Tuesday, December 29, 2015

Time Window Of Transition From First Farmer To Steppe Ancestry In Ireland Narrowed

As I've suspected since at least about four year ago, the modern Western European genetic profile, with lots of Y-DNA R-1b, lactase persistence, and steppe-like autosomal ancestry is a package that arrived sometime after the first wave Neolithic farmers of the megalithic culture and was in place by the Bronze Age in Western Europe, with the Bell Beaker People (whose own linguistic affiliation and origins are somewhat cryptic).

Both Paleolithic continuity theories and Neolithic continuity theories for the source of the modern Western European genotype are now basically ruled out by the ancient DNA.

The window of time in which this happened is narrowed to roughly 3000 BCE to 2000 BCE, i.e. Chalcolithic or early Bronze Age, and probably coincides with about 2500 BCE in Ireland when the Chalcolithic age began and Bell Beaker people appeared.

The Chalcolithic people were able to have such a large demographic impact because farming after thriving in Ireland from ca. 3700 BCE to 3400 BCE, then basically collapsed with farmers reverting to hunting and gathering for much of their sustenance.

As usual, I am skeptical that the wave of migration that brought this demographic transformation was in fact Indo-European Celtic, as obvious an assumption as that might seem, as opposed to a scenario in which the genetic shift is associated with a Bell Beaker linguistically Vasconic population and the language shift from a Vasconic substrate to Celtic occurs later ca. 1200 BCE around the time of Bronze Age collapse.
The Neolithic and Bronze Age transitions were profound cultural shifts catalyzed in parts of Europe by migrations, first of early farmers from the Near East and then Bronze Age herders from the Pontic Steppe. However, a decades-long, unresolved controversy is whether population change or cultural adoption occurred at the Atlantic edge, within the British Isles. We address this issue by using the first whole genome data from prehistoric Irish individuals. 
A Neolithic woman (3343–3020 cal BC) from a megalithic burial (10.3× coverage) possessed a genome of predominantly Near Eastern origin. She had some hunter–gatherer ancestry but belonged to a population of large effective size, suggesting a substantial influx of early farmers to the island. 
Three Bronze Age individuals from Rathlin Island (2026–1534 cal BC), including one high coverage (10.5×) genome, showed substantial Steppe genetic heritage indicating that the European population upheavals of the third millennium manifested all of the way from southern Siberia to the western ocean. This turnover invites the possibility of accompanying introduction of Indo-European, perhaps early Celtic, language. 
Irish Bronze Age haplotypic similarity is strongest within modern Irish, Scottish, and Welsh populations, and several important genetic variants that today show maximal or very high frequencies in Ireland appear at this horizon. These include those coding for lactase persistence, blue eye color, Y chromosome R1b haplotypes, and the hemochromatosis C282Y allele; to our knowledge, the first detection of a known Mendelian disease variant in prehistory. These findings together suggest the establishment of central attributes of the Irish genome 4,000 y ago.
Lara M. Cassidy, Rui Martiniano et al. "Neolithic and Bronze Age migration to Ireland and establishment of the insular Atlantic genome" PNAS (2015) (paragraph breaks and emphasis mine).

Eurogenes posts the results without original post comment, but there is lots of discussion in the comments to the post.

According to Bernard's post, the Y-DNA type for all three men was (to the extent of commonality): R1b1a2a1a2c aka R1b-L21, the most common Y-DNA type in the British Isles today, and a sister clade of the Yamnaya Y-DNA R1b haplogroup.

He notes (in French):
Ils appartiennent à l'haplogroupe du chromosome Y: R1b-L21. Cet haplogroupe est fréquent aujourd'hui dans les Îles Britanniques. On a retrouvé son haplogroupe "père" R1b-P312 dans tous les squelettes campaniformes d'Europe Centrale et son haplogroupe "oncle" R1b-Z2103 dans la plupart des squelettes de la culture Yamnaya dans les Steppes Pontiques. Ces haplogroupes sont absents chez les squelettes des chasseurs-cueilleurs et des fermiers Néolithiques d'Europe.
The mtDNA profile of the three Bronze Age individuals, two of which have mtDNA U5a, suggests that the Bronze Age impact may have been male dominated with Bell Beaker men marrying local women many of whom had hunter-gatherer matriline ancestors.

