In general, there are two hypothesis are in question about the human population in Southeast Asia: whether the raising of modern Southeast Asians are caused by immigration or local evolution. The former considers that the Southeast Asians originate from the hybrids between the indigenous Australo-Melanesian and the Mongolid whose probably came from southern China since Neolithic period. While the latter considers it was caused by local adaptation.
So far, there is no clear satisfactory hypothesis whether true immigration or local evolution is working for elucidating the historical development of human in Southeast Asia because our knowledge of the early human in this area, especially dating back between 70,000 and 100,000 years ago is very little.
Irishway 1-11-11 Sl