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A universal definition of life.
Any entity that has the ability to store and exchange information autonomously.
Perhaps as we move through the next millenium we will need a definition of life that is this general. It may be needed to classify artificial life or to classify alien life. We may find life forms so different to ourselves that the only recognisable feature is information management. It might also help us to identify the point at which a person is no longer alive.
Lint Porter
This was addressed by my high school biology teacher. It was something like :
1. metabolism
2. reproduction (to a highly self-same form)
The question was then raised: is FIRE alive? it breathes (conducts metabolism) and reproduces. But it doesn't reproduce to a highly self-same form; so fire is not alive, but biological organisms are. This touches on your "store and exchange information" point.
Viruses are also not alive, because they don't conduct metabolism.
peter lindsay 30+
Lint Porter
Our scientists have much different notions of life, in that case.
Viruses are much simpler than bacteria; and completely inert until they injecting RNA into a cell. They have no independent means of reproduction. Some of them are not even *contiguous* (e.g. the Hepatitis B virus comes in 2 pieces).
Biologists can actually build some viruses in a lab from scratch. That's not remotely true for a cell (though Craig Venter has bootstrapped the DNA of a cell).
If you're going to categorize a virus as life, you might as well define a prion as life. A prion is just a single (mis-shaped) protein.
peter lindsay 30+
Lint Porter
At the point that you have metabolism (energy consumption) and self-same reproduction, I would say that's life.
... The future might bring new ambiguous cases, if technology creates a reproducing robot (not just self-assembling, but actually self-reproducing from raw materials in the environment).
peter lindsay 30+
Gerald O'brian 50+
peter lindsay 30+
Gerald O'brian 50+
So I'd say living things are entities with knowledge about their environment encoded in them, as a result of mutation and selection.
Anne Thull
Mitch SMith 50+
The modulation of entropy.
Or to be needlessly complex:
A self-persistent pattern -
That which precipitates self-advantage sufficient to persist from this moment to the next.
I am sure ther are other models, but in biological examples we have this dynamic - that occurs in a separation of "self" and "else":
energy state of the instant -->sense-->determine advantage(means of persistence)-->potential agency-->act-->change of energy state (repeat until self is disrupted).
In higher organisms is gets a little more complex:
state-->sense-->percieve-->update map-->predict-->potential agency-->advantage evaluation-->potential agency-->act-->change of energy state.(repeat).
In social organisms there is also a step to de-code packaged perception(communication) that occurs after the perception step and enhances the potential agency .. it also causes a sub-branch to package perception(information) to be emmitted as part of agency.
edward long 100+
"Life is a thermodynamically open chemical system with a semi-permeable boundary. It contains an information-based complex system with emergent properties, part of which drives a metabolism based on a proton gradient. The said gradient generates the necessary potential difference across the semi-permeable boundary. The information is heritable and coded in such a way as to allow variation and thus evolution."
All I can add is that when you are finished doing what he said, you die!
Ed Schulte 50+
Andrew Kevins
I believe a sterile cloned animal would be alive based on my classification of anything that carries out cellular respiration being alive, I don't believe the ability to reproduce is necessary for a classification of living however it can be used as a guiding principle for classifying acellular forms, by which I mean that reproduction is a common trait amongst cellularly respiring life forms and therefor may help guide our classification of non-cellularly respiring forms.
Essentially, if some acellular form had the same properties as a cellularly respiring life form however was not a cell, that would be a pretty compelling argument to classify it as an acellular life form.
Here's an interesting one for you, what about Craig Venter's artificial bacteria cell? If you haven't seen the TED video do check it out, very good stuff!
