Genomic analysis of Germanic tribes from Bavaria show North-Central European ancestry

antiquity-europe

New open access paper Population genomic analysis of elongated skulls reveals extensive female-biased immigration in Early Medieval Bavaria, by Veeramah, Rott, Groß, et al. PNAS (2018), published ahead of print.

First, a bit of context on the Bavarii:

Europe experienced a profound cultural transformation between Late Antiquity and the Middle Ages that laid the foundations of the modern political, social, and religious landscape. During this period, colloquially known as the “Migration Period,” the Roman Empire gradually dissolved, with 5th and 6th century historiographers and contemporary witnesses describing the formation and migration of numerous Germanic peoples, such as the Goths, Alamanni, Gepids, and Longobards. However, the genetic and social composition of groups involved and the exact nature of these “migrations” are unclear and have been a subject of substantial historical and archaeological debate

In the mid 6th century AD, the historiographer Jordanes and the poet and hagiographer Venantius Fortunatus provide the first mention of a group known as the Baiuvarii that resided in modern day Bavaria. It is likely that this group had already started to form in the 5th century AD, and that it emanated from a combination of the romanized local population of the border province of the former Roman Empire and immigrants from north of the Danube (2). While the Baiuvarii are less well known than some other contemporary groups, an interesting archaeological feature in Bavaria from this period is the presence of skeletons with artificially deformed or elongated skulls.

bavarii-pca
Procrustes-transformed PCA of ancient samples using pseudohaploid calls based on off-target reads using an imputed POPRES modern reference dataset. Blue, green, and red male or female symbols are ancient Bavarian individuals with normal, intermediate, and elongated skulls, respectively. Orange circles are Anglo-Saxon era individuals. Large circles are medians for regions, dots are individuals. CE, central Europe; EE, eastern Europe; NE, northern Europe; NEE, northeastern Europe; NEW, northwestern Europe; SE, southern Europe; SEE, southeast Europe; WE, western Europe. Percentage of variation explained by PCs 1 and 2 for modern populations only is 0.25% and 0.15%.

Abstract (emphasis mine):

Modern European genetic structure demonstrates strong correlations with geography, while genetic analysis of prehistoric humans has indicated at least two major waves of immigration from outside the continent during periods of cultural change. However, population-level genome data that could shed light on the demographic processes occurring during the intervening periods have been absent. Therefore, we generated genomic data from 41 individuals dating mostly to the late 5th/early 6th century AD from present-day Bavaria in southern Germany, including 11 whole genomes (mean depth 5.56×). In addition we developed a capture array to sequence neutral regions spanning a total of 5 Mb and 486 functional polymorphic sites to high depth (mean 72×) in all individuals. Our data indicate that while men generally had ancestry that closely resembles modern northern and central Europeans, women exhibit a very high genetic heterogeneity; this includes signals of genetic ancestry ranging from western Europe to East Asia. Particularly striking are women with artificial skull deformations; the analysis of their collective genetic ancestry suggests an origin in southeastern Europe. In addition, functional variants indicate that they also differed in visible characteristics. This example of female-biased migration indicates that complex demographic processes during the Early Medieval period may have contributed in an unexpected way to shape the modern European genetic landscape. Examination of the panel of functional loci also revealed that many alleles associated with recent positive selection were already at modern-like frequencies in European populations ∼1,500 years ago.

bavarii-admixture
Supervised model-based clustering ADMIXTURE analysis for ancient samples based on phased haplotypes for individual 1,000 bp loci from the 5-Mb neutralome. Analysis is based on the best of 100 runs for K = 8, but NC_EUR is the ancestry summed across 1000 Genomes CEU, 1000 Genomes GBR, and GoNL populations (i.e., it represents a northern/central European ancestry). Blue, green, and red male or female symbols are ancient Bavarian individuals with normal, intermediate, and elongated skulls, respectively.

There is no Y-DNA data to keep confirming the North-Central origin of certain modern European subclades in Central and South-Central Europe.

