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Post by Admin on Mar 27, 2021 20:07:03 GMT
Franco-Cantabrians show a heterogeneous genetic landscape correlated to geography Because one of the major controversies regarding Basques is their internal genetic heterogeneity, we focused our analyses on the Franco-Cantabrian region to explore the internal genetic diversity in the region. A first PC separates all Franco-Cantabrian groups through a genetic cline, with all Basques in one extreme, the Spanish and French non-Franco-Cantabrians in the opposite one, and the Peri-Basques in an intermediate position (Figure 5A). The second PC, in turn, separates the regions from the western and eastern areas of the Franco-Cantabrian region. The PCA shows a remarkable micro-geographical genetic structure and clustering of the Basque groups. To obtain an external reference of similar size and sampling density at a micro-geographical scale, such as the present study, the Catalan samples from Biagini et al.28 were compared to our dataset. The PCA of Catalans does not show any geographical structure comparable to that of Basques and Peri-Basques (Figure S5), which may imply that the clustering observed in Basques is specific to them and unrelated to the sample strategy. To quantify and compare the genetic differentiation among the Franco-Cantabrian and Catalan groups, FST distances for each pairwise combination were estimated and shown in a multidimensional scaling (MDS) plot (Figure S6). Again, Franco-Cantabrians show a clear internal differentiation with distances in a range of 10−2, whereas Catalans showed no evidence of genetic structure or extreme internal differentiation with distances in the range of 10−3. Moreover, heterogeneity was tested within the region by performing analyses of molecular variance (AMOVAs) at different strata in the geography. Though the explained genetic variance was small, all the results were statistically significant, pointing to an internal differentiation of the region and especially in the Basque groups (Figure S7). In fact, the same analysis in Catalonia shows lower explained variance in all comparisons (Figure S7D). Figure 5 Population stratification of the Franco-Cantabrian region The analysis of genetic components performed in the region with ADMIXTURE mirrors the results described above (Figure 5B). At K = 2 (best K with the lowest cross-validation error), Basques present a main component (green) that is also present at substantial proportions in the Peri-Basque groups and marginally found in the external samples. At K = 3 and K = 4, internal different components appear within Basques. In K = 3, the Basque-related component splits in two specific components: a western component (blue) and an eastern component (green). These components are barely presented in the non-Franco-Cantabrian samples. Finally, at K = 4, another component arises, maximized in Araba and the surrounding groups (pink). Thus, these four components could be summarized in non-Franco-Cantabrian (orange), eastern-related Basque (green), central-related Basque (blue), and western-related Basque (pink) components. The distribution of these components among the samples evidences the correlation between genetics and geography in the region. To formally test for this correlation, we performed an isolation by distance (IBD) analysis. A Mantel test was applied between the FST values and the geographic distances, resulting in a positive and clear statistically significant result (R2 = 0.242; p = 0.0163; Figure S5B). Then, the spatially explicit statistical method, estimated effective migration surfaces (EEMS), showed a well-defined internal pattern of barriers (Figure S5A), both between the Basque and Peri-Basque area as well as within them. In fact, the pattern of the corridors with higher migration rate mirrors the observed relationships in the ADMIXTURE analysis and the PCA, between groups with overlapping standard deviations (Figures 5 and S5C). The same analyses were performed for the Catalan samples, and despite being a geographical region of similar size, the results show a non-significant and negative trend for the Mantel test (R2 = −0.151; p = 0.749) and the absence of barriers in the EEMS analysis (Figures S5A and S5B). Figure 6 Haplotype distribution and sharing within the Franco-Cantabrian region Finally, to refine the relationships between the populations within the area, we applied haplotype-based methods, and similar patterns of internal heterogeneity were observed (Figures 3 and 6; Table S1). Besides the differentiation of the Basque cluster in the fineSTRUCTURE dendrogram (Figures 3A, 3B, and S2), several internal clusters in the region can be defined mostly related to geography and language. On the one hand, three clusters are shown in the Basque branch (Figure 6A, right): one that encompasses the Central Basques plus an Eastern Basque and a Western Basque cluster. On the other hand, two clusters are shown in the Peri-Basque branch (Figure 6A, left): a Western and an Eastern Peri-Basque cluster, besides the Cantabrian samples (gCAN) that fall within the external Spanish cluster. Similar clusters are observed when performing the analysis reducing the dataset (Figures S2B and S2C). The differences found in Basques are also shown in the ancestry profiles calculated in the NNLS analysis (Figures 3B and 6B). Basque clusters are formed by exclusively Basque or Peri-Basque components, whereas Peri-Basques show also external ancestries. Focusing on Basques, the central group is defined exclusively by Basque ancestry, whereas Eastern and Western Basques present ∼25% of Peri-Basque ancestry. Despite some traces of Spanish and French ancestries in the Western Basque group, other external ancestries are absent in Basques, suggesting haplotype sharing within the region without external contributions.
