Monday, July 31, 2017

The Relationship Between The Bell Beaker Culture And Steppe Origins Is Still Opaque

We know from reliable ancient DNA that almost all of Europe (except Iberia) experienced an extreme shift in its population genetic makeup in a roughly one thousand year period after the first wave of farmers in Europe hit a serious slump, in the late Neolithic and early Bronze Age period. In some places, like the British Isles, the impact approximated total replacement.

This revived farming in Europe, coincided with a dramatic rise in lactase persistence, created a new predominant pigmentation phenotype in Europe, infused lots of steppe ancestry into the gene pool, brought a couple of major clades of Y-DNA R1 from very rare to predominant in Europe, and increased the frequency of some mtDNA H clades in Europe significantly. When it had run its course, modern Europe's gene pool was more or less in place. These events more or less coincide with the expansion of the Corded Ware culture in the East (associated with Y-DNA R1a) and with the expansion of the Bell Beaker culture in the West (associated with Y-DNA R1b).

This description doesn't do justice to how extreme what was going on must have been to produce the results that it did. One ethnic group waltzed in and took over and dominated an entire continent previously controlled by other ethnic groups, not just ruling them but at least partially replacing them. Maybe it was conquest. Maybe it was genocide. Maybe the existing people were experiencing an apocalyptic collapse and newcomers arrived and filled the vacuum. The story may have been different at different times and different places. But, it was an epic, vast and traumatic transformation.

Probably the only remotely similar transformation recent enough to have people who experienced who are still living it was the mass migration of Jews to Palestine in the 20th century, and the making of the modern Israeli state, although in the broader sweep of the human history and pre-history, there were many similar events (e.g. Cro-Magnon replacement of Neanderthals in Europe, the first wave Neolithic replacement of hunter-gatherers in Europe, Hebrew migrations into the Levant described in the Biblical Book of Numbers, Bantu expansion in Africa, Han Chinese expansion in Asia, European migration to the Americas and Australia respectively, South Arabian migration to northern Ethiopia, Inuit replacement of Paleo-Eskimos in the Arctic, Na-Dene migrations to the American Southwest).

We now have a lot more ancient DNA from the Bell Beaker culture. And, outside of Iberia, ancient DNA from Bell Beaker people suggests a population with almost as much steppe ancestry as the clearly Indo-European Corded Ware people who were their contemporaries in Eastern Europe.

But, in Iberia, which archaeological evidence points to as the place of origin of the Bell Beaker culture, there was a transition to the Western European clade of Y-DNA R1b (reaching a European peak in the Basque people of the same geographic vicinity), but the amount of steppe admixture is much lower, although not zero.

It isn't really obvious what kind of narrative explains this phenomena.

Were there two separate streams of steppe introgression/replacement with distinct origins? Perhaps an infiltration in Iberia, and an steppe invasion from Central Europe that experienced a culture (and perhaps language) shift to the Bell Beaker culture en route?

Was the Bell Beaker culture a predominantly indigenous invention, which people with steppe ancestry hijacked once it had gathered up steam.

Or, did the steppe ancestry people play an important part in giving rise to the Bell Beaker culture? Perhaps there was a founder population of steppe men in the original Bell Beaker formative community that provided strong cultural advantages to members of the culture, with a relatively modest demic impact. Perhaps those leaders were steppe people who only gained a demic advantage through founders effects when their children dominated the founding populations of Bell Beaker colonies (which native Iberians lacked an inclination to join). Then, did those Bell Beaker colonies perhaps transform non-Iberian societies more than they transformed Iberian ones where society was already relatively "advanced" (and hence less prone to falling sway to steppe cultural dominance)?

Are there other plausible narratives?

We still don't know why Western Europeans ended up with lots of Y-DNA R1b found further south on the steppe, while Eastern Europeans who derived from Corded Ware migrants ended up with lots of Y-DNA R1a. The Bell Beaker culture seems to be intimately tied to the rise of Y-DNA R1b in Western Europe, but we can't point to its origins on a map with any great specificity.

The ancient DNA evidence provides clues, but no really clear cut answers and ultimately, raises as more new questions than it does provide answers to old ones. And, of course, we are particularly looking through a glass darkly when we try to assign linguistic affiliations to already hard to fathom migration waves.

Did the Y-DNA R1a people of the steppe speak a different language (Indo-European or otherwise) from the Y-DNA R1b people of the steppe? They were certainly fairly well sorted patrilineages despite an absence of obvious physical boundaries between the two populations (although more ancient DNA suggests that the sorting was not complete).

Were the Bell Beaker people linguistically Indo-European, Vasconic, something else, or were they not linguistically homogeneous? 

If the Bell Beaker people, or some of them, were linguistically Vasconic, is that a language brought by steppe populations to Western Europe, or is it a language derived from the first farmers of the region (perhaps a language of Iberian farmers in particular, where the genetic impact on the Bell Beaker people was weakest, suggesting a potential that they rather than the locals could have experienced a language shift, and where the Vasconic languages were attested last historically).

If some or all of them were Indo-European linguistically, were the proto-Celtic or pre-Celtic, even though linguistic study of the Celtic and Italic languages suggests an early Iron Age time depth, rather than an early Bronze Age or Enolithic time depth? If so, what makes this language family look so young?

In the meantime, we are rapidly collecting more puzzle pieces in the hope of finding answers to these questions. 


Samuel Andrews said...

Yeah we live in really interesting times. Ancient DNA is like traveling back in time. None of what we're learning could have been discovered with just modern DNA.

Yes the heavily Steppe R1b P312 made a smaller demographic impact on Iberia than Britain/Ireland. But their impact on Iberia was still pretty big. Because think about it, when they arrived in Iberia they may have been only 50% Steppe and modern Iberians are estimated to be 20-30%.

Iberians might trace 50% of their ancestry back to the Eastern newcomers. That's not ~90% like in Ireland but it's still a lot.

Samuel Andrews said...

It'll be interesting to see how R1b U106 fits in the picture. I bet there was a 'R1b U106' nation like how NOrthern Bell Beaker was the 'R1b P312 nation' and Yamnaya was the 'R1b Z2103 nation.'

If so it would mean 'R1b U106 nation' was a lot less successful than 'R1b P312' nation.

andrew said...

You suggestion that the people who contributed steppe ancestry to the Iberians might have been 50% steppe is a very good one that works out numerically. I like it.