Wikipedia has agreed for many years that there are different views about manga’s history– those who start from the postwar years (the 1950s) and those who see continuity in manga as sequential art and go back much further. Some (your prof included) see it as starting in the late 19th century, or the early 20c century.
After reading (pdfs here) 1) Schodt’s Chapter 2 “A Thousand Years of Manga”; 2) Gravett’s 2nd chapter “Japanese Spirit, Western Learning” and 3) Ito’s article, what is your stance?
How far back does the history of manga go? What about the Frolicking Animals scroll or Hokusai Manga? How about kibyōshi and other forms of illustrated fiction?
What are the factors that are important? Sequential art? Style? Japanese origins?
Why is there so much disagreement about talking about the history of manga?