What is "alive"?

[thedarkshade]

That seems a bit too specific and limiting criterion for such a general concept as "life." Could we not imagine something that lacked a cell membrane, but yet if we saw it we would still want to call it life? If ET walked up to you and shook your hand, but you learned that he didn't have any cell membranes, would you really reject him as a lifeform?

What you are saying is pure imagination! You cannot even imagine any kind of organism without a membrane. What about protection against harmful factors? Just leave the cellular material out there without any protection?!! No no, you REALLY need a membrane!

[CDarwin]

then every time he touched metal he would collapse into a puddle. not advantageous from an evolutionary standpoint.

 

also, swimming would be a major problem for these organisms.

 

Not my point, I think obviously.

 

What you are saying is pure imagination! You cannot even imagine any kind of organism without a membrane. What about protection against harmful factors? Just leave the cellular material out there without any protection?!! No no, you REALLY need a membrane!

 

Indeed it is. And if I can imagine in even the vaguest terms something that might not require a membrane, think what nature could come up with. Recall Orgel's Second Rule, "Evolution is cleverer than you are."

[thedarkshade]

Indeed it is. And if I can imagine in even the vaguest terms something that might not require a membrane, think what nature could come up with. Recall Orgel's Second Rule, "Evolution is cleverer than you are."

Yeah yeah, but a membrane is vital. It's a fundamental necessity inside which everything (proteins and all) is located. Inside there!

Don't push it any more or it will break!

[lukey]

I'm reading a book about the origin of life. They listed characteristics of life as

Reproduction, Metabolism, Nutrition, Complexity, Organisation, Growth & Development, Information content, "Hardware/software" entanglement, Permanence and Change.

[lokanath]

A living entity is the one which can recieve inputs from outside, process them intelligently and give an output in a such a way as to continue its existence. Existence is what is experienced in between the cycle of evolution and involution. EVOLUTION is the process of a thing by which it moves from its subtle state to gross stste. INVOLUTION the process by which it moves from its gross state to subtle state again. This is a contiuous process which we call LIFE..

[thedarkshade]

Existence is what is experienced in between the cycle of evolution and involution.

It's good that you're keeping it this simple, because I personally have an addiction to complicate these concept due to the great influence philosophy has in me.

 

Philosopher classify existence as a unique property that only belongs to humans and is one element that makes humans different from any other living organism. The philosophical definition of existence is a bit different from the biological one. Existence in philosophy does not just mean having extension in time and space, but existence means having to ability to understand things that are beyond our physical reach! But anyway, that's just philosophy!

[mooeypoo]

A living entity is the one which can recieve inputs from outside, process them intelligently and give an output in a such a way as to continue its existence.

(emphasis not in original)

 

That would make any decently-programmed A.I alive as well. (actually, by this definition, I could count a few good computer viruses too that fit that)

 

Existence is what is experienced in between the cycle of evolution and involution. EVOLUTION is the process of a thing by which it moves from its subtle state to gross stste. INVOLUTION the process by which it moves from its gross state to subtle state again. This is a contiuous process which we call LIFE..

 

Who calls that life? I've never heard of involution in context of scientific description of Evolution' date=' or the evolutionary process. I know about it (in general, I suck at math) in context of mathematics (like here) and heard about it in terms of spirituality (and the development of 'consciousness' as a whole - the abstract concept of consciousness, as opposed to the individual life-form 'consciousness'), but never in relation to what life is biologically or even philosophically.

 

Expand on this? I don't quite understand how evolution/involution by your terms defines a valid life form.

[Eric 5]

All the enormous variety of organisms today comes from a single cell, just one! Which at some point begun to 'live'! But what conditions must be filled in order to be alive?

 

I still remember my first biology lesson in high school where we exactly talked about these conditions and we mentioned three:

 

1. A membrane

2. Energy Source

3. Reproductive Ability

 

I. A membrane is highly necessary for a lot of reasons. The must 'primitive' reason is that a membrane holds the entire protoplasm together. Then the membrane also protects the protoplasm from harmful outside factors. Them is also serves as a port where all the substances that are needed in a cell go in, and the substances that no longer are useful go out. It is very important due to selective ability that membrane has (semi-permability).

 

II. Energy is purely the fundamental condition needed to be filled so one cell (or organism) can keep living. Energy is needed to perform all the vital processes that happen in a cell and that make life possible. Of course energy is not needed in some physical processes (like diffusion or osmosis) which are passive, but energy indeed the key factor without which life just can't go on (at least no for long). After all, this is why we eat. Energy enters in different forms like carbohydrates, proteins, lipids etc.

 

III. And reproductive ability is the third main condition that makes possible the continuity of life. Due to reproduction organisms proliferate, generation after generation and so life goes on continuously as an entirety although individual organisms die all the time. It is by reproduction that life counters death.

 

Shade!

 

 

That is all fine as a definition of needs and activities of those organisms that are already alive. But what is it that animates the matter that comprise these organisms? That gets at the heart of the question of what is life or alive.

 

What is the quality or property that distinguishes living organisms from dead organisms and inanimate matter?

 

Existence is what is experienced in between the cycle of evolution and involution..

