What constitutes life?

[AltF4]

I read an interesting article I found off of Digg (which you can read here) that really got me thinking, what constitutes life? How do we exactly go about saying one thing is "alive" and another "not alive".


The question appears to be quite obvious when speaking about things we are very familiar with: IE humans, cats, dogs and mice clearly exhibit behaviors and qualities that rocks and stones do not. But there are many gray areas which demonstrate how fuzzy of a line the divider between "living" and not "living" can be:

Take for instance the problem with determining when someone (or something) is dead. How exactly do you determine when someone is dead? When their heart stops beating? Well, then you have an interesting phenomenon where people "die" and then come back to life quite commonly during certain procedures. Clearly we want our definition of "dead" to be such that it is irreversible. Someone should not be able to come back from the dead. But other forms of determining if someone is alive or not include less quantified approaches like loss of higher brain functions.

Secondly, this issue is manifested in the problem of classifying what does and does not classify as "life". Like mentioned previously, we all can agree that humans should fit under the classification of life, and that rocks should not. But what about a virus?

Life as we know it is comprised of cells, the basic building block of (at the very least) the majority of what we call life. These cells range in size, but are generally in the 200 nanometer ballpark. Viruses (and the new "nanobes" in the article mentioned in the beginning) are many times smaller than this, and are not comprised of the same building blocks. Many people use this to claim that they should not count as life, but on the other hand, they do still have DNA. I for one feel reluctant to call something with its own DNA "not life".

Viruses (which btw, should really be pluralized as "Virii") also seem to exhibit many of the qualities that we typically associate with living things, with the notable exception of needing a host to sustain itself. Making it a good topic for debate, indeed.


Lastly, are the implementation details important to being classified as life or not? Put it this way: All life as we know it is "carbon based", but why can't life be accomplished in another way? If we met an alien in a flying saucer which was not carbon based, surely we wouldn't classify them along with rocks as being "not alive" right?

Well, then why should robots be considered "not alive"? If you were to meet Data from Star Trek, would you classify him as alive, or not?



To begin actual debate, I hold the opinion that carbon chauvinism is silly and that a sufficiently sophisticated robot should certainly be classified as alive in a way no different than a human. This would stem from a classification of life based not on what it is made of, but what characteristics and behaviors they exhibit.

 

[Jack Kieser]

I don't think physical makeup is a definitive factor in 'being alive'; for instance, I consider the Geth from Mass Effect to be alive, even though they are a synthetic race. I've actually thought about the problem with Virii classification before (as part of a pro-life/pro-choice debate I had with a few friends, as a matter of fact), and it is indeed an intriguing question, as well.

Personally, I would consider something to be 'alive' if it can take an action, in some capacity, independent of outside stimulus. Rocks, for instance, can't do this (they can 'take action' in the form of transmuting into another type of rock, but that is through outside stimulus like heat and pressure), but Virii can (they search out cellular structures to inhabit on their own). As far as pronouncing a person dead, this definition has the fault that a person would be considered 'fully dead' when action can no longer be taken independent of anyone helping it, which can be interpreted liberally (when a person becomes brain dead) or conservatively (when all cellular functions stop).

 

[manhunter098]

Viruses actively search out host cells? I was of the belief that they simply floated around until they bumped into one and that would trigger them to infect it.

Either way, in my opinion for something to constitute life it needs to undergo some form of metabolic process and have DNA.

 

[AltF4]

Well, now, Jack... Without diverting this into a topic about Free Will (see my thread on that topic) nothing can act without stimulus. To do so would violate causality. So you really can't classify life using that.


Manhunter:

What is special about metabolic processes? Or better yet, what constitutes a metabolic process? (Perhaps there's already a rigorous definition for this from biology that I'm just not familiar with)

I agree that using that definition may be very accurate in classifying the life forms we're familiar with. But the problem I have with it is that it doesn't adequately cover forms of life we may not have observed yet.

As in my previous example, the problem with using implementation details to classify life is that we have no reason to believe the way we're familiar with is the only way. Little green men in flying saucers could conceivably be based off of a completely different infrastructure, and yet we'd still call them alive.

 

[manhunter098]

Well as I understand it, metabolism is pretty much just breaking down molecules and then using the energy produced for various biological processes. I think, that in order for something to have any of the more philosophical aspects of life, like free will, or acting on its own, etc, that it needs to be able to consume some chemical to be turned into energy, because without any energy it cannot do anything and is nothing more than a complicated lump of various compounds. I threw DNA in there because I feel that life needs to have something like that, but I suppose it doesnt necessarily have to be DNA filling that role, anything that would have the same effect as DNA would qualify for that I suppose.

