|
|
Post by Admin on Apr 27, 2024 20:08:06 GMT
Discovery of three pre-Bronze Age genetic clines that collapsed after Yamnaya expansion Principal Component Analysis (PCA) of ancient individuals from the Pontic-Caspian steppe and adjacent areas of Southeastern Europe, the Caucasus and West Asia reveals that most of the Eneolithic people of the steppe as well as the later Bronze Age Yamnaya fall on non-overlapping genetic gradients (Figure 1). Visual impressions from a two-dimensional PCA must be evaluated cautiously, as populations at intermediate PCA positions, may not, in fact, be mixtures of more extreme ones, and the plot may suggest alternative ways of modeling each population of interest. For example, PC1 correlates (from left to right) to the differentiation between inland West Asians (Caucasus and Iran) to East Mediterranean (Anatolian-European) populations10, but also to the differentiation between Siberians and European hunter-gatherers14. On the other hand, PC2 differentiates between Neolithic and earlier populations from northern Eurasia (top; including Europe and Siberia) and West Asia (bottom: Anatolia-Mesopotamia-Caucasus-Iran). The Eneolithic and Bronze Age populations occupy the middle of the PCA: how did the earlier groups surrounding them across these orthogonal directions combine to form them?  Figure 1: Three Eneolithic clines and their neighbors in space and time. (a) Map with analyzed sites. (b) PCA analysis using axes formed by a set of ancient West European hunter-gatherer (WHG), Siberian, West Asian, and European farmer populations. Selected individuals relevant to this study are projected37 (Methods). (c) qpAdm models fitted on individuals of the populations of the three clines. The Volga Cline is generated by admixture between Lower Volga (BPgroup) people with upriver Eastern hunter-gatherers (EHG). Populations of the Dnipro Cline have UNHG or UNHG+EHG admixture relative to the Core Yamnaya (the hunter-gatherer source along this cline is significantly variable). The Caucasus-Lower Volga Cline is generated by admixture between lower Volga people with those from the Neolithic Caucasus (Aknashen-related). To answer these questions in a statistically rigorous way, we implemented a new model competition tournament framework around qpWave/qpAdm methods2,30 to fit and distinguish among alternative models (Methods; Supplementary Information, section 2). Briefly summarized, the idea of this methodology is that an admixture model X that includes a set of sources describes the admixture history of a target population T well if it: (i) reconstructs the shared genetic drift of T with both distant outgroup populations and the sources of alternative competing models, but also (ii) renders these competing models infeasible by showing that they cannot model this shared drift with the sources of X. In our framework, models are evaluated against a conservative set of distant outgroups as an initial filtering step; if they fit poorly, they are rejected; if not, they are further evaluated by comparing them against each other in symmetrical fashion (all-against-all) to identify a smaller set of promising models. With this note of caution, we observe that in the PCA in the Eneolithic-Bronze Age steppe there are three clines (geographically denoted as “Volga”, “Dnipro”, and “Caucasus-Lower Volga”), which diverge, in PCA space, from an area that includes populations enclosed by the Lower Don (at the site of Krivyansky), Lower Volga (at Berezhnovka-2), and north Caucasus mountains (at Progress-2, Vonyuchka-1, and Sharakhalsun5). From these similar beginnings the three clines extend outward into distinct directions corresponding to their geographical neighbors: both towards the EHG and UNHG representing the pre-Eneolithic people that lived in the Volga-Don-Dnipro area of eastern Europe, and towards the CHG and Caucasus Neolithic representing the pre-Eneolithic people that lived in the Caucasus and West Asia. In what follows, we introduce the key populations of each of the three clines and show how these can be modeled in terms of proximate sources. We also infer the ancestry origins of the people of the three clines to discover what is shared among all of them and unique to each of them. Volga Cline |
|
|
|
Post by Admin on Apr 29, 2024 20:32:54 GMT
