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peter lindsay

Physics Teacher,


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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.

Topics: afterlife death life

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  • 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.

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