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Post by Admin on Mar 27, 2021 22:14:42 GMT
Discussion Our results show a clear genetic distinctiveness of the Basques within the European landscape in all the analyses performed, with evidence of continuous inbreeding reflected in their small Ne values, the large number and length of ROHs, and PI_HAT values (Figures 3C and S3), which suggests a pattern of genetic isolation in Basques in their recent history. In contrast, Peri-Basques show a transition between the Basques and the external Spanish and French populations (Figures 3, 5, 6, and S6A), as an example of intermediate area between open and isolated populations.29 Indeed, Basques do not show evidence of recent admixture events with non-Franco-Cantabrian groups, whereas Peri-Basques show gene flow at least since Medieval times (Figures 3B, 6B, S2E, and S2F). The inferred admixture events in these groups, involving potential Franco-Cantabrian-related and Spanish-related sources, mainly dated back to the so-called period of the Reconquista and the immediate next centuries. This was a long period characterized by the conflicts between the Islamic troops and the Christian kingdoms to maintain their territories in the Iberian Peninsula, expanding from the alleged Battle of Covadonga in 718 until the end of the Iberian Islamic rule with the fall of the Nasrid Kingdom of Granada in 1492.30 It led to a complex political and administrative situation in the history of the Iberian Peninsula, so these results might be echoing the consequences of the recurrent reorganization of the territory during these centuries along the Franco-Cantabrian region and specially the Peri-Basque area.
Nevertheless, our analyses support the notion that the genetic uniqueness of Basques cannot be attributed to a different origin relative to other Iberian populations but instead to a reduced and irregular external gene flow since the Iron Age as suggested by Olalde et al.19 The observed clines of post-Iron Age gene flow in the region suggest that the specific genetic profile of Basques might be explained by the lack of recent gene flow received. Our analyses confirm that Basques were influenced by the major migration waves in Europe until the Iron Age, in a similar pattern as their surrounding populations. At that time, Basques experienced a process of isolation, characterized by an extremely low admixture with the posterior population movements that affected the Iberian Peninsula, such as the Romanization or the Islamic rule, as observed in the present genetic landscape (Figures 3B, 4, and S4; Table S2). This does not exclude plausible previous periods of isolation, as attested by the presence of short ROHs and small Ne values (Figure S3) that support signals of ancient inbreeding in the region, even higher than in Sardinia, which is suggested to be isolated after Neolithic times. Thus, the increase of the Ne observed only in the external groups about 1,000 generations ago might be potentially linked to the role of the Franco-Cantabrian region as glacial refugium during LGM periods and the subsequent expansion.31 Although our results support the genetic continuity from the Iron Age19 in most of the present-day Basques, those located in the periphery of the Basque core area show signals of contacts compatible with the Roman Empire presence in the Iberian Peninsula (Figure 4; Table S2). These results are in agreement with archaeological and historical records. An important presence of the Roman Empire has been reported in the whole Franco-Cantabrian region, but the scholars suggest a much higher impact in the peripheral areas of the southern side, specially Nafarroa and Araba.32 Otherwise, North African influence only fit the models where southern and northwestern Iberians are included (Figure 4; Table S2). This confirms the reduced gene flow between the eastern and northern areas of the Iberian Peninsula with the North African incomers during the Islamic rule, as already reported by using uniparental markers33 and more recently through genome-wide data and haplotype-based methods.34
