April 5th, 2010, 02:28 PM
Assume you have a simple solar powered device. The device uses solar energy to absorb minerals from the ground, and it's computer chips have information on how to use those materials to construct an exact replica of itself. Would this living? Can all living things reproduce? What are the characteristics that all living things share?
descent with modification, i.e. reproduction with marginally flawed inheritance
My robot could occasionally have a flaw in its reproductions.
as long as it is an accidental flaw that can be inherited then yes, your robot could be considered alive
http://en.wikipedia.org/wiki/Asexual_reproduction
Would a plant reproducing with Asexual Reprod not be considered alive? After all, there would be no genetic flaws so bvy your logic it would not be considered alive.
Asexual reproduction still involves DNA replication, so some flaws will be passed on.
If anything, Marnix's definition is too broad not too narrow.
Wuh? Mutations still happen in asexually reproducing organisms...Originally Posted by CrimsonViper
The characteristics that define life are not straightforward definitions, but deeply ambiguous ones that continue to cause heated debate within scientific circles.
However, the general consensus continues to be one in which all life forms are composed of cells, have access to an energy source (require energy), reproduce, display heredity, respond to stimuli, evolve and adapt, and maintain homeostasis.
That said, viruses continue to be bodies raising contentious issues. Six of the seven essential characteristics are here met. However, they are not made up of cells, and therefore may be classified as both inanimate and living, depending on the precise classification.
Similarly, your solar powered device might also fall on the first hurdle by virtue of its non-cellular construct. Additionally, the act of replicating an exact copy of itself will also rule out a further common characteristic: evolution and adaptation. And, now that i think of it, does your replicated copy undergo growth?
From my university microbiology notes.
Life is defined as having the properties of
1. Reproduction
2. Evolution
3. Being a complex system based on organic molecules.
Having said that, I know damn well that the third condition is there only to exclude such things as computer programs and such things as the proposed robot. My own view is that the only two qualities that are essential are 1 and 2.
I read a scifi short story once about humans that had travelled a vast distance through the galaxy, and close to the speed of light, so that time passed slowly. When they reutrned to Earth, many millions of years had passed, and a full robot ecology had taken over. Robots that reproduced, but with occasional 'mistakes' so that natural selection could occur. If such a thing happened, those robots would be life.
I've always found it extremely weird that the very subject matter of biology - life - has no real standard definition. A quite bizarre situation I think. When something doesn't meet all the criteria in a particular definition of life, like viruses, it's often useful to ask if there is something wrong with the particular definition you are using rather than to exclude the candidate organism. Is the definition broad enough, for example?
Being chemical-based and possessing a metabolism could rule out the robots, I suppose.
Your definition seems arbitrary and incomplete. Must life reproduce? Could something exibit a nearly complete range of biological processes including growth and change but not reproduce? Would we call this non-life?
Likewise must something reproduce imperfectly in order to be called life?
what's so arbitrary about it ? do you know of any organism that does not reproduce (even if it's cloning or budding) ? and do you know of any organism that reproduces without some defect in the transcription of the genetic code ?Your definition seems arbitrary and incomplete. Must life reproduce? Could something exibit a nearly complete range of biological processes including growth and change but not reproduce? Would we call this non-life?
Likewise must something reproduce imperfectly in order to be called life?
unless you do, and you can point them out to me, your objections are hypothetical and not at all supported by any evidence
I can suggest something that reproduces and which is not living. Fire.
A forest fire spreads from clump of forest to clump. It grows. it consumes fuel, respires, excretes and reproduces.
The thing it does not do is change. There is no evolution. Life changes and evolves.
Well yes fire does change, depending on the conditions - for example, a flame can be bigger or smaller, and varied in colour.
But the changes are not passed on in "reproduction" - if you set fire to a forest using the yellow flame of a candle or the bluish flame of a gas torch, you get the same forest fire.
Read this definition of life by Bernard Korzeniewski.
I'm not sure if fire would meet these specs.In this formulation, life (a living individual) is defined as a network of inferior negative feedbacks (regulatory mechanisms) subordinated to (being at service of ) a superior positive feedback (potential of expansion).
But I am sure any proper definition of life must leave out such adventitious details as being based on carbon and water and DNA or organized in cells. You could just as well define a computer as "an electronic device capable of..." and then, when somebody builds a purely photonic, or phononic, or quantum machine capable of the same operations a million times faster, dismiss it as not being a computer because it doesn't run on electricity.