Dienekes' Anthropology Blog notes from the body text of the article the following ancestry proportions in the Bronze Age sample:
Linearbandkeramik (Early Neolithic; 35 ± 6%), Loschbour (WHG; 26 ± 12%), and Yamnaya (39 ± 8%), in the total Irish Bronze Age group. These three approaches give an overlapping estimate of ∼32% Yamnaya ancestry.
Typically of Middle Neolithic individuals, the Irish Neolithic sample is enriched in hunter-gatherer ancestry relative to early Neolithic individual, probably indicating a resurgence of local relict hunter-gatherer populations, whose status increased and facilitated introgression, when farming was temporarily discredit after the failure of the first wave of farming in Ireland.  But, she had no steppe ancestry.  The ancestry percentages aren't inconsistent with a near total replacement of Bronze Age men with proportionately fewer migrating Bell Beaker women.

Previous studies have shown an affinity to Iberian genetics in the British Isles and I haven't had time to read this closely enough to determine if these studies affirm that conclusion.  On the other hand, intriguing cultural and linguistic clues seem to connect the Balkans and Ireland, although the direction of transmission is not obvious.

In the PCA chart from the paper, the Hungary and German Late Neolithic and Bronze Age individuals are closer to the Irish samples than the Spanish Chalcolithic samples, which are at the Neolithic farmer side of an axis that has German Corded Ware and Steppe individuals at the other end of the axis.

Razib has meaty coverage with lots of context and analysis, most of which  I tend to agree with (he does not directly engage with the linguistic question).  He notes the relevance of legendary history which shouldn't be taken literally but provides useful information.  He provides the general context which is familiar to most of my readers. Particularly noteworthy is this little bit of insight:
But some inferences can be made with various techniques, the details for which you should read the supplements. The Neolithic female seems to be descended from Cardial, and not LBK, early European farmers. That is, the Irish Neolithic is connected to the Atlantic littoral, in keeping with Barry Cunliffe’s thesis in Facing the Ocean. Second, the excess hunter-gatherer ancestry in the Neolithic female exhibits greater affinities with the Loschbour hunter-gatherer from Luxembourg than hunter-gatherers from Central or Eastern Europe. This indicates that as with the the situation in Spain there was local admixture with hunter-gatherers over time.

Naturally this leads one to wonder if the early European farmer ancestry in the Bronze Age Irish samples was from the same group as that of the Neolithic farmer. The surprise is that there isn’t any strong evidence of admixture! Rather, there are better candidates for donor populations on the European continent. The most parsimonious explanation then is that the Bell Beakers mixed with early European farmers, and then rolled over the descendants of the Megalith builders in Ireland. But confidence in this sort of conclusion is weak, as the number of populations is finite, and one should be cautious about making too many inferences from a few samples (though modern Irish are actually a decent proxy for the Bronze Age Irish).
From off topic comments on this paper to another of my posts at this blog form Nirjhar007 on December 28, 2015:
Do you think its too early for that R1b to be IE?
Do you this goes along with this? 
Metallurgy arrived in Ireland with new people, generally known as the Bell Beaker People, from their characteristic pottery, in the shape of an inverted bell.[9] This was quite different from the finely made, round-bottomed pottery of the Neolithic. It is found, for example, at Ross Island, and associated with copper-mining there. It is thought by some scholars to be associated with the first appearance of Indo-Europeans in Europe (possibly Proto-Celtic),[10] though this theory is not universally accepted. 
The Bronze Age began once copper was alloyed with tin to produce true Bronze artefacts, and this took place around 2000 BC, when some Ballybeg flat axes and associated metalwork were produced. The period preceding this, in which Lough Ravel and most Ballybeg axes were produced, and which is known as the Copper Age or Chalcolithic, commenced about 2500 BC.
I think it is increasingly undeniable that the Chalcolithic demic change in Western Europe was due to the Bell Beaker People.

