EVOLUTION. “Salvador Luria mused about the viral influence on evolution in 1959. “May we not feel,” he wrote, “that in the virus, in their merging with the cellular genome and reemerging from them, we observe the units and process which, in the course of evolution, have created the successful genetic patterns that underlie all living cells?”
http://www.scientificamerican.com/article.cfm?id=are-viruses-alive-2004&page=3