A Source for the Birth Narratives in Matthew and Luke?

QUESTION:

What’s your take on the independence or interdependence of Mt 1-2 and Lk 1-2. Do you think Luke’s infancy narratives are based on Matthew’s? Or vice versa? Or on some other unknown earlier common source? Or neither and they’re both independent? It sounds like you’re advocating independence. But if they are separate and independent, then we have to account for common elements in the two. Some commonalities are easier to explain (e.g., location in Bethlehem [Micah 5.2]; mother’s name M...