https://phys.org/news/2018-05-million-year-old-evolutionary-arms-hiv.html > The study shows that over hundreds of millions of years, this battle for survival caused the genes to develop sophisticated shields to block viruses, which in turn forced the viruses to continually evolve and change to circumvent these defences. This provides insight into both how the viruses and the immune system has evolved. > Using sequencing technology, Barr and his research team found that the HERC5 gene from this 400 million-year-old fish called a coelacanth encodes for a protein that can potently block the primate version of HIV, known as simian immunodeficiency virus (SIV), but fails to block HIV.