There's a set of tiny travelers living in your DNA. Called transposons, they're stretches of DNA that are able to copy themselves, move to other places in your genome, and then insert themselves right in and make themselves at home.
They could keep doing this indefinitely, which would overwhelm their host DNA and kill their hosts. But they don't, and scientists have been unsure why.
Although they're able to continue to make more and more copies themselves, scientists weren't sure why they didn't do that indefinitely. Now, a team of biologists is proposing a solution to that mystery.
If they choose the wrong place to land, they can cause diseases such as hemophilia and colon cancer, yet they aren't generally harmful.