Science by Richard Bleil
A couple of times I’ve mentioned that there is a debate over whether or not viruses are actually living entities in my blogs. I thought it might be interesting to explain this in a little more detail. So, the question at hand is, “are viruses actually alive?” We won’t really resolve this today; biologists are clearly better experts on this topic than I, but hopefully it’ll be an interesting for my readers and spark a few synapses.
So, what is it that defines “alive”? Yes, I know, you can find a definition for life, but that’s not an interesting approach to an intellectual exercise. First, understand that unlike bacteria, which is a cellular life form, a virus is a molecular life form. Most consist of RNA segments and a few proteins, all molecules, although the simplest are nothing but the RNA segment without proteins. This is why viruses are so difficult to kill, since you can’t really kill a molecule. The idea is that the RNA is a “reverse transcriptase” RNA, meaning that once it’s inside a cell, it modifies the DNA of the cell causing it to create more viruses. But are viruses alive? Can a molecule, or small cluster of molecules actually be alive?
When I think of living organisms, I think of food. Every living organism on the earth requires water, and most either need to eat some source of food (like amoebas that take its prey by wrapping its body around it to internalize them and then digest them) or by creating its own fuel from an energy source (like plants and single-cell organisms that create sugar from sunlight). Viruses do not create their own food, consume prey, and every living organism on earth aside from viruses require water to live. This would support that viruses are not really alive, so, not alive 1 alive 0.
Living organisms reproduce and evolve. I had a student argue to me that this does not apply to viruses because they require a host body, but so do any parasitic organism. Tapeworms are clearly alive, but they require a living host. As I said above, viruses do reproduce by changing host cell DNA so that the cell will replicate the virus. What’s more, these viruses do evolve. Periodically, infected cells will interject changes into the virus which are then passed along. For example, our current pandemic is caused by the Covid-19 virus. Despite the claims of conspiracy theorists, the source of this virus is the evolution of a previously known SARS virus, specifically the SARS-CoV-2 virus. This evolution is why flu vaccines have such trouble keeping up. As the flu virus is transmitted from one host to another, changes in the virus means the vaccine might be useful against one strain, but not others. Ironically, our immune system works much the same way as viruses. The body will flood white blood cells with many antigens until one works. Once and antigen is found to work, the body begins producing that particular antigen favorably over the others. So, I would say that living and evolving supports viruses as a life form. So, not alive 1, alive 1. All tied up.
It’s been suggested that living organisms exhibit order. Cells, for example, have cell membranes to contain a small region of space and organelles for specific functions. Most viruses exhibit order. The protein sheath often has multiple components, a portion that will seek out and bind to specific cell types, a component to inject the DNA into the cell and of course the RNA that is injected. Some of these cells look remarkably like an alien lander, while the Covid-19 virus resembles a prickly sphere. So based on order, I would say this is alive. That brings the score to not alive 1, alive 2.
Living organisms apparently respond to external stimuli. We see this in plants that grow preferentially for their leaves to face the major source of life. Viruses don’t move towards or away from things like light or food sources. They can be destroyed if the conditions are not correct. For example, alcohol will destroy viruses, causing them to “denature”. However, the viruses don’t move to avoid alcohol, so I would say this looks like it is not alive. We’re tied up again, at not alive 2, alive 2.
Apparently, homeostasis, according to my source, is another requirement of life. This means that the organism can maintain conditions of life within a narrow range to deal with conditions they otherwise could not survive in. For example, regardless of the external temperature, we keep our bodies at a constant temperature to survive. I’m not sure I agree with the requirement of homeostasis; frogs and fish have been known to be able to survive complete freezing, their bodies shutting down and reinvigorating themselves on warming. Of course, viruses have no regulatory mechanism to maintain the necessary conditions to support life. So, if you count homeostasis as a necessary condition of life, then, no, viruses are not alive. So not alive 3, alive 2.
Energy processing, according to my source, is required for a living thing. To me, this means following the laws of thermodynamics. Yes, viruses’ bond to cells using potential energy, which is processing. What’s more, by creating chaos in the host body, as well as in its environment as pandemics spread (as we are seeing today), even the second law of thermodynamics is followed. I would say this supports the concept that they are alive. So not alive 3, alive 3 and again we’re tied.
Finally, my source claims regulation is a necessary condition of living. For example, our bodies regulate respiration rate, blood pressure and other systems to function properly. Even bacteria must maintain proper osmotic pressure and nutrients to survive. No regulation is possible in viruses, so I would say the score is not alive 4, alive 3.
So, are they alive or not? Our score seems to favor not alive just slightly over alive. If you consider that all of these conditions are required, then viruses are clearly not alive since even one violation would mean the list has failed. But they do evolve, use energy and reproduce. It’s not really my place to say, but hopefully it is sparking some thoughts in your mind. Mostly, I hope that now you understand why the question of whether or not viruses are actually alive is an active debate.