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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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  • 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.
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      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.
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          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).
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          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.

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