Viruses: Living or Non-living organisms

Are viruses living or non-living organisms

  1. Living

    7 vote(s)
    21.9%
  2. Non-living

    16 vote(s)
    50.0%
  3. Both

    9 vote(s)
    28.1%
  1. Do you consider a virus living or non-living organism?

    In middle school, I was taught that a virus was the smallest living organism.
    However, I see viruses as packages of genes coated in protein and that they are inert on their own. I think of viruses as stuck in a "Twilight Zone" between living and non living.

    I don't think that viruses are true living organisms because they do not grow by dividing, generate energy, creating protein, etc. Yet, some scientists believe they are living because they contain genes necessary for their replication.

    And there are some bacteria that are like viruses, unable to reproduce outside a host cell, such as Chlamydia or Rickettsia that are classified as living organisms. But they have the same limitations as viruses.



    p.s. I think there was a similar topic for some research paper that was posted in 2009. I can't seem to find it.
     
    Last edited: Feb 19, 2012
  2. jcsd
  3. Viruses are not considered to be "living" organisms in the fullest sense of the word. They replicate inside other living beings, but themselves are not living.
     
  4. bfman is exactly right.
     
  5. Ryan_m_b

    Staff: Mentor

    To be honest I don't think I've ever heard a solid definition of "life". Instead I've heard lists of attributes that if something has (or at least has some of them) it can be said to be alive. I would not class viruses as alive because they are not metabolically active and cannot reproduce themselves. The latter is different to needing a host to replicate because the distinction is that viruses literally are assembled by the host rather than growing in it.

    I also find it bewildering that people have voted "both" for a question that is essentially "A" or "Not-A"
     
  6. Pythagorean

    Pythagorean 4,582
    Gold Member

    "Towards a Mathematical Theory of Complex Biological Systems" by C. Bianca, 2011:

    my paraphrasing and comments in the parenthesis

    1. Wide range of participating entities (e.g. functional molecular groups)
    2. Nonlinear interactions between entities (characterized by feedback and dispersion)
    3. Heterogeneity (not sure how this is different form 1 given the paragraph on this)
    4. Self-Organization / ability to develop specific strategies (I don't think these should be the same)
    5. Active entities "play a game" at each interaction. (not really clear, but the author's paragraph talks about basically, changing internally as a result of external interacitons.
    6. System is not in equilibirum (I agree that would be bad for a living system)
    7. Entities belong to a wide variety of components (the entities have diverse functions)
    8. Time is a key variable (this seems irrelevant/obvious to me. It uses the words Darwinian evolution, but we've already established that implicitly with 4 and 5)
    9. multiscale approach (multi-scale optimization).
    10. small changes lead to large effects (an extension of 2: form nonlinearity to chaos)

    I think some of these are important and the idea develops a good framework for mathematical biology (which allows you to more concretely define things) but I think the number "10" was reached for. There's maybe four or five basic quantifiable principles here.

    We could lump:

    1, 3 and 7 together
    4, 5, 8 and 9 together
    2, 6 and 10 together

    (wow, that would bring it down to 3!)

    So far it seems that viruses would pass the test on these little quantifiers (but probably only in the presence of a "host"?), but then I have the feeling like they're life junk: amalgamates that must inevitably result from an ecology diverse degeneracy.

    But I also have another thought. In the spatiotemporal limit, we are all part of one system (we all came from the same ancestor, we're all driven by and interact with the same chemical and physical gradients). So the boundaries we define between "organisms" can often be fuzzier than we imagine it is. At some point, a transitions from a colony of single celled organism to a single multi-celled organism must have occurred.

    So my thought with viruses is then.. maybe they're just an extension of living things, moreso than a living thing themselves. An example of where the phenomena of "organism" leaks into and out of the environment through these fuzzy boundaries that define the organism.
     
  7. Seems like we need to make finer distinctions. I propose that a virus is dead until it contacts a cell and begins working. I'd further propose that it's not alive at that point either; that it has merely transformed the host cell into a new entity.

    In a very real way the infected cell is like a Zombie. It's no longer the cell it was and the mutated cell has to be considered the true organism with the virus particle as a mere "seed" or spore.
     
  8. Same, I personally don't think a virus is living or non living.

    A friend of mine said that saying that a virus is a living organism inside a host is almost like saying DNA nanobots are living organisms once inside a human body.

    http://www.sciencedaily.com/releases/2012/02/120216144238.htm
     
  9. Borek

    Staff: Mentor

    Trying to classify a virus as living or not is a futile effort. We (Homo sapiens) have a tendency to try to classify everything, even if the classification doesn't make sense and is based on a questionable definitions.
     
  10. Ryan_m_b

    Staff: Mentor

    I fail to see how a virus could be inside once in a host cell as often they have broken apart to shed their protein coat and release RNA. This RNA is then read by ribosomes that assemble more virus proteins, with the RNA is replicated by other processes, then the viral components self assemble. I don't think it is fair to say that any of that counts a virus as alive considering that when a virus replicates there is no whole virus at all.
    Agreed.
     
