The Eastern Eurasian Steppe was home to historic empires of nomadic pastoralists, including the Xiongnu and the Mongols. However, little is known about the region's population history. Here, we reveal its dynamic genetic history by analyzing new genome-wide data for 214 ancient individuals spanning 6,000 years. We identify a pastoralist expansion into Mongolia ca. 3000 BCE, and by the Late Bronze Age, Mongolian populations were biogeographically structured into three distinct groups, all practicing dairy pastoralism regardless of ancestry. The Xiongnu emerged from the mixing of these populations and those from surrounding regions. By comparison, the Mongols exhibit much higher eastern Eurasian ancestry, resembling present-day Mongolic-speaking populations. Our results illuminate the complex interplay between genetic, sociopolitical, and cultural changes on the Eastern Steppe.

During the Early Bronze Age, populations of the western Eurasian steppe expanded across an immense area of northern Eurasia. Combined archaeological and genetic evidence supports widespread Early Bronze Age population movements out of the Pontic–Caspian steppe that resulted in gene flow across vast distances, linking populations of Yamnaya pastoralists in Scandinavia with pastoral populations (known as the Afanasievo) far to the east in the Altai Mountains^1,2 and Mongolia³. Although some models hold that this expansion was the outcome of a newly mobile pastoral economy characterized by horse traction, bulk wagon transport^4–6 and regular dietary dependence on meat and milk⁵, hard evidence for these economic features has not been found. Here we draw on proteomic analysis of dental calculus from individuals from the western Eurasian steppe to demonstrate a major transition in dairying at the start of the Bronze Age. The rapid onset of ubiquitous dairying at a point in time when steppe populations are known to have begun dispersing offers critical insight into a key catalyst of steppe mobility. The identification of horse milk proteins also indicates horse domestication by the Early Bronze Age, which provides support for its role in steppe dispersals. Our results point to a potential epicentre for horse domestication in the Pontic–Caspian steppe by the third millennium bc, and offer strong support for the notion that the novel exploitation of secondary animal products was a key driver of the expansions of Eurasian steppe pastoralists by the Early Bronze Age.

The pace of transmission of domesticated cereals, including millet from China as well as wheat and barley from southwest Asia, throughout the vast pastoralist landscapes of the Eurasian Steppe (ES) is unclear. The rich monumental record of the ES preserves abundant human remains that provide a temporally deep and spatially broad record of pastoralist dietary intake. Calibration of human δ¹³C and δ¹⁵N values against isotope ratios derived from co-occurring livestock distinguish pastoralist consumption of millet from the products of livestock and, in some regions, identify a considerable reliance by pastoralists on C₃ crops. We suggest that the adoption of millet was initially sporadic and consumed at low intensities during the Bronze Age, with the low-level consumption of millet possibly taking place in the Minusinsk Basin perhaps as early as the late third millennium cal BC. Starting in the mid-second millennium cal BC, millet consumption intensified dramatically throughout the ES with the exception of both the Mongolian steppe where millet uptake was strongly delayed until the end of first millennium cal BC and the Trans-Urals where instead barley or wheat gained dietary prominence. The emergence of complex, trans-regional political networks likely facilitated the rapid transfer of cultivars across the steppe during the transition to the Iron Age.

Pastoralism in Central Asia directed the utilization of natural resources, yet information on livestock management strategies remain scarce. Carbon (δ¹³C) and oxygen (δ¹⁸O) isotope analyses of domesticated sheep teeth are used to identify animal management strategies. Sheep from Kent exhibit an inverserelationship where low δ¹⁸O values coincide with high δ¹³C values, consistent with the foddering of caprines in the winter for this location which occursalongside evidence for an extended lambing season. At the high altitude encampment of Turgen, Bronze Age sheep exhibit low δ¹⁸O values that coincide withhigh δ¹³C values, suggesting that livestock were moved to low altitude pastures in the winter months. Iron Age sheep sequences also have an inverserelationship, where low δ¹⁸O values coincide with high δ¹³C values, yet high δ¹³C values in the winter suggest that livestock were foddered. Our findingsindicate variation in livestock management strategies with distinct adaptations to local ecologies.

The initial movement of herders and livestock into the eastern steppe is of great interest, as this region has long been home to pastoralist groups. Due to a paucity of faunal remains, however, it has been difficult to discern the timing of the adoption of domesticated ruminants and horses into the region, though recent research on ancient dairying has started to shed new light on this history. Here we present proteomic evidence for shifts in dairy consumption in the Altai Mountains, drawing on evidence from sites dating from the Early Bronze to the Late Iron Age. We compare these finds with evidence for the rise of social complexity in western Mongolia, as reflected in material remains signaling population growth, the establishment of structured cemeteries, and the erection of large monuments. Our results suggest that the subsistence basis for the development of complex societies began at the dawn of the Bronze Age, with the adoption of ruminant livestock. Investments in pastoralism intensified over time, enabling a food production system that sustained growing populations. While pronounced social changes and monumental constructions occurred in tandem with the first evidence for horse dairying, ~1350 cal BCE, these shifts were fueled by a long-term economic dependence on ruminant livestock. Therefore, the spread into the Mongolian Altai of herds, and then horses, resulted in immediate dietary changes, with subsequent social and demographic transformations occurring later.

The role of migration and mobility of people across the steppe has often been cited as key to Bronze Age developments across Eurasia, including the emergence of complex societies in the steppe and the spread of material culture. The central Eurasian steppe (CES) is a focal point for the investigation of the shifting nature of pastoral societies because of the clear transition in archaeological patterning that occurred from the Middle (MBA) to Late Bronze Age (LBA). The spread of LBA (1700–1400 cal BC) Andronovo cultural materials found across wide swaths of the steppe provide indirect evidence for broad scale interactions, but the degree to which people moved across the landscape remains poorly understood. This study takes a first step into documenting human movement during these critical periods through strontium (⁸⁷Sr/⁸⁶Sr) and oxygen (δ¹⁸O) isotopic analyses of tooth enamel recovered from human individuals buried in the cemeteries of Bestamak (MBA) and Lisakovsk (LBA) in northern Kazakhstan. Strontium isotope results, referenced against the distribution of contemporary bioavailable strontium in the vicinity of both sites, suggest local communities engaged in small-scale mobility with limited ranges. Reduced strontium and oxygen isotopic variation visible in humans from Lisakovsk suggests mobility decreased from the Middle to Late Bronze Age likely indicative of a shift in resource and landscape use over time.