From Jordana Cepelewicz at Quanta:
All of viral evolution is murky: Different groups of viruses likely had very different origins. Some may have been degenerate “escapees” from cellular genomes, while others descended directly from the primordial soup. “Still others have recombined and exchanged genes so many times in the course of evolution that we will never know where they originally came from,” Fischer said.
As examples of this diversity, giant viruses could help illuminate more about how viruses operate and evolve. But even their own origins and evolutionary path are unsettled. One side holds that the giant viruses evolved from smaller viruses over 2 billion years by adding genes, through processes such as horizontal gene transfer and gene duplication. The other maintains that the viruses started out large from the very beginning — and may even have been autonomous organisms — before losing genes they no longer needed and diversifying into the strains we see today. More.
“All of viral evolution is murky”? Chances are, it’ll get murkier. In which case, the question isn’t whether evolution but what.
See also: Newly discovered complex viruses challenge what we think viruses are