be one of the smallest with only 246 nucleotides.

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No: this is more like comparing a Raspberry Pi to a full modern PC - all the same modern bits but simpler. Comparing to the first life on earth would be like the first computers, with radically different components and operating principals to achieve the same functions.

There is selection pressure to strip away genes you don't need because the investment for offspring is smaller. Environmental bacteria tend to lose genes quite quickly, e.g. when they enter simple growth medium in the lab because they don't have to "fight" for survival in harsh conditions.
So when you find organisms they kind of already have the 'minimum set' for their respective environment. The smallest DNA for a free-living organism is around 1.3 Mbp with 1354 encoding genes (Marine bacteria Pelagibacter ubique)

https://doi.org/10.1126/science.1114057 Publication figure 1 shows different species, also mycoplasmum, in a scatter plot genome size over number of genes.

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Spiegelman's Monster is the minimum viable RNA chain, made by selecting the fastest breeding viruses. 48 or 54 nucleotides is the smallest: https://en.wikipedia.org/wiki/Spiegelman%27s_Monster

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Yeah the base pairs of RNA can spontaneously form in nature and RNA can act like an enzyme or protein itself. Last I heard, evidence strongly hints that the world was an RNA (single strand) world before double stranding and then the more stable DNA double helix developed. But it's not conclusive.

Depends on your definition of an organism/virus, and what your function of interest is.

For example, if you're simply interested in things that can make more of themselves like viruses do: prions contain no genetic code at all and are simply misfolded proteins that cause other proteins of the same type to misfold into the same conformation.

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How does this selection pressure tie in with the large amount of non-coding DNA in complex organisms?

Reading Wikipedia on this didn't leave me with the impression that there is consensus on the why of DNA that doesn't code for proteins or change transcription sites.

Yes, even bacteria from u/FrostReaver 's answer is a parasite. Most organisms need something that was made by some other organisms. We divide life into things but because it's easier to analyze it that way, but they both depend on each other and influence each other (the same relationship as within parts of an organism).

So I wonder, is there any organism that if we put on say mars, it could function without any ecosystem? By function I mean not only survive but exponentially reproduce given available resources there. A follow up question would be if it would just deplete the resource it was feeding o and die after that, or could it bootstrap a whole ecosystem (theoretically, after many many millions of years).

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By definition, the only category of organism that meets those criteria are primary producers. This is because even a broth of carbohydrates used to culture an organism would need to be produced through photosynthesis, and so would therefore be requiring something made by another organism or ecosystem.

Rather than relying upon nutrients produced by other organisms, primary producers create their own. The most simple known primary producer are Cyanobacteria, and this phylum of microorganisms are thought to have played a key part in terraforming Earth and produce a huge amount of the oxygen we breathe.

Therefore, based on your parameters, I would say, Cyanobacteria are likely the most simple organisms that are self sufficient and contain minimal code. They would just need nitrogen, phosphorus, water, carbon dioxide and sunlight.

TLDR: all organisms except primary producers are in some way parasitic when you consider that they rely upon the outputs of other organisms within their ecosystem

It's always some magic term which once you know there's tons of knowledge to consume, thank you, I didn't know it.

Yes, but there's no 'proven' absolute minimum.

It also depends on what you want the thing to do, and what you call life. If you're just saying 'reproduction in an optimal environment', then the code could be pretty small if placed in a bath of ideal organic molecules.

That said, 1700 base pairs is pretty damned small, and a living environment (with all of its own mechanisms of production) probably is the most optimal environment.

Basically the plans for a virus vs that for bacteria are orders of magnitude in different complexity.

Virus: must have keys to a factory and plans that work in that factory to make more virii.

Bacteria: Must have plans for the entire factory.

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The issue really comes down to evolution.

The first organisms did not use photosynthesis, but rather chemiosythesis. There is only so simple that you can go if photosynthesis is the only way to produce

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I've seen this before, and I understand it, and I understand life can be created spontaneously by lightning striking in the perfect place. But what does that early early, minimal life do?? Is it about to hunt for "food"? How does it survive and replicate if it's just a few proteins that got shocked?

An MVC with 500k base-pairs … that’s quite far removed from self-replicating RNA strands!

