Notes:

"Further, Zeno of Citium says that there is nothing wrong with a man's rubbing his mother's private parts with his own, just as nobody would say that it is wicked for him to rub any other part of her body with his hand. And Chrysippus, also, in his Politics, decrees that a father may produce, children by his daughter, and a mother by her son, and a brother by his sister."

-Sextus Empiricus, Outlines of Pyrrhonism