There was this boy who went and asked his parents how he was born. His father said “We went to the store, and bought you.”
A bit puzzled, he went to see his grandparents and asked how his father was born. His grandfather said that they went into a store, found his father, and bought him.
More and more puzzled, he asked how his grandfather was born. The grandfather said that, similarly, he had been purchased from a store.
The boy went home and opened his journal that night. He wrote: “There has been no sexual intercourse in this family for three generations.”