What Defines Life: Is It DNA, RNA, or a Universal Programming?

[Skhandelwal]

I read that DNA is where life begins and therefore Viruses are hard to fight b/c they are RNA. Anyways...how is this claim supported? Aren't we programmed in certain way? Including electrons which carry information. How come everything is not a life? Or better yet, how can anything be life?

 

[Phred101.2]

Life is seen (by us who have the property of being alive), as a thing that moves around (mostly) looking for food, reproduces (copies itself), and processes external stimuli in order to have a "map" of itself and its surroundings.
The simplest concept of something "alive" is a thing that uses stored energy. It uses it to find more energy to store. This is an ongoing process, so its always a trade-off. Viruses don't carry around much energy except for the bit they use to get inside a cell or bacterium. Viruses co-opt other forms of life that follow the above general outline (they go around looking for more energy to store).

 

[jim mcnamara]

There are several slightly differing definitions of life, depending on what the guy doing the writing is dealing with.

For example, blue-green alage are considered alive by first definition definition above, but some folks would quibble about the 'stimulus' & 'moves' parts of the definition. And as Phred mentions there are things like viruses and prions that defy the first definition completely.

You'll have to learn that in Biology there is no one perfect definition for most broad terms, like 'what is life', you have to pick one that suits what you are working with, then convey it to anyone reading your work.

As long as you say 'this is my definition' and stick to it, then the most anyone else can say is:' such and such species/thing/gizmo is outside your definition'. What Phred & I showed with Phred's #1 definition. Notice we did not say it was wrong - just that it could be quibbled with: it didn't fit with viruses.

 

[Phred101.2]

You could say that having stored energy is a necessary condition, but it needs to use it both to store more, and (if it can), move around. Some things seem to be only like an arc of the "life" circle.

 

[jim mcnamara]

Quibble: I'm not sure you could say that prions store energy.
The PrP^{sc} protein acts as a catalyst or maybe enzyme, to transform
PrP^{c} into PrP^{sc}

I'm not also sure that prions are life anyway.

 

[mgb_phys]

As jim says - it depends on who you ask.
Chemists talk about respiration and energy. Maths/CS people talk about inheriting characterstics. The definition about having DNA is a bit circular - if aliens turned up with TNA they would still be alaive.

Not sure if prions/enzymes can pass-on favourable characterstics and so be considered alive.

 

[Skhandelwal]

Aren't these opinions? What the factual theories in existence considering this issue?

 

[Phred101.2]

Fact 1. Life uses energy
Fact 2. Life stores energy (storing energy requires energy)
Fact 3. Life reproduces itself (this uses energy)
Fact 4. Life maintains some 'map' of itself and its environment (this requires energy too)
Fact 5. Some life is mobile. (guess what mobility requires)

 

[AppleBite]

I would just like to modify the use of the word "mobile" into "responsive".
Not all forms of life are mobile (except when they grow in size) but what is meant by the term mobile is that a living organism has to be responsive to external stimuli.

 

[jim mcnamara]

Skhandelwal -

What you are seeing is exactly what you were told. It is not opinion, although it looks kinda like we are just throwing stuff out there.

Do you understand Math? If you know what the Axiom of Choice is, then you will understand what is going on here. There is a theorem - Goodman's Thoerem.

Goodman proved that if the axiom of choice vx3yA(x, y) ->
3fVxA(x, f(x)) is added to intuitionistic arithmetic (here
x, y9 and / are functionals of finite type), then no new arithmetic
theorems are obtained.

This is basic Math. The idea is that accepting or rejecting certain Axioms gives you different results - or not. We are essentially defining biological postulates, not voicing opinions necessarily. Read about Koch's postulates which define what is required to demonstrate the existence of a pathogen.

It is NOT opinion. It is the fact that it's diffcult to create a definition of life that always works because the huge number of weird things we find over time. Nobody really knew about prions or even suspected them prior to 1975, for example. They bent the rules.

 

[Skhandelwal]

So what you guys are trying to tell me is that we don't have an exact definition of life...the more life we discover, the better our definition gets. However, so far, scientists make us look "superior" to nonliving things b/c we have the ability to make a choice. But may be, we don't make choices at all...we are programmed that way in our DNA.

