Into the great wide open: How steppe pastoralist groups formed and transformed over time

The wider Caucasus region, between the Black and the Caspian Seas, connects Europe, the Near East and Asia. It displays a huge geographic, ecological, economic, cultural, and linguistic range today, from the steppe zone in the north, the Caucasus mountains in the center, to the highlands of today's Armenia, Georgia, Azerbaijan and Iran in the south. This diversity was no different in the past, where the archaeological record attests to many different influences from many surrounding regions.

"It is precisely this interface of different eco-geographic features and archaeological cultures that makes the region so interesting to study," explains Dr. Wolfgang Haak, senior author and principal investigator of the study. "By establishing a time series across many consecutive archaeological periods, we wanted to capture the time periods when, for example, the first farmers arrived in the region, or when the combination of new innovations in e.g., herd management, dairying, and mobility, enabled an autonomous nomadic lifestyle adapted to exploit the vast Eurasian steppe zone."

The team observes an alternating series of interaction and gene flow between inhabitants of the major eco-geographic zones of the mountainous upland regions and the steppes to the north of the Caucasus. "Initially, we find two distinct genetic ancestries among the hunter-gatherer groups north and south of the Greater Caucasus," adds lead author Ayshin Ghalichi, PhD candidate at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

This picture changed with the arrival of early farmers from northern Mesopotamia in the 6^th millennium BC, which led to two initial processes of mixture: one between these early farmers farmers and Caucasus/Iranian hunter-gatherers, which formed the predominant ancestry south of the Caucasus mountains, and a second one between the aforementioned hunter-gatherer groups, which resulted in the ancestry profile in the steppe zone north of the Caucasus. During the following 5^th and 4^th millennium BC, Eneolithic cultures emerged in the river valleys of the North-Pontic steppe and became archaeologically visible as they built characteristic earthen burial mounds, known as 'kurgans'. New Eneolithic groups arriving from the south led to a period of contact and exchange between both groups and resulted in the emergence of the Maykop culture phenomenon in the 4^th millennium BC, which represents a horizon of technical and social innovations in archaeology.

Into the great wide open

"This is a peak time of knowledge and technology transfer in the North Caucasus region, when we see very similar cultural elements in genetically different groups, but also many signs of mixing and mingling," explains Dr. Sabine Reinhold, co-lead author and principal investigator at the German Archaeological Institute in Berlin. "We uncover the moments when groups began to adapt their lifestyle to a more mobile economy, more suitable to the seemingly endless grasslands of Eurasia." Indeed, the archaeological record attest to critical innovations in herd management, dairying practices, and mobility such as wheels and wagons, of mobile architecture, and the incipient horse domestication, besides many more. "The global dairy industry today is built on the back of these Bronze Age innovations," says Prof. Christina Warinner, co-author and professor of anthropology at Harvard University. "They turned a somewhat niche practice into a multicontinental phenomenon."

Durable foodstuffs such as the early forms of cheese, together with innovations in transportation, made it possible to populate the Eurasian steppe permanently and establish continent-wide networks of communication. The combination of innovations paved the way for a fully nomadic pastoralist life-style at the turn the 3^rd millennium BC, practiced for instance by groups associated the Yamnaya cultural complex, which soon after expanded across the entire western steppe zone, as far as Mongolia in the east, and the Carpathian Basin in the west. Interestingly, it was also a time when Caucasus groups expanded to the south, such as the Kura-Araxes culture of Georgia, which extended to regions in east Anatolia, the Levante, and Iran, albeit with little or no connections to the steppe zone in the north.

The team also explored the social structure of prehistoric groups by analysing patterns of biological relatedness and consanguinity and found differences between the steppe and the Caucasus groups. The more stationary Caucasus groups showed higher levels of consanguinity and close connections between individuals buried in the same and/or nearby kurgans, whereas the steppe groups revealed very few of such connections, hinting at a different form of social organization of mobile pastoralist groups.

Dissolution and transformation

However, the turn to the 2^nd millennium BC represents another period of interaction between the steppe and Caucasus populations. Triggered by a period of aridification and possibly over-exploitation of the ecologically fragile steppe environment and unreliable levels of precipitation, the steppe zone became largely depopulated. The archaeogenetic study finds clear evidence of assimilation and mixture of Caucasus groups, while the resulting Middle and Late Bronze Age groups retreated further into the Caucasus highlands where they established a sedentary mountain economy. This transformation also formed the cultural and genetic basis for the present-day populations of the North Caucasus.

"Our integrated study is a beautiful example of human resilience, adaptability and innovation in the light of ecological, economic and socio-political changes," concludes Prof. Svend Hansen, director of the Eurasia Department of the German Archaeological Institute, and co-senior author of the study.