Rohan Zolokov
If you take away the capability of reproduction from a cell, then you get a form which is alive for maybe a few weeks then it is no more and never will be because we took its livelihood away. So yes it was alive. But not live. When you say it is alive then it implies the fact that it was brought to life. But when you say live than it means that it is capable of existing. And this cell is not, because we took away its reproductive function. After ran its course it will die. If you take away the reproductive function by host, from the virus, it will be no more because the reproduction itself is the life of the virus. The mechanism of reproduction is came to be in the universe, so forms that are more fragile than a granite slab can keep existing but not by keeping one individual alive but rather being able to reproduce and pass down itself to another. We must argue this “what is life and living” question not by one individual from a herd but by clusters. If a form came to existence by the universe trials and errors and it is capable to sustain itself by interacting with its surrounding and reproduce itself to be able to keep the interaction going then it is a living form. When a form came to existence by the universe trials and errors and it is capable to sustain itself by interacting with its surrounding but no longer (as a whole species) or never was able to reproduce, it is alive but not an ongoing living form. And most likely we will never meet this form in an alive state because it will die very quickly. And it will because of its fragile nature.
To look at the prion. I would not consider it alive since it does not pass the info to the next one how to create another prion. Maybe in a few million years it will but not just yet.
Andrew Kevins
With regard to the rock/moss situation, that's a little bit different to the virus situation because viruses, whether nucleic acid or software based, rely on their host to carry out the mechanisms of reproduction for them, whereas the rock is not carrying out reproduction for the moss, it is simply acting as some sort of input for the moss to grow from.
The same argument can be used for trees and soil. Soil only provides various inputs for trees such as nitrogen and water, even humans need food to function, even chloroplast containing bacteria rely on photons from the sun to provide energy for cellular respiration. No life form can survive independently of everything.
I suppose my point is whether reproduction is considered essential for a classification as living, in which case viruses may not not count, depending on your classification of reproduction, and software viruses in particular as their existence is dependent on a foreign entity (for lack of a better word) which itself has no means of reproduction.
Zared Schwartz
1) All living things are composed of cells and cell products.
2) New cells are formed only by division of preexisting cells.
3) All cells are basically similar in chemical makeup and in metabolic activities.
4) The activity of an organism is due to the collective activities and interactions of all of its cells.
Moreover, all organisms must maintain boundaries, metabolism, movement, responsiveness, digestion, excretion, reproduction, and growth in order to be define as alive.
peter lindsay 30+
2)Where did the first cell come from?
3)This is only relevant if you limit life to things that evolved on the Earth's surface. There are whole communities of living things that use quite different metabolic processes around mid-ocean ridges.
Cell theory was first coined in the mid 1600s so maybe we should move on.
Zared Schwartz
peter lindsay 30+
Zared Schwartz
peter lindsay 30+
Zared Schwartz
peter lindsay 30+
And any discussion regarding whether viruses or prions are alive is pointless?
Zared Schwartz
peter lindsay 30+
Ritchie Armer
Andrew Kevins
In fact, I think I may take another shot at it later tonight :)
Adrinn Chelton
So by this definition a virus would be a rudimentary or proto form of life. Since it doesn't act directly, but makes it's host act for it.
Life doesn't have to reproduce or even be capable of it, if it did a sterile human wouldn't fit the definition.
Andrew Kevins
What about a prion? It's basically a naked protein, can something that simple be considered alive?
Adrinn Chelton
If you use intrinsic to mean relating to the individual(self-determined) and keep it at that then I don't think a prion is fully alive, it is potentially alive though. Prions cause susceptible(similar) proteins to fold in unusual ways which damage the host, so they are more along the lines of an toxin. Albeit one that can reproduce itself similar to a virus, so possibly a proto life form? Maybe in a few billion years prion derived intelligent life will be pondering these questions.
Andrew Kevins
Viruses are acellular, if you consider viruses to be alive then there's an example of acellular life.
the reason I brought up cellular respiration is that viruses do not have cellular respiration, if you remove reproduction from the argument of life as well, I don't think viruses have much left that could classify them as living.
Rohan Zolokov
I`m not a biologist and also fairly new to these matters so please forgive me if my logic makes no sense and definitely feel free to correct me.
Rohan Zolokov
Regarding the living computer software, yes it does reproduce itself and it may also have the capability to adapt, however it did not came to "life" by itself. It had to be engineered. So at best we can call it artificial life. I think all life forms came about without (as far as we know it) engineering. They came to be by the interaction between matter. Of course you can take a bag of computer code and throw it up in the air and calculate, what are the chances that they will fall into the perfect combination to create a software "naturally". And most likely there is a number probably in 1 in the billions or something like that. I’m sure that in the not so distant future there will be living things that are half engineered and half naturally produced, and as I wrote this I just realized that there are already. We might consider the genetically altered plants, algae and so on into this half and half category.