Language might play a major role in the demographic processes of the populations, and in the present study, given the extraordinary traits of Euskara, the ethno-linguistic scenario of the region should be considered in the interpretation of the analyses performed. Our results are compatible with the Euskara as one of the main factors preventing major gene flow after the Iron Age and shaping the genetic panorama of the Basque region. The genetic continuity of Basques since the Iron Age also supports the hypothesis that the expansion of the Steppe ancestry did not completely erase Pre-Indo-European languages in Western Europe, as previously suggested in other studies.19 Before the arrival of the Romans to the Iberian Peninsula, the Euskara coexisted with other pre-Indo-European languages, such as Iberian. The contact with the Romans, and thus with Latin, was earlier and stronger in the Mediterranean watershed of the Iberian Peninsula followed by their expansion toward the Atlantic coast, with a later and lower impact in the Franco-Cantabrian area,35 as confirmed in our analyses (Figure 4; Table S2). Thus, it is expected that Latin had a deeper effect in the areas with stronger Roman rule, speeding the language replacement, whereas Euskara was scarcely affected. Once Latin was established in most of the Iberian Peninsula, Euskara might have acted as a cultural barrier to gene flow, leading to a genetic differentiation of the Basques and a low influence of the linguistic Romance substratum in Euskara.4,5
Together with a positive strong correlation with geography (Figure S5), our results confirm a clear internal heterogeneity in Basques and Peri-Basques, where East-West genetic clusters are evident along the Franco-Cantabrian region, showing a genetic cline from the core to the external areas with higher gene flow among the closest groups. This genetic substructure is more complex than the northern-southern orographic and administrative limits between the present-day Spanish and French territories, separated by the Pyrenees Mountains. Instead, haplotype-based methods enabled to accurately define a central Basque cluster plus Western and Eastern Basque and Peri-Basque genetic clusters (Figures 3B, 5, and 6), clarifying previous results that barely suggested this pattern in the Franco-Cantabrian region by using classical markers.36,37 Whereas the Eastern and the Central Basques do not show relevant gene flow with external sources, the groups from the Western Basque cluster present small levels of gene flow with them (Figures 3B, 4, 5, and 6). This genetic substructure reflects the historical and linguistic context between the Basques and the neighboring areas. Those from the central region are the most differentiated, due to the smaller influence from external sources along history regarding its farthest location.37,38 Moreover, the linguistic, political, and administrative situations in the central and the eastern areas have been quite stable along history.39 However, the western areas are characterized by a complex scenario, related to the reorganization of the administrative limits and the regression of Euskara due to the strong influence of surrounding Romance languages and mainly Spanish.32,39,40
Finally, the role of the Euskara dialects on the present-day Basque genetic substructure is more difficult to assess. Most linguist scholars agree on a western-eastern dialectal discontinuity with small distances among the closest dialects,41,42 resembling the genetic clusters observed in the present analysis. The most accepted hypothesis about their origin is that they emerged during the medieval period.4,42,43 Yet our results reveal a clearly defined genetic structure within Basques that might have been formed in earlier times. Indeed, a pre-Roman genetic substructure has been already suggested based on uniparental markers.6 Therefore, the diversification of the dialects and the genetic heterogeneity within the Basques might have in common their correlation to geography, and it might be worth to reconsider an earlier origin of the Euskara dialects in linguistic studies.
In this study, we disentangle long-standing controversies about the genetic uniqueness of Basques from a new perspective, providing finer and more-reliable conclusions that help to resolve the debate on the demographic history of Basques. This contributes to demystify the so often assumed genetic characteristics of Basques, even though little clear evidence was present to support their position as some sort of Proto-Europeans. Moreover, some new lines of evidence are presented to the archaeology and anthropology fields that can be further pursued. The genetic results presented here give support to the anthropological and chronological connections with the ancient remains, as well as the historical and linguistic relationships around the Euskara and its dialects. It is pivotal to emphasize the importance of a multidisciplinary approach when studying the evolution and demographic history of populations to contextualize the study, test hypotheses, and interpret the results. In this sense, it is crucial to encourage the integration and cooperative research among the different areas of knowledge with the aim of boosting complete, contrasted, and reliable studies.
