Talk:Life/Archive 1

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Definition

As a biologist I have taken out adaptation as one of the definitions of LIFE, there are thousands of organisms that can only live in their own niche, if this is changed then they will simply die out and go extinct, this does not mean that they were never alive simply because they were unable to adapt. I left Descent with modificationin but this should seriously be considered if it is fit to be in for a definition of life, Descent with modification is another term for evolution (and hense would be better fit in the evolution category)(SND)

Adaptation is an established criteria of the definition of life in scientific literature. If you wish to replace it, please document sources that show this definition is superior. -Gavin 19:19, 1 February 2006 (UTC)


I am changing this statement:

"Reproduction, the ability to create entities that are similar to, yet separate from, itself"

To:

"Reproduction, the ability to create entities that are similar to, yet separate from, itself or consisting solely of entities that exhibit the quality of reproduction."

I sort of agree with this, but, again, it is not an established definition. Frankly, I have long desired to change this sentance to "Entities that are a result of reproduction by other living entities." Every organism certainly exhibits this characteristic (except the first organism ever). -Gavin 19:19, 1 February 2006 (UTC)


For the sole purpose to encompass the fact that mules and the infertile are still alive, yet do not fit the prior definition of reproduction.

If my definition is incorrect please replace with the old definition or a more accurate definition.

If my definition is correct, then we can remove the section concerning mules, the infertile, and drones.

Keep in mind I used the "or" inclusively to indicate that if the first definition of reproduction is false, the other definition may apply to also define life from a reproductive standpoint.

I intend to revert your edits, but will wait for further comments first. -Gavin 19:19, 1 February 2006 (UTC)

I deleted this statement:

fire is alive. (This could be remedied by adding the requirement of locality, where there is an obvious feature that delineates the spatial extension of the living being, such as a cell membrane.)

I removed the above statement from the article because it is not true as the definition stands. Fire does not have any metabolism or response to stimuli. AdamRetchless

[Peak:] By removing "fire", you are doing a disservice to the integrity of the basic ideas of the original author. The main point is that the old-fashioned approach (based on a clever but ultimately haphazard collection of criteria) does not work very well. Fire responds to stimuli (e.g. wind), and it has "metabolism" in the sense identified ("consuming, transforming and storing energy/mass; ..."). Of course, one can define "metabolism" in a sophisticated way, but this section is about *unsophisticated* approaches. Please reconsider.
Thanks. Peak 06:57, 30 Mar 2004 (UTC)
Boy, am I out of touch with the common man? ;^) I can see your point. However, it doesn't take a biologist to realize that fire is not alive, so perhaps our "conventional" definition is lacking. For one, I think the common-sense definition includes the fact that living beings include a solid structure, whereas fire does not (it is gas, or maybe plasma). As for metabolism, fire obviously consumes fuel, but it doesn't produce any structures that further the "life" of the fire. Likewise, fire may change as a consequence of external factors, but it doesn't change in ways that promote its continuation. I don't think a person needs a degree in biology to understand these ideas, but perhaps they still fall in the "sophisticated" camp.
Anyway, I think that the real point should be that a list of traits is not a definition. The listed "exceptions" are relevant for those who are trying to make a comprehensive definition of life; several other phenomena are similar to life, and any definition needs to be sure to distinguish between these phenomena. BTW, crystalization also falls in this category of things that share some traits with life, but are not life. AdamRetchless 14:08, 30 Mar 2004 (UTC)

Otherwise, I intend to remove this...

Motion, either moving itself, or having internal motion

...from the definition if no-one objects. Anything that is growing, reproducing, and responding to stimuli is is necessarily moving. AdamRetchless 02:53, 30 Mar 2004 (UTC)

My definition: Life is a special kind of organization, of information. It uses self-reproduction as its main tool to stabilize and improve itself. In its profane meaning it forms structures out of dead mass, but in its meta sense and also since the invention of the "electronic brain" we extend the term of "life" to massless systems, too. Grasso

Assuming we get arount to designing a machine that is somehow able to make a copy of itself, allowing for imperfections, would we consider it to be alive? --Seb P.S. I think there's going to be quite some action in this area...

