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Thailand and Laos, located in the center of Mainland Southeast Asia (MSEA), harbor diverse ethnolinguistic groups encompassing all five language families of MSEA: Tai-Kadai (TK), Austroasiatic (AA), Sino-Tibetan (ST), Hmong-Mien (HM), and Austronesian (AN). Previous genetic studies of Thai/Lao populations have focused almost exclusively on uniparental markers and there is a paucity of genome-wide studies. We therefore generated genome-wide SNP data for 33 ethnolinguistic groups, belonging to the five MSEA language families from Thailand and Laos, and analyzed these together with data from modern Asian populations and SEA ancient samples. Overall, we find genetic structure according to language family, albeit with heterogeneity in the AA-, HM-, and ST-speaking groups, and in the hill tribes, that reflects both population interactions and genetic drift. For the TK speaking groups, we find localized genetic structure that is driven by different levels of interaction with other groups in the same geographic region. Several Thai groups exhibit admixture from South Asia, which we date to ∼600–1000 years ago, corresponding to a time of intensive international trade networks that had a major cultural impact on Thailand. An AN group from Southern Thailand shows both South Asian admixture as well as overall affinities with AA-speaking groups in the region, suggesting an impact of cultural diffusion. Overall, we provide the first detailed insights into the genetic profiles of Thai/Lao ethnolinguistic groups, which should be helpful for reconstructing human genetic history in MSEA and selecting populations for participation in ongoing whole genome sequence and biomedical studies.

Southern Thailand is home to various populations; the Moklen, Moken and Urak Lawoi’ sea nomads and Maniq negrito are the minority, while the southern Thai groups (Buddhist and Muslim) are the majority. Although previous studies have generated forensic STR dataset for major groups, such data of the southern Thai minority have not been included; here we generated a regional forensic database of southern Thailand. We newly genotyped common 15 autosomal STRs in 184 unrelated southern Thais, including all minorities and majorities. When combined with previously published data of major southern Thais, this provides a total of 334 southern Thai samples. The forensic parameter results show appropriate values for personal identification and paternity testing; the probability of excluding paternity is 0.99999622, and the combined discrimination power is 0.999999999999999. Probably driven by genetic drift and/or isolation with small census size, we found genetic distinction of the Maniq and sea nomads from the major groups, which were closer to the Malay and central Thais than the other Thai groups. The allelic frequency results can strength the regional forensic database in southern Thailand and also provide useful information for anthropological perspective.

The Maniq of southern Thailand is one of the last remaining practicing hunter-gatherer communities in the world. However, our knowledge on their genetic origins and demographic history is still largely limited. We present here the genotype data covering ∼2.3 million single nucleotide polymorphisms of 11 unrelated Maniq individuals. Our analyses reveal the Maniq to be closely related to the Semang populations of Malaysia (Malay Negritos), who altogether carry an Andamanese-related ancestry linked to the ancient Hòabìnhian hunter-gatherers of Mainland Southeast Asia (MSEA). Moreover, the Maniq possess ∼35% East Asian-related ancestry, likely brought about by recent admixture with surrounding agriculturist communities in the region. In addition, the Maniq exhibit one of the highest levels of genetic differentiation found among living human populations, indicative of their small population size and historical practice of endogamy. Similar to other hunter-gatherer populations of MSEA, we also find the Maniq to possess low levels of Neanderthal ancestry and undetectable levels of Denisovan ancestry. Altogether, we reveal the Maniq to be a Semang group that experienced intense genetic drift and exhibits signs of ancient Hòabìnhian ancestry.

