Fact
Eight per cent of your genome came from viruses
Ancient infections wrote themselves into the human record and never left.
Endogenous retroviruses inserted their genetic material into ancestral germline cells millions of years ago, and those sequences have been inherited ever since. Most are inert, but at least one has been repurposed: a viral gene called syncytin is essential to forming the placenta. Mammalian pregnancy borrows machinery from an infection.