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What is life?

What is life?
Joshua Matthews from Lancashire (Age: 5-14)

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2 Responses

  1. There is no agreement amongst scientists about what life is and how it should be defined. We know what it is when we see it on Earth but that’s because all life is fairly similar on Earth. This question is important because a lot of money has been spent searching for and considering the possibility of life on other planets. How would we know it when we see it, if we can’t define what it is? Also people are investigating how non-living chemicals became living cells. At what point in this evolution from non-living chemicals to “life as we know it”, do we call the system alive? The question also matters when we are considering whether viruses should be considered alive or not.

    It is possible to describe “life as we know it”; all life on earth does the following:
    Reproduce
    Replicate DNA
    Break down chemicals for energy
    Build up complex organic chemicals from small ones, organising them appropriately, for their own growth and reproduction
    Have a membrane of lipids (fats) which protect it from the external environment and allow it to regulate the internal environment.

    But, it is possible to imagine something doing some of these, or doing them differently to known life which you would still maybe call life. For example DNA is a large molecule that is used to store information, there is no reason why other molecules could not be used. If an alien life (or early life) form used a different molecule but did everything else we would still call it life. Also, Viruses have DNA which replicates (although the virus can’t do this without hijacking a host cell), but they don’t metabolise chemicals for energy.
    Is there a single essential quality that something must have to be called life, that nothing else has? Some would say that reproduction is that quality, if we could program a robot to construct copies of itself, it would be reproducing but would you call it alive? If a person never reproduces, are they not alive?
    What about things like, fire or stars, they use up energy, they are “born”, they die, and they can even reproduce.
    One of the problems with defining life is that we only know of one kind of life: Earth life. Imagine trying to define a car if we had only ever seen a two-seater sports car, we might get it completely wrong and say it has to have two seats as part of our definition. If we find other things which we can all agree are living then would have more information to base the definition on, but then again how can we agree if we don’t have a definition of life? Also we might all be too excited by the new discovery to worry about what to call it.
    Well my reply, has been very long, hasn’t answered your question and its brought up even more questions, isn’t science wonderful?

  2. Hi Bryan :).
    Yes, I wholeheartedly agree with you about Science! Further: Your answer does give a very thorough explanation of the constraints which the disciplines of science place on our visualisation of systems – clearly that is also an essential strength that the philosophy possesses too.
    Perhaps reproduction by a ‘natural’ utilisation of available resourses ( which excludes the intervention required for “robot re creations” keeps this line of enquiry more on track?
    Thankyou for an illuminating and thought provoking answer, truely a scientific analysis of a fundemental question
    Good Luck,
    Rockno3.

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