Is it offensive that the definition of life requires life to have cells?

[Donnie Darko]

I think it's so stereotypical and stupid that life has to be cellular to be considered life. I think viruses are alive.

[blike]

I think it's so stereotypical and stupid that life has to be cellular to be considered life. I think viruses are alive.

Why?

[Osiris]

Viruses can't reproduce... they are more like a trait or a characteristic a cell infected by it acquires. Although, viruses could be a key to evolution.

[ecoli]

I think it's so stereotypical and stupid that life has to be cellular to be considered life. I think viruses are alive.

 

I agree that our current definition of life is parochial and narrow-minded... especially considering the potentially limitness of exobiology...

 

However, I don't think I'd frame it exactly like you did, and without backing up my opinions. Why do you think viruses are alive?

[SkepticLance]

I agree with Donnie that viruses are alive. They are alive for several reasons.

 

1. They contain nucleic acids, and their existence depends on the nucleotide sequences of those substances, just as with all other life on Earth.

 

2. They use their nucleic acids to manufacture proteins, even if it is a host cell doing the 'work', and those proteins are used in their life processes.

 

3. The leading theory for the initial existence of viruses is that they 'devolved' from simple parasitic bacteria. Bacteria are generally regarded as alive. If viruses are not, at what point in devolution did they cease to live?

 

4. They reproduce using nucleic acid replication, creating new copies of themselves with the same proteins and same nucleic acid coding.

 

5. They undergo organic evolution. The only other (non life) thing to do this is certain computer programs, and they are not organic.

 

The argument against them being called 'alive' is their relative simplicity (a consequence of devolution), and their dependence on a host for most of their metabolism. A number of other organisms, which are considered to be alive, depend on a host for a lot of metabolism, also. Seems to me that calling those others alive, and not viruses is making a very subjective distinction.

[DrDNA]

I'm not offended.

But I have cells, so perhaps I'm not the right one to ask.

[Mr Skeptic]

I think it is a bit narrow-minded to require life to be based on cells, or even to be organic for that matter. I think a better definition would be a list of requirements. Here would be a (probably incomplete) list:

*Able to sense and respond to its environment.

*Able to acquire and use energy and materials.

*Able to self-repair or reproduce.

[DrDNA]

If "life" does not require cells, then would you require some alternate form of compartmentalization?

 

All "life", at least all "life" as we know it, is compartmentalized and also dependent on compartmentalization.

 

Certain of the hypotheses about the origins of life postulate that "life" as it origninated on earth likely required at least 2 primary elements; one, a blueprint that could be copied and amplified and two, compartmentalization.

So, does that help answer your question?

 

 

Sounds sort of like a virus doesn't it (sans a suitable host)?

 

BTW: I, personally, would not consider a little parasitic protein container filled with DNA (or RNA) a "life" form. I believe that under that definition, a little plastic container filled with DNA (or a microcentifuge vial containing DNA), should be considered a life form and I'm not about to give all that stuff in my freezer any rights or special privliges.

[SkepticLance]

Any definition of life will require a subjective, and hence unscientific, drawing of a line in the sand to say - here is life, and that side of the line is non life. We could argue all year about where to draw that line.

 

Life on Earth probably began as a broth of organic molecules in some pool about 4 billion years ago. Those chemicals interacted and reacted. Some, possibly on the surface of a clay or calcite particle, lined up to form a simple polymer. One such polymer happened by chance to have the ability to replicate itself - probably very crudely and with lots of errors. Some of the variations that resulted were unstable and vanished rapidly. Others were better and survived. From there on, natural selection could kick in, and develop new variations that were more stable, and better able to replicate with minimal errors. Over time, the first life resulted.

 

The point of this speculative discourse, is that life began from non life in the form of organic molecules, and slowly developed into simple life. Somewhere on that line of progression, we draw a line. Earlier than that line, we say, this is non life. Later, we say, this is life.

