Life

[doublecross]

I would like to start this discussion by asking people to contribute in one or both of two ways:
1) List what characteristics you think something must have to be considered life.   

This could either be what you consider to be a complete list, meaning that in your opinion, something is alive if, and only if, it meets all those criteria. Nothing that lacking even a single one could be considered life, and everything that meets all the criteria is life.  If you think you have a complete list, say so.

If not, just list some criteria (and please note that you don't believe it to be complete)


2) List things that seem iffy as to whether or not they are alive and/or suggest criteria that you are not sure if they are necessary or not.



Please refrain from directly responding to earlier posts, until I open the discussion up to that second portion. This part is just collecting first impressions.

[darkrobe]

Life must do the following three things (for argument purposes this is a complete list): Metabolize (aka be able to take up nutrients from the environment and transform it into new materials and waste products), Grow (aka reproduce or make more of itself), Evolve (change over time based on natural selection of said life forms natural variability)

thats my two cents

[nerd1]

if it can replicate on its own it is life.

[OldTrees]

The criteria for life change depending on how the word is being used.

To classification for the accumulation of knowledge? Use the biological definition of life.
To determine the legal significance of something? Use the legal definition of life.
To determine if something has certain moral relevance? Use the definition of life relevant to that moral relevance.
To find out if a game is the game of Life? Use the rules from the game of Life.

[Scaredgirl]

Wikipedia has a good answer to this:

Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes (i.e., living organisms) from those that do not.

I don't think it's very useful to ask people their opinions on what they think life is. A person could basically say anything to that, like "life is everything that is green" or "life is something that starts with a letter 'L'". My point is that we have a definition for word "life", therefore it's pretty pointless to ask any opinions on it. It's a bit like if we asked everyone's opinion on what gravity is, or their opinion on what day it is today.

[OldTrees]

@ScaredGirl

It is much closer to asking people the definition of "Wind". There are multiple answers that could be correct depending on the context.
"The wind blew through the trees"
"You must wind that watch"

However I agree that asking for opinions is not useful. Asking for beliefs about what the definitions are is more useful. Asking what the definitions are is even more useful.

[doublecross]

@Scaredgirl

The reason that I phrased the question as I did, is because really, as a society, we have not yet generated any definitions that hold up in all cases. As was pointed out earlier, different contexts use different definitions.   However, even within a given context, there are ample exceptions on both sides.  For this reason, it is not at all like asking someone what their opinion of gravity is.

The most common definition used in Biology is the following:

"Since there is no unequivocal definition of life, the current understanding is descriptive, where life is a characteristic of organisms that exhibit all or most of the following phenomena:
Homeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature.
Organization: Being structurally composed of one or more cells, which are the basic units of life.
Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
Adaptation: The ability to change over a period of time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present.
Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion, for example, the leaves of a plant turning toward the sun (phototropism) and by chemotaxis.
Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms."


Even this says that something must meet "all or most".  However, it is actually possible [depending on how one defines a cell], to find something that most people would not consider living, that meets all of these criteria, and it is easy to find things that most people don't consider living that meet more criteria than some things that most people do consider alive.




Additionally, there are ambiguities associated with any given criteria.

One of the most universally accepted criteria is REPRODUCTION:
If asked, most people would say that regardless of the other criteria, if something isn't capable of reproduction, it isn't alive.
However, what about the following cases:
1) A worker bee.

In the reproductive cycle of bees, a worker bee[female] is the fertilized offspring of a queen bee[female] and a drone[male], and the drones[male] are the unfertilized offspring of a queen[female].
Worker bees not only do not participate in the reproductive cycle, but are in fact sterile.

Would you consider a worker bee to be alive?
Follow up point: Interestingly enough, although a worker bee does not meet all the above stated criteria for life, the hive does, if you look at the entire hive as one unit.

2) A castrated bull.
This is not just a restatement of the previous example, because it was not always incapable of reproduction; its infertility happened at some point during its tenure in our world. Does it get its life status revoked?