The “Volga Cline” consists of sites on waterways that drain into the Caspian Sea and is suggestive of a zone of ongoing human contact within its region. The Eneolithic individuals fall at positions that correlate extraordinarily well to their position on the Volga River as one moves downstream: the Volosovo-attributed Sakhtysh (in the Upper Volga) and Murzikha (near the Kama-Volga confluence)14 constitute the upriver portion of the cline, situated in PCA space between EHG and UNHG. The Volga Cline then distinctly “bends” in PCA space and the knee of the cline is occupied by EHG groups, including those sampled in the northwest of Russia in Karelia2,19 and those of the Middle Volga, suggesting that this widely dispersed set of hunter-gatherers, which has also been called the Sidelkino Cluster based on its oldest representative19,22 were the major population of much of eastern Europe. Past the knee, in the downriver portion of the cline, the hunter-gatherer affinity decreases starting at the Middle Volga: Labazy, Lebyazhinka, Ekaterinovka, Syezzheye, then Khvalynsk (4500-4350 BCE) and Khlopkov Bugor, finally reaching the Lower Volga at Berezhnovka (4450-3960 BCE) (Fig. 1a). The decrease of hunter-gatherer affinity is counterbalanced by increased affinity towards populations of the Caucasus, suggesting that it is generated by an unsampled CHG-related source—that existed somewhere between Georgia (where the known CHG individuals were sampled8) and the Lower Volga— interacting with the northern EHG natives. Archaeological correlates for such south-north interactions do exist, and begin with the expansion of the Seroglazovo forager culture around the Lower Volga estuary ∼6200 BCE, with some ceramic and lithic typological parallels with Caucasus cultures, and continue to the unsampled North Caucasus Neolithic cemetery dated ∼4800 BCE near Nalchik.31,32  At the end of the cline, the four individuals from the newly reported Lower Volga site of Berezhnovka-2 can be grouped with the PG2004 individual of the Progress-25 site in the north Caucasus into a “Berezhnovka-2-Progress-2 cluster” (abbreviated to “BPgroup”). This proves that the CHG-related ancestry found at Progress-2 extended well into the steppe in the Lower Volga. The second individual from Progress-2 (PG2001) is grouped with another north Caucasus individual from Vonyuchka-15 into a related “Progress-2-Vonyuchka-1 cluster” (abbreviated as “PVgroup”). PVgroup and BPgroup are distinct (p=0.0006), but their genetic differentiation was small in magnitude (FST=-0.002±0.002; Extended Data Table 1) suggesting movement between the north Caucasus piedmont and Lower Volga sites. The two locations also shared a distinctive burial pose on the back with raised knees, later typical of Yamnaya and currently dated earliest in the Samara region at Lebyazhinka-5 and in a few graves at Ekaterinovka dated before 4500 BCE. It is clear from the PCA (Fig. 1b) that BPgroup differs from PVgroup in that the former is shifted towards the Afontova Gora-3 Upper Paleolithic individual from Siberia,33 West Siberian hunter-gatherers,4 and Central Asians such as a 7,500-year old Neolithic individual from Tutkaul (TTK) in Tajikistan.19 We will see below that Siberian/Central Asian ancestry was one of the constitutive elements of the Lower Volga-North Caucasus Eneolithic population represented by the two groups. A natural interpretation of the Volga cline is that upriver EHG-related ancestors and downriver Berezhnovka-related ones came together to form communities along the length of the river, resulting in a highly variable set of sampled individuals along the genetic gradient. While the origin of the upriver EHG ancestry is clear, as it has antecedents in eastern Europe for thousands of years,19 that of the downriver Berezhnovka group is less so, as (i) no earlier individuals from the Lower Volga have been sequenced, (ii) the genetic position of the Berezhnovka people is distinct from that of all preceding groups, and (iii) the BPgroup cannot be modeled as a clade with any contemporary or earlier groups (p<0.001). Whatever the origin of BPgroup, a point to which we will return below, we can use it as a proximate source and test Volga cline populations and individuals for consistency with a history of mixture of people related to the BPgroup and EHG (using Karelia2,19 as an EHG source well outside the Volga area and unlikely to be part of the riverine mating network), as suggested by the PCA. Seven Volga cline populations fit this model (p-values of 0.04 to 0.72) with the only consistently poor fits for Upper Volga, Murzikha, Maximovka, and “Klo” (the Khvalynsk individuals with low Berezhnovka relatedness) (p-values of 1e-66 to 0.006). Three of these populations (other than Klo which we discuss below) are arrayed in the upriver portion of the Volga cline, before its PCA “bend” (from EHG towards the UNHG). Individuals along the downriver portion of the cline can be well-modeled with only the two sources (BPgroup and EHG) (Fig. 1c). People on the Volga Cline buried at the Ekaterinovka cemetery likely died between 5050-4450 BCE (based on radiocarbon dates on three herbivore bones including a domesticated sheep in the graves of individuals we analyzed that are not expected to be affected by marine reservoir effects; Online Table 1). The Ekaterinovka people were already in the process of mixing with BPgroup-related people from the Lower Volga (24.3±1.3% on average). This contrasts to the earlier hunter-gatherer from Lebyazhinka, who had the lowest estimate of Berezhnovka ancestry on the Volga Cline of only 7.9±3.6%, providing a baseline of this component prior to the Eneolithic and which can also be modeled with only EHG-related ancestry (p=0.21) while Ekaterinovka cannot (p=2e-4). Mixing intensified over time so that 100-200 years later at the site of Khvalynsk34 which is ∼120km from Ekaterinovka (date range of 4500-4350 BCE based on two herbivore bones in the graves of individuals we analyzed), we observe a continuous gradient of admixture which we divide for convenience into three groups: “Khavlynsk high (Khi)” (76.8±1.9% BPgroup), “Khvalynsk medium (Kmed)” (57.3±1.7% BPgroup), and “Khalynsk low (Klo)” (41.2±1.6% BPgroup). Individuals on the downriver portion of the Volga cline exhibited a range of Berezhnovka ancestry from ∼14-89% (Fig. 1c) and thus were not clearly dominated by either the old EHG ancestors of the region or the Lower Volga newcomers. Genetic differentiation between Lower Volga (BPgroup) and Ekaterinovka was strong (FST=0.030±0.001; Extended Data Table 1) and quite probably reflected at least two different linguistic-cultural communities interacting with each other. A genetically Volga Cline individual not from the Volga Basin is from Csongrád-Kettőshalom in Hungary, whose direct date is 4331-4073 cal BCE. This individual is estimated to have 87.9±3.5% of its ancestry from the BPgroup (Fig. 1c) comparable to the most extreme “Khvalynsk high” individuals. The Csongrád individual is one among a group of steppe-like graves that appeared in Southeastern Europe in the late 5th millennium BCE including a cemetery at Giurgiuleşti,35 Moldova, from which one individual (I20072; 4330-4058BCE) is consistent with being a clade (p=0.90) with BPgroup, and another cemetery at Mayaky, Ukraine.36 Archaeological analysis has documented long-distance movement of Balkan copper to the Volga-Cline site of Khvalynsk,34 and the Csongrád and Mayaky individuals were plausibly part of the cultural exchange that mediated this process—a process our results show has no evidence of being contributed to genetically by people with ancestry typical of the Dnipro and Don basins. As we will now see, migrants with ancestry from the Lower Volga Eneolithic populations at the southern extreme of the Volga Cline did settle in the Dnipro area and generated the second major cline of the steppe. |
|
|
|
Post by Admin on May 2, 2024 12:05:47 GMT
(2) Dnipro Cline
The Dnipro Cline is formed at one end by Neolithic individuals living along the Dnipro River rapids whose union of calibrated radiocarbon dates is 6242-4542 BCE (UNHG), and at the other end by the Serednii Stih population represented by 13 individuals with good quality data whose union of radiocarbon date ranges uncorrected for freshwater reservoir effects are 4996-3372 BCE. The Dnipro Cline also includes the great majority of later Yamnaya individuals who expanded widely, most of whom are from a genetically homogeneous subset, and we used a large group of these individuals that have high quality data (n=104) to represent “Core Yamnaya” (Supplementary Information, section 2). Close to the Core Yamnaya in PCA are two Eneolithic groups: the Serednii Stih individual from Krivyansky in the Lower Don (4359-4251 BCE), and the PVgroup from the north Caucasus we discussed above as related to the Berezhnovka Lower Volga population. Nonetheless, the Core Yamnaya cannot be modeled as derived from either of these two earlier sources or indeed any other single source (p<1e-4). Their ancestry must have involved some admixture as their position along the highly variable Dnipro/Serednii Stih-associated cline also suggests. People from the Dnipro Cline as a whole are also fully distinct from those of the Volga Cline in PCA, and no pair of populations from the Volga and Dnipro clines form a genetic clade (p<1e-7). This distinctiveness spans a period of three millennia, beginning with earlier groups from Ukraine (UNHG), continuing with those of the Eneolithic Serednii Stih culture, and ending with the Yamnaya at the beginning of the Bronze Age, documenting the distinctiveness of the communities of these two great eastern European rivers and the relative lack of migration between them. A more geographically localized Yamnaya population of the Lower Don (n=23), many (n=17) of which are from the site of Krivyansky, bear no affinity to the Eneolithic individual from the area (Fig. 1). The Yamnaya can thus be traced neither to the north Caucasus (PVgroup), nor to the Lower Don (Krivyansky), nor to the Volga (BPgroup and the rest of the Volga cline). Yet, their position on the Dnipro cline, generated by populations of UNHG ancestry suggests that they emerged there, as a descendant community of people of the Serednii Stih culture.
