In relation to Sino-Austronesian models and the Longshan interaction sphere, Roger Blench (2014) suggests that the single migration model for the spread of the Neolithic into Taiwan is problematic, pointing out the genetic and linguistic inconsistencies between different Taiwanese Austronesian groups. The surviving Austronesian populations on Taiwan should rather be considered as the result of various Neolithic migration waves from the mainland and back migration from the Philippines. These incoming migrants almost certainly spoke languages related to Austronesian or pre-Austronesian, although their phonology and grammar would have been quite diverse.