Haplogroup R1a (R-M420), is a human Y-chromosome DNA haplogroup which is distributed in a large region in Eurasia, extending from Scandinavia and Central Europe to Central Asia, Siberia and South Asia.
The R1a (R-M420) subclade diverged from R1 (R-M173) 15-25,000 years ago, its subclade M417 (R1a1a1) diversified c. 3,400-5,800 years ago. The place of origin of the subclade plays a role in the debate about the origins of Proto-Indo-Europeans.
The Tocharians or Tokharians (US: /toʊˈkɛəriənˌ -ˈkɑːr-/ toh-KAIR-ee-ən, -KAR-; UK: /tɒˈkɑːriən/ to-KAR-ee-ən) were speakers of the Tocharian languages, a group of Indo-European languages known from around 7,600 documents from the 6th and 7th centuries, found on the northern edge of the Tarim Basin (modern-day Xinjiang, China). The name "Tocharian" was given to these languages in the early 20th century by scholars who identified their speakers with a people known in ancient Greek sources as the Tókharoi (Latin: Tochari), who inhabited Bactria from the 2nd century BC. This identification is now generally considered erroneous, but the name "Tocharian" remains the most common term for the languages and their speakers. Their endonym is unknown, although they may have referred to themselves as the Agni, Kuči, and Krorän or as the Agniya and Kuchiya known from Sanskrit texts.
Agricultural communities first appeared in the oases of the northern Tarim circa 2000 BC, represented by the earliest Tarim mummies. Genetic analysis reveals that nearly all (11 of 12, ~92%) of the early Tarim males carried R1a1a-M198, with additional individuals carrying R1b1b, establishing them within the paternal lineages of Ancient North Eurasian (ANE, ~72%) ancestry. However, the early Tarim mummies were not direct ancestors of the later-attested Tocharians. Instead, the Tocharian languages were likely introduced to the Tarim Basin later by Afanasievo-related migrants from the central steppes carrying the exact same paternal R-M17 during the Late Bronze Age (1600–1400 BCE).
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 start 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 populations of Europe, Central Asia, South Asia and West Asia. This ancestry is often referred to as Yamnaya ancestry, Yamnaya-related ancestry, Steppe ancestry or Steppe-related ancestry.
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.