HLA alleles uniquely distinguish populations like A36 and A43 in African Americans. Golla are ancient Dravidian pastoral caste in south India. Golla divided into seven endogamous subcastes across Chittoor district. Subcastes evolved from common parental stock via fission. Subcastes have small effective population sizes. High reproductive isolation and endogamy among subcastes. Consanguineous marriages with inbreeding coefficients from 0.0175 to 0.042. Average inbreeding coefficient of 0.029 matches small genetic isolates like Samaritans. Low migration rates promote genetic microdifferentiation through drift. High inbreeding increases homozygosity but not gene frequencies except via selection on recessives. Indian caste system 2000-3000 years old with short evolutionary history. Golla may predate Indo-Aryan invasion as Dravidians. Multiple invasions shaped India's population structure into tribes and castes. Castes further subdivided by geography, language, religion. HLA variation reconstructs phylogenetic relationships among populations.