Oh, boy. This is indeed a terrific question, and you will get a wide variety of answers–and that has a lot to do with how you view salvation. I agree with @Christy and Pete Enns that Augustine, one of the church Fathers that developed the doctrine of original sin, did so based on a faulty translation of Romans 5:12 “translated properly (as in the NRSV and other translations), says: “Therefore, just as sin came into the world through one man, and death came through sin, and so death spread to all because all have sinned”–Was There a "Fall" or Did Augustine Really Screw Everything Up?
The faulty translation says “in him” instead of “because.” Thus, Augustine thought that Paul was saying we all have guilt from Adam because of his sin. In stead, you have to read it in context. Paul was writing to the Roman church, comprised of both Jews and Gentiles. The Jews thought that they had to incorporate the Gentiles to their covenant, which required circumcision and other outward signs of Jewishness as a sign of faith. Paul agued that as we all are sinners since before even the first Jew came along, and we all are saved by faith anyway, there’s no reason to add that. As Dr Enns says, the issue of salvation wasn’t even the central theme here–circumcision was an outward sign of an inward covenant by faith (a la EP Sanders, writing about the New View on Paul, which affirmed that Jews also relied primarily on faith).
@Christy, feel free to correct me. There is much more you and others can add.
That’s not to say I don’t accept others with a different point of view. My own church believes as does Augustine, and so do most of my family (they are all YEC as well). There’s a lot more to maturity than getting all the theology right, and I learn a great deal from them.
Best wishes.
PS–if you would like good texts–"Evolution of Adam, “Inspiration and Incarnation,”: “The Bible Tells Me So,” and “Sin of Certainty” are good by Enns–the first 2 are particularly relevant. The thread on Denis Lamoureux has his own positions posted–he’s double doctorate in evolutionary biology and theology, as well as dentistry (so he researched on the development of teeth from scales, among other things). Lamoureux's Evolutionary Creation - #3 by Randy