Anatomically modern humans are known to have expanded into Southeast Asia at least 65,000 years ago –– leading to formation of the Hòabìnhian hunter-gatherer tradition. Although Hòabìnhian foragers are considered to be the ancestors of present-day hunter-gatherers from mainland Southeast Asia, the East Asian phenotypic affinities of the majority of present-day Southeast Asian populations suggest that diversity was influenced by later migrations involving rice farmers and millet farmers from the north. These observations have generated two competing hypotheses: [a] The Hòabìnhian hunter-gatherers adopted agriculture without substantial external gene flow; and [b] (the “two-layer” hypothesis) states that farmers from East Asia replaced the indigenous Hòabìnhian inhabitants ~4,000 years ago.
Studies of present-day populations have not resolved the extent to which migrations from East Asia affected the genetic makeup of Southeast Asia. From a Language point-of-view, the movement of Neolithic populations from southern China commenced as two separate migrations. One, ancestral to modern speakers of Tai and perhaps also Austroasiatic languages (the latter including Khmer and Vietnamese), spread by land into mainland Southeast Asia. Along with it spread rice, millets, and domesticated pigs and dogs. The other, ancestral to speakers of Austronesian languages such as Malay and Hawaiian, spread by sea into Taiwan, later the Philippines, and onward into Indonesia and Oceania, again carrying a cultural component of food production.
There is evidence indicating that the Hòabìnhian and Neolithic populations had already undergone some genomic mixing before Neolithic migrants expanded out of southern China. Moreover, in an archaeological site in northern Vietnam, skeletons of both populations are found buried together at ~1800 B.C. The Asian Neolithic population, however, appears to have been most prevalent among those skeletons. Two other important observations can be made from these studies. Mainland Southeast Asian populations such as Tais and Vietnamese Kinh received, perhaps unsurprisingly, another layer of quite heavy gene flow from China starting ~2,500 years ago. This was when the Warring States and subsequent Qin and Western Han (206 B.C. to 220 A.D.) Chinese empires conquered southern China and northern Vietnam, imposing Sinitic (Han) settlement, languages, and literacy on many of the indigenous Bronze and Iron Age societies to the south.
By sequencing 26 ancient human genomes, authors [see attached article & editorial] show that neither interpretation fits the complexity of Southeast Asian history: Both Hòabìnhian hunter-gatherers and East Asian farmers contributed to current Southeast Asian diversity, with further migrations affecting island Southeast Asia and Vietnam. These results help resolve one of the long-standing controversies in Southeast Asian prehistory. As is seen the world over, genetic admixtures between populations frequently occur. And they are influenced by agriculture and warring societies.
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Science 6 Jul 2o18; 361: 88–92 & pp 31–32 [Editorial]