Alive? How can I tell?

In Cecil’s current response to a query about stomping out viruses, he brings up the point that viruses aren’t stricty alive, as are bacteria – which, I believe, is biopolitically correct – and then he goes on to speak of them as parasites. Can one be a parasite without being alive? I was going to do myself in in the interest of trying to determine this issue, but I couldn’t figure out a good way of reporting the results to the teeming millions on this MB, so instead you unfortunately get a question here rather than an answer. Well, actually, two of them; my real question is:

GIVEN THAT BIOLOGY THESE DAYS THINKS IT’S PRETTY HARD-NOSED SCIENCE, EXACTLY HOW DOES ONE DRAW THE FINE LINE, AT PRESENT, BETWEEN LIFE AND NON-LIFE?

Ray (escaped from Conway’s game)


“The more the universe seems comprehensible, the more it also seems pointless.” – Steven Weinberg, Physicist

I thought that viruses weren’t considered alive because they lacked the full apparatus for reproducing, but had to use another cell’s protein-building machinery to build copies of themselves.

If I remember correctly, the requirements for life are:

  1. Made of cells
  2. Reproduces
  3. Reacts with its surroundings

There are two others but I don’t remember them from biology class.

A virus isn’t alive because it is not made of cells.


We must blame them and cause a fuss before somebody thinks of blaming us.
Sheila Broflofski

IMHO:

For Carbon Based Organisms:

Ingestion of nutrients, respiration, excreta, procreation.

Viruses cannot replicate themselves, lacking the requisite DNA, which is why they must invade an organism.
Once in the cell, they insert their RNA, and turn the cell into a virus factory.
Once the cell fills up with virus particles, it ruptures, spewing out the particles, and dying in the process. Repeat.

There was a fascinating episode on the Discovery Channel (I think) concerning this very subject.


VB

I could never eat a mouse raw…their little feet are probably real cold going down. :rolleyes:

I’m not a religious type-a-guy, but I do find it humbling that the human race will die out one day, from exposure to a NON-life form…

Cartooniverse ( always delighted to shed some sunshine wherever I go…rofl )


If you want to kiss the sky, you’d better learn how to kneel.

The definition of life is one of my pet peeves. I WANT it to be written in terms of chemistry or physics, since a definition should be founded on more basic concepts already established. Unfortunately, we have for our definition a list of properties - metabolism, adaptation to the environment, growth, reproduction, etc. It’s bad enough that no two authorities seem to agree on exactly what the list is, but when you look closely at something like, oh say, “metabolism” it is defined as (American Heritage Dictionary)
1 a : the sum of the processes in the buildup and destruction of protoplasm; specifically : the chemical changes in LIVING CELLS by which energy is provided for vital processes and activities and new material is assimilated b : the sum of the processes by which a particular substance is handled in the LIVING body c : the sum of the metabolic activities taking place in a particular environment <the metabolism of a lake>

I added the capitalization. Seems a bit cicular to use this word as one of the traits defining life. And really, it’s no wonder we get a circle - metabolism as a process is an abstraction of those processes observed to occur in things everyone just already knew were alive (before viruses were discovered.) Now we have viruses, and rather than sensibly remove metabolism from the list of requirements, we have gone the other way and removed viruses from the list of living things.

I expect a lot of this mindset comes from the discovery by a chemist that viruses can be crystalized, which originally shocked a lot of people - hey! You can’t crystalize living things!

I think excluding viruses from the designation “living” is extremely artificial. After all, YOUR metabolism is not complete: There are a lot of molecules you need to carry out “life functions” that your body must parasitize from other organisms, usually plants. This true for any heterotroph. Viruses have taken this to an extreme degree, and can only be said to “have metabolism” during the part of their life cycle when they are parasitizing all their molecules (besides DNA and a few enzymes) from a cell.

The designations are all arbitrary in the case of viruses, but their behavior, structure, and the conclusions we draw from studying them have far more in common with “the rest of” the living world than with any “other” nonliving system I’m aware of.

