(Below are quotes from historical extra Biblical writings giving evidence that the belief in two seedlines was an ancient belief, commonly held by both Jews and non Jews.)

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Extra-Biblical Evidence of Two Seedlines

Celtic Church in England taught that Eve was physically seduced by Lucifer

"Who died but was never born?" (Adam)
"Who gave but did not receive?" (Eve, milk)
"Who was born but did not die?" (Elias and Enoch)
"Who was born twice and died once? (Jonas the prophet, who for three days and three nights prayed in the belly of the whale. He neither saw the heavens nor touched the earth)"
"How many languages are there?" (Seventy-two)
"Who spoke with a dog?" (St Peter)
"Who spoke with an ass?" (Balaam the prophet)
"Who was the first woman to commit adultery?" (Eve with the serpent)
"How were the Apostles baptized?" (The Saviour washed their feet).

(The Celtic Church In Britain, by Leslie Hardinge, chapter titled"The Role of the Scriptures," page 48).
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Aramiac Targums give Evidence of physical seduction of Eve

To Gen 4:1, an ancient Targum adds the following words
italicized in red:

"And Adam knew his wife Eve, who was pregnant by Sammael [Satan], and she conceived and bare Cain, and he was like the heavenly beings, and not like earthly beings, and she said, I have gotten a man from the angel of the Lord."

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Protevangelium of James, from third century A. D.

"XIII. I Now it was the sixth month with her, and behold Joseph came from his building, and he entered into his house and found her great with child. And he smote his face, and cast himself down upon the ground on sackcloth and wept bitterly, saying: With what countenance shall I look unto the Lord my God ? and what prayer shall I make concerning this maiden? for I received her out of the temple of the Lord my God a virgin, and have not kept her safe. Who is he that hath ensnared me? Who hath done this evil in mine house and hath defiled the virgin? Is not the story of Adam repeated in me? for as at the hour of his giving thanks the serpent came and found Eve alone and deceived her, so hath it befallen me also. 2 And Joseph arose from off the sackcloth and called Mary and said unto her O thou that wast cared for by God, why hast thou done this ? thou hast forgotten the Lord thy God. Why hast thou humbled thy soul, thou that wast nourished up in the Holy of Holies and didst receive food at the hand of an angel? 3 But she wept bitterly, saying: I am pure and I know not a man. And Joseph said unto her: Whence then is that which is in thy womb ? and she said: As the Lord my God liveth, I know not whence it is come unto me."

(from "The Apocryphal New Testament," trans. by J. R. James, Oxford, Clarendon Press, 1924)

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From the Jewish Enclycopedia

Jewish Encyclopedia: Eve (Chava), In Rabbinical Literature:

"Cain's real father was not Adam, but one of the demons." (Pirke R. El. xxi., xxii.).

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Popular commentaries confirm the same thing.

     The Wycliffe Bible Commentary, page 1473: "
He (Cain) is said to have belonged to the family of the wicked one."

     Matthew Poole's Commentary on the Holy Bible, volume 3, page 936. "Which showed him (Cain) to be of that wicked one, of the serpent's seed: so early was such seed sown, and so ancient the enmity between seed and seed."

     Matthew Henry's Commentary, volume 6 page, 1077: "It showed that he (Cain) was as the firstborn of the serpent's seed."

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The Founding Fathers and others warned against influence of the false Jews and their Talmud.