Oh yes, there will be...
As to the question, since molecular biology effectively reduced cells to machines, I think we should not become carbon-chauvinists over the idea of self-replicating machines. Mentioning that, we should probably mention this "Life simulation" (you know the one, you can look at it for hours building patterns;). --Magnus Manske
Think it would be reasonable for me to insert a link to nanotechnology and clanking replicator? I consider those to be alive (well, nanotech isn't by _definition_ a self-replicating system, but it's usually assumed as such), but I wouldn't want to go too far out on the fringe before the more conventional parts of life's article get filled in first :) -BD
Read molecular assembler, and stop using the term "nanotechnology", it's worthless (means nothing). Molecular engineering is a better term, the Technological Singularity when invoked can be called by just that name.

I know reproduction is usually at the forefront in textbooks, but mules are definitely alive in my book, and some comment on that short-coming might be made. On the original wiki we settled on homeostasis the most likely defining characteristic, since it doesn't have any real counter-examples, but is somewhat vague. (The definition's been made much more rigorous since then.)

No mention of reverse entropy?

Why? Entropy is more of a basis for time, not life.
I submit that entropy is the key concept. The most fundamental quality of life is that it resists -- for a certain period and within a certain area -- the second law of thermodynamics; that is, life is a principle which DECREASES the entropy of a defined system.
Life increases entropy by converting complex material (food) to other complex material (cells) and Heat. It always increases the entropy of a system, never decreases it.
All of the various descriptions of life mentioned in the article are just that: descriptions. A definition must get to the essence. And the essence of life is that it creates order; once something ceases to live, it quickly decomposes into chaos, as the second law demands.
The fact that the descriptions of life are so varied shows that it is not a fluke, but an essential aspect of reality. It ought to be as disturbing to scientists as the quantum theory and the uncertainty principle were in the last century.
The punch line to this is: we will NEVER know for sure if there was life "Out there" before we arrived. NASA, in a futile attempt to "sterilize" space probes is creating the conditions under which life forms are evolving so they can survive and flourish in the vacuum of space. We are at this moment sending seeds out to other planets!! Life will not outlive the universe, but it will have a very good run. TheLeftReverend 02:14, 20 August 2005 (UTC)
Very articulate; I couldn't agree more with your statement as to the profoundity of the anti-entropic nature of life. I agree that's the fundamental aspect of it. This article could use a touchup by a biophysicist or condensed matter theorist; sadly, I'm not either of those so I'll have to leave it in its highly incomplete state. Ryanluck 09:06, 20 March 2006 (UTC)

I added a good definition "A self-replicating system that evolves through mutation" as it does, as you mentioned, get to the essence while ruling out all the silly things like fire and cars that fall under description-definitions. What do you guys think?


Shouldn't cells be moved to the terrestrial section? There's no a priori reason that life must have cells as we understand that word. Josh Rosenau 02:52, 15 January 2006 (UTC)


Simply: Something is alive as an organism if it can metabolise nourishment for energy without the direct use of another organisms protein or genetic material for anything other than an energy source. Aditionaly it is a species if it can reproduce.


This definition insures your finger is living but is not an organism. Parasites only use the products of there hosts for survival and are therefore separate organisms. Viruses are not organisms nor living.

Viruses

Hmm, the mule is already a shocking example, but how about an infertile person? Is that person not alive? And if he/she's not dead either, should we call the person undead? *g

To me, life are cell-based organisms that have a metabolism. So I'm not a carbon chauvinist, though maybe a cell chauvinist. And I'm not talking about memory cells holding a computer program. Neither am I intending to call jails alive! Ok, this seems more complicated now. Maybe we should just start an alphabetical list...

But now for something actually useful: A virus is said to be not alive because it doesn't grow. Does it not also fail to have metabolism or internal motion, and isn't it also unable to reproduce on its own? The latter (autonomous reproduction) was pointed out to my class in school, but now I think this would be a slippery slope - neither can, for example, wasps that lay their eggs into live caterpillars, reproduce on their own.

If a creatute cannot reproduce, it's genes cannot be passed on, thus making it "dead" in that it cannot contine it's own line of genes (not very punny pun unintended)-Melles Lord of Badgers

Prions

Definitely not alive. Just malformed parts of life.

5 attributes

Are there any biologists or other scientists who seriously consider mules dead and fire alive? It sounds like whoever slapped this hodgepodge of ideas together is simply trying to make a sardonic point: that the 5 attributes can't be strictly and mindlessly applied.

Fire isn't a form of "life" - it's inorganic. Mules are alive, even though they're all sterile. A man who gets a vasectomy or a bull that gets castrated, is still alive.

Come on, let's make this a serious article.

