Western Steppe Herders

In archaeogenetics, the term Western Steppe Herders (WSH), or Western Steppe Pastoralists, is the name given to a distinct ancestral component first identified in individuals from the Chalcolithic steppe around the turn of the 5th millennium BC, subsequently detected in several genetically similar or directly related ancient populations including the Khvalynsk, Repin, Sredny Stog, and Yamnaya cultures, and found in substantial levels in contemporary European, Central Asian, South Asian and West Asian populations.^[a][b] This ancestry is often referred to as Yamnaya ancestry, Yamnaya-related ancestry, Steppe ancestry or Steppe-related ancestry.^[6]

Western Steppe Herders are considered to be descended from a merger between Eastern Hunter-Gatherers (EHGs) and Caucasus Hunter-Gatherers (CHGs). The WSH component is modeled as an admixture of EHG and CHG ancestral components in roughly equal proportions, with the majority of the Y-DNA haplogroup contribution from EHG males. The Y-DNA haplogroups of Western Steppe Herder males are not uniform, with the Yamnaya culture individuals mainly belonging to R1b-Z2103 with a minority of I2a2, the earlier Khvalynsk culture also with mainly R1b but also some R1a, Q1a, J, and I2a2, and the later, high WSH ancestry Corded Ware culture individuals mainly belonging to haplogroup R1b in the earliest samples, with R1a-M417 becoming predominant over time.^[7][8][9]

Around 3,000 BC, people of the Yamnaya culture or a closely related group,^[2] who had high levels of WSH ancestry with some additional Neolithic farmer admixture,^[5][10] embarked on a massive expansion throughout Eurasia, which is considered to be associated with the dispersal of at least some of the Indo-European languages by most contemporary linguists, archaeologists, and geneticists. WSH ancestry from this period is often referred to as Steppe Early and Middle Bronze Age (Steppe EMBA) ancestry.^[c]

This migration is linked to the origin of both the Corded Ware culture, whose members were of about 75% WSH ancestry, and the Bell Beaker ("Eastern group"), who were around 50% WSH ancestry, though the exact relationships between these groups remains uncertain.^[11]

The expansion of WSHs resulted in the virtual disappearance of the Y-DNA of Early European Farmers (EEFs) from the European gene pool, significantly altering the cultural and genetic landscape of Europe. During the Bronze Age, Corded Ware people with admixture from Central Europe remigrated onto the steppe, forming the Sintashta culture and a type of WSH ancestry often referred to as Steppe Middle and Late Bronze Age (Steppe MLBA) or Sintashta-related ancestry.^[c]

The modern population of Europe can largely be modeled as a mixture of WHG (Western Hunter-Gatherer), EEF and WSH. According to a 2024 study, WSH ancestry peaks in Ireland, Iceland, Norway and Sweden.^[12] In South Asia, it peaks among the Brahmin, Bhumihar, Ror, Jat, and Kalash.^{[2][4][13][14]} The modern day Yaghnobis, an Eastern Iranian people, and to a lesser extent modern-day Tajiks, display genetic continuity to Iron Age Central Asian Indo-Iranians, and may be used as proxy for the source of "Steppe ancestry" among many Central Asian and Middle Eastern groups.^[15][16][17]

A summary of several genetic studies published in Nature and Cell during the year 2015 is given by Heyd (2017):

• Western Steppe Herders component "is lower in southern Europe and higher in northern Europe", where inhabitants have roughly 50% WSH ancestry on average. (Haak et al. 2015; Lazaridis et al. 2016)
• It is linked to the migrations of Yamnaya populations dated to ca. 3000 BC (Allentoft et al. 2015; Haak et al. 2015);
• Third-millennium Europe (and prehistoric Europe in general) was "a highly dynamic period involving large-scale population migrations and replacement" (Allentoft et al. 2015);
• The Yamnaya migrations are linked to the spread of Indo-European languages (Allentoft et al. 2015; Haak et al. 2015);
• The plague (Yersinia pestis) spread into Europe during the third millennium BC (Rasmussen et al. 2015), and it stemmed from migrations from the Eurasian steppes;
• Yamnaya peoples have the highest ever calculated genetic selection for stature (Mathieson et al. 2015);

