Why aren't viruses considered to be "alive"?

Life as the spontaneous generation from non-living matter (chemical) by chance - Darwin's “warm pond“.....

Not to mention huge kingdom of various viruses - more than 3500 different viruses! Seems to me that these guys have a strong plan to survive!

Viruses do furthermore offer a surprising and radical set of Darwinian choices; indeed high mutation rates are often credited with their robust survival strategies. A clean separation of viruses from the continuum of biochemistry seems unlikely. There is evidence that human DNA has many viral vestiges, thus elevating the virus kingdom to much more than some kind of biological passenger status. From generation to generation, viruses have introduced new genetic information into their victims and hosts.

The debate on defining life rarely has reached scientific consensus, despite volumes written cataloguing the various qualifications for being 'alive'. Of note however, the presence of similar molecules like DNA and RNA, even in the simplest life forms like viruses, is often suggestive of a single origin event--or at least, a whittling away of inferior encoding molecules from a multitude of less fit alternatives.

Although the only living candidate to store its key replicative information in RNA, viruses depend critically on adapting to the same code and cellular signals that govern their living hosts. Divergence into bizarre or out-of-family biochemistry would quickly prove fatal to any experiments that might widen to entirely new lifeforms, since the virus is ultimately just a parasite. That is the co-dependence of the simplest terrestrial experiment with its most complex manifestations.

The scientific community can agree on the important role that viruses have proven historically in the selection of future generations. If viruses are not alive, they certainly live with us.

source

Originally posted by Soylent Green Is People
cutwolf --

Going back to your original post, why are you so keen on the scientific world defining a virus as being "life". You seemed to inply that if a virus was considered "alive" it would increase the odds of finding life outside our planet. But a virus, by definition, needs to have a host cell to live, thus a virus could not live on a planet that does not already contain life...

...so it's safe to say that -- using the accepted scientific definition of a virus -- if a planet is found to have viruses, then it MUST have the bacterial or possibly even multi-cellular life to host those viruses.

In other words, if you find a virus, life is definitely present (although, I suspect that even a single cell bacteria will be much easier to detect that a virus, thus the bacteria will be found first, then possible viruses will be found later).

I was speaking in broader terms when I say that.

Scientists constantly say, "Life can't live here because it is too hot/cold/dark/etc."

They're assuming all life everywhere (if it exists) has the same characteristics and requirements as life on Earth.

I feel that logic is flawed, and if we'd stop thinking like that, we'd be more open to the possibility of unconventional life on other planets, which I think is how we'll discover it (if we discover it).

Originally posted by blue bird

Originally posted by X-tal_Phusion
3) No, they do not exhibit Darwinian evolution, therefore they are not "alive".


[edit on 28-5-2007 by X-tal_Phusion]

Please..

Viruses DO
1. survive
2. mutate


- DNA or RNA of virus can and evolve over time - that means that viruses increase their chance for evolutionary survival meaning adaptation to the environment........ so they stay from dawn of life till present in the game..

I was talking about computer viruses (not alive) as opposed to biological viruses (alive) in that post. I think you misunderstood me. I was demonstrating the differences between the two of them. Computer viruses can be programmed to mutate but there is no selection pressure by the environment to impact their competition against other computer viruses. Biological viruses can compete for resources when their environment changes.

Originally posted by blue bird
Life as the spontaneous generation from non-living matter (chemical) by chance - Darwin's “warm pond“.....

Not to mention huge kingdom of various viruses - more than 3500 different viruses! Seems to me that these guys have a strong plan to survive!

source

Let's not confuse the origin and evolution of viruses with spontaneous generation (I can see it coming, even you understand the primordial soup concept). We agree that biological viruses are alive; enough said. Good article you found, by the way.

Originally posted by X-tal_Phusion
Let's not confuse the origin and evolution of viruses with spontaneous generation (I can see it coming, even you understand the primordial soup concept). We agree that biological viruses are alive; enough said. Good article you found, by the way.

Oh no, no - I would never take ( evolutionary terms) honorary place from our dear bacteria.... after all virus need host -I just want to say, that virus coelvolve with their hosts from the dawn of life ( once momentum was gain and quality leap was made from 'primordial soup' ) be it bacteria or plant or insects or vertebrates.... with every walk from the tree of life.


Thanks X-tal...
computer viruses - sorry than

Originally posted by X-tal_Phusion
I was talking about computer viruses (not alive) as opposed to biological viruses (alive) in that post. I think you misunderstood me. I was demonstrating the differences between the two of them. Computer viruses can be programmed to mutate but there is no selection pressure by the environment to impact their competition against other computer viruses. Biological viruses can compete for resources when their environment changes.

Virus are only particles, they do not respond to environmental changes.

What resources would a virus fight over anyway? All it needs is a cell.

How about the cellular apparatus it needs in order to replicate? If virus A ends up in the same cell as virus B and A replicates faster than B, the cell could die before B gets a chance to replicate. No progeny = no contribution to the gene pool by virus B. In this case, you snooze, you lose. Computer viruses differ in that they are not reliant on physical structures in their hosts (thus rendering them immune to environmental influence, selection pressure and Darwinian evolution, thus excluding them from life). Biological viruses are competing for a physical resource that IS subject to environmental changes.

Living viruses compete for everything from who can replicate faster before the cell dies, to who can get through the cell membrane first, to whose enzymes are subject to inhibitors present in a host, etc. It's not simply a matter of, "You bind there, I'll bind here and we can share this cellular paradise." Like people, some viruses are real party animals. It's like sharing a house with strangers. Some want to take care of things to make sure the proverbial landlord (cell) won't evict them (or die) while others are wild, wreckless and trash the place in a relatively short period of time without a care in the world (I got what I wanted and I don't care about what anyone else in this symbiotic relationship needs!).

Let's not forget the container surrounding these cute little segments of DNA/RNA either... there is even competition before reaching the cell (eg, immune system). The battle for resources starts long before the cell is invaded. If something recognizes the virus for what it is, it can get gobbled up before it ever reaches its target. This is why some viruses have employed some pretty sneaky molecular measures to defend themselves against immune detection/response and other EXTRA-cellular dangers as well. Does this sound like something a purely chemical or physical system would do?

[edit on 28-5-2007 by X-tal_Phusion]

What makes and describes a virus as a non-living organism depends on a few things. First off, it would be incorrect to say that something is non-living just because it needs a host cell to reproduce. A virus behaves and has certain characteristics of known parasites (which also require a host to reproduce), and since we fully know that parasites are living organisms a virus' non-living structure cannot be explained in this manner. Think of it like this...when a man ejaculates he has a given amount of sperm cells that exit his body with his semen. These sperm cells need a host egg to bind with in order to reproduce and create life. If the definition of a non-living organism were simply that "it cannot reproduce without the assistance of a host", then a man's sperm cells would fall into that category as well. Essentially, the sperm needs the "host" cell of a female to finish the process of reproduction and cellular division, which following the parasitic explanation would mean that humans ourselves would be deemed as non-living parasites. We all know this is not true of course and that humans represent our own definition of a living organism, and because a female egg cell does go through the process of binary fission after fertilization we are not deemed as parasites ourselves. Parasites are also characterized as living organisms because although they do require a host to reproduce they also go through the process of cellular division and binary fission as I already mentioned.

With a virus it is especially difficult to trace the origin and classification of them very far back. In fact, by all accounts the fossil record is extremely tiny when it comes to the number of preserved viral particles. Classification of viruses ends at the Family level which essentially puts them in the same area as Eukarya, Archaea, and Eubacteria. This is another difficult thing about describing a virus as a living organism...we lack the fossil record to prove where a split occured from living organisms. Now, you can take a few things from this:

1. Because a virus needs a "host" for replication purposes, then you can draw the conclusion that viruses were probably not around before the advent of cellular evolution or would have evolved along with cells.

-or-

2. Viruses were once cells and carried out all the functions of cellular division, but somehow lost these basic cellular functions and held on to on the information needed to replicate themselves using host cells.

Another difficulty in describing a virus as a living organism is the fact that they lack the most basic of cellular structures beyond nucleic acids and proteins. Not only do they lack what is considered to be the most basic form: STRUCTURE but viroids, prions, and viruses do not metabolize in the same way at Eukaryotic and Prokaryotic cells do, and absolutely do require other cells for this process.

