To clarify, when breeding animals you often get superior offspring when you mate the father with the daughter. However, the failure rate is far greater than the good "nick."

I know a man who's grandfather was also his father.

His mother was also his sister.

When I met him, he lived with his uncle who was also his brother.

He was a genius . . .a farmer who had figured out the stock market. He was wealthy by our local standards, but lived like a pauper. His life was very isolated. He spent his entire life in the same homesteader shack in which he was born. I always had the sense that he was afraid of the world, afraid that everyone knew the family secret . . . that's why he never left the farm.

And everyone did know the family secret. No one ever spoke his name to me without mentioning his sordid beginnings. It was very sad that he could never escape the crime perpetrated by his grandfather/father . . .who was never prosecuted. In the 30's they just ignored that stuff.