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Post by Admin on Mar 29, 2022 21:07:41 GMT
Fig. 1.  Geographical location, mitochondrial haplogroup, PCA and admixture analysis of Uz_IA individuals. (A) Map showing the geographical location in South Uzbekistan of the three Uz_IA archaeological sites studied. The pie chart shows the distribution of mitochondrial haplogroups of Uz_IA individuals. (B) PCA of newly sequenced Uz_IA individuals along with published ancient populations from West and East Eurasia projected onto present-day populations. (C) ADMIXTURE ancestry components (K = 8) of Uz_IA and published populations from West and East Eurasia. The three main ancestry components are shown in green, red and violet representing ancestry maximized in Anatolian farmers, Iranian farmers, and Hunter Gatherers from West Siberia, respectively. Only the unrelated individuals having >20k SNPs are used for the analyses. The Dehkan site with only one individual (<20k SNPs) has been discarded from any further analyses. Only a subset of ancient samples, which are spatially and temporally important, is shown and supplementary figures of PCA and ADMIXTURE show all present-day and ancient populations. Results and Discussion In total, DNA from 27 ancient individuals was extracted and enriched for ∼1.2 million single-nucleotide polymorphism (SNP) targets (Fu et al. 2013; 2015). Full mitochondrial genomes were additionally enriched from all 27 samples using oligonucleotide probes (Fu et al. 2013) (supplementary table S1, Supplementary Material online). Mitogenomes from all 27 individuals (19–370 × fold coverage) had low contamination rates (0–2.7%) and a high haplogroup diversity among the Uz_IA population (fig 1A and supplementary table S1 and fig. S15, Supplementary Material online). The haplogroups suggest ancient Turan (i.e., the region comprising Iran and southern Central Asia, which includes present-day countries of Turkmenistan, Tajikistan, Uzbekistan, Afghanistan, and Kyrgyzstan) and Steppe-related maternal ancestry represented by six “U” and five “H” haplogroups (Narasimhan et al. 2019). Both of these haplogroups are also prevalent in present-day European, Caucasus, and Central and West Asian populations (supplementary fig. S15, Supplementary Material online). Another four D-haplogroups indicate a stronger genetic connection with present-day East Asian and Siberian populations (supplementary fig. S15, Supplementary Material online). Twelve other minor haplogroups of J, K, M, T, V, W, and X also indicate a high haplogroup diversity widely present in this region both in the ancient and present-day populations (Irwin et al. 2010; Narasimhan et al. 2019) (fig 1A and supplementary table S1, Supplementary Material online). We also identified the Y-haplogroup, R1a1 (n = 3), which additionally supports a connection to the present-day West-Central Asian and eastern European populations. Among the ancient populations, this haplogroup has been reported in Middle-to-Late Bronze Age (MLBA) populations in cultures having Steppe-related affinities such as Corded-Ware, Andronovo, and Sintashta (Allentoft et al. 2015; Haak et al. 2015; Mathieson et al. 2015; Underhill et al. 2015). We used nuclear DNA to further investigate the genetic relationships of IA Uzbekistan. We discarded individuals with <20k SNPs and checked the kinship relationships of those remaining, using only the individual with the highest number of SNPs from each kinship pair for further genetic analysis (supplementary table S2, Supplementary Material online). This resulted in a set of 15 unrelated individuals having 0.02–2.88 × fold coverage (27,900–723,918 SNPs). Increased Steppe Ancestry in Iron Age Compared with Bronze Age To assess the genetic affinities between Uz_IA individuals and ancient populations, we first performed principal component analysis (PCA) (Patterson et al. 2006) by projecting the ancient diverse Eurasian populations onto the present-day populations. The PCA results show that all the Uz_IA individuals lie on a cline extending from West Siberian Hunter Gatherers (WSHG) to Anatolian and Iranian farmer-related ancestry (fig. 1B and supplementary figs. S1–S3, Supplementary Material online) clustering closely with the geographically proximal ancient BA and IA populations from the Steppe and Central Asia, including ancient populations from Uzbekistan and neighboring regions of Turan and the Central Steppe (fig. 1B and supplementary figs. S1 and S2, Supplementary Material online). Despite being in proximity on the PCA to the previously published Uzbekistan BA populations (Bustan, Dzharkutan, Kashkarchi, Kokcha, and Sappali_Teppe), the Uz_IA populations lack a tight clustering. They overlap with Turan IA and historical time period populations with Steppe-related ancestry, suggesting the presence and influence of more Steppe-related ancestry in Uz_IA individuals than in BA Uzbekistan populations. To estimate the ancestral admixture and population structure, we used the model-based clustering method implemented in ADMIXTURE (Alexander et al. 2009). The same trends from the PCA are also observed in the ADMIXTURE (K = 8) analysis (fig 1C and supplementary figs. S4 and S5, Supplementary Material online), with three major sources of ancestries maximized in Iranian farmers, Anatolian farmers and WSHG (Steppe-related), as well as small amounts of West European Hunter Gatherer and East Asian-related ancestries (fig 1C and supplementary fig. S5, Supplementary Material online). The single individual from the Serkharakat site also shows high genetic similarity to Rabat individuals in PCA (fig. 1B and supplementary figs. S1–S3, Supplementary Material online), clustering with other Rabat individuals, and having similar admixture components in ADMIXTURE analysis (fig. 1C). We additionally investigated the genetic affinity between Rabat and Serkharakat using the outgroup-f3 test, that is, f3(Rabat, Serkharakat/Ancient Population; Mbuti) and f4-statistics test of the form f4(Rabat, Ancient Population; Serkharakat, Mbuti) (fig. 2B and supplementary fig. S6, Supplementary Material online). We noticed that Rabat and Serkharakat share strong genetic drift with each other, but both share greater genetic drift with Steppe MLBA and Afanasievo populations, indicating that the Serkharakat individual is not descended from Rabat individuals. In most cases, Uz_IA shows higher genetic affinity to the Late Bronze Age (LBA) populations with Steppe-related ancestry from Turan, Altai, and eastern European regions than to the other BA populations from Turan and Central Asia (fig. 2A and supplementary figs. S6, S8, and S9 and table S3, Supplementary Material online). This trend of higher Steppe-related ancestry in the Uz_IA samples is also supported by their closer proximity to present-day Europeans in the PCA, as well as higher values for f3(Uz_IA, Present-day Population; Mbuti) > 0, relative to Central Asian (including Turan) and Caucasus populations (supplementary figs. S3 and S7, Supplementary Material online). |
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Post by Admin on Mar 30, 2022 19:56:53 GMT
Results and Discussion In total, DNA from 27 ancient individuals was extracted and enriched for ∼1.2 million single-nucleotide polymorphism (SNP) targets (Fu et al. 2013; 2015). Full mitochondrial genomes were additionally enriched from all 27 samples using oligonucleotide probes (Fu et al. 2013) (supplementary table S1, Supplementary Material online). Mitogenomes from all 27 individuals (19–370 × fold coverage) had low contamination rates (0–2.7%) and a high haplogroup diversity among the Uz_IA population (fig 1A and supplementary table S1 and fig. S15, Supplementary Material online). The haplogroups suggest ancient Turan (i.e., the region comprising Iran and southern Central Asia, which includes present-day countries of Turkmenistan, Tajikistan, Uzbekistan, Afghanistan, and Kyrgyzstan) and Steppe-related maternal ancestry represented by six “U” and five “H” haplogroups (Narasimhan et al. 2019). Both of these haplogroups are also prevalent in present-day European, Caucasus, and Central and West Asian populations (supplementary fig. S15, Supplementary Material online). Another four D-haplogroups indicate a stronger genetic connection with present-day East Asian and Siberian populations (supplementary fig. S15, Supplementary Material online). Twelve other minor haplogroups of J, K, M, T, V, W, and X also indicate a high haplogroup diversity widely present in this region both in the ancient and present-day populations (Irwin et al. 2010; Narasimhan et al. 2019) (fig 1A and supplementary table S1, Supplementary Material online). We also identified the Y-haplogroup, R1a1 (n = 3), which additionally supports a connection to the present-day West-Central Asian and eastern European populations. Among the ancient populations, this haplogroup has been reported in Middle-to-Late Bronze Age (MLBA) populations in cultures having Steppe-related affinities such as Corded-Ware, Andronovo, and Sintashta (Allentoft et al. 2015; Haak et al. 2015; Mathieson et al. 2015; Underhill et al. 2015). We used nuclear DNA to further investigate the genetic relationships of IA