Around three million years ago, a huge evolutionary jump occurred: public lice that lived on gorillas began to inhabit human pubes. As we all know, you can get public lice from things other sex, so don't get all "my grandpa fucked gorillas!" on us - we can only assume that those early humans were either too cheap to stay at a clean hotel, or they used a bus station bathroom, and that's how the species jumped from one primate to another.