High-resolution stuff

I just emailed this to the authors of High-resolution genomic ancestry reveals mobility in early medieval Europe, a new preprint at bioRxiv [LINK].

I appreciate that Polish population history is not the main focus of your preprint, and also that you're constrained by the lack of relevant and suitably high quality ancient genomes from East-Central and Eastern Europe. However, I must say that your analysis of the Medieval Polish population and resulting conclusions about Polish population history don't reflect reality.

Your Poland_Middle_Ages genomic cluster is made up of just six samples that don't fully represent the genetic complexity of the core population of Medieval Poland.

As a result, you classified PCA0148 as one of the Poland_Middle_Ages outliers, even though this sample isn't an outlier when analyzed within the context of the full set of published Polish Medieval genomes.

Moreover, PCA0148 is very similar to several Polish Viking Age samples that show Scandinavian-specific genome-wide and Y-chromosome haplotypes, and probably likewise shows some Scandinavian-related ancestry.

This is important to note when attempting to recapitulate Polish population history, because it suggests that Scandinavian-related ancestry played a formative role in the shaping of the core Polish Medieval genetic cluster.

Thus, you might be correct when you claim that the six samples in your Poland_Middle_Ages cluster don't show any "detectable" Scandinavian-related ancestry, but this doesn't necessarily mean that this type of ancestry isn't a key part of the post-Iron Age Polish population history.

Below is a self-explanatory Principal Component Analysis (PCA) plot that illustrates my points. Interestingly, Figure 3c in your preprint shows very similar outcomes in regards to the post-Iron Age Polish population history. But the style and scale of your figure makes it difficult to spot the subtle but likely genuine Northwest European-related genetic shifts shown by PCA0148, the Viking context samples and present-day Poles relative to the Poland_Middle_Ages cluster.

However, I'm also skeptical that your Poland_Middle_Ages cluster doesn't carry any detectable or even significant Scandinavian-related ancestry. That's because I suspect that there might be some technical issues with your analysis that are masking this type of ancestry in the Polish samples.

Your top mixture model for the Poland_Middle_Ages cluster is, in all likelihood, an extreme statistical abstraction of reality, rather than a close reflection of it. That's because, due to a combination of historical, geographical and genetic factors, neither Italy.Imperial(I).SG nor Lithuania.IronRoman.SG are realistic formative source populations for the Medieval Polish gene pool.

One of the reasons why you ended up with such a surprising result is probably the lack of suitable samples from East-Central and Eastern Europe, especially those associated with plausibly the earliest Slavic-speaking populations.

It's also possible that basing your mixture model on formal statistics played a key part.

Formal statistics-based mixture models are known to be biased towards outcomes involving mixture sources from the extremes of mixture clines. If your analysis is affected by this problem, then this would help to explain why you characterized the Poland_Middle_Ages cluster as simply a two-way mixture between a Middle Eastern-related group from Imperial Rome and a Baltic population with a very high cut of European hunter-gatherer ancestry.

I do note that on page 6 of your manuscript you consider the possibility that the Southern European-related signal in the Poland_Middle_Ages cluster might only be very distantly related to Italy.Imperial(I).SG, and that it may even have spread across Poland with early Slavic speakers. This is a great point, and I think it should be emphasized and expanded upon, because I suspect that the problem runs deeper than this.

For instance, if the early Slavic ancestors of Poles carried substantially more Southern European-related ancestry than Lithuania.IronRoman.SG, and this ancestry was, say, more Balkan-related than Italian-related, then this might radically change your modeling of the Poland_Middle_Ages cluster. That's because these early Slavs would be positioned in a very different genetic space than Lithuania.IronRoman.SG, which could potentially require a significant signal of Scandinavian-related ancestry to get a robust mixture model.

Finally, it might be useful to consider Isolation-by-Distance as a partial vector for the Italy.Imperial(I).SG-related signal in Medieval Poland.

The full set of published Polish Medieval genomes includes a number of outliers with obvious ancestry from Western Europe and the Balkans. These people probably don't represent any large-scale migrations into Poland, but rather the movements of individuals and small groups. Over time, such small-scale mobility may have had a fairly significant impact on the genetic character of the Polish population.

Update 26/03/2024: I sent another email to Speidel et al., this time in regards to their analysis of present-day Hungarians.

Your preprint also claims that present-day Hungarians are genetically similar to Scythians, and that this is consistent with the arrival of Magyars, Avars and other eastern groups in this part of Europe.

