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.

[luckyme]

As soon as you list some necessary conditions to be called 'life' you run into situations that test a few of them.

'reproduce' is a good example. If we ran into an entity with an abundance of every other quality but lacked the ability to reproduce would it be a non-life form?

luckyme

[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

[Zeno]

[ QUOTE ]
As soon as you list some necessary conditions to be called 'life' you run into situations that test a few of them.

'reproduce' is a good example. If we ran into an entity with an abundance of every other quality but lacked the ability to reproduce would it be a non-life form?

luckyme

[/ QUOTE ]


Yes. But your response is somewhat sophomoric in my opinion. Definitions are required, especially in science and math, to give a basis for not only comparison and discussion, but as the framework for testing hypotheses, building theories, or acquiring data for example. Some definitions are more concrete than others say for an electron, the valve of the square of 4, an atom, H2O, to what is a fossil or a glacier or an island to what is life. Difficulties in defining natural phenomena or abstract concepts are neither prohibitive nor impossible in the scientific methodology developed by the human mind and should not be considered permanent roadblocks to knowledge. What’s the definition of a definition? Does 2+2 = 4? If you wish to wallow in ignorance as the defining nature of all phenomena and human constructs then we might as well stop all debate and discussion. In fact considering what most people state on this forum that may not be a bad idea.

Obviously I posted the life definition in response to Borodogs thread about the possible creation of “artificial life” by some scientists in the near future. If this does happen then a definition of what actually took place is of prime importance and sheds light on the implications and far reaching ramifications of said event.

-Zeno

[GoodCallYouWin]

Zeno :

I'm not sure how those links are supposed to disprove e=mc2 squared (the theory that all mass is fundamentally energy)...

[PLOlover]

watch the episode of star trek next generation where they want to dissassbmle Data for what is life and what is not lol.

[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)

[Zeno]

I suggest this slim volume by Erwin Schrödinger, What is Life? ( from Amazon )which is based on a series of lectures given by Schrödinger in the early 1940s. This slim volume provided inspiration, among others, to Crick and Watson.

-Zeno

[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.