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

On the other side of the equation, there are things capable of reproduction that most people would not consider to be alive.
1) Many crystals: Most crystals have the property that they can hijack crystal formation. If a crystal forms, it will usually form the crystal most stable under the present conditions- unless another crystal is present, in which case, it will tend to form the same type as the present crystal. One could call this a simple form of reproduction.
2) Computer virus: It spreads, and generates copies of itself.
3) Memes:   The ideas that are present in society today are those that were the most successful at getting remembered and repeated. Think back on a time that you heard something, and then felt compelled to tell it to several people. It does not take too much of a cognitive leap to see that this could be seen as the idea undergoing replication within its environment.



With all of the above criteria, it is possible to come up with examples on both sides (things that fail the criteria that we call alive, and things that meet the criteria that we normally wouldn't count).

Thus, I challenge your assertion that asking people to provide opinions instead of solid definitions is a silly exercise.  In fact, I would contend that anything else would represent a failure to comprehend the complexity of the issue.

[darkrobe]

I think for the stated goal of collecting first impressions first. asking for opinions is perfectly adequate. Whether this is a good topic or not probably depends on where it goes after people have given first impressions.

as for what you are saying Doublecross:

I think that in some cases. life is a group associated term. So if something is a part of a larger association that is life. then it itself is a part of life (even if it does not meet the requirements of life by itself)

So in the case of a Worker bee. it is part of a hive of bees, which you yourself said meets the definition of life, so a worker bee is a part of life.

also, in the assumption of life is that reproduction (or replication) doesnt have to be possible at all stages of growth. that at some point in the bulls life it was not able to preform in a reproductive way doesnt negate the fact  that it had the ability to reproduce and that it was created through a reproductive process

On a side not, I put down growth (not reproduction specifically) because if something is able to become larger and make more of itself in an individual sense. then i believe that qualifies as life.

also, none of your non life examples meet my stated definition of life because none of them metabolize. i think the memes is closest because you could make the argument that it could grow and change over time.

[doublecross]

I have argued in the past that I consider religion to be a meme, (and one of the most successful ones at that).

For the sake of argument, I will treat the fact that religion is a meme as a given (but am perfectly willing to defend that statement later).

Religion is a meme and thus capable of replication. To be clear, I am not saying that one religion can replicate into multiple (even though that has proven to be a true statement).   


What I *do* mean is that individual instances of the idea [i.e. one person thinking the idea] is able to create new instances of that idea [i.e. more people thinking the idea].   <= oversimplification for the sake of time.




However, what I didn't mention earlier is that religion (like many other memes), really could be said to have a metabolism.


Firstly, some terminology.
Meme was first coined as a biology term by Richard Dawkins.  He posited that just like we have genetic replicators (genes), there also exist mimetic replicators (memes). He argued that anything that in any way could effect the probability of having duplicates exist in the future should be able to follow the same principles of evolution that genes do.

If one considers the actual content of an idea to be the memetic equivalent of a genotype, then the way that people act because of the idea is the memetic equivalent of a phenotype.

The phenotype of religion is very complex, and hard to generalize, so for now I will focus on just one- Christianity.

It is clear that among the millions of things that are part of the staggeringly complex phenotype that is associated with the meme that is Christianity, many parts of it involve the conversion of matter not directly useful to the meme's continued existence and replication into things that are useful, and that it also creates waste.

One example would be the building of a church. I would seriously consider that to be an example of Christianity's metabolism.   I do not mean that metaphorically. I mean that to be a literal statement.



------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Similarly, how does a computer virus not have a metabolism? It does take computer processes and change their function to that of something useful to the virus, making physical changes to the world in the process, some of which serve no use to the virus and should be considered waste.


As to your other statement about something being a part of something that meets all those traits being considered life, I have 3 responses:

1) Well, yes, but that is not what I meant. The question really was referring to "what constitutes one specific entity of life" in the same way that most people would consider one person rather than a room full of people to count as a instance of life, or in the way that someone's gallbladder is alive, but is not 'life'.    In multicellular organisms, people tend not to consider any one particular cell as 'life' although in most cases it meets all the criteria of life.   
So, yes, that is one way to look at it, but it is in many ways sidestepping the issue.  One could classify an entire ecosystem of life that way- but that is not what is being asked.   It partially answers the question because it helps draw a line between [living] and [dead and or was never alive], which is relevant, but does not answer the other question of what constitutes one instance of life.