I am unsatisfied with the list of five attributes. First, I would like to know what justification there is for saying "an entity has traditionally been considered to be alive if it exhibits all the following phenomena at least once during its existence..." and then listing those five traits. Who first listed these traits? Even if we can't confidently find the "the first" use of this list, at least we could find some sort of authoratative source (a textbook perhaps) that uses this particular list. If this is the first time that this list has been collected as such, then the current structure is misleading and will need some major editing. In that case, the list should be changed such that it is clear that this list is NOT the traditional list of essential traits; instead, we should write that that the nature of life is often discussed in terms of posession of essential characteristics, such as those in the list. The special cases (mule, virus, fire, crystal) should be used to point out the difficulty of using any one of these traits as the defining trait. Then we can go on to point out that a list of characteristics is not a clear and coherent definition of life, then move on to present assorted attempts to provide a coherent definition of life. AdamRetchless 13:41, 4 Apr 2004 (UTC)

Anyway, I came here today because I'm looking for someplace to put the idea about when human "life" begins - as relates to abortion and abortion in the United States. There's a controversy between those who say abortion is always (or sometimes) murder, because it's killing a "living" human "baby" - and those who say it's sometimes (or always) not murder, on the specific grounds that whatever attributes the fetus might have, being "human" is not one of them (or something like that, maybe a pro-choicer can explain it better).

I think we need a sidebar discussion on what constitutes "human life" both legally and scientifically (they might not be the same in all jurisdicitons) - as background for the articles on abortion. If the US bans partial-birth abortion, our readers might have a renewed interest in a neutral discussion of the science, law, and ethics of the issue. --Uncle Ed 15:10, 22 Oct 2003 (UTC)

The definition of life is irrelevant to abortion. Of course a foetus is alive. That's not what's at issue. The issue is whether or not it's OK to kill it. And I say this as a "pro-choicer". Evercat 15:20, 22 Oct 2003 (UTC)
Good point, 'cat. Maybe "pro-lifers" have the wrong code name, then. Anyway, it might be around the meaning of what it is to be "human" that the question hinges. I have no POV whatever on the subject, despite what Erik has said elsewhere. My church says simply that we should avoid abortion -- not that it's a sin. We have much more interesting issues: like brainwashing, deprogramming, what is a cult and are we one?, the meaning of faith, the question of life after death, and oh yes, the identity of the Messiah -- then there's all the controversial issues I haven't even listed! --Uncle Ed 20:20, 22 Oct 2003 (UTC)
Even as a "pro-choicer" I would say that a foetus is a human life. The interesting question in my opinion is whether that makes it a person. That's a very seperate discussion, and I would hope this debate would really be discussed on abortion or related pages. I don't like the idea of life or person containing anything more than a passing reference to the abortion debate. :-) Evercat 15:34, 23 Oct 2003 (UTC)

That sounds good to me. The clean up of the life article has no real bearing on the abortion controversy. The fetus isn't dead; that's not the issue; I think we agree there. The fetus isn't even "non-human biological tissue" which suddenly "becomes human" like a Frankenstein monster created from frog's legs and an ape's body.

I'll try to make this my last post at talk:life and you or MyRedDice or someone can move and/or refactor to the appropriate talk page.

But, perhaps the ethical/legal issue has to do with "when human life begins" in the sense of "when does the fetus transform legally, morally and ethically" from a "freely killable life-form" (like a rat or a pig) into a "being with human rights" who may not be deprived of life except by due process or something like that.

Anyway, it's a good thing you and I are able to talk about this without arguing: unlike "E" and "J" (wink wink) -- not that I'm naming anyone... --Uncle Ed 21:14, 23 Oct 2003 (UTC)

Definition

Someone changed the definition from "An entity is" to "An entity or organism is", but adding organism here introduces a circularity of definition, since an organism is alive.Peak 05:55, 25 Dec 2003 (UTC)

I removed some parenthetical, argumentative statements from the "exceptions to common definition" section:

(although this would then discount fungi, and grasses from being life forms).

Fungi and grasses have cell membranes, so I don't understand how this could be an exception to the rule of having a defined border. Is this referring to symbiosis? Anyway, it isn't really appropriate for the section where it was inserted. AdamRetchless 02:26, 29 September 2005 (UTC) I also cut out this:

(Although it is colloquial to speak of flames "getting bigger," there are no discernable "generations" of flames of which to speak.)

