There is nothing indicated about the miraculous nature of Jesus’s birth in Paul or Mark. Scholars thereby generally conclude the virgin birth was a later invention by Matthew and Luke. The two genealogies of Joseph’s bloodline in Matthew and Luke might be a clue. Just as new believers are adopted into the family of God as cultic brothers and sisters, perhaps Jesus is being portrayed as being adopted into the Davidic Promise bloodline by his stepfather Joseph. Adopted children held a unique and special status in the ancient world, such as Julius Caesar adopting Augustus (Octavian).

One commenter shares:

• The Old Testament predicted that the Messiah would come from the line of David. Both Matthew and Luke provide genealogies of Jesus that confirm he was a descendent of David—therefore, a legitimate Messiah. He was a legitimate claimant to the throne of Israel. But they differ in an important way: Matthew follows the line of David’s son Solomon, while Luke follows the line of Nathan, another Son of David. The end result is two distinct genealogies.

One possible radical thesis is that Matthew read Luke or Luke read Matthew, and so wanted to write Joseph’s genealogy from a different point of view. Luke says in his introduction he had researched other written accounts.