What is the correct definition of life?

[seriously disabled]

After searching Google I couldn't find a definition of life that everyone agrees on.

 

Maybe trying to find a working definition of life is really a futile attempt but many times I get the impression that we just don't have a good (or working) theory of life.

 

I mean if scientists will one day be able to create life from scratch then maybe only then we will have a definition of life.

 

But right now do we even have a good theory of life? Do we know what differentiates living things from non-living (or inanimate) things?

 

After searching Wikipedia I have seen many different branches and outlines of biology and the life sciences but what I have not been able to find is a good and working general theory of what life really is.

Edited August 6, 2016 by seriously disabled

[Strange]

After searching Google I couldn't find a definition of life that everyone agrees on.

 

 

That is correct.

 

 

 

Do we know what differentiates living things from non-living (or inanimate) things?

 

Yes. But any attempt to define this in a rigorous way will be full of exceptions and special cases, and will not cover all cases.

 

There are many other things that cannot be rigorously defined in this way: art, religion, pornography, consciousness, etc. All abstract concepts that we recognise when we see them but find it impossible to define.

[ajb]

It is like good porn - you know it when you see it, but can't quite describe it to others.

[Phi for All]

Is there a scale that can be used to measure efficiency at using and dissipating heat, such that an obvious division is evident between animate and inanimate objects?

 

 

It is like good porn - you know it when you see it, but can't quite describe it to others.

 

"The smell of burning latex told me the condom was unlikely to provide further protection..."

[kisai]

Life isn't scalar, but a set of qualities. Definition is difficult because it is a decision of which qualities all members of the set must comprise.

 

Most likely its because the definition needs to be divvied up or expanded upon.

Edited August 6, 2016 by kisai

[StringJunky]

It is like good porn - you know it when you see it, but can't quite describe it to others.

It's very subjective.

[smhjn17]

You want a satisfactory theory of life? Why not analyze life through the perspective of biology, then chemistry and then physics. We will ultimately reach the level of energy, the quantum world! I know the hard part lies in explaining why all this orchestrates to form living matter, but if you build up from scratch you will realize that all the cells, organization in body, processes, senses, emotions, intellect is just the energy in the atoms expressing its information in different creative ways.

[iNow]

I always liked this explanation put forth here by a previously active member: http://www.scienceforums.net/topic/29095-what-is-alive/?p=383432

[ydoaPs]

After searching Google I couldn't find a definition of life that everyone agrees on.

That's because there isn't one. Once you get past molecules in the hierarchy, definitions don't seem to work for natural kinds. In practice, though we often talk about definitions, humans seem to use a family resemblance type theory of natural kinds. In the macro-level, definitions will always be either too broad or too narrow to capture all and only the phenomena they are intended to describe.

[StringJunky]

The evolution of life is a continuum of many forms from lifeless particles. Differentiating or defining the exact point at which one transits to the other is like asking: at what frequency does red become orange in the spectrum?

Edited August 8, 2016 by StringJunky

[koti]

Is there any existing or extinct life that could not reproduce? Is there any matter considered non-living that can reproduce? Isn't reproduction a single criterium which is enough to classify things by living and non living ?

[swansont]

Is there any existing or extinct life that could not reproduce? Is there any matter considered non-living that can reproduce? Isn't reproduction a single criterium which is enough to classify things by living and non living ?

What does it mean to reproduce? If a crystal grows and breaks in half, has it reproduced? Seems to me you need to have settled the definition of life before you can answer that.

[StringJunky]

Is there any existing or extinct life that could not reproduce? Is there any matter considered non-living that can reproduce? Isn't reproduction a single criterium which is enough to classify things by living and non living ?

Certain types of fatty acid-based vesicles can reproduce. These are hypothesised to be the initial principle structure of protocells; precursors of modern cells.These vesicles falsify the statement: only living things can reproduce. It is an insufficient property, on its own, to define life.

 

Reference: http://Self-Reproduction of Fatty Acid Vesicles: A Combined Experimental and Simulation Study

Edited August 20, 2016 by StringJunky

[koti]

I may be wrong but I always thought that reproduction has to involve DNA passing and inheriting? Crystals would be out of scope then, Im not familiar with the vesicles you are mentioning.

[Sophie Lux]

There is no inherent meaning of life, life occurred through natural processes and conditions.

 

Though this shouldn't devalue our lives, but rather empower them, rejoice in the fact that at this moment, you exist, because million years ago, stars died (as they all do eventually) spilling their chemically enriched contents out in cosmos, forming planets, including ours. Those very same elements make up your body. You are star stuff, we are all star stuff, and for a brief moment, amidts the chaos, through billions of years, those elements coalesced to form you. Our time in this planet is limited, love those who are around you, cherish it, savour it.

[Delta1212]

I may be wrong but I always thought that reproduction has to involve DNA passing and inheriting? Crystals would be out of scope then, Im not familiar with the vesicles you are mentioning.