The lack of a crisply delineated definition may speak to the wide, almost infinite, variety of life. Instead of "simply" defining Life = A+B+C, it may be more complicated, such as Life = (A+B+C) or (B+C+D) or (A+C+E+F).
I would suggest that, in the least, a living thing contains complete replication information and involves chemical reactions. I also get the impression that living things live in some sort of hostile environment due to the presence of other living things, and that they all have at least one means of defense or competition (although this may be hard to define further). That is, some minimum inherent understanding of self and non-self.
I don't think you would find this to be the consensus view among astrobiologists.On the other hand there is - demonstrably - no consensus view. At a recent astrobiology conference an attempt was made to define life. I believe over one hundred definitions were offered.
indeed - there's no inheritance involved, hence there can be no descent with modification
Just a small point here.
We do not need a final definition of life.
We just need one that works today. And today, the only living things known are carbon based, nucleic acid data based, water solvent etc. Our definition need only cover such life.
We do not need a definition to cover the famous phrase of Mr. Spock.
"Yes, Jim, it is life, but not as we know it."
If and when some new version of life is discovered, we can change our definition to fit. For now, one that just covers organic Earth life is fine.
Decent questions. Since we may one day create artificial minds, which may well consider themselves to be alive, defining life in terms of reproduction may well not be the way to go. Or would we consider these to be non-living minds?Your definition seems arbitrary and incomplete. Must life reproduce? Could something exibit a nearly complete range of biological processes including growth and change but not reproduce? Would we call this non-life?
Likewise must something reproduce imperfectly in order to be called life?
The definition agreed upon here is a requirement for life that emerged without design.
Marnix the original question was hypothetical as was your second response, The entire thread is based on speculation about some future entity and whether or not (assuming it were produced) it should be considered alive. Hypothetical situations seem quite appropriate.what's so arbitrary about it ? do you know of any organism that does not reproduce (even if it's cloning or budding) ? and do you know of any organism that reproduces without some defect in the transcription of the genetic code ?Your definition seems arbitrary and incomplete. Must life reproduce? Could something exibit a nearly complete range of biological processes including growth and change but not reproduce? Would we call this non-life?
Likewise must something reproduce imperfectly in order to be called life?
unless you do, and you can point them out to me, your objections are hypothetical and not at all supported by any evidence
I guess I missed the part where agreement was reached. Why must life not be designed? Does that mean the human designers can never make a new life form?Decent questions. Since we may one day create artificial minds, which may well consider themselves to be alive, defining life in terms of reproduction may well not be the way to go. Or would we consider these to be non-living minds?Your definition seems arbitrary and incomplete. Must life reproduce? Could something exibit a nearly complete range of biological processes including growth and change but not reproduce? Would we call this non-life?
Likewise must something reproduce imperfectly in order to be called life?
The definition agreed upon here is a requirement for life that emerged without design.
I agree. Could prions be defined as a toxic enzyme.
I never said that life cannot be designed, nor that human designers can never make new life. I said that descent with modification is logically a requirement for life that emerged without such intervention. Whether such emergence is possible is beside the point.I guess I missed the part where agreement was reached. Why must life not be designed? Does that mean the human designers can never make a new life form?
Yes, I see that now. Thank-you for the clarification. I see though that the original post and the thread included an example that would require a more inclusive definition that would include designed objects. So how about it? Must life reproduce? Can life be designed?
i'd venture as a guess : yes, and yes
No life doesn't have to reproduce. Mules are alive, and so are monks and nuns.
I would say that a living thing need not be capable of reproduction itself. It must either have arisen by reproduction from something capable of that function, or by design from something capable of design (which may or may not have the capacity to biologically reproduce). I suspect that life can be designed by life, and probably designed with great variety and with or without the capacity to reproduce. How we build an inclusive definition with all this in mind, I would really have to think about.
sorry, i phrased that badly, didn't i ?
what i meant (and TheBiologista already provided a similar answer) is that life has to be at least the result of reproduction, even if the organism in question can't or won't reproduce - but still i consider reproduction to be an essential ingredient of life
But, if "something" didn't reproduce to create new individuals, then mules, eunuchs, monks and nuns (as "species") would go extinct. It's not as though something could die, and then reassemble and reanimate itself. Right? :?
Don't think of them as species, think of them as naturally arising varieties within the species, the species will continue on even though these small segments of the population don't contribute to the offspring pool
As I said earlier. There are three conditions for life. Reproduction. Evolution. Complex organic systems.