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You’re thinking of “life” as if it were a soul, some chemicals gain a “spark of life” and then they are alive.

It’s more helpful to think of life as being those things which reproduce. This isn’t a perfect definition either, of course.

You have a primordial soup full of basic organic chemicals. Some bits of RNA, some proteins, some sugars. These chemicals are already undergoing natural selection, as more stable ones survive longer, but they aren’t undergoing evolution because there is no “descent with modification”. Maybe some chemicals, through chance, form a very simple precursor to a cell which dramatically increases their survival. They can absorb small molecules while protecting themselves from the environment. Great. Does not mean they are alive. Can that structure divide into two parts which can then both grow and divide again? That’s what makes something alive.

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Well first we must distinguish between “non-coding” and the pop-science concept of “junk” DNA. While the most interesting thing about DNA is its ability to code for genes, that is not the only thing it does.

Most of our DNA has some kind of function. That could be coding for RNA that isn’t supposed to be transcribed. It could be structural, like telomeres and centromeres. It could be about regulating transcription or replication.

All the same, human DNA is much more prone to accumulating dead genes than bacterial DNA due to our generation time. We can carry around a bunch of pseudogenes or ancient viruses that managed to get themselves added to our genome. Selection pressure is much less and much slower when it takes 20-40 years to reproduce as opposed to 20-40 minutes.

The chemosynthesis guys are considered primary producers also. Right?

I find the concept of prions to be useful in understanding this. Ofc, prions are complex proteins and massively more complex and durable than any early life-precursor would have been, but they can fold other proteins into copies of themselves. Early protoliving assemblages could have been amino acid assemblages that generally tend to replicate through a few stages, and more effective/ more complicated versions of them were able to keep replicating and working together until eventually they could form something that would be considered living.

Not sure if this helps, but I recently learned about viroids in my bio classes. From what I've gathered, viroids are basically just sequences of genetic material that can have virus-like effects. Most viroids don't have a shell (Envelope or capsid) like most viruses do, and they have far fewer genes. I believe that most viroids consists of just a few hundred base pairs. What's intriguing to me is that viroids don't actually code for anything. I think maybe some viroids code for one protein, but that's about it. Despite this, viroids can still wreak havoc on an organism. It's difficult to determine whether or not viroids are living things or organisms, but I think there is definitely some function there as you put it.

To sort of echo the other response in a different way, I find it easier to think of early life in a chemistry sense rather than a biology sense. Chemical reactions can "reproduce"(autocatalysis), and they can compete with other reactions over the starting ingredients for the reaction. We can get these sort of lifelike qualities from very simple structures that could be outcompeted by more complex and better replicating structures over time. If you're interested in more about origin of life research, I found that the YouTube channel "Professor Dave Explains" does a really good job of giving easy enough to understand explanations for stuff like this.

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I know one of the smallest genomes is for HEP D, its a satellite virus that only has like 3 genes. It uses the proteins from Hep A-C because it doesn't have them all. So to get D, you have to have another HEP. Pretty cool, honestly. It only has 1700 bp and is thought to maybe be a old plant virus called a viroid

Probably not. The last universal common ancestor (LUCA) of all life, circa 3.6 billion years ago, was bacteria-like and most likely to be free living (or somewhat colony forming). It's unlikely that a free living organism could have a genome as small as 438 genes. We also know that most major protein structural families data back to that period so a fairly complete repertoire of possible biochemical functions would have been within evolutionary reach to the LUCA. So it seems likely the LUCA was quite sophisticated from a biochemical function POV. We see that contemporary bacterial genomes tend to favour minimum levels of redundancy but that isn't the same as having smaller numbers of genes. Different types of bacterial genomes have very diverse counts of the number of genes present. Between these observations there's little reason to suspect that the LUCA's genome was minimal.

Anything older than the LUCA, such as pro-genotes (things before "modern" genomes appeared) or even earlier forms would have been substantially different to an organism with an organised genome of 438 genes. The further back in time you go towards the abiotic origin of life the more "weird" and less cellular early life probably was. There remains a reasonable chance that the earliest self replicating systems were just soups of nucleotide chains, which would arguably be the earliest life-like things on earth (circa 4.6 bya), and that's quite unlike a genome-containing cellular organism.