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Post by Admin on Mar 28, 2021 4:50:31 GMT
DNA from ancient remains seems to have solved the puzzle of one of Europe's most enigmatic people: the Basques. The distinct language and genetic make-up of the Basque people in northern Spain and southern France has puzzled anthropologists for decades. One theory proposed that they were an unmixed pocket of indigenous hunters. Now, a study in PNAS journal suggests they descend from early farmers who mixed with local hunters before becoming isolated for millennia. The Basques have unique customs and a language - Euskera - that is unrelated to any other spoken in Europe, or indeed the world. Nestled in a mountainous corner of Atlantic Europe, they also show distinct genetic patterns to their neighbours in France and Spain. It seemed logical that they were representatives of an older layer of population settlement, but just how far back their roots went has been a topic of debate. Mattias Jakobsson from Uppsala University in Sweden analysed the genomes of eight Stone Age human skeletons from El Portalón in Atapuerca, northern Spain. These individuals lived between 3,500 and 5,500 years ago, after the transition to farming in southwest Europe. The results show that these early Iberian farmers are the closest ancestors to present-day Basques. Go west Comparisons with other ancient European farmers show that agriculture was brought to Iberia by the same migrant groups that introduced it to central and northern Europe. These pioneers expanded from a homeland in the Near East, sweeping across Europe about 7,000 years ago to usher in the period known as the Neolithic. Once the farmers settled down, they mixed with local hunter-gatherers - the descendants of people who lived in Europe during the last Ice Age. Indeed, the El Portalón individuals had more hunter-gatherer ancestry than pioneer farmers from Germany, Hungary and Spain who lived several thousand years earlier. The new study also goes some way to explaining some of the differences between the Basques and their neighbours in France and Spain. After the initial farmer-hunter mixture was set, the ancestors of the Basques became isolated from surrounding groups - perhaps due to a combination of geography and culture. "It's hard to speculate, but we've been working with Basque historians and it's clear from the historical record that this area was very difficult to conquer," Prof Jakobsson told BBC News. This means the Basque area was largely unaffected by subsequent migrations that shaped genetic patterns elsewhere in Europe. Migration and isolation One of these movements occurred in the Bronze Age, when pastoralists from the Steppe - on the eastern periphery of the continent - travelled west en masse. This migration probably spread Indo-European languages across Europe, affecting the central and northern parts of the continent to a greater extent than the south. While the genomes of French and Spanish individuals showed evidence of this eastern genetic input, those of Basques did not. Another migration served to further differentiate Basques from their Spanish neighbours. In AD 711, a Muslim army crossed from North Africa into Iberia, beginning an occupation that lasted more than 700 years. Again, while a small amount of North African and Sub-Saharan ancestry can be detected in the Spanish, it is largely absent from the Basques. Previous studies have shown that people native to the Italian island of Sardinia are most genetically similar to the pioneer farmers of central Europe. The Sardinians also became isolated after the agricultural transition, but they lack the additional hunter-gatherer ancestry that characterises the Basques. Paradoxically, while archaeology shows that Europe's earliest farmers hailed from the Near East, populations living in that region today do not particularly resemble them genetically. This is because genetic patterns in Turkey and the Middle East were re-shaped by migrations from surrounding areas after the Early Neolithic. The proportion of hunter-gatherer ancestry varies across Europe, peaking at about 30% in Estonians and Lithuanians, but no "pure" indigenous Europeans remain. They appear to have been assimilated by the Neolithic migrants, who probably had greater numbers.
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Post by Admin on Mar 29, 2021 2:55:20 GMT
Ancient genomes link early farmers from Atapuerca in Spain to modern-day Basques Torsten Günther, Cristina Valdiosera, Helena Malmström, Irene Ureña, Ricardo Rodriguez-Varela PNAS September 22, 2015 112 (38) 11917-11922; first published September 8, 2015; doi.org/10.1073/pnas.1509851112Significance The transition from a foraging subsistence strategy to a sedentary farming society is arguably the greatest innovation in human history. Some modern-day groups—specifically the Basques—have been argued to be a remnant population that connect back to the Paleolithic. We present, to our knowledge, the first genome-wide sequence data from eight individuals associated with archaeological remains from farming cultures in the El Portalón cave (Atapuerca, Spain). These individuals emerged from the same group of people as other Early European farmers, and they mixed with local hunter–gatherers on their way to Iberia. The El Portalón individuals showed the greatest genetic affinity to Basques, which suggests that Basques and their language may be linked with the spread of agriculture across Europe. Abstract The consequences of the Neolithic transition in Europe—one of the most important cultural changes in human prehistory—is a subject of great interest. However, its effect on prehistoric and modern-day people in Iberia, the westernmost frontier of the European continent, remains unresolved. We present, to our knowledge, the first genome-wide sequence data from eight human remains, dated to between 5,500 and 3,500 years before present, excavated in the El Portalón cave at Sierra de Atapuerca, Spain. We show that these individuals emerged from the same ancestral gene pool as early farmers in other parts of Europe, suggesting that migration was the dominant mode of transferring farming practices throughout western Eurasia. In contrast to central and northern early European farmers, the Chalcolithic