The Bulgarians are part of the Slavic ethnolinguistic group as a result of migrations of Slavic tribes to the region since the 6th century AD and the subsequent linguistic assimilation of other populations.^[2][3][4][5]

Hellenthal et al, 2014 estimated from data of 94 modern populations a couple of analyses on Bulgarians inferred from an admixture event in 1000-1600 YBP between a Slavic and a Cypriot donor group: to a Polish donor group Bulgarains are of an estimated 59% Polish-like and 41% Cypriot-like admixture; to a Belarusian, Bulgarians are of 46% Belorussian-like and 54% Cypriot-like admixture.^[6][7] Early gene flows between southeastern and eastern Europe make it difficult to obtain a correct estimate, although young enough identical by descent segments confirmed such connection and that the East and West Slavs share more identical by descent segments with South Slavs than with Greeks, inter-Slavic populations (a group of Romanians, Gagauz), but less with Balts, while the South Slavs share similar number with East and West Slavs, but fewer with Greeks.^[8] Some of the phenomena that distinguish western and eastern subgroups of the South Slavic people and languages can be explained by two separate migratory streams of different tribal groups of the future South Slavs via both: the west and east of the Carpathian Mountains.^[9] The western Balkans was settled with Sclaveni, the east with Antes.^[10] Haplogroup R1a, the major haplogroup among Slavic tribes, reveals that the haplogroup of the Serbo-Croat group is mainly constituted by R1a-L1280 or R1a-CTS3402, while the Macedono-Bulgarian is exclusively made up of the R1a-L1029.^[11] A pattern of distribution of IBD segments between South Slavs and East and West Slavs suggests a shared ancestry or a modest gene flow.^[8]

The phenomenon of distinct genetic substrata in the West, East, and South Slavs would imply several mechanisms, including cultural assimilation of indigenous populations by bearers of Slavic languages as a major mechanism of the spread of Slavic languages to the Balkan Peninsula.^[8][12] About 55% of the Bulgarian autosomal genetic legacy is Mediterranean, about the half of which resembles the Caucasian, Middle Eastern and to a lesser extent the North African genetics.^[7] Combining all lines of evidence, it is suggested that the major part of the within-Balto-Slavic genetic variation can be mainly attributed to the assimilation of the pre-existing regional genetic components, which differ for West, East and South Slavic-speaking peoples.^[8]

Around 4% of Bulgarian genes are derived outside of Europe and the Middle East or are of undetermined origin (by 858 CE), of which 2.3% are from Northeast Asia and correspond to Asian tribes such as Bulgars,^[13] a consistent very low frequency for Eastern Europe as far as Uralic-speaking Hungarians. The percentage, however, may vary by regions as the less numerous Bulgars were concentrated around the northeast failing to settle throughout the country numerous tribes as the significant donor tribes.

Bulgarians, as some of their neighbours 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 18% 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:^[14]

Haplogroup frequencies of in Bulgarians**

A phylogenetic analysis determines that the population of Haskovo Province has shorter genetic distance against the population of the Czech Republic than to the Bulgarian provinces, and that only the population of Burgas Province is closer to Haskovo than the Hungarian population, furthermore only datasets of two more Balkan or Slavic foreign populations(Greece and Croatia) are used and all other Slavic populations are excluded from this analysis.^[40] The largest-scale study of the Hungarians (n=230) determined that^[41] the remaining Finno-Urgic peoples are genetically their furthest populations, and clearly confirmed that the closest Europeans to the Hungarians are the Bulgarians, however the same study determines the Yugoslavs as the nearest population to Bulgarians.^[42] According to DNA data for 17 Y-chromosomal STR loci in Macedonians, the Macedonian population has the lowest genetic distance against the Bulgarian population (0.0815).^[43]

According to an older study of 127 Bulgarian males, frequencies are the following: 30% R (17% R1a, 11% R1b, 2% R*); 27.5% I; 20% E; 18% J; 1.5% G; 1.5% H; 1% T.^[44]

According to another study involving 126 Bulgarian males, frequencies are the following: 30% I (25.5% I2a, 4% I1); 20,5% E; 17.5% R (R1b 11%, R1a 6%); 17.5% J (16% J2); 5.5% G; 4% Q; 1% L; 1% T; unknown 3%.^[45]

According to another study involving 100 Bulgarian males, frequencies are the following: 34% I (29% I2a, 3% I1); 30% R (16% R1a, 14% R1b); 21% E (20% E1b1b1a); 9% J; 2% G; 2% T; 1% N.^[46]

Complementary evidence exists from mtDNA data. Bulgaria shows a very similar profile to other European countries – dominated by mitochondrial haplogroups Hg H (~42%), Hg U (~18%), Hg J/Hg T (~18%), and Hg K (~6%).^[47] Like most Europeans, H1 is the prevailing subclade among Bulgarians.^[48] Most of the U-carriers belong to U5 and U4. The distribution of the subclades of Haplogroup H have not been revealed. 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.^[49]

MtDNA haplgroups of ~1000 Bulgarians:^[47]

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, autosomes. Although autosomal analyses often sample a small number of Bulgarians, by multiple autosomes multiple ancestral lines may be traced by an individual's 21 autosomes as opposed to one identical mtDNA or Y-DNA sex chromosome, whose inheritance although clinal, demonstrates genetic drift often in statistics. 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 auDNA 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 combined all lines of evidence, autosomal, maternal and paternal, including more than 6000 people for and at least 700 Bulgarians from previous studies, of which 13 were used for autosomal analysis (right image). The overall data situates the southeastern group (Bulgarians and Macedonians) in a cluster with Romanians, and they are at similar proximity to Gagauzes, Montenegrins and Serbs who are not part of another cluster but are described as 'in between' clusters.^[8] Macedonians and Romanians consistently appear to be among the most related to Bulgarians by au, mt, and Y-DNA^[8] a conclusion backed also by a pan-European autosomal study investigating 500,568 SNP (loci) of 1,387 Europeans and including 1 or 2 Bulgarians,^[50] other more or less extensive data sets situate Bulgarians and Romanians as their nearest .^[51][52][53] Per HLA-DRB1 allele frequencies Bulgarians are also in a cluster with the same populations.^[54] The Balto-Slavic study itself calculated genetic distance by SNP data of the multiple autosomes and ranked most proximal to Bulgarians the Serbs, followed by Macedonians, Montenegrins, Romanians, Gagauzes, Macedonian Greeks apart from Thessaloniki, the rest of the South Slavs, Hungarians, Slovaks, Czechs, and then by Greeks from Thessaloniki, Central Greece and Peloponnese.^[8] The East Slavs and Poles cluster together remaining less proximal to Bulgarians than Germans, among whom Slav admixture is also observed. Balts, however, according to the PCA analysis are less proximal to Bulgarians than Italians for example are.^[8] Bulgarians are also only modestly close to their eastern neighbours – the Anatolian Turks, suggesting the presence of certain geographic and cultural barriers between them.^[55] Despite various invasions of Altaic-speaking peoples in Europe, no significant impact from such Asian descent is recorded throughout southern and central Europe.^[56]

The study 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, which differed for present West, East and South Slavic-speaking people.^[8] For Slavic peoples correlations with linguistics came out much lower than high correlations with geography.^[8] The South Slavic group, despite sharing a common language, is separated and has a largely different genetic past from their northern linguistic relatives.^[5][8][12] Therefore, for the Bulgarians and most other South Slavs the most plausible explanation would be that their most sizable genetic components were inherited from indigenous Balkan pre-Slavic and pre-Bulgar population.^[5][8][12] The South Slavs are characterized 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.^[8] 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.^[8]

