Is “Married his sister Nüwa to reproduce humanity” true?

In later folk legends and popular literature, Fu Xi and Nüwa are often depicted as siblings who married after a great flood to reproduce humanity. However, a thorough search of early core texts such as the Classic of Mountains and Seas, Songs of Chu, Huainanzi, and Records of the Grand Historian reveals no indication of their sibling or marital relationship. This claim has no basis in early texts and was entirely fabricated by later generations.