'Steppe ancestry' can be classified into at least three distinctive clusters. In its simplest and earliest form, it can be modelled as an admixture of two highly divergent ancestral components; a population related to Eastern Hunter-Gatherers (EHG) as the original inhabitants of the European steppe in the Mesolithic, and a population related to Caucasus Hunter-Gatherers (CHG) that had spread northwards from the Near East. This ancestry profile is known as 'Eneolithic Steppe' ancestry, or 'pre-Yamnaya ancestry', and is represented by ancient individuals from the Khvalynsk II and Progress 2 archaeological sites. These individuals are chronologically intermediate between EHGs and the later Yamnaya population, and harbour very variable proportions of CHG ancestry.^[22][23][10]

The later Yamnaya population can be modelled as an admixed EHG-related/CHG-related population with additional (c. 14%) Anatolian Farmer ancestry with some Western Hunter-Gatherer admixture, or alternatively can be modelled as a mixture of EHG, CHG, and Iranian Chalcolithic ancestries. This ancestry profile is not found in the earlier Eneolithic steppe or Steppe Maykop populations. In addition to individuals of the Yamnaya culture, very similar ancestry is also found in individuals of the closely related Afanasievo culture near the Altai Mountains and the Poltavka culture on the Middle Bronze Age steppe. This genetic component is known as Steppe Early to Middle Bronze Age (Steppe EMBA), or Yamnaya-related ancestry.^[22][10]

Expansions of Yamnaya-related populations to Eastern and Central Europe resulted in the formation of populations with admixed EMBA Steppe and Early European Farmer ancestry, such as the ancient individuals of the Corded Ware and Bell beaker cultures. In the eastern Corded Ware culture, the Fatyanovo-Balanovo group may have been the source of a back migration onto the steppe and further to the east, resulting in the formation of the Srubnaya, Sintashta, and Andronovo cultures. The genetic cluster represented by ancient individuals from these cultures is known as Steppe Middle to Late Bronze Age (Steppe MLBA) ancestry.^[22][10]

The precise location of the initial formation of so-called 'Eneolithic steppe' ancestry, which can be modeled as a relatively simple admixture of EHG and Near Eastern (CHG-related) populations, remains uncertain.^[4][10] Admixture between populations with Near Eastern ancestry and the EHG on the Pontic-Caspian steppe had begun by the fifth millennium BC, predating the Yamnaya culture by at least 1,000 years.^[24][5]

This early, 'pre-Yamnaya' ancestry was first detected in Eneolithic individuals at the Khvalynsk II cemetery and directly north of the Caucasus mountains at the Progress 2 archaeological site; this ancestry is also detected in individuals of the Steppe Maykop culture, but with additional Siberian and Native American-related admixture.^[25][5]

The individuals from Khvalynsk comprise a genetically heterogeneous population, with some more similar to EHGs and others closer to the later Yamnaya population. On average, these individuals can be modelled as around three-quarters EHG and one-quarter Near Eastern ("Armenian related") ancestry. These three individuals belong to Y-chromosome haplogroups R1a (which is not found in later elite Yamnaya graves), R1b, and Q1a, the first two of which are found in preceding EHG populations, which suggests continuity with the preceding EHG population.^[24][10]

Three individuals from the Progress 2 site in the foothills north of the Caucasus also harbour EHG and CHG related ancestry, and are genetically similar to Eneolithic individuals from Khvalynsk II but with higher levels of CHG-related ancestry that are comparable to the later Yamnaya population.^[5][26]

Archaeologist David Anthony speculates that the Khvalynsk/Progress-2 mating network, located between the middle Volga and the North Caucasus foothills, makes a "plausible genetic ancestor for Yamnaya".^[26]

Early Yamnaya individuals, the Afanasievo population, and the individuals of the Poltavka and Catacomb cultures that followed the Yamnaya on the steppe comprise a genetically almost indistinguishable cluster, carrying predominantly R1b Y-DNA haplogroups with a minority of I2a.^[24][10]

When the first Yamnaya whole genome sequences were published in 2015, Yamnaya individuals were reported to have no Anatolian Farmer ancestry,^[2][27][24] but following larger studies it is now generally agreed that Yamnaya had around 14% Anatolian Farmer ancestry, with an additional small WHG component, which was not present in the previous Eneolithic steppe individuals.^[26][10][28]

