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I never understand why viruses are not life. Bacteria are life because they are essentially a single-cell organism and act like any cell in our body: they consu

I never understand why viruses are not life. Bacteria are life because they are essentially a single-cell organism and act like any cell in our body: they consume energy and produce waste. Viruses may not be a cell, but they can be damaged, they die, and they appear to be more than a simple chemical process.

SllX 9y ago
Our understanding of life, viruses, and the relation between them is incomplete which means our definitions and lexicon as they are interrelated is also lacking in resolution. Before the discovery of these Giant Viruses as I guess we are calling them now, you used to be able to make a useful distinction between cellular-based life, and viruses. Viruses were mere packets of information as far as our best understanding went with very simple mechanics. Cells are more complex, with a useful distinction being made between prokaryotes and eukaryotes when necessary, but each could be easily identified as being made up of one or more cells. As our understanding of life improves, so does our useful observations into that murky grey area between life and not-life, and I suspect we will have to potentially extend the definition of life but come up with a vocabulary that more usefully delimits the forms it can take from its most simplest forms into the murkier grey area where viruses start to resemble cell-based life. Science is a work in progress, and so must be the scientific lexicon. Consider further your use of the word "die" and is that really the word you would use when a virus expires? Maybe, if you consider them to be alive in the first place, but you might use the word "destroy" if you considered them to be more like an object, or at least not alive.
Santosh83 9y ago
Perhaps when we consider that viruses are unable to form complex structures like tissues, organs and entire organisms, we must rethink if they're the same level of "life" as cells? I don't think a single definition of life is useful or might even exist, just as I don't think a single universal physical theory is possible.
jayd16 9y ago
Would you consider prions to be life?
meuk 9y ago
From David Goodsells The Machinery of Life: "In 1944, the physicist Erwin Schrödinger presented a very simple definition of life that has withstood the test of time. He identified one property that all life shares: living things avoid decay into equilibrium."
simopaa 9y ago
If I recall what I've been taught correctly, the reason why viruses are not considered 'life' is that they have no metabolism of their own. https://www.cliffsnotes.com/cliffsnotes/subjects/sciences/why-aren-t-viruses-considered-living-things https://www.cliffsnotes.com/cliffsnotes/subjects/sciences/wh...
ohf 9y ago
Viruses are more like robots. They don't respond to stimuli. They just, do. The definition of "life" comes down to splitting hairs. We don't consider something "alive" if its behavior doesn't change when its environment does.
- ravenstine 9y ago
  Don't bacteriophages have to respond to some stimuli in order to attach itself to a host cell and inject genetic material?
  - zaarn 9y ago
    Bacteriophages attach to certain receptors, they don't respond to any stimuli. The entire process of injecting their RNA is simply a chemical reaction to being attached to a receptor. Basically, they just drift along until they hit a bacteria with the right receptor, then inject their genetic material and the empty hull is either discarded or simply continues to hang onto the cell. The outer hull of the phage doesn't do a lot.
- felipemnoa 9y ago
  >>Viruses are more like robots. A virus is just a computer program that needs a Von Neumann machine (CPU) to run on. Following this analogy we could define alive by saying that the combination of a program and a Von Neumann machine makes the entity alive.
  - dmurray 9y ago
    Except that they really do have a physical manifestation (from the article, the cylindrical tail, the polyhedral box containing the genes, the fibrils on the outside). In some way they are closer to being the USB stick containing the computer program, that can reproduce onto other USB sticks but needs a host computer to do so.
    - pluma 9y ago
      Everything[0] has a physical manifestation. A computer program has a physical manifestation on its storage medium. [0]: Let's not argue about whether it makes sense to say that abstract concepts also have a physical manifestation. Programs are concrete expressions encoded on a physical medium (whether using magnets, electrical charges or even the position of mechanical switches).
Neeek 9y ago
I thought the reason was that a virus has no means to reproduce without hijacking some other living thing's facilities with which to replicate itself.
- runeks 9y ago
  Humans also survive by ingesting other life forms (plants, animals). We couldn’t survive without vegetation either, because it converts our waste products into useful stuff (e.g. CO2 to oxygen).
  - Neeek 9y ago
    Ingestion isn't really reproduction though, even if the dependency is there. I'm not saying it's a perfect definition, just pointing out that it's never been "consume energy, produce waste".
- chii 9y ago
  but it's unclear that this definition really means anything, because you can say that humans lack the facilities to replicate itself, without access to food and water and air too!
  - Neeek 9y ago
    We have the organs to reproduce provided that we, you know, exist... I'm not arguing how correct the definition is, more that it's what is 'textbook' from my understanding, and not really do do with the consume energy, produce waste comment or ability to react to an environment like some other posts suggested.
- novia 9y ago
  Neither do rickettsia or chlamydia, two bacteria. Honestly, whoever was deciding on the definition of "what is life" knew ahead of time the kinds of things they wanted to include and they worked backwards from there. We want to exclude viruses because they are too mechanical. There's no magic to them. That's the way it appeared before we started finding all these giant viruses anyways.
whatshisface 9y ago
Words are only useful insofar as they point to groups of entities that the speaker and listener agree are being pointed to. So, we should ask "what is the most useful definition of life?" It's a short word, so it's valuable real-estate. What should the definition of life be? It's easy to get wrapped up into discussions about words, but don't forget that the things they point to is what's really interesting.
- jamesrcole 9y ago
  I agree. I think a source of confusion is the following. Everyone has built up, over their lifetime, an implicit mental notion of "life", which is based upon the sorts of characteristics of things they classify as being alive. Many (I'd say most) people think this mental notion is some objective category that exists external to their mind, some thing that has a kind of essence that is shared by all the instances of life. They see the task of defining life as defining the essence of this category, and see there being an objective question as to whether something (e.g. a kind of virus) fits this category. But this is to confuse a mental construct with what is out there. There are the objective properties of things like different types of viruses, different types of bacteria, of different types of mammals, and of all other natural phenomena. You can talk about what the similarities and differences are between the objective properties of a type of virus and a type of bacteria, for example, and there are simpler kinds of phenomena vs more complex ones, but there's no actual "life" category out there, separate from our mental constructs, to be objectively defined.
  - lawlessone 9y ago
    would it be safer to say everything in on spectrum between alive and not alive? Even chemicals "evolve" http://www.dictionary.com/browse/chemical-evolution http://www.dictionary.com/browse/chemical-evolution
- DelightOne 9y ago
  Thats "The Categories Were Made For Man, Not Man For The Categories". Sb trying to push sb else to use a definition meets the second part of the sentence.
HankB99 9y ago
Much the same as Pluto is no longer a planet. These things run on a continuum and the line has to be drawn somewhere.
novia 9y ago
The thinking on this has been changing recently as more discoveries are made. The linked article even alludes to it by calling viruses the fourth domain, implying that they are indeed life.
sorokod 9y ago
Well, it looks like that life is one of those non-binary sliding scale concepts. Accept this and move on.
lr4444lr 9y ago
Isn't replication through mitosis or miosis generally accepted as a requirement?