The hill tribes of northern Thailand comprise nine officially recognized groups: the Austroasiatic-speaking (AA) Khmu, Htin and Lawa, the Hmong-Mien-speaking (HM) IuMien and Hmong, and the Sino-Tibetan-speaking (ST) Akha, Karen, Lahu and Lisu. Except the Lawa, the rest of the hill tribes migrated into their present habitats only very recently. The Thai hill tribes were of much interest to research groups focusing on study of cultural and genetic variation because of their unique languages and cultures. So far, there have been several genetic studies of the Thai hill tribes. However, complete forensic microsatellite database of the Thai hill tribes is still lacking. To construct such database, we newly generated 654 genotypes of 15 microsatellites commonly used in forensic investigation that belong to all the nine hill tribes and also non-hill tribe highlanders from northern Thailand. We also combined 329 genotypes from previous studies of northern Thai populations bringing to a total of 983 genotypes, which were then subjected to genetic structure and population relationships analyses. Our overall results indicated homogenous genetic structure within the HM- and Tai-Kadai (TK)-speaking groups, large genetic divergence of the HM-speaking Hmong but not IuMien from the other Thai groups, and genetic heterogeneity within the ST- and AA-speaking groups, reflecting different population interactions and admixtures. In addition to establishing genetic relationships within and among these populations, our finding, which provides a more complete picture of the forensic microsatellite database of the multiple Thai highland dwellers, would not only serve to expand and strengthen forensic investigation in Thailand, but would also benefit its neighboring countries of Laos and Myanmar, from which many of the Thai hill tribes originated and where large populations of these ethnic groups still reside.

The great ethnolinguistic diversity found today in mainland Southeast Asia (MSEA) reflects multiple migration waves of people in the past. Maritime trading between MSEA and India was established at the latest 300 BCE, and the formation of early states in Southeast Asia during the first millennium CE was strongly influenced by Indian culture, a cultural influence that is still prominent today. Several ancient Indian-influenced states were located in present-day Thailand, and various populations in the country are likely to be descendants of people from those states. To systematically explore Indian genetic heritage in MSEA populations, we generated genome-wide SNP data (using the Affymetrix Human Origins array) for 119 present-day individuals belonging to 10 ethnic groups from Thailand and co-analyzed them with published data using PCA, ADMIXTURE, and methods relying on f-statistics and on autosomal haplotypes. We found low levels of South Asian admixture in various MSEA populations for whom there is evidence of historical connections with the ancient Indian-influenced states but failed to find this genetic component in present-day hunter-gatherer groups and relatively isolated groups from the highlands of Northern Thailand. The results suggest that migration of Indian populations to MSEA may have been responsible for the spread of Indian culture in the region. Our results also support close genetic affinity between Kra-Dai-speaking (also known as Tai-Kadai) and Austronesian-speaking populations, which fits a linguistic hypothesis suggesting cladality of the two language families.

Central Thailand is home to diverse populations with the central Thai constituting the major group, while the Mon, who migrated from southern Myanmar, are sparsely distributed within the region. A total of 338 individuals of eight central Thai (246 samples) and three Mon populations (92 samples) were newly genotyped. When combined with our previously published Mon data, this provides a total of 139 Mon samples. We found genetic similarity between the central Thai and Mon and weak sub-structuring among Thais from central, northern, and northeastern Thailand. The forensic parameter results show high discrimination values which are appropriate for forensic personal identification and paternity testing in both the central Thai and Mon; the probabilities of excluding paternity are 0.999999112 and 0.999999031, respectively, and the combined discrimination power is 0.9999999999999999999999 in both groups. This regional allelic frequency on forensic microsatellites may serve as a useful reference for further forensic investigations in both Thailand and Myanmar.

Tai-Kadai (TK) is one of the major language families in Mainland Southeast Asia (MSEA), with a concentration in the area of Thailand and Laos. Our previous study of 1,234 mtDNA genome sequences supported a demic diffusion scenario in the spread of TK languages from southern China to Laos as well as northern and northeastern Thailand. Here we add an additional 560 mtDNA sequences from 22 groups, with a focus on the TK-speaking central Thai people and the Sino-Tibetan speaking Karen. We find extensive diversity, including 62 haplogroups not reported previously from this region. Demic diffusion is still a preferable scenario for central Thais, emphasizing the extension and expansion of TK people through MSEA, although there is also some support for an admixture model. We also tested competing models concerning the genetic relationships of groups from the major MSEA languages, and found support for an ancestral relationship of TK and Austronesian-speaking groups.

