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On the xenobiological fundamentals of life; A question about the definition of life
Topic Started: Dec 28 2017, 12:43 PM (333 Views)
Lycaon
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All hail Odin! All hail the Allfather!
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So lately I’ve been diving a lot into the subject of xenobiology again, and one question that kept coming up was ‘how alien can something be while still being called life?’ The first step to answer that question obviously is to look at the definition of life, or more precise: to find out what the bare minimum of necessities is to call something alive. To quickly sum up what I found, most sources give seven of such necessities: reproduction, growth/development, metabolism, homeostasis, response to stimuli, adaptation/heredity and, the one my main question is actually about, being made up of cells.

So, to get to my actual question: why is being made up of cells a necessity? I get that all of life on earth is made up of them, but, in my view, it wouldn’t be impossible to have an alternative unit be the ‘building block’ for living systems somewhere else. What if viruses fulfilled the other necessities of our definition (they obviously lack in the reproduction and metabolism department, and maybe also in the growth part, but I’m not the best at virology), would we still not call them ‘alive’ because they aren’t made up of cells? Wouldn’t it be better to say that an internal environment that differs from the external environment be a better necessity? Or am I missing something here?

Having said that, I thought this’d be an interesting topic to discuss here. So, thoughts?
(Also, what do you guys think is the best definition of ‘life/alive/living’?)

~ OM :)
Edited by Lycaon, Dec 28 2017, 03:02 PM.
Lamna
 
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The true meaning of hypocrisy
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Yiqi15
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Welp, this'll go down the rabbit hole fast, so let me just stsrt off with crystals. While they obviously don't have consciousness or metabolise food matter, they can grow. Silcon-based lifeforms could see a structure similar to crystals.
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Beetleboy
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Yiqi15
Dec 28 2017, 01:18 PM
Welp, this'll go down the rabbit hole fast, so let me just stsrt off with crystals. While they obviously don't have consciousness or metabolise food matter, they can grow. Silcon-based lifeforms could see a structure similar to crystals.
Mm . . . maybe? Honestly I'm doubtful of silicon-based lifeforms being crystal-like. We're carbon-based lifeforms, and we don't look like a lump of coal.
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Lycaon
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All hail Odin! All hail the Allfather!
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Yiqi15
Dec 28 2017, 01:18 PM
Welp, this'll go down the rabbit hole fast, so let me just stsrt off with crystals. While they obviously don't have consciousness or metabolise food matter, they can grow. Silcon-based lifeforms could see a structure similar to crystals.
It won’t go down the rabbit hole if the premise is well understood. Any of those necessities on their own can’t be called life. It’s the combination of all of these basal necessities that makes something alive. So the fact that crystals grow isn’t enough to view them as living, as they lack the other necessities.
Also, alternate biochemistries is a different topic, as it isn’t at the basis of the definition of life, which is the topic at hand.
Edited by Lycaon, Dec 28 2017, 02:16 PM.
Lamna
 
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Flisch
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Lycaon
Dec 28 2017, 12:43 PM
So lately I’ve been diving a lot into the subject of xenobiology again, and one question that kept coming up was ‘how alien can something be while still being called life?’ The first step to answer that question obviously is to look at the definition of life, or more precise: to find out what the bare minimum of necessities is to call something alive. To quickly sum up what I found, most sources give seven of such necessities: reproduction, growth/development, metabolism, homeostasis, response to stimuli, adaptation/heredity and, the one my main question is actually about, being made up of cells.

So, to get to my actual question: why is being made up of cells a necessity? I get that all of life on earth is made up of them, but, in my view, it wouldn’t be impossible to have an alternative unit be the ‘building block’ for living systems somewhere else. What if viruses fulfilled the other necessities of our definition (they obviously lack in the reproduction and metabolism department, and maybe also in the growth part, but I’m not the best at virology), would we still not call them ‘alive’ because they aren’t made up of cells? Wouldn’t it be better to say that an internal environment that differs from the external environment be a better necessity? Or am I missing something here?

Having said that, I thought this’d be an interesting topic to discuss here. So, thoughts?
(Also, what do you guys think is the best definition of ‘life/alive/living’?)

~ OM :)
The main problem is that the "official" definition of life is pretty useless, because as you said it doesn't consider viruses alive.

If you look at the individual points, they're often interdependent on one another. Why does cell-based life metabolize? Because they need to grow in order to reproduce. So basically both growth and metabolism are dependent on reproduction, or to be more precise a specific kind of reproduction used by cell-based organisms. We do know reproduction without metabolism and growth is also possible.

So I think the definition of life should be boiled down to "capable of evolution", which basically encompasses two points: Reproduction and Heredity, meaning that traits are stored in some way* to allow for variation between individuals and thus to enable natural selection. This would include Von-Neumann machines as well as viruses and should essentially cover all forms of life we might eventually find.

*In some way means that it doesn't have to be a molecule, it could also be digitally stored, like in a computer program.
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Archeoraptor
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von-neumans machines?
Astarte an alt eocene world,now on long hiatus but you never know
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coming soon......a world that was seeded with earth´s weridest
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throw The Spec I gain strength to the inner peace
the is not good of evil only nature and change,the evolution of all livings beings"
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Rodlox
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Archeoraptor
Dec 29 2017, 11:04 AM
von-neumans machines?
autonomous robots, typically envisioned drifting from one star system to another, where they make landfall and mine the planet or moon for resources to make more of themselves - and when they reach a critical threshhold (such as no more planet or moon to mine), they move on to continue and repeat the process - only now there isn't one machine to reach another solar system...there are billions, most heading in different directions.
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