I think that much of this section is rambling, "original" arguments. AdamRetchless 02:26, 29 September 2005 (UTC)

Moved from article

This comment was moved from the article, because first, it was really phrased more as comment than actual content and hence should really be here on the Talk page, and second, as this is not really the focus of the article, these debates are already covered in other articles such as abortion etc. --Lexor|Talk 08:17, 14 May 2004 (UTC)

to the second definition above, there is contention as to whether life starts at birth or at the point of fertilization.

Extraterrestrial life

It says in this article that as of 2004 earth is the only place known to have human life. Well, 2004 has been over for only 2 weeks, and has there been any recent news during the past 2 weeks?? Georgia guy 01:11, 16 Jan 2005 (UTC)

I've updated it to "At this time," which is generally acceptable until news of extraterrestrial life is confirmed. 129.79.205.211 14:47, 23 December 2005 (UTC)

Life is not what we once thought it to be - New understanding

Bad news for the living.

(1) Your not really alive.

(2) It turns out your just a Bio-molecular machine: Bio(carbon based)- Molecular(atomic level construction)- Technological Machine(No soul, maybe not even spirit).

(3) Synthetic biology is up and running. That's man's ability to CREATE LIVING MACHINES. Living systems. Synthetic life as it were.

(4) You are so well made, you could of never guessed this to be true. For you look alive. Feel alive. Even Think and Talk as to being alive.

What is alive. We do not know yet. Every thing we look at is an intelligently design system of molecular devices that create a whole we call creature.

Scientist's are now using bacterium for their ability to create at the molecular level. If we feed it a new DNA software programming. It will create it for us. This is an old trick the virus does. Now we can do it. It's cheaper and easier. Billion dollar factories may no longer be needed. We can now just Grow it together.

References are always coming:

http://groups.msn.com/EvolutionBloopersVSGodCreates/general.msnw?action=get_threads

Do some web searches: Synthetic Biology, DNA computers, System biology, computational molecular biology, Biological computing, Biocomputers, Biological Computer Diagnoses Cancer(New) Biological energy conversion, Cellular computer models.

By: --Bio-molecular-Tony 23:36, 30 Apr 2005 (UTC) Jan 29,2005 Bio-molecular-Tony


(It's the 21 Century- wakee, wakee)

Have you had you daily genetically modified food today....


Daniel 03:16, 26 Mar 2005 (UTC)

Are you saying that anything alive isn't alive? What does being a Bio-molecular machine have to do with having a soul? Normally I'd say whatever we define as alive is alive, but after seeing this page I'd have to say that few know what they consider is alive, and thus we don't know what life is.

I figure a virus is alive. it starts out unable to reproduce, but it then eats a cell, grows considerably, and gains the ability to reproduce. Fire is not alive as it is not an entity, but an event. More specifically it is the event of live ash reproducing. There are only two actual attributes something must have in order to be alive. It has to move and grow in order to reproduce, and, according to the second law of thermodynamics, it has to have energy applied to do anything useful, thus leaving only reproduction and response to stimuli. I might be able to rule out that last one too if I find out exeactly what it means. I belive anything, including life and art, can be defined, even if every brain cell of every person who ever existed must be thuroughly incorperated into the definition to do it. Daniel 03:16, 26 Mar 2005 (UTC)


Get a life.


I was wondering, maby we are too cought-up in the science, and we need to take a step back. If we look at what people are trying to do, it looks like finding a set of laws that include everything they think is alive, and dosen't have what they dont think is alive. But people forget who created the word "life". Humans. So, if we created the word, we decide what the definition is. So the people who are trying to find this supposed set of laws are looking for somthing that dosent exist, because you don't look for the laws, you make them. With this law, what you think should be considered alive, it is alive because it is your mind and people can't tell you what to do with it.

What makes you think that the human mind doesn't follow laws of thought which need to be discovered? Should we abandon psychology? Logic? If it's all just thought then anything goes, right?

Molecular machine

Life is but a Molecular machine. Every plant, every animal, and yes every human. All that you see. All that is said to be alive. Is made of the greatest Molecular machines known to man. So called nature is but a forest of machinery on the molecular level.

When you "eat" food. Are you not getting new molecular parts for you own machinery. You can not eat dirt. So you must get it from those (Plants) that can.

Reference searches:

 Synthetic Biology

 System Biology

 Biology- energy conversion

 ENTROPY AND HEAT DEATH

 DNA programmed molecules

http://groups.msn.com/EvolutionBloopersVSGodCreates/general.msnw?action=get_threads&all_topics=0


http://www.worldpress.org/article_model.cfm?article_id=2153&dont=yes

Biomolecular computing is an interdisciplinary field of science which views biological systems like a PC....

