ERVs are indirect evidence of evolution, common descent. Retroviruses make a DNA copy of their RNA genome and then insert it into a random position in the host out of 3 billion positions, if its in a germline cell the host's offspring will have the ERV instead and if this offspring reproduces, its offspring will also have the ERV in the exact same position, this will keep repeating over and over every generation, which is why humans and chimps share 99.9% of their ERV insertions in the exact same position with the exact same mutations. It is literally impossible for evolution to not exist due to this. (99.9% is 203,000 ERV insertions shared between humans and chimps)