Several authors have also proposed that Kra-Dai speakers may actually be an ancient daughter subgroup of Austronesians that migrated back to the Pearl River delta from Taiwan and/or Luzon shortly after the Austronesian expansion. Later migrating further westwards to Hainan, Mainland Southeast Asia and Northeast India. They propose that the distinctiveness of Kra-Dai (it is tonal and monosyllabic) was the result of linguistic restructuring due to contact with Hmong-Mien and Sinitic cultures. Aside from linguistic evidence, Roger Blench has also noted cultural similarities between the two groups, like facial tattooing, tooth removal or ablation, teeth blackening, snake (or dragon) cults, and the multiple-tongued jaw harps shared by the Indigenous Taiwanese and Kra-Dai-speakers. However archaeological evidence for this is still sparse. This is believed to be similar to what happened to the Cham people, who were originally Austronesian settlers (likely from Borneo) to southern Vietnam at around 2,100 to 1,900 BP, and had languages similar to Malay. Their languages underwent several restructuring events to syntax and phonology due to contact with the nearby tonal languages of Mainland Southeast Asia and Hainan.