Where does life originate from?

[jgm340]

We already have computer programs which can self-reproduce: viruses.
Some even "evolve", randomly changing bits to avoid detection.

The only ways one might separate computer viruses from "life" proper are the following:
1) Computer viruses depend on an existing system (namely, computers of a particular architecture running the same software connected over networks).
2) Computer viruses had a creator, and did not arise spontaneously.

But (1) is not really a good argument, as humans depend just as much on their environment!

For example, oxygen was not "naturally" present in the Earth's atmosphere. Life didn't start out using oxygen: it was actually a poison which violently disrupted processes (just like it does today with forest fires). Bacteria actually filled the atmosphere with oxygen, and paved the way for further life to take advantage of it as an energy source: http://www.palaeos.com/Earth/Atmosphere/oxygen.htm

Aside from this, humans depend on trees, fish, cows, etc. just to stay alive. If you think about it, we can exist only in the narrowest of possible environments. So how is it fair to say that a biological virus isn't "alive" because it depends on human cells to do it's work for it, while we depend on plants to collect energy for us? How is it fair to say a computer virus isn't alive just because it depends on computers?

For number 2), why would we care how it was created? In fact, a lot of you are even arguing that one of the defining characteristics of a living thing is that it was created by another living thing (by reproduction)!

Humans and mosquitoes, along with some ancestral protist, worked to "create" the protist that causes malaria. Sure, there was a lot of "guess-and-check" involved with random genes mutating and reordering, but the malaria protist was certainly more likely to be "created" recently rather than 2 billion years ago (back when it's immediate ancestors and humans didn't exist).

In this sense, evolution is "intelligent" and "creative". Evolution is NOT just natural selection acting on randomly created possibilities.

The possibilities (as in DNA sequences) are created "intelligently" by the life that exists today. When you have a baby, it's more likely than not to have most of the great qualities you have. Certain sequences of DNA are far more likely to be created than others, meaning that the possible life forms on which natural selection acts are to no fathomable degree created randomly or spontaneously.

So, if a person writes a program, or genetically engineers their own organism, there's no rational way you can separate this from "natural" life on the basis of it being created.



Anyway, so here is my definition for life:

Life is a process which uses an external energy source in a controlled and roundabout way to decrease entropy locally, (rather than doing so in a quick, violent, and straightforward chemical process that increases entropy locally).

This definition has a lot of nice properties:
1) It rules out a lot of things which clearly aren't life, such as fire, and almost all non-life chemical reactions.
2) It gets to the core of what we think about when we think of life: controlled, organized chemical reactions. If a process is causing really organized glucose molecules to be formed in an otherwise disorganized slew of random molecules, then chances are it's alive.
3) There is no question that someone who can't reproduce is indeed alive.
4) It doesn't needlessly rule out non-DNA/RNA based life.

 

[Borek]

Don't you think most important part, that should be included in this list is genetic material (RNA or DNA), without which a cell cannot function.

That will mean limiting the definition to the life as we know it on Earth. That's not necessarily bad, we don't know other forms of life, but trying to start a general definition by narrowing it down to specific case doesn't sound logical to me.

 

[granpa]

Life is a process which uses an external energy source in a controlled and roundabout way to decrease entropy locally, (rather than doing so in a quick, violent, and straightforward chemical process that increases entropy locally).

doesnt a refrigerator do that?

 

[granpa]

I would like to point out that the original question was where does life come from.
Not what is the definition of life.
'life' as a physical process is different from 'life' as a word in the english language.

life as a physical process comes from reproduction and evolution.

the definition of the word 'life' is a completely different question especially when you consider that words are often used loosely to mean things very different from the core idea. (I personally think we should have a separate word for things that can't reproduce but have all the other attributes of life (self-maintenance) and another word for deliberate behavior directed toward self-preservation)

much of the arguing here just seems to be semantics.

 

[bobze]

Don't you think most important part, that should be included in this list is genetic material (RNA or DNA), without which a cell cannot function. The argument about virus is pretty blurry whether it is alive or not.

viruses contain genetic material, also they replicate using a host (not self replication). viruses could be considered as carrier of genetic material but have no metabolic processes, capable of mutation , replication using a host hence its below a cell (smallest unit ).

