Something we can quantify, eh? Hmm. That almost seems more line-in-the-sand-ish to me, at least if it’s of the form “Things that are alive have at least X units of Quantity A, while things that are not alive have less than X units.” Well, why not use Y as the dividing point? Or Z?
I still maintain that the difference is this: Living organisms themselves combine their complex prefabricated materials into a new organism, while inanimate things don’t, because they require some process not involving the inanimate thing in question to make the key connection. Can we agree on reproduction as the essential element, though?
The trick is that every test you devise will have advocates for moving the line. And that’s because there is a continuum from the inert to the animals se know. A virus is alive, clearly, but what of a dormant one? What of one that’s cut in half, but might randomly reattach and carry on? …
I’m puzzled by how many people seem to be assuming that a virus is alive. A virus cannot reproduce on its own; it relies on the use of mechanisms in other organisms to reproduce it. It may be that there is some reasonable definition of life which includes viruses, and certainly a virus is similar in some ways to things which are alive. But to start from the assertation that a virus is alive is to beg the question.
I made cited, salient points. Your rebuttal is terrible. You could at least try and come up with something to argue against the standard definition of life. There are many other definitions to choose from, some of which even support your incorrectly structured argument.
Instead you try and do exactly what you are blaming me for. Yet, my post has cites, IS about the OP, “What Defines Life?”, and, to boot, it is the funniest thing ever written. You could try a little harder, sheeesh.
The fact that there are so many definitions of “life” points to the fundamental problem: there is no single definition that can apply to all cases. As with trying to define “species”, the problem is difficult because, as Ty Cobb observed, there is a continuum involved.
At some point, barring divine intervention, it must have been the case that life arose from non-life. Such a transition from simple chemical reactions to something we might call “living thing” was almost certainly gradual. This means there will be a fuzzy region along the continuum in which certain entities cannot be definitively placed in either the “life” or “non-life” box. Viruses probably fall within this fuzzy region, exhibiting some characteristics which are only applicable to living things, and not exhibiting others.
The reality is that no matter what set of criteria you choose to define “life”, something out there will likely exhibit some, but not all, of those characters. The more rigidly you attempt to define the characteristic, the more likely you will be confounded when you actually look at the variety found in nature.
Look at the criterion of “reproduction”, for example. Under what circumstances? A single human is incapable of reproducing, yet most would consider a human (that wasn’t “dead”, anyway) to be “living”. A population of males (or females) would similarly, typically, be considered alive, but incapable of reproducing on its own. A population of mixed sexes can reproduce on its own, but then do we only consider the population as a whole alive? If the population can reproduce, is the characteristic of “living thing” simply assumed for each individual within that population, then?
Because of the vagueries involved, we wind up with assorted “working definitions”, again comparable to the case with species. In some circumstances, certain criteria are best considered. Viruses aren’t typically considered “living” in the “organism” sense. Individuals within a population are considered alive even though they may not necessarily exhibit all the characteristics that the whole population might. But there is unlikely to be a defintion of Life that will both apply universally and can be applied discretely.
I am no expert on this issue but I am well aware of the points you make in your response.
I am of the opinion that the standard definition for what life is given on Wiki is a fairly accurate and useful definition of the characteristics of life-forms on Earth.
There are many unanswered questions though and the standard definition does not perfectly define the borders of what could be life and the matter that makes up that life-form or other forms of life we might imagine but not yet encountered.
I do not think a virus, protein or protein prion are life-forms, for example. Even a single cell is pushing it. All the cells that share identical DNA would be a life-form IMHO, but possibly not a single cell. Would an ant or the colony be a life-form? These things are very interesting questions and certainly I do not have a clear answer.
However, trying to make the case that a DVD is a life-form because we use the word “replication” to describe both the inanimate objects copying process and a life-forms replication process is extremely disingenuous to the argument. Fractal analogies do not mean two processes are equatable and that is what Blake is trying to argue.
I am a staunch evolutionist. I think life started out from one or two points in Earth’s past. For the sake of argument, lets assume it happened once and a single cell arose from this start. That cell divided and divided and so on, until miraculously, we have the bio-diversity on Earth today.
Is this really bio-diversity though? All the individual life-forms we find today came from that single cell. Isn’t it really just one life-form? Aren’t our own individual consciousness’ just trying to divide something up that is really just one life-form with many different parts? What about alien life or created life, how will we define it?
Like what happens if we create AI? Does consciousness mean it is alive or can we have consciousness without life? It seems we can have life without consciouness so…?
Is there any chemical process/transformation that occurs in living things that does not occur currently in nature w/o living things?
Are there any molecules or atomic structures that only exist in living things due to the requirement of constant energy usage to maintain the structure?
Maybe something along these lines will get us most of the way there.
Chronos, I disagree. The method we’ve been using to define life has been to take certain cases that we know should fall into “alive” or “inanimate,” and then craft a definition of life, a general principle, that includes the former and excludes the latter. Now, I’m not up on my virology, so it may be that we don’t want to include viruses in the alive category, but viruses are such a liminal case that I think to not use them to refine our definition is silly.