Hey, I’m with the guy with all the 9s in his monicker. . .although I, of course, don’t know the subject like he does.

I think we should point out to the politicians and bureaucrats that, if viruses ain’t alive, why the devil should those biologers be getting all those grants of public money to study them thingies, huh? And if nanotechnologists are starting to build gismos that can march into biological cell structures and diddle things, oughtn’t the chemists to take some of that on down to shuffling amino acids? And then the software types could march in with their McAfee or Norton sort of virus-zapping algorithms. And then, if the biologers don’t then claim viruses as part of their menagerie, the latter can attack with Trojan Horses (Equus troyiani, or whatever) and take over the former’s scope of science.

Yes, it seems to me that viruses are much more attached to the ideas of life than to less complex chemistry of proclaimed non-life, although I wasn’t aware they could be crystallized. When they’re “crystallized”, do they exhibit any of their characteristic odd shapes? If so, then I would wonder what, exactly, the definition of crystallization ought to be.

My, probably older and more abridged, Amer. Her. dictionary (2nd Coll Ed, 1982), defines life as:

  1. The property or quality that distinguishes living organisms from dead organisms and inanimate matter, manifested in functions such as metabolism, growth, response to stimuli, and reproduction.

OK, ya wanna be that way, howdaya define death? Oh:

  1. The act of dying; termination of life.

The circles are getting shorter radii all the time.

The death of cells were mentioned in some above posts. One would kind of wonders what really constitutes the “death”, then, of a cell. Like we used to claim people and animals kicked off when their tickers stopped, but now we usually talk about brain death. Well, I ain’t seen either tickers or thinkers in biological cells.

And, oh yeah, that term, inanimate:

  1. Not having the qualities associated with active, living organisms; not animate.

animateadj. 1. Possessing life; living.

So none of these definitions are very operational. . .at least not in terms of physics and chemistry, as 9999er points out.

I agree, in that I think that once matter is configured complexly enough that it is able to change form in a more complex way than the comparatively uniform way that occurs in the case of crystallization, it should be categorized by a term that would include what we now term life. Granted, you would probably want to have a term also for the more restricted variety of such a beast as maintains its own DNA or something similar with which to replicate.

The Burrito says:

I think you’re talking here about CA.US’s prisons. They’re composed of cells. They keep reproducing at a rate higher than almost any colony of their species in the world. And they react with their surroundings – very much in the way of sustenance, i.e., for numerous 50,000-some-odd-population cities that live off them.

Vestal Blue:

So are viruses carbon-based “organisms” but not life forms? Each of those requirements can be sufficiently broadly defined to include viruses, don’t you think? The fact that a virus must get some help from a higher “living” organization/organism to procreate shouldn’t contradict that fact that it does “procreate” in this way.

But Blue somehow killed, i.e, de-animatized, let alone de-animated, (read, deadicated or made dead) his :rolleyes: Was that by checking ‘Disable Smilies’? Hopefully, mine here has a living cell beating for it, and it will replicate all over cyberspace.

And, well, I see that Cartooniverse, the sunshine-shedder, (Is that perverse-funnies) is raining on the parade of life with his glee in entropy’s finally quelling all these hopping, soul-bearing widgets.

Ray (What hath rotted God?)


“The more the universe seems comprehensible, the more it also seems pointless.” – Steven Weinberg, Physicist

The list I have of requirements of organisms(yes, I do think all organisms are considered alive) encompasses some of what has already been said, but I thought I’d put up the complete list anyways.

Requirements:
1)Specific organization
2)Ability to reproduce
3)Possession of DNA or RNA
4)All life forms have a water requirement
5)Irritability (response to stimuli)
6)The ability to maintain homeostasis
7)Nutritional requirement
8)Ability to grow and differentiate

As for viruses, I don’t think they fall under 5, 6, and 7 very well, but I’m not completely sure. They do have specific organization, but it is not cellularly based, as hightechburrito already pointed out.