No, because including DNA or RNA works on the a priori assumption that categorically all "life" would replicate in such ways. It is an a posteriori assumption that life is inexorably linked to these two nucleic acids and its not beyond the realm of possibility that in some dark and forgotten chasm of Earth there exists life which does not use DNA/RNA as a means of heritability (though small) and it is almost certainly a poor assumption to make for when and if we get out into the cosmos.

Really, as Granpa pointed out, the unifying feature of life and things which are life-like is the ability to evolve by natural selection. Again, as NS is the means for adaptive evolution and the conquest of biological complexity.

As I pointed out viruses "live" (pun intended ) in one of those shades of gray, between "living" and "nonliving". There are in deed cells which make their home here as well, Chlamydia, Rickettsia and species of Mycobacterium are obligate intracellular parasites--That is to say they are incapable of reproduction with fidelity outside of a host cell. Alive? How about another shade of gray.

Prion proteins 'reproduce' by a kinetic trap (an application of Le Chatelier) and are capable of natural selection acting upon them. Here there is "no" DNA/RNA transmitting hereditary material, rather changes in protein folding (alpha helica dominated or beta sheet dominated) which confer selective advantages to new "generations" of prions. More shades of gray.

So what we have, despite human-imposed definitions, is a continuum or spectrum (as someone else put it) going from something "not-living" to something with "life-like properties" to something we define as "living". The only unifying factor along that pathway is whether the "organism" (be it some primordial theoretical molecule or a modern cell) meets the criteria for natural selection; Namely, differential reproductive (replicative) success in a population of these organisms and introduction of variation at generational boundaries.

Meeting those two criteria then, NS can build upon any system layers of complexity that leads to some population of organisms we may wish to define as "living".

Edit: I see Borek beat me too it!

 

[cosmos 2.0]

That will mean limiting the definition to the life as we know it on Earth. That's not necessarily bad, we don't know other forms of life, but trying to start a general definition by narrowing it down to specific case doesn't sound logical to me.

It wouldn't be limiting. The general idea is, that life should carry on functioning in a conducive environment and able to pass on the blueprint to the next generation (with alterations if required) with which it was previously successful.That is done by RNA or DNA.As far i know, there is no organism including viruses that does not contain rna or dna m

 

[jgm340]

doesnt a refrigerator do that?

A refrigerator does not locally decrease entropy in a roundabout way.

It does so in a rather direct way. Similarly, when a crystal forms, it does so in a direct way, involving simple processes.

If you look at a living cell, on the other hand, it involves complicated enzymes and catalysts, and many steps before a waste product is generated. Something fits the definition of life better as the number of steps before a waste product is produced increases.

Moreover, the relative decrease in entropy is SO slight. The refrigerator itself has so much structure for just a small decrease in the random movement of a tiny number of air molecules.

A cell, on the other hand, has structure 99.999% of which would not exist had not the process by which the cell acts occurred. In other words, the processes which go on in the cell are the sole reason for the existence of much of its structure. Had the processes in the cell not occurred, much of that material would just be floating randomly about.

The fridge would still have been a giant hunk of organized metal, however, if it were never plugged in. Remember, life is a process, not a thing.

 

[granpa]

and what about the first primitive self-reproducing RNA-like molecule.
It was presumably surrounded by a sea of its subunits (which presumably had a natural tendency to stack in one dimensional structures) so all it had to do was arrange those units in some order.
Thats not exactly complicated.

 

[granpa]

life certainly does reverse entropy and over time as it evolves it becomes more and more complicated.
thats evolution.

but i don't think that being complicated is itself fundamental to the process of life
being complicated just follows from having genetic material and the ability to reproduce and evolve.

if on the other hand you are trying to define the word 'life' then that would be a semantic matter
and I really don't want to get into that.

you seem to be looking for something that is common to all the things that we use the english word 'life' to describe.
That is more semantics than physics.
When you learn a foreign language you learn that many things that are only 1 word in english are in fact 2 totally different things and are 2 words in the foreign language.
There is no reason to assume that all the things that we describe with the english word 'life' are in fact a single unified concept.

