Skeptics will sometimes claim that the existence of virgin birth stories in ancient pagan religions shows that Jesus’ virgin birth was fabricated by the early Christians.
There were apparently virgin birth stories for a number of figures in pagan religions and also some prominent historical figures. It may have been a mark of your importance, or maybe it was just a cool was to start a biography. At any rate, the stories were out there. Does that necessarily mean that Christ’s virgin birth was fictitious?
Is a virgin birth possible?
If you start with the idea of a God who can create a universe from scratch no other miracle is impossible. Can a virgin get pregnant naturally? No. Can God supply the necessary missing genetic material to create a baby? Of course. He made Adam’s DNA from scratch, so making half of Jesus’ shouldn’t be any trouble. (Actually, from the wording of the text, I wonder if Mary’s DNA was used at all. A question for another time.)
If a virgin birth is at least theoretically possible, is there any reason to doubt the claim that Jesus was conceived without the help of a human male? If you remove the anti-supernatural bias, I can see no reason we shouldn't believe the story, especially given how many other miraculous things occurred in Christ's life.
Why the pagan parallels?
Some have suggested that the ancient religions around Jesus’ time whetted the appetite for the gospel. I wonder if this might be a similar situation.
Instead of asking why Christ had to have a virgin birth, perhaps we should ask why the pagans had them. Could they have been there so that the pagans would see virgin births as pointing to someone important, someone worth listening to?* It’s worth thinking about.
* A careful, reasoned apologetic this is not. It's really just an interesting idea to consider. Maybe someone will be able to develop it some day.