Viruses are intricate collections of molecules that can infect all types of life forms, from plants and animals to microorganisms like bacteria. The origins of viruses in the evolutionary history of life are still a mystery to scientists. We don’t even know whether we can even consider them ‘alive.’ Because viruses cannot survive on their own and need living cells to multiply, many think of them as non-living entities. One thing is for sure though: they challenge our concept of what ‘alive’ even means.
Viruses are an inescapable part of life, especially in a global viral pandemic. Yet ask a roomful of scientists if viruses are alive and you’ll get a very mixed response.
The truth is, we don’t fully understand viruses, and we’re still trying to understand life. Some properties of living things are absent from viruses, such as cellular structure, metabolism (the chemical reactions that take place in cells) and homeostasis (keeping a stable internal environment).
This sets viruses apart from life as we currently define it. But there are also properties that viruses share with life. They evolve, for instance, and by infecting a host cell they multiply using the same cellular machinery.
Many viruses can cut the DNA of infected cells and intertwine their own genetic material so that they are copied along with the DNA of their host whenever the cell divides. This process is called lysogeny and it can be contrasted with the more destructive lytic strategy of viruses where they multiply in great numbers within a cell, only to burst the cell open and spread out to infect other cells.
There is an undeniable genetic and physiological connection between viruses and the organisms they infect. The discovery of giant viruses further blurs the distinction. These viruses can have as many genes as bacteria, some of which code for functions previously thought to be unique to cellular organisms.
Does this new information lead to confusion or clarity? Can we ever answer the elusive question of whether viruses are alive, instead of just a non-living part of the living world? If we approach this puzzle correctly, we may find that we are focusing on the wrong question. Is “life” a box-like category that we can place things in as we discover them, or is it something far more mysterious?