Question to all Murcers - What is the (scientific) definition of life ?

[Dogbert]

Not if you knew the people I know

[Dr Mordrid]

1. Prions don't need to react to dangers. Many/most of them are so stable they can survive being put in a ceramic kiln.

2. Evolving means being susceptible to mutation which by definition is a change in DNA or RNA sequence. Given the stable nature of prions they're unlikely to "evolve" much.

3. Machines can adapt to an environment if properly designed.

4. Interaction: see #3.

5. The IN-ability to reproduce does not disqualify one from being "alive". Post-menopausal women and men with vasectomies might argue this point.....

Prions don't qualify in my mind because of the absense of a cell wall (even virii have a protective outer wall) and the fact that they are just a defective form of an organic molecule (a protein).

As such they are better classified as a mutagenic toxin; a protein that can, in this case, hamper life processes by modifying a nerve cells RNA. More complex than the typical neurotoxin perhaps, but not any more alive than rattlesnake venom.

Dr. Mordrid

[KvHagedorn]

We could set up a definition of life as being anything with DNA. The purpose of life is to pass on DNA by reproduction. The meaning of life.. well that is just debate fodder.. but every life form has a purpose- to reproduce.

[cjolley]

What's the difference between light & dark?

Pitch Black -> easy
Bright Light -> easy

In between -> ????

Get used to the idea that many things are not black & white in this world.

chuck

[KRSESQ]

"We could set up a definition of life as being anything with DNA. The purpose of life is to pass on DNA by reproduction."

This of course assumes that DNA is the only possible genetic coding molecule possible. Just because it is predominant on Earth doesn't mean it will be predominent elsewhere in the universe.

Silicon-based lifeforms would have a radically different coding mechanism. An energy-based lifeform (if such a thing is possible) wouldn't have any known coding mechanism at all.

"IMHO you could be hospitalised if you suddenly decided that your car is alive and stopping it's engine would be murder "

What do we have when we finally create a car that can
a)locate a gas station and fuel itself when necessary,
b)locate a repair station and see to its own maintainence when necessary,
c)find its own way home when I have a little too much to drink, and
d)communicate with other autos in its immediate vicinity to prevent collisions?

The line between living and non-living gets a lot grayer.

Kevin

[mutz]

...chuckle. Dogbert you've done it! The first infinite thread!

For two reasons:

1. Life is observable, but it cannot be fixed in materia, space or time, as it is continuous transmutation, evolution of materia, space and time. Definitions require fixed demonstrable elements.

2. Since Dogbert is judge and jury, no definition will satisfy his transmuting criterion.

Note: Should 1. above fail, 2. will certainly not!

[Dogbert]

Worse, I'm not a judge, I''m just a part of the debate

[UtwigMU]

As I was told in school there is no accurate definition:

Crystals reproduce, some other process' consume oxygen, while some bacteria do not, amoeba divides, did it die etc...

[Drizzt]

Something is alive when it can change without external help.
A star is alive.
A fish is alive.
A tree is alive.
A dead body is alive.

A rock is not alive.
A skeleton is not alive.
An Iraqi is alive, but not for much time now.


After this, if you want you can start differentiating (suggest a better word, thanks) between alive-thinking and alive-not thinking.

An so on.

[mutz]

...try this:

Neutrinos are sub-atomic energy particles with mass that stream from our sun and other stars throughout the universe. They are so small that they pass through even the most dense of materials. They pass, for example, through the human body at the rate of three trillion neutrinos per square inch per second.

Neutrinos pass through everything in our universe. In their course, they are affected and deflected by everything they pass through in such a way that in the vast variations within their vast numbers they carry the message of everything they pass through to everything they pass through. You could call them the breath of the universe.

Every living thing that neutrinos pass through reacts to the message of neutrinos and is influenced and programmed by the neutrinos' passage, thereby influencing every living thing in its life.

Non-living things are not influenced by the message of neutrinos, though the message of non-living things is carried by neutrinos.

Therefore, anything affected, programmed and influenced by the message of neutrinos is alive.

[thop]

speaking of DNA i read once a nice theory that the only form of live is actually DNA itself. like a parasite. humans, animals etc. are just hosts.

[Wombat]

Parasite? Sounds like a pretty symbiotic relationship to me - I'll keep my DNA thanks.

mdhome: Life does not reverse entropy, at least not any differently than some mechanical processes. Although a lifeform may seem more organized than what came before it, it destroyed many things to get that far. Except for possibly some very small quantum-sized areas, entropy always increases monotonically in any closed system. A lifeform is not a closed system.

[Paddy]

I dont get the whole prion thing...
In most ENT (ear, nose and throat) operations they use disposable equipment as some bright spark announced that prions were concentrated in lymphoid tissue AKA tonsils.

Now, disposable tools are used because the theatre staff cant get the prions off by cleaning/disinfecting/irradiating the equipment. Now the bit I dont get is... 'If WE cant physically remove the prions from the bits of steel, then how the hell do they manage to infect people????'

That aside, we were always taught at school that alive things had to be able to move, feed, grow, respire, reproduce, respond to stimuli and something else probably stated above. Most comatose patients don’t fulfil that criteria.

I suppose ‘alive’ is synonymous with ‘conscious’ – something you didn’t want to get into…I don’t class proteins and virii as alive as they don’t appear to demonstrate any will of their own. They simply react in a reproducible way to their environment.

Do I think crystals are alive???? Hell no. and fire WTF???
I agree it is a woolly subject. I think the problem is that we try to define things by our own standards.

[Wombat]

Prions are generally extremely vulnerable, and/or extremely localized. You don't see prion "infections" fairly often. Often prions are created by the host as part of an inherited genetic defect, and may be transmitted to another person through transplants, open wounds, etc.

One interesting example is the Fore tribe. They would eat the brains of dead ancestors as part of their customs. Sometimes people died of a disease called kuru, a degenerative nervous disease that caused dementia, and the Fore tribe had an abnormally high incidence of this disease. Kuru was caused by a prions, and the prions would be in high concentration in the brains of those that died from kuru.

[Dogbert]

mutz, the neutrinos theory seems like something pretty cool. I need to read a little about before I comment about it, but 1 questions arises: what is accroding to the neutrinos theory 'alive' ?

Would a virus be affected by the neutrinos stream ?
If someone would be completely isolated (theoreticly) from the neutrinos stream, what would happen to him ?