Good theology should form a tight logical system. Different doctrines fit together, and partially explain one another, to make a cohesive picture. Bad theology often has holes left in it where different doctrines do not dove tail in logical ways with other doctrines.
Just because a doctrinal system is tight doesn’t mean it is correct. Human creativity and demonic false religion are both capable of forming tight systems of theology. Nevertheless, if your theology has gaps you should study to either close the gaps or adopt a more correct system.
One of my favorite places to demonstrate two doctrines that fit together well is the virgin birth and original sin. Paul teaches us that sin is passed down from the father’s side. The virgin birth described by Luke teaches us Jesus had no father other than the heavenly Father. Therefore putting the two ideas together, Jesus had no earthly father passing down original sin to Him. This is necessary since He was God’s perfect Lamb. If He had original sin, He would not be sinless or able to be our perfect, once for all, sacrifice.
Charles W. Short 
This doctrine is one of the more contentious in the bible.
Original Sin does not feature anywhere in the Torah./Old Testament. It is not taught or recognised anywhere within Judaism. Most importantly, Jesus was a Jew and he did not teach it and neither did his disciples.
It can be traced to Augustine of Hippo.
The Virgin Birth is another.
The gospel tradition is simply plagiarized from Isaiah 7:14 and corrupted. It refers solely to the future birth of a son to King Ahaz and has absolutely nothing to do with any future messiah. This is notwithstanding the misunderstanding surrounding the words Almah/Bethulah and Parthenos.
Theologian and Catholic spokesman Raymond Brown is on record that this is not regarded as a physical virgin birth and must not be taken literally.
Biblical inerantists and evangelical Christians realised there was no honest way to hide this error, hence duel prophecy hypothesis was developed.
Although Christianity flows from Judaism, it is not reasonable to assume it has to have had every aspect of Christianity contained within it.
But it is dishonest to say the doctrine of original sin traces to Augustine of Hippo. If you want to start with an earthly beginning point at least go back to Romans 5:12ff. Although with a little more understanding you could look back to Genesis 2:17 and begin to see the doctrine of original sin not overtly stated but implied between the lines.
Calling it plagiarism when the New Testament fulfills an Old Testament prophecy is silly. Your discussion saying the virgin conceiving is misunderstood is also a bit silly. Like so many other things you can find scholars who will agree with you. But you will find many times more that realize that interpretation is spurious and ignores the context.
Your statement about Evangelicals inventing a way around this is just fancy name calling. As is much of your comment.
Original Sin was never taught by Jews. Jesus was a Jew and most certainly did not teach
it and neither did his disciples. A point you did not address.
If you wish to consider its source in Romans, then the best you can say is this is an interpretation based uponPauline doctrine, but most certainly nothing that could be attributed to Jesus who taught the Law.
There is no fulfillment of prophecy, as I explained, and even a basic reading of the passage clearly shows that the prophecy was directed at King Ahaz, a point you did not even address, but rather deflect and suggest I am now making vague ad hominum remarks.
If you feel my understanding of the Virgin Birth is incorrect then please explain where I have gone wrong.
I spent a lot of time researching this issue and was surprised when I found the comments by Brown.
I can supply a link if you wish?
Surely, as a Pastor you have tackled such questions from fellow Christians before?
Are you unwilling to engage the central issues of my comment,Chip, simply because I am a non-believer?
I don’t chop up the Bible by who did what, instead I trust it, from beginning to end. Nevertheless I did address the statement Judaism didn’t teach original sin, by saying not everything true had to have Jewish roots. We don’t have record of everything Jesus taught, so I cannot answer whether He taught original sin or not.
Regarding the virgin birth, yes you explained you don’t believe it. And apparently you think all the world has to agree with you? I don’t agree. The words used do not confirm my side or your side. Believe what you wish, and I will do the same. such is the nature of faith. I believe the passage is based on Jesus, confirmed by the actual virgin birth recorded in Luke.
I am not interested in a link to a singular theologian. The search is not for what scholars say, or what you and I say, but it should be a search for the truth. I believe truth is found in Scripture. When Luke says in the NT, Isaiah was referring to Jesus, I believe it.
As a pastor, I can have open discussions with honest seekers. If you have settled on your perspective, then why are you bringing it up to me? Are you of the opinion that you must change my mind or show me the error of my belief, all the while claiming I am the one that cannot coexist?