incest
Incest can be traced back to the beginnings of literature. For example, the Olympian gods. Zeus himself was born from the love of two siblings, Kronos and Rhea, who in turn were fathered by Uranos and their mother Gaia. And dear Zeus continued the incestuous tradition, first marrying his sister Hera, and finally uniting with his mother Rhea. Or Oedipus. He unwittingly murdered his father Laius and then married his mother, Queen Iokasta. We see incestuous customs in many ancient cultures of India, through Egypt and Greece to America, and they seem to be of great interest in modern times. Yep, the search term statistics on the net are relentless!