The 'Two Layer' Hypothesis, or immigration hypothesis, is an

archaeological Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscape ...

hypothese that suggests the human occupation of mainland Southeast Asia occurred over two distinct periods by two separate racial groups, hence the term 'layer'.Reich, D., Patterson, N., Kircher, M., Delfin, F., Nandineni, M.R., Pugach, I.,... Stoneking, M. (2011). Denisova admixture and the first modern human dispersals into Southeast Asia and Oceania. The American Journal of Human Genetics, 89(4), 516-528. According to the Two Layer Hypothesis, early indigenous

Australo-Melanesian Australo-Melanesians (also known as Australasians or the Australomelanesoid, Australoid or Australioid race) is an outdated historical grouping of various people indigenous to Melanesia and Australia. Controversially, groups from Southeast Asia a ...

peoples comprised the first population of Southeast Asia before their genetic integration with a second wave of inhabitants from East Asia, including Southern China, during the

agricultural expansion Agricultural expansion describes the growth of agricultural land ( arable land, pastures, etc.) especially in the 20th and 21st centuries. The agricultural expansion is often explained as a direct consequence of the global increase in food and e ...

of the

Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several part ...

.Matsumura, 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), 135-148Matsumura, H., Hudson, M.J. (2005). Dental perspectives on the population history of Southeast Asia. American Journal of Physical Anthropology, 127(2), 182-209. The majority of evidence for the Two Layer Hypothesis consists of dental and

morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...

analyses from archaeological sites throughout Southeast Asia, most prominently

Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...

and

Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making it ...

. Recent genetic and archeologic evidence found that both Australo-Melanesian (South-Eurasian) and East Asian-related (East-Eurasian) populations migrated along a southern route, with the Australo-Melanesians using a coastal route along the coast of the

Indian peninsula The Indian subcontinent is a physiographical region in Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian Ocean from the Himalayas. Geopolitically, it includes the countries of Bangladesh, Bhutan, India, ...

into

Insular Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...

and Oceania, while East Asian-related groups used a route south or through the Himalayan mountain range into Mainland Southeast Asia, from where Basal-East Asians than expanded northwards and southwards respectively at 50,000BC. East Asian-related ancestry was far more widespread in Insular Southeast Asia than previously suggested, long predating the Austroasiatic and Austronesian expansions.

Early hypothese

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 (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

.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. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

and

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

, 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.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-Melanesians while researchers such as Turner argue that prehistoric Southeast Asians did not mix with either racial group.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-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age (Paleolithic, Mesolithic, Neolithic) and the Bronze Age (Chalcolithic). The concept has been mostly appl ...

. 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 Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flow ...

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

mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondrion, mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mit ...

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. Ethno ...

Polynesians Polynesians form an ethnolinguistic group of closely related people who are native to Polynesia (islands in the Polynesian Triangle), an expansive region of Oceania in the Pacific Ocean. They trace their early prehistoric origins to Island Sou ...

, 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 ( id, Sulawesi Selatan) is a province in the southern peninsula of Sulawesi. The Selayar Islands archipelago to the south of Sulawesi is also part of the province. The capital is Makassar. The province is bordered by Central Sul ...

, had ancestry from both, the South-Eurasian lineage (represented by Papuans and Aboriginal Australians), and the East-Eurasian lineage (represented by East Asians). 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 into

Maritime Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...

much earlier than previously suggested, as early as 25,000BC, long before the expansion of

Austroasiatic The Austroasiatic languages , , are a large language family in Mainland Southeast Asia and South Asia. These languages are scattered throughout parts of Thailand, Laos, India, Myanmar, Malaysia, Bangladesh, Nepal, and southern China and are t ...

and

Austronesian Austronesian may refer to: *The Austronesian languages *The historical Austronesian peoples The Austronesian peoples, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples in Taiwan, Maritime Southeast Asia, M ...

groups. Distinctive Basal-East Asian (East-Eurasian) ancestry was recently found to have originated in Mainland Southeast Asia 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 that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern Hemisphere, Eastern and Western Hemisphere, Western hemispheres, Oceania is estimated to have a land area of ...

could be estimated to ~25,000BC (possibly also earlier since 50,000BC). The pre-Neolithic South-Eurasian populations of Maritime Southeast Asia were largely replaced by the expansion of various East-Eurasian populations, beginning about 25,000BC from Mainland Southeast Asia. Southeast Asia was dominated by East Asian-related ancestry already in 15,000BC, predating the expansion of

and

Austronesian peoples The Austronesian peoples, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples in Taiwan, Maritime Southeast Asia, Micronesia, coastal New Guinea, Island Melanesia, Polynesia, and Madagascar that speak Au ...

References

External links

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

Early hypothese

Modern debates and controversies

See also

References

Further reading

External links