We genotyped 15 autosomal STRs loci in 1780 unrelated northeastern Thai individuals. Allele frequencies were computed and all of the loci reached Hardy-Weinberg equilibrium. The forensic parameter results showed high discrimination values which are suitable for forensic personal identification and paternity testing; the combined discrimination power and probability of excluding paternity were 0.9999999999999999999999 and 0.999998449, respectively. Genetic relatedness of northeastern Thais with comparable Thai and Asian populations using phylogenetic analysis revealed close genetic relationship between Mainland Southeast Asian populations and southern Chinese populations.

Purpose Laotians and Lao Isan are widely spread Lao groups who live in Laos and northeastern Thailand, respectively. We explored the genetic structure between them and other ethnic groups from Thailand to clarify historical patterns of admixture between Tai-Kadai and Austroasiatic speakers, and to expand the forensic reference database for the region. Subjects and methods We combined new genetic data for 554 individuals from 12 populations, typed for 15 autosomal short tandem repeats, with available data from 14 populations from Thailand, for a total of 1,153 raw genotypes belonging to 26 populations. We calculated forensic parameters and performed various analyses on genetic diversity, genetic structure, genetic admixture, and genetic relationships among the studied populations. Results Forensic estimators suggest a good power of discrimination with the combined power of exclusion ranging from 0.993628 to 0.999991 and a combined power of discrimination value greater than 0.99999999. Generally, the two Laotian groups were genetically similar, but the central Laotians from Vientiane have a closer genetic relationship to the Lao Isan than the northern Laotians from Luang Prabang. The Lao genetic ancestry forms the majority of the Lao Isan genetic makeup, while Austroasiatic ancestry is present at ∼10%-50%. Conclusions Lao Isan populations show signs of Lao ancestry and admixture with local Austroasiatic ancestry, which reflect historical migrations from Laos to Thailand. Lao speakers are genetically more homogeneous than Austroasiatic speakers, suggesting differential historical processes.

We have determined the distribution of Y-chromosomal haplotypes and haplogroups in the Yong population, one of the largest and well-known ethnic groups that began migrating southward from China to Thailand centuries ago. Their unique mass migration pattern provided great opportunities for researchers to study the genetic links of the transboundary migration movements among the peoples of China, Myanmar and Thailand. We analysed relevant male-specific markers, such as Y-STRs and Y-SNPs, and the distribution of 23 Y-STRs of 111 Yong individuals and 116 nearby ethnic groups including the Shan, Northern Thai, Lawa, Lua, Skaw, Pwo and Padong groups. We found that the general haplogroup distribution values were similar among different populations; however, the haplogroups O1b-M268 and O2-M112 constituted the vast majority of these values. In contrast with previous maternal lineage studies, the paternal lineage of the Yong did not relate to the Xishuangbanna Dai people, who represent their historically documented ancestors. However, they did display a close genetic affinity to other prehistoric Tai-Kadai speaking groups in China such as the Zhuang and Bouyei. Low degrees of genetic admixture within the populations who belonged to the Austroasiatic and Sino-Tibetan linguistic families were observed in the gene pool of the Yong populations. Resettlement in northern Thailand in the early part of the nineteenth century AD, by way of mass migration trend, was able to preserve the Yong's ancestral genetic background in terms of the way they had previously lived in China and Myanmar. Our study has revealed similar genetic structures among ethnic populations in northern Thailand and southern China, and has identified and emphasized an ancient Tai-Kadai patrilineal ancestry line in the Yong ethnic group.