 

[cosmos 2.0]

No, because including DNA or RNA works on the a priori assumption that categorically all "life" would replicate in such ways. It is an a posteriori assumption that life is inexorably linked to these two nucleic acids and its not beyond the realm of possibility that in some dark and forgotten chasm of Earth there exists life which does not use DNA/RNA as a means of heritability (though small) and it is almost certainly a poor assumption to make for when and if we get out into the cosmos.

is there any evidence here on earth, any other form of life (without Rna or dna) exists ?
I have nothing against broadening the scope to define life. But while broadening , we should realize the limits nature puts on kind of life that can exist and be successful

Prion proteins 'reproduce' by a kinetic trap (an application of Le Chatelier) and are capable of natural selection acting upon them. Here there is "no" DNA/RNA transmitting hereditary material, rather changes in protein folding (alpha helica dominated or beta sheet dominated) which confer selective advantages to new "generations" of prions. More shades of gray.

These are recently discovered group of proteins. we should make a distinction between ones that have genetic material and one that do not.
Are these proteins transmitted similar to any viruses , ricketsiae or mycobacterium. Can they be cultured or grown in the Lab like viruses or bacteria.
In the true sense they do not replicate, but converts already existing proteins and accumalates.

So what we have, despite human-imposed definitions, is a continuum or spectrum (as someone else put it) going from something "not-living" to something with "life-like properties" to something we define as "living". The only unifying factor along that pathway is whether the "organism" (be it some primordial theoretical molecule or a modern cell) meets the criteria for natural selection; Namely, differential reproductive (replicative) success in a population of these organisms and introduction of variation at generational boundaries.

Meeting those two criteria then, NS can build upon any system layers of complexity that leads to some population of organisms we may wish to define as "living".

well it all goes back to the origins of life, which is still not known as to whether complex molecules assembled themselves or any other way life organized itself.e continues we may never know.But one thing is clear Dna or Rna led to increase in complexity in the way life organized itself.

 

[jgm340]

and what about the first primitive self-reproducing RNA-like molecule.
It was presumably surrounded by a sea of its subunits (which presumably had a natural tendency to stack in one dimensional structures) so all it had to do was arrange those units in some order.
Thats not exactly complicated.

And it's questionable whether that would be considered life, or just part of the non-life processes which eventually led to the more complicated processes we call life. I'd go with the latter.

If we were to try to pinpoint the absolute first process which one could call life under my definition (indecisive as it is), it would probably be at the moment at which the probability of more complicated processes arising from existing processes became significant enough that it was almost certain that in the next month or so, something we would surely call life would exist.

 

[granpa]

well you seem to have made your mind up so I will stop trying to reason with you.

 

[Borek]

It wouldn't be limiting.

Yes it is limiting. Have you heard about PNA, p-RNA, and TNA?

http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=189

These we already know, plenty of other possibilities.

That is done by RNA or DNA.As far i know, there is no organism including viruses that does not contain rna or dna m

You are all the time presenting definition that is limited to the life as we know it. Or as you know it

 

[granpa]

the capacity to reproduce and evolve is necessary and sufficient for life to get started on any world. Everything after that is philosophy.

 

[jgm340]

well you seem to have made your mind up so I will stop trying to reason with you.

Don't be like that. You made a claim about the nature of life, which I didn't think accurately represented it. I offered an alternative definition.

Perhaps "complicated" could be replaced by something more accurate and meaningful. I want a condition that captures the fact that life seems to have an ulterior motive.

Although it feeds on an energy gradient, it's purpose is not simply to deplete that energy gradient.

Life *wants*, in some sense, its own processes to occur, in the same way that dried wood in the hot sun *wants* to burn, or how water *wants* to form a crystal when it gets cold. The formation of crystals and the combustion of flammable materials is tied directly with the basic chemical and physical properties of the materials involved. Any statement about the crystals "wanting to form" can be translated readily into a statement about water molecules having certain properties.

When one asks, however, "why does a cell seem to want to reproduce?", or "why does a cell seem to want to make these proteins?", the answer could not possibly boil down to a statement about the properties of a few common molecules. Any answer would involve not only an uncommon collection of molecules, but also the structure of the cell, many strange interactions working symbiotically, and many facts about its ancestors.

