The caste system transformed Indian genetics – David Reich

Geneticist David Reich explains how South Asia’s genetic landscape was shaped by the convergence of three ancestral populations—local hunter-gatherers, Iranian-related farmers, and steppe pastoralists—following the decline of the Harappan civilization approximately 3,800 years ago. While these groups initially underwent a period of intense mixing, the process "froze" between 2,000 and 3,000 years ago due to the cultural imposition of the caste system. This social shift toward endogamy prevented further large-scale genetic blending, preserving a unique gradient between Ancestral North Indians and Ancestral South Indians that remains visible today. Notable exceptions to this primary gradient include specific groups like the Patels, whose distinct genetic signature suggests additional ancestry from Central Asia. By analyzing these stable genetic snapshots, researchers can trace the historical transition from a fluid, mixing society to the rigid, stratified structure documented in early texts like the Rig Veda.