In my view the answer to the “are viruses alive” question is: 42! I see several issues with the question itself. First it presupposes that there are only two possibilities (“yes” and “no”), the other one, the real catch, is that “life” is in the eye of the beholder and depends on how you define “life”.

Having a computer background, I was raised on 1:s and 0:s, but very quickly realised that the “real world” the computers ultimately have to deal with is anything but binary or neatly categorised, it is a continuum with a lot of noise, and som chaos thrown in for good measure. Likewise I would like to see the question of virus and life like a long greyscale ranging from black (no life, like crystals) to white (mammals, with full reproduction and goal directed behaviour etc.). In my view viruses would certainly be placed on the lower half of that scale, but still not at the black extreme – let’s say I consider them “20% alive”. Possibly I would then consider prions “5% alive” or so.

Of course this is a simplified, if not simplistic, view, but so too is the “yes/no” debate. It is a bit like the old conundrum about photons: are they particles or waves? We now know the answer is “yes” (i.e. both), which we cannot properly visualise, but very well handle mathematically. So be it with “life”!

I have some thoughts regarding the ongoing debate over whether or not viruses are alive.

It's true that viruses need to be inside a living organism to reproduce, but all living things require a specific environment. Seeds require more than water to turn into a plant: they require nutriants, light, and a specific temperature range.

Even more to the point, certain species of wasp must plant their eggs inside spiders. They need living spiders to reproduce, but it's hard to argue they are not alive.

To some extent, the question while interesting is irrelevent. It doesn't really matter if a prion or virus is “alive” — it's a prion, or a virus. It is an entity on a spectrum of increasingly complex chemical reactions which start with hydrogen combining with oxygen on one end, and end with me commenting on a website when I am supposed to be working on the other. Somewhere in that spectrum is “life,” and it's probably impossible to specify exactly where it must be.

Personally, I think of life as a structure which reproduces itself and has no other origin in nature. This excludes fire or crystals, which “reproduce” but will also appear in the right conditions. I'll admit that it appears to exclude the very origin of life, however, and it's not quite perfect.

There is only one field I can think of where splitting “life” from “non-life” is an important problem: exobiology.

I understand that the Viking Mars landers each had three experiments designed to find life, and that on each lander two of these three experiments came up positive. As the protocols required all three experiments to return a positive, the results were declare inconclusive and remain unexplained to this day.

So really, the question might best be phrased this way:

If a virus were found off of the Earth, would you agree that extraterrestrial life had been found?