This line confuses me. I know you are saying it half-seriously, but you are partly serious, right? How do you think ‘tickers’ and ‘thinkers’ work? They themselves are obviously made out of cells which are doing all of the work. When the cells of the organ die, the organ will also start to die. Get it? Or did I take you too seriously? Has your question been answered yet?


“The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents.”
-H.P. Lovecraft, “The Call of Cthulhu”

Don’t think of life as an either/or scenario. IMO, the most accurate way to look at it is as the quality of “life” being a gradient. Viruses are less alive than ferrets but more alive than rocks.

Biology may be a “hard-nosed science”, but few questions in science have “yes or no” answers.


I used to rock and roll all night and party every day. Then it was every other day. Now I’m lucky if I can find a half an hour a week in which to get funky.

Unforgiven, I think what Nanobyte meant was, if cessation of heartbeat or brain function is used to define the death of a multicellular organism, what is the equivalent dividing line between “alive” and “dead” at the cell level? It’s a good question. I can tell you that in the lab where I work, we can tell that cells are dead because they look different under the microscope than they do when they’re alive. They develop a different optical property that’s hard to define. Sort of a loss of “sheen”. Of course for anything more quantitative, you would measure cell death not for a given cell but for a poulation of them, generally by what percentage of cells could take up a dye. I’ve never heard anyone grapple with the notion of what point in time a single cell can be said to die. Of course, just as with multicellular animals, any “point in time” is artificial anyway. The general cessation of metabolism, either cellular or organismic, doesn’t take place at a point but over a period of time. But with humans you often HAVE to give a more-or-less precise time of death for things like the death certificate. On a practical level, this is really the point in time where the dying process can no longer be reversed by any known means - hence the switch from ‘lack of heartbeat’ to ‘lack of brain activity’ as technology has improved.

Actually, there’s are very well studied viruses of E.coli that can insert their DNA into the bacterium’s chromosome and just lay dormant. As the bacteria reproduces itself (and therefore its chromosome), the virus is also reproduced. But when the bacterium is exposed to the environmental stress of UV light, the virus excises itself from the chromosome and becomes active again, packaging itself in protein to form the infective form (and destroying the cell in the process). Why UV light? Remember, E.coli lives in the guts. Exposure to UV means it has been shit out and is “seeing” sunlight, and hence is likely to die from exposure (and with it the virus) unless it can find its way into some new host. The virus is “abandoning ship” and spreading to the surrounding cells in hopes that at least one of them will make it. Cool, huh? So I’d say they have at least some capacity for number 5, response to stimuli. Number 6 assumes some sort of metabolic process. Number 7 depends on how you define “nutrient”. In a sense, when the virus commandeers cellular nucleotides from its host to make new viral genes, these nucleotides are nutrients for the virus, just as when you commandeer starches from a potato to make glycogen :). So really, number 6 is the only problem I see.

I don’t like this list actually. I would not find it surprising if there were something on another planet which we would all immediately recognize as “living” that nevertheless chooses to keep its genetic information in a molecule other than DNA. It might have something chemically similar to DNA, but to use the exact molecules we do is not necessary for the function of storing genetic information. This is why I want a more physical definition, something like “To be categorized as alive, the candidate object must exhibit stored information that can be translated under appropriate circumstances to produce a complete copy of the original object.” Or something like that. This particular definition has problems, too, but it’s the kind of thing I want, since it isn’t merely a description of things we’ve always seen in living organisms, but an abstraction of the concept that allows us to recognize life.

Sorry for the long post, but one last thing for Nanobyte. Viruses crystalizing just means that they will come together to form, well, a crystal, i.e. a material in which the units making it up (atoms, in the case of salt or gold, viral particles in this case) lay down in an ordered, symmetrical pattern.

I believe that NASA defines life as a self-contained chemical system that has the ability to replicate and the capacity to undergo gradual change. By this definition, I suppose, viruses can indeed be called living things. This definition also frees us from a requirement for DNA or RNA in considering extraterrestrial life.

