Paleovirology - ghosts and gifts of viruses past.

The emerging field of paleovirology aims to study the evolutionary age and impact of ancient viruses (paleoviruses) on host biology. Despite a historical emphasis on retroviruses, paleoviral 'fossils' have recently been uncovered from a broad swathe of viruses. These viral imprints have upended long-held notions of the age and mutation rate of viruses. While 'direct' paleovirology relies on the insertion of viral genes in animal genomes, examination of adaptive changes in host genes that occurred in response to paleoviral infections provides a complementary strategy for making 'indirect' paleovirological inferences. Finally, viruses have also impacted host biology by providing genes hosts have domesticated for their own purpose.