"Scientists estimate that they have discovered and documented less than 1 percent of all the living things on the planet. But for every organism in that unidentified 99 percent, at least 10 times as many unknown viruses are thought to exist—the vast majority of which are harmless to life and yet integral to it" - Viruses
Considering the primary function of virii is manipulation of genetic code, perhaps we should take into account these vast unknowns into our ideas about the theory of Evolution itself. It is certainly agreeable to reason that these little DNA programmers have had quite a significant long term impact on Evolution. Not sure what that would be though.
