The 'two layer hypothesis', or 'two layer model', states that eastern Asia was initially occupied by Australo-Papuans before being replaced by Neolithic agriculturalists, who possessed East Asian cranial morphology. Cranial morphometrics and dental characteristics of human remains were cited as evidence for the hypothesis.

Early hypotheses

The first fossilized skeletal remains and indication of early 'Proto-Australian' Southeast Asian inhabitants surfaced in 1920 during an excavation by Dubois on the island of

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

.Dubois, E. (1921). The proto-Australian fossil man of Wadjak, Java. Koninklijke Nederlandse Akademie van Weteschappen Proceedings Series B Physical Sciences, 23, 1013-1051. Despite this, a formal connection to mainland Southeast Asia and the suggestion of an initial population of Australomelanesoids was not suggested until 1952 by Koenigswald in his response to Hooijer,Koenigswald, G.H.R. (1952). Evidence of a prehistoric Australomelanesoid population in Malaya and Indonesia. Southwestern Journal of Anthropology, 8(1), 92-96. who sharply criticized the attribution of 'big toothed' dental remains to early Australo-Melanesians.Hooijer, D.A. (1950). Fossil Evidence of Austromelanesian Migrations in Malaysia? Southwestern Journal of Anthropology, 6(4), 416-422. The immigration hypothesis proposed by Koenigswald was formally termed the 'Two Layer' model by Jacob Teuku. In 1967, Teuku analyzed the cranial and dental proportions of 152 adult skeletal samples recovered from prehistoric sites in

Malaysia Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...

and

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

, the majority displaying robust jaws and teeth, prominent glabellae, and slender, elongated limbs. Teuku argued these characteristics correspond to the Australo-Melanesian population proposed by Koenigswald that predated the East Asian immigrants of the Neolithic; also suggesting the initial inhabitants were likely forced south of Southeast Asia's mainland by the second wave of migrants, due to resource competition or conflict.Matsumura, H., Hudson, M.J. (2005). Dental perspectives on the population history of Southeast Asia. American Journal of Physical Anthropology, 127(2), 182-209.Jacob, T. (1967). Some problems pertaining to the racial history of the Indonesian region: a study of human skeletal and dental remains from several prehistoric sites in Indonesia and Malaysia. Drukkerij Neerlandia.

Modern debates and controversies

The main controversy concerning the 'Two Layer' hypothesis is whether or not the evolutionary process truly involved the Australo-Melanesians. Archaeologists such as Matsumura suggest Southern Chinese people comprised the initial population of Southeast Asia, rather than Australo-MelanesiansMatsumura, H., Oxenham, M.F., Dodo, Y., Domett, K. Thuy, N.K., Cuong, N.L.,... Yamagata, M. (2008). Morphometric affinity of the late Neolithic human remains from Man Bac, Ninh Binh Province, Vietnam: key skeletons with which to debate the 'two layer' hypothesis. Anthropological Science, 116(2), 135-148 while researchers such as Turner argue that prehistoric Southeast Asians did not mix with either racial group, and instead Northeast Asians originated from Southeast Asians.Turner, C. (1992). The Dental Bridge between Australia and Asia: Following Macintosh into the East Asian Hearth of Humanity. Archaeology in Oceania, 27(3), 143-152. Though the early prehistoric Vietnamese and Malaysians both resembled the Australo-Melanesian samples the most, the Mán Bạc people had a greater resemblance to the Đông Sơn samples dating back to the

Iron Age The Iron Age () is the final epoch of the three historical Metal Ages, after the Chalcolithic and Bronze Age. It has also been considered as the final age of the three-age division starting with prehistory (before recorded history) and progre ...