 

[Kur]

I would call any chemical chain capable of splitting, reproducing with variation, and repeating the process, life.

Basically, any chemical that can evolve. This would be anything with DNA, RNA, or even some other simpler chemical chain or precursor to RNA. It is from this that all life on earth originated so it should be the bench mark of what constitutes life.

At least in terms of life on earth.

I agree that it is unlikely that an alien species would be carbon based, or resemble any animal on earth in any physical way. So to find what constitutes life for their world would require finding the simplest forms that those creatures evolved from.

As far as robots, androids, data from star trek, etc. I would not classify them as life, though I might call them alive. I would certainly afford a conscious entity (natural or robotic) the basic rights of life, but if it came down to the 'life' of the robot vs. the life of a person, the person wins. And I would define consciousness as an entities ability to project itself into the future and make decisions in the present based on that. There must also be a level of self awareness. Though I understand why a lot of people have a hard time defining what consciousness is, but we know it when we see it, usually.

No matter how sophisticated a robot may be, it is still just a construct, an unnatural tool created by humans. It can be reduced to a collection of the most basic parts and wires and be rebuilt to perfect working order.

Unless of course we create them with some sort of self replicating chemical chain as a base. A robotic DNA if you will. If robots could reproduce in such a sense I would probably call them life.

 

[Zero Beat]

As far as robots, androids, data from star trek, etc. I would not classify them as life, though I might call them alive.

Life seems to be a very fluid word in this thread. So I'll be careful..

In terms of robots, I'd go as far as saying "they're aware of what's going on." But that's about it.

 

[OffTheChain]

I would say an active brain best determines if something is alive as it is what regulates almost any function, robots can be programmed to feel what we do so as long as something is acting as a 'brain' I would say they are alive and in that case can die.

 

[derek.haines]

That's a **** good question (though it could descend into abortion debate terribly easily), and I'm not sure that I've any better answer to it than anyone else. I think that the capacity to make reasoned decisions about one's own self-preservation would be my basis for life. If a robot would value it's existence enough to defend itself, then I would not hesitate to call it alive.

 

[applejack]

I think that for something to be alive it needs to be able to have some type of choice. "I think, therefore I am." A virus is motivated only by survival needs, and is unable to survive or even reproduce without a host.

 

[manhunter098]

I think that for something to be alive it needs to be able to have some type of choice. "I think, therefore I am." A virus is motivated only by survival needs, and is unable to survive or even reproduce without a host.

I am relatively certain that bacteria do not think (nor have any other kind of free will independent of the possession of thought), they are more like a complex self sustaining chemical reaction factory that simply react to stimuli.

 

[applejack]

For the microscopic organisms I hold to the biological defintion of life, part of which says that the organism's species is able to reproduce by itself, and viruses are unable to do that still.

 

[Johnthegalactic]

In biology I was told life is the ability to respond to your environment, and some other stuff.
Such as living organisms cannot enter a crystal state and survive, hence, a frost bitten area must normally be removed, plus they must be able to reporoduce.
Tree's are living, sponges are, lol, my biology teacher got two people into a fight, when they said all animals go to heaven, she asked them if sponges do, one said yes, one was thinking of that thing they clean dishes with.
But, viruses reproduce,well more like replicate themselves, and can be crystalized and still function, but they require a host cell to replicate themselves.
Anyway, my biology teacher couldn't explain why they weren't living or dead.
I proposed the idea, that they are biological machines, organic machines that can replicate themselves and function without commands from an outside source.

Anyway, I thought that i would offer my input.

 

[Reaper0329]

A life in my opinion is anything self-aware or has potential to become self-aware. So while neither a cell nor a embryo is self-aware, the embryo will eventually (in the natural process) become offspring, a life. An advanced artificial intelligence is also a life, although an unnatural one in my opinion.

 

[~L~]

I think that for something to be alive it needs to be able to have some type of choice. "I think, therefore I am." A virus is motivated only by survival needs, and is unable to survive or even reproduce without a host.

I do not think this post is very clear. It seems to me,that you are saying nonsencience=dead.


I am very certain that ants do not think. But I'm also certain ants are considered alive.
Ants only react. Whether that be due to pheramones or other outside stimuli.