Of course, such a definition is fairly likely to exclude the possibility of alien life existing.

[koti]

Of course, such a definition is fairly likely to exclude the possibility of alien life existing.

Could you explain why ?

[Strange]

Because there is no reason to expect alien life to be based on DNA

[koti]

If it would be DNA or something profoundly different, there are exactly as many reasons to expect it as there are not to expect it. I would imagine that alien life forms would have some carrier of information passed from one generation to another. Ofcourse we can argue that aliens could have a basis of life which excludes generations, they could be plain energy, etc but still...

[StringJunky]

If it would be DNA or something profoundly different, there are exactly as many reasons to expect it as there are not to expect it. I would imagine that alien life forms would have some carrier of information passed from one generation to another. Ofcourse we can argue that aliens could have a basis of life which excludes generations, they could be plain energy, etc but still...

But wrt to the definition Strange is right; it's plausible: DNA is not necessarily an all-encompassing feature of every possible life-form. To be pedantic: viruses are RNA.

[Strange]

If it would be DNA or something profoundly different, there are exactly as many reasons to expect it as there are not to expect it. I would imagine that alien life forms would have some carrier of information passed from one generation to another.

 

 

Right. But you said "reproduction has to involve DNA passing and inheriting". It may be something other than DNA.

[koti]

Isn't this a strawman? - Im refering to Stringjunkies comment.

 

Strange - Whether we call it DNA or other hypothetical carrier whats the difference?

Edited August 28, 2016 by koti

[StringJunky]

Isn't this a strawman? - Im refering to Stringjunkies comment.

 

Strange - Whether we call it DNA or other hypothetical carrier whats the difference?

Molecular constitution and structure. DNA is DNA. Feels like your trying to wiggle out of this.

Edited August 28, 2016 by StringJunky

[Delta1212]

Isn't this a strawman? - Im refering to Stringjunkies comment.

 

Strange - Whether we call it DNA or other hypothetical carrier whats the difference?

What qualifies as a hypothetical carrier? You can't handwave a definition, so you need to define what a carrier molecule is, specifically. And then you are again precludin the possibility of certain hypothetical forms of life.

 

What if we come across something that replicates itself some way other than through a centralized carrier of genetic information? Something whose morphology creates a matching form for its "offspring"?

 

Prions aren't really considered alive. They'de just proteins, but prion disease is caused by proteins that are folded in such a way that that they cause other proteins to replicate the same fold. So it's certainly possibly to replicate a shape in a complex molecule without any kind of carrier. Perhaps given time and opportunity, some kind of complex life could grow out of that process.

 

And what about viruses, which do have a carrier of genetic information, RNA, but around which there is quite a bit of debate about whether they truly qualify as life since they don't reproduce themselves but inject their genetic code into cells which they begin producing viruses.

 

And if the sole criteria of life is that it reproduces and has DNA (or equivalent), does that preclude sterile individuals from qualifying as alive? This can be a concern even with traditional definitions of life, but at least there are a range of different characteristics taken into account so there is a bit of wiggle room for individuals that miss one or two traditional categories for one reason or another.

[koti]

Of course, such a definition is fairly likely to exclude the possibility of alien life existing.

I'm just trying to understand this statement.

What qualifies as a hypothetical carrier? You can't handwave a definition, so you need to define what a carrier molecule is, specifically. And then you are again precludin the possibility of certain hypothetical forms of life.

 

I realy do not either feel the need nor concider it scientific discussion to define alien "DNA"

 

What if we come across something that replicates itself some way other than through a centralized carrier of genetic information? Something whose morphology creates a matching form for its "offspring"?

 

Good for us. We'd find a cool, new life.

 

Prions aren't really considered alive. They'de just proteins, but prion disease is caused by proteins that are folded in such a way that that they cause other proteins to replicate the same fold. So it's certainly possibly to replicate a shape in a complex molecule without any kind of carrier. Perhaps given time and opportunity, some kind of complex life could grow out of that process.

 

Perhaps.

 

And what about viruses, which do have a carrier of genetic information, RNA, but around which there is quite a bit of debate about whether they truly qualify as life since they don't reproduce themselves but inject their genetic code into cells which they begin producing viruses.

 

They reproduce by injecting their genetic code - seems enough to consider them life.

 

 

And if the sole criteria of life is that it reproduces and has DNA (or equivalent), does that preclude sterile individuals from qualifying as alive? This can be a concern even with traditional definitions of life, but at least there are a range of different characteristics taken into account so there is a bit of wiggle room for individuals that miss one or two traditional categories for one reason or another.

 

That would very much be "life" but with a defect. Simple as that.

 

Molecular constitution and structure. DNA is DNA. Feels like your trying to wiggle out of this.

i dont think I can wiggle out of this one Stringjunky, nor do I want to

Edited August 28, 2016 by koti