The South Caucasus from the Upper Palaeolithic to the Neolithic: Intersection of the genetic and archaeological data

The genomic characterisation of human remains and the study of archaeological assemblages are complementary keys to understanding the evolution of ancient human groups. This article proposes a dialogue between these two approaches for the South Caucasus between the Upper Palaeolithic and the Neolithic periods. In the Upper Palaeolithic before the Last Glacial Maximum (ca. 40.-23. ka cal BP), genetic and archaeological data demonstrate the originality of the populations of the South Caucasus ( Caucasus_UP genome) compared with their neighbours in SE Europe and SW Asia and also show the existence of links between these different regions. For the post-LGM phase (ca. 20.9–11.7 ka cal BP), archaeological data suggest a certain continuity with the previous period during the cold phase of the Oldest Dryas, followed by a marked rapprochement with the Zarzian culture in the Zagros starting with the warming of the Bølling-Allerød. Genetic analyses, which are available only for the latter phase, reveal a new genome ( Caucasus Hunter-Gatherer or CHG ), that is very close to that of the ancestors of the Neolithic populations of the Zagros. For the Early Holocene (ca. 11.7–8.2 ka cal BP or 9700-6200 cal BCE), the CHG genome, which still characterises the populations of the South Caucasus, is difficult to distinguish in modelling from that of the Zagros (Iran_N ). However, archaeological data suggest that the spread of the Iran_N/CHG gene pool from Iran to Upper Mesopotamia and Central Anatolia was due to populations from the northwest Zagros, and not to those from the South Caucasus, who had only occasional contacts with the Fertile Crescent. At the beginning of the Middle Holocene (ca. 8.2–7.2 ka cal BP or 6200-5200 cal BCE), the appearance in the South Caucasus of animals and plants presenting a high level of domestication, as well as the introduction of new techniques (pressure knapping with a lever, pottery), are clearly due to the arrival of populations from the Fertile Crescent, as confirmed by genetic analyses. These analyses also show that there was not a replacement of local Mesolithic communities by Neolithic farmers, which the archaeological evidence confirms. • Genetics and archaeology prove the originality of Caucasus_UP peoples before the LGM. • Genetic models do not distinguish between the Iran_N and CHG genomes. • Archaeology shows that the westward expansion of Iran_N/CHG is due solely to Iran_N. • Neolithic farmers mixed with (and did not replace) the Caucasian hunter-gatherers.