 

Wherever we draw the line is a totally subjective and unscientific decision. I would personally draw the line at the point that a simple nucleic acid was able to replicate itself with minimal errors, and thus create offspring, which would in turn replicate, so that over time organic evolution took place.

 

By my drawing of the line, viruses are living. Others will disagree and make a different but equally subjective and unscientific drawing of the line elsewhere.

 

I argue that the two essential elements of life are reproduction resulting in genetic coding being copied, and organic evolution. Anything that shows both traits should be considered as life.

[Fred56]

I think that life is an emergent property of all the atoms, elements, organic compounds, compartmentalisations, and overall structure, that make up some living thing. Here's something I concocted a while ago about emergence:

 

The car is made up of a whole pile of what are, at first glance, simple parts. If you wander through an assembly plant, you find a lot of separate parts and sub-assemblies, none of which is a car, but you know it is part of a car. When all the parts needed are assembled (put into a certain configuration, or "structured" properly), a "car" emerges.

 

If that same car is crashed, or squashed up into a little cube, it becomes something that isn't a car, as we usually understand a car to be, even though it still consists of all the things it was originally made up of, they are just in a different configuration which cannot exhibit the emergent properties of "car-ness". A pile of parts isn't a car either.

 

i.e the whole can be more than the sum of its individual parts. The parts do not "determine" what a car is, the way the parts are put together does.

[Ophiolite]

I thought that thoughtful biologists had all but abandoned serious attempts to define life for many of the reasons touched upon implicitly and explicitly in several of the foregoing posts.

If you are determined, Donnie, to have viruses treated as life, would you also like to cast a vote for prions?

[Sisyphus]

I suspect that eventually "life" will be seen as a kind of process rather than a property of particular beings. That would address a lot of the ambiguities and and arbitrary demarcations we see currently, and probably help us deal with the uncertainties of exobiology.

[foodchain]

I personally consider also the virus to be life. I think I understand where you are coming from. I think a prime example in the history of science that is overlooked is prior to the discovery of life at underwater vents or vent communities as commonly denoted such was thought impossible for the existence of life. I don’t think life yet has a finite definition that covers every possibility. I think another part of the issue is that you have people behind the definitions of such things. What I mean by this is quite possibly that the current means of life on earth as we understand it is all we have really in which to gauge life. Now knowing that life can come to survive and become persistent or tenacious even in toxic/nuclear waste I have a hard time personally thinking of what the bounds are to life and or what it can or cant be or what it requires, such as what particular molecular structures or energetics of such or what not. I don’t even know what environments life can or cant survive in. I really think basically that life as we know it in current form is really what we attribute life to being and only being able to be at large. I think this is why the virus blurs such lines and gives people trouble in classifying it.

[Mr Skeptic]

I think that if a virus is alive then a computer virus is also alive.

[SkepticLance]

A few years back, when I did a paper on microbiology, we students were given a definition of life. This definition was stated to be the closest thing biology has to a universally accepted one. It included 4 essential components.

 

1. Complexity

2. Organic molecules

3. Reproduction

4. Evolution

 

The complexity bit was part of the definition purely and totally to exclude viruses. I consider this a bit like cheating. You re-state your definition to make it what you want it to be, rather than reflecting reality.

 

The organic molecules bit was there to exclude certain computer programs. Probably valid, since it is a bit hard to see how a computer program, at least in today's computers, can be alive.

 

Whenever a definition of life is debated, there are some who will try to make it include hypothetical extra-terrestrial life. This widens the scope of the definition to an impossible degree. I think we should limit the definition, at this point in history, to Earth life only. If and when we discover some extra-terrestrial biology, we can enlarge the definition. However, it may be thousands of years, if ever, before that is necessary. Stick to the data available in the mean time.

 

This follows the important principle that science is directed by empirically and objectively derived data, and not by 'logic' or speculation.

[waitforufo]

Offensive? Just who would be offended? I have seen political correctness take some strange paths but this one is beyond comprehension.

 

Do you, or someone you love, have a pet virus? Are you planning on starting people for the ethical treatment of viruses? If you are worried about offending viruses, why not prions? Wouldn’t want to hurt their feelings either.

 

Am I missing something here, or has the English language lost all meaning?

[Sisyphus]

This follows the important principle that science is directed by empirically and objectively derived data, and not by 'logic' or speculation.

 

I don't think that's what this is an example of. That would be true if we were making predictions, but we're not. We're assigning a definition.

 

That four-component definition of life you give is, I agree, rather cheating. It's taking the things we already consider to be "life" and devising a definition merely so as to include those things. It reminds me of defining "man" as "a featherless biped." Yes, it includes man and only man, but it doesn't have anything to do with what a man actually is. Similarly, that definition doesn't seem to be about what makes life special, but is merely a set of characteristics that happen to be shared by all agreed-upon living things.

[DrDNA]

Have we finally reached the ultimate point of politcal correctness ..........of offending viruses or prions?

 

Kill them I say...kill 'em all.

 

Which brings up a point....in order to "kill" them, they must first be "alive".....

[SkepticLance]

Sisyphus said

 

Similarly, that definition doesn't seem to be about what makes life special, but is merely a set of characteristics that happen to be shared by all agreed-upon living things.

 

That is all a definition has to be. What makes life special is getting into metaphysics. A scientific definition of life is merely a description that allows us to distinguish between life and non-life.

 

My personal definition would go something like :

 

"Life is any structure with the ability to reproduce itself, and undergo organic evolution."

 

I might have to add definitions of reproduction and of organic evolution, but I am sure that participants in this thread know what I mean. Note that the word 'organic' excludes computer programs.

 

This would clearly include viruses.

[pioneer]

Using a loose definition of life, fire has all the characteristics of life. It metabilizes organic materials. But can also eat inorganics and metals. It is able to sustain itself, as well as reproduce, as long as there is food. It can reproduce into separate entities, which can also reproduce. It can even become \a multicellular firery organism, as all the little fire cells merge into one huge firery organism. This can also reproduce, radiantly. If that isn't enough selective advantage, it can also give off tiny spores called embers, which can float in the air, land and come to life. It can dominate its environment with its many selective advantages.

 

We can kill the firery beast with water, which is the medium used by the other forms of life on the earth. Ironically, water can also cause the beast to appear, via lightning. Human have learned to tame it, like a beast of burden. But at times, the beast still breaks free and creates havoc. I like raising little fire ponies when I go camping. They dance and sing with the sound of hisses, crackles and pops.

[DrDNA]

Interesting proposition, Pioneer. But I would argue that fire contains no blueprint, no information (except *perhaps* a single 0 = no fire; and a single 1 = fire) and it is not compartmentalized (it is completely open to the system in which it resides). Hence the sun is not life either.

 

The earth on the other hand is compartmentalized.....and contains plenty of information in the form of DNA, RNA, fossil records, etc.........hmmmm.......

[SkepticLance]

To Pioneer

 

Re my definition of life, and fire.

 

Fire does not undergo organic evolution, so is not life.

[Mr Skeptic]

Fire cannot sense its environment, so it would not fall under my definition either.

[Fred56]

Maybe life is one of those complicated things that is just hard to define in a succinct way. It does seem difficult to pin some sort of "equation" on to, it just sort of squirms out of the way each time.

 

We are now at the beginnings of what might become a very important mathematical pursuit: complexity theory. There are many complex systems around (our planet and its climate, for example). The many forms of life are all examples of complex systems. This branch of Math is still quite "immature", so we have a ways to go before an "equation of life" appears on any blackboard.

[SkepticLance]

To Fred

 

It is not in the least difficult to define 'life'. It is just difficult to get a consensus on what is a correct definition. Witness this thread. At least three definitions, and no-one agreeing!