A time-honored method used by teachers to provoke discussion among young biology students at all levels is the question, “Are viruses alive?” If you have been fortunate enough to have any kind of comprehensive science education in your life, you’ve probably heard this question at least once, and if you’re the kind of weirdo that takes a biology course in college, or graduates with a degree in biology – or weirder yet, if you then go on and enter a post-graduate program in biology – then you’ve probably heard it more times than you may really want to think about. And there’s a good reason for that, because viruses are weird – they are big chunks of the basic genetic building blocks of life, DNA or RNA, often encapsulated in a protective protein jacket, occasionally not, and written in those chunks of DNA or RNA are functional genes. But that’s all they are – making those genes actually do anything requires them to piggyback on a functional cell, which almost always doesn’t go well for that cell. So viruses occupy a strange middle ground, having the same genetic material as cellular life as we know it, but unable to do anything with it by themselves.
As in all things, familiarity breeds contempt and we get sick of hearing this one after awhile, especially once we have all drawn our lines in the sand and taken a firm stance that viruses are not alive, or that they are. Discussions on down the line often just rehash these old arguments without further intellectual engagement with the question, which is too bad because it’s actually a very good question – not just on its own merits, but for deeper reasons as well.
To explain, the argument against viruses being alive typically hinges on their lack of cellular metabolism or structure – they cannot harvest energy from the environment, they cannot reproduce by themselves and they assemble spontaneously from component molecules within a host cell rather than dividing. This is a pretty convincing argument if you think that cellular processes are the defining features of life. That’s where I dug in my heels somewhere around the end of high school or early in college, and that’s where I stuck. But this argument deserves some reconsideration, because it is founded upon the idea that there is some fundamental, qualitative distinction between the biochemistry of a cell and the biochemistry of a virus that makes cells something different and special that we can call life.
We have spent the majority of human history convinced of our own specialness, and we’ve turned out to be wrong every time our specialness is put to the test. That’s not really our fault, because of the way our brains work, but it does mean that we’ve accumulated a long history of embarrassing errors about our place in nature. In the time of Shakespeare, we were the “paragon of animals;” unique, distinct from the dumb and mundane menagerie of the rest of the animal kingdom. But as we developed scientific systems for classifying organisms and identifying their relationships, we began a slow descent into banality. First we were primates – but special primates, distinct from the rest. And then it became clear that, really, we looked a lot like apes. That caused a fuss, but eventually it was accepted that we were apes, but still special, unique apes. Eventually, we had to accept that we were in fact another great ape, but chimpanzees, gorillas and orangutans were obviously a lot more similar to each other than to us, so we could live with that – until it became clear that, no, in fact we are much more closely related to chimpanzees than anything else. And worst of all, that means that chimanzees are more closely related to us than they are to anything else! The study of biology and taxonomy has destroyed our specialness.
Cosmology and astrophysics haven’t helped either, first destroying the geocentric solar system, then the heliocentric universe, and then making the universe so outrageously enormous that the presence of humans on this one little planet turns out to be far, far less than a rounding error.
The point is that science destroys specialness and obliterates the ego. For a lot of us, that’s part of what makes science so wonderful – the universe is an unbelievably vast place, where we are unbelievably unimportant, and that means that we’re unlikely to run out of things to do or learn. But it’s also very threatening. Biology and astrophysics say, “So, you think you’re pretty special, huh? What’s so special about you anyway?” And the answer turns out to be, well, pretty much nothing.
“Are viruses alive?” gets at the same question, but at a larger scale than mere human existence – it demands that we contemplate the specialness of being made of cells, and of life itself. What is special about cells? There are 15 times as many viruses in the oceans as there are prokaryotic cells – that seems to be enough metabolism to go around for all of the biotic particles in the world. Is there something fundamentally different about the biochemistry of a cell and the biochemistry of a virus?
It turns out that I don’t have as good an answer to this question as I thought I did. Humans, after all, are just another animal. Animals are nothing special, either – just a tiny proportion of the living organisms out there. And life itself is, after all, just chemistry.
Obviously, there comes a point where it gets impossible to function without drawing the line somewhere. Humans are obviously not the same as chimpanzees. Viruses are obviously not the same as cells. But reality doesn’t exist in discrete little boxes. It’s fine to have a line between categories, but at least we should know that we put that line down, and why we did so. I don’t think that’s where most students take this question, nor that educators intend them to do so. That’s what it makes it a perfect question to keep coming back to. The best questions, to me, are the ones with real depth. All of us, students, teachers, lay people, scientists, gain something from contemplating them.