How can ancient dental plaque help reveal the rise and spread of dairy pastoralism on the Eurasian steppes?

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Published in Ecology & Evolution
How can ancient dental plaque help reveal the rise and spread of dairy pastoralism on the Eurasian steppes?

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I grinned with excitement when I saw the results of our proteomic analysis of ancient human dental calculus from the North Caucasus. There was no doubt that this individual, an Early Bronze Age man excavated at the site of Sharakhalsun 6 and labeled SA6004, had consumed dairy. As a biochemist who studies the diets of ancient peoples, my work lies at the interface between archaeology, ecology, and anthropology, each of which provides pieces of a larger prehistoric puzzle that I am trying to solve about the initial spread of dairying across the Eurasian steppe. During my Ph.D. studies, I analyzed the remains of dietary proteins within the calcified dental plaque (dental calculus) of hundreds of ancient individuals, including several populations that practiced highly specialized forms of pastoralism that focused heavily on dairy products. Among all the individuals we analyzed, the ancient peoples who once inhabited the North Caucasus steppes clearly stood out, not just in the ubiquity of milk consumption (97% of analyzed individuals were positive for milk proteins) but in the sheer quantity of livestock milk peptides that we recovered from their calculus. From this man alone, we recovered more milk peptide spectral matches than the combined total of ten Bronze Age Mongolian pastoralists in a previous study!

Example MS2 of a beta-lactoglobulin peptide derived from milk, showing species-specific sequence differences between sheep and cattle. (Image credit: Ashley Scott)

Dental calculus is especially useful for studying ancient diets because, as a biomineralized substrate, it traps and preserves ancient biomolecules, allowing us to show direct evidence for the consumption of specific foods. Some milk proteins are known to survive exceptionally well in dental calculus and can be detected using tandem mass spectrometry. The peptide sequences of the constituent milk proteins are highly distinct for common dairying livestock, such as cattle, sheep, goats, and horses. For our team, understanding when and what animals were milked to produce dairy products is crucial for reconstructing the evolution of dairy pastoralism as a subsistence strategy that ultimately became a defining feature of human ecology in the steppe regions of Eurasia.

The teeth of the individual from Sharakhalsun 6 (associated with the Steppe Maykop complex) had an extraordinarily large build-up of dental calculus. At the time that I performed protein extraction and analysis, I did not yet know the detailed history of this individual, who lived approximately 4,500 years ago in the steppe region of the North Caucasus. We knew from our archaeologist colleagues that this person was biologically an adult male. He also holds the distinction of being the earliest known person to have been buried with a wagon, a technology that enabled high mobility and the transport of heavy cargo as herders moved their households - and even whole communities - to access new pastures for their grazing livestock. His skeleton also showed evidence of a large number of healed fractures, consistent with repeated injuries related to a moving wagon, unwieldy draft animals, or interpersonal violence.

Grave 18 from Mound 2 at the Sharakhalsun 6 kurgan cemetery. This man was buried seated on his wagon, which is the oldest dated wooden wagon known to date. Our findings show that he likely used his wagon to herd large flocks of sheep, from which he derived the dairy products that made up his diet. (Image credit: A. V. Yakovlev. Image credit: Nasledie, Stavropol)

While researching the deep past from a laboratory desk, it can sometimes be hard to connect the numbers and spectra I am seeing on my computer screen to the individual people who lived thousands of years ago. However, after seeing the abundance of milk evidence the man from Sharakhalsun 6, he suddenly seemed very real. He was no longer simply protein data on a screen - he was a full person, and I could catch a glimpse of this rugged, wagon-driving man who herded sheep on the North Caucasus steppe more than 4,500 years ago.

It is rare in archaeology to gain such an intimate portrait of an individual, and collectively the milk evidence we obtained in our study allowed us to see the broader pattern of their pastoralist lives. The earliest innovators of dairy pastoralism managed to exploit a previously untapped ecological niche in the steppes north of the Caucasus Mountains. While elsewhere, many ancient populations began to settle into major river valleys and transitioned into an agricultural-based subsistence, the early pastoralists were able to survive in a region ill-suited for agriculture, using domesticated livestock instead to transform vegetation into milk, a highly nutritious and renewable food source that can then be processed into more stable products, such as yogurt, cheese, and curds.