 

[jim mcnamara]

S -

Yes, you got it. I don't know if defintions get "better" or not but they do change. Your idea of better may not be what mine is.

 

[Phred101.2]

But may be, we don't make choices at all...we are programmed that way in our DNA.

Skhandelwal: this issue is something we still can't really say too much about. Except that we know neurons grow and connect to other neurons, and this is 'controlled' by signalling molecules -ultimately DNA 'produces' a neuron's environment but a neuron is also affected by the external world...

 

[ganstaman]

I read that DNA is where life begins and therefore Viruses are hard to fight b/c they are RNA. Anyways...how is this claim supported? Aren't we programmed in certain way? Including electrons which carry information. How come everything is not a life? Or better yet, how can anything be life?

I may have missed it, but I didn't see anyone make this correction yet. Viruses don't all have RNA. They can have DNA too (like HepB, for example). And that's hardly what makes them hard to fight -- I thought it was more that viruses are basically parasites feeding off our cells, so 'killing' them is hard to do without killing our own cells.

Also: Viruses may or may not be life. We may or may not have free will.

 

[Eshi]

I'm only a high school student, but having recently studied the nervous system I would have to say that there is free will, if free will is defined as the ability for the brain to analyze senses and make create different options, in some cases each with a probability of living, for example if u are on the edge of a cliff, and you look down, ur eyes perceive the depth and height at which you are and this information is transmitted to ur CNS(i'm pretty sure that this isn't an automated response) and you have the choice of going closer, which increases ur probability of falling(which is going to equal death in this hypothetical situation) and backing off which will increase ur chances of survival. So now u make the choice of stepping back, if u did the opposite you are taking a risk factor. Which surprisingly is also a tendency that humans have, since evolutionary speaking living things must take risks to survive sometimes(this tendency is what drives gambling addictions and the rush u get when u win). Now the only reason why you might step forward is because of an advantage you would gain from doing this, such as respect from the community(i.e. your friends being impressed with you). If there is no advantage, then you brain will tell you to back off, and if you do the opposite that usually means ur crazy. I would consider this free will, because u do have the choice. Free will really comes into play in situations where there isn't an advantage, such as taking a left or right at an intersection(and you u don't know where either leads), where u just have to guess, and that is what free-will really is, the ability to take risks and adapt

Hope this isn't too off-topic, kinda was just inspired to write after the last few posts. Everything i said of course can be debated, most advanced brain functions are still being researched more fully, so its tough to say anything about the 'big' questions. I also agree with post #8 by Phred and #9 by Applebite

 

[Phred101.2]

Right. Free will is something we perceive ourselves (and other forms of life) as having because it is an advantage to be able to choose (between chasing your lunch or waiting somewhere for it to come to you, for example). Or alternatively, life is compelled to do this (there is no choice), but this is because life needs to learn about things...

 

[ganstaman]

I'm only a high school student, but having recently studied the nervous system I would have to say that there is free will, if free will is defined as the ability for the brain to analyze senses and make create different options, in some cases each with a probability of living

I'm not really sure if that's how most would define free will. The argument against free will is that when the brain is "analyzing" and "creating options" all that's going on is some chemical reaction and some electric forces being passed around. It's not a "soul" that is doing the thinking, it's just a sac of chemicals acting solely on the laws of physics and chemistry.

If I make a robot that can sense its environment and create different options for how to react to what it senses, does it then have free will? Absolutely not -- it simply follows exactly what I programmed into it. That the brain is more complex to the point where we can't fully know what's going on doesn't mean that it's not analagous to my robot's software.

 

[Eshi]

If I make a robot that can sense its environment and create different options for how to react to what it senses, does it then have free will? Absolutely not -- it simply follows exactly what I programmed into it. That the brain is more complex to the point where we can't fully know what's going on doesn't mean that it's not analagous to my robot's software.

Yes, i agree with you, that's because robots do a linear process form(i.e. sense --> analzyze --> respond(action)) and the human mind is a cyclic cycle, right? So that means humans will sense something like heat and move away, then sense some more and continue doing this cycle. whereas the robot would just sense the fire move away and be done with that process. So the robot separates each process and the human kinda integrates multiple processes together and puts them on repeat?

 

[Phred101.2]

There is a sense, or an apprehension we have of "something" that does the thinking. Except of course, we can view thinking as a response, rather than a 'self-initiated' process by some "independent" being. This last (which is pretty much the classical view) then begs the question: where is this independent self? What is behind it (is there a higher "self of selves", and etc.)?
I personally think that this sense we have (of being independent of our thinking) is due to our advanced brain, which has so much circuitry that we have the capacity, unlike most other animals, to diverge from immediate concerns, and think (a lot) about things that aren't to do with finding food, or shelter, or getting a fire going, or any of the ongoing tasks that life requires. Once we started to just think, for the sake of it, we diverged from the usual environmentally-directed thought patterns, and learned to philosophise. This explains our belief in our 'free' ability to think and act because of it, rather than just responding (but it's probably an illusion).

 

[DaveC426913]

Life
1] metabolizes - consumes fuel and excretes waste
2] reproduces - makes copies of itself
3] responds to external stimuli
4] grows

 

[Phred101.2]

1) To "consume fuel", it needs a store of energy
2) Reproduction is an energy-using process
3) Responses to stimuli involve energy use
4) Growth is the "conversion" of energy to cellular material (proteins, carbohydrate stores, etc.)
Conclusion: life is something that stores energy and uses it for all of the above...

 

[DaveC426913]

1) To "consume fuel", it needs a store of energy
2) Reproduction is an energy-using process
3) Responses to stimuli involve energy use
4) Growth is the "conversion" of energy to cellular material (proteins, carbohydrate stores, etc.)
Conclusion: life is something that stores energy and uses it for all of the above...

While true, it does not exclude things that are not life. Basically, what you've defined is the set of energy-using systems of which life is a subset.

It does not serve as a useful definition.

 

[ganstaman]

Yes, i agree with you, that's because robots do a linear process form(i.e. sense --> analzyze --> respond(action)) and the human mind is a cyclic cycle, right? So that means humans will sense something like heat and move away, then sense some more and continue doing this cycle. whereas the robot would just sense the fire move away and be done with that process. So the robot separates each process and the human kinda integrates multiple processes together and puts them on repeat?

I may be misunderstanding you, but I think my answer is: no.

I think you're making a distinction that doesn't exist. Robots and humans sense, then analyze, then react, and then repeat it all. Why would you say the robot isn't integrating these? Does the robot stop sensing the heat once it moves away from the fire once?

 

[Phred101.2]

1) To "consume fuel", it needs a store of energy
2) Reproduction is an energy-using process
3) Responses to stimuli involve energy use
4) Growth is the "conversion" of energy to cellular material (proteins, carbohydrate stores, etc.)
Conclusion: life is something that stores energy and uses it for all of the above...

While true, it does not exclude things that are not life. Basically, what you've defined is the set of energy-using systems of which life is a subset.

It does not serve as a useful definition.

You mean things like batteries that store energy, or cars or robots? These do not respond to stimuli the same way. A robot cannot learn (they only respond in a preprogrammed way) and evolve due to the accumulation of ¨learning¨ (DNA modifications or mutations -group knowledge). How many robots can reproduce or grow? I´m sorry, but your blanket statement does seem a little trite, at least.

Why would you say the robot isn't integrating these

What does this integration represent? Is it an equivalent of what some organism does (say a blue-green alga), when it measures something (say the light near the water´s surface)?

 

[DaveC426913]

You mean things like batteries that store energy, or cars or robots? These do not respond to stimuli the same way. A robot cannot learn (they only respond in a preprogrammed way) and evolve due to the accumulation of ¨learning¨ (DNA modifications or mutations -group knowledge). How many robots can reproduce or grow?

The fact that life stores energy to do its functions is incidental (i.e. of little use) to its definition (since many things store energy for their functions).

It is those functions that makes life unique, and thus define it from cars and batteries and robots.