--Bio-molecular-Tony 08:57, 19 Apr 2005 (UTC)

A new definition

I heard a scientist define life as "a property of the DNA molecule". Is there space for that definition here? --JiFish 11:25, 23 May 2005 (UTC)

Maybe the working programming would be closer to the truth here.

http://www.sooty.ca/gene-hacking.html "Of course the programming language is DNA and its machine code runs all life on this planet."

http://www.weizmann-usa.org/site/News2?JServSessionIdr001=tdxgmh93y1.app13b&page=NewsArticle&id=5077

'The living cell contains incredible molecular machines that manipulate information-encoding molecules such as DNA and RNA in ways that are fundamentally very similar to computation,'

http://pard.technion.ac.il/archives/presseng/Html/PR_udicomuterEng_27_2.Html

'all biological systems, and even entire living organisms, are such computers.'

'Every one of us is a bio-molecular computer, that is, a machine in which all four components are molecules “talking” to one another in a logical manner.'

--Bio-molecular-Tony 01:30, 23 Jun 2005 (UTC)

Alphabets and fire?

First, the section "Life - Just a structure of alphabets." does not seem to belong here. If anything it seems to be one out of billions of philisophical viewpoints on the topic expressed by human beings over the thousands if not millions of years we've been capable of expressing them, and is not in any way neutral, nor scientific. If anything it would belong in a "Life (Philosphical)" article rather than a "Life (Biological)" one.

Second, while fire may not fit into the neat little box presented by biological science as "life as we know it," it does at least deserve an honorable mention. Perhaps something along the lines of this:

Many people also consider fire to be alive, as it displays attributes strikingly similar to those of living things;

  • 1. It grows by heating nearby matter until it combusts and becomes fuel for the fire.
  • 2. It consumes matter in order to continue growing (this is considered by some to be metabolism. Note that fire does not actively seek out fuel, but rather fuel becomes part of the fire by being heated by the fire itself).
  • 3. It has both internal and external motion
  • 4. and it reproduces (it can split into seperate localized fires that grow independantly of eachother)
  • 5. It reacts to stimuli in the sense that a chemical reaction can be accelerated or decelerated by external stimuli.

While these descriptions of attributes of fire are certainly subjective, they illustrate how fire can be percieved to partake in life as described by biology.

I'd add that and remove the alphabets section but I'm rather new here and don't feel comfortable making edits yet. Perhaps both fire and alphabets belong in a new article titled Life (Philosophical) which compares and contrasts non-scientific viewpoints on what constitutes "life."

Also the Unsolved problems in biology insert is incredibly difficult to read, perhaps someone who's skilled in wiki coding could clean that font up a bit? And perhaps move that box to somewhere that's not in the way? Peraps a single link to the Unsolved problems in biology article in the See Also section would be a better way to go?

Kris Wood 02:26, 24 Jun 2005 (PST)

I see some sophistry going on here. First of all, people are confusing the concept of "life" with the concept of "being alive." I do not think these terms of interchangeable. I think it is safe to say that all things that are alive are lifeforms (literally, "taking the form of life"), but it is not clear to me that all lifeforms are alive. "Raccoon" is a class of animals that is a lifeform, but obviously each particular raccoon need not be alive. (I can personally testify to the existence of dead raccoons. But it seems arbitrary--and, at least in English, contradictory--to assert that a dead raccoon is not a raccoon.)

Another word confusion that I see bandied about here is with the word "stimulus." A stimulus is *not* the same as a cause. One billiard ball does not "stimulate" another billiard ball to move--instead it causes it to move. I would argue (from my limited perspective) that the relationship of cause to effect is proportionate, whereas the relationship of stimulus to response is not. If I lightly prick a billiard ball with a pin, the ball is not going to move very far. However, if I lightly prick your finger with a pin, you are likely to recoil (far in excess of the "causal power" of the pin prick). The first example is a cause, the second example is a stimulus. This is why a stimulus is generally considered unique to biological organisms. If you want to argue that something (e.g., fire) is a counter-example, then you at least need to do so in a way that respects the terminology.

