

Itâ€™s not that having genetic material left behind by viruses is oddâ€”previous research had shown that viruses account for 8 percent of the human genome. But scientists thought most of that material came from retroviruses, which use their hostâ€™s DNA to replicate and leave some of their genetic material behind. Whatâ€™s weird about this is that filoviruses and bornaviruses are not retrovirusesâ€”theyâ€™re RNA viruses, which donâ€™t use the host to reproduce in the same way.