July 21, 2015

British origins (with ancient data)


bioRxiv http://dx.doi.org/10.1101/022723

Iron Age and Anglo-Saxon genomes from East England reveal British migration history

Stephan Schiffels, Wolfgang Haak, Pirita Paajanen, Bastien Llamas, Elizabeth Popescu, Louise Lou, Rachel Clarke, Alice Lyons, Richard Mortimer, Duncan Sayer, Chris Tyler-Smith, Alan Cooper, Richard Durbin

British population history has been shaped by a series of immigrations and internal movements, including the early Anglo-Saxon migrations following the breakdown of the Roman administration after 410CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences generated from ten ancient individuals found in archaeological excavations close to Cambridge in the East of England, ranging from 2,300 until 1,200 years before present (Iron Age to Anglo-Saxon period). We use present-day genetic data to characterize the relationship of these ancient individuals to contemporary British and other European populations. By analyzing the distribution of shared rare variants across ancient and modern individuals, we find that today’s British are more similar to the Iron Age individuals than to most of the Anglo-Saxon individuals, and estimate that the contemporary East English population derives 30% of its ancestry from Anglo-Saxon migrations, with a lower fraction in Wales and Scotland. We gain further insight with a new method, rarecoal, which fits a demographic model to the distribution of shared rare variants across a large number of samples, enabling fine scale analysis of subtle genetic differences and yielding explicit estimates of population sizes and split times. Using rarecoal we find that the ancestors of the Anglo-Saxon samples are closest to modern Danish and Dutch populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain.



eurologist said...

I would read this as such: even very late iron-age old British populations (not "Britons" as in the article) had very little ancient NE European HG admixture, but instead were more closely related to ancient W European HGs with of course some SE European/ Anatolian/ Levantine Neolithic admixture --- with a slightly more pronounced Levantine and Anatolian portion than C Europe's Neolithic admixture.

Also, as almost always, autosomal DNA does not favor intruders, while cultural artifacts do.

Finally, the PCA analysis again would have been much more conclusive with Spanish and Tuscan and Finnish and (if possible) S France removed, but far northwest Germany and northern Germany and the North Sea - facing Denmark included.

Maju said...

Interesting. However it is a true pity that they have not performed proper comparisons with a regional sample, particularly one including NW German, Frisians, Dutch and Danes (and skipping or going beyond the pan-European pointless PCA which does not help clarifying anything). That produces the problem that we don't know if the "purest" Anglo-Saxon individuals (O1, O2, HS2 and maybe HS1) are already admixed with native Britons or are unmixed immigrants from the Anglo-Saxon homeland in mainland NW Europe. The lack of Welsh samples in the PCA is also strange.

Said that, and assuming that these individuals are in fact actual immigrants, we can see among them a pure Briton (O4) and two admixed Anglo-Britons (O3 and HS3), indicating that they were already incorporating natives in the Anglo-Saxon ranks since 500 CE. It's true that these are females but that applies to the whole Anglo-Saxon ancient sample (all 7 samples were female).

Unknown said...

To what extent do inhumations of females represent the same population as those males who were cremated? There are some large cremation graveyards during the first 150 years of paganism. Whose burial customs were being followed?

Simon_W said...

Excellent paper. So, the British are predominantly of Insular Celtic descent, with the Germanic contribution being in the minority, though still substantial in certain places and individuals (up to 40% in East English individuals).

To me it's surprising that the Anglo-Saxon ancestry is quite evenly distributed in Britain, around 30% in eastern England, but still around 20% in Wales and Scotland. This certainly suggests a high amount of internal migration and mixture after the Anglo-Saxon incursions. Perhaps this occured rather recently, after the industrialisation.

The different affiliations of Anglo-Saxon individuals, with some being closer to the Dutch and others to the Danes, might perhaps reflect different tribal affiliations, the former Saxon, the latter Angles.

@ Eurologist

Consider this: In any decent West Eurasian PCA, Northwest Europeans are inbetween Middle Neolithic/Copper Age Europeans and Yamnaya/Corded Ware, with Western Hunter-Gatherers being complete outliers. This paper simply doesn't have anything to say about WHG, EHG and their relationship of modern Europeans.

Maju said...

@Simon: "with the Germanic contribution being (...) still substantial in certain places and individuals (up to 40% in East English individuals)".

That might be or... not. Because a flaw in this study is that the Anglosaxon individuals are not compared with modern or ancient references from the continental Anglosaxon area (the arch between Frisia and Jutland), so it could be that or could be half or even half of the half. What I say is that with the data of this study we can't say if the "Anglosaxon" individuals were 100% recent immigrants from the continental "Anglo-Saxony" or were already heavily diluted by admixture with natives. Only comparing with North Germans and such can the actual admixture be measured but this study avoids doing that.

"To me it's surprising that the Anglo-Saxon ancestry is quite evenly distributed in Britain, around 30% in eastern England, but still around 20% in Wales and Scotland".

Or that you're measuring something else. The Leslie et al. study showed a shared ancestry from the Rhineland area (which should be Celtic) but Welsh and Scotts lacked ancestry from North Germany. Anyhow this Saxon ancestry appeared to be low across the board, with Danish (Vikings) being a more important impactor, somewhat surprisingly.

Foof said...

I wonder how much of this discussion is more politics than science. Nobody asks about the Germanic contribution in France even though France is also named after a Germanic tribe of invaders, (Franks, 500 A.D.). In fact, genetically the French and English are very similar in genetic make-up, the main difference between these two cultures being the choice of lingua Franca for commerce. The Plantagenets with their roots in Angevin, France could very well have mandated the use of middle-French as the official language of Britain and this discussion might be moot point.