The potential Ostrogothic sample from Crimea was probably Hunnic, as the paper itself suggests, and both Ostrogoths and Gepids are known to have been allies of the Huns for a long time. It is also a well-known fact that East Germanic tribes migrated south- and eastward through eastern Europe, and then from the steppe westward.

Obviously, the PCA of a late Gepid sample – after a certain number of generations and admixture events with ‘local’ populations during the migrations – , and of a Crimean sample without a clear cultural identification, are of limited value today, until more samples are available.

Hence sadly no valid data yet to add to the debate of East Germanic nature, which mainly concerns its traditionally described origin in Scandinavia – i.e. close to North Germanic dialects – against a different origin (and dialectal branch) within Proto-Germanic territory.

NOTE. Just to be clear for future papers on Germanic tribes, I would expect East Germanic males to show either:
a) mainly R1b-U106, I1, and R1a-Z645 subclades, and to cluster closely to samples of Scandinavia during Antiquity, which would support a Scandinavian origin – a predominance of typically Scandinavian R1a-Z284 subclades would be more indicative of this origin, of course;
b) or mainly R1b-U106, R1b-P312, and I1 subclades and a PCA cluster close to West Germanic tribes, which would challenge its traditional dialectal identification.

I agree with the authors in that a few samples are able to describe certain migratory events, though, such as the emphasized female-biased long-distance migration in Bavaria, as well as the diverse ancestry of women versus men.

Related:

mtDNA suggest original East Germanic population linked to Jutland Iron Age and Bell Beaker

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Open Access article A mosaic genetic structure of the human population living in the South Baltic region during the Iron Age, by Stolarek et al., at Scientific Reports 8:2455 (2018).

About the site:

Kowalewko is a village in Wielkopolskie vojevodship, close to Poznan, in the middle reaches of the Samica Kierska river. Biritual Roman Age cemetery (site 12), dated from the mid-1st to the beginning of 3rd century AD, is located in the featureless arable fields at the South and West of the village

About the Wielbark culture:

Chronology spans almost all the Roman Iron Age, since ca. 20 AD to ca. 450 AD. The Wielbark culture is associated with the Goths and Gepids, who migrated from Scandinavia towards the Black Sea, and their successors, who, after several centuries, returned to the lands formerly occupied by their ancestors. Typical features of the culture include inhumation graves rich in goods of numerous ornaments frequently of noble metals, while no implements and weapons have been observed and iron objects very rarely. Less frequent cremations. Barrows recorded within cemeteries reflect emergence of elites. The Wielbark communities built stone constructions, including pebbled floors and circles. This culture is mainly known from cemeteries, as settlements, not fortified, are less recognized.

kowalewko
Location of Kowalewko and a scheme of the Kowalewko cemetery site 12, based on the Fig. 3 from the monograph by Tomasz Skorupka, Kowalewko 12. Biritual cemetery of a population of the Wielbark Culture (mid 1st to beginning of 3rd century AD), published in: Marek Chlodnicki [ed.], Archaeological rescue investigations along the gas transit pipeline, vol. II – Wielkopolska, part 3, Poznan 2001, generated using Corel Draw ver. 12.0, with the author permission. Sampled graves are marked with a red color. Europe and Poland maps were downloaded from Wikimedia Commons (https://commons.wikimedia.org), under the free licence, and modified with Corel Draw ver. 12.0.

Interesting excerpts with emphasis added (and some stylistic changes for abbreviations):

Analysis of genetic distances (see Fig. 2b) showed that both Jutland Iron Age (JIA) and Kowalewko (Kow-OVIA), are the closest to the Central Europe Metapopulation (CEM). However, it should be mentioned that many of the resulting genetic proximities did not reach statistical significance at the alpha level 0.05 (mainly due to the multiple comparisons), thus they should be interpreted with caution. Higher prevalence of the mtDNA haplogroup H in Kowalewko and Jutland Iron Age(its high level is also characteristic for the Bell Beaker Culture) than in the preceding Corded Ware Culture (CWC) and Unetic Culture (UC) supports the hypothesis assuming significant demographic changes in Central Europe after the LN/EBA period. This hypothesis is additionally strengthened by the results of AMOVA analysis indicating that there is some inconsistency between genetic distances and the chronology of the appearance of the studied populations in Central Europe, i.e., the older populations (BBC, CWC) contributed more to the genetic structure of CEM than the younger ones (UC).