I have even heard that a best and most basic way of looking at viral particles is to think of them along the line of crystal growth (which of course is non-living): they exhibit structural uniformity and are like a "growing chemical". Essentially a virus is non-living and non-dead, almost the equivalent of popular horror movies about the undead. Another way to think of how a virion could be described would be to compare it to modern day automobiles. A virus is little more than a transportation vehicle for genes, and take a look at the structure of even complex virusus such as Bacteriophages and notice that they are little more than carriers of genetic information.

So, there are essentially certain criteria that a virus must meet in order to be called a fully functional living organism, namely:

1. The ability to change and respond to any given environment (viruses do not change form in any way based on this)
2. Be able to reproduce (viruses need a host cell to do so)
3. Need to have a lifecycle themselves (viruses do not grow, develop or even die...they simply move on in one form or another)
3. Be able to use energy and the ability to obtain it on their own (viruses depend on host cells to fulfill their metabolic functions)

As you can see they do not meet any of the established criteria for living organisms, and contrary to what some people seem to think a "virus" is not an independant cell. If it were, it would have a cytoplasm, mytochondria, and all the other structures needed for life. As I have already noted the structure of a virus is nothing more than nucleic acids, proteins and a viral capsid (envelope) to contain the RNA or DNA.

[edit on 28-5-2007 by Jazzerman]

Originally posted by X-tal_Phusion
How about the cellular apparatus it needs in order to replicate? If virus A ends up in the same cell as virus B and A replicates faster than B, the cell could die before B gets a chance to replicate. No progeny = no contribution to the gene pool by virus B. In this case, you snooze, you lose. Computer viruses differ in that they are not reliant on physical structures in their hosts (thus rendering them immune to environmental influence, selection pressure and Darwinian evolution, thus excluding them from life). Biological viruses are competing for a physical resource that IS subject to environmental changes.

Well that only happens when they meet a host. In any other case they are in a dormant state and do absolutely nothing.

This is why some viruses have employed some pretty sneaky molecular measures to defend themselves against immune detection/response and other EXTRA-cellular dangers as well. Does this sound like something a purely chemical or physical system would do?

Yes it does. A virus doesn't think, it doesn't feel, it's not aware of anything. It's in a totally inactive state until it meets a host cell by chance where the features of it's shell provoke it's entrance into the cell. It has no will or anything like that. When it touches a cell, there is no sensory organ to detect the cell, no nerve to send a signal, and no brain to receive the signal and react. It's only a chemical reaction, cause and effect.

There are cristals that have the ability to reproduce (well, replicate), yet they are not alive.

[edit on 28-5-2007 by DarkSide]

Originally posted by DarkSide
Well that only happens when they meet a host. In any other case they are in a dormant state and do absolutely nothing.

Yes it does. A virus doesn't think, it doesn't feel, it's not aware of anything. It's in a totally inactive state until it meets a host cell by chance where the features of it's shell provoke it's entrance into the cell. It has no will or anything like that. When it touches a cell, there is no sensory organ to detect the cell, no nerve to send a signal, and no brain to receive the signal and react. It's only a chemical reaction, cause and effect.
[edit on 28-5-2007 by DarkSide]

Last time I checked, bacteria didn't think either. Viruses recognize their cellular targets through receptors present on the surface of the cell membrane (not unlike the binding of neurotransmitters in behavior: en.wikipedia.org...) and this is why viruses only infect certain cells (when's the last time your dog or cat caught your cold?).

Are the cells sending out engraved invitations to the viruses? "Here I am! Come infect me!" Nope. Basically, if a cell is unfortunate enough to present the target signaling molecule on its membrane, the virus sees that as a big, red flashing "Vacancy" sign after a long jouney of drifting past targets lacking these receptors. Viruses may not swim but they do know when it's time to pull over (bind to the receptor) check in for the night (endocytosis) and replicate.

You're right. Life is all a series of chemical reactions and whether its viral infection or behavior, biology cannot function without it!

Technically, if you take a step back from the molecular level, how different are we humans from viruses?

