Overview
Haplogroup R-BY173660 is a downstream R2a lineage that crystallized during the middle to late Holocene in the northwestern sector of the South Asian subcontinent. The estimated formation time coincides with the later Neolithic and early Chalcolithic phases of the Indus borderlands, when village based agricultural systems expanded along river valleys and foothill zones, and when sustained interaction with Iranian Plateau groups became a defining feature of regional demography. Modern occurrences of BY173660 are concentrated in northern and northwestern India as well as eastern Pakistan, especially among populations with deep historical ties to the Indus and its tributaries. This geographic footprint suggests that the lineage became embedded in communities that were either directly ancestral to or strongly influenced by the cultural processes leading toward the Indus Valley Civilization. The moderate internal structure of the clade indicates that it persisted through several phases of demographic expansion without completely losing its original phylogenetic identity. Despite the lack of ancient individuals assigned specifically to BY173660, multiple R2a bearers have been documented in prehistoric contexts spanning Baluchistan, the Kachi Plain and the Swat region. These findings support a scenario in which ancestral BY173660 populations were part of the broader tapestry of early Indus related and highland connected groups whose genetic signatures continued into later historic populations of northwestern South Asia.