The actual populations involved in the formation of the Yamnaya cluster remain uncertain. Proposed models have included admixture of an EHG/CHG population with European Farmers to the west (such as those of the Globular Amphorae culture or a genetically similar population), a two-way admixture of EHGs with an Iran Chalcolithic population, and a three-way admixture of EHG, CHG, and Iran Chalcolithic populations.^[5][13][10]

Lazaridis et al. (2022) conclude that Yamnaya ancestry can be modelled as a mixture of an as yet unsampled admixed EHG/CHG population with a second source from the south Caucasus, and rejects Khvalynsk Eneolithic as a source population for the Yamnaya cluster. The study also contradicts suggestions that European farmer populations of the Cucuteni-Trypillia and Globular Amphora cultures contributed ancestry to Yamnaya, as Yamnaya lack the additional hunter-gatherer ancestry found in European farmers, and carry equal proportions of Anatolian and Levantine ancestry, unlike European farmers who carry predominantly Anatolian ancestry.^[10]

Genetic evidence demonstrates a major and relatively sudden population turnover in Europe during the early third millennium BC, resulting in the rapid spread of steppe ancestry along with the Corded Ware and Bell Beaker cultures.^[2][9]

Corded Ware individuals have been shown to be genetically distinct from preceding European Neolithic cultures of North-Central and Northeastern Europe, with around 75% of their ancestry derived from a Yamnaya-like population.^[2][9]

The earliest Corded Ware individuals are genetically close to Yamnaya. Admixture with local Neolithic populations resulted in later individuals genetically intermediate between Yamnaya and individuals of the Globular Amphora Culture.^[9]

A 2021 study suggests that Early Corded Ware from Bohemia can be modelled as a three way mixture of Yamnaya-like and European Neolithic-like populations, with an additional c. 5% to 15% contribution from a northeast European Eneolithic forest-steppe group (such as Pitted Ware, Latvia Middle Neolithic, Ukraine Neolithic, or a genetically similar population), a cluster the authors term 'Forest Steppe' ancestry.^[9]

In the Bell Beaker culture, high proportions (c. 50%) of steppe related ancestry are found in individuals from Germany, the Czech Republic, and Britain. The genetic turnover is most substantial in Britain, where around 90% of the gene pool was replaced within a few hundred years.^[28][29]

The earliest Bell Beaker individuals from Bohemia harbouring Steppe ancestry are genetically similar to Corded Ware individuals, which suggests continuity between these two groups. Later Bell Beaker individuals have an additional c. 20% Middle Eneolithic ancestry.^[9][29]

Bronze Age individuals from the Sintashta culture in the southern Urals and the closely related Andronovo culture in Central Asia, as well as the Srubnaya culture on the Pontic Caspian steppe, all carry substantial levels of Yamnaya-related ancestry, with additional European Farmer admixture, an ancestry known as Steppe Middle to Late Bronze Age ancestry (Steppe MLBA), which developed with the formation of the Corded Ware culture who may also be included in this cluster. Individuals from the Sintashta, Andronovo, and Srubnaya cultures are all genetically similar and may ultimately descend from a secondary migration of the Fatyanovo population, an eastern Corded Ware group.^{[10][4][30][27]}

This Steppe MLBA cluster may be further divided into a 'Western Steppe MLBA cluster', who may be modelled as around two thirds Yamnaya-related ancestry and one third European Farmer ancestry, and a 'Central Steppe MLBA cluster', which can be modelled as Western MLBA with around 9% West Siberian Hunter Gatherer (WSHG) ancestry. It has been suggested that the Central Steppe MLBA cluster was the main vector for the spread of Yamnaya-related ancestry to South Asia in the early 2nd millennium BC.^[4]

The American archaeologist David W. Anthony (2019) summarized the recent genetic data on WSHs. Anthony notes that WSHs display genetic continuity between the paternal lineages of the Dnieper-Donets culture and the Yamnaya culture, as the males of both cultures have been found to have been mostly carriers of R1b, and to a lesser extent I2.^[28]

While the mtDNA of the Dnieper-Donets people is exclusively types of U, which is associated with EHGs and WHGs, the mtDNA of the Yamnaya also includes types frequent among CHGs and EEFs. Anthony notes that WSH had earlier been found among the Sredny Stog culture and the Khvalynsk culture, who preceded the Yamnaya culture on the Pontic–Caspian steppe. The Sredny Stog were mostly WSH with slight EEF admixture, while the Khvalynsk living further east were purely WSH. Anthony also notes that unlike their Khvalynsk predecessors, the Y-DNA of the Yamnaya is exclusively EHG and WHG. This implies that the leading clans of the Yamnaya were of EHG and WHG origin.^[32]