It remains a very open question what the earliest self-replicators that gave rise to cells might have been but all the options are pretty weird. Here's a somewhat decent summary of some models

https://www.bionity.com/en/encyclopedia/Origin_of_life.html

The earliest evolutionary organism would have to be a single molecule (probably RNA) able to reproduce itself with potential mistakes in a very specific environment (probably rich in organic molecules) that happened to be common enough at the time this organism appeared.

Anything with multiple molecules would most likely be too complex to appear first without previous evolution to learn to make those molecules and a container.

Because we don't know what was this early environment (there's some hypothesis, but no clear answer), we can't test what was the smallest RNA possible.

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They are using this approach or a very similar one to try to find LUCA ( the lasts universal common ancestor). Not necessarily the first living thing but the oldest living thing that all current organisms can trace their lineages back to.

So there's autotrophs and heterotrophs, which has to do with where you get your carbon (C atoms). If you're an autotroph, you can transform (or "fix") inorganic carbon (like in CO2) to organic carbon, which are molecules that contain hydrocarbons or hydrogen-carbon bonds. Heterotrophs can't do that. They have to consume organic carbon to use it.

This is what determines if you are a primary producer or not. If you are an autotroph, then you are a primary producer. If you are a heterotroph, you must consume other organisms to get your carbon and are a consumer (note that there are primary consumers, who consume primary producers).

Then there's where you get your energy. If its chemicals, then you're a chemotroph. If its light, then you're a phototroph. If its both, congrats, you're a mixotroph.

You can mix these up. You can be a photoautotroph that gets your energy from the sun and fixes carbon. Cool, you're probably a plant or cyanobacteria. You could also be a chemoheterotroph that must consume your carbon and obtains energy from the chemicals you consume. Dang, you're probably a human.

Chemosynthesis and photosynthesis refer to autotrophic processes so they are primary producers. But the reason isn't because they utilize chemicals to get energy, its because they fix carbon in the process.

Sorry for writing this all out. I'm trying to procrastinate. Thank you for your help.

The “RNA world hypothesis” was what I was taught in my upper level genetics class back in 2004, so unless I am out of the loop and it has been discarded in the 20 years since, it sounds accurate to me

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Oh wow thank you for the information

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probably yes. there are probably minimum functions that are required based on minimal protein combinations, and minimum basepairs necessary for read/write.

there is definitely a minimum. what that is... would take a bunch of testing. and that does not exclude future mutations producing reduced requirements either.

Ah okay thank you

what does a prion do?

makes non-prions into prions. self-replication is the most important step. from there, imperfection will enable natural selection.

Minimal genome experiments generate organisms that aren't free living so they aren't really aimed at generating something like the LUCA. Mostly these experiments are trying to discover the minimal set of house keeping genes that can maintain a living cell, there's no reason to believe the LUCA was like that, nor any reason to believe that the LUCA had a minimally sized genome.

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Okay now that actually makes perfect sense. Life is just an ongoing chemical reaction after all.

You made me understand primordial soup for the first time. I mean I understood what they meant but I never thought about it being an actual soup of all the required ingredients.

I understand a virus to be more like a chain letter than an "organism" -- a package of information that induces an information processing system to make copies of itself, but I believe you need the information processing system functioning, like a living cell, to make the copies or the virus doesn't do anything.

Is that as dangerous as it sounds?

Also consider that "life" is likely to be an arbitrary feature in this discussion.

If you have a molecule that happens to be an enzyme which builds itself, you have yourself a self-replicating thing. Is it "alive"? Definitely not.

Well that's one feature of "life" but it's one that most people tend to think of only in the context of life. But all the features we typically think of in the context of life exist in much simpler, not-alive things.

By looking for the simplest thing we consider "alive," no matter how we define that, it's likely to end up being much simpler than what we would feel comfortable calling "life."

You were probably contemplating primordial, when you should have been considering soup.

> doesn't really represent an organism because it requires the mechanisms of a cell to replicate.

Is there a specific definition of "organism" that includes this requirement? Not trying to be snarky I'm genuinely curious. I always thought that "organism" just meant a unit of "life" which just requires the ability to reproduce, and doesn't include the mechanism.