El Portalón individuals additionally mixed with local southwestern hunter–gatherers. The proportion of hunter–gatherer-related admixture into early farmers also increased over the course of two millennia. The Chalcolithic El Portalón individuals showed greatest genetic affinity to modern-day Basques, who have long been considered linguistic and genetic isolates linked to the Mesolithic whereas all other European early farmers show greater genetic similarity to modern-day Sardinians. These genetic links suggest that Basques and their language may be linked with the spread of agriculture during the Neolithic. Furthermore, all modern-day Iberian groups except the Basques display distinct admixture with Caucasus/Central Asian and North African groups, possibly related to historical migration events. The El Portalón genomes uncover important pieces of the demographic history of Iberia and Europe and reveal how prehistoric groups relate to modern-day people. Fig. 1. Overview of samples. (A) Geographic locations of ancient individuals used in this study. The dataset includes individuals sequenced as part of this study (from El Portalón) as well as individuals from the literature (1, 2, 10, 12, 19). The map template is modified from www.primap.com. (B) Temporal and cultural context of the ancient individuals; individuals from a hunter–gatherer context are shown in italics. The symbols and colors denoting each individual are used consistently throughout this paper. (C) PCA of ancient individuals and modern-day individuals across Europe (1). Only those ancient samples with more than 20,000 transversion SNPs overlapping with the modern-day SNP data are plotted (see also SI Appendix, section S8 and Dataset S1). Colored areas show kernel densities of modern-day groups with more than eight individuals. The first practice of farming started ∼11,000 years before present (yBP) in the Near East, before spreading west and north across Europe and transforming the way of life from small, mobile hunter–gatherer (HG) groups to larger sedentary, agrarian societies. Genomic studies of Stone-Age human remains from northern and central Europe have shown that the Neolithic transition was driven by migration, followed by subsequent admixture with HG groups (1⇓–3). More than 3,000 km away from the Near Eastern origin of farming practices, the Iberian Peninsula represents the western geographic extreme of the Neolithic transition, which reached the Spanish Mediterranean coast ∼7,650–7,550 yBP, the Iberian interior 7,350–7,250 yBP (4), and the Northern Cantabrian coast around 7,300–6,800 yBP (5). Investigations of mitochondrial DNA (mtDNA) haplogroup variation from Neolithic and Chalcolithic Iberian samples have been inconclusive, with some suggesting modern-day Near Eastern affinities (6) and others suggesting complex admixture between hunter–gatherers and farmers (7). The processes and consequences of the Neolithic transition in the Iberian Peninsula are, thus, contentious. The relationship of early Iberian farmers to their Central European counterparts and HG groups in Iberia, as well as their contribution to the present-day genomic variation in Iberia, is crucial to understanding the demographic history of the region. Of particular interest is the connection of Basques to different ancient groups in Iberia, to shed light on their long-debated origins (6⇓⇓⇓⇓⇓⇓–13). We investigated the remains of eight individuals from the Chalcolithic and Bronze Age periods excavated from the cave of the El Portalón de Cueva Mayor, of the Sierra de Atapuerca (Fig. 1A and SI Appendix, Fig. S1)—a site with a remarkably rich archaeological record, with human occupation from the Paleolithic to the historical period (14) (SI Appendix, section S1). The human remains were associated with offerings, such as domestic animals and pottery vessels corresponding to the pre-Bell Beaker culture, and were directly radiocarbon-dated to between ∼5,500 (Chalcolithic) and ∼3,500 cal yBP (Bronze Age) (SI Appendix, Table S1 and Fig. S2). Seven of the burials contained fragmentary human remains whereas one burial was a near-complete skeleton of a male child showing signs of chronic malnutrition (15) (SI Appendix, section S1).
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Post by Admin on Mar 29, 2021 5:16:26 GMT
Results and Discussion We generated genome-wide sequence data from all eight El Portalón individuals (Table 1 and SI Appendix, Table S2) ranging from 0.01× to 4.08×, with four individuals with a depth of coverage at >0.4×. All samples displayed features characteristic of ancient DNA (16): (i) The DNA was fragmented and (ii) cytosine deamination was consistently higher at fragment termini (SI Appendix, section S3). Mitochondrial (mt) DNA-based contamination estimates were <1.5% for all four >0.4× coverage individuals (Table 1). The eight individuals, genetically inferred to be four males and four females (Table 1), carried mtDNA haplogroups associated with early farmers of Europe (e.g., haplogroups K, J, and X) (10, 17), with hunter–gatherers (e.g., haplogroup U5) (18), or with both groups (e.g., haplogroup H) (17) (SI Appendix, section S4 and Dataset S2). Two Y-haplogroups were also determined (haplogroups H2 and I2a2a), but, given the small sample size, it is difficult to draw any solid conclusion (SI Appendix, section S5). The mtDNA- and Y-haplogroup composition of the El Portalón individuals is consistent with admixture between the incoming farmers and local HG groups, with contributions from both sexes (SI Appendix, sections S4 and S5). In addition, we inferred phenotype information from known genotype–phenotype associations, and we note that the phenotypes of the El Portalón individuals are in line with previous studies (SI Appendix, section S6) (1, 2, 10). The El Portalón mtDNA-haplogroup composition differs from a Chalcolithic sample of the El Mirador cave, also located in the Atapuerca cave system (6), which can be a consequence of somewhat limited sample sizes for this comparison. However, if this observation is supported by more extensive data from the two caves, it suggests stratification at a small geographic scale and complex population composition among early Iberian farmers, although detailed interpretations are limited for these single-locus comparisons.
