Life: A definition

[Zeno]

Decent article here on definition of life: Life


The salient points are:

"However, some initial agreement is possible. Living things tend to be complex and highly organized. They have the ability to take in energy from the environment and transform it for growth and reproduction. Organisms tend toward homeostasis: an equilibrium of parameters that define their internal environment. Living creatures respond, and their stimulation fosters a reaction-like motion, recoil, and in advanced forms, learning. Life is reproductive, as some kind of copying is needed for evolution to take hold through a population's mutation and natural selection. To grow and develop, living creatures need foremost to be consumers, since growth includes changing biomass, creating new individuals, and the shedding of waste.

To qualify as a living thing, a creature must meet some variation for all these criteria. For example, a crystal can grow, reach equilibrium, and even move in response to stimuli, but lacks what commonly would be thought of as a biological nervous system.

While a "bright line" definition is needed, the borderline cases give life's definition a distinctly gray and fuzzy quality. In hopes of restricting the working definition at least terrestrially, all known organisms seem to share a carbon-based chemistry, depend on water, and leave behind fossils with carbon or sulfur isotopes that point to present or past metabolism.

If these tendencies make for a rich set of characteristics, they have been criticized as ignoring the history of life itself. Terrestrially, life is classified among four biological families: archaea, bacteria, eukaryotes, and viruses. Archaea are the recently defined branch that often survives in extreme environments as single cells, and they share traits with both bacteria and eukaryotes. Bacteria, often referred to as prokaryotes, generally lack chlorophyll (except for cyanobacteria) and a cell nucleus, and they ferment and respire to produce energy. The eukaryotes include all organisms whose cells have a nucleus - so humans and all other animals are eukaryotes, as are plants, protists, and fungi. The final grouping includes the viruses, which don't have cells at all, but fragments of DNA and RNA that parasitically reproduce when they infect a compatible host cell. These classifications clarify the grand puzzle of existing life, but do little to provide a final definition. "

Another link with a reasonable definition:

Ask a Scientist

Of course asking a scientist is anathema to some people.



-Zeno, Scientist and a sentient terrestrial life form.

[GoodCallYouWin]

I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[Zeno]

[ QUOTE ]
I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[/ QUOTE ]

Really? Do you even know what you are stating? I don't think you do.

Life on Mars

Model Methanogens

That Meterorite

-Zeno

[Arnold Day]

[ QUOTE ]
[ QUOTE ]
I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[/ QUOTE ]

Really? Do you even know what you are stating? I don't think you do.

Life on Mars

Model Methanogens

That Meterorite

-Zeno

[/ QUOTE ]

What do your links have to do with what he said? I agree that living/not living will be a somewhat useless concept in the future. It is similar to how when you are a kid they teach you about the states of matter(solid, liquid, gas) but when you get older you see that many things don't belong to any of these categories.

[vhawk01]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[/ QUOTE ]

Really? Do you even know what you are stating? I don't think you do.

Life on Mars

Model Methanogens

That Meterorite

-Zeno

[/ QUOTE ]

What do your links have to do with what he said? I agree that living/not living will be a somewhat useless concept in the future. It is similar to how when you are a kid they teach you about the states of matter(solid, liquid, gas) but when you get older you see that many things don't belong to any of these categories.

[/ QUOTE ]

Wait...they don't? You mean like glass or chocolate or butter? [img]/images/graemlins/grin.gif[/img]

[Zeno]

[ QUOTE ]
I agree that living/not living will be a somewhat useless concept in the future.

[/ QUOTE ]

I do not know who you are agreeing with but the above statement is curious to a high degree. You are implying that at present living/not living is a useful concept but that at some point in the future this distinction will become useless. Science aside, I wonder what the legal communities response to this concept will be.

Are you a living being? How do you know?

Most observable matter on earth is in either of three states: gas, liquid or solid,( man in a laboratory can produce different states also, plasma and Bose-Einstein condensate etc) and in the universe as a whole more exotic states of matter do exist. States of Matter

-Zeno

[Alex-db]

[ QUOTE ]
I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[/ QUOTE ]

This is like saying "a car" is no different to "metal" and the definition is useless.

What do you have against defining "life" as a particular type of arrangement of matter (energy)

[vhawk01]

[ QUOTE ]
[ QUOTE ]
I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[/ QUOTE ]

This is like saying "a car" is no different to "metal" and the definition is useless.

What do you have against defining "life" as a particular type of arrangement of matter (energy)

[/ QUOTE ]


I agree, and I don't think the definitions are useless. HOWEVER, and it is a big however, it is important to understand that categorizing things like life is a tricky thing, and it does NOT imply concrete boundaries. There simply is no point at which something goes from non-life to life. It doesn't exist. This is a tricky point, and one that is seized upon by all manner of idiots as if it is some great refutation. This is why some of us are hesitent whenever the subject of 'definitions of life' are discussed. Much the same as any 'definitions of species.' We just don't want to be agreeing with anything that will be used against us later by unimaginative people.

But I certainly understand why it is important to be able to define things to have meaningful discourse.

[Piers]

[ QUOTE ]
I think the definitions of 'life' and 'non life' are mostly useless; consider that all matter is made fundamentally of energy... all things are composed of the same material there is nothing unique about 'life' as opposed to 'non life'. I'm not saying you can't make some arbitrary defintion if you want... it just doesn't matter.

[/ QUOTE ]

You could say the same thing about a banana and a lump or plutonium; they are both made of fundamental energy so no difference really. And of course you would be correct, except that the lump of plutonium would not taste as nice as the banana if you eat it but then we just the same stuff as well so it does not matter anyway.

I guess Zeno just wanted to make an arbitrary definition for some reason. Something to do with some article that took his fancy.

Personally I find a strict definition of life not worth the effort, just leave it to ones gut feeling otherwise its too confusing. Stuff like “are all sapient self aware entitles alive?” both yes and no answers can easily get you all muddled up.

[Siegmund]

I came to the conclusion some years ago that it didn't make much sense to ask "what is life," but rather, to ask "how alive is something".

I've only seen one attempt to quantify the aliveness of something, "Wesley's L": energy flux per unit mass, times the amount by which the object's entropy is reduced compared to a maximum-entropy arrangement of the same atoms. I ran across it in a book on computer artificial-life experiments probably 15 years ago. The citation in the appendix, if anyone cares, is J.P. Wesley, 1974. Ecophysics: the Application of Physics to Ecology. I may have to ILL it, now that you've reminded me of it...

I'm surprised I haven't seen a half-dozen other competing measures of aliveness.