March 25, 2005

Prehistoric Basques were closer to modern Near Easterners

This paper shows that 6th-7th century Basque mtDNA was similar to that of present-day Atlantic fringe populations, but both are not similar to prehistoric mtDNA dating back to 5000BP. Therefore, some population movement has taken place between 5000BP and the 6th-7th century, leading to the present-day distribution of mtDNA. Note that a "Near Eastern" tendency has already been found in Paleolithic Cro-Magnons from Italy, and ancient Etruscans. Here are some interesting findings of the article:
The first component, which accounts for 42.6% of the total variance, established a differentiation between the present-day populations of the Near East and those of Europe. Within Europe, the populations of the Mediterranean area (MdE, MdC and MdW) and those of Eastern Europe (NE and SE) are closer to those of the Near East. Regarding the prehistoric populations of the Basque Country, they are situated between the two groups (Europe and Near East), whereas the historical population of Aldaieta falls within the variability range of present-day European populations.


As we have seen, haplogroup K has a considerable bearing on the distribution of modern and ancient populations in both PC analyses. This haplogroup is at a high frequency in the prehistoric populations of the Basque Country (16% in Pico Ramos and around 23% in Longar and SJAPL) (Table 4), whereas the average value in present-day European populations is 4.8%, ranging between 3.6% and 7.7% (Richards et al. 2000).


As we have already seen, we did not find any individuals in the prehistoric populations that belong to lineage V (Izagirre & de la Rúa, 1999) and we found only one individual (2.7%) in the historical population of Aldaieta. On the other hand, Maca-Meyer et al. (2003) propose that the origin of haplogroup V should be displaced to Cantabria. Should this be the case, the presence of haplogroup V in the historical population of Aldaieta suggests the existence of genetic flow between the population of the Basque Country and that of the neighbouring region, at least since Late Antiquity.


The frequency of haplogroup H in the historical population of Aldaieta (48.6%) is similar to that displayed in the present-day Atlantic fringe populations. However, the prehistoric populations of the Basque Country studied prior to this show a lower frequency of haplogroup H, as in Longar it is 44% and in the other two prehistoric populations (SJAPL and Pico Ramos) its frequency is around 37% (Table 4).


Haplogroup J has been the main lineage of mtDNA related to the Neolithic expansion from the Near East around 10,000 years ago (Richards et al. 1996, 2000). A lower frequency of J has been displayed in the present-day Basque population (2.4%), whereas in all other regions of Europe its frequency ranges between 7% and 14%. However, in certain prehistoric populations from the Basque Country (SJAPL and Pico Ramos), and in the historical population of Aldaieta, the presence of this haplogroup is greater than in the rest of the European populations studied, displaying values of around 16%, although it is absent in the prehistoric population of Longar (Table 4). Nevertheless, haplogroup J is of no relevance in either of the first two components in the PC analysis performed in this paper (Fig. 4b and 5b).


Like us, Vernesi et al. (2004) detected a significant difference between the present-day population of Tuscany and the prehistoric one inhabiting the same area (Etruscan), with a gap of 2,500 years between them, finding only two haplotypes in common between both populations. It may be that this phenomenon is more widespread and has occurred in other regions of Western Europe. Data on more prehistoric populations are required in order to confirm this phenomenon. It should also be taken into account that these differences have only been detected in the mtDNA, as currently, the nuclear genome of prehistoric European individuals has not been studied at the population level.


Bearing in mind this temporal variation in the frequency of haplogroup H in the Basque Country, it is not correct to state that the widespread situation in the Upper Palaeolithic involved the existence of high frequencies of haplogroup H, simply due to the fact that present-day Basques present this characteristic. Another example is the case of haplogroup J. Given that the present-day Basque population is an outlier regarding the Neolithic component, it has been proposed that this region experienced a smaller genetic impact from Neolithic farmers. But if we accept that lineage J is a marker of migrations of Neolithic populations from the Near East, then the Basque Country also experienced the impact of these peoples, as is shown by the high frequency of haplogroup J in certain ancient populations.


As advised by Vernesi et al. (2004), this leads us to reconsider the supposition whereby the genetic patterns of present-day populations reflect the evolutionary processes experienced by their predecessors (Sokal et al. 1991; Richards et al. 2000, 2002, amongst others). Up until now it was thought that there was no evolutionary process subsequent to the Neolithic that altered the genetic composition of European populations (Barbujani & Bertorelle, 2001). However, our data on ancient DNA (as well as those of Vernesi et al. 2004) reveal a discontinuity between prehistoric and present-day populations, which leads us to reconsider the limitations involved in the reconstruction of evolutionary history on the basis of the genetic patterns of present-day populations.

Annals of Human Genetics (OnlineEarly)

Temporal Mitochondrial DNA Variation in the Basque Country: Influence of Post-Neolithic Events

A. Alzualde et al.


The Basque population has been considered an outlier in a large number of genetic studies, due to its hypothesized antiquity and greater genetic isolation. The present paper deals with an analysis of the mtDNA variability of the historical population of Aldaieta (VIVII c. AD; Basque Country) which, together with genetic data existing for other prehistoric populations of the Basque Country (4,5005,000 YBP), permits an appraisal of the hypotheses proposed for the origin of the genetic differentiation of the Basque population. Given that this is an aDNA study, application has been made both of standard precautions, to avoid contamination, and of authentication criteria (analysis of duplicates, replication in an independent laboratory, quantification of target DNA, sequencing and cloning of PCR products). The variability of the mtDNA haplogroups of the historical population of Aldaieta falls within the range of the present-day populations of Europe's Atlantic fringe, whereas the prehistoric populations of the Basque Country display clear differentiation in relation to all others. Consequently, we suggest that between 5,0001,500 YBP approximately, there may have been gene flow amongst the western European populations that homogenised mtDNA lineages.


1 comment:

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