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May 10, 2017

The Bronze age demographic transformation of Britiain

Filed under: Bell Beaker,Britain,Evolution,History,Human Genetics,Human Genomics — Razib Khan @ 8:52 am

In Norman Davies’ the excellent The Isles: A History, he mentions offhand that unlike the Irish the British to a great extent have forgotten their own mythology. This is one reason that J. R. R. Tolkien created Middle Earth, they gave the Anglo-Saxons the same sort of mythos that the Irish and Norse had.

But to some extent I think we can update our assessments. Science is bringing myth to life. The legendary “Bell Beaker paper” is now available in preprint form, The Beaker Phenomenon And The Genomic Transformation Of Northwest Europe. The methods are not too abstruse if you have read earlier works on this vein (i.e., no Nick Patterson authored methodological supplement that I saw). And the results are straightforward.

And what are those results?

First, the Bell Beaker phenomenon was both cultural and demographic. Cultural in that it began in the Iberian peninsula, and was transmitted to Central Europe, without much gene flow from what they can see. Demographic in that its push west into what is today the Low Countries and France and the British Isles was accompanied by massive gene flow.

In their British samples they conclude that 90% of the ancestry of early Bronze Age populations derive from migrants from Central Europe with some steppe-like ancestry. In over words, in a few hundred years there was a 90% turnover of ancestry. The preponderance of the male European R1b lineage also dates to this period. It went from ~0% to ~75-90% in Britain over a few hundred years.

If most of the genetic-demographic character of modern Britain was established during the Bronze Age*, then there has been significant selection since the Bronze Age. The figure to the left shows ancient (Neolithic/Bronze age) frequencies of selected SNPs, with modern frequencies in the British in dashed read. The top-left SNP is for HERC2-OCA2, the region related to brown vs. blue eye color, and also associated with some more general depigmentation. The top-right SNP is in SLC45A2, the second largest effect skin color locus in Europeans. The bottom SNP is for a mutation on LCT, which allows for the digestion of milk sugar as adults.

The vast majority of the allele frequency change in Britons for digestion of milk sugar post-dates the demographic turnover. In other words, the modern allele frequency is a function of post-Bronze Age selection. This is not surprising, as it supports the result in Eight thousand years of natural selection.

1000 Genomes derived SLC45A2 SNP frequency

At least as interesting are the pigmentation loci. The fact that the derived frequency in HERC2-OCA2 is lower in both British and Central European Beaker people samples indicates that the lower proportion is not an artifact of sampling. Britons have gotten more blue-eyed over the last 4,000 years. Second, SLC45A2 is at shocking low proportions for modern European populations.

HGDP derived SLC45A2 SNP frequency

In the 1000 Genomes the 4% ancestral allele frequency is almost certainly a function of the Siberian (non-European) ancestry. In modern Iberians the ancestral frequency is 18% (and it is even higher in Sardinians last I checked), but in Tuscans it is ~2%. Though not diagnostic of Europeans in the way the derived SNP at SLC24A2 is, SLC452 derived variants are much more constrained to Europe. Individuals who are homozygote ancestral for SNPs atSLC45A2 rare in modern Northern Europeans (pretty much nonexistent actually). But even as late as the Bronze Age they would have been present at low but appreciable frequencies.

This particular result convinces me that the method in Field et al. which detected lots of recent (last 2,000 years) selection on pigmentation in British populations is not just a statistical artifact. Though these papers are solving much of European prehistory, they are also going to be essential windows into the trajectory of natural selection in human populations over the last 5,000 years.

* In the context of this paper the Anglo-Saxon migrations tackled by the PoBI paper are minor affairs because the two populations were already genetically rather close. Additionally, the PoBI paper found that the German migrations were significant demographic events, but most of the ancestry across Britain does date to the previous period.

May 9, 2017

The Beaker is breaking!

The link is up, The Beaker Phenomenon And The Genomic Transformation Of Northwest Europe, but the paper is still processing:

I’ll update the post when I can read the paper.

Bell Beaker going to crash-land and blow our minds soon?

Filed under: Anthroplogy,Bell Beaker — Razib Khan @ 3:03 pm

I’m pretty sure that the Beak part is not a typo…. (if it is, Pontus better delete it)

May 5, 2012

Bell Beakers and R1b

Filed under: Ancient Europe,Anthroplogy,Bell Beaker,R1b — Razib Khan @ 11:20 pm

Over at Dienekes blog he has a post up about the extraction of R1b from a male who lived in Germany 4-5,000 in the past. This is important because R1b is one of the two most common male lineages (on the Y chromosome, passed from father to son) in Europe, and, it has inexplicably been underrepresented or absent in the ancient DNA samples. The other modal lineage is R1a (it too is underrepresented).

I have a pretty good grasp of variation on the autosomal dimension. A modest familiarity with uniparental lineages, Y and mtDNA. And finally, a rather weak understanding of archaeological patterns. Since mtDNA tends to be found at very high concentrations in subfossil remains you’ll get a good yield of that in the near future (as in the paper Dienekes covers). Y chromosomal information is more difficult. The problem with autosomal information is that you need more of it to make robust genealogical inferences (due to confounding with selection, as well as recombination breaking apart haplotypes), though if you manage to hit a functional region that can be very informative.

I assume in the year 2020, and perhaps well ...

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