Unique demographic history and population substructure among the Coorgs of Southern India

The fascinating genetic architecture of today's Indian population is the result of thousands of years of population mixing and eventual isolation. The Coorgs are one such small and religiously/socioculturally homogeneous community in Karnataka, India, whose origins and demographic history are much debated due to their stark sociocultural contrast with surrounding populations. Here, we analyzed Coorgs using both autosomal (n = 70) and uniparental markers (n = 144). Our analyses suggest population substructure among Coorgs and showed significant population drift in Coorg3 in both allele frequency and haplotype-based analysis methods. Further sharing of haplotype and identity by descent suggests a shared genetic history of Coorg1 with the Palliyar population, and founder event analysis clearly indicates that the founder event in Coorg1 was around 40 GBP (Generations Before Present). The demographic models based on fastGlobeTrotter and Moments highlighted the recent admixture of Coorg3 with the northwest Indian Sikh Jatt population (~23 GBP); and also showed that Coorg2 was formed by mixing Coorg1 and Coorg3 at ~11 GBP, explaining their current sociocultural homogeneity. F-statistics-based admixture graph models suggest an as yet unknown lineage in Coorg3. mtDNA analysis revealed about 40% South Asia-specific mitochondrial lineages in Coorgs; while Y chromosome analysis revealed a predominance of Eurasian, Middle Eastern, and Indian-specific haplogroups, suggesting male-mediated migration and eventual assimilation with native females. These insights into ancient and diverse genealogies among Coorgs not only explain their unique status in the Indian diaspora but also encourage further research to identify unknown migrations to the Indian subcontinent and thus further unravel its unique demography.