Seed of the Woman vs. Seed of the Serpent

If Cain was the serpent's + woman's biological boy, why are two "seeds" differentiated?

Genesis 3:15 KJV

"And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel."

Serpent's seed: Spiritual wickedness
Woman's seed: Biological (Jesus)

We are born of the flesh and hopefully also of the Spirit of God:

1 Peter 1:23 KJV

"Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever."

John 3:3 KJV

"Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God."

𝔄𝔫𝔱𝔦 𝔖𝔢𝔯𝔭𝔢𝔫𝔱 𝔖𝔢𝔢𝔡