High five for Dr. A but that would include and exclude some things that we do not and do consider life.
Then so be it.
The goal shouldn't be to make a definition that describes something we want to talk about: the goal should be to talk about things in accordance with the way nature "defines" them.
For example, if the definition of "life" fails to exclude viruses, you have to ask yourself why you want to exclude viruses. For another example, if it's impossible to define "dinosaur" such that it excludes birds, you have to ask yourself why you want to exclude birds.
Only if there's a relevant, natural reason to define a specific group of things should we be attempting to define it. We should also acknowledge that "definitions," in the strictest sense, are not part of nature, and so, shouldn't be regarded as binding on nature.
We need definitions to discuss and make decisions. When is a fetus considered alive? This would help us make decisions about the abortion issue. What was the first living cell? This would help us decide on a viable model.
Re: Definition of "Life" -- thresholds and subjective interpretations
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:Life is a characteristic of organisms that exhibit certain biological processes such as chemical reactions or other events that results in a transformation. Living organisms are capable of growth and reproduction, some can communicate and many can adapt to their environment through changes originating internally.[1] A physical characteristic of life is that it feeds on negative entropy.[2][3] In more detail, according to physicists such as John Bernal, Erwin Schrdinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena which are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form (see: entropy and life).[4][5]
An entity with the above properties is considered to be a living organism, hence, a 'life form'. However, not every definition of life considers all of these properties to be essential. For example, the capacity for evolution is sometimes taken as the only essential property of life; this definition notably includes viruses, which do not qualify under narrower definitions as they are acellular and do not metabolize.
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.
quote:The following points are made by Ers Szathmary (Nature 2005 433:469):
1) In investigating the origin of life and the simplest possible life forms, one needs to enquire about the composition and working of a minimal cell that has some form of metabolism, genetic replication from a template, and boundary (membrane) production. ... 3) Basically, there are two approaches to the "minimal cell": the top-down and the bottom-up. The top-down approach aims at simplifying existing small organisms, possibly arriving at a minimal genome. ... ... 6) The bottom-up approach aims at constructing artificial chemical supersystems that could be considered alive....
Another concept to throw in the pot is LUCA - the last universal common ancestor (or last universal ancestor)
wikipedia: LUCA
quote:The last universal ancestor (LUA, also called the last universal common ancestor, LUCA, the cenancestor or "number one" in slang) is the most recent organism from which all organisms now living on Earth descend. Thus it is the most recent common ancestor (MRCA) of all current life on Earth. The LUA is estimated to have lived some 3.5 to 3.8 billion years ago (sometime in the Paleoarchean era).[1][2]
It is possible that all of LUA's contemporaries became extinct and only LUA's genetic heritage lived to this day. Or, as proposed by Carl Woese, perhaps no individual organism can be considered a LUA, but the genetic heritage of all modern organisms derived through horizontal gene transfer among an ancient community of organisms.[7] Another hypothesis to explain the paucity of alternative life forms is panspermia, the inoculation of Earth by life carried on meteorites.
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.
Re: Definition of "Life" -- thresholds and subjective interpretations
There are several definitions of life, all of them with problems, because it is like defining "green" on a spectrum:
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. 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.
Re: Definition of "Life" -- thresholds and subjective interpretations
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:The real question is when does this continuum of life begin to be a distinct living breathing heart thumping thinking human being. On common moral grounds, it is important to be consistent at both ends of the spectrum of life. Thus the concept of beginning needs to be consistent with current medical practice in determining when a human life has ended. This criteria has been developed over a significant period of time with a lot of ethical input from all sides into the specific ethical considerations involved.
UNIFORM DETERMINATION OF DEATH ACT 1. [Determination of Death.] An individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brain stem, are dead. A determination of death must be made in accordance with accepted medical standards.
That's the legal nuts and bolts of it: either failure of {heart\lung} system or total brain failure. Any person with either of these failures is universally and legally considered to be dead. The word "irreversible" is used to refer to common medical practical limits to resuscitation.
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:
Self-replicating molecules
Consumes energy and materials to form new molecules
Held together into a consistent unit by some membrane
Divides into multiple membranes containing self-replicating molecules
Replication and division are imperfect, thus allowing selection and evolution to operate
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.
If the definition of life is a spectrum, then we create a problem with the definition of death.
Then so be it.
If that's the reality of it, why would you want the definition to reflect anything else?
Incidentally, I completely disagree with you that a spectrum for life makes death an ambiguous term. Death can only be defined in terms of life: so, however you define life, death is simply the cessation of it. So, death always adapts neatly to any definition of life that you could possibly care to conceive.
Further, the dichotomy of life and death is not the same as the dichotomy of life and non-life. Rocks and roadkill are two entirely different classes of things in regards to the definition of life.
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alaninnont writes:
When is a fetus considered alive? This would help us make decisions about the abortion issue.
The use of alive in this context is very different from the use of life in the context of the biological sciences. The human embryo fits every biological definition of life that I have ever heard, as do the human sperm and egg.
In the context of the abortion debate, the question isn’t about when the fetus fits the definition of life, but about when it is sufficiently human to be granted the same rights that humans have. (They made a very similar mistake in the movie Short Circuit, constantly saying that the robot, Number Five, was alive, when what they really meant was that Number Five was self-aware.)
