The Sindhi and Punjabi people of Pakistan exhibit significant steppe ancestry, a portion of which can be traced back to the region associated with the Sintashta culture. This ancestry is a result of migrations from the Eurasian steppes into South Asia over millennia, with the Sintashta culture playing a crucial role as a proposed Proto-Indo-Iranian culture and a conduit for this genetic flow.

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The Sintashta culture, flourishing in the Middle to Late Bronze Age (around 2100-1800 BCE) southeast of the Ural Mountains in present-day Russia, is widely accepted as the Proto-Indo-Iranian culture [1]. This archaeological culture is characterized by its advanced metallurgy, the earliest spoked-wheel battle chariots, and the burial of warriors with horses [1]. Genetic studies have revealed a strong connection between the Sintashta people and later Indo-Iranian-speaking populations, including those in South Asia [1].

Genetic analyses, such as Principal Component Analysis (PCA) and mixture models, show that many ancient and present-day South and Central Asians, particularly Indo-Iranian speakers, are strongly attracted to the main Sintashta genetic cluster [1]. This indicates a significant Sintashta-related ancestry in these populations [1]. Furthermore, the high frequency of Y-haplogroup R1a-Z93 in both Sintashta remains and many Indo-Iranian-speaking populations, including those in the Indian subcontinent, supports this genetic link [1].

The steppe ancestry in modern Indians, including Sindhi and Punjabi populations, is estimated to range from 5% to 30% depending on the specific group [3]. North Indian Brahmins and Jatts, for instance, show higher proportions (25-30%), while other groups may have lower percentages [3]. This ancestry is believed to have been introduced through movements from the Eurasian steppes, with the Sintashta culture and its descendants, such as the Andronovo culture, being key intermediaries [2] [3].

While Narasimhan et al. (2019) initially identified Central Steppe Bronze Age people as the primary source of steppe ancestry in Indians, more recent research suggests a more proximal mediator [2]. The TKM_IA sample from the Yaz II Iron Age culture site in Turkmenistan, dated to approximately 850 BCE, is considered a better fit as a direct source [2]. This TKM_IA sample itself is a mixture of Steppe Andronovo and BMAC (Bactria-Margiana Archaeological Complex) ancestry [2]. Further refinement points to populations similar to Loebanr_o, an outlier sample from the Swat Valley in Pakistan (circa 920 BCE), as the most proximal link for steppe ancestry in Indians [2]. Loebanr_o is estimated to have 50% ancestry from TKM_IA [2]. This suggests a migratory path of Steppe_MLBA > TKM_IA-like > Loebanr_o-like > Modern Indians [2].

The presence of steppe ancestry in the Indian subcontinent is a well-established fact in population genetics [3]. The timing of this influx is debated, but genetic dating tools like DATES suggest admixture events for Indo-European speakers in India occurring around 72 generations ago on average, which aligns with a post-1000 BCE movement for some groups [2]. The cultural and linguistic implications are significant, as this genetic flow is strongly associated with the spread of Indo-European languages into the region [1] [3].

In summary, the Sindhi and Punjabi people, as Indo-Iranian speakers, carry a notable genetic signature from the Eurasian steppes. This signature is consistent with the influence of the Sintashta culture and its successor cultures, which served as crucial links in the westward and southward expansion of steppe populations and their associated languages [1] [2] [3].

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