Fire can reproduce and is not life. A computer program can evolve, and is not life. Put the three together, and only life fits the definition.
I still have trouble with the third condition, personally. I am not sure the word 'complex' should be there. It is there, I suspect, because the authors wanted to eliminate viruses as living things. I am not sure that is valid.
My own view is that viruses should be considered to be alive. After all, they reproduce, evolve, and are based on nucleic acids. In my view that makes them living. The fact that they need other living cells to provide for their metabolic requirements is irrelevent. This is common among parasites.
Skeptic, I don't understand evolution as a requirement for life. While evolution seems to be a requirement for adaptation, why should we require it in a definition of life? to me it seems to be mixing up is (that populations do evolve over time) with should or must (it is not clear that a population must evolve). Do we say that satis disqualifies and organism from being considered life?
Maybe the formula for life is simple:
Maybe there are no definite "rules" to life!!!! Anything is possible and maybe it is possible for something to exist without a precedent!!!! Therefore, the law of Cause and Effect may not always be the case!
There might be "Cause and Effect" and then there might be "Chaos", where everything happens without reason.
After all, scientists have found species of animals that don't "need" water, although most animals and plants do. That's just evidence that there might be no definite rules after all!
I believe I have evidence for "Chaos" and I SWEAR on this case!:
About a few months ago, I was sitting on my computer in the computer room focused on surfing the internet. Behind me, I heard bells ringing from the room right next to the computer room, so I turned my head around to see what it was, and there was nobody there! I checked to see what was causing the bells to ring, and I concluded that no "force" strong enough can make those bells ring. So I sat back on the computer and got the thoughts out of my head. Next thing 3 or 4 minutes later, it happens again! Still, nobody there. About every five minutes, I would hear the bells again.
Now many people would tempt to conclude that it was a "ghost" causing all that.
But the thing is, it is quite possible that, all paranormal phenomenon recorded in history can actually be explained by "Chaos", where things don't have to happen for a reason.
Although most things happen for a reason, once in a while Chaos might happen, and although it does not appear that universal chaos happens often, but it is quite possible that it DOES happen.
(others have made similar points)
If so, your definition rules out, by absolute principle, the possibility of artificially creating a living organism. If a mule is ever assembled, atom by atom, in some incredibly advanced lab, your definition will dismiss it as non-living, even if it eats, drinks and runs around. Even if it is assembled as a young mule (at any stage, including a newborn colt or the mule zygote) that proceeds to develop, grow, mature and age, you will still refuse to call it a living animal, not because of what it is, but because of where it came from.
I'd rather have a definition that will set some criteria the organism itself (and not its provenance) must meet to be considered alive, then discuss whether or not it is possible to artificially create an entity which meets them.
To cypress
Re evolution as a part of the definition of life.
The reason this is needed is because other things reproduce. I mentioned fire. A forest fire spreads, and can move to other forests. Hence a form of reproduction. A fire also has many of the other characteristics of life, including nutrition, excretion, respiration, movement, energy emission etc. It does not evolve.
Evolution appears to be almost confined to life. As I mentioned, some computer programs can evolve, but they are not organic.
So as things stand right now, a definition based on reproduction, evolution and organic base covers all living things and nothing else.
Yet it would exclude possibilities that are far more life like than fire and fire does evolve as its offspring moves from one material to another as clearly the chemic processes of respiration have been altered. Your fire example seems cute but it also seems a poor justification for requiring evolution (change in offspring) in the definition of life. Few would argue that without evolution as a component, fire is life.
cypress
It is not about who believes what. It is about setting up a definition that works. Evolution is not just temporary change. It is a long term process that occurs over many generations. Fire does not evolve. However, fire does reproduce. You could even argue that it may be organic, since some fires depend on carbon chemistry.
If you defined life as an organic system that underwent reproduction and biological evolution - then you have a definition that includes all those we know to be living, and excludes all those we currently consider non living.
That is the aim.
Your definition excludes things we call life that are unable to reproduce and therefore also unable to evolve. Mules have been noted already.
Also the aim was to develop a definition that would help with a future hypothetical situation not the present actual situation. To that end the definition proposed does not help.
I don't think that is the aim.
A definition limited to the forms of life we know is not enough in my opinion, because we may soon discover other forms.
