The following is the best hypothesis as to how HIV began. As the years progressed, it began to spread around the world. New diseases among humans do occur from time to time. Just in the past 20 years, besides AIDS, we have now seen Legionaires Disease, Toxic Shock Syndrome, Chronic Fatigue Syndrome, and Ebola Virus. New diseases will always be seen from time to time.
Diseases are an ongoing part of nature.
All the evidence goes against HIV being a man-made virus. This virus was first thought to have begun in the late 1950's to early 1960's in Africa. During these years, we did not have the technology to study viruses, let alone create viruses. The tools to study viruses have primarily been developed in the 1970's, 1980's, and 1990's. Our technological capabilities to study viruses are still crude today.