The genetic heterogeneity of the Serednii Stih contrasts with the homogeneity of the Core Yamnaya (Fig. 1) which occupies one end of the Dnipro cline. The Core Yamnaya homogeneity is remarkable given that this cluster includes individuals sampled across 5,000 km from Hungary to southern Siberia, a vast slice of Eurasia across which the Yamnaya expanded but, for whatever reason, hardly admixed, at least initially, and at least for the elite subset of people afforded burial in kurgans, with any of the people that previously occupied it. Individuals of the Serednii Stih culture are arrayed along the Dnipro Cline with individuals of high or low Yamnaya affinity found at different sites. Closest to the Core Yamnaya genetically is a Serednii Stih individual from Vinogradnoe from the coast of the Azov Sea which we group with two other individuals from Oleksandria and one from Igren into an “SShi” cluster of greatest Yamnaya affinity. The sampled SShi group does not form a clade with the Core Yamnaya (p=2×10-7). A female from Kopachiv (I7585)38, represented by a long bone found loose in a Trypillia phase BI-II settlement, is part of a second “SSmed” cluster that is further along the Dnipro Cline; this group also includes three individuals from Oleksandria and three from Deriivka. The SShi and SSmed subsets are largely contiguous with each other, but individual I1424 from Moliukhiv Bugor (“SSlo”) is much further apart and close to the UNHG. The true variation within the Serednii Stih plausibly included individuals that fill gaps along the cline, e.g., between SSlo and SSmed, and even extended beyond the sampled variation, occupying the position of the Core Yamnaya itself. The Don Yamnaya largely overlap the Serednii Stih individuals, and the Don Yamnaya are discontinuous with the earlier Eneolithic individual from that location (p=7e-15). An interesting material correlate is seen in settlement continuity at stratified sites of the Konstantinovka culture on the Lower Don where the Don Yamnaya continued to settle in the same place as the earlier Serednii Stih, a continuity not seen in the Volga-Ural steppes, where most Eneolithic settlement sites exhibited no re-use by the Yamnaya.
qpAdm analysis reveals that all groups visually on the Dnipro Cline in the PCA can be well modeled with either UNHG or GK2 (individual I12490 from Golubaya Krinitsa in the Middle Don dated 5610-5390 BCE) at one extreme, and Core Yamnaya on the other (p-values between 0.07 and 0.85). Some populations of the cline (SSmed) can be modeled as Core Yamnaya and either GK2 (p=0.43) or UNHG (p=0.27); others, like the Don Yamnaya, can be modeled only as Core Yamnaya and UNHG (p=0.08) but not GK2 (p=0.0001); and others, like SShi, as Core Yamnaya and GK2 (p=0.08) but not UNHG (p=0.003). Thus, the hunter-gatherer end of the Dnipro Cline is not clearly UNHG or GK2. We therefore model individuals of the Cline with ancestry from any population from the UNHG-EHG cline (Fig. 1c), observing that individuals can be modeled as a mix in which UNHG ancestry predominates but EHG ancestry is also present in individuals (similar to GK2). This reflects the admixture of Caucasus-Lower Volga ancestry with hunter-gatherers of the Dnipro-Don (or UNHG-GK2) area, rather than other areas of eastern Europe (such as the Volga area) in which the hunter-gatherer population was EHG. Using Core Yamnaya as a source for the Serednii Stih is, of course, ahistorical, as they postdate the Serednii Stih, and so the model of Core Yamnaya + UNHG/GK2 admixture must be interpreted as admixture between local Neolithic residents of the Dnipro-Don area with a second, unsampled, Eneolithic source, which together account for the ancestry of the Core Yamnaya and—with even more UNHG/GK2 ancestry—of the Dnipro cline as a whole.
The Don, situated geographically between the Dnipro and Volga, is represented in our data by individuals from Golubaya Krinitsa (in the Middle Don) and Krivyansky (in the Lower Don). Golubaya Krinitsa contained two archaeologically contrasting styles of graves, one compared to Dnipro Neolithic graves and the other like Serednii Stih.39 The GK2 individual can be modeled as 66.6±4.7% UNHG and 33.4±4.7% EHG (p=0.39), suggesting that intermediate populations between the Dnipro hunter-gatherers (represented by UNHG) and the EHG existed not only in the Upper Volga (the upriver portion of the Volga cline), but also in the Middle Don. When we examine populations using the most ancient sources (Karelia, UNHG, and CHG) of the steppe and Caucasus, we see that the Eneolithic population of the Lower Don at Krivyansky and Neolithic individuals from Golubaya Krinitsa can all be well modeled with variable proportions of CHG-related ancestry (Fig. 2a). The most CHG-related ancestry is seen at Krivyansky (58.9±2.4%); there is less (25.3±2.1%) in three individuals which (Fig. 1) we group as GK1; and individual GK2 is consistent with having none or very little (4.0±2.2%), fitting the simpler EHG+UNHG model mentioned above. Thus, the Neolithic and Eneolithic individuals of the Don were a mixture of European hunter-gatherer ancestries (intermediate between the Dnipro-sampled UNHG and the Volga-sampled EHG, paralleling the intermediate geographic position of the Don) and southern CHG-related ancestry (Fig. 2a). When did the CHG-related ancestry reach the Don area? Its presence in a 14C-dated individual of the GK1 group (I12491/5557-5381 BCE) and others from the region7 suggest it was present there as early as the Neolithic. However, its absence from GK2 of similar 14C age proves that it was not a general feature of the Neolithic population. Both GK1/GK2 dates may be too early given that archaeologists of Golubaya Krinitsa interpreted people of the site as in contact with people of the much later Eneolithic Serednii Stih Culture.40 Moreover, an outlier Serednii Stih individual from Igren (I27930; 4337-4063 cal BCE) is consistent with all its ancestry coming from GK2; this could be an example of long-distance migration from the Don to the Dnipro, but also casts some doubt on the much older date of the GK2 individual, as genetic identity across more than a millennium in two different locations seems implausible given the diverse admixtures taking place throughout the steppe during the Eneolithic. The interpretation of the Golubaya Krinitsa population is further complicated by uncertainties as to their date due to freshwater reservoir effects in individuals who have a diet heavily reliant on freshwater fish. This can make nominal dates up to a millennium too old in this region.41 Further sampling along the Don would shed light on the distinctive processes and temporality of the ancestry change along this major river and place both the Golubaya Krinitsa individuals and those of Krivyansky on the Don mouth in their proper context.
Figure 2.
|
|
|
|
Post by Admin on May 5, 2024 16:03:03 GMT
 The three Eneolithic clines in the context of Eneolithic and Bronze Age admixture. Six 3-source models elucidate a complex history of admixture. Individuals plotted at the triangle edge fit (p>0.05); the simpler 2-source model is plotted for individuals with a negative coefficient from one of the three sources. The corners of each triangle represent the sources. Unplotted individual all give fits at P<0.05 and so should be viewed as poorly described by the model. (a) Caucasus and European hunter-gatherer admixtures in the “Old Steppe”: Krivyansky on the Lower Don received much more CHG-related admixture than upriver people of the Middle Don at Golubaya Krinitsa. In the Middle and Upper Volga and the Kama River, populations belonged to the old EHG cline with negligible CHG-related influence. (b) The “Don-Volga” difference. On the Lower Volga and North Caucasus piedmont, the BPgroup did receive CHG-related ancestry like its western Lower Don counterpart at Krivyansky; but, unlike Krivyansky, it also received ancestry from Central Asia; this eastern influence was higher still in the Bronze Age Steppe Maikop. (c) The “Volga Cline” vis-à-vis the Don: populations at Khvalynsk, Klopkov Bugor, and Ekaterinovka are clinal between the Berezhnvoka cluster on the Lower Volga and the upriver EHG-like populations of the Middle Volga (Labazy and Lebyazhinka). (d) the “Volga Cline” vis-à-vis Central Asia: a slight excess of Central Asian ancestry in the Khi subset of Khvalynsk. (e) the “Dnipro” cline: the Core Yamnaya are on one end of a cline that also includes the Don Yamnaya and Serednii Stih populations. The cline is formed by admixture from the “Caucasus-Lower Volga” (CLV) cline that is formed by differential admixture of Neolithic Caucasus and BPgroup people. The CLV Cline includes diverse people buried in kurgans at Berezhnovka, Progress-2, Remontnoye, and Maikop sites Klady and Dlinnaya-Polyana ∼5000-3000 BCE. (f) “West Asian”: CLV ancestry first appears in the Chalcolithic population at Areni-1 in Armenia and is also present in the Bronze Age at Maikop. The majority of the ancestry in both populations is from West Asian sources from the Mesopotamia-Caucasus (or Çayönü-Masis Blur-Aknashen) cline. Chalcolithic and Bronze Age Anatolians lack CLV ancestry but traces of it can be found in Bronze Age Central Anatolians. It has been suggested7 that the Yamnaya were formed by a substantial contribution of ∼65% Golubaya Krinitsa people from the Middle Don, that already had ∼20-30% CHG-related ancestry, with an additional ∼35% CHG-related ancestry. This scenario implies that they were formed in the Don area as the result of the CHG-related admixture observed there. Our results contradict this as the Core Yamnaya do not fit models with CHG-related and either GK1/GK2 sources (p<1e-6), suggesting that they have ancestry not accounted for by the model of ref.7 To understand the source of this ancestry, we fit the model of Fig. 2a (with the most ancient sources: Karelia, UNHG, and CHG) and observed that its failure (p=2×10-20) is explained by the fact that it severely underestimates their shared genetic drift with both Afontova Gora-3 from Upper Paleolithic Siberia (Z=-5.2) and Anatolian Neolithic (Z=-6.8).6 Thus, the Yamnaya must have Siberian- and Anatolian-related ancestry and cannot be a simple mixture of Caucasus- and Middle Don hunter-gatherers. A Volga source of the Siberian-related ancestry is strongly suggested by the fact that the Volga cline is shifted away from the Dnipro cline precisely in the direction of Siberian populations (Fig. 1b). That the Volga cline populations had such ancestry is proven by the fact that the model of Fig. 2a fails them precisely for the same reason as it does the Core Yamnaya as it also underestimates shared drift with Afontova Gora-3, e.g., for BPgroup (p=1×10-8 and Z=-4.5). This extra ancestry in BPgroup is also affirmed positively by the fact that it can be modeled as a mixture of Krivyansky and ∼24% Central Asian (Siberian-related) Tutkaul19 ancestry (p=0.13). When we fit both Krivyansky and the BPgroup with the same model that includes all relevant ancestries (Fig. 2b)—CHG, GK2, and Tutkaul—we see that indeed Krivyansky has little to no Central Asian ancestry (5.1±3.6%) but it can be fitted as 56.7±2.6% CHG-related and 43.3±2.6% GK2 alone (p=0.37), while BPgroup does have 29.3±2.2% Tutkaul ancestry. The model of Fig. 2b corrects for the missing Siberian-related ancestry in the Yamnaya, predicting shared genetic drift with Afontova Gora-3 reasonably accurately (Z=-1.7), but still fails (p=1e-9) as it does not predict shared drift with Anatolian Neolithic (Z=-6.1). Thus, while ancestry from the Volga can explain the Siberian relatedness of the Core Yamnaya it cannot explain the Anatolian Neolithic relatedness as this was not a component of Volga cline populations. Our new data resolve the extent of the spread of eastern “Central Asian” or “Siberian” ancestry into the Pontic-Caspian steppe. It was present, during the Eneolithic, on the Volga and in the North Caucasus Steppe, but further west on the Don there still existed populations without much or any of it like those at Krivyansky and Golubaya Krinitsa. When we repeat our modeling of the Volga Cline as a mixture of BPgroup and EHG sources but add either a western (UNHG) or eastern (Tutkaul) source (Fig. 2c,d) we see that individuals on the cline remain largely well-modeled as linear combinations of the two groups: Fig. 2c shows the characteristic “bend” of the Volga Cline with a portion showing variable Berezhnovka ancestry and the other (including many individuals from the Upper Volga and Murzikha) showing variable UNHG ancestry which increases further still in the GK2 individual from the Don. Fig. 2d shows that individuals of the Volga Cline have more Tutkaul ancestry than is explained by the simpler Berezhnovka-Karelia model; however, the deviations are small (4.4±2.6% Tutkaul ancestry for “Khi”). The Eneolithic Volga was an admixture zone between downriver BPgroup people with upriver EHG ones that included Central Asian ancestry mainly via BPgroup. Crucially, the Core Yamnaya fail all models of Fig. 2a-d (p<1e-8), and thus its origins must include a different blend of ancestry than the CHG-EHG-UNHG-Tutkaul ancestries involved in these models. As we will now see, this ancestry came from a third cline formed between the Caucasus Neolithic populations and those of the Lower Volga. |
