Answer the following question: Given the following passage  "All Iranian languages are descended from a common ancestor, Proto-Iranian. In turn, and together with Proto-Indo-Aryan and the Nuristani languages, Proto-Iranian descends from a common ancestor Proto-Indo-Iranian. The Indo-Iranian languages are thought to have originated in Central Asia. The Andronovo culture is the suggested candidate for the common Indo-Iranian culture ca. 2000 BC.",  answer the following question. Note that the answer is present within the text.  Question: What is Proto-Iranian to all Iranian languages?
Answer:
common ancestor