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What differentiates the living from the non-living?

  1. Aug 26, 2003 #1
    What physical property separates the two?
  2. jcsd
  3. Aug 26, 2003 #2
    That is a very interesting question, as any attempt to answer it using logic ends up with the conclusion that either everything is alive, including stones, or everything is dead, including ourselves. That can only mean one thing: "life" is a fundamental property of the universe and as such can't be reduced to anything more fundamental, not even physics.
  4. Aug 26, 2003 #3


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    Or that life is a subjective, relativist value.
  5. Aug 26, 2003 #4


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    Dearly Missed

    For a multicellular metazoan, it is that the collective cellular processes still work. This automatically means that such an organism dies in some parts before others (cf. "brain death"), but once the major processes fail, the others will eventually fail too.
  6. Aug 27, 2003 #5
    Doing my best to evade trying to
    define "life" I would say that
    what distinguishes that which is
    alive from that which is dead for
    me is that that which is alive
    must be engaged to some
    extent in the attempt to improve
    or elaborate upon it's status quo.

    That which is dead no longer exerts any effort of any kind on
    its own behalf and is at the
    mercy of any force that acts upon

    It is by virtue of this that I
    would never consider rocks, or
    minerals, or individual elements
    to be possessed of life.
  7. Aug 27, 2003 #6
    Well, since all "living things" are composed of elements, then perhaps life is a property related to complexity. After all, a cell is basically a very complex system of interactions and reactions. Of course, the cell is not a closed system, and a certain amount of interactions and reactions between it and its environment must take place. Maybe after a system becomes complex enough and parts of the system are dedicated to maintaining the system's continuity by interacting with and reacting to its environment, then it could be considered alive. But then, this is only my humble opinion.
  8. Aug 27, 2003 #7
  9. Aug 27, 2003 #8


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    Keep that heart-lung machine away from me!

    Arggg! Attack of the undead fishies...
  10. Aug 28, 2003 #9
    This is a good start.

    But there is more.

    Life als is able of reproducing itself, in more or less the same form.

    And life distinguishes itself from the environment.

    And life needs to take in sources of energy to sustain itself, it needs a form of metabolism.
  11. Aug 28, 2003 #10

    I agree with all except the first.
    The mule, I beieve is is, which is
    a cross between a donkey and a
    horse, I believe it is, is not able to reproduce.

    Likewise it seems resonable to
    propose that throughout evolution
    lifeforms came to be that were not
    able to reproduce, and these indi-
    viduals lineage died with them.
    Before these indiiduals died, how-
    ever, they were alive.
    Last edited: Aug 28, 2003
  12. Aug 28, 2003 #11
    So does a computer virus. Which is why they are called 'virus'. Are computer viruses alive?
    Yes, living beings are different from the environment by virtue of being alive. Like any fundamental principle, such as 'matter', 'space', 'time', life can only be defined tautologically.
    So does my car.

    What stands in the way of accepting life as a fundamental, irreduceable principle of the universe?
  13. Aug 28, 2003 #12

    Your car does not sustain itself.
    It can never make any effort on
    it's own behalf to do so. It
    cannot even desire to make such
    an effort.

    Nohing your car takes in goes to
    sustaining it in it's present
    state. All of its parts start to
    be acted upon by environmental
    agents as soon as they are made.
    It's downhill from there: no
    growth, no healing.

    A car cannot be used as an example
    of something that sustains itself
    by taking in nutrients.
    Last edited: Aug 28, 2003
  14. Aug 29, 2003 #13

    Another God

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    Douglas Adams at Digital Biota 2
    Life, seemingly like all things in our universe, is a phenomenon named by humans, which isn't bounded by a nice neat couple of lines of demarcation. Life, is a part of everything else which does something neat, but nothing which is unique nor removed from everything else which happens.

    Just like us humans like to have these neatly defined colours : Red, blue, green, yellow etc... when we find out what colour actually is, we quickly realise that there is no neat defined boundary of where Blue stops, and green starts...there is just a continuum. A morphing from one thing into another.

    Life, is a chemical reaction...it just happens to be a type which may become increasigly complex and self-propogating, so when seen in its most extreme form (Eukaryotes) it is easy to define. When u follow this easily defined 'life' back to its origins though...it becomes incresingly hard to find that magical line of demarcation.

    The same thing is apparent with 'What is human?' Whether u mean evolutionarily (it is obvious what is human now, but backwards in evolutionary time, the demarcating lines become more blurred, and no line is apparent), or whether u mean individually (Is a Zygote a human, an embryo, a fetus, a baby etc?) The lines simply do not exist.

    People need to start understanding this, or else find a real way to define these concepts (ie: Find God and ask him to tell us the lines.)

    Another interesting way of targetting this question is: What seperates a living organism, from a dead version of that same organism.
    ie: Poison someone, and figure out what it is precisely that makes them dead as opposed to the non poisoned person.
    What is the difference between viable and non-viable bacteria?
  15. Aug 29, 2003 #14
    The heading of the thread seemed
    targeted at discussing the polarities: whats the difference
    between that which we definitely
    consider alive, and that which
    we definitely consider dead. This
    is a different question than "what
    is life?" I didn't observe anyone
    getting confused about the parameters.
  16. Aug 29, 2003 #15

    Another God

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    OK then, how about: "Degrees of complexity"
  17. Aug 29, 2003 #16
    Life is Universe's way to increase entropy faster. Living beings actively try to decrease entropy (increase order) locally, at least by sustaining their own bodies. More complex organisms, for example we humans, also attempt to decrease entropy at our surroundings (buildings, cleaning). But all this has only local effect, and the entropy of the system as a whole actually increases; the more we increase order locally, the bigger is the entropy increase in the whole system.

    So living beings have a tendency to decrease entropy locally.
  18. Aug 29, 2003 #17
    The tone of that post was frankly
    exploratory; speculative, no
    assertions were made.
  19. Aug 29, 2003 #18

    This is true but it can't be used
    to distinguish that which is alive
    from that which is dead because
    of all the non-living natural
    forces a person could think of
    that do the same thing: the wind
    the tides and waves, rain, snow,
    UV rays etc.
  20. Sep 1, 2003 #19
    Hmm, don't forces of nature more like increase entropy, since they are destructive forces? Wind, rain and UV rays don't make buildings or maintain bodies; they erode them. They are tools of entropy a living being must fight against. From this point of view the natural forces seem like the exact opposite of the living.
  21. Sep 1, 2003 #20


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    Well, if you use the same terms as you did with life, they do locally and temporarily decrease entropy. Eg. in the formation of charged clouds for storms. Or they work to drive life along by providing energy, even though the ultimate product is, as you say, an increase in entropy.

    In things like ther formation of a snowflake for example, we see an increase in order from a natural process.
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