Genetic studies on Bulgarians

The European genetic structure (based on 273,464 SNPs). Three levels of structure as revealed by PC analysis are shown: A) inter- continental; B) intra-continental; and C) inside a single country (Estonia). D) European map illustrating the origin of sample and population size.

The Bulgarians are part of the Slavic ethnolinguistic group.^[1][2][3] However, the Bulgarians and most other South Slavs are characterized by a prevailing genetic substrate that is different than that of the East and West Slavs. The two groups are separated sharing only a modest gene flow.^[4][5] This phenomena of two genetically distinct groups of Slavic peoples is explained by the assimilation of previous indigenous Balkan populations by the medieval Slavic settlers in the Balkans.^[5][6][4]

Y DNA

Prevailing hgs among Euroepans

Bulgarians show the highest diversity of haplogroups in Europe, marked by significant (> 10%) frequencies of 5 major haplogroups (compared to Atlantic Europe, dominated by > 50% R1b). Most Bulgarians belong to three unrelated haplogroups, 20% of whom to I-M423 (I2a1b), 18% to E-V13 (E1b1b1a1b1a) and 17.5% to R-M17 (R1a1a), but the biggest part belongs to macro-haplgoroup R (~28%). The major haplogroups, groupped by age of around 20 kya, are:^[7]

Hg I-P37 (I2a1, aka. I2a) distibution mainly based on the map of Rootsi (2004) confirming that no Bulgarian samples data was considered for the map making.

• Haplogroup I-L460 (I2a) is presented at levels ~22% ^[8] according to 808 Bulgarian male samples. By higher levels may be defined the profiles of Ukrainians and all South Slavs other than Bulgarians.^[9] Evidence points to European origin for haplogroup I, and Levantine for its immediate ancestor- IJ. Its exclusive and now patchy distribution within Europe suggested a very early entry in to Europe during Palaeolithic colonization, which was confirmed by ~13,000 years old European Cro-Magnon remains belonging to I2a.^[10] Bulgarian Hg I2a most often belongs specifically to the P37.2, M423 branch ("Hg I2a1b"), representing 20% of Bulgarian males.^[8] According to some data, Bulgarian males who belong to M423, belong to CTS10228 Dinaric (I2a1b2a1), the prevalent clade in eastern Europe, and none of them belongs to the Disles L161 branch or the CTS595 branch found in west Europe and Sardinia.^[11] The Dinaric is descended by several 'only child' sublclades and it is suggested that its most recent common ancestor is aged only 2200 years^[12] making it the youngest and most common micro-group. It makes up an absolute majority among the highest populations. The largest marker group among Bulgarians is Dinaric-North, the largest SNP group is Z17855,^[11] being the prevailing clade in the eastern Balkans and rare elsewhere.^[13] Another major part are representatives of Dinaric-South S17250+, which is the most common subclade among west Balkan peoples and a minority northwards. These SNP groups separated before the Slavic expansion in the Balkans. Initially a Holocene expansion of I2 in SEE is supposed;^[14] however the homogeneity of Balkan Hg I2 and its star-like clustering suggests a far more recent expansion time. It was confirmed later that I2 started to resettle Eastern Europe only around 2,300 YBP.^[15] Around 2% of Bulgarian males belong to the subclade M223 (I2a2) found mostly around Germany. I2a2 is the most frequent haplogroup of European male remains dated to the Metal Ages, while I2a1 and I2a1b are most common on Mesolithic remains,^[10][16] as such they were the primary haplogroups of pre-historic European hunter-gatherers.

