New research from Dr. Katzourakis and hist Ph.D student, Pakorn Aiewsakun have discovered that retroviruses may be as old as 450 million years with recent genomic sequences from endogenous retroviruses, retroviruses within the genome of other organisms that is mostly dormant or broken.
The basic idea is that a retro viruses (a virus with RNA instead of DNA that infect the host and transcribes the RNA into DNA) can sometime infect a cell and then undergo a mutation that renders it nonfunctional. This virus then exist within the host genome and is subject to routine mutations like the rest of the genome.
By measuring the rate at which the genomes of the endogenous retroviruses mutate, a person can discover how long the virus has been dormant inside the genome. This is a similar method that scientist have been using to determine ancestry, for instance, looking at specific sites on the Y chromosome in males and by measuring mutation in the non-coding parts one can trace a single mutation in a male through his male descendants. This has been used to measure the early migrations and movements of people throughout the world.