Some mtDNA links between Europe and Asia

I was planning on writing up a more complete narrative for this post, but I don't think the evidence is -as of yet- strong enough to support very strong speculation. I will simply say that the recent results of Bramanti et al. for a U-dominated older mtDNA stratum in Central/North-eastern Europe can be reasonably extended to cover both North-western Europe and northern Eurasia up to Lake Baikal, the prehistoric limit between Caucasoids and Mongoloids.

This boreal zone of U dominance contrasts with that of the Neolithic and Bronze Age inhabitants, where the familiar mix of ten or so main Caucasoid haplogroups makes its appearance, in various proportions and in various degrees of admixture at the eastern end of its expansion. The eastern Caucasoids were probably derived from both (i) West Asia via the spread of the Neolithic economy to the east wherever it could be ecologically supported, (ii) in the more northern parts, from migrations across the steppe from Central and Eastern Europe.

More ancient DNA research is needed to establish (i) how complete was the U dominance in the pre-Neolithic northern zone, and (ii) when, and where did the other Caucasoid haplogroups break into it.

Anyway, here is the post as it stands:

Ricaut et al. (2004) discovered the presence of mtDNA haplogroup N1a (16147A, 16172C, 16223T, 16248T, and 16355T) in an Iron Age Scytho-Siberian skeleton from the Altai, reporting the presence of haplogroup N1a among Iranians and upper caste Havik Brahmins from India.

The same sequence was detected in a Neolithic Central European (DER1) of the Linearbandkeramik (LBK) culture, with reported modern matches in Egypt and Armenia. The following haplogroups were detected in the Neolithic LBK gene pool: H*, N1a, K, HV, T2, V, J, W, U3.

A later study by Gokcumen et al. (2008) discovered the presence of N1a in modern Kazakhs from the Altai:

The haplotypic variation within the seven N1a samples was relatively high (Table 2), with these haplotypes belonging to both the European and Central Asian branches of this haplogroup, as recently defined by Haak et al. (2005). Thus, the source of N1a haplotypes in Altaian Kazakhs was unclear, although they seemed to have originated west of this part of Central Asia (Gokcumen et al., 2007).

Haplogroup N1a was found to be a genuine signature of the Central European Neolithic by contrasting its high representation in the LBK with the overwhelming presence of haplogroup U (and especially U5 and U4) mtDNA among the Paleolithic and Mesolithic populations of the region.

A separate Neolithic Funnel Beaker (TRB) sample from Scandinavia (Malmström et al. 2009) included only three individuals belonging to haplogroups H, J, and T. Obviously, a sample of 3 is insufficient, but the absence of haplogroup U in it parallels that of the LBK. By contrast, the contemporaneous Mesolithic Pitted Ware culture, represented by 19 samples had single instances of J, and T (which may be due to admixture with the TRB), a single instance of haplogroup V, one of the few ones thought to be European in origin, and a gene pool that was apparently dominated by haplogroups U4 and U5. The picture emerging from the northmost European hunter-gatherers is one of a restricted set of haplogroups where U subclades were dominant (about 3/4).

N1a was also detected in medieval high-status Hungarians:

Commoners show a predominance of mtDNA haplotypes and haplogroups (H, R, T), common in west Eurasia, while high-status individuals, presumably conquering Hungarians, show a more heterogeneous haplogroup distribution, with haplogroups (N1a, X) which are present at very low frequencies in modern worldwide populations and are absent in recent Hungarian and Sekler populations.

While, as we saw, N1a was frequent among Neolithic Central Europeans, its absence in Hungarian commoners suggests that it was re-introduced -in the high status individuals- from Asia.

Interestingly, there has been European and Asian mtDNA evidence that allows us to have a good idea of the mtDNA landscape on which N1a-bearing people migrated from west to east:

The pre-farming foragers of Europe were dominated by mtDNA haplogroup U. The easternmost sample in the aforementioned study was from Samara, in European Russia and consisted of a U5a, and a U5a1 sample. How far to the west and east did the U-dominated population of pre-Neolithic northern Caucasoids extend?

Neolithic Siberians from Lake Baikal, the eastermost anthropologically attested limit of prehistoric Caucasoid populations had only U5a as a Western Caucasoid element in a population dominated by Eastern Eurasian mtDNA. Similarly, the Lokomotiv Siberian burials from Lake Baikal only had U5a in an other Mongoloid mtDNA gene pool. Yu Hong, a Sogdian in China (1,400 years ago) also belonged to haplogroup U5.

U5a was not limited to the territory of Central Europe to China in ancient times. It was the haplogroup of Cheddar Man, a Paleolithic Briton, and U5a1 or U5a1a has also been detected in a Mycenaean from Bronze Age Greece. Interestingly, U5a1 seems to have decreased in frequency in Britain from the 4th c. to the present.

Is it possible that negative selection is affecting mtDNA frequencies in Europe? U-haplogroup turns up in many ancient DNA samples, but the discovery that it was absent (or non-detectible) in Neolithic farmers raises the possibility that its reduced frequency may be due to demography, i.e., the overwhelming of Paleolithic foragers by Neolithic (and later) intruders.

We know that in the Bronze and subsequent ages, Siberians from Krasnoyarsk belonged to a rich assortment of Caucasoid haplogroups. It seems that newcomers from the West joined the U-dominated earliest settlers:

Twenty samples were found to belong to west Eurasian haplogroups (U2, U4,
U5a1, T1, T3, T4, H5a, H6, HV, K, and I), whereas the 6 remaining samples were attributed to east Eurasian haplogroups (Z, G2a, C, F1b and N9a).

At the other end of the Eurasiatic steppe, in the Bronze Age site of Eulau in Germany, the gene pool was also quite different from that of the Paleolithic inhabitants, with haplogroups K1b, U5b, I, H, X2, K1a2 detected.

Haplogroup X2 represents another link between the west and Siberia according to Reidla et al. (2003):

Overall, it appears that the populations of the Near East, the Caucasus, and Mediterranean Europe harbor subhaplogroup X2 at higher frequencies than those of northern and northeastern Europe (P less than .05) and that X2 is rare in Eastern European as well as Central Asian, Siberian, and Indian populations and is virtually absent in the Finno-Ugric and Turkic-speaking people of the Volga-Ural region. [...] the few Altaian (Derenko et al. 2001) and Siberian haplogroup X lineages are not related to the Native American cluster, and they are more likely explained by recent gene flow from Europe or from West Asia.

The Tubalar, Altaic speakers from the northeastern Altai showed a mixed Caucasoid-Mongoloid mtDNA gene pool, with the western component consisting of haplogroups H8, U4b, U5a1, and X2e:

Specifically, northeastern Altai appears to be a good candidate for the ancestral homeland of the haplogroup U4b, which is apparently ancient European. For some haplogroups, such as X2e, the relatively recent arrival to the Altai region is more likely.

Derenko et al. (2002) discovered a rich assortment of Caucasoid haplogroups in several populations from the Altai, including all aforementioned ones (H, HV1, J*, J1, J1b1, T1, T4, U1a, U2, U3, U4, U5a1, I, X and N1a):

The applied approach permitted identification of 60% of mtDNA types the majority of which had southern Caucasoid origin. Less than 10% of mtDNA types were of eastern European origin.

Derenko et al. (2003) also studied several populations from South Siberia where the Caucasoid component was much diminished (17%) with the following haplogroups present: H, U, J, T, I, N1a, X.