INTRODUCTION

Two of the major themes of stable isotopic research on the Eurasian steppes have involved investigating and documenting of the spread of millet (Svyatko et al. Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013; Motuzaite Matuzeviciute et al. Reference Motuzaite Matuzeviciute, Lightfoot, O’Connell, Voyakin, Liu, Loman, Svyatko, Usmanova and Jones2015) and the extent of freshwater fish consumption (Privat et al. Reference Privat, O’Connell and Hedges2007; Schulting et al. Reference Schulting, Ramsey, Bazaliiskii, Goriunova and Weber2014, Reference Schulting, Bronk Ramsey, Bazaliiskii and Weber2015; Shishlina et al. Reference Shishlina, Zazovskaya, van der Plicht and Sevastyanov2012, Reference Shishlina, Sevastyanov, Zazovskaya and van der Plicht2014, Reference Shishlina, van der Plicht and Turetsky2018; Svyatko et al. Reference Svyatko, Mertz and Reimer2015, Reference Svyatko, Schulting, Poliakov and Reimer2017a). While it began with individual sites and groups of prehistoric people, this research has also been targeting more general issues such as adoption of major economic practices and documenting changes in subsistence patterns over time and space (Svyatko et al. Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013; Motuzaite Matuzeviciute et al. Reference Motuzaite Matuzeviciute, Kiryushin, Rakhimzhanova, Svyatko, Tishkin and O’Connell2016). Most recently, there have been meta-analyses addressing various aspects of prehistoric life across the region, such as the transmission of domesticated cereals and the emergence of complex trans-regional political networks (Ventresca Miller and Makarewicz Reference Ventresca Miller and Makarewicz2019).

While the role of freshwater reservoir effects continues to be debated, stable carbon isotope (δ¹³C) analysis of human and faunal remains, especially when combined with radiocarbon (¹⁴C) dating, has proven very successful in tracing the spread and use of millet. This is because millets (Panicum miliaceum and Setaria italica) are the only plausible candidates for a significant increase in consumption of C₄ plants on the Eurasian steppes, whether directly or through foddered animals, and thus are relatively easily traced by δ¹³C values in human bone collagen. Obviously, ¹⁴C dating of samples which demonstrate a clear C₄ (millet) signal is crucial for understanding this process. In this contribution, we present a brief overview of isotopic studies focusing on the chronology of isotopic evidence for millet on the central Eurasian steppes, specifically within the Minusinsk Basin, and reiterate its appearance in the Late Bronze Age, from the 14th century BC.

Thus far, the earliest isotopic evidence for significant millet consumption in eastern China has been attributed to the Neolithic period (6200–5500 cal BC, Xiaojingshan and Yuezhuang sites; Hu et al. Reference Hu, Wang, Luan, Wang and Richards2008, Reference Hu, Luan, Wang, Wang and Richards2009), and in western China (Xinjiang) to the Bronze and Early Iron Age (from 2000 BC, Wang et al. Reference Wang, Fuller, Wei, Chang and Hu2016, Reference Wang, Wei, Chang, Yu, Zhang, Wang, Hu and Fuller2019; Qu et al. Reference Qu, Hu, Rao, Abuduresule, Li, Hu, Jiang, Wang and Yang2018; also summarized in Hu Reference Hu2018). By ca. 2700 cal BC, millet was used as fodder for domesticated stock in Dzhungar Alatau (southeastern Kazakhstan; Hermes et al. Reference Hermes, Frachetti, Doumani Dupuy, Mar’yashev, Nebel and Makarewicz2019). By the 17th–16th centuries BC millet consumption is isotopically recorded in southern Kazakhstan (Motuzaite Matuzeviciute et al. Reference Motuzaite Matuzeviciute, Lightfoot, O’Connell, Voyakin, Liu, Loman, Svyatko, Usmanova and Jones2015), and by the final Bronze Age in central Kazakhstan (Lightfoot et al. Reference Lightfoot, Motuzaite-Matuzeviciute, O’Connell, Kukushkin, Loman, Varfolomeev, Liu and Jones2015). To the northeast of this, in southern Siberia, millet apparently arrived in the Minusinsk Basin only during the 14th century BC (Svyatko et al. Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013), and by the 6th–7th centuries BC it is isotopically detected in the Tuva region (Murphy et al. Reference Murphy, Schulting, Beer, Kasparov and Pshenitsyna2013), though this is unlikely to mark their earliest appearance there. That said, clear isotopic evidence of significant millet consumption in Mongolia is also late, being mainly found from the 8th century BC (Wilkin et al. Reference Wilkin, Ventresca Miller, Miller, Spengler, Taylor, Fernandes, Hagan, Bleasdale, Zech, Ulziibayar, Myagmar, Boivin and Roberts2020).

In a recent synthesis, Ventresca Miller and Makarewicz (Reference Ventresca Miller and Makarewicz2019) propose that millet consumption in southern Siberia can be attributed to a much earlier period, namely, the late third to early second millennium BC (Early Bronze Age). This requires some discussion, as this conclusion, being a critical point for the perception of the history (economy, migrations, and cultural contacts) of southern Siberian populations, is inconsistent with the associated isotopic, paleobotanical and archaeological studies in the region. Their paper presents a meta-analysis of the existing stable isotope and paleobotanical data for the timing and spread of various cereals across a number of regions of the Eurasian steppe. The authors attempt not only to summarize the archaeological data, but also to demonstrate the use of cereals in regions which were previously considered to have been purely pastoral in terms of economy. This is particularly important for the Bronze Age archaeological complexes of the western and southern parts of Siberia, which have been traditionally seen as following a pastoral way of life (Gryaznov Reference Gryaznov1969).

As with any meta-analysis, there is a strong reliance on previously available data. Our main purpose in this brief paper is to correct a misunderstanding regarding the appearance of millet in southern Siberia at the end of the 3rd millennium BC, as this relies on a number of human stable carbon isotope (δ¹³C) values misattributed chronologically. Addressing one of the key regions of southern Siberia, the Minusinsk Basin, Ventresca Miller and Makarewicz (Reference Ventresca Miller and Makarewicz2019: p. e1) conclude that “low-level consumption of millet [was] possibly taking place in the Minusinsk Basin perhaps as early as the late third millennium cal BC” citing Svyatko et al. (Reference Svyatko, Murphy, Schulting and Mallory2007) in fig. 4 and table S5 as the source for the first millet signal in the Afanasyevo and Okunevo populations. In particular, they show two “Afanasyevo” and one “Okunevo” individuals demonstrating high δ¹³C values (i.e., > –17‰) that, in this region, are associated with consumption of the C₄ plant millet. The authors conclude that “in the absence of radiocarbon determinations from human individuals analyzed for carbon and nitrogen isotopes, some individuals in the EBA group could date to as late as c. 2000 cal BC”, and that “low-level millet consumption by hunter-gatherer populations in the ES [Eurasian Steppe] may have taken place in the Early Bronze Age (EBA) sometime during the late third to early second millennium cal BC” (Ventresca Miller and Makarewicz Reference Ventresca Miller and Makarewicz2019: p. e5). If true, this would present a very different picture of the transmission of millet into the region.

The paper cited, Svyatko et al. (Reference Svyatko, Murphy, Schulting and Mallory2007), was one of our first reports at an early stage of our research in the area, presenting preliminary stable isotope results for the Bronze to Early Iron Age populations of the Minusinsk Basin for the proceedings of the 2007 Annual Conference of the Association for Environmental Archaeology (Poznań, Poland). Cultural attributions were based on archaeological evidence. Subsequent research, however, demonstrated that the three supposedly early individuals showing a “millet signal” in fact dated to the later Karasuk (Late Bronze Age), Tagar (Early Iron Age) and medieval periods. The ¹⁴C dates were reported (Svyatko et al. Reference Svyatko, Mallory, Murphy, Polyakov, Reimer and Schulting2009; samples UBA-7902, UBA-7904 and UBA-7920), as a part of an extensive, targeted dating program involving 88 humans from the Minusinsk Basin, previously analysed isotopically. This exercise showed that the first clear “millet signal” (δ¹³C > –17‰) in the Minusinsk Basin appeared in the 14th century BC, as shown in Svyatko et al. (Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013, fig. 3). We recognize that there were issues in comparing the ¹⁴C dates and stable isotope results directly in our previous publications, though our reporting of the minimum and maximum values for each archaeological period and complex clearly showed that there were no δ¹³C values above –17.8‰ for any period prior to the Karasuk culture (Svyatko et al. Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013: table 2). To avoid further misunderstandings, we present the full dataset here (Figure 1 and SI Table 1). Another important point to emphasize here is that even after the 14th century BC, there was considerable variability in the consumption of millet, with some individuals showing little to no use, and this continued well into the Early Iron Age (cf. Murphy et al. Reference Murphy, Schulting, Beer, Kasparov and Pshenitsyna2013; Shishlina et al. Reference Shishlina, Pankova, Sevastyanov, Kuznetsova and Demidenko2016; Wilkin et al. Reference Wilkin, Ventresca Miller, Miller, Spengler, Taylor, Fernandes, Hagan, Bleasdale, Zech, Ulziibayar, Myagmar, Boivin and Roberts2020); similar observations have been made for central Kazakhstan (Lightfoot et al. Reference Lightfoot, Motuzaite-Matuzeviciute, O’Connell, Kukushkin, Loman, Varfolomeev, Liu and Jones2015). We have previously addressed the possibility of a freshwater reservoir effect on the ¹⁴C dates obtained (Svyatko et al. Reference Svyatko, Schulting, Poliakov and Reimer2017a), and, while it remains a possibility, we do not think it would have a major impact on the date for the introduction of millet into the Minusinsk Basin.

Figure 1 Boxplots showing (a) δ¹³C and (b) δ¹⁵N values by culture. The lighter gray circles and number in brackets indicate individuals that have been directly ¹⁴C dated.

Southern Siberia is one of the crucial regions of cultural genesis and interaction in the steppe zone; its importance for the Bronze and Early Iron Age of the Eurasian steppe belt has been continuously emphasized in the literature since the first expeditions by German scientists on Russian service (D.G. Messerschmidt, P.S. Pallas, W. Radloff) to the area in the 18th–19th centuries. For the 20th–15th centuries BC, this region and the adjacent southern part of West Siberia are represented by a number of autochthonous cultural complexes (Elunino and Okunevo) and those where bearers migrated from the west (Afanasyevo and Andronovo), as recently confirmed by ancient DNA (Allentoft et al. Reference Allentoft, Sikora, Sjögren, Rasmussen, Rasmussen, Stenderup, Damgaard, Schroeder, Ahlström and Vinner2015). According to archaeological and archaeozoological data, they all practiced a primarily stock-rearing economy (Gryaznov Reference Gryaznov1969).

Despite the role of cereal cultivation in supplementing the pastoral economy of Bronze Age communities in the south of West Siberia being originally discussed in the 1930s, the first reliable evidence of grain consumption was recorded only for the Late Bronze Age, 14th–9th centuries BC, in the Irmen Complex Milovanovo settlement where wheat impressions on pottery were found (Sidorov Reference Sidorov1986). This was the period when the Andronovo Complex was replaced by new material culture (including bronze sickles possibly used for harvesting cereals, as well as mattocks and quernstones) seen in the Irmen and Karasuk complexes. Importantly, this was associated with increased contacts between the populations of southern Siberia and the Central Plains of China. Prior to this time, there is evidence for interactions only between the Afanasyevo or Okunevo complexes of southern Siberia and the Dzhungar Basin (e.g., Qiemu’erqieke cemetery; Jia and Betts Reference Jia and Betts2010), and between Andronovo and Xinjiang, as summarized in Svyatko et al. (Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013; see also Jia et al. Reference Jia, Betts, Cong, Jia and Doumani Dupuy2017), both regions being part of the steppe world during the Bronze Age. The first connections between Siberia and China are only attributed to the Shang period (16th–11th centuries BC; Kuzmina Reference Kuzmina2007).

Isotopically, the appearance of millet in the Late Bronze Age cultural complexes of southern Siberia was first described in Svyatko et al. (Reference Svyatko, Schulting, Mallory, Murphy, Reimer, Khartanovich, Chistov and Sablin2013), where it was placed in the 14th century BC. That paper also discussed the context and implications of this conclusion, including intensified contacts between Karasuk groups and China, further detailed in later publications (Svyatko Reference Svyatko2014, Reference Svyatko2016). Subsequent recent research on earlier periods in the area and neighboring regions (Marchenko et al. Reference Marchenko, Orlova, Panov, Zubova, Molodin, Pozdnyakova, Grishin and Uslamin2015; Motuzaite Matuzeviciute et al. Reference Motuzaite Matuzeviciute, Kiryushin, Rakhimzhanova, Svyatko, Tishkin and O’Connell2016; Svyatko et al. Reference Svyatko, Polyakov, Soenov, Stepanova, Reimer, Ogle, Tyurina, Grushin and Rykun2017c) has provided no evidence for any significant contribution of millet to human diet. However a C₄ signal was detected for at least three 14th–13th centuries BC individuals out of 7 humans analysed from the Irmen Complex sites of Firsovo-14 and Plotinnaya in the upper Ob River Basin ca. 1500 km to the northwest of the Minusinsk Basin (δ¹³C = –16.4‰, –15.6‰, –15.5‰), with more systematic millet consumption only from the 5th century BC (δ¹³C = –18.2 ± 4.9‰, ranging from –24.6‰ to –14.1‰ for a group of 65 Early Iron Age individuals; Svyatko et al. Reference Svyatko, Papin and Poshekhonova2017b; Papin and Svyatko Reference Papin and Svyatko2018).

