Updated analysis of the Bronze Age population genetics from Bezdanjača Cave – the case of I2a1a male individuals

This case report presents an updated interpretation of genetic and chronological data from human remains discovered in Bezdanjača Cave, a Bronze Age burial site located in the Lika region of Croatia. The cave contains a complex necropolis with at least 57 graves and up to 200 individuals, which indicates its use as a collective burial site during the Middle and Late Bronze Age. Based on ancient DNA analysis, 13 males were identified among 38 analyzed individuals, with the majority belonging to the Y-chromosome haplogroup R1b, commonly associated with Bronze Age populations. However, two individuals were assigned to haplogroup I2a1a (I-Y3120). The I2a lineage has deep roots in Europe, and its presence has been confirmed in prehistoric contexts in Croatia and the region. However, newly obtained radiocarbon dates from occipital bones reveal that at least one of the two I2a1a individuals from Bezdanjača Cave dates to the Early Modern period (1645-1950 calibrated CE), which indicates that the remains were deposited in the cave much later than previously assumed. At the same time, these new data do not contradict the possible presence of the I2a1a lineage in Bronze Age populations in this area, as Bronze Age I2a1a samples have been reported from other archaeological sites in Croatia and the wider region. These findings, presented here for the first time, highlight the risks of assuming chronological homogeneity based solely on archaeological context and demonstrate the necessity of direct radiocarbon dating when integrating archaeological and genetic data. An interdisciplinary approach and careful chronological verification in ancient DNA research are essential to avoid misinterpretations in broader population genetic studies.