http://www.the-scientist.com/?articles.view%2FarticleNo%2F39244%2Ftitle%2FViruses-Reconsidered%2F

“Now, with the advent of whole-genome sequencing, researchers are beginning to realize that most organisms are in fact chimeras containing genes from many different sources—eukaryotic, prokaryotic, and viral alike—leading us to rethink evolution, especially the extent of gene flow between the visible and microscopic worlds. Genomic analysis has, for example, suggested that eukaryotes are the result of ancient interactions between bacteria and archaea. In this context, viruses are becoming more widely recognized as shuttles of genetic material, with metagenomic studies suggesting that the billions of viruses on Earth harbor more genetic information than the rest of the living world combined. (See “Going Viral,” The Scientist, September 2013.) These studies point to viruses being at least as critical in the evolution of life as all the other organisms on Earth.”