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The Scientist asks, Should giant viruses be the fourth domain of life?


Eukaryotes, prokaryotes, archaea, … and viruses?

Recently, there’s been a lot of discussion about giant viruses (as in “Biggest virus ever: We just don’t understand anything anymore!” The same issue of The Scientist from which we learned that the last universal common ancestor was “a sophisticated cellular organism,” not Darwin’s “primordial form” also asks, editorially, whether giant viruses should be the fourth domain of life.

More-recent discoveries of giant viruses with massive genomes have the potential to shake up evolutionary biology once again. Truly giant viruses, with bigger genomes than many bacteria and archaea, escaped detection for decades because microbiologists defined viruses, in part, by their ability to pass through filters with pores 0.2 μm in diameter. Didier Raoult (“Viruses Reconsidered”) describes the discovery of these megaviruses (0.4 μm) that, among other surprises, contain genes encoding the translational machinery for their replication. Woese added archaea to the tree of life based on rRNA sequencing. Viruses have no rRNA, and most biologists do not consider them to be living organisms. But Raoult argues that phylogenetic trees based on transfer RNA and RNA polymerase genes “show that viruses are at least as old as the three traditional domains proposed by Woese” and may warrant classification as a fourth branch of life.

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One of the giant viruses is Pandoravirus:


See also: The Science Fictions series at your fingertips (origin of life)

Robert Byers @ 3 Perhaps same logic may apply to any messy stuff found in biology including the so-called junk DNA. We humans have messed up ourselves through history. Can't complain now :( Dionisio
It all doesn't work because viruses were not created by god but are some monster twist on life after the fall. so they are just abberations on something else. its useless looking for a evolved ancestor. Robert Byers
In engineering software development, the analyst has to answer all possible questions when writing the tech specs for the programmers to work with. No ambiguity, no vague statements, no "perhaps" or "maybe" or words like that. Then on the quality assurance phase, the software has to go through a rigorous testing that covers as many possible scenarios and cases as one can think of. Do we take this same approach in science? Dionisio
Aren't these "domain of life" subjective arbitrary human concepts? Had they used a different criteria for sorting/grouping, would those so-called "domains" look different? Which sorting/grouping criteria is valid? Why? What evidences? What facts? Where are they listed and described? For any story about going from A to B, do we have the detailed step-by-step algorithm description of that transformation? Where is all that written in? Dionisio

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