GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2008-06 > 1212687542
From: ellen Levy <>
Subject: Re: [DNA] Iberian S116+
Date: Thu, 5 Jun 2008 10:39:02 -0700 (PDT)
I wanted to address the new Basque mtDNA study. A lot of information has been thrown into the discussion about Basque DNA, but no one has yet discussed this new study, or the aDNA evidence on ancient Basque and Iberians (also presented in my paper at JoGG).
I was highly disappointed by this new study by M.A. Alfonso-Sanchez. While some very intriguing DNA data was gathered, the authors engaged in much speculation while dismissing the theories of the aDNA researchers without a second thought (or reasonable argument either, in my opinion).
Three important facts to note here - one is the small sample size of 55 individuals.
Two is the particular population studied - Basques from Biscay providence and the northern part of Basque territory (northern Spain). It is important to note the location of the group because one of the author's theory is that the differences in haplogroup frequencies between the Basque groups is due to regional barriers and genetic substructuring based on these barriers.
Three is the very low diversity the researchers found among the lineages. If this is the alleged region where mtDNA haplogroups like V spread after the LGM, the low diversity today needs to addressed.
The authors found no U8 in their sample. Why is this relevant? Because U8 has been theorized to be a rare remnant of Paleolithic ancestry among the Basque. Interestingly enough, this rare remnant is rare indeed at only 1% among Basque, so if it is a remnant, it didn't survive in any great frequency. However, the failure to locate a very low frequency of this group in their sample may have been due to the very small sample size.
It would be interesting to read Dubut's study, entitled "MtDNA polymomrphisms in five French groups," Eur J Hum Genet 12:293-300. According to Alfonso Sanchez, in this study they found an incredible 8.1% of U8a!
Then the authors have to deal with the fact that they have found a very high frequency (more than 10%) of mtDNA haplogroup J in their sample, particularly J1c1 and J2a. This is unusual because J is less frequent in other Basque samples. In fact, the researchers note that the "Basque population features the highest frequencies for both mtDNA lineages within the European context." Also relevant is the fact that the ancient Basque studies also reveal a very high frequency of this haplogroup (16%).
While this J lineage is believed to have entered Europe during the Neolithic, the researchers completely ignore this fact. They don't even mention it in their study. Rather, they provide a unlikely scenario to describe all their results, including a low frequency of haplogroup V (again in keeping with aDNA studies, but not other Basque findings where V constitutes 20% of the mtDNA lineages) namely, Spatial heterogeneity dating all the way back to the LGM! And here is what they speculate about:
"... it is not difficult to connect the variability of modern maternal lineages with ancient habitat fragmentation processes probably originated in the LGM. Although Iberia was not among the most affected regions of the LGM, the polar front reached the Pyrenees and icebergs drifted into the Bay of Biscay, driving to temperatures around 15 degrees C lower than the average nowdays, and consequently, to extremely cold winters. The hostile environment created by extensive Pleistocene glaciations certainly limited the dispersal opportunities, which might have resulted in population fragmentation because of the existence of nonrandom breeding groups (departure from panmixia). Thus, long term population fragmentation could have promoted isolation and local genetic microdifferentiation by effect of genetic drift. This limitation of gene flow generated by the glacial conditions could have been reinforced by the complex orography of the Basque area..."
The authors go on to assert that this fragmentation dating all the way back to the Paleolithic is supported by the continuing existence of eigth distinct regional dialects for the Basque language. What is not explained is how a Neolithic group like J was present among the Basque all the way back to the Paleolithic period, thereby suffering severe fragmentation during the LGM, or how it allegedly reduced the frequency of haplogroup V as suggested by the study.
The scenario presented by the study has enough problems, but the researchers also propose the unlikely idea that minor regional dialect differences developed and were maintained among the Basque over a 12,000 year period or longer. There are so many problems with this idea that I hardly know where to start, but I'd like to hear from other listers before I say more. Also, the idea proposed by this study that Basque allegedly maintained very low diversity among their mtDNA lineages due to limited gene flow and/or high endogamy and consanguinity - again, since the last LGM. So apparently the researchers are suggesting that this tradition of marrying your first cousin which is so prevelant among modern-day Basque supposedly goes all the way back to the LGM.
Also, I highly recommend reading the ancient DNA studies on the Basque and Iberians before wading through this study. For whatever reason, Alfonso-Sanchez insists his scenario is more "appropriate" than those proposed by aDNA researchers who suggest temporal mtDNA variation due to post-Neolithic immigration and gene flow. Also note while reading the studies whether the aDNA data reflect the limited maternal lineages and very low diversity that Alfonso-Sanchez apparently finds in his sample of modern-day Basque.
|Re: [DNA] Iberian S116+ by ellen Levy <>|