This study aims to re-examine the conclusion that contemporary Bulgarians do not have significant Thracian ancestry, as stated in a 2021 preprint, by utilizing the same f3 approach but including additional populations, specifically Russia_Alan.SG, Bulgaria_Medieval, Bulgaria_EIA and Macedonia_IA. The aim is to test whether the presence of these additional populations alters the conclusions of the original study regarding the absence of Thracian ancestry in contemporary Bulgarians. The same software used by the previous study, ADMIXTOOLS version 2 and the updated version V54.1 of the „Allen Ancient DNA Resource (AADR)“ dataset, is also used in this study. The results of the f3 analysis indicate that the Russia_Alan.SG and Bulgaria_Medieval populations exhibit closer genetic affinities to Icelandic and Greek populations respectively than to contemporary Bulgarians. Furthermore, the contemporary Bulgarian population is significantly more closely related to the Bulgaria_EIA and Macedonia_IA, representing ancient Balkan DNA, than to the Bulgaria_Medieval and Russia_Alan.SG populations, purporting to represent proto-Bulgarian DNA.
In a 2021 preprint called „Significant (Z|-4|) admixture signal with a source from ancient Wusun observed in contemporary Bulgarians“, Svetoslav Stamov presents an analysis of ancient DNA data with the aim of providing insights into the history of the Bulgarians. One of the conclusions presented in the study is that „contemporary Bulgarians do not harbor Thracian-specific ancestry, since ancient Thracian samples share more SNPs with contemporary Greeks and even contemporary Icelanders than with contemporary Bulgarians“. However, the current study aims to re-examine this conclusion by utilizing the same f3 approach as Stamov, but including additional populations, specifically Russia_Alan.SG and Bulgaria_Medieval. We also utilize the f2 approach. We test whether the different populations alter the conclusions drawn in the original study regarding the absence of Thracian ancestry in contemporary Bulgarians.
Dataset and software for the analysis
It is a common practice in Svetoslav Stamov’s work to make conclusions based on limited sample size. In this instance, his assertion that there is „no substantial contribution coming from ancient Thracians to contemporary Bulgarians“ is based on a single DNA sample from the Iron Age in Bulgaria.
In order to evaluate the validity of Stamov’s conclusions, the same modern populations from the „Simons Genome Diversity Project“ will be utilized in this analysis. This will allow for a direct comparison to the data utilized by Stamov and an assessment of the accuracy of his conclusions. In order to maintain brevity and clarity in the analysis, the following modern populations will be included in the analysis: Dinka, Bulgarian, Yakut, Icelandic, Greek, and Polish. We are utilizing the same dataset as Svetoslav Stamov, in the updated version V54.1 from November 16th, 2022; and the same software, ADMIXTOOLS version 2.
In order to further examine the relationship between the study populations, the f3 statistic was applied using the methodology proposed by Patterson et al. in „Ancient Admixture in Human History“, 2012. We included the Russia_Alan.SG and Bulgaria_Medieval populations as additional reference groups. The results of this analysis indicate that the Russia_Alan.SG and Bulgaria_Medieval populations exhibit closer genetic affinities to Icelandic and Greek populations, respectively, than to contemporary Bulgarians. For f3, the higher the f3 score, the greater the genetic similarity between the second and the third population.
These are the results:
pop1 pop2 pop3 est se z p n <chr> <chr> <chr> <dbl> <dbl> <dbl> <dbl> <dbl> 1 Dinka.DG Bulgaria_IA Yakut.DG 0.127 0.00193 65.8 0 385997 2 Dinka.DG Bulgaria_IA Icelandic.DG 0.161 0.00221 72.6 0 381503 3 Dinka.DG Bulgaria_IA Bulgarian.DG 0.159 0.00218 73.1 0 381462 4 Dinka.DG Bulgaria_IA Greek_1.DG 0.162 0.00246 66.0 0 380652 5 Dinka.DG Bulgaria_IA Polish.DG 0.159 0.00248 64.3 0 380895 6 Dinka.DG Russia_Alan.SG Yakut.DG 0.131 0.00161 81.7 0 589601 7 Dinka.DG Russia_Alan.SG Icelandic.DG 0.157 0.00177 88.9 0 581891 8 Dinka.DG Russia_Alan.SG Bulgarian.DG 0.154 0.00169 91.4 0 581822 9 Dinka.DG Russia_Alan.SG Greek_1.DG 0.156 0.00181 86.3 0 580489 10 Dinka.DG Russia_Alan.SG Polish.DG 0.154 0.00185 83.0 0 580937 11 Dinka.DG Bulgaria_Medieval Yakut.DG 0.132 0.00174 75.8 0 492705 12 Dinka.DG Bulgaria_Medieval Icelandic.DG 0.163 0.00198 82.4 0 486820 13 Dinka.DG Bulgaria_Medieval Bulgarian.DG 0.159 0.00184 86.6 0 486761 14 Dinka.DG Bulgaria_Medieval Greek_1.DG 0.161 0.00209 77.0 0 485694 15 Dinka.DG Bulgaria_Medieval Polish.DG 0.159 0.00214 74.3 0 485999
Our analysis of the genetic data utilizing the software ADMIXTOOLS 2 reveals a proximity of the Russia_Alan.SG and Bulgaria_Medieval populations, which are thought to represent the ancestral proto-Bulgarians, to the Icelandic and Greek populations when compared to contemporary Bulgarians. This observation is consistent with the genetic proximity observed between the Bulgaria_IA population and the aforementioned populations. Based on this, if we apply the logic used by Stamov in his study, it can be inferred that contemporary Bulgarians do not exhibit genetic affinity specific to the proto-Bulgarian population.
