When did viruses/giruses evolve?

[CharonY]

I can find out, but from memory, Koonin is one of the corresponding authors and it was published 2017 in Science.

[CharonY]

In order to not derail the other thread further I am going to provide some lit here. The basic misunderstanding is that today we really only have viruses that rely on RNA for replication, hence, in an RNA world there can only be viruses. That is a misconception as replicating units would need to have more functions (and genomic studies point to number of likely early elements) thus, whatever existed in the RNA world would be quite different from what we understand as viruses. In short, one hypothesis assumes that proto cells existed that were based in RNA, but were preyed upon by RNA-viruses, which developed at that time. The development of DNA cells was (among other benefits, such as stability) a way to adapt to those viral particles.

My view was largely shaped by a paper published 2005 by Forterre (Biochimie 87:793-803) which I found to be an easy to understand introduction. For updated views I would recommend to look at a number of papers published authored or co-authored by Koonin.