APB:

So if you did accept the Unforgiven list, presence of homeostasis would define life? But an infinite number of chemical systems we would never associate with life maintain homeostasis.

And should I assume that crystallized viruses maintain their characteristic shapes while all being tesselated into something reminding one of a product of Escher? Or do they dissociate into unrecognizable arrays of their components, releasing all their individual rights to ownership thereof in complete communistic manner?

Fillet: Is that a definition applied within NASA over all of biology. . .or just over all contemplated exobiology?

Ray


“The more the universe seems comprehensible, the more it also seems pointless.” – Steven Weinberg, Physicist

As I understand it, the NASA definition applies to life in general (here or elsewhere).

According to my biology book (Modern Biology, from Holt, Rinehart, and Winston), there are six characteristics of life, and to be alive, an organism must meet all six:

  1. Must have cells/be a cell.
  2. Must have organization.
  3. Must use energy by means of metabolism.
  4. Must maintain homeostasis (stable internal conditions).
  5. Must grow.
  6. Must have the ability to reproduce.

A virus does not grow, does not maintain homeostasis, and does not have metabolism. Ergo, according to my biology book, it is not alive.

It is actually somewhat hard to “officially” tell if something is alive or not, at least without careful observation. One can make an argument that something already has reproduced, and already has grown, thus meeting those qualifications. Anything can be said to have structure. Maintaining homeostasis can be somewhat hard to judge, “conformers” (cold-blooded animals) do not control some of their internal conditions, but are still judged to maintain homeostasis. One would have to get out a microscope to judge if there are cells are not, and someone can always say “oh, your microscope isn’t powerful enough.” The metabolism takes place inside the cell, so that rests on the previous condition.

For practical purposes, obviously, that is not really a problem. If it looks alive and you think it’s alive, it probably is :wink:

You are doing what people have been doing since the beginning: Searching for the meaning of life.

Nanobyte,

Well, I think the idea of Unforgiven’s list is that something would have to have all the properties on it to be considered alive, not just any of them.

And viruses maintain their shape when they crystallize.

NASA’s definition is pretty good, except that the words “self-contained” are a little misleading. Thermodynamics forbids some obvious characteristics of life unless the living object is an open system. Also, the word “replicate” requires some qualification: I, personally, would reject anything that can’t evolve as not being life - hence the second part about gradual change. That means that the replication cannot be perfect replication. So given that a living thing’s replication must be no better than approximate, where do we draw the line? That is, how unlike the “parent” can the “offspring” be and still count as a valid replication?

These definitions always end up fuzzy when you look at them too closely. It’s very frustrating. Basically, it amounts to what DSP and a famous judge once said:
“I can’t exactly define life, but I know it when I see it.”

Oh yes, and about viruses. Vestal Blue said that they are not alive because they lack their own DNA; I feel compelled to point out that many viruses have their own DNA, e.g., papoviruses, adenviruses, herpesviruses, poxviruses…That said, many use RNA, and some have an amazing enzyme known as reverse transcriptase by which RNA is used as a template to create DNA and replicate the virus. These retroviruses include the HIV virus.

Also, APB9999 said something about e. coli being viruses…e. coli are bacteria. He also said however, something about viruses that can insert their DNA into a host cells’ DNA and then have it lie dormant until it is affected by something like ultraviolet light, or heat, or change in pH…This is known as the lysogenic cycle, and quite a few viruses employ it; the others use the lytic cycle, which simply goes in, replicates, and destroys the cell immediately. Oh, and from that same post, bacteriophage is the technical name for bacteria invading viruses, if anyone cares. My biology is actually becoming useful, or at least making me look somewhat smart, wow.

Ah, now I feel somewhat stupid, I misread APB9999’s post. He said viruses of e. coli, not e. coli viruses, my mistake :slight_smile:


A Freudian slip is when you say one thing and mean your mother.

Um, did I?

Nah, I just can’t read :slight_smile:


A Freudian slip is when you say one thing and mean your mother.