Viruses: Dead or Alive

An ongoing question in virology is whether viruses are to be considered living creatures.  Its easy to tell that a groundhog is alive but a book is not.  But what properties does a groundhog have that a book does not?  We can look up basic properties of living things in a biology textbook, and yet it remains difficult to define life in a simple sentence.

I would argue that a virus is not alive. Viruses are completely dependent on host cells to replicate.  That said, in absence of the host cell the virus clearly lacks most of the properties of a living thing.  (Does stealing those properties from a living thing count towards being alive?)  Life seems to emerge from a collection of parts where the whole is greater  than the sum of the parts.  This emergent property, life, is present in animals, plants, bacteria etc, but in a virus infected cell, that property remains a part of the cell, not the virus.

Alive or not, viruses are an integral part of biology.  They help us understand life and they certainly have an effect on living things.


28 thoughts on “Viruses: Dead or Alive”

  1. I agree that this is largely a philosophical discussion, but a very interesting one! Im enjoying reading everyone’s thoughts. A common theme appears to be that viruses exhibit many of the properties of life when actively infecting, but are more like chemicals without the host. So that begs the question: can something be considered alive sometimes but not always? A bacterial spore by itself does not display properties of life, but once activated, becomes a vegetative, metabolically active and growing bacterial cell. Are these essentially the same in terms of properties of life?

  2. I find the ventilators/dialysis argument for a virus’s being alive to be a fascinating one, and one that I had not truly considered myself. Nonetheless, humans who are kept alive by ventilators and/or dialysis are known to have the internal mechanisms necessary to perform these functions on their own, and while some may be born without these facilities in place and thus require artificial assistance for their whole lives, the better example of the rest of the human species seems to prevent the full diminishing of the humanity of these dependent individuals. Still, though, this argument serves as an example in the related argument of how human technology in life support may blur the line of what deserves to hold the title of ‘alive’ (the most well-known example of this debate being the one surrounding Terri Schaivo).
    Returning to the point, however, viruses cannot be alive because, in addition to their dependence on hosts for function, they themselves have no cells, which to me is a strong enough point in itself to refute their being considered ‘alive.’

  3. I thought the question itself was a philosophical one; like, “Is a fetus a human being?” A virus has the potential to life, but unlike a fetus, a virion can exist outside a host, without depending on the host prior to “invasion”. Now, just because a virus borrows most of the properties of life doesn’t man they are simply chemicals, because once entered the host, the virus can develop clever ways of avoiding detection by the host’s immune system, entirely colonize the host, and so on. All of the comments above point out the alive and dead aspects of viruses accurately, so my take on this is, maybe there is no absolute “live OR dead” line. Maybe there is a whole spectrum of aliveness. And perhaps viruses score 3 out of 10 there.

  4. Before doing the assigned reading of Chapters 1 and 19, I automatically disagreed with Mr. Esteban’s opinion that viruses are non-living things. I thought that since they have single or double RNA or DNA and are able to reproduce, it instantly categorized them as living since these are characteristics of all living organisms. However, I decided that because viruses depend solely on a host cell for survival and thus cannot function by themselves, they are not living. “Stealing” from a host cell should not make a virus living. If it can’t survive without being a dependent, it is not alive.

  5. Since a virus is fully dependent upon a host cell and has no “metabolic machinery” i would have to say that a virus is not alive. Although i am open to the argument that it can be considered alive because of its huge impact in the “living” world and it has an effective method of reproduction. If you think about it, like viruses, we are all dependent on something in order to be alive.

  6. In my opinion, viruses are living organisms. Even though many characteristics would suggest otherwise, the fact that they possess genetic material, have evolved over time and are able to reproduce is enough reason for me to believe that viruses are living things. The livelihood of a virus, like any other living parasite, largely depends on its host. I don’t believe that just because viruses are dependent on hosts to “live” is proof that they should not be classified as living organisms.

  7. In Chapter 1, a cell is defined as “life’s fundamental unit of structure and function” because it is the smallest unit able to carry out all of life’s processes: reproducing, processing energy, responding to its environment, and so on. With that definition in mind, it seems clear to me that while viruses do possess some qualities of living things and functioning cells, they lack metabolic processes, organelles, the ability to reproduce… the list continues. These are all things that would qualify something as a cell: the simplest form of life… things a virus does not have. The post above me does make a valid point… sometimes it is hard to draw the line between life and death. However, the above post also utilizes the example of human beings: complex organisms made up of many organ systems and thousands upon thousands of cells. Viruses are not nearly this complex; therefore, in my opinion, the method of determining whether they are dead or alive is also much less complex and cannot be put on par with a human being. Viruses don’t live up to the standards of even being a single fully functioning cell, and so they are not alive.

  8. I do not believe that viruses are alive. Although they are very parasitic in nature ( i.e. they rely on their hosts to stay alive), they are, as the book noted, just a packaged genome when without a host. They rely on a host to be able to do the one thing that is common among all living things, metabolize. Their inability to metabolize without a host makes them nonliving.

