The Relativity of Life
I always think of the line in "The Princess Bride" when the hero is declared to be "mostly dead" when I discuss this idea of life and death or should that be life vs death ?
Actually, it all started about twenty years ago when I read an article about an organism called the Tardigrade in one of the Scientific journals. In the article it was stated that a Tardigrade could be freeze dried and then when it was placed in water would resume swimming or walking around (whatever Tardigardes do!). I then spent the next fifteen or so years looking for the elusive Tardigrade ( a supposedly common inhabitant of ponds). I must confess that it was really not I who was doing most of the looking but my High School Biology students who had been guaranteed extra credit for a confirmed (by me) discovery. It was not until a few years ago that one of my students at The Summer Institute for The Gifted made a confirmed find. Of course it was in a drop of pond water and seemed to be walking on those stubby little appnedages, but it may in fact have been swimming!
To get to my point, was the Tardigade dead when it was freeze dried? Or, was it in a state of suspended animation (whatever that is)? Or, is it in fact capable of coming back to life after being dead? As you can see all of these ideas pose some rather awkward scenarios !
Now, the definition of life is also a rather interesting area to pursue. What does a thing have to do to be alive? Some say that if it does not carry on metabolism, reproduction, evolution, and response it is not alive. That is the basic premise of the "Cell Theory".
Of course the lowly Virus poses a problem because it does not carry on metabolic activities, cannot reproduce by itself (it in fact makes its host cell do the reproducing for it), does evolve rather quickly and is capable of responding sometimes to highly specific hosts. Is it alive or just a rather sophisticated chemical ?
Then we have a whole array of seeds and spores that can remain "dormant" for eons before producing a new organism. Are they alive during that period, just sleeping or again capable of returning to life under the proper circumstances ?
So, the idea of life being relative does have meaning. In my humble opinion the lowly Tardigrade and all of those things that can appear to be dead are in fact alive as long as they are "viable", where viable is defined as the ability to carry on some if not all of the activities associated with life. Does this mean that a virus is a living thing? Yes, although I must admit that it is probably the "ulitmate parasite". In most cases the virus is entirely inert outside of the host cell and in some cases inside the host cell or organism. The fact that it can lose its viability when the conditions are not correct implies something more that just a pile of chemicals when not in the host. Of course one could argue that the pile of chemicals was just very fragile when placed in a harsh environment, like the air, but considering the tremendous similarity in the structure of most viruses and the tremendous difference in their sensitivities I think the answer lies more in their life characteristics than their chemical structure.