Cast bronze model of a flock of sheep from the hoard of Gamdlistskaro in Georgia. (Image credit: Joni Apakidze, German Archaeological Institute, Eurasia Department)

Much about the lives of these early pastoral nomads still remains unknown. This is in part because historical records were primarily recorded by agricultural societies, and there are few surviving accounts of the lives of herders recorded by pastoralists themselves. However, archaeologists have long suspected that the arrival of animal husbandry in the Northern Caucasus played a vital role in the development and spread of the earliest forms of steppe mobile pastoralism. These mobile lifeways would eventually contribute to the great Bronze Age steppe expansions and the subsequent emergence of the Silk Roads, but, until now, when and under what conditions milk-based subsistence arose on the steppes remained unanswered questions.

Previous archaeological work in the region had provided some context about the movement of people and the spread of subsistence strategies. But unequivocal evidence of dairying remained elusive. Scant archaeological settlement data, limited findings of animal remains, and an isotopically complex landscape have complicated attempts to trace the rise of dairy technology. Our solution for addressing this was to directly analyze the dietary proteins preserved in the dental calculus of people who lived in the Caucasus region and surrounding areas spanning a period of nearly 6,000 years, from the Neolithic to the Greco-Roman periods. Our study, “Emergence and intensification of dairying in the Caucasus and Eurasian steppes,” identified the spread and arrival of dairying technologies to the North Caucasus, and documented the changing use of dairy livestock through time, ultimately finding that past steppe societies had milked sheep, goats, cattle, and horses at different periods in the region’s history.

Eden Hill, a biomolecular archaeology Ph.D. candidate at the Max Planck Institute for Evolutionary Anthropology, subsampling ancient dental calculus for analysis. Dental calculus is analyzed in a clean environment to help reduce possible sources of contamination. (Image credit: Ashley Scott)

To our surprise, we identified a striking and unexpected pattern of dairy consumption that unfolded as we performed multiple rounds of sample extractions and analyzed the data over the course of several months. In the North Caucasus, we found that dairying had begun much earlier than expected, starting already in the 5th millennium BCE during the Eneolithic. Dairying continued throughout all subsequent periods and among all cultural groups, but it changed through time – starting with a focus on sheep milk among the Eneolithic, Maykop, and early Yamana groups, and later diversifying to also include goat and cattle milking from the early 3rd millennium BCE onwards among the late Yamnaya, North Caucasus Culture, Catacomb, and Lola groups. In the South Caucasus, we detected dairying intermittently from the Chalcolithic onwards, and we found that dairying arrived rather late – after 2500 BCE – in the forest steppe to the north and regions east of the Urals.

Sheep being herded today in Azerbaijan. Sheep and other dairy livestock have long been integral to daily life in the foothills north and south of the Caucasus mountains. (Image credit: Emily Hammer)

The lack of cattle milking among the Maykop came as a surprise because their material culture so strongly focuses on cattle-associated imagery and equipment, including bull figurines, cattle nose loops, and even burials containing entire oxen teams. By contrast, the perishability of sheep secondary products, such as milk, cheese, and wool, has made sheep less visible in the archaeological record, and this appears to have contributed to a biased understanding of the relative importance and roles of different livestock at Bronze Age Eurasian sites.

We found that the transition from sheep dairying to a more diversified dairying strategy based on sheep, goat, and cattle milk products first occurred among the Yamnaya in the early 3rd millennium BCE. The Yamnaya were the first cultural group to become fully and permanently mobile, utilizing wagons to spread across the entire Pontic-Caspian region and beyond. It could be that the need for additional pastures to support these herds, especially as the climate became drier after 3000 BCE, may have driven the heightened mobility of the Middle and Late Bronze Age periods. Although Yamnaya-related groups were a major factor in the spread of dairying technology across Eurasia, we find that they inherited a regional dairying tradition that had already been underway for a millennium prior to their expansions.

Interestingly, the only horse milking we observed in our study was from a 9th century BCE Iron Age cemetery of pre-Scythian nomads. This cemetery was related to the recent repeopling of the North Caucasus steppe after a centuries-long hiatus caused by a catastrophic drought that began ca. 1700 BCE. At the time, the Greeks referred to this region as being populated by ‘horse milk drinkers,’ a characterization we were pleased we could confirm.  

The recovery of dietary proteins from ancient dental calculus has transformed our understanding of the rise and spread of dairy pastoralism on the Eurasian steppe. Who would have ever thought that something as mundane as dental plaque could hold the key to unlocking the forgotten stories of our distant past?

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