The human demographic history of Mainland Southeast Asia (MSEA) has not been well studied; in particular, there have been very few sequence-based studies of variation in the male-specific portions of the Y chromosome (MSY). Here, we report new MSY sequences of ∼2.3 mB from 914 males and combine these with previous data for a total of 928 MSY sequences belonging to 59 populations from Thailand and Laos who speak languages belonging to three major Mainland Southeast Asia families: Austroasiatic, Tai-Kadai, and Sino-Tibetan. Among the 92 MSY haplogroups, two main MSY lineages (O1b1a1a* [O-M95*] and O2a* [O-M324*]) contribute substantially to the paternal genetic makeup of Thailand and Laos. We also analyze complete mitochondrial DNA genome sequences published previously from the same groups and find contrasting pattern of male and female genetic variation and demographic expansions, especially for the hill tribes, Mon, and some major Thai groups. In particular, we detect an effect of postmarital residence pattern on genetic diversity in patrilocal versus matrilocal groups. Additionally, both male and female demographic expansions were observed during the early Mesolithic (∼10 ka), with two later major male-specific expansions during the Neolithic period (∼4–5 ka) and the Bronze/Iron Age (∼2.0–2.5 ka). These two later expansions are characteristic of the modern Austroasiatic and Tai-Kadai groups, respectively, consistent with recent ancient DNA studies. We simulate MSY data based on three demographic models (continuous migration, demic diffusion, and cultural diffusion) of major Thai groups and find different results from mitochondrial DNA simulations, supporting contrasting male and female genetic histories.

The Maniq and Mlabri are the only recorded nomadic hunter-gatherer groups in Thailand. Here, we sequenced complete mitochondrial (mt) DNA genomes and ~2.364 Mbp of non- recombining Y chromosome (NRY) to learn more about the origins of these two enigmatic populations. Both groups exhibited low genetic diversity compared to other Thai populations, and contrasting patterns of mtDNA and NRY diversity: there was greater mtDNA diversity in the Maniq than in the Mlabri, while the converse was true for the NRY. We found basal uniparental lineages in the Maniq, namely mtDNA haplogroups M21a, R21 and M17a, and NRY haplogroup K. Overall, the Maniq are genetically similar to other negrito groups in Southeast Asia. By contrast, the Mlabri haplogroups (B5a1b1 for mtDNA and O1b1a1a1b and O1b1a1a1b1a1 for the NRY) are common lineages in Southeast Asian non-negrito groups, and overall the Mlabri are genetically similar to their linguistic relatives (Htin and Khmu) and other groups from northeastern Thailand. In agreement with previous studies of the Mlabri, our results indicate that the Malbri do not directly descend from the indigenous negritos. Instead, they likely have a recent origin (within the past 1,000 years) by an extreme founder event (involving just one maternal and two paternal lineages) from an agricultural group, most likely the Htin or a closely- related group.

Ancient migrations in Southeast Asia The past movements and peopling of Southeast Asia have been poorly represented in ancient DNA studies (see the Perspective by Bellwood). Lipson et al. generated sequences from people inhabiting Southeast Asia from about 1700 to 4100 years ago. Screening of more than a hundred individuals from five sites yielded ancient DNA from 18 individuals. Comparisons with present-day populations suggest two waves of mixing between resident populations. The first mix was between local hunter-gatherers and incoming farmers associated with the Neolithic spreading from South China. A second event resulted in an additional pulse of genetic material from China to Southeast Asia associated with a Bronze Age migration. McColl et al. sequenced 26 ancient genomes from Southeast Asia and Japan spanning from the late Neolithic to the Iron Age. They found that present-day populations are the result of mixing among four ancient populations, including multiple waves of genetic material from more northern East Asian populations. Science , this issue p. 92 , p. 88 ; see also p. 31