--CHuRL [:Why, "at least in English, contradictory"? Contradiction doesn't depend on English languagenish (NB - new word: sensor alert, but you're welcome). And if I lightly crack your skull with a stick, can you still hear me?---shtove 04:42, 3 December 2005 (UTC)]

Good call, I was indeed thinking in terms of cause (Newtonian action vs reaction) and not biological reaction. Had I taken the time to click the link for stimuli in the article I would have understood that and not taken the time to rant about it. :) Thanks for pointing that out!

-- Kris Wood

Bio-molecular-Tony

Living systems (Life) and fire have some notable similarities, and differences.

In my viewpoint, Creatures are not alive at all. For that is an old misunderstanding of what is biology. Let me make a comparison to help clear the confusion.

Lightening strikes is like fire. In a lightening strike, high levels of energy will moved to one place to another. All things strive to achieve equilibrium (Laws of Thermodynamics). It is not alive. It is not a machine. It is not really intelligently controlled. The earth as a whole could be said to be a working system.

Fire is as non-living and non-mechanical as lightening. Life is built and functions on chemistry, but under a controlled way. Fire is not a controlled chemical reaction. Our electronics uses electricity in a controlled way. Lightening is electricity not in any controlled way.

Our electronics is intelligent use of energy under controlled conditions. Our designs are called machines.

So what then is this so-called life we see. Is it not intelligently controlled use of chemical energies, in a molecular chemical way? Are we not machines built on chemistry? Could chemistry ever be called something alive? Think about it hard. It hurts, but this new view is needed for us to move forward in science.

Bio-molecular-Tony

--24.42.133.215 13:04, 7 August 2005 (UTC)


A candle flame

The article states that "This definition, in use by most biochemists, makes it clear that fire is not alive, because fire releases all the oxidative energy of its fuel as heat."

This is not true. A candle flame uses a tiny but life supporting part of the energy for convection that transports freshly vaporized wax to the reaction zones. 84.160.201.148 12:11, 9 October 2005 (UTC)

Yes and doesn't a candle flame also die down or burn faster in different conditions?raptor 12:46, 3 July 2006 (UTC)

Unsolved Problems in Biology?

The sidebar ("Unsolved Problems in Biology") reads: "Did life start on this planet or was there an extraterrestrial intervention?" Call me cynical, but I doubt that this is serious topic of biology. Even ignoring the dubious reference to "extraterrestrial intervention," I think that the overriding assumption in biology is that life *did* start on this planet, but that it is not yet known how (hence the need for some of the *other* questions raised in the sidebar). Even if, some time down the road, it was decided that life must have originated from somewhere other than earth, it does not then follow that an alien species "intervened" to bring it here (nor could such an intervention ever serve to explain the origin of life in general). For that reason alone, the question is simply not relevant to modern-day biology. But FURTHERMORE, even if (again, some time down the road), such an explanation was deemed plausible and even likely, determining whether or not it happened would be a problem primarily for historians, not biologists. (Of course, the science of biology can always be brought to bear on such issues, but saying that therefore it is a "problem of biology" is just ridiculous.)

In light of this I am removing the question from the sidebar.

--CHuRL

I'm still in favor of removing the sidebar altogether and instead putting a link to its main article in the see also section at the bottom. The sidebar itself serves no purpose except to clutter this fine artcle on life, just as it clutters a few other articles around wikipedia for no aparent reason. The sidebar's article itself has been nominated for deletion. The article it refers to would still be accessable via the link, and we'd have more room on the page.

-- Kris Wood

Neutral?

This article repeatedly attempts to define life in a way as to separate it from the non-living. It goes back and forth, suggesting a possible definition, then giving exceptions, then suggesting another million other definitions, then more exceptions. The organization makes it look exactly like what it is trying to do: make life unique and precious. This hardly seems neutral to me. If we can allow a small section on something as arbitrary as "extraterrestrial life", surely we can stick in yet another concise definition of life that doesn't bother with this futile attempt: "The only difference between living and non-living is complexity." Or do we need a separate article on why people need to define life? — BRIAN0918 • 2005-09-20 02:46