Southeastern Europeans share large numbers of common ancestors that date roughly to the times of the Slavic expansion around 1,500 years ago. The eastern European populations with high rates of (IBD) are highly coincident with the modern distribution of Slavic languages including Hungary, Romania, Greece and Albania, so it is speculated for Slavic expansion, anyway it was concluded that additional work and methods would be needed to verify this hypothesis. This study detects a considerable connection between Bulgarians and North Slavs that is the result of migrations no earlier than 1500 years ago.^[53] A study on genetic admixture filtered to 474,491 autosomal SNPs and including 18 Bulgarians concluded that there is a recent excess of identical by descent sharing in Eastern Europe, and recent period of exchanged segments speculating that this may correspond to the Slavic expansion across this region. A signal at a low frequency among Balkan Slavs was detected that may have been inherited from the medieval Slavic settlers, but it was confirmed that this issue requires further investigation.^[8] 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.^[8] The South Slavs share significantly fewer identical by descent segments for length classes with Greeks than with the group of East-West Slavs.^[8] 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 Slavic gene flow across the wide area and physical boundaries such as the Carpathian Mountains, including Hungarians, Romanians and Gagauz.^[8] Notably, the number of common ancestors within the last 1,000 to 2,000 years is particularly high within eastern and Slavic-speaking Europe.^[57] A high number of shared IBD segments among East Europeans that can be dated to around 1,000–2,000 YBP was revealed. The highest percentage of the total number of shared pairwise IBD segments is detected between the group of East-West Slavs and South Slavs (41% from the total number of IBD segments detected); Baltic speakers, Estonians (40%) and "inter-Slavic" Hungarians, Romanians and Gagauz (37%). East-West Slavs share these segments with Western Europeans (32%), Volga region populations (30) and North Caucasus (21%). South Slavs also share 41% with East-West Slavs and 37% with Inter-Slavic populations, they also share 31% with Western Europeans and 30% with Greeks. However, per one pair of individuals East-West Slavs share more IBD with Balts than with South Slavs, but not with the rest and the same amount with inter-Slavic as with South Slavs. Per one pair of individuals South Slavs keep sharing most IBD with East-South Slavs and the same amount with the inter-Slavic, followed by Greeks and Western Europeans.^[8]

For Bulgarians the prevailing donor group in admixture with up to more than 40% are a northeastern group, consistent with the medieval Slav expansion, the date of the admixture event is set at 900-1300 CE. The Slavic frequency of the Bulgarians is determined lower than that of Poles and Hungarians, higher than that of Greeks and roughly the same as Romanians.^[7] In the publication by Hellenthal et al., based on a database of 94 modern populations, the authors inferred over 40% of the total autosomal make-up of the Bulgarians to a legacy of the "Slavic (500-900CE)" expansion.^[7] The same publication provided the following two analyses on oneway admixture of the Bulgarian autosomal makeup:

1. 46.0% Belorussian-like (including 23.2% Lithuanian, 19.3% Polish, 2.3% Finnish) and 54.0% Cypriot-like (including 14.8% Greek, 12.7% Cypriot, 11.9% Arab, 4.1% Italian, 3.3% Georgian, 2.0% Sardinian, 2.8% Iranian)
2. 59.0% Polish-like (including 54.5% Polish, 4.0% English) and 40.9% Cypriot-like (including 15.3% Cypriot, 14.9% Arab, 3.5% Georgian, 2.4% Sardinian, 1.4% Hezhen, 1.3% Greek).^[6]

The genetic diversity among Bulgarians is the reason of more inherited diseases^[58] The blood type of 21,568 Bulgarians is 37% A+, 28% 0+, 14% B+, 7% AB+, 6+ A-, 4% 0-, 2% B-, 1% AB-,^[59] a distribution similar to Sweden, the Czech Republic and Turkey.

Despite the most common haplogroup among Bulgarians is 14000 years old^[60] 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 of skeletal remains from Loschbour cave in Luxembourg.^[61]

Three out of four samples from Bulgarian Neolithic(6,500-5000 ybp) from Smyadovo came out mtDNA haplogroup H and the other one is T2e, while another 5,500-4,000 old sample from Durankulak is U52a2. Several mtDNA Bulgarian samples considered part of the Yamna culture came out haplogroups H, T2a1b1a, U2e1a, U5a1 and K.^[35]

