http://www.newscientist.com/article...RSS|NSNS|2012-GLOBAL|online-news#.UoqIg42ZXcB
...
The new study is important, says Magiorkinis, because it emphasises that modern humans can differ from one another significantly in the non-coding parts of their genomes. "The results show that we can find individuals today who share loci with Denisovans or Neanderthals, but not with other humans alive today," he says.
This shows how vital it is to know whether an individual possesses or lacks a certain sequence rather than just assuming it is present, says Jonathan Stoye at the MRC National Institute for Medical Research in London. "Such properly analysed data will be necessary to establish whether there is any real link between endogenous retroviruses and disease," he says.
Belshaw and Magiorkinis's team is now exploring just how widespread this retroviral DNA is in the modern human population and whether the viruses themselves are ever active. "Within the next five years, we should be able to say for sure whether these ancient viruses play a role in modern human diseases," says Belshaw.
"We know these viruses cause disease in other animals, including mice," says Belshaw. There is also some evidence that the viruses are in an active state in tissue taken from people with motor neurone disease. "But it's never been proven that they can cause disease in humans," he says.