ask any christian who's the biological father of jesus and they will still answer "god".
Any Christian would know that Jesus has no biological father. He is who He is, or in first person pronoun, the famous I am who I am. John 1:1-2 - In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God.
Of course the next question to follow would be, what about Mother Mary? The answer is of course in John 1:14 - And the Word became flesh and dwelt among us, and we beheld his glory, the glory of the only begotten son of the Father, full of grace and truth.
Without coming to earth through the womb of a woman, He couldn't be a man in flesh. With a biological father, he couldn't be the Son of God. The whole rationale traces back to Adam, a man and the first Man, not born out of the womb of a woman but created out of soil. Therefore, Jesus Christ is not only known as Son of God, but also Son of Man.
I'm not preaching any religion here, just to discuss a point. Before jumping into conclusion to accusation of irrationality, think rationally. How could the first man come from the womb of a woman by insemination? If that's impossible, then it's possible that another man could come without insemination. It's a possibility, not a proven certainly. It's up to individual believe and faith.