Ok, so Jesus parents were named Joseph and Virgin Mary. "Virgin" implies Mary was a virgin so she had not had sex with Joseph. So my theory is: Mary gets drunk and crazy, has sex with a random guy, and ends up getting pregnant. Because she hasn´t had sex with Joseph and can't claim the child is his, she comes up with the idea that it is Gods child. One thing leads to another and it gets blown out of proportion and thus, Christianity is born.