Yeah, OK, so what's ERV?
Endogenous Retro Virus
Viruses that have become part of the genome. See Prediction 4.5 (about 2/3 the way down) for details.
The distribution of ERVs among the primates is illustrated there.
It's not proof of common descent, in the sense of proving the Pythagorean Theorem. However, when dealing with natural phenomena, we *never* have proof in that sense. All we have is proof in the legal sense of "beyond a reasonable doubt".
When you consider that in addition to the illustrated primate phylogenetic tree, the same kind of results have been found everywhere that genomes have been tested, doubt of common ancestry becomes highly unreasonable.