However, present-day Hungarians are overwhelmingly derived from Slavic and German peasants from near Hungary. This is not a controversial claim on my part; it's backed up by historical sources and a wide range of genetic analyses.

Hungarians still show some minor ancestry from Hungarian Conquerors (early Magyars), but this signal only reliably shows up in large surveys of Y-chromosome samples.

The Scythians that you used to model the ancestry of present-day Hungarians are of local, Pannonian origin, and they don't show any eastern nomad ancestry. So they're either acculturated Scythians, or, more likely, wrongly classified as Scythians by archeologists.

And since these so-called Scythians lack eastern nomad ancestry, the similarity between them and present-day Hungarians is not a sign of the impact from Avars, Hungarian Conquerors and the like, but rather a lack of significant input from such groups in present-day Hungarians.

Citation...

Speidel et al., High-resolution genomic ancestry reveals mobility in early medieval Europe, bioRxiv, Posted March 19, 2024, doi: https://doi.org/10.1101/2024.03.15.585102

See also...

Wielbark Goths were overwhelmingly of Scandinavian origin

Para-Turbo-Balto-Slavic?

I'm seeing increasing numbers of Bronze and Iron Age samples from Central Europe and surrounds with this peculiar set of traits:

- shared genetic drift with present-day Balto-Slavic speakers to the exclusion of most other Europeans

- and yet, an unusually low level of Yamnaya-related steppe ancestry

- so much so, in fact, that they're often outside the range of modern European genetic variation.

As far as I can tell, currently the best examples of this unusual population are HUN_Mako_EBA_o:I1502 (Mathieson et al. Nature 2015) and HUN_EIA_Prescythian_Mezocsat_o1:I18241 (Patterson et al. Nature 2021). Both are from the Carpathian Basin in what is now Hungary.

I ran a series of qpAdm mixture models to try and learn more about their origins. The most robust outcomes, out of about 50 different attempts, are these:

right pops:
CMR_Shum_Laka_8000BP
MAR_Taforalt
IRN_Ganj_Dareh_N
Levant_PPNB
TUR_Barcin_N
Iberia_Southeast_Meso
UKR_Meso
England_Meso
RUS_Karelia_HG
RUS_West_Siberia_HG
MNG_North_N
TWN_Hanben
BRA_LapaDoSanto_9600BP

HUN_Mako_EBA_o
Baltic_LTU_Narva 0.149 ∓0.028
POL_Globular_Amphora 0.613 ∓0.028
Yamnaya_RUS_Samara 0.238 ∓0.029
chisq 10.836
tail prob 0.370463
Full output

HUN_EIA_Prescythian_Mezocsat_o1
Baltic_LTU_Narva 0.186 ∓0.028
POL_Globular_Amphora 0.592 ∓0.027
Yamnaya_RUS_Samara 0.222 ∓0.029
chisq 12.492
tail prob 0.253499
Full output

Combining the two genomes produces a very similar result:

HUN_EBA-EIA_o
Baltic_LTU_Narva 0.160 ∓0.023
POL_Globular_Amphora 0.612 ∓0.023
Yamnaya_RUS_Samara 0.227 ∓0.023
chisq 14.653
tail prob 0.14524
Full output

Importantly, when I move RUS_Karelia_HG from the right pops to the left pops, to test whether HUN_EBA-EIA_o really has steppe ancestry, as opposed to closely related hunter-gatherer ancestry, I still get a very similar outcome:

HUN_EBA-EIA_o
Baltic_LTU_Narva 0.158 ∓0.027
POL_Globular_Amphora 0.605 ∓0.033
RUS_Karelia_HG 0.014 ∓0.038
Yamnaya_RUS_Samara 0.223 ∓0.053
chisq 10.461
tail prob 0.234171
Full output

So these largely Globular Amphora-related individuals do harbor as much as a quarter of steppe ancestry, which is to be expected considering the massive genetic turn-over that most of Europe experienced just before their time as a result of population expansions from the Pontic-Caspian steppe.

Nevertheless, this is ~20% less steppe ancestry than in the present-day populations of the region, and it clearly shows in any decent Principal Component Analysis (PCA) of West Eurasia. For instance:

At the same time, the relatively close genetic relationship between these ancients and present-day Balto-Slavic speaking populations shows up in fine-scale intra-European PCA.

