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The definition of living beings

  1. Jul 27, 2007 #1
    sorry for asking question that might be considered as stupid but I keep on thinking for the definition of living beings

    Life, term used to summarize the activities characteristic of all organisms—ranging from such primitive forms as cyanobacteria (formerly known as blue-green algae) to plants and animals. These activities fall into two major categories: reproduction and metabolism.
    Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

    Using this definition, a fire would "reproduce" and "metabolise"

    The other major activity of living organisms is metabolism, the physical and chemical processes by which energy from the outside world is used in such activities as reproduction (including growth),
    Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

    I am unable to satisfy my self in nearly all definition of living beings that I ever find. The closest one is given by a friend of mine: "anything that can be killed" But I am sure there are better ones.
  2. jcsd
  3. Jul 27, 2007 #2


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    Well, the definition does say it describes "organisms". Fire is not an organism.
  4. Jul 27, 2007 #3


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    You've defined life (broadly), but you haven't defined "reproduce" or "metabolise".

    A fire does not "reproduce" in the strict sense of the term.
  5. Jul 27, 2007 #4
    I suppose that how fire "reproduce" is similar with vegetative reproduction, cell fission, and sponges, and others. There is a chemical reaction inside of fire, an oxidation I suppose, which I could loosely identify as "metabolism". I took a hard time in getting the essence, as in ancient greek philosophy, of what is life. I know I am being somewhat unscientific and going against anything conventional, but I really want to know.
  6. Jul 27, 2007 #5


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    The modern definition is generally based on inheriting characteristics.(1)

    A fire can reproduce but it doesn't pass on any of the charactersitics of the original fire to it's offspring - you can't tell from a burning cigar if it was lit from a match or a burning oil tanker!

    (1) Unless you are from the Southern USA - of course.
  7. Jul 29, 2007 #6
    sorry I dont get, the jokes (1) >.< I am not from USA or anywhere near

    So a living things is a thing which is able to inherit characteristic.

    how about a infertile organism (due to many reasons like, accident or sickness or old ages), are they a living things?

    And when a living things stop living? if living things is a thing that able to inherit characteristic, then an animal which is to old to reproduce is no more a living things.
  8. Jul 29, 2007 #7
    Life is a characteristic of organisms that exhibit some of the following phenomena:

    Homeostasis - keep your internal environment at a constant state
    Organization - being composed of one or more cells (basic unit of life)
    Metabolism - consumption of energy by converting nonliving material into cellular components and decomposing organic material.
    Growth - A higher rate of synthesis than catalysis.
    Adaptation - The ability to change over time in response to the environment
    Response to stimuli - Self-explanatory
    Reproduction - The ability to produce new organisms.

    In order for something to be called life, it doesn't need to follow all of these, it is just that life is a characteristic of organisms that exhibit these phenomena.

  9. Jul 29, 2007 #8
    Actually, it is not that I do not know what is living things. it is that I am just unsatisfied with the current definition. I know my question could be annoying to most people, so I tried to be careful, but sometimes it just cant be help. so I am sorry.

    Moridin, are you sure that your definition is perfect? that following some or more of that characteristic, something is worthy to be called as a living things? and to do that, I will push any given definition to its limit.

    (I am not sure about this, but) according to gaia theory, the earth could keep its "internal environment at a constant state"
    And this way, a virus is able to reproduce.
    and how about a factory that could produce robots to make sure that it is able keep producing robots (that able to make sure that ... )

    One of the things that add to my confusion is, when an offspring begin to live?
  10. Jul 29, 2007 #9


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    The problem with the old - Homeostasis, Organization, Metabolism, Growth, Adaptation, Response to stimuli ,Reproduction,
    defintiion is that all of these can be easily applied to other things from stars to fire.
    The arguement against the inheritance definition is that is can also be applied to say a generic algorithm or computer virus, but you can make the case that these are just as alive as a phage virus.

    As for an infertile organism, the definition of course applies to class of things not necessarily to an individual. Ungulates are hoofed mammals, but a cow doesn't stop being a cow if you cut it's feet off!
    The question about when something begins to live or die is not the same as the definition of life. It is probably best to consider that from athermodynamic/chemistry point of view, although that doesn't give you a precise answer.

    The southern USA was a joke about some American states where the religous authorities have banned the teaching of evolution.
  11. Jul 29, 2007 #10
    so mqb_phys, is the conclusion is that there are currently no such definition that i demand? no solid definition that cant be argued against?

    and thx for explaining the joke, I found it hilarious for a modern society to ban a teaching.
  12. Jul 29, 2007 #11


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    It's very difficult to come up with a simple mathematical style definition for a complex process like 'life'.
    The definition used by a biochemist, a physicist, a transplant surgeon and a laywer in a murder case would all be very different.
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