2) This is similar to point 1, but different enough I figured it could be its own number.
If someone was asked to sort the following items into two groups: human, cell, bee, hive, family, puppy, tree, colony, forest
Most people would come up with-
Group 1: human, bee, puppy, tree
Group 2: hive, family, colony, forest
and people would probably be split evenly about where to put cell, and a few people might put tree in group 2, and a few might put hive in group 1.

With the exception of the people who might sort this on the ground of animal v. non-animal (who would account for those who swapped tree and hive), most people would naturally sort based on what they felt to be a single entity.   If asked, most would probably say that while both groups were alive, there is an inherent difference between the two groups- group 2 may be alive, but group 1 lists individual living organisms.   When trying to define life, the goal is not just to divide life from non life, but also to define the boundaries of what is an organism.


3) I put the following examples up to your definition that "if something is part of a larger association that is life. then so it itself is a part of life (even if it does not meet the requirements of life by itself) "
a) Someone with a mechanical heart, artificial respirator, and dialysis.     
b) The dialysis machine from example a)
c) The air in someone's lungs at any given moment
d) The physical structure of a beehive (not counting any of the bees)


b,c, and d   are all parts of something that is alive, although they don't meet the requirements by themselves. Are they life? Are they alive?   [I will assume I don't need to ask you if you think they count as individual organisms], although that is a question I am curious to ask about a.

[darkrobe]

Perhaps the first part of your argument is best answered by clarifying what i mean Metabolism.

from wikipedia: Metabolism is the set of Chemical Reactions that happen in living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism uses energy to construct components of cells such as proteins and nucleic acids.

It not as simple as initiating some change in the environment.

I think I can further argue against Religion being life (and im doing this seriously and I do not mean to make this comparison to anger anyone ) the same way I could argue that a virus is not life.
Viruses replicate themselves through living beings. they insert their genetic material into a cell (which is living) and the cell mistakenly reproduces the virus.

I could argue that this "entity" you name christianity does not build a church. the ideas or memes that are the makeup of this "religion" are inserted into living beings, aka humans, and humans build the church. and through the church christianity grows. however it is not life because it itself did not do the building (metabolizing).

a computer virus does not have metabolism cause it is not involved in chemcal reactions also, i do know for a fact, but i am unaware of a *Edit COMPUTER* virus that changes over time on its own. based on natural selection.

And I will get to the other points in a bit but I have some errands to do.

[darkrobe]

Lets see. I think It is much more difficult to identify an individual instance of life. thats really all i was trying to say with my statement. that When you are talking about life you are talking about a a group of things that together have the potential to metabolize grow and evolve.

So I guess under my definition. the thing that is life is the Hive (the group of bees, not the physical structure) and a worker bee is a component of said life, not life. similar to the way carbon is not life, but makes up carbon lifeforms. This is going to get me into a lot of trouble but maybe I can say that an "individual" unit of life is the smallest group of something that can perform the metabolize grow and evolve functions.

When I say "part of life". what I meant is more along the lines of something that is a component of an "individual" unit of life, not that it is life.

[doublecross]

I know that there is what appears to be a two man argument going on. Please don't let this discourage anyone from jumping in or replying to any part of the discussion, even something several posts back. Please put this message at the top of all posts, until it seems clear that it is no longer relevant.

Well, now I am contesting the science of your claim [I do not intent this to be a complete rebuttal- I am purposefully only addressing certain points right now]

Firstly, the statement that viruses do not change over time due to natural selection is just flat out wrong. The first example that comes to mind is the Common Cold, which mutates so much that immunity becomes obsolete after less than a year.

Moving on.

With almost any term or distinction, it is perfectly clear what that term means- until you zoom in on it at least.
To give an example of what I mean, green and blue are both useful words, and there are many cases where everyone would agree that something is blue, and many cases where everyone would agree that something is green.  However, when one zooms in on the line, it turns out, there is not a clear line. It is easy to find colours that some would call green and others blue. 

