What is life?

[lunakilo]

The question came up in another thread while talking about abiogenesis/creation.

A proponent of creation remarked that life from non-life was absurd.

I don't personally see a clear line between living and non-living beings/things.
I mean, a rock is not alive, and a tree is (provided it has not died thi is), but what about a virus or other micro organisms?
Where is the line that seperates living things from non-living things?

[Storm]

Well, given the placement of the thread, I feel comfortable bringing theology into it.

As a panentheist, "I have no use for that distinction." I believe that the cosmos is saturated with arn (life force). There are biological life forms, non-biological life forms, and undifferentiated forces, but all lives.

[Mr Spinkles]

Originally Posted by lunakilo

Where is the line that seperates living things from non-living things?

I think what is important is whether or not something can catalyze copies of itself. For some molecules this may take a long time and the "copies" may not be very exact, and the process may not be very robust (it only works in a narrow range of conditions). Thus we have clear examples of living and non-living things, and we also have a continuum in between living and non-living .... and that is exactly how we need to think about life in order to understand how living things come from non-living things, IMO.

[Willamena]

Originally Posted by lunakilo

The question came up in another thread while talking about abiogenesis/creation.

A proponent of creation remarked that life from non-life was absurd.

I don't personally see a clear line between living and non-living beings/things.
I mean, a rock is not alive, and a tree is (provided it has not died thi is), but what about a virus or other micro organisms?
Where is the line that seperates living things from non-living things?

I see "life" tied to "essence" or "nature." Where it is in the nature of a thing to be able to generate its own structure, like the plant that develops from the seed, we see "life." Non-life just sits there.

If you see a rock as "not alive," doesn't that imply a clear line between living and non-living?

[Mr Spinkles]

Originally Posted by Willamena

I see "life" tied to "essence" or "nature." Where it is in the nature of a thing to be able to generate its own structure, like the plant that develops from the seed, we see "life." Non-life just sits there.

If you see a rock as "not alive," doesn't that imply a clear line between living and non-living?

It's more complex than that though, Willamena. Not everything outside biology is a rock which just sits there. Take the Sun, for example, it's a raging beast with violent mood swings. What about tornadoes, volcanoes, and indeed, computers with artificial intelligence?

Physical systems can be very complex, but as argued persuasively in The Selfish Gene, Darwinian selection can only act on replicators. So only replicators have the potential (through evolution) to develop structures that have function and use them for a purpose. Other complex structures with unpredictable behavior may arise in Nature, but because of Darwinian selection on replicators living structures are markedly different, in a way humans intuitively recognize as functional / purposeful.

From a physics perspective, living things are engines: they sit between a heat reservoir (the Sun, ultimately) and a cold reservoir (space, ultimately) and "siphon off" useful work as energy flows from hot to cold. Like an engine, they do this without destroying themselves. But they are a special engine, in that they use the useful work they generate to make more engines like themselves. By Darwinian selection this leads to a spontaneous increase in the efficiency of such engines, if and when they arise, and thus an increase in the rate of flow of energy in the universe from hot to cold. Thermodynamically, living things are a clever route the universe sometimes discovers while trying to bring hot reservoirs into equilibrium with cold reservoirs (maximize entropy, or disorder).

[Quintessence]

Folks that think non-life becoming life is absurd need to study more biology (and physics and chemistry, but especially biology). That's really all I have to say to them. Even us current life integrates stuff that is "non-life" into our "life" form. All the universe is about exchanges of energy. The universe doesn't care if humans decide to call one component of the exchange "life" and another component "non-life," the exchanges of energy happen regardless. That these exchanges do happen should tell us that life is not categorically different from non-life in an extreme way; they are not like oil and water.

[johnhanks]

Originally Posted by Willamena

I see "life" tied to "essence" or "nature." Where it is in the nature of a thing to be able to generate its own structure, like the plant that develops from the seed, we see "life." Non-life just sits there.

It's in the nature of a snowflake to generate its own structure, but we don't call it alive.

Originally Posted by Willamena

If you see a rock as "not alive," doesn't that imply a clear line between living and non-living?

'Fraid not. Yes, a rock is very clearly on the non-life side of the divide, a cat just as clearly on the life side. But rather than a sharp line separating them, there's a broad strip with very fuzzy edges. Viruses do not represent a step in the emergence of life from non-life, but they demonstrate very clearly that entities can exist which have some but not all of the properties of living things.

A major error creationists make when they dismiss abiogenesis is to assume that the properties of living cells have to come as an all-or-nothing package.

[Willamena]

Originally Posted by Mr Spinkles

It's more complex than that though, Willamena. Not everything outside biology is a rock which just sits there. Take the Sun, for example, it's a raging beast with violent mood swings. What about tornadoes, volcanoes, and indeed, computers with artificial intelligence?

Right. And this is where allowance for the whole universe--everything open to our knowledge of it, even the rock--to be alive can be accommodated, in moving beyond the idea that biology and flesh define life. Essence entails the whole world, already generated, and nothing is permanent. All it takes is to slip a little concept of "existence" or "god" behind it to give it permanence--but that's probably a story for another thread.

Originally Posted by Mr Spinkles

Physical systems can be very complex, but as argued persuasively in The Selfish Gene, Darwinian selection can only act on replicators. So only replicators have the potential (through evolution) to develop structures that have function and use them for a purpose. Other complex structures with unpredictable behavior may arise in Nature, but because of Darwinian selection on replicators living structures are markedly different, in a way humans intuitively recognize as functional / purposeful.

Sounds interesting. But I'm open to defining "life" in non-Darwinian terms.

[Mr Spinkles]

Originally Posted by Willamena

Right. And this is where allowance for the whole universe--everything open to our knowledge of it, even the rock--to be alive can be accommodated, in moving beyond the idea that biology and flesh define life. Essence entails the whole world, already generated, and nothing is permanent. All it takes is to slip a little concept of "existence" or "god" behind it to give it permanence--but that's probably a story for another thread.

Well we can call everything in the universe "alive" if you like, but then we would miss many important, consequential distinctions. Also please note that nothing I said above requires life to be made of "flesh".

Originally Posted by Willamena

Sounds interesting. But I'm open to defining "life" in non-Darwinian terms.

I am also open to defining life in any way that is useful and consistent with fact. Is there a non-Darwinian definition which does this?

[Gjallarhorn]

Life is gauged by oneself. A dog is closer to yourself than a tree or rock, and are therefore "more alive". A tree's processes are easy to see within a human lifespan as opposed to a rock, and is therefore "more alive". It says nothing about reality, and everything about the limitations and simplifications of one's own mind.