When one asks, for example, "why does this cell seem to want to reproduce?", you can't really understand it by only looking at that cell. I mean, reproduction is expensive energy-wise. The best answer I can think of is that statistically speaking, you are much more likely to come across a cell that wants to reproduce than one which does not: almost all cells in existence were created by other cells which must have had the ability to reproduce.

I feel as though a definition of life ought to capture that aspect of complexity, while ruling out static results of life, such as art, music, etc.

Then again, the concept of "memes" as ideas with a life of their own may be an important concept for higher life. After all, what makes someone human has a lot to do with what they learn. Intellectual thought seems like a self-perpetuating end in itself. Perhaps consciousness is a form of life itself...

 

[granpa]

you are asking 'what is the meaning of life'.
no doubt there is some religious motive here as well.

thats as philosophical as it gets
I just do physics

the question you should be asking yourself is 'am i even asking the right question'.

 

[Siv]

How are you defining "self aware"? Does it just mean the system responds to stimuli in an extremely compicated fashion? Because otherwise I don't even know how you expect to prove that other humans are self-aware, let alone a machine. I'm not saying solipsism is a tenable philosophical position, but it's outside the realm of science to address the question as far as I can see.

Sentience is a very controversial topic, isn't it ?

There's no way we can prove that someone does or does not have sentience. You can't prove that computers or mobile phones dont have sentience. Many scientists and philosophers feel that its very much a material thing, no need to invoke any magic to explain it. Just a property of a certain degree of complexity.

Its true that sentience is far from being an easy thing to define or measure, so using it as a parameter to differentiate living from non-living is really a no-go.

 

[Siv]

Perhaps "complicated" could be replaced by something more accurate and meaningful. I want a condition that captures the fact that life seems to have an ulterior motive.

Although it feeds on an energy gradient, it's purpose is not simply to deplete that energy gradient.

Life *wants*, in some sense, its own processes to occur, in the same way that dried wood in the hot sun *wants* to burn, or how water *wants* to form a crystal when it gets cold. The formation of crystals and the combustion of flammable materials is tied directly with the basic chemical and physical properties of the materials involved. Any statement about the crystals "wanting to form" can be translated readily into a statement about water molecules having certain properties.

When one asks, however, "why does a cell seem to want to reproduce?", or "why does a cell seem to want to make these proteins?", the answer could not possibly boil down to a statement about the properties of a few common molecules. Any answer would involve not only an uncommon collection of molecules, but also the structure of the cell, many strange interactions working symbiotically, and many facts about its ancestors.

When one asks, for example, "why does this cell seem to want to reproduce?", you can't really understand it by only looking at that cell. I mean, reproduction is expensive energy-wise. The best answer I can think of is that statistically speaking, you are much more likely to come across a cell that wants to reproduce than one which does not: almost all cells in existence were created by other cells which must have had the ability to reproduce.

I feel as though a definition of life ought to capture that aspect of complexity, while ruling out static results of life, such as art, music, etc.

The problem arises because you want to create an artificial and concrete line between living and non-living when non exists.

Although religious folks would like there to be some magical god-given property to life, life simply is a label we give to a certain level of organized complexity.

A cell no more wants to replicate than wood wants to burn. It really does not help at all to project human wishes and desires onto everything.
The elegance of evolution by random mutations and natural selection is precisely the fact that a "non-intelligent" process can give rise to so much organized complexity and beauty. Organisms which survive and replicate more effectively than other organisms do better simply because, by default, more of them remain after a period of time. See the simple elegance of that theory ? Darwin really was a genius.

 

[granpa]

some questions like 'have you stopped beating your wife' are best left unanswered.
the only possible answer is that its the wrong question to ask.

I strongly advise you (and anyone else) to leave the whole thing alone till you clearly understand the issues involved.
And it is perfectly clear to me, just from the fact that you are asking the question in the first place, that you don't understand the issues.

Like I said, the question you should be asking yourself is 'am I asking the right question'.

the philosophy forum:
https://www.physicsforums.com/forumdisplay.php?f=112

meaning of life:
https://www.physicsforums.com/showthread.php?t=435874&page=2

consciousness:
https://www.physicsforums.com/showthread.php?t=423084

 

[Siv]

Well, "Where does life come from?" really is not such a bad question. But its rarely ever asked innocently, is it ? Esp on forums like these

 

[johng23]

some questions like 'have you stopped beating your wife' are best left unanswered.
the only possible answer is that its the wrong question to ask.

Ummm...what? :uhh:

 

[bobze]

The problem arises because you want to create an artificial and concrete line between living and non-living when non exists.

Although religious folks would like there to be some magical god-given property to life, life simply is a label we give to a certain level of organized complexity.

A cell no more wants to replicate than wood wants to burn. It really does not help at all to project human wishes and desires onto everything.
The elegance of evolution by random mutations and natural selection is precisely the fact that a "non-intelligent" process can give rise to so much organized complexity and beauty. Organisms which survive and replicate more effectively than other organisms do better simply because, by default, more of them remain after a period of time. See the simple elegance of that theory ? Darwin really was a genius.

Good post

 

[Siv]

Good post

Thank you.

 

[granpa]

Ummm...what? :uhh:

you haven't been following the thread have you.

I was responding to post 50

Don't be like that. You made a claim about the nature of life, which I didn't think accurately represented it. I offered an alternative definition.

Perhaps "complicated" could be replaced by something more accurate and meaningful. I want a condition that captures the fact that life seems to have an ulterior motive.

Although it feeds on an energy gradient, it's purpose is not simply to deplete that energy gradient.

Life *wants*, in some sense, its own processes to occur, in the same way that dried wood in the hot sun *wants* to burn, or how water *wants* to form a crystal when it gets cold. The formation of crystals and the combustion of flammable materials is tied directly with the basic chemical and physical properties of the materials involved. Any statement about the crystals "wanting to form" can be translated readily into a statement about water molecules having certain properties.

When one asks, however, "why does a cell seem to want to reproduce?", or "why does a cell seem to want to make these proteins?", the answer could not possibly boil down to a statement about the properties of a few common molecules. Any answer would involve not only an uncommon collection of molecules, but also the structure of the cell, many strange interactions working symbiotically, and many facts about its ancestors.

When one asks, for example, "why does this cell seem to want to reproduce?", you can't really understand it by only looking at that cell. I mean, reproduction is expensive energy-wise. The best answer I can think of is that statistically speaking, you are much more likely to come across a cell that wants to reproduce than one which does not: almost all cells in existence were created by other cells which must have had the ability to reproduce.

I feel as though a definition of life ought to capture that aspect of complexity, while ruling out static results of life, such as art, music, etc.

Then again, the concept of "memes" as ideas with a life of their own may be an important concept for higher life. After all, what makes someone human has a lot to do with what they learn. Intellectual thought seems like a self-perpetuating end in itself. Perhaps consciousness is a form of life itself...

the question he is asking isn't 'where does life come from' but 'what is the meaning of life' and is clearly religious in nature.

hence my response:

some questions like 'have you stopped beating your wife' are best left unanswered.
the only possible answer is that its the wrong question to ask.

I strongly advise you (and anyone else) to leave the whole thing alone till you clearly understand the issues involved.
And it is perfectly clear to me, just from the fact that you are asking the question in the first place, that you don't understand the issues.

Like I said, the question you should be asking yourself is 'am I asking the right question'.

the philosophy forum:
https://www.physicsforums.com/forumdisplay.php?f=112

meaning of life:
https://www.physicsforums.com/showthread.php?t=435874&page=2

consciousness:
https://www.physicsforums.com/showthread.php?t=423084

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

A loaded question is a question which contains a controversial assumption such as a presumption of guilt.[1]
Such questions are used rhetorically, so that the question limits direct replies to be those that serve the questioner's agenda.[2] The traditional example is the question "Have you stopped beating your wife?"

 

[mishrashubham]

As for me, I think I can describe life as an organized set of chemical reactions whose sole purpose is to make sure that these reactions continue to exist.

 

[Ivan Seeking]

There is no doubt that whatever happens in the cell is just a chemistry, but we are still far from knowing all details.

