Are viruses alive?

Robot One of my sons asked me this question a few days ago. I said no, but I’m happy that others agree with me:

Ten reasons to exclude viruses from the tree of life. 2009 Nature Reviews Microbiology 7: 306-311
When viruses were discovered, they were accepted as missing links between the inert world and living organisms. However, this idea was soon abandoned as information about their molecular parasitic nature accumulated. Recently, the notion that viruses are living organisms that have had a role in the evolution of some essential features of cells has experienced a renaissance owing to the discovery of unusually large and complex viruses that possess typical cellular genes. Here, we contend that there is strong evidence against the notion that viruses are alive and represent ancient lineages of the tree of life.

Viruses do not reproduce by division, but are replicated by the self-assembly of preformed components. This, not size, differentiates them from cellular living organisms such as bacteria. A virus-infected cell is more like a car factory than a womb.
Also, unlike living organisms, no virus has the means of generating its own energy – they are all energy pirates.

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10 Responses to Are viruses alive?

  1. jobadge says:

    hurray. I keep getting asked this by my OU students, especially as viruses are included in their list of ‘living things’ at the beginning of their text book on biology!

  2. elementaryteacher says:

    I would like to simplify this discussion. I teach Grade 3, and we don’t discuss viruses. But as someone very interested in science, I would like to bring it down to the level of a young child. Just by chance, I once saw a Sesame Street episode which was teaching kids how to tell what is alive, and what’s not. They brought it down to three questions.

    1) Does it eat?
    2) Does it breathe?
    3) Does it grow? (or perhaps in this case, reproduce?)

    I presume it does eat. I presume it must have some form of respiration. Does it need oxygen? Does it not need oxygen? Do viruses grow once they are created? Or, as you say, if they are assembled like machines, perhaps they do not grow?

    If a virus is not alive, what does that make it? A replicating mineral? By necessity, aren’t things either animal, plant, protist, or mineral? If a virus is not a mineral, what category would it properly be called? Or would they be a category completely to themselves?

    Eileen

  3. David Raikow says:

    I consider viruses to be intermediate, not transitional, between organisms and non-living structures. Hence I do not consider them to be alive. They are replicated, but do not self-replicate. Their construction consumes resources, but they do not consume resources. They can persist for extended lengths of time, theoretically forever, but require no expenditure of energy to maintain their structure.

    Though their replication is totally depended on cells, viruses remain a facinating example of evolution. They can persist because they are a structure that favors their own replication in an envrionment replete with the mechanism to do so.

    I don’t doubt that viruses first appeared shortly after genetic material appeared, and had thus the potential to affect the evolution of life. But they’re likely to only be an accident of the mechanism of genentic replication. I find it hard to beleive that they could be directly part of root origin of life. They would have had to lose self-replicating components without retaining vestiges, and there are none.

    That is, unless there was another non-living chemical mechanism of assembling organic structures, from which some viruses evolved an independedt means of self-replication. Then the virsues of today would be descendants of the original “chemical” to “biological” transitional forms. But that’s just a wild speculation.

  4. I also believe that viruses are not living. But then what is a spore? Or a plant seed? And what about sperm and eggs – are they living or not? These are some of the many obstacles to my belief that viruses are not living. Remember what André Lwoff said: “a virus is a virus”.

    One more thing….why do we use the term ‘live virus vaccine’? I kept saying that while teaching a class yesterday at NYU, and the students laughed, because earlier, I harped on my belief that viruses are not living.

    profvrr

  5. Richard Badge says:

    IMHO viruses and people are just complicated ways of making more replicators: given their environment, neither is necessarily more “alive” than the other.

    Given the similarities between viruses people (nucleic acid genomes,encoding proteins)surely the debate about what’s alive shouldn’t be staged here… prions anybody?

  6. Eileen says:

    Thank you for your reply about this. I’m just having a little trouble with conceptually understanding one point. It sounds like if a virus is a parasite that it is taking nourishment from a host. How is this different than eating? I suppose one doesn’t necessarily need a mouth to eat. If it’s not “eating,” but merely “attacking” how would that make it any different from a chemical attack? I’m not understanding why it needs a host at all, if it is not alive.

    Please help? (sorry to be having such trouble with this concept!)

    Eileen

  7. ajcann says:

    Viruses don’t eat or breathe, but they are parasitic on organisms who do. Viruses don’t grow either, any more than a television set or a pencil grows.
    If a virus is not alive, what does that make it? It makes it a virus!

  8. ajcann says:

    Yes, it’s a misnomer, in which case, killed virus vaccine is too :-)
    Another good one is “growing virus stocks”.
    But neither of them bother me, although they are misleading. The one that really gets me is the adjectival usage of the noun “virus” ;-)

  9. Absolutely. Viral capsid, not virus capsid. My colleagues here insist on using virus….but Jane Flint prevailed during the writing of “Principles of Virology”. Can you believe, ASM did not want to use ‘viral’!!!

  10. ajcann says:

    Fair enough. I regard all this as semantic waffle and would prefer not to get dragged into it. However, the question of viruses and “life” is a perennial evergreen and appears on many biology curricula, so it has to be addressed.

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