Wielbark Goths were overwhelmingly of Scandinavian origin

When used properly, Principal Component Analysis (PCA) is an extraordinarily powerful tool and one of the best ways to study fine-scale genetic substructures within Europe.

The PCA plot below is based on Global25 data and focuses on the genetic relationship between Wielbark Goths and Medieval Poles, including from the Viking Age, in the context of present-day European genetic variation.

I'd say that it's a wonderfully self-explanatory plot, but here are some key observations:

- the Wielbark Goths (Poland_Wielbark_IA) and Medieval Poles (Poland_Middle_Ages) are two distinct populations

- moreover, the Wielbark Goths form a relatively compact Scandinavian-related cluster and must surely represent a homogenous population overwhelmingly of Scandinavian origin

- on the other hand, the Medieval Poles form a more extensive and heterogeneous cluster that overlaps with present-day groups all the way from Central Europe to the East Baltic, and that's because they are likely to be in large part of mixed origin

- I know for a fact that at least some of these early Poles harbor recent admixture, because their burials are similar to those of Vikings and their haplotypes have been shown to be partly of Scandinavian origin (see here)

- one of the Wielbark females is an obvious genetic outlier (Poland_Wielbark_IA_outlier), and basically looks like a first generation mixture between a Goth and a Balt.

Please note that the PCA is only based on relatively high quality genomes, so as not to confuse the picture with spurious results and noise. Also, all outliers with potentially significant ancestry from outside of Central, Eastern and Northern Europe were removed from the analysis. The relevant datasheet is available here.

However, sanity checks are always important when studying complex phenomenon like fine-scale genetic ancestry. To that end I've prepared a graph based on f3-statistics of the form f3(X,Cameroon_SMA,Estonia_BA)/(X,Cameroon_SMA,Ireland_Megalithic), that reproduces the key features of my PCA. The relevant datasheet is available here.

Polish groups from the Middle Ages are marked with the MA suffix, while the Iron Age Wielbark Goths are marked with the IA suffix.

If you're wondering why I plotted the f3-statistics that I did, take a look at this (all groups largely of Scandinavian origin are emboldened):

f3(X,Estonia_BA,Cameroon_SMA)
Poland_Legowo_MA 0.226406
Poland_Ostrow_Lednicki_MA 0.225996
Poland_Plonsk_MA 0.225017
Poland_Trzciniec_Culture 0.224215
Poland_Lad_MA 0.224142
Poland_Viking 0.223838
Poland_Niemcza_MA 0.223659
Poland_Weklice_IA 0.223549
Poland_Kowalewko_IA 0.222584
Poland_Pruszcz_Gdanski_IA 0.222324
Sweden_Viking 0.222091
Russia_Viking 0.222042
Poland_Maslomecz_IA 0.221914
Norway_Viking 0.221825
Denmark_EarlyViking 0.221257
Denmark_Viking 0.221174
England_Viking 0.220979

f3(X,Ireland_Megalithic,Cameroon_SMA)
Poland_Maslomecz_IA 0.219816
Poland_Weklice_IA 0.219501
Denmark_Viking 0.2192
Poland_Kowalewko_IA 0.219176
Poland_Ostrow_Lednicki_MA 0.218916
Norway_Viking 0.218854
Poland_Pruszcz_Gdanski_IA 0.218684
Sweden_Viking 0.218626
Denmark_EarlyViking 0.218529
England_Viking 0.218308
Russia_Viking 0.217999
Poland_Viking 0.217914
Poland_Plonsk_MA 0.217756
Poland_Lad_MA 0.217719
Poland_Legowo_MA 0.21765
Poland_Niemcza_MA 0.217001
Poland_Trzciniec_Culture 0.216551

Interestingly, the Middle Bronze Age samples associated with the Trzciniec Culture (Poland_Trzciniec_Culture) show a closer genetic relationship to Medieval Poles than to Wielbark Goths or Northwestern Europeans. This is indeed the case both in terms of genome-wide and uniparental markers, including some very specific lineages under Y-chromosome haplogroup R1a.

But that's a much more complex issue that I'll leave for another time. So please stay tuned.

See also...

Slavs have little, if any, Scytho-Sarmatian ancestry

Best of 2008: Corded Ware DNA from Germany

One of the biggest hits of the year for this blogger was the discovery of Y-DNA haplogroup R1a among three Corded Ware skeletons from a burial site in Eulau, eastern Germany. It's an important result, because it links one of Europe's most dominant Y-haplogroups to a major Late Neolithic archeological complex.

All three individuals were confirmed to be paternally related via their shared Y-STR haplotype. Nevertheless, the outcome appears far from a random coincidence. Consider that in Europe today R1a shows its highest frequencies in Poland and Western Russia, which are both located in former Corded Ware territory, and where the Eulau R1a haplotype appears to have its closest modern matches. Moreover, the Corded Ware culture is often classified as an Indo-European culture by archeologists and linguists, while at the same time R1a has been posited as a marker of the early Indo-Europeans by some geneticists. Needless to say, I'm expecting R1a to be a common, and perhaps dominant marker among Corded Ware samples when more of them make it to the lab.

The consensus haplotype of the three individuals (based on most complete profile) gave two exact matches in in an European population sample of 11,213 haplotypes in a set of 100 populations (as of July 2008, Release ‘‘23’’ from 2008–01-15 14:44:25): one individual from Poland (1/939 from Gdansk) and one from Russia (1/48 from Tambov).

...

The Y haplotype was predicted using the Web-based program Haplotype Predictor (9). The three individuals of grave 99 belong to haplotype R1a, with a probability of 100% based on the Y-STR profile of individual 3 (10). To confirm haplogroup status, we further amplified an 85-bp fragment covering the Y-SNP marker SRY10831.2 characteristic for R1a (11). Primer sequences are given in Table S6. Sequences and sequenced clones from independent extract of all three individuals show the specific G to A transition identifying R1a (Fig. S5).

The mitochondrial DNA (mtDNA) lineages of the Eulau skeletons belonged to haplogroups K1b (3), X2 (2), H, I, K1a2, and U5b. Most of these maternal markers aren't particularly common in Europe today, and the overall result appears decidedly unusual compared to the mtDNA frequencies of modern European populations, largely because of the low frequency of H.

I'm quite certain this is at least partly due to the small sample size and presence of several related individuals skewing some of the frequencies. However, it's interesting to note that this pattern of discontinuity between mtDNA gene pools from different time periods has also been reported in other studies, some with larger samples, and focusing on different regions of Europe. So it might well be a signal of significant shifts in mtDNA frequencies during European prehistory and early history, possibly as a result of major migrations leading to significant population replacements.

Interestingly, one of the ancient K1b lineages most closely matched a haplotype shared by two modern Shugnans from Tajikistan. Exactly how the Corded Ware individual is related to these two Central Asians isn't clear yet, but Shugni is an Indo-Iranian language, so some kind of early Indo-European relationship is possible.

Citation...

Wolfgang Haak et al, Ancient DNA, Strontium isotopes, and osteological analyses shed light on social and kinship organization of the Later Stone Age, PNAS, Published online before print November 17, 2008, doi:10.1073/pnas.0807592105