About one year ago, I realised that haplogroup R1b originated somewhere between Central Asia and the Middle East, then moved through the Pontic steppe where it became associated with Indo-European culture, before pushing its way through the Danube valley and Western Europe.
It all made sense. The older subclades of R1b were found East. R1b1a was found among the Levantines and R1b1* in central Africa with a trail leading back to Egypt and the Middle East 12,000-15,000 years ago. The highest diversity of R1b1b1 and R1b1b2 was found in Anatolia and the Caucasus, and the split between these two haplogroups occurred around Anatolia. Both subclades were found in Russia, Central Asia and Pakistan, an obvious sign that they had been part of the Indo-European migrations, at least in Asia.
One thing kept bugging me with this nice theory. How did R1b lineages come to replace most of the older lineages in Western Europe ? I tried to explain that with a series of factors (polygamy, status, war...), but somehow that still didn't explain why R1b reached tremendous frequencies in places like Ireland, Wales, Cornwall, Brittany or the Basque country, and not elsewhere. I think I have come up with a reasonable answer to this mystery.
I was looking at a map of metal-rich zones in Europe, and more specifically where copper, tin, silver and gold mines had been established in the Copper and Bronze Age. The richest regions were the Anatolia, North Caucasus, the Carpathians (Romania), the Balkans (especially central Bulgaria), the Alps, and the Atlantic fringe of Europe ( Ireland, Wales, Cornwall, Brittany). This was exactly the migration route I had established a year ago for R1b1b2. R1b people were evidently metal workers.
The second element that dawned on me is that the Atlantic fringe from Galicia to the Scottish Highlands, must have been poor agricultural land for early farmers. This may be why farming spread later to these regions, and that aboriginal Megalithic cultures thrived there more than anywhere else. What does that have to do with R1b ? The Proto-Italo-Celts that brought R1b lineages to Western Europe from the North Caucasus and Pontic steppes had an economy relying on stockbreeding and herding more than farming. The European Bronze Age is characterised by the sharp diminution in agriculture and an increase in domesticates. The steppe culture was replacing the Neolithic lifestyle.
Where else could this have the most dramatic effect on the population structure than in the Atlantic fringe, where the Neolithic/Chalcolithic population was sparser than elsewhere due to the late adoption of agriculture and low yield of the farms ? The arrival of the metal-hungry, horse-riding and warlike Indo-Europeans with their bronze swords and axes was a death sentence to the locals. The green pastures of the Atlantic were a boon for the flocks of cattle and herds of sheep of the Indo-Europeans. It was like a milder-climate version of the steppes with the added bonus of being rich in copper and tin, the two components of bronze.
Mitochondrial DNA analysis of R1b regions
To verify my hypothesis, I checked the mtDNA frequencies around Europe to see which region had the most maternal lineages typically associated with the Pontic-Caspian steppes, Caucasus and northern Anatolia. The most easily identifiable Indo-European mtDNA lineages are I, U2, U3, U4 and W. The Indo-Europeans also had plenty of H, U5, and some K, T and V as well. Unfortunately, these haplogroups being the same as in the Neolithic European population, they are useless for comparison.
Here are the combined percentage for these five haplogroups for populations from Anatolia to the steppes, based on a Europe-wide study by Simoni et al.. Note that Simoni did not test for U2, so percentages should be a bit higher in southern Russia and the Caucasus.
- 17.7% for the Volga-Finnic people (mostly U4 with some I)
- 12.57% for European Russians (Helgason data)
- 24% for the Adygeys of the North Caucasus (very high incidence of I and U3)
- 19.9% for the Georgians of Central Caucasus (well balanced haplogroup distribution)
- 15.9% for the Turks (well balanced too)
- 16.7% for the Bulgarians (U3 and U4)
A high presence of Pontic-Caspian/Caucasian mtDNA in regions of Western Europe where R1b is high would indicate a migration on a large scale, not just a military conquest by men or a diffusion of royal/noble paternal lineages.
Ireland is an interesting case because it is the remotest part of Europe from the Pontic-Caspian region, and yet one where R1b makes up over 80% of male lineages. I wasn't expecting to find a link because I thought that R1b men would have intermarried to frequently with local European women for steppe mtDNA to survive in substantial level in the westernmost region of Europe.
Helgason's study gives respectively 2.34% of I, 0.78% of U2, 0% of U3, 2.34% of U4 and 2.34% of W. 7.80% in total. Compared with other Western European countries, Ireland has more steppe/Indo-European mtDNA than France/Italy (5.26%), Iberia (5.4%), Scandinavia (6.52%) or England/Wales (7.69%), and only slightly less than Germany (8.74%) and the Alps (Austria/Switzerland, 9.04%).
H1, a haplogroup typical of the Paleolithic Western European population is surprisingly low in Ireland - in fact lower than anywhere else in Europe except Bulgaria and Turkey. This could mean that a major population replacement happened in Ireland, not just for paternal linages but also maternal ones.
Helgason's data for Cornwall (11.6%), Wales (3.3% - only hg I), mainland Britain (7%), Belgium (6.3%), France (5.4%) and Denmark (3.1%) confirms an exceptionally high incidence of IE maternal lineages in Cornwall, but not in Wales, by north-western European standards. Cornwall is one of the richest regions of Europe for tin, one of the most valuable metals during the Bronze Age. The Indo-Europeans would have settled in the region in great numbers to secure the resource. The data for modern Wales does not reflect the ancient population because modern Welsh descend mostly from ancient Britons from present-day England, pushed west by the Anglo-Saxons.
I couldn't find data for Brittany. Like for Wales, the modern population of Brittany hardly reflects on the ancient people, because Brittany was resettled by immigrants from Britain during the late Roman period.
Helgason's study separates data for North and South Germany. As expected by the pattern of Danubian migration, South Germany has much more Pontic/Caucasian-specific mtDNA (12% against 4.6%). Austria has 9.4%, Switzerland 8.4% and Alpine Italy 7.9%. The number of IE mtDNA diminishes as one moves away from the Danube.
In Spain, Galicians (12.3%), Catalonians (26.6% ! => all U4 and W) stand out remarkably against Central Spaniards (4.4%), Southern Spaniards (6.5%) and Portuguese (7.5%). Cantabrians (10.3%) also have a higher than average number of Pontic/Caucasian mt-haplogroups. Catalonia has the highest percebtage of R1b in Spain along with the Basque country.
The Basques, on the other hand, have 0% of I/U2/U3/U4/W according to Helgason and 1.8% in Maca-Meyer's study. The Basque country is the only high R1b region that lacks its mtDNA equivalents. The best explanation is that the Basque was not settled by Indo-Europeans, but that its male rulers (and aristocracy) became Indo-European and married local princesses/women. The founder effect would have amplified quickly with time if the R1b royalty/nobility produced a lot of sons (gender bias) or took a lot of local wives (polygamy). This is surely why the Basques did not lose their pre-IE language and identity. In any case, the weighed average for Y-DNA and mtDNA is lower among the Basques than for most of Western Europeans.
Overall, we see that the regions of Western and Central Europe with the highest frequencies of Pontic-Caspian/Caucasian mtDNA are found around the Alps (12% peak in southern Germany), in Catalonia (Pyrenees region) and in the metal-rich, rocky, pasture lands unsuitable for primitive agriculture of Ireland, Cornwall, Cantabria and Galicia.
It is probably not a coincidence that Ireland, Cornwall or Galicia have retained a stronger Celtic identity than other places in Europe.