Altho this appears to be framed as a debate, it really is a question. Then maybe not. Thinking about spores, it really is alive. Altho the bacterium forms a hard, protective protein covering, there must be some metabolic activity going on inside, or else it would “live” forever. Which is another question: how long does a spore live? Anyway, I was thinking what would be a definition of “living” that would be all inclusive. First I thought metabolic activity, but viruses do not have such activity until they inhabit a living creature, but they do have either DNA or RNA. Therefore, “life” would be any thing that has either metabolic activity or either DNA or RNA. But prions have neither, being pure amino acids. Yet, you cannot exclude them as they cause disease. However, they are a part of a living being. So, “life” would be some thing that has metabolic activity, or DNA/RNA, or is part of something else that is living. However, that appears to be too general. Can we say any of our organs are “life”? Every part of our body has metabolic activity, DNA/RNA, and is part of a living being, but we don’t consider that the part equals the whole. We’re alive, but is our skin “life”?
Viruses don’t live forever either, but how long does a virus live? If it never invades a living body, I suppose that the ribonucleic acid would eventually degenerate, but I don’t know.
So, there are three questions here: (1) How long do spores live? (2) How long do viruses live (3) What is an all-encompassing definition of life that is not too general. The dictionary definitions of life are not satisfying: the condition that distinguishes animals and plants from inorganic objects and dead organisms or a state of existence. The dictionary also gives distinguishing manifestations, but those are characteristics and not the essence of life.
Someone had to say it.
Re-Viruses
There is some debate as to whether a virus is actually alive. They can only reproduce by using the cells of other organisms. My Anthropology teacher pointed out a few things that straddle the line between living and nonliving things. Gotta go check my notes.
The problem is that biologists haven’t yet come up with a conclusive definition what ‘alive’ really means. Right now the common point of view is that in order to be alive, an orginism must have the ability to self-replicate. This would exclude viruses as they rely on host cells to propigate, pushing them off into the relm of sucessful protien and DNA ‘shells’.
If you want to take to a materialistic point of view, you can argue that nothing is really ‘alive’ and that we’re just a complex series of chemical reactions which has managed to convince itself that it exists.
No one has attempted to answer my first two questions re spores and viruses. I don’t want to know the meaning of life (why we exist) but what is life. The M-W definition (1c) is too restrictive, as it eliminates viruses, spores, and prions. Most people will concede that the former two, anyway, are alive. But are they capable of "metabolism, growth, reaction to stimuli and reproduction? A spore is not while it is a spore. A virus is incapable of growth. A prion is not capable of any of the above. Definition 1a is a tautology and absolutely meaningless.
While prions are organic, they are not living things unto themselves. A prion is a bit of misfolded protein. It does not grow, breathe, eat, move, or respond to environmental stimuli. It does, in a sense, reproduce itself. But so do crystals.
Depends on the spore.
Again, never mind how long a virus lives. The question is whether it lives at all.
As far as a definition of life goes, I'm going with the classic. All living things-grow,move,breathe(this a bit of a simplification, I know) ,eat (again a simplification), move, respond to environmental stimuli (even an amoeba will move towards food), and reproduce (no, spaying or neutering your pet does not classify it as nonliving). This may describe what life does, rather than what life is, but that's the best you'll get. It's also a tremendously useful yardstick.
Fire is the classic test. Fire grows and moves. It eats by consuming fuel, and uses oxygen. It may start other fires. However, it does not respond to stimuli. Nor, does it truly breathe.
For more on the question of what life is I suggest viewing certain episodes of Star Trek.
PS Life-Noun 1 A board game 2 A breakfast cereal that Mikey likes.
I agree with DocCathode. Self-replication is much too loose a criterion (rf crystals). But on the other hand metabolism is way too strict.
I am not a biologist, so I won’t venture any guesses.
In my opinion as a biologist, you can’t divide the world into “living” and “non-living.” There are some things that are definitely alive, some things that are entirely inert and some things, like viruses and Bob Hope, that are kind of in the middle. Prions and crystallized viruses are certainly not “alive,” but they aren’t really in the same category as Al Gore’s political career, either.
I don’t think you’re likely to find any practicing scientists worrying about the definition of “life.” Like “art,” I know “life” when I see it, and it’s pretty hard to define “life” in such a way that no one can come up with a counter-example.
Well, since no one has even attempted to answer my questions about how long spores and viruses exist (I avoid the use of “live”), coincidentally in today’s newspaper there was an article that said the anthrax virus “can live for many years in the ground.” That pinpoints it. The article said “live” BTW.
“Well, since no one has even attempted to answer my questions about how long spores and viruses exist (I avoid the use of “live”), coincidentally in today’s newspaper there was an article that said the anthrax virus “can live for many years in the ground.” That pinpoints it. The article said “live” BTW.”
Ahhh, newspapers.
I’m agreeing with Bob. You can’t draw a firm line.
What’s so important about defining ‘life’ anyway? I have to say, I’d feel awfully guilty if I had to define clearing a virus as ending ‘life’.
Whatever defentition that comes up can be knocked down. You could say that a woman who is on birth control is not alive, since she can’t reproduce.
Quoth barbitu8: “…there was an article that said the anthrax virus ‘can live for many years in the ground.’”
Huh? CNN.com told me that anthrax is caused by a bacterium, Bacillus anthracis, and I just can’t believe that the media or the internet lied to me. Are there two things called “anthrax” or something?
Achernar- Yes, there are two things known as anthrax. The first is the disease. The second is a metal band.
Barbitu8-Spore is a pretty broad category. IANA biologist but I’m thinking that life span depends on the species of the spore in question. The question is analogous to asking ‘How long do verterbrates live?’. That depends on the vertrebrate-humans aprox 80 years, dogs aprox 20 years, etc.
Anthrax is, of course, a bacterium. I don’t know if I blindly just typed what the paper said or if it was a slip. But where do spores normally reside: in the ground? I thought they float in the air. Viruses, I guess, reside, when not in animals or plants, in the air.