 

[Phred101.2]

The fact that life stores energy to do its functions is incidental (i.e. of little use) to its definition

You think? I would say that because life is obliged to store energy and use the store to find more energy (to store), defines it pretty closely. It has to grow (extend), and perhaps move around to do this. Also it necessarily must be able to determine (discriminate or measure) its environment to do this, and measure its own internal ´environment' simultaneously. Bacteria do this. Learning is the accumulation of this measurement and discrimination, and storage of this too (in DNA and protein). How does a car or a battery or a machine -a robot, do this?

 

[DaveC426913]

I have 47 gadjillion distinct objects on a (large) tray and I want to separate them into life and non-life. (The act of separating the two is the embodiment of having a definition. If we have a non-ambiguous definition of life vs. non-life we can do this, if we do not, we cannot.)


I keep all things that (metabolize and reproduce and grow and respond) on the tray, and toss everything else off the tray. I have 11 brazillion objects left.

I decide to enact your criteria and (from the remaining 11 brazillion objects) remove all that do NOT store energy for these functions.

How many do I have left? Exactly 11 brazillion.

"Storing energy" does not contribute to our isolating the set of things that are life from the things that are not life. Thus it is an irrelevant criteria in defining life vs. non-life.

 

[Phred101.2]

"Storing energy" does not contribute to our isolating the set of things that are life from the things that are not life. Thus it is an irrelevant criteria in defining life vs. non-life.

So there is no way to distinguish a battery or a jar full of some chemicals (that have a potential energy say, if someone opens the jar and chucks a lit match in), from a bacterial culture? There is no way to tell if a bit of wood or a rock is alive or not, because containing energy is an irrelevant distinction? How do you personally decide if something, say, is not alive? Just for argument´s sake, what criteria do you look for?

I keep all things that (metabolize and reproduce and grow and respond) on the tray

How can you hope to determine that things are metabolising or reproducing, for example, surely this must be impossible?

Frankly I think you are completely wrong, actually incorrect, and you definitely need to review what you know about this subject (you´re talking rubbish, in other words).

1. Things contain or store energy. All things made of matter can be converted to some kind of energy.
2. Life stores energy. It has to use energy to do this.
3. Life uses energy to find more energy, things can store energy (have or contain some), but only life (is obliged to) goes around looking for more of it. All by itself.
4. Life tracks its environment by using energy to maintain a map of external and internal information
5. Life grows (extends itself) by converting energy into more ´life´.
6. Life reproduces, this requires energy.
7. Life shares information with others. This sharing is not an energy-free process.

 

[DaveC426913]

So there is no way to distinguish a battery or a jar full of some chemicals (that have a potential energy say, if someone opens the jar and chucks a lit match in), from a bacterial culture?

?

Of course there is - the four criteria defined: metabolism, reproduction, stimulation and growth.

 

[DaveC426913]

1. Things contain or store energy. All things made of matter can be converted to some kind of energy.
2. Life stores energy. It has to use energy to do this.
3. Life uses energy to find more energy, things can store energy (have or contain some), but only life (is obliged to) goes around looking for more of it. All by itself.
4. Life tracks its environment by using energy to maintain a map of external and internal information
5. Life grows (extends itself) by converting energy into more ´life´.
6. Life reproduces, this requires energy.
7. Life shares information with others. This sharing is not an energy-free process.

Again, I am not saying these things aren't true, I'm simply saying that the "uses energy" part doesn't help to distinguish life from non-life.

Take #6 for example:
"Life reproduces, this requires energy."

Do you know of any circumstance in the universe where a process "reproduces" without "requiring energy"? If there are no processes that reproduce without requiring energy, then this criteria does not narrow the choices by any. After applying it, you have the same number of items on your tray as you had before.


Or #4:
"Life tracks its environment by using energy to maintain a map of external and internal information"

Do you know of any process in the universe where a system "tracks its environment to maintain an external and internal map" - but does NOT "use energy" to do so? If you do NOT know any, then this criteria does not help narrow the definition any. same items on tray.

Simply put, you are confusing properties of life with definitions of life. What you are listing is properties that life has. But those properties do not help narrow the definition of life.

 

[Phred101.2]

So what criteria are used to distinguish that something has "metabolism, reproduction, stimulation and growth" ?
How can we differentiate between something that "uses" energy, say some star, from something that grows, or metabolises. The key difference is the way life (is obliged) to use energy (for all the above reasons).

