It is absolutely amazing that if an ERV is found that is not degraded much from the “parent” sequence it is likely to be found only within that species or in very closely related species (exactly as if it had incorporated itself into the genome very recently). But if an ERV is found that is highly degraded it will likely be found in almost all closely related species (exactly as if it had incorporated itself into the genome of a common ancestor a long time ago).
There has yet to be a scientific explanation proffered for this phenomena that doesn't include common descent.
The Earth is only 6000 years old, LOL!