Are Viruses Alive?

Julie McMahon

By Grennan Milliken

Influenza, SARS, Ebola, HIV, the common cold. All of us are quite familiar with these names. They are viruses—a little bit of genetic material (DNA or RNA) encapsulated in a protein coat. But what we don’t really understand, and what scientists have struggled with since the study of virology began, is whether viruses are actually living or not. A paper published today in Science Advancesjust might change that. By creating a reliable method of studying viruses’ long evolutionary history—hitherto nearly impossible—researchers have found new evidence that strongly suggests viruses are indeed living entities.

Scientists have long argued that viruses are nonliving, that they are bits of DNA and RNA shed from other cells. Indeed, based on everything else we know about what it takes to qualify as life, a virus doesn’t seem to fit the bill. There are many life processes, such as the ability to metabolize, that viruses do not do. Viruses seem to carry out only one life process, reproduction, but even then, individual viruses don’t carry translational machinery, namely, the proteins needed to read their DNA and RNA and build new viruses. They invade a cell and hijack its genetic tools to do it for them.

But within the last decade, developments in virology have started to reveal more and more that viruses might in fact be alive. One was the discovery of mimiviruses, giant viruses with large genomic libraries that are even bigger than some bacteria. To put this in perspective, some viruses, like the Ebola virus, have as few as seven genes. Some of these giants have genes for the proteins that are required for translation—those readers of DNA and RNA that in turn build new viruses. This throws the lack of translational machinery argument for classifying them as nonliving on its head.

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