 

[derek.haines]

It seems to me that what we really need is different definitions of life to fit each type of life. Bacteria and viruses are biologically alive, but subsist only through little more than programmed responses to stimuli--they are incapable of such complex thought as "I think therefore I am." Insects would be a step up from this, able to deviate from those programmed instinctual habits for their own survival, but still not capable of understanding perhaps that they are even truly alive.

Most non-human animals would be another step up, allowing for an element of free will but still largely governed merely by instinct. Humans sit atop this plateau, mixing fully between random freely allowed choice and instinctual governing. For robots, it would be necessary to harbor a completely different definition.

I don't think there's just one blanket definition that can be thrown over the whole of "life" to call it alive.

 

[AltF4]

Here are some commonly proposed definitions of "life", ripped right from Wikipedia. We can use this to help things along.

1. Living things are systems that tend to respond to changes in their environment, and inside themselves, in such a way as to promote their own continuation.[7]
2. Life (a living individual) is defined as a network of inferior negative feedbacks (regulatory mechanisms) subordinated to a superior positive feedback (potential of expansion, reproduction)[8]
3. Life is a characteristic of self-organizing, self-recycling systems consisting of populations of replicators that are capable of mutation, around most of which homeostatic, metabolizing organisms evolve.
4. Type of organization of matter producing various interacting forms of variable complexity, whose main property is to replicate almost perfectly by using matter and energy available in their environment to which they may adapt. In this definition "almost perfectly" relates to mutations happening during replication of organisms that may have adaptive benefits.
5. Life is a potentially self-perpetuating open system of linked organic reactions, catalyzed simultaneously and almost isothermally by complex chemicals (enzymes) that are themselves produced by the open system.

 

[derek.haines]

Those are pretty good definitions, and for the most part they fit almost every imaginable type of organism--including robots. I'd call into question the final one on the list, as organisms from other planets might not be governed by enzymes or specific chemical reactions, but the rest of them seem solid.

 

[AltF4]

But are they? The fun part about this topic is that we already have a rough estimate of what it means to be "alive" versus "not alive". But putting exact terms on it is difficult. We want our definition to include humans under life, and include rocks under not life, yes?

Well, #2 could potentially include crystals (a rock). Crystals take minerals from the outside world, change them, and use them to grow and expand.

#1 is VERY general. Robots would certainly fall under this category, as well as lots of regular machines without even computers running them.

 

[derek.haines]

So that would question the "aliveness" of a alien gas creature, for example. I can't help but feel that the definition for life will ultimately end up being more one of philosophy than biology, but it's always going to depend on who you're talking to. This debate will no doubt really be brought out further as artificial intelligence continues to advance.

As an aside, I discovered this website: http://www.beyondbooks.com/lif72/2c.asp
It's a bit on the silly side, but there's some good information in there, and it does specifically address the question of whether or not a virus meets the criteria for life. If a virus can still be considered life, yet not meet all of the criteria for it, then why couldn't some even odder potential alien lifeforms?

 

[Peeze]

Just gonna attack this from a simple perspective but, if it can be killed it's alive, since death is the opposite of life?

 

[derek.haines]

To understand death don't we first have to define life?

 

[EC_Joey]

I'm going to deviate from popular belief and current scientific thought here.

I see everything that we define as "life" as complex systems that act against the tendency of the universe to move towards disorder.

What we define right now as "life" possesses characteristics that people have already posted, but the most important of these is the ability to reproduce. All the other characteristics contribute to this one purpose, because you are more likely to reproduce if you "live" longer. I believe these characteristics of "life" are simply methods of keeping matter organized and collected, rather than disorganized and dispersed. Your body keep foreign materials out, while utilizing those that are needed.

However, the complex system that is your body cannot keep this process up forever, it will eventually fail. So in order to continue this process of perpetuating organization and order, your body tells you to reproduce, and thereby give form to another body. This continues the rebellion against the universe's tendency towards disorder and chaos.

I think the concept of "life" has been romanticized to the point that it is regarded as spiritual. It is a notion that has been used to give human beings a feeling of being special, much like how humans used to believe that the universe revolved around the Earth.

 

[derek.haines]

I have trouble defining life as the "ability to reproduce". I guess, "potential" is a better word for it, because to use "ability" would mean that people who are sterile would technically not be alive... Reproduction is even a sketchy idea, because many creatures don't reproduce in a classical sense but rather clone themselves, more or less.

