A review of: Reasons to include viruses in the tree of life. Hegde NR, Maddur MS, Kaveri SV, Bayry J. Comment on Nature Reviews Microbiology. 2009 Apr;7(4):306-11
As we all are aware there is a debate which has been on-going for decades, Are viruses alive? There has been a previous post by Nikie Pontefract on Ten Reasons to Exclude Viruses from the tree of life, this paper although very short raises opinions for why viruses should be included in the tree of life as a direct response to Moreira and Lopez-Garcia’s paper (2009). As I was one of the people who also reviewed this paper for the seminar I decided it would be a good idea to review a paper which was pro viruses being classified as living organisms.
This paper selects but a few of the main points raised by Moreira and Lopez-Garcia (2009) and uses them to turn and suggest reasons why viruses should be included in the tree of life.
In the original article they stated that viruses are not alive because they are polyphyletic this means that they derive from more than one ancestral type, however this paper they suggest that because of the rapid evolution of viruses it would make sense that they are polyphyletic. This is only one example used but the authors do explain a more plausible comparisons being between viruses and spermatozoa or ova neither of which would survive without a host, the most interesting point raised by the authors was Darwin’s theory of ‘survival of the fit test’: those organisms that cannot adapt to a particular condition become extinct. The authors remind us that non-living organisms do not follow this theory and if viruses are non-living then they should not be able to adapt to a particular condition. This is not true for most viruses as they constantly mutate to adapt, Human immunodeficiency virus being an example of this.
This paper does show some valid reasons for why viruses should be included but too few, in my opinion this was a very rushed article just to get an opposing opinion out there. It does not unfortunately take the time like Moreira and Lopez-Garcia (2009) to formulate an equally lengthy or informative read which is a shame because it would have been very interesting……
Further Refrence: Moreira and Lopez-Garcia. Ten Reasons to exclude viruses from the tree of life. Nature. Vol 7. 2009.
3 comments:
Alright Dan,
The polyphyletic thing confuses me. Why can't alive organisms come from more than on ancestor? I was reading a paper for the john spicer groupwork on scleractinian corals and the whole time they went on about them being polyphyletic and seemed to think it was ok.
Hey,
yeah i got confused about this too!
in the original paper (10 reasons not to nclude viruses...) the authors say that 'a phylogenetic tree is a conceptual representation of evolutionary relationships amoung taxa' that can 'only be be inferred by studying characteristics that have been inherited from the last common ancestor of the taxa'. so because viruses do not share any homologous characteristics with cells, they cant be included because basically they have nothing in common with everything else already considered part of the tree.
does that make sense? i think i've confused myself again now!
so, everyhthing already in the tree of life comes from one ancestor but because viruses are so different and dont share anything in common with everything else they must be from a different ancestor (which the authors claim is impossible) or maybe nothing at all, therefore they are not alive...
Hi Matt, Nikie
This is the thing, polyphyletic groups last common ancestor is often not a member of the same group. we generally classify species as coming from a single common ancestor. In this review the authors are arguing that because viruses evolve rapidly and they 'gene rob' means it would make perfect sense that they are polyphyletic and alive.
Dan
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