. Analyzing cranial and dental remains, Matsumura concluded based on chronological differences that the Mán Bạc people were immigrants affiliated with peoples near the

Yangtze River The Yangtze or Yangzi ( or ) is the longest river in Eurasia and the third-longest in the world. It rises at Jari Hill in the Tanggula Mountains of the Tibetan Plateau and flows including Dam Qu River the longest source of the Yangtze, i ...

region in Southern China. Molecular anthropologists have used classical genetic markers and

mtDNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...

to analyze the similarities between early Chinese and Southeast Asians. Such genetic markers suggest the genetic layout of Southern Chinese peoples is quite similar to that of Southeast Asians. Other controversies completely reject the 'Two Layer' hypothesis. Using dental evidence, Turner’s Sundadont/Sinodont hypothesis suggests the “Sundadont” trait seen in present-day Southeast Asians is a result of long-standing continuity. Turner created a cluster analysis of MMD values in order to test existing hypotheses of origins, concluding that all Southeast Asians,

Micronesians The Micronesians or Micronesian peoples are various closely related ethnic groups native to Micronesia, a region of Oceania in the Pacific Ocean. They are a part of the Austronesian ethnolinguistic group, which has an Urheimat in Taiwan. Eth ...

Polynesians Polynesians are an ethnolinguistic group comprising closely related ethnic groups native to Polynesia, which encompasses the islands within the Polynesian Triangle in the Pacific Ocean. They trace their early prehistoric origins to Island Sout ...

, and Jomonese form their own branch and descend from a common ancestor. The Australians and Melanesians, however, are scattered over the African and European branch along with a side branch of Tasmanians and Solomon Islanders. Howell analyzed crania of major racial branches worldwide, and linked Australian and Melanesian cranial morphology most closely with African cranials. Howell discovered, however, that the size and features of present-day Asian cranial morphology differed significantly from that of Australians, Melanesians, and Africans. Several studies in 2021 concluded that East Asian-related ancestry originated and expanded from Mainland Southeast Asia at about 50,000BC. East Asian-related ancestry was far more widespreaded in Southeast Asia than previously suggested. Ancient remains of hunter-gatherers in Maritime Southeast Asia, such as one Holocene hunter-gatherer from

South Sulawesi South Sulawesi () is a Provinces of Indonesia, province in the South Peninsula, Sulawesi, southern peninsula of Sulawesi, Indonesia. The Selayar Islands archipelago to the south of Sulawesi is also part of the province. The capital and largest ci ...

, had ancestry from both the Papuan-related and East Asian-related branches of the Eastern non-African lineage. The hunter-gatherer individual had approximately ~50% "Basal-East Asian" ancestry, and was positioned in between modern East Asians and Papuans of Oceania. The authors concluded that East Asian-related ancestry expanded from

Mainland Southeast Asia Mainland Southeast Asia (historically known as Indochina and the Indochinese Peninsula) is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to th ...

into

Maritime Southeast Asia Maritime Southeast Asia comprises the Southeast Asian countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. The terms Island Southeast Asia and Insular Southeast Asia are sometimes given the same meaning as ...

much earlier than previously suggested, as early as 25,000BC, long before the expansion of Austroasiatic and Austronesian groups. Distinctive Basal-East Asian (East-Eurasian) ancestry was recently found to have originated in

at ~50,000BC, and expanded through multiple migration waves southwards and northwards respectively. Geneflow of East-Eurasian ancestry into

and

Oceania Oceania ( , ) is a region, geographical region including Australasia, Melanesia, Micronesia, and Polynesia. Outside of the English-speaking world, Oceania is generally considered a continent, while Mainland Australia is regarded as its co ...

could be estimated to ~25,000BC (possibly also earlier since 50,000BC). The pre-Neolithic Papuan-related populations of Maritime Southeast Asia were largely replaced by the expansion of various East Asian-related populations, beginning about 25,000BC from

. Southeast Asia was dominated by East Asian-related ancestry already in 15,000BC, predating the expansion of Austroasiatic and

Austronesian peoples The Austronesian people, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples who have settled in Taiwan, maritime Southeast Asia, parts of mainland Southeast Asia, Micronesia, coastal New Guinea, Island Melan ...

References

External links

Maps of early Austronesian settlement routes
{{Southeast Asia , state=collapsed Prehistoric migrations Archaeological theory Archaeology in Asia Peopling of Southeast Asia Pleistocene Holocene

Early hypotheses

Modern debates and controversies

See also

References

Further reading

External links