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Life?


alan2here
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There are some verry narrow desciptions of life where it must involve growing and breathing and the such. I think that a formal desription should be wider than that but not as wide as I am preposing, however I would like some feedback on some of my ideas.

 

 

From my POV life is a system that is mathamatically chaotic and is a lurning\evolution system.

 

For example for bacteria each lifeform is changed all the time accoding to the rules of physics and able to make two inperfect coppies of itself.

 

The result of this is that if it gets into a state that is too wrong it breaks up and fails to be a lifeform anymore (dies), a behaviour of the system that results in the life really being life as we know it is that the least able bacteria in this system are removed due to competition for food. Not only because this is familier to us but also because the system would have no goal if this didn't occur and the only outcome would be that given enough time every possible stable varieation (lifeform) would occur.

 

 

Life could however be more abstract such as in the following made up example:

 

Signals are created from vibrational interactions between atombs. Natural formations in this system are created by paterns of atomic spin and vibration. Stable paterns can effect each other and can also be effected by unstable chaotic vibrations. Patterns can create copies of other paterns they see but not of themselves.

 

 

Such a system could occur over the top of the physical systems visable to us in the same way that waves occur over the main bulk of the ocean, a whole civerlisation could rise and fall covering several cubeic miles of the matter around us or in the flame of a candle in a few seconds and we would never know.

 

 

Imagine a cold planet dwelling society. Earth could look like a burning inhospitable fireball to them as they may be verry slow moving and so percieve things on earth such as tectonic plate movements as being fast and see earth as a bright, hot dwarf star heated by our local groups main star the sun (or sol to use the proper word). Maybe such a society would percieve liquid as being just like gas and think of both in the same way we think of plasma.

Edited by alan2here
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Yes, various speculations about very different forms of life are the basis for a huge amount of science fiction (that is, real science fiction, not allegorical/fantastical stuff like star trek, where it's all about the different forehead wrinkles), and something which is very interesting to me, as well. And you're right: broader definition of "life" is usually needed. I generally think along the lines of, "a self-replicating pattern of localized negative entropy" or something like that. It's vague, but it has to be. Even here on Earth life isn't especially well-defined. The line we draw between the living and the nonliving is blurry and arbitrary. We are definitely alive and a rock is definitely not, but there's a whole lot in between, and not really an obvious place to draw that line. The convention is somewhere between viruses and bacteria, but it doesn't have to be. In addition to discussing hypothetical extraterrestrial life, it often comes up when talking about abiogenesis on our own planet. i.e., the first "life" necessarily arose from "nonlife," but that nonlife would have to have many characteristics of life and be capable of becoming life, so isn't it essentially living as well? And so on.

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Simple and for the same reason plasmids are not considered alive. It does not have a metabolism. Truth is, however, that "alive "is not really a physical property itself, but rather a collection of properties. Simply put: there is no clear-cut demarcation between alive and not-alive. As with many biological aspects everything exists in continua (to put it simply).

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But that's precisely the reason viri aren't alive - because they cannot do anything without the help of a cell with a metabolism.

But they can do more than a rock can, even if the rock were helped by a cell.

 

A virus is not alive only due to formal classification. But informally far as nature is concerned, a virus might well be alive, even if just very slightly. That it has a "borrowed" metabolism I don't think is a good enough reason to deny it the life classification. Maybe it runs on life fumes. :)

 

However, this problem might be related to the same kind of confusion when science has its own meanings for words that are different from the general use, such as "theory". In other words, maybe a virus is alive by general language, but under scientific definition it's not alive, but they're not really talking about the same exact thing.

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Does a virus rely on a cell in a parasitical relationship or as we rely on air or is there someting fundermental that justifies this being a valid (not a contrived) reason why a virus is not alive?

Edited by alan2here
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Our reliance on air is different - the air doesn't actually *do* anything for us, but merely acts as a substrate or an ingredient.

 

Think of it like cooking. An organism is like a cook who does stuff to make a cake, but still requires milk, eggs, flour, etc. A virus is like a guy who breaks into the kitchen and forces the cook to follow a recipe he has - he hijacks the system and provides the instructions, but cannot be said in any meaningful way to be the one who cooked the cake.

