Genome studies show that several ethnic groups in western Indonesian archipelago have significant Austroasiatic genome markers, despite none of these groups speaking Austroasiatic languages. Thus this could mean, that there was either once a substantial Austroasiatic presence in Island Southeast Asia, or Austronesian speakers migrated to and through the mainland. The substantial presence of Austroasiatic ancestry in western Indonesian archipelago suggests that the western branch of Austroasiatic migration from Indochina might have taken place in pre-Neolithic era. The contesting suggestion argues for Austroasiatic-Austronesian admixture — which probably took place in the Malaysian peninsula or southern Vietnam, intermixing there before continuing to western Indonesia.
