But what of their deeper origins? Each STD, be it a virus, bacteria or protozoan, has taken a different evolutionary path to its present day existence. Many were likely present in other animals first, later mutating to survive in humans. Once the trans-species leap was made, the proliferation of each disease became tied to a complex array of factors including the movement of people – facilitated by ships, roads, airplanes, urbanization and globalization – and the sexual practices they brought with them, to name only a few. For a glimpse into the development of a new STD with worldwide implications, we need only look back as far as 1981, when the Centers for Disease Control first reported what would later be known as the Human Immunodeficiency Virus, or HIV. Today, there are approximately 40 million people infected with HIV worldwide, a staggering number considering the first human case probably occurred as recently as 1930, when a hunter in the Belgian Congo may have come into contact with blood infected with the Simian Immunodeficiency Virus, the chimpanzee forebearer of HIV.