The Nephalim
The Nephilim were on the earth in those days—and also afterward—when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown.
[Our anthology begins here] The Lord saw how great the wickedness of the human race had become on the earth,and that every inclination of the thoughts of the human heart was only evil all the time. 6 The Lord regretted that he had made human beings on the earth, and his heart was deeply troubled. 7 So the Lord said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them.” 8 But Noah found favor in the eyes of the Lord.
Human beings shared habitat with other advanced hominids from Europe through Asia until as late as 40,000 years ago: might ancient people have carried a folk-knowledge of this through oral tradition?
Recent archeological and DNA evidence proves that humans interbred with both Neanderthals and Denisovens:
National Geographic: Why Am I Denisovan?