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What is alive?

Michael Daunt liz.daunt at sympatico.ca
Fri Sep 20 11:21:20 EST 1996



Kevin W L Croft <kcroft at server.blo.su.oz.au> wrote in article
<3241C1C8.7BA4 at server.blo.su.oz.au>...
>(snip)
> With metabolism and boundary, cells are alive, multicellular organisms
> are alive, maybe organs are alive (James Grier Miller thinks they are,
> but for different reasons).
> Viruses are not alive.  They don’t maintain "…active thermodynamic
> disequilibrium …" with the environment.  Outside the cell, they are like
> crystals.
> Prions are not alive for the same reason.  (However, the issue of their
> being only protein is still subject to dispute.)
> Interestingly, the definition I have given recognises that life can be
> turned on and off.  For example, some plant seeds may be so "dormant" as
> to not qualify as alive.  Yet they retain the potential for life.
> I regret that this post is so long.  I look forward to your comments.
> 
> Kevin W L Croft

This is interesting.  I agree that we are getting to the heart of the
matter.  It seems to me that this whole discussion of what is life is
really begging the question.  We have this discussion because of a built-in
assumption that there is a boundary between life and non-life.  This comes
from our every day experience in our "macro"-world (for want of a better
word).  This is a common-sense approach.  As we walk down the street, we
can tell what is alive and what is not alive.  But I think in the
micro-world we are going to have to put an arbitrary limit on it.  Thus,
crystals will be non-life by definition, because our definition excludes
anything without a membrane (assuming that this is where the boundary is
drawn).  This would also follow for prions and viruses.  Or the definition
may be anything whose structure is determined by DNA or RNA.  This would
include viruses in the definition of life, but would probably exclude
prions.

Anyway, I really enjoyed your discussion.

Michael Daunt
liz.daunt at sympatico.ca


 



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