 

 

Mooeypoo is right. What definition of involution are you using? I just looked in the "American Heritage College dictionary and did not find a definition of involution that fits the context in which you are using it.

 

Also, the question I would have to ask you is, "What is doing this experiencing of existence?

 

One other thought. Don't you find it ironic that those that are alive are trying to find out what it means to be alive? Maybe a good start would be to examine what makes us alive and aware of being alive, and then tackle the bigger question of what makes everything else alive.

[mooeypoo]

One other thought. Don't you find it ironic that those that are alive are trying to find out what it means to be alive? Maybe a good start would be to examine what makes us alive and aware of being alive, and then tackle the bigger question of what makes everything else alive.

 

 

Actually, this is a great philosophical question... I am not sure all life try to understand what it is to be alive. At least as far as we know from the limited experiments we were able to conduct (and I am talking out of my *** on this one in respect to proof, these are just things I've *heard about*.. take it with limited 'trust') -- no other animal is curious about these things.

 

In other words, I am not sure that is good to 'define' (or support even) the definition of life. It might support our definition of *intelligent* life, or "advanced" life.. but I am not sure cocroaches (which are alive), or fish, or amoeba, or dogs for that matter, are curious about their meaning of life.

 

But it's also a bit separate from the discussion, I think. It might be a good topic to talk about in another thread.

[CharonY]

Some good points were put forth here. Basically the textbook definitions of life (usually at least requiring a membrane enclosed plasma, metabolism and the ability to reproduce) are more a description of known life forms than a true definition applicable for the actual identification of life. This is a severe limitation as definitions go. In the end it borders more to a philosophical question as ultimately "alive" is not a measurable quality but rather a denominator of a bunch of qualities that we intuitively associate with something we call a living organism.

In practical terms, though, there are not many examples of "borderline" examples that exhibit only some of the ascribed properties. The most known ones are viruses that don't have metabolism nor membrane (capsules usually do not count).

 

And just as a sidepoint, someone mentioned that respiration falls under excretion (I think). It does not. Now carry on

[lucaspa]

What is the criteria that is used to determine whether something is alive or not?

 

In the context of abiogenesis (life from non-life), the definition is usually that something alive must have all four of the following characteristics:

1. Metabolism (anabolism and catabolism)

2. Response to stimuli

3. Growth

4. Reproduction.

 

I said "usually" because many researchers in the abiogenesis field have added a characteristic:

 

5. RNA/DNA directed protein synthesis

 

Some researchers add the characteristic"

 

6. Has a lipid bilayer membrane.

 

Or at least a means of separating the living thing from it's environment. Some people have proposed micropockets within rock formations.

 

Other researchers eliminate conditions 1-3 and say that something is "alive" if it can self-replicate.

 

A living entity is the one which can recieve inputs from outside, process them intelligently and give an output in a such a way as to continue its existence. Existence is what is experienced in between the cycle of evolution and involution. EVOLUTION is the process of a thing by which it moves from its subtle state to gross stste. INVOLUTION the process by which it moves from its gross state to subtle state again. This is a contiuous process which we call LIFE..

 

Lokanath, "evolution" doesn't have the definition in science that you have given it here. Neither does "involution". "involution" in biology refers to tissues folding in upon themselves to make a pocket.

 

Before you try imposing your particular views upon biologists and state those opinions as "fact", you need to learn first what has already been done in the field of abiogenesis and biology. Otherwise all you are doing is spouting nonsense.

 

In another thread I already showed that your definition and application of "subtle form" is contradicted by observations. Sorry, but this just isn't "life".

[Mr Skeptic]

If you freeze something that was alive in a reversible manner is it still alive? I ask because frozen things lose many of the attributes normally held by living things.

[lucaspa]

If you freeze something that was alive in a reversible manner is it still alive? I ask because frozen things lose many of the attributes normally held by living things.

 

Good question. I do this all the time with the adult stem cells. Are they still "alive" while frozen? They don't have any of the 4 characteristics; they are frozen. When I thaw them all the characteristics return.

 

So, how do we consider this? Do we go from "alive" to "non-alive" while they are frozen and then back to "alive" again when they are thawed? Or do we consider them as generally "alive" but in an artificial state while frozen?

 

This is a lot like "angels dancing on the head of a pin" when applied to frozen cells. It's just not important. However, when we get to humans we run into those ethical and legal minefields again. We've already seen the controversy over frozen blastocyts generated during in vitro fertilization. And the controversy just gets worse if we try freezing adult humans. Are they still "human" while frozen?

[stevo247]

If you freeze something that was alive in a reversible manner is it still alive? I ask because frozen things lose many of the attributes normally held by living things.

 

That situation is very similar to this one:

 

The question of what is alive becomes difficult when talking about seeds. Some seeds can remain viable for thousands of years but seem 'dead' until a little water is added. There's been a whole load of study over the years to figure out exactly what makes one seed dead, and another still alive. I don't think the answer has been found yet.

[Mr Skeptic]

But don't seeds have just a tiny bit of metabolism?