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It’s just an RNA chain really.

The original bacteriophage virus used to harvest the first chain only infected certain bacterium such as E. Coli, fwiw.

The actual replication environment is highly specific and required special solutions.

Eh. Not really any more than there is a concrete definition of "species".

Lots of biologists don't refer to viruses as organisms, but there's a fair argument that they're no less alive than any other parasite.

I'd say, noting this is tangential to my field of study, that the (EDIT: agreed upon) minimum requirement is a cell membrane. Viruses may have capsules, but it's not quite the same. I believe this to be unnecessarily arbitrary, but it's consistent with keeping viruses out of the alive category

Yup. Its theorised that that was how life originally came about too: self-replicating nucleotide structures. All the other stuff came afterwards as imperfect copying resulted in changes (and increasing complexity) over time.

No, but a virus doesn't have the ability to reproduce. It has the ability to be reproduced. But so does many things, such as chairs, phones, books, and possibly other stuff. Much like a virus however, neither chairs, phones or books can reproduce.

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Not really. It was grown in highly specific conditions in a lab. If it got out, it would probably be broken down incredibly quickly.

It really depends who you ask. Some consider viruses to be alive, others do not.

True, a virus can't function unless it's inside a cell with access to those nutrients/cofactors, and existing proteins and other components. But a bacteria also can't function unless it's in an environment with appropriate nutrients/cofactors and existing proteins and other components. The only difference is that those proteins etc already exist when the bacteria is born (divides into daughter cells), while a virus has to go and find them. Does that difference define life?

But then, if you consider a virus to be alive, what about self-replicating plasmids? They're really not much different from a virus. What about transposable elements in a genome? Are they alive too? They're not much different than a virus in latent phase.

The definition of life is something that sounds like it should be easy, and high school textbooks do give a precise definition. But the reality is a lot more complicated and murky than it seems.

Viruses require very specific environments to reproduce (the inside of the right kind of cell), but so does humans. Put humans in 2000 degrees, and they won't reproduce. Put them in the vacuum of space, and they won't reproduce. Without food, humans won't reproduce. Without water, humans won't reproduce. How is that fundamentally different from viruses?

A much more convincing argument for viruses not being alive is that they don't have a metabolism.

Viruses aren't dead but they don't fit the definition of alive either, it's just a coded set of genetic information that uses the cells processes to reproduce. They float without direction until they hit a cell they can hijack

There is another organism on this planet that follows the same pattern. Do you know what it is?

For that matter, what about a prion? Does nothing when not in the presence of similar amino acid chains that are in a vulnerable conformation, but makes more of itself when those resources are available.

Then again, prions don't breathe and eat and grow, and that is how we know they're not alive.

In those conditions humans are dead, so they do not fulfill the definition of life.

A virus has no ability to reproduce, and as such it is not life.

Virologist and professor Vincent Racaniello refers to viruses as “obligate intracellular parasites.”

One of the fascinating areas of research is in using bacteriophages to break up biofilms. https://www.frontiersin.org/articles/10.3389/fmicb.2022.825828/full

Sounds a lot like a retrotransposon, which aren't particularly dangerous.

A chair requires a very specific environment to reproduce. Inside a carpentry shop with a human carpenter capable of measuring, cutting, and machining new parts to assemble, or otherwise a factory designed to create more chairs. /s

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Would replication of RNA/DNA not be sufficient to be considered an organism?

I see why the parasite/virus case is similar. Does the difference stem from the necessity of a host for viral replication?

The problem is that parasites can range such a gamut that range from selfish genetic elements like transposons all the way up to like, head lice and remora. It's not clear where the line is between organisms and not, because it's really a gradient that depends on your opinion to draw a line. "Capable of living on it's own" is a good line to draw, though, when you're asking how many genes you need to live. It would be like asking how much money you need to live in NYC and including people in a survey who live with their parents. Not totally relevant to the question being asked.

Do you happen to have a link to one of these papers? Sounds interesting

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There's not really any single paper about it, so much as it being one of the most commonly held beliefs among biologists looking at how life might originate.

There are a lot of variations to the idea too though: some might argue that DNA came first, while others suggest that life actually started with proteins, and DNA/RNA came later. So far as I understand, the protein theory is most widely supported, and is partly why scientists get excited when they find amino acids somewhere.

Yeah, that’s why I used quotes for organism. I consider them closer to nano-robots than a cell. But they still use DNA

If you're counting viruses as an "organism", which the biological community does not, then the minimum amount of code required is none. Prions are misfolded proteins that have no DNA/RNA whatsoever and are able to "function" in much the same way as a virus by causing other proteins to misfold.

I've heard some think it's best to define an infected cell as the living virus, treating virions as reproductive material. I don't know how widespread this idea is, but I thought it was an elegant way to define them as living.

In my opinion, that's enough, but the taxonomists of the world disagree.

There are so many organisms that are obligated to have a host to survive. Granted, they mostly need one condition or another that the host provides, rather than invading its cells, but I much find the distinction between virus and obligate pathogen to be just one that is being held onto rather than one that is meaningful. I'm open to someone giving me a real definition, though I've never encountered one I feel satisfying.

Worth noting, my opinion on the lack of consensus for species is that there genuinely can't be one. Humans try to classify biology, but biology doesn't care. You can look at the clostridium or clostridioides clades or the bacillus cereus groups and see examples of biology laughing at us trying to name a species when there is so much intermingling and genetic transfer or so little genetic difference between "species". Dengue virus subtypes might be even clearer, though that's an example of what should arguably be four species being lumped into a single one. Also, why would a non living entity be granted living entity taxonomy like "species" or "genius"? I think that's a matter of convenience, but it does raise an eyebrow because viruses have evolutionary histories as rich as bacteria or animals.

Then there's the "there's no such thing as a tree" argument, that I personally subscribe to.

Long story short, between understood "convention", attempts at classification (taxonomy) that can only approach but never reach the truth, the complicated phylogenetic nature of the world - the fuzzy line between the same and different, and the general resistance to change, I don't think there's really a clear answer for what constitutes an organism and why. Again, I'm open for debate or education.

Viruses don't have a metabolism. Generally speaking, using energy is part of being alive. Also, a virus doesn't replicate its own DNA. It co-opts the replication mechanisms of a host cell and forces the cell to do the replication.

Keep in mind it lacks a lot of defensive mutations

If the wrong mutations from this cell however occured elsewhere either by exposure or naturally replicated similar genes that'd certainly be concerning

There exist self-replicating strands of RNA. All they are is RNA in solution that can gather and assemble loose nucleotides into copies of itself.

But if a virus is alive, then they could probably be considered alive too.

Off topic, but I really appreciate when people like you who seem to know what they’re talking about share some insights that laymen like myself can understand. Just makes me want to read up on things

There are no easy dividers like these to separate life from non-life. The short answer is that it depends on how you define life. Others define it in another way and include viruses among live organisms. Just like there is no clear definition on what a game is.

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Everything alive is dependent on something else in their environment to stay alive. If you define life by function instead of properties you can arrive at a different conclusion.

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It seems that you are referring to hepatitis D, a very interesting virus. It’s the smallest known virus to infect humans and it’s genome only codes for one protein, HDAg (hepatitis D antigen) which can be produced in two sizes. In order to replicate it needs not only the human cell but there must also be a co-infection with hepatitis B since hepatitis D “steals” the surface antigen (HBsAg) from hepatitis B so that both viruses have identical viral membranes.

From the other discussion in this thread I see a lot of argument whether viruses are alive or not. This is not particularly interesting to any person infected with hepatitis D (and B simultaneously) since it behaves in very “alive” manner and seriously impacts the life of the infected.

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anyone interested in more abstract mathematical models related to this question can consult, e.g., this page

https://www.moshesipper.com/the-artificial-self-replication-page.html

and this wiki shows the efforts of a community to find small self-replicating and other interesting patterns in Conway's Game of Life

https://conwaylife.com/wiki/

Right? The concept of "life" is surprisingly tricky. But I personally would not consider prions to be alive.

I will say though, prions definitely "eat", when they destroy the normal form of the protein. They "grow" by increasing their population, much like bacteria / viruses. Breathing is not a requirement for life.

