Who was Cain's father?

Yet another post, inspired by a Twitter conversation....

Here's R. Yochanan on BT Avoda Zara 22B:

When the serpent came unto Eve he infused filthy lust into them

Asked @Marksofla:

R' Yochanan says that the nachash had sexual relations with Chava. Is this from a medrash somewhere?

First, any non-halachic information found in the Talmud is, by definition, a medrash, so the short answer is, yes, it is a found in a midrash somewhere, and that somewhere is the Talmud itself, which discusses the illicit relationship between Eve and the snake in three places.

And where does the story of Eva and the sexy snake come from? Seemingly from an earlier idea that Cain was the product of an illicit union between Eve and a wicked angel disguised as the snake, an idea that itself appears to be very old and appears to have gotten its start with an interpretation of Genesis 4:1.

The verse reads: וְהָ֣אָדָ֔ם יָדַ֖ע אֶת־ חַוָּ֣ה אִשְׁתֹּ֑ו וַתַּ֙הַר֙ וַתֵּ֣לֶד אֶת־ קַ֔יִן וַתֹּ֕אמֶר קָנִ֥יתִי אִ֖ישׁ אֶת־ יְהוָֽה׃.

Some things are curious about this verse.

(1) Why does Eve refer to her newborn as an ish? Ish is a full grown man, not an infant.

(2) What did Eve mean when she said "I have acquired a man with YKVK (the Lord?)" 

For that matter, the whole story of Cain and Abel is puzzling. Why, for instance, did he kill his brother, and why was his sacrifice rejected?

An answer is given by Targum-Pseudo-Johnathan (dating uncertain) on the spot: And Adam knew that his wife Eve had conceived via Samael the angel of the Lord and she became pregnant and gave birth to Cain. He resembled the upper ones (angels), not the lower ones so she said I have acquired a man (kaniti ish) indeed (or via) an angel of the Lord.

The answer, or interpretation/drash given by TPJ seems based on the idea that ish often means angel (Cain resembled the upper ones) and on the understanding that the Torah uses ellipses (thus "via an angel of") and on a convention that the word YKVK can sometimes refer to a wicked angel (as it is understood for example in Exodus 4:24). 

TPJ solves another problem by explaining that "knew" is not being used in 4:1 in the usual biblical sense, as a euphemism for sexual relations, but literally: Adan knew that his wife had conceived via Samel

The idea that Cain was the son of a wicked angel solves the problem in Exodus 4:1, gives a reason for the rejection of the sacrifice, and also explains why Cain killed his brother (He was evil from birth, and the son of the devil, see?) This idea seems to have been in circulation at the end of the first Temple period as it pops up in a variety of places:

• First epistle of John: (first century): Do not be like Cain, who belonged to the evil one and murdered his brother
• TPJ 3:6: And the woman saw Samel and was afraid

Later, or at the same time, the idea seems to have developed that the snake that tempted her was actually the wicked angel in disguise: 

• Pirquei deR. Eliezer (dating unclear): The serpent came unto her and she became pregnant with Cain as it says... What did he know? That she was already pregnant from someone else.
• Apocalypse of Moses (first century) The devil answered me through the mouth of the serpent
• 3 Baruch (first century)(probably) Satanel, when he dressed himself as the serpent
• Macabbes 4 (between first century BCE and first century CE) "I was a pure virgin and did not go outside my father's house; but I guarded the rib from which woman was made. No seducer corrupted me on a desert plain, nor did the destroyer, the deceitful serpent, defile the purity of my virginity.

All of the sources above are older than BT Avoda Zara, by the way.

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