There's a reason our immune system doesn't simply keep all viruses out of the body. Any organism that did so would have offspring without as much random varia

There's a reason our immune system doesn't simply keep all viruses out of the body. Any organism that did so would have offspring without as much random variation. That would greatly decrease the chances of surviving random threats including new viruses. So when going back in time, don't change anything. And should science ever make it possible to design offspring, don't make it impervious to viruses.