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Short answer: probably.

Long answer: all life, the simplest example of which is the cell, must be able to locally reduce entropy while increasing the entropy of it's environment. So far that we're aware, this includes metabolic processes, which take simple (comparatively) molecules, restructure and recombine them, and poop out less energetic small molecules. To do this requires big molecular machines, or proteins and enzymes. These big molecules are coded like a computer (in this metaphor, it may be helpful to think of the protein/enzyme as executable code, etc.) by DNA, which again for this metaphor may be thought of as binary. The binary must be translated from 1 & 0 to a programming language, RNA in this case. The RNA may then input executable code. This requires tremendous effort, at least 50 separate proteins (again, coded commands) and only makes binary to code language to executable code. That's one pathway. One fundamental requirement. When you ask about energy metabolism like fermentation, or membrane construction, or things like that, the process gets even more whackadoodle. This is to give you an idea of the complex requirements for the basic concept that life locally reverses entropy. Now consider that for each amino acid of a protein/enzyme (the big machines, the executable code) there are 3 base pairs of DNA called a codon. Each protein can have between 100 and 1 million amino acids. That means that, not counting things like RNA, a genome must be massive for a living thing to actually be alive. Indeed, the smallest confirmed genome of a living thing was isolated from an endosymbiotic organism (a critter that lives in the cell of another critter), Nasuia, that has around 190,000 base pairs of DNA. This thing can only synthesize around 10 amino acids using their DNA. So that's probably the minimal genome possible.

But if these would really be the "origin of life" why are they only found in plants?

There is a book by Freeman Dyson called "Origins of life". He talks about the possibility of a self replicating polynucleotide as the supposed origin of life on earth.

I work with viruses, some virologist like 'genetic material replicating and closed in a membrane' which makes me laugh

Isn't this basically the "RNA world" hypothesis? There should definitely be papers on that. Recently there was a new paper on the question how it could actually have been possible for the RNA bases to emerge from inorganic molecules. For a long time the RNA world hypothesis was (is) very popular yet from a chemistry point of view it is quite hard for RNA bases to form from inorganic starting materials (if I understood correctly). Whereas amino acids form comparatively easy from such starting materials. That's why some hypothesized that proteins might have been the origin of life. Yet protein can't replicate themselves. Even prions need existing correctly folded proteins to convert them into their prion state. That's the cool thing about ribozymes. They can self replicate.

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This is not a universal sentiment in the biology community and some like myself count viruses as oganisms. And I maintain not counting them is very very stupid. They have lineages, code which evolves over time, and self replicate in the right conditions. Just like every other "organism". If we're counting obligate parasites' as organisms, there's no reason to not count viruses. And there are some viruses bigger than some bacteria with thousands of genes.
Prions on the other hand don't really evolve, it's just the same misfolded protein constantly.

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By these definitions for eat and grow, a fire is alive. I'd consider prions no more alive than fire, while still being as dangerous as fire.

The virus can reproduce, it just requires a very specific environment to do so, including specific molecules that are only produced by other life, such as ribosomes.

Humans require very specific environments to survive, including a long list of chemicals that are only produced by other life, such as vitamins.

The requirements for the virus are a lot more specific, but there is nothing fundamentally different in them.

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No, the virus cannot reproduce.

It simply does not have the parts to reproduce. Only instructions on how to produce it. A virus is even worse at reproducing than Ikea chairs:, the chairs bring both the parts and the manual, the virus only comes with the manual. The extremely specific conditions you mention do not allow the virus to reproduce, it allows the host cell to produce the virus.

You might not like the definition of the word, but it is what it is.

Behold, a man!

But yes, examples like fire (nice idea on that one btw) are why "life" is weirdly tricky to define.

I think the answer lies in quantum physics, we may find some mechanism there that exists in typical life but doesn't exist in atypical thing like viruses and self-replicating RNA. Either that, or it lies in chemistry and we just haven't found the right experiment to make the discovery with. Because the line between "a mix of compounds/elements that can do complex things" and "life" has to be drawn somewhere right?

I get the edges are very blurry when defining what something is or isn't in biology, but I wouldn't equate destroy or alter with consume, or grow with reproduce, either.

