peter lindsay

Physics Teacher,

This conversation is closed.

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.

  • thumb
    Aug 24 2012: Some things can't be defined.
    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.
    • thumb
      Aug 30 2012: "Some things can't be defined"

      Such as?
      • thumb
        Aug 30 2012: Nothing living can be defined without defining the whole system of life.

        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.
        • thumb
          Aug 30 2012: But perhaps definitions are not arrogant attempts to fully encompass everything knowable about a thing. Perhaps they are parochial explanations required in some context.
          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.
  • thumb
    Aug 22 2012: I like this portion of the trial of Data on Star Trek to clarify these issues:


  • thumb
    Aug 28 2012: An astrobiologist at The Open University in the U.K. by the name of Sohan Jhetta has contributed this definition:
    All I can add is that when you are finished doing what he said, you die!
  • Aug 26 2012: Hi Rohan,

    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.
  • thumb
    Aug 26 2012: If a species cannot both reproduce and enjoy copious amounts of drugs, it is infact a half life.
    • Aug 26 2012: I don't know Ritchie, I've had numerous attempts at reproduction, both sexually and asexually, that have not resulted in fruitful offspring, however I feel like I have quite a full life.

      In fact, I think I may take another shot at it later tonight :)
  • thumb
    Aug 25 2012: I throught my life have sort the answer to this question, as i'm sure many people have. At certain periods of my life I found myself going through bouts of depression and anxiety over this very question. I have also found that people with a lesser mind do not understand the concept of a life with definition, but this is not ofcorse based on any hard evidence or proper reasearch on my part. After much soul searching and research I found what I believe works for me and that is sex and drugs. Now life is great.......... Also, the younger the better :)
  • Aug 24 2012: Life is interaction between matter which is able to sustain itself and reproduce to keep its interaction (its own existence) going. This definition is of course is regards to living things. On a larger scale Life is everything there is. And the definition for that would be: Life is the interaction between all forms and their environments. This very interaction then creates an interdependence for all participants.

    To simplify it even more: Life is participation.

    peace,wisdom,prosperity for all...
  • Aug 23 2012: You don't need to go so far as to alien life form in order to define life.

    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. ;)
  • Sep 3 2012: ...

    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.
    • thumb
      Sep 3 2012: I find it very interesting that several people in this conversation have quite categorically stated that viruses are not alive and they have all been US citizens. In AUS the question is considered very much unanswered. We are taught that the jury is out on viruses from junior high level of science. It's an interesting contrast between two very similar cultures.
      • Sep 3 2012: ...

        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.
        • thumb
          Sep 3 2012: So where do you draw the line between living and non-living? At some stage in the evolutionary process a capsule of nucleic acid developed a semi-permiable membrane over thousands of generations, Which generation suddenly became life?
      • Sep 5 2012: I don't think that's well-defined in the PAST (as life was developing) ; but today it's fairly well defined ... in the sense that there are zero (or very few) ambiguous cases today.

        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).
        • thumb
          Sep 5 2012: You realise that if you go into it a bit beyond highschool level there are around 20 kingdoms of living things, many of them don't fit into your definition.
  • thumb
    Aug 30 2012: I don't know what a universal definition is. But I think definitions are not supposed to be universal at all. They should be useful, instead.
    • thumb
      Aug 30 2012: Universal in the sense that it defines life in a way that could be applied to ecosystems that are totally different to the Earth. The current one really only works here.
      • thumb
        Aug 31 2012: Gotcha.
        So I'd say living things are entities with knowledge about their environment encoded in them, as a result of mutation and selection.
  • thumb
    Aug 30 2012: Energy allows life to exist in many variations and dimensions.
  • thumb
    Aug 29 2012: Life:
    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.
  • Aug 26 2012: Hi Adrinn

    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!
    • Aug 27 2012: Hi Andrew

      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.
  • Aug 26 2012: Cell theory:
    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.
    • thumb
      Aug 26 2012: 1)We already have non-cellular life forms on Earth
      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.
      • Aug 27 2012: Unless it is proven false, we should not discount cell theory.
        • thumb
          Aug 27 2012: It certainly describes the majority of life on Earth so far but it may limit our ability to identify life elswhere, if we stick rigidly to it.
      • Aug 28 2012: We cannot just drop a theory in just a mist of doubt for this doubt could just be for nothing. Besides, if we do not have some time of system, then, how would we know the concept of life at all.
        • thumb
          Aug 28 2012: I'm just concerned that if we do ever get to another system we might walk strait past the most developed being there because they don't have cells.
      • Aug 29 2012: If they do not have cells, they are not alive. If you want to dispute this, you would have to prove it. If we can not go to another system without a standardized system, then, we would not know what anything is.
        • thumb
          Aug 29 2012: So the concept of a silicon based crystalline life form that stores information in the form of metal ions in co-ordinate bonds is of no interest?
          And any discussion regarding whether viruses or prions are alive is pointless?
      • Aug 29 2012: Viruses are practically parasites to the living. They are not alive. Prions are similar to viruses, and they are also not alive. The system we have may or may not be accurate for other worlds; however, if we do not have a system, which we can modified, then we would be even more lost in that world.
        • thumb
          Aug 29 2012: You seem very comfortable with the "viruses are not alive" thing but I can't find one biologist on staff that agrees with you. If we assume evolution is correct, at some stage there must have been an intermediate between an unprotected strand of nucleic acid and the first true cell. I just find the presence or absence of an encapsulating membrane a fairly arbitrary point to use for classification of life.
  • Aug 26 2012: That which is capable of acting upon it's environment with intrinsic purpose. I think that would suffice.