Table 1. Sequence information for the eight ancient individuals in this study
Individual Genome coverage mt coverage mt haplogroup Y haplogroup Biological sex Age (C14 cal yBP) Contamination estimate (95% CI) (41) ATP2 4.08 341.2 U5b3 H2 XY 4,849–4,628 0.1 (0–0.3) ATP3 0.03 14.4 K1a2b — XY 5,466–5,312 0 (0–7.2) ATP7 0.04 16.8 J1c1b1 — XX 5,295–4,894 9.2 (3.8–14.6) ATP9 0.41 35.4 U5b1b — XX 3,700–3,568 1.4 (0–3.3) ATP16 1.11 68.7 X2c — XX 5,211–4,866 1.4 (0.2–2.7) ATP17 0.03 3.6 H3 — XY 4,957–4,821 — ATP20 0.01 3.6 U5a1c — XX 4,239–4,000 — ATP12-1420 1.21 230.8 H3c I2a2a XY 4,960–4,829 0.5 (0–1.1) CI, confidence interval; —, not determined.
Principal component analysis (PCA) of the El Portalón farmers together with relevant published Chalcolithic, Neolithic, and Mesolithic European genome-wide sequence data (1, 2, 10, 12, 19) (Fig. 1 A and B) and a large set of modern-day Europeans (1) (Fig. 1C and SI Appendix, section S7) revealed a distinct separation of hunter–gatherers and early farmers irrespective of their geographic location (Fig. 1C). The closest extant populations to hunter–gatherers from Iberia, Scandinavia, and Central Europe are Northern Europeans; however, the hunter–gatherers fell outside the range of modern-day European genetic variation (Fig. 1C). In contrast, early farmers from Iberia, Scandinavia, and Central Europe grouped with modern-day Southern Europeans, consistent with outgroup f3 statistics (SI Appendix, Fig. S8). These results demonstrate that early European farmers, including those in Iberia, emerged from a common group of people (SI Appendix, section S11 and Dataset S3). This observation indicates that farming was brought to Iberia via migration, similar to the process in Scandinavia (2, 3) and Central Europe (1).
We fitted an admixture graph model for ancient individuals with the greatest genome coverage (20) (using the Denisovan genome as an outgroup and ascertaining genetic variants in Yorubans) (21) (SI Appendix, section S9), which confirmed the known connection between Scandinavian hunter–gatherers (Motala12) and a Paleolithic Siberian (MA1) (1, 2). Chalcolithic farmers (Iberian ATP2 and the Tyrolean Iceman) and Scandinavian Neolithic farmers (Gok2) traced a substantial amount of their genetic ancestry to European HG groups, in contrast to the earliest farmers of Central Europe (NE1 and Stuttgart) (Fig. 2A), and this increase in HG admixture across Europe was significant as a function of time (Fig. 2B) (R2 = 0.69, P = 0.001). The best fitting source for the HG admixture into the El Portalón individuals was the common ancestor of the nearby La Braña Mesolithic individual and a Mesolithic individual from Luxembourg (Loschbour) (Fig. 2A) whereas contemporary farmers from Central Europe (Iceman) and Scandinavia received their (best-fit) HG admixture from Scandinavian hunter–gatherers (Fig. 2A). These inferred admixture events demonstrate that different farmer populations had different HG groups as the best proxy for the source of admixture (D-tests showed similar results of multiple admixture events in different parts of Europe) (SI Appendix, section S11 and Dataset S4). These analyses showed that, whereas early farmers—who were likely more numerous than the hunter–gatherers (SI Appendix, Fig. S9)—spread across Europe, they assimilated HG populations, a process that continued locally for several millennia (2, 17).
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