We need a host to survive. Without the earth to mine for resources so we can reproduce, we'd be none existent.
Through the same definition, couldn't humans, and all life for that matter, be declared as 'not life' ?

What happens if a virus strain figures out how to reproduce using resources other than a living cell? Are we just going to say, oh, well... they're life now? BS. Viruses are living things just like we are... just because they are pure predator, requiring an external living thing to survive, doesn't make it any less than a life form.

Remember, we can't survive without external living things...
either viruses are life-forms, or we aren't.

Well, a virus is a virus because it can't reproduce using food. Basically, we can eat and drink and whatever and our bodies can produce offspring. A virus can't do that - it has to rely on the host cell's mechanisms not only for nutrients, but for the entire reproductive process.

Originally posted by MastaG
What we're doing is dividing the whole world in two extremes - yes and no, black and white.. [It's really late here, and I'm too drowsy to remember the name of the philosophy I'm talking about;]

Boolean logic is what you were looking for.
And would go something like this… If a virus is not dead it must be alive. If a virus can be killed it must be alive. If a virus can not be killed it must not be a life form.

Originally posted by Cutwolf
1. A virus particle attaches to a host cell.
2. The particle releases its genetic instructions into the host cell.
3. The injected genetic material recruits the host cell's enzymes.
4. The enzymes make parts for more new virus particles.
5. The new particles assemble the parts into new viruses.
6. The new particles break free from the host cell.
[...]
[edit on 5-27-2007 by Cutwolf]

Having studied biochemistry to me this still is just more of a perceived idea.
One person sees proactive behaviour another.. (me) sees molecules reacting when they come into contact with the right molecules.
natrium meets air, protein on shell meets lipids in cell membrane. to me there is no difference yet on this scale. Not in a practical sense anyway.

(1)It enters the cell because proteins on it's capsule react with the lipids in the cell membrane.
(2)The shell get's dissolved by enzymes. It doesn't get released (intent)
(3)Absorbed genetic material, it's often said injected but according to what I am supposed to know, a cell reacts to new genetic material by absorbing it into it's make-up.
(4)The enzymes the host cell creates.
(5)The host cell assembles the new viruses.
(6)Breaking free is a result of the cell being over full and bursting whatever viruses are complete survive, the ones mid assembly when it bursts don't.

I have to admit though the nanomechanical aspects of some larger viruses are amazing and seem very living. but still when you observe it only happens on contact.

Originally posted by Johnmike
It would have to be the virus, I think. The virus is parasitic and therefore needs a host (the bacteria).

[edit on 27-5-2007 by Johnmike]

Being parasitic I'd have to say I think you're wrong on the viruses conclusion, the logic is fine but the conclusion contradicts your own logic. single celled lifeforms (inc. bacteria) would have to have come first, if viruses came first what did they use to multiply and survive up to the arrival of single celled lifeforms?

As for killing viruses.. destroying molecules sounds more accurate. if the molecules get destroyed by a reaction then no rna/dna can get into a cell.
It would just be free floating, inert. and without the protein molecules from the shell it won't be able to get past the cell membrane.

as for black and white, yes and no, As i've said before I concider them a seperate stage between living life and inert material.


[edit on 29/5/2007 by David2012]

Let me see if I'm understanding this correctly. Please inform me if I'm not...

Originally posted by Johnmike
Well, a virus is a virus because it can't reproduce using food.

We don't reproduce using food either. We need food to survive, as do viruses. They must thrive on something inside of their parent host to maintain the necessary energy to keep reproducing. They don't just magically manufacture other viral cells.

Basically, we can eat and drink and whatever and our bodies can produce offspring. A virus can't do that - it has to rely on the host cell's mechanisms not only for nutrients, but for the entire reproductive process.

So what you're really saying here is that the only thing that separates us from viruses is the ability to consciously make the decision to eat or not to eat? How is the Earth any different with us on it than we are with a virus in us? I'm confused. If you could enlighten me, I'd be ever so grateful.

Thanks in advance for any and all help on understanding this.

TheBorg

Originally posted by X-tal_Phusion
Last time I checked, bacteria didn't think either.

They don't, but bacteria are more "alive", they react to changes in their environment, move, communicate, need energy to survive, etc.