|
|
|
Post by Admin on May 8, 2024 7:23:31 GMT
(3) Caucasus-Lower Volga Cline (CLV)
The Yamnaya are on the edge of the Dnipro cline, having less UNHG/GK2-related ancestry than other cline populations; thus, they cannot be modeled in terms of them alone (Fig. 1), but must have possessed more of a second source of ancestry. We found that the only consistently fitting (p=0.67) two-way model for the Core Yamnaya involved 73.7±3.4% of the SShi subset of the Serednii Stih population and 26.3±3.4% from a population represented by a sample of two individuals from Eneolithic burial sites at Sukhaya Termista I (I28682) and Ulan IV (I28683), dated 4152-3637 BCE near the village of Remontnoye, north of the Manych Depression on the watershed between the Lower Don and Caspian. The Remontnoye population is on neither the Volga nor Dnipro clines and is neither genetically close (Fig. 1) nor forms a clade (p<1e-10) to any other single sampled population. We determined that it had at least two sources: a southern one from the Caucasus—either descendants of the Aknashen Neolithic in Armenia6, or ancestors of people of the Bronze Age Maikop5 culture—and a northern one from a population from the low-EHG end of the Volga Cline such as the BPgroup. The Caucasus component is about half when using either Aknashen (44.6±2.7%; p=0.66) or Maikop (48.1±2.9%; p=0.44) as the proxy for the southern source. We also observed that the main cluster of Maikop individuals, including those buried in kurgans in Klady and Dlinnaya-Polyana, can be modeled as having 86.2±2.9% (p=0.50) Aknashen ancestry. Thus, there exists a Caucasus-Lower Volga (CLV) cline: Aknashen-Maikop-Remontnoye-Berezhnovka. These four populations are arrayed in order of decreasing Caucasus Neolithic component, concordant with their south-to-north geographical location. However, there were also populations of the CLV cline that bucked this latitudinal trend, such as the people of the North Caucasus at Progress-2 and Vonyuchka-1 that, unlike their Maikop neighbors, had little Caucasus Neolithic ancestry and were most like the people of Berezhnovka-1 in the Lower Volga. These violations of the genetic-geographic pattern prove long-range connectivity across the CLV area; they also caution us not to easily interpret genetic position along the CLV cline as predictive of position within the CLV geography.
What was the proximal source for the southern ancestry of the intermediate populations of the CLV cline? Aknashen makes a poor choice, as it is both geographically remote from the steppe and earlier by two millennia (5985-5836 BCE) than Remontnoye. Neither is Maikop a good proximal source; it is geographically closer, but postdates (3932-2934 BCE) Remontnoye.
Settlements at Meshoko and Svobodnoe, dated 4466-3810 BCE,42 provide a temporally, geographically, and archaeologically plausible source, as they exhibit exchanges of exotic stone, copper, and stone mace heads with Volga Cline sites, setting the context for the expansion of Aknashen-like ancestry northward and Berezhnovka-like ancestry southward. These settlements are temporally earlier than Maikop and later than two individuals from Eneolithic Unakozovskaya (ref.5 4607-4450 BCE, and this study) in the North Caucasus; however, unlike Aknashen and Maikop, the Unakozovskaya population is not a good genetic source for Remontnoye, as the model BPgroup+Unakozovskaya fails (p<0.001) by overestimating (Z=3.8) shared genetic drift with the CHG. The Unakozovskaya was not exactly the same genetically as the Maikop who succeeded them (p=2e-11) but were genetically similar (Fig. 1) and can be modeled as 95.3±6.3% Maikop and 4.7±6.3% CHG (p=0.46). Thus, there were three elements of ancestry in the North Caucasus in the Eneolithic: (i) Aknashen-related ancestry was dominant, representing the spread of the Neolithic from the south across the Caucasus mountains; (ii) there was some variation in CHG-related ancestry as suggested by the Maikop-Unakozovskaya contrast; and (iii) there was also a small component of northern Lower Volga ancestry of about one seventh in the Maikop on average. Thus, in the north Caucasus there lived, side by side, both “high steppe” ancestry people genetically close to the Lower Volga Berezhnovka population (individuals at Progress-2 and Vonyuchka-1), as well as “low steppe” ancestry people in which the Lower Volga ancestry had been diluted by the greater contribution of the (Aknashen-related) Caucasus Neolithic.