Also I don't think you can compare a nematode's, or a blue-green algae's internal "map of self" (whatever biochemical or neural representation it may have), with anything that doesn't have or maintain such a thing, or doesn't use it to exploit (to measure) the environment. Are you saying inanimate objects do this too (like the sun, say)?

It is a bit trite, I suppose, to just say "Life uses (and stores) energy", when actually it is more the way it does this, and how it depends on both its internal store and the energy (food) it finds, to store more of it, in an ongoing (teleological) process. I think that's succinct enough, because all the rest follows, more or less, from this "requirement". Telic processes are what ensues from Life having a unique "relationship" with its food (the environment).

Arguably, the distinction is that inanimate things don't have this teleological feature. Life appears to have a purpose, which is different from, say a fire. A fire can be said to have a purpose in that it "wants" to burn all the fuel it can, but there is no directed or purposeful (or intelligent) feature present after all, just our observation of its character or behaviour, which we tend to ascribe to some intelligence (because that's what we do -humans are incurable anthropomorphics, sorry about the big word...)

 

[DaveC426913]

Life appears to have a purpose, which is different from, say a fire. A fire can be said to have a purpose in that it "wants" to burn all the fuel it can, but there is no directed or purposeful (or intelligent) feature present after all, just our observation of its character or behaviour, which we tend to ascribe to some intelligence (because that's what we do -humans are incurable anthropomorphics, sorry about the big word...)

Yes, I was about to raise the point that it is very common to anthropomorphize phenomena. Fire is often invoked as a loophole in definitions of life because it supposedly does all those things. But it does not. For example, fire does not reproduce unless one means figuratively.


But I disagree with your supposition that life appears to have purpose. I think that leads down a road to a philosophical definition of life, which I also think is of little use.

 

[Phred101.2]

Your restrictions don't seem to leave a lot of room, though. How is the distinction made then (you said you could select things off a tray -what sort of criteria are applied when you do this?).
We can "tell" the difference between a bit of rock, and say some worms, or a bird (rocks don't move around "by themselves"). How do we make this distinction, or how do we discriminate 'dead' things from 'live' things - something we do continually?

If there is no use in distinguishing the way something uses energy, or appears to be directed to a purpose (unlike something inanimate, which has only its existence, but no awareness), then what do we use (what do you specifically use as a discriminatory feature, or set of features? I think you do use the same features I listed, like every other observer does).

Is awareness (thanks to a store of biochemical energy, a map, and so on) a unique property, perhaps?

 

[DaveC426913]

Your restrictions don't seem to leave a lot of room, though.

Isn't that the point?

How is the distinction made then (you said you could select things off a tray -what sort of criteria are applied when you do this?).

We can "tell" the difference between a bit of rock, and say some worms, or a bird (rocks don't move around "by themselves"). How do we make this distinction, or how do we discriminate 'dead' things from 'live' things - something we do continually?

Worms eat and excrete; we keep them on the tray. Rocks do not; we discard them.

Is awareness (thanks to a store of biochemical energy, a map, and so on) a unique property, perhaps?

Again, awareness is a property of some forms of life, but we can't use it to define life because it will rule out very simple lifeforms that don't have a meaningful amount of awareness. They do react to stimulation though, which is one of the criteria I listed. That might count as awareness, depending on how loosely you wish to interpret the term.

 

[Phred101.2]

I think awareness is the ability to measure, or to observe, or to 'receive' messages (information), and to 'send' information too (to other observers).
All living things do this...

I disagree with your supposition that life appears to have purpose. I think that leads down a road to a philosophical definition of life, which I also think is of little use.

But teleology is an ergodic function, ergodics is certainly a scientific subject.
You claim that 'worms eat and excrete', presumably their use of energy, and the 'purpose' they exhibit doing this (as every living thing that exhibits trophism does), is irrelevant, or meaningless? Or just not very useful as a way to define or describe life?

 

[DaveC426913]

I think awareness is the ability to measure, or to observe, or to 'receive' messages (information), and to 'send' information too (to other observers).
All living things do this...

Yes, this is embodied by the words stimulation/irritation, which is one of the criteria I listed. Living things in some way get information from the world around them (be it as simple as: it's very hot over here) and react to it (move away from the hot place). So we agree on this criteria.