Because the slight EEF ancestry of the WSHs has been found to be derived from Central Europe, and because there is no CHG Y-DNA detected among the Yamnaya, Anthony notes that it is impossible for the Maikop culture to have contributed much to the culture or CHG ancestry of the WSHs. Anthony suggests that admixture between EHGs and CHGs first occurred on the eastern Pontic-Caspian steppe around 5,000 BC, while admixture with EEFs happened in the southern parts of the Pontic-Caspian steppe sometime later.^[7]

As Yamnaya Y-DNA is exclusively of the EHG and WHG type, Anthony notes that the admixture must have occurred between EHG and WHG males, and CHG and EEF females. Anthony cites this as additional evidence that the Indo-European languages were initially spoken among EHGs living in Eastern Europe. On this basis, Anthony concludes that the Indo-European languages which the WSHs brought with them were initially the result of "a dominant language spoken by EHGs that absorbed Caucasus-like elements in phonology, morphology, and lexicon" (spoken by CHGs).^[7]

During the Chalcolithic and early Bronze Age, the Early European Farmer (EEF) cultures of Europe were overwhelmed by successive migrations of WSHs. These migrations led to EEF paternal DNA lineages in Europe being almost entirely replaced with EHG/WSH paternal DNA (mainly R1b and R1a). EEF mtDNA however remained frequent, suggesting admixture between WSH males and EEF females.^[33][34][35]

Western Steppe Herders are believed to have been light-skinned. Early Bronze Age Steppe populations such as the Yamnaya are believed to have had mostly brown eyes and dark hair,^[27][36] while the people of the Corded Ware culture had a higher proportion of blue eyes.^[37][38] A study from 2022 suggested that the skin tone of WSH peoples had brown eyes, brown hair, and intermediate complexions. The authors noted that the use of an “intermediate” skin tone phenotype, are those commonly found in present-day Mediterranean populations, as opposed to “pale” ones in present-day Northern Europeans.^[39]

The rs12821256 allele of the KITLG gene that controls melanocyte development and melanin synthesis,^[40] which is associated with blond hair and first found in an Ancient North Eurasian individual from Siberia dated to around 15,000 BC, is later found in three Eastern Hunter-Gatherers from Samara, Motala and Ukraine, and several later individuals with WSH ancestry.^[28] Geneticist David Reich concludes that the massive migration of Western Steppe Herders probably brought this mutation to Europe, explaining why there are hundreds of millions of copies of this SNP in modern Europeans.^[41] In 2020, a study suggested that ancestry from Western Steppe Pastoralists was responsible for lightening the skin and hair color of modern Europeans, having a dominant effect on the phenotype of Northern Europeans, in particular.^[1] In general, the inhabitants of the Southern Arc had darker pigmentation on average than those of the north (Europe outside the Southern Arc and the Eurasian steppe). When examining composite pigmentation phenotypes, researchers observed that while average pigmentation did indeed differentiate between populations of the Southern Arc and the north, light phenotypes were found in both areas at similar early dates, growing in parallel in the more recent millennia of history, making light pigmentation in West Eurasia the result of constant selection pressure across time.^[42]

A study in 2015 found that Yamnaya had the highest ever calculated genetic selection for height of any of the ancient populations tested.^[24][37] A 2024 study argues that the different amounts of Yamnaya/Steppe-like ancestry in Northern and Southern Europeans is responsible for the difference in height.^[43] In addition, "based on osteological evidence, the Yamnaya people were tall and had dolichocephalic crania (the average male was 175.5 cm in height), while the representatives of Catacomb culture were stockier and had more brachycephalic crania."^[44]

More than 25% of five ancient DNA samples from Yamnaya sites have an allele that is associated with lactase persistence, conferring lactose tolerance into adulthood.^[45] Steppe-derived populations such as the Yamnaya are thought to have brought this trait to Europe from the Eurasian steppe, and it is hypothesized that it may have given them a biological advantage over the European populations who lacked it.^[46][47][48]

Eurasian steppe populations display higher frequencies of the lactose tolerance allele than European farmers and hunter gatherers who lacked steppe admixture.^[49]

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