The Khon Mueang represent the major group of people present in today’s northern Thailand. While linguistic and genetic data seem to support a shared ancestry between Khon Mueang and other Tai-Kadai speaking people, the possibility of an admixed origin with contribution from local Mon-Khmer population could not be ruled out. Previous studies conducted on northern Thai people did not provide a definitive answer and, in addition, have largely overlooked the distribution of paternal lineages in the area. In this work we aim to provide a comprehensive analysis of Y paternal lineages in northern Thailand and to explicitly model the origin of the Khon Mueang population. We obtained and analysed new Y chromosomal haplogroup data from more than 500 northern Thai individuals including Khon Mueang, Mon-Khmer and Tai-Kadai. We also explicitly simulated different demographic scenarios, developed to explain the Khon Mueang origin, employing an ABC simulation framework on both mitochondrial and Y microsatellites data. Our results highlighted a similar haplogroup composition of Khon Mueang and Tai-Kadai populations in northern Thailand, with shared high frequencies of haplogroups O-PK4, O-M117 and O-M111. Our ABC simulations also favoured a model in which the ancestors of modern Khon Mueang originated recently after a split from the other Tai-Kadai populations. Our different analyses concluded that the ancestors of Khon Mueang are likely to have originated from the same source of the other Tai-Kadai groups in southern China, with subsequent admixture events involving native Mon-Khmer speakers restricted to some specific populations.

The Tai-Kadai (TK) language family is thought to have originated in southern China and spread to Thailand and Laos, but it is not clear if TK languages spread by demic diffusion (i.e., a migration of people from southern China) or by cultural diffusion, with native Austroasiatic (AA) speakers switching to TK languages. To address this and other questions, we obtained 1,234 complete mtDNA genome sequences from 51 TK and AA groups from Thailand and Laos. We find high genetic heterogeneity, with 212 haplogroups. TK groups are more genetically homogeneous than AA groups, with the latter exhibiting more ancient/basal mtDNA lineages, and showing more drift effects. Modeling of demic diffusion, cultural diffusion, and admixture scenarios consistently supports the spread of TK languages by demic diffusion. Surprisingly, there is significant genetic differentiation within ethnolinguistic groups, calling into question the common assumption that there is genetic homogeneity within ethnolinguistic groups.

The migration of the Tai-Kadai speaking people from southern China to northern Thailand over the past hundreds of years has revealed numerous patterns that have likely been influenced by routes, purposes and periods of time. To study the effects of different migration patterns on Tai-Kadai maternal genetic structure, mitochondrial DNA hypervariable region I sequences from the Yong and the Lue people having well-documented histories in northern Thailand were analyzed. Although the Yong and Lue people were historically close relatives who shared Xishuangbanna Dai ancestors, significant genetic differences have been observed among them. The Yong people who have been known to practice mass migration have exhibited a closer genetic affinity to their Dai ancestors than have the Lue people. Genetic heterogeneity and a sudden reduced effective population size within the Lue group is likely a direct result of the circumstances of the founder effect.

Since prehistoric times, Mon-Khmer speaking people have been recognized as indigenous ethnic groups living in northern Thailand. After the period of Tai colonization in the thirteenth century CE, the Mon-Khmer inhabitants were fragmented; some were expelled to rural areas while some were integrated into the mainstream of Tai society. Autosomal STR variations revealed that the present-day Mon-Khmer people could be genetically divided into two clusters. This finding appears to be consistent with the level of historical contact with the Tai majority ethnic groups. The cluster consisting of the Khamu, Lua, Paluang and Htin people, indicate that they have lived in remote areas and have had little historical contact with the Tai people. In this way, they appeared to have maintained aspects of their Mon-Khmer ancestral genetic bloodline but have genetically diverged from the Tai people. The cluster comprised of the Mon and Lawa people had an exclusively close relationship with the Tai people during the establishment of the prosperous Lan Na Kingdom. A fraction of the Tai genetic component investigated among the Mon people and some Lawa populations reflected the evidence of genetic admixture. However, some Lawa people, who have lived in the mountainous area of Mae Hong Son Province have exhibited a unique gene pool, which might have been shaped by the founder effect that occurred during their historical fragmentation. The rise of the genetic assimilation of the hill-tribe Karen people into the Mon-Khmer and the Tai gene pools indicated that different languages, cultures, and geographical distances have lost their power as barriers of inter-ethnic marriages in the present day.