But teleology is an ergodic function, ergodics is certainly a scientific subject.
You claim that 'worms eat and excrete', presumably their use of energy, and the 'purpose' they exhibit doing this (as every living thing that exhibits trophism does), is irrelevant, or meaningless? Or just not very useful as a way to define or describe life?

I don't follow your words but I do think we may be crossing wires here. I am taking your words of 'purpose' and 'meaning' at face value. I do not believe that life has purpose or meaning except that assigned to it arbitrarily by thinking creatures with philosophy or religion.

 

[Phred101.2]

Living things in some way get information from the world around them

I would say that the "some way" involves energy, its "storage and usage" specifically. But this is irrelevant, according to your definition.

I do not believe that life has purpose or meaning except that assigned to it arbitrarily by thinking creatures

How do thinking creatures manage this? If the use of the energy store they all carry around, or the apparent purpose that thinking creatures 'observe' in other lifeforms (and other members of their own lifeform), is of no help, or is actually irrelevant?

I believe that both energy 'storage' and the teleology, are necessary features that 'thinking creatures' project onto them, to distinguish between living things, and non-living things. The projection doesn't create these things, they are intrinsic to all life, not created by an observer.

You can select things off the tray that are 'dead' because they do not exhibit either of these features (behaviours). A rock does not move around under its own power, or consume other things and then grow, or exhibit any sort of purposeful behaviour. We can distinguish between a rock and a bunch of insects, because of these behaviour distinctions. This is how you, me, and all living things see the world (to whatever extent they 'see', or measure it), surely?

BTW 'ergodics' is the study of evolving systems: complexity theory and emergent behaviour are included in this.

 

[DaveC426913]

You can select things off the tray that are 'dead' because they do not exhibit either of these features (behaviours). A rock does not move around under its own power, or consume other things and then grow, or exhibit any sort of purposeful behaviour. We can distinguish between a rock and a bunch of insects, because of these behaviour distinctions. This is how you, me, and all living things see the world (to whatever extent they 'see', or measure it), surely?

How does one determine 'purposeful'? Does lichen exhibit more definably purposeful behaviour than a rock?

 

[Phred101.2]

How does one determine 'purposeful'?

Are you saying that we, or you, are unable to make a distinction between "purposefulness" and "non-perposefulness", or that the distinction (if we make it), is irrelevant, or of no use to us?

Does lichen exhibit more definably purposeful behaviour than a rock?

Yes it does, if you observe it carefully or closely enough. A drop of pond water is teeming with lifeforms that we need a microscope to see; is something like that (or the bacteria living all over most organisms) not life, or not 'exhibiting' behaviour because we can't see it without some instrument?

 

[DaveC426913]

Are you saying that we, or you, are unable to make a distinction between "purposefulness" and "non-perposefulness", or that the distinction (if we make it), is irrelevant, or of no use to us?

Yes it does, if you observe it carefully or closely enough. A drop of pond water is teeming with lifeforms that we need a microscope to see; is something like that (or the bacteria living all over most organisms) not life, or not 'exhibiting' behaviour because we can't see it without some instrument?

But it seems that the definition is circular.
Life exhibits purposeful behaviour.
How do you define purposeful behaviour?
Well, it's behaviour that life exhibits and non-life does not.

Purposeful is a judgement call.

 

[Phred101.2]

Purposeful is a judgement call

What's a "judgement call", though? Is it the capacity of an observer to judge something (like whether there is enough light to make sugars, or enough heat, or too much)?
What else can observers do except observe --process the 'information' that is projected at them?

 

[DaveC426913]

What's a "judgement call", though? Is it the capacity of an observer to judge something (like whether there is enough light to make sugars, or enough heat, or too much)?

No, a judgement call means there's no objective, independent criteria for true or false, i.e. it's subject to the observer. You might decide something on my tray is exhibiting purposeful movement and who am I to say it's not purposeful? The first question I'm going to ask is 'what - in your judgement - makes it purposeful'?

Which means we're back to not having a definition.

