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Post by Admin on Mar 26, 2021 22:54:32 GMT
The Basques are a unique population in Western Europe; their language is not related to any Indo-European language. Furthermore, genetically speaking, they have been considered to have distinct features. However, until now there was no conclusive study to explain the origin of their singularity. Now, an international research team led by UPF has confirmed that the Basques' genetic uniqueness is the result of genetic continuity since the Iron Age, characterized by periods of isolation and scarce gene flow, and not its external origin in respect to other Iberian populations. The study, led by David Comas, principal investigator at UPF and at the Institute of Evolutionary Biology (IBE: CSIC-UPF), has involved the most comprehensive geographic sampling to date of the Basque population, with over 600,000 genetic markers throughout the genome for each individual. The result of the multidisciplinary study, which involved a team of linguists and geneticists, reveals in the journal Current Biology that the cultural barrier of the language promoted the isolation of the Basque population from subsequent population contacts, such as the influence of the Roman empire or the Islamic occupation of the peninsula, and even acted as an internal barrier in some cases due to the use of dialects. "Sampling included microregions within the Basque Country and also the surrounding areas. Thus, we obtained samples from a geographic region where Euskera has always been spoken, others where it has been spoken historically but has been lost, and regions where it has never been spoken," points out André Flores-Bello, first author of the article. He also stresses that "our study is clear proof of the importance of the interaction between different disciplines such as linguistics, genetics and archaeological evidence when it comes to reconstructing our history." The work compares the Basque people with other contemporary European populations and with data from ancient DNA. The results show that the Basques' genetic makeup is similar to other populations of Western Europe but with slight differences. These differences are due to a scarce gene flow as of the Iron Age, i.e., less mixing has occurred with other populations. David Comas, full professor of Biological Anthropology at the UPF Department of Experimental and Health Sciences (DCEXS), details that "for example, we find no influences from North Africa which are appreciated in most populations of the Iberian Peninsula, and neither do we find traces of other migrations such as the Romans." The question of how genetically different the Basques are from one another has also been broached. In the Basque Country, they have found that the geographically closest settlements are genetically more similar. This correlation between genetics and geography is common, because neighboring settlements have a shared history. What is unique here is that there is a great deal of compartmentalization within an extremely small geographic region, which is not common in populations of this size. This genetic heterogeneity matches the Basque dialects. "To date it was thought that they were formed from the Middle Ages but we postulate that they may have arisen much earlier and are therefore related to the genetic structure," explains David Comas, head of the Human Genome Diversity research group of the IBE. With the new methods available, we are increasingly able to reconstruct history on a smaller scale. "The large number of markers and samples we employ together with sophisticated computation enable us to solve issues that we could not broach until now and pave the way towards knowledge of the more local, more recent history of our species," Comas concludes. Explore further The genetic imprint of the Palaeolithic has been detected in North African populations More information: André Flores-Bello et al, Genetic origins, singularity, and heterogeneity of Basques, Current Biology (2021). DOI: 10.1016/j.cub.2021.03.010
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Post by Admin on Mar 26, 2021 23:19:11 GMT
Genetic origins, singularity, and heterogeneity of Basques André Flores-Bello Frédéric Bauduer Jasone Salaberria Jaume Bertranpetit Lluis Quintana-Murci David Comas 6 Published:March 25, 2021 DOI:https://doi.org/10.1016/j.cub.2021.03.010 Summary Basques have historically lived along the Western Pyrenees, in the Franco-Cantabrian region, straddling the current Spanish and French territories. Over the last decades, they have been the focus of intense research due to their singular cultural and biological traits that, with high controversy, placed them as a heterogeneous, isolated, and unique population. Their non-Indo-European language, Euskara, is thought to be a major factor shaping the genetic landscape of the Basques. Yet there is still a lively debate about their history and assumed singularity due to the limitations of previous studies. Here, we analyze genome-wide data of Basque and surrounding groups that do not speak Euskara at a micro-geographical level. A total of ∼629,000 genome-wide variants were analyzed in 1,970 modern and ancient samples, including 190 new