David Tarkhnishvili
Alexander Gavashelishvili
Oleksij Yanchukov
(Ilia State University)
Human dispersal around the Black Sea area
in early postglacial time
Wide use of genetic markers since last 30 years, and fast development of the genomic technologies during the last decade strongly accelerated research in human population genetics and triggered revision of some traditional views on history and, especially, pre-historic past of the human being. Currently, we have sufficiently good knowledge about the timing and location of early divergence of anatomically modern humans, we can follow the waves of human migrations from Africa to Eurasia and farther, and track genetic introgression between anatomically modern humans, Neanderthals, and Denisovians in different parts of the World. Thanks to genomic data, we have growing evidence of dispersal of early agriculture and technologies. However, we still know little details about dispersal of hunter-gatherers in early Holocene time, which obviously had a strong impact on the modern pattern of human allele distribution. Our studies, published in four papers between 2014 and 2021, try to fill this gap to a certain extent. The focus of these papers was to check whether and how the landscape separating the modern settlements is correlating with the genetic patterns of the humans from rural area. The assumption is that the landscape peculiarities, such as mountainous terrain, snow cover, or thick forest cover, do not have a substantial impact on the dispersal of modern humans, but could well be important for hunter-gatherers 11 – 15 Kya. Our early studies showed that the distribution of patrilineally inherited Y-chromosome haplogroups in the Caucasus is associated with the landscape type, with less correlation to a spoken language or ethnicity, hence, suggesting that the landscape genetic pattern is much more conservative than any other anthropological dimensions. Another paper validated the impact of the landscape on the genetic connectivity of rural populations. It showed that both clonally inherited and recombinant genetic pattern is, above all, associated with a weighted geographic distance where the impeding factors were snow cover in winter, terrain ruggedness, and forest cover, hence suggesting that the population network, at least in high mountain areas, was largely formed due to very early (prior to the agriculture expansion) movements of humans in the postglacial period. The two following papers suggest the critical importance of glacial refugia in the formation of the current allele distribution throughout the entire Old World. The most recent large wave of out-of-Africa migration has occurred ca. 45 kya, just prior to fast decrease of temperature during the last glacial wave. This climatic change captured humans in more or less isolated refugial areas, mostly grasslands and light forests, separated by large areas of cold deserts and other landscapes difficult to cross. Closeness to multiple refugia explains different level of genetic diversity in different parts of Eurasia with a high confidence level. Recent genomic data analysis supported the view that the current genetic pattern was formed largely in the early postglacial period and undergone relatively little changes after Neolithic time. In the Black Sea area, the glacial human refugia existed in three partly separated areas: in southern Anatolia, in Transcaucasian depression from Black to Caspian Sea, and in Balkans. Migration from these three areas shaped current population of the region; the proportion of ancient alleles from each of these three areas in the modern rural populations correlates strongly with the closeness to each of these ancient migration sources. It was shown that this early migration from Balkans to the Caucasus went through the grassland area in the modern Ukraine rather than through Anatolia, whereas the ancient people from the southern Caucasus expanded northwards rather than to Anatolia. The migrants from southern Anatolia, however, drove large part of their alleles to the southern Caucasus populations.