Post by Admin on Aug 5, 2023 17:05:09 GMT
Discussion
There are only a few reports on the genetic makeup of the populations inhabiting East-Central Europe in the first millennium CE. The majority of them are based on mitochondrial DNA [37, 38, 72, 73]. Whole-genome analyses of individuals living in this region in the IA and the early MA are scarce [1, 66, 74] and, for the region of contemporary Poland, very limited.
Presented here whole-genome analyses of the individuals from the IA group together with our previous observations [37, 38] and numerous archaeological findings consistently support earlier hypotheses assuming that the Wielbark culture was associated with immigrants from Northern Europe who spread within the region of present-day Poland and mixed with the autochthonous IA population. Most of the data collected for the IA and MA groups are in line with the hypothesis assuming genetic continuity from the IA to the early MA in East-Central Europe and suggest that the migration from east in the sixth CE was not necessary to form the genetic pool of the MA group. However, based on these data, one cannot exclude additional migrations from the Eastern Europe, either during the Migration Period or later.
Most of the collected data including f4 statistics and qpAdm models showed that the genetic makeup of the Wielbark culture-associated people was related with the ancient northern European populations including Denmark_IA and Norway_IA. This result is consistent with our earlier observation of matrilineal connections between IA_Kowalewko and the IA population from Jutland Peninsula [37]. Here, we further showed that the Wielbark culture-associated IA populations could not be derived from the preceding the EBA_Unetice populations alone. It means that the migration from northern Europe was necessary to the formation of the IA group genetic pool.
In addition, f4 statistics and qpAdm models revealed that the MA population could not be formed by people living earlier in the same region and approximated by Poland_EBA_Unetice, Czech_EBA_Unetice or Lithuania_BA. Putative northern ancestors of the Wielbark culture-associated people (approximated by Denmark_IA or Norway_IA) also could not explain the genetic makeup of all MA_X populations. The valid two-way models for all MA_X populations were obtained only for Poland_EBA_Unetice or Czech_EBA_Unetice and IA_Maslomecz. The latter population represents the north incomers with the highest admixture of the autochthon IA population since IA_Maslomecz was formed at the last stage of migration of the Wielbark Culture-associated peoples through the territory of contemporary Poland. It further means that the autochthonous IA genetic component was indispensable to model the whole MA group and that it is possible to explain the genetic makeup of the MA group without a need for separate migration from east in sixth CE or later. f4 statistics demonstrated also that neither the MA nor the IA group was statistically significantly more shifted towards Poland EBA Unetice or Czech EBA Unetice. This observation indicates that the latter two could be a common ancestral component for the IA and MA populations. However, qpAdm models showed that the EBA related ancestry in the IA and MA populations was minor.
The above results are consistent with the hypothesis assuming migration from north and genetic continuity in the region of contemporary Poland from the IA to the MA. Accordingly, we observed that majority of the ancestry of the MA populations could be derived from the preceding IA populations in particular IA_Maslomecz. The MA populations, compared with the IA populations, had lower genetic affinities to ancient northern Europeans and higher to ancient Eastern Europeans (see Additional file 2: Table S11). Still, the MA populations showed close relations with ancient north and north-western Europeans indicating the continuity of the northern European genetic component. That is why, to model some of the MA populations, Denmark_IA could be used as the only source. However, high genetic contribution of the IA populations to the MA populations suggests not only the continuation of the common north European ancestry but also genetic continuation of the autochthon IA population which mixed with the incomers. The possibility that the autochthon IA population could be closely related with the MA populations was additionally supported by modelling the IA populations as mixture of Hungary_Szolad_Migration_Period and the MA populations, where majority of the ancestry was derived from MA populations (~ 80%).
Our Y-chromosome analyses revealed significant differences between the two studied groups. The patrilineal genetic structure of the IA group members was dominated by I1 Y-hg lineages. Many identified I1 clades are now the most common Y-hg in present-day Nordic populations, reaching a 28–38% frequency [75, 76]. An increased I1 Y-hg frequency was previously reported in the context of Anglo-Saxon migrations to Britain [77,78,79]. This further supports the Northern European origin of the Wielbark culture-associated people. The Y-hg I1 frequency dropped significantly in the MA group in favour of the Y-hg R1a. The R1a-S198 marker exceeded a 40% frequency in the MA group, with R1a-M458 being the most common lineage. Today, both R1a-S198 and R1a-M458 are most frequent in the east-central Europe population [80]. We found that all IA group individuals with Y-hg R1a belonged to the R1a-M458 lineage. These results, together with the earlier report on R1a-S204 lineage detection in an individual associated with the Late Bronze Age Urnfield culture [26], strengthen the evidence that R1a-S204 Y-hg lineages, which are dominant in present-day East-Central European populations (Polish, Czech, Belarusian, Ukrainian) [80], were already present in East-Central Europe, at least since the Late Bronze period.