Uzbekistan. We discarded individuals with <20k SNPs and checked the kinship relationships of those remaining, using only the individual with the highest number of SNPs from each kinship pair for further genetic analysis (supplementary table S2, Supplementary Material online). This resulted in a set of 15 unrelated individuals having 0.02–2.88 × fold coverage (27,900–723,918 SNPs). Increased Steppe Ancestry in Iron Age Compared with Bronze Age To assess the genetic affinities between Uz_IA individuals and ancient populations, we first performed principal component analysis (PCA) (Patterson et al. 2006) by projecting the ancient diverse Eurasian populations onto the present-day populations. The PCA results show that all the Uz_IA individuals lie on a cline extending from West Siberian Hunter Gatherers (WSHG) to Anatolian and Iranian farmer-related ancestry (fig. 1B and supplementary figs. S1–S3, Supplementary Material online) clustering closely with the geographically proximal ancient BA and IA populations from the Steppe and Central Asia, including ancient populations from Uzbekistan and neighboring regions of Turan and the Central Steppe (fig. 1B and supplementary figs. S1 and S2, Supplementary Material online). Despite being in proximity on the PCA to the previously published Uzbekistan BA populations (Bustan, Dzharkutan, Kashkarchi, Kokcha, and Sappali_Teppe), the Uz_IA populations lack a tight clustering. They overlap with Turan IA and historical time period populations with Steppe-related ancestry, suggesting the presence and influence of more Steppe-related ancestry in Uz_IA individuals than in BA Uzbekistan populations. To estimate the ancestral admixture and population structure, we used the model-based clustering method implemented in ADMIXTURE (Alexander et al. 2009). The same trends from the PCA are also observed in the ADMIXTURE (K = 8) analysis (fig 1C and supplementary figs. S4 and S5, Supplementary Material online), with three major sources of ancestries maximized in Iranian farmers, Anatolian farmers and WSHG (Steppe-related), as well as small amounts of West European Hunter Gatherer and East Asian-related ancestries (fig 1C and supplementary fig. S5, Supplementary Material online). The single individual from the Serkharakat site also shows high genetic similarity to Rabat individuals in PCA (fig. 1B and supplementary figs. S1–S3, Supplementary Material online), clustering with other Rabat individuals, and having similar admixture components in ADMIXTURE analysis (fig. 1C). We additionally investigated the genetic affinity between Rabat and Serkharakat using the outgroup-f3 test, that is, f3(Rabat, Serkharakat/Ancient Population; Mbuti) and f4-statistics test of the form f4(Rabat, Ancient Population; Serkharakat, Mbuti) (fig. 2B and supplementary fig. S6, Supplementary Material online). We noticed that Rabat and Serkharakat share strong genetic drift with each other, but both share greater genetic drift with Steppe MLBA and Afanasievo populations, indicating that the Serkharakat individual is not descended from Rabat individuals. In most cases, Uz_IA shows higher genetic affinity to the Late Bronze Age (LBA) populations with Steppe-related ancestry from Turan, Altai, and eastern European regions than to the other BA populations from Turan and Central Asia (fig. 2A and supplementary figs. S6, S8, and S9 and table S3, Supplementary Material online). This trend of higher Steppe-related ancestry in the Uz_IA samples is also supported by their closer proximity to present-day Europeans in the PCA, as well as higher values for f3(Uz_IA, Present-day Population; Mbuti) > 0, relative to Central Asian (including Turan) and Caucasus populations (supplementary figs. S3 and S7, Supplementary Material online). Fig. 2.  f4-statistics of Uz_IA populations. (A) Outgroup-f3 test (f3(Uz_IA, X; Mbuti) > 0) showing the 25 populations with the highest affinity (most positive) to Uz_IA samples. Most of these populations are from the Central Steppe, and among them MLBA populations from Kazakhstan show the highest affinity. Horizontal bars represent two standard errors. (B) Results of f4-statistics of the form f4(Rabat/Serkharakat, X; Rabat/Serkharkat, Mbuti). The plot shows the significant Z-scores of the f4-statistics test results. The negative values show a greater affinity of both Rabat and Serkharakat to the ancient populations compared with each other. The ancient populations are subgrouped as BMAC, Central Steppe EMBA (CS_EMBA), Central Steppe MLBA (CS_MLBA), Eastern Steppe EMBA (ES_EMBA), Steppe LBA (Steppe_LBA), Western Steppe EMBA (WS_EMBA), Western Steppe MLBA (WS_MLBA), Steppe MLBA with additional affinity to BMAC (ST_MLBA_oBMAC), and Steppe MLBA with additional affinity to West Siberian Hunter Gatherer (ST_MLBA_oWSHG). The individuals are grouped similar to Narasimhan et al. (2019). |
