Here are the findings from this recent paper:
1. The very derived downstream clades of R1b like R1b1a2a1a2c were well-established in Ireland by 3750 before the present. There is no evidence the ancient specimens in the paper were the first generation in Ireland, so it is likely they were present by 2000 BCE.
2. The population of the Central European migrants to Ireland, who were herders, and had some Steppe-derived ancestry, were MUCH higher, compared to hunter gatherers. In other words, R1b is so common in Ireland because of massive migration of such people.
3. This is emphatically NOT consistent with pioneer colonization and elite dominance.
4. The current distributions in many parts of Western Europe are due to a LACK of invasions since (no Anglo-Saxon or Roman penetration.) In other words, this was a second but more prounounced founder effect of sorts.
5. This is consistent with comparisons to more centrally located, easy to reach locales, like Italy, where the genomes show greater variability in
both autosomes and Y DNA, due to introgressions that occurred after the late Neolithic and early Bronze Age migrations. (Cavalli-Sforza's admonishment to understand the difference between an expansion and an "impansion" come to mind.)
6. In Western Europe, Bell Beaker culture is the most likely candidate for the spread of R1b and related autosomal genes.
7. R1b and this Western European expansion is strongly scientifically correlated to lactose persistence, which likely provided the demographic advantage to propagate in larger numbers in places like Hibernia.
8. As an addendum, the megaliths of Western Europe are indeed likely linked to early cardial cultures, who bore of mix of HG and farming genes, which correlate to I-M26 in Ireland and Sardinia.
WOW!
Two insights that may help explain R1b-L21 clade dominance in Ireland relative to other places.
ReplyDelete1. All native fauna of Ireland, not just humans, were wiped out during 13,000 years of much taller than skyscraper sized glaciers centered around the LGM until about 13kya. There were no Irish refugia during the LGM so it had to be entirely repopulated by people and fauna that had the ability to make multiple sea passages. The situation for flora is only marginally better. So, despite good weather for hunter-gatherers, the local ecology in Ireland was very impoverished which meant that Ireland could only support very small hunter-gatherer populations on the order of 3,000-5,000 people for the entire island.
2. Peak first wave Neolithic population in Ireland was about 100,000-200,000 people reached around 3,700 BCE. But, a few centuries later, and something on the order of a thousand years before the Bell Beaker people arrived, the farming economy/ecology of Ireland collapsed. Almost everyplace that experienced the Neolithic revolution experienced this collapse to some greater or lesser extent, but Ireland hit bottom deeper and for a longer time that most of Continental Europe, and in short order Ireland was predominantly hunter-gatherer again after the collapse, which implies a particularly small population since Ireland's shallow ecology is ill suited to feeding hunter-gatherers. It probably didn't fall all of the way down to 3,000-5,000 people and some herding and gardening probably persisted. But, this first wave farming collapse in Ireland was a bigger bottleneck, for example than the ones that hard hit European regions received from the Black Plague or the Irish Potato Famine bottleneck. Realistically, the population of Ireland probably fell 75%-90% during the sustained collapse of farming.
3. As a result, for the Bell Beaker migrants ca. 2500 BCE, Ireland was virtually virgin territory at ca. 4-10+ times below its carrying capacity when cultivated using Bronze Age farming and herding technologies. If early Bell Beaker migrants arrived with a modest initial population and increased at near maximal rates of natural increase for fifteen generations or so from 2500 BCE to the 2000 BCE sampling date, it doesn't take all that many migrants to totally overwhelm the hunter-gatherer populations that they encounter when they arrive who derive mostly from failed first farmers with a healthy dollop of Western European hunter-gatherers who mostly arrived in Ireland during the many thousands of years of the Mesolithic era. For example, if 1,000 Bell Beaker migrants arrived in 2500 BCE and experienced natural population growth of 3% per year until it reached its Bronze Age farming technology carrying capacity of 100,000-200,000, it would take five or six centuries to do so. So, Bell Beaker people could easily swamp the native hunter-gatherers even if the initial group of migrants was outnumbered 5-1 by the natives.
4. The same dynamics apply in Continental Europe as well, but the greater ease with which people and megafauna could expand from the the refugia that did exist on the Continent gave it a richer ecology which meant that the hunter-gatherer carrying capacity of Continental Europe was much higher in a given area of land relative to Bronze Age farmers than it was in Ireland. The comparative lack of competition from hunter-gatherers would have allowed the Bell Beaker people to have far more unchecked growth in Ireland in a shorter period of time than in most of Continental Europe, which allowed them to be much more dominant in their contribution to modern Irish population genetics than almost anywhere else in Europe.
This is a good summary of an important (dare I say breakthrough) study. As far as the addendum goes I would caution that no where in the actual study does it speculate on the Y haplogroup that would have accompanied the Neolithic specimen had there been male samples present in the human remains recovered and determined to be that of a Neolitic woman. The suggestion that they would be I-M21 is but one possibility. It could also be that they would have been all or some of the G2a subclades that have become synonymous with the spread of farming to Europe in the Neolithic. That would include Spain and Sardinia. Today the population of Ireland is 1-2 percent HG G. I myself am in a G subclade of CTS-342 and my most distant male ancestor was from Westmeath with no connection to the English Planter population that settled Ireland in the 1600s. We need to await further ancient Irish Neolithic samples beforer concluding which EEF Y HGS settled Ireland in the Neolithic
ReplyDeleteNice summary Moore
ReplyDeleteAndrew, I've read your proposals that a problem of identifying R1b as IE is its presence in basques. However, many argue its reflection in Basques is simply a founder effect, and the tight , recent branching of P312 supports its IE origin.
What do you think ?