Distribution of E-M78 according to Semino (2004) (no data on Bulgarians used, probable frequency)

• Haplogroup E-V68 (E1b1b1a) is presented at levels ~19.5%.^[17] The ultimate origin of E-V68 points to northeastern Africa, specifically near the Nile and Lake Alexandria.^[18] Thus this haplogroup represents a more recent Bronze Age "out of Africa" movement into Europe via the Balkans. Holocene movement into the Near East is proposed, then several thousand years ago, a movement into the Balkans.^[18] Through the long-term migrations the sub-Saharian maternal lineage Hg L was lost lacking completely today in the Balkans. All V68-postive Bulgarians were recorded as M78-positive. The presently mostly European V13 (E1b1b1a1b1a) originated in western Asia according to the most plausible scenario^[19] and is presented at ~18% among Bulgarian males.^[8] According to deeply traced data its internal structure is divided among Z5016, Z5017 and S17461.^[11] Recent findings of V13 in a Neolithic context in Iberia (dated to ~ 7 kya) give a terminus ante quem.^[20] However, it might have really begun to expand in the Balkans somewhat later, perhaps during the population growth of the Bronze Age.^[21] Like I-P37 above, it is spread throughout Europe but peaks in the Balkans, only the Albanians, Greeks, Macedonians, Macedonian Romani, Montenegrins and Serbs may have it at higher levels than Bulgarians.^[22]

Hg R-M420 (R1a) distribution per Underhill 2009, which confirmes that no data of Bulgarian samples was considered in the map making

• Haplogroup R-M420 (R1a) is identified at 17.5%.^[8] It is the dominant group among most Slavs, Hungarians, Romanians and the Indostan area. The M458 branch, which is most common in Poland and the Czech Republic, is present in Bulgarians at 7.5%.^[8] The R1a subclades that are limited to Europe and separated from their Asian relative ~5000 ^[12] years ago, make up 97% of Bulgarian R1a, divided by the largest clades the Bulgarian R1a structure would be nearest to the Estonian and Czech by composition.^[23] M458 and Z280 both constitute 45% of Bulgarian R1a, 7% constitute their parent Z282 and only 3% is constituted by the Asian branch Z93, that is the most common subclade from China to Anatolia.^[23] The most common Bulgarian subclade appears to be the L1029 subclade (R1a1a1b1a1b1) of M458, prevailing in most of the eastern Balkans and various spased parts of central and northern Europe.^[11][24]
• Haplogroup R-M343 (R1b): present in Bulgarians at ~11%.^[8] R1b is the most frequently occurring haplogroup in western Europe, though the Bulgarian internal structure is heterogeneous and 4% of Bulgarian males carry western subclades, at least 2% are carriers of U152.^[8] The ancestral L23 and Z2103 branch show a clear relationship with Anatolia and the Near East,^[25] Z2103 was found on 4 out of 6 males of the Yamna culture in Europe.^[26] Despite most Bulgarians belong to Z2103, the majority of them belong to its subclade Z2110^[11] (R1b1a1a2a2c1a), which today is limited around Europe. The overall evidence suggests that the macro-haplogroup R arose in southern or central Asia descending from Haplogroup IJK. The subsequent path into Europe, and the major settlement is thought to have happedned in the Bronze Age by the Kurgan hypothesis, R1 clades are found at minority levels in Europe since the Mesolithic; a subsequent Balkan entry of R1b into Europe is a major theory.
• Haplogroup J-M172 (J2) is presented at levels 10.5%.^[17] Higher levels of it are observed in the Balkans as far as Bosniaks,^[27] Italians, while Anatolia and the surroundings are dominated by the group.^[28] Whilst its origin is north Levantine, its current pattern reflects more recent events connecting the Aegean and western Anatolia during the Copper and Bronze Ages, as well as Greek settlement around the Mediterranean. Several subclades within J2 are present: J-M410 (J2a) is represented at 6% and J-M12 (J2b) at 4%,^[8] the prevailing is the L26 deep subclade of J2a, it is furtherly divided into M67, M92, L24 and other subclades.^[11]

Finally, there are also some other Y-DNA Haplogroups presented at a lower levels among Bulgarians ~ 20% all together, as G-P15 (G2a) at ~5%, I-M253 (I1, mostly Scandinavian L22, Yutland Z58 and continental Z63)^[11] at ~4%, J-M267 (J1) at ~3.5%, E-M34 (E1b1b1b2a1) at ~2%, T-M70 at ~1.5%, at less than 1% Haplogroup C-M217, H-M82, N-231, Q-M242, L-M61, I-M170, E-M96(excl. M35), R-M124, E-M81, E-M35.^[8]

