I did a little dig on the wheat and tares a few years ago. The farmer sowed good seed (wheat) in his field, but his enemy sowed tares among the wheat. Tares look just like wheat, but are a different type of plant entirely, and are actually poisonous. Line of Adam (Seth, etc), and the line of the serpent (Cain, Cannites). Noah was perfect in his generations, meaning his DNA was not contaminated with "tares." And when Daniel interpreted the King's dream of the statue, he explained that the toes of iron mixed with miry clay were from "them" mingling themselves with the seed of men.
So "they" left their first estate (heavenly realms), bred with mankind and animals, wreaking havoc on the DNA of God's creation. Perhaps that's why the Bible says "you must be born again," to straighten out the mixed genetics (just a theory), and restore our spiritual relationship with God (definitely).