The Khon Mueang (KM) are the largest group of northern Thai people. Our previous mtDNA studies have suggested an admixture process among the KM with the earlier Mon-Khmer-speaking inhabitants of this region. In this study, we evaluate genetic affinities and admixture among 10 KM populations in northern Thailand lying along the historical Yuan migration route, and 10 neighboring populations belonging to 7 additional ethnic groups: Lawa, Mon (Mon-Khmer-speaking groups), Shan, Yuan, Lue, Khuen and Yong (Tai-speaking groups) by analyzing 15 hypervariable autosomal short tandem repeat loci. The KM exhibited close relationships with neighboring populations, especially the Tai-speaking groups, reflecting an admixed origin of the KM. Admixture proportions were observed in all KM populations, which had a higher contribution from the parental Tai than the Mon-Khmer groups. Different admixture patterns of the KM along the migration route might indicate high heterogeneity among the KM. These patterns were not directly associated with geographical proximity, suggesting other factors, like variation in the timing of admixture with the existing populations may have had an important role. More genetic data from different marker systems solely transmitted through the male or female lineages are needed to complete the description of genetic admixture and population history of the KM. © 2011 The Japan Society of Human Genetics All rights reserved.

The Kra-Dai linguistic family includes Thai and Lao as well as a great number of languages spoken by ethnic minorities in Southeast Asia. In Thailand, a dozen of other Kra-Dai languages are spoken in addition to Thai, the national language. The genetic structure of the Kra-Dai-speaking populations in Thailand has been studied extensively using uniparentally inherited markers. To extend this line of genetic investigation, this study used 15 autosomal microsatellites of 500 individuals from 11 populations, belonging to nine Kra-Dai ethnicities, namely, the Kaleung, Phu Thai, Saek, Nyo, Lao Isan, Yuan, Black Tai, Phuan and Lue. These ethnolinguistic groups are dispersed in three different geographic regions of Thailand, that is, Northern, Northeastern and Central. The results show a very low average of pairwised F(st) (0.0099), as well as no population substructure based on STRUCTURE analysis, indicating genetic homogeneity within the Kra-Dai-speaking group, possibly owing to shared linguistic ancestry. The Mantel test, an analysis of molecular variance, and the approximate Bayesian computation procedure employed to evaluate potential factors for driving genetic diversity revealed that language is the predominant factor affecting genetic variations, whereas geography is not. The result of distance-based clustering analyses and spatial analysis of molecular variance revealed genetic distinctions of some populations, reflecting the effects of genetic drift and gene flow on allele frequency within populations, in concordance with the result of R-matrix regression. The genetic and linguistic affiliations of the contemporary Kra-Dai-speaking groups are consistent with each other despite certain deviation due to various evolutionary factors that may have occurred during their migrations and resettlements.

The present study describes the initial phase of the Thai Twin Registry (TTR) in Khon Kaen University, a pioneer research university located in the Northeast of Thailand. The initial steps of the study included the analysis of dermatoglyphic information in Thai twins for answering the research question: Are monozygotic (MZ) and dizygotic (DZ) twins different in dermatoglyphic variables? Subjects were 212 twin pairs (81 MZ and 131 DZ), consisting of 155 males and 269 females. Four types of fingerprint pattern (FP) — that is, arch, radial loop, ulnar loop, and whorl — were classified and analyzed and compared between MZ and DZ twins. The arch radial loop and whorl frequencies differ between MZ and DZ twins. When comparing FP in each finger, only the right little finger shows a statistically different FP, while the FP similarity average from 10 homologous fingers of co-twins was greater in MZ than DZ twins. By using the Area Under the Receiver Operating Characteristic curve analysis, the MZ twins could be differentiated from DZ twins by the FP similarity. Summarizing, this valuable report about TTR was conducted by analysis of FP data, which indicated that the MZ and DZ twins exhibited FP pattern and FP similarity differences. Other dermatoglyphic studies of the existing FP database, such as finger ridge count, finger ridge density, and minutia, will be considered for ongoing research at the TTR.

