Are viruses alive?

[Dale R. Worley]

In article <3935 at news.duke.edu> una at phy.duke.edu (Una Smith) writes:
   Viruses are _not_ self-replicating.  They are (we think) evolved
   from self-replicating, living cells.  In the course of evolution
   viruses have discarded all but a very few genes, and now depend
   on the host cells which harbor them to replicate the viral DNA 
   and build the viral coat proteins.

Viruses *are* self-replicating, in the right environment, just as we
need oxygen to be self-replicating.  It's just that viruses require
other living things in the environment.

The crucial thing is that the virus genome replicates *independently*
of the genome of its prey.  The reason that the various chromosomes
inside me are classed as all one living thing is that they
(more-or-less) have to replicate together, forcing them in to a
certain amount of altruism toward eachother, making them behave as a
coordinated system.  The virus genome can replicate independently, and
so it doesn't act in a coordiated system with my genome.

In article <robison1.711564533 at husc9> robison1 at husc9.harvard.edu (Keith Robison) writes:
   A friend and I recently got into this discussion.  If viruses are
   alive, are plasmids?   Transposons?

That's a touch one, because they replicate in two different ways --
One is the spreading of copies throughout the organism they inhabit,
which is independent of the organism's main genome.  The other is the
production of new organisms carrying the plasmid/whatever, which is
coordinated with the replication of the main genome.

Dale Worley		Dept. of Math., MIT		drw at math.mit.edu
--
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