The origins and implications of this population are still a mystery to me. I don't think it's native to the Carpathian Basin. Indeed, my qpAdm models suggest that it may have moved into this region from somewhere to the northeast, because its ancestry is best modeled with ancient groups from present-day Lithuania, Poland and Russia.

I'm adamant that these people weren't Balto-Slavic speakers, and certainly not proto-Slavs. Rather, I suspect that much like the Welzin warriors of Bronze Age North-Central Europe, they were closely related to a contemporaneous group that eventually gave rise to proto-Slavs. At best, they may have somehow contributed to the ethnogenesis of Balto-Slavs.

By the way, using the Global25 to model their ancestry is highly problematic, because of the strong Balto-Slavic genetic drift that affects some of the dimensions. So be careful when you try it, or better yet, don't try it at all, and stick to formal stats in this particular instance.

See also...

Tollense Valley Bronze Age warriors were very close relatives of modern-day Slavs

Population genetics is a state of mind

Years of blogging about population genetics has seriously eroded my faith in the peer review process.

During the past decade I've witnessed an inordinate amount of crap published in basically all of the major science journals. Often the work is misguided in some way, sometimes even quite strange, and occasionally outright wrong.

Back in 2014, a team of scientists from the UK published a paper in Science emphatically titled A Genetic Atlas of Human Admixture History. These people were Garrett Hellenthal, George B. J. Busby, Gavin Band, James F. Wilson, Cristian Capelli, Daniel Falush, and Simon Myers. See here.

The thing that really sticks out for me in this paper is Figure 3, which shows the present-day Polish population as largely a mixture between Northern European- and Turkish-related ancestries. Incredibly, the Turkish-related ratio appears to be about 25% and dated to 438 CE.

This is not just inexplicable, but utterly wrong. It's a result that is impossible to reproduce with any standard population genetics methods.

In fact, in terms of deep ancient ancestry, present-day Poles are very similar to present-day Scandinavians, and even to Viking Age, Iron Age and Bronze Age Scandinavians. This is easy to demonstrate, for instance, with f4-statistics, in part based on samples from the Hellenthal et al. paper.

Chimp Yamnaya_Samara Swedish_modern Polish_modern -0.000311 -1.574
Chimp Yamnaya_Samara Ollsjo_Bronze_Age Polish_modern -0.000044 -0.152
Chimp Yamnaya_Samara Sealand_Iron_Age Polish_modern -0.000072 -0.293
Chimp Yamnaya_Samara Sealand_Viking_Age Polish_modern 0.000078 0.525
Chimp Yamnaya_Samara Gotland_Viking_Age Polish_modern -0.000141 -1.322

Chimp Barcin_N Swedish_modern Polish_modern -0.000318 -1.662
Chimp Barcin_N Ollsjo_Bronze_Age Polish_modern 0.000216 0.798
Chimp Barcin_N Sealand_Iron_Age Polish_modern -0.000023 -0.104
Chimp Barcin_N Sealand_Viking_Age Polish_modern -0.000186 -1.310
Chimp Barcin_N Gotland_Viking_Age Polish_modern 0.000083 0.788

Chimp Karelia_HG Swedish_modern Polish_modern -0.000134 -0.540
Chimp Karelia_HG Ollsjo_Bronze_Age Polish_modern 0.000056 0.162
Chimp Karelia_HG Sealand_Iron_Age Polish_modern 0.000047 0.153
Chimp Karelia_HG Sealand_Viking_Age Polish_modern 0.000424 2.241
Chimp Karelia_HG Gotland_Viking_Age Polish_modern 0.000134 0.959

Simply put, if Poles have ~25% ancestry from a Turkish-related source, then so do Swedes, Norwegians and basically all other Northern Europeans going back hundreds and even thousands of years. This is obviously not the case, and it's also not what Hellenthal et al. claimed anyway.

A year later, a team of scientists that again included Garrett Hellenthal, George B. J. Busby, James F. Wilson, Cristian Capelli and Simon Myers, published another, similar paper in Current Biology. And guess what? This paper also claimed that present-day Poles had Turkish-related ancestry, but this time dating to a somewhat later period. See Busby et al. 2015 Figure 4.C here.

I've got most of the samples from that paper, so I can analyze them myself, and I think I know what the problem is. Basically, the Turks are mixed. So what appears to have happened is that Busby et al. got things backwards.

