“These findings show that this medically important group of viruses is at least up to half a billion years in age—far older than previously thought,” Katzourakis said in a press release. “They date back to the origins of vertebrates, and this gives us the context in which we should consider their present-day activity and interactions with their hosts.”
“We’re up against the limits of our ability to determine their age,” Michael Worobey of the University of Arizona, who was not involved in the work, told Nature.
Michael Emerman of the Fred Hutchinson Cancer Research Center in Seattle, who also was not involved in the work, told Nature that this analytical approach is applicable to animals other than fish. “Almost every animal has a retrovirus, and their evolution occurred with these viruses,” he said. “You can’t consider the evolution of a species without the evolution of their pathogens.”