Consider this. You are a neuroscientist with a special interest in the brains of psychopaths. Knowing your interest, your mother suggests you check your own family tree for skeletons in the closet. Some of your ancestors were strange indeed, she says. You do that and discover that, among other psychos, Lizzy Borden, the Axe Murderess, is in your family tree. You check DNA in your immediate family and are astonished at what you find.