SllX 9y ago

Our understanding of life, viruses, and the relation between them is incomplete which means our definitions and lexicon as they are interrelated is also lacking in resolution. Before the discovery of these Giant Viruses as I guess we are calling them now, you used to be able to make a useful distinction between cellular-based life, and viruses. Viruses were mere packets of information as far as our best understanding went with very simple mechanics. Cells are more complex, with a useful distinction being made between prokaryotes and eukaryotes when necessary, but each could be easily identified as being made up of one or more cells. As our understanding of life improves, so does our useful observations into that murky grey area between life and not-life, and I suspect we will have to potentially extend the definition of life but come up with a vocabulary that more usefully delimits the forms it can take from its most simplest forms into the murkier grey area where viruses start to resemble cell-based life. Science is a work in progress, and so must be the scientific lexicon. Consider further your use of the word "die" and is that really the word you would use when a virus expires? Maybe, if you consider them to be alive in the first place, but you might use the word "destroy" if you considered them to be more like an object, or at least not alive.

Santosh83 9y ago

Perhaps when we consider that viruses are unable to form complex structures like tissues, organs and entire organisms, we must rethink if they're the same level of "life" as cells? I don't think a single definition of life is useful or might even exist, just as I don't think a single universal physical theory is possible.

jayd16 9y ago

Would you consider prions to be life?

meuk 9y ago

From David Goodsells The Machinery of Life: "In 1944, the physicist Erwin Schrödinger presented a very simple definition of life that has withstood the test of time. He identified one property that all life shares: living things avoid decay into equilibrium."

simopaa 9y ago

If I recall what I've been taught correctly, the reason why viruses are not considered 'life' is that they have no metabolism of their own. https://www.cliffsnotes.com/cliffsnotes/subjects/sciences/why-aren-t-viruses-considered-living-things https://www.cliffsnotes.com/cliffsnotes/subjects/sciences/wh...

ohf 9y ago

Viruses are more like robots. They don't respond to stimuli. They just, do. The definition of "life" comes down to splitting hairs. We don't consider something "alive" if its behavior doesn't change when its environment does.