individuals from 18 sampling locations in the Basque area. For the first time, local- and wide-scale analyses from genome-wide data have been performed covering the whole Franco-Cantabrian region, combining allele frequency and haplotype-based methods. Our results show a clear differentiation of Basques from the surrounding populations, with the non-Euskara-speaking Franco-Cantabrians located in an intermediate position. Moreover, a sharp genetic heterogeneity within Basques is observed with significant correlation with geography. Finally, the detected Basque differentiation cannot be attributed to an external origin compared to other Iberian and surrounding populations. Instead, we show that such differentiation results from genetic continuity since the Iron Age, characterized by periods of isolation and lack of recent gene flow that might have been reinforced by the language barrier. Introduction The Franco-Cantabrian region, which includes the western part of the actual border of Spain and France through the Pyrenees, has drawn the attention of several disciplines due to its relevant role in European human history. This region was one of the most densely populated glacial refugia in Europe during the last glacial maximum (LGM), and it is related to pivotal archaeological discoveries, especially the oldest known European cave paintings.1 One of the most interesting features of the region is the presence of the Basques. They have been historically distributed along the western edge of the Pyrenees, spanning across the present Spanish and the French territories currently organized in seven provinces: Gipuzkoa; Bizkaia; Araba; and Nafarroa in the southern side of the Pyrenees and Zuberoa; Lapurdi; and Nafarroa Beherea located in the northern side. Basques have presumably stood out due to their historical, anthropological, and biological traits that define their singularity and isolation within the European context. A remarkable feature is Euskara, with its five main dialects (Figures 1 and S1; Table 1), which is a non-Indo-European language isolate with no close relationship to any other extant language.2,3 Beyond its current distribution, Euskara was historically spoken in the seven present provinces, before its geographic regression due to the pressures of Romance languages.4 Moreover, an archaic Euskara-related language is suggested to have been spoken in a much wider area in earlier periods. This area would include the neighboring Northern Spanish areas and the southern half of Aquitaine in France (Figure S1).5 Whereas Euskara has been pointed as a possible cultural barrier between Basques and neighboring populations, its dialects might have also acted as an internal barrier.6 They show reduced interintelligibility, and a standard language (batua in Euskara) was not established until 1968 and was widely used only since the 1980s. Figure 1 Geographic distribution of the Franco-Cantabrian region and the areas included in the study Our dataset includes a total of 190 samples from 18 areas in the present-day Spanish and French territories of the Franco-Cantabrian region. Both Euskara and surrounding Romance speaking groups were considered. All four grandparents of the individuals were born in the same geographical region of the collected sample. n represents the number of individuals genotyped for each region. See also Figures 1 and S1.
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Post by Admin on Mar 27, 2021 1:22:09 GMT
Although numerous studies have focused on the genetics of Basques, a lively debate on their population history is still ongoing (see, for instance, Laayouni et al.7 and Rodríguez-Ezpeleta et al.8). Such an interest in the genetics of Basques started with the remarkable observation of a high frequency of the Rh-negative blood group,9 a genetic variant associated with the hemolytic disease of the newborn, which was confirmed in following studies.10 Subsequent studies using more genetic markers revealed that Basques were particularly differentiated within the European genetic context.11,12 These results, together with archaeological, cultural, and linguistic data, were interpreted as Basques descending from an ancient population that remained isolated in the region.13 However, other studies have not provided evidence of a genetic distinctiveness for the Basque population, suggesting genetic homogeneity through Europe.14
The origins of Basques have also been controversial. Some studies based on uniparentally inherited markers have proposed that Basques represent isolated Pre-Neolithic European groups that stayed in the region after the resettlement of Europe from the glacial refugia in the post-LGM periods.15,16 Conversely, other studies have shown the influence of the Neolithic migrations in the Basque area, refuting the Paleolithic genetic continuity.17 Exhaustive analysis of uniparental genomes showed a continuity since Pre-Neolithic times and a pre-Roman genetic structure in Basques.6,18 In support of this, ancient DNA data have suggested that Basques can actually be explained as a common Iberian Iron Age population, with an important genetic influence of the post-Neolithic Steppe pastoralists ancestries but lacking admixture from subsequent incoming populations, such as Romans or North Africans.19