    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.
    • Aug 26 2012: If cellular respiration is not necessary, and reproduction is not necessary (which I assume is a viruses intrinsic purpose) then can you classify a virus as a life form, rudimentary or otherwise?

      What about a prion? It's basically a naked protein, can something that simple be considered alive?
      • Aug 26 2012: Well I'm glad to have some debate, I made no mention of cellular respiration as being either necessary or not. I think life could possibly exist in a form other than cellular, this is of course speculation so it remains to be seen. I was speaking to the individual nature of what is alive rather than to what perpetuates life, I agree that reproduction is needed for life to continue past a single generation, but it's not required to regard something as alive in the present.

        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.
        • Aug 26 2012: Hi Adrinn,

          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.
      • Aug 26 2012: I have never heard of prions before. Thank you for bringing it up. I looked it up immediately. What I found is that prions are bordering between nonliving and living just as viruses and scientist still debating if they are considered alive or not. Personally form the information I got in the last 20 minutes about prions I would consider a virus to be more closely to be alive then a prion. It seems to me that the prion does not have the information of how to reproduce although the virus does. It looks to me as if the prion is a “bad” type of protein which if interacts with another “good” protein the interaction causes the “good “ protein to turn into a prion. But this turn is not because of the splitting of information from the first prion to the other, but because of the molecular structure of the prion. When the prions structure “collides” with the “good” proteins structure it causes the “good “ protein to “fall” (unfold) apart into the very same structure as the prion itself. Although a virus does have the information of how to make another one of itself, but lacking the resources to make one.
        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.
    • Aug 26 2012: Are there any living species that does not reproduce? The human which is sterile in your example is only a random occurrence. But for the human to be it had to be produced first by another. So the human species is indeed reproductive and this reproduction sometimes has glitches with sterile end results.
      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.
      • Aug 26 2012: Very true, sterile life is a random occurrence and you are right in a broad sense that life is able to reproduce, but can that be the deciding factor in determining an individual is alive?
        • Aug 26 2012: No since the mentioned sterile human, is alive because of his past, and not because of his future. The way of production of this human is the proof of its aliveness.
      • Aug 26 2012: Hi Rohan,

        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)?
        • Aug 26 2012: Hi Andrew
          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.
        • Aug 26 2012: Would a sterile, cloned animal be alive?

          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.
  • Aug 26 2012: Is a prion alive?
    • thumb
      Aug 26 2012: That is part of the problem. Are you infected with a prion bourne disease or are you poisoned with a chemical called a prion?
  • thumb
    Aug 23 2012: Life is living in love; love of living, love of our lovers; love of nature, love of our times and circumstances and the opportunity to learn something new.

    Anything that has the potential to die has life.
  • thumb
    Aug 23 2012: MRS GREN

    Nutrition- as in it eats.
  • thumb
    Aug 23 2012: Animated matter that is aware of being aware
    • Aug 26 2012: A bacteria is not self aware, but it is alive
      • thumb
        Aug 26 2012: Maybe so don't know if that is true or not? What about a virus?
        • Aug 26 2012: Are you asking if a virus is aware or if it is alive? It is not aware of it's own existence, as to whether it is alive... If you define life as including the ability to utilise energy and self-replicate, then no.
      • thumb
        Aug 26 2012: Ok I'm revising my definition to animated matter.
  • thumb

    Gail .

    • 0
    Aug 23 2012: Being demands movement and movement causes learning.

    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.
  • thumb

    Gail .

    • 0
    Aug 23 2012: Life = being. Not necessarily "a" (physical) being.
  • thumb
    Aug 23 2012: "Any entity that has the ability to store and exchange information autonomously."

    Define "autonmously".
    Also, where does a sterile animal stand in that definition?
  • thumb
    Aug 23 2012: I think defining liiving things is still a major grey area as are most concepts in biology, it's messy and complicated, where do viruses fall for instance?
    • thumb
      Aug 23 2012: Any entity that has the ability to store and exchange information autonomously.
      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.
      • thumb
        Aug 23 2012: Yes so by that definition software could be considered living, even some mattresses could be considered living but I think living things such as organisms have additional properties which make them more complicated like self replication and adaptability.
        • thumb
          Aug 23 2012: Some computer software is self-replicating and adaptive. BTW if you think your mattress might be alive you could try spraying it with a pesticide.;-)
      • thumb
        Aug 23 2012: On a PhD student salary my mattress looks like Swiss cheese punctured with springs. I don't have the fancy memory foam that conforms to me, I conform to my mattress. There may be software that can do all that I don't doubt it, I just wanna point out that with these additional properties the term now narrows to a smaller range of phenomena. However I have to point out that biological adaptation might be different than software adaptation although I can't say for sure since I don't know that much about software adaptation.
  • thumb
    Aug 23 2012: Well, that is a hard question! why? Because we define life more with our senses than by reason! for many life has to be made of meat. Built a robot with meat and the same with iron, and you will have debates about the iron one. We can only define life when we became more objective with the world!
    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?