  9. I think that viruses are not alive. They are simply living off of the host they infect and can not function alone. And if they can’t function alone at all, viruses are not alive.At first, I likened them to parasites( which they are in a sense), but they differ from living parasites in that t hey can not hold their own metabolic processes or reproduce without a host.
    So, viruses, I think, are not alive.

  10. Although viruses are not capable of many of the most basic functions of all other organisms, I believe it is still reasonable to refer to them as a life form. This evaluation depends entirely on their use of the genetic code to propagate and evolve. Since life is based around this universal language of DNA, any unit which plays an otherwise unfulfilled role in genetic development could be considered living. It is not necessary for the living, changing DNA to possess its own reproductive machinery.

  11. I believe that viruses are a sort of pseudo-lifeform that (as Biology 8th edition by Campbell, Reese, etc) “lead a kind og borrowed life”. DEspite the fact that they evolve to some extent and have gentic material (RNA or DNA depending on the particular virus), like most parasites, viruses are entirely dependent on their hosts, without which they can neither carry out metabolic activities nor reproduce, abilities which are intrinsic to living organisms.

  12. The issue of whether viruses are alive seems to me a question of semantics more than anything else: the criteria we use to define “reproduction” are really at stake. Reproduction, agreeably one of the most important characteristics of a living thing, is analogous to replication, which is a virus’ attempt to proliferate or spread copies of itself. As we know, viruses depend on hosts to replicate– this dependence, as Rachel Trenchard said above, should not “prevent them from being considered alive…” Why must reproduction entail an independent process rather than a parasitic process in which a host must be involved? To answer the question of whether viruses are alive, we must first clarify our definition of the term “reproduction.”

  13. I do think viruses should be considered to be alive. Obviously they live in a very simplistic way, but it seems to me that they show too many defining characteristics of life to be dismissed as lifeless. As stated in Chapter 1, some of the main “properties and processes we associate with life” are order, evolutionary adaptation, response to the environment, and reproduction, all of which are present in viruses to different extent.
    I don’t think the fact that viruses have to rely on a host to reproduce and function really matters in the argument. The fact that viruses have a purpose – to reproduce and multiply – is what matters, not how they achieve that goal. There is nothing that is not alive in this world (to my knowledge) that actively tries to reproduce and thrive.

  14. I wanted to say something very similar to Rachel Trenchard above. I will add to what Rachel said, that we could even look at the entire human race, how we interact with each other and with resources in the globe, and we see that we are in a way similar to parasites of the earth. For viruses their earth might be limited to the insides of hosts, plants, humans, animals, etc.
    In addition, the incredibly creative behaviors (about which Professor Esteban talks about in his post “Storming the Castle,” are aimed at reproduction. Very often, we say the basis of human behavior is in reproduction. Also, their reproduction centers on the same material, DNA or RNA, that ours and other living things use. I would say these are some strong reasons they should be considered alive.

  15. I think that viruses are alive. One commonality among all living things is the necessity to interact with the environment. All life processes, whether directly or indirectly, are carried out with aide from an outer environment. As humans, we may seem like independent life forms, but absolutely none of our life processes would be possible without exchange with our surroundings, starting with the simple necessity of sunlight. From this perspective, viruses could be the smartest life form; reducing their existence to nothing but reproduction, which is the most important process of an organism.

  16. As many posts have noted, viruses are reliant on their hosts for many of life’s basic functions. I don’t believe this dependence should prevent them from being considered alive however. In a way viruses are no different from humans who use ventilators or dialysis to maintain their body’s regulation; these people are reliant on something else to perform one of the main properties of life yet we still consider them to be living beings. Using this logic I think that the fact that under some circumstance a virus can perform the most basic properties of life –to reproduce and adapt-is enough to consider it alive.

  17. Its interesting to note the particular language you used here: “these young ones in turn,grow,develop and reproduce.” The terms are certainly used for most organisms, but not usually for viruses. The language for viruses is much less “biological” and more “mechanical.” Viruse dont age, but the viral particles may become degraded over time outside of the host. They dont grow or develop, rather they are assembled and sometimes undergo biochemical steps of maturation. Rather than reproduction, we tend to talk about replication. To me the language hints at a non-living, almost mechanical thing.

  18. At first glance it may seem as though viruses are alive because they contain the universal genetic code, something that all living things have in common. In addition, they respond to stimuli and evolve. However, when looking at more of the properties of life, a virus cannot be be deemed alive because it cannot reproduce on its own and it cannot grow and develop fully without a host cell. This dependence on the host cell on two of the important properties of life cause me to believe that a virus is not alive despite the fact that it does have other properties of life.

  19. I do not believe that viruses are living, but they do, as many other have said, have some properties of living organisms, such as possessing their own genetic code. But they are unable to perform basic life functions, such as replication and the inability to resupply their energy stock (ATP) without acting as a parasite to a host. On their own, they are not “living” but when acting as a parasite, they are able to do many of life’s functions. But, living beings need to be able to do these functions on their own to be considered living, and since viruses cannot, I would not consider them living beings.