The overall profile of the 808 Bulgarian samples, according to the highest level of phylogenetic analysis calculating distribution of hgs R1a1a7, R1а1, R1b1a2, R2a, I, E1b1, E1b1b1, E1b1b1a, E1b1b1b, J2b, J2a, J2a1b, J1, G, T, NO, C, H, Q, L, A and B, is positioned nearest to the Romanians per 147 their samples,^[8] also backed by studies as early as 2000,^[29] however the analysis did not involve neighbouring Macedonians, Serbians and related Montenegrins. The largest-scale study of the 147 Romanians itself concludes that they are closer to Ukrainians and Hungarians than to the Bulgarian group sampled by the study.^[30] The largest-scale Y-DNA analysis of at least 219 Hungarians determined that the remaining Finno-Urgic peoples are genetically their furthest populations and confirmed that by a large lead the closest Europeans to the Hungarians are the Bulgarians, furthermore the same study determines the Yugoslavs as the nearest population to Bulgarians.^[31] Other Y-DNA studies concluded that Bulgarians are more distant to Romanians and Hungarians, and closest either to Macedonians, Serbs, Bulgarian Turks or Gagauzes, followed by some Balkan populations.^{[5][32][33][34]}

mtDNA

Prevailing mtDNA hgs

Complimentary evidence exists from mtDNA data. Bulgaria shows a very similar profile to other European countries – dominated by mitochondrial haplogroups Hg H (~42%), Hg U (~22%), Hg T (~11%), Hg J (~8%) and Hg K (~6%).^[35] Like most Europeans, H1 is the prevailing subclade among Bulgarians.^[36] The subclades of Haplogroup H may have not been studied but subclusters H1b and H2a are more common in Eastern than in Western Europeans.^[37] Recent studies show greater diversity within mt Haplogroups than once thought, as sub-haplogroups are being discovered, and often separate migrations and distributions of the Y-DNA haplogroups. While the Y-DNA variation in Europe is clinal, the mitochondrial is not.^[38]

The results of the mitochondarial analyses find the Bulgarians more related to North Slavs. The mtDNA PCA analyses find the Bulgarians more often in a cluster with Central Europeans than with Balkan peoples. According to such a mtDNA PCA analysis of 855 Bulgarian samples, comparing distribution of hgs H, H5, HV, HV0, R0a, J, U1, U2, U2e, U3, U4, U5a, U5b, U6, U7, U8, K, N1, N2, X, M, Т1, Т2, the Bulgarians came out most related to the Poles, followed by Ukrainians, Croats, Czechs, while neighbouring Turks, Romanians and Greeks remained more or very distant.^[39] Several other pan-European mtDNA PCA analyses of the same Bulgarian samples indicate that the neighbouring populations except the Macedonians are distant from the Bulgarians. According to these the Bulgarians are most related by mtDNA either to Hungarians, Szekelys, Slovaks or to Macedonians, followed either by Ukrainians, Croats or Czechs, while neighbouring populations such as Turks, Romanians, Serbs and Greeks remain more distanced.^[40][41][42] Italians from the northern and central part also remain related according to these studies. A pan-Slavic mtDNA plot analyzing genetic distance, situates Bulgarians as sharing their position with Czechs, Romanians, Macedonians and Hungarians, while other close groups to them are Slovaks, Estonians and Latvians.^[4]

auDNA and overall

Network of 29 populations constructed with the Neighbor-net approach from FST distances based on the variation of autosomal SNPs.

Balto-Slavic comparision by A (atDNA), B (Y-DNA) and C (mtDNA plot).

Pan-Euorpean autosomal plot.

Admixture analysis of autosomal SNPs of the Balkan region in a global context on the resolution level of 7 assumed ancestral populations: the African (brown), South/West European (light blue), Asian (yellow), Middle Eastern (green), North/East European (dark blue) and beige Caucasus component.

