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what is alive?

Johnjoe McFadden j.mcfadden at surrey.ac.uk
Thu Sep 19 08:10:38 EST 1996


Steve McGrew writes:     

   Wouldn't it make sense to consider "living" to be a matter of degree?  
>For example, a dried lotus seed or a frozen spore *must* be considered to be 
>alive to some degree, since it has the capacity for doing all the things 
>living things do.  A person in a coma is less alive than one who is engaged in 
>a lively conversation.  A virus is perhaps less alive than a eukaryotic 
>organism, which in turn may be less alive than a dog.  And, a cancer cell is 
>certainly alive, but perhaps to a lesser degree than the organism whose stem 
>cells it arose from.
>        Certainly we could cook up a definition for "life" that would provide 
>a basis for calculating the "degree of aliveness" of a system, so that each 
>animal, plant, virus, autonomous robot and river system can be allocated its 
>own aliveness.
>        I think a lot of the problem people have with the concept of "what is 
>alive" may come from the idea that there is a "spirit" that enters leaves the 
>body upon birth and leaves upon death: an on/off kind of quantity called 
>"life".  In the context of current medical, biological, biochemical and 
>cybernetic knowledge, that idea is nonsense.  If "life" is to be something 
>science deals with, it must be measurable, quantifiable-- and probably not a 
>binary quantity.
>

.....................................
I don't like this 'degree of alive' notion and agree with Arthur Chandler's
comments that life does appear to be a binary phenomenon - alive or dead. If
we allowed degrees then we would expect a smooth transition between living
and dead things - but there is not. The simplest self-replicating organisms
are bacteria - extrodinarily complex compared to the most complex inaminate
systems. Therealso  doesn't seem to be any transitional state between being
alive and dead - that would surely imply that the process should be
reversible but death is unfortunately irreversible.

I know that I run into dangers of circularity here by including a patient in
a coma or a dormant spore as being alive even if  by my earlier argument
(life = ability to resist or initate movement (as used by Aristotle with
movement including growth and replication)) they can't move much BUT they
still retain the potential for being alive and doing what living thigs do -
unlike death, their state IS reversible. I don't have any problem with
living things having periods of inactivity which would include
coma/dormancy/hibernation. But it is clear that if patients/seeds are killed
then an irreversible process (loss of life) has taken place and the living
state cannot be regenerated. Why not?

Mike O'Hara argues that my definition of lfe (life = ability to resist or
initate movement) would also include rocks or earthquakes that under certain
circumstances are certainly capable of imposing their will upon you. Richard
Dawkins (I can't remember which book) graphically illustrated the point I'm
making by asking you to imagine holding a rock in one hand and dropping it
and holding a (live) dove in the other and also dropping that. Clearly the
dove would be able to demonstrate its 'inner will' by flying away whereas
the rock's movement is subject only to exterior forces. But what about an
earthquake or a stick of dynamite - wouldn't the latter impose its will upon
you if you held it after lighting the fuse? In a way it does and we have to
look deeper to understand the difference. If we add up all the exterior
forces acting upon the rock then we could predict its movement. For the
dynamite we would have to take into account the chemical reactions taking
place within the lighted stick to predict its movement and its effect on its
environment. For the dove - if we add up all the chemical reactions could we
predict it would fly up into the air? Maybe so, but what if it noticed a
juicy morsal of food on the floor - it would fly down. How could we predict
both behaviours by analysing its chemistry alone? It seems to have an
independent 'will'.

I am certainly not advocating anything unscientific (ie soul) to explain
life but I am suggesting that a full explanation requires something new in
our understanding. To throw another cat into melee - I think it has
something to do with determinism.

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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