It's like defining "fire" as "rapid oxidation of wood", and then you see a grassfire and you have to conclude that it's not fire. I'd even think twice about the word "oxidation" (in the narrow sense of combining with oxygen), because iron can burn in chlorine gas. Note added later: I can even imagine, on a planet with a methane atmosphere, gas cookers fuelled by oxygen - now you have a fire where the fuel gets reduced rather than oxidized.
I think a definition should give a formal frame to the intuitive notion of life we have. Something along the lines of homeostasis, nutrition, and interacting with the environment. Gosh, even nutrition is tricky - some crane flies don't feed at all in their adult form, they just multiply and die.
And I have two remarks to make about your specific wording:
1) "Organic", AFAIK, means carbon-based. What about silicon-based life which may have existed on Earth before we carbon-based lifeforms took over, and which possibly exists somewhere in the universe?
2) "Biological evolution". "Biological" means "related to life". This makes your definition circular.
A final note: I have just come across a very interesting idea called the clay theory. It describes a curious phenomenon which probes the limits of what we do or do not consider life.
First to Cypress
If we are talking of individuals, then no definition will fit. Personally, I don't have any children. Does that make me non living?
However, if we are talking of populations over several generations, rather than individuals, that problem disappears.
Lescek
I have encountered that clay theory before. I doubt it is quite relevent to the current discussion. Clay itself cannot be considered living by the definition I offered, and its role in abiogenesis, if correct, is that of a catalyst.
Homeostasis as a characteristic for life has possibilities. However, nutrition and interacting with the environment also occur with fire.
Your other points.
Silicon based life. If we encounter it, we will change the definition. However, that is not required right now.
'Biological evolution'. OK. I see your point. Just call it evolution.
Hey, I didn't call you Septic!
This is what IMO a definition should avoid: being unnecessarily narrow by holding on to inessential properties just because they happen to appear in all the known instances of the thing we are trying to define. Can you imagine a penal code that only forbids killing people with a knife, and has to be amended when a killer uses a gun or a baseball bat?
Leszek
Apologies about my spelling.
Science progresses. Each step builds upon what has already been learned. However, there is no need to anticipate, when what we anticipate may not be true.
There is no need at this point in time to include silicon based life in our definitions. After all, there may well be no such thing as silicon based life. Carbon is a very special element, and we may well discover that the only life possible is carbon based. You do not know, and neither do I.
Let's not make a rod for our backs, and let us stay within what we know is real, without entering the world of open slather speculation.
A definition of life is not about what kinds of life are extant or possible. That is for empirical research do discover. A definition of life is about what is and what is not life.
You are right, we don't know (I mean we = you and me; perhaps some researchers already know, one way or other) if silicon-based life is possible. But if we include "being organic, i.e. carbon-based" in our definition of life as such, then by that definition silicon-based organis... erm... systems are not life, even if we find them growing, blooming, running around, eating each other, and bearing fruit and offspring on some distant planet. And that would be making a rod for our own backs: imposing upon ourselves the obligation to pronounce such a flourishing biosphere "inanimate automata", or at best "pseudo-life" simply because it's based on a different element.
I want the statement "Silicon-based life cannot exist" to be a synthetic proposition, which can be empirically disproved (e.g. by discovery or creation of such life) or confirmed (by studying the properties of silicon compounds and finding that they all lack some essential property). Finding that it is true or false will be (or perhaps has been) a major discovery.
If we accept your definition with all its logical consequences, that statement will be an analytical proposition, proved by the definition alone, and a trivial tautology. The term "silicon-based life" will no longer describe something that may or may not be possible - it will be an oxymoron, like "rectangular circle" or "two-digit even prime".
Am I making sense?
The mule does not evolve, as such. Does cypress evolve? Both are products of evolving populations. They are the product of evolution. Populations of cells within both creatures can also evolve.
Re silicon life.
I am not saying it can or cannot exist. I do not know. If we discover a living rock on a moon circling the primary planet of alpha centauri, we can alter our definition of life. That is trivial.
However, that is not a 'problem' we are likely to face for centuries. Follow the KISS principle, and stick to what we know. Carbon based life.
Another interesting feature to add to the list would be the thermodynamic properties of life. Schrödinger in the 1940s said that life "feeds on negative entropy" - although, as I understand it, he meant free-energy.
I think this is where we have a very fundamental difference of views on what a definition is, or should be.
I feel your idea is wrong, and you probably feel the same way about mine. I wish I had the time to go into a lengthy and enjoyable discussion about it, but I don't - so let's agree to differ.
Peace and clarity,
Leszek.
metabolism? surprised no one has mentioned it yet...
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