Define the term "life"

Discussion in 'Biology & Genetics' started by crazylenny, Aug 3, 2003.

  1. KitNyx Registered Senior Member

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    Both donkeys and viruses fit my definition of life. I do not think the need or want to reproduce is a prerequisite for life. As long as the "creature" in question strives for its own survival.

    dinokg - I specifically attempted to come up with a definition that would include that. If a "being" lived indefinitely, why would it need to reproduce to insure the survival of it's species?

    - KitNyx
     
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  3. dinokg Registered Senior Member

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    Even robotic life would have to have some way of reproducing.
    I think they would just build each other to continue their way of life.

    But I do remember hearing somewhere that really advanced robotic and nanotechnology would be almost identical to a biological creature. At least as fair as the way it lives and the way its body works. So even robotic life might develop a method of reproduction similair to biological life eventually.

    Now theres something to think about.

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  5. KitNyx Registered Senior Member

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    Why...we reproduce because we are mortal. In order to continue our species we must reproduce. Why would it be necessary for a being that does not age as we do to procreate? It's continued existance continues it's species.

    - KitNyx
     
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  7. river-wind Valued Senior Member

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    woohoo- 'new' study creates life-like plasma. Not proof of how life came about on Earth, but yet another example of self-replicating structures which react to their environment and which can be created from non-living matter

    http://www.newscientist.com/news/news.jsp?id=ns99994174
     
  8. river-wind Valued Senior Member

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    Problem here is adaptation rates. If the environment in which this ageless individual living in changes, then he will need to adapt to it to survive. however, this is not an easy task -copying that change across every cell int he body is next to impossible, when dealing with a DNA-level alteration.

    What requires much less work is to produce a single cell with the needed alteration, and then re-grow your entire form from that one, changed cell.

    bing-bam-boom- you've got reproduction. however, now you have the ageless guy and his new, slightly modified self competing for resources. You went through the whole thing of creating this new version of him so that he can survive (ie his old self will die soon anyway), so to prevent the old guy from taking the new guy with him, you kill off the old guy, and the new guy flourishes.

    At least to me, that seems a reasonable explination for reproduction, death, and why aging appears to be genetically controlled. It's an evolutionary advantage, allowing for faster mutation and adaptation of the species population. We don't reproduce because we die, we die because we reproduce. we reproduce to adapt.
     
  9. paulsamuel Registered Senior Member

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    biologist's perspective

    individuals do not evolve, ageless or not.

    your argument appears to be teleological.

    the evolutionary perfection is to make exact genetic copies of oneself.

    mistakes in copying are incidental to the process.

    aging and especially dying are mal-adaptive (an individual would essentially be sacrificing all reproductive potential)

    aging (and dying) are incidental
     
    Last edited: Sep 18, 2003
  10. spuriousmonkey Banned Banned

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    another biologists perspective:



    dying certainly seems to have an evolutionary advantage. And to me it seems to be an adaptive one. Death became an essential part of sexually reproducing multicellular organisms.
    They essentially decided to subdivide the roles of different cells. A breach was made between the somatic cells, which give rise to all the differentiated cells of the body, and between the germ line cells, whose only function is reproduction (well, not even reproduction, just to make egg cells and sperm cells).

    One of the more primitive multicellular organisms with sexual reproduction is volvox. There are many different kind of species, with all slightly different strategies. But one of which is to create a set of germ line cells who differentiate into eggs and sperm, and purely somatic cells, which encompass the germ cells and are there for feeding and such. Once the eggs and sperm are released there is no function left for the somatic cells.

    They cannot reproduce anymore. Hence, there is no need to be alive from an evolutionary viewpoint and they die. In fact they would eat up precious resources for the next generation if they would remain alive forever after having reproduced.
     
  11. river-wind Valued Senior Member

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    Re: biologist's perspective

    IMO, only because of the definition of the word evolution. An individual is certainly able to adapt- take a pair of siblings, one from Alaska and one from Arizona , and place them in New Jersey. The person from Alaska will feel very warm on average, while the person from arizona will fell very cold on average. The same temputature, similar genetic material, and (presumably), similar environments during childhood.

