Eve being seduced by the Serpent is what brought about the fall of man and the sexual birth; so in order for God to restore fallen man, another birth was needed to redeem him. This other birth was the virgin birth that produced the Redeemer Jesus, and by His death on the cross of Calvary, the new birth was made available to us (John 3: 3).
Cain’s entrance into this world came about by the sexual birth via Eve’s encounter with the Serpent. The Serpent was not a human, but was an animal who closely resembled man in his stature; thus we can clearly see that Cain’s birth in Eden did not come about by the instrumentality of a human male, but that a non-human father was responsible for it.
A similar thing happened when God brought salvation to this world by the Redeemer. Mary’s husband was Joseph, even as Eve’s husband was Adam. As Adam had no part to play in the birth of Cain, so Joseph had no part to play in the conception of Jesus. Adam was not the genetic father of Cain, and neither was Joseph the genetic father of Jesus. The Bible makes quite plain that as Cain had a non-human father, so Jesus had a non-human father, for we read the following in Matthew 1: 18: Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost.