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Post by Admin on Jul 28, 2020 0:31:17 GMT
A West-to-East Cline of Decreasing Anatolian Farmer-Related Ancestry We studied the genetic transformations accompanying the spread of agriculture eastward from Iran beginning in the 7th millennium BCE (41, 42). We replicate previous findings that 9th to 8th millennium BCE herders from the Zagros Mountains of western Iran harbored a distinctive West Eurasian-related ancestry profile (9, 27), while later groups across a broad region were admixed between this ancestry and that related to early Anatolian farmers. Our analysis reveals a west-to-east cline of decreasing Anatolian farmer-related admixture in the Copper Age and Bronze Age ranging from ~70% in Anatolia to ~31% in eastern Iran, to ~7% in far eastern Turan (Fig. 1; (13), Fig. S10, Table S8–S16). This suggests that the archaeologically documented spread of a shared package of plants and animal domesticates from diverse locations across this region was accompanied by bi-directional spread of people and mixture with the local groups they encountered (3, 41, 43, 44). We call this the Southwest Asian Cline. In the far east of the Southwest Asian Cline (eastern Iran and Turan) in individuals from the 3rd millennium BCE, we detect not only the smallest proportions of Anatolian farmer-related admixture but also admixture related to West Siberian Hunter Gatherers (WSHG) (plausibly reflecting admixture from unsampled hunter-gatherer groups who inhabited this region prior to the spread of Iranian farmer-related ancestry into it). This shows that North Eurasian-related ancestry impacted Turan well before the spread of descendants of Yamnaya Steppe pastoralists into the region. We can exclude the possibility that the Yamnaya were the source of this North Eurasian-related ancestry, as they had more EEHG-than WSHG-related ancestry, and also carried high frequencies of mitochondrial DNA haplogroup type U5a as well as Y chromosome haplogroup types R1b or R1a not represented in Iran and Turan in this period ((13), Table S93-S94). People of the BMAC Were Not a Major Source of Ancestry for South Asians From Bronze Age Iran and Turan, we obtained genome-wide data for 84 ancient individuals (3000–1400 BCE) who lived in four urban sites of the Bactria Margiana Archaeological Complex (BMAC) and its immediate successors. The great majority of these individuals fall in a cluster genetically similar to the preceding groups in Turan, consistent with the hypothesis that the BMAC coalesced from preceding pre-urban populations (5). We infer three primary genetic sources: early Iranian farmer-related ancestry (~60–65%), and smaller proportions of Anatolian farmer- (~20–25%) and WSHG-related ancestry (~10%). Unlike preceding Copper Age individuals from Turan, people of the BMAC cluster also harbored an additional 2–5% ancestry related (deeply in time) to Andamanese Hunter-Gatherers (AHG). This evidence of north-to-south gene flow from South Asia is consistent with the archaeological evidence of cultural contacts between the Indus Valley Civilization and the BMAC and the existence of an IVC trading colony in northern Afghanistan (although we lack ancient DNA from that site) (45), and stands in contrast to our qpAdm analyses showing that a reciprocal north-to-south spread is undetectable. Specifically, our analyses reject the BMAC and the people who lived before them in Turan as plausible major sources of ancestry for diverse ancient and modern South Asians by showing that their ratio of Anatolian farmer-related to Iranian farmer-related ancestry is too high for them to be a plausible source for South Asians (p<0.0001, χ2 test; (13), Fig S50–S51). A previous study (26) fit a model in which a population from Copper Age Turan was used a source of the Iranian farmer-related ancestry in present-day South Asians, thus raising the possibility that the people of the BMAC whom the authors correctly hypothesized were primarily derived from the groups that preceded them in Turan were a major source population for South Asians. However, that study only had access to 2 samples from this period compared to the 36 we report with this study, and it lacked ancient DNA from individuals from the BMAC period or from any ancient South Asians. With additional samples, we have the resolution to show that none of the large number of Bronze and Copper Age populations from Turan for which we have ancient DNA fit as a source for the Iranian farmer-related ancestry in South Asia. Steppe Pastoralist-Derived Ancestry Arrived in Turan by 2100 BCE Our large sample sizes from Central Asia, including individuals from BMAC sites, are a particular strength of this study, allowing us to detect outlier individuals with ancestry different from those living at the same time and place, and revealing cultural contacts that would be otherwise difficult to appreciate (Fig. 2). Around ~2300 BCE, we observe three outliers in BMAC-associated sites carrying WSHG-related ancestry and we report data from the third millennium BCE from three sites in Kazakhstan and one in Kyrgyzstan that fit as sources for them (related ancestry has been found in ~3500 BCE Botai culture individuals (26)). Yamnaya-derived ancestry arrived by 2100 BCE, since from 2100–1700 BCE we observe outliers from three BMAC-associated sites carrying ancestry ultimately derived from Western_Steppe_EMBA pastoralists, in the distinctive admixed form typically carried by many Middle to Late Bronze Age Steppe groups (with roughly two thirds of the ancestry being of Western_Steppe_EMBA origin, and the rest consistent with deriving from European farmers). Thus, our data document a southward movement of ancestry ultimately descended from Yamnaya Steppe pastoralists that spread into Central Asia by the turn of the 2nd millennium BCE. Fig. 2. Outlier analysis reveals ancient contacts between sites. We plot the average of Principal Component 1 (x-axis) and Principal Component 2 (y-axis) for the West Eurasian and All Eurasian PCA plots, as we found that this aids visual separation of the ancestry profiles. (A) In the Middle to Late Bronze Age Steppe, we observe in addition to the Western_Steppe_MLBA and Central_Steppe_MLBA clusters (indistinguishable in this projection), outliers admixed with other ancestries. The BMAC-related admixture in Kazakhstan documents northward gene flow onto the Steppe and confirms the Inner Asian Mountain Corridor as a conduit for movement of people. (B) At Shahr-i-Sokhta in eastern Iran, there are two primary groupings: one with ~20% Anatolian farmer-related ancestry and no detectable AHG-related ancestry, and the other with ~0% Anatolian farmer-related ancestry and substantial AHG-related ancestry (Indus Periphery Cline). (C) In individuals of the BMAC and successor sites, we observe a main cluster as well as numerous outliers: outliers >2000 BCE with admixture related to WSHG, outliers >2000 BCE on the Indus Periphery Cline (with an ancestral similar similar to the outliers at Shahr-i-Sokhta), and outliers after 2000 BCE that reveal how Central_Steppe_MLBA ancestry had arrived. (D) In the Late Bronze Age and Iron Age of northernmost South Asia, we observe a main cluster consistent with admixture between peoples of the Indus Periphery Cline and Central_Steppe_MLBA, and variable Steppe pastoralist-related admixture. An Ancestry Profile Widespread During the Indus Valley Civilization We document 11 outliers—3 with radiocarbon dates between 2500–2000 BCE from the BMAC site of Gonur, and 8 with radiocarbon dates or archaeological context dates between 3300 BCE to 2000 BCE from the eastern Iranian site of Shahr-i-Sokhta—that harbored elevated proportions of AHG-related ancestry (range of 11–50%) and the remainder from a distinctive mixture of Iranian farmer- and WSHG-related ancestry (~50–89%). These outliers had no detectable Anatolian farmer-related ancestry, in contrast with the main BMAC (~20–25% Anatolian-related) and Shahr-i-Sokhta (~16–21%) clusters, allowing us to reject both the BMAC and Shahr-i-Sokhta main clusters as sources for them (p<10−7, χ2 test; (13), Table S83). Without ancient DNA from individuals buried in IVC cultural contexts, we cannot make a definitive statement that the genetic gradient represented by these 11 outlier individuals, which we call the Indus Periphery Cline, was also an ancestry profile common in the IVC. Nevertheless, our result provides six circumstantial lines of evidence for this hypothesis. (i) These individuals had no detectable Anatolian farmer-related ancestry suggesting they descend from groups further east along the Anatolia-to-Iran cline of decreasing Anatolian farmer-related ancestry than any individuals we sampled from this period. (ii) All 11 outliers had elevated proportions of AHG-related ancestry, and two carried Y chromosome haplogroup H1a1d2 which today is primarily found in southern India. (iii) At both Gonur and Shahr-i-Sokhta there is archaeological evidence of exchange with the IVC (46, 47), and all the outlier individuals we directly dated fall within the time frame of the mature IVC. (iv) Several outliers at Shahr-i-Sokhta were buried with artifacts stylistically linked to Baluchistan in South Asia whereas burials associated with the other ancestries did not have these linkages (13). (v) In our modeling, the 11 outliers fit as a primary source of ancestry for 86 ancient individuals from post-IVC cultures living near the headwaters of the Indus River ~1200–800 BCE as well as diverse present-day South Asians, whereas no other ancient genetic clusters from Turan fit as sources for all these groups ((13), Fig S50). (vi) The estimated date of admixture between Iranian farmer-related and AHG-related ancestry in the outliers is several millennia before the time they lived (71 ± 15 generations, corresponding to a 95% confidence interval of ~5400–3700 BCE assuming 28 years per generation (13, 48). Thus, AHG-and Iranian farmer-related groups were in contact well before the time of the mature IVC at ~2600–1900 BCE as might be expected if the ancestry gradient was a major feature of a group that was living in the Indus Valley during the IVC.
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Post by Admin on Jul 28, 2020 6:37:19 GMT
Ancestry Clines in Eurasia Established After the Advent of Farming The late hunter-gatherer individuals from northern Eurasia lie along a west-to-east hunter-gatherer gradient of increasing relatedness to East Asians (Fig. 3). In the Neolithic and Copper Ages, hunter-gatherers at different points along this cline mixed with people with ancestry at different points along a southern cline to form five later clines, two of which were in the south (the Southwest Asian Cline and the Indus Periphery Cline which are described in the previous section), and three of which were in northern Eurasia (Fig. 3). Furthest to the west in the Steppe and Forest Zone there was the European Cline, established by the spread of farmers from Anatolia after ~7000 BCE and mixture with Western European Hunter-Gatherers (19). In far eastern Europe at latitudes spanning the Black and Caspian Seas there was the Caucasus Cline, consisting of a mixture of Eastern European Hunter-Gatherers and Iranian farmer-related ancestry with additional Anatolian farmer-related ancestry in some groups (49). East of the Urals we detect a Central Asian Cline, with WSHG individuals at one extreme and Copper Age and Early Bronze Age individuals from Turan at the other. Fig. 3. Ancestry Transformations in Holocene Eurasia. (A) Ancestry clines before and after the advent of farming. We document a South Eurasian Early Holocene Cline of increasing Iranian farmer- and West Siberian hunter-gatherer related ancestry moving west-to-east from Anatolia to Iran, and a North Eurasian Early Holocene Cline of increasing relatedness to East Asians moving west-to-east from Europe to Siberia. Mixtures of peoples along these two clines following the spread of farming formed five later gradients (shaded): moving west-to-east: the European Cline, the Caucasus Cline from which the Yamnaya formed, the Central Asian Cline which characterized much of Central Asia in the Copper and Bronze Ages, the Southwest Asian Cline established by spreads of farmers in multiple directions from several loci of domestication, and the Indus Periphery Cline. (B) Following the appearance of the Yamnaya Steppe pastoralists, Western_Steppe_EMBA (Yamnaya-like) ancestry then spread across this vast region. We use arrows to show plausible directions of spread of increasingly diluted ancestry (the arrows are not meant as exact routes which we do not have enough sampling to determine at present). Rough estimates of the timing of the arrival of this ancestry and estimated ancestry proportions are shown. A Distinctive Ancestry Profile Stretching from Eastern Europe to Kazakhstan in the Bronze Age Beginning around 3000 BCE, the ancestry profiles of many groups in Eurasia were transformed by the spread of Yamnaya Steppe pastoralist ancestry (Western_Steppe_EMBA) from its source in the Caucasus Cline (9, 49) to a vast region stretching from Hungary in the west to the Altai mountains in the east (7, 8) (Fig. 3). Over the next two millennia this ancestry spread further while admixing with local groups, eventually reaching the Atlantic shores of Europe in the west and South Asia in the southeast. The source of the Western_Steppe_EMBA ancestry that eventually reached Central Asia and South Asia was not the initial eastward expansion but instead a secondary expansion, which involved a group that had ~67% Western_Steppe_EMBA ancestry and ~33% ancestry from a point on the European Cline (8) (Fig. 3). We replicate previous findings that this group included people of the Corded Ware, Srubnaya, Petrovka, and Sintashta archaeological complexes spreading over a vast region from the border of eastern Europe to northwestern Kazakhstan (8, 19, 21), and our dataset adds more than one hundred individuals from this Western_Steppe_MLBA cluster. We also detect a further cluster, Central_Steppe_MLBA, which is differentiated from Western_Steppe_MLBA (p=7×10−6 by qpAdm), due to carrying ~9% additional ancestry derived from Bronze Age pastoralists of the central Steppe of primarily of WSHG-related ancestry (Central_Steppe_EMBA). Thus, individuals with Western_Steppe_MLBA ancestry admixed with local populations as they integrated eastward and southward. Bidirectional Mobility Along the Inner Asian Mountain Corridor As in Iran/Turan, the outlier individuals provide crucial information about human interaction. First, our analysis of 50 individuals from the Sintashta culture cemetery of Kamennyi Ambar V reveals multiple groups of outliers whom we directly radiocarbon dated to be contemporaries of the main cluster but were genetically distinctive, indicating that this was a cosmopolitan site (Fig. 2). One set of outliers had elevated proportions of Central_Steppe_EMBA (largely WSHG-related) ancestry, another had elevated Western_Steppe_EMBA (Yamnaya-related), and a third had elevated EEHG-related ancestry. Second, in the central Steppe (present-day Kazakhstan), an individual from one site dated to 2800–2500 BCE, and individuals from three sites dated to ~1600–1500 BCE, show significant admixture from Iranian farmer-related populations that is well-fit by the main BMAC cluster, demonstrating northward gene flow from Turan into the Steppe at the same time as there was southward movement of Central_Steppe_MLBA-related ancestry through Turan to South Asia. Thus, the archaeologically documented spreads of material culture and technology both north and south along the Inner Asian Mountain Corridor (50, 51), which began as early as the middle 3rd millennium BCE, were associated with substantial movements of people (Fig. 2). Third, we observe individuals from Steppe sites (Krasnoyarsk) dated to ~1700–1500 BCE that derive up to ~25% ancestry from a source related to East Asians (well-modeled as ESHG), with the remainder best modeled as Western_Steppe_MLBA. By the Late Bronze Age, ESHG-related admixture became ubiquitous as documented by our time transect from Kazakhstan, and ancient DNA data from the Iron Age and from later periods in Turan and the central Steppe including Scythians, Sarmatians, Kushans, and Huns (25, 52). Thus, these 1st millennium BCE to 1st millennium CE archaeological cultures with documented cultural and political impacts on South Asia cannot be important sources for the Steppe pastoralist-related ancestry widespread in South Asia today (since present-day South Asians have too little East Asian-related ancestry to be consistent with deriving from these groups), providing an example of how genetic data can rule out scenarios that are plausible based on the archaeological and historical evidence alone ((13), Fig S52). Instead, our analysis shows that the only plausible source for the Steppe ancestry is Steppe Middle to Late Bronze Age groups, who not only fit as a source for South Asia but who we also document as having spread into Turan and mixed with BMAC-related individuals at sites in Kazakhstan in this period. Taken together, these results identify a narrow time window (first half of the second millennium BCE) when the Steppe ancestry that is widespread today in South Asia must have arrived.
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Post by Admin on Jul 28, 2020 20:52:28 GMT
Three Ancestry Clines That Succeeded Each Other in Time in South Asia Previous work has shown that South Asians harbor ancestry from peoples related to ancient groups in northern Eurasia and Iran, East Asians, and Australasians (9). Here we document the process through which these deep sources of ancestry mixed to form later groups. We begin with the pre-2000 BCE Indus Periphery Cline, described in an earlier section and detected in 11 outliers from two sites in cultural contact with the Indus Valley Civilization (Fig. 4). We can jointly model all individuals in this cline as a mixture of two source populations: one end of the cline is consistent with being entirely AHG-related, and the other is consistent with being 90% Iranian farmer-related and 10% WSHG-related (Fig. 4, (13)). People fitting on the Indus Periphery Cline form the majority of the ancestors of present-day South Asians. Through formal modeling, we demonstrate that it is this contribution of Indus Periphery Cline people to later South Asians, rather than westward gene flow bringing an ancestry unique to South Asia onto the Iranian plateau, that explains the high degree of shared ancestry between present-day South Asians and early Holocene Iranians (9, 13, 27). Fig. 4. The Genomic Formation of South Asia. (A) The degree of allele sharing with southern Asian hunter-gatherers (AASI) measured by f4(Ethiopia_4500BP, X; Ganj_Dareh_N, AHG) and with Steppe pastoralists measured by f4(Ethiopia_4500BP, X; Central_Steppe_MLBA, Ganj_Dareh_N) reveals three ancestry clines that succeeded each other in time: the Indus Periphery Cline prior to ~2000 BCE, the Steppe Cline represented by northern South Asian individuals after ~2000 BCE, and the Modern Indian Cline. (B) Modeling South Asians as a mixture of Central_Steppe_MLBA, AHG (as a proxy for AASI), and Indus_Periphery_West (the individual from the Indus Periphery Cline with the least AASI ancestry). Groups along the edges of the triangle fit a two-way model, and in the interior only fit a three-way model. The 140 present-day South Asian groups on the Modern Indian Cline are shown as small dots. (C) Groups that traditionally view themselves as being of priestly status in this and the preceding panel are shown in red (“Brahmin,” “Pandit,” and “Bhumihar” but excluding “Catholic Brahmins”), and tend to have a significantly higher ratio of Central_Steppe_MLBA to Indus_Periphery_Cline ancestry than other groups. (D) Plot of the proportion of Central_Steppe_MLBA ancestry on the autosomes (x-axis) and the Y chromosome (y-axis) shows that the source of this ancestry is primarily from females in Late Bronze Age and Iron Age individuals from the Swat District of northernmost South Asia, and primarily from males in most present-day South Asians. We next characterized the 2000 BCE Steppe Cline, represented in our analysis by 117 individuals dating to 1400 BCE - 1700 CE from the Swat and Chitral districts of northernmost South Asia (Fig. 2, Fig. 4). We found that we could jointly model all individuals on the Steppe Cline as a mixture of two sources albeit different from the two sources in the earlier cline. One end is consistent with a point along the Indus Periphery Cline. The other end is consistent with a mixture of about 41% Central_Steppe_MLBA ancestry and 59% from a subgroup of the Indus Periphery Cline with relatively high Iranian farmer-related ancestry ((13), Fig S50). To understand the formation of the Modern Indian Cline, we searched for triples of populations that could fit as sources for diverse present-day South Asians groups as well as peoples of the Steppe Cline. All fitting models include as sources Central_Steppe_MLBA (or a group with a similar ancestry profile), a group of Indus Periphery Cline individuals, and either AHG or a subgroup of Indus Periphery Cline individuals with relatively high AHG-related ancestry (13), Fig S51). Co-analyzing 140 diverse South Asian groups (10) that fall on a gradient in PCA (13), we show that while there are three deep sources, just as in the case of the earlier two clines the great majority of groups on the Modern Indian Cline can be jointly modeled as a mixture of two populations that are mixed from the earlier three. While we do not have ancient DNA data from either of the two statistically reconstructed source populations for the Modern Indian Cline, the ASI or the ANI, in what follows we co-analyze our ancient DNA data in conjunction with modern data to characterize the exact ancestry of the ASI, and to provide constraints on the ANI. The ASI and ANI Arose as Indus Periphery Cline People Mixed with Groups to the North & East To gain insight into the formation of the ASI, we extrapolated to the least West Eurasian-related theoretical extreme of the Modern Indian Cline by setting the Central_Steppe_MLBA ancestry proportion to zero in our model. We estimate a minimum of 55% ancestry from people on the Indus Periphery Cline (by representing the Indus Periphery Cline by the individual on it with the most Iranian farmer-related ancestry, which we call Indus_Periphery_West), and modeling the reminder of the ancestry as deriving from an AHG-related group (13). We find that several tribal groups from southern India are consistent with ~0% Central_Steppe_MLBA ancestry (13). The fact that these individuals match the most extreme possible position for the ASI not only reveals that nearly direct descendants of the ASI live today in South Asia, but also allows us to make a precise statement about the ancestry profile of the ASI. In particular, the fact that they harbor substantial Iranian farmer-related ancestry (via the Indus Periphery Cline), disproves earlier suggestions that the ASI might not have any ancestry related to West Eurasians (11). Using the DATES software, we estimate an average of 107 ± 11 generations since admixture of the Iranian farmer-related and AHG-related groups in one of these groups: Palliyar. This corresponds to a 95% confidence interval of 1700–400 BCE assuming 28 years per generation (53). Thus, the ASI were note fully formed at the time of the IVC, and instead must have continued to form through mixture after its decline as material culture typical of the IVC spread eastward (54) and Indus Periphery Cline ancestry mixed with people of less West Eurasian relatedness. We also obtained additional evidence for a late (Bronze Age) formation of the ASI by building an admixture graph using qpGraph, co-modeling Palliyar and Juang (an Austroasiatic-speaking group in India with low West Eurasian-relatedness) (Fig. 5). The graph fits the component of South Asian ancestry with no West Eurasian relatedness (AASI - “Ancestral Ancient South Asians”) as an Asian lineage that split off around the time that East Asian, Andaman Islander, and Australian aboriginal ancestors separated from each other, consistent with the hypothesis that eastern and southern Asian lineages derives from an eastward spread that in a short span gave rise to lineages leading to AASI, East Asians, Andamanese Hunter Gatherers, and Australians (55) (Fig. 5). The Juang cannot be fit through a mixture of ASI ancestry and ancestry related to Austroasiatic language speakers, and instead can only be fit by modeling additional ancestry from AASI, showing that at the time Austroasiatic groups formed in South Asia, groups with less Iranian farming-related ancestry than in the ASI were also present. Austroasiatic languages are hypothesized to have spread into South Asia in the 3rd millennium BCE (based on hill cultivation systems hypothesized to be associated with the spread of Austroasiatic languages (42), and thus the ancestry profile of the Juang provides an independent line of evidence for a late (Bronze Age and plausibly post-IVC) formation of the ASI. Fig. 5. Admixture Graph Model. The largest deviation between empirical and theoretical f-statistics is |Z|=2.9, indicating a good fit considering the large number of f-statistics analyzed. Admixture events are shown as dotted lines labeled by proportions, with the minor ancestry in gray. The present-day groups are shown in orange ovals, the ancient ones in blue, and unsampled groups in white. (The ovals and admixture events are positioned according to guesses about their relative dates to help in visualization, although the dates are in no way meant to be exact.) In this graph we do not attempt to model the contribution of WSHG and Anatolian farmer-related ancestry, and thus cannot model Central_Steppe_EMBA, the proximal source of Steppe ancestry in South Asia (instead we model the Steppe ancestry in South Asia through the more distally related Yamnaya). However, the admixture graph does highlight several key findings of the study, including the deep separation of the AASI from other Eurasian lineages, and the fact that some Austroasiatic-speaking groups in South Asia (e.g. Juang) harbor ancestry from a South Asian group with a higher ratio of AASI-related to Iranian farmer-related ancestry than any groups on the Modern Indian Cline, thus revealing that groups with substantial Iranian farmer-related ancestry were not ubiquitous in peninsular South Asia in the 3rd millennium BCE when Austroasiatic languages likely spread across the subcontinent. To shed light on the formation of the statistically reconstructed ANI, we return to the Swat Valley time transect that formed the Steppe Cline after 2000 BCE. The Modern Indian Cline intersects the Steppe Cline at a position close to the position of the Kalash, the group in northwest South Asia with the highest ANI ancestry proportion (56) (Fig. 4). The DATES-based estimate of admixture in the Kalash is 110 ± 12 generations (56), suggesting a post-IVC date of formation of the ANI paralleling the post-IVC date of formation of the ASI. Further evidence for a post-IVC integration of Steppe ancestry into South Asia comes from ancient individuals on the Steppe Cline (along which the ANI could theoretically have formed) whose admixture date for Steppe ancestry is also post-IVC. Specifically, we estimate the date of admixture into the Late Bronze Age and Iron Age individuals from the Swat District of northernmost South Asia to be on average 26 generations before the date that they lived, corresponding to a 95% confidence interval of ~1900–1500 BCE. This time scale for the arrival of Steppe ancestry in the region is consistent with our observation of 6 outlier individuals in Turan who lived between ~2000–1500 BCE and who carry this ancestry in mixed form (Fig. 2), and with our finding that the R1a Y chromosome associated with Central_Steppe_MLBA ancestry in South Asia is also present in the Swat District Late Bronze and Iron Age individuals (2 copies). Taken together, these results show neither of the two primary source populations of the Modern Indian Cline, the ANI and ASI, was fully formed before the turn of the 2nd millennium BCE. Steppe Ancestry in South Asia is Primarily from Males and Disproportionately High in Brahmins In the Late Bronze Age and Iron Age individuals of the Swat Valley, we detect a significantly lower proportion of Steppe admixture on the Y chromosome (only 5% of the 44 Y chromosomes of the R1a-Z93 subtype that occurs at 100% frequency in the Central_Steppe_MLBA males) compared to 20% on the autosomes (Z = −3.9 for a deficiency from males under the simplifying assumption that all the Y chromosomes are unrelated to each other since admixture and thus statistically independent), documenting how Steppe ancestry was incorporated into these groups largely through females (Fig. 4). However, sex bias varied in different parts of South Asia, as in present-day South Asians we observe a reverse pattern of excess Central_Steppe_MLBA-related ancestry on the Y chromosome compared to the autosomes (Z = 2.7 for an excess from males) (13, 57) (Fig. 4). Thus, the introduction of lineages from Steppe pastoralists into the ancestors of present-day South Asians was mediated mostly by males. This bias is similar in direction to what has been documented for the introduction of Steppe ancestry into Iberia in far western Europe, although the bias is less extreme than reported in that case (58). Our analysis of Steppe ancestry also identified 6 groups with a highly significantly elevated ratio of Central_Steppe_MLBA-to-Indus_Periphery_West-related ancestry compared to the expectation for the model at the Z < −4.5 level. The strongest two signals were in Brahmin_Tiwari (Z = −7.9) and Bhumihar_Bihar (Z = −7.0). More generally, there is a notable enrichment in groups that consider themselves to be of traditionally priestly status: 5 of the 6 groups with Z < −4.5 were Brahmins or Bhumihars even though they comprise only 7–11% of the 140 groups analyzed (p<10−12 by a χ2 test assuming all the groups evolved independently). We caution that this is not a formal test as there is an unknown degree of shared ancestry among groups since they formed by mixture, and because our decisions about which groups to include in the analysis was not made in a blinded way; for example, we excluded four “Catholic Brahmin” groups with strong evidence of substantial shared ancestry in the last millennium (10) which makes them not statistically independent (Table S5, Fig. 4 (13)). Nevertheless, the fact that traditional custodians of liturgy in Sanskrit (Brahmins) tend to have more Steppe ancestry than is predicted by a simple ASI-ANI mixture model provides an independent line of evidence, beyond the distinctive ancestry profile shared between South Asia and Bronze Eastern Europe mirroring the shared features of Balto-Slavic and Indo-Iranian languages (59), for a Steppe origin for South Asia’s Indo-European languages prior to ~2000 BCE.
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Post by Admin on Jul 29, 2020 4:21:32 GMT
Discussion Our analysis reveals that the ancestry of the greater South Asian region in the Holocene was characterized by at least three genetic gradients. Prior to ~2000 BCE, there was the Indus Periphery Cline consisting of people with different proportions of Iranian farmer- and AASI-related ancestry, which we hypothesize was a characteristic feature of many IVC people. The ASI formed after 2000 BCE as a mixture of a point along this cline with South Asians with higher proportions of AASI-related ancestry. Between about 2000 and 1000 BCE, people of largely Central_Steppe_MLBA ancestry expanded toward South Asia, mixing with people along the Indus Periphery Cline to form the Steppe Cline. Multiple points along the Steppe Cline are represented by individuals of the Swat Valley time transect and statistically we find that the ANI, one of the two primary source population of South Asia, can fit along the Steppe Cline. After 2000 BCE, mixtures of mixed populations—the ASI and ANI—mixed themselves to form the Modern Indian Cline, which is represented today in diverse groups in South Asia (Fig. 4).
Our finding based on admixture linkage disequilibrium ((13), Fig S59) that the mixture that formed the Indus Periphery Cline occurred by ~5400–3700 BCE—at least a millennium before the formation of the mature IVC—raises two possibilities. One is that Iranian farmer-related ancestry in this group was characteristic of the Indus Valley hunter-gatherers in the same way as it was characteristic of northern Caucasus and Iranian plateau hunter-gatherers. The presence of such ancestry in hunter-gatherers from Belt and Hotu Caves in northeastern Iran increases the plausibility that this ancestry could have existed in hunter-gatherers further east. An alternative is that this ancestry reflects movement into South Asia from the Iranian plateau of people accompanying the eastward spread of wheat and barley agriculture and goat and sheep herding as early as the 7th millennium BCE and forming early farmer settlements such as those at Mehrgarh in the hills flanking the Indus Valley (60, 61). However, this is in tension with the observation that the Indus Periphery Cline people had little if any Anatolian farmer-related ancestry, which is strongly correlated with the eastward spread of crop-based agriculture in our dataset. Thus, while our analysis supports the idea that eastward spread of Anatolian farmer-related ancestry was associated with the spread of farming to the Iranian plateau and Turan, our results do not support large-scale movements of ancestry from the Near East into South Asia following ~6000 BCE (the time after which all ancient individuals from Iran in our data have Anatolian farmer-related ancestry even though South Asians have very little). Languages in pre-state societies usually spread through movements of people (62), and thus the absence of much Anatolian farmer-related ancestry in the Indus Periphery Cline suggests that the Indo-European languages spoken in South Asia today are unlikely to owe their origin to the spread of farming from West Asia.
Our results not only provide negative evidence against an Iranian plateau origin for Indo-European languages in South Asia, but also positive evidence for the theory that these languages spread from the Steppe. While ancient DNA has documented westward movements of Steppe pastoralist ancestry providing a likely conduit for the spread of many Indo-European languages to Europe (7, 8), the chain-of-transmission into South Asia has been unclear because of a lack of relevant ancient DNA. Our observation of the spread of Central_Steppe_MLBA ancestry into South Asia in the first half of the 2nd millennium BCE provides this evidence, and is particularly striking as it provides a plausible genetic explanation for the linguistic similarities between the Balto-Slavic and Indo-Iranian sub-families of Indo-European, which despite their vast geographic separation, share the Satem innovation and Ruki sound laws (63). If the spread of people from the Steppe in this period was a conduit for the spread of South Asian Indo-European languages, then it is striking that there are so few material culture similarities between the central Steppe and South Asia in the Middle to Late Bronze Age (i.e. after the middle of the 2nd millennium BCE). Indeed, the material culture differences are so substantial that some archaeologists recognize no evidence of a connection. However, lack of material culture connections does not provide evidence against spread of genes, as has been demonstrated in the case of the Beaker Complex, which originated largely in western Europe, but in Central Europe was associated with skeletons that harbored ~50% ancestry related to Yamnaya Steppe pastoralists (18). Thus, in Europe we have an unambiguous example of people with ancestry from the Steppe making profound demographic impacts on the regions into which they spread while adopting important aspects of local material culture. Our findings document a similar phenomenon in South Asia, with the locally acculturated population harboring up to ~20% Western_Steppe_EMBA-derived ancestry according to our modeling (via Central_Steppe_MLBA groups) (Fig. 3). Our analysis also provides a second line of evidence for a linkage between Steppe ancestry and Indo-European languages. Steppe ancestry enrichment in groups that view themselves as being of traditionally priestly status is striking as some of these groups including Brahmins are traditional custodians of literature composed in early Sanskrit. A possible explanation is that the influx of Central_Steppe_MLBA ancestry into South Asia in the mid-2nd millennium BCE created a meta-population with varied proportions of Steppe ancestry, with people of more Steppe ancestry (or admixing less with Indus Periphery Cline groups) tending to be more strongly associated with Indo-European culture. Due to strong endogamy, which kept groups generally isolated from neighbors for thousands of years (7), some of this population substructure persists in South Asia among present-day custodians of Indo-European texts.
