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Friday, September 18, 2015

Recent admixture in West Eurasia (including Europe)


A new open access paper at Current Biology looks at the role of recent admixture in the formation of the present-day West Eurasian gene pool. It appears to be an updated version of a paper from last year which I found somewhat disappointing (see here). This effort is a lot better; it's more detailed and sophisticated, and the authors are more cautious with their interpretations of the data.

That's it for now, but I'll have a lot more to say about these results soon at my other blog when more ancient DNA data rolls in from southern Europe and the Near East.

Below is Figure 4A from the paper, which shows the proportions of admixture from outside of Europe and West Asia among a wide variety of West Eurasian groups.

Citation...

Busby et al., The Role of Recent Admixture in Forming the Contemporary West Eurasian Genomic Landscape, Current Biology, DOI: http://dx.doi.org/10.1016/j.cub.2015.08.007

27 comments:

Tesmos said...

Were there Belgian people tested? I can see a green spot but the country is gray.

Davidski said...

They're not Belgians. They're white Americans from Utah. The reason they're sitting in Belgium is because overall that's where they cluster.

They're mostly of British origin, but some of the individuals come out totally Scandinavian and others part Polish and Italian, which pushes them south and east of the UK on a map of Europe.

Arch Hades said...

Does this paper give dates of the admixture? Wow look at the difference between Greece and Italy in terms of geneflow from the Levant.

Davidski said...

Yes, it does. It's open access. You need to go through it carefully because it covers a lot of detail, including two sets of migrations; within West Eurasia and into West Eurasia.

But I think it's still a work in progress, and quite frankly to get really precise with this stuff we'll need lots of ancient DNA.

A lot of the migration edges seem exaggerated in this paper. Recent admixture from the Levant in France? Yeah, maybe, in areas where the French don't live.

Arch Hades said...

How is West African Ancestry in Southern Italy and Spain 5% but there's no North African Ancestry? That must be an error or something. The percentages should be reversed.

Davidski said...

Maybe they colored it wrong? It does seem very high.

Like I said, they'll probably refine it in the future, and maybe even use ancient DNA.

Matt said...

Visually, that is what in fact, the S3 Figure (source of proportions and dates of admixture shown in Figures 2 and 3) and showing the contributions to each of their clusters seems to show, a strong North African and Levant contribution to an Itali8 cluster, and less to other Italian clusters. But not really any West African cluster membership in the South Italian groups. The Sicilian cluster seems more notable for its lack of membership in the NW European cluster and sharing with SE Europe / West Asian clusters than Africa related clusters. Similar results for the Spanish clusters.

Not totally sure how they got to those estimates in that Figure4A from the estimates for clusters shown in S3 (although that confuses me a little as S3 is either labeled incorrectly, or has multiple estimates for some populations).

The unit of populations under analysis in the paper are mainly clusters who share chunks, named for the main population contributing to them and the number of individuals in them - e.g. ceu71 is a combination of 43 ceu, 8 english, 7 irish, 6 scottish, 4 welsh, 2 french, 1 german, while ukrai48* is 20 ukrainian, 16 polish, 8 belorussian, 1 chukchi, 1 chuvash, 1 koryake, 1 lithuanian.

Figure 4A is "For each geographic sampling location, we estimated the proportion of ancestry coming from outside of West Eurasia by averaging GLOBETROTTER’s admixture inference across individuals from a sampling location. The sampling locations of each point are shown in Figure S4A; Caucasus populations are spread out to aid visibility. Points are stacked vertically in cases where multiple ancestries are present in a population.". But that wouldn't necessarily seem to lead to the same estimates by eyeball.

*for ukrain48 it's odd that a few of these samples nominally from quite East Eurasian groups got assigned to the cluster, which must be because they have large amounts of recent ancestry of East European derivation, but because they few does not seem to affect the results for composition for that cluster.

Davidski said...

Matt, those Siberians in the Ukrainian cluster are self-reported Siberians, but in large part of East European origin. They're probably the descendants of recent Slavic settlers in Siberia who shacked up with the natives.

Not really sure if there's any use including such people in an East European cluster, but whatever.

Matt said...

Yep, sorry if I wasn't clear, that's more or less what I was saying ("large amounts of recent ancestry of East European derivation" in those individuals).