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Post by Admin on Mar 30, 2022 21:27:25 GMT
The outgroup-f3 analysis shows the highest genetic affinity between Uz_IA and the Steppe_MLBA population (fig. 2A and supplementary fig. S8, Supplementary Material online). Among the Early-to-Middle Bronze Age Steppe (Steppe_EMBA) populations, Uz_IA shows the highest affinity with the Afanasievo population in outgroup-f3 statistics and an overall greater affinity to Western_Steppe_EMBA populations than to Central_Steppe_EMBA populations (supplementary fig. S8, Supplementary Material online). Among the Steppe_MLBA populations, Uz_IA shows higher genetic affinity to Central_Steppe_MLBA than to Western_Steppe_MLBA populations (supplementary fig. S8, Supplementary Material online). The f4-statistics of the form f4(Ancient Population, Ancient Population; Uz_IA, Mbuti) also suggest a greater affinity between Steppe MLBA populations and Uz_IA compared with the BMAC populations and other ancient BA populations from the Steppe region except for the Afanasievo population (supplementary fig. S9, Supplementary Material online). We conclude that Uz_IA populations were thus derived from an LBA/IA Steppe pastoralist group that admixed with later IA populations in eastern Asia and Turan, principally derived from populations related to the Central_Steppe_MLBA. We observe a greater genetic affinity of Uz_IA to present-day Europeans than to the present-day Uzbekistan populations (supplementary fig. S7, Supplementary Material online). This higher genetic affinity for European populations is due to the similar components of Anatolian farmer and Steppe-related ancestries observed both in Uz_IA and European present-day populations. Lower genetic affinity for the present-day Uzbekistan populations indicates substantial demographic changes through several admixture events over the past ∼2,000 years whereby present-day Uzbekistan populations now show additional ancestries derived from East Asian and Siberian populations (Irwin et al. 2010; Yunusbayev et al. 2015). Considering the greater inflow of Steppe ancestry during the IA into this region, the present-day populations reveal an interruption of genetic continuity since the Iron Age in southern Uzbekistan.
We then modeled the potential ancestry components using qpAdm to further investigate the admixture amount and ancestral sources in the Uz_IA individuals (Patterson et al. 2012). This admixture modeling was done in two stages: the first stage involved distal modeling, which included ancient pre-Copper Age populations as sources of admixture, and the second stage used proximal modeling where we focused on BA and IA populations as sources. The distal models included up to five sources, and we identified three major ancestries related to Iranian farmers (∼31–39%), Anatolian farmers (∼30–34%), and Steppe-related ancestry (WSHG) (∼15–17%); and three minor ancestries of West European Hunter Gatherer (∼7–12%), East Asian (∼5-7%), and South Asian Hunter Gatherer represented by Onge population (∼8%) (table 1). Both Rabat and Serkharakat show similar models except that the Serkharakat individual also shows affinity for South Asian Hunter Gatherers represented by Onge population.
Table 1.Feasible Five-Way qpAdm Distal Models for Rabat and Serkharakat as Target Population.
Uz_IA Tail Source1 Prop1 Source2 Prop2 Source3 Prop3 Source4 Prop4 Source5 Prop5
Rabat 0.304 Iron_Gates_HG 0.073 Ganj_Dareh_N 0.39 Anatolia_N 0.323 West_Siberia_N 0.167 Han 0.047
Rabat 0.255 Iron_Gates_HG 0.071 Ganj_Dareh_N 0.361 Anatolia_N 0.336 West_Siberia_N 0.162 Shamanka_EN 0.07
Serkharakat 0.135 Karelia 0.252 Ganj_Dareh_N 0.376 Anatolia_N 0.32 Shamanka_EN 0.052
Serkharakat 0.119 Iron_Gates_HG 0.121 Ganj_Dareh_N 0.306 Anatolia_N 0.331 West_Siberia_N 0.157 Onge 0.084
Serkharakat 0.330 Iron_Gates_HG 0.118 Ganj_Dareh_N 0.376 Anatolia_N 0.301 West_Siberia_N 0.151 Shamanka_EN 0.054
NOTE.—The distal models were run for one to five sources, feasible models worked only with four and five sources with a cut-off of P > 0.05 and pnest < 0.05 where P value (Tail > 0.5) suggests the admixture from n-source model where “n” is the number of source populations and P-nest (<0.5) indicates the higher ranking n-source model is significantly better than the n−1-source model. In this table, Prop is the admixture proportion and Tail is the P value.