Our findings also shed light on the origin of its second-largest language group in South Asia, Dravidian. The strong correlation between ASI ancestry and present-day Dravidian languages suggests that the ASI, which we have shown formed as groups with ancestry typical of the Indus Periphery Cline moved south and east after the decline of the IVC to mix with groups with more AASI ancestry, most likely spoke an early Dravidian language. A possible scenario combining genetic data with archaeology and linguistics is that proto-Dravidian was spread by peoples of the IVC along with the Indus Periphery Cline ancestry component of the ASI. Non-genetic support for an IVC origin for Dravidian languages includes the present-day geographic distribution of these languages (in southern India and southwestern Pakistan), and a suggestion that some symbols on ancient Indus Valley seals denote Dravidian words or names (64, 65). An alternative possibility is that proto-Dravidian was spread by the approximately half of the ASI’s ancestry that was not from the Indus Periphery Cline, and instead derived from the south and the east (peninsular South Asia). The southern scenario is consistent with reconstructions of Proto-Dravidian terms for flora and fauna unique to peninsular India (66, 67).
We finally highlight a remarkable parallel between the prehistory of South Asia and Europe. In both regions there were exchanges between people related to Southwest Asian people and local people; mixtures of these groups led to the Indus Periphery Cline in South Asia and the European Cline in Europe. In both subcontinents, people arriving in the 3rd and 2nd millennia BCE who descended from mixtures of people related to Yamnaya Steppe pastoralists and European farmers mixed further with local populations: in South Asia forming the ANI, and in Europe forming groups like that of the Beaker Complex. In both cases, mixtures of these mixed populations—those with Steppe pastoralist-related admixture and those without—drive the modern ancestry clines in both regions (Fig. 3). However, there are also profound differences between the Bronze Age and Neolithic spreads of ancestry across the two subcontinents. One is that the maximum proportion of local ancestry is higher in South Asia (AASI ancestry of up to ~60%) than Europe (WEHG ancestry of up to ~30%) (7), which could reflect stronger ecological or cultural barriers to the spreads of people in South Asia than in Europe, allowing the previously established groups more time to adapt and mix with incoming groups. A second difference is the smaller proportion of Steppe pastoralist-related ancestry in South Asia than in Europe, its later arrival by ~500–1000 years, and a lower male sex bias in the admixture, factors that help to explain the continued persistence of a large fraction of non-Indo-European speakers amongst people of present-day South Asia today. The situation in South Asia is somewhat reminiscent of Mediterranean Europe where the proportion of Steppe ancestry is considerably lower than that of northern and central Europe (Fig. 3), and where many non-Indo European languages are attested in classical times (68). Further studies of ancient DNA from South Asia and the linguistically related Iranian world will extend and add nuance to the model presented here.
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Post by Admin on Jul 30, 2020 23:12:08 GMT
Bactria-Margiana Archaeological Complex (BMAC) When Victor Sarianidi first excavated the BMAC sites, his hypothesis was that it represented a migration from Syro-Anatolia to the east. Then, as in the following decades more information became available from previous cultures in the area, the debate about its origin opened with the option of a more native development. We still don’t have DNA from the earliest neolithic times, but we do have samples from the 5th-4th mill. to compare to the later BA ones from the BMAC proper. If we assume that the samples from Sarazm (c. 3500 BCE) represent a more “native” (but we don’t know if Mesolithic or only Neolithic) type, we can use them to first look at the other Eneolithic samples. Geoksiur_Eneolithic are loosely dated to 5000-2000 BCE, but they’re more “eastern” than the other 2 groups, so probably they are a bit older: Geoksiur_Eneolithic Sarazm_Eneolithic:I4290 42.4% Ganj_Dareh_N 28.8% Sarazm_Eneolithic:I4910 14.8% Hajji_Firuz_ChL 12% West_Siberia_N 2% Seh_Gabi_ChL 0% Distance 1.7415% Then we have the Anau and the Parkhai samples, from the 4th mill. Tepe_Anau_Eneolithic Ganj_Dareh_N 42.8% Sarazm_Eneolithic:I4290 33.2% Seh_Gabi_ChL 13.8% Sarazm_Eneolithic:I4910 6.2% Hajji_Firuz_ChL 4% West_Siberia_N 0% Distance 2.2718% Parkhai_Eneolithic Ganj_Dareh_N 35.8% Sarazm_Eneolithic:I4910 29.4% Seh_Gabi_ChL 21.4% Sarazm_Eneolithic:I4290 13.4% West_Siberia_N 0% Hajji_Firuz_ChL 0% Distance 2.1556% So now let’s compare these to the later BMAC proper samples: Gonur1_BA Seh_Gabi_ChL 39% Geoksiur_Eneolithic 27% Sarazm_Eneolithic:I4290 18.6% Shahr_I_Sokhta_BA2 14% West_Siberia_N 1.4% Distance 