I mean, sure. Maybe such a thing exists, but if we don't know of that, we're just making things up.

Not that it matters, but I don't personally draw a line between a bunch of molecules and an animal. Granted, that's not a common opinion

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If there is a virus that can self-replicate, that's news to me. Which viruses do that?

You have a version of these within your genome as well. Look up retrotransposons and other genetic mobile elements.

The poster is referencing deltavirus, which also doesn’t produce its own capsid. Its only not a viroid because it steals a capsid from HepB.

There doesn't have to be any fundamental measurable difference between something that is or is not life. Reality doesn't really care about our need to define things.

This probably gets into more philosophy than science maybe, but there's not really a clear-cut line between "life" and "non-life" which is why it's hard to classify where viruses fall. If you instead think of life as less of a binary state and more like a process of self-preservation/self-propagation, then viruses certainly fit that bill. I would imagine the usage of the term "organism" predates thinking of life as a process and more of a state.

> they could potentially go even further, if there are genes sets where knocking out only single components was lethal, but knocking out the whole set was survivable, so there's potential to go even further.

That’s got to be maddening, having to account for various combinations within your original problem.

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There are several measurable differences between cells and viruses.

Defining what viruses are, and thus whether or not they're considered "life", is quite scientifically important. We need to define things based on what their uses and limitations are. Viruses are already known to have unique characteristics; if we further define those characteristics and are able to distinguish them from organisms, we can potentially discover new things about life, or new things about almost-life as a whole that fits certain parameters. We dont know what we don't know. Everyone freaking out over labels is missing the point, as usual.

I honestly think that most microbial stuff (prions, viruses, even bacteria to some extent) is closer to machinery than anything a layman would consider "life."

Sure, it's autonomous self-replicating machinery that actively seeks and processes its own fuel, but... well, you could design a macroscale machine that does this.

You wouldn't want to, because you'd be Ted Faro, but it's possible.

When you hear "consume" or "metabolize", it doesn't just mean destroying or altering a molecule. The important bit is that energy is removed from the molecule and used by the "organism" in question. Fire definitely does count for that particular one, as the reaction to burn something is almost exactly what we do in our bodies. We burn our food, just much more slowly. A prion though, does not meet that criteria. It does alter a molecule (the non-dangerous form of the prion protein), and energy is removed (the dangerous form of the prion is at a slightly lower energy level, I believe), but the original prion doesn't do anything with that energy. It is unchanged.

Viruses can be fairly complex, but imagine the very basic form of what they are: A string of DNA floating around and getting into cells, and causing them to produce more copies of itself. Obviously viruses are more than just rogue DNA, but that's their function - they corrupt other cells. They don't eat, photosynthesis, reproduce, etc. They're much closer to a chemical reaction, like how fire causes wood to create more fire, except orders of magnitude more complicated.

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I've heard one interpretation that a virus particle could be thought of as analogous to a seed, and that an infected cell effectively becomes a virus organism.

This is undeniable. But when we're talking about definitions, aren't we talking about human constructs, attempts to approximate truth? Isn't it the same impulse that birthed the scientific method? Drawing lines between things is *useful!

Plus, anything that provides conversation like this thread is worth talking about, if you ask me.

I think you're on the right track, here. A virus needs a cell to function. A bacterium needs a nutrient-rich environment to function. An animal needs gravity oxygen, water, and food. Plants and animals are *environments for other kinds of life, so it's no wonder that the question is difficult to answer. When asked in the other direction, you're confronted with whether the Earth itself is alive.

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Heck, who's to say that having achieved sapience, those self-replicating machines aren't alive? Racists, that's who!

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> OP, the virus mentioned doesn't really represent an organism because it requires the mechanisms of a cell to replicate

There are a slew of obligate parasitic eukarotes that this definition disqualifies as an organism.

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I had no idea geneticists also did tiny code challenges, as well as programmers.

Though thinking about it, genetics is just soggy programming

Adding to this awesome answer: ecologically speaking, the investment for offspring is much less dependent on sheer DNA mass for complex organisms than it is for bacteria. Bacteria optimize things unheard of for complex organisms, they have crazy selection pressure.

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