Trying to define life is a useful exercise; it forces people to look in more detail at something they take for granted. I agree that complexity is an important part of many living systems, but not all complex systems are alive. The article should probably discuss the features of the most simple system that we would want to call "alive" and why living systems can evolve towards greater complexity. There is no obvious boundary between the living and the non-living. I'd probably be willing to call a set of self-replicating polymers "alive", and such a minimal life form would not be nearly as complex as what we usually think of when we think of life. --JWSchmidt 04:16, 20 September 2005 (UTC)
Well, if there is no boundary between living and non-living, shouldn't we merge Life with Rock? :) — BRIAN0918 • 2005-09-20 04:31
The argument for abandoning use of the life/non-life distinction seems to go like this: some people have imagined that life is due to a Vital Force. Since nobody can find such a force, but rather we find that everything is made from dead matter, we should give up on the idea of "life". The problem with such arguments is that they are built upon the wrong conceptualization of what life is. Life is not due to some additional non-material stuff that is added to material objects like using pixie dust to allow objects to fly. Life arises (see: Emergence) in material systems from special configurations of the non-living components. The science of Biology and the new field of Artificial life are concerned with careful study of of how life can arise from non-life. Most of the time, people just make use of "rules of thumb" for thinking about the disctinction between life and non-life. The problem with these "definitions" of life is that they are useful approximations that can only usefully be applied to a restricted set of circumstances. Thus, we have the content of the Life article where the various "rules of thumb" are listed and people point out how they are limited. I understand the objection about efforts to find a simple way to define life so as to show that life is unique and precious. However, people have evolved so as the feel that life is precious and we have also inherited a huge cultural support system for that feeling. Would it make the article "neutral" if it included an explicit statement about why people often prefer an explanation for life in forms such as "it flows from the finger of God"? --JWSchmidt 13:59, 20 September 2005 (UTC)
"Due to" connotes debt, and nothing more; you should use, "Owing to", connoting cause. It's a close argument, so the distinction is worth it. From: your friendly lawyer.--shtove 04:48, 3 December 2005 (UTC)

A virus should be considered alive...

...after it co-opts the machinery of a host cell for replication. It meets all the standard criteria for life, including the existence of a cell. The cell just happens to be stolen. A free virus, on the other hand, is not alive because it lacks a cell. This transition from potentially alive to alive exists throughout nature. A Judean date palm seed that was unearthed last year had the potential for life for 2000 years, but did not realize that potential until someone put it in the right environment to sprout. Don't biologists categorize viruses as "sometimes alive"? If so, I think this should be reflected in the article.

Also, I think fire and stars should be removed from the "Exceptions to the conventional definition" section. They are not alive and, therefore, not exceptions.

Any comments would be welcome before I jump into this article with my machete. --Gavin 05:21, 5 January 2006 (UTC)

I agree, and also have beef with this:
(most) mules and people who are infertile cannot reproduce and thus would not qualify as lifeforms. Also worker bees and other organisms living in colonies would not qualify; only the queen and the drones (or the whole colony) can be considered 'alive'.
1. Mules and infertile people are products of species that are capable of reporducing. Maybe the "reproduction" definition should be rewritten to be more inclusive.
2. Worker bees are capable of reproducing (correct?), they just don't.
71.65.54.92 05:40, 5 January 2006 (UTC)
If reproduction is replaced with the product of reproduction, all lifeforms would be included. To be living, an entity doesn't need to be able to reproduce, but it certainly must be the product of reproduction. This would remove an entire class of exceptions. Can anyone point to a flaw in this argument? --Gavin 06:10, 5 January 2006 (UTC)

"biologists categorize viruses as 'sometimes alive'" <-- If you want to say this in a Wikipedia article it is up to you to document it as a fact. If you bother to do the required literature search, expect to find many more published statements by virologists who do not take this position. "including the existence of a cell" <-- saying that a virus is using the metabolic resources of a cell does not mean that the virus is a cell or has a cell. It means that the genetic instructions of the virus are being expressed by the infected cell. That host cell is part of another organism. The infected cell does not become part of the virus upon infection. About viable seeds; if a seed can grow that means it contains living cells. Such a seed contains a living embryo. The seed is alive and has the potential to grow. --JWSchmidt 14:15, 5 January 2006 (UTC)

I remember long ago when I studied biology, I didn't like the rather arbitrary cutoff of what is considered alive, between bacteria and viruses. Personally, viruses seem far more alive than inanimate to me. The cell part of the definition seems inessential (it is the fact that the object is held together in some way that is more significant, and a virus manages this adequately. The thing that really sets viruses apart is that they are parasitic on such a small scale, requiring the machinary inside another organism's cells. To me, this makes them no less alive than larger parasites are. If life is considered from the selfish gene point of view, the genes that characterise viruses have just found an unusual way to ensure their replication from one generation to the next. Elroch 01:16, 24 May 2006 (UTC)

The article's Introduction

I see some stuff in the article's introduction about life beginning at conception. I find this strongly biased in favor of sexual creatures. It completely excludes non-sexual life such as ferns, mushrooms, and many single-celled creatures.

