the most common and the most believed theory of how HIV came into existence is the " Hunter" theory. in this theory, SIV was given or transferred to humans from chimps when the chimps blood got in a hunters cut or wound or raw chimp meat was consumed by hunters. during those processes, SIV was transferred to a hunter. usually the human body would fight off the disease very easily, but in some cases(depending on the person and the immune system) the SIV would have spread in the body causing strains at first and then leading to HIV then later into AIDS. there has been many bans on the butchering and consumption of ape and chimpanzee meat to stop any diseases like HIV to happen again.