Christians regulary affirm that Jesus was "conceived by the Holy Spirit, born of the Virgin Mary." This faith is embedded as a cornerstone of all the major Christian creeds and is central to the Christmas story, read and re-told countless times at this season in both word and song. Surprisingly, the gospel of Mark has no account of the birth of Jesus. It opens with Jesus as an adult, traveling from Nazareth down to the Jordan River to be baptized by John. Since Mark is our earliest gospel the question arises--what is the origin of the idea of Jesus' virgin birth? When and where did it originate?

In contrast to Mark both Matthew and Luke give us different versions of the "Christmas story," but they both agree on the source of Mary's pregnancy. In Matthew's account Joseph...