ravenstine 9y ago
Don't bacteriophages have to respond to some stimuli in order to attach itself to a host cell and inject genetic material?
- zaarn 9y ago
  Bacteriophages attach to certain receptors, they don't respond to any stimuli. The entire process of injecting their RNA is simply a chemical reaction to being attached to a receptor. Basically, they just drift along until they hit a bacteria with the right receptor, then inject their genetic material and the empty hull is either discarded or simply continues to hang onto the cell. The outer hull of the phage doesn't do a lot.
felipemnoa 9y ago
>>Viruses are more like robots. A virus is just a computer program that needs a Von Neumann machine (CPU) to run on. Following this analogy we could define alive by saying that the combination of a program and a Von Neumann machine makes the entity alive.
- dmurray 9y ago
  Except that they really do have a physical manifestation (from the article, the cylindrical tail, the polyhedral box containing the genes, the fibrils on the outside). In some way they are closer to being the USB stick containing the computer program, that can reproduce onto other USB sticks but needs a host computer to do so.
  - pluma 9y ago
    Everything[0] has a physical manifestation. A computer program has a physical manifestation on its storage medium. [0]: Let's not argue about whether it makes sense to say that abstract concepts also have a physical manifestation. Programs are concrete expressions encoded on a physical medium (whether using magnets, electrical charges or even the position of mechanical switches).

Neeek 9y ago

I thought the reason was that a virus has no means to reproduce without hijacking some other living thing's facilities with which to replicate itself.

runeks 9y ago
Humans also survive by ingesting other life forms (plants, animals). We couldn’t survive without vegetation either, because it converts our waste products into useful stuff (e.g. CO2 to oxygen).
- Neeek 9y ago
  Ingestion isn't really reproduction though, even if the dependency is there. I'm not saying it's a perfect definition, just pointing out that it's never been "consume energy, produce waste".
chii 9y ago
but it's unclear that this definition really means anything, because you can say that humans lack the facilities to replicate itself, without access to food and water and air too!
- Neeek 9y ago
  We have the organs to reproduce provided that we, you know, exist... I'm not arguing how correct the definition is, more that it's what is 'textbook' from my understanding, and not really do do with the consume energy, produce waste comment or ability to react to an environment like some other posts suggested.
novia 9y ago
Neither do rickettsia or chlamydia, two bacteria. Honestly, whoever was deciding on the definition of "what is life" knew ahead of time the kinds of things they wanted to include and they worked backwards from there. We want to exclude viruses because they are too mechanical. There's no magic to them. That's the way it appeared before we started finding all these giant viruses anyways.

whatshisface 9y ago

Words are only useful insofar as they point to groups of entities that the speaker and listener agree are being pointed to. So, we should ask "what is the most useful definition of life?" It's a short word, so it's valuable real-estate. What should the definition of life be? It's easy to get wrapped up into discussions about words, but don't forget that the things they point to is what's really interesting.

jamesrcole 9y ago
I agree. I think a source of confusion is the following. Everyone has built up, over their lifetime, an implicit mental notion of "life", which is based upon the sorts of characteristics of things they classify as being alive. Many (I'd say most) people think this mental notion is some objective category that exists external to their mind, some thing that has a kind of essence that is shared by all the instances of life. They see the task of defining life as defining the essence of this category, and see there being an objective question as to whether something (e.g. a kind of virus) fits this category. But this is to confuse a mental construct with what is out there. There are the objective properties of things like different types of viruses, different types of bacteria, of different types of mammals, and of all other natural phenomena. You can talk about what the similarities and differences are between the objective properties of a type of virus and a type of bacteria, for example, and there are simpler kinds of phenomena vs more complex ones, but there's no actual "life" category out there, separate from our mental constructs, to be objectively defined.
- lawlessone 9y ago
  would it be safer to say everything in on spectrum between alive and not alive? Even chemicals "evolve" http://www.dictionary.com/browse/chemical-evolution http://www.dictionary.com/browse/chemical-evolution
DelightOne 9y ago
Thats "The Categories Were Made For Man, Not Man For The Categories". Sb trying to push sb else to use a definition meets the second part of the sentence.

HankB99 9y ago

Much the same as Pluto is no longer a planet. These things run on a continuum and the line has to be drawn somewhere.

novia 9y ago

The thinking on this has been changing recently as more discoveries are made. The linked article even alludes to it by calling viruses the fourth domain, implying that they are indeed life.

sorokod 9y ago

Well, it looks like that life is one of those non-binary sliding scale concepts. Accept this and move on.

lr4444lr 9y ago

Isn't replication through mitosis or miosis generally accepted as a requirement?