What is Life? A comment on Viruses

There have been many definitions of “life”. I think the simplest definition of life is this one: Life is a system that acquires the substances and energy needed to continue to exist and to reproduce. If it fails to do this, it ceases to exist. Any such system is an organism.

By that definition, a virus is alive. It’s the simplest form of life: a packet of genetic information that drifts about until it latches onto a cell that it can invade. It then uses the cell to acquire the substance and energy it needs in order to reproduce.

Since a virus needs another organism to survive and reproduce, it is a parasite. Most parasites either do not harm their hosts or provide some benefit. A few (mostly microbes) are necessary for their host’s well-being and even continued existence. A few parasites harm their hosts, and some kill their hosts. A parasite species will survive only as long as its hosts do not die out.

It’s likely that many viruses, like many microbes, are not merely beneficial but necessary for their hosts’ well being. We know enough about bacteria, for example, to know that without them we would have trouble digesting much of our food. We don’t know that much about viruses. But we do know that some of them kill bacteria that are dangerous to us. We also know that viruses can transport bits of DNA between species, and that this sometimes results in beneficial changes to an organism’s genome.

What all this amounts to is that we are woefully ignorant of viruses’ roles in the web of life. The handful that bother us create the impression that we would be better off without them. That is certainly a false impression. We just don’t know enough. Yet.

Footnote: Very early on, some computer programmers wrote small programs with a rather strange property: they would use the computer's operating system to write copies of themselves into every available memory space. Rewriting these programs so that they would send copies of themselves to other computers was the next step. Thus the computer virus. Are they alive? Most of them are not. To be alive, the program would have to also prevent the computer from shutting down, thus maintaining the energy it needs for continued existence.