Re: use of including them in that cluster, their methodology just places individuals in their dataset in clusters together without considering what population they're from. Which is probably a pretty cool methodology when you want to compare FSTs between the clusters, because the clusters are genetically "real" while self described populations are not necessarily. So if they're in the dataset they're in the cluster. Question being whether they were worth being in the dataset, I guess? Does not seem to have produced strange outcomes, anyway. Whatever, exactly.

Simon_W said...

I've already commented on this paper on Dienekes' Blog. It may take a while until the comments get approved, but I don't want to repeat myself here. However, since this is a blog on Polish genes, let me just repeat that to me figure 4C is the most fasciniating one. Among other things you can clearly discern the Slavic expansion. Surprisingly, it looks bimodal, with a western, Lithuanian-like center and an eastern Ukrainian-like center. The former suggests that the origin of the more western Slavs shouldn't be sought too far in the south. So probably not near the Carpathians, as some have suggested, but more to the north. Also noteworthy that there is a Slavic arrow into Germans, but not the other way round.

Davidski said...

Estimating levels and dates of admixture between closely related populations based on modern DNA is not a precise science, and that's putting it mildly, no matter what anyone claims.

alex D said...

Nice link but why do the authors continue down the migration period path?
Wasn't that used by people to sure up the racist doctrines of the uber-germanic ideology? very outdated thinking.

Davidski said...

Well, a couple major Germanic tribes got their asses handed to them by the Huns during the Migration Period.

And in this paper Norwegians also show admixture from North Siberia, which can be seen on the map I posted above.

alex D said...

Without a doubt it's an interesting paper, but they should have stayed well away from the Völkerwanderung I have not seen much evidence to date.

Simon_W said...

Still, on a second thought some stuff in Figure 4C looks outlandish. Like that >50% migration edge from England to Norway. And that's dated to the common era! Simply not credible. The more likely explanation is that Norwegians used to be quite British-like before that minor eastern admixture arrived.

Simon_W said...

The Völkerwanderung for sure was very real, though the effect of Germanic tribes in countries which didn't switch to Germanic tongue afterwards, was negligible. But in Germanic countries a detectable Germanic influence can be expected, though that needn't be everywhere >50%.

alex D said...

Ok but

a) you should know by now that you can take anything coming out of that period in Germany/Prussia and it's sub affiliates with a grain of salt (in the 40's they still thought Charlemagne spear was real).

b) Even if they were well intentioned sourcing from ancient texts does not mean that are accurate - Roman writer's may not have even visited the place, geography may be off, finding a people/army in a area does not mean everyone has moved to that area invasion != migration.

c) Language is not a good way to identify people it can change in a single generation.

d) Take Ötzi for example 5,300 years old and still has relatives up the road.

That being said all may be possible, but I was just suggesting that the writers should let science do the talking.

Simon_W said...

The term Völkerwanderung didn't originate in NS Germany, but in the late 18th century. It has survived from then to the present modern historical and archeological scholarship and is still taught in schools. And even if critical questions are surely legitimate, the outright denial of the Völkerwanderung sounds fringe, like conspiracy theories. Historians have already noted long ago that some of the migrating tribes numbered less than 100'000 people, compare this to the millions of inhabitants in the decaying Roman empire, it's negligible. And to what extent southern Germans, Austrians, Englishmen etc. are descended from Germanics and to what from Romano-British and Gallo-Romans etc. is open to debate, but the available evidence so far seems to suggest a non-negligible Germanic impact, regionally varying of course. In the meantime it may help to note that the Germanic tribes were not Germans. Especially the East Germanic tribes like the Goths were about as German as the Danes, i.e. simply not. But also the West Germanic tribes were not simply Germans, because the German ethnicity didn't yet exist back then. So even with anti-German resentments it's not necessary to play down the existence and migration of these tribes. That said, I haven't read that paper in detail, but I would recommend caution with appealing to the Völkerwanderung as the explanation of some of these migration edges. For instance that strong edge from Germany to Ireland definitely needs another explanation.

alex D said...