 

Mokele

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A better analogy is a computer virus. A computer virus can replicate itself, but only if it has a computer. Without a computer, a computer virus can do nothing. With a computer, however, the computer virus can hijack the computer and force it to make more copies of itself. A biological virus works in exactly the same way, except that it has its own specific physical form (whereas a computer virus can be bits on a hard drive, bits on a CD, bits in an optical cable, etc). If viruses are alive, why not computer viruses?

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So this is different from some bactera that need us to survive (and therefore reproduce) or other parasites that require the recources of there host because a virus requires controll of the host where as a parasite does not?

 

A human brain cell is an organism itself but cannot live alone in the same way a single bee cannot live away from it's colony. The brain cell cannot reproduce itself into another human body without the whole body in the same way that the bee requires the whole nest that maintains the queen to create a new colony.

 

So the reason for virus not being classified as life is that they require other lifeforms not genetically identical to themselves to help them reproduce?

Edited by alan2here
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So the reason for virus not being classified as life is that they require other lifeforms not genetically identical to themselves to help them reproduce?

 

No, the reason is that the virus requires the other lifeform to reproduce the virus. The virus has no ribosomes, so it cannot make proteins. It doesn't produce its own energy, it doesn't have the machinery to acquire energy from the environment (ie, it doesn't take food into itself). It lacks the enzymes to make even the most simple chemicals. All the pieces of the virus, were made/assembled by a living cell, and all the atoms of the virus, acquired by a living cell. Again, would you consider a computer virus alive?

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So this is different from some bactera that need us to survive (and therefore reproduce) or other parasites that require the recources of there host because a virus requires controll of the host where as a parasite does not?

 

Basically, think of most parasites (like tapeworms) as predators who are just small enough to live on/in their prey and eat it. Unlike a virus, which needs to hijack its hosts' biochemistry to reproduce, all a parasite gets from us is food and shelter. To use the cook metaphor, a parasite is just the guy that steals a slice of the cake before it leaves the kitchen, rather than the guy holding the gun to the cook's head.

 

A human brain cell is an organism itself but cannot live alone in the same way a single bee cannot live away from it's colony. The brain cell cannot reproduce itself into another human body without the whole body in the same way that the bee requires the whole nest that maintains the queen to create a new colony.

 

Yep - a lot of people who work on hive insects call them "super-organisms" due to precisely this similarity.

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I think it's important to note that the term "life" is just a product of human language, and the distinction between life/non-life doesn't necessarily map onto reality... It's just a word we made up to describe stuff, not an underlying truth of the universe.

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No, the reason is that the virus requires the other lifeform to reproduce the virus.....All the pieces of the virus, were made/assembled by a living cell, and all the atoms of the virus, acquired by a living cell.

The scary thing is the creator of any new virus would seem to be the affected lifeform itself, if what you say is true.

 

In that manner, it's nothing like a computer virus, whose existence is never spawned by a computer, but rather a slick geek behind the monitor.

 

The virus has no ribosomes, so it cannot make proteins. It doesn't produce its own energy, it doesn't have the machinery to acquire energy from the environment

How then, did its first ancestor get the energy to put a gun to the cook's head?

 

If a virus doesn't produce its own energy, does it at least borrow or extract it?

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The scary thing is the creator of any new virus would seem to be the affected lifeform itself, if what you say is true.

 

In that manner, it's nothing like a computer virus, whose existence is never spawned by a computer, but rather a slick geek behind the monitor.

 

Don't confuse the origin of a virus with how it makes more copies of itself. And, just so you know, geeks have made biological viruses as well. However, other than the original virus, the infected cell makes more biological viruses, and the infected computer makes more computer viruses.

 

How then, did its first ancestor get the energy to put a gun to the cook's head?

 

If a virus doesn't produce its own energy, does it at least borrow or extract it?

 

Viruses have a few proteins, which allow them to enter the host cell in various ways. The proteins are made by the previous host cell, following the instructions contained in the virus DNA/RNA. Then they take control of the cell in various ways, or lie dormant in it. If they take control of the cell, the virus forces the cell to create the proteins and copies of DNA/RNA required to make more viruses.