Computing the frequency of common point mutations of several mtDNA Thracian remains from Romania with haplogroups H17, H22 and HV has resulted that the Italian (7.9%), the Albanian (6.3%) and the Greek (5.8%) have shown a bias of closer genetic kinship with the Thracian individuals than the Romanian and Bulgarian individuals (4.2%), but it was noted that more mtDNA sequences from Thracian individuals are needed in order to perform a complex objective statistical analysis.^[62] From seven Thracian samples aged about 3 millennia from Gabova Mogila and Shekerdja Mogila in Sliven Province, and from Bereketska Mogila in Stara Zagora Province, two were identified as belonging to mtDNA Haplogroup D, presumably associated with East Asia. Haplogroup W5a was found among two individuals and H1an2. H14b1 was also found.^[63] 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 individual. Haplogroups U for the Krushare man, U2e for the Vratitsa individual have been identified. Those individuals were from Thracian burial sites and are dated at around 450-1500 BC.^[64] Unofficial analysis of the raw data claims that the first one is positive for Y-DNA Haplogroup E-Z1919 or H-Z14031 (H1b1). It also claims that according to the SNPs all the four samples came out male and also in the man from Krushare Haplogroup J-PF5197 (J2a1a1a1b2) was found, while another man's haplogroup came out negative for E, I and J and remained unknown but is likely R1.^[65][66] According to an autosomal analysis of DNA Land, the Svilengrad man came out 100% Mediterranean islander,^[67] while the Stambolovo man appears to be 99% Balkan.^[68] One of the surprising results are of 3,500-3,100 years old samples from Vratitsa, which came out 60% Northwest European 24% Southwestern European(22% Sardinian),5% Ashkenazi, 5% Mbuti, 3% Native American, 3% South/Central European, 1% North Slavic,^[69] along with a 2,400 years old sample from Krushare that is 32% Southwestern European, 26% Northwestern European, 26% Balkan, 5% Central Indo European, 3% Mbuti, 3% Finnish, 3% North Slavic, 1% Ambiguous, 1% Amazonian,^[70] in comparison a sample from Iron Age Montenegro is surprising in the opposite direction and came out 64% North Slav and 50% Yamnaya.^[71] For the man from Krushare the authors explicitly stated "However, the DNA damage pattern of this individual does not appear to be typical of ancient samples, indicating a potentially higher level of modern DNA contamination.". While the Svilengrad man still shows the highest proportion of Sardinian ancestry, the Krushare more resembles the hunter-gatherer individuals.

20 samples from medieval Bulgarian sites were alleged as originally Bulgar, but there is no evidence for that.^[72] They were from a burial site from the Monastery of Mostich in Preslav, Nozharevo, Tuhovishte and most came out European mtDNA haplogroup H, including H1, H1an2, H1r1, H1t1a1, H2a2a1 H5, H13a2c1, H14b1, HV1, J, J1b1a1, T, T2, U4a2b, U4c1 and U3 with the half belonging to Haplogroup H. It was shown a short genetic distance between these samples and modern Bulgarians.^[73]

After at least 20 mediaval(10-14th century) mtDNA samples from Cedynia and Lednica in Poland, possibly Slavic, had been studied, the 855 sampled modern Bulgarians come out overally the closest group to these samples out of 20 other European nations and moreover, they share the highest value of haplotypes with the medieval Polish population more than any other compared nation does. Those medieval haplogroups included H, H1a, K1, K2, X2, X4, HV, J1b, R0a, HV0, H5a1a, N1b, T1a, J1b and W. The samples came out distant from modern Polish population, but nearest to the modern Bulgarian and Czech population.^[74] 20 medieval(9-12th century) samples from Slovakian sites Nitra Šindolka and 8 from Čakajovce were compared to modern population and Bulgarians, and Portuguese came out nearest to them by genetic distance, however all these came out distant to modern Slovak population.^[75]

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.^[76] This process of genetic shaping continued into recorded history, such as the Slavic migrations.^[77]

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 (52%) 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.^[78] The impact of Yamnaya culture is estimated at 20-30%, which is most common among the Slavs.

According to Genographic Project's autosomal study called Your Regional Ancestry based on nine regional affiliations, the Bulgarians regional ancestry results are as follows: 47% Mediterranean and 20% southwest Asian impact, which reflect the strong influence of neolithic agriculturalists from the Fertile Crescent; 31% Northern European component that reflects Paleolithic hunter-gathers' ancestry; 2% Northeast Asian component which shows there have been some mixings with Asiatic invaders.^[79]