The Remontnoye and Berezhnovka people, like the Maikop people, were buried in kurgans. Thus, the kurgan burial rite was widespread 5000-3000 BCE among people of diverse ancestry from both the edges and middle of the CLV Cline, suggesting that—regardless of its ultimate origin and whether it was culturally adopted or spread by migration—it was common among the people of the CLV region.22 In contrast, a distinctive position of the body on the back with knees raised and the floor of the burial pit covered with red ochre was shared by all the steppe groups including Serednii Stih, groups on the Volga Cline, and Remontnoye, while the Maikop burial position was contracted on one side. Thus, some funeral customs united Maikop with the steppes and others separated them.
The discovery of the CLV Cline suggests a solution to the question of the origin of the Dnipro Cline and thus the genetic origins of the Yamnaya. Most of their ancestors were people of the CLV Cline, similar to the sampled Remontnoye individuals. These CLV ancestors were drawn into the Dnipro-Don region and mixed with local groups to form Serednii Stih people and eventually the Yamnaya. It must be emphasized that the CLV and Dnipro-Don sources need not have been identical to the sampled Remontnoye and SShi populations or have lived close to the sampling locations of these two populations. The Dnipro Cline can be fit (Fig. 2e) by a 3-way model in which the GK2 admixed with groups of mixed Aknashen and Berezhnovka ancestry. We note the aforementioned caveat that either of GK2 or UNHG could be contributing to the Dnipro Cline, but chose GK2 in Fig. 2e as this model has a higher p-value (p=0.93) for the Core Yamnaya than the alternative with UNHG as the source (p=0.04); however, we do not take this as evidence that the GK2 population was a better source than the UNHG as we have far better data for UNHG (n=35 individuals) than GK2 (n=1), which provides more power to detect slight but qualitatively unimportant oversimplifications in models. Note also, that GK2 is itself ∼2/3 UNHG in ancestry, and that the proportion of either GK2 (22.5±1.8%) or UNHG (17.7±1.3%) is similar, and about one fifth. A full exploration of 3-way models (Supplementary Information section 2) reveals that the Yamnaya could have been formed from diverse (but similar) distal sources which include populations of (i) Neolithic or Chalcolithic age from Armenia6,9 and Azerbaijan43,44 representing the “Caucasus Neolithic”, (ii) GK2, UNHG, or Serednii Stih representing the Dnipro-Don area, and (iii) BPgroup or PVgroup representing the Lower Volga-north Caucasus Eneolithic. What is invariant among the class of 2- and 3-way models for the Core Yamnaya is that they posit their descent from people of the CLV Cline (the remaining four fifths of their ancestry) who admixed with Dnipro-Don people of substantial UNHG ancestry.
Our results show that movement of people and culture we document as having occurred along the CLV Cline was the vector by which Caucasus-derived ancestry like that present in the Aknashen Neolithic population flowed into the steppe and into the ancestors of the Yamnaya45. Crucially, the successful Remontnoye+SShi model predicts shared genetic drift with the Anatolian Neolithic outgroup well (Z=-0.8). CLV cline populations can account for both Siberian-related (via the Lower Volga component) and Anatolian Neolithic-related (via the Caucasus Neolithic component) affinities of the Yamnaya. Archaeological evidence shows that Balkan copper was traded during the late 5th millennium BCE across the steppes to North Caucasus farmer sites (Svobodnoe) and to the Volga (Khvalynsk), while Neolithic pots like those from Svobodnoe appeared in Dnipro-Don steppe sites connected with the Seredni Stih culture (Novodanilovka), documenting an active period of cultural exchange that was the context for the movement of groups of mixed BPgroup/Aknashen-related ancestry into the Dnipro-Don steppes.
|
|
