Did viruses precede other life?

I think I was probably in on that thread, but was banging my bonce against a different set of brickwork so I might have missed the details.It seems to me that it maybe is a bit bold to claim that viruses came before the earliest life. The evidence seems (I haven't looked at the paper in full yet) to be consistant with viruses having a common ancestor, and that they evolved early on alongside very early replicators.ps thanks for the cat link by the way, I was hoping for a creationist to bite at the bait - but no luck

Sorry for not getting back quickly, this is partly due to Euro 2004 football on the telly, but mainly due to my slothlike laziness!I can see what you are saying about different chemistry, but I think (definitely relating to this paper) that this could be a bit of a red herring. For a start the paper is talking about protein motifs, so the period of history they are looking at has chemistry very similar to life today ie nucleic acid encoding for protein.Although early life (ie before the split between Achaea, Bacteria and Eukaryotes) was undoubtably very 'virus-like' in some ways - like having a small genome and a simple structure - to define this stage of life as being viruses would require a redefinition of what a virus is.That said, I believe the evidence that viruses evolved early has strong implications for the history of life on this planet. For example, the Woese model of having a pool of many different protocells being the progenitors of the three domains needs an efficient method of horizontal transfer - viruses are great candidates.Not quite the universal role for viruses envisaged by SUnderwood (I'm not sure, but I think genetic studies would have picked up the significant events he's talking about), but a vital role non-the-less!

Hello SUnderwood,Good to see this topic up and running again.A few points:As you can see from my previous posts to Razd I don't think it's unreasonable to think that HGT drove early evolution (ie before the split into the three distinct domains): the 'bushiness' of the 'tree' of life () at this stage is testament to the amount of genes whizzing from organism to organism. I also don't dispute the evidence that suggests there being a transfer of genes from symbionts to the nucleus of hosts. But I have a few reservations about making the bold claims you seem to be making.

1. Although I accept that there does seem to be transfer of genes from parasite to hosts (and presumably visa versa), the extent to which this happens and its' evolutionary significance is unclear. To quote from one of your cited papers:
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   just how important remains to be seen

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2. It is clear that transfer of genes from the protobacterial progenitors of mitochondria and chloroplasts was central to the evolution of a separate Eukaryotic 'identity'. However, extrapolating this to suggest that it supports a role for HGT in 'macro' events further down the line is an error. I simply don't think that the evidence is there.
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3. Once past the promiscuous beginnings of life, genetic phylogenies tend to demonstarte a very vertical pattern of gene transference. If you have any evidence for large scale HGT I honestly would be interested to see it.
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4. The evidence to date is that the best candidate mechanism for generating change (on a large or a small scale) is gene duplication and changes in gene expression patterns. While viruses and other transposable elements do have a role in such duplication events the effect is very much vertical - gene duplications run in families.

To sum up: an interesting idea, but nothing to shout about (yet)Cheers Edit: Got my laterals and verticals mixed up - which can be quite painful I can tell you!This message has been edited by Ooook!, 09-30-2004 10:35 AM