In sum, a small number of key datapoints cited by Ventresca Miller and Makarewicz (Reference Ventresca Miller and Makarewicz2019) are inaccurate regarding the timing of the appearance of significant consumption (i.e., clearly detectable isotopically) of C₄ crops in southern Siberia. The presence of cereals—both wheat and millet—in the local diets has only been reliably recorded archaeologically and isotopically following the transition from Andronovo to Irmen and Karasuk cultural traditions. At present, there are no direct data for southern Siberia indicating the consumption of millet prior to the 14th century BC, at least 600 years later than suggested in Ventresca Miller and Makarewicz (Reference Ventresca Miller and Makarewicz2019). Beyond setting the record straight for a few stable isotope values, the issue is of wider relevance since it links in with larger discussions concerning the cultural exchanges and transmissions across the Eurasian steppe, particularly regarding links with China.

The 2nd millennium BC was a highly dynamic period in Eurasian prehistory, characterised by intensified East-West migrations and exchanges in material culture and ideas. This was the time of a dramatic increase in human population and settlements in China, a “revolutionary” development towards the emergence of Chinese civilization and the formation of early states. The latest research in key archaeological sites of the Inner Asian Mountain Corridor (Wang et al. Reference Wang, Wei, Chang, Yu, Zhang, Wang, Hu and Fuller2019, Reference Wang, Liu, Duan, Zhang, Liu, Reid, Zhang, Dong, Wang, Ruan, Li and An2020) demonstrates that during the 2nd millennium BC millets spread westward out of the Yellow River Basin to Xinjiang, southern Kazakhstan, Minusinsk Basin and Europe. This dynamic period apparently witnessed the first steps of formation of the so-called “Isotopic Millet Road” (Wang et al. Reference Wang, Wei, Chang, Yu, Zhang, Wang, Hu and Fuller2019) which extended from North China to Central Asia (including Siberia). This was likely driven by increased East–West contacts, including resource transfer, warfare, marriage, migration, and the rise of the Xia and Shang dynasties. The Gansu Corridor is the most likely route by which millet ultimately arrived into the Minusinsk Basin in the mid-2nd millennium BC. Millets were already in use in southeast Gansu region in the 6th millennium BC (Dadiwan site, Barton et al. Reference Barton, Newsome, Chen, Wang, Guilderson and Bettinger2009) and in northwest Gansu by at least 2000 BC (Atahan et al. Reference Atahan, Dodson, Li, Zhou, Hu, Bertuch and Sun2011; Ma et al. Reference Ma, Dong, Jia, Wang, Cui and Chen2016; see summary in Liu et al. Reference Liu, Pollard, Schulting, Rawson and Liu2021). Interestingly, at around the same time as a millet signal is detected in the Minusinsk Basin at ca. 1400 BC, there appears to be a parallel decrease in δ¹³C values in Gansu, suggesting the reciprocal arrival of wheat there (Ma et al. Reference Ma, Dong, Jia, Wang, Cui and Chen2016; see also Liu et al. Reference Liu, Pollard, Schulting, Rawson and Liu2021). Whether this can be linked to climate change as proposed by Ma et al. (Reference Ma, Dong, Jia, Wang, Cui and Chen2016) is a subject for further research. In any case, this was undoubtedly a major milestone in the development of the regional economy and the long-distance cultural exchanges that are at the heart of the Eurasian steppe.

Regardless of our remarks, the paper by Ventresca Miller and Makarewicz (Reference Ventresca Miller and Makarewicz2019) has important implications for the study of particular localities and ways of adoption of cereal cultivation traditions in the Eurasian steppe belt and represents a major contribution towards our understanding of the regional prehistoric economies and societies. Needless to say, only further research in particular areas, especially the ¹⁴C dating of human and/or animal remains suggestive of millet consumption, and the remains of the crops themselves, will provide us with the precise chronology and pathways of the spread of millet in Siberia.