Paul Wexler's thesis is that the Eastern dialects of Yiddish actually independently descend from early Jewish Slavic languages (e.g. https://en.wikipedia.org/wi

Paul Wexler's thesis is that the Eastern dialects of Yiddish actually independently descend from early Jewish Slavic languages (e.g. https://en.wikipedia.org/wiki/Knaanic_language https://en.wikipedia.org/wiki/Knaanic_language), and the Western dialects are derived from the Eastern ones, "... a hypothesis that has been widely rejected by other Yiddish and Germanic linguists and geneticists", says his WP bio.