 

[Chaco]

Alt, this question is commonly used towards abortions. Many people who are against abortions have different time lines of when life begins, is it a certain amount of months,days, etc. You see that if they can ever truly define when life begins, you could not have an abortion beyond that point. It would be considered murder. So when this has been brought up in courts, the answer is always the same. "We do not truly know when life begins?" So, really how could you classify when exactly life begins? They would have to define a certain time in the developmental cycle to be the point at which life begins. I really don't believe that they can make an accurate assumption at what point life begins.

 

[EC_Joey]

I have trouble defining life as the "ability to reproduce". I guess, "potential" is a better word for it, because to use "ability" would mean that people who are sterile would technically not be alive... Reproduction is even a sketchy idea, because many creatures don't reproduce in a classical sense but rather clone themselves, more or less.

I'm not saying the ability to reproduce determines whether something is alive or dead. My main point is that all things considered "alive" struggle to maintain order in a universe of disorder. Reproduction only serves to assist in this purpose.

 

[AltF4]

Chaco:

No, I think that's a slightly different question. When debating abortion, you try to determine when the developing child (for lack of a better term) becomes "human". It is certainly "alive" in the sense that we are using the term here. It is made of cells which are reproducing. At any developmental stage, it is "alive" in the same way that we say bacteria is alive. The debate with abortions entails determining when those collections of cells becomes human.


Essentially my position is one stemming from materialism. There is no higher meaning to the word "life" or "human". We are all just collections of atoms interacting according to the laws of nature. It doesn't matter if you're a dog or a rock. So labels we put on things are just arbitrary constructs that are inherently inaccurate, because the world is under no obligation to facilitate our want for categorization.

 

[EC_Joey]

Essentially my position is one stemming from materialism. There is no higher meaning to the word "life" or "human". We are all just collections of atoms interacting according to the laws of nature. It doesn't matter if you're a dog or a rock. So labels we put on things are just arbitrary constructs that are inherently inaccurate, because the world is under no obligation to facilitate our want for categorization.

My thoughts are essentially the same, but I can think of no examples apart from life-forms which actively perpetuate order. By this I refer to processes that run counter to entropy.

For example, every cell in our bodies creates proteins from specific arrangements of amino acids. While this may occur randomly without the presence of life, a cell is like a factory in this sense, collecting building blocks and fitting them together to create a functional product, rather than depending on this process naturally occurring.

 

[AltF4]

I see what you're getting at, Variola. But I can't come up with a good definition of life using the concept of entropy that wouldn't include crystals.

Crystals clearly become more ordered over time, and they grow too. But we don't want to be classifying rocks as life.

 

[Kur]

Such as living organisms cannot enter a crystal state and survive, hence, a frost bitten area must normally be removed....

There are some species of frogs and toads which freeze completely solid during the winter in parts of north eastern US and Canada.

There are also many simple life forms that completely dehydrate and many years later (over 100) can be revived by simply putting them in water.

Do some research on the "Water Bear" or "Tardigrade" you will be amazed at just what some life can survive.

I see what you're getting at, Variola. But I can't come up with a good definition of life using the concept of entropy that wouldn't include crystals.

Crystals clearly become more ordered over time, and they grow too. But we don't want to be classifying rocks as life.

Maybe we do?

It was mentioned early in this debate that extraterrestrial life may not be carbon based. If it was based on some other element, say, silicon, then that life may very well be not much more than a crystal.

Maybe there are some silicon based life forms growing on earth right now, several miles under the earths crust, or at the bottom of the ocean. Probably not likely, but entirely possible.

We have a tendency to associate life with soft squishy things. We envision aliens as basically humans but with exaggerated features like large eyes, green skin, big heads, etc. When in reality why would life that is not related to anything on earth, look like anything on earth?

I wonder if we would know an alien if we saw one. I wonder if aliens would even be of a size we can comprehend. Why would they not be microscopic? Does intelligence really require a large size? It does to a degree by our standards of life but a microscopic crystal alien may only need to be a few microns wide to get the job done.

Just something to think about.

 

[manhunter098]

But any form of life also has to be somehow active. So even a silicon based life form, would still process chemicals for energy much like a carbon based life form. Its structure might not really be something we can understand, but to fit a given definition for life it still needs to fit that definition. Just because its silicon based doesnt exempt it from needing to fulfill the conditions determined to qualify as life.

Also, its entirely possible that silicon based life wont work, but we dont know for sure, the entire idea with silicon based life though is that it could work with oxygen or sulfur, since silicon has very similar properties to carbon.