Are they a critical part of the origin of life?:-"By incorporating giant viruses into phylogenetic trees, we are now able to begin understanding their role in the evolution of life. Some giant virus genes are highly similar to each other, and to those of other microbe groups, suggesting these genes—and giant viruses—have an ancient origin. Some researchers, such as Patrick Forterre of Paris?Sud University and the Institut Pasteur in France, believe that giant viruses are the origin of the eukaryotic nucleus;8 the previously established theory of viral eukaryogenesis posits that large DNA viruses played this role.
 
"Forterre and others even speculate that DNA was "invented" by viruses, helping to convert a world of RNA-based organisms to one where DNA became the pervasive unit of heredity. In part due to its catalytic potential, RNA is hypothesized to have been the molecular basis of first life on Earth. (See "RNA World 2.0," The Scientist, March 2014.) Forterre argues that early RNA cells and ancient RNA viruses, perhaps derived from these early cells, coexisted at that time and that early RNA cells were likely to have been parasitized by these viruses. Evolving a genome of DNA could have guarded these viruses against attacks from their hosts, which may have begun to evolve RNA-specific defenses to protect themselves against viral infection. Then, as viruses borrowed and returned the genetic material of their hosts, they would have shared DNA genes, which are more stable and would have therefore been favored by natural selection.
 
"While all of these theories are just that, and much work is needed to understand the origin and evolution of life on Earth, it is clear that the long-neglected viruses are central to answering these questions."-http://www.the-scientist.com//?articles.view/articleNo/39244/title/Viruses-Reconsidered/