Are Viruses Alive?

Sep 29, 2015

Julie McMahon

By Grennan Milliken

Influenza, SARS, Ebola, HIV, the common cold. All of us are quite familiar with these names. They are viruses—a little bit of genetic material (DNA or RNA) encapsulated in a protein coat. But what we don’t really understand, and what scientists have struggled with since the study of virology began, is whether viruses are actually living or not. A paper published today in Science Advancesjust might change that. By creating a reliable method of studying viruses’ long evolutionary history—hitherto nearly impossible—researchers have found new evidence that strongly suggests viruses are indeed living entities.

Scientists have long argued that viruses are nonliving, that they are bits of DNA and RNA shed from other cells. Indeed, based on everything else we know about what it takes to qualify as life, a virus doesn’t seem to fit the bill. There are many life processes, such as the ability to metabolize, that viruses do not do. Viruses seem to carry out only one life process, reproduction, but even then, individual viruses don’t carry translational machinery, namely, the proteins needed to read their DNA and RNA and build new viruses. They invade a cell and hijack its genetic tools to do it for them.

But within the last decade, developments in virology have started to reveal more and more that viruses might in fact be alive. One was the discovery of mimiviruses, giant viruses with large genomic libraries that are even bigger than some bacteria. To put this in perspective, some viruses, like the Ebola virus, have as few as seven genes. Some of these giants have genes for the proteins that are required for translation—those readers of DNA and RNA that in turn build new viruses. This throws the lack of translational machinery argument for classifying them as nonliving on its head.

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13 comments on “Are Viruses Alive?

  • Well yes…. and err, no. There is no black and white answer. The examples provided above are smeared across a spectrum of abilities that could be defined as life. Some at one end of the spectrum could be considered life. Some at the other end of the spectrum are not life. The answer to the question is not Either / Or. Each virus would need to be considered on the evidence.

    For example, if you could build a virus in a lab from spare parts, then is that alive. This was done in 2002 when scientist reconstructed the polio virus with off the shelf spare parts.

    Scientists have built the virus that causes polio from scratch in the lab, using nothing more than genetic sequence information from public databases and readily available technology.

    I suspect the definition of what is alive should include an ability to reproduce independently. Most viruses can’t do this. Those that can’t, are not alive.

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  • 3
    Darvick says:

    Life is an interesting concept. When we try to definition it in black-and-white terms we end up with loose ends. To me that suggests that perhaps the concept itself is flawed. Maybe we need to look at things in a different way. It reminds me of the Dwarf-planet debate. There is no really good way to define a planet. They tried, but I think they failed when they settled for complex definitions stuck on the concept of planet. In that argument, the concept: Planet was a flawed concept. In both cases, we have past president for using these terms and that’s all that really holds them up… Time to look at things in new ways. Instead of Life, perhaps we define a scale of chemical complexity? Perhaps we define Planets in the same way – on a scale of gravity and chemical composition?

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  • Yes, the living vs nonliving question is a continuum, not binary. Nature really doesn’t make a sharp boundary between life and nonlife; it’s just us who like to think there is one. Just like there was no obvious first human born of nonhuman parents, there can be no firm dividing line between life and non-life when the whole story of evolution is one of gradual change. We could choose an arbitrary dividing line, but I can’t believe it would be all that helpful. Yes, a virus that has DNA or RNA that codes for some of its own proteins is cool, and that is probably a useful checkoff item for aliveness, but whether that crosses some nonlife/life threshold is probably not a useful question.

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  • Darvick
    Oct 1, 2015 at 6:31 pm

    Perhaps we define Planets in the same way – on a scale of gravity and chemical composition?

    I think you would have problems with chemistry and gravity because of differences caused by variations of size to mass.

    The definition of a planet as being massive enough to collapse into a spheroid shape, distinguishes it from the irregular shapes of asteroids and comets.
    Defining it as orbiting a star distinguishes from moons (whose structure can be influenced by the parent planets), which may be a similar size and mass.

    As you say:- Like life – there is a continuum of structures, with a system of classification imposed upon it.

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  • Nor women over 50.

    I think a definition based on a localised entropy drop surrounded by a ring of raised entropy relative to the regional entropy would do it.

    Er…no….that’s still tough.

    A virus is a component in a living system. Simulations of RNA World show the automatic generation of little helper entities that make RNA World living entities more accurate copiers. (RNA World copying is pants with barely viable replicators). Viruses seem very like these entities.

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  • David R Allen
    Oct 2, 2015 at 7:34 am

    What do you think would define life. I can see that your above examples means mine needs a bit of work. Would you modify mine, or do you have some other suggestion.

    While the ability to reproduce is part of the definition of “life” for the purpose of categorisation, there are numerous side branches where this ability is disabled.

    There is the example of sterile hybrids – mules, some hybrid plants, soldier and worker phenotypes in social insects, where the reproduction is specialised in a queen.

    If we think in terms of the gene-pool, rather than the individual, the concept of dead-end side branches providing “kin-support” to the community, or simply as individual dead-ends, is easily accommodated.

    Viruses are simply a life form, which hi-jacks parts of other species’ cells, to facilitate their own reproduction.

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  • I wonder if an Extended Phenotype type argument could be made for an extended human family? Particularly one that mixed reproducers with pure helpers, like longer lived women/grandmothers, and a third son who is gay….

    I’m happy not to call viruses life forms. I think something in between would be a great way to break down resistance to abiogenesis. At the creation of life definitions are fuzzy.

    I do though think thermodynamics is the key to a more revealing definition.

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  • 11
    Pinball1970 says:

    I am happy with Viruses being classed as alive.

    If we found replicators on Mars no matter how basic we would say we had found life would we not?

    I think difference between finding just chemical building blocks, water, volcanic activity on Mars say and finding those with active replicators would be huge.

    I think defining intelligent life is more difficult and as for conscious beings…

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  • I think thermodynamic behaviours are the most basic definers of life. The problem in a system of separate parts is defining what are elements of the system and what constitutes the environment they are in (the other parts?).

    My brain hurt, so I am going to see what others think elswhere.

    Reproduction is of course essential as a potentiality (once or through others as Alan explains.) Though a live once undying entity could be us one day. The ultimate weed.

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  • Dawkins had an excellent short article in the book This Idea Must Die! A collection of Edge essays by people who take on a specific idea and say why they think its time has passed. His idea that must die was essentialism by which he means the Platonic idea that words pick out ideals and that questions like “is gay marriage really marriage?” or “is a fetus a person?” have actual scientific answers. They don’t. Word definitions are fluid and are nothing more than social conventions. As Chomsky says these questions are the equivalent of asking “do submarines swim?”. In English they don’t in Japanese they do but in neither case is anything substantive at stake.

    This case may be a bit different in that there can be legitimate issues at stake for how we choose to define a scientific concept. So in that sense perhaps its an interesting question but otherwise not really.

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