Your point is a valid one. I’ve been taking care to insert the word “capability” in the appropriate places to ensure that we include those organisms who may lack for one reason or another the right opportunity, such as a lone human being, who could reproduce if there were only a mate present. Now, that leaves us with, for example, a person born with a disorder that renders him sterile. Obviously we want to include him in our definition of “alive,” and a definition comprised solely of a refined concept of reproduction cannot do that. So perhaps an inclusive or, namely, we consider something to be alive if either or both of the following conditions hold:
It is clear beyond all doubt that the organism can communicate.
The organism can reproduce, with a suitably adjusted definition for reproduce.
I’m not sure I like the first part, because it leaves it up to our capability to determine whether or not the capability for communication is present. Other ideas?
Yeah, but that doesn’t mean we can’t try to find one anyway.
This is what I was aiming at; there are simply scads of chemical reactions going on all the time. Let’s say we’re talking about A plus B being converted into C. If we re-create this in a test tube, , starting with only A and B, over time, we’d see the amount of A+B decrease, and the amount of C increase. Eventually, a state of equilibrium would be reached and the concentration of all three compounds would remain static.
In a living organism, this equilibrium would never be reached except in death; C could be further converted into D, or exhaled, such that, as long as you kept up a regular supply of A and B (by eating it, say), the reaction would continue in one direction, and equilibrium would never be reached.
Here’s another analogy. Stand up. Now lean forward. Now lean forward a little more. And a little more. Now, pick yourself up off the floor. Fell down, didn’t ya?Lean too far forward and you fall down, right? Well, what if, just as you started to fall, you took a step forward? You wouldn’t fall down. Of course, you’d then have to take another one, and then another one, but as long as you kept accelerating, even though you were leaning forward, you wouldn’t fall down. That kind of “metastable state”-on a chemical scale- constitutes my definition of life.
I don’t want to say you are not going anywhere with this but your analogy is apples and oranges.
In your first example you have a closed system, carrying out a chemical reaction. In the second you have an open system carrying out a chemical reaction. In the first you have a limited supply of A and B and the second you have an unlimitted supply. If you had an unlimitted supply of A and B in the first example you would get the same results.
You may have something here but you haven’t logically illustrated it yet.
Just so you know, I am pretty sure you are trying to re-invent the theory of life is defined as reverse entropy or something like that. Look that one up and you might find the information to fully realize your thoughts.
I looked up the Wiki quote on this, life is “A system converting entropy to negentropy, using flow of energy.” cite It is a very interesting thought.
I agree; it was clumsily worded. However, your response is not much better, since you’re talking about a chemical process with an unlimited supply of precursors, and you ignore the effect of an ever-increasing supply of product. Such a thing doesn’t exist; even stars burn out eventually.
My point was that living things never reach equilibrium, until they die. I purposefully kept entropy out of the picture because it is tossed about a little too glibly as a catch-all fudge factor; I’ve been a chemist for the past 25 years, and I still can’t really fathom it.
Chronos, I think that that is the point of this thread. Many people do intuitively consider viruses (why do I question whether this should be viri?) to be alive, correctly or incorrectly. I think that it is because they are biological entities, and they will reproduce. Most people don’t look into the mechanics of their reproduction, as you have. When flu vaccines are being distributed, we are mollified that the vaccines are made from “dead viruses” and therefore we won’t become infected. People’s perceptions of this may be incorrect, but I don’t find it to be puzzling.
Your focus on the use of other organisms in reproduction brings up a point that I had touched upon earlier; symbiotic diseases. For instance, cedar-apple rust is a sybiotic disase between apple trees and Eastern White Cedar. Is this disease “alive”? It requires both hosts to reproduce. Should we consider the spores to be not alive, unless both hosts are present?
I am coming to the conclusion that the word “life” is ambiguous enough to have little or no technical meaning; that it is a fuzzy line that we draw in the water to differentiate one entity from another.
Just because there is a fuzzy line doesn’t mean the word “life” has no value.
We just have 3 sets instead of 2:
Clearly non-life
Not sure
Clearly life
Possibly, if we try hard enough, we can reduce the size of the “not sure” set.
Is God alive? No, seriously. For the sake of argument God exists. Is God carbon-based? Does God reproduce (Son of God is really “alias of God,” no?) Does God eat?
Switch with me now to the movie “Short Circuit.” Is Johnny Five alive (a robot that through fortuitous malfuncion becomes self aware).
I like Sentient Meat’s definition. Should we OR it with “anything that is self-aware?”
I didn’t say that it doesn’t have value, just that it seems to have little or no technical meaning. As much as that seems to be splitting hairs, I am really starting to think this way. In terms of your set theory, the boundary separating “Clearly life” from “Clearly non-life” is the fat and indistinct line that represents “Not sure”. There is value in saying that everything on one side is clearly alive, and clearly not-alive on the other side. However (to this non-scientist at least), technical meaning is rolled into the refinement of the definition of that line.
If we use the entropy definition, how many types of things are in the “not sure” set?
I believe fire is in the “non life” set based on the entropy definition (correct me if wrong on this one).
A virus would appear to be in the “life” set, which intuitively is fine by me, but I’m not a biologist so maybe someone with more knowledge can explain why this is a problem.
