These are remnants that are no longer used, and the integrity of the genetic text starts to erode. One of my favorite stories concerns the
ice fish of Bouvet Island. These creatures live in the cold waters of the Antarctic. They are the only vertebrates without red blood cells to carry oxygen to nourish their tissues. If you look at the genes for hemoglobin, the oxygen-carrying proteins in red blood, one of those genes is completely gone and another is a broken remnant, rotting away. From this we understand that the ancestors of these fish had red blood, but these guys have left that red-blooded lifestyle behind.