    Their DNA hasn't changed, so they haven't "evolved", however, they have adapted to their own local environments.
    Yeah, I know, but that is due to a philosophical difference between the two of us. I have found that there are manythings in life which seem to be due to a plan or design, but when you look into it more, they exsist in the way that they do, because that is the way that works- any other attempt along the evolutionary path would have resulted in the end of the genetic line, so the way that works is the way that survives.
    my expirience disagrees with this assertion. Were this the case, sexual reproduction would not take place.
    again, I would argue that is explicitly not the case.
    an individual will be giving up reproductive possibility only if his/her children are considered seperate entities from the original. In asexual reproduction, the offspring are near identical copies of the original - if they are better suited toi survive due to a subtle change, what is the advantage of keeping the original parent around? All in all, the two beings are the same being- one came from the other, and is a near identical copy. Why have the two individuals compete with each other for reasources, and weaken each other for it, when you could sacrifice one individual, and in doing so, strengthen the position of the other to survive? The survival of one constitutes the survival of both, if the two individuals are identified as pretty much the same being.
     
  12. paulsamuel Registered Senior Member

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    evolutionary biologist's perspective

    spurious: there appears to be a chance for a fruitful discussion here.

    When you say 'evolutionary advantage' and 'adaptive' it implies selective advantage for the individual. Since fitness is measured by reproductive success, being dead lowers fitness to zero. As long as there is some positive fitness value by being alive, then dying is mal-adaptive. This is completely regardless of any future resource use needed by the next generation (unless one includes inclusive fitness, which can lead to another pet-peeve of mine, which is; THERE IS NO SUCH THING AS ALTRUISM!!).

    This also points to the reason why organisms age and die. Fitness peaks in an organism when it first reaches reproductive age and decreases after that (this is ecological theory based on life history tables). After reproductive age, fitness is zero and blind to natural selection. Aging results from a decline in the force of natural selection which occurs incrementally throughout the organism's life. Medawar and Haldane have published lots on this.
     
  13. paulsamuel Registered Senior Member

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    a reply to river wind

    in response to my assertion that individuals do not evole, you stated;

    you appear to be mixing up 2 definitions of adaptation. They are homonyms.


    I found it difficult to understand your response to my suggestion that your argument appeared to be telological, however I assure you that evolutionary processes are NOT goal directed OR progressional.

    Your response to my statement ('the evolutionary perfection is to make exact genetic copies of oneself.')

    is really not a valid argument becuase the exact opposite can be said and would be more correct, i.e., if it wasn't the case, then we wouldn't see so many organisms (many more orders of magnitude greater than sexual reproducers) that reproduce this way. However, biologically, you make a valid point. Theories on why sexual reproduction came about can be found in published work of John Maynard Smith and Richard Dawkins (The Selfish Gene). One theory is that sexual reproduction arose to provide genetic variability. Regardless of these theories, the consequence of reproduction is to get your genes into the next generation. One can regard fitness as how successful an individual is in getting genes into the next generation, the most fit being the individual with the most genetic representation in the next generation. Therefore the fittest individual is the one with all his genes, unaltered, in the next generation.

    when I stated that 'mistakes in copying are incidental to the process,' I meant the process of replication, i.e. hundreds of millions of cells copying hundreds of millions of bases of DNA hundreds of millions of times per hour, where mistakes are bound (and I mean this literally) to happen. to which you replied,
    and I would ask, where do you think these mistakes are coming from?

    finally in response to my assertion that dying is mal-adaptive (please see my previous post in response to spuriousmonkey)
    you said,
    You appear to be mixing selective advantage of the parent and the offspring. Perhaps it would be an evolutionary advantage of the offspring if the parent dies, but this does not mean that it's advantageous to the parent that it dies, and it appears that this is what you are asserting. You might want to look into trade-offs, an aspect of behavioral ecology, in which a parent maximizes reproductive output. Is it more selectively advantageous to reproduce once then sacrifice oneself for the offspring (this happens in some organisms where the offspring eat the mother), or to stay around for more chances at reproduction? The answer depends on many different ecological factors and life history traits, i.e. if the chances are that a parent will die (just by chance) before the next reproductive cycle, it might be advantageous to put all reproductive effort into one clutch. Also, you might want to look into the evolutionary aspects of iteroparity vs. semelparity.
     