1.1578% Dzharkutan1_BA Geoksiur_Eneolithic 36.6% Seh_Gabi_ChL 33.8% Shahr_I_Sokhta_BA2 15% Sarazm_Eneolithic:I4290 12.2% West_Siberia_N 2.4% Distance 1.0491% So what we see is that the BMCA did receive a good amount of migration from the west between the Eneolithic and the Bronze Age (34-39% from around West Iran) and a smaller amount of migration from the Indus Valley (~15%), but the native component is still the largest. This is probably in agreement with more recent archaeology that has been able to establish the intensive cultural contacts between these 3 regions from the Eneolithic, with cultural exchange happening probably in every direction. The Scythians and the language of the steppe One interesting but not commented thing in the paper is that it better documents the genesis of the Scythians in Central Asia. We already knew that the Scythians were largely descended from Sintashta/Andronovo people, but also had some NE Asian (much more the Eastern Scythians than the Western ones) and some “southern” admixture. In this paper we might have references for those sources and early (presumably) proto-Scythian samples. Taking a look at the Western Scythian/Sarmatian samples using Eurogenes Global 25 datasheets, we see that they are closest to samples from Kazakhstan c. 1600-1500 BCE like Taldysay_MLBA2, ID I4794, 1600-1400 BCE, Y-DNA J2a1h2 (same as Tepe_Hissar_ChL:I2337, Iran, 3641-3519 calBCE) or Kyzlbulak_MLBA2, ID I4784, 1618-1513 calBCE, Y-DNA Q1a2b2). These two samples can be modelled as: Taldysay_MLBA2 Sintashta_MLBA 58.4% Parkhai_EBA 16.4% West_Siberia_N 10.4% Tepe_Hissar_ChL 7.6% Xibo 7.2% Distance 2.9151% Kyzlbulak_MLBA2 Sintashta_MLBA 47.6% Parkhai_EBA 27.3% West_Siberia_N 24.7% Xibo 0.4% Tepe_Hissar_ChL 0% Distance 2.2969% In turn, Sarmatians can be modelled mostly as a mix of the above samples and the Srubnaya people they encountered on their migration to the western steppe: Sarmatian_Pokrovka Kyzlbulak_MLBA2 43.1% Srubnaya_MLBA 40.2% Taldysay_MLBA2 7.4% Xibo 6.1% Armenia_EBA 3.2% Distance 1.8709% Or using the same sources as above: Sarmatian_Pokrovka Sintashta_MLBA 67.8% Parkhai_EBA 15.8% West_Siberia_N 9.2% Xibo 7.2% Tepe_Hissar_ChL 0% Distance 1.9752% The interesting thing about this is this genetic data is that it continues to provide more information for linguists to work with. Why? Because we can now more accurately tell the place and time when specific contacts or migrations happened, and that provides valuable information for linguistic research. To the point: we don’t know exactly how Indo-Iranian languages arrived to SC Asia, but we do know quite accurately that they were spoken there from at least 1800 BCE. If, for the sake of simplicity and to avoid controversies, we follow the steppe hypothesis, Indo-Iranian formed right there through the migration of Andronovo tribes, in the contact zone with BMAC. David Anthony, following Lubotsky, refers to 55 non-Indo-Iranian words borrowed into common Indo-Iranian, among them the words for bread, ploughshare, canal, brick, camel, ass, sacrificing priest, soma and Indra, and concludes: The BMAC fortresses and cities are an excellent source for the vocabulary related to irrigation agriculture, bricks, camels and donkeys; and the phonology of the religious terms is the same, so probably came from the same source.¹ The Scythian language is poorly known and hardly attested. However, it seems quite clear that it was an Indo-Iranian language, most likely on the Iranian branch, and more related to East Iranian. However, given the date of the formation of the ancestors of the Scythians, we’re probably taking about a very early form of Indo-Iranian, on the Iranian branch, but still older than Avestan and close to the split with Indo-Aryan. And given that Vedic is older than Avestan, that language was more or less as close to Vedic as to Avestan, even if it was in the Iranian branch. A late PIE language, ancestral to both Balto-Slavic and Indo-Iranian splits (more or less coinciding with the split of R1a-Z645 into Z93 and Z283) c. 3000 BCE somewhere in Eastern Europe (western Ukraine, Poland, maybe Belarus…), with pre-Indo-Iranian moving east from there (carrying R1a-Z93) and then from Kazakhstan moving south to become proto-Indo-Iranian through contacts with BMAC. Scythians, already speaking an early form of Indo-Iranian move west all the way to the Pontic steppe, where they arrive somewhere after 1000 BCE (?). This language is spoken throughout the steppe until the arrival of Uralic and Turkic groups. So this is the question for linguists: Are the similarities between Balto-Slavic and Indo-Iranian better explained by the first scenario alone, or by the second scenario alone, or by both, with two different layers of influence corresponding to each? And basically the same question could be asked for the relationship between proto-Uralic the hypothetic late PIE from the 3rd mill or the early Indo-Iranian from the late 2nd and 1st mill. 1 – Anthony, D. (2007), The horse, the wheel, the language.
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