Whilst haploid markers such as mtDNA and Y-DNA can provide clues about past population history, they only represent a single genetic locus, compared to hundreds of thousands present in nuclear, autosomal chromosomes. Analyses of autosomal DNA markers gives the best approximation of overall 'relatedness' between populations, presenting a less skewed genetic picture compared to Y DNA haplogroups. This atDNA data shows that there are no sharp discontinuities or clusters within the European population. Rather there exists a genetic gradient, running mostly in a southeast to northwest direction. A study compared all Slavic nations and combinined all lines of evidence, autosomal, maternal and paternal, including more than 6000 people for the chromosomal data and at least 700 Bulgarians from previous studies, and 296 for its autosomal analysis scanning a small number of SNP groups, of which 13 were Bulgarians. It claims that the major part of the Balto-Slavic genetic variation can be primarily attributed to the assimilation of the pre-existing regional genetic components.^[4] For Slavic peoples correlations with linguistics came out much lower than high correlations with geography.^[4] The South Slavic group, despite sharing a common language, is separated and has largely different genetic past from their northern linguistic relatives genetically.^[4][5][6] Therefore, the Bulgarians and most other South Slavs are more often included in Balkan genetic clusters and the most plausible explanation would be that their most sizable genetic components were inherited from the assimilated pre-Slavic and pre-Bulgar population,^[4][5][6] predominantly of indigenous Balkan origin, which is also the similar case of most European peoples, whose genetic structure is dependent on geography rather than on language, dominant regional genes often predate the arrival of the current linguistic family by milleniums.^[38][43][44] The southeastern group (Bulgarians and Macedonians) is situated together in a cluster with Romanians and is related to other South Slavs by au, mt, and Y-DNA,^[4] a conclusion backed also by a pan-European autosomal study sampling 2 Bulgarians,^[44] (illustriations on the right) another more extensive autosomal study situated Bulgarians and Romanians as their nearest.^[45] Another pan-Slavic Y-DNA study concludes that most of the Southern Slavic group is distinct from their Northern Slavic relatives, whose homogenity on the other hand stretches form the Alps to Volga end even as far as the Pacific Ocean in Russia.^[5] This means that there is a paternal genetic rather than a geogrpahical factor separating these Slavic peoples. The South Slavs are charctarized by featuring NRY hgs I2a and E plus 10% higher Mediterranean k2 autosomal component, while the Eastern and Western Slavs are characterized by the k3 component and hg R1a.^[4] The current differientaion of high I-P37 and lower R-Z282 among South Slavs and vice versa among North Slavs suggests it was present prior to the Slavic settling in the Balkans as no relevant migrations occur later to change the frequencies.^[4][46][47] The contribution of the Y chromosomes of peoples who settled in the Balkans before the Slavic expansion is the most likely explanation of the phenomenon according to the other study on Y-haplotypes, concluded by its two separate analyses because of the complicity of the methods tracing the alleles.^[5] The presence of two distinct genetic substrata in the genes of East-West and South Slavs would conclude that assimilation of indigenous populations by bearers of Slavic languages was a major mechanism of the spread of Slavic languages to the Balkan Peninsula.^[4] A modest signal among Balkan Slavs was detected that may be inherited from the Slavic settlers, but it was confirmed that even this issue requires further investigation.^[4] Though Southern Slavs are often more related to non-Slavic populations than to other Slavs, the short genetic distance of South Slavs does not extend to populations throughout the whole Balkan Peninsula and they are differentiated from all Greek sub-populations that are not Macedonian Greek.^[4] They share significantly fewer IBD segments for length classes with them than with the group of East-West Slavs.^[4] Most of the East-West Slavs share as many such segments with the South Slavs as they share with the inter-Slavic populations between them. This might suggest gene flow across the wide area and physical boundaries such as the Carpathian Mountains, including Hungarians, Romanians and Gagauz.^[4] Bulgarians are also only modestly close to their eastern neighbours – the Anatolian Turks, suggesting the presence of certain geographic and cultural barriers between them.^[48] Despite various invasions of Altaic-speaking peoples in Europe, no significant impact from such Asian descent is recorded throughout southern and central Europe.^[49]

Ancient DNA

A simplified model for recent demographic history of Europeans. The panels indicate a possible demographic scenario consistent with the observed signals. (A) Mesolithic HGs present in mainland Europe prior to the arrival of agriculture. (B) Initial spread of farming from the Middle East beginning from 7,000 YBP into SE Europe. (C) Expansion of farming to N Europe from SE European gene pool and establishment of main S-N gradient of genetic diversity. Wave of migration also reaches Sardinia. (D) Continuous population expansion and admixture with local HGs as well as additional migrations continues to shape genetic diversity in mainland Europe, but Sardinia remains mostly isolated (IBD: isolation by distance).

