Things that don't move shouldn't be considered alive

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Re: Things that don't move shouldn't be considered alive

Postby Angua » Thu May 05, 2011 5:00 pm UTC

The way I see it, viruses aren't 'alive' as they don't really carry out any of their own metabolism - sure they use genes to make sure their proteins are made, but all of the actual work is being done by the cell, not them - you can't even see a virion generally once it integrates into the cell to start replicating. You can't really say that about anything else.

Also, I like the idea of viruses being DNA/RNA that has escaped from the cell.
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Re: Things that don't move shouldn't be considered alive

Postby Gigano » Thu May 05, 2011 6:55 pm UTC

BlackSails wrote:
Gigano wrote:
BlackSails wrote:If viruses fail being alive because they cant independently reproduce, then there are several species of bacteria that we also need to rule as "not alive", because they cannot independently reproduce.

(Also, I cannot independently reproduce)


As has been addressed the definition should only be applied to single cells, not necessarily the organism in its entirety. Your somatic cells can reproduce (multiply) independently; this is not so for an individual virus.


There is still my first point, that there are bacteria that are obligate intracellular parasites.


Those bacteria are likely to have evolved in the same way that mitochondria and chloroplasts have evolved to reside only within other cells after an endosymbiosis-like evolution. Ultimately they would lose their motile components because they simply weren't necessary anymore (i.e. the selective pressure on having motile components was lost). I do not know such a bacterium, so if you could provide me with a species I'd be grateful. It's not that I do not believe you, rather I am interested in them.
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Re: Things that don't move shouldn't be considered alive

Postby Seli » Mon May 09, 2011 10:54 am UTC

qetzal wrote:@Interactive Civilian,

I don't think I'm especially knowledgeable in this area. I'm a molecular biologist, but I don't really do any work directly related to evolution. So please don't look at my thoughts as anything more than that.

I agree that there's value in Dawkins' metaphor. I just worry that it's potentially misleading (to ourselves and to others) to suggest that any single class of molecules is somehow the most fundamental.

That said, genes do have a critical property that all other biomolecules lack. DNA and some RNAs are the only biomolecules where a chemical modification (i.e. a mutation) can be heritably passed on to an organism's progeny. Proteins, lipids, carbohydrates, and other biomolecules can all undergo chemical modification, and those modificatios can alter an organism's phenotype, but they can't be heritably passed on to the next generation. (Perhaps there are a few cases where certain very specific non-nucleic acid modifications might be passed on epigenetically, but I wouldn't consider that equivalent.)


I don't believe the metaphor is misleading. It is important to keep in mind genes are not the molecules themselves, those are just the carriers at any point in time.

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Re: Things that don't move shouldn't be considered alive

Postby zmatt » Tue May 10, 2011 2:30 pm UTC

A virus is a machine, a biological one, but a machine. It is a device built out of proteins that is designed to inject a payload into cells. That is how I have thought of them. Either that or as they only fulfill part of the requirements to be alive the are undead and therefore zombies.
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Re: Things that don't move shouldn't be considered alive

Postby gmalivuk » Tue May 10, 2011 2:48 pm UTC

zmatt wrote:A virus is a machine, a biological one, but a machine.
So's your mom.
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Re: Things that don't move shouldn't be considered alive

Postby Velifer » Tue May 10, 2011 3:10 pm UTC

gmalivuk wrote:So's your mom.

How did you know?
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Re: Things that don't move shouldn't be considered alive

Postby TheChewanater » Tue May 10, 2011 7:30 pm UTC

gmalivuk wrote:
zmatt wrote:A virus is a machine, a biological one, but a machine.
So's your mom.

In that case, in what way is your mom distinct from an Xbox that makes her a living thing and not it?
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Re: Things that don't move shouldn't be considered alive

Postby gmalivuk » Tue May 10, 2011 10:26 pm UTC

Nothing. My mom hasn't been a living thing since 2003.

But the point is, using the word "machine" to explain your belief that something isn't alive doesn't actually accomplish anything, since biological machines are all *anyone* is.
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Re: Things that don't move shouldn't be considered alive

Postby Velifer » Wed May 11, 2011 12:22 pm UTC

gmalivuk wrote:Using the word "machine" to explain your belief that something isn't alive doesn't actually accomplish anything.

It provides support to those who would claim the opposite. Bacteria are little bags where some processes happen that give rise to interesting emergent properties. So are bureaucracies. Attach some magic words like modus ponendo ponens, and voilà! Bureaucracy is a living thing, and so are thunderstorms.
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Re: Things that don't move shouldn't be considered alive

Postby drw@xkcd » Wed May 11, 2011 5:33 pm UTC

life is a process rather than a thing; (currently) living things are just one of a range of phenomena consequent to that process it is probably more useful examine the products of life rather than try and define what is alive and what is not


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