The controversies about the Basques have not only been focused on their distinctiveness and their origins but also on their internal genetic heterogeneity. Genome-wide data in Basque groups have shown contradictory results, with some studies suggesting that French Basques are markedly different from Spanish Basques, the latter being similar to other Iberian populations;7 whereas other data were interpreted as showing internal homogeneity within Basques and marked genetic differentiation from non-Basque groups.8
These remarkable contradictory results might be explained by a limited methodology and resolution. The low number of samples used in these analyses to represent the Basque groups and their neighboring areas has supposed the major limiting factor. Furthermore, they have been based on the allele frequencies of classical genetic markers, the phylogeny of uniparental genomes, or a reduced number of sample and markers.13 To overcome the limitations in the previous studies, we adopt a robust genome-wide study design that enables us to unravel the controversial population history of Basques, including their uniqueness, their origins, and their genetic structure. The unique and exhaustive dataset of the whole Franco-Cantabrian region presented here (Figures 1 and S1; Table 1) limits any possible sampling biases affecting the previous studies and affords an exhaustive analysis at micro-geographical and wide-scale level. Moreover, the ethno-linguistic information considered in our sampling allowed us to interpret the results beyond the genetic data, considering how cultural factors could be involved in shaping the genetics of the Basques and surrounding populations. Finally, we leverage the more-precise haplotype-based methods to uncover fine-grained genetic structure and admixture patterns.20,21
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Post by Admin on Mar 27, 2021 3:05:24 GMT
Basques display marked differentiation in the European/Mediterranean landscape We first studied Basques in a wide-scale context to assess their genetic variability within a large and diverse population panel, which includes a complete dataset of West Eurasia and North African samples. In a principal-component analysis (PCA), the Basque samples fall in the opposite edge of the North African samples and in the periphery of Europe, similarly to Sardinians, with the Peri-Basque groups (surrounding traditionally Gascon- and Spanish-speaking areas; see sample collection in STAR Methods) being in an intermediate position (Figure 2A). Using admixture analyses, considering the global genetic ancestry components of these populations (Figure 2B), a differential genetic pattern is observed in Basques. In K = 6, Basques present mainly two components: a major component (green), which is also present in European samples and is found at low frequencies in the Middle East/Caucasus and North Africa, plus a minor component (pink) found at high frequencies in Central/Eastern Europe. The other components found in the rest of European groups are not present in Basques (frequencies <1%). The Peri-Basque samples show a similar pattern to Basques but with low frequencies of other external components absent in Basques. From K = 7 onward, a new specific component appears, maximized in Basques and with frequencies over 50% in Peri-Basques. This component is also observed in Spanish and French samples, although it is virtually absent in the other external European samples. Figure 2 Contextualizing the Franco-Cantabrian region Using the haplotype-based analyses implemented in fineSTRUCTURE, we detected marked levels of differentiation in Basques (Figures 3 and S2; Table S1). First, the Basque groups cluster together within the large European branch but in a differentiated external cluster (Figures 3A and S2). This result points to low haplotype sharing between this cluster and the rest of European groups, showing a clear internal and specific genetic profile of Basques. Second, the Peri-Basque groups also exhibit a differentiation from the other external populations, clustering internally with Europeans but forming a specific branch with the exception of the Cantabrian samples (gCAN), which cluster with Spanish samples (Figures 3A and S2). To discard putative artifacts due to the overrepresentation of Franco-Cantabrian samples in the fineSTRUCTURE analysis, we performed a random sampling of the Franco-Cantabrian region (50 samples, including Basques and Peri-Basques) and obtained similar results (data not shown). Furthermore, the ancestry profile calculated in the non-negative least squares (NNLS) analysis mirrored the results above (Figure 3B). Basques share haplotypes exclusively with the internal groups in the Franco-Cantabrian region. Peri-Basques mainly share haplotypes internally with the groups in the region but also with the non-Franco-Cantabrian Spanish and French groups, acting as a buffer zone between Basques and the surrounding external populations. The intermediate ancestry profile observed in Peri-Basques suggests gene flow between the Franco-Cantabrian region and the external groups. Therefore, potential admixture events were tested in Peri-Basques by using