Clues to Ancient Viruses: The Evolution of Innate Immunity to Primate Retroviruses

Within the past century a number of “emerging viruses” with pathogenic properties have entered the human population. However, it is unlikely that novel pathogenic viral infections of humans are unique to modern history. We can trace the history some ancient viral infections from “fossils” left behind in primate genomes in the form of defective integrated proviruses. However, other ancient viral infections can be inferred from their effects on the evolution of host antiviral genes. The genetic conflict of antiviral genes with virally-encoded antagonists of these host defenses viruses results in patterns of adaptive evolution of the host genes. These patterns can be used to deduce when a given gene was under positive selection, and consequently when possible Darwinian selection due to a pathogenic viral challenge acted during primate evolution. We suggest that selection to survive the pathogenic effects of these ancient viruses has shaped our repertoire of antiviral defenses in ways that impact our resistance or susceptibility to modern day emerging viruses.