It is impossible to come up with a single definition of life such that abiogenesis, the Bread of Life, anti-abortionism and Number Five is alive will all be satisfied.
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alaninnont writes:
We need definitions to discuss and make decisions.
I repeat my original statement:
Bluejay, post #16, writes:
Only if there's a relevant, natural reason to define a specific group of things should we be attempting to define it.
There is absolutely no legitimate need for any definition that does not conform to reality, so, definitions must reflect the way things actually are. If the way things actually are is that life is only discernible as a spectrum of increasing chemical interconnectedness, then, as I have grown fond of saying,
Re: Definition of "Life" -- thresholds and subjective interpretations
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.
The above ontological example models the zero premise to BB theory. It does so by applying the relative uniformity assumption that the alleged zero event eventually ontologically progressed from the compressed alleged sub-microscopic chaos to bloom/expand into all of the present observable order, more than it models the Biblical record evidence for the existence of Jehovah, the maximal Biblical god designer. -Attributed to Buzsaw Message 53
The explain to them any scientific investigation that explains the existence of things qualifies as science and as an explanation -Attributed to Dawn Bertot Message 286
Does a query (thats a question Stile) that uses this physical reality, to look for an answer to its existence and properties become theoretical, considering its deductive conclusions are based against objective verifiable realities. -Attributed to Dawn Bertot Message 134
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.
Is life just a synergy between active cells that breaks down at death?
Thats like saying making love is the biological transfer of genetic material through the coitus of a male and female homo sapien.
While technically accurate it's not so sexy Sheldon!
Edited by 1.61803, : add sheldon
"You were not there for the beginning. You will not be there for the end. Your knowledge of what is going on can only be superficial and relative" William S. Burroughs
Hi Im new here but I found this a very interesting thread!
If you look at the seven pillars you need some programming or code to get that done. A code to survive or to get alive (or just a code with a purpose). So the P says it all. Without a P(rogram) how would a cell know how to improvise, compartmentalise, handle energy, regenerate, adapt and seclude?
So summarised you could say; life = organic material with a programming code with some purpose built in (duplication, survival, adaptation, energy transition etc)??.
quote:So summarised you could say; life = organic material with a programming code with some purpose built in (duplication, survival, adaptation, energy transition etc)??.
. Ok, but the "code" for all known life forms is not a "program": it is the synthesis of a prior existing natural system. Then we go to the first form of life... Which was the natural system that furnished its code? It was a life, a half life, or a non-living system? How it emitted its code to the primordial soup? Which were the natural systems at that soup?
There is no doubt that the producer of the first biological system (aka terrestrian life) was this astronomical system surrounding us to which Earth belongs as a part of it. Because Earth alone have no important properties of life, like self-reproduction. If the solar system has no all required forces and elements for building the first biological life, then, we need look to the galaxy. If still is missing some force or element, there is no other alternative than looking for the Universe. But our calculations suggests that this "code" exists at all these natural systems, included atoms systems, so, while biological life is based on DNA, universal life is based on a Matrix/DNA.
Following this line of reasoning, the Matrix/DNA Theory arrived to a never imagined before solution : LUCA, the last universal common ancestor never existed at Earth, but, the Earth was part of it. We included the theoretical model of LUCA, a natural system half-mechanical, half-biological. It is the building block of galaxies but in the way that nucleotides of DNA is a building block of humans.
There is no way for a exactly definition of life by the same motive pointed by RAZD in the electromagnetic spectrum which also we can point it at a human body... there is no an exactly moment that separates the shape of a teenager from an adult, or a baby from a child. What we call "life" is only the biological organization of matter, but there is life also at electromagnetic organization, as the astronomical mechanical organization. What is a continuum of transformations can not be separated into exactly parts.
And since that the definition of life pulls the issue about life origins, at Matrix/DNA Theory we arrived to a definition: life began when waves of light penetrated dark matter and they began interactions. Because we discovered that the first emanation of the code for life in this Universe was in shape of a light wave, and the first "material life", was the small amount carried by light plus mass coming from dark matter. It is like a computer and a human consciousness: mass furnished the hardware ( which can be the brain) and light the software ( which can be the mind).
The first wave of light was here at the moment of the Big Bang. So it came from beyond this Universe and so, the answer for "what is life" ill not be find inside this Universe. We will need waiting for NASA and its spacecrafts.
There was no origins of life and universe, astronomical systems are half-alive, light waves contains the code for life and DNA is not a code: Matrix/DNA Theory
Islam? If not, then to what are you referring? How can we look at the seven pillars when we have no idea which seven pillars you are talking about?
Also, we must be careful not to be misled by language. When DNA sequences were discovered they appeared to be some kind of code, so we started called them that. Just because our von Neumann machines (AKA, "computers" -- there are many different ways you could design a computer; ours are based on the von Neumann design) also have code doesn't mean that computer code and DNA code are the same thing. Nor does that necessarily mean that they are utilized in the same manner; eg, computer code is a series of instructions for moving binary data about in order to accomplish various tasks, whereas if anything DNA "code" is mostly pure data which translates to amino acid sequences.
Analogies are nice for helping us to explain and understand things, but we mislead ourselves when we take analogies too far.
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