Among the people living in the five deep Southern Thai provinces, Thai-Malay Muslims (MUS) constitute the majority, while the remaining are Thai Buddhists (BUD). Cultural, linguistic and religious differences between these two populations have been previously reported. However, their biological relationship has never been investigated. In this study, we aimed to reveal the genetic structure and genetic affinity between MUS and BUD by analyzing 15 autosomal short tandem repeats. Both distance and model-based clustering methods showed significant genetic homogeneity between these two populations, suggesting a common biological ancestry. After Islamization in this region during the fourteenth century AD, gradual albeit nonstatistically significant genetic changes occurred within these two populations. Cultural barriers possibly influenced these genetic changes. MUS have closer admixture to Malaysian-Malay Muslims than BUD countrywide. Admixture proportions also support certain degree of genetic dissimilarity between the two studied populations, as shown by the unequal genetic contribution from Malaysian-Malay Muslims. Cultural transformation and recent minor genetic admixture are the likely processes that shaped the genetic structure of both MUS and BUD.

Though the Y-chromosome O2a-M95 lineage is one of the major haplogroups present in eastern Asian populations, especially among Austro-Asiatic speaking populations from Southwestern China and mainland Southeast Asia, to date its phylogeny lacks structure due to only one downstream SNP marker (M88) assigned to the lineage. A recent array-capture-based Y chromosome sequencing of Asian samples has yielded a variety of novel SNPs purportedly belonging to the O2a-M95 lineage, but their phylogenetic positions have yet to be determined. In this study, we sampled 646 unrelated males from 22 Austro-Asiatic speaking populations from Cambodia, Thailand and Southwestern China, and genotyped 12 SNP makers among the sampled populations, including 10 of the newly reported markers. Among the 646 males, 343 belonged to the O2a-M95 lineage, confirming the supposed dominance of this Y chromosome lineage in Austro-Asiatic speaking populations. We further characterized the phylogeny of O2a-M95 by defining 5 sub-branches: O2a1*-M95, O2a1a-F789, O2a1b*-F1252, O2a1b1*-M88 and O2a1b1a -F761. This updated phylogeny not only improves the resolution of this lineage, but also allows for greater tracing of the prehistory of human populations in eastern Asia and the Pacific, which may yield novel insights into the patterns of language diversification and population movement in these regions.

BackgroundThe Mon-Khmer speaking peoples inhabited northern Thailand before the arrival of the Tai speaking people from southern China in the thirteenth century A.D. Historical and anthropological evidence suggests a close relationship between the Mon-Khmer groups and the present day majority northern Thai groups. In this study, mitochondrial and Y-chromosomal DNA polymorphisms in more than 800 volunteers from eight Mon-Khmer and ten Tai speaking populations were investigated to estimate the degree of genetic divergence between these major linguistic groups and their internal structure.ResultsA large fraction of genetic variation is observed within populations (about 80% and 90% for mtDNA and the Y-chromosome, respectively). The genetic divergence between populations is much higher in Mon-Khmer than in Tai speaking groups, especially at the paternally inherited markers. The two major linguistic groups are genetically distinct, but only for a marginal fraction (1 to 2%) of the total genetic variation. Genetic distances between populations correlate with their linguistic differences, whereas the geographic distance does not explain the genetic divergence pattern.ConclusionsThe Mon-Khmer speaking populations in northern Thailand exhibited the genetic divergence among each other and also when compared to Tai speaking peoples. The different drift effects and the post-marital residence patterns between the two linguistic groups are the explanation for a small but significant fraction of the genetic variation pattern within and between them.