By comparing the genetic data of modern day cancer patients to that found in fossils of our genetic ancestors, the Neanderthals and Denisovans, researchers learned that the same viruses that infect us today also infected Neanderthals more than half a million years ago.
The find suggests that that some viruses that infect us today have their origins in our ancestors, and the link establishes the possibility for research into whether modern diseases like HIV and cancer have roots in the past.
About 8 percent of human DNA is made of endogenous retroviruses (ERVs), which are DNA sequences from viruses that pass from generation to generation. These ERVs are found in part of the DNA sequence with no known function; this seemingly useless DNA is often referred to as junk DNA.
"I wouldn't write it off as 'junk' just because we don't know what it does yet," said study co-author Gkikas Magiorkinis, of Oxford University's Department of Zoology. "Under certain circumstances, two 'junk' viruses can combine to cause disease -- we've seen this many times in animals already. ERVs have been shown to cause cancer when activated by bacteria in mice with weakened immune systems."