Matrilineal haplogroup analysis revealed another aspect of demographic processes that occurred in east-central Europe in the first millennium. The lack of significant differences between the patterns of mt-hg frequencies in the IA and MA groups shows that populations inhabiting East-Central Europe before and after the Migration Period had similar matrilineal genetic structures. This result is consistent with several earlier reports on the genetic continuity of mt-hg lineages in East-Central European populations between the IA and MA periods [72]. Although the overall pattern of mt-hg frequencies was roughly the same in both groups, in the MA group, we found several lineages very specific to present-day Eastern European populations (Ukrainian, Russian) [81] (H5a2, H5e1a, H1c, U4a2, and U5a1b1e), which were absent or present at very low frequencies in the IA group. The increases in the H5a2, H5e1a, and U5a1b1e mt-hgs suggest that after the Migration Period, there was at least some movement of peoples from East to Central Europe; however, this observation could also be explained by the smaller sample size of the IA group studied here.
Considering the above, one can speculate that the observed differences in the patterns of Y-hg frequencies at the beginning and end of the first millennium CE as well as the stability of the mt-hg frequency profiles are products of androcentric and paternalistic social structures, characteristic to this period. Usually, the men migrated and the women were local. This phenomenon may also explain the low incidence of Y-hg R1a in the IA group. There are many examples in history showing that a relatively small group of male immigrants can subjugate a local community (e.g. the history of the colonization of North and South America). Thus, a small number of individuals with Y-hg R1a in the IA group does not necessarily mean a low frequency of this haplogroup in the autochthonous IA population. It may, however, indicate a natural phenomenon of excluding local men from communities dominated by male immigrants.
Here, we provide several pieces of evidence that the ancestors of the medieval populations lived in the region of present-day Poland during the IA. There are, however, several aspects that need further elucidation. Firstly, how and when the ancestors of the MA populations with Y-hg R1a appeared. The times when Y-hg R1a-M417 dominated in this territory are associated with the spread of the Corded Ware culture (from 3000 to 2300 BC) [82]. Later, it was replaced by the Unetice culture (from 2300 to 1600 BC) [82] that was associated with the populations in which Y-hg R1a was very rare. From then until the IA, there were many archaeological cultures in this region from which no genetic data is available as cremation became the dominant burial practice. Here, we showed that the IA and MA populations inherited only a small percentage of genetic ancestry from the people associated with the Unetice culture. Therefore, the ancestors of the autochthonous IA populations with Y-hg R1a would have either had to be revived in the BA period or come from east during the BA or IA period. At this point, it should be noted that based on our results, one cannot explicitly rule out additional waves of migration after the IA. Thus, one of the reasons for the increase in the frequency of Y-hg R1a could also be migrations from Eastern Europe after the Migration Period.
Although they seem less likely one cannot exclude the alternative scenarios that do not assume the presence of the ancestors of the medieval populations in the region of contemporary Poland during the IA. One possibility is the numerous waves of migration from northern Europe in both IA and medieval times. According to this scenario, the medieval populations could have arisen as a result of the migration of individuals carrying genetic components similar to those possessed by the autochthonous IA populations. In this case, the immigrants would not be direct descendants of the autochthonous IA populations. Another scenario may assume the occurrence of a bottleneck effect that could make the IA and MA populations similar to each other under the conditions of reduced genetic diversity. There is also possibility that both the IA and medieval populations shared a common ancestral population that has not yet been studied. This common ancestry could explain the genetic similarities between the two populations without the direct presence of the ancestors of the medieval populations in the area of present-day Poland in the IA. Certainly, the basic limitation hindering the verification of the scenarios presented above is the lack of aDNA samples from people living in the period between the disappearance of the Unetice culture and the beginning of the IA and from people belonging to the Przeworsk culture.