But, I also continue to think that the Bell Beaker people were not Proto-Celtic IE people, despite the trend in most of the 20th century's anthropology to think of Bell Beaker is something other than a folk migration, and that instead there was a subsequent language shift around the time of Bronze Age collapse with much less demic impact.  Mostly this is because I don't think that Basque people who exemplify the Western European Chalcolithic source were ever proto-Celtic speakers and because of the Vasconic substrate in place names in Western Europe and the thousand year division between Bell Beaker derived territory and Corded Ware territory culturally.

I do think that the geographic range of Celtic closely tracks places that had a Vasconic substrate, however, and is distinct as an IE language family largely due to that substrate influence.  It isn't impossible to imagine that the Bell Beaker people were linguistically Vasconic, and I do think that the language of the first farmers was probably closer to Vasconic than IE was, but I don't think that the megalithic first farmer language survived anywhere (except perhaps on a few Mediterranean islands like Sardinia) into historically attested times.

In other Bell Beaker news, Bell Beaker mtDNA is closer to Minoan mtDNA than to somewhat similar Androvo and Unitice mtDNA.  Rossen mtDNA is considerably more dissimilar.  This follows suggestive evidence from Y-DNA and other sources of Minoan-Bell Beaker similarity, although neither case has really been conclusive.

I suspect that the Minoans were part of the Aegean wave of an Anatolian demic transition between first farmers and early metal age farmers.  Even if they weren't directly ancestral to the Bell Beaker people, they probably had common origins and quite possible belonged to the same language family.


Nirjhar007 said...

Thank you for the post!.
Chalcolithic in Ireland arrived with Bell Beakers, originally from the continent, so it is not excluded that they brought some steppe DNA arrived in the third mill. BC, but I don't understand from the paper where is the
proof of EHG and Yamnaya, because the rose component is also WHG and the green component is originally Caucasian or near, as admitted by the paper itself.
It is remarkable that the closest triangles in the PC map B are of Bell Beaker and Unetice, a culture heir of Bell Beaker according to some scholars. It is curious that Sintashta/Andronovo are closer than CW and

About Celts in Ireland, the main theory is that they arrived in the Iron age in small numbers:
It seems there was also a recent memory of Gaelic invasion, and curiously they have a possible Scythian origin, as mentioned in Khan's blog:
Genetically, it is rather R1b-U152 which is connected with Celts (and apparently also Italics),
with 5-10% in certain parts of Ireland. The fact that it is not found in the Bronze Age site can be interesting.

andrew said...

Interesting links, of which I had not been aware, that tend to support my analysis. See also my riff on the Irish origin myth in a later post.

capra internetensis said...


The proof is not in the ADMIXTURE components but in the D statistics:

Mbuti, Eastern_HG : Rathlin1, Ballynahatty -0.0422 -8.864
Mbuti, Yamnaya : Rathlin1, Ballynahatty -0.0326 -9.039

Which can't be explained by an increase in WHG:
Mbuti, Western_HG : Rathlin1, Ballynahatty 0.0072 1.609

So there is clearly a real and major increase in EHG ancestry. On the other hand there are no statistics using CHG (presumably the genomes came out too late to be included) so (as with Bell Beaker) it is not clear how much is really Yamnaya and how much is related CHG + EHG ancestry from other sources.

Overall they appear close to Copper/Early Bronze Age Central Europeans, especially Bell Beaker:

Mbuti, Ballynahatty : Irish_Bronze, Bell_Beaker 0.0007 0.217
Mbuti, Ballynahatty : Irish_Bronze, Unetice -0.0018 -0.568
Mbuti, Ballynahatty : Irish_Bronze, Corded_Ware -0.0061 -1.638

Mbuti, Yamnaya : Bell_Beaker, Irish_Bronze 0.0005 0.215
Mbuti, Yamnaya : Unetice, Irish_Bronze -0.0051 -2.287
Mbuti, Yamnaya : Corded_Ware, Irish_Bronze -0.0175 -6.682