Monday, June 11, 2012

Pre-Neolithic Ancient DNA In Southern Europe

The Newly Discovered Ancient DNA Data

Maju calls attention to two new instances where ancient mtDNA of haplogroup H have been found in human remains dated to before the Neolithic revolution in Southern Europe (one in what is now Basque Spain, the other in Greece). Earlier this year there was another find of this kind in Southwest Europe. Maju also references two unpublished reports, one in Morocco and the other in Southwest Europe.

The Greek find is particularly notable, as it is the only known case to date of pre-Neolithic mtDNA H that is not from Southwest Europe, or the portion of North Africa directly across the straight of Gibraltar from Southwest Europe, and because it might even be pre-Epipaleolithic. The mtDNA H found in Danubian Neolithic populations would presumably have originated with an mtDNA H heavy population somewhere in Southeast Europe by the time that the Neolithic revolution expanded from that area into the rest of Europe in previously mtDNA U dominated areas. The phylogeny of mtDNA haplogroup H doesn't do much to help us discern if that lineage had arrived in the Epipaloelithic, the Neolithic, or perhaps earlier, as the error bars on the mtDNA mutation rate dating are too great.

What Kind of Societies Could Have Expanded In The Epipaleolithic?

The find is suggestive of a pan-Mediterranean mtDNA H region in the Epipaleolithic that was distinct from both northern parts of the European continent, and sub-Saharan parts of the African continent, a pattern suggestive of a maritime society's spread. 

An alternative possibility is that the spread was driven by the role of "pre-farming" of wild plants sufficient to supplement a pre-existing fishing diet or a diet in particularly compact and abundant hunting and gathering territories, but not sufficient to provide enough subsistence in previously more nomadic hunting and gathering societies where the wild resources were not rich enough to permit a near sedentary lifestyle.  At the "A Remote Period Indeed Blog" pre-Neolithic use of flour in the New World and in Gravettian Italy suggest that this kind of pre-farming of wild cereals may have been fairly sophisticated at some times and places prior to the advent of full fledged farming economies.

Why Does Early mtDNA Haplogroup H matter so much?

In modern Europe mtDNA H is the most common haplogroup of mtDNA (on the order of a half of the total), so the timing of the expansion of mtDNA H is critical to making sense of the extent to which there was population replacement in the Neolithic revolution, as opposed to heavy integration of existing populations into it and cultural technology transfers. Further North in Europe, pre-Neolithic mtDNA is overwhelmingly a few subtypes of mtDNA haplogroup U.

If mtDNA H is Paleolithic, then close to 80% of Europe's mtDNA has pre-Neolithic origins.  If mtDNA H is Neolithic, then close to 70%+ of Europe's mtDNA has Neolithic origins, indicating much greater levels of female population replacement with the advent of the Neolithic.  The origins of mtDNA H define the difference between genocidal class population replacement of women, and merely multiple mass migrations in the Neolithic and the several millenia afterwards over multiple waves of migration.

Possible Demographic Models

* CP Neolithic Replacement With Genetically Similar Populations.

The Cardial Pottery Neolithic could have replaced a population that as a result of population replacing pre-Neolithic migrations was similar in mtDNA to the incoming populations to start with (because the pre-Neolithic migrations may have happened only a few centuries or millenia earlier), making the demic transition invisible from ancient DNA studies of the precision available to subtype those ancient DNA samples.

* A Culturally Transmitted CP Neolithic

But, it is possible that the Cardial Pottery Neolithic either had a much smaller demographic replacement component than the Danubian Neolithic and was mostly cultural. 

* Epipaloelithic Maritime Society Expansion From Somewhere

It could be that an mtDNA H rich population expanded from somewhere (e.g. the Franco-Cantabrigian refugium, the Balkans, the Near East, elsewhere) along both of the Mediterranean coast between the end of the Last Glacial Maximum and the Neolithic revolution, perhaps initially as part of a fishing culture than ultimately expands inland (this could be driven by improved fishing methods, or by pre-farming activity only possible in areas where semi-sedentary hunting and gathering is possible with pre-farming supplementation).

But, at least some of the ancient mtDNA H samples do seem to be somewhat inland - within a week or two of walking-, implying either a shift in the carrier's method of acquiring food, or perhaps bride trading between coastal and inland populations that were otherwise relatively static in their lifestyles.

* Augnirican Sources Kept Confined To Southern Europe

Another possibility is that mtDNA has a deeper origin in the Southern European region dating all the way back to the arrival of modern humans in Europe (basically the Augnirican era), ca. 40,000 years before present in round numbers.

But, this begs the question: Why have numerous ancient DNA samples (both pre-LGM and post-LGM) failed to reveal mtDNA haplogroup H further to the north, at least after the northern portion of the European continent was repopulated after the LGM and before the Neolithic? The ancient DNA samples over a very long time frame in Europe are sufficiently numerous that mere random sampling error seems like an unlikely source for this pattern.

* Gender Assymmetry In Replacement Rates

Of course, a scenario in which Europe has mostly Paleolithic source mtDNA with only modest replacement of women, and mostly Neolithic source Y-DNA with profound replacement of men, is entirely possible and has historical precedent.

In general, mtDNA tends to be more conservative in a particular place than Y-DNA, even though naively, one might expect the opposite in patrilocal societies where men stay in the communities where they were raised and bring in brides from other communities in the region (however large or small that region might appropriately be considered at the time).

This is because a significant number of historical transformative, relatively long distance migrations appear to have been male dominated, rather than involving entire intact families that did not admix much with their neighbors.

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