At the end I still like to stick with the definition that a living thing is a form which is capable to reproduce and sustain itself at least for long enough to be able to complete one reproductive cycle. And life is the interaction between non reproducing and reproducing forms.
Adrinn Chelton
Rohan Zolokov
Andrew Kevins
interesting concept with the software virus, can a software virus be considered life if it reproduces only within an artificial cell (a computer) which itself has no means of reproducing?
Also, how about a cross species such as a mule? Is it considered life as a sterile species (I'm kinda cheating there because mules are not species, rather the failed mating of 2 disparate species)?
Rohan Zolokov
We might consider it alive but that would be artificial life only. To answer the other part if the “host computer” does not reproduce I`m not sure but there is a type of moss which is living in rocks. This moss is alive although it would not be able to exist without that very rock. The rock would be the non-reproducing host.
For the mule. It is alive since it came to be. The cross mating is just as random as thee sterilization in a human being.
Adrinn Chelton
What about a computer program which thought of itself as alive? Would it be alive since it came to be? Arguably it was created by life, humans.
Andrew Kevins
peter lindsay 30+
Ritchie Armer
Rohan Zolokov
To simplify it even more: Life is participation.
peace,wisdom,prosperity for all...
Frans Kellner 100+
To define is to close it within borders that really doesn't exist within the natural world.
The thing is that nothing in itself exists separately but is defined by what it is not.
So anything is defined by everything.
Gerald O'brian 50+
Such as?
Frans Kellner 100+
If I say:"that's a rose.", I may point at a picture or the real thing, you may think that you know what is a rose because you saw one before and you associate the word with the appearance as you remember.
But to really know a rose you need to understand the rosebush, the way they multiply, the environment of the plant and its history. You have to know the elements and light, cell building/differentiation, the universe - you have to understand being itself to know a rose.
You don't know a thing by describing its morphology alone. Color, smell, you even have to describe yourself as well.
Gerald O'brian 50+
A rose is also a symbol in litterature, politics, ... more than a living thing, more than a bunch of atoms.
But to give a definition of a rose is to share some understanding of it.
I think everything can and should be defined.
Definition of a rose : a horny bush planted in public gardens to keep children off the lawn.
Feyisayo Anjorin 50+
Anything that has the potential to die has life.
Stewart Gault 30+
Moves
Respires
Sensitivity
Grows
Reproduces
Excretes
Nutrition- as in it eats.
pat gilbert 50+
Andrew Kevins
pat gilbert 50+
Andrew Kevins
pat gilbert 50+
Gail . 50+
For me, a well-lived life is one spent learning, which is how I try to spend my days. Those who choose willful ignorance or intellectual laziness aren't really living. They're just existing.
Gail . 50+
Gerald O'brian 50+
Gerald O'brian 50+
Define "autonmously".
Also, where does a sterile animal stand in that definition?
Budimir Zdravkovic 20+
peter lindsay 30+
By this most general of definitions viruses are alive if they are in the appropriate environment. But so is some computer software in its environment.
Budimir Zdravkovic 20+
peter lindsay 30+
Budimir Zdravkovic 20+
Jon Ho
Indeed, have you ever heard of liquid crystal? A couple of centuries ago some Austrian botanist called Reinitzer discovered liquid crystal. Now, liquid crystal displays all the properties of being alive; it seemed to be able to grow, move, divide, copulate, and so on and so forth.
So. here you have it. ;)
Pedro Silva
Now we have trouble defining when human life starts, how can we define other? What happen when we find an alien life that simply doesn’t born, doesn’t eat, doesn’t multiple? Better yet, will they consider us as living things? how will we prove to them that we are living things?
Debra Smith 200+
http://youtu.be/3PMlDidyG_I
http://youtu.be/0f0hns2AVW0