Viral Origins

Alec Redwood aredwood at cyllene.uwa.edu.au
Thu Feb 4 22:44:27 EST 1999


Yes this is a theory, as percentage of DNA in most/all/many (not sure about
all) animals has DNA sequences from viruses in it.  HIV is a retrovirus and has
the capacity to intergrate into host DNA and there is plenty of retroviral DNA
in humans that is apprently no longer a virus.  There is a theory that viruses
might have first come out of animals and then gone back in.  In animals there
are regions of DNA called transposons that are capable of "moving T/O the
genome.  It is possible that these transposons are precursor viruses or vis a
versa (ie were once viruses).  In addition it is known that many viruses pick
up bits of DNA from the host and incorporate them into their own genetic
structure.  This is quite common and many viruses have means of tricking or
avoiding the immune response by mimicking or inhibiting it with it's own
weapons.  Hence these viruses could be said to be "part" human (or other
animals depending on the DNA source).

One of the most interesting talks in immunology I have ever gone to was on a
species of wasps that "grows" it's own viruses.   When it lays eggs in a
caterpiller the egg passes through the sack containing the virus.  Hence egg is
laid covered in virus.  The virus coating mimics the coating of the "blood"
vessels in the host and hence the egg is not seen as a foreign body.  In
addition the virus then goes on to damage the immune system of the host so that
when the egg hatches the nest stage of the wasp can live quite happily in the
defensless host.  This is an excellent example of a reason that an animal may
want to create it's own virus (of course in this case it is a simbiotic
relationship) but it gives a teilological reason for the production of a new
(ie virus) life form.

Comments anyone....maybe a virologist, this is not my area?.  But it is a good
question.

Jason Merrique wrote:

> I heard of a theory a while back that stated that Virusses could have first
> evolved as part of another species and then later developed as separate
> "self replicating"(?) entities (?). Is this theory based on any kind of
> substantial evidence? And if it is, which species might they have developed
> as part of? And is it possible that modern (multi cellular, higher) animals
> can have evolved to produce virusses (self propagating or otherwise?
> I use the phrases self replicating and self propagating definetly for want
> of a better word......
>
> I must tell you that I'm an upper sixth A-level student (pre university) and
> am probably out of my depth here. I was just very intrigued by the theory,
> and wanted to find out more. So please don't ridicule me for my ignorance :]
>
> Any information would be brilliant, thanks in advanced :]




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