 

The most that I know of a virus using energy is that one had a "motor" that squeezes the virus' nucleic acid into its capsid. Even so, it requires energy produced by the host cell in the form of ATP.

Edited by Mr Skeptic
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And, just so you know, geeks have made biological viruses as well.

But surely they can't have done so without first starting either with genetic material extracted from a real living organism, or from a pre-existing virus.

 

If I'm correct, then it's still far different because we're able to manufacture a computer without the need of a pre-existing computer, and a digital virus without the need of a pre-existing digital virus.

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A definition of life cannot occur without it matching the expectations of the person doing the defining. Thus, a universla definition cannot exist.

 

Currently, a definition of life will include organic life on Earth, and exclude such things as fires and computer programs. One definition I saw was :

"Life is a complex organic chemical system capable of reproduction and evolution."

 

The qualities often mentioned, like respiration, excretion, nutrition etc., cannot be used in a definition, since a forest fire exhibits all those. Reproduction and evolution are two vitally important qualities of life, but both these can be seen in certain computer programs. Thus the addition of a statement such as "complex organic chemical system".

 

The definer in this case used the word 'complex' to exclude viruses. Personally, I think that is unjustified. I do not care that a virus cannot reproduce without the use of a host cell. It still displays the qualities of being organic, reproducing, and evolving. Lots of parasitic organisms cannot operate without a host to assist reproduction. eg. Mycoplasma bacteria.

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We've discussed this a few times.

 

http://www.scienceforums.net/forum/showthread.php?t=31518

http://www.scienceforums.net/forum/showthread.php?t=32625

 

 

In one of those threads, the following was offered in response to "what defines life":

No, I'll stick with the 4 criteria:

1. Metabolism

2. Response to stimuli

3. Growth

4. Reproduction

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iNow

All four of those criteria are shown by a forest fire. Yet a forest fire can hardly be called life.

 

The forest fire exhibits metabolism because it breaths, liberates energy, excretes waste etc.

Responds to stimuli by flaring up with more fuel, or driving before the wind.

Grows whenever fuel is available.

Reproduces by budding off new fires.

 

This makes those criteria invalid as a definition of life. Any valid definition will exclude non life such as fires, and computer programs.

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Metabolism? That's a bit of a stretch, especially since metabolism has such a specific definition, as what you're referring to is chemistry. I also think your "response to stimuli" point misses the mark (as that's also accounted for by basic chemistry), but hey, I'm not a biologist.

 

 

http://en.wikipedia.org/wiki/Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism, on the other hand, uses energy to construct components of cells such as proteins and nucleic acids.

 

The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed into another by a sequence of enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable but thermodynamically unfavorable reactions by coupling them to favorable ones, and because they act as catalysts to allow these reactions to proceed quickly and efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells.

 

The metabolism of an organism determines which substances it will find nutritious and which it will find poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The speed of metabolism, the metabolic rate, also influences how much food an organism will require.

 

A striking feature of metabolism is the similarity of the basic metabolic pathways between even vastly different species. For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all organisms, being found in species as diverse as the unicellular bacteria Escherichia coli and huge multicellular organisms like elephants. These striking similarities in metabolism are most likely the result of the high efficiency of these pathways, and of their early appearance in evolutionary history.

Edited by iNow
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A definition of life cannot occur without it matching the expectations of the person doing the defining. Thus, a universla definition cannot exist.

 

Currently, a definition of life will include organic life on Earth, and exclude such things as fires and computer programs.

Such a definition is possible. Really, anything ca be defined if we abandon preconceptions a bit.

 

http://en.wikipedia.org/wiki/Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life.

Problem with using this definition is that it uses the word life, so perhaps it's not as good candidate for defining life.
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Life's metabolism is different from a burning forest fire. Life has specific anabolic reactions, which are powered by specific catabolic reactions, both of which are carefully controlled and assisted by organic catalysts. A forest fire burns everything it touches (catabolic reactions), and if there are any anabolic reactions they are random.

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