Something can be useful as a word, and still not actually have clearly defined parameters.

What then is a chemical reaction?     A computer virus causes changes to the physical world on the microscopic scale, often changing magnetic states or manipulating individual electrons. I will admit that most chemists would not call that a chemical reaction, but say that it comes close, because most electric charge is fundamentally the main thing that factors into chemical reactions.

You say that memes are not living, and go on to say that they do not cause physical changes.
Ignoring the claim about genes being living or not, I will address the claim that they are not responsible for physical changes, and more specifically, not chemical reactions.
I make two main rebuttals to this point.

1) To say that a meme can not be credited with the physical changes that have a multi-step causal chain connecting them to the meme would be akin to saying that no prototypical effects could be associated with the genes that caused them, and that all you could credit to the gene is the formation of protein.   

However, we can clearly establish that a given gene is linked to a given effect. Or course, any gene in isolation would not cause the effect- the prototypical effect can occur only in the context of the organism. This does not in any way decrease the validity of saying that GENE caused TRAIT.

I don't really see how it is different to say that IDEA [meme] caused METABOLIC EVENT. Just like with genes, one can trace the chain of causality back to the meme, and, just like genes, the effect only takes place in the context of the rest of the organism.

2) For a second, let us not treat an idea like an abstract object, and look at the actual science going on. Unless you are planning on rejecting neuroscience, you will agree that the brain handles thinking through a combination of neurons [with extreme significance on the ways in which they are connected to each other], as well as various chemicals that modify the function of, or interaction between neurons, including hormones and neurotransmitters, and including complex substances such as re-uptake inhibitors.

Almost everything that goes on inside the brain is chemical, ranging from the specifics of what causes a neuron to fire, to the actual mechanism of what happens at the neurotransmitter receptor sites, to the way that neurotransmitters get broken down.   

Additionally, neurons themselves are full of the usual storm of chemical reactions that are characteristic of almost any cell, as well as much more specialized chemical reactions related to the action potential and the refractory period.

I should elaborate: When a neuron fires, it undergoes a large change in polarity [after first a small change in polarity caused it to fire in the first place]. After that, there is a very short period during which the neuron cannot fire, and is busy re polarizing itself. This is called the refractory period.   Several chemical reactions are involved in the refractory period.


The reason I am saying all this is that an idea is not just some abstract concept. It must actually have some physical component, or, by definition, it would not be a part of our universe.

The physical existence of an idea, its body if you like, is a specific pattern of neurons and chemicals. At any given moment, every idea in your head has a set of neurons that are part of that idea. If something other than the normal action of the brain were to change one of those neurons, it would change that instance of the idea.
If you don't like that, or it doesn't feel right, I offer the following logical proof:
* An instance of an idea in a human consists of thought.
* The mechanical process that we perceive as thought fundamentally involves the manipulation of neurons and neuron-affecting chemicals in the brain.
* Thus, an instance of an idea in a human exists in the manipulation of neurons and neuron-affecting chemicals.
Q.E.D
That proof was probably not necessary, but I am going for completeness.


Anyways, even if you refuse to accept that memes (ideas) are responsible for macroscopic changes, such as building a church, by their very nature, ideas as they exist in people, not only cause, but FUNDAMENTALLY CONSIST OF, chemical reactions as they pertain to neurons.   
Thus, you must accept that ideas are DIRECTLY INVOLVED IN AND ARE DIRECTLY RESPONSIBLE FOR CERTAIN METABOLIC EVENTS.

I will leave aside the discussions of viruses as life, and certain other points, for now.

EDIT: To respond to your second post, which got posted while I was composing this, what about a cell? That can metabolize and grow, but in multi-celled organisms, I don't think it would constitute the smallest unit of life, in the way that I think you meant earlier.

EDIT #2: Also, to your earlier point about how something doesn't necessarily need to be able to replicate/reproduce NOW, it just needed to at some point, what if I change the example to a Bull that was born sterile?