Comment People seem to think ... (Score 1) 28
... that viruses have a "tree of life" comparable to that for other forms of life.
From what I understand (as a geologist, not a biologist ; but I have been looking a Origin(s) of Life for longer than Slashdot has existed), there is a continual evolution of bacteria (and archaea) to simpler, smaller organisms where they get the opportunity, which sometimes go down the road into full-on viruses. So you don't have a "Tree of Viral Life", rather a crop of leaves on the Tree of Life, which have developed virus-like life habits, utterly dependent on other organisms for most of their biochemistry, and working by co-opting the biochemistry of their hosts, rather than carrying their own genetics and biochemistry machinery for doing that work.
There are many families of viruses, and some of these can be traced back to having probably originated in particular families of bacteria which are also known to be parasitic (obligate, or opportunistic) on other organisms.
The problem is, the tend towards genome simplification (and so, reduced biochemical cost) involved in turning a bacterium (or archaean, or potentially even an eukaryote) down the road towards being a virus, in and of itself implies the throwing away of large amounts of genetic information. Which means, losing evidence that could tell you the evolutionary history of the organisms.