Was the Maikop culture the PIE homeland?

Discussion
This study presents the first large archaeogenetic dataset from present-day Georgia. Extending previous data6,8,41,42, this temporally continuous genomic time transect allowed us to provide comprehensive insights into the population history of the South Caucasus.

Our comparative models for Georgia and Armenia during the Early Bronze Age demonstrate that previous mixture events between metapopulations related to the CHG and the farmers of Anatolia resulted in a homogeneous population throughout the South Caucasus not only specific to present-day Armenia. The trace amounts of EHG-related ancestry observed in EBA Armenia and Georgia indicate that it did not disappear after the Chalcolithic period when it was observed in Armenia 43.

We find that EHG ancestry resurged again in the Middle Bronze Age. Two lines of evidence suggest that this increase can be associated with specific populations, namely the pastoralist groups from the steppe adjacent to the North Caucasus, which are 1) fitting sources in our proximal modeling (Figure 3C) and also sources for the newly arriving Y haplogroup Z2103. Notably, we observe no geographically stratified signal of EHG (steppe ancestry) in the Late Bronze/Early Iron Age that could indicate an eastwards or westwards migration route across the Caucasus (Table S9), but one limitation is that our dataset underrepresents the western end of Georgia. The admixture timing and the model fit of the group ‘Steppe_Catacomb’ correlate with deteriorating climatic conditions in the Caucasus-Steppe region, which led to the breakdown of stock specialization and, ultimately, its abandonment at the end of the 2nd millennium BC 44,45. In addition to such ‘push’ factors,, the farming and metallurgical societies of the South Caucasus that had developed since the 6th millennium BC and could have attracted groups with similar economies. It has also been suggested that steppe mobility into the South Caucasus played a role in language innovation in Indo-European-speaking Armenia 8. However, recent linguistic evidence also supports a northward expansion of Indo-European languages from a region south of Caucasus postdating the divergence of the Armenian language. In the case of Georgia, Kartvelian, a distinct non-Indo-European language family that has existed since approximately 13,000 years ago 47, persists until today. It further diversified after the MBA/LBA admixture, and the described gene flows may have contributed to its proposed structural relationship with Indo-European languages 48,49.

The simultaneous rise in Anatolian/Levantine ancestry in the Middle Bronze Age indicates a separate and parallel admixture event. This gene flow likely reflects a continuous demographic process of prolonged contact between the South Caucasus and Anatolia, as previously documented 6,7.

Together, the two MBA admixture events mentioned above have lastingly shaped the gene pool of the South Caucasus, as evidenced by the PCA, qpAdm modeling, and uniparentally-inherited markers, which reached present-day population diversity levels 50 shortly after the Bronze Age. It is worth noting that pairwise comparisons by period reveal differences, particularly between the latest and earlier groups (see Supplementary Figure 2A). However, as the proximal modeling indicates, these differences can be explained by a decreasing Steppe-Anatolian/Iranian ancestry ratio over time (see Figure 3C). Given that Armenia and, to some extent, Iran are the southernmost enclaves of steppe ancestry in southwest Asia 8, this genetic signal is interpreted as an increase in gene flow from Anatolia and Iran. The historical relevance of this finding can be proposed at the base of the continuous political influence exerted on the region by the successive empires that extended across Southwest Asia, including the Median, Achaemenid, and Sasanian empires. The Iberian, Colchis, and Armenian kingdoms were among those influenced.

With half of the aDNA dataset dating to the Late Antique and Early Middle Ages (c. 50-800 AD), we were able to assess the potential influence of important historical events such as the Roman conquest, Christianization, and increased contact with nomadic tribes from the Eurasian steppe. According to a recent study 51, approximately 7% of historical individuals in Europe and Southwest Asia had non-local ancestry. Our results for this period broadly fit this observation, but with a higher fraction of around 15%, most of which indicates individual mobility from neighboring areas such as Anatolia and the North Caucasus, and a smaller fraction explained by trans-Eurasian mobility networks. However, these figures cannot be extrapolated to the entire area of Georgia, as our sampling concentrates on Iberian urban centers such as Mtskheta (Samtavro) and Tbilisi and their surroundings. The Greek Historian Strabo refers in his Geography (Book 11, Chapter 3) to this area as the confluence of the Aragvi River’s two branches - the Dariel Pass’s main route - which since antiquity has been considered a crucial passageway controlling the migration on either side. Although generally known as a rural area, it has the earliest evidence of Christianization and served as a defensive system for the capital. Our analyses combining haplotype sharing and ancestry modeling revealed a mixed social organization with rural endogamic communities together with genetically more diverse communities of unrelated individuals in urban sites, including the ’ancestry outliers’ buried according to the same rites as the ‘locals’ (see SI Material 1). Notably, the individuals with a high Anatolian/Levantine ancestry component were buried in the urban necropolis of Samtavro and mostly date to the 5th century AD, which is about a century after Christianity became Iberia’s official religion.

Finally, we generated new insights into the practice of ACD in the Early Medieval Caucasus. A recent study using geometric morphometric analysis between medieval Hungary and Georgia concluded that ACD was not associated with the Huns but rather with the Sarmatians and Alans in the North Caucasus 40. Furthermore, due to the lack of craniometric data from infants and children with ACD (only one 7 to 9-year-old child from Samshvilde), it has not been possible to establish that such individuals were born into the community. Also, burials of individuals with ACD did not indicate sex bias, higher status, nobility, or poorer health status 52. Here, we show not only the local ancestry of the majority of ACD cases but also their biological relatedness, establishing that ACD has been practiced locally and was passed on to the next generation. However, a person with ACD was more likely to have migrated - directly or through recent ancestors - from across the Eurasian steppe. This observation parallels the findings from a study on Early Medieval deformed skulls from Bavaria, whose collective ancestry derived from Eastern Europe 26. Here, our modeling analyses of the ACD in Georgia support the hypothesis of Sarmatian and Alan origin in some cases, but with haplotype sharing we identify direct genealogical links to individuals from the Avar and Hun periods in the Carpathian basin. Remarkably, all the outlying ACD individuals, with the exception of the possibly contaminated SVL005, had their deformation carried in a different way (‘tabular’) than the one associated with the Huns (‘annular’) 53.

LEIPZIG, GERMANY—According to a Cosmos Magazine report, a DNA study of 131 sets of human remains from 38 sites across the Caucasus region spanning a period of 6,000 years detected genetic differences between populations living to the north and south of the Caucasus Mountains. Researchers led by Ayshin Ghalichi of the Max Planck Institute for Evolutionary Anthropology and Sabine Reinhold of the German Archaeological Institute determined that the DNA of people living to the north was linked to hunter-gatherers from the east. But to the south of the mountains, eastern hunter-gatherer DNA mixed with populations of East Anatolian farmers, whose DNA increased over time.



The researchers suggest that the migrating farmers from Anatolia may have introduced farming techniques to the southern Caucasian population. This interaction may have also led to the development of animal husbandry and West Eurasian steppe cultures, they explained. But by the late Bronze Age, the steppe cultures declined as new populations moved into the region some 3,000 years ago. Read the original scholarly article about this research in Nature.

doi.org/10.1038/s41586-024-08113-5