Some form of Judaism believes that Serpent and Eve had mated and Kain was an offspring of this relationship. Therefore, Eve is called a mother of all living, but not Adam, because he was not a father of all humanity. "Genesis 4:1: ‘ And Adam knew
his wife Eve, who was pregnant by the Angel Sammael, and she conceived and bare
Cain; and he was like the heavenly beings, and not like the earthly beings, and
she said, I have acquired a man, the angel of the Lord." - from Targum of Jonathan.
The rivalry between Abel and Kain was caused by two brothers having two different daddies. The hatred between two classes of people was brought to the offspring. Some interpretation from Judaism said that the war is between children of Serpent and Adam, and has nothing to do with Christian Messiah. Some more radical rabbinic stories said that the fall from grace was that both Adam and Eve had inappropriate 3-way sexual relationship with a Serpent and were not pure afterward. This was also a cause for their mutual shame. Two years ago I posted on the Serpent Seed here from Midrash, but I do not feel to look for the links again.
The stories between Adam, Eve, and Serpent having sexual relationship is old over 1000 years. They were also known to medieval Christianity and Renaissance. It is not recent invention.