An alternative approach to infer genetic relatedness between populations is the use of f2 statistics, which do not rely on the inclusion of an outgroup population. Specifically, the lower the f2 score, the greater the genetic similarity between populations. Here we add the populations Bulgaria_EIA and Macedonia_IA, published in 2022.
These are the results:
pop1 pop2 est se 1 Bulgaria_EIA Bulgarian.DG 0.00316 0.000443 2 Bulgaria_EIA Greek_1.DG 0.00353 0.000882 3 Bulgaria_EIA Icelandic.DG 0.00582 0.000492 4 Bulgaria_EIA Polish.DG 0.00689 0.000902 5 Bulgaria_EIA Yakut.DG 0.0375 0.000436 6 Bulgaria_IA Bulgarian.DG 0.157 0.000945 7 Bulgaria_IA Greek_1.DG 0.156 0.00129 8 Bulgaria_IA Icelandic.DG 0.159 0.000946 9 Bulgaria_IA Polish.DG 0.160 0.00136 10 Bulgaria_IA Yakut.DG 0.191 0.000810 11 Bulgaria_Medieval Bulgarian.DG 0.0278 0.000722 12 Bulgaria_Medieval Greek_1.DG 0.0273 0.00113 13 Bulgaria_Medieval Icelandic.DG 0.0278 0.000794 14 Bulgaria_Medieval Polish.DG 0.0295 0.00120 15 Bulgaria_Medieval Yakut.DG 0.0584 0.000746 16 Macedonia_IA Bulgarian.DG 0.00220 0.000408 17 Macedonia_IA Greek_1.DG 0.00195 0.000863 18 Macedonia_IA Icelandic.DG 0.00397 0.000477 19 Macedonia_IA Polish.DG 0.00523 0.000896 20 Macedonia_IA Yakut.DG 0.0355 0.000405 21 Russia_Alan.SG Bulgarian.DG 0.0138 0.000570 22 Russia_Alan.SG Greek_1.DG 0.0136 0.000981 23 Russia_Alan.SG Icelandic.DG 0.0149 0.000619 24 Russia_Alan.SG Polish.DG 0.0170 0.00105 25 Russia_Alan.SG Yakut.DG 0.0418 0.000556
The results of the pairwise f2 statistics indicate that:
- The population of Bulgaria_EIA is more closely related to the contemporary Bulgarian population than to the contemporary Greek population.
- The population of Bulgaria_EIA, Bulgaria_IA, and Macedonia_IA exhibit a closer relationship with the contemporary Bulgarian and Greek populations, whereas the Icelandic, Belarusian, and Yakut populations exhibit a more distant relationship.
- The contemporary Bulgarian population is significantly more closely related to the Bulgaria_EIA and Macedonia_IA (representative of ancient Balkan DNA) than to the Bulgaria_Medieval and Russia_Alan.SG populations (purportedly representative of proto-Bulgarian DNA)
- The Bulgaria_Medieval and Russia_Alan.SG populations (purportedly representative of proto-Bulgarian DNA) exhibit a closer relationship with the contemporary Greek population than with the contemporary Bulgarian population.
The study by Svetoslav Stamov, published in a bioRxiv preprint in 2021, makes incorrect claims about the genetic makeup of contemporary Bulgarians. Using a newer version of the same dataset and similar analytical methods, this critique demonstrates that contemporary Bulgarians do in fact harbor significant ancestry from ancient Thracians. Furthermore, the analysis provides evidence that Bulgaria_Medieval and Russia_Alan.SG, the populations cited by Stamov as being of proto-Bulgarian origin, are not more closely related to contemporary Bulgarians than to other populations such as Greeks and Icelanders. These findings refute Stamov’s conclusion that contemporary Bulgarians do not harbor Thracian-specific ancestry. This critique serves as a reminder that conclusions made from genetic data should be made with care and scrutiny, especially when based on small sample sizes or limited genetic markers.