Changes in the occurrence of mtDNA haplogroups U5a/U5b in Central Europe are also worth noting. At LN and EBA, the prevailing haplogroup was U5a for BBC/CWC/UC. Next, there was a dominance of U5b for the Kow-OVIA/JIA during IA and now U5a is again more popular (CEM). The first alteration in the U5a/U5b prevalence between the LN/EBA and the IA supports the hypothesis of demographic changes right after the LN, proposed by Brandt et al (2013). The second conversion indicated by our results suggests another crucial demographic event that should occur between the IA and present.

On the basis of the above observations, one may assume that in the IA, specific genetic substructures were formed in Central Europe. Because the demographic history of fossil populations often has a local character33,34, it is worth considering the range of the observed changes. These considerations should also take into account the hypothesis on the migrations that most likely occurred between the 3rd and 6th century AD. In this context, it seems necessary to compare Kow-OVIA and JIA with other populations from the IA, in particular those located east of Vistula, and with the populations that inhabited this region during the Middle Ages.

kowalewko-mtdna
PCA2 vs. PCA3 on the haplogroup frequencies of ‘European Population Transect’ populations

Finally, we found that the genetic structures of female and male subpopulations of Kow-OVIA were significantly different. This fact cannot be explicitly determined based on the results of individual analyses; however, it is quite evident if one considers the whole set of data presented here including the Fisher test on haplogroup frequencies. The analyses of both mtDNA haplogroups and genetic distances indicated that women from Kowalewko were related closer to the EN/MN populations, and the men were closer to the CWC and UC. This observation may explain why the genetic relationships of Kow-OVIA with other ancient European populations were more complex and more difficult to define as it was in the case of JIA. In analyzing Kow-OVIA, we observed multiple overlapping effects of two subpopulations with different genetic affinities. One would speculate that the genetic profile of Kow-OVIA-F resulted from exogamy that was described for the CWC population. This is, however, not the case. We found that the genetic differences between women and men were maintained for the entire observation period, i.e., for 200 years (approximately 8 generations). Such a composition of the genetic structure of Kow-OVIA could exist only if at least one subgroup (Kow-OVIA-F or -M) was periodically exchanged. It would further mean that Kowalewko played some specific roles in that region. According to the recent archaeological studies, the colonization pattern in IA Greater Poland could be linked with the existence of a centralized organization system32. Kowalewko could have been one of the important elements of this system. For example, it could have functioned as a garrison for the population closely associated with the JIA, such that warriors stayed in the garrison for only a few years and were then replaced by others. Other scenarios are also possible; however, verification of any hypothesis requires more detailed studies.

All in all, we know that Wielbark probably represented the initial migration period of East Germanic tribes, traditionally believed to be from Northern Scandinavia, into territory later inhabited by Slavic tribes (and potentially earlier by a Balto-Slavic community).

Other than that, the results show some potential for a stable genomic situation in the Germanic homeland in terms of mtDNA, common after the Bell Beaker expansion, which probably brought Pre-Germanic to Scandinavia.

Nevertheless, only a comprehensive study of all Germanic regions from that period (whole genomic and Y-DNA) might shed light onto the real origin of East Germanic peoples, and thus their contended dialectal position, since we already know that certain modern Slavic and Germanic populations cluster closely to some Bronze Age communities of the same region, so differences during the Iron Age may be already quite subtle.

In my humble opinion, too many hypotheses in the paper for few interesting data – as is more and more usual in genetic papers. I guess journals expect that to get more attention, although serious reviewers should actually encourage the opposite, and only informal blogs like this one should come up with far-fetched theories, instead of rebutting them…

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