Now it seems that "8% of human genetic material comes from" bornaviruses (BDV) that invaded one or some of our more recent ancestors. They've found them in all sorts of mammals and birds.
What's more, BDV lives only in the brain and infects only neurons. So if I'm reading this right, 8% of our chromosomes consists of a virus that lives only in the brain.
Researchers said, "These data yield a testable hypothesis for the alleged, but still controversial, causative association of BDV infection with schizophrenia and mood disorders."
Oh, boy. The brain roils, and not just the virus part. By this time, the viruses are assimilated, so it's not really viruses we're talking about but chunks of human DNA that were inserted by a virus a long time ago. It's not like we can take antiviral medication to get rid of it.
And it's not like we would want to. It is probably a net benefit to us. I mean, the mitochondrial invasion was a huge success for eukaryota ever since. Maybe the reason the virus was able to naturalize in our brain, so to speak, is that those who had it had more babies, evolution 101.
We might, however, find a way to unexpress parts of it, if it turns out to be related to mental illnesses. And that's a cool conjectural prospect for down the line.