  14. paulsamuel Registered Senior Member

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  15. certified psycho Beware of the Shockie Monkey Registered Senior Member

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    life-defined

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    The property or quality that distinguishes living organisms from dead organisms and inanimate matter, manifested in functions such as metabolism, growth, reproduction, and response to stimuli or adaptation to the environment originating from within the organism.
    The characteristic state or condition of a living organism.
    Living organisms considered as a group: plant life; marine life.
    A living being, especially a person: an earthquake that claimed hundreds of lives.
    The physical, mental, and spiritual experiences that constitute existence: the artistic life of a writer.

    The interval of time between birth and death: She led a good, long life.
    The interval of time between one's birth and the present: has had hay fever all his life.
    A particular segment of one's life: my adolescent life.
    The period from an occurrence until death: elected for life; paralyzed for life.
    Slang. A sentence of imprisonment lasting till death.
    The time for which something exists or functions: the useful life of a car.
    A spiritual state regarded as a transcending of corporeal death.
    An account of a person's life; a biography.
    Human existence, relationships, or activity in general: real life; everyday life.

    A manner of living: led a hard life.
    A specific, characteristic manner of existence. Used of inanimate objects: “Great institutions seem to have a life of their own, independent of those who run them” (New Republic).
    The activities and interests of a particular area or realm: musical life in New York.

    A source of vitality; an animating force: She's the life of the show.
    Liveliness or vitality; animation: a face that is full of life.

    Something that actually exists regarded as a subject for an artist: painted from life.
    Actual environment or reality; nature.

    adj.
    Of or relating to animate existence; involved in or necessary for living: life processes.
    Continuing for a lifetime; lifelong: life partner; life imprisonment.
    Using a living model as a subject for an artist: a life sculpture.
     
  16. spuriousmonkey Banned Banned

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    Re: evolutionary biologist's perspective

    maybe, but recent discussions with marine microbiologists have made me think. In case of the volvox there is a clear evolutionary advantage if the 'parent' dies off as fast as possible. Life as plankton is determined by the availablity of recources. If a volvox would carry a 'gene' (in the loose definition of gene) thate instructs the death of the parent, then the offspring would have a great advantage and hence the original volvox has benefitted. It created a higher chance of success for its offspring. It not only helps the offspring after all. It helps both the offspring and parents. Or as a matter of fact it could also be stated that it helps purely the parent.

    The success of the parents is reflected in the fitness of the offspring. If actions of the parents after the reproductive age benefit the reproductive succes then I see no problem for natural selection to work. It is after not as if the parent has to add an extra gene after it already reproduced. The genetic material required has always been there from the start.


    The reverse situation we might find in humans. The grandparents linger on well past the reproductive age because they tend to be a valuable asset for their secondary reproductive success: the reproductive success of their children.

    I probably fucked it up somewhere here in this reasoning, but I am sure someone is willing to point it out for me.
     
  17. paulsamuel Registered Senior Member

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    reply

    sounds right to me and a good example of inclusive fitness. however you don't need a 'death' gene, as Haldane and Medawar point out, being blind to natural selection is enough.
     
  18. spuriousmonkey Banned Banned

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    but this death is an active death. It is regulated by genes.
     
  19. paulsamuel Registered Senior Member

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    reply

    if you're saying that they've found this death gene, i would ask for a reference.
     
  20. spuriousmonkey Banned Banned

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    I would have to look it up for this particular case, but in any organism cells usually die for 2 reasons. By immune repsonse initiated cell death and by apoptosis.

    And apoptosis is always regulated and I doubt the volvox kills itself by means of its immune system.


    but i will look up some stuff...because i am not quite sure
     
  21. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Dam haven’t been here in awhile, what been going down? Huuuum, huuuum, aaaaah, oooooh, huuuum, ok dare I ask if you two do not know about Telomeres?
     
  22. netkk Registered Member

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    Well, don't be so sure viruses aren't classified as living, sure they are. Viruses are one of the simplests forms of life (they're not the simplest anyway).
    The problem comes when you define life as cells. If life=cells then viruses aren't alive. But this live=cells is a quite old idea.
    Those alive "things" are called acellular forms.
     
  23. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Oh so a virus is alive? What about prions?
     

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