Below are three plots from a Principal Component Analysis (PCA) largely based on data from Busby et al., featuring samples from England, Germany, Norway, Poland and Turkey. The first plot is based on dimensions 1 and 2, the second plot on dimensions 1 and 3, and the third plot on dimensions 1 and 4. The relevant data file is available here.

Note that the Europeans are more or less symmetrically related to the Turks, which means none of these European populations has significantly more Turkish-related ancestry than the others. Indeed, it's the Turks who show more variation in the first (horizontal) dimension, suggesting that they might have variable levels of European ancestry.

I chose the aforementioned papers to make my point here because they made quite an impression on me. In other words, they really pissed me off.

For the sake of completeness, I'm now going to try and get in touch with the authors and ask them how on earth they managed to make these Poles Turkish-related, and also why they never corrected their mistake.

See also...

Don't believe everything you read in peer reviewed papers

Yamnaya-related ancestry proportions in present-day Poles

Modeling ancient ancestry proportions in present-day Europeans with the qpAdm software is now a lot more difficult. The reasons for this are updates to qpAdm as well as the availabiity of more useuful outgroups or right pops.

This isn't necessarily a bad thing, because users are forced to work harder to find successful models, which is likely to lead to some interesting discoveries. But it can be very frustrating.

I don't think that settling for poor statistical fits or using a small number of outrgoups are acceptable short cuts. Perhaps sequencing modern-day samples in exactly the same way as the ancient samples, and thus increasing the compatability between them, might help?

Limiting qpAdm runs to higher quality SNPs from transversion sites does help, but perhaps largely because of the significant reduction in markers?

In any case, I've now given up on running such analyses, at least until I see some serious pointers on the topic from Harvard's qpAdm experts. But before I put this project to bed for the time being, I'd like to share some new results for Poles from eastern and western Poland, respectively.

right pops:

CMR_Shum_Laka_8000BP
MAR_Taforalt
IRN_Ganj_Dareh_N
Levant_PPNB
GEO_CHG
TUR_Barcin_N
RUS_Piedmont_En
SRB_Iron_Gates_HG
WHG
RUS_Karelia_HG
MNG_North_N
RUS_Ust_Kyakhta

left pops:

Polish_East
CWC_Baltic_early 0.572±0.024
SWE_TRB 0.428±0.024
chisq 11.776
tail prob 0.300296
Full output

Polish_West
CWC_Baltic_early 0.587±0.021
SWE_TRB 0.413±0.021
chisq 11.165
tail prob 0.34478
Full output

Even using transversion sites, this is one of the very few combinations of ancient reference samples that works for the Poles with these right pops. That is, the combination of early Corded Ware samples from the East Baltic (CWC_Baltic_early) and Funnel Beaker samples from Scandinavia (SWE_TRB). The former are obviously the proxy here for Yamnaya-related ancestry.

Adding any sort of hunter-gatherer population to this model doesn't help or even makes things worse (for instance, see here and here). It is possible to add Baltic hunter-gatherers to a similar model after dropping CWC_Baltic_early in favor of closely related samples from the Early to Middle Bronze Age Pontic-Caspian steppe. Note, however, that the statistical fits are somewhat poorer.

Polish_East
Baltic_LTU_Narva 0.032±0.014
PC_steppe_EMBA 0.483±0.019
SWE_TRB 0.485±0.019
chisq 17.143
tail prob 0.0465198
Full output

Polish_West
Baltic_LTU_Narva 0.031±0.011
PC_steppe_EMBA 0.491±0.015
SWE_TRB 0.477±0.016
chisq 22.444
tail prob 0.00757421
Full output

Interestingly, but not surprisingly, the ancestry of many present-day Northwestern European populations can be modeled in basically the same way. That's because ancient ancestry proportions are more closely correlated with latitude than longitude across much of the European continent.

English_Kent
CWC_Baltic_early 0.527±0.024
SWE_TRB 0.473±0.024
chisq 13.042
tail prob 0.221357
Full output

Icelandic
CWC_Baltic_early 0.586±0.023
SWE_TRB 0.414±0.023
chisq 16.517
tail prob 0.085751
Full output

Scottish
CWC_Baltic_early 0.583±0.021
SWE_TRB 0.417±0.021
chisq 12.144
tail prob 0.275536
Full output

A zip file with the qpAdm output from this analysis and a list of the most relevant ancients is available here. I might try to run a few more populations over the next few days, but probably only from the northern half of Europe, so please check the zip file in a week or so to see what else is in there.

