Viruses and DNA transfer

Here's an intriguing thought. About 8% of our DNA is made up of ERVs. What's that?

ERV stands for "endogenous retroviruses." ERVs pass on with the rest of our DNA, but they initially came from...viruses. Some of them were even shared with other human species. Even more intriguingly, the HML2 family of viruses, which appear to be shared with Neanderthals and Denisovans, may be linked to cancer and the severity of AIDS.

So, do old viruses play a role in modern disease? More interesting still is the prospect that that viral DNA may actually do something- and that it may be possible to "catch" inherited traits the same way as one catches a cold. Could we find something in these viruses that could be used in gene therapy...and do we want to, given germ line gene therapy (passed on to offspring) is an ethical and even spiritual can of worms?

At the very least we may be able to come up with some more accurate predictors of cancer risk.