Laurent Sagart
Laurent Sagart (2002) considers Hakka and southern Gan Chinese to be sister dialects that descended from a single common ancestral language (Proto-Southern Gan) spoken in central Jiangxi during the Song Dynasty. In Hakka and southern Gan, Sagart (2002) identifies a non-Chinese substratum that is possibly Hmong-Mien, an archaic layer, and a more recent Late Middle Chinese layer. Lexical connections between Hakka, Kra-Dai, and Hmong-Mien have also been suggested by Deng (1999).