A joke taken from 'The Diary of A Young Girl - Anne Frank'

After a Bible lesson about Adam and Eve, a thirteen year-old boy asked his father, 'Tell me, Father, how did I get born?'
'Well,' the father replied, 'the stork plucked you out of the ocean, set you down in Mother's bed and bit her in the leg, hard. It bled so much she had to stay in bed for a week.'
Not fully satisfied, the boy went to his mother. 'Tell me, Mother,' he asked, 'how did you get born and how did I get born?'
His mother told him the very same story. Finally, hoping to hear the finner points, he went to his grandfather. 'Tell me, Grandfather,' he said, 'how did you get born and how did your daughter get born?' And the third time he was told exactly the same story.
That night he wrote in his diary: 'After careful inquiry, I must conclude that there has been no sexual intercourse in our family for the last three generations!'