Aside from that, it may even be a political message from the pro-life camp of American politics. I think that the word "conception" should be removed from the article's introduction. Zaorish 19:32, 27 January 2006 (UTC)

The change was introduced by 68.102.26.204 at 06:35, 27 August 2005 diff and his contributions do have a religious slant. I've changed it to fertilisation, although the original version says birth. The IP address in question does have a history of vandalism. The IP address maps to Wichita, Kansas, US geolocation. - Samsara contrib talk 19:56, 27 January 2006 (UTC)

Distinguishing life from non-life

I find the definitions unsatisfactory – for reasons others have given and more.

Why couldn’t life be non-corporeal? No cells, no organism, no metabolism. What if AI develops on the internet and starts talking to us? Think of Hal from 2001, A Space Odyssey. What if it declares (indignantly) “I am alive.”? Definitions of life would become irrelevant. If it demands some rights, it will be not only accorded life status but human status. Perhaps it will grow but is that essential? Presumably it will evolve but is that required for us to concede it is alive? It would no doubt have to use energy but so do all machines.

As a systemic definition, Francisco Varela and Humberto Maturana's is descriptive and restrictive. Stuart Kauffman's depends on the meaning of “autonomous” which he seems to draw empirically from practical biology. From the mentions of fire and computer programs and much else it is evident that we are seeking a distinction between life and non-life. I have a couple of suggestions.

One difference between life and non-life is that a life-form has a problem – it has to avoid joining the non-living. It has to work at staying alive. To succeed it has to ensure that available resources match its needs. Non-life has no problem. It becomes life when it is eaten (or as light, absorbed) and takes no steps to avoid it.

Another difference between life and non-life is in interaction. For life forms it is active, not passive, and it is active in three distinct ways: competition, cooperation and coercion. It seems to me that these three kinds of interaction do not exist outside of life, that there is no other kind of active interaction and that all three pervade life at all levels, operating at the macro level (lions, daffodils), the micro level (germs, blood cells), and at the molecular level within living cells (viruses, hormones).

It also seems to me that of the three forms of interaction, competition is paramount, that the other two serve and moderate competition, that competition may occur without the other two but the other two cannot occur without competition being present. For example you coerce (say, point a pistol) in order to extract something (money, sex) that will give you competitive advantage. For example you cooperate (say, in a fishermen’s coop) in order to better compete (in the fishing industry).

I think the “problem of matching needs and resources” and the “three forms of active interaction” are clear markers of the systemic difference from non-life. They also resolve some of the boundary problems (mules are life, viruses are life; genes are life, mitochondria are life, fire does not get a look in).

But they are just my thoughts. I do not know if anyone else has made these connections. – Pepper 150.203.2.85 05:15, 13 February 2006 (UTC)

Wording

"It would be relatively straightforward to offer a practical set of guidelines if one's only concern were life on Earth as we know it." I don't think it would be straightforward to define life on Earth (viruses? the abortion debate?). I also don't think it's NPOV to say it would be straightforward. Kai 06:17, 27 February 2006 (UTC)

current event

This article documents a current event.
Information may change rapidly as the event progresses.

Should the article be indicated as a current event? :) →AzaToth 21:36, 20 March 2006 (UTC)

bacteria has been shown to survive on the moon

Terrestrial bacteria apparently survived on the moon for 3 years - see Surveyor 3 and Forward-contamination. We have an example of life surviving (albeit not thriving) without life-support in an environment external to Earth. Should the paragraphs in the article on "The possibility of extraterrestrial life" be changed to reflect this? RevJohn 04:39, 8 April 2006 (UTC)

Information-based definition

It would be good to include one of the definitions of life based on information that I am sure I have seen somewhere. The basic idea being that life is something which has an detailed digital description of itself and is able to preserve that description from one generation to the next (or in most cases mixtures of closely related descriptions) in a suitable environment. Elroch 01:05, 24 May 2006 (UTC)

Article structure: Moving beyond the definition

Life is notoriously difficult to define. However this article is about life, and not about its definition. As such it should move on quickly from the definition (or difficulty there of), to text about life itself. If the article can't do that, it should be renamed to something like Definition of life controversy or something equally bland. —Pengo 00:28, 3 July 2006 (UTC)

Good Idea raptor 12:47, 3 July 2006 (UTC)
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