[PLAIN]http://star.psy.ohio-state.edu/coglab/Pictures/miracle.gif
http://star.psy.ohio-state.edu/coglab/Miracle.html

 

[johng23]

you haven't been following the thread have you.

Sure I have, just seemed like you were suggesting that if someone's beating their wife, you should look the other way.
I guess maybe I misinterpreted it. I was assuming that it was a known fact that the person beat their wife in the past.

 

[granpa]

you've never heard that joke before?
groucho marx is famous for it.
you have heard of groucho marx haven't you?

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

A loaded question is a question which contains a controversial assumption such as a presumption of guilt.[1]
Such questions are used rhetorically, so that the question limits direct replies to be those that serve the questioner's agenda.[2] The traditional example is the question "Have you stopped beating your wife?"

 

[Borek]

No, that's classic example of the question that if you decide to answer (especially in terms of Yes/No), you always put yourself in the bad light.

 

[minorwork]

As for me, I think I can describe life as an organized set of chemical reactions whose sole purpose is to make sure that these reactions continue to exist.

What instrument measures purpose, in what units is purpose/intent expressed, and what do you use to calibrate the instrument?

Life, then, covers rocks weathering, stars aging, atoms interacting, and most anything then. Isn't that definition too broad? If you were to send an unmanned probe to Mars, what sort of sensor, what instrument, what detector would test best for life and, most important, what indication would it give for the absence of life. How do we test for past life especially in the case of Mars?

 

[granpa]

organic life doesn't have a purpose in that sense but it does have a function that it is optimized for.

(its a local optimum not a global optimum)

 

[Siv]

What instrument measures purpose, in what units is purpose/intent expressed, and what do you use to calibrate the instrument?

If we draw a line at a certain level of organized complexity that involves replication, and call all those things to the right of that line as "alive" and all the things to the left as "not alive", then that's easy. Use that very line to "measure" life.

 

[minorwork]

If we draw a line at a certain level of organized complexity that involves replication, and call all those things to the right of that line as "alive" and all the things to the left as "not alive", then that's easy. Use that very line to "measure" life.

So my Mars probe has to look for a line and find things on the right side of the line. Probably better things to look for. http://en.wikipedia.org/wiki/Life_on_Mars#Viking_experiments". One showed an increase in CO2 from Martian soil being exposed to water and nutrients. The designer of this experiment, called the Labeled Release experiment, said this indicated life. Maybe, but other scientists dispute his conclusion since the CO2 evolved could have resulted from a non-life explanation, that being the presence of super oxidants in the soil.

organic life doesn't have a purpose in that sense but it does have a function that it is optimized for.

(its a local optimum not a global optimum)

How does organic life know of this function and when it has achieved optimization?

To clarify what you mean by organic, do you mean containing the molecules that the Viking experiment did NOT detect with its mass spectrometer and gas chromatograph? Are you referring to general carbon chemistry?

I have to ask this because of the increased ability of the self-replicating programs known as computer viruses, and especially the http://en.wikipedia.org/wiki/Stuxnet" that can be said to be optimized for its function of replicating and installing a PLC rootkit in industrial software in order to cause damage to the process under the PLC's control. Can a replicating, evolving computer program be alive?

 

[Siv]

So my Mars probe has to look for a line and find things on the right side of the line. Probably better things to look for. http://en.wikipedia.org/wiki/Life_on_Mars#Viking_experiments". One showed an increase in CO2 from Martian soil being exposed to water and nutrients. The designer of this experiment, called the Labeled Release experiment, said this indicated life. Maybe, but other scientists dispute his conclusion since the CO2 evolved could have resulted from a non-life explanation, that being the presence of super oxidants in the soil.

Sure.
My point was that, any search for life should depend on how we define it.

A lot of people assume that something magical appears in an organism if its alive. Which is not true, really.

 

[LivaN]

You have already been given excellent explanations above. bobze explained it very well in post 26. You are hand waving, which doesn't belong in this forum.

No, not for my specific question. I was not hand waving, or if it appears that way it was not my intention.

granpa's post #32 put things into perspective, and #33 answers my question.
Thanks to grandpa for a good explanation.