To the VIRO-NET
On March 17, Mike Perdue commented in reference to virus evolution...
...I just wanted to make a short comment on the discussion that brought flu
in as an example. I don't think you can place viruses into a specific
host-parasite relationship that says that the virus will "evolve" in one
direction or the other.......
Evolution is NOT a directed process, especially the evolution of
viruses. Viral evolution is dependent random genetic drift. As Mike
Perdue suggests, a virus does not benefit by completely killing its
host--unless it can transfer rapidly from host to host. This transfer is
more productive if it is laterally (to a new host) than serially (to the
same host). The viral survial paln is quite different than other
organisms. The high population of a viral strain lowers the effects of mutation on
the stability of the viral population. Since viruses replicate at very
high numbers within their host, they can incur significant mutations,
partly due to the streamlined genome; these mutations are random--natural
selection then acts upon a randomly mutated population of viruses. The
natural selection forces are determined, for the most part, by the host.
Thus as Mike Perdue mentions, there is not a host-virus evolutionary
direction. Viral evolution occurs first via random genetic mutation not
a host-virus relationship. The latter acts only after mutation has
altered in the viral strain.
William Jewell College
Liberty, MO 64068
Email mowjmat at coop.crn.org