There are only a few reports on the genetic makeup of the populations inhabiting East-Central Europe in the first millennium CE. The majority of them are based on mitochondrial DNA [37, 38, 72, 73]. Whole-genome analyses of individuals living in this region in the IA and the early MA are scarce [1, 66, 74] and, for the region of contemporary Poland, very limited.
Presented here whole-genome analyses of the individuals from the IA group together with our previous observations [37, 38] and numerous archaeological findings consistently support earlier hypotheses assuming that the Wielbark culture was associated with immigrants from Northern Europe who spread within the region of present-day Poland and mixed with the autochthonous IA population. Most of the data collected for the IA and MA groups are in line with the hypothesis assuming genetic continuity from the IA to the early MA in East-Central Europe and suggest that the migration from east in the sixth CE was not necessary to form the genetic pool of the MA group. However, based on these data, one cannot exclude additional migrations from the Eastern Europe, either during the Migration Period or later.
Most of the collected data including f4 statistics and qpAdm models showed that the genetic makeup of the Wielbark culture-associated people was related with the ancient northern European populations including Denmark_IA and Norway_IA. This result is consistent with our earlier observation of matrilineal connections between IA_Kowalewko and the IA population from Jutland Peninsula [37]. Here, we further showed that the Wielbark culture-associated IA populations could not be derived from the preceding the EBA_Unetice populations alone. It means that the migration from northern Europe was necessary to the formation of the IA group genetic pool.
In addition, f4 statistics and qpAdm models revealed that the MA population could not be formed by people living earlier in the same region and approximated by Poland_EBA_Unetice, Czech_EBA_Unetice or Lithuania_BA. Putative northern ancestors of the Wielbark culture-associated people (approximated by Denmark_IA or Norway_IA) also could not explain the genetic makeup of all MA_X populations. The valid two-way models for all MA_X populations were obtained only for Poland_EBA_Unetice or Czech_EBA_Unetice and IA_Maslomecz. The latter population represents the north incomers with the highest admixture of the autochthon IA population since IA_Maslomecz was formed at the last stage of migration of the Wielbark Culture-associated peoples through the territory of contemporary Poland. It further means that the autochthonous IA genetic component was indispensable to model the whole MA group and that it is possible to explain the genetic makeup of the MA group without a need for separate migration from east in sixth CE or later. f4 statistics demonstrated also that neither the MA nor the IA group was statistically significantly more shifted towards Poland EBA Unetice or Czech EBA Unetice. This observation indicates that the latter two could be a common ancestral component for the IA and MA populations. However, qpAdm models showed that the EBA related ancestry in the IA and MA populations was minor.
The above results are consistent with the hypothesis assuming migration from north and genetic continuity in the region of contemporary Poland from the IA to the MA. Accordingly, we observed that majority of the ancestry of the MA populations could be derived from the preceding IA populations in particular IA_Maslomecz. The MA populations, compared with the IA populations, had lower genetic affinities to ancient northern Europeans and higher to ancient Eastern Europeans (see Additional file 2: Table S11). Still, the MA populations showed close relations with ancient north and north-western Europeans indicating the continuity of the northern European genetic component. That is why, to model some of the MA populations, Denmark_IA could be used as the only source. However, high genetic contribution of the IA populations to the MA populations suggests not only the continuation of the common north European ancestry but also genetic continuation of the autochthon IA population which mixed with the incomers. The possibility that the autochthon IA population could be closely related with the MA populations was additionally supported by modelling the IA populations as mixture of Hungary_Szolad_Migration_Period and the MA populations, where majority of the ancestry was derived from MA populations (~ 80%).
Our Y-chromosome analyses revealed significant differences between the two studied groups. The patrilineal genetic structure of the IA group members was dominated by I1 Y-hg lineages. Many identified I1 clades are now the most common Y-hg in present-day Nordic populations, reaching a 28–38% frequency [75, 76]. An increased I1 Y-hg frequency was previously reported in the context of Anglo-Saxon migrations to Britain [77,78,79]. This further supports the Northern European origin of the Wielbark culture-associated people. The Y-hg I1 frequency dropped significantly in the MA group in favour of the Y-hg R1a. The R1a-S198 marker exceeded a 40% frequency in the MA group, with R1a-M458 being the most common lineage. Today, both R1a-S198 and R1a-M458 are most frequent in the east-central Europe population [80]. We found that all IA group individuals with Y-hg R1a belonged to the R1a-M458 lineage. These results, together with the earlier report on R1a-S204 lineage detection in an individual associated with the Late Bronze Age Urnfield culture [26], strengthen the evidence that R1a-S204 Y-hg lineages, which are dominant in present-day East-Central European populations (Polish, Czech, Belarusian, Ukrainian) [80], were already present in East-Central Europe, at least since the Late Bronze period.
