There is always something in science where an idea is mindlessly debated over, where one side continually seems to be engaged in obfuscation on behalf of advancing their cause, or in less polite terms, of muddying the waters. This seems especially true for whether or not viruses are alive. For those that do not know or fail to remember, viruses are particles containing DNA or RNA surrounded by a protein coat. They are often associated with disease, but in fact, most viruses do not cause disease. Now, an old article on the question (found here), written by Luis P. Villarreal and published in Scientific American, was recently brought to my attention. While Villarreal does explain why viruses were originally thought to not be alive, or in his words, underwent a “demotion”, he chooses to air his own position with the exit clause, that a “precise scientific definition of life is an elusive thing”. Let us examine exactly what Villarreal has an issue with (italics mine):
Their [viruses] demotion to inert chemicals came after 1935, when Wendell M. Stanley and his colleagues, at what is now the Rockefeller University in New York City, crystallized a virus— tobacco mosaic virus—for the first time. They saw that it consisted of a package of complex biochemicals. But it lacked essential systems necessary for metabolic functions, the biochemical activity of life.
I think the key word here is “metabolic”. What certainly is the most distinguishing feature between a virus and other organisms is the apparent lack of an ability to do any kind of work for itself outside of infecting a host and using its machinery to replicate. Even other parasites condescend to do some of their own biochemical reactions (perhaps we can entertain bestowing appreciation on these critters for being many times less lazy). As for the phrase “inert chemicals”, Villarreal borders on the fallacious. As a point of fact, such little gems are a running theme in the article. We can bear witness to non-sequiturs such as this (italics mine):
Molecular biologists went on to crystallize most of the essential components of cells and are today accustomed to thinking about cellular constituents—for example, ribosomes, mitochondria, membranes, DNA and proteins—as either chemical machinery or the stuff that the machinery uses or produces. This exposure to multiple complex chemical structures that carry out the processes of life is probably a reason that most molecular biologists do not spend a lot of time puzzling over whether viruses are alive. For them, that exercise might seem equivalent to pondering whether those individual subcellular constituents are alive on their own. This myopic view allows them to see only how viruses co-opt cells or cause disease.
I am sure that any student of logic can tell you that an opinion of a truth claim is not at all the same thing as making a truth claim. What molecular biologists think of viruses is immaterial to whether or not viruses are alive. Their opinions may of course bias them, but when Villarreal utilises a false dichotomy in his non-sequitur, the subtitles with words is not likely to be at play.
The error prima facie fatalis, first fatal error, made by Villarreal is the lack of a distinction between what is alive and what can replicate (italics not mine):
Debates over whether to label viruses as living lead naturally to another question: Is pondering the status of viruses as living or nonliving more than a philosophical exercise, the basis of a lively and heated rhetorical debate but with little real consequence? I think the issue is important, because how scientists regard this question influences their thinking about the mechanisms of evolution.
Well, no there are two distinct truth claims made. The first concerns if viruses are alive while the second concerns if viruses are important in evolution. They have no bearing of each other: a virus could not be alive and still be important in evolution, an idea which Villarreal spends no time pondering, relying instead on a host of logical fallacies (is the truth of something really determined by what scientists think?). If we entertain his idea that a virus is alive because it can replicate and hence be applicable to evolution, then the bar is set rather low for entry into the ‘living’ club. DNA or RNA can be replicated in a test tube via the polymerase chain reaction (PCR), yet you would be hard-pressed to label them as “living”. But such a reductio ad absurdum entirely escapes his attention.
Let us demystify this area by exploring the possibility that a virus is not alive because it cannot metabolise. Metabolism is the key distinction and sets the bar much higher, as after all, it necessarily leads to respiration and excretion, other processes which define life. Chuck viral DNA into a test tube with a few proteins and chemicals, and you will get more viral particles, something that is considered impossible even with a single celled bacterium.
There is no doubt that viruses are important in evolution. It certainly does not follow that they should be considered alive. His error seconda facie fatalis, second fatal error, is his inconsistency and disposition to create straw men. Do viruses have a “potential for life” much like a seed, or are they “on the verge of life”, failing to “reach a critical complexity”? Indeed, the entire premise of the article rests on the assumption that considering a virus to not be alive is bad for science, in particular evolutionary biology.
Brothers and sisters of the evolutionary world, join together and prove him wrong by welcoming, with open arms and a generous dose of flowers, viruses into your consideration whilst acknowledging that the reception of this news would be rather cold and lacking in life. Villarreal seems to take such a position as his concluding statement: “Regardless of whether or not we consider viruses to be alive, it is time to acknowledge and study them in their natural context—within the web of life.” I really don’t know why he wasted so many words.