GLOBETROTTER, considering Basques and all the external clusters inferred by fineSTRUCTURE as surrogates (Figures S2D–S2F). Single admixture events involving two sources were detected for all Peri-Basque targets, with close dates between the 11th and 16th centuries. Similar sources were described in each target cluster: a major source represented by mainly Basque and Spanish ancestries and a minor source that is predominantly represented by Spanish ancestry. Moreover, the confidence intervals for the dates estimated from bootstrapping resulted in overlapped and quite large ranges in each Peri-Basque target, especially in Bigorre (gBIG) (Figures S2E and S2F). This might evoke a single but continuous pulse of admixture in the Peri-Basques and a general large-scale demographic event that affected the area in recent historical times, between the 11th and 16th centuries. Figure 3 Haplotype-based analyses To explore further the genetic differentiation of Basques, we performed an analysis of runs of homozygosity (ROHs). Basques show the overall highest total number (NROH) and total length (SROH) of ROHs, even higher than Sardinians, which are reported to carry long ROHs22 and show ROH values slightly above the European average,23 and followed by the Peri-Basque groups (Figures 3C and S3A). In the intermediate ROH categories, the total proportion of samples represented in the external populations is very small (Figure S3A). This shows that these categories are more common in the isolated groups, Basques and Sardinians, as well as in the Peri-Basques, although in the external groups, the values observed could be more related to cryptically inbred outliers.24 These results are in agreement with the exploration of the proportion of identity-by-descent sharing between samples (PI_HAT) within the groups (Figure S3B). Moreover, the estimation of the effective population size (Ne) over time showed Basques with low and stable values, whereas external groups (i.e., Spanish and French) show a dramatic increase around one thousand generations ago (Figure S3C). These results suggest a pattern of isolation together with inbreeding in Basques and to a lower extent in Peri-Basques. Such patterns of isolation, which by all other evidence is much more recent (see Discussion), seems to have been deep enough to erase the traces of an apparent Ne Paleolithic growth in the surrounding populations.
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Post by Admin on Mar 27, 2021 4:52:31 GMT
Post-Iron Age demographic processes explain the genetic uniqueness of Basques Then, analyses including ancient samples were performed to throw light on the origin of the genetic singularity of Basques. The PCA projection of ancient samples shows Basques closer to Pre-Neolithic hunter-gatherers and European Neolithic farmers but also to some post-Neolithic Steppe herders associated to the Pontic-Caspian Steppe Yamnaya ancestry (Figure S4A). ADMIXTURE analysis (K = 4; lowest cross-validation error; Figure S4B) show Basques and Peri-Basques with the lowest proportions of Levant- and Iran-related Neolithic components, together with a slightly higher proportion of the Anatolian/European farmer component compared to other European populations. When testing for the shared drift with ancient samples, outgroup f3-statistics show high shared drift between Basques and the three major ancient components in Europe (i.e., Paleolithic hunter-gatherers, Neolithic farmers, and post-Neolithic Steppe herders related to the Yamnaya ancestry; Figure S4C). We then modeled Franco-Cantabrian groups and other European populations with these ancient samples by using qpGraph (Figure S4D). The model fit each tested European population, with Z scores close to 0 for all the 100 permutations performed. The inferred admixture proportions for the three ancient components do not show differences of Basques compared to the general European context (Figure S4E), following the Northern-Southern European expected cline of these ancient components.25 Moreover, no internal differences regarding the proportions of these ancient components were observed when modeling the Franco-Cantabrian groups individually (Figure S4F). This suggests that the genetic singularity of Basques might rely on demographic processes after the Iron Age, such as recent historical influences in Roman and Islamic periods. Therefore, qpAdm analysis was performed to formally test plausible post-Iron Age admixture models that might explain the singularity of Basques. This analysis shows that Basques can be mostly explained with the Iron Age samples from the Iberian Peninsula,19 with very limited influence of Roman Empire samples26 in some groups next to Peri-Basques (Figure 4; Table S2). These Roman-related proportions increase the farther the target populations are from the Franco-Cantabrian region. Moreover, no significant results were observed for any model considering North African samples27 in the region (Figure 4; Table S2). Overall, these results suggest that Basques might have received limited gene flow during recent historical events in the Iberian Peninsula. Figure 4 Modeling potential post-Iron Age gene flow in the Iberian Peninsula
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