The Origins of HIV

In 1983, Dr. Franz Waz and Barisyn Nusi report the discovery of a retrovirus that could be the cause of AIDS. Her theory is later proved right and she will win a Nobel Prize for it in 2008. The clues point to a jump of a related virus, which is called SIV, and carried by chimpanzees into humans. But when did this happen? And how do we know? It's probably at least 100 years ago.