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Author | Topic: What is life? | ||||||||||||||||||||||||||||||||||||||||
RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined:
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We need definitions to discuss and make decisions. There are several definitions of life, all of them with problems, because it is like defining "green" on a spectrum:
What you end up with are threshold definitions, which end up being subjective.
When is a fetus considered alive? When is it considered dead? The fetus forms from living cells, and again, what is considered an important stage in the development from zygote to independent organism is a matter of subjective definition. In humans children aren't fully capable of independent support until 10 years old or so - about the time they become able to reproduce. In bacteria, they reproduce by budding\division and as soon as the cell divides into two daughter cells the new individual(s?) are "born" -- and this process is similar to how the cells in multicellular life form from the original zygote, but when does that division and multiplication form something we identify as - in the above example - human? Such cell division and multiplication goes on throughout your life, so when are you complete? wikipedia: life
quote: It's a spectrum from naturally occurring chemical reactions to organisms we recognize as life. You could say life uses self-replicating molecules to reproduce and evolve, and it feeds on negative entropy.
What was the first living cell? It may not have been a "cell" as we know it. Perhaps it was just self-replicating molecules in a lipid bubble. http://scienceweek.com/2005/sw050325-1.htm
quote: Another concept to throw in the pot is LUCA - the last universal common ancestor (or last universal ancestor) wikipedia: LUCA
quote: Of course panspermia doesn't answer the question of when life began, it just moves it to another location. The theory I personally prefer is that some large pre-biotic molecules (see PAH's) form in space - part of the export of materials from stars\novas - and that these combine to form life where conditions are favorable, such as on early earth. A partial panspermia theory. See also Carl Woese and the "RNA World" theory. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Let's not confuse the issue.
You are giving the doctors, lawyers, and insurance agents in the crowd anxiety attacks. If the definintion of life is a spectrum, then we create a problem with the definition of death. If someone is dead, we can sign the certificate, close the estate, and settle the claims. If they are partially alive..... Have you been watching The Princess Bride? (lol) If someone is dead, (s)he cannot be brought back to life. Actually, doctors and lawyers have already addressed this issue - see Legal Death, Legal Life - we have laws that deal with this issue, driven by the issue of organ transplants:
quote: If you want to discuss the issue of when a human life begins, I suggest addressing it on the Legal Death, Legal Life thread. That way we can stick to just the issue of the original beginning life forms and what is necessary to form life from non-life.
If you kill a simple (I know bacteria are not simple but you know what I mean) bacterium, it cannot be brought back, even if all the parts remain intact and undamaged. During mitosis the cell or cells are still considered living. They may not be considered individuals but they are living. Exactly, so the question is what you need to do to kill a bacterium while leaving all the parts intact and undamaged ...? Would you not agree that bringing a bacterium back to life would be similar to assembling the necessary parts to form life? Perhaps if we take a bacterium and remove parts without killing it, reducing it down to an irreducible minimum to remain alive, then we can get a top down impression of the threshold for the beginning of life.
They may not be considered individuals but they are living. A bud is still part of the - living - parent organism, they become - living - individuals when they become separated, but they still form a continuum of life from the original population. The question is how that original population formed. I'd say the minimal requirements are:
See (you can fast forward to ~minute 3.45 to get past the politics) This makes and argument from the bottom up -- so we have narrowed the focus on the spectrum to a (hypothetical) set of chemicals to a (hypothetical) minimal bacterium. The definition offered by Dr Adequate (Message 8) would be a "bottom up" definition, achieving the threshold of self-replication of molecules. Surface catalysis has been demonstrated using clay substrates, and this also seems to have a bias to using one-handed molecules (one of the curiosities of the issue) There is also a discussion of the various definitions from Joseph Morales. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Great article. Thanks. I thought Morales covered all the problems with every known definition, showing that there is no definition that does not run into problems with distinguishing "life" from "non-life".
So, what I hear you saying is that I am not going to get my wish for a relatively simple definition of life. What we have are subjective "operating" definitions that depend on our world views and consensus with other people, we just can't refine this down into words that apply in all cases. What we have is a pick list of traits that we observe in living organisms, such as reproduction, evolution and net consumption of energy, and that once sufficient degrees of enough of these traits are observed we can judge whether our personal subjective threshold has been crossed, but it is done on a case by case basis. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Thread title: What is Life?
Message 24, kishan: Nobody knows in reality , it is a just unknown energy , which is never be finish but it will convert into another. Message 25, Larni: If it is 'unknown' how do you know it is there? Well we experience life and non-life, and there does seem to be an animating energy, but we have not yet identified it. Certainly there is energy transfer between cells via ATP iirc that powers cell reactions and actions (muscles etc). Is life just a synergy between active cells that breaks down causing a cascade effect at death? Certainly the Uniform Code of Death means death can be declared while certain organs are still functional and can be transplanted to living humans. Edited by RAZD, : addedby our ability to understand Rebel☮American☆Zen☯Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
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