the difference between life and non-life

[theradwun]

Sorry if this question has already been posed, just point me in that direction if you're terribly annoyed at my redundancy.
I'm only looking for simple answers.  I guess I'm most curious of the atheists'/naturalists' point of view.

What is the difference between life and non-life?

I'm not at all a biologist.  I'm assuming a naturalist sees a difference between a rock and a human, and I'm wondering what distinguishes them (as far as one being living and the other being "not-living").

[AlP]

Hi theradwun. I'm not a biologist either but I think a reasonable definitions would be that living things reproduce whereas things that are not living do not.

[Kylyssa]

But then again there are things that lie somewhere in between such as prions.

[Will]

Active DNA.

[theradwun]

Active DNA.

Well then I have to ask what is active DNA?

[theradwun]

^^  And I understand I asked for simple answer.  The point was to start simple.

[Renegnicat]

The first thing I'd like to point out is that there are no actual dead-straight divisions to anything in this universe. Rather, there is a gradual escalation of complexity. Keep in mind that even the unbelievably small is extroadinarily complex. And as things grow in size, they grow astronomically in complexity and in interaction.

But to say there is any inherent straight line that can be drawn, where everything on one side is dead, and everything on the other side is living is not realistic. Especially since, the only difference that can be observed between humans and a rock is a rather large difference in the degree of complexity. But all things possess complexity. And aside from that, to quote what's his face:

"We're all made from the same stuff." -- Whatsisface

.

Was that helpful?  

[Will]

Well then I have to ask what is active DNA?

DNA which is still involved in ongoing processes. All throughout mu body, DNA is replicating and providing "instructions" on how my body functions and continues on. When I die some day, those actions and reactions will halt.

Still, my definition is based only on what I currently understand and have been exposed to. It is entirely possible that life could exist without DNA. If we ever come across something without DNA that can self-replicate, adapt, mutate, and have other traits which are common among known life-forms, I would need to reevaluate my understanding.

[LARA]

I have to wonder why this is in Philosophy rather than Science?  

But anyway...

I think it's an excellent question, theradwun.

Life from a biological perspective is generally described as a thing that eats, excretes, reproduces and reacts to stimuli.  But then as the other posters have pointed out, there are matters of complexity, things that reproduce without needing the other processes, etc.  Generally if you look at something such as a prion which is a protein capable of inducing mass replication of itself in a biological organism that results in diseases like Kuru, BSE and scrapie, it's not considered alive because even though it's capable of reproducing in the right environment, it doesn't qualify for the eating, excreting and reacting to stimuli criterion.  

The next level from there would be things such as RNA and DNA, but these molecules aren't generally found freely floating about, but are associated with RNA & DNA viruses, bacteria (DNA), higher animals (DNA) etc.  So is an RNA virus alive?  It doesn't eat, excrete or react to stimuli but only hijacks the hosts DNA to replicate itself.  It doesn't satisfy the criterion.

On to a bacteria.  It eats; by taking in necessary nutrients through it's cell wall (the actual biochemical processes are pretty complex), excretes; by emitting waste products through it's cell wall, reproduces by binary fission and reacts to stimuli by simple actions such as moving towards a light or food source and away from a gradient of a toxic chemical.  It does satisfy the criterion and is alive.

Now compare a rock to a bacteria.  A rock is simple chemically, made of of a few minerals.  A bacteria, though infinitesimally tiny, is much more chemically complex and it is ordered as well. It has a cell wall, flagella for motility, a plasma membrane, and free floating genetic material, among other things. These are orderly and arranged in a packet that can reproduce itself.  Under a microscope the difference in complexity and organization between a mineral and a living thing are very apparent.

[Whitney]

I have to wonder why this is in Philosophy rather than Science?  

good point, moving....

[Squid]

Life itself is defined by the possession of particular characteristics to distinguish it from "non-life".  These are laid out by Audesirk et al. (2002) into 7 characteristics:

1. Organized structure consisting largely of organic molecules
2. Respond to stimuli from their environment
3. Maintain homeostasis
4. Acquire materials and energy from the environment and convert them to different forms
5. Growth
6. Reproduce themselves using DNA
7. Evolve

Hope that helps.

Audesirk, T., Audesirk, G. & Byers, B. (2002). Biology: Life on Earth (6th ed.). Upper Saddle River: Prentice Hall.

[LARA]

Interesting list Squid, these are getting more specific than the ones I learned.  Of course I was answering off the top of my head for the definition rather than going back to the college texts.

A lot depends on the definition and your source of course.  But what happens if we were to, say, find what appears to be an extraterrestrial organism that uses a slightly different molecule than DNA to store it's genetic information?  The potentially alive organism in question would automatically be excluded from being considered life by this more narrow definition just on the basis of lacking DNA.

And the structure is necessarily defined as being composed largely of organic molecules. I suppose that any highly complex future computer system would also necessarily be excluded from the "life" category by the materials it was composed of, even though it could in some ways be considered as qualifying for the other criterion.

I am of course, keeping in mind that the text was titled "Life on Earth" on all my examples are, at this time, mostly hypothetical.

I do, however, think that while such a narrow definition for life will at present suffice, we might perhaps someday come up against very interesting tests as humanity reaches out into space and the fields of computer science and AI.

[joeactor]

Hmmm... great topic.

I'd have to agree with many of the definitions, but they seem very "Earth-centric"

Granted, that's all we've got access to, but what about non-DNA/RNA life forms?
How do you define "organic molecules".

Surprised nobody has mentioned "Fire" yet (consumes, replicates, born, dies, reacts to environment, etc...)

Off to watch "Andromeda Strain",
JoeActor

[theradwun]

I have to admit I'm pretty lost in this discussion; I think I have a more specific question for those who seem so informed. (And I think this is where the philosophy would come in...)

Do scientists make a distinction between "things" which simply react to their environment and those that make decisions according to their environment?  
Take, for instance, me and a rock.  I pick up the rock and throw it.  The rock had no choice in the matter.  If I (or anything else) didn't move it, it would never have moved.
But if someone tried to pick me up and throw me, I make a decision... I fight them off physically and stop them from throwing me, or I try to reason with them as to why they shouldn't throw me, or I let them throw me.  

I'm not sure how to ask this question, but what do scientists make of decision-making capabilities?

[Whitney]

I have to admit I'm pretty lost in this discussion; I think I have a more specific question for those who seem so informed. (And I think this is where the philosophy would come in...)

Do scientists make a distinction between "things" which simply react to their environment and those that make decisions according to their environment?  
Take, for instance, me and a rock.  I pick up the rock and throw it.  The rock had no choice in the matter.  If I (or anything else) didn't move it, it would never have moved.
But if someone tried to pick me up and throw me, I make a decision... I fight them off physically and stop them from throwing me, or I try to reason with them as to why they shouldn't throw me, or I let them throw me.  

I'm not sure how to ask this question, but what do scientists make of decision-making capabilities?

I don't quite understand your question.  A rock is not alive and doesn't have the ability to make decisions however a flower is alive and doesn't have the ability to make decisions.  Are you asking if there is a special scientific classification for creatures which are self aware?  If you are just asking what scientists think of being self aware then that certainly would be a philosophical question however there wouldn't be an answer since scientists wouldn't necessarily agree with each other as it is not a scientific question.