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what is alive?

Johnjoe McFadden j.mcfadden at surrey.ac.uk
Wed Sep 18 07:56:14 EST 1996


I wrote: 
>... Life is a lot more wonderful that a computer virus or a chain mail
letter - not just more
> complex - it differs at more fundamental levels.
.......................

Ed Rybicki, PhD  comments:

How?

and  Mario Vaneechoutte comments:

'Wonderful' isn't useful either. Again very anthropocentric.

I still don't see problems for calling this living information. As a
consensus, we can use 'life' only when we refer to biological living
information.

.......................

This may come down to a question of semantics. Ed and Mario may be happy
with a definition of life that includes computer viruses, chain mail letters
and sequels to the movie Rambo (which certainly proliferated) - but I am not
- its just not very useful when trying to work out what makes living
organisms special. I also consider that plants or animals that are incapable
of replication, eg. infertile hybrids such as mules or indeed an infertile
person, are clearly still ALIVE. Now what it is that defines this life (in
the absence of replication)  is of course the billion dollar question - but
I'll have a go.

 Aristotle mused on this very question more than 2000 years ago and proposed
that the defining quality of life was the ability to 'initiate movement'  -
movement in his sense was rather broad and included (though did not depend
on) growth and replication. This ability to initiate (or to resist) movement
was an indication of a inner will that Aristotle ascribed to a soul. I am
certainly not advocating any living soul but I believe there is something
very profound in this  - living organisms have the ability to resist
external forces - both  stones and a salmon may move within a stream but
only the salmon can leap upstream. How living organisms impress their 'will'
(its hard not to be anthropomorphic!) on their environment is I think tied
up with information, the second law of thermodynamics and the ability of
living organisms to resist its progress within the confines of their own
bodies (though not of course within the entire system). Replication of
genetic information is an aspect of this deeper level - but its not the
whole story.

Johnjoe


Johnjoe McFadden, PhD
Molecular Microbiology Group
School of Biological Sceinces
University of Surrey,
Guildford, Surrey GU2 5XH, UK.

tel: 44-(0)1483 300800 extn.2671
fax: 44-(0)1483 300374

e-mail: j.mcfadden at surrey.ac.uk




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