For the proximal model, we first performed admixture-f3 tests, a three-population test whereby a significantly negative value indicates the target is a mixture of ancestry related to the other two populations. We found that admixture-f3(Population1, Population2; Uz_IA) < 0 (z < −3.0), where the test population includes temporally and spatially preselected ancient populations used for proximal qpAdm modeling. The top 25 negative admixture-f3 tests predominantly show a pattern where the Uz_IA population appears to be a mixture of ancestry present in BMAC and MLBA populations (supplementary fig. S14, Supplementary Material online). In proximal source modeling, Uz_IA can be modeled as single source with Ksirov_H_Kushan, a population present within a similar geographical region and time period, indicating a similar ancestry profile as that found in Uz_IA individuals (supplementary table S4, Supplementary Material online). A previous genomic study found that the Kushan individuals (30–380 CE) from South Tajikistan possessed a mixed ancestry of LBA Steppe herders (∼43.5%), BMAC populations (∼16.8%), and Anatolian farmers (∼39.7%) (Narasimhan et al. 2019). Some archaeological texts and records from the Ksirov site in Tajikistan have been regarded as a link between the Kushan and the Yuezhi people (Liu 2001; Narasimhan et al. 2019). Our Uz_IA individuals also show similarities with the Ksirov site in Tajikistan and present a similar ancestral profile having an East Asian-related component probably originating from the ancestors of the LBA Steppe pastoralists. Some archaeologists suggest a wider spread for the Yuezhi people and their origins around the northern region of the Tianshan Mountain Region in present-day Northern Xinjiang (Liu 2001), so it may be possible that the Yuezhi people were also derived from the ancestors of Steppe LBA populations with some East Asian ancestry, but additional sampling is needed within this region to fully explore the Yuezhi-related migration and settlement in Bactrian region. Although Kushan period coins were not found in the archaeological record, making it difficult to determine whether this population was directly related to the Kushan Empire that controlled the region during this time period. In a two-way admixture model, Uz_IA can be modeled as a mixture of a Copper Age population (Seh_Gabbi_Iran_Calc) and a Steppe MLBA-related (Georgievsky2_LBA, Priobrazhenka_LBA, and Zevakinskiy_MLBA) ancestry as well as a Ksirov_H_Kushan-related ancestry (supplementary table S4, Supplementary Material online). Finally, using the three proximal sources, many working admixture models reflected a general admixture of Steppe MLBA/LBA-, BMAC-, and Iranian_Chalcolithic-related ancestry. Similar admixture models were also attained for the previously published Kushan individuals (Narasimhan et al. 2019).
In Central Asia, Steppe-related ancestry arrived in the BMAC region by ∼4100 BP (de Barros Damgaard, Martiniano, et al. 2018; Narasimhan et al. 2019) and an increased Steppe-related ancestry in Uz_IA populations compared with those dating to the BA supports an increase of contact and admixture with groups from the northern and eastern Steppe of Central Asia. This increase in Steppe-related ancestry in Uz_IA is also observed in other nomadic groups of the Central Steppe such as the Scythians and Sakas and even in the Xiongnu, which were widely present in the Eastern Steppe (de Barros Damgaard, Marchi, et al. 2018). Presence of BMAC-related ancestries further indicate an interaction of Saka- and BMAC-related people which suggests that this mixed ancestry is not only present in Uzbekistan but also in large parts of the Central Steppe region (de Barros Damgaard, Marchi, et al. 2018; Narasimhan et al. 2019). Thus, Uz_IA populations in South Uzbekistan are derived from an LBA Steppe pastoralist population that admixed with a local IA population after the BMAC period. This ancestry was also quite prominent in the late IA Steppe region indicating a high degree of interaction and movement of people in this region.
