Retroviruses are nearly 500 million years old, according to new research by scientists at Oxford University. According to a new study published in Nature Communications, the evolutionary arms race between retroviruses and their hosts began several hundred million years before scientists previously thought.

To detail the history of retroviruses -- the group of viruses that includes HIV -- scientists combined new modeling techniques with a penetrating survey of genomic fossil records of the foamy-like viruses. Foamy and foamy-like viruses are viruses that diverge alongside their host. They are endogenous retroviruses, as their distinctiveness emerges from within.

The innovative modeling and fossil survey allowed researchers to overcome one the main challenges of studying the evolutionary history of viruses -- their accelerated evolution. Their rapid adaptation makes studying recent virus history easy, but the quality works to complicate an accurate view of more ancient viral history.

"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," study author Aris Katzourakis, a zoologist at Oxford, explained in a news 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."

Katzourakis believes the latest revelations will force scientists to adapt the way they interpret previous and ongoing studies of viral evolution.

"We need to consider the adaptations that vertebrates have developed to combat viruses, and the corresponding viral countermeasures, as the product of a continuous arms race that stretches back hundreds of millions of years," he said.