Simon_W I agree with your comments and yes the theory when it was in the context of invasions and the fall of Rome I have no problem with. In fact it one could argue Cassiodorus started the theory got mulled about in various places and later the 16th onwards came into fashion with German/German-state writers (Lazius or Schmidt I forget?) and anyway ended with the accumulation of dodgy science which did more harm to it than good.
I just couldn't understood why they took valid scientific data and automatically linked it with a theory which we have little knowledge of, most likely was more complex and where little (if any) scientific data exists.

alex D said...

I should add Jutes,Saxon,Angles are pretty scientifically well attested for on the British isles it's just so lacking on the continent.

Simon_W said...

It can't be generalized that evidence is very lacking on the continent. Archeologically the Alamannic presence in Southwestern Germany and adjacent areas is well attested, and also their relations with the Elbe Germanic area. That's just the subject I know best, because it relates to my own roots. I own a thick exposition catalogue with plenty of Alamannic finds. But I know there are also archeological traces of the Goths and Huns and whatnot, and of the Frankish expansion etc. It isn't credible to me that the Anglo-Saxon case is somehow special. But some Germanic tribes got assimilated to the indigenous Romance cultures, and then their influence vanished or merged with the local traditions.

Simon_W said...

Another dreaded topic is the ethnic interpretation of the archeological cultures in Poland, but that's not directly related to the Völkerwanderungs-topic. At least I'd say it would be strange to argue that there were never any Germanic tribes east of the Oder-Neisse line, just because that happens to be the modern-day Polish-German border.

Simon_W said...

I was digressing. Well, in my opinion Busby et al. needn't have offered any historical interpretation for their results, but they were entitled to do so. And since their postulated migrations fall partly into the first millennium AD, it's natural that they thought of the Völkerwanderung. I mean, the German word „Völkerwanderung“ literally means just „migration of peoples“, nothing evil, and to my knowledge it's still a valid notion in archeology and history. And imho the fact that a concept was once misused for bad actions doesn't scientifically invalidate that concept. Besides, to me it's dubious that the concept was the culprit at all. Was it not rather the other way round? Chauvinism led to the wrong interpretation of the Völkerwanderung as a proof for the supremacy of Germans. And by the way, for the National Socialists it wasn't the only proof, but just the endpoint of a long history of Aryan migrations that dominated the ancient world. In fact, the Indo-Europeans really did dominate a lot of the ancient world, the Nazis have just misconceived them as a Nordic and German race.

Suevi said...

Do we have any verifiable evidence for Völkerwanderung from Central Europe? All the written sources from the Early Medieval Period, which relate to the Slavs are scarce. Many Medieval authors suggest that Slavs are descendants of ancient Venedi, who lived somewhere along the Vistula and Baltic coast (see for example Tabula Peutingeriana). This of course needs to be confirmed or denied by Y-DNA and mtDNA continuity since the Iron Age until the Middle Ages. There are no inscriptions from the Iron Age found in the Central Europe, at the time people were illiterate, so linguistics is not of much help here. Cultural elements can be adopted from different ethnic groups, so any conclusions based just on cultural changes seem to be biased. We know exactly where Slavic-Germanic border was in the 7-8th century AD and this should be our starting point.

Suevi said...

Cultural elements can be adopted from different ethnic groups, but language...hmm? We know that Slavic, which derived from PIE is very archaic, so definitely it wasn't invented ~1500 years ago. We know that groups such as Lusatian Sorbs could preserve their language being under domination of much more developed German culture for 1000+ years. Why supposedly Central European Germanic-speaking people ceased to exist and in the 7-8th century AD we have exclusively Slavic lands? The only proof could be in massive DNA change.

Suevi said...

So we have 3 scenarios:
- Slavs arrived from somewhere and settled in Central Europe replacing former inhabitants; could be confirmed or denied by Iron Age and Medieval DNA analysis
- all Germanic-speaking Central Europeans within the area of 500,000+ km2 adopted Slavic language (highly unrealistic scenario); only possible if significant Slavic population with inviting culture came to Slavicise Germanic-speaking tribes
- proto-Slavs were always present in Central Europe, perhaps conquered by Germanic-people in the 300s (see Jordanes), but never really spread from their Central/East European homeland until the 500-600s

Suevi said...

This topic is highly politicized since the late 18th century. Prior to the German nationalism and expansionism, there's been little doubt that Slavs in Central Europe are autochthonous population.