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Post by Admin on Mar 31, 2022 17:55:10 GMT
Genetic Continuity of Bronze Age Ancestry in Iron Age Uzbekistan with Low East and South Asian Connection Compared with the Bronze Age, Iron Age Central Asia shows increased migrations and cultural exchanges supplemented by technological advances (de Barros Damgaard, Marchi, et al. 2018; de Barros Damgaard, Martiniano, et al. 2018; Narasimhan et al. 2019). Despite major migrations of Steppe-related people into this region, two major components of BA populations, Anatolian and Iranian farmer-related ancestries, still form the majority of Uz_IA ancestry (∼64–70%) in ADMIXTURE and qpAdm analyses (fig. 1C and table1). The two MLBA populations from Uzbekistan (Kashkarchi_BA, Kokcha_BA) and other Steppe_MLBA populations share a closer relationship with Uz_IA than with the BMAC and Indus periphery, Gonur2_BA populations, as shown with f4-statistics analysis (supplementary table S3, Supplementary Material online). These MLBA populations have significantly higher Steppe-related ancestry, suggesting a greater interaction with Steppe groups from the Central Steppe region of Kazakhstan in the MLBA period. Thus, a probable genetic connection from the north of Uzbekistan (e.g., Kazakhstan) is evident, bringing Steppe-related ancestry down into this region. Overall, similar core genetic profiles within Uzbekistan from the BA to the IA suggest continuation of BA ancestry into the IA with no mass replacement, although with an increased influx of Steppe-related ancestry, likely from the north of Uzbekistan, possibly using the Inner Asian Mountain Corridor route. The ADMIXTURE and qpAdm analyses of UZ_IA suggest two major ancestral components related to Iranian and Anatolian farmers (fig. 1C and table 1). These two components also show significantly positive f4-statistics (f4(Rabat/Serkharkat, X; Anatolia/Iran_N, Mbuti)) compared with the BMAC populations (supplementary fig. S10, Supplementary Material online). Among these two ancestries, we observe a relatively higher Anatolian farmer-related ancestry (∼30–34%) in Uz_IA individuals than that found in Neolithic and BA populations in Turan (Bustan_EN: ∼9% and BMAC: ∼26%), and a lower amount of Iranian farmer-related ancestry in Uz_IA (∼31–39%) than found in Bustan_EN: ∼73–85% and BMAC ∼59% populations (Narasimhan et al. 2019). In proximal qpAdm modeling, we also observed that the two- and three-source models always required an Anatolian farmer-related ancestry source (e.g., Hajji_Firuz_C: ∼53%), suggesting an increase in Anatolian farmer-related ancestry in Uz_IA compared with the BMAC populations (supplementary table S2, Supplementary Material online). In addition, we find an increase in Iranian farmer-related ancestry compared with the LBA Steppe populations similar to the other Kushan period individuals (Narasimhan et al. 2019), implying later admixtures with the IA populations from Turan and Iran. This region was traversed extensively by people across Inner Asian Mountain Corridor and the diverse ancestries may also be the result of these movements of people across Central Asia (Frachetti 2012). Some of the Central Asian populations also show higher affinities with East and South Asian populations apart from the Steppe, Anatolian, and Iranian farmers-related populations (Narasimhan et al. 2019). In the f4-statistics test, the Uz _IA populations share more alleles with ancient East Asian populations than with BMAC populations (supplementary fig. S11, Supplementary Material online). This pattern is also observed in both ADMIXTURE and qpAdm analyses (fig 1C and table 1), with the contribution of East Asian-related ancestry ∼5–7% (table 1). Additionally, the ADMIXTURE (fig. 1B) and qpAdm models both suggest an ancestry component derived from South Asian Hunter Gatherer ancestry (Onge) (table 1 and supplementary table S4, Supplementary Material online). Between Rabat and Serkharakat, the distal qpAdm model suggests more South Asian Hunter Gatherer ancestry in Serkharakat compared with the Rabat individuals (table 1). In comparison with BMAC populations which contained ∼2% ancestry being derived from Onge, an f4(Rabat/Serk; Gonur2_BA/Saidu_Sharif_H, Mbuti) statistics test of Uz_IA with other BA populations shows more shared drift with Onge for the Serkharakat compared with the Rabat (supplementary fig. S13, Supplementary Material online). Therefore, we find relatively more East Asian ancestry in Uz_IA compared with the BMAC populations and relatively similar amounts of South Asian HG ancestry. Additional sampling across this region would provide more clarity for South and East Asian genetic affinities. Conclusions In this study, by using the genomic data of 27 Southern Uzbekistan individuals including 15 unrelated individuals from the late IA around the Kushan time period, we report an increase in Steppe-related admixture in the IA compared with BA populations in the Bactria region. The source of Steppe-related ancestry was likely identified as LBA Steppe populations, who admixed with local LBA populations associated with the earlier BMAC populations prevalent in this region. However, the migration and admixture with Steppe-related sources did not replace the previously present Iranian and Anatolian farmer-related ancestry; in fact, we find genetic continuation of BA ancestry with the addition of Steppe-related ancestry. The Uz_IA population also shows a minor genetic connection with populations in South and East Asia, suggesting movement of these ancestries into South Uzbekistan. In addition, increased Anatolian farmer-related ancestry compared with the BA points to additional admixture with local populations having Anatolian farmer related-ancestry after the decline of the BMAC settlements. This mixed-genetic ancestry had a widespread presence as it is also observed in Kushan-related populations and other Central and Eastern Steppe populations. Future genomic studies in Central Asia will provide more insights into the Iron Age genetic and cultural diversity of this region. Supplementary Material Supplementary data are available at Molecular Biology and Evolution online. |
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Post by Admin on Jul 17, 2022 17:35:50 GMT
PMCID: PMC6748862EMSID: EMS84309PMID: 29743352
The First Horse Herders and the Impact of Early Bronze Age Steppe Expansions into Asia
Abstract
The Yamnaya expansions from the western steppe into Europe and Asia during the Early Bronze Age (~3000 BCE) are believed to have brought with them Indo-European languages and possibly horse husbandry. We analyze 74 ancient whole-genome sequences from across Inner Asia and Anatolia and show that the Botai people associated with the earliest horse husbandry derived from a hunter-gatherer population deeply diverged from the Yamnaya. Our results also suggest distinct migrations bringing West Eurasian ancestry into South Asia before and after but not at the time of Yamnaya culture. We find no evidence of steppe ancestry in Bronze Age Anatolia from when Indo-European languages are attested there. Thus, in contrast to Europe, Early Bronze Age Yamnaya-related migrations had limited direct genetic impact in Asia.
The vast grasslands making up the Eurasian steppe zones, from Ukraine through Kazakhstan to Mongolia, have served as a crossroad for human population movements during the last 5000 years (1–3), but the dynamics of its human occupation—especially of the earliest period—remain poorly understood. The domestication of the horse at the transition from the Copper Age to the Bronze Age ~3000 BCE, enhanced human mobility (4, 5) and may have triggered waves of migration. According to the “Steppe Hypothesis,” this expansion of groups in the western steppe related to the Yamnaya and Afanasievo cultures was associated with the spread of Indo-European (IE) languages into Europe and Asia (1, 2, 4, 6). The peoples who formed the Yamnaya and Afanasievo cultures belonged to the same genetically homogenous population, with direct ancestry attributed to both Copper Age (CA) western steppe pastoralists, descending primarily from the European Eastern hunter-gatherers (EHG) of the Mesolithic, and to Caucasian groups (1, 2), related to Caucasus hunter-gatherers (CHG) (7).
Within Europe, the “Steppe Hypothesis” is supported by the reconstruction of Proto-IE (PIE) vocabulary (8), as well as by archaeological and genomic evidence of human mobility and Early Bronze Age (3000–2500 BCE) cultural dynamics (9). For Asia, however, several conflicting interpretations have long been debated. These concern the origins and genetic composition of the local Asian populations encountered by the Yamnaya- and Afanasievo-related populations, including the groups associated with Botai, a site that offers the earliest evidence for horse husbandry (10). In contrast, the more western sites that have been supposed by some to reflect the use of horses in the Copper Age (4) lack direct evidence of domesticated horses. Even the later use of horses among Yamnaya pastoralists has been questioned by some (11) despite the key role of horses in the “Steppe Hypothesis.” Furthermore, genetic, archaeological, and linguistic hypotheses diverge on the timing and processes by which steppe genetic ancestry and the IE languages spread into South Asia (4, 6, 12). Similarly, in present-day Turkey, the emergence of the Anatolian IE language branch including the Hittite language remains enigmatic, with conflicting hypotheses about population migrations leading to its emergence in Anatolia (4, 13).
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