Despite the most common haplogroup among Bulgarians is I2a1b at 20%, 8000 years old hunter-gatherer samples of the same haplogroup came out genetically very distant from Bulgarian and Balkan individuals by an autosomal analysis.^[50]

Four mtDNA samples from Bronze Age Bulgaria considered part of the Yamna culture came out haplogroups T2a1b1a, U2e1a, U5a1 and K.^[51]

Medieval gene flow within West Eurasia is shown by lines linking the best-matching donor group to the sources of admixture with recipient clusters (arrowhead). Linecolors represent the regional identity of the donor group, and line thickness represents the proportion of DNA coming from the donor group. Ranges of the dates (point estimates) for events involving sources most similar to selected donor groups are shown.

Four samples from Iron Age Bulgaria were studied, the official study confirmed only that the two are male and mtDNA of two individuals - U3b for the Svilengrad man and HV for the Stambolovo man, those men were from Thracian burial sites, some of them victims of a ritual sacrifice, and are dated at around 450-850 BC.^[52] Unofficial anlysis of the raw data claims that the first one is positive for Y-DNA Haplogroup E-Z1919. It also claims that according to the SNPs all the four samples came out male and also haplogroup J2-M410 was found among them, while another man's haplogroup came out negative for E, I and J and remained unknown but is likely R1.^[53][54]

13 samples from medieval Bulgarian sites were alleged as originally Bulgar, but there is no evidence for that.^[55] They were from a burial site from the Monastery of Mostich in Preslav, Nozharevo, Devnya, Tuhovishte and came out European mtDNA haplogroups H, H1, H5, H13, HV1, J, J1, T, T2 and U3 without any East Eurasian haplogroups found.^[40]

After 34 mediaval(10-14th century) mtDNA samples from Sedynia and Lednica in Poland, possibly Slavic, had been studied, the ~900 sampled modern Bulgarians come out overally the closest group to these samples out of 20 other European nations and morever, they share the highest value of haplotypes with the medieval Polish population more than any other comapared nation does. Those medieval haplogroups included H, H1a, K1, K2, X2, X4, HV, J1b, R0a, HV0, H5a1a, N1b, T1a, J1b and W.^[41]

Samples from three prehistoric European ancestor groups compared to modern peoples

Further evidence from ancient DNA, reconsiderations of mutation rates, and collateral evidence from autosomal DNA growth rates suggest that the major period of European population expansion occurred after the Holocene. Thus the current geographic spread and frequency of haplogroups has been continually shaped from the time of Palaeolithic colonization to beyond the Neolithic.^[56] This process of genetic shaping continued into recorded history, such as the Slavic migrations.^[57]

Recent studies of ancient DNA have revealed that European populations are largely descending from three ancestral groups. The first one are Paleolithic Siberians, the second one are Paleolithic European hunter-gatherers, and the third one are early farmers and later arrivals from the Near East and West Asia. According to this, Bulgarians are predominantly (~ 2/3) descending from early Neolithic farmers spreading the agriculture from Anatolia, and from West Asian Bronze Age invaders and cluster together with other Southern Europeans. Another of the admixture signals in that farmers involves some ancestry related to East Asians, with ~ 2% total Bulgarian ancestry proportion linking to a presence of nomadic groups in Europe, from the time of the Huns to that of the Ottomans. A third signal involves admixture between the North European group from one side and the West Asian - Early farmers' group from another side, at approximately the same time as the East Asian admixture, ca. 850 AD. This event may correspond to the expansion of Slavic language speaking people. The analysis documents the hunter-gatherer admixture in Bulgarians at a level from ca. 1/3.^[58]

See also

• Genetic history of Europe

References

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