World's largest virus found, bigger than bacteria:

http://news.nationalgeographic.com/news/2013/07/130718-viruses-pandoraviruses-science-biology-evolution/

Perhaps a fourth kind of life on Earth.

looking at the diagram of that virus it struck me that it superficially resembles a living cell.
It makes me wonder; could all viruses have evolved from living cells that turned parasitic and became so specialized as parasitic that they lost their cytoplasm and protein-making machinery because they became totally dependent on the host's cytoplasm and protein-making machinery which they specialize in hijacking? -just a speculative thought. Don't know if there would be any evidence for that one.

Originally posted by humy
looking at the diagram of that virus it struck me that it superficially resembles a living cell.
It makes me wonder; could all viruses have evolved from living cells that turned parasitic and became so specialized as parasitic that they lost their cytoplasm and protein-making machinery because they became totally dependent on the host's cytoplasm and protein- ...[text shortened]... ijacking? -just a speculative thought. Don't know if there would be any evidence for that one.

Or it could have been the other way round, virus like creatures first then membranes, etc. Don't know how that would have worked though, since present day viruses need bacteria to reproduce.

Originally posted by sonhouse
Or it could have been the other way round, virus like creatures first then membranes, etc. Don't know how that would have worked though, since present day viruses need bacteria to reproduce.

Perhaps the way it could happen the other way around is if the viruses started off as very simple by consisting of not much more than genetic material only and 'infected' lifeless microscopes that regularly spontaneously formed in tidal pools but then some viruses evolved to have a symbiotic with those microspheres and, in the process, not only gave them life and made them living cells, but became an inseparable part of the cells while other viruses evolved to simply be parasitic on these new cells?

So I think we now have three credible theories here:

1, viruses evolved from living cells that first turned parasitic then evolved to loose their cytoplasm.

2, living cells evolve from viruses that combined with lifeless microspheres.

3, viruses and cells have independent origins (cells via abiogenesis; viruses via “viroabiogenesis” -which is a word I just made up) and neither one ever evolve from the other.

The most probable is that living cells came first and virus' originated later from a mutation of of RNA floating around in cells. They may have even originated multiple times. I know virus' come in strains/families, does anyone know if they all share at least some genes?

I am also of the opinion that there are probably other kinds of weird life that don't fit our current categories that have simply not been discovered yet because we don't know how to look for them. Unless something causes a disease or other significant interaction with life we tend not to notice it.

I typed "evolution of viruses" into google and one of the first links was this page which is reasonably accessible, and says there are probably multiple origins:

http://www.mcb.uct.ac.za/tutorial/virorig.html