In response to Mary's post about fossil viruses...Coming at this from a biochemistry/molecular biology perspective, viruses are considered very ancient entities (not really life forms). It's not surprising that there wouldn't be a fossil record of their presence on ancient Earth, since they are impossibly small packets of protein and DNA, and such molecules degrade rapidly outside of host organisms. Some viruses have the ability to incorporate themselves into their host's DNA and effect mutations leading to evolutionary changes - or a dim outlook for the host should this incorporation lead to disease - one of the theories supporting their ancient origins. To be truthful, I've never really considered the history of viruses, so I can't say a lot off the top of my head. However, my training as a biochemist suggests to me that viruses have been around a whole lot longer than we have and their ability to adapt and evolve is likewise superior. With that comforting thought, I'm off. regards, Julia
