Evolution of viruses and cells: do we need a fourth domain of life to explain the origin of eukaryotes?

The recent discovery of diverse very large viruses, such as the mimivirus, has fostered a profusion of hypotheses positing that these viruses define a new domain of life together with the three cellular ones (Archaea, Bacteria and Eucarya). It has also been speculated that they have played a key role in the origin of eukaryotes as donors of important genes or even as the structures at the origin of the nucleus. Thanks to the increasing...