This interpretation is misleading. Sarno et al. modeled Bulgarian ancestry using various ancient reference groups, including Bronze/Iron Age samples from Bulgaria (“BGR_IA”), but they stress that modern Bulgarians are a genetic mosaic shaped by multiple waves of migration.
Their haplotype-based analysis finds signals from Mesolithic hunter-gatherers, Neolithic farmers, Bronze-Age Steppe migrants and later historical events (Roman, Slavic, etc.)
Balkan Thracians’ contribution to today’s gene pool “remains largely unknown” due to limited data https://www.nature.com/article...
The study never claims “only 12% Thracian” in modern Bulgarians; rather it shows the specific “Bulgarian Iron Age” component
Crucially, these “Iron Age” samples are few (approximately 4 individuals from Bulgarian necropolises) and may not represent all Thracian groups. Equating “BGR_IA” with the historical Thracians is uncertain
Sarno et al. do not definitively measure “Thracian DNA” in Bulgarians, But only a small local Iron-Age reference group.
Moreover, Sarno et al. emphasize that later migrations had major impact. Their haplotype results indicate significant ancestry from Roman/Byzantine-era and Medieval Balkan populations in modern Bulgarians
https://www.technologynetworks... Reich notes that Slavic-era gene flow accounts for a large fraction of Balkan ancestry, Thus even if the Iron-Age component is modest, it is overshadowed by subsequent Slavic and medieval inputs.
Sarno et al. themselves highlight contributions from post-Roman and Medieval population processes shaping Bulgarians, So the “12–15%” figure refers only to the narrow BGR_IA proxy, not the totality of pre-Slavic Balkan ancestry.
Olalde et al. 2023 found that roughly half of Bulgarian ancestry derives from Slavic migrations, with the remainder from earlier Balkan and Roman-era populations. Olalde reports ~19% from Early Iron Age Balkan “natives” plus ~23% from Roman-era Balkans, totalling ~42% pre-Slavic
Thus Bulgarians inherit on the order of ~50–60% of their genome from pre-Slavic Balkan lineages (which include Thracian ancestors), far above the 12–15% figure quoted for just the BGR_IA component.
~40% of Bulgarian Y-chromosomes belong to haplogroups E-V13 or I-M423 (common autochthonous Balkan lineages) https://www.researchgate.net/p... Notably, haplogroup E-V13 appears to have been present in the Balkans since the Mesolithic:
Bulgarian brides with artificially elongated skulls were found buried in 5th–6th century Bavaria, With their genomes matching modern Bulgaria and Romania https://www.pnas.org/doi/full/...
Thus, There is a continuity between modern and medieval Bulgarians.