Parallel evolution of viruses?

[Fishteacher73]

I have been poking about and not really been able to find any theories regarding the genesis of viruses. It seems reasonably well accepted that they evolve with the host that they plague. The question arises because there is no fossil evidence so only extant viruses are known. Is it plausable for them to have started in the same primordial ooze as self-replicating molecules like what is believe to be the origin of life and simply hitched a ride after cyanobacteria took off?

Any ideas or holes or other theories out there?

[bumab]

I've heard a few ideas:
Viruses evolved in the "primoridial ooze" before life created an inhosibitable environment to ambiogenisis, and utilized existing cells as a food source, essentially skipping the step whereby they needed to establish their own method for replication.
Viral molocules are genetic misfits that somehow popped out of an existing genome with the coding already present for protien coats and insertion into host genomes.

The real trick for viral evolution (as I see it) is host population density. Viruses undoubtably evolve, and do so independent of the host as we see in interspecies transfer. It's actually to the viruses advantage to evolve a multi-species host base, as viral infection is detrimental to the host's fitness, and over time, the host population will suffer as a result. If host population is sufficiently dense, the viral molocules can evolve to be highly virulent and effective reproducers. This also goes if the virus can attack many species. If host population is low, then the viral molocules either die out by killing their food supply, or they evolve low virulence to lessen their effect on the host. There are many examples of viruses that have evolved to become less virulent over time (the rabbit virus in Australia, for one). However, if a virus becomes less host specific, it can evolve more independently, and thus (presumably) more effectivally. I'll bet this is the direction of viral evolution, however, their simplicity and few genes might limit their adapatability.


Because of all that, I would imagine viral molocules could evolve either way, and probably did- ooze and the selfish gene route. Didn't Dawkin's bring that up? It's been a while since i read that...