Are the cells sending out engraved invitations to the viruses? "Here I am! Come infect me!" Nope. Basically, if a cell is unfortunate enough to present the target signaling molecule on its membrane, the virus sees that as a big, red flashing "Vacancy" sign after a long jouney of drifting past targets lacking these receptors. Viruses may not swim but they do know when it's time to pull over (bind to the receptor) check in for the night (endocytosis) and replicate.

But they pull over and replicate only because they hazardly came into contact with the cell.

Originally posted by TheBorg
We don't reproduce using food either. We need food to survive, as do viruses. They must thrive on something inside of their parent host to maintain the necessary energy to keep reproducing. They don't just magically manufacture other viral cells.

Originally posted by TheBorg
So what you're really saying here is that the only thing that separates us from viruses is the ability to consciously make the decision to eat or not to eat? How is the Earth any different with us on it than we are with a virus in us? I'm confused. If you could enlighten me, I'd be ever so grateful.

No, we do reproduce using food. Or at least, the nutrients and energy in food. what separates us from viruses is the fact that we take things from food and build with it. We construct new offspring, in a sense, from what we consume. The big thing is that we can synthesize proteins. A virus can't do so, but it needs to be able to if it wants to make more copies of itself. While we can create new cells, structures, offspring, and whatnot on our own, a virus lacks this ability. The only reason it can replicate is because it "uses" the mechanisms in a host cell that build new structures (especially proteins). That's why viruses are a bit creepy - they don't attack you, as much as they hijack your own cells and use them against you.

Adaptation is the name of the game when it comes to viral existance. As I briefly explained before, viruses more than likely came sometime after the development of of early cellular life on Earth, and more than likely started as bits of genetic code that adapted to a parasitic like existance through the process of evoluntion. One characteristic of most cellular life on earth is that fragments of RNA and DNA can both be found inside that particular life-form. On the other hand, the genetic material carried by a virus can be either DNA or RNA, but never both.

Another key aspect in the debate about whether a virus is a living organism that has been brought up in this thread is whether or not a viral particle uses food for reproduction. No known virus has the organelle called "Ribosomes", which translate mRNA into a polypeptide chain using functioning amino acids delivered by the tRNA. Because of this it cannot synthesize proteins...a basic function of life on Earth. Once a virus acquires any form of energy it is not able to hold onto it in the form of adenosine triphosphate (Definition found here: Adenosine Triphosphate ), which regular cellular function requires. So, they are required to derive all of their energy and metabolic functions from a host cell.

Nevertheless, and on a slightly different hand viruses have been known to evolve and sometimes at alarming rates. There are several RNA based viruses whose mutation rate shows them evolving a new genome every time they replicate! By the time HIV has made its rounds in the human body there are some estimates that over 900 Billions mutations have occured due the the nature of the virus using the CD4+ cell against itself. Retroviruses (like HIV), pararetroviruses, retrotransposons, and retroposons more than likely all carried a common ancestor that may have evolved in the switch from RNA to DNA based genetics using Reverse Transcriptase. It does leave one to wonder whether the process of evolution itself can be a justification and basis for life, however, that definition alone is not enough to justify viral life and you can see my previous post for some easy ways scientists use to classify life. See here for a fairly good description of Life as we know and describe it: LIFE .

The nature of a virus is to exist; nothing more, nothing less. Whether it is able to create further viruses is merely by the chance meeting of a host cell. Although this has always posed somewhat of a quagmire to me, as it seems to directly contradict something brought up in the Second Law of Thermodynamics...Entropy.

[edit on 30-5-2007 by Jazzerman]

Originally posted by Johnmike
While we can create new cells, structures, offspring, and whatnot on our own, a virus lacks this ability. The only reason it can replicate is because it "uses" the mechanisms in a host cell that build new structures (especially proteins). That's why viruses are a bit creepy - they don't attack you, as much as they hijack your own cells and use them against you.

And we humans don't "use the mechanisms" on the Earth to do what we want? I'm trying to understand how we're any different from a virus. We're the most prevalent macro-virus in the known universe, since we incorporate everything that we come into contact with.

TheBorg

If viruses aren't alive, how does stuff like this happen?