If anyone wants to challenge my results, note that these and very similar samples are freely available to the public via Harvard University here and here.

Update 22/08/2020: From Nick Patterson (Broad) in the comments:

My general advice for qpAdm is 1) Work on the right hand set. Don't include irrelevant population (except for one population as an outgroup); picking the best RHS can dramatically reduce s. errors on the admixture weights. 2) If qpAdm gives a very low p-value try and understand why, sometimes it is telling you that the target is not a mixture of the sources but sometimes the assumptions are violated, for example recent gene-flow from left pops -> right.

See also...

Ancient ancestry proportions in present-day Europeans

Don't believe everything you read in peer reviewed papers

Case in point, here's a quote from a recent paper at the Journal of Human Genetics (emphasis is mine):

The Mordovian and Csango samples have a moderate to slight orientation toward the Central-Asian and Siberian Turkic groups. This could suggest the more significant East Eurasian or Turkic ancestry of these populations, which should be further investigated. German samples are inhomogeneous, and some of the German samples also show this tendency, which can be the result of the recent 20th century Turkish immigration into Germany [42].

Nope, these German samples don't show anything even remotely resembling recent Turkish ancestry. The authors of the paper, Ádám, V., Bánfai, Z., Maász, A. et al., should've been able to figure this out, even with the standard analyses that they ran. Failing that, the peer reviewers at the Journal of Human Genetics should've noticed that the authors were confused.

Moreover, if the authors and peer reviewers actually bothered to take a closer look at metadata for these samples, which were sourced from the Estonian Biocentre, they'd see that they're not even from Germany. In fact, they represent self-reported ethnic Germans from Russia.

My own quick and dirty analysis of these individuals suggests that many of them harbor East Slavic and/or Volga Finnic ancestries. Indeed, only some of them can pass genetically for run of the mill Germans from Germany. The Principal Component Analysis (PCA) below is self-explanatory. It was plotted with the Vahaduo Custom PCA tools freely available here. The relevant PCA datasheet can be gotten here.

That's not to say, of course, that some Germans don't have recent Turkish ancestry, because an increasing number of Germans nowadays do, nor that people with German heritage in Russia shouldn't identify as Germans, because that's entirely their choice.

This blog post isn't about what it takes to be German, and this is not something that I ever want to discuss for obvious reasons. The point I'm making here is that the authors and peer reviewers of the said paper at the Journal of Human Genetics were sloppy and half-arsed in their approach. And, sadly, this isn't an isolated case in peer reviewed scientific literature dealing with human population genetics.

I feel that the Estonian Biocentre is also partly to blame for this cock up, due to its somewhat peculiar sampling and labelling strategies. For instance, its scientists rely solely on self-reported identity to establish the ethnic origins of their samples, and they apparently never remove genetic outliers from their datasets or even try to identify them.

Unfortunately, I fear that this relaxed approach will eventually lead to basic errors and even unusual conclusions in a number of so called peer reviewed papers.

I first raised this issue with the Estonian Biocentre about five years ago, when I noticed that some of the supposedly Polish individuals in its dataset were genetically more similar to various groups from northern Russia than to Poles from Poland. These individuals also showed significant Siberian ancestry, which was very unusual indeed. Where the hell did the Estonian Biocentre find Poles who resembled people from near the Arctic Circle, you might ask? Apparently in Estonia.

OK, I can imagine that sampling ethnic Poles from Estonia may have been easier for the Estonian Biocentre than sampling Poles from Poland. And Estonian Poles certainly make for interesting and useful data points. However, as you can see in the PCA below, some of these individuals (labeled Polish_Estonia by me) aren't representative of the native Polish population, and yet the Estonian Biocentre not only lumps them with their Poles from Poland, but even labels them with the word "Poland". The relevant PCA datasheet can be gotten here.

However, based on my communications with some of the scientists at the Estonian Biocentre, including head honcho Mait Mestpalu, it seems that nothing will ever change there in regards to this issue. Who knows, perhaps some day we'll see a paper based on Estonian Biocentre data in the Journal of Human Genetics claiming that Poles originated near the Arctic Circle? I wouldn't be shocked if that actually happened.

Citation...

Ádám, V., Bánfai, Z., Maász, A. et al. Investigating the genetic characteristics of the Csangos, a traditionally Hungarian speaking ethnic group residing in Romania. J Hum Genet (2020). https://doi.org/10.1038/s10038-020-0799-6

See also...

Like three peas in a pod