August 18, 2010

Ancient Megalithic mtDNA from France

An extremely interesting paper, the first one on Megalithic remains, and a link between the Megalithic people and the early central European Neolithic Linearbandkeramik, where N1a was unexpectedly detected as a major component a few years ago. I'll probably have more to say on this after I read the paper.


From the paper:
We reproducibly retrieved partial HVR-I sequences (nps 16,165 to 16,390) from three human remains (Prisse´ 1, 2, and 4, Table 1), one adult and two children deposited during different stages of use of the burial chamber. Corresponding sequences could be unambiguously assigned to haplogroups X2, U5b, and N1a (Table 2 and Supporting Online Information).
Haplogroup U5b subclusters are believed to have spread from central-southern Europe post-LGM. Haplogroup X2 is believed to have spread from the Near East and Mediterranean Europe; it is one of those mystery haplogroups that turn up in the Taklamakan desert as well as Native Americans. Together with the clearly invasive nature of N1a, these results are consistent with migrationism.

The authors write:
The widespread distribution of the N1a lineage in Early and Middle Neolithic northwestern Europe may indicate genetic continuity from Mesolithic populations.
This scenario would support a Mesolithic contribution to the earliest Neolithic of Atlantic Europe. This would imply that the N1a lineage was already common in
indigenous north European populations and that the spread of the Neolithic was principally the result of cultural diffusion. Although so far the N1a lineage has not
been encountered among late European hunter-gatherers in central and north Europe (Bramanti et al., 2009; Malmstro¨m et al., 2009), it is worth noting that less
than half of the hunter-gatherers’ paleogenetic data come indeed from the pre-Neolithic period (predating LBK expansion). Finally, no paleogenetic data currently
exist for the Mesolithic period in Western Europe. This prevents any conclusion being drawn about N1a occurrence during the Mesolithic period in those regions.
Of course we won't know if N1a occurred in France prior to the Neolithic until we test pre-Neolithic French samples. However, if N1a was present in France prior to the Neolithic, then why wasn't it present in central-northern Europe where substantial sample sizes exist? This would require a partition of pre-Neolithic populations of Europe, and also existence of N1a in both the Linearbandkeramik (that spread on a south-north vector) and in Mesolithic French. So, while we wait for pre-Neolithic Western Europeans to come up N1a, I'm willing to wager that they will not, and that N1a spread into France with the Neolithic or the later spread of Megalithic cultures.


American Journal of Physical Anthropology DOI: 10.1002/ajpa.21376

News from the west: Ancient DNA from a French megalithic burial chamber

Marie-France Deguilloux et al.

Recent paleogenetic studies have confirmed that the spread of the Neolithic across Europe was neither genetically nor geographically uniform. To extend existing knowledge of the mitochondrial European Neolithic gene pool, we examined six samples of human skeletal material from a French megalithic long mound (c.4200 cal BC). We retrieved HVR-I sequences from three individuals and demonstrated that in the Neolithic period the mtDNA haplogroup N1a, previously only known in central Europe, was as widely distributed as western France. Alternative scenarios are discussed in seeking to explain this result, including Mesolithic ancestry, Neolithic demic diffusion, and long-distance matrimonial exchanges. In light of the limited Neolithic ancient DNA (aDNA) data currently available, we observe that all three scenarios appear equally consistent with paleogenetic and archaeological data. In consequence, we advocate caution in interpreting aDNA in the context of the Neolithic transition in Europe. Nevertheless, our results strengthen conclusions demonstrating genetic discontinuity between modern and ancient Europeans whether through migration, demographic or selection processes, or social practices.



Observer said...

After that I'm pretty sure that N1a had a significant adaptive disadvantage, it becomes less and less likely, that such a change is even possible without a strong selective trend.

Also, that this haplotype was found in such frequencies in different prehistoric populations can't be chance neither.

After all, N1a is now extremely rare almost everywhere - it reaches nowhere a high frequency.

Are there any theories about selective, adaptive, functional disadvantages, I mean concrete ones, for N1a already?

German Dziebel said...

What's interesting about N1, X2 and U5 is that they are low frequency lineages found across 3-4 continents: X2 in America, Europe, West Asia and (as "X1") Africa; N1 in Asia, Europe and Africa, U5 in Asia (Yakut), Europe and Africa (Fulbe). U5 and N1 are usually interpreted as signatures of back migration to Africa. The same is probably true of X2/X1. We're probably talking about the time when Upper Paleolithic technologies spread from the East to Europe and North Africa at 45-40K. Sometimes we see very granular and hyper-localized spikes in frequencies, e.g. X in Druze, U5 in Saami, so I wouldn't assign too much significance to the higher frequency of N1 in some ancient remains. It can in fact be lineage fragmentation through bottlenecks.

Mason said...

The whole pdf is here: