text: Because most HERVs have no function, are selectively neutral, and are very abundant in primate genomes, they easily serve as phylogenetic markers for linkage analysis. They can be exploited by comparing the integration site polymorphisms or the evolving, proviral, nucleotide sequences of orthologs. To  estimate when integration occurred, researchers used distances from each phylogenetic tree to find the rate of molecular evolution at each particular locus.  It is also useful that ERVs are rich in many species genomes (i.e. plants, insects, mollusks, fish, rodents, domestic pets, and livestock) because its application can be used to answer a variety of phylogenetic questions.