 

[Phred101.2]

In which case, how do we, or any group of observers, end up making decisions (like whether something that's wriggling around might be good to eat for instance, or worth chasing, or as in our case, here on this forum)?

 

[DaveC426913]

In which case, how do we, or any group of observers, end up making decisions (like whether something that's wriggling around might be good to eat for instance, or worth chasing, or as in our case, here on this forum)?

?
What does this subjective, goal-driven action have to do with the task of creating a definition of life? We're talking pure academics here, not survival techniques.

 

[Phred101.2]

?
What does this subjective, goal-driven action have to do with the task of creating a definition of life? We're talking pure academics here, not survival techniques.

What does this discussion (which I claim is also a "subjective, goal driven action" -and you appear to be claiming also that there is a "purpose" to all this activity, or maybe you are also claiming that there isn't any such thing as "purpose" at the same time, I can't quite figure this out) have to do with goals or purpose? We aren't able to make decisions based on this 'activity' according to you...
What's your definition of 'pure' academics btw?

Your definition does not seem to allow for the (observed) behaviour of life to 'preserve' itself. Without purpose, no organism would bother to expend energy looking for food, or move away from danger. We would simply stay inside a burning building, or remain 'unmoved' by an oncoming flood, or violent storm, or an attacking wild animal (a lion say); since we can't make a 'judgement', there is no point in having or even defining purposeful behaviour, because its an illusion; no lifeforms have this property, they simply sit around waiting for whatever might come along, but can't decide what to do if something does...

 

[DaveC426913]

I think we've gotten mired in a meta-discussion; we're now talking about how our own discussion is an example of the topic we're arguing.

Hmm.

I'm going to go back to this point:

In which case, how do we, or any group of observers, end up making decisions (like whether something that's wriggling around might be good to eat for instance, or worth chasing, or as in our case, here on this forum)?

I don't see how the answer to this is directly relevant. It seems to be more about the application of our definition of life. We should first try to define life.

 

[Rade]

On another thread I defined life this way, I think it works for all known examples of it that exist on earth:

life = entities with self generated action mediated by nucleic acid (either DNA or RNA)

see here:
https://www.physicsforums.com/showthread.php?t=114399

There are many other threads on this forum about this important question. If we do not know what life is, the word Biology has no meaning. So, if you study Biology, then I say you study entities with self generated action mediated by nucleic acid (either DNA or RNA). Of course how you can study such entities comes in many forms, which is what makes Biology such a great field of study, and so much more complex than any other natural science.

 

[DaveC426913]

On another thread I defined life this way, I think it works for all known examples of it that exist on earth:

life = entities with self generated action mediated by nucleic acid (either DNA or RNA)

That would be the definition of life-as-we-know-it.

But it still seems self-referential to me.

 

[Phred101.2]

We should first try to define life.

I agree. This is supposedly the point of this thread, and I'm keen to see how well we do or how far we can all (as a group, say) agree on what each has to offer to the discussion.

First, I think it's probably important to define the question: what is it asking?
"How do we define" life, or how do we notice what it is, or what we are? How much of a problem is there with life trying to define itself (us, or any other organism)?
What about the possibility of being 'observed' --by something that isn't alive, as far as we can define, or 'notice'? How does the world 'see' life, in other words (or maybe that's a bit too obtuse or obscure for some).

Anyways, if you start with the assumption that you already know the answer --it's something you were born with, or some kind of innate knowledge (like knowing how to move around, or see or hear things)-- then it shifts to: What is this innate knowledge? Selecting live and dead things and sorting them (as on a tray), must involve some decision-making; what decisions get made, and why or how?

I don't personally think it's helpful to try to exclude things that are obvious characteristics; what's the point of doing that?
e.g. "moves around" (except for the life that doesn't, but this kind of 'non-motile' life isn't static, it is an active thing), or "has purpose", or "uses energy", etc.. Life does all this, so why is it 'important' to classify it as "irrelevant" --which I don't think is the case either? I don't see how something can be defined by describing what it doesn't do, except in a limited way; or that defining its characteristics away (as not meaningful) --so excluding them-- is going to get to any sort of useful goal here.

 

[DaveC426913]

We strive for the most concise definition. If something can be expressed with one rule as easily as several rules, we go with the one rule.