  11. What about Prions?
     
  12. But I also have another thought. In the spatiotemporal limit, we are all part of one system (we all came from the same ancestor, we're all driven by and interact with the same chemical and physical gradients). So the boundaries we define between "organisms" can often be fuzzier than we imagine it is. At some point, a transitions from a colony of single celled organism to a single multi-celled organism must have occurred.

    So my thought with viruses is then.. maybe they're just an extension of living things, moreso than a living thing themselves. An example of where the phenomena of "organism" leaks into and out of the environment through these fuzzy boundaries that define the organism.[/QUOTE]

    Well written, I like it. A fuzzy line of almost life. Lots of grey areas in this universe.
    DC
     
  13. A a College Biology professor, the debate about a virus being living or non-living is ongoing. The reproduction is the complicated issue, because all viruses use the host's cell DNA/RNA replication machinery, ie, enzymes, nucleotides. Even the enzyme itself is incorporated into the virus' envelop. They therefor are not self sufficient for the own reproduction, which is a characteristic for living things. They also do not carry out all the cool little processes that eukaryotic cells do to produce energy. They lead a "borrowed" life, so to speak.

    Prions, on the other hand, are nonliving particles. They are proteins that are capable of misshaping others simply by their contact with them.
     
  14. bobze

    bobze 650
    Science Advisor
    Gold Member

    I'd like to second this as well. Whether they are "living" or "non-living" isn't important. We like to shove things in boxes, which sometimes lets us loose sight of the big picture.

    People do it when trying to ponder the origins of life as well. Evolution doesn't have a requirement that something be "alive" to evolve--Viruses get by just fine in their niche and evolving without meeting what we deem necessary for something to be alive.
     
  15. Moonbear

    Moonbear 12,265
    Staff Emeritus
    Science Advisor
    Gold Member

    Viruses fit perfectly in the gray area. I also agree that defining them into living or non-living really has no impact on studying them and what they do. That discussion is mainly useful in the high school biology setting to introduce students to the idea that not everything can be easily categorized and that biological molecules to organisms exist on a continuum.
     
  16. Pythagorean

    Pythagorean 4,582
    Gold Member

    I see it the other way around. Theoretically, if life is ever formally defined a (i.e. a quantitative set of measurements on a system) it would be interesting to see where viruses fall on the test.
     
  17. I'd class viruses as 'living' because they are obligate parasites. Also, IIRC, viruses do range from stripped-down, minimal monsters to much larger whatsits...
     
  18. bobze

    bobze 650
    Science Advisor
    Gold Member

    That's the point though Pythagorean--Life isn't amenable to "definitions", it occurs across a spectrum. Its not binary, its shades of gray.

    Probably the most simple and inclusive definition for life we could come up with is something capable of biological evolution.
     
  19. Ryan_m_b

    Staff: Mentor

    Hmm however by this definition products of genetic algorithms would be classed as alive.
     
  20. Moonbear

    Moonbear 12,265
    Staff Emeritus
    Science Advisor
    Gold Member

    It's sort of like when I assign final grades in a course, and someone emails me that they are only some smidgen of a percentage point from the cut-off for the next letter grade and pleads for a grade bump. The answer is that wherever the cut-off is set, there will be someone with a grade close to that cut-off, especially in a large course. The same holds for how we define life. In a way, the definitions try to take into account things we have a gut feeling are "alive" but no matter how we define it, something will just miss the cut off and be the topic of this same debate.

    The only potential value in defining a cut off for what is alive would be to foist some topics over onto the chemists that the biologists don't want to deal with. Biology is the study of life, so if it's not alive, and it involves chemical reactions of some sort, maybe we can make it the problem of the chemists instead. Of course, in reality, that's why fields like biochemistry exist, and why chemists work on biological problems and biologists work on chemical problems, because again, there's a range of topics that bridge the two subjects and are not easily defined as one or the other, nor do I think they should be.
     
  21. Pythagorean

    Pythagorean 4,582
    Gold Member

    Yes! I'm glad you agree with my point! This is not something special about life (or else we would have a clear cut distinction, right? :)

    This is the same problem with, say, conductors vs. insulators. There is no perfect conductor or insulator. Everything exists in between (i.e. they are two ideals we have invented for studying them). But we can still identify regions where we say "oh that's definitely not a conductor" (even though electrons do actually move across the substance).

    So life will have the same kind of spectrum... but the point is we still have yet to quantify it mathematically; and once we do, we would expect a rock to be at one end, animals to be at the other, and viruses to be somewhere in between.

    But the point I was discussing, was whether the measure would be useful or not:

    ...and I am contending that it would be useful to have a quantitative test for living things. Quantitative classification is always useful to prediction, even if we accept that near the boundaries between regions (living/non-living or conductor/insulator) there are some problems with a rigid definition.

    Even in Moonbear's example above, she outlines how the distinctions are useful, even though the boundaries are fuzzy. That's the nature of EVERYTHING we study! Not just life!
     
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