Genesis 6:5 Now the giants were upon the earth in those days; and after that when the sons of God were wont to go in to the daughters of men, they bore children to them, those were the giants of old, the men of renown.LXX
Giants, before and after the flood. Some say that the sin in the garden of Eden, as taught by the dragon, was intercourse: hence the sudden desire for clothing. How else can one explain the seed of the woman versus the seed of the dragon/enchanter? The woman Eve was the mother of all humans. So, the sons of God would have been the dragon and his angels on Earth.
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Others say that Japheth was the Titan Iapetus... similarity of names?
Titans & Titanesses | Theoi Greek Mythology
After them, came the Giants of Pelasgian Legend.
Giants | Theoi Greek Mythology
The personification of Heaven and Earth... obvious poetic license.
Seas give birth to rivers... also poetic license.
Zeus made sweet love... the evangelization of Crete, etc.