[stevo247]

It looks like water is needed in order to stimulate metabolism:

 

The seed is metabolically inactive (quiescent) in the mature, dry state and can withstand extremes of drought and cold. For example, dry seeds can be stored over liquid nitrogen at -150 degrees Celsius (-238 degrees Fahrenheit) for many years without harm. Upon hydration of a seed, metabolism commences as water enters its cells, using enzymes and structural components present when the seed was dry. Respiration to provide energy has been observed within minutes of water uptake.

 

http://www.biologyreference.com/Re-Se/Seed-Germination-and-Dormancy.html

[mooeypoo]

Good question. I do this all the time with the adult stem cells. Are they still "alive" while frozen? They don't have any of the 4 characteristics; they are frozen. When I thaw them all the characteristics return.

 

So, how do we consider this? Do we go from "alive" to "non-alive" while they are frozen and then back to "alive" again when they are thawed? Or do we consider them as generally "alive" but in an artificial state while frozen?

 

This is a lot like "angels dancing on the head of a pin" when applied to frozen cells. It's just not important. However, when we get to humans we run into those ethical and legal minefields again. We've already seen the controversy over frozen blastocyts generated during in vitro fertilization. And the controversy just gets worse if we try freezing adult humans. Are they still "human" while frozen?

 

I can't find references now, but there's a sort of frog that freezes itself completely in winter and gets thawed up in spring, regularly, and is alive.

 

How would we define that, too? You don't have to go to stem cells (which are also 'separated' from the host body so the question of life is even more complicated) -- what about that frog?

 

Those are.. good questions.. I am not sure we can answer them without going into philosophy, or fixing the current definition of what is life....

 

~moo

 

EDIT:

 

Found something: http://axiomsun.com/home/video/frog_reborn_after_freezing_itself_for_the_winter.html

[Mr Skeptic]

Perhaps life has to be measured as a continuum rather than a binary state. If something is mostly dead then it is a little bit alive Like a tree actually, most of them is dead wood, but it is still vital to the tree. We also have many dead cells, and "non-living" stuff like water and crystals. Just about any small enough piece is not alive, so we are made of non-living things, right?

 

In fact, I've recently read that we're basically made of protein crystals. They didn't say it like that, but rather that the proteins frequently self-assemble because of their structure. The special shapes are due to the patterns the proteins make, and also because the structure contains other different proteins that change the pattern they arrange in. Some even need to be seeded before they start to form because they don't stick together strongly enough until they start forming their pattern. There are, of course some that are different and require some help to form their patterns. This was in relation to surface-style proteins in particular, but I think it applies to others as well.

 

Anyhow, the more we understand it the more I think we are complex biochemical machines.

[Taq_is_hot]

Aw, too bad I didn't see this thread before I posted in the other one about life! I say that "life" is just a label we put on the most complex systems in the universe. If you want to hear my perspective in more detail, I practically wrote a whole book in the origin of life thread.

[CDarwin]

Perhaps life has to be measured as a continuum rather than a binary state. If something is mostly dead then it is a little bit alive Like a tree actually, most of them is dead wood, but it is still vital to the tree. We also have many dead cells, and "non-living" stuff like water and crystals. Just about any small enough piece is not alive, so we are made of non-living things, right?

 

This is a bit literary of me (I'll pretend its anthropological), but I just came across a quote in Things Fall Apart, by Chinua Achebe that expresses that notion from the Ibo perspective quite interestingly: "A man's life from birth to death was a series of transition rites which brought him nearer and nearer to his ancestors."

 

The Ibo notion is of "life" and "death" is not, as you said, binary states, but a continuum. I think that as the science emerges that might well turn out to be the most accurate way to view the phenomena.

[lucaspa]

We also have many dead cells, and "non-living" stuff like water and crystals. Just about any small enough piece is not alive, so we are made of non-living things, right?

 

Except on the skin, "dead" cells don't last long. They are dissassembled. We don't have any crystals in us.

 

In fact, I've recently read that we're basically made of protein crystals. They didn't say it like that, but rather that the proteins frequently self-assemble because of their structure.

 

And the reason they didn't say "crystals" is because that would be wrong. Yes, proteins do interact to form larger structures. Hemoglobin, remember, is 4 proteins and the heme molecule, not a single protein. But these are NOT crystals. Saying they are is stating an error. Sometimes an analogy doesn't help but makes things worse. That's the case here.

 

Anyhow, the more we understand it the more I think we are complex biochemical machines.

 

Was there any doubt? Yes, at the cellular or organismal level we are a set of chemical reactions. That's what "biochemistry" is: figuring out the chemistry of living things. Notice I said "cellular or organismal level". A philosophical question that arises because of our ability to reason and manipulate abstract thought at the level we do is: are we only biochemical machines?

 

This is analogous to the question addressed by Star Trek: was Data "only" a machine?

[insane_alien]

aren't bones crystaline? and enamel?

[halogirl]

i feel that to define life, that life has to be able to do something, that the things that make it up, perform a job to keep that thing alive. sorry to be so vague.

[insane_alien]

so, to be alive it has to keep itself alive?

 

that doesn't really define 'alive' its just kind of circular.

[noz92]

The NASA definition of life: "Life is a self-sustained chemical system capable of undergoing Darwinian evolution."