Are Viruses Alive?
Scientists have a compulsive urge to do a few things: meet, argue, categorize things, and drink insane amounts of coffee. I recently found myself ensnared in a very typical argument with my partner: are viruses dead or alive? This is not an unusual event in our relationship — we tend to have epic battles concerning the Middle East, medicine, music, microbes, the cosmos, what animals are the cutest — essentially anything that can be debated ad nauseam for extended periods of time (whilst drinking coffee, of course). Alexis is a first year medical student, and therefore suffering from a disorder that I diagnosed: Medical Student Syndrome. This condition is characterized by the need to discuss all the medical things, all the science things, and all the mysteries of the universe, at all times. And as a scientist, I love to argue, so the relationship is beautifully symbiotic.
The question of whether or not viruses are alive has been hotly debated in the scientific community for many years, so in full disclosure, there is nothing particularly unique about the topic. However, I think it deserves some thought, especially after a long year of Ebola and Measles outbreaks, not to mention the annual influenza events that plague us.
Viruses are an evolutionary enigma, the origins of which are uncertain despite being extensively studied. Researchers have found that nearly every life form has a virus capable of invading it, and viruses appear to be the most ubiquitous biological entity on the planet, outnumbering every other life form combined. And to further complicate matters, viruses have an exhaustive taxonomy, which makes this topic difficult to succinctly discuss.
In the argument of alive vs. dead, it’s important to know what classifies a biological entity as “alive.” For example, a chunk of granite is not living. While it is made up of various elements, it cannot create it’s own energy or reproduce. A cell, however, is capable of reproducing, creating its own energy source, and eventually dying. In 2002, Science magazine published an essay outlining the seven pillars of life, concluding that in order to be categorized as living, the organism must have the following: Program, Improvisation, Compartmentalization, Energy, Regeneration, Adaptability and Seclusion. Simply, these pillars stand for the ability to reproduce and pass genes from one generation to the next, as well as the ability to change in response to environmental demands. Living entities must be compartmentalized in a way that makes chemical reactions possible in order to create energy to sustain vital functions; in addition, they must possess the ability to keep one biological process from causing harm to another biological process (ie, you don’t want to digest vital components of your being). Furthermore, “living” entities must have the ability to regenerate systems after wear and tear (ie, replacement of muscles cells in the heart).
My argument is that viruses are not in fact alive. In brief, viruses are extremely tiny biological agents that require life forms to reproduce and evolve. They infect animals, plants, bacteria, and microorganisms — all of which are known as hosts. They infect by taking up residence in the cells of a host organism where the virus essentially uses the host’s mechanics against the host. In some ways, viruses are almost parasitic hijackers, somewhat alien space invaders. Without a living host cell to replicate in, the virus is nothing but a bit of encapsulated genetic material. This is because viruses are acellular, meaning they do not have cells of their own. It is true that viruses are capable of evolving, but at someone else’s expense. They do not reproduce with one another or by themselves (without the help of a living cell) in order to pass their genes on to another generation.
Alexis’ views are actually not so different from mine, mostly because she admits that she believes that viruses are not necessarily alive in the traditional sense, but they are more living than dead. This is because viruses are equipped with DNA or RNA and are capable of evolving according to natural selection, which is included in the seven pillars of life. A good example of this is the incredible way HIV evolves inside its host to render a single anti-retroviral medication ineffective. It is for this reason that a large cocktail of anti-retroviral drugs is necessary to treat the disease. However, she also views the natural world through a philosophical lens. All organisms have certain requirements for function — on earth, we as humans require oxygen, water and food to thrive, and plants require carbon dioxide, water and sunlight. So she asks, why can’t it just be that viruses require prefabricated cells in order to reproduce in the same way humans need their environment to thrive? And while viruses are metabolically inactive at times, the same is true for seeds, spores and certain types of bacteria. Thus, she argues, viruses just require a different form of environment and enrichment than other living things.
I suppose that I have to concede to a couple of points. First, I agree that viruses are not dead. But I cannot refer to them as living either. While it’s hard to imagine that there could be life on other planets due to the harsh environments and toxic mix of chemicals that exist, there could be organisms that thrive in those settings. Maybe viruses are just ancient aliens living off the inhabitants of Earth. Pondering this makes me think of deep sea organisms that live without sunlight in extremely cold temperatures and survive for millions of years in spite (or because of) these unrelenting conditions. But then I remember, even the creatures living in the deep sea have cells with cell walls and the ability to reproduce on their own in spite of their different requirements for life. The fact remains, viruses don’t even have a chance to be biologically relevant without the cells of another organism, and to me, that doesn’t constitute life.
Let’s first define life. According to the online Merriam-Webster Dictionary, life is “an organismic state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction.”
Viruses are not living things. Viruses are complicated assemblies of molecules, including proteins, nucleic acids, lipids, and carbohydrates, but on their own they can do nothing until they enter a living cell. Without cells, viruses would not be able to multiply. Therefore, viruses are not living things.
When a virus encounters a cell, a series of chemical reactions occur that lead to the production of new viruses. These steps are completely passive, that is, they are predefined by the nature of the molecules that comprise the virus particle. Viruses don’t actually ‘do’ anything. Often scientists and non-scientists alike ascribe actions to viruses such as employing, displaying, destroying, evading, exploiting, and so on. These terms are incorrect because viruses are passive, completely at the mercy of their environment.
Update: See a more recent post for my thoughts on this question.