To whom it may concern,

I am currently a 1st year student of Biology in the National University of Ireland, Maynooth. During my studies we have talked alot about viruses. One thing which troubles me is the question, are viruses alive? In my opinion they are, i feel that many biologists will not accept that they are as the whole definition of LIFE would have to be changed, however the definition of life has changed many times over the past few centuries, why can't it again? I would really like to hear your opinion on this!

               Jason Mc Dermott

The problem with viruses is that they don't have essential enzymes that allow them to self-replicate. They need to infect other organisms and use their enzymes. So it isn't really a self-sustaining living organism.

However, I do see your point about the possibility of viruses being alive. Their sole purpose is to reproduce, much as other living organisms and that seems to me very much like life.

I think the problem here is where to draw the line. Is a virus alive when they're reproducing (i.e. with the help of enzymes in other organisms), but not alive when they're dormant? Is it possible to have a part-time living organism?

On the other hand do we really need to draw the line?

As we understand phylogeny and evolution better, it is becoming increasingly difficult to separate individual groups from another. For instance, dinosaurs and birds. There isn't a clear cut separation of birds from dinosaurs because we now know that some dinosaurs had many characters that we previously thought was bird specific.

Unfortunately, we live in a classification world and we do need to draw the line somewhere. It may change in the future when we understand the history of viruses better.

Does that mean that I (and all other obligately sexual organisms) am (are) not alive, since I (they) cannot self-replicate without using another organism?

Last edited by Paolo Viscardi (17th May 2007 07:51:04)

Viruses can't reproduce without the help of an organism of a different species/phylum/kingdom, whatever, another bacteria or a eukaryote cell or something. Sexual organisms are different from that because most of us can reproduce within our own species, subspecies, whatever. My thoughts on the matter anyway.

Hello Jason, you have really put forward a tough question and it is no surprise that different members of the forum here have different opinions! The problem here, as with many such philosophical questions is defining LIFE.

As you said the definition of life has continually changed and currently the most popular definition is limited to self-sustaining organisms. However, consider that many non-viral parasitic organisms including multicellular life such as plants and animals are certainly regarded as alive but could not survive without their hosts.

So if we go with the most basic definition viruses can be viewed as alive. As Manabu said:

"Their sole purpose is to reproduce, much as other living organisms "

Now, what about prions?

Prion proteins do not reproduce. The presence of the mutant form induces permanent conformational changes in the wildtype protein, but that does not involve genomics and thus in my book it is neither reproduction nor "alive".

I'd agree about the "alive" bit, but surely by changing the form of the wildtype protein into what is, effectively, a replica of itself the prion does actually reproduce?

all comes down to what we mean by reproduce - potatoes, potatoes, tomatoes, tomatoes!

In summary, Jason's orginal question "Are viruses alive?" might be better expressed as "Is 'alive' defined in such a way as to include viruses?"  Put that way, it's clear that the question is about definitions rather than facts.