  20. I thought it was vital to know the characteristics of living things in order to answer the question.All living things reproduce,grow and develop,respond to stimuli,evolve and most importantly,made up of cells.

    Viruses have either DNA or RNA genetic material that they replicate. these young ones in turn,grow,develop and reproduce in order to commandeer their host’s body.Moreover,they carry out meetabolic processes that ensure their survival according to their changing environment.

    However, none of these proccess can occur independent of a host.The virus’ genetic material is in essence the host’s genetic material and most importantly,viruses are not cells.Therefore, in my opinion,viruses are dead.

  21. At the start of reading chapter 19, I was convinced that viruses were alive. They replicate to infect their host, and they contain a genetic code, which only living things are said to contain. However, it is hard to believe that viruses are alive, considering they depend on a host cell to carry out their functions of producing proteins etc. I believe that once viruses attach to a host cell, they act as though they are alive, replicating themselves and sometimes killing the host cell in an attempt to infect the host. Also, viruses evolve similarly to the theory “survival of the fittest”. However, I would have to say that viruses are “nature’s most complex associations of molecules” rather than living beings.

  22. As much as professor Daestebans argument revolving around “emergent properties” makes sense and to some degree demonstrates that viruses are not alive, I beg to differ and would argue that viruses are alive. I would do this very simply and I presume swiftly too, simply by adding on to one of the professors claims as follows:

    Although in the absence of a host cell, viruses lack MOST (perhaps not all) of the properties of a living thing, they do exhibit those basic properties of life (such as reproduction) within a host cell. Whether stolen or not, viruses, at one point, do exhibit the properties of life which I believe only living things are SAID to demonstrate!

    Nevertheless, the point that “emergent properties remain a part of the cell, not the virus”, leads me to think of viruses as chemicals… substances that are not alive but can induce changes in living things – particularly cells.

    so… I guess I should say that viruses may be alive but only upto some extent.

  23. After reading chapter 19, I would say that viruses are alive. My main reasoning for this is that they contain a genetic code. And although they do depend on another host cell to reproduce, a virus does have a unique genetic code. No matter how “lifeless” they may seem when not infecting another cell, viruses continue to evolve and do attempt to reproduce and expand their population in the only way they know how. To me, viruses are one of the simplest living beings in this respect.

  24. I would have to agree with you in saying that viruses are not living. They do show some characteristics of living organisms, but they are also missing too many other characteristics of being a living organism to be considered alive. In Chapter 1 of our reading, I took special attention to Figure 1.3 which showed some properties of life. Though they reproduce, they are entirely dependent on a host; they are also known to respond to their environments, but not in the ways that other living organisms do; they are capable of adapting on an evolutionary standpoint, but still they require another organism for this evolution to take place; etc. Viruses definitely walk the thin line in being considered a living organism, but as of right now, I think that they have yet to make the leap into being considered alive.

  25. I agree that a virus, itself, is not alive. It can only survive via host cells otherwise it cannot function or spread. Even though it has taken over the host cell, the virus depends on the host cell’s properties to spread whatever disease it carries. There is a line in the text reading “How did viruses originate…they depend on cells for their own propagation, it seems likely that viruses are not the descendants of precellular forms of life but evolved after the first cell appeared”. I agree with this statement, in that before taking over a host cell, viruses are “nothing”. They are unknown and not alive. But once in the host cell, they come to life and can cause harm, spreading diseases evolving into even more complex forms of viruses. The host cell carries the properties of life, not the virus itself. It would be nothing without the host cell.

  26. Viruses share many characteristics with living things. Viruses respond to stimuli, have genetic makeup, and even evolve. However, to be truly scientific, we must apply the rigid definition of life, and if one or more of the criterion of life is not met, viruses are not alive. Since viruses lack the ability to thrive and reproduce autonomously, they cannot be called alive.

  27. I also do not think we can consider viruses to be living. One line I think really captures the reason why is your statement that “Life seems to emerge from a collection of parts where the whole is greater than the sum of the parts.” If, hypothetically, scientists were to isolate one human organ, they would not consider it to be living because it lacks basic properties of living things. For example, the heart, an organ that is vital, cannot reproduce (among other things), and therefore is not alive. However, when the heart is placed in the context of the body with other non-living organs, life emerges. Similarly, a virus alone is not living, but when it interacts with a host cell, life can emerge.

  28. My opinion is that viruses are not alive. They do not react to stimuli, undergo internal regulation, or undergo other life processes without a host. Though they do reproduce, there are many other non-living things which do in a sense reproduce: waves and crystal, for instance. Viruses differ from living parasites in that unlike tape worms which can carry out metabolic processes while living outside a host, they owe all their life properties to their hosts. This separates them from parasites that rely on their hosts for nutrition or shelter.

    The closest to life that a virus can reach is the pro-phage state of a lycogenic virus, where the virus temporally exists in the form of an infected cell, which does undergo the processes of life.

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