According to 23andme’s Twitter
Image reads,
Approximately 8% of DNA is originally from viruses, which infected your ancestors and became integrated into their cells.
.. Should a retrovirus happen to infect a germ line cell – i.e., a sperm or an ovum – the retroviral DNA will be copied into the offspring’s DNA. And their offspring. That’s called an “endogenous retrovirus”. Some cause or contribute to cancers – and sometimes (for example) that DNA even gets co-opted for a useful purpose.
.. Estimates vary – many of the retroviral sequences have been modified by mutation over the aeons, making it hard to find them all – but recent estimates do come to about 8% of the human genome having a retroviral origin. There’s a fair chunk of virus in all of us.