Matrilineal haplogroup analysis revealed another aspect of demographic processes that occurred in east-central Europe in the first millennium. The lack of significant differences between the patterns of mt-hg frequencies in the IA and MA groups shows that populations inhabiting East-Central Europe before and after the Migration Period had similar matrilineal genetic structures. This result is consistent with several earlier reports on the genetic continuity of mt-hg lineages in East-Central European populations between the IA and MA periods [72]. Although the overall pattern of mt-hg frequencies was roughly the same in both groups, in the MA group, we found several lineages very specific to present-day Eastern European populations (Ukrainian, Russian) [81] (H5a2, H5e1a, H1c, U4a2, and U5a1b1e), which were absent or present at very low frequencies in the IA group. The increases in the H5a2, H5e1a, and U5a1b1e mt-hgs suggest that after the Migration Period, there was at least some movement of peoples from East to Central Europe; however, this observation could also be explained by the smaller sample size of the IA group studied here.
Considering the above, one can speculate that the observed differences in the patterns of Y-hg frequencies at the beginning and end of the first millennium CE as well as the stability of the mt-hg frequency profiles are products of androcentric and paternalistic social structures, characteristic to this period. Usually, the men migrated and the women were local. This phenomenon may also explain the low incidence of Y-hg R1a in the IA group. There are many examples in history showing that a relatively small group of male immigrants can subjugate a local community (e.g. the history of the colonization of North and South America). Thus, a small number of individuals with Y-hg R1a in the IA group does not necessarily mean a low frequency of this haplogroup in the autochthonous IA population. It may, however, indicate a natural phenomenon of excluding local men from communities dominated by male immigrants.
Here, we provide several pieces of evidence that the ancestors of the medieval populations lived in the region of present-day Poland during the IA. There are, however, several aspects that need further elucidation. Firstly, how and when the ancestors of the MA populations with Y-hg R1a appeared. The times when Y-hg R1a-M417 dominated in this territory are associated with the spread of the Corded Ware culture (from 3000 to 2300 BC) [82]. Later, it was replaced by the Unetice culture (from 2300 to 1600 BC) [82] that was associated with the populations in which Y-hg R1a was very rare. From then until the IA, there were many archaeological cultures in this region from which no genetic data is available as cremation became the dominant burial practice. Here, we showed that the IA and MA populations inherited only a small percentage of genetic ancestry from the people associated with the Unetice culture. Therefore, the ancestors of the autochthonous IA populations with Y-hg R1a would have either had to be revived in the BA period or come from east during the BA or IA period. At this point, it should be noted that based on our results, one cannot explicitly rule out additional waves of migration after the IA. Thus, one of the reasons for the increase in the frequency of Y-hg R1a could also be migrations from Eastern Europe after the Migration Period.
Although they seem less likely one cannot exclude the alternative scenarios that do not assume the presence of the ancestors of the medieval populations in the region of contemporary Poland during the IA. One possibility is the numerous waves of migration from northern Europe in both IA and medieval times. According to this scenario, the medieval populations could have arisen as a result of the migration of individuals carrying genetic components similar to those possessed by the autochthonous IA populations. In this case, the immigrants would not be direct descendants of the autochthonous IA populations. Another scenario may assume the occurrence of a bottleneck effect that could make the IA and MA populations similar to each other under the conditions of reduced genetic diversity. There is also possibility that both the IA and medieval populations shared a common ancestral population that has not yet been studied. This common ancestry could explain the genetic similarities between the two populations without the direct presence of the ancestors of the medieval populations in the area of present-day Poland in the IA. Certainly, the basic limitation hindering the verification of the scenarios presented above is the lack of aDNA samples from people living in the period between the disappearance of the Unetice culture and the beginning of the IA and from people belonging to the Przeworsk culture.